DK165229B - PROCEDURE FOR CONTINUOUS COMBINATION OF BODIES AND / OR TOWERS OF THERMOPLASTIC PLASTIC MATERIALS - Google Patents

Description

in

DK 165229B

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method for continuous welding of thermoplastic foam plastics rods and / or tubes along which the plastic surfaces to be welded are first melted by heating and then compressed.

A known method is flame coating, which in practice is used exclusively for textile coating of plastic films. In this method, foam film is passed over a relatively large cooled roll over 10 so that the foam film covers at least one third of the roll surface, which is obtained by two guide rollers. Between these two guide rollers, the melting of one side of the foam foil takes place by means of gas flames. The textile material is then fed via a second guide roller and joins under the pressing pressure of the second guide roller, which presses against the large cooled roller, with the molten surface of the foam film.

A disadvantage of this method is that not only does a thickness loss occur during the fusion of the cells present on the surface - which, moreover, cannot be completely avoided in the welding of foams - but also a thickness loss due to burning .

In another known method, the so-called heating element welding, metallic heaters heat in direct contact with the joining surfaces and with correspondingly good heat transfer the plastics until plastic moldability is achieved. Upon reaching the corresponding temperature, the heating elements are removed from the joining surfaces and these are connected to each other by means of compression pressure. While this approach requires only short clock times and is suitable for joining solid profiles as well as pipes, it also has the disadvantage that it is not very well suited to a continuous working method.

Therefore, there has been no lack of attempts to design the heating element weld in such a way that a direct contact is obtained.

DK 165229B

2 with the heating element during a continuous process. In such a method as e.g. can be used with polyethylenes with cross-linking, contacting the plastic surfaces to be welded with highly heated rollers, thereby obtaining a uniform melting of the surfaces to be welded without having to find a thickness loss as a result of firing, as is the case with the aforementioned flame-caching methods. After the surfaces to be welded are melted, they are compressed or pressed together and a durable weld joint is obtained. However, with many thermoplastic plastics materials, such as polyethylenes without cross-linking, there is the disadvantage that plastic debris will sooner or later become stuck and adhere to the highly polished rollers, so that no particularly clean process or impeccable procedure is no longer ensured. welding seam, except that the roller may be in such a state after a short time that the process can no longer be continued.

20 German Patent No. 1,704,012 discloses an apparatus for welding two foam plastic blocks. These plastic blocks are clamped on two separate sliding tables, after which they are pushed together and held in the pushed position. Then, the abutting end faces are welded together by means of a heat wire which is inserted between the two plastic blocks and moved from one end to the other end of the weld seam following immediately after a separation sword which presses them against each other. surfaces of the plastic blocks apart so that the heating wire can move forward freely. It is thus not as in the present application for continuous manufacture of sheets or blocks on the basis of rods and tubes.

The method according to the invention is characterized in that the plastic surfaces which are to be heated for melting are first disposed in such a distance around a electrically heated heat conductor serving as a heat source that they form a heating channel which surrounds

DK 165229 B

3, which may be closed at the beginning and end, and that the plastic surfaces are then connected by pressure.

5 In this way, it is possible to continuously produce sheets or blocks of rods or tubes by a relatively easy and inexpensive procedure. This is because the rods and tubes in question can be manufactured by means of a relatively small and inexpensive extruder, after which the tubes are welded together 10 in a very inexpensive manner to form sheets or blocks of the desired thickness and width. By means of the method according to the invention, it is possible to make even large plates in small quantities.

Thus, the present invention is very important from a practical point of view. Extrusion of foam sheets requires extruders which are very expensive. The maximum thickness of such extruded sheets is approx. 8 cm and the width is 1 m. By means of the present invention it is possible to use a small, cheap extruder with a performance of approx. 50 kg per hour just to produce e.g. rectangular tubes with a side width of 8 cm. These tubes are then welded together to form sheets of the desired thickness and width, meaning that a manufacturer of such sheets is capable of producing only small quantities of such sheets in accordance with a customer's desire.

The rods and / or tubes to be welded according to the present invention may consist of any thermoplastic plastic material. However, the method according to the invention preferably finds application to such thermoplastic plastics materials which can only be unsatisfactorily bonded with adhesives or solution welding methods, ie. eg. with polyolefins such as non-crosslinked polyethylenes from the low density polyethylenes group. Also, due to their small dielectric loss factor (0.0005), polyethylenes cannot be welded by high frequency * weighing.

