PROCESS AND APPARATUS FOR MANUFACTURING BEAD SUB-ASSEMBLIES

Abstract: There is disclosed apparatus for manufacturing a bead sub-assembly comprising an upper mould plate (10) and a lower mould plate (12), at least one of said upper and lower mould plates being moveable so that the plates can cooperate to define a mould cavity (14) substantially corresponding to the shape of the sub-assembly and delivery means (32) for delivering a desired quantity of a mouldable composition (18) to the mould cavity.

Description: PROCESS AND APPARATUS FOR MANUFACTUR ING BEAD SUB-ASSEMBLIES This invention relates to the field of bead sub-assemblies, in particular to methods and apparatus for the manufacture of annular bead sub-assemblies for use in tyres. The manufacture of tyres for automobiles - such as cars and freight vehicles - air craft, or other heavy load bearing wheeled carriages, such as caravans, involves the incorporation of "bead sub-assemblies" into the body of the tyre in order to retain the tyre on the wheel. The bead sub-assembly comprises a bead wire or wires and a suitably shaped bead filler. At the present time, the bead sub-assembly is manufactured off-line and thus the bead sub-assembly must be brought to the tyre building machine. Furthermore, the present bead sub-assembly manufacture involves four or five fabrication steps. Typically, an extrusion operation is performed to coat the bead wires with rubber, thereby joining a number of wires together with the rubber into a flat layer. The flat layer is then formed into a hoop (of square cross section). A separate extrusion operation is performed to produce the bead filler, which is cut to length and attached to the rubber coated bead wire hoop, using the natural adhesion of the rubber. The two ends of the bead filler are joined using the natural adhesion. Finally, the sub- assembly is partially cross-linked in an oven to improve dimensional stability so that it will not be damaged by the forces applied during the tyre building operation. This cross- linking process is necessary because the sub-assembly is otherwise joined only by local adhesive forces. The overall process is labour intensive and hence quite expensive, since two extrusion processes are involved, together with an assembly step and transfer of the assembly to and from the oven. The present invention addresses the described problems and considerations and provides convenient apparatus and methods for manufacturing bead sub-assemblies in just two or three fabrication steps, involving injection moulding or compression moulding techniques. According to a first aspect of the invention there is provided apparatus for manufacturing a bead sub-assembly comprising an upper mould plate and a lower mould plate, at least one of said upper and lower mould plates being moveable so that the plates can cooperate to define a mould cavity substantially corresponding to the shape of the sub-assembly and delivery means for delivering a desired quantity of a mouldable composition to the mould cavity. In one embodiment the delivery means comprises a metering valve positionable above the lower mould plate and adapted to deliver a desired quantity of a substantially formed charge of the mouldable composition to said lower mould plate. A mould cavity may be defined by a mould stack, e.g. a pair of mould plates (one an upper plate, one a lower plate), which can be placed into a press prior to moulding. The apparatus may have a flow region through which the mouldable composition is delivered whilst the mould plates are in cooperation. The apparatus may comprise a flow member spaced from one of said mould plates so as to define at least a portion of the flow region. The apparatus may further comprise a reciprocable member adapted to reciprocate between a first position in which the reciprocable member defines a cavity connecting the flow region to the mould cavity and a second position in which the reciprocable member prevents the delivery of the mouldable composition to the mould cavity. The reciprocation of the reciprocable member may remove excess mouldable composition from the sub-assembly. The reciprocable member may be positioned around the periphery of the lower and upper mould plates. The mouldable composition may be a rubber compound. According to a second aspect of the invention there is provided a method for manufacturing a bead sub-assembly comprising the steps of : forming an annular bead wire structure from at least one bead wire; and moulding a mouldable composition around the annular bead wire structure in a mould cavity formed when a lower mould plate is in cooperation with an upper mould plate. The mouldable composition may be a rubber compound. The annular bead structure may be positioned in the lower mould plate, a substantially formed charge of the mouldable composition delivered to said lower mould plate and the lower and/or the upper mould plates moved so that said plates cooperate to form the mould cavity. This process is a compression moulding process. A metering valve may be positioned above the lower mould plate, the substantially formed charge being delivered from said metering valve. A mould stack may be used to define a mould cavity. An injection moulding process may be employed in which the mouldable composition is delivered through a flow region to the mould cavity whilst the mould plates are in cooperation. The delivery of the mouldable composition to the mould cavity may be controlled by reciprocating a reciprocable member between a first position in which the reciprocable member defines a cavity connecting the flow region to the mould cavity and a second position in which the reciprocable member prevents the delivery of the mouldable composition. The reciprocation of the reciprocable member may remove excess mouldable composition from the sub-assembly. Methods and apparatus in accordance with the invention will now be described with reference to the accompanying drawings, in which : Figure 1 shows cross-sectional views through a first embodiment: (a) depicting the delivery of a charge of mouldable composition to a lower mould plate, and (b) depicting the subsequent moulding closure process (compression moulding); Figure 2 shows