GB2073650A

GB2073650A - Plastic housing comprising inwardly directed projections

Info

Publication number: GB2073650A
Application number: GB8110060A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-04-15
Filing date: 1981-03-31
Publication date: 1981-10-21
Also published as: FR2481997B1; SE432220B; IT1143546B; GB2073650B; IT8167508A0; SE8102371L; FR2481997A1

Abstract

A plastic housing is manufactured by injection molding and comprises at the inner side thereof one or a plurality of projections (8) for the mounting of further elements. The housing shell (1) includes in the area of projection(s) (8) an enlargement of its surface by molding therein one or a plurality of folds, depressions, recesses, grooves or any other similar shape which permit bulging out of the shell (1) during its removal from the mould core (not shown) so that the projection(s) (8) can be removed from opening(s) in the core without being damaged, after which the shell (1) returns to its original shape. Such bulging out of the shell (1) can be effected by means of an additional lift projection (11) which cooperates for this purpose with the core. Alternatively, the bulging can be effected by means of lift pins or compressed air. <IMAGE>

Description

SPECIFICATION Plastic housing comprising inwardly directed projections and method for the production thereof The invention relates to a plastic housing to be manufactured by injection molding and comprising at the inner side thereof one or a plurality of projections serving in the mounting of further elements as a stop or arresting means.

The manufacture of such housing proves to be extremely difficult and in such cases where the housing chamber is provided as a blind hole it is almost impossible because demolding of the injection molded housing cannot be effected in the usual way because of the projections.

Plastic housings comprising inwardly arranged stops, projections and the like have already been known. The latter are however provided at a location at the inner wall of the chamber where it is possible to arrange the stops, projections and the like in the junction plane of a double pin so that one portion of the pin is introduced into the chamber from one side and the other portion of the pin from the other thus effecting molding of the projection or projections. In this connection it is frequently necessary that the two pins cut each other, i.e. they have to pass -each other on a portion of their length in tight contact relative to each other on one side.In order to avoid that such pins, which are frequently less than 1 mm thick, hit upon each other with their heads when closing the tool, it is necessary to provide these portions with bevels or to shape them as cones. The production of such tools for injection molding is therefore rather time consuming also for an experienced toolmaker and is mastered only by the best of the trade. The costs of such a tool are therefore extremely high and the production costs of the housing produced by the injection molding process are correspondingly high.

It is therefore the aim of the present invention to provide a plastic housing to be manufactured by injection molding having inwardly directed projections, which does not necessitate a complicated and expensive tool but can be manufactured by means of a simple tool comprising corresponding recesses for the projections and thus can cost savingly be produced.

The problem accdrding to the invention is solved in that in the plastic housing manufactured by injection molding having inwardly directed projections the housing shell includes in the area of the projection(s) an enlargement of its surface beyond the necessary extent by molding one or a plurality of folds, depressions, recesses, grooves or any other similar shape.

This enlargement of the area near the projection makes possible a bulging out of the wall during the course of the demolding process whereby the inwardly directed projection is drawn out from the mold opening of the mold core and the mold core is removed from the housing without damaging the projection.

The invention is based on Applicant's surprising discovery that the plastic material molded by the injection molding process, such as polyamide possesses an elasticity immediately after crystallization shortly afterwards changing to fragile brittleness, which disappears only when humidity, or water, respectively, is incorporated and only then will yield the characteristics typical for polyamide (nylon). This elasticity immediately after crystallization permits a reversible deformation of the enlarged wall for the very short duration of the demolding process while in view of the elasticity still present the bulged out wall portion returns immediately into its original shape so that in the finished housing, when ejected from the mold, no changes can be observed in spite of the short deformation during the demolding process.

The bulging out of the housing wall enlarged in the'shape of a fold, an impression, a recess, groove or the like makes use of the elastic deformability of this enlarged wall portion without however expanding the wall material in its length.

The latter would not be possible anyway in the necessary extent as the elasticity of the plastic material atthe time of the demolding of the finished housing would not be sufficient.

It has shown to be particularly advantageous if the new plastic housing according to the invention shows the enlargement of the wall in the shape of a fold, an impression, a recess, groove or any similar shape in the housing wall on one side of the projection. By bulging out this wall portion, the projection is lifted out of its opening in the molded core so that the molded core may be drawn out of the housing without damaging the projection.

It has shown to be particularly suitable if the enlargement of the housing wall is provided on the side of the projection which, as seen in the demolding direction of the core, is provided behind the projection.

The elasticity very essential in the present invention of the plastic material immediately after crystallization (solidification) in the form which makes possible a reversible bulging out of the enlarged wall is particularly well shown in polyamide plastic material (nylon). Considering however that most of the other tenacious plastic materials have the same characteristics and behave similarly, the plastic housing according to the invention may also be produced by other common molding materials.

