CH661474A5 - METHOD AND DEVICE FOR CONNECTING THE EDGES OF PLASTIC RAILS. - Google Patents

Description

The invention relates to a method and a device for connecting the edges of webs made of plastics, in particular PVC and copolymers, wherein the edges to be connected are either arranged overlapping one another or running side by side and covered on at least one side by a certain plastic strip to be connected and wherein the so-welded assembly so formed is heated to soften and compressed at the same time.

Such methods are already known and are carried out, for example, in such a way that the edges of the plastic webs to be welded are heated in a high-frequency field, softened on their inner surfaces and then pressed together from the outside. Although these methods of high-frequency welding provide durable welded edges, they require a significant amount of high-frequency energy and are therefore expensive. In addition, the maximum permissible radio frequency energy in many countries is limited by official regulations in order to avoid interference with other facilities operating on the frequencies concerned.

Of course, so-called source welding is also known, in which the overlapping and weldable edges of the plastic sheets are provided with a liquid source welding agent and are thereby plasticized on their surface, so that when the edges are pressed together, the edges are welded. Using suitable sweat welding agents it can be achieved that the solvent evaporates practically completely, which results in durable welded edges.

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 a tendency to stick to the heated components that cause thermal welding and have therefore so far been necessary In this process, a compromise between temperature and contact pressure is aimed at, so that on the one hand a sufficient softening of the facing surfaces of the edges to be welded is ensured, but on the other hand sticking of the outer surfaces of the heated edge areas to the heated components is avoided. In addition, with these welding methods there is a risk of initially undetectable temperature deviations due to voltage fluctuations in the power grid. Caused by this compromise, the strength and durability of the edges of plastic sheets welded with this type of thermal welding are often objectionable, especially with plastic sheets that

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

3rd

66 i 474

be used on the outside of structures and are exposed to aggressive weather conditions.

The present invention has set itself the task of avoiding the previous disadvantages of thermal welding. The method according to the invention is characterized in that before being pressed together, the arrangement to be welded is covered with a separating layer on each of the two free outer surfaces, and then the arrangement is pressed over the entire length between heated rails during an adjustable welding time and with an adjustable welding pressure, whereupon by the lightly adhering separating layers are removed from the outer surfaces of the welded arrangement.

The invention is explained in more detail below in some exemplary embodiments with reference to FIGS. 1 to 4. Show of this:

Figure 1 is a schematic, exploded in the vertical direction for the welding of an arrangement of overlapping edges of two plastic sheets.

2 shows a further exemplary embodiment for welding double-walled plastic sheets;

3 and 4 are an elevation and a plan view of the inventive device in a schematic representation.

In the description, the term PTFE is used below, which is common among experts for a material made of polytetrafluoroethylene.

The present method is first described with reference to FIG. 1 for welding the edges of two plastic sheets 10 and 11, the overlapping edges 12 and 13 of which are to be welded to one another. As is usual with thermal welding, the welding is carried out by means of a lower and upper heated rail 14 and 15, however, before the heated rails 14 and 15 are pressed together, the edges 12 and 13 to be welded are welded onto each of the two free outer surfaces Separation layer 16 or 17 covered. Then the edges 12 and 13 are pressed over their entire length between the heated rails 14 and 15 during an adjustable welding time and welding pressure. Now that the outer surfaces of the edges 12 and 13 to be welded cannot touch the heated rails 14 and 15, there is no danger that they will stick to the hot rails 14 or 15. The edges 12, 13 to be welded are heated through the two separating layers 16 and 17, which is practically possible without loss of heat or time if the material of these separating layers 16, 17 is selected appropriately. However, the presence of the two separating layers 16, 17 makes it possible to choose the temperature of the heated rails 14 or 15 to be significantly higher than in the previously conventional thermal welding with “naked” heated pressing tools, since at the risk of the material of the plastic sheets 10 or 11 no longer has to be considered. The permissible higher temperature of the heated rails 14, 15 also enables the welding time to be shortened.

Accordingly, in the present method, the edges of the two plastic sheets 10 and 11 to be welded are pressed over their entire length between the heated rails 14 and 15 during the suitably selected welding time and with the suitably selected welding pressure until an intimate connection of the softened inner sides of the Margins 12 and 13 takes place.

