Patent Publication Number: US-10307807-B2

Title: Extrusion press

Description:
TECHNICAL FIELD 
     The present invention relates to an extrusion press, more particularly relates to an extrusion press device extruding aluminum or aluminum alloy or other metal material through a die, especially an electric powered extrusion press using electric power to drive the extrusion operation. 
     BACKGROUND ART 
     An extrusion press is used for extruding aluminum frame parts or other metal products. In past extrusion presses, the starting material, that is, the billet, was loaded into a fixed container. This was then pushed by an extrusion stem driven by a ram cylinder (hydraulic cylinder). The billet was made to pass through a die positioned to the outlet of the container to thereby be extruded to a predetermined cross-sectional shape. Specifically, the billet loaded in such a molding machine is supplied by a billet loader. The billet loader grips a billet sent from a billet carrier arranged at the side of the molding machine and conveys it to the billet loading opening of the container. It loads the transferred billet into the container pushed by the extrusion stem in the state with the billet and loading opening centered. After that, the billet is extruded under pressure whereby it is formed into the shape of the final product. 
     Among the products extruded by an extrusion press, there are aluminum frame members and other long products. In the case of long products, the extrusion stem pushes the billet for a long period of time. For this reason, a hydraulic cylinder able to operate with a long stroke at a high pressure has been used for the ram cylinder for pushing the extrusion stem. However, such a conventional extrusion press device has been driven by hydraulic pressure, so there were challenges such as protection of the environment (against noise, oil leakage, etc.), reducing energy consumption (lowering running costs), etc. To meet these challenges, realization of a press using the electric powered drive system employed in plastic injection molding machines or die cast machines for die casting aluminum alloys has been demanded. In the case of an electric powered drive system, in general, it is necessary to convert the rotary motion of a first stage drive device comprised of an electric motor to linear motion or back and forth linear motion. 
     In conventional hydraulic cylinder devices, the larger output capacity sought from an extrusion press, for example, 9800 kN (that is, 1000 tf) or more, can be continuously output. However, no mechanism has yet been realized for converting rotary motion to linear motion taking the place of conventional hydraulic cylinder devices. Therefore, electric powered drive systems have not been applied to extrusion presses. 
     A conventional extrusion press is a machine using a motor and pump to drive a plurality of hydraulic devices to produce an extruded product. During the extrusion process of course and also processes other than the extrusion process, for example, even in the discard cutoff step, billet loading step, etc. as well, the same pump and motor are used as sources of drive power. Here, the extrusion-use pump and motor utilizing hydraulic devices and an auxiliary pump and motor have to be kept constantly operating in an idling mode even when not directly required for operation of the extrusion press device. Power loss therefore occurs. 
     Further, when a machine user uses a machine for a long time, maintenance and inspection are required for continued operation. Comparing when the drive source is a hydraulic source and when it is only an electric motor, it is believed that the time required for maintenance would be overwhelmingly longer in the case of a hydraulic source. The reason is that when using hydraulic equipment for many years, the hydraulic fluid degrades, the valves become worn, fluid leaks from the pipe joints, and other trouble occurs at the pumps, valves, manifolds, piping, and numerous other parts. Much time is required for identifying the causes of the trouble and taking measures against them. In this way, there were the following defects in conventional hydraulic drive type extrusion presses: 
     (1) Since hydraulic fluid was used as the medium for the drive force, realization of the speed and precision of position crucial to mechanical operation was difficult. 
     (2) The energy loss was relatively great and cooling water was required for preventing a rise in fluid temperature, so the running costs swelled. 
     (3) A hydraulic circuit has many high pressure components and generates high noise at the time of operation. 
     (4) Since a large amount of hydraulic fluid is used, leakage of the hydraulic fluid causes problems in maintenance, the environment, and costs while disposal of the hydraulic fluid causes problems in the environment and costs. 
