METHOD AND DEVICE FOR THERMOPLASTIC WELDING

Abstract: To obtain a flashless welded joint between two ends of a thermoplastic profile welding is carried out under application of heat and pressure in a mold which is closed at least in the region of the two ends to be welded together.

Description: Method and Device for Thermoplastic Welding The present invention relates to a method for the flashless welding of thermoplastic profiles. It also relates to a device for welding such profiles and to an endless profile welded by the method according to the invention. To prepare endless profiles from pre-cut lengths of open-ended materials, a splicing operation is required. For profiles made of a thermoplastic material, welding is the most convenient splicing method. According to the conventional welding method, the two belt ends to be welded are brought into simultaneous contact with a heated metal blade until the material flows, after which they are pressed together and held under pressure until the softened end-surface material solidifies. While this method is simple, it suffers from several disadvantages: 1) The pressing-together of the softened ends produces a substantial flash all around the joint, which has to be carefully removed. 2) When applied to flexible thermoplastic material, it is difficult to maintain proper alignment of the two- ends during the welding operation. 3) The "hot blade" method does not permit controlled, uniform heat¬ ing of the belt ends and therefore does not produce joints of uniform quality. It is thus one of the objects of the present invention to over¬ come the drawbacks and difficulties of the prior art methods and to provide a method that produces substantially flashless welded joints of high, uniform quality and precisely aligned profile ends. According to the invention, this is achieved by providing a method for producing a flashless, welded joint in a thermoplastic profile, comprising the steps of providing a piece of profile of predetermined length, with ends cut to have complementary surfaces, inserting the ends of said profile into an open mold, with the complementary surfaces of said ends facing one another at a distance, applying heat to said complementary surfaces, bringing said comple¬ mentary surfaces together in said open mold, closing said mold at least in the region of said brought-together complementary surfaces and applying pressure in said region in the plane of said surfaces, and allowing the thus-produced substantially flashless, welded joint to solidify under pressure. The invention further provides a device for producing a flashless, welded joint in a profile of predetermined length, with ends cut to have complementary surfaces, comprising two members, at least one of which has an at least partly open guide and molding groove adapted to snugly fit and accommodate said profile along at least some portions of at least one of the surfaces thereof, the other of said two members having at least one surface substantially aligned with at least one of the profile-fitting surfaces of said guide groove, at least one of said two members being movable in translation relative to the other member, means to immobilize one end portion of said profile relative to one of said two members, means to immobilize the other end portion of said profile relative to the other one of said two members, means to apply heat to said complementary surfaces, means to produce a translational movement of at least one of said members to bring together said two complementary surfaces after having been heated, and means to close at least a portion of said open guide and molding groove and to apply pressure in the region and the plane of said brought-together complementary surfaces. The invention will now be described in connection with certain preferred embodiments with reference to the following illustrative figures so that it may be more fully understood. With specific reference now to the figures in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental under¬ standing of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the drawings: Fig. 1 is a schematic perspective view of the device according to the invention; Fig. 2 illustrates the device in an initial stage of its use; Fig. 3 is a partial view, in cross section along plane III—III in Fig. 2; Fig. 4 is a similar view, in cross section along plane IV—IV in Fig. 2; Fig. 5 shows the device with both profile ends immobilized; Fig. 6 shows the device with the hot-air nozzle in operation; Fig. 7 is a partial view, in cross section along plane VII—VII in Fig. 6; Fig. 8 shows the device in the final stage of its use; and Fig. 9 is a partial view, in cross section along plane IX—IX in Fig. 8. Referring now to the drawings, there is seen in Fig. 1 a stationary member 2, fixedly mounted on the base of the device (not shown). The stationary member has an open guide and molding groove 4 (see