IL22887A - Process and apparatus for the manufacture of reinforced workpieces of synthetic material - Google Patents

Description

A process and apparatus for the manufacture of reinforced workpieces of synthetic material JOSSF BICHL Ci 21971 It is known that the properties of high-polymer substances can be improved and their strength can be increased by the use of various kinds of embedded reinforcements. For instance, plastics materials have been developed Yihich are reinforced with glass fibers, e.g., with rovings, which extend in the longitudinal direction of tubes, rods, sections or the like. The reinforcements result in a substantial improvement in the tensile, bending, compression and impact strengths to values which are much higher than in the non-reinforced plastics material.

It is desirable, however, to reinforce plastics materials not only with continuous, linear longitudinal reinforcements, but also in a transverse direction. For this purpose, reinforcements of glass, asbestos, textiles, including nylon, perlon, etc., and of metal wire, have been cut into relatively short lengths, which agree with the length of any natural or synthetic fibers which are employed, or natural fibers are used. These fibers or the reinforcements cut into short sections are sucked, in most cases with the aid of an air stream, into a preform screen, which is thus flocked. The resulting preform is consolidated with a binder and then impregnated with plastics material, which is cured when the workpiece has been molded to the desired shape. In such ?iorkpieces, the short reinforcing fibers are in a random arrangement in the plastics material in random positions obtained during the manufacture of the preform.

In another known process of making tubes and woven glass fabrics or strips are wound, ¥;hich are then cured. The winding process has the disadvantage that it cannot be performed continuously because the mandrel must be pulled out of the workpiece when a certain length has been produced.

In another process, which is based on the same principle, longitudinally extending rovings are applied parallel to the tube axis in alternation with wound layers applied to the mandrel.

As has been set forth hereinbefore9 it is also known to introduce continuous reinforcements in the form of glass strands, glass rovings, textile filaments or threads, yarns, ply ya , strings, braids, ribbons, ropes, plaits and other linear textile products, made from natural and synthetic fibers, into the space between a core and a shell, and to introduce at the same time synthetic resin with the aid of feed screas into this space so that hollow workpieces are obtained, which have a longitudinal reinforcement. These workpieces, however, lack a transverse reinforcement, vihich is essential for the required strength to the workpieces. This transverse reinforcement is also absent in proposal to introduce into an extrusion die a tube, which is held by a core having a conical end portion. The core is surrounded by a shell, which defines with the core a space through which synthetic resin is supplied. The tube has beads, which accommodate thinner tubes, through which reinforcements in the form of filaments or wires are supplied. The tube and the thinner tubes for supplying the linear reinforcements terminate before the throat of the extrusion die shortly - - after the conical end portion of the core so that tubes of plastics materials, particularly synthetic resin, are obtained, in which filaments or wires are embedded. In this process, the embedded reinforcements can lie only on ishe surface of the resulting synthetic resin tubes whereas the internal portions of the tube are not reinforced in the longitudinal and transverse directions* It is an object of the present invention to provide a process in which workpieces of plastics materials are stiffened by continuous, linear, embedded reinforcements and the above-mentioned transverse reinforcement is provided by additional embedded reinforcements, thich deviate from the longitudinal direction of the workpiece.

The invention consists in a process £>r inanufacturing reinforced tubes, section bars or the like workpieces froa plastic materials by extrusion, wherein continuous longitudinal reinforcing elements are fed to an extrusion die through tubes which extend in parallel to the longitudinal direction of the workpiece, additional reinforcements being short lengths of wire, textile or mineral fibres, or pliable textile or mineral filaments, or the like, are admixed to the plastics material and this latter mixture is fed into the extrusion die through an annulus surrounding the die, and while being so fed, is constrained to move initially in a direction parallel to tie longitudinal direction of the workpiece and then radially inwards until it enters the extrusion die.