     To deal with these problems, PLT 1 proposes a completely electric powered type extrusion press. In this prior art, the extrusion drive device is provided with four electric powered extrusion-use main motors for driving a single extrusion stem. Four wire drums are driven to rotate by the respective electric powered extrusion-use main motors so as to make the crosshead to which the extrusion stem is fastened move back and forth. Each wire drum has first ends of 10 single strand wires fastened to it. The other ends are fastened to a crosshead fastening member. Each wire is strung straight without anything interposed between the wire drum and the crosshead connecting member. The four wire drums are made to simultaneously rotate to wind up the wires in a simple manner and make the crosshead move back and forth. In this prior art, rotary motion is converted to linear motion by the plurality of wires being wound up on the wire drums, but the wires are just linearly connected, so the output is insufficient. For this reason, four electric powered extrusion-use main motors had to be used. Further, 10 wires had to be attached between each wire drum and crosshead connecting member by a uniform tension (unless uniform tension, the load will be applied to a specific wire and cause breakage or other issues). Installation and adjustment were extremely troublesome. 
     CITATION LIST 
     Patent Literature 
     PLT 1: WO2011/074106A 
     SUMMARY OF INVENTION 
     Technical Problem 
     As explained above, in a conventional extrusion press, there were the problems of poor precision and energy efficiency, a detrimental effect on the environment, troublesome adjustment, and other problems, so improvement of an electric powered extrusion press for solving these problems has been sought. The present invention was made in consideration of the above-mentioned situation and has as its object to provide an electric powered extrusion press which is excellent in precision, is improved in energy efficiency, has no detrimental effect on the environment, is improved in maintenance ability and operating ability, and reduces noise. 
     The present invention has as its object the provision of a compact extrusion press powered electrically. 
     Solution to Problem 
     An electric powered extrusion press pushing an extrusion stem by extrusion force generated by an electric powered drive device so that pressure is applied to a billet and a predetermined product is extruded through a die, wherein the electric powered drive device is provided with one or more freely rotatable wire drums, an electric powered extrusion-use main motor makes the wire drums rotate to wind up wires and thereby give thrust to movable pulleys in the extrusion direction so that a crosshead and extrusion stem are driven to advance through an extrusion movement part provided with the movable pulleys, is provided. 
     Preferably, a wire is wound around each wire drum from the two ends. The two ends of the wire are fastened by connection to the wire drum through fixed pulleys and movable pulleys. 
     Alternatively, a wire is wound around each drum from one end part. One end part of the wire is fastened to the wire drum, while the other end part is fastened to a fastening location. 
     Preferably, one or more electric powered drive devices are arranged in the extrusion direction in series and are connected through the components for transmitting the extrusion force and components for receiving the reaction force of the extrusion force to enable all sorts of capabilities of extrusion force to be handled. 
     The combined pulleys are given the function of a speed reducer. 
     A wire slack preventing device is attached. 
     A tail end electric powered drive device is provided with a high speed movement mechanism enabling the crosshead to advance and retract at a high speed. 
     Among the components of the electric powered drive devices, the components for transmitting the extrusion force and the components for receiving the reaction force of the extrusion force comprise stronger parts endurable against the loads acting on the electric powered drive devices, the further away from the main crosshead of the extrusion press. 
     Advantageous Effect of Invention 
     The present invention does not use any hydraulic devices for its main parts but uses an electrically powered drive system, so the maintenance ability can be improved, energy can be saved, and the operating efficiency and performance of the machine become excellent. Further, the source of noise changes from the main pumps to the main motors, so the noise can be reduced. Therefore, the work environment is improved, the machine becomes good in operability, and a greater improvement to the productivity of the extruded product is realized. 
     Further, since the load transfer medium is a single through wire, even if connected to a plurality of pulleys, it passes over the pulleys by the same tension so is automatically adjusted in tension. There is no need for the troublesome adjustment of tension like in the prior art. On top of this, since a plurality of pulleys are connected in parallel, the assembly acts as a speed reducer, it becomes possible to lower the speed reduction ratio of the speed reducer used from the main motor to the wire drum to boost the power, and the electric powered drive device as a whole can be configured from more compact drive parts. 
     Furthermore, by arranging a plurality of electric powered drive devices in the extrusion direction in series and connecting the movement parts of the crosshead (later explained extrusion movement parts  15 ) in series, even if a larger extrusion ability is required, this can be realized without the need to make the individual drive parts larger. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic side view showing an extrusion press of a first embodiment of the present invention. 
         FIG. 2  is a plan view of  FIG. 1  seen from above. 
         FIG. 3  is a partial enlarged view of  FIG. 1 . 
         FIG. 4  is a cross-sectional view seen from A-A of  FIG. 1 . 
         FIG. 5  is a side view seen from B-B of  FIG. 1  and a rear view seen from the rear. 
