Vulcanization mold and method for using such a vulcanization mold

Abstract

Vulcanization mold for a vehicle tire provided with a profiled tread, in particular a pneumatic vehicle tire, with mold segments (1) forming the tread of the vehicle tire, which have slats (3) for forming incisions in the tread, which are each anchored in the mold segments (1), have an initial shape forming the incisions in the intended shape and consist of a shape memory alloy. The sipes (3) consist of such a shape memory alloy that by heat treatment of the sipes (3) on the inside (1a) of the mold segments (1), any sipes (3) that may have been bent during the molding of the tire return to their original shape.

Description

The invention relates to a vulcanization mold for a vehicle tire provided with a profiled tread, in particular pneumatic vehicle tires, having mold segments which form the tread of the vehicle tire and have sipes for forming sipes in the tread, which sipes are respectively anchored in the mold segments, have a starting shape which forms the sipes in the intended shape and consist of a shape memory alloy. The invention further relates to a method for applying such a vulcanization mold.A vulcanization mold of the type mentioned at the beginning is known, for example, from JP 2010023325 A. The lamellae inserted in the shape segments of the segment ring consist of a shape memory material, for example a Ni-Ti alloy or a Pd-Ti alloy. These shape memory alloys are designed such that the material for the lamellae has a restoring force of about 400 MPa under the temperature conditions during vulcanization. Under temperature conditions after vulcanization, after demolding the tire from the mold, the material has a recovery force of about 100 MPa. The sipes are in particular made of shape memory materials which can be easily deformed in a temperature range of 80° to 180°, so that the sipes can be more easily removed from the rubber material of the tread when the mold segments are pulled away from the tire after the vulcanization process. At this time, the temperature of the tire after vulcanization is set within the above-mentioned lower temperature range. The shape memory material of the sipes therefore ensures that demolding of the tire from the vulcanization mold is possible and therefore facilitated during each heating cycle under a certain deformation of the sipes.In conventionally designed sipes, which consist, for example, of steel sheet and are inserted in a large number in the mold segments, in particular when forming tread profiles for winter tires, it occurs again and again that, when the vulcanized tire is removed from the mold, the steel sheet sipes permanently deform as a result of the pull-out forces acting on them. With a very large number of sipes in the mold segments, time consuming verification is required to determine which sipes are bent such that they must be replaced to avoid sipes being less accurately formed in subsequently cured tires, thereby compromising the grip performance of the tire and overall the quality of the tire. In the vulcanization mold known from JP 2010023325 A, it is difficult to adjust the shape memory material to the temperature provided for demolding the tire.The invention is based on the object of ensuring in a simple manner, in a vulcanization mold of the type mentioned at the beginning with sipes made of a shape memory alloy, that any sipes bent during demolding of a vulcanized tire are available again as exactly aligned and non-curved sipes during the subsequent vulcanization process.The object set is achieved according to the invention in that the sipes consist of a shape memory alloy such that, by heat treatment of the sipes on the inner side of the mold segments, any sipes which are bent during the molding of the tire return to their initial shape.In the invention, therefore, the sipes consist of a shape memory alloy which enables phase transformation by a subsequent heat treatment carried out after demolding of a tire in order to restore any bent sipes to their initial shape again. Such heat treatment is therefore carried out when required.In a preferred embodiment, the shape memory alloy has a phase transition temperature >180° C. This temperature is advantageously above the usual vulcanization temperature, so that the sipes desirably remain stable during the vulcanization process and can exactly form the sipes in the tread.Shape memory alloys based on Ni-Ti or Cu, such as a Cu-Al-Ni alloy, are particularly well suited for the lamellae. In these alloys, the desired behavior of the lamellae can be trained particularly well and the alloy composition can be adjusted particularly well.It is furthermore advantageous if the lamellae have a material thickness of 0.30 mm to 2.00 mm, preferably of 0.40 mm to 0.80 mm, over a major part of their radial extension, in particular over their entire radial extension. Within these material thickness ranges, the desired shape memory effect can be adjusted particularly well with the shape memory alloys mentioned.The lamellae are furthermore preferably anchored in the vulcanization mold or the mold segment by a hard solder. Conventional hard solder materials are suitable, in particular those which contain metal components which ensure a good connection to the shape memory material of the lamellae.The invention further relates to a method for applying a vulcanization mold according to one or more of claims 1 to 5, wherein this method is characterized in that the heat treatment of the inside of the mold segments takes place at a temperature which is higher than the vulcanization temperature acting in the vulcanization mold, in particular by up to 20° higher.The heat treatment is therefore preferably carried out in a temperature range >180° C. to 200° C.Infrared radiators, for example, are suitable for the heat treatment, since such radiators are capable of generating and radiating heat at the required temperature.Further features, advantages and details of the invention will now be described in more detail with reference to the schematic drawing which represents an exemplary embodiment. Figure shows FIG. 1 is a view of a portion of a mold segment of a tire curing mold, FIG. 2 is an enlarged sectional view taken along the line II--II of FIG. 1; and FIGS. 3a to 3c are sectional views analogous to FIG. 2 illustrating the mode of operation of the invention by way of example.FIG. 1 shows an inner view of a section of a mold segment 1 of a segment ring of a vulcanization mold for a vehicle tire, in particular for a pneumatic vehicle tire, having elements which form part of the profile of the tread of the vehicle tire, said segment having an inner side 1 a. According to FIG. 1, these elements include webs 2 for forming grooves and a lamella 3, which is designed in the example in the form of a wave, for forming a cut running continuously between two grooves and running in the form of a wave, in the tread. The lamella 3 is firmly anchored in the material of the mold segment 1 and, like the webs 2, protrudes from the inner side 1 aof the mold segment 1 in a known manner in the direction of the mold cavity. Blades 3 usually have a material thickness b of 0.30 mm to 2.00 mm, in particular 0.40 mm to 0.80 mm, and can be provided locally, for example at their outer ends with sections having a thickness greater than their material thickness b. Instead of wave-shaped lamellae 3, straight lamellae or lamellae with one of the known three-dimensional structures can be anchored in shape segments 1.Fins 3 according to the invention consist of a shape memory alloy and are anchored in the mold segments 1 by a bonding layer 4 of brazing material 4. The usual metal alloys are used as hard solders, which contain metal components that ensure a good connection to the material of the lamellae 3, for example brass hard solders.As is known, the shape memory effect of shape memory alloys results from crystallographically reversible martensite-austenite phase transformation. After deformation, shape memory alloys are capable of deforming back to a previously stamped shape. Shape memory alloys which are suitable for lamellae 3 use the two-way effect; the material is reminiscent of a previously present component shape by heating and upon cooling.At the usual vulcanization temperatures of 120° C. to 160° C., the sipes 3 form the sipes in the tread in the usual manner. FIGS. 2 and 3 a show this stable initial state of a sipe 3. However, when the fully vulcanized vehicle tire is removed from the vulcanization mold, high forces may be required in order to pull the sipes 3 out of the now vulcanized rubber material of the tread. Above all in the case of tread strips in which a plurality of sipes 3 produce sipes, there is the possibility here that sipes 3 bend, in particular partially, during demolding (arrow P 1 between FIGS. 3 aand 3 b). FIG. 3 bshows schematically and by way of example a bent lamella 3.Bent sipes 3 cause during the subsequent vulcanization process that the respective sipes are no longer formed exactly in the tread of the tire to be vulcanized, thus suffering the grip performance of the tire and, overall, the quality of the tire. The shape memory alloy of which the blades 3 consist makes it possible to restore the bent blades 3 to their original shape again by an external heat treatment of the inside of the mold segments before the subsequent vulcanization process, as indicated schematically by the arrow P 2 between FIGS. 3 band 3 c. The heat treatment is carried out at a temperature which is higher than the vulcanization temperature mentioned, therefore in particular in the range from 180° C. to 200° C. Infrared emitters, for example, are suitable for the heat treatment.Suitable materials for the lamellae 3 are shape memory alloys based on Ni-Ti or Cu, such as Cu, Al, Ni alloys. The phase transition temperature of the material used is known to be determined by the ratio of the alloy composition. In Ni-Ti alloys, the ratio of nickel to titanium causes the level of phase transition temperature, and the alloy composition should be adjusted accurately.The selection of the alloy composition therefore makes it possible to influence the level of the phase transition temperature and thus the level of the required temperature of the heat treatment.List of reference characters1 Mold segment 1a Inner side 2 Web 3 Lamella 4 Connecting layer b Material thicknessReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedJP 2010023325 A [0002, 0003]

