EA001743B1 - Method and arrangement for manufacturing of electrically heat-weldable plastic tube fittings - Google Patents

Abstract

1. A method for manufacturing of electrically heat-weldable plastic tube fittings in an injection mould, whereby - 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, characterized in that - a guide bushing (11, 12) is disposed in connection 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 process is started by introducing moulding compound around the core (1) in the moulding space (3) in a manner knownper 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the holding power of the actuator, such as a spring (15, 16), and that - after the injection moulding, the core (1) is withdrawn from the mantle (2), the mantle (2) including the guide bushing (11, 12) is opened, and the finished fitting is removed from the injection mould. 2. A method as claimed in claim 1, characterized in that the recess (7, 8) in each pin (9, 10) is disposed to extend through the core (1). 3. A method as claimed in claim 1 or 2, characterized in that the pin (9, 10) and the guide bushing (11, 12) are disposed to rise under the plastic pressure to the desired level above the core (1). 4. A method as claimed in claim 1, 2 or 3, characterized in that the resistance wire (4) is wound into contact with the peg (5, 6). 5. An arrangement for manufacturing electrically heat-weldable plastic tube fittings in an injection mould, comprising the core (1) and the mantle (2) of the injection mould and a moulding space (3) provided between these, the electrically heated resistance wire (4) being wound about the core (1), the arrangement comprising: - pegs (5, 6), the ends of the resistance wire (4) being attached in connection with these, - recesses (7, 8) provided in the core (1), - pins (9, 10) for supporting the pegs (5, 6), the pins being fitted in the recesses (7, 8), characterized in that the arrangement further comprises - guide bushings (11, 12), which are disposed to support the pins (9, 10), - a recess (13, 14) in the mantle (2) for each guide bushing (11, 12), the guide bushings (11, 12) being supported through the recesses (13, 14) on the mantle (2) of the injection mould, and - an elastic actuator, such as a spring (15, 16) in each recess (13, 14) behind the guide bushing (11, 12), the actuators (15, 16) serving to retain the guide bushings (11, 12) and with these the pins (9, 10) in position, the pins (9, 10) and further the guide bushings (11, 12) being disposed to rise from the recesses (7, 8) under the action of the plastic pressure against the holding power of the actuator (15, 16) during the injection moulding step. 6. An arrangement as claimed in claim 5, characterized in that the recess (7, 8) in each pin (9, 10) is disposed to extend through the core (1). 7. An arrangement as claimed in claim 5 or 6, characterized in that each pin (9,10) and guide bushing (11, 12) is disposed to rise under the plastic pressure to the desired level above the core (1), a stopper (17, 18) having been positioned at this point.

Description

The invention relates to a method defined in the restrictive part of the first independent claim, and intended to support the ends of the resistance wire in the manufacture of plastic fittings connected to electric welding pipes in a mold.

The invention also relates to a device for implementing the proposed method and defined in the second independent claim.

Weldable thermoplastic fittings, i.e. couplings, are designed to precisely fit plastic pipes made of similar material to each other. Such pipelines made of plastic pipes are used, for example, as gas pipes in the manufacturing industry.

The fitting has a housing with one or more transitional parts for connected plastic pipes. The transition parts, in turn, are made with landing channels into which plastic pipes are inserted. Landing channels are connected by pipe sections. The fitting, in particular the adapter parts, is equipped with a resistance wire. The resistance wire is located in the landing channel of each transitional part, being passed along its inner surface and extends at least along the length of the junction of one landing channel with a plastic pipe. The connected sections of the pipe are located in the landing channels of the fitting. The electric current required for welding is passed through the resistance wire for a certain period of time, as a result of which the fitting, the adapter part and the plastic pipe installed in the bore channel will be softened and melted in the joint zone, and then harden, forming a strong single unit.

Plastic pipe fittings are manufactured using injection molding technology. Before the casting step, a resistance wire is placed inside the mold. The resistance wire is held on the forming rod either by means of a pre-cast assembly casing or by means of supporting fingers.

