GB2122530A - Tyres - Google Patents

Abstract

A method of moulding a hollow tyre comprises moulding two parts, at least one having a hollow recess 14 therein, and joining the two parts to form a hollow tyre. The two parts may be joined by means of pegs 17 and sockets 16, by a screw thread, by adhesive, or by passing a heated blade between the two parts. The two parts of the tyre may be identical so that a single mould may be used to produce both parts. An illustrated device for joining the halves comprises a turntable 19 driven via a belt 22 from a motor 21. The halves of a tyre are clamped together on the turntable and during rotation of the turntable fixed electrically heated blades 30, 30 project between the halves to heat soften the joining surfaces to allow bonding when the blades are withdrawn. <IMAGE>

Description

SPECIFICATION Tyres The invention relates to tyres.

It is known to manufacture tyres of relatively small dimensions as solid tyres by moulding scrap plastics material such as PVC.

For larger tyres, however, such as tyres for wheelbarrows, a solid tyre may be too rigid and unacceptably heavy. It would obviously be preferable to mould the tyre with a hollow interior but this is not possible and hitherto the only method of producing a hollow tyre from scrap plastics material has involved extruding a tube of plastics material and then joining the ends of the tube together. This does not produce a tyre having a satisfactory finish because distortion can arise since the outer edge of the tube has to extend along a longer path than the inner edge of the tube and the joint between the ends, which is not easy to produce, is clearly visible in the finished tyre.

We have now discovered an alternative solution to the problem and accordingly the invention provides a method of moulding a hollow tyre comprising moulding two parts, at least one having a hollow recess therein, and joining the two parts together to define a hollow tyre.

Preferably each part has a recess and in the finished tyre the two recesses co-operate to define the hollow interior of the tyre.

Preferably each part comprises a side wall and part of an inner and outer rim of the tyre so that the joint between the parts extend circumferentially around the tyre. It can thus be concealed in a tread pattern of the tyre.

Preferably the two parts are identical so that a single mould can be used to produce both parts.

Mechanical means may be provided for securing the parts together.

The parts may for example be provided with a screw-thread formation but it is preferred that the two parts are provided with peg and socket interconnections.

Each part may for example have three pegs and three sockets spaced apart around the tyre part circumferentially, the pegs alternating with the sockets.

The parts can readily be secured together by means of adhesive but this requires the use of solvent based adhesives and consequent stringent safety precautions. It is necessary to provide fume extractor fans in the area where adhesive is used, and the adhesive cannot be used in the vicinity of injection moulding machines because of the possible fire risk unless the injection moulding machines are flame-proofed.

For this reason attempts were made to join the parts by means of welding techniques such as ultrasonic welding or high frequency welding. However these methods were not very effective since it was difficult to localise the welding and there was a tendency to melt a larger area of the parts of the tyre than was desirable, leading to deformation of the tyre.

Accordingly, the tyre parts are preferably joined together by passing a heated member over the faces to be joined and then urging the faces together.

Preferably the member comprises a heated blade which is inserted between the two parts.

There may be more than one blade. For example, a first blade may extend radially inwardly between the two parts, from the outer periphery of the tyre, a second blade passing radially outwardly between the two parts, from the inner periphery of the tyre.

Preferably relative movement is provided between the blades and the tyre such that, with respect to the tyre, the blades travel circumferentially around the tyre to cover all the surfaces of the two parts of the tyre that contact one another.

Where two parts have peg and socket interconnections, the blades may be arranged to cut through the pegs as they move relative to the tyre, since the pegs are only required to locate the two parts together immediately prior to permanent attachment of the parts together by heating of the abutted faces.

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

The principle of the invention may be applicable to articles other than tyres.

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 side view of one part of an embodiment of wheelbarrow tyre according to the invention; Figure 2 is a cross-section on line ll-ll of Fig. 1 showing an entire tyre; Figure 3 is a cross-section on line Ill-Ill of Fig. 1, again showing an entire tyre; Figure 4 is a plan view of apparatus for manufacturing this embodiment of tyre according to the invention; and Figure 5 is a side view of the apparatus of Fig. 4 being used to join together two halves of a tyre according to the invention.

The tyre which is the subject of this embodiment, and which is suitable for use as the tyre of a wheelbarrow, is injection moulded in two identical parts from scrap PVC. One of the two identical parts is shown in Fig. 1.

Each part comprises one side wall 10 (see Figs. 2 and 3) of the tyre and also provides part 11 of the outer rim of the tyre and part 1 2 of the inner rim of the tyre. The outer rim has a tread formation in the form of a series of circumferentially extending ribs 1 3.

The part shown in Fig. 1 contains a circumferentially extending recess 1 4. Strengthening webs 1 5 bridge the recess at intervals. At three locations spaced equi-distant around the part there are three sockets 16. Alternating with these sockets are three pegs 1 7. The sockets and pegs are tapered and are of similar dimensions.

One two identical parts have been moulded, it is possible to fit the two parts together by fitting the pegs of a first part into the sockets of a second part. The sockets of the first part receive the pegs of the second part.

This results in a complete tyre with a hollow interior. A neat finish to the tyre is provided because the outer joint line is concealed by the tread formation and the inner joint line will eventually be concealed by the wheel hub when the tyre is fitted to a wheel.

Figs. 2 and 3 are cross-sections on lines Il-lI and Ill-Ill respectively, but taken through two tyre parts assembled together to form the complete tyre. Thus the finished recess within the tyre is indicated in Fig. 2 by the reference numeral 1 8. Fig. 3 illustrates how each peg 1 7 mates with an associated socket 16.

