Patent Publication Number: US-2022226874-A1

Title: Extrusion press systems and methods

Description:
BACKGROUND 
     The properties of a material are affected by the processing used to form and shape the material. Processing includes heat treatment, deformation, and casting. Heat treatment is the process of subjecting a metal or alloy to a particular schedule of heating and cooling that causes desirable physical or chemical changes. Deformation is the process of forcing a piece of material to change its thickness or shape, and some deformation techniques include forging, rolling, extruding, and drawing. Casting is the pouring of melted metal into a mold so that the metal conforms to the shape of the mold when it solidifies. Heat treatment, deformation, and casting can be used in combination, and in some cases particular alloying elements are added to influence such processing in a desirable way. 
     Seamless metal tubing, such as copper tubing, is typically manufactured using various methods such as cast-and-roll, up-casting, or extrusion processes. To lower the cost of manufacturing metal tubing produced by conventional extrusion and casting techniques, manufacturers increase the size of billets used for forming the metal tubing. These billets are typically 100 to 1,000 pounds or more. Manufacturers thus require very large facilities to house the specialized large-scale machinery needed to processes the billets to form metal tubing. The sheer size of the equipment, and the billets processed by the equipment, causes the extrusion process to have large start-up and maintenance costs. Furthermore, limitations of the processes, such as extruding only one billet at a time, lead to manufacturing inefficiencies including limits on the amount of tubing produced per run and system component wear caused by the constant start-up and shut-down of the manufacturing process with respect to separate runs for each billet. 
     SUMMARY 
     Disclosed herein are systems, devices, and methods for extruding materials. In certain embodiments, the systems, devices, and methods allow for continuous extrusion of a plurality of billets. Such continuous extrusion allows for relatively smaller billets to be used to produce a desired quantity of extruded material, and therefore the scale of such continuous extrusion press systems can be smaller than conventional extrusion processes. The systems, devices, and methods allow for continuous seamless extrusion of the plurality of billets. 
     In one aspect, the systems, devices, and methods of the present disclosure include a method for continuously loading and extruding a plurality of billets, the method comprising loading a first billet at a receiving end of an elongate mandrel bar, transporting the first billet along the mandrel bar and through gripping elements that secure in place and prevent rotation of the mandrel bar, wherein at any given time at least one gripping element is gripping the mandrel bar, and extruding the first billet to form an extruded material by pressing the first billet through a rotating die, wherein the first billet is followed by an adjacent second billet that forms a part of the extruded material. The rotating die heats the billet as the billet advances through the rotating die. In certain implementations, a substantially constant pushing force is provided against the first billet in a direction towards the rotating die. In certain implementations, the rotation speed of the rotating die may be adjusted. 
     In certain implementations, the method further includes transporting the first billet along the mandrel bar and through cooling elements that clamp to the mandrel bar and deliver cooling fluid to the mandrel bar, wherein at any given time at least one cooling element is clamped to the mandrel bar. The billet may be transported along the mandrel bar via a track that intermittently moves depending on the position of the first billet relative to the gripping elements and the cooling elements. In certain implementations, the cooling fluid is transported to a mandrel bar tip provided on a second end of the mandrel bar opposite the receiving end, and the cooling fluid is returned to the cooling elements after passing through the mandrel bar tip. The mandrel bar tip may be positioned within the rotating die prior to receiving the first billet. In certain implementations the cooling fluid is water. 
     In certain implementations, continuously loading the plurality of billets further comprises the gripping elements alternately gripping the mandrel bar to allow one or more billets to pass through the gripping elements. In certain implementations, a downstream gripping element grips the mandrel bar and an upstream gripping element is open, and the method includes loading the one or more billets onto the mandrel bar and past the open upstream gripping element, closing the open upstream gripping element, and advancing the one or more billets to the downstream gripping element. In certain implementations, the method then includes opening the downstream gripping element, advancing the one or more billets past the open downstream gripping element, and closing the downstream gripping element. 
     In certain implementations, continuously loading the plurality of billets further comprises the cooling elements alternately clamping the mandrel bar to allow one or more billets to pass through the cooling elements. In certain implementations, a downstream cooling element clamps the mandrel bar and delivers cooling fluid to the mandrel bar, and an upstream cooling element is open, and the method includes loading the one or more billets onto the mandrel bar and past the open upstream cooling element, closing the open cooling gripping element, and advancing the one or more billets to the downstream cooling element. In certain implementations, the method then includes opening the downstream cooling element, advancing the one or more billets past the open downstream cooling element, and closing the downstream cooling element. 
     In certain implementations, the method further includes, during the extruding, preventing a portion of the first billet that has not yet entered the rotating die from rotating. A centering insert may grip the portion of the first billet to prevent rotation of said portion, and the centering insert may have an adjustable position relative to the rotating die. The centering insert may be cooled with a cooling fluid. 
     In certain implementations, the method further includes quenching the extruded material when the extruded material exits the rotating die. The extruded material may be quenched using water. In certain implementations, the water contacts the extruded material within approximately 1 inch of the rotating die. In certain implementations, the rotating die comprises a plurality of stacked die plates. In certain implementations, the material is copper, or the material is selected from the group consisting of copper, aluminum, nickel, titanium, brass, steel, and plastic. The plurality of billets may extend along substantially the entire length of the mandrel bar. In certain implementations, the method includes flooding the interior of the extruded material with nitrogen. Each of the plurality of billets may be loaded onto the mandrel bar by a human or by an automated loading device. 
     In one aspect, there is provided a method for continuously loading and extruding a plurality of billets, the method comprising receiving a first billet at a receiving end of an elongate mandrel bar, transporting the first billet along the mandrel bar and through cooling elements that clamp to the mandrel bar and deliver cooling fluid to the mandrel bar, wherein at any given time at least one cooling element is clamped to the mandrel bar, and extruding the first billet to form an extruded material by pressing the first billet through a rotating die, wherein the first billet is followed by an adjacent second billet that forms a part of the extruded material. 
     In certain implementations, the first billet is transported along the mandrel bar via a track that intermittently moves depending on the position of the first billet relative to the cooling elements. In certain implementations, the cooling fluid is transported to a mandrel bar tip provided on a second end of the mandrel bar opposite the receiving end, and the cooling fluid is returned to the cooling elements after passing through the mandrel bar tip. The mandrel bar tip may be positioned within the rotating die prior to receiving the first billet. In certain implementations, the cooling fluid is water. 
     In one aspect, an extrusion press system comprises a mandrel bar having a first end and a second end, the first end for receiving a billet having a hole therethrough and the second end coupled to a mandrel bar tip, a cooling element coupled to the mandrel bar, the cooling element having a port through which cooling fluid is delivered into the interior of the mandrel bar for cooling the mandrel bar tip, a gripping element coupled to the mandrel bar, the gripping element comprising moveable grips for securing in place and preventing rotation of the mandrel bar, and a rotating extrusion die configured to receive the billet from a centering insert having a plurality of notches that frictionally engage the billet to prevent the billet from rotating prior to entry of the billet into the rotating extrusion die, wherein the mandrel bar tip is positioned within the rotating die. 
     In certain implementations, the extrusion press system further includes a press-ram element having moveable first and second arms that together grip the billet and provide a substantially constant pushing force in the direction of the rotating die. The substantially constant pushing force may cause the billet to enter the rotating die at a predetermined rate. In certain implementations, the extrusion press system further comprises a motor coupled to a spindle that controls the rotation speed of the rotating extrusion die. 
     In certain implementations, the mandrel bar comprises an opening proximate to the cooling element ports, which opening receives the cooling fluid. The mandrel bar may further comprise notches about the mandrel bar on either side of the opening, wherein the notches are configured to receive an o-ring to substantially prevent the cooling fluid from leaking. The mandrel bar may further comprise a mandrel bar sleeve about the opening that substantially prevents the cooling fluid from leaking. In certain implementations, the mandrel bar comprises a grip portion that is correspondingly shaped to mate with the gripper of the gripping element. In certain implementations, the mandrel bar comprises an inner tube therein that receives the cooling fluid from the cooling element and through which the cooling fluid is delivered to the mandrel bar tip. The cooling fluid may be returned to the cooling element from the mandrel bar tip along a space within the mandrel bar between the outer surface of the inner tube and the inner surface of the mandrel bar. In certain implementations, the cooling fluid is water. 
     In certain implementations, the extrusion press system further comprises a track along which the billet is transported, wherein the track intermittently moves depending on the position of the billet relative to the gripping elements and the cooling elements. The track may include upper rolling wheels located above the track and configured to contact an upper surface of the billet. In certain implementations, the extrusion press system further comprises a quench tube provided at an exit of the rotating extrusion die. The quench tube quenches the extruded material when the extruded material exits the rotating extrusion die. In certain implementations, the extruded material is quenched using water. The water may contact the extruded material within approximately 1 inch of the rotating extrusion die. 
     In one aspect, a system is provided for controlling at least in part the extrusion of a plurality of billets, and the system includes a processor configured to provide instructions to an extrusion press system for loading a first billet at a receiving end of an elongate mandrel bar, transporting the first billet along the mandrel bar and through gripping elements that secure in place and prevent rotation of the mandrel bar, wherein at any given time at least one gripping element is gripping the mandrel bar, and extruding the first billet to form an extruded material by pressing the first billet through a rotating die, wherein the first billet is followed by an adjacent second billet that forms a part of the extruded material. 
     In certain implementations, the processor is further configured to provide instructions to an extrusion press system for intermittently moving a track upon which the first billet is placed based on the location of the first billet with respect to the gripping elements. In certain implementations, the processor is further configured to provide instructions to an extrusion press system for adjusting a rotation speed of the rotating die. In certain implementations, the processor is further configured to provide instructions to an extrusion press system for monitoring a cooling fluid delivery system. In certain implementations, the processor is further configured to provide instructions to an extrusion press system for adjusting the advancing and retraction speeds of press-rams that deliver the plurality of billets to the rotating die. 
     In one aspect, a non-transitory computer-readable medium is provided for controlling at least in part the extrusion of a plurality of billets, the non-transitory computer-readable medium comprising logic recorded thereon for loading a first billet at a receiving end of an elongate mandrel bar, transporting the first billet along the mandrel bar and through gripping elements that secure in place and prevent rotation of the mandrel bar, wherein at any given time at least one gripping element is gripping the mandrel bar, and extruding the first billet to form an extruded material by pressing the first billet through a rotating die, wherein the first billet is followed by an adjacent second billet that forms a part of the extruded material. 
     In certain implementations, the non-transitory computer-readable medium further comprises logic recorded thereon for intermittently moving a track upon which the first billet is placed based on the location of the first billet with respect to the gripping elements. In certain implementations, the non-transitory computer-readable medium further comprises logic recorded thereon for adjusting a rotation speed of the rotating die. In certain implementations, the non-transitory computer-readable medium further comprises logic recorded thereon for monitoring a cooling fluid delivery system. In certain implementations, the non-transitory computer-readable medium further comprises logic recorded thereon for adjusting the advancing and retraction speeds of press-rams that deliver the plurality of billets to the rotating die. 
     In one aspect, an extrusion press system comprises a mandrel bar having a first end and a second end, the first end for receiving a billet having a hole therethrough and the second end coupled to a mandrel bar tip, cooling means for delivering cooling fluid into the interior of the mandrel bar for cooling the mandrel bar tip, gripping means for securing in place and preventing rotation of the mandrel bar, and rotating extrusion means for extruding the billet, wherein the rotating extrusion means receives the billet from centering means having a plurality of notches that frictionally engage the billet to prevent the billet from rotating prior to entry of the billet into the rotating extrusion means, wherein the mandrel bar tip is positioned within the rotating extrusion means. 
     In certain implementations, the extrusion press system further includes pressing means for gripping the billet and providing a substantially constant pushing force in the direction of the rotating extrusion means. The substantially constant pushing force may cause the billet to enter the rotating extrusion means at a predetermined rate. In certain implementations, the extrusion press system further includes means for controlling the rotation speed of the rotating extrusion means. 
