GB2185712A - Moulding of solid bodies - Google Patents

Abstract

To eliminate the risk of the occurrence of voids therein during the moulding of a solid plastics body, which voids may result in subsequent change in the shape of the body, an inner body (28) whose configuration corresponds to the desired finished product but whose dimensions are smaller than the latter is moulded on a core pin in a first mould (not shown). The resultant aperture (30) in the inner body (28) is then employed with a core pin (32, 34), or a succession of such core pins, to locate the inner body (28) in a larger mould (40) (or a succession of progressively larger moulds) to enable a surrounding layer or a succession of surrounding layers to be moulded around the body (28) to achieve the desired eventual configuration and dimensions. <IMAGE>

Description

SPECIFICATION Moulding of solid bodies This invention concerns the moulding of bodies from plastics materials, such as polyvinyl chloride, polypropylene, nylon and other materials which can be moulded (e.g. by injection moulding) so as to re sult in a relatively solid product, such as a ball or bowling bowl. Although, in in general, reference is made herein to rounded solid bodies such as balls or bowls which will roll and in general can be used;for example, in games, this is notto be taken to mean that the invention may not be applied to bodies of other shapes, such as cubes, pyramidal bodies, polyhedrons and the like, especially where relatively large bodies of these shapes may be required.

In the moulding of relatively large solid bodies of plastics materials, one encounters the problem that the solidification of the moulded product, whether this be effected by allowing the product to cool within the mould or by cooling it after removal from the mould, occurs progressively, and often quite slowly, from the outer surface of the moulded article inwards. Thus, almost immediately after introduction the plastics material into the mould, an external skin solidifies on the moulded product. Often the product can be removed from the mould quite quickly, but it may be many hours later before the product has cooled throughout its entire mass. Ex perienceshowsthatthiscan have a deleterious effect on the eventual product.During cooling the plastics material tends to shrink, so one has an external shall initially solidified, with interior plastics material subsequently solidifying and shrinking. As a result, it is notfeltto be a practical proposition to mould relatively large solid bodies, because empty voids occurwithin the mass ofthe plastics material, and although upon removal from the mould the product may present a satisfactory appearance, the product may subsequently change its shape from what was intended, and in the case of a ball or bowl the balance ofthe product may be unsatisfactory.

An object of the present invention is to provide a method of moulding a solid bodywherebythe above-discussed difficulties or problems are eliminated or obviated, it being possible, by use of the method, to achieve a product which is free of or substantially free of voids, so that the shape thereof cor responds precisely to what is required.

With this object in view, the present invention provides a method of moulding a solid plastics body which comprises moulding an inner body portion having a configuration corresponding app roximately or substantiallyto the desired finished configuration, but of smaller dimensions than the desired finished product, with an aperture therein for a core pin, and thereafter, by use of the or successive core pins, locating the inner body within a mould having a larger mould space (or a succession of moulds having successively larger mould spaces) and moulding a surrounding plastics layer around the inner body portion or a succession of surround ing plastics layers therearound, to achieve the des ired finished body size and configuration.

After removal from the core pin or the last ofthe core pins, the aperture left thereby may optionally be filled. This filling of the aperture, when this is effected, may, of course, be effected by plugging the aperture, e.g. by means of a mushroom-shaped element, or by injecting a suitable plastics filling.

The invention further includes a plastics body made by the method aforesaid such a body comprises, of course, an inner body portion having a configuration corresponding approximately or substan- tiallytothe desired external configuration butof smaller dimensions than the body and, around said inner body portion, a surrounding plastics layer which, or a plurality of successive surrounding plastics layers the outer one of which, determines the outer configuration ofthe body.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure lisa fragmentary sectional elevation illust- rating part of a first mould suitable for use in carrying outthe method of the invention according to afirst example; Figure2 is a view comparable with Figure 1 but illustrating a second mould used in carrying out the said first example of the method of the invention; Figure 3 is a sectional elevation, to an enlarged scale, illustrating the product produced bythe method illustrated in Figures 1 and 2; Figure 4 is a view comparable with Figure 1 but corresponding to a second example; Figure 5is a view comparable with Figure 2, but again corresponding to the second example of the method ofthe invention; and Figure 6 is a sectional elevation, to an enlarged scale, illustrating the product produced bythe method illustrated in Figures4and 5.

Referring firstly to Figure 1, in moulding a solid spherical body (e.g. a ball such as a billiards or snooker ball) of a plastics material (e.g. of rigid polythene, polypropylene, nylon orthe like) one starts with a suitable injection mould 12 having therein an appropriate number of approximately spherical mould cavities, indicated generally by the numeral 10, corresponding to the desired number of articles desired to be produced upon each operation ofthe mould 12. In the illustration, only one such cavity 10 is shown but it will readily be understood to those skilled in the art that any practical number may be present.

