METHOD OF AND APPARATUS FOR SPLICING THERMOPLASTIC ARTICLES

Abstract: A method and apparatus are provided for forming a joint in an elongate article formed from a thermoplastic material, for example an escalator handrail (120) or a conveyor belt, which also includes a plurality of reinforcing cables and a slider fabric. End parts of the article (120) are held in a mold (12) and heated to remelt the material. Portions adjacent the end parts are chilled, at ends of the mold, to prevent remelting. The molten end parts then fuse, and the molten joint is then cooled to resolidify the material and form the joint. With reinforcing cables (126) being present, these can be cut into an interlace pattern, which advantageously is provided in just a layer of the article rather than extending through the full depth of the article. A top layer (160) can then be replaced by a separate top cap of the material of the body of the article. Where a slider is present, to provide an effective interlacing effect, a bottom layer or portion of a handrail is cut at an inclined angle, to form an inclined joint in the slider.

Description: Title: Method of and Apparatus for Splicing Thermoplastic Articles FIELD OF THE INVENTION This invention relates to a method of and an apparatus for splicing articles formed from a thermoplastic material, such as a handrail for an escalator or the like. This invention more particularly relates to a method and apparatus for splicing together extruded articles including a plurality of elongate inextensible members and a slider fabric layer, such as handrail sections or conveyor belts BACKGROUND OF THE INVENTION Handrails for escalators, moving walkways and other transportation apparatus are usually produced in indefinite lengths. A conventional handrail has three main components, namely the main body of the handrail, which is commonly formed from a rubber or other thermoset material; a plurality of steel, reinforcing cables, which act as a stretch inhibitor to define a neutral axis and to give the handrail a desired stiffness in a longitudinal direction, while enablin it to flex in a vertical direction, so as to be capable of travelling around pulley wheels, drive mechanisms etc; and a slider fabric that is commonly bonded to the handrail within a T-shaped channel on the bottom of the handrail, the function of the slider being to provide a low coefficient of friction between the handrail and a supporting and correspondingly shaped guide. Conventional handrails also commonly included various layers of fabric reinforcement. Conventionally, handrails have been produced in a piece wise fashion. As the main material of the handrail body is a thermoset material, this has caused little difficulty. After production of each section within a mold, the handrail is moved forward, and the next section formed after it. For a particular application, to form a splice at an installation site, a so-called "field splice", an appropriate length of handrail is selected, and the ends prepared for splicing together. Commonly, this involves cutting the ply containing the steel cables and interlacing them. The slider fabric is cut appropriately. The ends are then assembled in a mold, the mold is filled with fresh material, and the mold is then heated, to cause the material to set. In production of the handrail, if the length required is known, then in the factory a "factory splice" can be made. A length of handrail is produced with the ends left uncured, so that an invisible, smooth splice can be made using a production mold. Proposals have been made for forming handrails for escalators and the like from a thermoplastic polymeric material, such as polyurethane, and one example is shown in U.S. Patent 4,618,387 (Fisher et al.) assigned to Westinghouse Electric Corp. It is first noted that the practical utility of this method is questioned, since the patent only shows and describes a C-shaped section for a handrail having the main body formed from the elastomeric material and a plurality of steel cables or other inextensible members. No mention is made of the fabric slider that, as a practical matter, is required for any conventional handrail. It is not seen how even a test loop of handrail could have been made and tested, if the slider was not present. To applicant's knowledge, there is no practical way of bonding this slider to the handrail after formation of a complete handrail loop, nor indeed after the forming of any length of handrail. It has, to applicant's knowledge, to be formed with the handrail at the time that the other elements of the handrail are assembled. In any event, the main proposal in this U.S. Patent 4,618,387 is to cut the two ends of the handrail square, and then heat fuse them together. It is not clear how this is intended to be effective, but it is suggested that as the interfaces are short, only a small amount of elastomeric material will extrude from the periphery of the joint and require removal. This method by itself is believed to be almost certainly inadequate, and indeed, a test sample prepared by the present inventors showed that a distinct plastic hinge developed at the break in the steel cables. A large part of the strength of a handrail is derived from the steel reinforcing cables. A simple, square butt joint would require the elastomeric material to provide the strength across the joint, and this would be unacceptable. To allow for this, the disclosed method also provides for cutting a number of longitudinally extending, parallel grooves between the existing cables. Short lengths of the cables are then placed in the grooves and a thin sheet of material is disposed over the grooves. Heat is then applied to the sheet on the joint area to cause the sheet to melt and flow into the grooves to surround them. Again, it is not entirely clear how it is intended for this to be achieved, nor how the correct profile would be maintained. Such a technique is clearly impossible when the slider is present and if the slider is to be continuous, and it is clear that this method can only readily be practised on a handrail assembly without the slider fabric. A further disadvantage to this technique is that, in the area of the joint, there will be, approximately, twice the density of reinforcing cables as in the rest of the handrail, giving the joint area a stiffness and