NL7906592A - Thermoplastic pipe couplings with resistance coil for welding - has wire at inner surface fixed inseparably in moulding - Google Patents

Abstract

A sleeve consisting of a material which will not bond to the injection moulding for which it forms the core, has a sprial groove on its outer surface in which a resistance wire is wound. The moulding forms a coupling for pipes etc. to which it can be welded when an electric current is laid on to the coil. A number of lengthways extending grooves intersect the spiral groove, so that bridges are formed in the moulding which hold the wires immovably in place, when the core is extracted. For pref. the lengthways grooves intersect the spiral grooves at an angle. They may be interrupted and they are near enough equal to the depth at which the inner faces of the coil wires are located. The core is a thin walled sleeve which can be removed by deformation or by breaking into pieces. To provide couplings which accurately weld the components together without danger of shortcircuiting, and in which the wires, although they are at the inner surface of the socket, cannot be displaced by rough treatment or careless handling.

Description

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Py a - 1 - N.O. 28.116 .--———— -1 A. de Jong in Eefde j \

Brief designation: Method for manufacturing a connecting molding, in particular fitting and a connecting molding manufactured according to the method.

The invention relates to a method for manufacturing a connecting molding, in particular fitting, provided with a heating wire, through which an elec- triangular current is passed to effect a weld connection between the connector molding and an object to be connected thereto, the heating wire being laid in a spiral groove in the outer surface of a core and the heating wire over the core being the molding; is formed, the core being of a material which is resistant to the states prevailing during the molding and the states mentioned do not combine with the material used for the molding. Such a method is known from German 'Auslegeschrift1' 1.048.106. By welding pipes of a thermoplastic plastic by welding, use is often made of moldings provided with an electric heating element in the form of a spiral-wound metal heating wire secured against the inner wall surface of the socket part of the fitting The internal diameter of the molding is slightly larger than the pipes to be joined, so that the molding can be fitted over the 20 pipe ends 25, after which an electric current is passed through the spiral heating wire. As a result of the heat development in the heating wire, the material of the molding and the pipes melts at the surfaces facing each other.

According to the said German "Auslegeschrift", the mounting of spiral heating wire is effected by embedding 7906592-1. Hereby it must be ensured that between the windings the material of the molding does not run through, but grooves remain, while the individual wire bonds of the heating wire winding are kept at a predetermined distance during the molding operation. Therefore, in German "Auslegeschrift" 1,048.1Q6 it has been proposed to wind the winding wire together with a spacer wire on a core, after which the molding is formed directly with the wound wires, for example by an injection molding process.

The known method has the drawback, however, that when winding the heating wire together with the spacing wire, care must be taken that the two wires are always wound against the steel core of the injection mold or press mold with the same stiffness, since otherwise the metal heating wire is almost entirely covered locally by too much plastic during the injection molding or pressing and consequently does not heat uniformly everywhere, while furthermore not enough melt is formed to form the space between the inner walls of the fitting and the outer wall of the inserted pipe fill the end sufficiently, leading to a faulty weld.

Torch manufacture according to the known method of large series is economically more or less only possible if during the injection molding or pressing the released steel bypass cores are wound again with a blank heating wire together with the spacing wire, which is time consuming.

In order to meet this drawback, it has been proposed in German "Auslegeschrift" 1,048,106 to use a core in which a spiral groove is arranged in the external surface so that the spiral rib defining the spiral groove has the function of takes up the spacing thread.

However, the above solutions have the drawback that the heating wire is embedded very little in the molding. By inserting a pipe end into a fitting or during careless transportation with other hard objects, the 7906592 # 4 3 metal heating wire can be easily damaged due to the low adhesion to the inner surface of the fitting, if the special installation or transport instructions are not observed taken. One or more wire turns can be pushed out of the shallow bed and slide over each other, so that by using a bare resistance wire a short circuit is caused by electric heating, whereby the place where the wire is slid away is not heated sufficiently for the formation of enough melt to properly fill the space between the inner wall of the fitting and the outer wall 10 of the inserted pipe end, resulting in a faulty weld. The use of insulated wires avoids the danger of a short circuit, however, due to the displacement of the wire turns, the heating is no longer uniform. The object of the invention is to provide a method of the type mentioned in the preamble, whereby the above-mentioned drawbacks are avoided.

According to the invention, this object is achieved in that a number of thickenings of the molding material are applied along each thread winding of the heating wire winding, in which thickenings the heating wire is at least partly incorporated.

As a result, the spiral wire winding is fixed not only during the manufacture of the molding but also in the finished nozzle. 25

Preferably, the thickenings are applied during molding of the molding.

In a preferred method according to the invention, the core on its external surface is provided with interrupted or not longitudinal grooves which are at an angle to the spiral-shaped groove and which have a depth substantially corresponding to the diameter of the heating wire.

In another embodiment of the method according to the invention, the core is a thin-walled sleeve and / is removed from the shaped molding by deformation or breaking.

7906592 4% 4

A hollow connection molding, in particular fitting, which is provided on the inner surface with a spiral heating wire winding, through which an electric current can be passed to effect a welding connection between the molding and an object to be connected thereto, has the feature that there are, on the inner surface of the molding, interrupted or uninterrupted longitudinal bridges which are at an angle to the faces of the wire turns of the heating wire winding and which at least partially clamp the wire turns. 10

The length bridges are preferably integral with the molding.

