DE19941084A1 - Plastic electric welding socket with integral heating coil for joining venting pipes forms a gap between the coil and pipe end during welding - Google Patents

Abstract

When the opposing ends (4) of the plastic venting pipes to be joined are inserted into the welding socket the distance between the heating coil (2) and the outside of the venting pipe is 0.2-2mm. An Independent claim is made for a process for welding the claimed socket onto the end of a plastic pipe in which the pipe end is inserted into the socket and leaves a gap (7) between itself and the heating coil (2) which fills with softened material from both the pipe end (4) and the socket.

Description

The invention relates to an electro welding fitting with integrier The heating coil for welding to a plastic pipe. The invention also relates to a method for welding an electric welding plastic fittings with the end of a plastic tube.

Electrofusion fittings with an integrated heating coil are for Welding on pressure pipes known, just like the fitting one have considerable wall thickness and practically no tolerance in that Welding fitting can be used. It therefore arises more directly Contact between the partially exposed heating coils of the Fittings and the pipe wall and thus direct heat transfer on the pipe. It was previously thought that this fit exactly ability to create a flat welded connection in the heating system zone is required.

While with pressure pipes, which are already with electrofusion fittings were welded, and the corresponding fittings with narrow toles satchel is worked so that there is good contact of the heating coil with the outside of the pipe to be welded on (or, if necessary, inside of the pipe) is possible, ventilation pipes have a much smaller wall strength as pressure pipes. While the ratio of the outside diameter to the wall thickness d / s for the electrical welding fittings in the pressure range generally 7 to 9 and up to 18 in special cases,  this value is essential for plastic pipes in the ventilation area Lich higher, e.g. B. at 70. These relatively thin-walled tubes can not be manufactured so precisely that they are just like printing pipes by contact with the heating coils of the fitting z. B. outside can be softened. It was therefore believed that a Welding through direct contact with the heating coil in the case of ventilation pipes cannot be reached because of the for the Er direct heat transfer required or not in sufficient measure is possible.

It has now been found that ventilation pipes made of plastics with electro-welded fittings made of plastic despite lack of con cycle between the pipe end inserted into the fitting and the Heating coil can be welded if the distance between the exposed heating coil and the outside of the tube is not is larger than 2.0 mm. It has been shown that despite the lack the material contact between the heating coil and the pipe surface there is sufficient heating of the outside of the pipe to soften it and also welding the softened pipe outside (or inside of pipe with fitting inserted) with the Inside of the fitting is reached, one for ventilation sufficient tightness and strength. This is surprising because of the gap width between the ver welding parts could not be expected that the softened materials of both parts except for material contact approach and a material closure sufficient for welding and achieve joining pressure.

According to the preferred embodiment of the invention Electric welding fittings is the distance between adjacent turns of the Heating coil larger than twice the diameter of the heating wire. In addition to plasticizing the outside of the fitting inserted pipe is the plastic material of the fitting between  the turns of the heating coil u. a. through contact with the heater coil warmed to softening, so that u. a. in these areas between the turns bridges to the softened outside form the pipe end, which after cooling one for the occurring Sufficient connection between the two parts results from axial forces also has sufficient tightness for ventilation pipes. Preferential the distance between adjacent turns of the heating coil is larger than three times the diameter of the heating wire. In general this distance is in the range of 2 to 30 times the heating wire diameter. The distance between the heating coil and the Outside of the pipe end in the welding position preferably in the range of 0.2 to 2.0 mm, especially in the range from 0.4 to 1.5 mm.

In one embodiment of the fitting according to the invention is this in the area of the heating coil, i.e. H. in the heating zone by an external clamp under a radial com pressure pressure kept. Especially with continuous softening the fitting wall in the area of the heating coil is softened Material pressed inwards by the clamp and thus with the also softened material of the tube wall welded. The clamp can be a simple slotted ring after the weld solution remains on the fit. But it can also consist of two one on the one hand by a hinge and on the other hand by a clamping lever bound halves and after the weld has cooled dismantled and used again. The welding takes place automatically when the material is sufficiently softened so that a sufficient joining pressure between the softened materials both parts can take effect.