cross-sectional views through a second embodiment: (a) depicting the injection of mouldable composition, and (b) depicting the moulded bead sub-assembly after separation of the mould plates; Figure 3 shows a cross-sectional view through a third embodiment: (a) depicting the injection of mouldable composition, (b) depicting the opening of the mould press after injection, and (c) depicting the mould stacks after removal thereof from the mould press; and Figure 4 shows a cross-sectional view through a fourth embodiment. The present invention comprises a method for manufacturing a bead sub- assembly comprising the steps of : forming an annular bead wire structure from at least one bead wire; and moulding a mouldable composition around the annular bead wire structure in a mould cavity formed when a lower mould plate cooperates with an upper mould plate. The annular bead wire structure can be formed from a bead wire or wires (typically a bundle of wires) by, for example, simply bending the wire or wires into the annular shape and securing the free end with a suitable tie. Thereafter, the sub-assembly is produced by moulding with a suitable mouldable composition, usually a rubber compound. The moulding may be performed in one or two steps - in other words, the entire manufacturing process may be reduced to a convenient two or three step process. The resultant sub-assembly is inherently robust, since the moulded rubber compound is of a homogeneous shape and can completely encapsulate the bead wire assembly. Figures la and lb show a portion of an apparatus for moulding the sub- assembly in two steps by compression moulding. The apparatus comprises an upper mould plate 10 and a lower mould plate 12, at least one of said upper 10 and lower 12 mould plates being moveable - in Figure lb, it is the upper mould plate 12 which is moveable - so that the plates 10,12 can cooperate to define a mould cavity 14 substantially corresponding to the shape of the sub-assembly; and delivery means (not shown) for delivering a desired quantity of a mouldable composition 18 into the mould cavity 14. It will be appreciated that Figure la shows a cross-section taken through less than one half of the mould plates 10,12. In order to produce an annular bead sub- assembly the mould cavity 14 defined by the plates 10,12 must be circular. In this two step moulding process the bead wire structure 20 is positioned in the lower mould plate, a substantially formed charge of mouldable composition 18 is delivered to the lower mould plate 12, and the upper mould plate 10 is then moved so that the plates 10,12 cooperate to form the mould cavity 14, thereby causing the mouldable composition to flow into the form of the mould cavity 14. The delivery means can comprise a metering valve positioned above the lower mould plate, the substantially formed charge being delivered from the metering valve. In the present context, the substantially formed charge is of a substantially annular form, so that the mouldable charge is delivered into the circular groove 14a of the lower mould plate 12 which corresponds to one half of the mound cavity 14. Preferred examples of suitable metering valves are described in International Publication No. WO 96/33390, which discloses metering valves comprising a valve body having a metering cavity, a material inlet to the metering cavity and an outlet for metered material, and comprising an operating member reciprocable relative to the valve body comprising a plug closure for the outlet and having a material delivery action by which the contents of the metering cavity are delivered from the outlet, the outlet having a reduced cross- section as compared to the metering cavity and the operating member being extendable out of the metering cavity away from the reduced cross-section outlet to open the outlet to deliver the contents of the metering cavity. International Publication No. WO 96/33390 describes embodiments of metering valves suitable for delivering substantially formed charges of viscous or viscoelastic fluids in various shapes, including an annular form. Such embodiments and variations thereon should be considered to be elements of the present application. Having delivered the substantially formed charge 18 to the lower mould plate 12, the metering valve is removed and the upper mould plate 10 moved so as to cooperate with the lower mould plate 10 (Figure lb). After moulding is completed, the formed bead sub-assembly is removed using ejection plate 22. It is understood that various alternative ejection methods, such as airstreams and ejection pins, might be employed in place of an ejection plate. Figures 2a and 2b depict apparatus for moulding the sub-assembly in a single step by injection moulding. The apparatus comprises, as before, an upper mould plate 24 and a lower mould plate 26, at least one of the upper and lower mould plates 24,26 being moveable - in Figure 2a it is the lower mould plate 26 which is moveable - so that the plates 24,26 can cooperate to define a mould cavity 28 substantially corresponding to the shape of the sub-assembly 30, and delivery means (not shown) for delivering a desired quantity of a mouldable composition to the mould cavity 28. In this one step embodiment, the mouldable composition is delivered through a flow region 32 to the mould cavity 28 whilst the mould plates 24,26 are in cooperation. Conveniently, the apparatus comprises a flow member 34 spaced from the upper mould plate 24 so as to define at least a portion of the flow region 32. In the embodiment shown in Figures 2a and 2b the flow member 34 is a circular plate separated from the upper mould plate 24 by a plate separator 36. The circular plate has an aperture 34a at its origin through which the mouldable composition is injected. This configuration is particularly convenient because of its constructional simplicity. Furthermore, a single "fill" or injection of mouldable composition at the origin of the circular plate 34 results in the mouldable composition flowing radially through the flow region 32. In this way the delivery of mouldable composition to the mould cavity 28 is homogeneous around the circumference of the annulus defined by the mould cavity 28. The apparatus further