DE1291109B - Process for welding plastic pipes and welded joint formed according to the process - Google Patents

Description

The invention relates to a method for welding Plastic pipes and a welded joint formed according to the process, in particular for the connection of pipes of small diameter and smaller Wall thickness.

Various methods are already known to make pipes, preferably Plastic pipes, with the help of connecting pieces that cross the pipe ends connect to. For example, one has the connection by way of gluing with the help tried a suitable solvent; this method has the disadvantage that it does not represents a sufficiently tight connection when the plastic pipes are exposed to high pressures be acted upon; in addition, there is also sufficient security against tensile stress not guaranteed, an immediate load on the connection is not possible. Another method consists in welding the pipe parts to be connected by means of a hot air gun, through which the position to be welded from the outside on the Softening point are heated. Great care must be taken with this method be to the required temperatures in certain latitude and depth exactly to be observed. The procedure is time consuming and does not guarantee achievement the strength required for plastic pipes that are subject to high internal pressures are; It is very difficult to use this method with thin-walled pipes because there is a risk of adversely affecting the structure.

It has also already been suggested that the separation points of the plastic parts to heat on hot metal parts and the connection by subsequently sliding into one another to achieve, with a welding of the nested parts take place target. Here, too, the greatest care is required to maintain the necessary temperatures to reach exactly; this method is also time consuming and does not guarantee any there is sufficient strength in the weld zone, and there is also thin-walled pipes the risk of a negative influence on the structure. It has already been suggested the parts to be joined by mutual rotation up to the softening temperature to be heated and welded.

Such a method is only possible for small parts; the welding long pipes are not feasible because of their unwieldiness; you can also use elbows not be associated with pipes. This method also has the same disadvantages like the above.

Another known method uses electrical heating a resistance wire. A wire helix is used in one of the parts to be connected injected, which is heated externally by an electric current. By heating the wire helix becomes the material of the parts to be welded at the parting surfaces softened and welded.

A double helix is required here, both ends of which are after are led out to be connected to a power source. These Coils are exposed to corrosion from the outside. A tightness between the connected parts can only be reached if the welding zones of the neighboring wires merge into one another. If this is not the case, then there is between the wires a helical area in which the two wires are not connected to each other, which in the case of plastic pipes that are underneath high pressure results in a leak. If reliable tightness and high Strength of the connection point is to be achieved, this type of connection is especially not suitable for pipes with a smaller diameter.

It is also already known to use electroinductive pipes to be connected to one another Ways to weld; Here the frontal welding was initially suggested, in which a metal ring or metal wire is used, which is attached to the face of the Pipe rests and made of a matched to the plastic to be welded Metal alloy. The metal insert is heated by an induction coil and melted. After the melting temperature of the metal and the plastic has been reached the pipe ends are pressed against each other, so that the molten metal is pushed out and the melted end faces are firmly bonded together. This Method cannot be used for pipes with small diameters and high pressures, because the welding at the end is disadvantageous for the load-bearing capacity of the pipe Structural change occurs. The removal of the molten metal is also difficult, since any residues call the tightness into question. In no case can use this method on thin-walled pipes for obvious reasons frontal welding is not possible because of the small wall thickness. It is also already known that the ends of the pipes are used when welding plastic pipes Provide overlapping connecting pieces, between which a self-contained metallic insert is arranged in which to generate the welding temperature Induction shock of suitable frequency is generated. The well-known metallic insert is designed as a ring. Since the ring rests on the surface of the pipe, if there is a bilateral open to the outside between the pipe and the connecting part, the wall thickness of the ring corresponding to the air gap created by the liquefied Plastic must be bridged during the welding process, causing the air to break down of the plastic, in particular the polyamides, leads and thus has a disadvantageous effect. Another disadvantage is that the edges of the ring are only narrow Can form welding zones, so that the pipes connected in this way only over a certain Have tensile strength and even at high pressures inside the pipe it is not sufficient have a secure sealing effect. If the well-known ring; e provided with perforations there is probably a certain increase in tensile strength, but the Sealing effect practically not increased at high pressures, as only the narrow welding zones can form self-contained welding zones at the edge of the ring.

