SYNTACTIC FOAM TYRE INSERTS FOR FLAT-PROOF TYRES AND APPARATUS FOR MANUFACTURING A PORTION THEREOF

Abstract: In order to make a vehicle tyre relatively flat-proof, a flexible, pressurised, closed-cell, syntactic foam tyre insert is fitted within the tyre to extend over the tread and adjoin­ ing sidewall areas. The tyre insert comprises a plurality of preformed elastomeric spheres compressed and moulded together into the configuration of the interior of the tyre cas­ ing, or a segment thereof. Each such elastomeric sphere is pressure moulded from a castable plastic resin in a mould (24) to form a hollow, thin-walled, seamless, pressurised, elastomeric sphere. The elastomeric spheres are coated with a liquid resin to fill any voids between said elastomeric spheres after they are compressed, and to bond said elas­ tomeric spheres together when cured. The pressurised elastomeric spheres are manufactured in an apparatus which simultaneously rotates the mould (24), having a spherical mould cavity 24c, about two perpendicular axes of said cavity 24c to provide a uniform, thin-walled sphere.

Description: Title: "Syntactic foam tyre inserts for flat-proof tyres and apparatus for manufacturing a portion thereof" THIS INVENTION relates to tyres for vehicle wheels. The need for a flat-proof tyre has been evident ever since the invention of the automobile. Many such tyres have been proposed, but for one reason or another, they have not been completely successful, and tyres today are subject to flats just as they were when the automobile was first developed. One proposed "flat free" tyre was made by filling a tyre casing with a conventional plastic foam, the foam replacing the conventional air-filled inner tube. Foam-filled tyres, however, proved to be too heavy for passenger car use and did not provide a comfortable ride. Foam-filled tyres also produced a relatively high build-up of heat when operated at high speeds over long distances. Heat proved to be deleterious to the tyre and to the foam. As a result, foam-filled tyres are generally restricted to military use, mining vehicles, or public works equipment where the aforesaid problems can be tolerated. It is therefore an object of the present invention to produce a foamed plastic tyre insert that will be free of the problems associated with prior foamfilled tyres. Another object of this invention is to provide a tyre that will not go flat when punctured. Yet another object is to provide an apparatus for manufacturing a component of the foamed tyre insert of the present invention. According to one aspect of the invention, there is provided a tyre insert made of a relatively light weight syntactic foam, said foam comprising a plurality of preformed elastomeric shapes compressed and moulded together into the configuration of the interior of a tyre casing or a segment thereof, said elastomeric shapes being formed by moulding a castable plastic resin in a chamber pressurised with a gas to form a hollow, thin-walled, seamless elastomeric sphere pressurised with a gas, said shapes being coated with a liquid resin to fill void space between said elastomeric shapes when compressed, and to bond said elastomeric shapes together when cured. According to another aspect of the invention, there is provided a relatively flat-proof tyre comprising a tyre casing and one or more tyre inserts according to the invention According to a further aspect of the invention, there is provided an apparatus for moulding elastomeric spheres from a resin or plastic by simultaneously rotating a mould for said sphere about two perpendicular axes of said sphere, said apparatus comprising: a bracket rotatably mounted within a frame, said bracket being rotatable about the axis of a pair of shafts passing through said frame and connected to said bracket; a sphere mould rotatably mounted to said bracket for rotation about an axis of said mould, said mould axis being perpendicular to the axis of said bracket shafts; and power transmission means to simultaneously rotate said bracket and mould as aforesaid, when either said bracket or said mould is rotated. According to a yet further aspect of the invention, there is provided a process for the pressurised rotational casting of a hollow, thin-walled, seamless, elastomeric sphere under pressure in a mould having a male and female end and a semi-spherical mould cavity in said male and female ends, said process comprising: charging one of said semi-spherical mould cavities with a predetermined amount of a castable liquid plastic resin; mating said male and female ends of said mould so that the semi spherical cavities therein form a spherical mould cavity; pressurising said spherical mould cavity with a gas; and simultaneously rotating the mould about the vertical and horizontal axis thereof to cause the castable liquid plastic resin to be evenly distributed about the walls of the mould cavity so that upon curing, a seamless moulded elastomeric sphere having a uniform wall thickness will be produced. According to a still further aspect of the invention there is provided a process for the compression moulding of hollow, thin-walled, gas pressurised elastomeric spheres in a tyre insert mould having a tyre insert mould cavity to produce a syntactic foam tyre insert, said process comprising: coating said spheres