GB2084508A

GB2084508A - Moulding

Info

Publication number: GB2084508A
Application number: GB8129461A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-09-30
Filing date: 1981-09-30
Publication date: 1982-04-15

Abstract

A plastics article such as a tyre is reinforced by moulding a core from scrap plastics material, and then moulding an outer skin for the article from fresh plastics material. This, for example, makes it possible to manufacture a tyre which is white on the outside, but with the core being formed from scrap material, so that the minimum amount of expensive fresh plastics material need be used.

Description

SPECIFICATION Moulding The invention relates to moulding, and particularly to the moulding of plastics articles, for example tyres.

Many products, including plastics tyres such as are used on golf trolleys, pushchairs and the like, are moulded from plastics scrap material. The scrap usually includes at least some coloured plastics material, and it has been found impossible to use scrap material to produce tyres in any desired colour. Indeed in order to produce a reasonably uniform colour in the tyres it has been found necessary to add a black pigment since this is the only colour which satisfactorily masks the various assorted colours which may be found in the scrap.

If it is desired to produce tyres in colours other than black, for example white, it has been found necessary to use pure fresh plastics material.

The price of fresh plastics material is five or six times higher than the price of scrap plastics, and so the cost of white tyres is a great deal more than the cost of black tyres.

I have now discovered that a tyre having a white appearance can be made more cheaply than known white tyres.

The invention provides a method of manufacturing a plastics article comprising the steps of moulding a core for the article from scrap plastics material, and then moulding an outer skin for the article from fresh plastics material.

The article may comprise from 70% to 80% by weight of scrap material and from 30% to 20% by weight of fresh material.

With my invention it is possible to manufacture a tyre which is white on the outside, or any other desired colour, but with the core of the tyre being formed from scrap material, so that only the minimum amount of expensive fresh plastics material need be used.

Even though two moulding operations are necessary, and the labour costs are therefore higher, the difference in price between fresh material and scrap material is so great that it is still possible to produce a tyre having a white appearance which is significantly cheaper than known white tyres.

Preferably the outer skin is moulded by forming at least one passage or channel in the moulded core, placing the core in a mould, and injecting fresh plastics material such that it flows through the or each passage or channel and then around the outside of the core.

Where the article is a tyre, it is preferred that the or each passage or channel extends from the inner rim of the core to the outer rim of the core.

The core may be formed or provided with one or more lugs arranged to abut part of the mould used to mould the outer skin, to locate and retain the core in a predetermined position during moulding of the skin.

The lugs may be visible after moulding of the skin, thus for example producing a decorative effect on the tyre.

The plastics material may be PVC.

The invention includes a tyre moulded by the method according to the invention.

By way of example, a specific embodiment of the invention will now be described, with reference to the accompanying drawings, in which:~ Figure 1 is a cross-section through a mould illustrating the moulding of a core for a tyre; Figure 2 is a side view of the moulded core; Figure 3 is a cross-section through another mould showing the core in position in the mould ready to receive the outer skin, the cross-section being taken through the injection point of the mould; Figure 4 is a cross-section similar to Figure 3 but taken at a different location; and Figure 5 is a side view of a tyre manufactured according to an alternative embodiment of the invention.

The mould shown in Figure 1 comprises two halves, 10 and 1 When the mould halves are placed together as shown, they define an annular chamber 12 in the general shape of a tyre. An inlet passage 13 passing through the mould half 1 1 leads into the chamber 12. The cross-section of the tyre comprises a generally rectangular portion 14, and a generally semi-circular portion 15 intended to seat in the rim of a wheel.

By injecting plastics material into the chamber 12 through the passage 13, cooling the mould, and removing the hardened plastics material, one produces a plastics core as shown at 17 in Figure 2, having the general shape of a tyre.

Part of the mould, not visible in Figure 1, is shaped to provide three channels in the core, at the location indicated by reference numeral 16 in Figure 2. There is a channel 1 6a down each side of the tyre, and the semi-circular portion 15 is absent at location 16, providing a cross-channel 1 6b.

Because the passage 13 leads into the inner rim of the core, any mark left by the sprue will be concealed when the finished tyre is mounted on a wheel.

The core 17 is moulded from scrap plastics material, which may be of a mixture of colours.