The invention is based on the object of avoiding these disadvantages and to achieve a welding in particular thin-walled pipes, which both in terms of tensile strength as well as in terms of tightness under high tensile loads and high internal pressures ensure a satisfactory, tight and tight connection. This is achieved according to the invention in that the metallic insert is flush with it the inner surface of the overarching Connector in whose inner wall is embedded and the inner part without air gaps in the overarching one Part is inserted and that the length of the insert is a multiple of the circumference of the pipe to be welded.

Due to the flush embedding of the insert in the inner wall of the Connecting part, an air gap between pipe and connecting part is avoided, so that the disadvantages caused by the presence of air are avoided during the welding process because the connecting part can be pushed over the pipe without any air gap. Simultaneously a double closed connection zone is created, the length of which is a multiple of the pipe circumference, which leads to a substantial increase in tensile strength and also the tightness of the welded joint leads to all stresses that occur enough.

Another feature is that the metallic insert under Bias is embedded in the sleeve material, in the liquefied plastic material contracts radially and anchored in the pipe surface. When heated, the Due to its contraction, the insert partially enters the pipe surface, whereby an optimal welding is guaranteed.

Further features emerge from the other subclaims.

The inventive arrangement and design of the as an insert Serving wire is sufficiently wide, due to the winding width of the wire conditional welding zone created, which also maximum requirements for strength and tightness is sufficient.

To achieve a perfect welded connection and as protection against corrosion the inwardly exposed insert, it is advantageous to the insert with a, for example to provide plastic coating applied in the fluidized bed process, the drawings show various embodiments of the one used to carry out the method Metal inserts, and it means A b b. 1 illustration of a known ring-shaped Metal insert in section, Dept. 2 representation of an inventive, in turns running metal wire as an insert, A b b. 3 representation of a wire according to From b. 2 with a modified form of winding, A b b. 4 illustration of a wire according to Dept. 2 in a further modification of the winding shape, Ab b. 5 Representation of a welded connection, in the case of two pipes with a connecting sleeve containing the metallic inserts are welded, A b b. 6 Representation of a T-shaped connector with injected metallic inlays, A b b. 7 illustration of a connector with one from metallic inlay consisting of several coiled wires lying next to one another, A b b. 8 modified representation according to A b b. 7, A b b. 9 a one-sided sleeve for butt joints and repair purposes with a corrugated ring as a metallic insert, whose shafts are perpendicular to the axis.

The A b b. 1 shows a known metallic, self-contained Insert 1, which consists of an annular body. With this deposit 1 result at the ring edges 2 and 3 self-contained zones in which the to be united Bodies are welded together. The width of the welding zone is proportional small amount; This also increases the strength and tightness of the weld limited. In the welding connection according to the invention, according to A b b. 2 a sinuous one Wire 4 used.

The weld zone is shown here by the dashed lines 5 shown.

In the embodiment according to A b b. 3 is the wire 6 in turns out, whose legs are directed parallel to each other and in such a Distance from each other are that one self-contained, indicated by the dashed line Lines given welding zone 7 results, the width of which is greater than the length of the turns of the wire 6. This welding zone ensures with absolute Tightness a high load capacity in the direction of pull.

In a modified embodiment according to A b b. 4 is the wire 8 out in turns which run parallel to the axis in their apex area 9 and are arranged obliquely in its central region 10, so that a Welding zone results in a particularly large width, as it is for high tensile loads necessary is.

The cross-sectional shape of the wire used can be round; he can however, it can also be flattened in order to minimize the radial extent of the softening zone in the wire to reach.

The ratio of the length to the width can, for. B.

1: 2 to 1: 3, the width of course being parallel to the axial direction of the connection.