flexing characteristic quite different from the rest of the handrail, which it is believed would result in unusual and undesirable wear characteristics. It is suggested this can be alleviated by feathering the joint, but this would simply relieve the abrupt change in stiffness, rather than eliminating it. The problem of splicing together the ends of a selected length of an endless member is known in many other fields of technology. In particular, there are many proposals in the conveyor belt field for splicing belts together. U.S. Patent 3,481,807 is one example, which shows various interlacing techniques. It shows cutting of reinforcing cables so that the junctions in individual cable runs are staggered along the length of the belt. It also shows this characteristic for outer cables, combined with overlapping or interlacing of ends of inner cables. This method is intended to be applied to a rubber belt, with a covering material that can be replaced and vulcanized. It does not address the problem of applying this technique to a belt formed from a thermoplastic material, particularly the problem that the whole body of a thermoplastic belt could melt and run away if it is heated without being contained. Further, many, although not all, thermoplastic materials are strongly hygroscopic. For such materials, it is necessary to maintain sufficient pressure that retained water does not vaporize. SUMMARY OF THE INVENTION Accordingly, it is desirable to provide a method and apparatus for splicing together selected lengths of an extruded handrail. Ideally, the method should provide for formation of a joint that is largely undetectable to a user. Moreover, it is desirable that the spliced joint provide the same high or good bond strength for the cables, peel strength for the slider fabric and thermoplastic layers, and lip strength as in the extruded handrail, and that the integrity of the body be retained in the splice area. In accordance with one aspect of the present invention, there is provided a method of forming a joint in an elongate article, which is of generally uniform cross-section, is formed from a thermoplastic material and has end parts, the method comprising the steps of: (1) placing the end parts of the article in a mold having a mold cavity with a cross-section corresponding to the cross-section of the article, and enclosing the end parts of the article within the mold; (2) while maintaining portions of the article adjacent the end parts cool, to prevent melting thereof, heating the end parts of the article to melt the thermoplastic material, thereby to fuse the end parts together; (3) while continuing to maintain said portions of the article adjacent the end parts cool, cooling the molten end parts of the article to resolidify the material and to form a joint. The mold has a cavity that corresponds to the cross-section of the article in the sense that they have similar and related profiles, although it is not essential for the dimensions of both the mold cross- section and the cross-section of the handrail to be identical. As detailed below, at least for some materials and applications, it is advantageous to have the mold slightly oversized with respect to the profile of the article and this has been found to give good results. Preferably, the method is applied to an elongate article including a plurality of elongate inextensible members, wherein the method includes the additional step of, prior to step (1), cutting the inextensible members to at least two different lengths, to form an interlace pattern at the joint, with the inextensible members terminating in a plurality of planes transverse to the elongate article. As the material is a thermoplastic, the elongate inextensible members or cables are preferably cut with a corresponding portion of the material of the body of the article, whereby where the cable end parts are interlaced there are no substantial voids in the body of the material. In a preferred aspect of the present invention, the method is applied to an elongate handrail having a generally C-shaped external section and defining an internal T-shaped slot, and including an internal slider fabric around the T-shaped slot, the handrail having, in a cross- section, a main top portion and side legs extending down there from around the T-shaped slot with the inextensible members being located in the top portion above the T-shaped slot, wherein the method comprises forming the interlace pattern in the top portion of the handrail. In accordance with another aspect of the present invention, there is provided an apparatus for forming a joint in an elongate article of substantially uniform cross-section and formed from a thermoplastic material, the apparatus comprising a mold defining an elongate cavity having a cross-section corresponding to the cross-section of the elongate article, which mold comprises a central section and first and second end sections on either side of the central section; a main heating means for heating end parts of the article in the central section of the mold to cause remelting and fusing of the end parts of the article; a main cooling means for cooling the end parts of the article to resolidify the material and form the joint; and end cooling means, for the first and second end sections, for cooling portions of an elongate article adjacent the end parts thereof, to prevent melting, wherein the mold comprises at least two parts which are displaceable between an open configuration in which an article can be inserted into the mold and a closed configuration for forming a joint. In a preferred aspect of the invention, the main heating means, the main cooling means and the end cooling means are all integral with the mold. Conveniently the cooling means are provided by appropriate ducts in the central and end sections of the mold, through which cooling water flows. The heating means is provided by ducts within the central section in which elongate electric heating elements are located. However, it is conceived that the heating and /or the cooling means could be separate from the mold, and more particularly could be incorporated in press platens used to maintain the mold closed. This would then simplify the design of the mold, although the thermal paths for heating and cooling would likely be longer. Preferably, the mold comprises a top