This process gives the desired success because the plastics material provided with the additional reinforcements can be moved in a direction parallel to the axis of the workpiece for such a distance that the additional reinforcements assume an orientation which is parallel to the direction of flo . The additional reinforcements need not be divided into relatively short length sections. For instance, pliable reinforcements in the form of filaments or strands or textile material v/ill readily follow the changes in direction imparted to them in the process according to the invention. This is not always the case with metal wire. In these cases it will be suitable to supply the additional reinforcements in the form of pieces of finite length or of any kind of fibers. In carrying out the process, the plastics material provided with the additional reinforcements may emerge from an annular gap, is spaced around the cross-section of the norkpiece and extends parallel to the axis of the workpiece, and the plastics material emerging from this annular gap may be initially deflected towards the axis of the workpiece ia a direction ^hich is inwardly with respect to this axis, and may then be deflected to move in an axial direction along paths tjhich are equidistant with respect to the periphery of the workpiece so that the additional reinforcements extend transversely to the longitudinal axis of the workpiece. In this operation, continuous reinforcements may be pre-stressed. This applies particularly to the longitudinal reinforcements but also to the additional reinforcements if they have the above-mentioned pliability and elasticity. !lhen the plastics material provided with the relatively large cross-section into the annular gap, which is much narrower and extends at right angles to the supply duet, the resulting flow conditions in the flowing plastics material tend to orient a major portion of the additional reinforcements in the direction of flow. It has been found that when said annular gap is of sufficient length, a major portion of the additional reinforcements contained in the plastics material assume the desired preliminary orientation. As the plastics material is subsequently deflected towards the workpiece axis, the reinforcements contained in the plastics material approach the extrusion die substantially in a transverse direction whereas the finished workpiece is axially forced out of said die. As the change in direction in the extrusion die is rather abrupt, the major portion of the reinforcements which have entered the die in a transverse position retains this position in the resulting work-piece. Thus, with reinforcements in the form of sections of finite length, e.g., of fibers, which are initially contained in the plasties material in a random orientation, the process according to the invention resulte in a surprising and extrem-ely simple manner in an orientation of these fibers in positions which are substantially equidistant viith respect to the boundary surface of the uorkpiece by an ingenious control of the flow path for the plastics material so that the fibers cross the continuous longitudinal reinforcements approximately at right angles. In a workpiece having a cross-section in the form of a circular ring, e.g., in a tube, the additional reinforcements will appear in a - 7 - 226872 peripheral orientation and, in view of the continuous axial displacement, in a helical orientation, and will he crossed by the rovings, which are parallel to generatrices of the tube. Other Individual fibres may be arranged in the longitudinal direction ©f the tube or other workpiece. Besides, the orientation of the ibres may be modified in accordance with the desired object by the provision of obstructions in the flow path. fhe invention also provides an apparatus for carrying out the process aforesaid, which comprises an extrusion die designed to be supplied with plastics material through an annular passage, and tubes extending parallel to the longitudinal axis of the workpiece and to each other, which tubes open into the die and serve for supplying continuous longitudinal reinforcements, the annular passage having a narrow portion which is parallel to the axis of the workpiece and being succeeded in the direction of low of the plastics material by a portion radially extending inwardly, which terminates in the extrusion die.

The continuous, longitudinal, linear reinforcements introduced into the die from the rear must not be inwardly displaced toward a core which defines a cavity in the work-piece when they meet the plastics material containing the additional reinforcements but must lie at predetermined points in the cross-section of the wall of the finished workpiece. For this purpose, guides for the continuous, longitudinal, linea reinforcements are provided, preferably adjacent to the junction between the radially inwardly extending portion of the annular passage and the die cavity, and extend parallel to the axis. These longitudinal guides may be arranged in such a manner relative to the space left between a core and an outer ring of the die that solid and hollow bodies having any desired cross-sectional shapes, inclusive of irregular cross-sectional shapes, may be produced. In accordance with the subsequent stress conditions the continuouso longitudinal, linear reinforcements may be arranged with a greater density in some areas than in others, and the pattern in which the linear reinforcements are embedded in the cross-section of the workpieces, e.g., of a wall of a hollow body, Ba be selected as desired.

The invention includes also some of the features which will be described hereinafter and is directed to the overall combination of these features as well as to all partial combinations thereof which are technologically useful and feasible, even though the novel technical effects may not be set forth and described in detail hereinafter. Besides, all details shown in the drawings are included per se and in their functional relation.