The method for the production by injection molding of a plastic housing according to the invention is characterized in that the projection or the projections are molded in the corresponding opening(s) of the molded core and in the apea of the projection the housing shell of the plastic housing is provided with an enlargement of its surface beyond the necessary extent by molding one or a plurality of folds, depressions, recesses, grooves of any other similar shapes, and then after molding the outer limiting wall of the mold is removed from the housing shell provided with the enlargement of its surface, the projection is lifted by bulging out the housing shell from the opening of the core and the housing is demolded whereupon the housing shell returns to its original shape.

For bulging out the enlarged wall any method may be applied. It has however shown to be particularly advantageous if in the method of the invention the projection is lifted from the opening of the molded core by means of compressed air whereby the housing shell is bulged out.

In another embodiment of the methodaccording to the invention, the projection is lifted from the opening of the molded core by means of a lift pin which is adjacently provided in-the core, which bulges out the enlarged shell so that the molded core may subsequently be withdrawn from the housing. The advanced movement of the lift pin makes sure that the projection is not damaged in the process of the withdrawal of the molded core.

In accordance with another particularly advantageous embodiment of the method of the invention, demolding is effected in that at least one additional lift projection-is molded to the housing shell of the plastic housing near the projection(s) in a corresponding opening of the molded core, which lift projection will turn out, during the demolding process, from its lower position in the molded core for bulging out said housing shell and at the same time will lift the projection(s) from their lower positions.

In such an embodiment, a damage of the projection or of the projections is avoided, which is very essential in delicately molded projections.

Therefore, the lift projection constitutes only a demolding help and does not play any role as a limiting stop or the like. For this reason, a possible damage of this lift projection is of no consequence for the molded housing.

It has further on shown to be particularly advantageous if in the method of the invention the lift projection is molded at the side(s) of the projection(s) in the housing shell. It is particularly advantageous if the lift projection is provided, as seen in the demolding direction of the housing, in front of the projections.

The lift projection molded to the housing includes suitably a greater depth projecting into the housing than the projection(s) additionally molded to the housing. In this way, it is safeguarded that during the demolding process the lifting projection will sufficiently bulge out the enlarged housing shell to the outside so that the additional projection(s), which are required in the housing as later arresting means, are lifted without any damage from the corresponding openings of'the molded core.

It has further on shown to be very advantageous if in the method of the invention the lift projection additionally molded to the housing shell is provided with an undercut edge almost perpendicular to the molded core plane.

In view of this embodiment, the lift projection turns, under the demolding pressure acting in axial direction, out from the lower position of the molded core and at the same time lifts the housing shell provided with the enlargement so that it bulges out outwardly thus lifting the further projection(s) molded to the housing shell at the side of the lift projection without any damage from the lower position of the molded core and the molded core is then withdrawn from the housing.

With the aid of this method according to the invention, such plastic housings may be produced considerably cheaper as they do not require complicated molds for the formation of the projection provided in the housing and the undercuts thereof. By the method of the invention particularly cheap insulation housings for electrical engineering purposes may be produced, which are provided with inwardly directed. projections for mounting, locking and arresting purposes. The housings produced in accordance with the method of the invention are particularly suited for insulation purposes, especially for plugs wherein the contact elements are retained by the molded projections.

The method according to the invention makes possible a substantial decrease of the production costs of such insulation portions and in case of housings having blind hole openings the production of projections provided in such blind holes is made possible only-by the invention.

The plastic housing produced in accordance with the method of the invention is therefore characterized according to a particularly advantageous embodiment of the present invention in that an additional lift projection is molded to the housing shell in the vicinity of the projection(s). This lift projection includes suitably an undercut edge almost perpendicular to the molded plane; and relative to the #other projections the lift projection possesses a greater depth projecting into the housing.

Based on the exemplified embodiments shown in the attached drawings, the present invention will be described in detail in the following: In the drawings, Figures 1, 3 and 5 show embodiments of plastic housings according to the invention, wherein the upper cover wall each is provided with a corresponding enlargement of its surface beyond the necessary extent by providing one or a plurality of folds, depressions, recesses, grooves or any other shape, which makes possible a bulging out of this portion of the wall.

In Figure 1 ,the upper wall portion 1 is provided with a flat groove-like deformation. In the interior, wall portion 1 includes the projection; for demolding of the molded core provided in the interior of the housing, wall-portion 1 is bulged out after the removal of the outer mold wall.

In Figure 2, the plastic housing according to Figure 1 is shown with cover wall 2 bulged out.

In Figure 3, the cover wall including the inwardly directed projection is provided with a fold-like inwardly directed recess 3, which makes possible an outwardly directed bulging out 4, as shown in Figure 4. Through this bulging out, the inwardly directed projection is lifted from the molded core so that the molded core may then be drawn out from the housing without damaging the projection molded to the housing shell. In-view of the elasticity, fold-like bulged out wall 4 returns after demolding of the housing immediately to its original state as shown in Figure 3.

In Figure 5, another embodiment of a plastic housing according to the invention is shown, wherein inwardly directed lateral folds 5 makes possible the lifting up or bulging out, respectively, of the upper side 6 and of the under side 7 of the housing.