The mould 12isatwo-part mould being composed of an upper cavity die part 14 and a lower core die part 16,these having therein respective mating depressions which, when the mould 12 is closed, regi sterto form the individual mould cavities 10, with the split line on the equators of the spherical cavities.

Channels 18 are provided in the mating surfaces of the two die parts 14,1 6for plastics material (not shown in this figure) to be supplied into the cavities 10 by conventional injection techniques.

The core die part 16 has, in register with each of its depressions, a respective opening 20 which accommodates a respective core pin 22. Each core pin 22 extends right across the cavity 10 substantially perpendicularto the split line and has a reduced dia meter end piece 23 abovethe level of the split line. A tubular ejector sleeve 24 is provided around each core pin 22 in the respective opening 20.

Each cavity 10 is, of course, of a configuration (i.e.

substantially spherical) corresponding approximately orsubstantiallyto the desired eventual product, i.e. a solid ball. However, such cavity 10 is significantly smallerthan the desired size ofthe eventual product, and is of a volume such as to rece ive a filling of plastics material, upon injection, which will solidify throughout its masswithoutforming any voids.It will thus be appreciated that in carrying out a first step in an example of the method of the invention (the understanding of which example is facilitated by Figures 1 and 2) one injects a suitable plastics material into the mould cavities 10 and after a short period,sufficientforatleastan external skin to form of the plastics material, the mould parts 14, 16 are separated and the ejector sleeves 24 are actuated to push the resultant substantially spherical moulded articles upwards relative to their core pins 22 and ejectthem from the cavities.

One such article is indicated at 28 in Figure 2. Upon ejection from its mould each such article 28 posesses a diametrically-extending aperture 30 justvacated by its respective core pin 22, each such aperture 30 having, approximately midway along its length a shoulder 31 corresponding with the transition to the reduced diameter end piece 23 of the core pin 22.

The article 28 so far moulded, which constitutes an inner body portion of the body required to be moulded, is then allowed to cool. Once cool, the article 28 is placed upon a fresh core pin 32 in a second mould 40.

As shown in Figure 2, the second mould 40 comprises a core die part 38 and a cavity die part 42, these die parts defining a cavity 44which is largerthan the article 28 and (in the illustrated case) of configuration and diameter corresponding to the desired finished article. The fresh core pin 32 projects through an opening 39 in the core die part 38. It is basically oflarger diameterthan the core pin 22, but has an extension 34forfitting snugly intothe aperture 30 and defining afirstshoulder36forthe article 28to rest on and a second shoulder 37 to abut the shoulder3l formed inside the aperture 30 through the article 28. As previously, where it extends through the opening in the core die part 38, this new core pin 32 is a snug fit in an ejector sleeve 50.

It will readily be understood that once the inner body portion 28 has been fitted into its respective cavity 44 on the extension 34 of the core pin 32, injection of plastics material into the cavity 44 ofthe mould 40, byway of passage 46, introduces a surrounding layer 60 (see Figure 3) around the inner body portion 28. This surrounding layer 60 may be of the same plastics material as the portion 28, or it may be different.Obviously, it may be harder or softer, and it may be of the same oradifferentcolour.What is importantto note is the fact that the newly injected mass or layer 60 is of relatively narrow radial thickness, so that cooling will proceed relatively rapidly, little shrinkage will occur, and the finished product will correspond precisely to the desired shape and configuration as defined by the cavity 44 in the mould 40.

The product 28,60 (Figure 3) produced in the mould 40, is, of course, ejected by means of the ejector sleeve 50 in the same way as the product (i.e. the inner body portion 28) produced in the mould 12, and is allowed to cool. If the article is required to have an aperture (e.g. in the case where it is to be used, for instance, as a decorative ball of the top of a flag post or in a like environment) apertures 30,62 (Figure 3) vacated by the pin 32 may be leftvacantfor use in subsequently fitting to the post, for instance.

However, if, for instance, and in the example being described, the ball is required for playing a game, the vacated aperture30,62 is plugged, for example with a suitable pre-moulded mushroom-shaped plug 64 (Figure 3) which abuts the shoulder 31 inside the aperture 30, or by introducing (e.g. by injection) a suitable plastics filling. The exterior surface ofthe ball is subsequently suitably smoothed and polished to achievethefinished article. In some cases, as in the illustrated example, an additional infill of plastics material may be required in the region previously lying adjacentthe opening of the mould supply pas sage 46, as indicated at61 in Figure 3.

It will readily be appreciated, however, that should one require a larger product than that which is obtained from the mould 40 of Figure 2, one may repeat the step of Figure 2, but now using yet a further mould, and core pin, in a manner analagous to what has been described with reference to Figure 2, to mould afurtherlayerofappropriatethicknessonto the product, and this may be repeated as manytimes as may be desired until a finished article of desired external dimensions and configuration is achieved.

