GB2157224A - Device for vulcanization of automobile tyres - Google Patents

Abstract

A device for vulcanization of automobile tyres comprises a mould (1, 2) for accommodating a tyre (4) to be vulcanized, a UHF energy emitter (10) provided with a waveguide and adapted for introduction into the interior of the tyre and rotation therein, and a membrane for pressure-moulding. The waveguide is detachable and its rotatable portion carrying the UHF energy emitter is capable of linear displacement perpendicularly to the longitudinal plane of the tyre, the membrane being secured on this movable portion of the waveguide. <IMAGE>

Description

SPECIFICATION Device for vulcanization of automobile tyres This invention relates to devices for vulcanization of tyres and can find application for fabricating pneumatic tyres in a wide range of types and sizes, for example, automobile, farm machine and aircraft tyres.

It is known that vulcanization is the most labour and power consuming process in the art of tyre production. Because rubber as the main ingredient in the tyre structure features a rather low thermal conductivity, the normally employed in vulcanizatiion surface heat transfer between the tyre, heated metal mould and rubber membrane results in extended duration of the vulcanization process and low thermal efficiency thereof.

New capabilities for invigorating the vulcanization process are offered by heating the entire bulk of the tyre being vulcanized through the use of microwave or UHF energy. In this case the rate of heating is largely determined by the characteristics of the electromagnetic field regardless of the dimensions of the tyre being vulcanized, whereby the power efficiency of the process is substantially improved.

The invention is directed toward the provision of a device for vulcanization of automobile tyres which comprises a mould for accommodating a tyre to be vulcanized, a UHF energyy emitter provided with a waveguide and adapted for introduction into the interior of the tyre to rotate therein, and a membrane for pressure-moulding, in which device, according to the invention, the waveguide is detachable and its rotatable portion carrying the UHF energy emitter is capable of linear displacement perpendicularly to the longitudinal plane of the tyre, the membrane being secured on this movable portion of the waveguide.

The advantages offered by the proposed device reside in that the detachable arrangement of the waveguide and its attachment on the movable portion of the membrane assures mechanized and easy removal and placement of the tyre while maintaining a steady orientation point, as well as provides for the arrangement of the UHF energy emitter inside the tyre to promote efficient heating of the tyre being vulcanized.

Preferably, the emitter is pivotably secured for articlation in the plane of the tyre; it is further advisable that the emitter be spring-biased to facilitate its withdrawal from the plane of the waveguide.

This provides for automation of the vulcanization process and makees it possible to arrange the emitter in close proximity to the inner surface of the membrane.

In order to avoid a possible electric breakdown which may lead to a loss in the intensity of the electric field and consequently in reduced amount of UHF energy applied, the waveguide may preferably have the form of a hollow cylinder.

A more thorough heating of the bulk of the tyre being vulcanized may be attained by making use of an additional insert interposable between the tyre and the mould, the total thickness of the insert and tyre at any point of their cross-section being preferably invariable.

The invention will now be described in greater detail with reference to various specific embodiments thereof taken in conjunction with the accompanying drawings, in which: Figure 1 is a sectional view of a device for vulcanization of tyres using a UHF energy source in its initial position with half-moulds drawn apart; Figure 2 is a view of the device according to Figure 1 during vulcanization with the half-moulds brought together; Figure 3shows the device in a position for removing the vulcanized tyre from the mold; Figure 4 is a modified form of the device according to the invention provided with hollow waveguides; and Figure 5 is an alternative embodiment of the device according to the invention generally similar to that shown in Figure 4 but provided with additional emifers and dielectric inserts.