Then the pressing process of the edges 12, 13 is ended, the heated rails 14 and 15 are separated from one another and then the separating layers 16 and 17, which are slightly adhering to the edge regions, are removed from the plastic sheets 10 and 11 welded together with their edges 12, 13. With a suitable choice of these separating layers 16, 17 there is no danger that they will be welded to the outer surfaces of the edges 12, 13, that is to say the removal of these separating layers 16, 17 is possible without difficulty. For example, a flat ruler is pushed between the separating layers 16 and 17 and the welded plastic sheets over the entire length of the separating layers 16, 17, which already eliminates the adhesion of the separating layers 16, 17 to the edge areas 12, 13.

In the present method of thermowelding PVC and mixed polymer plastic sheets, for example, separating layers 16, 17, which consist of a glass fiber fabric that is coated on at least one side with PTFE, have proven effective. Unarmed separating layers can also be used. Such separating layers have, for example, a thickness of 0.5 mm and are easily flexible and can be rolled up. If a separating layer of this type which is coated on one side only with PTFE is used, the coated side must of course face the outer surfaces of the edges 12, 13 to be welded. Since on the one hand the melting point of PTFE is significantly higher than the plastic sheets to be welded together at the edges, and on the other hand experience has shown that a PTFE layer has only a very low tendency to adhere to heated surfaces, such a separating layer in the present process ensures that sticking does not occur on the welded edges 12, 13, still on the heated outer surfaces of the rails 14 and 15 respectively. Instead of the coated glass fiber fabric, other heat-resistant materials can of course also be used if it is ensured that the expansion of the separating layer is negligibly small at the temperatures used.

With the present thermal welding process, it is also possible to weld two plastic webs together along their edges if they do not overlap each other, but butt against each other with their front edges. One or each plastic strip is then placed on the outer surfaces of the edge areas for the purpose of welding to the outer surfaces of the edges of the two plastic sheets. Before carrying out the thermal welding, however, in accordance with the present method, the free outer surfaces of the one or two plastic strips are covered with a separating layer, so that they do not touch the surfaces of the heated rails.

The use of the present method for the welding of the edges of plastic webs that butt against one another with their end edges also enables, for example, the permanent connection of large-area double-walled plastic webs. For example, FIG. 2 shows the welding of such double-walled plastic sheets, which are plastic sheets each consisting of a lower and upper plastic layer 20, 21 or 24, 25 and a different type of intermediate layer 23 or 26, for example a so-called Spacer fabric can be to pass liquid or gaseous media through the double-walled plastic sheet. In order to connect the butt-jointed end edges of these double-walled plastic sheets 20, 21 or 24, 25 to one another, but not to impair the flow of the medium through the middle layer 23 or 26 over the end edges, the edge regions of the two double-walled parts to be connected are used Plastic sheets each have a plastic strip 27 or 28 placed with the intention of the plastic strip 27 with the two

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

661474

4th

Welding plastic layers 20 and 24, or insolubly connecting the plastic strips 28 to the plastic layers 21 and 25. According to the present method, the outer sides 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, respectively. Here, too, the separating layers 29 and 30 can easily be pulled off from the outside of the plastic strips 27 and 28 welded to the two double-walled plastic sheets after the welding process has been completed.

In the present thermal welding process using the separating layers described, as already mentioned, a higher temperature can be used than in the previous thermal welding. It is then expedient, when pressing the heated rails 14 and 15, to take suitable measures to ensure that they cannot fall below a predetermined and adjustable distance. In this way it can be achieved that when mutually overlapping edges are welded, as in the exemplary embodiment according to FIG. 1, a wide squeezing of the edge regions 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 the double-walled plastic sheets indicated in the exemplary embodiment according to FIG. 2.

The present method according to the above description has proven itself in practice and enables the edges not only to be welded to simple flat plastic sheets, but also in particular to produce large-area plastic covers consisting of many individual welded-together sheet sections, as determined, for example, for roofs of buildings are. In this case, there is often the need to weld two such web segments along longitudinally curved edge regions, which necessitates a device which can be adjusted correspondingly flexibly to such needs. The exemplary embodiment of such a device for carrying out the present method described below accordingly consists of assemblies which are mutually adjustable accordingly and which allow the use of curved heating rails.

