NL8602937A - METHOD AND APPARATUS FOR CONTINUOUS, FLAT WELDING OF FOILS, SHEETS, RODS AND / OR TUBES OF THERMOPLASTIC PLASTICS. - Google Patents

Description

VO 8430

Method and device for continuous, flat welding of films, plates, rods and / or pipes from thermoplastic plastics.

The present invention relates to a method and an apparatus for continuous, flat welding of thermoplastic plastics films, plates, rods and / or pipes to one another, wherein the plastic surfaces to be welded are first melted by heating and then pressed together.

A known method which is exclusively used in practice in textile foaming foils is the flame coating. In this method, the foam film is passed over a relatively large, cooled roller such that the foam film covers at least 1/3 of the roll-jacket surface, which is achieved by means of two guide rollers. Between these two guiding rollers, one side of the foam film is melted by means of gas flames. The textile material is then fed over the second guide roller and connects under the contact pressure of the second guide roller, which presses against the large, cooled roller, with the melted surface of the foam film. A drawback of this method is that a thickness loss does not only take place by melting together the cells located on the surface, which, incidentally, can never be completely avoided when welding foams together, but that a thickness loss is also caused by combustion.

In another known method, the so-called heating element welding, metallic heating devices in direct contact with the joining surfaces and a particularly good heat transfer heat the plastic up to the plastic deformability. After this temperature has been reached, the heating elements are removed from the joint and the joint parts are joined together by pressing pressure. Although the method requires only short working times and is suitable for joining solid profiles as well as pipes, it has the drawback that it is not very suitable for a continuous method.

Attempts have therefore been made to perform the heating element welding in such a way that a continuous process is possible in direct contact with the heating element. In such a method 8602937-2, which can be used, for example, with wetted polyethylenes, the plastic surfaces to be welded are contacted with highly heated rollers, whereby a uniform melting of the surfaces to be welded is achieved, without loss of thickness by burning off. should increase, as is the case with the flame-coating process discussed above. After the surfaces to be welded have melted, they are pressed together, respectively. compressed and provide a durable weld connection. With many thermal plastics, e.g. in the case of those made of non-wetted polyethylene, however, this has the drawback that sooner or later plastic residues will stick to the smoothly polished roller and stick, so that neither a further clean process nor a correct weld seam is left out, completely. the roller can already be in such a state after a short time that a continuation of the process can no longer take place.

The object of the invention is therefore to provide a method and a device with which it is possible to weld, in a burn-free, continuous manner, also those thermoplastic plastics, which tend to so-called "lubrication" and which is more important. , also applies to foamed plastics, where the danger of unwanted residual adherence of plastic to the roller is particularly great.

This problem is solved according to the invention by a method, characterized in that the plastic surfaces to be heated until melting are passed over a spacing device at a distance around the electrically heated heating conductor serving as the heat source, so that the welding plastic surfaces together with the spacing device form a heating channel, which surrounds the heat source and which may also be closed at the beginning and at the end, and by a device for applying this method, which is characterized, in that it has at least one electrically heatable heating source, furthermore a spaced-apart device and a device for compressing the fused surfaces.

1002937 t% -3-

The films, plates, rods and / or pipes to be welded according to the present invention can consist of any thermoplastic plastic. Preferably, however, the method according to the invention is applied in that thermoplastic plastic, which is only applied with adhesives or the soft welding method. insufficient bonding, ie for example with polyolefins such as polyethylene, in particular non-wetted polyethylenes from the group of "low density" polyethylenes. It should be noted at this point that, due to its small dielectric loss factor (0.0005), polyethylene cannot be welded at high frequencies.

Of particular interest is the new method for welding films, plates, rods and / or pipes, which consist of the aforementioned thermoplastic plastics, in particular polyethylene, and which are in the form of foams and preferably have a density with regard to the foam of less than 3 50 kg / m, in particular less than 20 kg / m.

The device serving for applying the method according to the invention mainly consists, as has already been indicated above, of a heat source, a spacer device arranged in front of it and a device arranged after the heat source for compressing the melted surfaces.

