GB2072568A

GB2072568A - Moulded components

Info

Publication number: GB2072568A
Application number: GB8010111A
Authority: GB
Original assignee: Global Castors and Hardware Ltd
Current assignee: Global Castors and Hardware Ltd
Priority date: 1980-03-26
Filing date: 1980-03-26
Publication date: 1981-10-07
Also published as: BE887981A; NZ196404A; JPS56150509A; IT1195804B; SE8101881L; AU6825281A; DK76081A; FR2479072A1; GB2072568B; ZA811327B; DE3107336A1; IT8167294A0

Abstract

A component is moulded from a flexible material and has a fixing lip (6) which projects, internally or externally, from a surface (4) of the component. The lip (6) is inclined to the surface (4) and is moulded with a back clearance space (10). The cross-sectional shape of the lip (6) is contained within an included angle A which is preferably less than, and is not greater than, an included angle B of the back clearance space (10). During ejection of the moulded component from the mould the lip (6) is pushed back into the clearance space (10) by a stationary part of the mould cavity. <IMAGE>

Description

SPECIFICATION Moulded components This invention relates to moulded components designed for clip-fixing on to, or into, another component. It is particularly concerned with such components which are moulded with an integral fixing lip which projects, either internally or externally, for engagement with a groove or recess in the other component when fitted thereto. The invention also relates to a method of, and novel tooling for, moulding such a component.

The moulding of the projecting lip of such a component presents problems normally necessitating a compromise in the design of the component, either generally or as regards the shape of the lip, and/or in the moulding procedure used. The lip has either to snap-off a mould part during core withdrawal or ejection of the moulded component from the mould, or it has to be moulded between two relatively movable core mould parts each of which partially defines the lip.

In the former case the component has to be designed with sufficient flexibility in the region of the lip for it to snap-off the mould part by which the lip is defined, the optimum shape of lip often cannot be used, a long moulding cycle time is unavoidable as the moulding must cool sufficiently for it not to be damaged when snapped-off the mould part, and the optimum design of the component generally and/or the lip region thereof cannot usually be achieved. In the latter case the component is more favourably designed in the foregoing respects but it still has to be designed to suit the moulding procedure. That procedure is normally considerably complicated by the necessity for two-way core withdrawal with increased tooling costs, and the design of the component in any case often precludes this method of moulding the lip.

The main object of the invention is to provide a moulded component, and a method of moulding a component, with a clip-fixing lip which materially overcomes the foregoing disadvantages and problems in a successful manner.

To this end a fixing lip projecting inwardly or externally from a surface of a component moulded from flexible material is inclined to that surface and moulded with a back clearance space, and has a cross-sectional shape lying within an including angle which is preferably less than, and certainly not greater than, an included angle of said back clearance space.

The invention also includes a method of moulding such a component wherein withdrawal of, or ejection of the component from, a mould part by which the lip and the clearance space are defined during moulding occurs in a direction such that the mould part moves relatively to the component along said surface in the general direction in which the lip projects therefrom.

Put more generally, a projecting fixing lip in accordance with the invention is moulded with back clearance such that, during relative separating movement at the end of the moulding procedure of the component and a mould part by which the lip is defined during moulding, the lip can move into and be received by the progressively opened up back clearance to allow such movement. Thus, in particular, such movement does not necessitate radial flexing of the component as a whole in the region of the lip. Various shapes and dispositions of the lip are possible within the purview of the invention, the main essential feature of which is that the lip is moulded with a back clearance adequate to receive the lip without general flexing of the component as a whole in the region of the lip.Thus the limitation of prior fixing lips which have to snap-off the defining mould part, namely that material flexing of the adjacent region of the component as a whole must occur, is overcome.

Following on from this, the invention has the special advantage that a component can be moulded with internal and external lips both defined by one and the same mould part. This has not previously been possible.

The back clearance results in a stepped formation of said component surface, with the inclined lip at the stepped region. In other words, when the surface is cylindrical it will be stepped with portions of different diameters which merge through the lip which projects with respect to the "top" step diameter portion and is inclined generally in a direction away from that portion. In the case of an internal lip the "top" step diameter is the smaller diameter, whereas the converse is the case with an external lip.

