Abstract:
An extrusion system for extruding a layer of a plastic or rubber material onto a work piece without having to continuously adjust the extrusion system during the “set-up” mode to “full-run” mode, wherein the extruded layer exhibits a predetermined cross-section size and a uniform wall gauge concentricity.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an extrusion system containing a fixed center die module which requires no mechanical adjustments, for continuously extruding a molten material or a formable mass to provide a tubular structure having a predetermined cross-section size and a uniform wall gauge concentricity. More particularly, the present invention relates to a crosshead extrusion system.  
           [0002]    Hoses made primarily of polymeric materials are widely used for transporting various fluids such as water, gasoline, coolants, power steering fluids, transmission fluids, etc. Typically, these hoses are used in automobiles, trucks, buses, aircraft, locomotives and water craft to transmit such fluids. Generally, for such applications it is necessary to provide high pressure hoses having multiple layers, including reinforcing layers, in order for the hoses to withstand the pressures and temperatures involved, and to meet the various federal and state emission regulations, and still exhibit dimensional stability and rugged durability required for today&#39;s fuel powered internal combustion engines. For example, U.S. Pat. No. 4,330,017 to Satoh describes an automobile fuel hose comprising a two-ply rubber tube covered with a reinforcing fiber layer and further with a protective rubber layer. The hose is constructed from a very thin inner layer of a fluorine-containing rubber which is resistant to fuel, and an outer layer of a synthetic rubber such as epichlorine rubber or ethylene-acrylic rubber which is less resistant to gasoline, but is superior in cold resistance. The extrusion system of the present invention can be used in the manufacture of any polymeric hose, e,g, garden hoses, air pressure hoses, and industrial hoses such as those used in connection with hydraulic presses and the like.  
           [0003]    U.S. Pat. No. 5,566,720 to Cheney et al. proposes a multiple layer hose comprising a first layer made up of a melt processible fluoroplastic terpolymer wherein the innermost surface is capable of prolonged exposure to hydrocarbon-containing fluids, and a second layer composed of a resinous thermoplastic material such as polyamide which is bonded directly to the outwardly oriented surface of the first layer.  
           [0004]    U.S. Pat. No. 5,524,673 to Noone et al. describes an elongated tubing which includes a first layer of an extrudable, melt-processible thermoplastic material, and a second layer of an extrudable, melt-processible thermoplastic material wherein the second layer is capable of sufficiently permanent laminar adhesion with the first layer to prevent delamination during the desired lifetime of the tubing. At least one of the first and second layers is resistant to permeation of hydrocarbons. In addition to the first and second layers, the tubing includes a third layer adhered to the second layer.  
           [0005]    Typically, multi-layer tubular structures are manufactured using extrusion processes and, more particularly, using crosshead extrusion processes as described in U.S. Pat. No. 4,361,455 to Arterbum. Such crosshead extrusion systems are employed not only in the manufacture of rubber tubes and hoses, but also for coating cylindrical work pieces with highly viscous materials such as unvulcanized rubber as described in U.S. Pat. No. 4,832,588 to Rasmussen, and in the manufacture of coated wire and cables as described in U.S. Pat. Nos. 5,183,669; 5,780,066; 5,882,694; and 5,980,226 all to Guillemette; and 5,830,516 to McAlpine et al.  
           [0006]    Typically, in the manufacture of rubber tubing or rubber-coated wire, the molten rubber material is extruded by means of a crosshead extrusion system which receives a stream of molten rubber material and causes the molten rubber material to be distributed around the circumference of a wire or tube. In the present invention, the term molten is used to define a formable mass and is not intended to specifically suggest that the formable rubber material is in a molten or liquid state. A variety of crosshead devices have heretofore been known in the art for manufacturing hoses and for applying rubber coatings around the circumference of a wire or tubular member. Furthermore, it is known in the art to simultaneously extrude more than one layer of molten rubber to provide a multi-layer tube. Such a process is accomplished by means of multi-layer crosshead extruder devices such as that described in U.S. Pat. No. 4,798,526 to Briggs et al. Such devices typically utilize two or more crosshead extruders for co-extrusion of multiple layers.  
           [0007]    It is also known in the art that it is extremely difficult to establish an even and balanced flow of molten material around the circumference of a wire, mandrel or tube. For example, it is known that conventional crosshead extrusion methods pose several inherent problems such as lengthy “set-up” time which is the time spent adjusting the extruder for a desired circumferential size and uniform wall gauge concentricity. After the adjustments are made and remade several times and the “set-up” is finally complete, the material being extruded from “set-up” mode to “full run” mode has, typically, become hotter on the inside, or extrude side, of the crosshead, thus causing concentricity of the tubular structure to be comprised. In addition, the overheated plastic or rubber material frequently becomes discolored and exhibits other undesirable characteristics. . . . Furthermore, it is known that splitting and reblending of the molten material can cause the molten material to blend together unevenly forming undesirable weld or joint lines in the finished product. Accordingly, there is a need for an extrusion system which overcomes the inadequacies and undesirable characteristics of the prior art extrusion systems.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention provides a new and improved crosshead extrusion system wherein the crosshead extruder housing is designed to accept a fixed center or non-adjustable die module which is capable of balancing the flow of molten material to the die and maintaining this balance from a “set-up” mode to a “full-run” mode. Die modules are known, however, such die modules are notorious for requiring continuous adjustment of the die module in the housing in order to provide hoses having acceptable cross-section size with a uniform wall gauge concentricity. It has now been found that a tubular member having a predetermined cross-section size and a uniform wall gauge concentricity can be extruded in an extrusion system, particularly, a crosshead extrusion system which employs the die module or torpedo of the present invention. The die module of the present invention has a fixed center and requires no mechanical adjustments while providing a balanced flow of molten or formable material to the die and maintains this balance from a “set-up” mode to a “full-run” mode. The tubular member formed using the extrusion system of the present invention has a predetermined cross-section size and a uniform wall gauge concentricity.  