         FIG. 6A  is a schematic view of the wire layout in the case of fastening the two ends of the wire to a wire drum.  FIG. 6B  is a schematic view of the wire layout viewing  FIG. 6A  from the same direction as  FIG. 1 . 
         FIG. 7  is a schematic view of the wire layout when fastening just one end of the wire to the wire drum. 
         FIG. 8  is a partial enlarged view of a stem slide mechanism of  FIG. 1 . 
         FIG. 9  is a schematic side view showing a second embodiment in the case of provision of four extrusion drive devices of the present invention. 
         FIG. 10  is a plan view of  FIG. 9  seen from above. 
         FIG. 11  is a rear view of  FIG. 9  seen from the rear. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Below, an extrusion press of embodiments of the present invention will be explained in detail based on the drawings. 
     First Embodiment 
       FIGS. 1 to 8  schematically show a first embodiment of an extrusion press according to the present invention (stem slide type extrusion press).  FIG. 1  is a side view showing the schematic configuration of the extrusion press of the first embodiment.  FIG. 2  is a plan view of the device of  FIG. 1  seen from above.  FIG. 3  is a partial enlarged view of  FIG. 1 .  FIG. 4  is a cross-sectional view seen from A-A of  FIG. 1 .  FIG. 5  is a side view seen from B-B of  FIG. 1 .  FIG. 6  is a rear view seen from the rear. The extrusion press of the present invention is provided with an electric powered extrusion drive device converting rotary motion to linear motion. The extrusion press of the present invention pushes an extrusion stem by the extrusion force from the electric powered extrusion drive device. In general, it pushes an approximately 400 to 500° C. billet and extrudes it through a die to a product of a predetermined shape. 
     First, referring to  FIGS. 1 and 2 , an extrusion press  10  of the present embodiment is provided with an end platen  1  positioned at a front end part and a fixed platen  2  positioned near a center of the extrusion press. The billet  8  is extruded through a die  20  built into the end platen  1  to be formed into a predetermined shape. Here, the end platen  1  side is designated as the “front” and the fixed platen  2  side is designated as the “rear”. In the present embodiment, the end platen  1  and the fixed platen  2 , as shown in  FIGS. 1 and 4 , are connected by the four tie rods  4  arranged at the four corners. Between the end platen  1  and the fixed platen  2  and near the end platen  1 , a container holder  18  is arranged. The container holder  18  supports a container  3  into which a billet  8  is loaded. At the fixed platen  2  side, a crosshead  7  is slidably supported by the four tie rods  4 . The four tie rods  4  pass through the crosshead  7  at the four corners. The die  20  is arranged between the end platen  1  and container  3 . At the end platen  1 , a container operating device  14  is provided. The container  3  is driven by a container operating device  14  provided with a container operating motor  17  through a ball screw  46 ′ and ball screw nut  47 ′ to move in the front and rear directions. 
     At the center of the container side of the crosshead  7 , an extrusion stem  13  is attached. The extrusion press  10  of the present embodiment uses a stem slide system. The “stem slide system” is a system enabling the extrusion stem  13  to move up and down by the stem slider  11  so as to enable loading of the billet by the billet loader.  FIG. 8  is a detailed enlarged view of a stem slide type mechanism. A stem slide motor  12  is installed at the crosshead  7  and turns a ball screw  64  through a wheel  61 , timing belt  62 , and wheel  63 . A ball screw nut  65  is fastened to a stem slide  9  supporting the extrusion stem  13 . By rotation of the ball screw  64 , the extrusion stem  13  can move up and down through the ball screw nut  65 . In the present embodiment, the extrusion stem  13  is driven by the stem slide motor  12 , but the stem slide motor  12  is preferably a variable speed inverter motor or AC servo motor. 
     As shown in  FIGS. 1 and 3 , at the fixed platen side of the crosshead  7 , a hollow cylindrical (may also be polygonal shape or solid shape or other shape) extrusion movement part  15  is connected. The extrusion movement part  15  passes through a center hole of the fixed platen  2  and is supported by the fixed platen  2  to be able to slide. At the end part of the extrusion movement part  15  in the opposite direction to the fixed platen  2 , as shown in  FIGS. 1 and 3 , a movable pulley  41  is attached. The extrusion movement part  15  is fastened at the left side end part of  FIG. 3  to the crosshead  7  and is fastened at the right side end part to a span  24 . At the span  24 , a shaft of the movable pulley  41  is attached through a bearing. Movement of the extrusion movement part  15  and the span  24  in the extrusion direction is guided by the center hole of the fixed platen  2  and the four support columns  49  shown in  FIG. 4 . 