     In certain implementations, the mandrel bar comprises an opening proximate to the cooling means, which opening receives the cooling fluid. The mandrel bar may further comprise notches about the mandrel bar on either side of the opening, wherein the notches are configured to receive an o-ring to substantially prevent the cooling fluid from leaking. The mandrel bar may further comprise a mandrel bar sleeve about the opening that substantially prevents the cooling fluid from leaking. In certain implementations, the mandrel bar may further comprise a grip portion that is correspondingly shaped to mate with the gripping means. In certain implementations, the mandrel bar comprises an inner tube therein that receives the cooling fluid from the cooling means and through which the cooling fluid is delivered to the mandrel bar tip. The cooling fluid may be returned to the cooling means from the mandrel bar tip along a space within the mandrel bar between the outer surface of the inner tube and the inner surface of the mandrel bar. In certain implementations, the cooling fluid is water. 
     In certain implementations, the extrusion press system further comprises a track along which the billet is transported, wherein the track intermittently moves depending on the position of the billet relative to the gripping means and the cooling means. The track may include upper rolling wheels located above the track and configured to contact an upper surface of the billet. In certain implementations, the extrusion press system further comprises quenching means provided at an exit of the rotating extrusion means. The quenching means quenches the extruded material when the extruded material exits the rotating extrusion means. In certain implementations, the extruded material is quenched using water. The water may contact the extruded material within approximately 1 inch of the rotating extrusion means. 
     In one aspect, a method for continuously extruding a plurality of billets comprises transporting, along a non-rotating mandrel bar, the plurality of billets from a first end of the mandrel bar to a second end of the mandrel bar, and extruding the plurality of billets by pressing each of the plurality of billets through a rotating die, wherein friction from the rotation of the rotating die against the non-rotating plurality of billets generates heat for deforming the plurality of hollow billets, wherein a mandrel bar tip is positioned within the rotating die at the second end of the mandrel bar. In certain implementations, the method includes, during the extruding, preventing a portion of a respective one of the plurality of billets that has not yet entered the rotating die from rotating. In certain implementations, a centering insert grips the portion of the respective billet to prevent rotation of said portion, and the centering insert has an adjustable position relative to the rotating die. In certain implementations, the method further includes cooling the mandrel bar tip during the extruding. 
     In one aspect, a die for extruding a material includes a die body having a passage defining an entrance and an exit, with the diameter of the exit being smaller than the diameter of the entrance, and an interior surface extending around the passage from the entrance to the exit. A base is coupled to the die body, and rotation of the base causes the die body to rotate. 
     In certain implementations, the die body is configured to receive a billet of material for extrusion, and the billet is not pre-heated before entering the die body. Rotation of the die body creates friction between the interior surface and a billet advanced through the entrance and into the interior passage of the die body. The friction heats the billet to a temperature that is sufficient to cause deformation of the billet material. In certain implementations, the die body is configured to receive a mandrel tip through the entrance such that the mandrel tip is positionable within the interior passage of the die body. The interior surface of the die may include an angled portion configured to be positioned near a corresponding tapered outer surface of the mandrel tip. The die body is configured to receive a billet pressed through the interior passage of the die body to form an extruded product, the extruded product having an outer diameter corresponding to the diameter of the exit of the die body and an inner diameter corresponding to a diameter of the mandrel tip. 
     In certain implementations, the die body includes a plurality of die plates coupled together to form a stack. Each die plate has a circular bore through the center of the plate, and perimeters of the bores form the interior surface in the die body. The perimeter of the bores are angled at different angles with respect to an axis extending through the die body from the entrance to the exit. An angle of the perimeter near a front face of each plate in the die body is greater than an angle of the perimeter near a back face of an adjacent plate. The stack may include a non-uniform die plate having a bore perimeter angled at first angle near a front face of the plate and angled at a different second angle near a rear face of the plate. At least one of the die plates is formed from two different materials, with a first material forming a perimeter of a bore in the die plate and a second material forming an outer portion of the die plate. The first material may be a ceramic material, a steel, or a consumable material. In certain implementations, a front face of the die body near the entrance is configured to mate with a centering insert having a diameter substantially equal to the diameter of the entrance. The centering insert and a perimeter of the entrance may be formed from the same material. The centering insert does not rotate when the base and die rotate. In certain implementations, the base comprises a circular bore having a diameter greater than the diameter of the exit of the die body. A motor may supply a rotational force to the base. 
     In one aspect, a die includes a means for extruding a material, and the means for extruding includes a passage means defining an entrance and an exit, where the diameter of the exit is smaller than the diameter of the entrance, and an interior surface means extending around the passage means from the entrance to the exit. The die also has a means for coupling the means for extruding to a rotation means, and rotation of the means for coupling causes the means for extruding to rotate. 
     In certain implementations, the means for extruding is configured to receive a billet of material for extrusion, and the billet is not pre-heated before entering the die body. Rotation of the means for extruding creates friction between the interior surface means and a billet advanced through the entrance and into the passage means of the means for extruding. The friction heats the billet to a temperature that is sufficient to cause deformation of the billet material. The means for extruding is configured to receive a rod tip means through the entrance such that the rod tip means is positionable within the passage means of the means for extruding. The interior surface means of the means for extruding includes an angled portion configured to be positioned near a corresponding tapered outer surface of the rod tip means. The means for extruding is configured to receive a billet passed through the passage means of the means for extruding to form an extruded product, the extruded product having an outer diameter corresponding to the diameter of the exit of the means for extruding and an inner diameter corresponding to a diameter of the rod tip means. 
     In certain implementations, the means for extruding comprises a plurality of plate means coupled together to form a stack. Each plate means has a circular bore through the center of the plate means, and perimeter of the bores form the interior surface means in the means for extruding. The perimeters of the bores are angled at different angles with respect to an axis extending through the means for extruding from the entrance to the exit. An angle of the perimeter near a front face of each plate means in the means for extruding is greater than an angle of the perimeter near a back face of an adjacent plate means. The stack may include a non-uniform plate means having a bore perimeter angled at a first angle near a front face of the plate means and angled at a different second angle near a rear face of the plate means. At least one of the plate means is formed from two different materials, with a first material forming a perimeter of a bore in the plate means and a second material forming an outer portion of the plate means. The first material may be a ceramic material, a steel, or a consumable material. A front face of the means for extruding near the entrance is configured to mate with a centering means having a diameter substantially equal to the diameter of the entrance. The centering means and a perimeter of the entrance may be formed from the same material. Wherein the centering means does not rotate when the means for coupling and the means for extrusion rotate. The centering means includes gripping means that prevent rotation of a billet passing through the centering means. In certain implementations, the means for coupling comprises a circular bore having a diameter greater than the diameter of the exit of the means for extruding, and a power means may supply a rotational force to the means for coupling. 
     Variations and modifications of these embodiments will occur to those of skill in the art after reviewing this disclosure. The foregoing features and aspects may be implemented, in any combination and subcombination (including multiple dependent combinations and subcombinations), with one or more other features described herein. The various features described or illustrated herein, including any components thereof, may be combined or integrated in other systems. Moreover, certain features may be omitted or not implemented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects and advantages will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which: 
         FIG. 1  shows a side elevation view of an illustrative extrusion press system; 
         FIG. 2  shows a side elevation view of an illustrative billet feed track assembly for use with the extrusion press system of  FIG. 1 ; 
         FIG. 3  shows a perspective view of an illustrative fluid clamp; 
         FIGS. 4 and 5  show front and side elevation views, respectively, of the fluid clamp of  FIG. 3 ; 
         FIG. 6  shows a schematic view of an illustrative mandrel bar having an opening or port for receiving cooling fluid; 
         FIG. 7  shows a perspective view and various cross-sectional and side views of an illustrative mandrel bar sleeve; 
         FIG. 8  shows a perspective cross-sectional view of an illustrative mandrel bar having an inner tube for delivering cooling fluid to a mandrel bar tip; 
         FIG. 9  show a schematic diagram of an illustrative fluid delivery system; 
         FIG. 10  shows a perspective view of an illustrative mandrel bar grip; 
         FIGS. 11 and 12  show front elevation views of the mandrel bar grip of  FIG. 10  in a gripping position ( 11 ) and a non-gripping position ( 12 ); 
         FIG. 13  shows a schematic view of an illustrative mandrel bar having a portion that mates with a mandrel bar grip; 
         FIG. 14  shows a perspective view of the mandrel bar portion of  FIG. 13 ; 
         FIG. 15  shows a perspective view of an illustrative press-ram assembly having guide members; 
         FIG. 16  show a perspective view of an illustrative press-ram platen; 
         FIGS. 17-19  show front, side, and rear elevation views, respectively, of the press-ram platen of  FIG. 16 ; 
         FIG. 20  shows a perspective view of an illustrative press-ram platen; 
         FIGS. 21-23  show front, side, and rear elevation views, respectively, of the press-ram platen of  FIG. 20 ; 
         FIG. 24  shows an illustrative rotating die and centering ring in an extrusion orientation; 
         FIG. 25  shows an illustrative cross-sectional view of the rotating die and centering ring of  FIG. 24 ; 
         FIG. 26  shows an illustrative cross-sectional view of the rotating die and centering ring of  FIG. 24 ; 
         FIG. 27  shows a cross-sectional view the rotating die of  FIG. 24  with a mandrel bar positioned therein; 
         FIG. 28  shows a cross-sectional view of a billet being extruded through the rotating die of  FIG. 27 ; 
         FIGS. 29 and 30  show a perspective view and a top plan view, respectively, of illustrative mandrel bar tips; 
         FIG. 31  shows an illustrative flowchart for pre-processing a billet for use in the extrusion press system of  FIG. 1 ; 
         FIG. 32  shows an illustrative flowchart for pre-processing a mandrel bar tip for use in the extrusion press system of  FIG. 1 ; 
         FIGS. 33-36  show illustrative flowcharts for operating the extrusion press system of  FIG. 1 ; 
         FIG. 37  shows a block diagram of an illustrative computer system for operating the extrusion press system of  FIG. 1 ; 
         FIG. 38  shows a cross-sectional view of a magnetic data storage medium encoded with a set of machine-executable instructions for performing the methods of the present disclosure; 
         FIG. 39  shows a cross-sectional view of an optically readable data storage medium encoded with a set of machine-executable instructions for performing the methods of the present disclosure; 
         FIG. 40  shows a simplified block diagram of an illustrative system employing a programmable logic controller of the present disclosure; and 
         FIG. 41  shows a block diagram of an illustrative system employing a programmable logic controller of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     To provide an overall understanding of the systems, devices, and methods described herein, certain illustrative embodiments will be described. Although the embodiments and features described herein are specifically described for use in connection with continuous extrusion press systems, it will be understood that all the components, connection mechanisms, manufacturing methods, and other features outlined below may be combined with one another in any suitable manner and may be adapted and applied to systems to be used in other manufacturing processes, including, but not limited to cast-and-roll, up-cast, heat treatment, other extrusion, and other manufacturing processes. Furthermore, although the embodiments described herein relate to extruding metal tubing from hollow billets, it will be understood that the systems, devices, and methods herein may be adapted and applied to systems for extruding any suitable type of extruded product using billets. 
     The extrusion press system operates using frictional heat generated from a non-rotating hollow billet coming into contact with a rotating die to facilitate deformation and extrusion of the billet. There is thus no requirement of pre-heating the billets or the rotating die before the extrusion. The amount of heat generated is generally determined by the rate at which the billets are fed into the rotating die (e.g., controlled by the press-ram speed of the press-ram elements  130 ,  140  of  FIG. 1 ) and the rotation speed of the die (e.g., controlled by the rotation speed of the spindle  172  of  FIG. 1 ), as well as the interior profile of the rotating die. Higher press-ram speeds and spindle rotation speeds generate relatively greater amounts of heat. 