part and a bottom part, wherein the top part of the mold comprises top parts of the main central section and of the first and second end sections, and the bottom part of the mold comprises bottom parts of the main central section and of the end sections. More preferably, the top parts of the end sections are joined to the top part of the central section but are generally thermally insulated therefrom, and the bottom parts of the end sections are joined to the bottom part of the central section but are generally thermally insulated therefrom. Conveniently, this is achieved, by integrally forming the top parts of the central section and the end sections from metal, with the parts joined by a narrow web providing insulation, with the bottom formed similarly. Advantageously, each of the top and bottom parts of each of the end and central sections includes a duct means, for passage of a liquid coolant. The duct means preferably comprises suitably arranged bores extending through the various sections. Also, the top and bottom parts of the central section advantageously include second elongate bores and heating elements located in the second elongate bores, as the heating means. Preferably, the apparatus is adapted for forming a joint in an elongate handrail having a generally C-shaped external section and defining an internal T-shaped slot, and comprising a main body formed of a thermoplastic material, a stretch inhibitor reinforcing the handrail, and a slider fabric bonded to the main body and around the T-shaped slot, wherein the apparatus includes an elongate mandrel extending through the central and end sections and having a profile corresponding to the T-shaped slot. The apparatus can also be configured to form a joint in a conveyor belt. In the handrail as originally extruded, the cables are bonded to the thermoplastic material. This bond strength can be maintained, by cutting the interlace pattern so as to leave thermoplastic around the end part of each cable, and without removing or damaging the thermoplastic on each cable end part. While a metal mandrel defining the T-shaped slot within the middle of the handrail section may provide some conductive cooling effect, no specific attempt is made to cool the mandrel from the interior. It is preferred to cool the joint mainly from the exterior, to avoid distortion of the handrail profile. As detailed below, it may be necessary to continuously heat the mandrel from the interior, to ensure that cooling does indeed occur mainly from the exterior. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, which show a preferred embodiment of the present invention and in which: Figure 1 shows a perspective, end view of the handrail; Figure 2 shows a side view, partly cut away of the end of the escalator handrail, along line 2-2 of Figure 1; Figure 3 shows a perspective view of a band saw for cutting the handrail; Figures 4a and 4b show successive cutting steps for one end part of a handrail; Figures 5a and 5b show two end parts of the handrail, prior to cutting an interlace pattern in the end parts; Figure 6 is a perspective view of the two end parts of the handrail, showing cutting of an interlace pattern; Figure 7 is a perspective view showing assembly of the two end parts, and a mandrel forming part of the apparatus of the present invention; Figure 8 is a perspective view showing an apparatus of the present invention in an open configuration; Figure 9 is an end view of the apparatus of the present invention; Figure 10 is a plan view of the apparatus of the present invention showing cooling order paths; Figure 11 is a perspective view of the apparatus of the present invention in a press; Figure 12 is a perspective view of the apparatus and the press, showing movement between open and closed positions; and Figure 13 and 14 are side views similar to Figure 2 showing interlace patterns for the side legs of the handrail. DETAILED DESCRIPTION OF THE INVENTION An apparatus in accordance with the present invention is shown in Figures 8 - 12 and generally indicated by the reference 10. The apparatus 10 has a main, central molding section 12 and first and second protective end sections 14, 16. The main and central section 12 comprises respective top and bottom parts 12a, 12b. Correspondingly, the protective end sections 14, 16 have top and bottom parts 14a, 14b, 16a, 16b. An elongate mandrel 18 is secured to the top part 12a. These individual parts or elements will now be described in greater detail. The top part 12a is generally rectangular in plan. It comprises a main base portion 22. Extending along the length of the top part 12a there is a raised central portion 24. This raised central portion 24 has outer sides each having a vertical wall portion 26 and an inclined wall portion 28. The inclined wall portions 28 continue into a planar mating surface 30. Cut into the mating surface 30 is an elongate trough 32 configured to correspond to the external profile of a handrail. At the bottom of the trough 32, there is a shallow rectangular slot 34. Further, at the bottom of the slot 34 there is a further shallow rectangular depression (not shown) into which bolt holes 38 open. The depression 36 serves as a pry slot, for prying the mold apart. Additionally, on either side of the trough 32, there are two small, generally semi circular grooves 40 closely spaced from the trough 32 to accept excess material during molding. The mandrel 18 is secured by bolts (not shown) in the slot 34, as shown in Figure 9. It is shown separated in Figure 8, to show the structure, but in use would remain bolted to the top part 12a. With all the parts formed from aluminum or other metal, this can provide a good conductive path between the mandrel and the top part 12a. As detailed below, this can require continuous operation of mandrel heating elements to obtain the desired cooling scheme. Alternatively, the mandrel can be insulated from the top part 12a, by an insulating spacer or the like. The top part 12a includes elongate bores 44, in which are inserted electric heating elements 46. The top part 12a also includes cooling ducts 48. (Figure 10) The ducts 48 include two longitudinally extending ducts 48a and two transverse ducts 48b, connected to respective inlet and outlet ports 50, 52. The bottom part 12b of the mold 12 is complementary to the top part 12a (Figure 