Moulding of the lip with back clearance as described involves the use of novel mould tooling. Thus, according to another aspect of the invention a moulding tool has a moulding cavity defining a component to be moulded with a projecting fixing lip, the tool having a mould part with a stepped moulding surface which, in the stepped region thereof, defines both the fixing lip which is inclined to that surface and also a back clearance for the lip, such back clearance being adequate to receive the lip as a result of flexing thereof during relative separating movement of the mould part and the moulded component at the end of a moulding operation.

A specific and especially advantageous exemplary application of the invention, providing a marked commerical advantage, is to a component providing the moulded plastics body of a castor, either a wheeled castor or a so-called "glide" or "slipper" castor as used for supporting furniture or the like. In this application of the invention the body is moulded with a bore having an intermediate internally projecting lip for snap-on fixing of the body to a mounting spindle, which spindle will normally be a length of metal rod peripherally grooved for engagement with the lip when the spindle is pushed into the moulded body. However, it will be appreciated that the other component with which the lip engages may in many cases also be a moulded component.

The invention will now be further described with reference to the accompanying drawings which illustrate, by way of example, an embodiment of the invention and a modification thereof. In the drawings: Figure 1 is a plan view of a glide castor having, for fixing to a mounting spindle, an internal lip in accordance with the invention; Figure 2 is a cross-sectional view on the line Il-Il in Fig. 1 showing the glide fitted to the mounting spindle; Figure 3 is a fragmentary view showing a detail of Fig. 2 to a large scale; and Figure 4 is a cross-sectional view similar to Fig. 2 but of a component embodying said modification and the moulding tool as the component is moulded.

The embodiment illustrated in Figs. 1 to 3 is a glide or slipper castor, and the construction shown is basically similar to that described in Patent Specification No.

1,496,170. It comprises a plastics moulded body component I with a convex lower ground-engaging surface 2 and an upstanding boss 3 with a blind bore 4 for a mounting spindle 5. The spindle 5 inserted in the bore is retained therein, to fix the glide castor on to the spindle, by means of an integral moulded fixing lip 6 formed in accordance with the present invention.

An upper dished cap-like plastics moulded component 7 fits on to the body and at its periphery seats on a peripheral seating 8 on the moulded body component 1. This cap moulding 7 has an apertured region 9 which surrounds and is formed for snap-on engagement with the boss 3. To provide for such engagement the boss 3 has an end section 3a of increased outer diameter, over which the moulded cap 7 snaps-on to hold the two moulded components 1 and 7 together as a two-part assembly.

The novel shape of the fixing lip 6 is shown in the enlarged detail view of Fig. 3. The lip 6 projects inwardly of the bore 4 and thus projects from the surface thereof, while being inclined to that surface in a direction outwardly of the bore. It is moulded with a back clearance space 10, to which end the bore is of stepped form with the step therein providing the root region of the lip 6, the outer portion 4a of the bore 4 being of correspondingly increased diameter. The bore 4 is moulded at its blind end with a domed convex central region which provides an end thrust surface for the spindle 5 which turns freely in the fitting bore 4 inwardly of the lip 6 which, for fixing to the spindle 5, engages an annular groove 12 in the spindle.

Reverting to Fig. 3, the lip 6 is of tapering cross-section with a radiused peak 13 and substantially straight inner and outer side flanks 14 and 15. The flanks 14, 15 subtend an including angle A which is materially less than the included angle B of the back clearance space 10, which included angle is subtended by the wall of the bore portion 4a and the outer flank 15 of the lip 5. The space 10 has a small bottom radius and is large enough, due to the difference between the angles A and B, to accommodate the lip 6 by flexing of the latter to allow withdrawal of the moulding core from the bore 4, and core withdrawal does not necessitate any radial flexing of the boss 3 as a whole so that the boss can be contained radially within the mould as the core is withdrawn past the lip 6.

As the core is withdrawn past and flexes the lip 6 the back clearance space 10 opens up progressively sufficiently to receive it, due to the accompanying withdrawal of the portion of the core which defines the clearance space within the mould cavity.

Thus, the same mould part can be used to mould the boss 3 both internally and externally, in other words a separate core part is not required. In the embodiment illustrated the angles A and B are respectively 20" and 35", and it will be appreciated that for the clearance space 10 to be large enough to receive the lip 6 the angle A must not be greater, and is preferably less, than the angle B.