comprises a reciprocable member 36 adapted to reciprocate between a first position (shown in Figure 2a) in which the reciprocable member 36 defines a cavity 38 connecting the flow region 32 to the mould cavity 28 and a second position (not shown) in which the reciprocable member 36 prevents the delivery of the mouldable composition to the mould cavity. In Figure 2a the second position is attained by an upward movement of the reciprocable member 36. An additional benefit is that reciprocation of the reciprocable member 36 removes excess mouldable composition from the (forming) sub-assembly by virtue of its "trimming" or "cropping" action. The reciprocable member 36 is positioned around the periphery of the lower and upper mould plates 24,26 (and the flow member 34, when said flow member 34 is a circular plate). In Figure 2a, the reciprocable member 36 is in the form of a cylindrical collar. The fit of this collar to the mould plates 24,26 and flow member 34 is determined by the precise operational characteristics of the apparatus, as would be readily appreciated by those skilled in the art. Thus, it is desirable that the clearance between the reciprocable member 36 and the lower mould plate 26 and flow member 34 is sufficiently small to prevent mouldable composition escaping from the apparatus. The precise tolerances will depend upon the nature of the mouldable composition and the backing pressure used to inject the mouldable composition into the apparatus. In use, the bead wire structure 37 is positioned in the circular groove 28a of the lower mould plate 26 which corresponds to one half of the mould cavity 28. The mould plates 24,26 are moved into mutual cooperation and clamped in place. The mouldable composition is injected, using known and conventional means, through an aperture 34a in the flow member 34. The mouldable composition then flows radially through the flow region 32 and then through the (substantially cylindrical) cavity 38 defined by the reciprocable member 36, entering the mould cavity 28 via a small circumferential aperture 28b. The reciprocable member 36 is then moved upwards to a second position in which the delivery of mouldable composition to the mould cavity 28 is prevented, and excess mouldable composition is "cropped" from the circumferential aperture 28b. After the moulding process is completed, the mould plates 24,26 are undamped and the moulded bead sub-assembly 30 is removed. Figure 3 shows various stages in the moulding of bead sub-assembly using a modified version of the apparatus of Figure 2. The principle difference between the apparatus of Figure 2 and the apparatus of Figure 3 is that the latter utilises three mould stacks 40,42,44 to define three mould cavities. Each mould stack can be considered to comprise an upper mould plate (e.g. 40a) and a lower mould plate (e.g. 40b). Otherwise, the apparatus of Figure 3 shows many of the features already described in relation to Figure 2: identical numerals are used to denote such shared features. Note that the flow member 39 is a circular plate which is now separated from a portion of the press 45, rather than from the upper mould plate. In operation, bead wire structures are placed into the mould cavities. The mould stacks 40,42,44 are placed in the apparatus in the configuration shown in Figure 3 a by traversing the mould stacks 40,42,44 into a press (shown generally at 46) and clamping the press 46. The mouldable composition is then delivered to the mould cavities by delivery means (not shown) such as a screw or a ram injection unit. Next, the reciprocable member 36 prevents the delivery of further mouldable composition to the mould cavities and crops excess mouldable composition. The reciprocal member 36 is connected to press columns 48,50 by guide bushes 52,54. Next, the press 46 is opened and the mould stacks 40,42,44 removed from the press 46. Finally, the completed bead sub-assemblies are removed from the mould stacks 40,42,44. The entire injection cycle (traversal of mould stacks into press, clamping, injection of mouldable composition, cropping and opening of press) can be performed in ca. 19s. Figure 4 shows a variation on the apparatus of Figure 3: once again, identical numerals are used to denote identical features. The apparatus of Figure 4 has an upper portion (in this instance the flow member 34) which is of greater diameter than the mould stacks 40,42,44 and a lower portion 58 on which the mould stacks 40,42,44 are placed. Furthermore, the reciprocable member 36 has a detachable lower part 36a which can be changed for different lower parts of different internal diameter. In this way, the apparatus can be adapted to accommodate mould stacks of different sizes. It will be apparent to those skilled in the art that numerous modifications to the apparatus and methods described might be performed whilst retaining the capability to injection mould in a single step. For example, the circular plate flow member might be separated from the lower mould plate 26 rather than the upper mould plate 24, the fill being performed from below, and the upper mould plate being movable. In the above described embodiment the mould plates are positioned horizontally - giving rise to the "upper" and "lower" nomenclature. In principle, the mould plates might be positioned vertically. Another modification is to employ delivery means which injects mouldable composition at the periphery of the mould plates, rather than at their centres. In this instance a flow member or members would be positioned around the periphery of the mould plates. It may, in this instance, be desirable to inject mouldable composition at several points around the periphery, in order to improve the homogeneity of the mouldable composition in the mould cavity. The bead sub-assemblies produced by the present invention are robust, due to the substantially homogeneous bead filler configuration. Furthermore, the process is relatively inexpensive since relatively uncomplicated apparatus can be used to manufacture the bead sub-assemblies, and since labour costs are reduced. Indeed, the process can be made fully automatic by employing robotic loading and unloading of the bead wire structures/moulded bead sub-assemblies.