with a resin; filling said mould cavity with said spheres; compressing said spheres to substantially eliminate void space between said spheres without substantially increasing the pressure within said spheres, said coating filling any void space not filled by compression; and curing the resin coating to produce a unitary syntactic foam tyre insert. A preferred form of flat-proof tyre embodying the present invention comprises a conventional tyre casing and one or more tyre inserts comprised of preformed elastomeric shapes in the form of spheres compressed and moulded together into the configuration of the interior of the tyre casing or a segment thereof. The elastomeric spheres are hollow and are cast in a pressurised mould cavity from a castable plastic resin to produce a pressurised elastomeric sphere. These elastomeric spheres are coated with a liquid resin and compressed in a mould to form the tyre insert. The liquid resin coating will fill any void spaces between the spheres compressed, and will bond the spheres together when the liquid resin is cured. The resultant mass is referred to as a flexible, pressurized closed cell, "syntactic" foam. The pressurised elastomeric spheres are preferably manufactured in an apparatus which simultaneously rotates the mould for the sphere about two separate axes which are perpendicular to each other. The apparatus comprises a bracket rotatably mounted within a frame having a pair of horizontal shafts passing through the frame and connected to the bracket. The frame is rotatable about the axis of the shafts. A sphere mould is mounted on the bracket and is rotatable about the vertical axis of the mould which is perpendicular to the horizontal axis of the said shafts. A power transmission means is associated with the bracket and frame to simultaneously rotate the sphere mould about said horizontal and vertical axes to ensure a uniform distribution of the resin within the mould cavity and thereby produce a sphere having a uniform wall thickness when the resin is cured. Embodiments of the invention are described below, by way of example, with reference to the accompanying drawing, in which: FIGURE I is a front elevational view of the apparatus of the present invention. Preferred embodiments of the invention make use of pre-formed hollow elastomeric spheres. These hollow elastomeric spheres of the present invention may be made by any moulding or casting technique known in the art which will produce a unitary, hollow sphere, having relatively thin walls ranging from about 0.01 inch to about 0.025 inch, and weighing about 0.8 to about 6 grams. A moulding or casting technique which may be used to produce such spheres is to charge a spherical mould cavity with the desired quantity of castable liquid resin, and then increase gas pressure within the mould. The mould is simultaneously rotated about its opposing axes to produce a hollow seamless sphere having a uniform wall thickness as the sphere is cured within the mould. An apparatus for simultaneously rotating a sphere mould about opposing axes thereof is shown in Figure 1. A frame 10 is provided having a first upstanding leg IOa and a second upstanding leg lOb. A rotatable U-shaped bracket 12 is provided between the upstanding frame legs I 0a and b. The Ushaped bracket has a first leg 12a parallel to and spaced away from the first upstanding frame leg lOa, a second leg 12b parallel to and spaced away from the second upstanding frame leg lOb, and a horizontal leg 12c connecting said first and second bracket legs. A first shaft 14a passes through the first legs of the frame and bracket, and a second shaft 16a passes through the second legs of the frame and bracket. The shafts are fixed to the bracket legs by means of bolt heads 14c and 16c welded thereon, and are rotational within the frame legs by means of bearings 14b and 16b adjacent to or within said frame legs, to permit the bracket 12 to be rotatable about the horizontal axis of the shafts 14a and 16a. Power to rotate shaft 16a and bracket 12, is provided by motor 18, in association with a V-belt 20 and V-belt pulleys 22a and 22b. A sphere mould 24 is rotatably attached to the horizontal bracket leg 12c and has a downwardly projecting shaft 26 which passes through mould bearing 28 and through horizontal leg 12c. The sphere mould 24 has a female end 24a, a cylindrical male end 24b, and a mould cavity 24e which forms a sphere when the female end and male end are mated. A passageway 24d is provided in the female end of the mould for communication with an external source of pressurised gas and with the tolerance between the male and female ends when mated. An O-ring is provided around the circumference of the male end to prevent the pressurised gas from escaping out along the circumference thereof when mated with the female end. The top of the female end of the mould is provided with a shaft 30 and a gas valve 32 of the type used on automobile inner tube tyres to allow pressurised gas to be injected into the mould without the release of gas out of the valve when the source of pressure is removed. A power transmission means is provided for transmitting the power to rotate bracket 12 about the horizontal axis of shafts 14a and 16a, and to rotate the sphere mould about the vertical axis thereof. The power transmission means is in