Moreover, although a spherical article has been illustrated the article can be of any desired solid shape, for instance cubic, pyramidal, polyhedral and so forth. As has already been mentioned, the method of the invention is specifically useful forthe production of billiards or snooker balls, e.g. for use on children's oryouth'stables. Another particularly suitable application of the method is in the production of bowling balls, for instance for use in outdoor but more likely indoor bowls, in which case the bowls may be moulded so as not to be accurately spherical but may each have a predetermined bias. Then the element plugging the aperture vacated by the core pin may simulate the usual central inset disc in a traditional bowl.

A particular additional advantage ofthe method of the invention lies in the factthatwhere one is manufacturing and supplying a rangeofsizesofso-called junior billiard tables which require balls of different sizes, the moulds of the invention can be used selectively according to the size of ball required to be moulded. Thus, for instance if one has four moulds ofprogressivelyincreasing sizes, one may use only the smallerthree of these for producing small sized balls, and then use all four for producing large sized balls.

Referring now to Figures 4,5 and 6 these figures illustrate a modification, the details of which will readily be understood from the foregoing description, similar reference numerals having been allocated to similar parts for ease of explanation.

In this case, however, the depression in the core die part rt 1 6 of the fi rst m ou Id 12 is shaped, as at 52, to provide a recess which forms a disc-like protrusion 54 on the inner body part 28. Then in the second mould 40, the inner end of the ejector sleeve 50 abuts wholly against this protrusion 54 which, of course, is still visible when the product of the mould 40 is ejected from the mould. If the eventual product is to be a ball, the appropriate plug 64 (Figure 6) is inserted into the space vacated by the pin 32 and the ejector sleeve 50.

In both of the described examples, of course, the arrangement may be such thatthe core pin used in the larger mould (mould 40 in Figures 2 and 5) isthe same as that used in the smaller mould, for instance by provision of appropriate adapters around the pin or by use of appropriate configurations of ejector.

Moreover, in thefirst mould, the core pin may not always extend diametrically right through the cavity and thence the moulded product. It may, for example, extend only halfway through, or some other portion of the entire distance. Other minor modifications of the method and the product, are, of course, possible.

Claims (6)

1. A method of moulding a solid plastics body which comprises moulding an inner body portion having a configuration corresponding approximately or substantiallyto the desired finished configuration, but of smaller dimensions than the desired finished product, with an aperture therein for a core pin, and thereafter, by use of the or successive core pins, locatingtheinnerbodywithin a mould having a larger mould space (or a succession of moulds having successively larger mould spaces) and moulding a surrounding plastics layer around the inner body portion or a succession of surrounding plastics layers therearound, to achieve the desired finished body size and configuration.

2. A method according to claim 1 wherein, after removal from the core pin or the last ofthe core pins, the aperture left thereby is filled.

3. A method according to claim 2 wherein the filling ofthe aperture is effected by plugging the aperture by means of a mushroom-shaped element.

4. A method according to claim 2 wherein the fil- ling is effected by injection of a suitable plasticsfilling.

5. A method of moulding a solid plastics body substantially as hereinbefore described with referenceto and as illustrated in Figures 1 to 3, or in Figures 4to 6, of the accompanying drawings.

6. A moulded plastics body substantially as hereinbefore described with reference to and as illustrated in Figure 3, or in Figure 6, of the accompanying drawings.

6. A moulded plastics body made by the method of any of claims 1 to 5.

7. A moulded plastics body comprising an inner body portion having a configuration corresponding approximately or substantially to the desired external configuration but of smaller dimensions than the body and, around said inner body portion, a surrounding plastics layer which, or a plurality of successive surrounding plastics layers the outer one of which, determines the outer configuration ofthe body.

8. A moulded plastics body substantially as hereinbefore described with reference to and as illustrated in Figure 3, or in Figure 6, ofthe accompanying drawings.

Amendments to the claims have been filed and have the following effect: (a) Claims 1 to 8 have have been deleted (b) New or textually amended claims have been filed asfollows: CLAIMS

1. A method of moulding a solid plastics body which comprises the steps of moulding, around a core pin inserted into a first mould, an inner body portion having a configuration corresponding approximately or substantially to the desired finished configuration, but of smaller dimensions than the desired finished product, and removing the core pin to leave an aperture therein, and thereafter, by inser- tion of the or successive core pins into the aperture, locating the inner body portion within a second mould having a larger mould space (or a succession of moulds having successively larger mould spaces) and moulding a surrounding plastics layer around the inner body portion (or a succession of su rrou nding plastics layers therearound) to achieve the des ired finished body size and configuration, and finally removing the core pin orthe last of the core pins and filling the aperture left thereby.

2. A method according to claim 1 whereinthefilling ofthe aperture is effected by plugging the aperture by means of a mushroom-shaped element.

3. A method according to claim 1 whereinthefilling is effected by injection of a suitable plasticsfilling.

4. A method of moulding a solid plastics body substantially as hereinbefore described with referpence to and as illustrated in Figures 1 to 3, or in Fig urns 4to 6, of the accompanying drawings.

5. A moulded plastics body made by the method of any of claims 1 to 4.