NZ196404A

NZ196404A - Moulding a projecting lip

Info

Publication number: NZ196404A
Application number: NZ196404A
Authority: NZ
Inventors: M J James
Original assignee: Global Castors & Hardware Ltd
Priority date: 1980-03-26
Filing date: 1981-03-04
Publication date: 1984-03-16
Also published as: BE887981A; JPS56150509A; IT1195804B; SE8101881L; AU6825281A; DK76081A; FR2479072A1; GB2072568B; ZA811327B; DE3107336A1; IT8167294A0; GB2072568A

Description

1 96 4 0 4 Priority Briefs): Ak CompSeto Specification Fi'sd: | Class: . JournrJ, ft 155-5 ■ tiit «,S.q C33/00, few X) 31/00 f|5 HW1984 N.Z. NO.

NEW ZEALAND Patents Act, 1953 COMPLETE SPECIFICATION "MOULDED COMPONENTS" 4 MAR Mt We, GLOBAL CASTORS AND HARDWARE LIMITED, A British company of King Alfred Way. Cheltenham, Gloucestershire, GL52 6QP, England. do hereby declare the invention, for which we pray that a Patent may be granted to us , and the method by which it is to be performed, to be particularly described in and by the following statement _ 1 _ (Followed by 1A.) - lA- 196^4 "MOULDED COMPONENTS" This invention relates to moulded components designed for clip-fixing on to another component. It is particularly concerned with such components which are 5 moulded with a blind bore and an integral fixing lip which projects into the bore 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 internal 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 to snap-off a mould part 15 during core withdrawal or ejection of the moulded component from the mould, as the alternative of moulding the lip between two relatively movable core parts cannot be employed with a blind bore.

Thus at present the component has to be designed 20 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 the 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 2 5 the mould part, and the optimum design of the component generally and/or of the lip region thereof cannot usually 1 O <C /! n /! _ 2 - I / u i U 4 be achieved.

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

According to the invention, in a method of moulding a component from a flexible material with a blind bore and an internal fixing lip which projects into the bore, wherein the lip is moulded with a 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 a progressively opened up space vacated by the back clearance forming section of the mould part, thereby allowing such movement without radial flexing of the component as a whole in the region of the lip.

The invention includes the resultant moulded component, and in particular such,a component wherein said internal lip is inclined to the bore axis so as to project towards the open outer end of the bore and is moulded with a back clearance space such that, in relation to the cross-sectional shape of the lip, the lip can flex to permit insertion into the bore of a member which fits the bore on the inner side of the lip with the so-flexed lip wholly received in said clearance space.

Various shapes and dispositions of the lip are possible within the purview of the invention, the main 196$©4 •> 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 with prior fixing lips 5 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 10 by one and the same mould part. This has not previously been possible.

The back clearance results in a stepped formation of the blind bore, with the inclined lip at the stepped region. In other words, when the bore is cylindrical it 15 will be stepped with portions of different diameters which merge through the lip which projects with respect to the inner and smaller diameter portion of the bore.

Moulding of the lip with back clearance as described involves the use of novel mould tooling. Thus, 20 according to another aspect of the invention a moulding tool has a moulding cavity defining a component to be moulded with a blind bore and an internally projecting fixing lip, the tool having a mould part with a stepped moulding surface which, in the stepped region thereof, 25 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 1 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 commercial 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 often used for supporting furniture or the like. In this application of the invention the body is moulded with a blind 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 /H 1 96404 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 II - II in Figure 1, showing the glide castor fitted to the spindle; Figure 3 is a fragmentary view showing a detail of Figure 2 to a larger scale; and Figure 4 is a cross-sectional view similar to Figure 2 but of a component embodying said modification and the moulding tool as the component is moulded.

The embodiment illustrated in Figures 1 to 3 is a glide or slipper castor. It comprises a plastics moulded body component 1 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 when inserted in the bore 4 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 1 964 0 4 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 Figure 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 Figure 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 1 96 4 0 4 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 Figure 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 | Q 3, C 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 19a to which a core pin 19b and a surrounding body portion 19c are 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 ejection 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 moulding and the mould part 19. 1 96 40

Claims

WHAT WE CLAIM IS:

1. A method of moulding a component from a flexible material with a blind bore and an internal fixing lip which projects into the bore, wherein the lip is moulded with a 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 a progressively opened up space vacated by the back clearance forming section of the mould part, thereby allowing such movement without radial flexing of the component as a whole in the region of the lip.

2. A method of moulding according to claim 1, wherein said component is also moulded with an external lip, each of the internal and external lips 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.

3. A component moulded from a flexible resilient material according to the method of claim 1 or claim 2, wherein said internal lip is inclined to the bore axis so as to project towards the open outer end of the bore and is moulded with a back clearance space such, in relation to the cross-sectional shape of the lip, that the lip can flex to permit insertion into the bore of a member which fits l?6404- - 10 - the bore on the inner side of the lip with the so-flexed lip wholly received in said clearance space.

4. A component according to claim 3, wherein an including angle of the or each lip and within which the cross-sectional shape thereof lies is less than an included angle of the back clearance space.

5. A component according to claim 3 or claim 4, wherein said blind bore is cylindrical and presents an internal stepped annular formation with the inclined internal lip at the stepped region thereof and different diameter portions of the bore merging through that lip.

6. A component according to claim 5 in combination with a grooved spindle, wherein said internal lip is designed to retain the spindle in said bore of the component and to provide snap-in fixing of the spindle in the component with the internal lip engaging the groove in the spindle.

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 or a moulded

T. c.\o<—» I o<- "Zj a«y—©fte——fe&e—preceding—elaimc^ 1 96 - ii - wherein said flexible material is a synthetic plastics material. a component to be moulded with a blind bore and an internally 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 during the ejection step of a moulding operation.

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

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

12. A method of moulding a component with a blind bore and an internally projecting fixing lip, substantially 9. A moulding tool having a moulding cavity defining as herein described. 1 96^4 - 12 -

13. A moulding tool for moulding a component with a blind bore and an internally projecting fixing lip, substantially as herein particularly described with reference to Figure 4 of the accompanying drawings. GLOBAL CASTORS AND HARDWARE LIMITED By Their Attorneys HENRY HUGHES LIMITED BY" .-v.