The heat source preferably consists of an electrically heatable heating conductor, in particular in the form of a wire or metal strip. Preferably, the thread, resp. the metal strip 25 of a chromium-nickel alloy, a chromium-nickel-aluminum alloy or an iron-chromium-nickel alloy. However, all other metals, resp. metal alloys or non-metallic heating conductors, e.g. silicon carbide heating conductors are used, which are normally used in resistance heating.

The temperature to which the heating conductor is heated fluctuates over a wide range of e.g. 600-1200 ° C and depends on the material to be welded and the speed at which the plastic surfaces to be welded are guided along the heating conductor. At high throughput rates and / or difficult-to-melt thermoplastic plastics, it can be advantageous, respectively. it is necessary that two or more heating conductors are arranged one behind the other in the direction of movement of the plastic surfaces to be welded.

8602937 * i -4-

In order to avoid sagging of the heating conductors and thus an uneven heat radiation, it is preferred according to the invention that the heating conductor, in particular when they are used in the form of wires or metal strips, always by means of a tensioning device , ie also in a heated state, are tense. The tensioning device, which is preferably simultaneously designed as a power supply connection, preferably operates the spring force of a spring or pressure-calculated spring. The power supply can be controlled or responds according to a preferred embodiment by means of a thermo-element. be arranged in the vicinity of the heating conductor.

A spacing device is provided shortly before the heating conductor for forming a heating channel and for passing the plastic surfaces to be welded at a certain distance without contact with the heating conductor. This spacing device is preferably wedge-shaped and positioned such that the cutting edge of the wedge faces the oncoming material and the back of the wedge faces the heating conductor.

The length of the wedge and of the heating conductor depends on the width of the surfaces to be welded. The cutting edge of the wedge is preferably slightly rounded so as not to damage the arriving material.

The back of the wedge is preferably convex and also rounded at its longitudinal edges to avoid material damage.

Of course, however, the back of the wedge can also be made concave, in which case the sides are preferably also rounded. Since this spacing wedge simultaneously serves as a heat protection shield, it may be expedient to remove the spacing wedge in the longitudinal direction of one or more bores, respectively. provide passages to allow a cooling medium to pass through the spacing wedge, if excessive heating of the spacing wedge is to be feared during longer operation. The spacing wedge can be used for special purposes, e.g. if a heating channel which is practically closed on all sides is desired, both side surfaces are extended along one plane, such that the flat extension corresponds to the mirror image of the side surface of the wedge.

8602937 * Λ -5-

Preferably, the wedges of the wedge are polished to a high gloss to reduce friction.

According to another embodiment of the invention, the spacing device may also be formed by a pair of rollers, the roller diameter and the roller length having to be adjusted in accordance with the relevant requirements. Spacing pairs of rollers are particularly used according to the present invention when e.g. already relatively thick and wide foam plates, for example those with a thickness of 8 or 16 mm and a width of 10 1 m or above, have to be welded together or when e.g.

endless, wide foam films should be coated with a suitable homogeneous decor film to keep friction on the spacer device as low as possible. When using spaced-apart pairs of rollers, which preferably run on ball bearings, it may also be desirable to cool them. In such cases, at least one of the two rollers is hollow and designed such that a cooling medium can be passed through it. Since the spacing rollers are preferably in contact with each other to co-form the longitudinally closed heating channel, it may be advantageous if the rolls are covered with an elastic plastic jacket, this jacket being relatively thin. can be kept.

Instead of the spaced wedge or the spaced pair of rollers, both of which are then preferably used in particular, when films, plates, rods and / or tubes of elastic foam materials are to be welded together, it is of course possible to one e.g. want to weld plates, rods or tubes from homogeneous thermoplastics, also use a simple metal or ceramic plate rounded on the longitudinal sides or an advantageously dimensioned tube as spacer. then, however, may have to be smoothly polished on the 30 contact surfaces.

With the aid of the spacing device, it is thus possible to feed the plastic surfaces to be welded at some distance along the heat source, thereby melting the plastic surfaces on the surface. Shortly after passing the heat source, 35 dg of melted surfaces are then melted by means of appropriate device 8602937 -6-

-V

rings, for example, pressure rollers, compressed, respectively. compressed.

The welding process is finished after cooling.