     The rotating die forms the outer diameter of an extruded tube produced by the extrusion press system, and a mandrel bar tip positioned within the rotating die forms the inner diameter of the extruded tube. In certain embodiments, chilled process water, or any other suitable cooling fluid, is used to cool the process elements including the rotating die, the centering insert, the billets, and the gear box oil, as well as the extruded tubing product. Unlike conventional extrusion techniques, the extrusion press system of the present disclosure does not require any container within which to hold the billet for extrusion. Therefore the billets to be extruded preferably have sufficient column strength to withstand the pressure applied by the press-ram elements during the extrusion process. A programmable logic controller, or PLC, controls all or a subset of movements of the extrusion press system while the system is set in automatic mode. 
     The extrusion press systems, devices, and methods described herein may provide for continuous extrusion of a plurality of billets to produce a seamless extruded tubing product according to various seamless tubing standards including, for example, the ASTM-B88 Standard Specification for Seamless Copper Water Tube. The seamless extruded tubing of the present disclosure may also comply with the standards under NSF/ANSI-61 for Drinking Water System Components. 
       FIG. 1  shows an extrusion press system  10  according to certain embodiments. The extrusion press system  10  includes structural sections referred to herein as the mandrel carriage section  80  and the platen structure section  90 . The mandrel carriage section  80  includes a mandrel bar  100 , fluid clamps or cooling elements  102  and  104 , mandrel grips or gripping elements  106  and  108 , and a billet delivery system  110  shown in detail in  FIG. 2 . The mandrel carriage section  80  is supported by a physical carriage structure, which is not shown in  FIG. 1  to avoid overcomplicating the drawing, but which carriage structure serves as a mount for the components of the mandrel carriage  80 . The platen structure section  90  includes an entry platen  120  and a rear die platen  122 , press-ram platens  130  and  140 , a centering platen  150 , and a rotating die  160  that presses against the rear die platen  122 . The platen structure section  90  is supported by a frame  190  that also serves as a mount for the motor  170  and related gearbox components (not shown). The direction along which billet loading, transport, and extrusion occurs according to the extrusion press system  10  is denoted by directional process arrow d 1 . The extrusion press system  10  may be operated, at least in part, by a PLC system that controls various aspects of the billet delivery subsystem  20 , extrusion subsystem  40 , and quenching or cooling subsystem  60  of the extrusion press system  10 . 
     The mandrel grips  106 ,  108  comprise a mandrel bar gripping system  105  designed to hold the mandrel bar in place while allowing a plurality of billets to be continuously fed along and about the mandrel bar  100  to provide for continuous extrusion. The billets may be formed from any suitable material for use in extrusion press systems including, but not limited to, various metals including copper and copper alloys, or any other suitable non-ferrous metals such as aluminum, nickel, titanium, and alloys thereof, ferrous metals including steel and other iron alloys, polymers such as plastics, or any other suitable material or combinations thereof. The mandrel grips  106 ,  108  may be controlled by the PLC system to securely hold the mandrel bar  100  such that at any given time during the extrusion process, at least one of the mandrel grips  106 ,  108  is gripping the mandrel bar  100 . The mandrel grips  106 ,  108  set the position of the mandrel bar  100  and prevent the mandrel bar  100  from rotating. When the mandrel grips  106 ,  108  are in a gripping or engaged position, thereby gripping the mandrel bar  100 , the mandrel grips  106 ,  108  prevent billets from being transported along the mandrel bar  100  through the grips. 
     The mandrel grips  106 ,  108  operate by alternately gripping or engaging the mandrel bar  100  to allow one or more billets to pass through a respective mandrel grip at a given time. For example, the upstream mandrel grip  106  may release or disengage the mandrel bar  100  while the downstream mandrel grip  108  is gripping the mandrel bar  100 . At any given time, at least one of the mandrel grips  106 ,  108  is preferably gripping or otherwise engaged with the mandrel bar  100 . One or more billets queued or indexed near the upstream mandrel grip  106 , or being transported along the mandrel bar  100 , may pass through the open upstream mandrel grip  106 . After a specified number of billets has passed through the open upstream mandrel grip  106 , the gripper  106  may close and thereby return to gripping the mandrel bar  100 , and the billets may be advanced to the downstream gripping element  108 . The downstream gripping element  108  may remain closed, thereby gripping the mandrel bar  100 , or the downstream mandrel grip  108  may open after the upstream mandrel grip  106  re-grips the mandrel bar  100 . Although two mandrel grips  106 ,  108  are shown in the extrusion press system  10 , it will be understood that any suitable number of mandrel grips may be provided. 
     The fluid clamps  102 ,  104  comprise a mandrel bar fluid delivery system  101  designed to supply cooling fluid along the interior of the mandrel bar  100  to the mandrel bar tip during the extrusion process. The fluid clamps  102 ,  104  also receive cooling fluid from the mandrel bar  100  that has returned from the mandrel bar tip. Any suitable cooling fluid may be used, including water, various mineral oils, brines, synthetic oils, any other suitable cooling fluid, including gaseous fluids, or any combination thereof. The fluid clamps  102 ,  104  may be controlled by the PLC system to continuously supply process cooling fluid to the mandrel bar during the extrusion process while allowing a plurality of billets to be continuously feed along and about the mandrel bar  100 . The fluid clamps  102 ,  104  operate such that there is no or substantially no interruption to the supply of process cooling fluid to the mandrel bar tip during the extrusion process. Similar to the operation of the mandrel grips  106 ,  108  discussed above, when the fluid clamps  102 ,  104  are clamped to or engaged with the mandrel bar  100 , the fluid clamps  102 ,  104  prevent billets from being transported along the mandrel bar  100  through the fluid clamps. 
     The fluid clamps  102 ,  104  operate such that at any given time during the extrusion at least one of the fluid clamps is clamped to or engaged with the mandrel bar  100  and thereby delivers cooling fluid into the mandrel bar  100  for delivery to the mandrel bar tip. When a billet passes through one of the fluid clamps  102 ,  104 , the respective fluid clamp discontinues delivering (and receiving) cooling fluid and releases or disengages the mandrel bar  100  to allow the billet to pass therethrough before re-clamping the mandrel bar  100  and continuing to deliver (and receive) cooling fluid. While one of the fluid clamps  102 ,  104  is unclamped or disengaged from the mandrel bar  100 , the other fluid clamp continues to deliver cooling fluid to the mandrel bar. 
     For example, the upstream fluid clamp  102  may release the mandrel bar  100  while the downstream fluid clamp  104  is clamped to the mandrel bar  100 . At any given time, at least one of the fluid clamps  102 ,  104  is preferably clamped to the mandrel bar  100  to continuously deliver cooling fluid. One or more billets queued or indexed near the upstream fluid clamp  102 , or being transported along the mandrel bar  100 , may pass through the open upstream fluid clamp  102 . After a specified number of billets has passed through the open upstream fluid clamp  102 , the fluid clamp  102  may close and thereby return to clamping the mandrel bar  100  and delivering cooling fluid, and the billets may be advanced to the downstream fluid clamp  104 . The downstream fluid clamp  104  may remain closed, thereby clamping the mandrel bar  100 , or the downstream fluid clamp  104  may open after the upstream fluid clamp  102  re-clamps to the mandrel bar  100 . Although two fluid clamps  102 ,  104  are shown in the extrusion press system  10 , it will be understood that any suitable number of fluid clamps may be provided. 
     The billet delivery system  20  includes the billet feed track assembly  110  of  FIG. 2 . The billet delivery system  110  ensures that a continuous supply of billets, such as billet  30 , is present for the extrusion process. When additional billets are needed, the PLC system will cycle the proper mandrel bar grips  106 ,  108 , fluid clamps  102 ,  104 , and billet delivery rollers (e.g., the billet feed track assembly  110 ) to ensure that the billet supply is continuous. The section of the mandrel carriage  80  located between the mandrel grip  106  and the entry platen  120  may continuously index to minimize the gap between billets fed into the ram platen sections  141  of the platen structure  90 . For example, at this location of the mandrel carriage  80 , the track assembly  110  may continuously cycle the track  202  to feed billets into the platen structure  90 . 
     The billet feed track assembly  110  includes a chain or a track  202  positioned about sprockets  204  and  205 . One or more of the sprockets  204 ,  205  may be coupled to a motor (not shown) that operates to move or cycle the track  202  in a loading direction, d 2 . The track  202  and sprockets  204 ,  205  are supported by a base rail  206  and a low rail  208 , which together couple to a frame  210 . An upper portion  210   a  of the frame  210  includes top roller wheels  212  that provide an upper bound for a passing billet  30 . For example, as show in  FIG. 2 , the mandrel bar  100  includes a billet  30  loaded thereon, where the billet  30  moves via contact with the track  202  and is stabilized by the top roller wheels  212 . The billet feed track assembly  110  may have any suitable length. For example, the track assembly  110  may extend along substantially the length of the mandrel bar  100  within the mandrel carriage section  80 . In certain embodiments, there may be provided a plurality of track assemblies that together operate to feed billets along the mandrel bar  100  and into the platen structure section  90 . For example, there may be track assemblies provided along the mandrel bar  100  between each of the fluid clamps  102 ,  104  and the mandrel grips  106 ,  108  such that one or more billets can be independently cycled through respective fluid clamps  102 ,  104  and mandrel grips  106 ,  108 , without requiring transport of other billets as would occur if there were only a single track assembly. 
     Returning to  FIG. 1 , the mandrel bar  100  extends along substantially the length of the extrusion press system  10  and is positioned to place the mandrel bar tip within the rotating die  160 . The adjustment to properly position the mandrel bar tip within the rotating die  160  is accomplished by moving the mandrel carriage section  80 , thus moving the mandrel bar  100 . The adjustments to the mandrel bar  100  and the mandrel carriage section  80  may be towards or away from the die  160 . The mandrel bar  100  and the mandrel carriage section  80  preferably cannot be adjusted while the extrusion press system  10  is in operation, although it will be understood that in certain embodiments the mandrel bar  100  and/or mandrel carriage section  80  may be adjusted during operation. 
     As discussed above, the extrusion press system  10  includes a platen structure section  90  having an entry platen  120  and a rear die platen  122 , press-ram platens  130  and  140 , a centering platen  150 , and a rotating die  160  pressed against the rear die platen  122 . Near the entry platen  120  is the press-ram assembly  141  that includes a first press-ram platen  130  and a second press-ram platen  140 . The first and second press-ram platens  130 ,  140  feed billets into the centering platen  150 , which grips the billets and prevents the billets from rotating prior to entering the rotating die  160 , which presses against the rear die platen  122 . The entry platen  120  and the rear die platen  122  are coupled by a series of tie rods  124  that act as guides for the press-ram platens  130 ,  140  and the centering platen  150 , each of which includes bearings  126   a ,  126   b ,  126   c  that move along the tie rods  124 . The rear die platen  122  and the entry platen  120  have mounting locations  127  through which the tie rods  124  are fixed. The entry platen  120 , rear die platen  122 , and tie rod structure  124  are supported by the frame  190 . The frame  190  also holds the spindle  172  and motor  170 . At the exit of the rotating die  160  is a quench tube  180  for rapidly cooling the extruded tubing. 
     The press-ram platens  130 ,  140  operate by gripping the billets and providing a substantially constant pushing force in the direction of the extrusion die stack  160 . At any given time at least one of the press-ram platens  130 ,  140  grips a billet and advances the billet along the mandrel bar  100  to provide the constant pushing force. The press-ram platens  130 ,  140  form the final part of the billet delivery subsystem  20  before the billet enters the centering platen  150  and the rotating die  160  of the extrusion subsystem  40 . Similar to the billet feed track section before the entry platen  120 , the section prior to the press-ram platens  130 ,  140  preferably continuously indexes the billets to minimize any gaps between a billet that is gripped the press-ram platens  130 ,  140  and the next billet. 