Fig. 3) of a cross-sectional shape configured to snugly fit the profile 6 to be spliced by welding. In Fig. 4, a V-belt profile 6 is shown accommodated in the groove 4. Further seen in Fig. 1 is a second member 12 which is movable in translation, being guided by two guide rods 14 on which it is sliding- ly mounted. Movement of the member 12 is effected by a hydraulic or pneumatic cylinder 16 mounted on a bracket (not shown) fixedly attached to the above-mentioned base. In Fig. 2 the movable member 12, too, is preferably provided with a guide groove, 5, similar in size and shape, and in alignment with, the groove 4 of the stationary member 2. Each of the members 2, 12 is provided with a clamping means 18 and 20, respectively, shown in Fig. 1 in the open position. When in the course of the welding operation these clamping means are brought down onto the profile end portions as located in their respective members, these ends are immobilized relative to these members. Thus profile end A is immobilized with respect to the stationary member 2 by clamping means 18, and profile end B is immobilized with respect to the movable member 12 by clamping means 20. A pressure pad 22, as seen above the gap 23 left between the ends A and B, completes the circumference of the profile partly formed by the molding groove 4. The purpose of this pad will be explained further below. Located in the plane of the gap 23, there is seen a hot-air nozzle 24. Shown in Fig. 1 in its working position in which it blows hot air into the gap, it is used to soften the complementary surfaces 26, 28 of the ends A and B respectively, prior to the actual welding thereof. After the softening operation and prior to the below described welding stage, the nozzle 24 is withdrawn, to make way for the descending pad 22. The following is a step-by-step description of the method according to the invention. The first step consists in preparing a piece of thermoplastic profile of the required length, having two end portions A and B, and two complementary surfaces 26,28 (Fig. 2). In a preferred embodiment of the method, a butt surface perpendicular to the profile's center axis is produced. The end portion A is then inserted into the guide groove 4 of the stationary member 2 (Fig. 2) to a predetermined point advantageously indicated by a mark (not shown) and is then immobilized by clamping it down with the aid of the clamping means 18. The position of the belt inside the groove 4 with matching contours is clearly seen in Fig. 4, which also shows the clamping means 18 as clamped down. The next step is illustrated in Fig. 5, showing the other end portion B inserted into the guide groove 5 and immobilized relative to the movable member 12 by clamping means 20. The complementary surfaces 26,28 now face one another at a short distance. The hot-air nozzle 24 is then swung into position above the gap 23, as shown in Figs. 6 and 7, and hot air is forced into the gap. - 1 - softening the two complementary surfaces 26 and 28. It is obvious that the particular form of the hot air nozzle can be adapted to match the complementary surfaces 26,28. In Fig. 8, the movable member 12 is pneumatically pushed towards the stationary member 2, until the complementary surfaces 26,28 meet under controlled pressure and, having been thoroughly softened, fuse. While the movable member 12 still moves, the nozzle 24 is swung away, to make room for the pressure pad 22 which now descends, completing the groove 4 above the welding joint in forming the circumference of the profile while exerting pressure in the plane of the joint (see Fig. 9), and turning this part of the open groove 4 into a closed mold, thus preventing the formation of flash. Pressure on the pad 22 and the movable member 12 is maintained until the joint region has solidified. This process is advantageously accelerated by the provision of a system of cooling ducts. After solidification is completed, the clamping means 18,20 and pressure pad 22 are opened and the now endless profile removed from the device, following which the cylinder 16 is activated to return the movable member 12 to its initial position. While the profile used to explain the device according to the invention was a V-belt profile, other profiles, too, can be welded using the device. Such profiles include round, rectangular, hollow, reinforced profiles, etc. ' The angle of cut of the ends A and B can be any pair of comple¬ mentary angles, allowing the continuity of the profiles. As the guide and molding groove 4 and the guide groove 5 are different for each profile, it is advantageous to design the members 2 and 12 as two-part blocks each, the upper part having the required groove and being exchangeable. Clearly, the profile and size of the clamping means 18,20 and pressure pad 22, too, is determined by the profile. While hot air has been found very suitable as heating medium for softening the thermoplastic