In an embodiment of the invention, the heating wire winding in the center of the molding has a greater pitch than in the remainder thereof. 15

The invention will be explained in more detail below with reference to the drawing, in which: Fig. 1 shows an injection-molded core according to the invention, the right part of which is drawn in section before a heating wire is wound up; Fig. 2 illustrates a cross-section of an embodiment of a molding according to the invention; Fig. 3 shows a cross-section of the molding according to line III / 3, and Fig. 4 shows a molding according to the invention with pipe ends to be slid to be inserted therein, the left part showing the assembly for the heating, while the right one part illustrates the composition after the melting process.

Fig. 1 shows a thin-walled sleeve 1, which forms part of the injection-molded core. This thin-walled sleeve 1 fits with its internal diameter on the steel core of the injection mold or compression mold, while the external diameter almost corresponds to that of the pipes to be joined together *.

A spiral groove 2 is arranged in the outer wall surface of the sleeve, the cross section of which corresponds to the wire diameter of the possibly blank 7906592 to be laid therein.

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5 metal heating wire 3 · The thin-walled sleeve 1 is provided with end flanges 4, to which are attached electrical connection plugs 5 which are electrically connected to the heating wire 3.

A plurality of longitudinal grooves 6 are arranged in the outer wall surface of the sleeve in substantially perpendicular or oblique direction 5 with respect to the spiral groove 2, in which the bare metal heating wire is wound.

After the heating wire 3 has been wound on the sleeve 1, the connecting molding 7 (see Fig. 2) is formed around the sleeve 1 in the injection mold. ^ 0

The thin-walled sleeves can be produced in large series by injection molding or another process, preferably from thermoplastic plastic or another material which does not combine or fuse with the plastic of the fitting to be molded or pressed and which is then serially coated with a blank - J5 metal heating wire are wrapped.

The spiral groove 2 provided in the outer wall surface of the sleeve 1 has a pitch which must conform to the heating pattern required for the welding and is of such a size that the heating wire 3 is more or less recessed and fitting into the groove, so that it is no longer possible to injection-mold or press plastic material of the fitting arbitrarily around the wire, while the spacing back 8 between the girder-shaped groove 2 ensures that in the fitting between the turns of the bare metal heating wire 3 the required distance is maintained during the molding of the fitting to avoid short circuits during the electrical current flow. Drill the grooves 6 in the outer wall surface of the sleeve 1, bridges 9 are formed during the injection molding or pressing of the molding, which firmly fix the bare metal heating wire to the inner wall surface of the fitting in a regular pattern, because the said grooves 6 are cut so deeply that the bridges 9 formed thereby enclose bare metal heating wire 3 on site almost wholly or completely. 35

Bridges 9 may or may not be interrupted, depending on the design of the grooves 7906592 * X-6 6.

After the injection molding or pressing has ended, the thin-walled sleeve 1 is removed from the fitting by deforming or breaking, after which the spent sleeves 1 can be used again and again as raw material for new sleeves to be manufactured. 5

In Fig. 2, the molding 7 is shown with the heating wire 3 attached to the inner surface thereof, which attachment is effected by the bridges 9 of the same material as the molding.

Fig. 3 shows a cross-section of a part of the molding 7, in which the heating wire 3 and the bridges 9 are clearly visible.

Fig. 4 shows how the connection between two pipes 10 and 11 is established. The pipes 10 and 11 are inserted into the corresponding holes of the molding 7, until they abut against the cams 12 of the molding 7. Because the windings of the heating wires 3 are firmly fixed by means of the bridges 9, when inserting pipes 10 and 11 into fitting 7 »the metal heating wire must not be damaged or shifted. 20

The cams 12 in the molding 7 are formed during injection molding or pressing, because the material of the molding 7 is pressed through the holes 13 of the thin-walled sleeve 1.

After the pipes 10 and 11 have been inserted into the molding, an electrical voltage or current source is connected to the heating wire 3 with the aid of the connecting plugs 5 ·

Due to the heat generated in the heating wire 3 as a result of the current flowing through this heating wire, the material of the pipes 11 and 12 and of the molding melts at the location of this heating wire, so that the molding 7 and the pipes 10jq and 11 melt together, of which the result to the right of fig. 4 is clearly shown.

The spiral-wound single bare metal heating wire 3 can also be used as a spiral-wound bifilar metal heating wire. 35

Although in the figures it is shown that the pitch of the 7906592

Claims (7)

1. Method of manufacturing a connector, especially fitting, provided with a heating wire, through which an electric current is passed to effect a weld connection between the connector and an object to be connected thereto, whereby the heating wire is laid in a spiral groove in the external surface of a core and the molding is formed over the core with heating wire, the core of which is a material which is resistant to the prevailing forming conditions and The said states do not unite with the material used for the molding, characterized in that a number of thickenings of the molding material 20 are provided along each thread winding of the heating wire winding, in which thickenings the heating wire is at least partly received. Method according to claim 1, characterized in that the thickenings are applied during the molding of the molding. 25 Method according to claim 2, characterized in that the core on its external surface is provided with interrupted or not longitudinal grooves which are at an angle with respect to the spiral groove and which have a depth substantially corresponding to the diameter of the heating wire. Method according to any one of the preceding claims, characterized in that the core is a thin-walled sleeve and is removed from the shaped molding by deformation or crushing. 55 Hollow connection molding, in particular fitting, provided on the inner surface with a helical heating wire winding, through which an electric current can be passed to effect a welding connection between the molding and an object to be connected thereto, characterized that there are, on the inner surface of the molding, 5 bridges, broken or not, which are at least partially clamping the wire turns at an angle to the surfaces of the wire turns of the heating wire winding. 6. Yer connector molding according to claim 5, characterized in that the length bridges are integral with the molding piece. Yer binder molding according to claim 5 or 6, characterized in that the heating wire winding in the center of the molding has a greater pitch than in the remaining part thereof. 7906592