The in Figs. 3 and 4 schematically shown device consists of a frame-like structure which has a plurality of vertical stands 35, each of which has a bottom rail 36, a double column 37 and an upper crossbeam 38. As indicated in FIG. 4, three such stands 35 are provided in the present exemplary embodiment, which are connected to one another by the longitudinal beams 39 and 40 at the lower and upper ends of the double columns 37. The front ends of the three floor rails 36 are also connected to one another via a longitudinal bar 41, and the front ends of the upper transverse bars 38 also have a corresponding connection to the longitudinal bar 42. Thus, the three stands 35 together with the longitudinal beams 39, 40, 41 and 42 form a rigid frame-like structure which is sufficiently stable and can absorb the pressures occurring in the present method, but both in a workshop and at a construction site, for example for the production of a Roof covering can be applied using plastic sheeting. In practice it has been found to be expedient that the individual stands 35 of such a device should have a mutual distance of approximately one meter and the device shown in FIG. 4 with three such stands 35 next to one another for welding plastic sheets up to a width of about two meters is suitable. Through the

If more than three such stands 35 are arranged next to one another, the edges of plastic webs of greater width can of course also be welded to one another in accordance with the present method.

The front ends of the bottom rails 36 of the three stands 35 each have a support 43 on a support table 44, which is composed here, for example, of suitable hollow profiles 45 and extends over the entire length of the three stands 35, as can be seen from FIG. 4. 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 electrical heating rods 49 embedded therein, is screwed onto this support table. The hollow rail 46 can be provided on both sides with openings 50, the purpose of which will be explained below.

The upper part of the welding tool is arranged mirror-image and consists of the hollow beam 51 with the thermally insulating holder 52 for the heating rail 53 with the electrical heating elements 54 embedded therein.

This hollow beam 51 can also be expediently provided with lateral openings 55.

The upper part of the welding tool 51, 52, 53, 54 is fastened to the piston rod 56 of a pressure cylinder 57 and can be pulled up or pushed down as required by appropriate control of this cylinder 57. The pressure cylinder 57 is attached to the vertical beam 58, which in turn is fastened in an adjustable manner to the upper cross beam 38 and can be moved both forwards and backwards and sideways on this cross beam 38. In this way, it is possible, as indicated in FIG. 4, to arrange the pressure cylinders 57 of the three stands 35 so as to be displaced relative to one another in such a way that the attachment of a curved upper welding tool 51, 52, 53, '54 is possible, in which case, of course the lower part of the welding tool 46, 47, 48, 49 on the support table 44 would have to be arranged correspondingly offset from the center line of this support table 44. In any case, this construction of the crossbeams 38 of the stands 35 enables both straight and curved heating rails to be attached, as is desired, for example, for welding non-rectilinear edge regions of plastic sheets.

3 and 4 for welding the edges of large-area plastic sheets according to the present method, it is necessary to cover the mutually facing surfaces of the heating rails 48 and 53, each with a separating layer. For this purpose, for example, as indicated in FIG. 4, the lower separating layer 60 is wound on a rotatable roller 61 attached to the support table 44 and is pulled over the lower heating rail 48 in the direction of the arrow 62 before the welding process begins, and wound on the rotatable roller 63 at the other end of the: support table 44. The plastic web is then pulled off from a supply roll 64 in the direction of arrow 65, inserted into the gap between the already covered lower heating rail 48 and the not yet covered upper heating rail 53 and held there in a suitable manner. From the outside, the second plastic sheet is then placed on the edge area of the first-mentioned plastic sheet in such a way that the edge areas on both sides overlap, approximately in the manner shown in FIG. 1. The upper separating layer is now placed on the overlapping edge region, for which purpose a further rotatable roller can be provided on each end of the supporting table 44 in a manner similar to that already described for the lower separating layer 60. Only then is the heating bar 53 of the upper welding tool lowered by actuating the pressure cylinder 57 and with the provided one

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

5

661 474

Pressure placed on the overlapped edge to be welded. By adjusting the pressure in the pressure cylinders 57 accordingly, the contact pressure of the two heating rails 48, 53 on the overlapped edge regions of the two plastic sheets to be welded can be determined.

