ZACSEK, Gábor (Veder u. 2, Budapest, H-1035, HU)
GYARMATI, József (Barcsay út 20, Budapest, H-1181, HU)
ZACSEK, Gábor (Veder u. 2, Budapest, H-1035, HU)
| CLAIMS 1. Tyre vulcanizing mould (1) having an inner tread forming surface (3) provided by groove forming ribs (4) emerging from the surface (3), and a sharp corner (6) is formed at least at the junction of the tread surface (3) and a rib (4), and the mould (1 ) is provided by means for removing gas from the sharp corner (6) and the surface (3), characterized in that said means for removing gas from the sharp corner (6) and the surface (3) comprises an air pocket (7) formed in the surface (8) of the groove forming ribs (4), near said corner (6). 2. Tyre vulcanizing mould (1) according to claim 1., characterized in that said air pocket (7) comprises a cavity extending parallelly to the line of the corner (6) provided at the junction of the surface (3) and the tread grooves forming ribs (4) and having a depth sequentially decreasing toward the corner (6). 3. Tyre vulcanizing mould (1 ) according to claim 1, characterized in that said air pocket (7) comprises a cavity extending parallelly to the line of the corner (6) provided at the junction of the surface (3) and the groove forming ribs (4) and having a depth gradually decreasing toward the corner (6). 4. Tyre vulcanizing mould (1) according to claim 1., characterized in that said air pocket (7) comprises a cavity extending parallelly to the line of the corner (6) provided at the junction of the surface (3) and the groove forming ribs (4) and provided by an air channel (4a) directed to the corner (6) and machined into the ribs (4) defining tread grooves. 5. Tyre vulcanizing mould (1 ) according to claim 1., characterized in that said air pocket (7) comprises a cavity arranged near the corner (6) provided at the junction of the surface (3) and the groove forming ribs (4) and provided by an air channel (4b) directed to the corner (6) and machined into the ribs (4) defining tread grooves. 6. Method for removing gas from the surface (3) of a tyre vulcanizing mould (1 ) and diverting the gas accumulated between the tread surface (5) of a green tyre (2) and the tread forming surface (3) of the mould (1) at the line of a corner (6) formed by junction of tread grooves defining ribs (4) emerging from the tread surface (3) of the mould (1) and of said surface (3), while forcing the tread surface (5) of a green tyre toward the tread forming surface (3) of the of the mould (1), characterized by forming said air pocket (7) in the surface (8) of the rib (4) adjacent the corner (6) and diverting the gas accumulated between the tread surface (5) of a green tyre (2) and the tread forming surface (3) of the mould (1) from the tread forming surface (3) and from the corner (6) into air pockets (7) formed in the surface (8) of a tread groove forming rib (4) near the corner (6), while forcing the surface (5) of the green tyre (2) toward the tread forming surface (3) of the mould (1). 7. Method according to claim 6., characterized by forming said air pocket (7) as a cavity extending parallelly to the line of the corner (6) provided at the junction of the surface (3) and the tread groove forming ribs (4) and having a depth continuously decreasing toward the corner (6). 8. Method according to claim 6., characterized by forming said air pocket (7) as a cavity extending parallelly to the line of the comer (6) provided at the junction of the surface (3) and the groove forming ribs (4) and having a depth gradually decreasing toward the corner (6). 9. Method according to claim 6., characterized by forming said air pocket (7) as a cavity extending parallelly to the line of the corner (6) provided at the junction of the surface (3) and the groove forming ribs (4) and providing said cavity (6) by an air channel (4a) directed to the corner (6) and machined into the ribs (4) defining tread grooves. 10. Method according to claim 6., characterized by forming said air pocket (7) as a cavity arranged near the corner (6) provided at the junction of the surface (3) and the groove forming ribs (4) and providing said cavity (6) by an air channel (4b) directed to the corner (6) and machined into the ribs (4) defining tread grooves. |
MOULD
The invention relates to a tyre vulcanizing mould having an inner tread forming surface provided by ribs emerging from the surface and defining tread grooves therebetween, and a sharp corner is formed at the junction of the tread forming surface and the rib, and the mould is provided by means for removing gas from the sharp corner and the surface, and further relates to a method for removing gas from the surface of tyre vulcanizing mould and diverting the gas accumulated at the line of a corner formed by junction of ribs emerging from the tread surface of the mould and of said tread forming surface, while forcing the tread surface of a green tyre toward the tread forming surface of the of the mould.
