MXPA00002276A - Method and arrangement for supporting the ends of a resistance wire in an injection mould during manufacturing of electrically heat-weldable plastic tube fittings - Google Patents

Abstract

The invention relates to a method and an arrangement for supporting the ends of a resistance wire in the manufacture of electrically heat-weldable plastic tube fittings in an injection mould. In the method, an electrically heated resistance wire (4) is wound about the core (1), the ends of the resistance wire (4) are connected to pegs (5, 6), pins (9, 10) are fitted into recesses (holes) (7, 8) provided in the core (1), and the pegs (5, 6) are supported on the core (1) by means of pins (9, 10) connected to them. In accordance with the invention, a guide bushing (11, 12) is disposed in contact with each pin (9, 10) and the connected peg (5, 6), each guide bushing (11, 12) is supported in a recess (13, 14) provided in the injection mould (2), an elastic actuator such as a spring (15, 16) is disposed to act on each guide bushing (11, 12) so that its holding power presses the guide bushing, the peg and the pin into position against the core (1), the injection moulding operation is started by introducing injection moulding compound around the core (1) in the moulding space (3) in a manner known i(per se), whereby, as the injection moulding compound reaches each pin (9, 10), the plastic pressure lifts the pin (9, 10), the peg (5, 6) and the guide bushing (11, 12) from the core (1) against the holding power of the actuator, such as a spring (15, 16), and after the injection moulding the core (1) is withdrawn from the mantle (2), the mantle (2) including the guide bushings (11, 12) is opened and the finished fitting is removed from the injection mould.

Description

METHOD AND DISPOSITION TO SUPPORT THE EXTREMES OF A RESISTANCE WIRE IN AN INJECTION MOLD DURING THE MANUFACTURE OF TUBE ACCESSORIES PLASTIC ELECTRICALLY WELDED BY HEAT The invention relates to a method, as defined in the preamble of claim 1, for supporting the ends of a resistance wire during the manufacture of electrically heat-weldable plastic tube fittings in an injection mold. The invention also relates to an arrangement, as defined in claim 6, for the application of the method. Heat-weldable thermoplastic fittings, ie sleeves, are intended to be tightly packed together with plastic tubes made of similar material. Said pipes made of plastic tubes are used, e.g., as gas pipes in the processing industry. The accessory comprises a body with one or more fitting parts for the plastic tubes to be joined. The adaptation parts, in turn, comprise adjustment cavities in which the plastic tubes are adjusted. The adjustment cavities are joined by tube sections. The accessories, in particular the adaptation parts, are equipped with a resistance wire. The resistance wire is arranged in connection with the adjustment cavity of each adaptation part so that it passes through the adjustment cavity in the vicinity of its internal surface and extend at least over the length of the connection between a cavity of fit and plastic tubes. The sections of tubes that will be joined are arranged in the adjustment cavities and plastic tubes. An electric current suitable for heat welding is arranged to pass through the resistance wire for a certain time, and then both the fitting, the fitting part, as well as the plastic tubes are mounted in the adjustment cavity which will be plasticized and fused in the joint area, subsequently solidifying to form a strong hermetic unit. The accessories of plastic tubes are manufactured with injection molding techniques. Prior to the molding step, the resistance wire is disposed within the injection mold. The resistance wire is supported on the molding core either by means of a pre-molded adjusting body or by support pins. In a first method, a first thin pre-casting, ie, an adjustment body, is first manufactured around the molding core in an injection mold, and then cooled, a resistance wire is wound around the body. The adjustment body is preferably provided with depressions for connecting pins, in which the ends of the resistance wire are joined. After the resistance wire including the connection pins has been fixed in its position in the adjustment body, it is returned to the injection mold and a second molding is carried out, whereby the accessory assumes its final shape. The connection pins extend beyond the molded accessory and through it, electric current is supplied in the resistance wire by heat welding. This method involves the problem that the molding is carried out in two steps. This slows down the production process and implies an increase in production costs. In a second method, the resistance wire is wound directly onto a molding core, as described, for example, in the patent specification EP 260 014. In this embodiment, the molding core has been provided with depressions, in the which connects the connection pin by means of the support pins during the molding time. The support pins are removed, either totally or partially, from the depressions after molding. The portion of the pin located within the depressions in the core is removed by cutting it. The pin is provided with a concentration such as a slot in the cut. The cut is carried out by means of the molding core: the core is removed from the finished and cooled fitting, the pins are cut in the contraction. The upper part of the pin remains inside the connecting pin, while the rest remains inside the depressions in the