     As discussed above, the press-rams  130 ,  140  continuously push billets into the rotating die  160 . The press-rams  130 ,  140  alternate gripping and advancing billets towards and into the rotating die  160  and then ungripping the advanced billets and retracting for the next gripping/advancing cycle. There is preferably an overlap between the time when one press-ram stops pushing and the other press-ram is about to start pushing so that there is always pressure on the rotating die  160 . The press-rams  130 ,  140  advance and retract via press-ram cylinders coupled to the respective press-ram. As shown there are two press-ram cylinders  132 ,  142  per press-ram. A first set of press-ram cylinders  132  is located to the left and right of the entry platen  120  (although the right-side press-ram cylinder is hidden from view by the left-side press-ram cylinder). The first set of press-ram cylinders  132  couples with the first press-ram platen  130  and is configured to move the first press-ram  130  along the tie rods  124  as the first press-ram  130  advances billets and then retracts for subsequent billets. A second set of press-ram cylinders  142  is located on the top and bottom of the entry platen  120 . The second set of press-ram cylinders  142  couples with the second press-ram platen  140  and is configured to move the second press-ram  140  along the tie rods  124  as the second press-ram  140  advances billets and then retracts for subsequent billets. Although two press-ram cylinders are shown for each of the first and second press-ram platens  130 ,  140 , it will be understood that any suitable number of press-ram cylinders may be provided. In certain embodiments, press-ram cylinders may be coupled to both press-rams  130 ,  140 . 
     The centering platen  150  receives billets advanced by the press-rams  130 ,  140  and holds the billets to prevent their rotation during the extrusion process prior to entry of the billets into the rotating die  160 . When the centering platen  150  is positioned in place for the extrusion process, the centering platen  150  becomes part of the extrusion die  160 . That is, a centering insert  152  of the centering platen  150  substantially abuts the rotating die  160 . The centering platen  150  itself, however, and the components therein including the centering insert  152 , do not rotate with the rotating die  160 . The centering platen  150  prevents billets that are no longer held by the second press-ram  150  from rotating while the die  160  rotates by gripping the billets and thereby preventing the billets from rotating prior to entry of the billets into the rotating die  160 . 
     The rotating die  160  may have a unibody design, or may include a plurality of die plates stacked together. In certain embodiments, the die includes a base plate, a final plate, a second intermediate plate, a first intermediate plate, an entry plate, and a steel end holder, and the die plates are bolted together to form the die  160 . The rotating die  160  is bolted to or otherwise coupled with the spindle  172 , which is operated by the motor  170 . A gear box is bolted to the rear die platen  122  and contains the spindle  172  as well as the drive chain, motor drive gear, gear oil reservoir, and gear oil heat exchanger, which are not shown in  FIG. 1  to avoid overcomplicating the figure. In certain embodiments, the spindle motor  170  and the spindle/die gear tooth ratio is 2.5:1, although it will be understood that any suitable gear ratio may be used for the rotation of the rotating die  160 . 
     At the extrusion end of the extrusion press system  10  is a quench box  185  bolted or otherwise coupled to the exit side of the gear box on the rear die platen  122 . In certain embodiments, within the quench box  185  is a quench tube  180  for rapidly quenching or cooling the extruded material as it exits the rotating die  160 . Water may be used as the quenching or cooling fluid, and the water may contact the extruded material sometime after the exit of the extruded material from the rotating die  160 . For example, in certain embodiments, the extruded material is quenched with cooling fluid within approximately 1 inch of exiting the rotating die  160 . Any suitable cooling fluid may be used for quenching an extruded material, including water, various mineral oils, brines, synthetic oils, any other suitable cooling fluid, including gaseous fluids, or any combination thereof. The quench tube  180  may be formed of one or more tubes having a channel therein for delivering the cooling fluid to the extruded material. In certain embodiments, the quench tube  180  further includes an end cap or other structure through which the cooling fluid is delivered to the extruded material. Any suitable quench tube may be used the extrusion press system of this disclosure, including, for example, the quench tubes described in copending, commonly-assigned U.S. patent application Ser. No. ______ (Attorney Docket No. 109965-0006-101), filed concurrently herewith, and entitled “SYSTEMS AND METHODS FOR COOLING EXTRUDED MATERIALS,” the disclosure of which is hereby incorporated by reference herein in its entirety. 
     In certain embodiments, nitrogen gas, or another suitable inert gas, is delivered to the interior of an extruded material as the material exits the rotating die. For example, nitrogen gas may be delivered to the interior of extruded tubing using a cap placed on the leading end of the extruded tubing as it exits the rotating die. Injecting gaseous or liquid nitrogen into the rotating die assembly, or the interior of the extruded material itself, can minimize oxide formation by displacing the oxygen-laden air. 
     Although not shown in  FIG. 1 , the billet delivery subsystem  20  of the extrusion press system  10  may include a billet delivery table with a plurality of billets prepped for loading onto the extrusion press system  10 . The billets may be loaded automatically, for example, by an automated process or may be loaded by hand. 
     The various components of the extrusion press system  10  of  FIG. 1  will now be described with respect to  FIGS. 3-30 .  FIG. 3  shows a perspective view of the fluid clamp  102  of  FIG. 1  according to certain embodiments. The fluid clamp  102  includes a housing  302  having a base  304  and end plates  306   a  and  306   b  coupled via four tie rods  308 , although it will be understood that any suitable number of tie rods may be used, and in certain embodiments other fixation techniques may be used to secure the elements of the fluid clamp in addition to, or in place of, the tie rods  308 . Supported by the tie rods  308  is an inlet/outlet fluid clamp  312 , through which cooling fluid such as water enters and exits the fluid clamp  102 , and a blank fluid clamp  314 , each of which is actuated by a respective cylinder  309 ,  310  located between the respective clamp  312 ,  314  and its end plate  306   a ,  306   b . Situated below the housing  302  are carriage rails  305  that secure the fluid clamp  102  onto the carriage structure that supports the mandrel carriage section  80  of  FIG. 1 . The inlet/outlet fluid clamp  312  includes taps  316  formed in a top surface  312   a  therein that extend to an insert piece  318  that is inserted into an inner portion of the inlet/outlet fluid clamp  312 . As can be seen in  FIG. 3 , the blank fluid clamp  314  has a clamping surface  314   a  and the insert  318  within the inlet/outlet fluid clamp  312  has a clamping surface  318   a . The clamping surfaces  314   a  and  318   a  frictionally engage a respective surface of the mandrel bar, such as the mandrel bar  100  of the extrusion press system  10 . In certain embodiments, the clamping surfaces  314   a ,  318   a  may engage a mandrel bar sleeve (e.g., mandrel bar sleeve  360  of  FIG. 7 ) provided about a portion of the mandrel bar. 
       FIGS. 4 and 5  show front and side elevation views, respectively, of the fluid clamp  102  of  FIG. 3 . As shown in  FIGS. 4 and 5 , for example, the taps  316  in the inlet/outlet fluid clamp  312  extend from the top surface  312   a  of the clamp  312  and into ports  320  formed in the insert  318 . The fluid clamp  102  delivers cooling fluid to the mandrel bar via the inlet/outlet fluid clamp  312  through the taps  316  and the ports  320 . Also shown in  FIG. 4  are the clamping surfaces  314   a  and  318   a  of the inlet/outlet fluid clamp  312  and the blank fluid clamp  314 . Although the fluid clamp  312  includes two taps  316  in fluid communication with two ports  320  of the insert  318 , it will be understood that any suitable number of taps and ports may be provided for delivering cooling fluid to the mandrel bar. Alternatively, or additionally, in certain embodiments the taps  316  may be provided through other surfaces of the fluid clamp such as the front (or rear) surface  312   b  or the lateral surfaces  312   c  of the inlet/outlet fluid clamp  312 . 
     In certain embodiments, the clamping surfaces  314   a  and  318   a  of the blank fluid clamp  314  and the insert  318  of the inlet/outlet fluid clamp  312  are structured to mate with a corresponding portion of a mandrel bar.  FIG. 6  shows a schematic view of a mandrel bar  340  having an opening or port  344  for receiving and/or returning cooling fluid from a fluid clamp according to certain embodiments. As shown in  FIG. 6 , for example, the mandrel bar  340  includes portions  342  and  348  having two respective port sections  342   a ,  342   b  and  348   a ,  348   b  for receiving and/or returning cooling fluid from a fluid clamp such as fluid clamp  102 . In certain embodiments, port sections  342   a  and  348   a  are configured for the return of cooling fluid to a fluid clamp, and the port sections  342   b  and  348   b  are configured for the receipt of cooling fluid from the fluid clamp. Alternatively, port sections  342   a  and  348   a  may receive cooling fluid, and port sections  342   b  and  348   b  may return the cooling fluid. In still further embodiments, port sections  342   a / 348   b  may receive cooling fluid and port sections  342   b / 348   a  may return cooling fluid, or vice versa. Any suitable receiving/returning arrangement of port sections may be used such that at least one of the respective ports receives cooling fluid and another returns the cooling fluid to the fluid clamp. 
     The inset of the mandrel bar portion  342  shows port section  342   a  with an opening or port  344  for receiving and/or returning cooling fluid from the fluid clamp  102 . The mandrel port  344  is sized to correspond with the respective port  320  of the fluid clamp  102 . About the mandrel port  344  are a series of notches  346  receiving o-rings and thereby preventing cooling fluid from escaping or otherwise leaking from the mandrel bar  340  via the port  344 . The two mandrel bar portions  342 ,  348  correspond, for example, to the portions of the mandrel bar that interface with the two fluid clamps  102 ,  104  of the extrusion press system  10  of  FIG. 1 . As discussed above, in certain embodiments a mandrel sleeve  360  may be provided to engage the clamping surfaces of a fluid clamp. The mandrel sleeve  360  may also work together with the o-rings to prevent fluid leakage from the mandrel bar  340  and the fluid clamp. As shown in  FIG. 7 , for example, a mandrel sleeve  360  includes ports  360  through which cooling fluid is delivered and/or returned between the mandrel bar  340  and a fluid clamp. The mandrel sleeve  360  also includes a slot  364  that allows for flexibility as the sleeve  360  is positioned on the mandrel bar  340  about the portions  342 ,  348  that receive and/or return cooling fluid. The o-rings in notches  346  may create a substantially fluid-tight seal between the mandrel bar  340  and the inner surface  360   a  of the mandrel bar sleeve  360 . 
     Also shown in  FIG. 6  is an inner tube  350  that runs along the length of the mandrel bar  340  and which delivers the cooling fluid to the mandrel bar tip, which is positioned within a rotating die. The cooling fluid that is received through the openings or ports  344  in the mandrel bar  340  travels through an opening  354  in the inner tube  350  such that the cooling fluid is delivered along the inside of the tube  350  to the mandrel bar tip, where it then travels back out of the tube  350 , but within the mandrel bar, to the openings or ports  344  from which it was received. The direction of cooling fluid travel is shown in in  FIG. 8 , which depicts a perspective cross-sectional view of the mandrel bar  340  and the inner tube  350  of  FIG. 6  for delivering cooling fluid to the mandrel bar tip. The cooling fluid travels along the inside of the inner tube  350  in the direction of arrow W1 towards the mandrel bar tip and then returns in the direction of arrow W2 in the outer space  352  between the outer surface  350   a  of the inner tube  350  and the inner surface  340   a  of the mandrel bar  340 . In certain embodiments, a portion of the inner surface of the mandrel bar, such as the inner surface  340   a  of mandrel bar  340 , may be threaded for receiving the mandrel bar tip, although the mandrel bar tip may be coupled to the mandrel bar using any suitable technique. In certain embodiments, a spacer may be provided about the inner tube  350  that centers the inner tube  350  within the mandrel bar  340  along any suitable length of the mandrel bar  340 . Where the mandrel bar has threads, the spacer may be threaded to the mandrel bar, although the spacer may also press against non-threaded portions of the mandrel bar. 