In the device described, the electrically heated rails 48 and 53 are fastened to the hollow beams 46 and 51 via suitable, thermally insulating brackets 47 and 52. These hollow beams 46, 51 are provided on both sides with openings 50 and 55, respectively, so that vapors or gases generated during the welding process, for example, can be sucked out through the hollow beams 46, 51. This suction process simultaneously cools the hollow beams 46, 51, which is advantageous for avoiding undesired thermal distortions. As already stated above, the use of the so-called separating layers in the present method permits the use of higher temperatures for the thermal welding of plastic sheets, although it must be ensured that the heating rails 48 and 53 do not bend due to material expansion. To achieve this,

The heating rails 48 or 53 can also consist of layers of metals with different coefficients of expansion such that the thermally caused expansions largely compensate for one another at the intended operating temperature. Of course, as indicated in FIG. 4, there is also the possibility of preventing the heating rails or the entire welding tool from bending, as a result of additional pressure cylinders 57 'which are arranged on the longitudinal bar 42 between the three stands 35.

It should also be pointed out that the support table 44 is not only used for fastening the lower part of the welding tool. It is also advantageous to attach additional devices, for example spacers to limit the maximum feed of the piston rods 56 and thus the upper part of the welding tool relative to the lower part thereof, which is necessary when welding double-walled plastic sheets according to the method described with reference to FIG. 2 . Any desired clamping devices for the plastic sheets to be welded can also be arranged on the support table 44.

5

10th

15

20th

25th

30th

.35

40

45

50

55

60

65

S

3 sheets of drawings

Claims (7)

661474 1. A method for connecting the edges of webs of plastics, in particular PVC and copolymers, the edges to be connected either being overlapping one another or running side by side and covered on at least one side by a plastic strip which is intended to be connected to them, and wherein the thus formed, arrangement to be welded for softening is heated and pressed together at the same time, characterized in that That the arrangement to be welded is covered on each of the two free outer surfaces with a separating layer before being pressed together, And then the assembly is pressed over the entire length between heated rails during an adjustable welding time and with an adjustable welding pressure, - whereupon the lightly adhering separating layers are removed from the outer surfaces of the welded arrangement. 2. The method according to claim 1, wherein the edges to be joined butt butt together, characterized in that a plastic strip is placed on both sides of the edges and welded to the two edges, after each with a separating layer, the free outer surfaces of the two plastic strips have been covered. 2nd PATENT CLAIMS 3. The method according to claim 2, characterized in that when connecting the edges of double-walled plastic sheets with intervening porous spacing material, the gap remaining when the heated rails are pressed together between them is limited. 4. The method according to claim 1, characterized in that an at least one side with PTFE or other corresponding heat-resistant plastic-coated glass fiber fabric or other corresponding heat-resistant material is used as the separating layer and the coated side is turned towards the edges to be connected. 5. Device for performing the method according to claim 1, characterized - By a frame-like structure of a plurality of identical stands (35) arranged next to one another, each of which consists of a bottom rail (36), a vertical column (37) and an upper crossbeam (38) and which are interconnected by a plurality of longitudinal beams (39, 40, 41,42) are rigidly connected, - By means of a support table (44) which extends over all the supports (35) and which is fastened to the base rails (36) of the individual supports (35) with one support (43) each, - by a lower part of a welding tool fastened on the support table (44), which consists of a hollow beam (46) and a thermally insulating holder (47) arranged thereon with a heating rail (48) having metallic, embedded electrical heating rods (49), - by an upper part of a welding tool, which is arranged as a mirror image of the lower part, which consists of a hollow beam (51) and a thermally insulating holder (52) arranged thereon with a heating rail (53) having metallic, embedded electrical heating elements (54), - By a pressure cylinder (57) which is adjustable forwards and backwards and sideways on the upper crossbeam (38) of each stand (35) and has a piston rod (56) for holding the hollow beam (51) of the upper part of the welding tool is set up - And by at least one roller structure (61, 63) at the two ends of the support table (44), set up for pulling a separating layer (60) into the gap between the two parts of the welding tool. 6. Device according to claim 5, characterized by a suction device which is connected to the, with lateral holes (50, 55) provided with hollow beams (46, 51) of the two parts of the welding tool. 7. Device according to claim 5, characterized by heating rails (48, 53) which consist of materials of different thermal expansion such that at least a partial compensation of the expansion takes place at the operating temperature.