8). It has a mating surface 60, intended to abut the mating surface 30. Extending from this mating surface 60 are inclined walls 62 which continue into vertical walls 64. The walls 64 are intended to slidingly engage the vertical wall portions 26, so as to locate the parts 12a, 12b, laterally. A rounded trough 66 is formed in the part 12b, corresponding to the trough 32, so as to form a complete mold cavity corresponding to the desired handrail section. As for the top part 12a, the bottom part 12b includes bores 70 for heating elements 72. It also includes a network of ducts (not shown), again comprising longitudinal ducts and transverse ducts, with the arrangement corresponding to that for ducts 48a, 48b. The transverse ducts are connected to inlet and outlet ports 80, 82 for providing cooling flow through the top part 12a, as detailed below. The end sections 14, 16 generally correspond to one another, and for simplicity, just the first end section 16, as shown in Figure 8 is described. As detailed below, the end sections 14, 16 are intended to be kept cool at all times, even when the central section 12 is heated. For this reason, they are thermally isolated from the central section 12. Firstly, profiles of the top and bottom parts 16a, 16b of the end section 16, generally correspond to the main, central section 12. Thus, the top part 16a shows a main base portion 84 and a raised central portion 85. It has vertical wall portions 86 and inclined wall portions 88, continuing into a planar mating surface 90. Unlike the central section, the mating surface 90 is provided with no grooves for excess material. It includes a trough-shaped part 92, which provides a continuation of the trough 32. It also includes a rectangular slot 94 as a continuation of the slot 34 in the central section. The bottom part 16b, correspondingly, has a mating surface 100 with inclined wall portions 102 and vertical wall portions 104. At the middle of the mating surface 100 there is a rounded trough 106, to complete the handrail section, and as a continuation of the trough 66. The end parts 16a, 16b are provided with respective through bores with one shown at 108 in Figure 10, for cooling water, and inlets and outlets 109, 110. They also include bores, for passage of heating elements. The mandrel 18 includes bores 19, for electric heating elements 20. A description will now be given of the formation of a splice joint in a handrail, in relation to Figures 1 - 7. The end parts can be prepared using a bandsaw, knife, hot knife or other suitable or conventional cutting means. Here, the main handrail body is indicated at 120. This body 120 includes a top portion 122 and side legs 124. Within the top portion 122, there is a planar array of reinforcing cables 126 as elongate inextensible members. The handrail defines a generally T-shaped slot 128, which is lined with a slider fabric 130. The two end parts of the handrail are designated by the reference 131 and 132. The handrail is formed from a thermoplastic polyurethane elastomer (TPU), although it will be appreciated that any suitable thermoplastic could be used. Two end parts 131, 132 are first cut, with straight, square cuts. Firstly, complementary portions of the side legs 124 are removed from the two end parts by means of corresponding inclined cuts 132, extending through just the side legs 124 of each end part. The second end part 132 will require the making of a complementary horizontal cut 136 immediately below the top portion 124. For each end part, a part of the top portion 122, as indicated 140, is removed by a horizontal cut 142. This is effected by means of a band saw. As shown in Figure 3, a jig 144 including a mandrel 146 is provided. The mandrel 146 conforms to and is a close fit within the T-shaped slot 128, so as to securely retain an end part 131 or 132 on the jig 144. The horizontal cut 142, or other cuts, such as the cuts 134 can then be made precisely. For this purpose, the mandrel 146 could be slotted, or the handrail can be otherwise supported. Note that instead of removing top parts 140, an interweave pattern can also be provided in the top. This cut 142 is made immediately above the array of cables 126. Together with two transverse vertical end cuts, this removes a top layer from both end parts 131, 132. This then leaves a thin, bottom part 148 of the top portion 122, as an intermediate layer containing cables 126 in each of the handrail end parts 131 and 132. These bottom parts are then cut to form a desired interlace pattern, as best shown in Figures 6 and 7. Now, it will be appreciated that, in known manner, a key factor in determming the strength of an interlace pattern is the strength of the cables and the relative shear strength between the cables and the polymer of the handrail. These two factors together determine what length of the cable is required to be embedded in the polymer, in order that, when increasing load is applied to the cable, failure will occur through breakage of the cable, rather than failure of the bonding of the cable to the polymer. An ideal interlace pattern has the cables overlapped sufficiently that the cable joints are spaced apart by more than this critical distance. Referring to Figure 6 it can be seen that there are four planes 150, 151, 152 and 153, at which there are cable breaks. In plane 150, there is a break in the two outer cables 126a and two intermediate cables 126e. In plane 151, there is a break in the three central cables 126b. At plane 152, there is a break in four outer cables 126c, arranged in pairs adjacent the outermost cables 126a. At the plane 153, there is a break in four inner cables 126d, arranged in pairs on either side of the three central cables 126b. It will be appreciated that while a preferred interlacing arrangement is shown, any suitable arrangement can be provided. It can be noted that corresponding to the plane 150, edge parts 155, including the outer cables 126a, of the second end part 132 are retained, but are removed for the first end part 131. The interlacing pattern is cut not just with reference to the cables but with reference to the cables as embedded in the polymer. As detailed below, the polymer is to be remelted during the final splicing step. Rather, each cable is cut, or group of cables cut, to incorporate a corresponding portion of the body of the