In another embodiment, the electrowelding is fitting to produce the weld in the area of the heating coil at least one pressure acting on the end face of the fitting body kept under compression. With sufficient through  softening of the fitting walls, this is axially together pressed, which also causes the softened material of the fitting pressed inside against the softened pipe wall and ver is welded. The pressure body is, for example, a two-part Ring with hinge that resiliently against the ring-shaped End face of the fitting is pressed. The pressure body can also consist of several partial bodies distributed over the circumference.

In contrast to the previously known electric welding sleeves is the ratio of outer diameter to wall thickness d / s the fittings according to the invention in the range from 18 to about 100, preferably from 40 to 90. These relatively thin-walled, in particular electric welding used to connect ventilation pipes fittings cannot be as precise as with thick-walled fittings with d / s ratios of 9 or 11, for example are, apart from the fact that the tubes are often out of round or become. The electrowelding must therefore have an air gap take place over an essential, generally over extending part of the pipe circumference. The wall thickness of the Fittings and the ventilation pipe at the welding end are preferred wise in the range of 3 to 6 mm, especially in the range from 2 to 4 mm. In contrast, the wall thickness of fittings in the Print area greater than 6.5 mm. With an inside diameter of For example, 200 mm is 26 mm.

In a further embodiment of the invention Electric welding fittings is in the fitting wall in the area of Heating coil embedded a radially preloaded pressure body. This body exerting internal pressure has the same function like the clamp above, but is already from manufacturing contained in the fitting and remains in it after the Welding. The radially biased pressure is preferred body a wire coil or a slotted ring. As soon as the  Softening progressing from the inside to the outside of the fitting wall zone reaches the pressure element, it moves the softened element Material of the fitting wall between the turns of the heating coil inside, creating the gap between the fitting wall and pipe wall bridges and the weld connection is made. Conveniently are the turns of the wire coil to the turns of the heating coil staggered so that the turns of the wire coil caused displacement of the softened plastic material between the heating coil turns and is not hindered by them becomes.

The manufacture of the fitting of this type according to the invention can be done, for example, in such a way that first the core Heating wire is wound with the desired winding spacing, then on the core a plastic layer covering the heating wire is applied. On this plastic layer in the solid state the pre-formed wire coil will then have a smaller turn knife than the outer diameter of the plastic layer mentioned hung up. For this purpose, the wire coil must be widened so that it after application is under tension. Then then applied the outer layer so that the wire coil is complete is embedded.

In another embodiment of the elec The welding coil is located under an axial projection tension. When softening the plastic material in the area the heating coil contracts them, which softens them Material is pressed in between the turns and the Gap bridged so that welded connections to the softened pipe be produced on the outside.

In general, the plastic is used here upcoming fittings and pipes made of polyethylene, polypropylene, heavy flammable polypropylene or polyvinylidene fluoride.  

Preferably the wire of the heating coil is more than 50% its circumference embedded in the plastic and it lies in the rest free. The heating coil is thus on the inside (or the outside) of the fitting firmly anchored, so that its material by immediate bare heat transfer from the heating coil is softened. The free lying part of the heating wire transfers heat through radiation and Convection to the surface of the opposite tube wall, see above that this too is softened before bridging and a Material contact of both parts occurs.

The electrowelding fitting according to the invention has in general the heating coil on the inside of the fitting wall. In individual cases the heating coil can also be attached to the outside of the fitting wall to be in order. In this case, the pipe to be welded on pushed the fitting.

The task is invented in the aforementioned method solved according to the invention in that art softened by the heating material of the fitting through the gap until it comes into contact with the also softened plastic material on the surface of the Tube end is moved. The softening of the pipe surface follows essentially by heat radiation or by convection through the gap, while it was previously assumed that for expansions contact with the pipe wall opposite the fitting the exposed heating coil is required. The fiction appropriate displacement of the softened material takes place essentially due to the thermal expansion of the softened material and the Wire material of the heating coil, which thereby softened deeper Plastic penetrates and displaces it.