The core 17 is next placed in a further mould as shown in Figure 3. This mould also has two halves, 18 and 19. Together they define a further annular chamber 20 which has substantially the same internal diameter as the core 17, but has a larger external diameter and is of greater thickness, so that the chamber 20 extends around the outside of the core 1 7, and over the sides of the core 17. An inlet passage 21 communicates with the chamber 20.

Since the internal diameter of chamber 20 is substantially the same as that of the core, the core is held in position by engagement of semi-circular portion 15 in the correspondingly shaped part of the chamber 20; as best seen from Figure 4, which is a cross-section through the chamber 20 and core 17 at a point spaced around the core 17 from the region 16.

It will be seen from Figure 3 that the core is placed in the chamber 20 with the region 16 in registration with the entry point of the inlet passage 21.

Fresh white plastics material is then injected through the passage 21 and this plastics material passes into the channel 1 6b, through the channels 1 6a, and then around the outside of the core 17 and over the sides of the core 17. When the mould has been cooled, opened, and the sprues have been removed, a tyre results which has a white outer rim and white sides, with only a small semicircular scrap area exposed around the inner rim.

This scrap area is concealed when the tyre is attached to the wheel.

In some cases it may be necessary to provide means to assist in maintaining the core 17 securely in position in the second mould and reduce any tendency for the core to move out of position under the high injection pressures which may be used, for example of the order of 1,000 psi.

One embodiment of the invention which provides this assistance involves modifying the core mould shown in Figure 1 by providing, on each half 10, 1 a plurality of cavities spaced uniformly apart around the circumference of the mould cavity, for example as shown in dotted lines at 22 in Figure 1. These cavities cause the core to be formed with a plurality of spaced apart lugs on each side face. the depth of the cavities, and hence the height of the lugs, is such that when the core is placed in the mould shown in Figures 3 and 4, the lugs abut the side walls 23 (see Figure 4) of the core to locate and maintain the core in position while high pressure skin material is flowing around the core.

These lugs will be visible in the finished product, but as shown on the tyre 24 of Figure 5, the lugs 25 can be arranged to give a pleasing patterned effect.

The invention is not restricted to the details of the foregoing embodiments. For instance the channels 1 6a and 1 6b may be cut into the core after the core has been moulded. Alternatively, one or more passages through the core may be cut or moulded.

It is not essential for plastics material to be fed into the chambers 12 and 20 at a single location.

Depending on the dimensions and weight of any given tyre being produced, there may be two, three, four or more passages into the chambers, e.g. spaced evenly apart around the chambers.

Although twelve lugs 25 are shown in Figure 5, different numbers may be used, and the shape and configuration may differ. The lugs could for example be formed to display lettering; for example giving the name of the manufacturer.

The principle of the invention is not restricted to the manufacture of tyres, and the invention may also be used to manufacture other articles utilising a mixture of scrap plastics material and fresh plastics material.

Claims

1. A method of manufacturing a plastics article comprising the steps of moulding a core for the article from scrap plastics material, and then moulding an outer skin for the article from fresh plastics material.

2. A method as claimed in Claim 1, in which the article comprises from 70% to 80% by weight of scrap material and from 30% to 20% by weight of fresh material.

3. A method as claimed in Claim 1 or Claim 2, in which the outer skin is moulded by forming at least one passage or channel in the moulded core, placing the core in a mould, and injecting fresh plastics material such that it flows through the or each passage or channel and then around the outside of the core.

4. A method as claimed in Claim 3, when used to manufacture a tyre, in which the or each passage or channel extends from the inner rim of the core to the outer rim of the core.

5. A method as claimed in any one of the preceding claims, in which the core is formed or provided with one or more lugs arranged to abut part of the mould used to mould the outer skin, to locate and retain the core in a predetermined position during moulding of the skin.

6. A method as claimed in Claim 5, when used to manufacture a tyre, in which the lugs are visible after moulding of the skin, thus providing a decorative effect on the tyre.

7. A method as claimed in any one of the preceding claims, in which the plastics material is PVC.

8. A method substantially as hereinbefore described with reference to Figures 1 to 4, or Figures 1 to 4 as modified by Figure 5, of the accompanying drawings.

9. A plastics article when manufactured according to any one of the preceding claims.

10. A plastics article as claimed in Claim 9 comprising a tyre.

11. A tyre substantially as hereinbefore described with reference to Figures 1 to 4, or Figures 1 to 4 as modified by Figure 5, of the accompanying drawings.