According to a particularly preferred embodiment of the invention, at least two, preferably a number of, plates 5 are arranged one above the other, so that, for example, one can simultaneously weld 2, 3, 6 or 10 foam plates, depending on the desired thickness of the end product. This makes it possible in a simple manner to weld relatively thin foam plates with a very low volume weight, which up to now could only be manufactured in a continuous process up to a thickness of at most 8 cm, into plates of any desired thickness. .

Accordingly, according to the present invention, for example, foam tubes of "low density" polyethylene 3 with a volume weight of less than 50 kg / m can be welded to plates of any width, the width of the tube faces being welded together can be varied by appropriate compression of the foam tubes, for example by the distances of the juxtaposed welding devices according to the invention, the dimensioning of the spacing device and the distances between the pressure rollers which may be present behind the heating source to be. However, because the welding devices according to the invention can be arranged not only next to each other, but moreover also one above the other, by means of such a welding grid construction the foam tubes can simultaneously be welded side by side and one above the other, so that a block consisting of foam tubes is obtained. .

However, the method according to the invention can also be used advantageously for making composite films.

Polyethylene films 30 can be joined with another film in a particularly elegant manner, in order to improve in this way the disadvantageous and noticeable aroma, gas and fat permeability of polyethylene films.

Likewise, polyethylene foam films can be coated on one or both sides with textile materials.

8602937 - 7- -c.

Furthermore, according to the present invention, one can use a continuous process, e.g. in a double belt installation, in which the welding device according to the invention is integrated, produce layered elements with an otherwise only mail (if possible) 5 glueable polyethylene foam core and metals or other coatings to which the melted polyethylene adheres.

The present invention is explained below with reference to Figures 1-8, without however being limited thereto.

Fig. 1 shows a vertical longitudinal section through the welding devices arranged according to the invention in a double belt installation for welding foam plates together; FIG. 2 shows a vertical section through a grid construction according to the invention with three welding devices along the cutting line C-D in FIG. 3 for welding adjoining foam tubes; Fig. 3 shows a horizontal longitudinal section along the cutting line A-B in Fig. 2; Fig. 4 shows a vertical section through a grid construction according to the invention with a horizontal and three vertical welding devices for simultaneously welding foam rods arranged one above the other; Fig. 5 shows in a schematic perspective view the preferred wedge-shaped embodiment of the spacing device according to the invention with an electrically heated heating conductor in the form of a metal strip arranged above it; Fig. 6 is a schematic perspective view of an embodiment of the welding device according to the invention for welding together homogeneous films; Fig. 7 is a schematic perspective view of an embodiment of a welding device according to the invention for welding foam films together with a wedge-shaped, spaced device; Fig. 8 is a schematic perspective view of an embodiment of the welding device according to the invention for joint welding of foam films with spaced rollers.

8602937 -8-

As already mentioned, Fig. 1 partly shows a vertical longitudinal section through a double belt installation with the upper conveyor belt 4 conveyed over rollers 3 and lower conveyor belt 6 conveyed over rollers 5.

Between the upper and lower conveyor belt 4,6 there are four foam plates 7a, 7b, 7c and 7d to be welded, which are welded together to form a foam plate 7 after passing the wedge-shaped spacer 2 and the electrically heated heating conductor 1. Arrow 8 indicates the transport direction.

Depending on the desired thickness of the welded plates, several welding devices according to the invention can also be arranged one above the other. However, it is of course also possible to set up the installation in such a way that only one welding device is present and with that only two output plates are welded together to form the correspondingly thicker plate.

Foam plates of different thicknesses can also be welded together with a corresponding construction of the installation. The double belt installation can be open on the sides or closed by two other corresponding conveyor belts, which also run on rollers. The additional lateral conveyor belts will then be fitted if one wishes to avoid lateral deflection of the foam and thereby increase the pressure for compressing the melted surface. Normally, ie also without the lateral conveyor belts, the foam plates are already under such pressure shortly after introduction into the double belt installation that, due to their flexibility, after passing the welding devices, they are sufficiently self-expanding. strongly compressed.