In the first case, first, in a mold, a thin assembly casing is cast around the forming rod, which is then cooled and a resistance wire is wound on it. Recesses for connecting pins to which the ends of the resistance wire are attached are preferably made in the assembly casing. After the resistance wire with connecting pins is installed on the assembly casing, this device is transferred to another mold, in which the fitting is cast, receiving it in the completed form. The connecting pins protrude from the molded fitting, and through them, at the stage of welding, electric current is supplied to the resistance wire. The disadvantage of this method is the presence of two stages of casting, which reduces productivity and causes an increase in production costs.

In the second case, the resistance wire is wound directly onto the forming rod, as shown, for example, in the description of patent application EP 260014. Here, in the forming rod, recesses are made in which connecting pins are installed during the casting by means of supporting fingers. After casting, the support fingers are removed from the indentations in whole or in part. The part of the finger located in the recess of the rod is removed by cutting. To do this, the finger is performed with a narrowing, for example, in the form of a groove. Cutting is performed using a forming rod: when removing the rod from the finished chilled fitting, the fingers are cut off at the points of their narrowing. The upper part of the finger remains with the connecting pin, and the cut off part remains in the recess of the molding rod, from where it is removed before the next casting operation. In this regard, the remainder of the finger removed from the molding rod causes a problem, since, in order not to interfere with the subsequent casting process, the parts of the fingers remaining in the rod must be carefully removed. An additional technological stage, which consists in removing the remainder of the finger, complicates the method. The finger can be completely removed from the recess of the shaft using a suitable tool. In addition, the finger and the recess can be threaded, and then, after casting, the finger is unscrewed from the recess. This technique eliminates the problem associated with the need for an additional step of removing the finger from the recess using the tool after the casting stage.

The objective of the invention is to obtain new, solving the above problems, method and device for supporting the ends of the resistance wire in a mold in the manufacture of plastic fittings that can be electrically welded to pipes. To solve this problem, the method proposed in accordance with the invention is characterized by the features defined in the characterizing part of paragraph 1 of the claims. In turn, the device made according to the invention is characterized by the features of the distinctive part of the corresponding independent claim. In the dependent claims, preferred embodiments of the invention are disclosed.

The invention is described in more detail below with reference to the attached drawings.

In FIG. 1 shows a vertical section of the proposed device for supporting the resistance wire in the manufacture of electrically welded plastic fittings in a mold, before the casting process;

in FIG. 2 - the same after the casting process;

in FIG. 3 is a longitudinal section through a fabricated thermoplastic fitting;

on figa in top view shows the end of the resistance wire attached to the pin, turning during the casting process;

in FIG. 4B is a plan view showing the end of a resistance wire attached to the pin in position at the end of the casting process;

in FIG. 5 shows a second embodiment of the proposed device.

A device for supporting the ends of a resistance wire in the manufacture of electrically weldable plastic fittings in a mold is illustrated in FIG. 1 and 2. The foundry mold includes a core 1 and a sheath 2 with a molding space 3 between them. The resistance wire 4 intended for electric heating is wound onto the rod 1, both ends 4a, 4b thereof being attached to the corresponding pins 5, 6. Two recesses 7, 8 are made in the rod 1, preferably in the form of holes or channels. The pins 5, 6 are connected to the corresponding fingers 9, 10 installed in the recesses 7, 8. Using the fingers 9, 10 and pins 5, 6, the resistance wire 4 is held in the winding position around the rod 1 during molding. In addition, the resistance wire 4 tightly fits the rod 1 in the area where the transitional parts of the fitting for those pipes to be connected are formed at the casting stage. The ends of both pins 5, 6 will protrude from the resulting fitting (see FIG. 3) to ensure that the energy source is connected during the pipe connection, as described below.

The device for supporting the ends 4a, 4b of the resistance wire 4 also contains two guide bushings 11, 12 mounted to support the fingers 9, 10, respectively. For the guide bushings 11, 12, holes 13, 14, respectively, exit into the molding space 3 in the shell 2 of the mold. The guide bushings 11, 12 are located in these holes 13, 14 essentially vertically above the surface of the shaft 1 with the possibility of movement towards the recesses 7, 8. This device also contains elastic force elements in the form of springs 15, 16 (in particular, coil springs) placed in holes 13, 14, respectively. The springs are located behind the guide bushings 11, 12 in such a way that on one side they abut against the ends of the holes formed, for example, by plugs 17, 18, and on the other hand, into the rear surfaces of the guide bushings 11, 12. Pressure of the springs 15, 16 is transmitted through the guide bushings 11, 12 and pins 5, 6 to the fingers 9, 10, holding them in the recesses 7, 8. The fingers 9, 10 and the guide bushings 11, 12 are arranged to move up against the direction of action of the springs 15, 16 under molding pressure mixtures at the stage of injection molding with the release of fingers 9, 10 and h recesses 7, 8. At the beginning of the injection molding stage, the springs 15, 16 prevent the molding sand from getting between the fingers 9, 10 and the guide bushings 11, 12.