handrail. This is shown in Figures 6 and 7. Accordingly, when the two end parts are assembled together, in the plane of the cables, there are essentially no voids, other than reasonable tolerances resulting from cutting, and there is no need, apart from such tolerances etc. to replace any of the body of the handrails around the cables. A further advantage of this technique is that it ensures that adhesive between the cables and the thermoplastic is not damaged or removed during formation of the interlace pattern. While Figures 4a and 4b show an inclined splice for the portion of the handrail including the slider fabric, it will be appreciated that a number of different joint mechanisms can be provided in the side legs 124 of the handrail. Alternative profiles are shown in Figures 13 and 14. In Figure 13, there is shown an arrangement that provides for a number of generally rectangular fingers or projections on each end which are interwoven or interdigitated. As for the top portion, these are defined relative to a number of vertical planes. A central plane 170 has, on one side planes 171 and 172, and on the other side, planes 173 and 174. It will first be appreciated that, while vertical planes are shown, this is not essential. It is possible to use a variety of inclined planes, and not all the planes need be parallel to one another; the planes could be inclined either as seen from the side, or as viewed in plan. Thus, there are top and bottom fingers 175 and 176, extending from the two ends and two middle fingers 177 and 178. Again, the ends of the fingers terminate in different planes, to provide a desired stress pattern and to transfer longitudinal tension loads, in shear, between the adjacent fingers. Figure 14 shows an alternative arrangement using triangular fingers. Again, the whole joint is defined in relation to a central plane 172, and planes 171-174 on either side. Top and bottom, triangular fingers or projections 180 and 181 extend to the planes 172 and 173 closest to the central plane 170, while two triangular fingers 182 and 183 extend to the outermost planes 171 and 174. As before, for the joints above Figures 13 and 14, the necessary cuts can be formed by sawing, cutting with hot or cold knives, or otherwise, as appropriate. To reinforce the joint, a saddle or patch can be provided for the slider fabric 130, and such a saddle is indicated at 164 in Figure 6. The saddle 164 could be wide enough to line the joint over the full width of the handrail. The length of the saddle 164 should be such as to provide adequate reinforcement. The saddle 164 could be a sheet cut from the slider fabric 130 and could be prepared by coating with TPU or suitable adhesive, which can be done manually or otherwise. The end parts 131, 132 are then assembled in the mold apparatus 10. The section at the joint is then complete. In the case where material is removed by saw cuts: a replacement sheet 158 allows for the material removed by the cuts 136. A replacement top cap 160 replaces the parts 140 removed from each end part. This replacement cap 160 is cut with a band saw or knife or hot knife; and allowance is made. when cutting it, for the thickness of the band saw if used; i.e. the kerf which is removed material from the end parts 131, 132; where a knife is used, such an allowance is not required. More complex handrail constructions may have one or more internal fabric plies. Then, the ends of the handrail are prepared in the same manner, with each additional ply of fabric being separated from the handrail by horizontal cuts above and below it. The plies of fabric can be joined in an abutting or overlapping configuration. The joints are spaced longitudinally from one another along the handrail, so as not to be aligned with one another. Generally, these additional plies are provided to improve the lip strength of the handrail, and not the longitudinal strength, so that the strength of the longitudinal joint for these plies is not critical. However, for some applications, it may be desirable to provide some form of interlocking fingers, as for the joints described above, for additional fabric plies. Any standard pressure tool can be used and Figures 11 and 12 show a press-tool 56, which has a top part pivotable between open and closed positions. As detailed below, the pressure should be sufficient to maintain the mold closed, while permitting excess material to escape. As detailed below, the mold is slightly oversized, so that initially the TPU is not pressurized. Cooling water is then passed through both the top and bottom parts of the first and second protective end sections 14, 16. The function of this is to keep the portions of the handrail in the ends 14, 16 cool to prevent the handrail remelting at this point. Simultaneously, the heating elements are energized, so as to heat the main central section 12. This remelts the polymer within the central section 12, causing it to bond together and form a unified joint. Now, it is known that TPU is strongly hygroscopic. A finished handrail, formed from TPU will, in normal usage, have absorbed moisture from the atmosphere. Accordingly, care needs to be taken when remelting the handrail to form the spliced joint, to ensure that vaporization of water and generation of vapour bubbles does not occur, and the pressure is selected accordingly. To this end, the mold is dimensioned so that, before thermal expansion causes the end parts to expand significantly, they contact the interior of the mold, which then pressurizes the TPU. More particularly, the dimensions are such that at all times while the end parts are molten, the pressure is sufficient to prevent the generation of vapor bubbles, i.e. the end parts will be pressurised before they melt as vapor bubbles can only be released from molten thermoplastic. The pressure will be determined by the applied load and the dimensions of the mold. As the portions adjacent the end parts are kept cool and do not melt, they will not exert pressure on the mold. The clearance in the mold is chosen so that the pressure thus generated will prevent generation of vapour bubbles at the temperature for forming the splice. Now, if there is any excess material, this simply opens the mold slightly; that is, the top and bottom central parts 12a, 12b will ease apart slightly in the vertical direction, to permit