The invention relates to a valve insert of an air venting valve and an air venting valve for removing air from a vulcanizing mould, for example from a vulcanizing mould of a vehicle tyre. The invention also relates to a method of operating of a vulcanizing mould of a vehicle tyre.

In vulcanising moulds of vehicle tyres a tyre blank smaller than the inner dimensions of the mould is placed inside the mould, after which the mould is closed. After closing, the tyre blank is caused to expand, whereby it presses against the surface of the mould in its plastic state getting the size and shape of a tyre. During the vulcanizing process, air between the tyre blank and the mould surface has to be removed in order for the surface of the tyre blank to come into a tight contact with the mould surface. The vulcanizing mould comprises venting ducts or bores through which air can be removed from the space between the tyre blank and the mould surface. Typically the vulcanizing mould comprises several hundreds of venting ducts for removing air completely at each point of the mould so that no air pockets remain between the tyre and the mould. The drawback with the use of the venting ducts is that rubber material of tyre flows into the venting ducts during the vulcanization process. As a result, the outer surface of the finished tyre comprises threadlike projections that must be removed after the vulcanization, which increases the manufacturing costs and time of the tyre. Alternatively, the projections can be left on the tyre surface, which in turn weakens the aesthetic appearance of the tyre. The threadlike projections may also break off and remain in the venting duct which impairs or prevents the air removal from the mould.

The venting ducts of the vulcanization mould can be provided with air venting valves to prevent entry of tyre material into the venting ducts during the vulcanization process. The air venting valve typically comprises a valve sleeve and a venting duct arranged inside the valve sleeve. A movable valve insert provided with a valve disc is placed in the venting duct. A coil spring for pressing the valve disc away from the mould wall towards the tyre blank is arranged around the valve insert. Thus, air is able to exit from the mould via a clearance between the valve disc and the valve sleeve and further via a clearance between the stem of the valve insert and the inner surface of the valve sleeve. As the tyre material being vulcanized moves towards the mould surface, it pushes the valve disc towards the closed position and finally presses the valve disk against the valve sleeve thus closing the venting duct so that the tyre material being vulcanised cannot access the venting duct. The coil spring opens the air venting valve while the tyre blank is being removed from the mould.

The drawback with the openable and closable air venting valves is that in certain production conditions the tyre material enters the venting duct of the venting valve and thus may cause the sticking of the valve insert. This, in turn, impairs or totally prevents the air venting through the venting valve. The produc- tion conditions which can cause the sticking of the valve insert may be e.g. process disturbances or the change to a different type of tyre raw material.

If the sticking of the valve inserts occurs, some or all of the venting valves can be removed and replaced with traditional valve sleeves without valve inserts and with venting bores of desired diameter. When the problems causing the sticking of the valve insert have been solved, the valve sleeves can be replaced again with venting valves having movable valve inserts. A disadvantage of this method is that the replacement of the venting valves is quite time consuming and difficult.

The object of the present invention is to provide a solution by means of which the problems described above can be reduced.

The object according to the invention can be achieved by a valve insert accord- ing to claim 1 , air venting valve according to claim 6 and a method according to claim 10. The valve insert according to the invention comprises a valve stem arranged to be inserted into a valve sleeve of the air venting valve. The first end of the valve stem is provided with a valve disk and the second end of the valve stem is provided with means for detachably attaching the valve insert to the valve sleeve. The valve insert comprises a venting bore for removing air from the vulcanizing mould. An opening of the venting bore is located on a front surface of the valve disk.

Significant advantages can be achieved by means of the invention. The valve insert according to the invention can be used in venting valve which is provided with movable valve insert after the movable valve insert has been removed from the valve sleeve and vice versa. This enables a fast change between two different venting technologies, i.e. the traditional technology, in which the venting ducts of the mould remain open throughout the vulcanization pro- cess, and the technology, in which the venting ducts are closed by the movable valve insert of the venting valves. Since the valve insert is detach- ably attached to the valve sleeve, the valve inset can removed and replaced with a different type of a valve insert quickly and easily as the replacement of the valve insert is much easier than the replacement of the entire air venting valve.

In the following, the invention will be described in more detail by means of examples with reference to the attached drawings, wherein fig. 1 shows an air venting valve according to an embodiment of the invention, figs. 2 and 3 show a valve insert of the air venting valve of fig. 1 , fig. 4 shows the air venting valve of fig. 1 which is provided with a different type of a valve insert. Fig. 1 shows an air venting valve 1 for removing air from a vulcanizing mould 2, e.g. a vulcanizing mould of a vehicle tyre. Typically the vulcanizing mould 2 comprises 1000-4000 air venting valves 1 . The air venting valve 1 comprises a valve sleeve 3 and a valve insert 4 inserted into the valve sleeve 3. The valve sleeve 3 is attached to a venting duct 5 of the vulcanizing mould 2 e.g. by a press fit. The valve sleeve 3 is cylindrical. The outer diameter of the valve sleeve 3 is typically 1 .5-4 mm.

