CH636174A5 - Plastic collar which can be electrically welded - Google Patents

Description

The invention relates to an electrically weldable sleeve made of a thermoplastic for connecting line elements by means of a heating wire arranged in turns on the inner wall of a sleeve-shaped sleeve body, which, when pushed onto the socket of the line elements to be connected, partially softens together with the socket by heat generated in the heating wire and is welded to them.

Today, pipeline networks are often manufactured using piping elements made of thermoplastic. Here the task arises, the line elements, including pipe sections, fittings, control elements, for. B. Valves and other workpieces can be understood, assembled and connected to their nozzle drip and pressure tight. It is generally known to use cylindrical sleeves with a sleeve-shaped sleeve body made of a thermoplastic material for connecting the stubs of these line elements, which are partially melted together with the stubs of the line elements and welded to one another. The sleeve body can be part of a line element or a separate part. For the partial melting and welding of the parts to be connected, an electrical heating wire is arranged in turns in the area of the inner wall of the sleeve-shaped sleeve body. By supplying electrical energy to this heating wire, a metered amount of heat is generated which is sufficient to connect the socket body and the connecting piece.

To meter the amount of heat required for welding the sleeve and the socket, welding devices are used which supply the electrical energy proportional to the amount of heat required to the heating wire embedded in the sleeve body. Various embodiments of these welding devices are known which adhere to a specific welding time when controlled to constant voltage or constant current. Devices with a temperature measuring point on the sleeve itself are also known, as are simpler devices which only limit the welding time. Devices are also known in which the ambient temperature of the welding sleeve is also taken into account for regulating the welding time.

The sleeve, which can be electrically welded with the aid of such devices, with the heating wire inserted in the sleeve body appears to be a relatively simple element. It is only important to ensure that when the heating wire is inserted, the individual turns are separated from one another by a sufficiently large plastic mass so that reliable turns are avoided. On the other hand, to achieve a good connection of the parts to be welded, the thermoplastic

25th

30th

35

40

45

50

55

60

65

see sleeve body granted a shrink reserve, which is triggered during the welding process, so that the sleeve body lies snugly against the parts to be connected. As the socket body shrinks during welding, the heating wire, which is heated during the welding process, expands against the shrinking movement of the socket body. These two opposing movements can cause individual turns of the heating wire to buckle and thus cause a short circuit, as a result of which the thermoplastic material of the sleeve body is damaged or can catch fire. Furthermore, the linear expansion of the resistance wire causes the winding to be removed from the welding zone. The distance between the turns can be so great that a complete melting of the inner wall in the welding zone is questioned. Such phenomena can occur especially in the case of electrically weldable sleeves with a larger sleeve diameter, e.g. B. over 200 mm in diameter can be observed. Undoubtedly, the thermal expansion of the heating wire plays a significant role here, since the total length of the heating wire turns is a considerable length, e.g. B. 10 m and more.

Various measures are known to avoid the above-mentioned disturbances when welding sleeves with a larger diameter. For example, the total length of the heating wire can be reduced in that the heating wire has multiple threads, e.g. B. in four courses, is inserted into the sleeve body. This reduces the total elongation of the heating wire, which also reduces the risk of short circuits. However, this increases the complexity of the circuitry.

It is also known to use a lacquered or tape-insulated heating wire. Although this does not reduce the thermal expansion of the heating wire, the insulation is intended to prevent a short circuit in the event of any short circuit. However, the insulation of commercially available heating wires is so thin that it is not sufficient to effectively prevent short circuits in the event of short circuits.

There is also the risk that at higher heating wire temperatures, enamel insulation will charr and emit solvent vapors. These released gases lead to the formation of voids in the welding zone. In contrast, gases are usually not released in a ribbon-insulated heating wire.

The invention is based on the object of designing an electrically weldable sleeve of the type described at the outset such that, on the one hand, short turns are largely impossible, and on the other hand the heating wire turns remain stationary in order to thereby prevent malfunctions, especially with sleeves with a large diameter.

According to the invention, this object is achieved by

that the heating wire has a coefficient of thermal expansion of less than 10-10 "6.

The invention is shown in the drawing in one embodiment and described below. Show it:

Fig. 1 shows a longitudinal section of a schematically illustrated electrically weldable sleeve for connecting two pipe sockets of line elements and

Fig. 2 is an enlarged view of section II in Fig. 1, but for an electrically weldable sleeve with a two-part sleeve body.

