CS152791A3 - Process for producing plastic coated fittings by injection moulding - Google Patents

Description

Technical field

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing plastic-coated injection molding fittings in which a female threaded body is screwed into an injection-molding device with the outer plastic body.

Background Art

A known method of this kind is to produce flush-mounted plastic sleeves as part of a transition piece for connecting plastic pipes for liquid media with fittings made of metal materials, especially in the field of sanitary and heating technology, wherein one end of the flush-mounted sleeve has an offset hole to weld the plastic tube and the other end of the sleeve has a cast metal sleeve with a threaded fitting thread (see German Utility Model No. 8716394). In order to form a tensile and torsional connection between the metal sleeve and the concealed plastic tube, the sleeve being formed by spraying plastic on the sleeve, the connecting sleeve has a radial notch at its rear end which is provided with at least one recess located approximately parallel to the longitudinal the connecting sleeve axis and into which the plastic material of the sleeve body flows, whereby the shaped sleeve is achieved by the connecting sleeve and the sleeve body. Furthermore, the outer surface of the connecting sleeve is provided with projections or grooves surrounding the circumference thereof, into which the plastic material of the concealed sleeve flows when the sleeve is sprayed. In spite of these surface finishes, which are made with great workload to be used for this purpose, and those between the plastic body and the metal body have been shaped, however, the paths of material flow may open as a result of the shrinkage between the contacting surfaces of the different materials. which causes the concealed sleeve to become unusable as a connecting element between the plastic pipes and the screwed or unsheathed sleeve. a screwable armature. In another known transition piece of the type described above, a flameproof enclosure is provided to form a positive connection between the metal connection tube and the sleeve bodies injected thereon, the latter being formed by a recess of the grooves, bores and the like. , provided on the front inner end of the connection sleeve, and recesses in the form of grooves, bores and the like, provided at the front inner end of the connection sleeve, and recesses in the form of grooves, bores and the like. on the outer surface of the connecting sleeve. These depressions are at least partially connected to the recesses on the front and can inject the injection molded plastic. (See German Utility Model 88 10285). Here too, considerable effort is required in order to provide a mechanically rigid and sealing connection between the plastic body and the metal body. Furthermore, it has also been proposed to connect a connector for a plastic con- junction with this hose by pouring or crimping so that the end of the hose is inserted into the injection mold for the connector body and the surface of the connector material is melted, both parts of of the same plastic material.

However, this method of manufacture is unsuitable for making plastic-coated fittings, in particular transition pieces for connecting plastic pipes with fittings made of metallic materials, since it does not result in a mechanically rigid and tight permanent connection of said parts. This is due to the fact that the hose intended to be injected has at least one collar which is. pressed into this part of the hose before connecting the connecting piece near the end of the hose. This part is to be surrounded by a plastic body. This measure is intended to increase the resistance to tensile forces acting on the coupling piece. It is therefore an object of the present invention to improve the method described above in such a way that a durable connection between the threaded inner sleeve body for screwing the fitting and the outer plastic sleeve body which remains completely tight even under extreme mechanical and thermal loads.

SUMMARY OF THE INVENTION

This object is achieved in accordance with the invention in that the outer sleeve body is produced by injection from a low melting olefinic plastic, whereupon a core is inserted into the sleeve bore, the outer surface of which corresponds to the inner surface of the fitting to be manufactured, and then between the core and the sleeve. the inner surface of the outer plastic sleeve body injects a higher melting point olefin plastic to form the inner sleeve body, which melts the surface of the outer plastic sleeve body and connects to it;

The essence of the invention is that the two sleeve bodies to be joined by injection molding are of different plastics, which are joined together during the casting process but differ at least in their melting point so that the outer sleeve body melts at a lower temperature than the inner sleeve body. In this way, it is ensured that the outer sleeve body first produced by the injection molding is melted by the higher melting material injected subsequently into the injection mold, by surface injection molded subsequently into the injection mold, by the higher material melting temperature of the inner sleeve body. that this melting leads to a permanent bonding of the two different materials, which resists even higher thermal stresses and mechanical stresses. Polypropylene (PP), which has a melting point of about 170 ° C, has proven to be useful as the outer sleeve material, while polyamide / PA / with a melting point of about 300 ° CPolyamide can advantageously be used as the inner sleeve material. to blend with the carbon fibers with non-glass fibers to achieve tensile and shear strength corresponding to the brass. 5

In a particularly advantageous and inexpensive manner, such an embodiment of the process according to the invention has been avoided, in that the inner surface of the outer sleeve body, for example in the form of ribs, groove grooves, notch recesses, etc., has been discarded since the fusion connection between the two sleeves is sufficiently tight in torsion, and there is no need to bend the injected material when it is cooled, since both materials are olefins. An embodiment of the invention

The steps used to carry out the process according to the invention assume that the outer sleeve body of propylene is first sprayed in a suitable injection mold, after which the core is removed from the sleeve body cavity, the core being a smooth outer surface. inserts another smaller diameter core, the outer surface of which corresponds to the negative shape of the inner surface of the fabricated fitting or transition piece; it usually has a thread into which a metal connecting fitting is later screwed.

After insertion of the second core, the cavity between the outer sleeve body and the core surface is ejected by Ultramid T, a polymer whose melting point is about 300 ° C and which is internally bonded by the outer sleeve body by melting its surface.

After the inner sleeve body has cooled, the core is removed and the fitting as a whole removed from the mold. Can it be used immediately, or? subsequent machining is no longer necessary.

Claims (5)

I 6 PATENT CLAIMS A method for producing injection-molded plastic fitting in which an internal threaded body of a fitting is threaded in an injection molding tool non-movably with an outer plastic sleeve body, characterized in that the outer sleeve body is injection molded from a low melting olefin plastic, whereupon a core having an outer surface corresponding to the inner surface of the fitting to be inserted is inserted into the socket opening, and an olefin plastic having a higher melting temperature is injected between the core and the inner surface of the outer plastic sleeve body to form the inner sleeve body; , exposing the surface of the outer plastic sleeve body to it. 2. A process as claimed in claim 1, wherein the low melting olefin plastic used is polyolefin as the higher melting olefin plastic. 3. Process according to claim 2, characterized in that carbon fibers are added to the polyamide in a proportion which increases the tensile and shear strength of the material to a value corresponding to brass. 7 4. A method according to any one of claims 1 to 3, characterized in that the outer plastic sleeve body and the inner sleeve body are produced in the same injection molding using two different cores. 5. A method according to any one of claims 1 to 4, wherein at least the inner radial surface of the outer plastic sleeve body which is fused to the outer surface of the inner sleeve body is provided as a smooth surface without grooves, grooves, recesses, and grooves. of recesses.