     An embodiment with a different method of stringing a wire  32  of  FIGS. 6A and 6B  and  FIG. 7  will be explained. The method of stringing the wire over the pulleys is not limited to this. It is sufficient that movable pulleys be used so that the power is boosted.  FIG. 6A  shows an embodiment in the case where the two ends of one wire  32  are fastened to a wire drum  31 . The wire  32  fed out from the wire drum  31  is alternately wrapped around a movable pulley  41  and a fixed pulley  40  and further a movable pulley  41  and finally passes through two balance pulleys  42 ,  42  and is closed (joined together). In the case of  FIG. 6A , there are two sets of four movable pulleys  41  and three fixed pulleys. Here, the balance pulleys  42  are used for maintaining the balance and for balancing. The shaft of each movable pulley  41  is supported by a bearing, bush, or slide bearing or other such rotation support part. The shaft of the movable pulley  41  is fastened through the rotation support part to the extrusion movement part  15 . The extrusion movement part  15  is designed to move by exactly the distance of movement of the movable pulleys  41 . If the wire drum  31  rotates in this way, the movable pulleys  41  move in the extrusion direction corresponding to the speed by which the wire  32  is wound up and the extrusion movement part  15  moves. Note that the force for making the extrusion movement part  15  move becomes a multiple of the number of movable pulleys  41 . This is well known as the mechanical advantage of a pulley system (rope and pulley system) using a movable pulley and fixed pulley. 
       FIG. 7  shows the case of using a single wire for making the extrusion movement part  15  move wherein one end of the single wire is fastened to the wire drum  31  and the other end is fastened to the fastening location  44 . Wire with one end fastened to the wire drum  31  is strung over these pulleys in the order of the movable pulleys  41  and fixed pulleys  40  and a movable pulley  41  and finally is fastened to a movable pulley  41 , fixed pulley  40 , or fastening location  44  of the fixed platen etc. In the case of  FIG. 7 , there are eight movable pulleys  41  and seven fixed pulleys  40 . In the case of the embodiment of  FIG. 7 , no balance pulleys  42  are used. The fastening location  44  corresponds to a balance pulley  42 . 
     Below,  FIGS. 1 and 2  explain in detail an embodiment of the extrusion press  10  of the present invention.  FIG. 2  is a plan view of the device of  FIG. 1  seen from above. In the present embodiment, as shown in  FIG. 2 , one each extrusion drive device  52  is arranged at the left and right of the extrusion press. At the extrusion drive devices  52 , freely rotatable wire drums  31  are arranged above the fixed platen  2 . Specifically, the extrusion press  10  is fastened on a machine base  6 . Above the fixed platen  2 , there is a base  30 . On the base  30 , the extrusion drive devices  52  (see  FIG. 2 ) are fastened. At the extrusion drive devices  52 , wire drums  31  are mounted. The wire drums  31  are driven through speed reducers  35  and clutch couplings  37  by electric powered extrusion-use main motors  36  (AC servo motors are preferable). Reference numeral  38  is a coupling. There is an extrusion stem  13  arranged coaxially with the container  3 . The extrusion stem  13  is attached to the crosshead  7 . Furthermore, at the opposite side of the crosshead  7  from the extrusion stem  13 , an extrusion movement part  15  is fastened. At the extrusion movement part  15 , movable pulleys  41  are attached through bearings, slide bearings, etc. The movable pulleys  41  are attached to the rear end part of the extrusion movement part  15  and move together with the extrusion movement part  15 . Further, at part of the fixed platen  2 , fixed pulleys  40  and balance pulleys  42  are fastened. The wire drums  31 , movable pulleys  41 , fixed pulleys  40 , and balance pulleys  42  are connected by single wires. The electric powered extrusion-use main motors  36  make the wire drums  31  rotate, whereby the extrusion movement part  15  moves. Due to this, the extrusion stem  13  is designed to move back and forth in the extrusion direction. 