In a preferred embodiment of the method, the Material shift due to the extent of the softened material force of the fitting directed radially inwards (or outwards) supported. This force can, for example, by the outside  Fitting on pre-stressed clamp or by the embedded kill; also radially preloaded pressure body can be exerted.

In another embodiment, the shift is supported Exercise of the softened material by using the softened material axial compression force exerted by the fitting. Through the upsetting becomes the softened material between the turns of the heating coil also pressed inwards, making it a welded joint with the Outside of the superficially softened pipe end comes.

You can also move the material through the Ent tension of the heating coil fixed in the fitting is supported zen made possible by the softening of the surrounding material becomes. The pre-tension of the heating coil in the solid plastic mat rial of the fitting can lead to the softening of the The heating coil compresses axially or radially tert, which also makes the softened bridging material of the gap is pressed inwards. There is an all-over (bubble-free) welding to achieve an axial force not a coherent, airtight connection between pipe and fitting required but desired.

Some embodiments of the Er described in more detail. Show it

Figure 1 shows the axial section of a first embodiment of an electric welding sleeve for connecting two ventilation pipes.

Figure 2 shows the axial section of part of a second embodiment of the electrofusion socket.

Fig. 3 is the axial section of a third embodiment of the electric welding sleeve according to the invention similar to FIG. 1; and

Fig. 4 shows a part of an electric welding according to the invention with one end of the pipe to be welded and an auxiliary device used.

The electric welding sleeve 1 shown in Fig. 1 has on the inside a partially exposed heating coil 2, the two connections 3 for contact plug of a power source (not Darge asserted) ends. The heating coil 2 is divided into two heating zones for welding to one pipe end 4 each. The right side of FIG. 1 shows the pipe end inserted into the sleeve 1 before welding to the sleeve. It can be seen that the outer side of the tube end 4 has no contact with the heating coil 2 . The left side of Fig. 1 shows the sleeve 1 after welding with the end 4 of the ventilation pipe. After the presentation, the heating coil is completely embedded in the welding area after welding. In practice, air inclusions can also be present, which, however, do not significantly impair the axially non-positive connection between the sleeve 1 and the pipe end 4 .

The illustration in FIG. 2 corresponds to the left part of FIG. 1, but with a clamp or a slotted pressure ring 5 resting on the outside of the sleeve 1 in the area of the welding zone. This exerting a radial force on the welding zone pressure ring has the softened sleeve material in the heating zone inwardly pressed into contact with the likewise softened upper surface of the pipe end 4 , whereby a welded joint sufficient for ventilation pipes has been created. It should be noted that the surface of the pipe end, as usual, must be freed from a superficial oxide layer, e.g. B. by means of a commercially available surface peeling device.

In the embodiment shown in FIG. 3, a radially preloaded metal wire coil 6 is embedded in the electrical welding sleeve in the region of each welding zone. On the right side of FIG. 3, the state before softening of the plastic material in the welding zone is again shown, in which the pretension of the helix 6 is absorbed by the material and cannot yet be material-displacing. The left side of FIG. 3 shows the state after heating the heating coil 2 and softening of the material in the heating zone up to the area of the coil 6 . It can be seen that the softened plastic material of the sleeve was pressed inwards by the prestressed coil 6 , so that the air gap 7 in the area of the coil 6 has disappeared and the plastic material of the sleeve 1 has been welded to the outside of the pipe end 4 .