As the core moulding the bore 6 with the lip 6 can be withdrawn while the boss 3 is still radially contained, it is possible to provide a similar fixing lip externally of the boss 3, in order to retain the cap moulding 7, and to mould both lips (and the body component as a whole above the lower surface thereof) using one and the same mould part. Such a modification is illustrated in Fig. 4, where the internal lip 6 to retain the spindle 5 is supplemented by an external lip 16 of generally similar form and which acts to retain the cap moulding 7 when the latter is snapped into position on the body moulding 1. As a result of this modification a simple two-part mould 17 can be employed, with a lower part 18 which merely defines the lower ground-engaging surface 2 of the body and an upper part 19 which defines the rest of the body moulding, in particular the boss 3 with both the lips 6 and 16. The mould part 19 consists of a backplate 1 9a to which a core pin 1 9b and a surrounding body portion 19carve rigidly fixed.

After the mould has been opened the moulding is ejected from the part 19 by an ejector sleeve 20, moved by an ejector plate 21 in the normal manner, during such ejec tion the lips 6, 16 simultaneously flexing independently of the rest of the moulding into the respective back clearance spaces which progressively open up behind them to allow the relative ejection movement of the mould ing and the mould part 19.

Claims

1. A component moulded from a flexible material and having a fixing lip projecting from a surface of the component, the lip being inclined to said surface, moulded with a back clearance space and having a cross sectional shape lying within an including an gle which is not greater than an included angle of said back clearance space.

2. A component according to claim 1, wherein said including angle of the lip is less than said included angle of the back clearance space.

3. A component according to either one of the preceding claims, wherein said surface is cylindrical and has a stepped annular forma tion with the inclined lip at the stepped region thereof, thus presenting different surface di ameter portions which merge through the lip which projects with respect to the "top" step diameter portion and is inclined generally in a direction away from that portion.

4. A component according to claim 3, wherein the lip is an internal lip in a stepped circular bore of the component, said "top" step diameter then being a smaller diameter portion of the bore.

5. A component according to claim 3, wherein the lip is an external lip on an outer surface of the component, said "top" step diameter then being a larger diameter surface portion of the outer surface.

6. A component according to claim 4, wherein the lip is designed to retain a spindle in said bore of the component and to provide snap-in fixing of the spindle in the compo nent.

7. A castor having a body provided by a moulded component in accordance with claim 6, said spindle being a mounting spindle of the castor.

8. A method of moulding a component in accordance with claim 1, wherein withdrawal of, or ejection of the component from, a mould part by which the lip and the clearance space are both defined during moulding oc curs in a direction such that the mould part moves relatively to the component along said surface in the general direction in which the lip projects from the surface.

9. A method of moulding a component with a fixing lip which projects from a surface of the component, wherein the lip is moulded with a back clearance such that, during rela tive separating movement at the end of the moulding procedure of the component and a mould part by which the lip is defined during moulding, the lip can move into and be received by a progressively opened up back clearance of the lip, thereby allowing such movement without radial flexing of the component as a whole in the region of the lip.

10. A method of moulding according to claim 8 or 9, wherein said component is moulded with internal and external lips, each such lip being moulded with a back clearance space into which the lip can be received during said movement of the corresponding mould part which defines both lips during moulding.

11. A moulded component or method of moulding a component according to any one of the preceding claims, wherein said flexible material is a synthetic plastic material.

12. A moulding tool having a moulding cavity defining a component to be moulded with a projecting fixing lip, the tool having a mould part with a stepped moulding surface which, in the stepped region thereof, defines both the fixing lip which is inclined to that surface and also a back clearance for the lip, such back clearance being adequate to receive the lip as a result of flexing thereof during relative separating movement of the mould part and the moulded component at the end of a moulding operation.

13. A moulded component having an internal fixing lip substantially as herein particularly described with reference to Fig. 3 of the accompanying drawings.

14. A castor having a moulded body with an internal fixing lip for a mounting spindle, substantially as herein particularly described with reference to Figs. 1 to 3 of the accompanying drawings.

15. A method of moulding a component with a projecting fixing lip, substantially as herein described.

16. A moulding tool for moulding a component with a projecting fixing lip, substantially as herein particularly described with reference to Fig. 4 of the accompanying drawings.