Vulcanization of a green tyre built on a tyre building machine is performed in a tyre vulcanizing mould having a mould cavity, which must be filled by the green tyre to the full to obtain a defect free product. When some air or other type of gas remains between the surface of the mould cavity and the surface of the tyre a gas bubble/deformity occurs resulting in the tyre to be possibly discarded. The term "deformity" in this description means a difference occurring between the surface of the mould and that of the tyre, where the surface of finished tyre does not flush the surface of the mould perfectly. For venting gases from the mould cavity air escapes with slit vent pin or cartridges therein can be applied on the inner surface of the vulcanizing mould, which lead the gases into the environment through the wall of the mould. Vulcanizing moulds formed by segments are designed in such a way that the small elements of the surface bossing of the tyre are fitted and fixed to each other. Air can escape through the butt joint having a size between 0,02 and 0,03 mm. Rubber material of the tyre generally flows in the gap of the joints resulted in an aesthetical failure.
Publication document DE 196 28 166 A1 discloses a vent pin having a tubular body one end of which is closed by a surface provided with air escape holes of 0,12 mm in diameter. The aim of these holes is to escape displaced gases through these holes during filling the cavity of the mould by the material of the green tyre. The principal disadvantage of such solutions is that the rubber flowing in the air vents will presents a hairy appearance of the tread surface of the tyre, detrimentally affecting the exterior of the product. A further significant disadvantage is that the rubber hair torn in the vent hole clogs the hole, consequently, its regular cleaning is to be performed detrimentally influencing the productivity and raising the production costs as well.
This drawback is intended to overcome by the solution disclosed in the publication document JP 2006-150602A applying a closing plug arranged in the air vent holes. Around this closing plug the gas flows into the vent hole until the rubber expanding in the mould cavity pushes in the plug closing the hole in its full cross sectional area. The disadvantage of this solution is that after closing of the hole some gas bubble may as well remain in the mould cavity. Its further disadvantage is that an accidental influx of the rubber into the hole causes the breakdown of the plug resulting in an aesthetical failure and its cleaning or changing is inevitable, moreover, its build-up is relatively complex as well, hence its mounting is cumbersome and expensive. Patent document JP 57-128532 disclose an air escape vent having an insert made from a particulate material, e.g. granulated polyethylene, or sintered metal particles. Gases escape through the gaps between the particles. This solution counteracts both forming of larger rubber hairs and clogging the vent. A similar solution is known from the patent document DE 180 00 81. There is a common drawback with solutions described above, namely, numberless vent holes must be formed in the wall of the mould cavity significantly raising the production costs and time as well.
Therefore, the object of the present invention is to provide a vulcanizing method and vulcanizing mould obviating the occurrence of gas bubbles/deformities during vulcanizing tyres, so that the tread surface of the tyre does not contain any surface deformation caused by air escaping process and eliminating the drawbacks of the prior art solutions at the same time, so that diverting the air from the mould cavity without having rubber hairs on the surface of the end product, and without diverting the gases being present in the mould cavity into the environment through the wall of the mould, hence sparing time and costs for creating several vent holes, consequently, our aim is to achieve an air vent process enabling good quality tyre production even without air escape holes on the tread surface.
These objects can be achieved by providing a tyre vulcanizing mould according to the invention having an inner tread surface provided by groove forming ribs emerging from the surface , and a sharp corner is formed at least at the junction of the tread surface and the rib , and the mould is provided by means for removing gas from the sharp corner and the surface and said means for removing gas from the sharp corner and the surface comprises an air pocket formed in the surface of the groove forming ribs , near said corner .
Said air pocket preferably comprises a cavity extending parallelly to the line of the corner provided at the junction of the surface and the tread grooves forming ribs and having a depth sequentially decreasing toward the corner.
Said air pocket advantageously comprises -a cavity extending parallelly to the line of the corner provided at the junction of the surface and the groove forming ribs and having a depth gradually decreasing toward the corner.
Said air pocket preferred embodiment comprises a cavity extending parallelly to the line of the corner provided at the junction of the surface and the groove forming ribs and provided by an air channel directed to the corner and machined into the ribs defining tread grooves.
Said air pocket preferably comprises a cavity arranged near the corner provided at the junction of the surface and the groove forming ribs and provided by an air channel directed to the corner and machined into the ribs defining tread grooves.
A method for removing gas from the surface of a tyre vulcanizing mould is also provided, comprising the steps of: diverting the gas accumulated between the tread surface of a green tyre and the surface of the mould at the line of a corner formed by junction of tread grooves defining ribs emerging from the tread surface of the mould and of said surface , while forcing the tread surface of a green tyre toward the tread forming surface of the of the mould and forming said air pocket in the surface of the rib adjacent the corner and diverting the gas accumulated between the tread surface of a green tyre and the tread forming surface of the mould from the tread forming surface and from the corner into air pockets formed in the surface of a tread groove forming rib near the corner , while forcing the surface of the green tyre toward the tread forming surface of the mould. The method according to the invention can also comprise the step of forming said air pocket as a cavity extending parallelly to the line of the corner provided at the junction of the surface and the tread groove forming ribs and having a depth continuously decreasing toward the corner.