FIG. 4 shows a representation corresponding to the right side of FIG. 1. A two-part clamp 8 is firmly clamped onto the pipe end 4 at a short distance from the sleeve 1 . The two half-shells of the clamp 8 are connected by a hinge (not shown) and fixed non-slip on the tube end 8 by closing a clamp 8 ^a . In the clamp 8 axially parallel bores 8 ^{b are} contained, in which piston rods 9 with pressure elements 10 are slidably mounted. A helical compression spring 11 in each bore 8 ^b presses the pressure body 10 onto the end face 1 ^{a of} the sleeve 1 . The device 8-11 is applied with upsetting voltage before the heating of the heating coil 2 . When the sleeve material softens in the area of the heating zone, the upsetting pressure causes the softened plastic material to be at least partially pressed inwards and welded to the likewise softened outside of the pipe end 4 . After cooling, the device 8-11 is dismantled.

The electrowelding fittings according to the invention include not only the sleeves shown, but also reducers, closure sleeves, corner pieces, T-pieces, etc. Instead of the pressure ring 5 , the compression can also be effected by hand with a plier-like tool after a sufficient softening takes place is.

Claims (17)

1.Electrical welding fitting made of plastic with an integrated heating coil for welding to a plastic pipe, characterized in that the plastic pipe is a ventilation pipe and the outside or inside of the end ( 4 ) of the ventilation pipe inserted in the welding position is at least partially a distance from the heating coil ( 2 ) in the range of 0.2 to 2.0 mm. 2. Electric welding fitting according to claim 1, characterized in that the adjacent turns of the heating coil ( 2 ) are kept at a distance. 3. Electric welding fitting according to claim 1 or 2, characterized in that it is held in the area of the heating coil 2 by an externally applied clamp ( 5 ) under a radial compression pressure. 4. Electric welding fitting according to claim 1 or 2, characterized in that it is held in the region of the heating coil ( 2 ) by a pressure body ( 10 ) acting on the end face of the fitting under a compression pressure; 5. Electric welding fitting according to one of claims 1 to 4, characterized in that its ratio of outside diameter to wall thickness d / s in the range from 18 to 100, preferably from 40 to 90 lies. 6. Electric welding fitting according to one of claims 1 to 5, characterized in that the wall thickness of the fitting ( 1 ) and the ventilation pipe at the welding end ( 4 ) is in the range of 2 to 6 mm. 7. Electro welding fitting according to one of claims 1 to 6, characterized in that in the fitting wall in the area of the heating coil ( 2 ) a radially prestressed pressure body ( 6 ) is embedded. 8. Electro welding fitting according to claim 7, characterized in that the radially prestressed pressure body ( 6 ) is a wire coil or a slotted ring. 9. Electro welding fitting according to claim 8, characterized in that the turns of the wire coil ( 6 ) are arranged offset to the conditions of the heating coil ( 2 ). 10. Electric welding fitting according to one of claims 1 to 6, characterized in that the heating coil ( 2 ) is under an axial bias, 11. Electric welding fitting according to one of claims 1 to 10, characterized in that the plastic under polyethylene, poly propylene, flame retardant polypropylene and polyvinylidene fluoride is selected. 12. Electric welding fitting according to one of claims 1 to 11, characterized in that the wire of the heating coil ( 2 ) is embedded to more than 50% of its circumference in the plastic and is otherwise exposed. 13. Electric welding fitting according to one of claims 1 to 12, characterized in that the heating coil ( 2 ) is arranged on the inside of the fitting wall. 14. A method for welding an electric welding fitting made of plastic with an integrated, partially exposed heating coil with the end of a plastic tube, characterized in that the tube end in the welding position in or on the fitting is at least partially separated from the heating coil by a gap and softened by the heating Plastic material of the fitting is pushed through the gap ( 7 ) until it joins with the softened material on the surface of the pipe end ( 4 ). 15. The method according to claim 14, characterized in that the material displacement by a circumferential of the softened material of the fitting ( 1 ) supports radially inward or outward force. 16. The method according to claim 14, characterized in that the material shift through to the softened area trained axial compressive force supports. 17. The method according to claim 14, characterized in that the material shift is supported by the relaxation of the heating coil ( 2 ) fixed in the fitting ( 1 ).