In all the embodiments shown in Figures 1 through 6, the groove, the depression or the fold, respectively, provides as much wall material each as is necessary to make possible a bulging out and thus an exit of the projection(s) from the opening of the molded core. Without the wall encrease, according to the invention, in the form of grooves, depressions, folds and the like in the area of the projection(s), such a deformation would not be possible based on elasticity or flexibility of the material alone.

The bulging out essential in the method of the invention of the wall portion in the area of the projection(s) may be performed, as shown in the beginning, with the aid of compressed air, which is introduced through a corresponding opening in the molded core in the area of the enlarged shell of the plastic housing after the removal of the outer mold limitation.

The second possibility for obtaining the necessary bulging out of the enlarged housing shell is effected by means of an advancing pin provided in the molded core, which lifts the enlarged housing shell and thus lifts the projection(s) out of the openings of the molded core before the molded core is drawn out from the molded housing.

An essentially simpler way of bulging out the enlarged housing shell for an undamaged removal of the projections molded to it in the interior may be described in detail by Figures 7 through 10.

In the housing shown in Figure 7, which is shown partly open, projection 8 may be recognized, which projects inwardly from cover wall 1 and, as shown in Figure 8 by dotted lines, is positioned in opening 9 of molded core 10. In addition to projection 8, and-as seen in the molded direction of the housing in front of projection 8, an additional lift projection 1 1 is provided at the enlarged housing shell in a corresponding opening of the molded core, which is indicated in Figure 8 by dotted lines and carries reference numeral 12.

This lift projection 1 1, molded to the housing shell of the plastic housing with an undercut edge almost perpendicular to the molded core plane and provided relative to projection 8 with a greater depth projecting into the housing is turned in the demolding process out of its opening in the molded core and thus lifts the enlarged housing shell 1 so that projection 8 is lifted out of its opening 9 in molded core 10 without damaging its undercut edge. The molded core 10 is then, as shown in Figure 9, withdrawn from the housing, or otherwise, the housing is shifted by means of a wiper not shown from molded core 10, and in view of the elasticity of the plastic material the bulged out housing shell 1 including projection 8 molded thereto as well as lift projection 11 returns to the originally molded position as shown in Figure 10.

The housings shown in the drawing constitute insulating housings for electric plug connections.

Claims

1. Plastic housing to be manufactured by injection molding and comprising inwardly directed projections, wherein the housing shell includes in the area of said projection(s) an enlargement of its surface beyond the necessary extent by molding one or a plurality of folds, depressions, recesses, grooves or any other similar shape.

2. Plastic housing according to claim 1, wherein said enlargement of said housing shell is provided on one side of said projection.

3. Plastic housing according to claim 2, wherein said enlargement of said housing shell is provided on the side of said projection which, as seen in the demolding direction of the molded core, is provided behind said projection.

4. Plastic housing according tq one of claims 1 through 3, wherein an additional lift projection is molded to said housing shell near said projection(s).

5. Plastic housing according to claim 4, wherein said lift projection includes an undercut edge almost perpendicular to the plane of said core.

6. Plastic housing according to one of claims 4 or 5, wherein said lift projection projects to a greater depth into said housing than said projection(s).

7. Plastic housing according to one of claims 1 through 6, wherein said housing is manufactured from polyamide material.

8. Method for the production by injection molding of a plastic housing according to one or a plurality of claims 1 through 7, wherein said projection is molded in a corresponding opening of said core and in the area of said projection the housing shell is provided with an enlargement of its surface beyond the necessary extent by molding one or a plurality of folds, depressions, recesses, grooves or any other similar shapes, and after molding the outer limiting wall of the mold is removed from said housing shell provided with the enlargement of its surface, the projection is lifted by bulging out said housing shell from the opening of said core and the housing is removed whereupon said housing shell returns to its original shape.

9. Method according to claim 8, wherein said projection is lifted from the opening of said molded core by means of compressed air whereby said housing shell is bulged out.

10. Method according to claim 8, wherein said projection is lifted from the opening of said molded core by means of a lift pin which is adjacently provided in said core and which bulges out the shell provided with the enlarged surface.

11. Method according to claim 8, wherein said projection is lifted from said opening of said molded core by means of two lift pins provided on both sides of said projection in said molded core, which bulges out said shell provided with the enlarged surface.

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12. Method according to claim 8, wherein at least one additional lift projection is molded to the inner side of the housing shell of said plastic housing near said projection(s) in a corresponding opening of said molded core, which lift projection will turn out, during the demolding process, from its lower position in the molded core for bulging out said housing shell and at the same time will lift said projection(s) from their lower positions.

13. Method according to claim 12, wherein said additional lift projection is molded with an undercut edge almost perpendicular to the molded core plane to the housing shell of said plastic housing.

14. Method according to claim 12 or claim 13, wherein said lift projection is provided at the side(s) of said projection(s ) in said housing shell.

15. Method according to one of claims 1 2 through 14, wherein said lift projection is molded to a greater depth projecting into said housing than said projection(s) in said housing shell.

16. Plastic housing substantially as described with reference to and as illustrated in the accompanying drawings.