WO1991007266A1

WO1991007266A1 - Process for the production of conventionally non-deformable tubular cavities in injection-moulded plastics articles

Info

Publication number: WO1991007266A1
Application number: PCT/DE1990/000797
Authority: WO
Inventors: Lutz Ballhause; Gerhard Schellenberg; Friedemann Schroff; Dieter Egert
Original assignee: Robert Bosch Gmbh
Priority date: 1989-11-18
Filing date: 1990-10-20
Publication date: 1991-05-30
Also published as: DE3938396A1

Abstract

The process of the invention calls for hollow preforms to be joined to form the required cavities, placed in a mould cavity for the plastics article and the plastic subsequently introduced into the mould cavity, in particular by injection.

Description

Method for producing conventionally non-demoldable, tubular cavities in plastic injection molded parts

State of the art

The invention relates to a method for producing conventionally non-demoldable cavities, according to the preamble of the main claim.

Plastic molded parts with tubular cavities are required in many ways. The vehicle construction is to be mentioned here, namely both the inner and outer parts and functional elements. These include, for example, fuel distributors of injection engines. Furthermore, molded plastic parts with tubular cavities in the furniture sector are required, for example in armrests and fittings, in components of sports equipment or toys, in household appliances and household goods in a wide variety of designs.

Depending on the field of application, these cavities can be closed at the end, bent in many ways, or have different lateral connecting pieces. In vehicle construction in particular, such as in the case of fuel distributors, it is necessary for the respective cavity to be absolutely gas-tightly sealed at internal pressure. In a first known manufacturing process, different pipe sections are produced separately by the cavities in the pipe sections being formed by corresponding cores. These pipe sections can still be demolded in the longitudinal direction, such as aluminum pipes manufactured in an extrusion process. The end product is then created by assembling the individual pipe sections using, for example, appropriate flanges and seals. This process is complicated and time-consuming.

In a second manufacturing process, so-called "lost" cores are used. These cores have the dimensions of the cavity and consist, for example, of low-melting metal alloys, but also of salt or plastic-metal mixtures. Such cores are, for example, inserted into the molding space of an injection molding machine and extrusion-coated with plastic. The finished product is then placed in a melting device, for example in a tempered bath, and the core or cores are melted out by strong inductive support.

This method is also complex, since for this purpose a "lost" core must first be produced, which, apart from creating a cavity, can no longer serve any other purpose.

In a third manufacturing process, the so-called internal gas pressure process, a gas, for example nitrogen, is blown into the molded part in a plastic injection molding machine or in the tool of this machine, which gas is contained in the molded part produced by the plastic forms a cavity. This method can only be used to a limited extent since the cavity formed by the gas cannot be defined or controlled geometrically. The formation of cavities by overmoulding insert parts is basically also prior art. However, this involves the encapsulation of one-piece metal pipes, which can possibly be bent, but no sealing is required, since hoses are attached directly to the corresponding pipe ends protruding from the molded parts.

Furthermore, the connection of two tubes lying against one another with their flanges is also known, the two flanges lying against one another being extrusion-coated in the form of a “barrel tire”. However, this encapsulation poses further sealing problems.

However, by all the known methods it is not possible to form conventionally non-demoldable tubular cavities in plastic injection moldings.

Advantages of the invention

According to the present invention, preformed hollow bodies are joined to form the desired cavities, placed in a molding space for the plastic molded part and then the plastic is introduced into the molding space, in particular injected.

This means that no additional work steps, in particular connection steps, are necessary compared to the known first production process. There is also no need to seal any connection points, for example flange connections. A mechanically stable and tight connection is created, which is ensured by the extrusion-coated plastic.

Compared to the known second manufacturing process - H -

no cores are melted out, i.e. no residues resulting from the melting are also to be expected. The molded part remains clean even in its cavities. In addition, production is cheaper in many cases.

Compared to the gas pressure process, the present invention stands out due to geometrically precisely defined cavities.

The present invention is intended primarily for entire systems of pipe sections. The individual parts are put together before being inserted into the molding space, it being possible to use corresponding connecting elements, such as T-pieces, branches or the like. The joints need ^'only so closely to lie to each other that no flowing around Kunst¬ polymer melt ^-' n penetrates the cavities. The complete sealing of the entire system is achieved by overmoulding the inserted hollow body system after the melt has solidified. It also does not require a mechanically fixed connection between the individual elements of the system. This is also done by the overmolded plastic.

Metal is preferably used for straight or slightly curved pipe sections. On the other hand, connecting pieces or connecting elements or also sharp deflections can be made of plastic. There should be no limit to the inventive idea here.

In any case, however, the system with the hollow bodies should be kept at a sufficient distance from the inner wall of the molding space, so that it is ensured that every hollow body is actually encapsulated with plastic. The surface of the inserted hollow body should not penetrate through the outer skin of the extrusion coating, since this could possibly lead to sealing problems. The inserted hollow bodies are preferably fixed within the injection molding tool by means of movable tool cores which engage in connection openings in the hollow bodies. Corresponding sealing surfaces are formed on the extrusion coating around these connection openings, on which neighboring components are sealed off for encapsulation.

The special features of the present invention can be found in the following:

- Formation of complicated cavities within injection molded parts by joining part hollow bodies;

- Fixing the hollow body within the tool by means of tool cores at the connection openings and sealing the

Connection components opposite the extrusion coating.

Claims

1. A method for producing conventionally non-demoldable tubular cavities, such as U-tubes, tubes with closed ends, long, thin tubes without draft angles, in plastic injection molded parts, characterized in that preformed hollow bodies to the the desired cavities are joined, placed in a molding space for the plastic molding and then the plastic is introduced into the molding space, in particular is injected.

2. The method according to claim 1, characterized in that pieces of pipe are used as a hollow body for tubular cavities.

3. The method according to claim 1 or 2, characterized in that the hollow body or before the insertion into the mold space to a desired system, for example by T-pieces, branches. Like. Are connected.

4. The method according to claim 3, characterized in that the connecting elements are molded from plastic.

5. The method according to at least one of claims 1 to 4, characterized in that with the hollow bodies in any case. The distance from the walls of the mold space is maintained, the hollow bodies being fixed by means of cores which form corresponding openings or connecting pieces to adjacent hollow bodies.