the form of a stationary miter gear 34a mounted onto stationary shaft 14a, and engaged with a rotatable miter gear 34b rotatably mounted on said horizontal bracket leg 12c by bearing 36. The rotatable miter gear has a shaft 38 downwardly extending therefrom for engagement with a V-belt pulley 42 and V-belt 40 which are engaged with the mould shaft 26, connected to the male end of said mould, to provide a source of energy for rotating the mould about its vertical axis. In operation, the mould is opened and a predetermined amount of castable plastic resin is placed in the semi-spherical mould cavity in the male end of the mould. The moulds are then closed and pressurised. Motor 18 is actuated to rotate shaft 16a by means of V-belt 20 and V-belt pulleys 22. The rotational energy on shaft I 16 causes bracket 12 to rotate about the horizontal axis of shaft l4a and l6a. When this rotation commences, the rotatable miter gear 34b rotates around the stationary miter gear 34a, which causes miter gear shaft 38 to rotate causing V-belt pulley 42 and V-belt 40 to rotate causing mould shaft 26 to rotate causing mould 24 to rotate about the vertical axis of said mould. As a result, the sphere mould will be rotated simultaneously about its horizontal and vertical axes to cause the liquid castable resin within the mould cavity to be evenly distributed about the walls of the mould cavity so that upon curing, the moulded elastomeric spheres will be seamless and have a uniform wall thickness. The seamless feature of the spheres will eliminate any possible problem of the pressure within the spheres from leaking through a seam. Alternatively, the rotational power of motor 18 may be applied to miter gear shaft 38 rather than to horizontal shaft 16¯. FIGURE I illustrates a second sphere mould 44 in parallel with mould 24. The second sphere mould 44 is identical in construction and operation to sphere mould 24. Additional sphere moulds may be provided along the length of horizontal bracket leg 12c to increase the production of spheres. When more than one mould is utilised, a top mould bracket 46 and bearings 48 and 50 are provided to stabilise the moulds and to provide for their rotation. The pressure within the spherical mould is provided by pressurised gas, such as air or nitrogen which will not react with and degrade the resin from which the spheres are manufactured. The spheres may be coated or impregnated with a gas barrier, such a polyvinyl alcohol, butyl rubber, or polyisobutylene to prevent any gas migration out of the spheres. Polyurethane is the preferred resin and nitrogen is the preferred gas used for pressurising the spheres because of its low rate of migration through polyurethane. Any other resin, gas or gas barrier suitable for use with the present invention and determined by routine experimentation, may also be used. The diameter of the spheres ranges from about z inch to about 2 inches when used for automobile tyres, but may be smaller or greater, depending upon the size of the tyre and the use to which it is put. When the elastomeric spheres are ready to be moulded into a tyre insert embodying the present invention, they are coated with a liquid resin which is preferably of the same composition used to manufacture the elastomeric spheres, for example polyurethane and the coated spheres are compressed in a mould corresponding to the configuration of the interior of a tyre casing or a segment of such casing. The spheres occupy about 50% of the volume of the tyre insert mould, the remainder of the mould being occupied by voids between the spheres. The spheres are compressed to about 50% of the mould volume to substantially reduce the weight of the inserts by eliminating the voids without substantially increasing the pressure in the interior of the spheres. The coating of liquid resin on the spheres will fill any remaining void space not filled by compression to form a unitary syntactic foam when the liquid resin is cured. The strength of the elastomeric spheres may be increased by admixing therewith, suitable amounts of glass, quartz, aramid, or carbon fibres, or mixtures thereof. Such fibres may also be admixed with the liquid plastic resin used to coat the elastomeric shapes to provide additional strength. Such fibres should be utilised in amounts, lengths and diameters that will not detract from the elastomeric nature of the tyre insert. Thus, a relatively flat-proof tyre may comprise a tyre casing having a tyre tread and side walls and an insert embodying the invention bonded to the interior of the casing over the tread and sidewall regions, or simply located within the tyre casing so as to extend over these regions. While the present invention has been described in terms of a tyre insert designed to be inserted into the interior of a tyre casing, tyre tread and sidewalls and suitable reinforcements therefor may be bonded directly onto the insert to form the flat-proof tyre. A tyre embodying the present invention may be mounted onto a one piece drop centre rim or a two piece wheel which will separate into two halves along a plane perpendicular to the rotational axis of the wheel. These two halves are installed in the open centre of the tyre, drawn together, and secured around their circumference by fastening means to form the wheel. When a tyre in accordance