Referring now to Figures 1 and 2, there is shown a device for the vulcanization of automobile tyres in its initial position. The device comprises a vulcanizing mould formed by two half-moulds 1 and 2. These vulcanizing moulds, as well as other types of moulds, such as collapsible moulds, are well known to those experienced in the art. They are normally fashioned as metal containers which include side plates and shape forming metal inserts 3. For shape forming and pressure-moulding of a tyre 4 use is made of a rubber membrane 5 secured in an upper clamping disk 6 and in a lower bead ring 7. A housing 8 unitized with the lower bead ring 7 and being generally a presure-sealed cavity to accommodate parts and components of the device assumes a bottom position prior to vulcanization.For applying a UHF energy to theinterior of the tyre 4 a detachable waveguide comprised of several parts and an emitter 10 are used, the waveguide being mounted on a rod member 9. In the case under consideration, the waveguide is made up of three interlinkable parts. A rotatable part 11 of the waveguide bears on a casing 12 that embraces this part 11 and is connected to a drive motor 13 through a gear coupling 14 secured on the rotatable part 11 of the waveguide and a pinion 15 engageable with this gear coupling 14, the pinion being arranged on a spline shaft secured to the bottom wall of the housing 8. The rotatable part 11 can be displaced upwards and downwards substantially vertically by moving the rod member 9 to which it is keyed.A middle part 18 of the waveguide can be moved vertically and is attached on the housing 8 and provided with a connector assembly 19 disposed outside the housing 8 and serving to connect to a lower stationary part 20 of the waveguide for transmitting UHF energy from a UHF generator 21. In order to protect the generator 21 from high pressures of a pressing agent, a low loss dielectric partition 22 is provided in the middle portion 18 of the waveguide.

The emitter 10 is pivotably mounted on the rotatable part 11 of the waveguide; it is spring biased in the radial direction by a coil spring 23 to be forced to the waveguide for minimizing the outer diameter of the membrane 5 to facilitate placing of the uncured tyre 4. The emitter 10 is of any known suitable design, such as in the form of a rod aerial, and may have dimensions approximating the torusshaped inner surface of the tyre 4. The above pivotal arrangement and the spring are such that during rotation the emitter 10 could assume the required position under the action of a centri-fugal force.

The device embodying the present invention operates as follows.

In the initial position seen best in Figure 1 the pressure disk 6 is at the top and the membrane 5 is stretched. The uncured tyre 4 is placed on the lower half-mould 1. After fixing the bead of the uncured tyre 4 on the lower bead ring 7, a gaseous agent, such as air under a pressure of between 0.05 and 0.15 MPa (0.5 to 1.5 kglcm2) is fed to the interior of the membrane 5. The half-moulds 1 and 2 are drawn together for the rod member 9 and consequently the waveguide and the upper clamping disk 6 to move downwards. To eliminate damage during engagement of the gear coupling 14 with the pinion 15 the latter is spring-biased by a spring 24 seated on a spline shaft 25. For fast orientation of the teth of the gear and pinion, bevels are made thereon.When the half-moulds are completely drawn together, pressure inside the membrane is increased to the one that conforms to the preselected operating conditions, i.e. to between 2.0 and 3.0 MPa (20 to 30 kg1cm2). The electric motor 13 is then energized for the UHF energy emitter 10 to enter into the interior of the membrane 5 under athe action of a centrifugal force arising during rotation at a constant speed and exceeding the force produced by the coil spring 23.

The source 21 of UHF energy is there-after energised to heat and vulcanize the tyre 4 (Figure 2).

Subsequent to vulcanization (Figure 3) the source 21 of UHF energy and the drive motor 13 are deenergised for the emitter 10 to return to its initial position under the action of the coil spring 23.

During opening of the mould the tyre 4 is released from the shape forming inserts 3 and the upper half-mould 2. The waveguide is moved upwards axially together with the disk 6 to again stretch the membrane 5. Then the ring 7 is raised to free the tyre 4 from the lower half-mould 1. Thereafter, the tyre is removed from the membrane in any known suitable manner, whereupon all the parts and elements of the device assume their initial position.

In view of the foregoing, it is evident that the device provides for easy placement and removal of a tyre from the UHF vulcanizer. The UHF energy emitter may be placed as close to the inner surface of the membrane as necessary.

The construction of the vu Icanizer described with reference to Figures 1 to3 is preferable for use in or modification of the known vulcanizing apparatus, since such modification would require the minimum of effort. However, because the wave guide cooperates with the rod member throughout a considerable portion of its length, an electric break-down may occur between the inner and outer waveguide of UHF energy. This disadvantage is obviated in an alternative vulcanizer construction illustrated in Figure 4.

