DE3325339A1 - Process and device for welding the edges of plastics webs - Google Patents

Abstract

The present process of so-called thermal welding serves for welding the edges of webs of plastics, especially PVC and copolymers, the edges to be welded being heated until they soften and simultaneously pressed together. In order to use higher temperatures in the welding, according to the present process the edges to be welded are covered on both free outer surfaces with one separating layer in each case before being pressed together and then the edges are pressed together over the entire length between heated rails for an adjustable welding time and with an adjustable welding pressure. Subsequently the separating layers adhering lightly at the edge regions can be stripped off the webs welded together at their edges. A device of frame-like design is provided for carrying out this process, having a support table for the two-part welding tool and a roll stack for drawing in the separating layers. <IMAGE>

Description

Method and device for welding the edges of

Plastic Sheets The present invention relates to a method and a device for welding the edges of thermoplastic sheets, in particular PVC, ie of polyvinyl chloride, and copolymers, with the to Welding edges heated until they soften and pressed together at the same time will.

Such methods are already known and are, for example carried out in such a way that the edges of the plastic webs to be welded in heated by a high frequency field, softened on their inner surfaces and then are pressed together from the outside. These methods of high frequency welding deliver durable welded edges, but require a considerable amount of high-frequency energy and are accordingly expensive. In addition, the maximum allowable high frequency energy is in many countries limited by government regulations to avoid interference with others to avoid facilities working on the frequencies concerned.

So-called source welding is of course also known, whereby the overlapping edges of the plastic sheets to be welded together provided with a liquid solvent welding agent and thus on their surface are plasticized, so that when these edges are pressed together, a weld occurs the edges takes place. Using suitable solvent welding agents can be achieved that the solvent practically completely evaporates, which is durable welded Margins results.

Also the so-called thermal welding (e.g. hot gas, heating wedge) of the Edges of plastic sheets has already been proposed, but it has been found that both PVC sheets and plastic sheets made of copolymers have the tendency own, on the heated components causing the thermal welding to stick. For this reason, a compromise between temperature had to be made in this process up to now and contact pressure are sought, so that on the one hand a sufficient softening of the facing surfaces of the edges to be welded is guaranteed, on the other hand but sticking of the outer surfaces of the heated edge areas to the heated ones Components is avoided. There is also a danger with these welding methods of initially undetectable temperature deviations due to voltage fluctuations in the power grid. This compromise is caused by strength and durability the edges of plastic sheets welded with this type of thermal welding often objectionable, especially with plastic sheeting on the outside of Structures are used and are exposed to aggressive weather conditions.

The present invention has set itself the task of the previous Avoid the disadvantages of thermal welding. The method according to the invention is characterized in that the to be welded before pressing together The edges on both free outer surfaces are covered with a separating layer each, and then the edges along their entire length between heated rails during one adjustable welding time and pressed together by adjustable welding pressure whereupon of the webs welded together at their edges, those at the Separating layers that adhere slightly to the edge are peeled off.

The invention also relates to a device for welding the edges of sheets made of PVC and other plastics by means of thermal welding.

The invention is based on a few exemplary embodiments below 1 to 4 explained in more detail. 1 shows a schematic, vertical view Direction exploded view for the welding of the overlapping Edges of two sheets of plastic; Fig. 2 shows a further embodiment for the Welding of double-walled plastic sheets; dough. 3 and 4 an elevation or a plan view of the device according to the invention in a schematic representation; In the description below, the # designation PTFE is used, which is used in specialist circles is common for a material made of polytetrafluoroethylene.

The present method is initially based on FIG. 1 for welding the edges of two plastic webs 10 and 11 described, the overlapping Edges 12 and 13 are to be welded together. As with thermal welding Usually, the welding takes place by means of a lower and an upper heated one Rail 14 or 15, however, these are heated here before they are pressed together Rails 14 and 15, the edges 12 and 13 to be welded on both free outer surfaces each covered with a separating layer 16 or 17. Then the edges 12 and 13 are over their entire length between the heated rails 14 and 15 during an adjustable Welding time and adjustable welding pressure compressed. Since now the outside areas of the edges 12 and 13 to be welded, the heated rails 14 and 15, respectively, do not can touch no risk of sticking to the hot rails 14 or 15 takes place. The heating of the edges to be welded 12, 13 takes place through the two separating layers 16 and 17, respectively, but this is the case with a suitable one Choice of the material of these separating layers 16, 17 with practically no loss of heat or time is possible.