     The extrusion press system  10  includes a cooling system  400  for cooling the various components of the press system  10  during operation. Although the cooling system  400  of  FIG. 9  will be described as using water as the cooling fluid, it will be understood that any suitable cooling fluid may be used. The extrusion press cooling system  400  is designed to deliver cooled water in sufficient quantities and pressures to cool the process components and the extruded product. In certain embodiments, there may be two main water systems on the press, mandrel water and press water. With respect to the mandrel water, the mandrel water system is supplied water from the holding tank. The heat exchangers cool the process water by exchanging the heat generated during the extrusion process with chilled water from the chiller water system. The process water flows in a serial circuit through the heat exchangers and chilled water flows in a parallel circuit through the heat exchangers, and the two water systems never come into physical contact with each other. All of the water is made available to the mandrel water system. A pressure relief valve limits the system pressure. The water not used the mandrel system is diverted to the holding tank, which cools the process water in the holding tank. The water is pumped through the inside of the mandrel bar through the inner water tube (e.g., inner tube  350  of  FIGS. 6 and 8 ) to the mandrel bar tip and returns down the length of the outer space of the inside of the mandrel bar as discussed with respect to  FIGS. 6 and 8 . As the water has circulated through the mandrel cooling system, it is returned into the holding tank which is the other source of cooling the process water to the holding tank. Preferably at no time is the mandrel process water supply interrupted while the press is running. The press water system is supplied water from the holding tank. Flow and pressure is regulated by a relief valve with excess water being returned to the holding tank. The press water is pumped to a manifold where it is routed to cool various components of the system, including the rotating die, by means of a high velocity water spray from a cooling ring which water is routed to cool the gear box hydraulic oil before going to cool the die. The centering insert  152 , by means of a constant flow through a centering insert holder, the billets through a flood system as it enters the Inconel, and the tube being extruded by use of the quench tube which spray quenches the tube. The quench tube is housed inside the spindle. The process water from the above operations returns back to the holding tank. 
       FIG. 10  shows a perspective view of the mandrel grip  106  of  FIG. 1  according to certain embodiments. The mandrel grip  106  includes a front plate  502  and back plate  504  separated by a spacer  506 . Within the front plate  502  is a cut-out gripping portion  508  and a top grip  510  and bottom grip  512 , although it will be understood that alternatively, or additionally, in certain embodiments the grips  510 ,  512  could be positioned side-to-side rather than top-to-bottom within the mandrel grip  106 . The mandrel grip  106  also includes a cylinder  514  and piston rod  515  coupled to a cylinder mount  516 . The cylinder  514  operates to control the gripping and ungripping of the top grip  510  and bottom grip  512  with respect to the mandrel bar  100 . 
       FIGS. 11 and 12  show front elevation views of the mandrel grip  106  of  FIG. 10  in a closed or engaged gripping position ( FIG. 11 ) and a non-gripping or open position ( FIG. 12 ). As shown in  FIG. 11 , for example, the top grip  510  and the bottom grip  512  are in a gripping position and engaged about a mandrel bar portion  518 , which is the portion of the mandrel bar to which the grippers  510 ,  512  grip. When the mandrel grip  106  is in an open or non-gripping position, as shown in  FIG. 12 , the top grip  510  and the bottom grip  512  are displaced from one another relative to the gripping position and are thereby displaced from the mandrel bar portion  518 , such that there is clearance along the mandrel portion  518 , and within the gripping cutout  508 , for a billet to pass therethrough. 
     In certain embodiments, the top grip  510  and the bottom grip  512  are structured to mate with a corresponding portion of a mandrel bar, such as the mandrel bar portion  518  of the mandrel bar  540 .  FIG. 13  shows a schematic view of a mandrel bar  540  having portions  518  that may be shaped or otherwise configured to mate with the top grip  510  and the bottom grip  512  of the mandrel grip  106 . The particular shape of the mandrel bar portions  518  may aid the mandrel grip  106  in forming and maintaining a secure grip of the mandrel bar  540  to prevent the mandrel bar  540  from rotating or otherwise moving or displacing during operation of the press system when the mandrel bar  540  is gripped by the mandrel grip  106 . As shown in  FIG. 13 , for example, the two grip portions  518  may correspond to the portions of the mandrel bar that interface with the two mandrel grips  106 ,  108  of the extrusion press system  10  of  FIG. 1 . 
     A perspective view of the portion  518  of the mandrel bar  540  is shown in  FIG. 14 . The mandrel bar portion  518  is shaped to mate with a mandrel grip such as mandrel grip  106  and includes a rounded circumference portion  550  and various straight edges  552  and  554  that mate with the top and bottom grips of a mandrel grip. The mandrel portion  518  also includes various insets or cut-outs  556  and  558  shaped to mate with complementary grippers. As shown in  FIG. 14 , the mandrel portion  518  is hollow and includes an inner surface  540   a  for receiving an inner tube such as the inner tube  350  discussed above with respect to  FIGS. 6 and 8 . 
     In certain embodiments, the mandrel bar extends along the length of the extrusion press system  10 , terminating at a mandrel bar tip positioned within the rotating die. The mandrel bar may have a substantially continuous cross-section along its length or may have portions thereof (such as portions  342 ,  348 ,  518  and mandrel bar sleeve  360 ) shaped for interfacing with components of the press system such as the fluid clamps  102 ,  104  and the mandrel grips  106 ,  108 . In certain embodiments, the mandrel bar may be modular and may comprise a plurality of attachable sections that together form the mandrel bar for use with an extrusion press system. For example, the mandrel bar  540  of  FIG. 13  may be configured to attach to other mandrel bars, or sections of mandrel bars, such as the mandrel bar  340  of  FIG. 6 , which shows a portion of a mandrel bar  340  used to couple with fluid clamps. In order to attach these modular portions of a mandrel bar together, the mandrel bar  540  is provided with ends  542  and  544  that receive the complementary ends of another mandrel bar. 
       FIG. 15  shows a perspective view of the press-ram assembly  141  of  FIG. 1  having guide members for guiding the press-ram assembly  141  along the tie rods  124  according to certain embodiments. As shown in  FIG. 15 , for example, the first press-ram platen  130  and the second press-ram platen  140  include guide members  600  and  610 , respectively. The guide member  600  of press-ram platen  130  has hanging plates  602  coupled to bearings  604 , which bearings  604  are configured to move the press-ram  130  along tie rods such as tie rods  124  of  FIG. 1 . The guide member  610  of press-ram platen  140  also includes hanging plates  612  and various bearings  614  configured to move the press-ram  140  along tie rods  124 . The hanging plate  614  of guide member  610  is positioned above where the tie rods  124  are located and the hanging plate  602  of guide member  600  is located below the position at which the tie rods  124  are located. These guide members  600 ,  610  allow the press-ram platens  130 ,  140  to move along the tie rods  124  as the extrusion process operates such that the press-ram platens  130 ,  140  can grip and advance billets into the rotating die and then retraction to begin the next cycle. 
       FIG. 16  shows a perspective view of the press-ram platen  130  of  FIG. 1  according to certain embodiments.  FIGS. 17-19  show front, side, and rear elevation views, respectively, of the press-ram platen  130  of  FIG. 16 . The press-ram platen  130  includes a grip mounting plate  620  and first and second billet gripper link arms  622  and  624  that are coupled to a cylinder  626  about a pivot  625 . The cylinder  626  operates to move the first and second link arms  622 ,  624  with respect to one another and about the pivot  625 . The grip mounting plate  620  is coupled to the link arms  622 ,  624  and separated by a spacer  621  therebetween. As shown in  FIG. 19 , first and second grips  630 ,  632  are mounted to the first and second link arms  622 ,  624 , and are supported by a bottom mount  634  and top mount  635 . In certain embodiments, the gripping surfaces  630   a ,  632   a  of the first and second grips  630 ,  632 , can have a serrated or otherwise textured surface for improving the frictional contact between the gripping surfaces  630   a ,  632   a  and a gripped billet. 
       FIG. 20  shows a perspective view of the press-ram platen  140  of  FIG. 1  according to certain embodiments.  FIGS. 21-23  show front, side, and rear elevation views, respectively, of the press-ram platen  140  of  FIG. 20 . The press-ram platen includes a grip mounting plate  640  and first and second billet gripper link arms  642  and  644  that are coupled to a cylinder  646  about a pivot  645 . The cylinder  646  operates to move the first and second link arms  642 ,  644  with respect to one another and about the pivot  645 . The grip mounting plate  640  is coupled to the link arms  642 ,  644  and separated by a spacer  641  therebetween. As shown in  FIG. 23 , first and second grips  650 ,  652  are mounted to the first and second link arms  642 ,  644 , and are supported by a bottom mount  654  and top mount  655 . In certain embodiments, the gripping surfaces  650   a ,  652   a  of the first and second grips  650 ,  652  can have a serrated or otherwise textured surface to increase the frictional contact between the gripping surfaces  650   a ,  652   a  and a gripped billet. 
     In certain embodiments, one or both of the first and second press-rams  130 ,  140  may include centering links. For example, centering links may be coupled to the link arms  622 ,  624  and/or the cylinder  626  of the first press-ram  130  for synchronizing movement of the respective arms of the press-ram  130  about the pivot  625 . This prevents, for example, operation of the cylinder  626  from extending one arm about the pivot point  625  while the other arm remains still. When the movement of the arms  622 ,  624  is synchronized about the pivot  625  using the centering links, both arms move together when gripping and releasing the billets. 
     A billet pressed through the die  160  is extruded by heat generated from friction and forces applied to the billet by an interior surface of the die  160 . Before a billet is pressed into the die  160 , the die and the centering insert  152  are pressed together to form a sealed mating interface for extrusion, and this orientation is shown in  FIG. 24 . During extrusion, the die  160  rotates while billet  702  is pressed through the die. The billet  702  is held by grippers on the centering insert  152 , which does not rotate, and thus the billet  702  does not rotate as it enters the rotating die  160  at the entrance  716  to the die. The rotation of the die  160  creates friction with the outer surface of the non-rotating billet  702  as it is pressed through the die, and the friction heats the billet  702  to a temperature sufficient for the billet material to deform. For example, a metal billet may be heated by the friction to a temperature grater than 1000° F. for deformation. The temperature requirements of different materials and different metals may vary, and billet temperatures less than 1000° F. may be suitable in some applications. In contrast to other extrusion systems, the extrusion assembly in  FIG. 24  does not require pre-heating of billets before extrusion, as the rotation of the die  160  and the friction created by contact with the non-rotating billet  702  provide energy that heats the billet to a deformable temperature. 
     While the billet  702  and centering insert  152  do not rotate during the extrusion process, the die  160  and base  700  to which the body of the die is connected are rotated by a motor-driven spindle. As the billet  702  is advanced through the centering insert  152 , it passes through the entrance  716  of the die  160  and contacts an interior surface of the die, shown in more detail in  FIGS. 25-28 . In addition to the die  160  and the inner surface details shown in  FIGS. 24-28 , other die designs or inner surface profiles may be implemented in a rotating die. For example, a die assembly for an extrusion system may be the die assembly described in copending, commonly-assigned U.S. patent application Ser. No. ______ (Attorney Docket No. 109965-0005-101), filed concurrently herewith, and entitled “EXTRUSION PRESS DIE ASSEMBLY,” the disclosure of which is hereby incorporated by reference herein in its entirety. A torsional force is applied to the outer surface of the billet  702  due to the interference contact between the rotating die  160  and the billet  702 . The grippers on the centering insert  152  resist this torsional force and prevent the billet  702  from rotating before it enters the die  160 , creating friction and producing the energy that heats the billet  702 . 
     The interior surface of the die  160  exhibits a tapered profile that narrows the interior passage through the die  160  from the entrance  716  to an exit  718 . Thus, when force is applied to the billet  702  to press the billet through the die  160 , the material of the billet  702  is extruded as the outer diameter of the material is forced to decrease to pass through the interior of the die  160  from entrance  716  to exit  718 . The dimensions of the die  160  and interaction between the interior surface of the die  160  and the billet  702  is described in more detail below with respect to  FIGS. 25-28 . 