molding core, from where they are removed before following the molding operation. In this assembly, the removal of the rest of the pin from the molding core is a problem: in order not to deteriorate the molding of the next fitting, these remaining portions must be carefully recovered. The additional operation step consisting of the removal of the remaining pin is another problem. Optionally, the pin is completely removed from the depressions of the core by means of an appropriate tool; the pin and the depression, for example, are threaded, the pin being screwed out of the depression after molding. This embodiment involves the problem of an additional operation step: the removal of the pin from the depression with a tool after the molding step. The purpose of the invention is to provide a new method and arrangement for supporting the ends of a resistance wire in the manufacture of electrically heat-weldable plastic tube fittings in an injection mold, which solves the problems described above. To achieve this, the method according to the invention is characterized by the aspects defined in the characterization clause of claim 1. The arrangement according to the invention, in turn, is characterized by the aspects defined in the characterization clause of claim 6. Preferred embodiments of the invention are described in the remaining claims. The invention is explained in more detail below with reference to the accompanying drawings, of which Figure 1 is a vertical cross-sectional view of the support arrangement of a resistance wire of the invention in the manufacture of plastic pipe fittings. electrically heat-weldable in an injection mold prior to the injection molding operation, Figure 2 is a vertical cross-sectional view of the end support arrangement of a resistance wire of the invention in the manufacture of accessories of electrically heat-weldable plastic tubes in an injection mold after the injection molding operation, and Figure 3 is a vertical cross-sectional view of the finished thermoplastic fitting, and Figure 4A is a top view of the end connection of the resistance wire the plug and the screw of the plug in the step of injection molding and the Figur a 4B is a top view of the position of the resistance wire and the pin at the end of the injection molding step, Figure 5 shows a second support arrangement for the end of the resistance wire, however, illustrating a single pin and Barrette. An arrangement for supporting the ends of a resistance wire in the manufacture of electrically heat-weldable plastic tube fittings in an injection mold as illustrated in Figures 1 and 2. The injection mold comprises a core 1 and a mantle 2, and a molding space 3 provided therebetween. The electrically heated resistance wire 4 is wound around the core 1. The resistance wire 4 is attached to the end 4a, 4b of the plug 5, 6. The core 1 has been provided with two depressions 7, 8, or perforations, preferably holes. The plugs 5, 6 are connected with a pin 9, 10, which is fixed in the depressions 7, 8, with the help of the pins 9, 10 and the pins 5, 6, the resistance wire 4 is retained in the position around the core 1 during molding. The resistance wire 4 is additionally fixed in the area of the core 1, where the fitting parts of the fitting are formed in the molding passage for the tubes to be joined. The ends of both pins 5, 6 project from the finished fitting (see Figure 3), to allow the connection of a power source during the joining of the tubes, as described below. The arrangement for supporting the ends 4a, 4b of the resistance wire 4, further includes two guide bushings 11, 12, arranged to support two pins 9, 10, respectively, and the depressions 13, 14, such as the holes or perforations for each guide bushing 11, 12, in the mantle 2 of the lining of the molding space 3. With these depressions 13, 14, the guide bushings 11, 12 are supported essentially vertically against the surface of the core 1 and move towards in front of the depressions 7, 8 in the mantle 2 of the injection mold. The arrangement also comprises a flexible actuator arranged in the connection with each depression 13, 14, in this case a spring, particularly a spiral spring 1, 16. It is arranged behind the guide bushing 11, 12, in a depression, such as a hole, being thus supported, on the one hand, by the lower depression, that is, in this case the retention means of the hole 17, 18 act as a depression, and on the other hand, by the rear surface of the guide bushing 11, 12. Under the action of the rear spring, the spring 15, 16, the guide bush 11, 12 is pressed and also passed through the pin 9, 10 and the pin 5, 6, which are retained in their position in the depression 7, 8. The pins 9, 10 and also the guide bushings 11 , 12 are arranged to rise against the action of springing backward of the spring 15, 16 in the depressions 7, 8 under the pressure of the molding compound during the injection molding step. At the beginning of the injection molding step, the springs 15, 16 ensure that the molding compound does not enter the space between the pin 9, 10 and the guide bushings 11, 12. An elastic actuator may also be provided in some other form by means of coil springs 15, 16, as described above. The purpose of the elastic actuator is, on the one hand, to retain the pin 9, 10 in the position of the depression 7, 8 before initiating the step of injection molding and, on the other hand, during the step of injection molding, to produce both molten plastic and that which is introduced into the mold space 