Forming said air pocket as a cavity extending parallelly to the line of the corner provided at the junction of the surface and the groove forming ribs and having a depth gradually decreasing toward the corner.
Forming said air pocket as a cavity extending parallelly to the line of the corner provided at the junction of the surface and the groove forming ribs and providing said cavity by an air channel directed to the corner and machined into the ribs defining tread grooves.
Forming said air pocket as a cavity arranged near the corner provided at the junction of the surface and the groove forming ribs and providing said cavity by an air channel directed to the corner and machined into the ribs defining tread grooves.
The invention will further be described in details by advantageous embodiments of the invention shown in the drawings attached. In the drawings:
Figure 1. is a cross sectional view of a fragment of the tyre production mould with air pockets according to the present invention,
Figure 2a. shows the expansion process of the green tyre arranged in the mould during forming, Figure 2b. shows the filling in of the corner,
Figure 3.-4. shows further embodiments of air pockets showed in negative form created in the tyre, Figure 5. a cross section area of the tyre produced by the vulcanizing mould according to the invention.
In Figure 1. a cross section of a fragment of the tyre vulcanizing mould with air pockets according to the present invention is shown. The tyre vulcanizing mould 1 has inner tread forming surface 3 provided by ribs 4 emerging from the surface 3 and defining tread grooves or slots therebetween. A sharp corner 6 is formed at the junction of the tread surface 3 and the rib 4. In contrast of the prior art solutions, the mould 1 is provided by air pockets 7 for removing gas from the sharp corner 6 and the tread surface 3, said air pockets 7 are machined into the surface of the ribs 4 defining tread slots, near the sharp corners 6.
Figure 2a shows that the green tyre 2 arranged in the mould 1 expands toward the inner tread surface 3 of the mould 1 and a surface 8 of the rib 4, as depicted by arrows T in the figure. Since the tread surface 3 (being e.g. a continuous toroidal or annular surface) is not even, that is it is provided with ribs 4 having different directions according to the tread slots of the tyre 2 being produced, there are sharp corners 6 at the junctions of the tread surface 3 and ribs 4, near which the air filling the space between the tread surface 3 of the mould 1 and tread surface 5 of the tyre 2 is trapped, and this prevents the rubber from filling the sharp corners 6 if gas bleeding is absent. As it was described above by the solutions according to the prior art the gas escapes through gas vent holes provided in the tread forming surface 3, but the material of the tyre 2 may enter into these vents resulting in possible clogging of the vents. Figure 2a shows how the material of the tyre 2 approaches the corners 6 during filling in process. Figure 2b depicts how perfectly the material of the tyre 2 fills in a corner 6, while pushing the gas into the air pocket 7. With a preferred embodiment of the tyre vulcanizing mould 1 according to the invention shown in Figure 1 - 2b the air pocket 7 comprises a cavity extending parallelly to the line of the corner 6 provided at the junction of the tread forming surface 3 and the tread forming ribs 4 and perpendicularly to the surface of the drawing, having a depth sequentially decreasing toward the corner 6. In a further preferred embodiment the air pocket 7 comprises a cavity extending parallelly to the line of the corner 6 provided at the junction of the tread forming surface 3 and the tread forming ribs 4, having a depth gradually decreasing toward the corner 6. Air pocket 7 may be formed as a cavity extending parallelly to the line of the corner 6 provided at the junction of the tread forming surface 3 and the tread forming ribs 4, and provided by an air channel 4a directed to the corner 6 and machined into the ribs 4 defining tread slots (Fig. 3 - 4). In a further preferred embodiment the air pocket 7 comprises a cavity formed near the corner 6 at the junction of the tread forming surface 3 and the tread forming ribs 4, and provided by an air channel 4b directed to the corner 6 and machined into the ribs 4 (Fig. 3)
Air pockets 7 do not remove the gases from the mould 1 , but forming a cavity for the gas in the mould 1 enable the gas to accumulate in the cavity instead of trapping at the sharp corners 6. Since the air pockets 7 are placed in the surface 8 of the ribs 4, the gas progressively expelling from the tread surface 3 accumulates in the air pockets 7 arranged near the corners 6, rather than in the corners 6. The material of the tyre 2 advances into the pockets 7 until the pressure of the gas accumulated in the given pocket 7 becomes equal to the surface pressure exerting by the material of the tyre 2. Then the shape of the tyre 2 can be stabilized in the area of the pocket 7. This practically means that the local shape of the tyre 2 forms a beading 9 being in undercut position in relation to the surface 8 of the rib 4. But this beading 9 does not cause any deformation in the tread surface 5 of tyre 2 filling the mould 1 , since a tread slot 10 of the tyre 2 defined by a rib 4 projects from a surface being substantially perpendicular to the tread surface 5, and thus it does not affect the rolling features of the tread surface 5.