     The cross section view of the die  160  in  FIG. 25  shows the die  160  and the centering insert  152  positioned for extrusion. While the die  160  is shown in  FIG. 25  as a single, unibody component, the die may also be composed of multiple die plates having bores and interior surfaces that form the passage and inner surface of the die, as discussed below with respect to  FIG. 26 . In this orientation, the opening  716  of the interior passage  720  in the die  160  is aligned with the centering insert  152  to receive a billet pressed through the opening  722  of the centering insert  152  and into the die  160  along the center axis  724  of the interior passage  720 . The inner surface  726  narrows the interior passage  720  from the largest diameter of the passage at the opening  716  to the smallest diameter at the exit  718 , and the narrowing of the passage  720  causes the narrowing deformation and extrusion of a billet pressed into the die  160  during operation. The extrusion requires friction energy to be produced at the interface of the inner surface  726  to heat the billet, and the energy is provided by the interaction of the rotating surface  726  and the non-rotating billet pressed into the die. 
       FIG. 26  shows the die  160  in an alternate construction of die plates that form the body of the die  160 . The die  160  in  FIG. 26  includes a steel end holder  706 , an entry plate  708 , a first intermediate plate  710 , a second intermediate plate  712 , and an exit plate  714 . Each plate includes a bore through the center of the plate, and the bores are stacked adjacent one another to form the interior passage  720  of the die  160 . The interior surfaces surrounding the bores of the plates are angled to form the profile of the inner surface  726  and narrow the interior passage  720  from the entrance  716  to the exit  718 . One potential advantage of using the plate construction is the ability to exchange individual plates when areas of the inner surface  726  begin to wear, rather than having to replace the full die  160 . To reduce the effects of wear on the plates, each plate may also be constructed from two different materials, with one material outlining the center bore of the plate and forming the inner surface  726  and a second material forming an outer perimeter of the plate. Wear-reducing materials, such as ceramic materials or steel, may be used to form the bore perimeter, or a consumable material may be used and periodically replaced. Because the centering insert  152  does not rotate when the die  160  rotates, the material surrounding the bore in steel end holder  706  and forming the front face  738  of the die  160  may be the same as or similar to the material of the centering insert  152  to reduce the effect of wear as the two materials come into contact during extrusion. 
     To reduce the cost-increasing effect of the friction wear on each of the plates in the die  160 , the plates may be designed to focus the wear on one or more plates that are replaced more often than the remaining plates. Such a design may allow the die to be operated by producing multiple copies of a single plate and a single plate for the rest of the plates in the stack. For example, in the stack shown in  FIG. 26 , the second intermediate plate  712  exhibits a non-uniform surface profile around the center bore through the plate. The inner surface of plate  712  includes a first portion  740  that is angled at a sharper angle than the other inner surfaces in the die plate stack and a second portion  742  that is angled similarly to other inner surfaces in the stack. The sharp angle of the first portion  740  creates a greater decrease in diameter at that section of the inner surface relative to the other plates in the stack, and thus creates a greater friction force and potential for wear at the first portion  740 . This wear may be decreased by positioning a corresponding angled portion of a mandrel bar within the passage  720  near the portion  740  to further reduce costs created by the need to replace the plate  712 . In certain implementations, the angle of the bore perimeter on each plate may increase from the back face of first plate to the front face of the next plate towards the exit of the die. For example, in  FIG. 26 , the angle of each inner perimeter near the front face of each plate is greater than the angle of the inner surface near the back face of the adjacent plate positioned nearer the entrance of the die. This design may be desired, for example, to focus work and stress towards the exit of the die  160 , and may result in a need to replace plates near the exit  718 , for example plates  714  and  712 , more often than plates that are nearer the entrance  716 . 
     In addition to focusing work and stress within the die  160 , mechanical and thermal properties of the billet materials may dictate the number and design of plates in a die assembly. For example, a billet material having high thermal conductivity may heat up to a deformable temperature more quickly than a material having a low thermal conductivity, and thus a shorter die with fewer plates may be used for the high conductivity material. In addition, the tapering angles of the inner surface of a die may be greater for the high conductivity material as a result of the quicker heating of the billet. In other implementations, dies of equal size having the same number of plates may be used, and the tapering angles of the dies may differ to accommodate the different thermal properties and heat the billets to a deformable temperature while still focusing work and wear to a desired area of the die surface and the surface of a mandrel tip within the die, or while spreading the work and wear over the surfaces. 
     Whether a unibody or die plate stack die is implemented, a billet pressed through the die  160  produces an extruded tube product through exit  718  of the die  160  having an outer diameter that is similar to the diameter d1, the diameter at the narrowest portion of interior passage  720 . The inner diameter of the extruded product is selected by advancing the mandrel bar  100  into the die  160  with a mandrel bar tip, such as mandrel bar tip  800 , having an end dimension selected to create the inner diameter of the tube product at the end of the mandrel bar  100 . 
       FIG. 27  shows the die  160  with the mandrel bar  100  and mandrel bar tip  800  advanced through the centering insert  152  and into the center passage  720  of the die  160 . As discussed above with respect to  FIG. 1 , gripping elements in an extrusion press system may be used to hold the mandrel bar  100  and in the orientation shown in  FIG. 27  and to resist rotation while the die  160  is rotated and a billet passes over the mandrel bar  100 . 
       FIG. 28  shows the die and mandrel bar configuration of  FIG. 27  as the billet  702  is passed through the die  160  and extruded to form tubing  728 . During extrusion, the die  160  is rotated while the mandrel bar  100  and centering insert  152  are held stationary. The billet  702  is pressed into the die  160  in the direction of arrow A and contacts the interior surface  726  of the die  160  at a first contact point  730 . The interference contact between the interior surface  726  and the billet  702  begins at the contact point  730  and generates the energy that heats the billet  702  to a plastic deformable temperature. The design of the inner surfaces and the profile of the interior die surface may differ for different applications, and in particular for the extrusion of different materials. Depending on the material properties of billets used for extrusion, for example heat transfer properties that may affect the heating of the billets during extrusion, the inner profile of die plates in a die body may be varied to focus or spread work and wear over the die plates. In addition, the die rotation speed may be varied for a particular extrusion to increase the efficiency of the die and avoid exceeding material properties of the billets. For example, a die rotation speed between about 200 rpm and about 1000 rpm may be used. In certain implementations, a slower rotation speed, for example about 300 rpm, may be desired to avoid applying a high level of torsional sheer to a billet while still heating the billet to a sufficient temperature for deformation. A faster speed, for example about 800 rpm, may be used for a material that is not adversely affected by a higher torsional sheer or that requires more energy, and thus greater friction, to heat to a deformation temperature. In other implementations, die rotation speeds in excess of 100 rpm may be desired for extrusion. 
     As the billet  702  is advanced over the middle portion  732  of the mandrel bar tip  800 , the taper of the interior surface  726  applies a compression force to the outer surface of the billet  702  that presses the billet  702  inwards towards the mandrel bar tip  800 . Because the billet  702  is in a plastic deformation state, the material in the billet extrudes in the direction of end portion  734  of mandrel bar tip  800  as the die  160  decreases the outer diameter of the billet  702  from the original diameter d2 to a final outer diameter d3. When the billet  702  reaches the middle portion  732 , the taper of the mandrel bar tip  800  towards the end portion  734  causes the inner diameter of the billet  702  to extrude and decrease from the original diameter d4 as the billet advances further over the mandrel bar tip  800 . The tapered surface of the mandrel bar tip  800  in the middle portion  732  may be positioned near a sharp angled portion of the inner surface  726 , for example near a first sharp angle portion  740 , as discussed above with respect to second intermediate plate  712 . This orientation positions the tapered middle portion  732 , and the area in which the inner diameter of a billet passing over the mandrel bar tip  800  is decreased, in the same location as the greatest compression force produced by inner surface  726  over die  160 . 
     When the extruding billet  702  reaches the end portion  734 , the inner diameter of the billet is reduced from the original diameter d4 to the final diameter d5 of the end tubing product  728 . As the billet  702  passes over the end portion  734 , the outer diameter of the billet  702  continues to decrease to the final outer diameter d3 when the extruded tubing product  728  exits the die at exit  718 . At the point of exit, the formation of the extruded product  728  is complete. Due to the friction and heating within the die  160 , the product  728  is at a heightened temperature upon exit from the die  160 , and a cooling element may be applied to prevent further deformation or increase operational safety of the extrusion press, eliminate the escape of extruded material, or maintain desired material characteristics. A bore  736  in the base plate  700  is shown in  FIG. 28  with a diameter larger than the diameter of the die exit  718 . This configuration may be preferable in order to allow cooling elements and cooling fluid to reach into the base plate  700  and contact the extruded product  728  as soon as it exits the die  160  for earlier cooling. After the product  728  exits the base plate  700  and passes through a cooling system, the extrusion process is complete, and the product  728  may be gathered for post-processing. 
       FIGS. 29 and 30  show a perspective view and a top plan view, respectively, of mandrel bar tips according to certain embodiments. Mandrel bar tip  800  includes a connector  802  that couples with a mandrel bar to form the mandrel bar tip of the mandrel bar. The mandrel bar tip  800  also includes various extrusion contact surfaces  804  that contact the inner surface of a hollow billet as the billet passes over the mandrel bar tip  800 , which is positioned within a rotating die. The mandrel bar tip  800  has a terminal contact surface  806  with a diameter D1 that sets the inner diameter of the extruded tubing. During the extrusion process, the rotating die rotates against the billet and thereby generates heat, which softens the billet to allow for plastic deformation of the billet. During operation of the extrusion press system  10 , the combination of the rotating die  160  and the mandrel bar tip  800  causes the plastic deformation zone of the billet to generally occur in the plastic deformation zone  808  of the mandrel bar tip  800 . 
     The mandrel bar tip  800  may have any suitable diameter along the extrusion surfaces  804  as well as the terminal contact surface  806 . For example, in certain embodiments, as shown by mandrel bar tip  820 , the terminal contact surface  826  may have a setting diameter D2 that is relative larger than the setting diameter D1 of mandrel bar tip  800 . In certain embodiments, each of the contact surfaces  804  of the mandrel bar tip  800  may correspond to the respective profile of the various die plates within the rotating die. 
       FIG. 31  shows a flowchart for pre-processing a billet for use in the extrusion press system  10  of  FIG. 1  according to certain embodiments. At step  1010 , the billet is cast using any suitable casting process. For example, casting a billet may include the use of a casting furnace for producing a billet of desired proportions. The cast billet may then be straightened using a roll straightening process at step  1020 , followed by machining the rolled billet at step  1030 . Machining the rolled billet includes, for example, clearing any rough edges or surfaces of the billet. At step  1040 , the machined billet may be strain hardened and sized. Strain hardening may include compressing the billet to induce strain hardening effects that allow the billet to withstand the pressing forces exerted onto the billet during the extrusion process by press-rams (e.g., press-ram platens  130 ,  140  of  FIG. 1 ), as well as the rotation and shear stresses induced by a rotating die (e.g., rotating die  160  of  FIG. 1 ). At step  1050  the billet may again be straightened using any suitable straightening device. At step  1060  the billet ends are trimmed. The trimming allows for removing imperfections or other deformations at the ends of the billet, for example, that may have been introduced during the prior processing steps or during casting. The billet may then be cleaned at step  1070  using any suitable cleaning solution such as a water soluble degreasing solution or combination of cleaning solutions. At step  1080  the inner diameter of the billet may be lubricated with any suitable lubrication fluid including graphite lubricants, petroleum-based composites or non-petroleum synthesized compounds, any other suitable lubrication fluid or combinations thereof. 