excess material to flow out to the grooves 40. It has also been discovered that, if high pressures are used, excess material can cause the ends of the handrail to be forced or extruded from the mold slightly. This will also relieve the pressure. It will be appreciated that, there will be a pressure drop ΔP between the main handrail section and the grooves 40. This pressure drop ΔP will be a function of the flow rate of material, the width of the channel forced between the two parts of the mold, and the length, ΔL (marked in Figure 9) between the main cavity in the mold and the grooves 40. In general, the pressure drop ΔP will be the difference between the pressure within the main cavity of the mold and ambient pressure. However, it will be realized that, when the mold opens slightly and material is flowing to the grooves 40, the area of the mold, as seen in plan view, on which the pressure of the molten TPU acts is increased. Thus, the molten TPU will act not only within the cavity, but also on the surfaces defming channels extending out to the grooves 40. As a constant load is maintained, then the average pressure within the mold must necessarily drop slightly. Nonetheless, the pressure is still sufficient to prevent any moisture from turning into steam or vapour bubbles. When sufficient excess TPU has flowed outwardly to the grooves 40, the two mold parts will reclose, nipping off the flow. Again, the pressure within the cavity will be determined such that the pressure multiplied by the length (acted upon by the molten material) and width of the mold is equal to the applied load. The mold is heated to a sufficient temperature and this is held for a sufficient time, to give a good joint. At the end of this time, all the heating elements are turned off, except for the heating elements 20 for the mandrel 18, and cooling water is then passed through the top and bottom parts 12a, 12b, to resolidify the material around the actual joint. When the spliced joint is completely cool, the cooling water can then be turned off and the mold opened. As the TPU cools, it shrinks and the pressure reduces down to ambient. At all times, the pressure is sufficient to prevent steam bubbles forming. When the joint has been sufficiently cooled all the water flows are turned off, any heating elements still operative are turned off, and the mold is opened. If there is any excess material present, this is readily trimmed with a knife and the edges of the handrail can be quickly and simply cleaned up, so that the handrail then presents a smooth uniform appearance, and the joints should be undetectable to an ordinary user. The interlacing of the cables provides a strong joint having characteristics comparable to the main body of the handrail. Also, during formation of the splice, the temperature is maintained high enough to ensure good integration of the various layers of the thermoplastic, so that the thermoplastic layers merge completely with one another throughout the splice. The preferred material for the handrail is a polyurethane thermoplastic elastomer. Such material adheres well to the cables, provides a good gloss finish which is durable and wear resistant, shows good resistance to tearing, and good adhesion to the slider fabric. However, thermoplastic polyurethane expands significantly when heated. For this reason, the mold is made oversized by an appropriate amount. This oversizing is along the whole length of the mold, which has proven satisfactory. Preferably, the oversizing is at the low limits of the ranges given. Providing a uniform sizing along the length of the mold has been found to give a uniform finish to the splice and the splice is not visually noticeable. Accurate measurement along the length of the splice may show dimensional variations of the order of a few thousandths of an inch, but as these occur over distances of the order of a few inches, they are not detectable to an ordinary user. Effectively, due to greater thermal expansion in the joint area, this will shrink more when it cools. This results in the joint area being of slightly smaller dimensions than the main part of the handrail, but joined to the main handrail body by smoothly tapered sections that are not readily discernible to an ordinary user. It is important when forming the interlace pattern for the joint, that the different portions of the pattern be cut reasonably exactly, so that the amount of material present corresponds to that needed to refinish the joint. If there is too much material present, so that there is substantial flow out through the edges of the mold, then the flow sideways tends to displace the cable ends sideways. This displaces the cable ends and significantly distorts the joint, so as to affect the mechanical properties of the joint. Ideally, any flow of excess material is minimal, so that the cable ends remain substantially unmoved, with the cable ends aligned with one another and in a desired array, to give a strong joint. The inclined cuts 134, or other formation in the slider fabric, are provided, so as to avoid a purely square cut in the slider fabric 130. By providing an inclined cut, it is believed that the joint will travel more smoothly and be less susceptible to damage in use. Also, this effectively enables tension loads to be transferred across the joint in the slider fabric 130. If a square or butt joint is provided in the fabric 130., tension loads, e.g., when the handrail is bent backwards in some drive assemblies, will tend to open the joint. A saddle for the fabric will reinforce the joint and transfer the tension loads. While the invention has been described in relation primarily to handrails, it is to be appreciated that it is applicable to any article formed from a thermoplastic material and having a constant cross- section. For example, it could be applied to conveyor belts, which often have many properties similar to handrails. Typically a conveyor belt will include reinforcing cables or other stretch inhibitor, to give the desired strength and elastic properties to the conveyor belt. It may often include a fabric layer bonded to one side of it. A conveyor belt typically has a simple rectangular section, so it is a simple matter of forming an interlace pattern through the complete depth of the conveyor belt, and then assembling this together in a suitable mold.