The device shown in Figure 4 is generally similar to the one described with reference to Figures 1 to 3 and therefore need not be described in detail.

However, in order to preclude electric break-downs during transmission of UHF energy, the waveguide may have the form of a hollow detachable cylinder.

An upper rotatable part 26 of this cylinder is connected to a middle non-rotatable part 27 capable of vertical displacement by means of a gear coupling 28 and rolling bearings 29. The upper portion of the rotatable part 26 of the waveguide is connected to the upper clamping disk 6 of the membrane 5 through rolling bearings 30. Annular projections of the lower end of the rotatable part 26 of the waveguide disposed between annular projections of the non-rotatable part 27 define an annular labyrinth seal preventing the penetration of UHF energy to the inside of the bearings 29, which penetration may otherwise cause sparking and damage of these bearings. Further, radial labyrinth seals 31 are provided to protect the bearings 30 and the rotating drive of the waveguide inside the housing 8 from being acted upon by UHF energy.

The modified form of the device according to the invention, although featuring a number of advantages over the prior art constructions, may sometimes fail to provide uniform heating, for example, when the tyre structure involves the use of a metal cord. Therefore, in a number of situations it is advisable to assure additional heating on the outside of the tyre being vulcanized without resorting to applying heat to the outer surface of the mould, for which purpose another alternative modification of the device will be described with reference to Figure 5.

The modification of the device shown in Figure 5 is generally similar to those described previously.

However, in order to dispense with outside heating of the mould, it contains an insert 32 of a dielectric material, such as glass fiber, capable of dielectric permittivity, like that exibited by the rubber parts of the tyre being vulcanized. In this case at the boundary between the rubber and dielectric no reflection of UHF energy occurs, which energy may therefore spread to the dielectric causing losses therein, heating of the shape forming surface of the mould and preventing the removal of heat from the tyre 4 being vulcanized. The insert 32 has a variable thickness throughout its length, the total thickness of the insert and tyre at each cross-sectional point thereof being substantially invariable. When vulcanizing tyres with metal cord reinforcements or breakers, the rotatable part 26 of the waveguide preferably accommodates additional emitters 33 and 34 facing the ends of the dielectric inserts 32 to function together with these dielectric inserts 32 as waveguide transmission lines conducting UHF energy for exposing the outer surface of the tyre to UHF radiation. In this manner unifrom UHF energy heating of the tyre is carried out to vulcanize metal cord reinforced tyres.

Claims (7)

1. A device for vulcanization of automobile tyres comprising a vulcanizing mould to accommodate a tyre to be vulcanized, a UHF energy emitter provided with a waveguide and adapted for introduction to the interior of the tyre to be vulcanized for rotation therein, and a membrane for pressure-moulding, said waveguide being detachable and its rotatable portion carrying the UHF energy emitter is capable of linear displacement perpendicularly to the longitudinal plane of the tyre, the membrane being secured on this movable portion of the waveguide.

2. A device as claimed in claim 1 wherein the UHF energy emither is arranged pivotably for articu lation in the plane of the tyre underthe action of a centrifugal force produced by rotation of the wave guide and is spring-biased for the withdrawal from the plane of the waveguide.

3. A device as claimed in claim 1 wherein the waveguide has the form of a hollow detachable cylinder, at the point of detachment the connection having the form of a labyrinth seal.

4. A device as claimed in claim 1 having a rod member for displacing the membrane wherein the waveguide is arranged coaxially on said rod, the membrane being secured by one end on the rod member and by the other end on the waveguide.

5. A device as claimed in any of the preceding claims 1 to 4wherein the waveguide is capable of rotating at a constant speed.

6. A device as claimed in claim 1 wherein an insert is provided inside the mould but outside the tyre, the insert having a variable thickness through out its length for the total thickness of the insert and tyre at every point of cross-section to be substantial ly invariable.

7. A device for vulcanization of automobile tyres substantially as described in the description and illustrated in the accompanying drawings.