However, the presence of the two separating layers 16, 17 makes it possible to choose the temperature of the heated rails 14 and 15 significantly higher than in the previously common thermal welding with "bare" heated press tools, there at the risk of the material of the plastic webs 10 and 11 sticking to it Consideration must be taken more. The 'permissible higher temperature of the heated Rails 14, 15 also enable the welding time to be shortened.

In the present method, the to be welded are accordingly Edges of the two plastic sheets 10 and 11 over their entire length between the heated rails 14 resp.

15 during the appropriately selected welding time and with the appropriate selected welding pressure pressed together until an intimate connection of the softened Inside of the edges 12 and 13 takes place. Then the pressing process of the edges 12, 13 finished, heated rails 14 and 15 are removed from one another and then -be the slightly adhering separating layers 16 from the edges 12, 13 ′ that are welded together and 17 subscriptions. With a suitable choice of these separating layers 16, 17 there is no risk of that the same are welded to the outer surfaces of the edges 12, 13, so that the removal of these separating layers 16, 17 is possible without difficulty. For example a flat ruler is placed between the separating layers 16 or -17 and the ones that are welded together Plastic sheets pushed through over the entire length of the separating layers 16, 17, with which the adhesion of the separating layers 16, 17 to the edge regions 12, 13 is already eliminated.

In the present process of thermal welding of PVC and mixed polymer plastic sheets For example, separating layers 16, 17 made of a glass fiber fabric have proven successful that is coated with PTFE on at least one side. Likewise, unarmored Separating layers are used.

Such separating layers have a thickness of 0.5 mm, for example and are easily flexible and rollable. If one only coated with PTFE on one side Separation layer of this type is used, of course, the coated side must match the outer surfaces facing the edges 12, 13 to be welded. On the one hand, the melting point of PTFE is significantly higher than that to be welded together at the edges Plastic sheeting, and on the other hand, according to experience, a PTFE layer only one-very-a-time has little tendency to adhere to heated surfaces, ensures a such a separating layer in the present method that sticking neither to the welded together edges 12, 13, still on the heated outer surfaces of the rails 14 or 15 can take place. Instead of the coated fiberglass fabric you can Of course, other heat-resistant materials can be used if guaranteed is that the expansion of the separating layer at the temperatures used is negligible is small.

With this thermal welding process, it is also possible to to weld two plastic sheets together along their edges, if they do not overlap one another, but butt against one another with their front edges.

One or one plastic strip is then applied to the outer surfaces of the edge areas placed for the purpose of welding to the outer surfaces of the edges of the two plastic sheets. Before the thermal welding is carried out, however, according to the present process, each with a separating layer, the free outer surfaces the one or two plastic strips covered, making the same the surfaces Do not touch the heated rails.

The use of the present method for welding the edges of plastic sheets that butt against each other with their front edges, also enables, for example, the permanent connection of large double-walled Plastic sheeting. For example, in Fig. 2 the welding of such double-walled Plastic webs shown, which are plastic webs, each consist of a lower and an upper plastic layer 20, 21 and 24, 25 and one different types of intermediate layer 23 or 26, for example a so-called spacer fabric can be to liquid or gaseous media through the double-walled plastic sheet pass through. Around the butt abutting front edges of this double-walled Plastic webs 20, -21 or 24, 25 to one another. connect, but with the flow of the medium through the middle layer 23 or 26 over the front edges to affect, is to be connected to the edge areas of the two double-walled Plastic sheets each with a plastic strip 27 or 28 placed with the intention of to weld the plastic strip 27 to the two plastic layers 20 and 24, or the plastic strip 28 with the plastic layers 21 and 25 insoluble associate. According to the present method, the outside of the Plastic strips 27 and 28 are covered with a separating layer 29 and 30, respectively, and then the welding process is carried out by pressing the heated rails 14 and 15 against them. Here too, after the welding process has been completed, the separating layers 29 and 30 can easily from the outside of the welded to the two double-walled plastic sheets Plastic strips .27 or 28 can be pulled off.

In the present thermal welding process using the As already mentioned, a higher temperature can be used than with previous thermal welding. It is then useful when pressing together the heated rails 14 and 15 by suitable measures guarantee, that the same do not fall below a predetermined and adjustable distance can. In this way it can be achieved that each other during the welding overlapping edges as in the embodiment of FIG. 1, a wide squeeze the edge areas is avoided. Such a limitation of the smallest distance when pressing the heated rails together is particularly important when using the present method for thicker plastic sheets, such as those in the exemplary embodiment according to Fig. 2 indicated double-walled plastic sheets, important.