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DK 165229 B

Of particular interest is the method of welding according to the invention of rods and / or tubes consisting of the above-mentioned terraoplastic plastics materials, especially polyethylenes, which are in the form of foams and preferably have a density 5 in connection with the foams of less than 50 kg / m 3, and in particular below 20 kg / m3.

For the practice of the method according to the invention, an electrically heatable heat conductor is used, especially in the form of a wire or metal strip. Preferably, the wire or metal strip consists of a chromium-nickel alloy, a chromium-nickel-aluminum alloy, or an iron-chromium-nickel alloy. However, all other metals or metal alloys or non-metallic thermal conductors, e.g. silicon carbide heat conductors which are known in the art in resistance heating. The temperature at which the heat conductor is heated varies within a wide range from e.g. 600 to 1200CC and adhere to the materials to be welded and the rate at which the plastic surfaces to be welded pass the heat conductor. At high throughput rates and / or high melting thermoplastic plastic materials, it may be advantageous or necessary to place two or more heat conductors one after the other in the direction of movement of the plastic surfaces to be welded. In order to avoid a hanging of the heat conductor and thus a uniform heat radiation, it is preferred that the heat conductor, especially when in the form of wires or metal strips, is permanently biased, ie. also in the heated state, by means of a clamping device. This clamping device, which may preferably also be formed as a power supply connection, is suitably operated by the spring force of a spring which is placed under pressure or tension. Current The supply can be controlled or regulated by means of a thermocouple located near the heat conductor.

For the purpose of forming a heating duct and passing the plastic surfaces to be welded past the heat conductor in a 35

DK 165229 B

5 a certain distance without contact with the heat conductor, a spacer device is placed shortly before the heat conductor. This spacer is preferably wedge shaped and arranged so that the cutting edge of the wedge is facing the material arriving, while the wedge back faces the heat conductor.

, The length of the wedge and the length of the heat conductor depend 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 material arriving. The wedge back is preferably convexly formed and evenly rounded at its longitudinal edges to avoid material damage. However, the wedge back may also be concave, with the side edges preferably also rounded. Since this spacer wedge simultaneously serves as a heat shield, it may be convenient to provide the spacer wedge with one or more longitudinal bores or passageways so that a refrigerant can be passed through the spacer wedge if prolonged heating is feared for prolonged use. spacer wedge. The spacer wedge can, for special applications, e.g. when a heating channel closed from practically all sides is desired to be extended at its two side surfaces in a surface-forming manner and in such a way that the surface-forming extension corresponds to mirror images of the side surfaces of the wedge. For the purpose of reducing the friction, the wedge side pieces are preferably highly polished.

The spacer may also be formed by a pair of rollers, whereby the roll diameter and roll length are adjusted in accordance with the relevant requirements. Since the spacer rolls are preferably in contact with each other to form the longitudinally closed heating channel, it may be advantageous if the rollers are coated with a sheath of resilient plastic material, whereby this sheath can be kept relatively thin.

Of course, instead of the spacer wedge or spacer roll pair, a single metal or ceramic plate rounded at the longitudinal sides may also be used, or a

DK 165229 B

6 correspondingly dimensioned pipe, which must then be highly polished on the contact surfaces.

Thus, by means of the spacer device, it is possible to pass the plastic surfaces to be welded past the heat source at a certain distance, thereby melting the plastic surface on the surfaces. Shortly after the passage of the heat source, the molten surfaces are then compressed or compressed by suitable devices, e.g. pressure rollers. After cooling, the welding process is complete.

By means of the present invention, e.g. low density polyethylene plastic tubes with a weight of less than 50 kg / m3 are welded together to plates of any width, whereby the width of the pipe surfaces being welded may be varied by corresponding compression of the foam pipes, e.g. by means of the distances between the adjacent welding devices, the dimensioning of the spacer and the distance between the pressure rollers, which may be arranged after the heat source. Since the welding device can not only be arranged side by side but also above one another, by means of such a welding grid device, foam pipes can be simultaneously welded side by side and above each other so that a block of foam pipes is obtained.