Welding of foam tubes together is preferably effected in the production method shown in FIGS. 2-4. The frames 9 (see Figs. 2 and 4), for example made of pipes, are arranged in a vertical arrangement (see Fig. 2) and in fig. 4 additionally in a horizontal arrangement, the wedge-shaped spacing devices 2, of which in fig. .2 and 4 the 35 wedge-shaped cross sections can be seen. In the center behind the wedge-spaced devices, the respective heating conductors 1 are arranged (see Figures 3 and 5), which are always kept in tension by means of spring tensioning devices (not shown). The distances between the wedge-shaped, spaced-apart devices and the lateral limiting rods 10, the distance of which from each other decreases slightly in the conveying direction, are preferably chosen such that the foam tubes, after passing the welding devices, are joined in a wide plane welding.

In order to exert an additional pressure on the melted tube surfaces, a pair of rollers is preferably located shortly behind the welding devices, that is transversely, ie at a right angle to the transport direction, the rollers of which are spaced apart and between which the foam tubes are fed.

As shown in Fig. 2, a number of 15 welding devices can of course be arranged next to each other, so that, for example, 20 foam tubes can be welded together into one plate without difficulty. The same applies to the grid embodiment shown in Fig. 4, with which simultaneously a plurality of tubes arranged next to and above one another, e.g. until a square block can be welded together. For practical reasons, however, it may be advantageous if, first of all, 10 or 20 foam tubes are juxtaposed side by side according to the product method shown in Fig. 2 and then the resulting plates are welded one above the other, as shown in Fig. 4, but without the vertically arranged welding devices, or by using the above described double belt installation.

Using the devices shown in Figures 6, 7 and 8 it is possible to manufacture composite films in a simple manner, either from two different homogeneous films or from a foam film and a homogeneous film or a textile fabric. Of course, with these devices two foam films can also be welded together. If desired, it is also possible to switch two such devices behind or next to one another, e.g. would like to coat a foam film on both sides. Fig. 8 shows how, e.g. can replace the wedge-shaped spacer device by a pair of rollers running relative to each other.

Further embodiments of the object of the invention automatically follow from the above-mentioned embodiments for those skilled in the art. The method according to the 8602937-10 invention and the welding device for welding foils, plates, rods and / or tubes of foam material, in particular that of polyethylene, are particularly suitable.

8602937

Claims (10)

Method for continuous surface welding of films, plates, rods and / or pipes of thermoplastic plastics, wherein the plastic surfaces to be welded are first melted and then compressed, characterized in that the plastic surfaces to be heated until melting are mixed a spaced-out remote device around the electric heat conductor serving as the heat source such that the plastic surfaces to be welded together with the spaced-out device form a heating channel, which surrounds the heat source and, if necessary, also at the beginning and may be closed at the end. Method according to claim 1, characterized in that the films, plates, rods and / or tubes to be welded consist of a polyolefin, preferably a polyethylene, in particular of a non-wetted polyethylene. Method according to claims 1 and 2, characterized in that the foils, plates, rods and / or pipes to be welded consist of an elastically foamed "low density" polyethylene, preferably such with a 3 volume weight below 50 kg / m . Welding device for applying the method according to claims 1-3, characterized in that it comprises at least one electrically heatable heat source (1), furthermore a spacer device (2) arranged therefor and a device for compressing has the fused surfaces. Welding device according to claim 4, characterized in that the electrically heatable heat source (1) is a heating conductor in the form of a wire or a metal strip, preferably of a chromium-nickel alloy, a chromium-nickel-aluminum alloy or an iron-chromium-nickel alloy. Welding device according to claims 4 and 5, characterized in that the electrically heatable wires or metal strips are always tensioned by means of a tensioning device, i.e. also in the heated state. Welding device according to claims 4-6, characterized in that the spacing device (2) is designed as a wedge-shaped heat protection shield. 8602937 -12- * '* Welding device according to claim 7, characterized in that the wedge-shaped heat protection shield has in the longitudinal direction one or more passages present for the passage of a cooling medium, preferably in the form of one or more suitable bores. Welding device according to claims 4-6, characterized in that the spacing device is formed by a pair of rollers, wherein the rollers are preferably mounted on ball bearings and have an elastic plastic jacket. Welding device according to claim 9, characterized in that the rollers consist of hollow rollers flowing with cooling medium. 8602937