Claims: CLAIMS 1. Apparatus for manufacturing a bead sub-assembly comprising an upper mould plate and a lower mould plate, at least one of said upper and lower mould plates being moveable so that the plates can cooperate to define a mould cavity substantially corresponding to the shape of the sub-assembly and delivery means for delivering a desired quantity of a mouldable composition to the mould cavity. 2. Apparatus according to claim 1 in which the delivery means comprises a metering valve positionable above the lower mould plate and adapted to deliver a desired quantity of a substantially formed charge of the mouldable composition to said lower mould plate. 3. Apparatus according to claim 1 in which a mould cavity is defined by a mould stack. 4. Apparatus according to claim 1 or claim 3 having a flow region through which the mouldable composition is delivered whilst the mould plates are in cooperation. 5. Apparatus according to claim 4 comprising at least one flow member spaced from one of said mould plates so as to define at least a portion of the flow region. 6. Apparatus according to claim 4 or claim 5 further comprising a reciprocable member adapted to reciprocate between a first position in which the reciprocable member defines a cavity connecting the flow region to the mould cavity, and a second position in which the reciprocable member prevents the delivery of the mouldable composition to the mould cavity. 7. Apparatus according to claim 6 in which reciprocation of the reciprocable member removes excess mouldable composition from the sub-assembly. 8. Apparatus according to claim 6 or claim 7 in which the reciprocable member is positioned around the periphery of the lower and upper mould plates. 9. Apparatus according to any previous claim in which the mouldable composition is a rubber compound. 10. A method for manufacturing a bead sub-assembly comprising the steps of: forming an annular bead wire structure from at least one bead wire; and moulding a mouldable composition around the annular bead wire structure in a mould cavity formed when a lower mould plate is in cooperation with an upper mould plate. 11. A method according to claim 10 in which the mouldable composition is a rubber compound. 12. A method according to claim 10 or claim 11 in which the annular bead structure is positioned in the lower mould plate, a substantially formed charge of the mouldable composition is delivered to said lower mould plate and the lower and/or the upper mould plates are moved so that said plates cooperate to form the mould cavity. 13. A method according to claim 12 in which a metering valve is positioned above the lower mould plate, the substantially formed charge being delivered from said metering valve. 14. A method according to claim 10 or claim 11 in which a mould stack is used to define a mould cavity. 15. A method according to claim 10, claim 11 or claim 14 in which the mouldable composition is delivered through a flow region to the mould cavity whilst the mould plates are in cooperation. 16. A method according to claim 15 in which the delivery of the mouldable composition to the mould cavity is controlled by reciprocating a reciprocable member between a first position in which the reciprocable member defines a cavity connecting the flow region to the mould cavity, and a second position in which the reciprocable member prevents the delivery of the mouldable composition. 17. A method according to claim 16 in which the reciprocation of the reciprocable member removes excess mouldable composition from the sub-assembly.

Inventors: FREAKLEY PHILIP KENNETH, FREAKLEY, PHILIP, KENNETH
Applicants: FREAKLEY PHILIP KENNETH, UNIV LOUGHBOROUGH, FREAKLEY, PHILIP, KENNETH, LOUGHBOROUGH UNIVERSITY INNOVATIONS LIMITED
Application year: 1998
Main classification: B29D30
IPC codes: B29C45, B29D30