Claims: WE CLAIM: 1. A method of forming a joint in an elongate article, which is of generally uniform cross-section, is formed from a thermoplastic material and has end parts, the method comprising the steps of: (1) placing the end parts of the article in a mold having a mold cavity with a cross-section corresponding to the cross-section of the article, and enclosing the end parts of the article within the mold; (2) while maintaining portions of the article adjacent the end parts cool, to prevent melting thereof, heating the end parts of the article to melt the thermoplastic material, thereby to fuse the end parts together; (3) while continuing to maintain said portions of the article adjacent the end parts cool, cooling the molten end parts of the article to resolidify the material and to form a joint. 2. A method as claimed in claim 1, when applied to an elongate article including a plurality of elongate inextensible members, wherein the method includes the additional step of, prior to step (1), cutting the inextensible members to at least two different lengths, to form an interlace pattern at the joint, with the inextensible members terminating in a plurality of planes transverse to the elongate article. 3. A method as claimed in claim 2, wherein the elongate inextensible members are cut with a corresponding portion of the material of the body of the article, whereby where the end parts of the elongate inextensible members are interlaced there are no substantial voids in the body of the material and a bond between the elongate inextensible members and the material is not disturbed. 4. A method as claimed in claim 3, wherein the interlace pattern is formed in an intermediate layer of the article extending into both end parts of the article, wherein the end parts of the elongate inextensible members and associated portions of the body of the article substantially fill the intermediate layer and leave no substantial voids. 5. A method as claimed in claim 4, wherein a second, top layer is defined in the end parts, adjacent and above the intermediate layer, and wherein during cutting of the end parts to form the interlace pattern, the portions of the end parts forming the second, top layer are removed, and wherein, to complete the joint, a top cap portion, corresponding to the second layer, is inserted into the mold. 6. A method as claimed in claim 1, when applied to an article formed from a hygroscopic thermoplastic which may contain water, wherein the temperature conditions along the mold are such that the article expands and contacts the mold to pressurise the end parts, before the thermoplastic melts, the end parts being pressurised to a pressure high enough to prevent vaporization of water in the molten thermoplastic. 7. A method as claimed in claim 4, when applied to an elongate handrail having a generally C-shaped external section and defining an internal T-shaped slot, and including an internal slider fabric around the T- shaped slot, the handrail having, in cross-section, a main top portion and side legs extending down therefrom around the T-shaped slot with the inextensible members being located in the top portion above the T-shaped slot, wherein the method comprises forming the interlace pattern in the top portion of the handrail. 8. A method as claimed in claim 7, wherein the interlace pattern is formed in an intermediate layer of the top portion above the slider fabric. 9. A method as claimed in claim 8, wherein the end parts of the handrail, above the intermediate layer, include a second, top layer which is removed during formation of the interlace pattern and wherein a top cap portion of the handrail is provided to complete the cross-section. 10. A method as claimed in claim 9, wherein, for each end part, a lower portion including the slider is cut to form a pattern selected from one of: an inclined joint in the slider fabric; and an interdigitated pattern. 11. A method as claimed in claim 10, which includes providing a saddle for the slider, extending over at least part of the width of the handrail. 12. A method as claimed in claim 10 or 11, wherein, in step (2), the end parts of the article are heated to a temperature such as to form a bond between the thermoplastic material layers, which provides a peel strength comparable to the peel strength of the original handrail. 13. A method as claimed in claim 10 or 11, wherein an inclined joint is formed and wherein, in forming the inclined joint, a horizontal cut is made beneath each intermediate layer, and a replacement bottom sheet is provided to allow for the thickness of the cut. 14. A method as claimed in claim 7, when applied to a handrail formed from a hygroscopic thermoplastic which may contain water, wherein the temperature conditions along the mold are such that handrail expands and contacts the mold to pressurise the end parts, before the thermoplastic melts, the end parts being pressurised to a pressure high enough to prevent vaporization of water in the molten thermoplastic. 15. A method as claimed in claim 7, wherein the mold cavity is dimensioned so as to be slightly oversized as compared to the cross-section of the article at ambient temperature, the cross-section of the mold being such that a resultant joint has dimensions generally similar to dimensions of the elongate article. 16. A method as claimed in claim 15, when applied to a handrail formed from a hygroscopic thermoplastic which may contain water, wherein the temperature conditions along the mold are such that the handrail expands and contacts the mold to pressurise the end parts, before 5 the thermoplastic melts, the end parts being pressurised to a pressure high enough to prevent vaporization of water in the molten thermoplastic. 