In Fig. 1, two pipe sockets 1,2 are shown, which are part of pipe elements, not shown. A sleeve 3 is pushed over the pipe socket 1, 2; the sleeve 3 and the pipe socket 1,2 are made of a thermoplastic. The sleeve 3 has a sleeve-shaped sleeve body 4. In the immediate vicinity of the inner wall 5 of the sleeve body 4, a heating wire 6 is embedded in windings which are spaced 7 from adjacent windings. The ends of the heating wire 6 are connected to contacts 8, which are arranged in a bore arranged at the ends of the sleeve body 4

636 174

9 are embedded. Lines of a welding device, not shown, can be connected to the contacts 8, through which the heating wire 6 can be fed with metered electrical energy.

In Fig. 1, the pipe socket 1,2 and the sleeve 3 are shown before they are welded. If electrical energy is supplied by the welding device, heat is generated in the heating wire 6, which should lead to a partial softening of the sleeve body and the pipe socket 1, 2, so that the parts are welded. Since in the manufacture of the sleeve 3, the sleeve body 4 has a shrink reserve, e.g. B. is issued by expansion, this is free when the sleeve body 4 is heated, as a result of which the sleeve body 4 performs a shrinkage, through which the gap 10 existing before welding between the inner wall 5 of the sleeve body 4 and the outer wall 10 of the pipe socket 1, 2 is canceled.

As can be seen from FIG. 1, the turns of the heating wire 6 need not be distributed uniformly over the entire inner wall of the socket body 4. In particular, the distance between the turns can be larger in the area of the connecting pieces.

In order to avoid the difficulties mentioned at the beginning when welding sleeves 3, in particular of larger diameter, the invention is based on the consideration that the heating of the heating wire 6 takes place much faster than the softening and thus the shrinking of the sleeve body 4. If it is possible to keep the thermal expansion of the heating wire 6 small at this relatively short point in time, the occurrence of interturn short-circuiting or other deformations can be avoided. As soon as the sleeve body is softened and the shrinkage begins, the heating wire 6 can expand in the softening thermoplastic material.

If, instead of the heating wires previously used, a heating wire 6 with a low coefficient of thermal expansion is used, all difficulties which could arise immediately when heating wire 6 starts to be avoided are avoided.

5 Various alloys with a low coefficient of thermal expansion are known today; these are iron-nickel alloys with a nickel content of 30-50% by weight. With such alloys, thermal expansion coefficients smaller than 10-10 "6 can be achieved, but smaller values, eg 1.5-10" 6, can also be achieved. Heating wires 6 with a negative coefficient of thermal expansion can also be used. It is essential, however, that the thermal expansion of the heating wires 6 that are usually used is considerably reduced in order to achieve the desired effect.

xs The enlarged section shown in FIG. 2 shows a sleeve 3, the sleeve body of which consists of two parts, an inner sleeve part 15 on the one hand and an outer sleeve part 16 on the other hand. The inner sleeve part 15 has on its outer side a helically extending, annular disk-shaped web 17, in the windings of which the heating wire 6 is laid. The ends of the heating wire 6 are connected to the contacts 8 in the same way as shown in FIG. 1. After inserting the heating wire 6, the outer sleeve part 16 is sprayed onto the inner sleeve part 15, whereby a compact sleeve body is created. 1, a heating wire 6 with a small coefficient of thermal expansion can be used in the same way in the embodiment according to FIG. 2. With the sleeve described, it is possible, even with large pipe diameters, for. B. 200-500 mm, to achieve a reliable 30 weld, which is not only drip-tight, but also pressure-tight.

M

1 sheet of drawings

Claims (3)

636 174 PATENT CLAIMS 1.Electrically weldable sleeve made of a thermoplastic for connecting line elements by means of a heating wire arranged in turns on the inner wall of a sleeve-shaped sleeve body, which, when pushed onto the connecting piece of the connecting elements, softens together with the connecting piece by heat generated in the heating wire and welded to it is characterized in that the heating wire (6) has a coefficient of thermal expansion of 10 less than 10-10 '". 2. Socket according to claim 1, characterized in that the heating wire (6) has a coefficient of thermal expansion of less than 2.0-10 "°. 3. Socket according to claim 1, characterized in that the 15 heating wire (6) has a negative coefficient of thermal expansion. 20th