The purpose of the elastic force organs is to, on the one hand, hold the fingers 9, 10 in the recesses 7, 8 before the start of the injection molding stage, and on the other hand, allow these fingers to move during injection molding under the anti-spring force the pressure introduced into the molding zone of the molten plastic. It should be further noted that the elastic force with which the elastic power organs act through the guide sleeves 11, 12 on the pins 5, 6 and fingers 9, 10 should be of such a value that no extrusion of these elements 11, 12, 9, 10 , 5, 6 back into the molten molding sand when the molding space 3 is filled with molten plastic and when the plastic supply pressure drops at the end of the injection molding stage.

Elastic force elements can be made in a different way than in the form of the coil springs 15, 16 described above. Thus, the force element can be made, for example, in the form of a hydraulic or pneumatic cylinder, due to which through the guide bushings 11, 12 and pins 5, 6 the fingers 9, 10 are held in recesses 7, 8 at the beginning of the injection molding stage, when the pressure of the molten plastic composition acts against the pressure of the cylinder. The cylinder is controlled mainly mechanically so that it is pulled up together with the guide sleeve 11, 12, pin 9, 10 and pin 5, 6 at the casting stage and is in the upper position at the end of this stage, thereby preventing the extrusion of these elements into the molten plastic and their fixation in the molding composition in exactly the desired position.

In a preferred embodiment of the invention, the recesses 7, 8 for the fingers 9, 10 are made in the mold core 1 through. Due to this, during the molding process, the pressure of the plastic will act on the fingers 9, 10 directly through the holes of the recesses 7, 8 on the opposite side of the rod 1.

In a preferred embodiment of the invention, the fingers 9, 10 and the guide bushings 11, 12 are mounted with the possibility of lifting to the desired level above the surface of the rod 1 under the action of the pressure of the plastic. For this purpose, in the holes 13, 14 of the guide bushings 11, 12 are the stoppers 19, 20, respectively made, for example, in the form of a pin or ring structure. The stop 19, 20 is installed at a distance from the surface of the rod 1, as well as from the rear surface of the guide sleeve 11, 12, pressed against the finger 9, 10 under the action of the spring 15, 16, so the guide sleeve 11, 12 can rise to the desired height, at least at least a height sufficient to allow the finger 9, 10 to completely exit the recess 7, 8 during injection molding. Thus, upon completion of the casting stage, the rod 1 can be immediately removed from the shell 2 and the resulting fitting.

In a preferred embodiment of the invention, each finger 9, 10 is made with a flange 21, 22 or a similar annular protrusion located in the upper part of the finger outside the recess 7, 8, i.e. on the surface of the rod 1 or above it. The pin 5, 6 is connected to the pin 9, 10 on the outside of the flange 21, 22, thus constituting a single coaxial element. The guide sleeve 11, 12 rests on the flange 21, 22. When there are gaps 23, 24 between the flanges 21, 22 and the rod 1, respectively, as shown in FIG. 1, during injection molding, the molding composition will act on the flanges 21, 22 through the gaps 23, 24 and raise the fingers 9, 10, even if the recesses 7, 8 in the rod are not made through. It should be noted that the cross-sectional area of the end of the guide sleeve 11, 12 is essentially equal to the area of the flange 21, 22, so the pressure of the filled plastic will not act directly on the end of the guide sleeve 11, 12; this pressure acts on the flange 21, 22 through its lower surface and then on the guide sleeve 11,12 and the spring 15, 16 in contact with it against the direction of the force of its elasticity.