Claims

Vulcanization mould for a vehicle tyre provided with a profiled tread, in particular pneumatic vehicle tyres, having mould segments (1) which form the tread of the vehicle tyre and have sipes (3) for forming sipes in the tread, which sipes are respectively anchored in the mould segments (1), have a starting shape forming the sipes in the intended shape and consist of a shape memory alloy, characterized in that the sipes (3) consist of a shape memory alloy such that, by heat treatment of the sipes (3) on the inner side (1a) of the mould segments (1), any sipes (3) bent during the forming of the tyre return to their starting shape.Vulcanization mould according to claim 1, characterised in that the shape memory alloy has a phase transition temperature greater than 180°C.Vulcanization mould according to claim 1 or 2, characterised in that the lamellae consist of a shape memory alloy based on Ni-Ti or Cu, such as a Cu, Al or Ni alloy.Vulcanization mold according to one of Claims 1 to 3, characterized in that the lamellae (3) have a material thickness (b) of 0.30 mm to 2.00 mm, preferably of 0.40 mm to 0.80 mm, over a large part of their radial extent, in particular over their entire radial extent.Vulcanization mould according to one of Claims 1 to 4, characterized in that the lamellae (3) are anchored in the mould segment (1) by brazing material.Method for applying a vulcanization mould according to one or more of Claims 1 to 5, characterized in that the heat treatment of the inner side (1a) of the mould segments (1) is carried out at a temperature which is higher than the vulcanization temperature acting in the vulcanization mould, in particular is higher by up to 20°C.Method according to claim 6, characterised in that the heat treatment takes place in the temperature range greater than 180°C to 200°C.Method according to claim 6 or 7, characterised in that the heat treatment of the inner side (1a) of the mould segments (1) is effected with at least one infra-red radiator.

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