with the preferred embodiment of the present invention in punctured by a nail or some other foreign object, a few elastomeric spheres will collapse, but the loss of pressure in these few spheres is insignificant in view of the great number of spheres comprising each tyre insert. As a result, the tyre will not go flat but can continue to be used despite the presence of the object causing the puncture. An insert in accordance with the preferred embodiment, when designed for use with a conventional automobile tyre, will weigh about 8 pounds when completely filling the tyre. A conventional automobile tyre weighs about 25 pounds and the metallic wheel walls will weigh about lû pounds. This yields a total weight of about 43 pounds which is below a 50 pound limit on the tyre and wheel combination to avoid the problems associated with prior foamed tyres and to make such tyres acceptable for conventional automobile use. The weight of tyres embodying the present invention may be reduced even futher by using spheres of differing diameter to manufacture said inserts, by using a conventional inner tube of reduced diameter in association with the inserts, or by using tubeless tyres in association with said inserts. When using spheres of differing diameters to manufacture said insert, spheres of smaller diameter are arranged in the inserts so they will be closer to the tyre tread than the larger spheres, when the insert is inserted into the tyre casing. The larger spheres will thus be further away from the tyre treads and will be closer to the centre of the wheel than the smaller spheres. By this arrangement the overall weight of the insert can be reduced because the larger spheres weigh less than smaller spheres having the same volume. The depth of the layer of the smaller diameter spheres is selected so that when the tyre of the present invention is punctured by a nail or some other foreign object the depth of the puncture will not reach the larger diameter spheres, but will be limited to the smaller diameter spheres. In this manner, the amount of deflation due to the puncture will be relatively minor because it will be limited to the spheres of small diameter. Rather than using spheres of larger diameter to reduce tyre weight, a conventional automobile inner tube of reduced diameter may be substituted therefor. When using a conventional inner tube said tyre insert is manufactured so that it may be used as a liner between the tyre casing and the inner tube adjacent to the tyre tread and sidewalls. In this case, the tyre insert may be bonded to the interior of the tyre casing, or simply held in place against the interior surface of the tyre casing by the pressure within the inner tube. The depth of such a liner is selected so that when the wheel is punctured by a nail or some other foreign object, the puncture will not reach the inner tube, but will be limited to a few small spheres in the liner which will thereby limit the amount of deflation caused by the puncture. The insert liner is moulded to accommodate the shape of the inner tube when inflated. Use of the insert liner of the present invention in combination with a conventional inner tube of reduced diameter has the additional advantage of being able to compensate for any pressure loss in the insert liner due to gas migration or punctures by increasing the pressure in the inner tube. The insert of the present invention may also be used with tubeless tyres. Said insert may be bonded to the interior of the tyre over the tyre tread area and the side walls by means of a suitable bonding agent, or may be held in place against said interior surface over the tyre tread area and the side walls by the pressure within the tubeless tyres. The inserts are manufactured to have sufficient depth so that when the tyre is punctured, the puncture will not reach the tubeless area, but will be limited to a few spheres in the liner which will thereby limit the amount of deflation caused by the puncture. Loss of pressure in the insert due to gas migration or punctures can be compensated for by increasing the pressure within the tyre. Whilst, in the above description a tyre has had a unitary insert embodying the invention fitted within it, it will be appreciated that a tyre may be provided with a multi-part insert arrangement, comprising two or more insert parts which, for example, fit together within the tyre to provide the assembled insert arrangement. In particular, the insert arrangement may comprise a plurality of similar or identical sectors which are fitted together, end to end, around the internal circumference of the tyre. References to a tyre insert above are also intended to extend to such multi-part insert arrangements. The present invention is described in terms of elastomeric, hollow, thinwalled spheres under pressure. While the spherical configuration is preferred, the invention is not limited thereto, but contemplates pressurised, elastomeric, hollow, thin-walled shapes of any configuration or shape, which may, upon routine testing, be found to be suitable for use with the present invention. The features disclosed in the foregoing description, in the following claims and/or in the accompanying drawings may, both separately and in any combination thereof, be material for realising the invention in diverse forms thereof.