     As shown in  FIG. 2 , on the fixed platen  2  of the extrusion press  10 , one each extrusion drive device  52  is carried at the left and right. Each extrusion drive device  52  is provided with one wire drum  31 . Each wire drum  31  is driven through a speed reducer  35  and clutch coupling  37  by an electric powered extrusion-use main motor  36  (AC servo motor is preferable). 
     As shown in  FIG. 6A , a wire drum  31  has the two end parts of a wire  32  fastened to and wound around it. The wire  32  starting from each of the end parts is first wound around a movable pulley  41  then is wound around a fixed pulley  40 . It is then further alternately wound around the movable pulleys  41  and the fixed pulleys  40 . The wire  32  starting from the end parts is wound around the four movable pulleys  41 . After that, the wire is wound around the balance pulleys  42 ,  42 , joined, and closed. In this way, a single through wire is wound around a plurality of pulleys, so it passes through the pulleys by the same tension and is automatically adjusted in tension, so there is no need for the troublesome adjustment of tension like in the prior art. The movable pulleys  41 , in the case of  FIG. 6A , are bundled into groups of four at the left and right. They are connected at the two sides of the extrusion movement part  15  and convert rotary motion to linear motion. The connecting parts may, for example, be bearings or slide bearings or other such parts. In the case of  FIG. 5 , the pulleys are bundled into groups of six at the left and right. The shafts of the fixed pulleys  40  and the balance pulleys  42  are attached to the fixed platen  2  through bearings so as to be able to freely rotate. Each wire drum  31  winds up the wire  32  to move the movable pulleys  41  and extrusion movement part  15  in the extrusion direction. Due to this, the extrusion stem  13  is made to advance through the crosshead  7 . One or more wire drums  31  may be mounted corresponding to the capacity of the extrusion press  10 . Each wire drum  31  is driven through a speed reducer  35  and clutch coupling  37  by an electric powered extrusion-use main motor  36  (AC servo motor is preferable). In each extrusion drive device  52 , the wire drum  31  is connected to an output shaft of the speed reducer  35 . The input shaft of the speed reducer  35  is connected through the clutch coupling  37  to the output shaft of the extrusion-use main motor  36 . The speed reducer  35  and the clutch coupling  37  may also be other machine elements for transmitting power. 
     When using a wire drum  31  to make the extrusion stem  13  move, the speed is greatly reduced by the speed reducer  35 , so is low. However, it is preferable to move the drum at a high speed to shorten the operating time until making the extrusion stem  13  contact the billet  8 . Furthermore, a wire drum  31  is used for moving the extrusion stem  13  only in the extrusion (advancing) direction, so movement of the extrusion stem  13  in the pullback (retracting) direction is also necessary. For this reason, a crosshead high speed movement mechanism  45  is provided. In the present embodiment, the crosshead high speed movement mechanism  45  is provided with a crosshead high speed movement motor  43  (AC servo motor or inverter motor is preferable), a ball screw nut  47 , a ball screw  46 , etc.  FIG. 3  shows details of the crosshead high speed movement mechanism  45 . The rotation of a pulley  21  attached to the crosshead high speed movement motor  43  is transmitted through a timing belt  22  to a pulley  23 . The pulley  23  is fastened to the right end part of the ball screw of  FIG. 3  whereby the ball screw  46  is made to rotate. The rotation of the ball screw  46  makes the span  24  set fastened at the right end part of  FIG. 3  of the extrusion movement part  15  move at a high speed in the extrusion direction through a ball screw nut  47  fastened to the span  24 . In the present embodiment, the mechanism for converting rotary motion of the crosshead high speed movement motor  43  to linear motion is comprised of the ball screw  46  and ball screw nut  47 , but it may also be a known mechanism of a rack and pinion etc. In the present embodiment, the crosshead high speed movement mechanism  45 , as shown in  FIGS. 4 and 5 , is supported fastened to the fixed platen  2  through four support columns  49 , but it may be supported by another support method as well. Furthermore, when using the crosshead high speed movement mechanism  45  to move the extrusion stem  13  at a high speed, the wire ends up slackening, so to prevent the wire from becoming slack at this time, as shown in  FIG. 1 , each wire drum  31  is provided with a wire windup device  50 . A wire windup motor  51  of the wire windup device  50  is connected to the wire drum  31  through a chain etc. The wire windup motor  51  is made to operate simultaneously with the operation of the crosshead high speed movement motor  43  to drive the wire drum  31  so that the wire does not become slack. The wire windup device  50  forms a wire slack preventing device. 