The preferred connection of the end 4a of the resistance wire 4 to the pin 5, and thereby to the corresponding pin 9, is shown in FIG. 4A and 4B, in which section AA is shown in FIG. 1. The end 4a of the resistance wire is attached to the pin 5 and the pin 9 so that the wire 4 is wound around the pin 5 and the finger 9. When at the injection stage, the pin 5 and the pin 9 rise under the pressure of the molten plastic in the direction against the holding force of the guide sleeve 11 (FIGS. 1 and 2), such as the spring force of spring 15, the resistance wire 4 is unwound from pin 5 and pin 9 and thereby releases its additional length to the amount necessary to raise pin 5 and pin 9. As shown in FIG. 4A, the end 4a of the wire 4 is welded at point a to the pin 9, in particular to the edge of the flange 21 belonging to the pin 9, and the wire 4 is wound on the flange 21, for example, with an incomplete revolution, in particular with a half revolution. When the pin 5 and pin 9 rise from the recess 7 during the casting process (Figs. 1 and 2), they also rotate in this recess in the direction of arrow B, allowing the wire 4 to be wound off the flange 21, due to which, on the one hand, the attachment of the end is retained 4a of the wire 4, and on the other, the wire 4 is still sufficiently released to allow the pin 9 to rise from the recess 7. The length of the pin 9 and the minimum depth of the recess 7 is, for example, 5 mm, the diameter of the flange 21 may be 10 mm If the resistance wire 4 is wound 1/4 turn around the flange 21, then when the pin 9 and the flange 21 are rotated 90 ° in the direction of arrow B, more than 7 mm of the length of the wire 4 is released.

In a second preferred embodiment of the invention shown in FIG. 5, each finger, indicated by 25, has a flange 26 or a similar annular protrusion. The finger 25 is located in the recess 27 in the rod 1 so that the flange 26 is located on the surface of the rod 1 or above it, as in the previous embodiment. The guide sleeve 29 rests on the flange 26. In this embodiment, one or more grooves or recesses 30 are made on the lower surface of the flange 26. At the injection molding stage, the plastic pressure will thus be transmitted through the recess 30 to the lower surface of the flange 26 and further to the guide sleeve 29 and to the corresponding spring (not shown in FIG. 5), lifting pin 25 with pin 28 from recess 27. With the exception of the design of flange 26, the described example basically corresponds to that shown in FIG. 1, 2, however, the recess 27 for the finger 25 is not through in the shaft 1 (even if this is possible).

According to the invention, in the method for supporting the ends of the resistance wire in the manufacture of plastic fittings connected to electric welding pipes, the following steps are performed (see FIGS. 1, 2 and 3):

a) the resistance wire 4 intended for electric heating is wound onto a rod 1, in the zone of which location during the casting process adapter parts 33, 34 of the fitting will be formed (see Fig. 3) for pipes to be connected;

b) the ends 4a, 4b of the resistance wire 4 are connected to the pins 5, 6, for example, by spot welding. Typically, one end of the resistance wire 4 is first attached to the first pin 5, the wire is preferably bent around it, then the wire is wound onto the surface of the rod 1, and then the second end of the wire is wound onto the second pin 6 and attached to it (see Fig. 4A and 4B);

c) the fingers 9, 10 are placed in the recesses 7, 8, made in the rod 1, for example, in the form of holes;

d) accordingly, the pins 5, 6 are located above the rod 1;

d) the guide bushings 11, 12 are placed in contact with the corresponding fingers 9, 10 and pins 5, 6. Most preferred is the location of the guide bushings on the flanges 21, 22 belonging to the fingers 9, 10;

e) each guide sleeve 11, 12 is placed in the corresponding hole 13, 14, made in the shell 2;

g) a spring 15, 16 or a similar power element is installed to act on the corresponding guide sleeve 11, 12 so that the force of the spring acts on the sleeve 11, 12, pin 5, 6 and pin 9, 10 towards the rod 1. In particular , the spring 15, 16 presses on the guide sleeve 11, 12 in the direction of the flange 21, 22 of the pin 9, 10;

h) a known method initiate injection molding by introducing a molten molding composition into the molding space 3 through the hole 40, distributing the molding composition around the rod 1;