The shape of each pocket 7 can be dimensioned by taking into account the alteration (decreasing) of the corner filling radius of the tyre 2 filling the mould 1 , attempting to allow gases to be continuously removed from the sharp corners 6 into the pockets 7 arranged near the corner 6 during the whole of the filling process of the corner 6. With a preferred embodiment of the pocket 7 depicted in Fig. 1 , the depth of the pocket 7 continuously decreases toward the corner 6. The total volume of the pockets 7 can be determined by taking into account the fact, that the gas initially having environmental pressure, temperature and a given volume at the start of moulding and remained in the mould 1 between the tyre 2 and the tread surface 3 of the mould 1 , tends to be warmed and pressurized during moulding. According to the general gas law (expressed as p*V = nRT), the total volume of the pockets 7 to be created can be determined approximately as follows:
V = nRT/p,
where p is pressure of the gas at the end of the moulding process, which is at least equal to the internal pressure of the material of the tyre 2 at the end of moulding, R is the universal gas constant (8,314 J/mol.K), T is the temperature of the gas at the end of moulding as experimentally determined, and V is the volume of the gas at the end of moulding, that is equal to the total volume of the pockets 7, approximately. The adequate size of each pocket 7 may be adjusted experimentally, by virtue of their positions and the volume V as calculated.
Consequently, removing gas from the tread surface 3 of tyre 2 vulcanizing mould 1 and diverting the gas from the line of a corner 6 formed by junction of ribs 4 emerging from the tread surface 3 of the mould 1 and of said surface 3, accumulated between the tread surface 5 of the tyre 2 and the tread surface 3 of the mould 1 , is performed according to the present invention in such a way that, while forcing the tread surface 5 of a green tyre 2 toward the tread forming surface 3 of the of the mould 1 , diverting the accumulated gas from the tread forming surface 3 and from the corner 6 into an air pocket machined into the surface of a tread slot forming rib 4 near the corner 6, rather than preparing air vent holes in the tread forming surface 3 of the mould 1 and expelling the gas out through these vents. Thus, the rubber hair forming in the tread surface 5 and frequent and expensive cleaning of the mould 1 resulting in a loss of production can be omitted as well.
Air pockets 7 are shaped advantageously as a cavity extending parallelly to the line of the corner 6 formed at the junction of the tread forming surface 3 and the ribs 4 forming tread slots, the depth of which decreases continuously toward the corner 6. However, it is possible to form the pockets 7 as a cavity extending parallelly to the line of the corner 6 formed at the junction of the tread forming surface 3 and the ribs 4 forming tread slots, the depth of which decreases gradually toward the corner 6. Further, the pockets 7 can be formed as a cavity extending parallelly to the line of the corner 6, so that it is provided by an air channel 4a machined into the tread slot forming rib 4, through which the gas can be diverted into the pocket 7 from the corner 6. When the pocket 7 is formed as a cavity arranged near the corner 6, it may be provided by an air channel 4b machined into the tread slot forming rib 4 and extending toward the corner 6, through which the gas can be diverted into the pocket 7 from the corner 6.
Fig. 3 and 4 show some further exemplary embodiments of the vulcanizing mould 1 according to the invention provided by air pockets 7. It is to be noted, that depending on the requirements occurring by the geometry of the mould 1 many different variations of pocket 7 can be formed in the same mould 1.
In Fig. 5 a cross section area of the tyre produced by the vulcanizing mould according to the invention is shown. As it can be seen clearly in this figure, the material of the tyre 2 intruding into the pockets 7 forms headings 9 on the side surface of the tread grooves 10 of the tyre 2 shaped by the ribs 4, however, these headings 9 are not in connection with the tread surface 5, so that they do not affect the running properties of the tyre 2.
The main advantage of the vulcanizing mould 1 according to the present invention over prior art solutions is that it does not contain any air vent that can get clogged or must be changed and can cause aesthetical problems, therefore, the mould need not be removed from the production line to repair, consequently no time losses and the surface of the tyre 2 is nice and uniform, and the proper forming of the pockets 7, beside diverting the gas, may improve the sliding-gripping properties of the tyre 2, too, resulting in a better road-holding capacity e.g. in rainy circumstances. Further, by the method according to the invention, the occurrence of gas bubbles/deformities during vulcanizing tyres can be obviated, so that the tread surface of the tyre does not contain any surface deformation caused by air escaping process and eliminating the drawbacks of the prior art solutions at the same time, so that diverting the air from the mould cavity without having rubber hairs on the surface of the end product, and without diverting the gases being present in the mould cavity into the environment through the wall of the mould, hence sparing time and costs for creating several vent holes, consequently, achieving an air vent process enabling good quality tyre production even without air escape holes on the tread surface.
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