     The extrusion press  10  is provided with a machine base  6 . On the machine base  6 , an end platen  1 , fixed platen  2 , wire drums  31 , speed reducers  35 , extrusion-use main motors  36 , etc. are installed and fastened. Looking at the center axis of the extrusion press  10 , as shown in  FIG. 2 , the extrusion press  10  is configured substantially symmetric to the left and right. In the extrusion stage, the end platen  1 , fixed platen  2 , container  3 , extrusion stem  13 , crosshead  7 , and extrusion movement part  15  are arranged so that their center axes match the center axis of the extrusion press. 
     Furthermore, the extrusion press  10  is provided with a billet loader (not shown), shear device  27 , die slide device (not shown) for making the die move, etc. The billet loader supplies the billet  8  between the container  3  and extrusion stem  13 . The shear device  27  is placed on the end platen  1  and cuts off the discard of the unnecessary part of the end part of the product after extrusion of the billet  8 . 
     The application and object of the die slide device are (1) to make the die  20  move in the horizontal direction perpendicular to the center axis of the extrusion press and (2) at the time of end of extrusion, cut off the product extruded to the rear of the end platen from the die  20 . As the actual operation of (2), a platen saw (not shown) set in the space at the front equipment side in front of the end platen  1  is used to cut the product at the time of end of the extrusion operation. After that, the product is sent to a front table by a conveyor device at the space at the front equipment side. At this time, the remaining material of the product as shaped by the die remains inside the end platen  1 . This remaining material is cut off from the die by making the die  20  move to the die changing position by the die slide device at the time of changing the die  20 . That is, the remaining material of the product is cut off from the die stack at the front surface of the end platen and the cutting surface of the front surface of the die  20 . The remaining material in the die stack is cut off from the die  20  by another cutting device or manual operation after unloading the die stack from the machine. 
     The container  3  is made to move straight back and forth (advance and retract) by a container operating device  14  comprised of a container operating motor  17 , ball screw  46 ′, and ball screw nut  47 ′. The rotary motion of the container operating motor  17  is converted to linear motion by the ball screw  46 ′ and ball screw nut  47 ′ (similar to  FIG. 8 ). The container operating motor  17  is preferably an inverter motor or AC servo motor. In the case of the front loading type, the container operating device  14  is provided at the fixed platen  2 . This is due to the fact that in the case of the front loading type, the stroke of movement of the container is large. The shear device  27  is powered by an electric motor and converts rotary motion to linear motion through a chain or other windup drive mechanism. The die slide device is powered by an electric motor and converts rotary motion to linear motion through a power transmission mechanism comprised of a ball screw and ball screw nut. The stem slider  11  is also powered by an electric motor and uses a mechanism for converting rotary motion to linear motion through a power transmission mechanism comprised of a ball screw and ball nut. The die changer for changing the die and billet loader are also powered by an electric motor. Due to these configurations, the extrusion press can be made fully electric powered. In all power transmission mechanisms powered using electric motors and comprised of a ball screw and ball nut, a timing belt and pulleys were used, but a chain and sprockets can also be used. The same is true in the second embodiment explained below. 
     Second Embodiment 
     The second embodiment will be explained using  FIGS. 9 to 11 . In the second embodiment, the case of four extrusion drive devices will be explained. The two extrusion drive devices of the electric powered extrusion press are further provided with two extrusion drive devices (total four) so two devices each are arranged in series and connected. The fixed platen  2  and fixed platen  21  are connected by the four connecting rods  58  shown in  FIG. 11 . In  FIG. 11 , there are four connecting rods  58 , but the number may also be greater. Further, the extrusion movement part  15  is fastened at one end part (left side in  FIG. 9 ) at the crosshead  7  and at the other end part (right side in  FIG. 9 ) at the movable pulleys  48  of the extrusion drive devices  53 . The movable pulleys  41  of the extrusion drive devices  52  are connected in the middle of the extrusion movement part  15 . Further, in the extrusion press of the present embodiment, the extrusion drive devices  52 ,  53  can make the extrusion movement part  15  move back and forth. The extrusion movement part  15  is a hollow cylindrical shape (may also be polygonal shape or solid shape or other shape) and may also be a certain thickness. Preferably, the parts of the extrusion drive devices  52  are thick and the parts of the extrusion drive devices  53  may be narrowed somewhat. This is because double the extrusion force is taken at the parts of the extrusion drive devices  52 . Further, the same can be said for the components transmitting the extrusion force and the components receiving the reaction force of the extrusion force. 