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The invention is described below with reference to the drawing, in which: FIG. 1 is a vertical longitudinal sectional view of a double-band system with welding devices for welding foam sheets together by the method according to the invention; FIG. Fig. 2 is a vertical section through a grating device with three welding changes after cutting ten in a C-D in Fig. 3 to 35 welding foam pipes arranged one after the other; 3 is a horizontal longitudinal section along section line A-B in FIGS. 2, 7

DK 165229 B

FIG. 4 is a vertical section through a grating device having a horizontal and two vertically arranged welding devices for simultaneous welding of side-by-side and superimposed foam rods, and 5 FIG. with electrically heated heating elements in the form of a metal strip.

10 In FIG. 1 is a section of a vertical longitudinal section through a double belt system with an upper conveyor belt 4, and a lower conveyor belt 6 conveyed on rollers 5. Between the upper and lower conveyor belt 4, 6 are four foam sheets. 7a, 7b, 7c and 7d, and which, after the passage of a wedge-shaped spacer 2 and an electrically heated heat conductor 1, are welded to A foam plate 7. An arrow 8 shows the direction of transport. Depending on the desired thickness of the welded plate, several 20 welding devices can also be placed one above the other. Of course, it is also possible to arrange the system so that there is only one welding device, and thus only two output plates are welded together to the corresponding thick plate. By suitable arrangement of the plant, foam sheets of different thickness 25 can also be welded together. The dual belt system may be open at the sides or closed with two more clearly similar conveyor belts which also run over rollers. The additional lateral conveyor belts will be provided if you want to prevent the foam from folding to the side and thereby increasing the pressure to compress the molten surfaces. Usually, ie. even without lateral conveyor belts, the foam sheets are already pressurized shortly after insertion into the dual belt system so that, due to their flexibility after passage of the welding device, they are compressed with a satisfactory strength due to their own expansion.

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The welding of foam pipes to those of FIG.

1, preferably referred to in FIG. 2-4. On a e.g. of tubes made of frame 9 (see Figs. 2 and 4), the wedge-shaped spacer means 2 are arranged horizontally (see Fig. 2) and also vertically in Figs. 4. In FIG. 2 and 4, only the wedge inserts of the spacers 2 can be seen. In the middle and behind the wedge-shaped spacer devices, the corresponding heat conductors 1 are arranged (see Figures 3 and 5). These heat conductors 1 are held in the tensioned state by means of unshown 10 spring biasing devices. The distance between the wedge-shaped spacers and spacers 10, whose spacing decreases slightly in the direction of transport, is preferably thus selected, for the foam pipes after the passage of the welding devices 15 are welded together across wide surfaces. In order to exert further pressure on the molten pipe surfaces, preferably shortly after the welding devices and perpendicular to the direction of transport there is a pair of rollers whose rollers are spaced apart and between which the foam tubes are passed.

20 In the same way as shown in FIG. 2, of course, several welding devices may also be arranged side-by-side, so that one can easily weld simultaneously, e.g. 20 foam tubes for one plate. The same applies to the one shown in FIG. 4, with tubes which have been simultaneously placed in a number of four side by side and above each other, i. that e.g. can be welded a square block. For practical reasons, however, it may be advantageous to first weld 10 or 30 20 foam pipes adjacent to each other at the same time as in FIG.

2, and then such sheets are welded on top of each other in the manner shown in FIG. 4, but without the use of the vertical welding devices, but using the double-band system described above.

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Claims (3)

A process for continuous welding of rods 5 and / or tubes of thermoplastic foam plastic along surfaces to produce sheets or blocks, wherein the plastic surfaces to be welded are first melted and then compressed, characterized in that the plastic surfaces which should be heated to melt, first passed at a distance 10 about a heat-acting electrically heated heat conductor (1) to form a heating channel which surrounds the heat source and which may be closed at the beginning and end, and that the plastic surfaces thereafter connected by pressure. Process according to claim 1, characterized in that, as rods and / or tubes, those consisting of polyolefin, preferably of a non-crosslinked polyethylene, are used. A method according to claim 1 or 2, characterized in that, as rods and / or tubes, those consisting of a low density foamed polyethylene, preferably a polyethylene having a volume weight of less than 50 kg / m 2 are used. 25 30 35