The present method, as described above, has has proven itself in practice and not only enables the edges to be welded simple flat plastic sheets, but also especially the production of large, plastic covers consisting of many individual welded-together track sections, as they are for roofs, for example. are determined by buildings. This often occurs the need for one, two such path segments along curved edge regions with one another to weld what a correspondingly flexible adjustable to such needs Establishment required. The embodiment described below such a device for performing the present method exists accordingly from assemblies that are mutually adjustable and enable the use of curved heating rails.

The device shown schematically in FIGS. 3 and 4 consists from a frame-like structure which has a plurality of vertical uprights 35, the each has a bottom rail 36, a double column 37 and an upper cross beam 38 having. As indicated in FIG. 4, there are three in the present exemplary embodiment such stand 35 is provided, which with the longitudinal beams 39 and 40 on the lower or upper end of the double pillars 37 together are connected. The front ends of the three floor rails -36 are also connected to one another via a longitudinal beam 41 connected and likewise the front ends of the upper crossbeams 38 have a corresponding connection with the longitudinal beam 42. Thus, the three uprights form 35 together with the longitudinal beams 39, 40, 41 and 42 - a rigid frame-like structure, which on the one hand is sufficiently stable and the pressures occurring in the present process can record, and on the other hand both in a Werkhal1 # #ls ~ on a construction site can be used, for example, to produce a roof covering by means of plastic sheets is. In practice it has been found to be useful that the individual stands 35 such a device have about a mutual distance of one meter and the device shown in FIG side by side for the. Welding of plastic sheets up to a width of about two meters is suitable. By arranging more than three such Columns 35 next to one another can of course also be the edges of plastic sheets welded together with a larger width according to the present method will.

The front ends of the bottom rails 36 of the three uprights 35 support over a support 43 a support table 44, which here for example from suitable Hollow profiles 45 is composed and extends over the entire length of the three uprights 35 extends, as can be seen from FIG. Screwed firmly to this support table 44 is the lower part of the welding tool, which consists of a hollow beam 46 with a thermally insulating holder 47 for the heating rail 48 with the embedded therein electric heating rods 49 consists. The hollow bar 46 can have openings on both sides 50, the purpose of which will be explained below.

The upper part of the welding tool is arranged in a mirror image and consists of the hollow beam 51 with the thermally insulating # bracket 52 for the heating bar 53 with the electrical heating rods 54 embedded therein. Also this hollow beam 51 can conveniently with side openings 55 be provided.

The upper part 51 to 54 of the welding tool is on the piston rod 56 of a pressure cylinder 57 attached and can this by appropriate control Cylinder 57 can be pulled up or pushed down as required. The printing cylinder 57 is attached to the vertical beam 58. This bar 58 is at the top Crossbar 38 adjustably attached and can-be 'both forwards and backwards as well as move sideways on the crossbar 38. In this way it is possible as indicated in FIG. 4, the pressure cylinders 57 of the three uprights 35 so against one another shifted to arrange that the attachment of a curved upper welding tool 51 to 54 is possible, in which case of course also the lower part of the welding tool 46 to 49 on the support table 44 correspondingly offset to the center line of this support table 44 must be arranged. In any case, this construction enables the crossbeam 38 the stand 35 allows the attachment of both straight and curved heating rails 53, as is the case, for example, for the welding of non-rectilinear Edge areas of plastic sheets is desirable.

When operating the device according to FIGS. 3 and 4 for welding = sen it is the edges of large-area plastic strips according to the present method necessary, the facing surfaces of the heating rails 48 and 53 with each to cover with a separating layer. For this purpose, for example, as indicated in Figure 4, the lower separating layer 60 on a rotatable roller attached to the support table 44 61 and is wound in the direction of the arrow before the start of the welding process 62 pulled over the lower heating rail 48 and on the rotatable roller 63 wound at the other end of the support table 44.

Then the plastic web is from a supply roll 64 in the direction of the arrow 65 withdrawn, into the gap between the already covered lower heating rail 48 and the one not yet covered upper heating rail 53 inserted and recorded there in a suitable manner. The second plastic sheet is then from the outside so placed on the edge area of the first-mentioned plastic sheet that the overlap edge areas on both sides, for example in the manner shown in FIG. Now the upper separating layer is placed on the overlapping edge area, for which in a manner similar to that already described for the lower separating layer & 0 Xan two ends of the support table 44 each have an additional rotatable roller Only then is the heating bar 53 of the upper welding tool activated the pressure cylinder 57 is lowered and with the intended pressure on the to be welded placed on the overlapped edge. By setting the pressure in the pressure cylinders accordingly 57, the contact pressure of the two heating rails 48, 53 on the one to be welded overlapped edge areas of the two plastic sheets are determined.