       FIG. 32  shows a flowchart for pre-processing a mandrel bar tip, such as the mandrel bar tip  800  or  820  of  FIGS. 28 and 29 , for use in the extrusion press system  10  of  FIG. 1  according to certain embodiments. At step  1110 , the mandrel bar tip may be heated using any suitable heating process. For example, the mandrel bar tip may be placed in a furnace or heated with a blowtorch until the mandrel bar tip is greater than approximately 1,000 degrees Fahrenheit. Following this heat treatment, at step  1120 , the mandrel bar tip may be quenched in lubricant and agitated to ensure a consistent deposit of the lubricant. In certain embodiments the lubricant is a graphite lubricant, although any other suitable lubricant or combinations thereof may be used. At step  1130 , the mandrel bar tip is allowed to cool after quenching. At step  1140 , any excess lubricant is removed from the mandrel bar tip. The mandrel bar tip is then be reheated at step  1150  to greater than approximately 1,000 degrees Fahrenheit and quenched in lubricant and agitated at step  1160  to ensure a consistent deposit of the lubricant. In certain embodiments, the mandrel bar tip is quenched using a second lubricant that is different than the first lubricant used in step  1120 . For example, the lubricant used in step  1120  may be a graphite lubricant and the lubricant used in step  1160  may be a petroleum-based composite or non-petroleum synthesized compound, or any other suitable lubricant that is different than the first lubricant. In certain embodiments, the lubricant used in step  1160  may be the same as that used in step  1120 . At step  1170 , the mandrel bar tip is allowed to cool after the quenching step  1160 . In certain embodiments, after completing process step  1170 , the process steps  1150 ,  1160 , and  1170  may be repeated. In such embodiments, the lubricant used in the repeated quenching step may be the same as that used in the prior step  1160 , which lubricant may be the same as or different than that used in the first quenching step  1120 . 
       FIGS. 33-36  show various flowcharts depicting processes for operating an extrusion press system, such as the extrusion press system  10  of  FIG. 1 , according to certain embodiments. Steps  1210  through  1240  depict certain exemplary steps of the billet delivery subsystem  20  of the extrusion press system. Step  1250  depicts certain exemplary steps of the extrusion subsystem  40  of the extrusion press system, and step  1260  depicts certain exemplary steps of the quenching subsystem  60  of the extrusion press system. It will be understood that the steps of the flowcharts of this disclosure are merely illustrative. Any of the steps of the flowcharts may be modified, omitted, or rearranged, two or more of the steps may be combined, or any additional steps may be added, without departing from the scope of the present disclosure. 
     Process  1200  begins at step  1210 , where one or more billets are loaded about the receiving end  100   a  of the mandrel bar near the first or upstream fluid clamp  102 . Each of the billets of the present disclosure is hollow along the length of the billet, which allows the billets to be placed onto the stationary mandrel bar  100  such that the billet moves and is transported along and about the mandrel bar  100 . In certain embodiments, the billet delivery subsystem  20  of the extrusion press system  10  may include a billet delivery table with a plurality of billets prepped for loading onto the extrusion press system  10 . The billets may be loaded automatically by an automated process or may be loaded by hand. Once loaded, the billets may be transported along the mandrel bar by a billet feed track assembly such as the track assembly  110  shown in  FIG. 2 , which includes a track  202  that intermittently moves depending on the position of particular billets relative to the fluid clamps  102 ,  104  and the mandrel grips  106 ,  108 . 
     At step  1220  the billets are transported along the mandrel bar and through the fluid clamps, which when engaged to the mandrel bar deliver cooling fluid to the mandrel bar tip. At any given time, at least one of the fluid clamps is preferably clamped to or otherwise engaged with the mandrel bar to provide a continuous or substantially continuous delivery of cooling fluid to the mandrel bar. The steps for passing one or more billets through the respective fluid clamps of the extrusion press system are shown in  FIG. 34 . For example, at step  1400 , one or more billets are transported to a first upstream fluid clamp such as fluid clamp  102  of extrusion press system  10 . The PLC system determines whether the first fluid clamp is engaged with the mandrel bar at decision block  1402 . If the first fluid clamp is engaged with the mandrel bar, the PLC system then determines whether the second fluid clamp is engaged with the mandrel bar at decision block  1404 . In certain embodiments, both fluid clamps may be engaged with the mandrel bar when billets are not being passed through the fluid clamps. If the second fluid clamp is engaged, then at step  1410  the first fluid clamp is disengaged. However, if the second fluid clamp is not engaged, at step  1404 , the PLC system determines that the second fluid clamp is transporting billets therethrough and waits for the billets to clear the second fluid clamp at step  1406 . Then at step  1408  the second fluid clamp is engaged and the process continues to step  1410  where the first fluid clamp is disengaged. After the first fluid clamp is disengaged at step  1410 , or if the first fluid clamp was already determined to be disengaged at decision block  1402 , the process continues to step  1412  where one or more billets are advanced through the first fluid clamp. While the first fluid clamp is disengaged to allow the billets to pass therethrough, the second fluid clamp is engaged to the mandrel bar and delivering cooling fluid to the mandrel bar. After a desired number of billets have been advanced through the first fluid clamp, the first fluid clamp is engaged with the mandrel bar at step  1414  and the billets are transported to the second fluid clamp at step  1420 . 
     The process  1220  with respect to the second fluid clamp is substantially similar to that performed by the PLC system for the first fluid clamp and is also shown in  FIG. 34 . At step  1420 , one or more billets are transported to a second, downstream fluid clamp such as fluid clamp  104  of extrusion press system  10 . The PLC system determines whether the second fluid clamp is engaged with the mandrel bar at decision block  1422 . If the second fluid clamp is engaged with the mandrel bar, the PLC system then determines whether the first fluid clamp is engaged with the mandrel bar at decision block  1424 . In certain embodiments, both fluid clamps may be engaged with the mandrel bar when billets are not being passed through the fluid clamps. If the first fluid clamp is engaged, then at step  1430  the second fluid clamp is disengaged. However, if the first fluid clamp is not engaged, at step  1424 , the PLC system determines that the first fluid clamp is transporting billets therethrough and waits for the billets to clear the first fluid clamp at step  1426 . Then at step  1428  the first fluid clamp is engaged and the process continues to step  1430  where the second fluid clamp is disengaged. After the second fluid clamp is disengaged at step  1430 , or if the second fluid clamp was already determined to be disengaged at decision block  1422 , the process continues to step  1432  where one or more billets are advanced through the second fluid clamp. While the second fluid clamp is disengaged to allow the billets to pass therethrough, the first fluid clamp is engaged to the mandrel bar and delivering cooling fluid to the mandrel bar. After a desired number of billets have been advanced through the second fluid clamp, the second fluid clamp is engaged with the mandrel bar at step  1434 . 
     Returning to process  1200  of  FIG. 33 , at step  1230  the billets are transported along the mandrel bar and through mandrel grips, which when engaged to the mandrel bar secure the mandrel bar in place and prevent rotation of the mandrel bar. At any given time, at least one of the mandrel grips is preferably clamped to or otherwise engaged with the mandrel bar. The steps for passing one or more billets through the respective mandrel grips of the extrusion press system are shown in  FIG. 35 . For example, at step  1500 , one or more billets are transported to a first upstream mandrel grip such as mandrel grip  106  of extrusion press system  10 . The PLC system determines whether the first mandrel grip is engaged with the mandrel bar at decision block  1502 . If the first mandrel grip is engaged with the mandrel bar, the PLC system then determines whether the second mandrel grip is engaged with the mandrel bar at decision block  1504 . In certain embodiments, both mandrel grips may be engaged with the mandrel bar when billets are not being passed through the mandrel grips. If the second mandrel grip is engaged, then at step  1510  the first mandrel grip is disengaged. However, if the second mandrel grip is not engaged, at step  1504 , the PLC system determines that the second mandrel grip is transporting billets therethrough and waits for the billets to clear the second mandrel grip at step  1506 . Then at step  1508  the second mandrel grip is engaged and the process continues to step  1510  where the first mandrel grip is disengaged. After the first mandrel grip is disengaged at step  1510 , or if the first mandrel grip was already determined to be disengaged at decision block  1502 , the process continues to step  1512  where one or more billets are advanced through the first mandrel grip. While the first mandrel grip is disengaged to allow the billets to pass therethrough, the second mandrel grip is engaged to the mandrel bar. After a desired number of billets have been advanced through the first mandrel grip, the first mandrel grip is engaged with the mandrel bar at step  1514  and the billets are transported to the second mandrel grip at step  1520 . 
     The process  1230  with respect to the second mandrel grip is substantially similar to that performed by the PLC system for the first mandrel grip and is also shown in  FIG. 35 . At step  1520 , one or more billets are transported to a second, downstream mandrel grip such as mandrel grip  108  of extrusion press system  10 . The PLC system determines whether the second mandrel grip is engaged with the mandrel bar at decision block  1522 . If the second mandrel grip is engaged with the mandrel bar, the PLC system then determines whether the first mandrel grip is engaged with the mandrel bar at decision block  1524 . In certain embodiments, both mandrel grips may be engaged with the mandrel bar when billets are not being passed through the mandrel grips. If the first mandrel grip is engaged, then at step  1530  the second mandrel grip is disengaged. However, if the first mandrel grip is not engaged, at step  1524 , the PLC system determines that the first mandrel grip is transporting billets therethrough and waits for the billets to clear the first mandrel grip at step  1526 . Then at step  1528  the first mandrel grip is engaged and the process continues to step  1530  where the second mandrel grip is disengaged. After the second mandrel grip is disengaged at step  1530 , or if the second mandrel grip was already determined to be disengaged at decision block  1522 , the process continues to step  1532  where one or more billets are advanced through the second mandrel grip. While the second mandrel grip is disengaged to allow the billets to pass therethrough, the first mandrel grip is engaged to the mandrel bar. After a desired number of billets have been advanced through the second mandrel grip, the second mandrel grip is engaged with the mandrel bar at step  1534 . 
     Returning to process  1200  of  FIG. 33 , at step  1240  the billets are gripped and then advanced using press-rams. The press-rams provide a substantially constant pushing force against the gripped billets in a direction toward the rotating die. The PLC system controls the rate at which the press-rams operate and thereby controls the entry of billets into the rotating die. The steps for grabbing and advancing billets using press-rams of the extrusion press system are shown in  FIG. 36 . For example, at step  1600  a billet is gripped by a first, upstream press-ram such as press-ram  130  of the extrusion press system of  FIG. 1 . The first press-ram is advanced toward a second, downstream press-ram at step  1602 . The PLC system determines whether the second press-ram has been retracted to a receiving position to receive the billet at decision block  1604 . If the second press-ram is not in position then at step  1606  the first press-ram continues advancing the billet until the second press-ram is in position. If the second press-ram is in position, at step  1604 , then the billet is gripped by the second press-ram at step  1608 . The first and second press-rams continue advancing the billet together at step  1610 . This may ensure that a continuous or substantially continuous pushing force is applied to the billet in the direction of the rotating die. At step  1612  the first press-ram releases the billet (while the second press-ram continues to advance the billet) and at step  1614  the first press-ram is retracted to a receiving position to thereby grab a subsequent billet. This arm-over-arm process allows the rotating die to receive a constant stream of billets at a determined feed rate. Prior to the first press-ram gripping the billet at step  1600 , the feed track assembly may continuously index the track to minimize the gaps between adjacent billets queued to be advanced by the press-rams. 
     At step  1250  the billets are extruded to form an extruded material. The press-rams of step  1240  advance billets through a centering insert (e.g., centering insert  152  of  FIG. 1 ) having a plurality of notches that prevent the billets from rotating prior to entry of the billets into the rotating die. Once a billet enters the rotating die, the die simultaneously heats the billet and sets the outer diameter of the billet as the billet is extruded to form the extruded material. The mandrel bar is positioned to place the mandrel bar tip within the rotating die. The mandrel bar tip sets the inner diameter of the extruded material. The position of the mandrel bar with respect to the die can be controlled by the PLC system. The PLC system can also control the rotation speed of the rotating die using a motor  170  coupled to the spindle  172 . 