The invention will now be explained more full with reference to an embodiment shown by way of example in the drawings. The longitudinal reinforcement of the hollow work-piece consists of rovings of glass fibers and the transverse reinforcement consists of length sections of such rovings.

Fig. 1 is a vertical sectional view showing an extruder for carrying out the process according to the invention.

Fig. 2 is partly an end elevation and partly a sectional vieu taken on line II—II of Fig. 1» Fig. 5 is partly an end elevation and partly a broken~av/ay sectional view taken on line III—III of Fig, 1.

Fig. 4 is a diagram illustrating the orientation of the reinforcing fibers flowing through the extruder.

Fig* 5 are fragmentary transverse sectional views shoeing portions of t?jo finished orkpieces.

Fig. 6 shows the overall arrangement.

The extruder shoran in Fig. 1 consists of detachably connected parts to facilitate the replacement and maintenance of such parts. It includes a hollow cylindrical die block lj which has a longitudinal cavity, through which a core 3 extrends, which defines a cavity of the finished work-piece and leaves an annular gap. A cover 2 secured to the free end face of the die block has a central opening with a rounded edge. A disc 4 ^hich has also rounded edges is secured to the adjacent end of the core 3. The generally funnel-shaped opening which is thus obtained serves for the introduction of linear reinforcements, which extend in the longitudinal direction of the v;orkpiece through openings 6 of a member 5 and through guide tubes 8 to and through the bushing 10. The guide tubes 8 are held in a predetermined position in the annulus surrounding the core 3 by a further annular member 7 and an end ring 9. The guide tubes 8 have an extension 14» which extends into the bushing 10. The purpose of this extension will be explained hereinafter.

The plastics material which is to be extruded contains reinforcements in the form of fibers or fiber sections and is supplied under pressure through the duct 11. Feed screws or presses having one or more rams may be used to generate the pressure. The duct 11 merges into an annular gap, v ch is spaced around the longitudinal cavity of the die block. The length of the gap 12 is determined empirically. The annular gap 12 is much narrower in cross-section than the duct 11 so that the flow of the plastics material is throttled at the entrance to the gap 12. As a result, reinforcements admixed to the plastics material will assume in the gap 12 an orientation Yihich is substantially parallel to the direction of flow of the plastics material in this gap.

The annular gap 12 is continued by a passage 13t ¾hich extends inwardly' -; and substantially radially towards the workpiece axis and in the bushing 10 extends radially inwardly into the die passage. The passage 13 opens into the die passage within the area in which the extensions of the guide tubes 14 for the longitudinal, linear fibrous reinforcements are extended beyond the outer end face of the die block 1 and the core portions adjacent to said outer end face towards the outlet of the die, where the linear reinforcements emerge from the die.

As the cavity 13 having the shape of an annular disc opens into an annular gap 17 (see Fig. 1) between an extension 18 of the core 3 and the shell 19, the additional reinforcements 16 are introduced into the stream of plastics material along a helical path (see Figs. 1 and 5) because the synthetic resin flows radially between the nozzles 14 and is deflected into an axial direction so that direction into an axial and peripheral direction, in conjunction with the action of the core. The lead of the helix will depend on the ratio of the cross-sectional areas of the centripetal and axial flou passages and can be determined by a suitable selection of these cross-sections. If the cross-section between parts Is, 19 exceeds the cross-sections between parts 13» 12, 11, the lead of the helical flow will be larger than in the opposite case, here the additional reinforcements 16 lie virtually in planes which are at right angles to the longitudinal axis 20-20 of the entire arrangement.

The longitudinal, linear fibrous reinforcements 15 are unwound from supply reels, not shown, and emerge from the guide tubes 14 behind the junction between the annular gap portion 13 and the die passage in the bushing 10 so that the longitudinal linear reinforcements 15 contact at the end of the tubes 14 a plastics material hic moves in the same direction as the linear fibrous reinforcements (to the left in Pig. 1). As a result, the linear fibrous reinforcements are embedded in the plastics material in the desired distribution over the cross-section of the workpiece wall.