belt material to the fusing point, other media are also possible, e.g., a flat electric heating element insertable into the gap 23 and producing radiant or contact heat or heat generated by electromagnetic fields. It will be evident to those skilled in the art that the invention 1s not limited to the details of the foregoing illustrative embodi¬ ments and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the Invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims: WHAT IS CLAIMED IS: 1. A method for producing a flashless, welded joint in a thermo¬ plastic profile, comprising the steps of: providing a piece of profile of predetermined length, with ends cut to have complementary surfaces; inserting the ends of said profile into an open mold, with the complementary surfaces of said ends facing one another at a distance; applying heat to said complementary surfaces; bringing said complementary surfaces together 1n said open mold; closing said mold at least in the region of said brought-together complementary surfaces and applying pressure in said region in the plane of said surfaces, and allowing the thus-produced substantially flashless, welded joint to solidify under pressure. 2. The method as claimed in claim 1, comprising the further step of immobilizing said ends after the insertion thereof into said open mold. 3. The method as claimed in claims 1 and 2, comprising the further step of ceasing application of said pressure and opening said mold to facilitate removal of said now welded profile from said mold. 4. The method as claimed in claim 1, wherein said heat is produced by at least one jet of hot gas. 5. The method as claimed in claim 1, wherein said heat is radiant heat impinging on said surfaces. 6. A device for producing a flashless, welded joint in a profile of predetermined length, with ends cut to have complementary surfaces, comprising: two members, at least one of which has an at least partly open guide and molding groove adapted to snugly fit and accommodate said profile along at least some portions of at least one of the surfaces thereof, the other of said two members having at least one surface substantially aligned with at least one of the belt-fitting surfaces of said guide groove, at least one of said two members being movable 1n translation relative to the other member; means to immobilize one end portion of said profile relative to one of said two members; means to immobilize the other end portion of said profile relative to the other one of said two members; means to apply heat to said complementary surfaces; means to produce a translational movement of at least one of said members to bring together said two complementary surfaces after having been heated, and means to close at least a portion of said open guide and molding groove and to apply pressure 1n the region and the plane of said brought-together complementary surfaces. 7. The device as claimed in claim 6, wherein one of said members is stationary and the other one movable. 8. The device as claimed -in claim 7, wherein said open guide and molding groove is provided in said stationary member. 9. The device as claimed in claim 6, wherein said means to immobi¬ lize said profile end portions are clamping means actuable by fluid- pressure-operated cylinders. 10. The device as claimed in claim 6, wherein said means to apply heat to said complementary surfaces is a hot-air nozzle locatable in a position close to said complementary surfaces to be welded and removable from said position after the application of said heat. 11. The device as claimed in claim 6, wherein said means for producing said translational movement of said movable member is a fluid-pressure-operated cylinder. 12. The device as claimed in claim 6, wherein said means to close at least a portion of said open groove is a pressure pad actuable by a fluid-pressure-operated cylinder, which pad is so dimensioned and configured that at least in the region of said brought-together complementary surfaces said profile is fully enclosed by surfaces of said groove in conjunction with at least one surface of said pad, pressure being applied by said pad to said region in the plane of said brought-together complementary surfaces and maintained until said heat-and pressure-produced joint has solidified. 13. A thermoplastic profile structure as spliced by welding according to the method of claim 1. 14. A method for producing a flashless, welded joint in a thermo¬ plastic profile substantially as hereinbefore described, and with reference to the accompanying drawings. 15. A device for producing a flashless, welded joint in a thermo¬ plastic profile of predetermined length, substantially as hereinbefore described, and with reference to the accompanying drawings.

Inventors: HARAN MOSHE, SCHANIN JONATHAN, HARAN, MOSHE, SCHANIN, JONATHAN
Applicants: FENRIR AG
Application year: 1991
Main classification: B29C65
IPC codes: B29C65