i) during injection molding, when the molten composition reaches each finger 9, 10 (through the through hole 7, 8 in the rod 1 and / or through the gap 23, 24 between the flange 21, 22 and the rod 1, acting on the lower surface of the flange 21, 22, and / or through the recesses 30 in the flange 26, acting on its lower surface), the pressure of the plastic will raise the pin 9, 10, pin 5, 6 and the guide sleeve 11, 12 from the rod 1, counteracting the force of the elastic force, such as a spring 15, 16 (see Fig. 2). The finger 9, 10, pin 5, 6 and the guide sleeve 11,12 will preferably be at least approximately in the upper position, and the pins 5, 6 will clearly protrude from the formed fitting;

j) after the injection molding stage, the rod 1 is removed from the shell 2, the shell 2 is opened, the guide bushings 11, 12 are removed, and the finished fitting is removed from the mold.

In the proposed device, the casting mold is intended for the manufacture of a thermoplastic fitting comprising a housing 32 in the form of a straight cylinder and two transition parts 33, 34 located at the ends of the housing 32, as shown in FIG. 3. In turn, the transition parts 33, 34 have landing channels 35, 36 into which plastic pipes are inserted. The landing channels 35, 36 are communicated with each other either directly or through a short tubular section 37. The fitting, in particular the transitional parts 33, 34, is equipped with a resistance wire 4, which is located in the area between the connected pipe, the landing channel 35, 36 of each transitional part 33, 34 and fitting. Resistance wire 4 passes through the bore channel 35, 36 along its inner surface and extends, at least along the length of the junction of one bore channel with a plastic pipe. The sections of the connected pipes are installed in the landing channels 35, 36 of the fitting. The electric current required for welding is supplied to the pins 5, 6 and, thus, passed through the resistance wire 4 for a certain period, as a result of which the fitting sections, adapter parts 33, 34 and plastic pipe sections in the zone inserted into the bore channels 35, 36 the joints will be softened and melted, and then harden, forming a strong single unit.

The invention is described above with a number of examples of its preferred implementation, however, it can be used in another way within the scope of the inventive concept defined in the attached claims.

Claims (7)

CLAIM 1. A method of manufacturing plastic fittings connected to pipes by electric welding, including winding onto the rod a resistance wire intended for electric heating, attaching the ends of the resistance wire to the pins, inserting fingers into recesses or holes made in the rod, and holding the pins on the rod using connected to them fingers, characterized in that in contact with each finger and a pin connected to it, a guide sleeve is installed, which is located in the hole made in the mold, establish an elastic force element, for example a spring, for acting on each guide sleeve so that the spring force acts on the guide sleeve, pin and finger towards the rod, begin the injection molding process by introducing the molding composition into the molding space around the rod by a known method, which, when the molding composition reaches each finger, the pressure of the plastic raises the fingers, pins and guide bushings above the rod in the opposite direction to the direction of elastic force organ, for example a spring, and after injection molding, the rod is removed from the shell, the shell containing the guide bushings is opened, and the resulting fitting is removed from the mold. 2. The method according to p. 1, characterized in that the recess for each finger is performed in the rod through. 3. The method according to claim 1 or 2, characterized in that the finger and the guide sleeve are arranged to be raised under the action of plastic pressure to a predetermined level above the rod. 4. The method according to claim 1, or 2, or 3, characterized in that the resistance wire is wound onto the pin in contact with it. 5. A device for the manufacture of plastic fittings connected to pipes by electric welding, containing a core and a shell of a mold with a molding cavity between them, designed to electrically heat the resistance wire, wound around the core, pins to which the ends of the resistance wire are attached, and fingers for supporting the pins placed in the recesses made in the rod, characterized in that it is equipped with guide bushings for the fingers placed in the holes made in the foundry shell spring molds for each guide sleeve, and an elastic force element, for example, a spring installed in each hole behind the guide sleeve and designed to hold the guide sleeve with the corresponding finger in the position of the finger in the recess and to allow the guide sleeve and finger to be lifted from its recess under the action of the pressure of the plastic in the opposite direction to the direction of the force of the elastic force body during the process is molded under pressure. 6. The device according to claim 5, characterized in that the recess for each finger is made through the rod. 7. The device according to claim 5 or 6, characterized in that it is equipped with a stopper to enable the lifting of each finger and the guide sleeve under the action of plastic pressure to a predetermined level above the rod.