3 of the mold, its pressure acting against the retention energy of the actuator. Furthermore, it should be noted that this retention energy, by means of which the elastic actuator has been arranged to act on the guide bushing 11, 12 and through it on the pin 9, 10 and the pin 5, 6, should be of, and in order of magnitude in such a way that does not press these means 11, 12; 9, 10; 5, 6 back into the melt molding compound, as the molding space 3 is being filled with a molten plastic the supply pressure of the plastic remains at the end of the injection molding step. The elastic actuator used is, for example, a hydraulic or pneumatic cylinder, by means of which the guide bushing 11, 12 and through it, the pin 9, 10 and the pin 5, 6 are kept inserted in the depressions 7, 8, the pressure of the molten plastic composition acts against the cylinder pressure in the injection molding step. The cylinder is preferably driven mechanically so that it is pushed together with the guide bushing 11, 12, the pin 9, 10 and the pin 5,6 as the injection molding step proceeds, and remains in the upper position. At the end of the injection molding step, this means that it is thus prevented from re-pressing on the molten plastic and solidifying precisely in the desired position in the molding compound. In a preferred embodiment of the invention, the depressions 7, 8 on the pins 9, 10, are arranged to extend through the core 1 of the injection mold. Therefore, during the step of injection molding, the pressure of the plastic will act on the pin 9, 10 directly through the depressions 7, 8 on the opposite side of the core 1.

In a preferred embodiment of the invention, the pins 9, 10 and the guide bushings 11, 12 are arranged to rise to the desired level above the surface of the core 1 under the action of the plastic pressure. For this purpose, a retainer 19, 20 is disposed at a distance from the surface of the core 1 and, at the same time, from the rear surface of the guide bushing 11, 12, supported on the pin 9, 10 or the like, under the action of the spring 15, 16 so that the guide bushing 11, 12 can be raised to the desired height, i.e., at least at a level of sufficient height to allow the pin 9, 10 to be completely withdrawn from the depressions 9; , 10 in the step of injection molding. Therefore, after the injection molding step, the core can be removed directly from the mantle 2 and from the finished fitting. In a preferred embodiment of the invention, each pin 9, 10 includes a flange 21, 22 or a similar annular projection. They are arranged in the upper portion of the pin 9, 10 so that they remain outside the depressions 7, 8 and, therefore, on the surface of the core 1 or above it. The pin 5, 6 is connected to the pin 9, 10 on the other side of the flange 21, 22. The pin 5, 6 and the pin 9, 10 constitute a uniform coaxial part. The guide bushing 11, 12 is arranged to rest on the flange 21, 22. If the flange 21, 22 is arranged so as to form a space 23, 24 between the flange and the core 1, as illustrated in the figure 1, the injection molding compound should act on the flange 21, 22 through the space 23, 24 in the molding step and the impulse pin 9, 10, even if the depressions 7, 8 in the pin 9, 10 they do not extend through the core 1. It should be noted that the cross-sectional area of the end of the guide bushing 11, 12 essentially levels out the area of the flange 21, 22 and, therefore, the pressure of the plastic to be injected will not act directly on the end of the guide bushing 11, 12, the pressure will be applied through the bottom surface of the flange 21, 22, to the flange 21, 22 and, further, to the guide bushing 11, 12 and spring 19, 20 connected thereto, and acting against the springback factor. A preferred connection of the end 4a of the resistance wire 4 to the pin 5 and especially to the associated pin 9 is illustrated in FIGS. 4A and 4B. These figures show AA in detail as a top view of Figures 1 and 2. The end 4a of the resistance wire is attached to the pin 5 and the pin 9 so that the resistance wire 9 is wound around the pin 5 and the pin. As the pin 5 and the pin 9 rise in the injection molding step under the pressure of the molten plastic against the holding energy of the guide bushing 11 (see Figures 1 and 2), such as the springing factor toward behind the spring 15, the resistance wire is unwound from the pin 5 and the pin 9, and therefore, the resistance wire acquires additional length to the required degree by raising the pin 5 and the pin 9. In the figure 4A, the end 4a of the resistance wire 4 is spot welded at the point a on the pin 9, particularly at the edge of the flange 21 belonging to the pin 9, and the resistance wire 4 has been wound, v.gr ., less than one turn, such as half a turn around the flange 21. As the pin 5 and the pin 9 rise from the depression 7 in the molding step (see Figures 1 and 2), they also roll in relation to depression 7 (address B) and it is released the resistance wire 4, ie, it is unwound from the flange 21, and because of this, the junction of the end 4a of the resistance wire 4 remains intact, although there is still enough resistance wire 4 free to allow the pin 9 to rise from the depression 7. The length of the pin 9 and, at the same time, the minimum depth of the depression 7, is for example, in the order of 5 mm in diameter of the flange 21 being eg, 10 mm. When the resistance wire 4 is wound a quarter of a turn around the flange 21, the 90 ° rotation of the pin 9 and the flange 21 in the B direction produces