Claims: CLAIMS 1. Atyre insert made of a relatively light weight syntactic foam, said foam comprising a plurality of preformed elastomeric shapes compressed and moulded together into the configuration of the interior of a tyre casing or a segment thereof, said elastomeric shapes being formed by moulding a castable plastic resin in a chamber pressurised with a gas to form a hollow, thin-walled, seamless elastomeric sphere pressurised with a gas, said shapes being coated with a liquid resin to fill void space between said elastomeric shapes when compressed, and to bond said elastomeric shapes together when cured. 2. A tyre insert according to claim I wherein said gas is selected so that its rate of migration through said pressurised shapes is relatively low. 3. A tyre insert according to claim I or claim 2 wherein said shapes or the outer surface of said inserts are coated or impregnated with a gas impermeable barrier to prevent or reduce migration of pressurised gas out of said shapes. 4. A tyre insert according to any preceding claim, wherein said shapes are spheres which have a diameter of 0.5 inch to 2 inches, a uniform wall thickness of 0.010 inch to 0.025 inch, and a weight of 0.8 to 6 grams, said spheres being coated with liquid polyurethane and compressed to at least 50% of the uncompressed volume of said spheres and cured to bind said spheres together, said liquid polyurethane filling any void space between said compressed spheres to form a unitary mass upon curing. 5. A relatively flat-proof tyre comprised of a tyre and one or more tyre inserts as set forth in any of claims I to 4. 6. An apparatus for moulding elastomeric spheres from a resin or plastic by simultaneously rotating a mould for said sphere about two perpendicular axes of said sphere, said apparatus comprising: a bracket rotatably mounted within a frame, said bracket being rotatable about the axis of a pair of shafts passing through said frame and connected to said bracket; a sphere mould rotatably mounted to said bracket for rotation about an axis of said mould, said mould axis being perpendicular to the axis of said bracket shafts; and power transmission means to simultaneously rotate said bracket and mould as aforesaid, when either said bracket or said mould is rotated. 7. An apparatus for moulding elastomeric spheres from a resin or a plastic by simultaneously rotating a mould for said spheres through axes which are vertical and horizontal with respect to one another, said apparatus comprising: a frame having first and second upstanding legs; a rotatable U-shaped bracket rotatable within said frame and having a first leg parallel to and spaced away from said first upstanding frame leg, a second leg parallel to and spaced away from said second upstanding frame leg, and a horizontal leg connecting said first and second bracket legs; a first shaft passing through said first legs of the frame and bracket, and a second shaft passing through said second legs of the frame and bracket, said shafts being fixed to said bracket legs, and rotational within said frame legs to permit said bracket to be rotational about the horizontal axis of said shafts; ; a sphere mould rotatably attached to said horizontal bracket leg and having a shaft projecting away from said mould to engage a drive chain for rotating said mould about the vertical axis thereof, said mould having a mould cavity, a gas valve and a passageway, said passageway communicating with said gas valve and a mould cavity to provide a means for the pressurisation of said mould cavity; and power transmission means to simultaneously rotate said bracket and mould as aforesaid, when either said bracket or said mould is rotated. 8. A process for the pressurised rotational casting of a hollow, thin-walled, seamless, elastomeric sphere under pressure in a mould having a male and female end and a semi-spherical mould cavity in said male and female ends, said process comprising: charging one of said semi-spherical mould cavities with a predetermined amount of a castable liquid plastic resin; mating said male and female ends of said mould so that the semispherical cavities therein form a spherical mould cavity; pressurising said spherical mould cavity with a gas; and simultaneously rotating the mould about the vertical and horizontal axis thereof to cause the castable liquid plastic resin to be evenly distributed about the walls of the mould cavity so that upon curing, a seamless moulded elastomeric sphere having a uniform wall thickness will be produced. 9. A process for the compression moulding of hollow, thin-walled, gas pressurised elastomeric spheres in a tyre insert mould having a tyre insert mould cavity to produce a syntactic foam tyre insert, said process comprising: coating said spheres with a resin; filling said mould cavity with said spheres; compressing said spheres to substantially eliminate void space between said spheres without substantially increasing the pressure within said spheres, said coating filling any void space not filled by compression; and curing the resin coating to produce a unitary syntactic foam tyre insert. 10. The process of claim 8 or claim 9 wherein said gas is selected so that its rate of migration through said pressurised spheres is relatively low, and wherein said spheres or the outer surface of said inserts are coated or impregnated with a gas impermeable barrier to prevent or reduce the migration of pressurised gas out of said spheres.

Inventors: SHONER, DOUGLAS
Applicants: SHONER, DOUGLAS
Application year: 1986
Main classification: B60C7
IPC codes: B60C5, B29D30, B60C7