The advantage of the method according to the invention is that due to the use of a closed metal insert also a closed one Can reach welding zone, which an absolute tightness of the welded joint guaranteed, whereby by appropriate shaping and use of one in turns extending wire or a suitable perforated sheet metal strip also each desired width of the weld zone and thus the required strength is achieved can be. Here is the temperature in the self-contained metal insert during the induction current the same size everywhere, so that a perfectly uniform Welding is inevitably obtained.

Section 5 shows one produced by the method according to the invention Welded connection in which the two thin-walled plastic pipes 11 and 12 through a connecting piece 13 are welded together. In the connector 13 the self-contained metal inserts 14, 15 made of wire are embedded; they are during the spraying of the connector 13 on the spray mandrel, the is not shown in the drawing, held. This spray mandrel runs easily conical outwards; two spray mandrels are used, one of which is the Insert 14, the other the insert 15 takes up.

As a result of the taper, the inserts 14 and 15 are not on the shown, held outwardly slightly conically widening spray mandrel. In order to be able to use pipe connections where tightness is of particular importance, a weld also at the end faces of the two pipes 11 to be connected and 12, a ring 16 is injected in the middle of the connector 13, on which the end faces of the tubes 11 and 12 come to rest. When creating a Induction current takes place simultaneously in the inserts 14, 15 and 16 one simultaneous welding of the tubes 11 and 12 each with the connecting piece 13 and a welding of the end faces of the tubes 11 and 12 through the insert 16.

The A b b. 6 shows a T-shaped connector in which in FIG In the manner described above, the metal inserts 18, 19, 20 are injected. Here too the inserts 16 can be used for additional welding of the pipe end faces.

The A b b. 7 and 8 show parts of a connector 21 in which self-contained deposits are arranged. At the A b b. 7 these deposits exist from several adjacent, self-contained, corrugated wire rings, z. B. 22, 23, 24, which, like the A b b. 7 shows interlock. At the A b b. 8 are two self-contained, corrugated wire rings 25 and 26 in the connector 21 injected in such a way that they almost touch each other once with their apexes and have the greatest possible distance with the adjacent winding apices, so that during the welding both after Dept. 7 and after Dept. 8 a closed Large-width welding zone is created.

Fig. 9 shows a one-sided sleeve 27, as used for butt joints and repair purposes is required. In the sleeve is the insert 28 for connection with the pipe and on the face of the sleeve, the insert 29 for connection with injected into a mating sleeve. The frontal insert 29 can consist of a corrugated ring, whose shafts are arranged perpendicular to the axis of the socket (left illustration of the A b b. 9), or from a disc-shaped ring (right illustration of Fig. 9) exist.

Claims (8)

Claims: 1. Method for welding plastic pipes with the pipe ends overlapping connectors and a self-contained metallic insert in which an induction current is used to generate the welding temperature is generated by a suitable vibration frequency, characterized in that the metallic insert flush with the inner surface of the overlapping connector is embedded in the inner wall and the inner part without air gaps in the overarching one Part is inserted and that the length of the insert is a multiple of the circumference of the pipe to be welded. 2. The method according to claim 1, characterized in that the metallic Insert is embedded under prestress in the sleeve material, in the liquefied Plastic material contracts radially and anchored in the pipe surface. 3. Welded connection according to claim 1 or 2, characterized in that that the metallic insert consists of a wire of oval cross-section to at Injection molding of the overlapping connector reduces the flow resistance of the plastic reduce and avoid air inclusions. 4. Welded connection according to claim 3, characterized in that the wire is bent in a wavy line. 5. Welded connection according to claim 4, characterized in that the bent wire has obliquely directed legs. 6. Welded connection according to claim 4, characterized in that the bent wire has axially parallel legs. 7. Welded connection according to claim 4, characterized in that the legs of the bent wire parallel to the axis in the area of their bend apex and run obliquely to the pipe axis in the middle between the bend vertices. 8. Welded connection according to claim 3, characterized in that a plurality of the bent wires are arranged so that the one turn apex like a mesh intertwine and the adjacent turn vertices the largest possible Have distance.