Fig. 2 is partly an end elevation and partly a transverse sectional view showing the extruder intended for carrying out the process according to the invention. In the embodiment shown by uay of example, this extruder is arranged to manufacture a hollow body 17' , which has a rectangular cross-section flith a protruding bead. Longitudinal, linear reinforcements 15 are embedded in the workpiece wall one beside the other with a regular spacing. A gap corresponding to the cross-section of the hollow body 17' is left between the core 3 and the guide members 25* 26. Pipes 27, 28 and ledgelike fittings 29 connecting them maintain the members 25, 26 and the hollow body 178 at the required temperature.

Fig. 3 is partly an end elevation and partly a transverse sectional view showing the guide tubes 14 and 8 for the longitudinalv linear reinforcements 15. These tubes determine the final distribution of the longitudinal reinforcements in the workpiece wall 17'. It is apparent from the top half of Fig. 3 that the tubes 14 extend in the extruding direction beyond the junction between the annular gap 13 and the die passage.

Fig. 4 is a diagrammatic representation of the process by union the further reinforcements mixed with the plastics material and consisting of fibers, or sections of fibers, or of fibrous textile products or wires or the like are given an orientation which is transverse to the, longitudinal axis 20-20 of the workpiece, unless the additional reinforcements are continuous. The additional reinforcements 16 arriving in the duct 11 are embedded in the plastics material more or less at random and by the throttling effect at the junction to the narrow annular gap 12, which is concentric with the workpiece axis, are compelled to assume an orientation in the direction of flow of the plastics material. This orientation of the reinforcements lb in the direction of flow is maintained in the portion 13 of the annular gap. As has been explained hereinbefore, the reinforcements 16 embedded in the workpiece extend in a and in any case cross the direction of the continuous reinforcements.

These linear reinforcements 159 which are supplied and inserted in the longitudinal direction are protected by the tubes 14 at the junction between the annular gap 13 and the passage defined by the bushing 10 so that the additional reinforcements 16 are embedded in position between the tubes 14.

Fig. 5 shows in transverse sectional views tuo finished plastics materials tubes made by the process according to the invention. The continuousfl linear reinforcements 15 extend in a longitudinal directions and the generally shorter additional reinforcements 16 lie between the reinforcements 15 and consist generally of fibers or fiber sections, either of crude fibers or textile fiber products. The arrangement in the right-hand half of Fig. 5 differs only in that the longitudinal, linear reinforcements 15 are arranged in two courses whereas in the left-hand half the spaced-apart longitudinal reinforcements are arranged only in a single circular course.

The process according to the invention may be used to manufacture workpieces having a w de range of cross-sectional shapes. These ¾orkpiece may be manufactured in an extreaoly simple manner and have much improved mechanical properties. The shape of the uorlipieces as ¾ell as the arrangement of the longitudinal reinforcements and the materials may be selected as desired. The reinforcements in the form of fibers or fiber strands may consist of any suitable material, such as asbestos, glass fibers, glass filaments, glass i>70ol9 slag ?/ool, textile fibers, linear textile products in the form of threads or filaments, yarns ply yarns* strings, ropes, ribbons etc. from natural and/or synthetic fibers or mixed fibers,, or wires0 tvdsted wires, twisted or untwisted metal stript or the like. The longitudinal linear fibrous reinforcements are suitably prestressed to enable the build-up of the back-pressure required for the filling of the extrusion die ^ith the plastics material. This back-pressure is essential for obtaining a vjo kpiece having a satisfactory surface finish and for filling the die completely so as to expel all air. when the longitudinal reinforcements consist of rovingsp these may be pre-impregnated by drawing them through a bath of viscous resin before they enter the extruder, In this case the rovings are generally impregnated uitfa a so-called A-stage resin or resol. Alternatively, rovings may be used hich are impregnated with a 8-stage resin or resitol ? eh has been pre-cured by thermal and/or chemical action end is almost or entirely dry. The plastics material mixed with the short reinforcements may also be an A-stage or fistage material. The longitudinal reinforcements and/or the additional reinforcements need not consist of the same materialB and different resins may be used5 provided that they are compatible. The finished workpiece may be advanced in the extruder by the action of the pressure with which the plastics material is supplied or by a withdrawing device or both. The length of the workpiece made in a continuous operation corresponds to that of the rovings which are 1 Thus, the nature of the invention resides in that sections of linear reinforcements which are distributed more or less at random in a stream of plastics material* particularly synthetic resin0 are initially supplied with a stream of plastics material (premix) in a direction which is radial with respect to the longitudinal axis of the work-pieces, and are then distributed as uniformly as possible over a cross-section which exceeds the cross-section of the workpiece and is preferably equidistant theretof whereafter the reinforcementtsections are deflected to move in the axial direction and parallel to the workpiece axis until the rein orcement sections have an axial orientation; they are subsequently deflected on all sides radially toward the workpiece axis and centripetally supplied to a cavity, which corresponds to the cross-section of the workpiece, and this cross-section is filled with plastics material, said reinforcement sections and longitudinal reinforcements. Any heat treatment which is required during this process or during the further processing of the workpiece need not be illustrated because such treatments are known per se. Heating coils which may be required for this purpose are indicated at 26-29 in Fig. 1.