     At step  1260  the extruded material is quenched as it exits the rotating die. This step includes rapidly cooling the extruded material by spraying cooling fluid such as water, or any other suitable cooling fluid, at a high velocity from a quench tube onto the extruded material. Despite the temperatures generated during the extrusion process of step  1250 , upon exiting the quench tube, the extruded material is relatively cool enough to the touch that it can be handled without causing burns. Furthermore, in certain embodiments, nitrogen gas, or another suitable inert gas, is delivered to the interior of the extruded material as the material exits the rotating die. For example, nitrogen gas may be delivered to the interior of extruded tubing using a cap placed on the tubing as it exits the rotating die. Injecting gaseous or liquid nitrogen into the rotating die assembly, or the interior of the extruded material itself, can minimize oxide formation by displacing the oxygen-laden air. 
     It will be understood that as one or more billets proceed through the process  1200  thus described, other billets may be advancing through the extrusion press system at any of the other steps of the process  1200 . For example, as a first set of billets, including one or more billets, is transported through the fluid clamps at step  1220 , another set of billets, including one or more billets, may be contemporaneously loaded onto the mandrel bar at step  1210  or transported through mandrel grips at step  1230  or any other step appearing in process  1200 . In this way the extrusion press system is operable to continuously feed a plurality of billets into a rotating die to extrude the billets to form an extruded material. 
       FIG. 37  shows a block diagram of a programmable logic control system for operating the extrusion press system of  FIG. 1  according to certain embodiments. As discussed above, the extrusion press system  10  comprises the functional subsystems of a billet delivery subsystem  20 , an extrusion subsystem  40 , and a cooling or quenching subsystem  60 . Operation of certain components in any one or more of these subsystems  20 ,  40 ,  60  may be controlled by the PLC system  1700 . Various operational steps of the subsystems  20 ,  40 ,  60  are described above with reference to process  1200  of  FIGS. 33-36 . 
     Instructions for carrying out the methods of this disclosure for extruding a material may be encoded on a machine-readable medium, to be executed by a suitable computer or similar device to implement the methods of the disclosure for programming or configuring PLCs or other programmable devices with a configuration as described above. For example, a personal computer may be equipped with an interface to which a PLC can be connected, and the personal computer can be used by a user to program the PLC using suitable software tools. 
       FIG. 38  shows a cross-section of a magnetic data storage medium  1800  which can be encoded with a machine executable program that can be carried out by systems such as the aforementioned personal computer, or other computers or similar devices. Medium  1800  can be a floppy diskette or hard disk, or magnetic tape, having a suitable substrate  1801 , which may be conventional, and a suitable coating  1802 , which may be conventional, on one or both sides, containing magnetic domains (not visible) whose polarity or orientation can be altered magnetically. Except in the case where it is magnetic tape, medium  1800  may also have an opening (not shown) for receiving the spindle of a disk drive or other data storage device. 
     The magnetic domains of coating  1802  of medium  1800  are polarized or oriented so as to encode, in manner which may be conventional, a machine-executable program, for execution by a programming system such as a personal computer or other computer or similar system, having a socket or peripheral attachment into which the PLC to be programmed may be inserted, to configure appropriate portions of the PLC, including its specialized processing blocks, if any, in accordance with the present disclosure. 
       FIG. 39  shows a cross-section of an optically-readable data storage medium  1810  which also can be encoded with such a machine-executable program, which can be carried out by systems such as the aforementioned personal computer, or other computers or similar devices. Medium  1810  can be a conventional compact disk read-only memory (CD-ROM) or digital video disk read-only memory (DVD-ROM) or a rewriteable medium such as a CD-R, CD-RW, DVD-R, DVD-RW, DVD+R, DVD+RW, or DVD-RAM or a magneto-optical disk which is optically readable and magneto-optically rewriteable. Medium  1810  preferably has a suitable substrate  1811 , which may be conventional, and a suitable coating  1812 , which may be conventional, usually on one or both sides of substrate  1811 . 
     In the case of a CD-based or DVD-based medium, as is well known, coating  1812  is reflective and is impressed with a plurality of pits  1813 , arranged on one or more layers, to encode the machine-executable program. The arrangement of pits is read by reflecting laser light off the surface of coating  1812 . A protective coating  1814 , which preferably is substantially transparent, is provided on top of coating  1812 . 
     In the case of magneto-optical disk, as is well known, coating  1812  has no pits  1813 , but has a plurality of magnetic domains whose polarity or orientation can be changed magnetically when heated above a certain temperature, as by a laser (not shown). The orientation of the domains can be read by measuring the polarization of laser light reflected from coating  1812 . The arrangement of the domains encodes the program as described above. 
     A PLC  1700  programmed according to the present disclosure may be used in many kinds of electronic devices. One possible use is in a data processing system  1900  shown in  FIG. 40 . Data processing system  1900  may include one or more of the following components: a processor  1901 ; memory  1902 ; I/O circuitry  1903 ; and peripheral devices  1904 . These components are coupled together by a system bus  1905  and are populated on a circuit board  1906  which is contained in an end-user system  1907 , which may include a terminal unit  1407  for operating an extrusion press system. 
     System  1900  can be used in a wide variety of applications, including as instrumentation for an extrusion press system, or any other suitable application where the advantage of using programmable or reprogrammable logic is desirable. PLC  1700  can be used to perform a variety of different logic functions. For example, PLC  1700  can be configured as a processor or controller that works in cooperation with processor  1901 . PLC  1700  may also be used as an arbiter for arbitrating access to a shared resources in system  1900 . In yet another embodiment, PLC  1700  can be configured as an interface between processor  1901  and one of the other components in system  1900 . It should be noted that system  1900  is only exemplary. For example, in certain embodiment a user terminal may be provided near the extrusion press system. In other embodiments, a networked arrangement may be provided that may allow the user terminal to be remote from the extrusion press system. 
       FIG. 41  is a block diagram of a computing device  2200  used for carrying out at least some of the extrusion press logic processing described above according to certain embodiments. The computing device  2200  comprises a PLC system such as PLC  1700 , and at least one network interface unit  2204 , an input/output controller  2206 , system memory  2208 , and one or more data storage devices  2214 . The system memory  2208  includes at least one random access memory (RAM)  2210  and at least one read-only memory (ROM)  2212 . All of these elements are in communication with a central processing unit (CPU)  2202  to facilitate the operation of the computing device  2200 . The computing device  2200  may be configured in many different ways. For example, the computing device  2200  may be a conventional standalone computer or alternatively, the functions of computing device  2200  may be distributed across multiple computer systems and architectures. The computing device  2200  may be configured to perform some or all of the extrusion press logic processing described above, or these functions may be distributed across multiple computer systems and architectures. In the embodiment shown in  FIG. 23 , the computing device  2200  is linked, via communications network  2150  or local area network  2124  to third parties  2224  through the communications network  2150 . 
     The computing device  2200  may be configured in a distributed architecture, where databases and processors are housed in separate units or locations. The computing device  2200  may also be implemented as a server located either on site at the extrusion press facility or external to the extrusion press facility. Some such units perform primary processing functions and contain at a minimum a general controller or a processor  2202  and a system memory  2208 . In such an embodiment, each of these units is attached via the network interface unit  2204  to a communications hub or port (not shown) that serves as a primary communication link with other servers, client or user computers and other related devices. The communications hub or port may have minimal processing capability itself, serving primarily as a communications router. A variety of communications protocols may be part of the system, including, but not limited to: Ethernet, SAP, SAS™, ATP, BLUETOOTH™, GSM and TCP/IP. 
     The CPU  2202  comprises a processor, such as one or more conventional microprocessors, and one or more supplementary co-processors, such as math co-processors, for offloading workload from the CPU  2202 . The CPU  2202  is in communication with the network interface unit  2204  and the input/output controller  2206 , through which the CPU  2202  communicates with other devices such as other servers, user terminals, or devices. The network interface unit  2204  and/or the input/output controller  2206  may include multiple communication channels for simultaneous communication with, for example, other processors, servers or client terminals. Devices in communication with each other need not be continually transmitting to each other. On the contrary, such devices need only transmit to each other as necessary, may actually refrain from exchanging data most of the time, and may require several steps to be performed to establish a communication link between the devices. 
     The CPU  2202  is also in communication with the data storage device  2214 . The data storage device  2214  may comprise an appropriate combination of magnetic, optical and/or semiconductor memory, and may include, for example, RAM, ROM, flash drive, an optical disc such as a compact disc and/or a hard disk or drive. The CPU  2202  and the data storage device  2214  each may be, for example, located entirely within a single computer or other computing device; or connected to each other by a communication medium, such as a USB port, serial port cable, a coaxial cable, an Ethernet type cable, a telephone line, a radio frequency transceiver or other similar wireless or wired medium or combination of the foregoing. For example, the CPU  2202  may be connected to the data storage device  2214  via the network interface unit  2204 . 
     The CPU  2202  may be configured to perform one or more particular processing functions. For example, the computing device  2200  may be configured, via the PLC, for controlling at least in part one or more aspects of the billet delivery subsystem  20 , extrusion subsystem  40 , and quenching subsystem  60 . 
     The data storage device  2214  may store, for example, (i) an operating system  2216  for the computing device  2200 ; (ii) one or more applications  2218  (e.g., computer program code and/or a computer program product) adapted to direct the CPU  2202  in accordance with the present invention, and particularly in accordance with the processes described in detail with regard to the CPU  2202 ; and/or (iii) database(s)  2220  adapted to store information that may be utilized to store information required by the program. 
     The operating system  2216  and/or applications  2218  may be stored, for example, in a compressed, an uncompiled and/or an encrypted format, and may include computer program code. The instructions of the program may be read into a main memory of the processor from a computer-readable medium other than the data storage device  2214 , such as from the ROM  2212  or from the RAM  2210 . While execution of sequences of instructions in the program causes the CPU  2202  to perform the process steps described herein, hard-wired circuitry may be used in place of, or in combination with, software instructions for implementation of the processes of the present invention. 
     The term “computer-readable medium” as used herein refers to any non-transitory medium that provides or participates in providing instructions to the processor of the computing device (or any other processor of a device described herein) for execution. Such a medium may take many forms, including but not limited to, non-volatile media and volatile media. Non-volatile media include, for example, optical, magnetic, or opto-magnetic disks, or integrated circuit memory, such as flash memory. Volatile media include dynamic random access memory (DRAM), which typically constitutes the main memory. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM or EEPROM (electronically erasable programmable read-only memory), a FLASH-EEPROM, any other memory chip or cartridge, or any other non-transitory medium from which a computer can read. 
     Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to the CPU  2202  (or any other processor of a device described herein) for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer (not shown). The remote computer can load the instructions into its dynamic memory and send the instructions over an Ethernet connection, cable line, or even telephone line using a modem. A communications device local to a computing device (e.g., a server) can receive the data on the respective communications line and place the data on a system bus for the processor. The system bus carries the data to main memory, from which the processor retrieves and executes the instructions. The instructions received by main memory may optionally be stored in memory either before or after execution by the processor. In addition, instructions may be received via a communication port as electrical, electromagnetic or optical signals, which are exemplary forms of wireless communications or data streams that carry various types of information. 
     The foregoing is merely illustrative of the principles of the disclosure, and the systems, devices, and methods can be practiced by other than the described embodiments, which are presented for purposes of illustration and not of limitation. It is to be understood that the systems, devices, and methods disclosed herein, while shown for use in extrusion press systems, may be applied to systems, devices, and methods to be used in other manufacturing processes including, but not limited to, cast-and-roll and heat treatment processes. Furthermore, the disclosure could be implemented as a post-processing step of another manufacturing process, including other extrusion processes, or could be implemented concurrently with another manufacturing process. 
     Variations and modifications will occur to those of skill in the art after reviewing this disclosure. The disclosed features may be implemented, in any combination and subcombination (including multiple dependent combinations and subcombinations), with one or more other features described herein. The various features described or illustrated above, including any components thereof, may be combined or integrated in other systems. Moreover, certain features may be omitted or not implemented. 
     Examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the scope of the information disclosed herein. All references cited herein are incorporated by reference in their entirety and made part of this application.