The apparatus shown in Figs. 4 and 5 is used to permanently fix the tyre parts together and comprises a turntable 1 9 mounted for rotating about a vertical axis on support bearings 20. The turntabie can be slowly rotated by the drive pulley 21 of an electric motor (not shown), the drive pulley 21 being ocupled by means of a toothed belt 22 to a driven gear 23 which is secured to the turntable 19.

The turntable 1 9 has a hollow recess in its upper face shaped to receive one half 24 of a tyre. This tyre half is identical to that shown in Fig. 1.

A second identical tyre half 25 is fitted on to the top of the tyre half 24, the two halves being neatly located together by means of peg and socket interconnections such as those shown in Fig. 3.

A heavy metal cap 26, similar in shape to the turntable 19, is then fitted over the tyre half 25 thus applying pressure which tends to urge the two halves together.

Adjacent the outer periphery of the tyre parts there is mounted a first blade 27 which is rotatably mounted by means of a vertically extending pivot post 28 which is in turn rotatably mounted in a bearing 29. The blade 27 consists of a thin portion 30 which is capable of passing between the tyre halves, and a thicker body portion 31, which contains two thermostatically controlled electric heating elements 32.

The blade 27 can be swivelled clear of the tyre halves, or swivelled in the opposite direction to engage between the tyre halves as shown in Fig. 4, by means of an air ram (not shown).

The turntable 1 9 and cap 26 are annular as shown in Fig. 4, and adjacent the inner periphery of the turntable 1 9 and cap 26 there is mounted a second blade 33. This blade is identical to the glade 27. In other words it can be heated by thermostatically controlled heaters 32 and it can be swivelled on a vertical pivot post 28 by means of an air ram (not shown) between a position in which it is clear of the tyre parts and the position shown in Fig. 4 in which it projects between the tyre parts.

In order to join two tyre parts together, the heated blades are swivelled into the position shown in Fig. 4 and the electric motor is then operated to rotate the turntable for a full revolution. This causes the abutting faces of the two tyre parts to be melted. The inner blade 33 melts a region extending from the inner periphery of the tyre to slightly beyond the centre line of the tyre and the outer blade 27 melts a region extending from the outer periphery of the tyre to slightly beyond the centre line of the tyre.

Since the blades are relatively narrow in relation to the circumferential dimensions of the tyre, each blade melts a relatively small circumferential area at a time, the melting occurring progressively in the circumferential direction. As each melted region leaves the blade which has carried out the melting, the melted faces tend to stick together because of pressure applied by the cap 26.

Once the joining process has commenced, the peg and socket interconnections are no longer required, and in fact the pegs are cut through by the blades as the tyre rotates.

Once the tyre has completed a revolution and the joining process is complete, the air rams are actuated to swivel the blades clear of the tyre and the jointed tyre can then be removed.

The invention is not restricted to the details of the foregoing embodiment. For example alternative means may be provided for securing the two tyre parts together. One part may for example be provided with a circumferentially extending screw-threaded flange which screws into a circumferentially extending screw-threaded channel in the other part.

Also, the two parts may permanently be attached together by adhesive or welding.

Means may be provided to apply additional pressure to the tyre via the cap 26. For example pressure rollers may be provided which bear down on the cap 26. The temperature to which the blades are heated may lie in the range 1 80 C to 220"C.

Claims (16)

1. A method of moulding a hollow tyre comprising moulding two parts, at least one having a hollow recess therein, and joining the two parts together to define a hollow tyre.

2. A method as claimed in Claim 1, in which each part has a recess and in the finished tyre the two recesses co-operate to define the hollow interior of the tyre.

3. A method as claimed in Claim 1 or Claim 2, in which each part comprises a side wall and part of an inner and outer rim of the tyre so that the joint between the parts extends circumferentially around the tyre.

4. A method as claimed in Claim 4, in which the joint is concealed in a tread pattern of the tyre.

5. A method as claimed in any one of Claims 1 to 4, in which the two parts are identical so that a single mould can be used to produce both parts.

6. A method as claimed in any one of Claims 1 to 5, in which mechanical means are provided for securing the parts together.

7. A method as claimed in Claim 6, in which the parts are provided with a screwthread formation.

8. A method as claimed in any one of Claims 1 to 6, in which the two parts are provided with peg and socket interconnection.

9. A method as claimed in Claim.8, in which each part has three pegs and three sockets spaced apart around the tyre part circumferentially, the pegs alternating with the sockets.

10. A method as claimed in any one of the preceding claims, in which the two parts are connected together by means of adhesive.

11. A method as claimed in any one of Claims 1 to 9, in which the tyre parts are joined together by passing a heated member over the faces to be joined and then urging the faces together.

1 2. A method as claimed in Claim 11, in which the member comprises a heated blade which is inserted between the two parts.

1 3. A method as claimed in Claim 12, in which there is more than one blade.

14. A method as claimed in Claim 13, in which a first blade extends radially inwardly between the two parts, from the outer periphery of the tyre, a second blade passing radially outwardly between the two parts, from the inner periphery of the tyre.

1 5. A method as claimed in Claim 14, in which relative movement is provided between the blades and the tyre such that, with respect to the tyre, the blades travel circumferentially around the tyre to cover all the surfaces of the two parts of the tyre that contact one another.

16. A method as claimed in Claim 15 where the parts have peg and socket interconnections, in which the blades are arranged to cut through the pegs as they move relative to the tyre.

1 7. A method of moulding a hollow tyre substantially as herein described, with reference to the accompanying drawings.

1 8. A tyre when moulded by the method as claimed in any one of the preceding claims.