The general arrangement is shown in Fig. 6. The arrangement shown in Figs. 1 and 2 is indicated at 21, the wound-up rovings are indicated at 22 and a double-acting plunger press for a continuous supply of plastics material, particularly synthetic resin, at 25. The plant further comprises conventional means, known per se, e.g., a saw 30 for cutting the finished workpiece 17 'into sections of desired lengthy cooling beds 51? ^orkpiece supports in the form of rollers 32p etc The invention is not restricted to the embodiment which has been shown. For instance 9 the supply duct 11 for the plastics material and the additional reinforcements may be displaced to the left or right from the vertical center plane of the extruder in fig. 3 so that the plastics material and the additional reinforcements are tangentially admitted to the passage 12 and a swirling flow results in the passage 12 and the succeeding passages. /26

Claims (4)

1. 7 22887/2v 1. A process for manufactaring reinforced tubes, section bars or the like workpieces from plastic materials by extrusion* wherein continuous longitudinal reinforcing elements are fed to an estrusion die through tubes which extend in parallel to the longitudinal direction of the workpiece, additional reinforcements being short lengths of wire, textile or mineral fibres or pliable textile or mineral filaments, or the like, are admixed to the plasties material and this latter mixture is fed into the extrusion die through an annulus surrounding the die, and while being so fed, is constrained to move initially in a direction parallol to the longitudinal direction of the workpiece and then radially inwards until it enters the extrusion die.

2. A process as claimed in Claim 1, therein the mixture of plasties material and additional reinforcements is moved in a direction parallel to tie axis of the workpiece for such a distance that the additional reinforcements assume an orientation which is parallel or approximately parallel to the direction of flow of the mixture.

3. & process as claimed in Claim 1 or 2, wherein the mixture of plastics material and additional reinforcements is made to emerge fro© an annular gap, which is spaced around the eross-section of the workpiece and extends parallel to the axis of the workpiece, and then initially deflected toxmrds the axis of the workpiece in a direction which converges towards this axis, and thereafter in an axial direction along paths which are equidistant from the periphery to the workpiece so that the additional reinforcements extend transversely to the - 18 - 22887/2 * longitudinal axis of the workpiece.

4. A process as claimed in any of Claims 1 to 3» wherein the longitudinal continuous reinforcements are prestreesed. 5* A process of manufacturing workpieces of plastics materials I substantially as described hereinbefore with reference to, or as illustrated in the accompanying drawings. β. An apparatus for carrying out the processes claimed in any of Claims 1 to 5, comprising an extrusion die designed to be supplied with plastics material through an annular passage, and tubes extending parallel to the longitudinal axis of the work piece and to each other, which tubes open into the die and serve for supplying continuous longitudinal reinforcements, the annular passage having a narrow portion which is parallel to the axis of the workpiece and being succeeded in the direction of flow of the plastics material by a portion radially extending inwardly, which terminates in the extrusion die* 7. An apparatus as claimed in Claim 6, comprising guides, parallel to the axis of the workpiece, for the continuous longitudinal reinforcements, preferably adjacent to the junction between the radially inwardly extending portion of the annular passage, and the die passage. 8. Apparatus for manufacturing workpieces of plastics material, substantially as described hereinbefore with reference to, or as shown in the accompanying drawings. For the Applicants m. REHH0U3 /dO r PARSHBRS