more than 7 mm of the released wire 4. In a second preferred embodiment of The invention, illustrated in Figure 4, each pin 25 includes a flange 26 or an annular projection. The pin 25 fits in the depression 27 in the core 1 so that the flange 26 is on the surface of the core (or optionally above it, as in the example of the preceding embodiment). The guide bushing 29 abuts the flange 26. In this embodiment, one or more grooves or cavities 30 are provided in the lower surface of the flange 26. In the injection molding step, the plastic pressure should be applied, therefore, through the cavity 30 toward the lower surface of the flange 26 and further into the guide bushing 31 and the associated spring (not shown in this figure) by driving the pin 26 including the pin 28 of the depression 27. Except by the design of the flange 26, this arrangement corresponds to those at the beginning of figures 1 and 2; however, the depression 27 in the pin 25 does not extend through the core 1 (even if this were feasible). With reference to Figures 1 and 2, the following steps of the process are carried out in the method of the invention to support the ends of the resistance wire in the manufacture of electrically heat-weldable plastic tube fittings: a) The wire of electrically heated resistance 4 is wound around the core 1 in the area of the core 1 in which the fitting parts 33, 35 of the fitting can be formed in the molding step (see Figure 3) for the tubes to be joined. b) The ends 4a, 4b of the resistance wire 4 are connected to the pins 5, 6, eg, by spot welding. Usually one end of the resistance wire 4 is first attached to the first pin 5 and the wire is preferably wound around it, and then the resistance wire is wound on the surface of the core 1, and only then the second end of the wire The resistance is joined to the second pin 6 and is also wound around it (see Figures 4A and 4B). c) The pins 9, 10 are fixed in the depressions, such as in the holes 7, 8 provided in the core 1. d) At the same time, the pins 5,6 are supported on the core 1 with the help of the pin 9, 10 included in each pin. e) The guide bushing 11, 12 is disposed in relation to each pin 9, 10 and the pin 9, 10. More preferably, the guide bushing 11, 12 is arranged to rest on the flange 21, 22 belonging to the pin 9, 10. f) Each guide bushing 11, 12 is supported in a depression 13, 14 provided in the mantle 2. g) The spring 15, 16 or a similar actuator is arranged to act on the guide bushing 11, 12 so that its retention energy presses the guide bushing 11, 12, the pin 5, 6 and the pin 9, 10 in the position against the core 1. In particular the spring 15, 16 presses the guide bushing 11, 12 against the flange 21, 22 of the pin 9, 10. h) The injection molding is initiated by introducing the molten molding compound through the opening 40 into the molding space 3 in a manner known per se, the molding compound extends around the core 1. i) During the injection molding process, as the compound fused or reaches each pin 9, 10 (either through a depression 7, 8 extending through the core 1 and / or through a space 23, 24 between the flange 21, 22 and the core 1, acting on the lower surface of the flange 21, 22 and / or through the cavities 30 in the flange 26 acting on the lower surface of the flange 26), the pressure of the plastic should drive the pin 9, 10, the pin 5,6 and the guide bushing 11, 12 of the core 1 against the clamping energy of an elastic member, such as a spring 15, 16, as illustrated in Fig. 2. The pin 9, 10, the pin 5, 6 and the bushing guide 11, 12, should preferably remain at least almost in the upper position, the pins 5, 6 are projected differently from the finished accessory. j) After the injection molding step, the core 1 is removed from the mantle 2, the mantle 2 and the guide bushing 11, 12 are opened and the finished fitting is removed from the injection mold. In this arrangement, the injection mold is intended for the manufacture of a thermoplastic fitting comprising a straight cylindrical body 32 and two fitting parts 33, 34 disposed at the ends of the body 32, as shown in Figure 3. The parts of adaptation 33, 34, in turn, include adjustment cavities 35, 36, in which the plastic tubes are fixed. The adjustment cavities 35, 36 are interconnected either directly or with a short section of tube 37. The attachment, in particular the adapter parts 33, 34, are equipped with a resistance wire 4. The resistance wire 4 is arranged in the area of connection between the tube to be connected, the adjustment cavity 35, 36 of each adaptation part 33, 34 and the accessory. The resistance wire 4 passes through the adjustment cavity 35, 36 and the surroundings of its internal surface and extends at least over the length of the connection between an adjustment cavity and the plastic tube. The sections of tubes can be joined by being fixed in the fitting cavities 35, 36 of the fitting. An electric current suitable for heat welding is connected to the pins 5, 6, and is arranged to pass through the resistance wire 4 for a certain period, and then both the fitting, the fitting parts 33, 34 and the tubes of plastic are fixed in the adjustment depression 35, 36 which will be plasticized and fused in the bonding area and subsequently solidified to form a hermetic, uniform unit. The invention was described above by means of a number of preferred embodiments, however, the invention can, of course, be applied in many forms within the scope of the idea of the invention defined in the appended claims.