17. A method as claimed in claim 7, when carried out using a mold comprising at least two mold parts displaceable between open and closed configurations, wherein an external pressure is maintained on the mold 10 parts pressing the mold parts together into the closed configuration, which external pressure permits any excess thermoplastic material to displace the mold parts to enable the excess material to flow out of the mold cavity, whereby internal pressure within the cavity is reduced sufficiently to enable the mold parts to resume the closed configuration. 15 18. A method as claimed in claim 17, when applied to a handrail formed from a hygroscopic thermoplastic which may contain water, wherein the temperature conditions along the mold are such that the handrail expands and contacts the mold to pressurise the end parts, before the temperature of the end parts is high enough to vaporize water in 20 molten thermoplastic, and the external pressure maintains an internal pressure sufficient to prevent generation of water vapor bubbles in the end parts. 19. An apparatus for forming a joint in an elongate article of substantially uniform cross-section and formed from a thermoplastic 25 material, the apparatus comprising a mold defining an elongate cavity having a cross-section corresponding to the cross-section of the elongate article, which mold comprises a central section and first and second end sections on either side of the central section; a main heating means for heating end parts of the article in the central section of the mold to cause remelting and fusing of the end parts of the article; a main cooling means for cooling the end parts of the article to resolidify the material and form the joint; and end cooling means, for the first and second end sections, for 5 cooling portions of an elongate article adjacent the end parts thereof, to prevent melting, wherein the mold comprises at least two parts which are displaceable between an open configuration in which an article can be inserted into the mold and a closed configuration for forming a joint. 20. An apparatus as claimed in claim 19, wherein the mold comprises a 10 top part and a bottom part, wherein the top part of the mold comprises top parts of the main central section and of the first and second end sections, and the bottom part of the mold comprises bottom parts of the main central section and of the end sections. 21. An apparatus as claimed in claim 20, wherein the top parts of the 15 end sections are joined to the top part of the central section but are generally thermally insulated therefrom, and wherein the bottom parts of the end sections are joined to the bottom part of the central section but are generally thermally insulated therefrom. 22. An apparatus as claimed in claim 21, wherein the top parts of the 20 central section and the end sections are integrally formed from metal and are joined by a narrow web providing insulation, and wherein the bottom parts of the end sections and the bottom part of the central section are integrally formed from metal and are joined by a narrow web providing insulation. 25 23. An apparatus as claimed in claim 21, wherein for each of the central and end sections, the top and bottom parts have complementary mating surfaces which abut one another in use, in the closed configuration, and an elongate trough is formed in each mating surface, forming part of the cross- section of the elongate article. 24. An apparatus as claimed in claim 23, wherein at least one of the top and bottom parts of the central section includes an overflow groove means. 5 25. An apparatus as claimed in claim 21, wherein each of the top and bottom parts of each of the end and central sections includes a duct means, for passage of a liquid coolant. 26. An apparatus as claimed in claim 25, wherein for the end sections, the duct means comprises a straight bore extending through the respective 10 one of the top and bottom parts thereof, and for the central section, the duct means comprises a pair of longitudinally extending bores and a pair of transverse bores connected to ends of the longitudinal bores, with the transverse ducts each having one end opening to the exterior to form a connection port. 15 27. An apparatus as claimed in claim 25 or 26, wherein the top and bottom parts of the central section include second elongate bores and the heating means comprises heating elements located in the second elongate bores. 28. An apparatus as claimed in claim 21, adapted for forming a joint in 20 an elongate handrail having a generally C-shaped external section and defining an internal T-shaped slot, and comprising a main body formed of a thermoplastic material, a stretch inhibitor reinforcing the handrail, and a slider fabric bonded to the main body and around the T-shaped slot, wherein the apparatus includes an elongate mandrel extending through the 25 central and end sections and having a profile corresponding to the T-shaped slot. 29. An apparatus as claimed in claim 28, wherein the mandrel is secured to the top parts of the central and end sections and extends beyond the mold. 30. An apparatus as claimed in claim 29, wherein both the top and bottom parts of the central and end sections and the mandrel include heating elements. 31. An apparatus as claimed in claim 28, wherein the mold has a uniform internal cross-section for the central and end sections of the top and bottom parts, which cross-section is slightly larger than the cross-section of the handrail at ambient temperature.

Inventors: BALL DAVID S, BALL RONALD H, CAUNCE A STUART, KENNY ANDREW O, WEATHERALL DOUGLAS J, BALL, DAVID, S., BALL, RONALD, H., CAUNCE, A., STUART, KENNY, ANDREW, O., WEATHERALL, DOUGLAS, J.
Applicants: BALL DAVID S, BALL RONALD H, CAUNCE A STUART, KENNY ANDREW O, WEATHERALL DOUGLAS J, BALL, DAVID, S., BALL, RONALD, H., CAUNCE, A., STUART, KENNY, ANDREW, O., WEATHERALL, DOUGLAS, J.
Application year: 1997
Main classification: B29C65
IPC codes: B29C65, B29K105, B29L29, F16G3