In the setup described, the rails are electrically heated 48 or 53 via suitable, thermally insulating. Brackets 47 and 52 to the Hollow beams 46 and 51 attached.

These hollow beams 46, 51 have openings 50 and 55, respectively, on both sides provided, so that resulting from the hollow beams 46, 51 during the welding process Vapors or gases can be extracted.

This suction process also cools the hollow beams 46, 51, which is advantageous in avoiding undesirable thermal distortions is. As already stated above, in the present method through the application the so-called separating layers the use of higher temperatures for thermal welding permissible for plastic sheeting, but it must be ensured that none Bending of the heating rails 48 and 53 caused by material expansion occurs.

In order to achieve this, the heating rails 48 and 53 can also be made from Layers of metals with different expansion coefficients exist in such a way that that at the intended operating temperature, the thermally caused expansions largely compensate. Of course there is also the possibility how indicated in FIG. 4 by additional pressure cylinders 57 'which are attached to the longitudinal beam 42 are arranged between the three uprights 35, a possible bending of the heating rails or the entire welding tool.

It should be noted that the support table 44 is not only is used to attach the lower part of the welding tool. He. is also beneficial to attach additional devices, such as spacers to limit the maximum advance of the piston rods 56 and thus of the upper part of the welding tool relative to its lower part, which occurs when welding double-walled plastic sheets according to the method described with reference to Figure 2 is required. Also possibly desired clamping devices for the plastic webs to be welded can be arranged on the support table 44.

Claims (8)

PATENT CLAIMS @ Process for welding the edges of webs made of plastics, in particular PVC and copolymers, the ones to be welded Edges are heated until they soften and at the same time pressed together, thereby marked - that the edges to be welded open before pressing together both free outer surfaces are covered with a separating layer each - and then the edges along the entire length between heated rails during an adjustable Welding time and with adjustable welding pressure are pressed together, - whereupon of the webs welded together at their edges, those at the edge areas slightly adhesive separating layers are peeled off. 2. The method according to claim 1, characterized in that the to welding edges overlap each other. 3. The method according to claim 1, characterized in that the to The edges of the welded edges butt against each other with their front edges, each with a plastic strip placed on the outer surfaces of the edge areas and with the two edges on each the outer surfaces welded is, according to each with a separating layer the free outer surfaces of the two plastic strips have been covered. 4. The method according to claims 1 and 3, characterized in that that when welding the edges of double-walled plastic sheets with intermediate porous spacer material that remains when the heated rails are pressed together Gap between them is limited. 5. The method according to claim 1, characterized in that that as a separating layer - at least one side with PTFE - or something else accordingly heat-resistant plastic coated glass fiber fabric or other equivalent Heat-resistant material is used and its coated side is the one to be welded Edges is turned. 6. Device for carrying out the welding process Edges of sheets made of plastics, characterized - by a frame-like structure of several, juxtaposed identical stands (35) - each of which consists of a floor rail (36), a vertical column (37) and an upper cross beam (38) and which are rigidly connected to one another by several longitudinal bars (39,40, 41,42) are connected, - by a support table extending over all the uprights (35) (44) each with a support (43) on the bottom rails (36) of the individual stands (35) is attached, - By one, which can be fastened on the support table (44) lower part of a welding tool, which consists of a hollow beam (46) and one on top arranged thermally insulating holder (47) with a metallic, embedded electrical heating rods (49) having heating rail (48) consists, - by a, the upper part of a welding tool arranged in mirror image to the lower part, that of a hollow beam (51) and a thermally insulating one arranged thereon Holder (52) with a metallic, embedded electrical heating rods (54) Heating rail (53). consists, - . by one pressure cylinder (57) each, which is forward and backward as well as laterally adjustable attached to the upper transom (38) of each upright (35) and has a piston rod (56) which is used to hold the hollow beam (51) of the upper part of the welding tool is set up, - and by at least a roller assembly (61, 63) at both ends of the support table (44) for pulling a separating layer (60) into the gap between the two parts of the welding tool. 7. Device according to claim 6, characterized by a suction device, those with the side holes (50,55) provided with hollow beams (46,51) of the two Parts of the welding tool is connected. 8. Device according to claim 6, characterized by heating rails (48,53) which consist of materials with different thermal expansion in such a way that at least partial compensation of the expansion at the operating temperature takes place.