     Separate from the crosshead high speed movement mechanism  45  and the extrusion drive devices  53 , wire windup devices  50  may also be provided. The wire windup devices  50  can make the wire drums  31  rotate forward and reverse to wind up or feed out wires  32  on or from the wire drums  31 . The wire windup devices  50  are provided at the wire drums  31  of the extrusion drive devices  52 ,  53 . At the next stages (1) and (2), a crosshead high speed movement mechanism is used. 
     (1) Stage at the time of start of the extrusion process from when a billet  8  advances until it abuts against the die  20  where no extrusion load acts on the extrusion stem  13 . 
     (2) Stage at the time of retraction of the extrusion stem  13  when the crosshead high speed movement mechanism  45  drives the extrusion stem to retract at a high speed through the extrusion movement part  15 . At this time, it is necessary to operate the wire windup devices  50  to wind up and feed out the wires  32 . 
     In the second embodiment, as drive units, extrusion drive devices are mechanically connected. By controlling the speeds of the motors of the extrusion drive devices to synchronize them, it is possible to transmit the composite pushing load of the plurality of extrusion drive devices to the extrusion stem. 
     In the above case, the case where two each extrusion drive devices  52 ,  53  were provided in series, that is, a total of four, was explained, but in the case where further greater numbers of extrusion drive devices  52 ,  53  are provided in series, the configuration is the same. 
     The stem slide type extrusion press falls under the category of rear loading types of short stroke types. The extrusion press  10  of the present embodiment was explained with reference to the example of a stem slide type of extrusion press, but the fact that the present invention can also be applied to a short stroke type front loading type or a conventional type not provided with a stem slider, should be easily understandable to a person skilled in the art. Further, the configuration of the present invention, as explained above, was explained with reference to the example of a direct type extrusion press, but person skilled in the art should be able to easily understand that the present invention can be similarly applied to an indirect type extrusion press. 
     As explained above, the present invention has the following effects. The present invention does not use any hydraulic devices for its main parts but uses an electrically powered drive system, so the maintenance ability can be improved, energy can be saved, and the operating efficiency and performance of the machine become excellent. Further, the source of noise changes from the main pumps to the main motors, so the noise can be reduced. Therefore, the work environment is improved, the machine becomes good in operability, and a greater improvement to the productivity of the extruded product is realized. 
     Further, since the load transfer medium is a single through wire, even if connected to a plurality of pulleys, it passes over the pulleys by the same tension so is automatically adjusted in tension. There is no need for the troublesome adjustment of tension like in the prior art. On top of this, since a plurality of pulleys are connected in parallel, the assembly acts as a speed reducer, it becomes possible to lower the speed reduction ratio of the speed reducer used from the main motor to the wire drum to boost the power, and the electric powered drive device as a whole can be configured from more compact drive parts. 
     Furthermore, by arranging a plurality of the electric powered drive devices in the extrusion direction in series and serially connecting the movement parts of the crosshead (extrusion movement part  15 ), even when a greater extrusion ability is demanded, realization becomes possible without any need to make the individual drive parts larger. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1 . end platen 
               2 . fixed platen 
               3 . container 
               4 . tie rod 
               6 . machine base 
               7 . crosshead 
               8 . billet 
               10 . extrusion press 
               11 . stem slider 
               12 . stem slide motor 
               13 . extrusion stem 
               14 . container operating device 
               15 . extrusion movement part 
               17 . container operating motor 
               18 . container holder 
               20 . die 
               21 . fixed platen 
               27 . shear device 
               30 . base 
               31 . wire drum 
               32 . wire 
               35 . speed reducer 
               36 . extrusion-use main motor 
               37 . clutch coupling 
               40 . fixed pulley 
               41 . movable pulley 
               42 . balance pulley 
               43 . crosshead high speed movement motor 
               44 . fastening location 
               45 . crosshead high speed movement mechanism 
               46 . ball screw 
               47 . ball screw nut 
               48 . movable pulley 
               49 . support column 
               50 . wire windup device 
               51 . wire windup motor 
               52 . extrusion drive device 
               53 . extrusion drive device 
               58 . connecting rod