Claims (10)

1. CLAIMS 1. A method for supporting resistance wire ends in the manufacture of electrically heat-weldable plastic tube fittings in an injection mold, whereby - an electrically heated resistance wire (4) is wound around the core (1), - the ends of the resistance wire (4) are connected to the pins (5, 6), - the pins (9, 10) are fixed in the depressions (holes) (7, 8) provided in the core (1), and - the pins (5, 6) are supported on the core (1) by means of the pins (9, 10) connected thereto, characterized in that - the bushing guide (11, 12) is arranged in relation to each pin (9, 10) and the connected plug (5, 6), - each guide bushing (11, 12) is supported in a depression (12, 14) provided in the injection mold (2), - an elastic actuator, such as a spring (15, 16), is arranged to act on each guide bushing (11, 12) so that its retention energy presses the guide bushing, the pin and the pin in the position against the core (1), - the injection molding process is initiated by introducing the molding compound around the core (1) in the molding space (3) in a manner known per se , so that - as the injection molding compound reaches each pin (9, 10), the pressure of the plastic drives the pin (9, 10), the pin (5, 6) and the bushing d guide (11, 12) from the core (1) against the holding force of the actuator, such as a spring (15, 16), and that - after injection molding the guide bushing (11, 12) opens , and the finished accessory is removed from the injection mold. A method according to claim 1, characterized in that the depression (7, 8) in each pin (9, 10) is arranged to extend through the core (1). A method according to claim 1 or 2, characterized in that the pin (9, 10) and the guide bushing (11, 12) are arranged to rise under the pressure of the plastic to the desired level above the core (1). ). 4. A method according to claim 1, 2 or 3, characterized in that the resistance wire (4) is wound in contact with the pin (5, 6). An arrangement for supporting the ends of a resistance wire in the manufacture of accessories of electrically heat-weldable plastic tubes in an injection mold, comprising the core (1) and the mantle (2) of the injection mold and a molding space (3) provided therebetween, the electrically heated resistance wire (4) being wound around the core (1), the arrangement comprising - the pins (5, 6), the ends of the resistance wire (4) being connected in relation thereto, - the depressions (7, 8) provided in the core (1), - the pins (9, 10) to support the pins (5, 6), the pins being fixed in the depressions ( 7, 8), characterized in that the arrangement further comprises - guide bushings (11, 12), which are arranged to support the pins (9, 10), - a depression (13, 14) in the mantle (2) for each guide bush (11, 12), the guide bushings (11, 12) being supported through the depressions (13, 14) on the mantle (2) of the injection mold, and - an elastic actuator, such as a spring (15, 16) in each depression (13, 14) behind the guide bushing (11, 12), the actuators (15, 16) serve to retain the guide bushings (11). , 12) and, with these, the pins (9, 10) in their position, the pins (9, 10) and in addition the guide bushings (11, 12) being arranged to rise from the depressions (7, 8) under the action of the pressure of the plastic against the retention energy of the actuator (15, 16) during the injection molding step. 6. An arrangement according to claim 5, characterized in that the depressions (7, 8) in each pin (9, 10) are arranged to extend through the core (1). 7. An arrangement according to claim 5 or 6, characterized in that each pin (9, 10) and the guide bushing (11, 12) is arranged to rise under the pressure of the plastic to the desired level above the core (1), a retainer (17, 18) having been placed in this point. 8. An arrangement according to claim 5 or 7, characterized in that each pin (9, 10) comprises a flange (21, 22) or a similar projection. An arrangement according to claim 8, characterized in that the flange of the pin (25) is provided with a groove or cavity (30) on its bottom surface. A method according to any of claims 5 to 9, characterized in that the resistance wire (4) is wound in contact with the pin (5, 6), especially with the pin (9, 10).