           [0009]    A critical feature of the new crosshead extrusion system is the construction of a fixed center die module or “torpedo” which resides inside the extruder housing. The torpedo is designed to split the molten material coming from the screw into two substantially equal parts or controlled flow, and then split each of these two parts into two more substantially equal parts, thereby providing four substantially equal parts or controlled flow, thus allowing for a balanced volume flow to the die. Another feature of the crosshead extrusion system is the outside part or the body of the crosshead extruder which is designed to accept “non adjustable” dies. Also the extruder is designed with dual controllable temperature zones in the front of the crosshead body to control the temperature of the material flowing through the body of the extruder. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 is a cross-sectional view of the crosshead extrusion system of the present invention;  
         [0011]    [0011]FIG. 2 is a perspective view of the fixed center die module of the present invention;  
         [0012]    [0012]FIG. 3 is a front view of the die module of the present invention;  
         [0013]    [0013]FIG. 4 is a right side view of the die module of the present invention;  
         [0014]    [0014]FIG. 5 is a left side view of the die module of the present invention;  
         [0015]    [0015]FIG. 6 is a bottom view of the die module of the present invention;  
         [0016]    [0016]FIG. 7 is a cross-sectional view of the die module taken along line  7 - 7  of FIG. 6;  
         [0017]    [0017]FIG. 8 is a top view of the die module of the present invention; and  
         [0018]    [0018]FIG. 9 is a cross-sectional view of the die module taken along line  9 - 9  of FIG. 8.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0019]    Turning to the drawings, FIG. 1 illustrates a cross-sectional extrusion system of the present invention. The extrusion system  10  comprises a housing  12  having a tapered interior wall surface  14 , the circumference of the interior wall surface being smaller in the front of the housing  12  than in the rear of the housing. The housing  12  is adapted with a threaded surface  28  at the front of the housing  12  to threadedly secure a die head (not shown) to the housing  12 . As shown in FIG. 1, an extrusion module  18  is placed in the interior of the housing  12  such that the frusto-conical exterior surfaces  22  of the module  12  mates with the tapered interior wall surface  14  of the housing  12 . The extrusion module  12  has a tubular bore  32  with a uniform circumference extending through module  12  for transporting a wire, mandrel, or tube (not shown) in accordance with the present invention. The module  18  is secured in the housing  12  using a nut (not shown) which is threadedly locked onto the housing  12  using threaded surface  26 .  
         [0020]    Molten material such as plastic and/or vulcanized or unvulcanized rubber is delivered under high pressure and temperature to the interior of the housing  12  through conduit  40 . The pressure and temperature employed are those typically used in conventional extrusion systems for similar material plastic or rubber materials. The molten material is distributed by diverter  38  in the fixed center die module through channels  42  between raised surfaces  24  to uniformly divide the molten material into two substantially equal parts or equal flow. The molten material continues to be distributed forward through the channels  44  wherein the two equal parts or flow of molten material are eventually uniformly divided into four equal parts of molten material. Finally, the molten is directed to tubular bore  32  where, in one aspect of the invention, it is evenly distributed and coated onto a cylindrical body such as a hose, a wire or a mandrel, to provide a tubular structure of molten material having a predetermined cross-section and uniform wall gauge concentricity. In another aspect of the invention, the molten material may be employed to provide an unsupported hose. In a preferred aspect of the invention, one or more temperature controlling zones  20  are employed in the housing  12  to aid in controlling the wall gauge concentricity of the extruded material. Most preferably, the housing  12  is constructed with dual temperature controlling zones, and the temperature of the temperature controlling medium is monitored and controlled to assure of proper temperature.  
         [0021]    The extrusion system of the present invention can be employed in a conventional extrusion system for the extrusion of a single or multiple layer hose using a mandrel to configure the interior circumference of the hose, or the extrusion system can be used in a cross-head extrusion system to coat wire or cable in an extrusion/coating operation. The present extrusion system also can be employed to provide an unsupported tube. The extrusion system of the present invention has been found to be particularly useful in extruding a layer of vulcanized or unvulcanized rubber material on a mandrel employing a cross-head extruder. The hose is then reinforced with a reinforcing layer such as braided fiber e.g. glass fiber, polyester fiber, polyamide fiber, partially acetyl-formed polyvinyl alcohol fiber or the like to form a high pressure hose such as that used as a power steering hose in the automotive industry.  
         [0022]    While the extrusion system of the present invention is shown and described herein certain specific structure, it will be obvious to those skilled in the art that certain modifications may be made without departing from the spirit and scope of the invention concept as indicated by the scope of the appended claims.