The valve insert 4 of the venting valve 1 comprises a valve stem 6, first end of which is provided with a valve disk 7 and the second end with means 8 for de- tachably attaching the valve insert to the valve sleeve. The valve insert 4 is attached to the valve sleeve 3 by a detachable connection, for example detachable snap connection. The valve insert 4 is shown in more detail in figs. 2 and 3. The first end of the valve sleeve 3 comprises a conical seat surface 9 against which the valve disk 7 is arranged. The air venting valve 1 shown in fig. 1 is provided without a spring for moving valve insert 4.

The means for detachably attaching the valve insert to the valve sleeve comprises an elastically compressible and/or elastically deformable retainer member 8 provided at the second end of the valve stem 6. The retainer member 8 is arranged to be compressed when the valve insert 4 is removed from and insert- ed into the valve sleeve 3.

The retainer member 8 comprises a slot 10 at the second end of the valve stem 6, by means of which the compression of the retainer member 8 is achieved. The slot 10 extends from the second end of the valve stem 6 towards the first end of the valve stem 6. Additionally, the retainer member comprises a collar 1 1 at the second end of the valve stem 6. The slot 10 extends through the collar 1 1 . The outer diameter of the collar 1 1 in the uncompressed state of the retainer member is larger than the inner diameter of the opening 12 of the second end of the valve sleeve 3. The collar 1 1 comprises a first surface 13, which is arranged to abut the edge of the opening 12, when the valve insert 4 is inserted into the valve sleeve 3. The first surface 13 is conical. Further, the collar 1 1 comprises a second surface 14, which is arranged to abut the edge of the opening 12, when the valve insert 4 is removed from the valve sleeve 3. The second surface 14 is conical. When the valve disk 7 is against the seat surface 9, the retainer member 8 is against the edge of the opening 12 at the second end of the valve sleeve 3, thus retaining the valve insert 4 stationary in the valve sleeve 3. The valve insert 4 comprises a venting bore 15 for removing air from the vulcanizing mould 2. The opening 16 of the venting bore 15 is located on a front surface 18 of the valve disk 7, i.e. on the surface of the valve disk which faces the interior 17 of the vulcanizing mould 2. The opening 16 of the venting bore 15 is completely surrounded by the edge of the front surface of the valve disk 7. Typ- ically, the opening 16 of the venting bore 15 is located in the centre of the front surface 18 of the valve disk 7. The other opening of the venting bore 15 is located on a bottom of the slot 10. The diameter of the venting bore 15 and the opening 16 thereof can be selected as desired. The end of the valve sleeve 3 is at the same level as the front surface 18. Fig. 4 shows an air venting valve 1 ' which comprises a valve sleeve 3 similar to that of fig. 1 . The valve insert 4' is of a different type than the valve insert shown in figs. 1 -3. The valve insert 4' does not comprise a venting bore through which air can be removed from the mould 2. The air venting valve V comprises a spring member 19 such as a coil spring for urging the valve insert 4' towards an open position, in which air can be removed from the vulcanization mould 2 through the clearance between the valve disk 7' and the seat surface 9, and further through the clearance between the outer surface of the valve insert 4' and the inner surface of the valve sleeve 3. The spring member 19 is arranged around the stem 6' of the valve insert 3. The valve sleeve 3 comprises a support surface 20 for the spring member 19. The spring member 19 is arranged between the support surface 20 and the back surface of the valve disk 7'. One end of the spring member 19 is arranged against the support surface. The other end of the spring member 19 is arranged against the back surface of the valve disk 7'. The support surface 20 surrounds the valve stem 6', 6 (fig. 1 ). The valve stem 6' is longer than that in the embodiment of figs. 1 -3 so as to achieve the opening movement of the valve insert 4'. The retainer member 8 limits the opening movement of the valve insert 4'. During the vulcanization process the tyre to be vulcanized expands and urges the valve insert 4' to a closed position, in which the valve disk 7' is against the seat surface and no air is allowed to flow through the venting valve 1 '. The retainer member 8 of the valve insert 4' can be similar to that of figs. 1 -3. If, for some reason, during the operation of the vulcanizing mould tyre material enters the space between the valve insert 4' and the valve sleeve 3, the valve insert 4' may stick in the valve sleeve 3, which impairs or totally prevents the air removal through the venting valve 1 '. In this case the valve insert 4' can be detached and removed from the valve sleeve 3 and replaced with a different type of a valve insert, e.g. with the valve insert 4 shown in figs. 1 -3.

The removal of the valve insert 4' is performed by pushing the retainer member 8 from the venting duct 2 of the vulcanizing mould 1 towards the interior of the vulcanizing mould 1 . The retainer member 8 is elastically compressed and deformed as it abuts the opening 12 and passes through the opening 12 of the valve sleeve 3. When the retainer member 8 has been brought through the opening 12, the valve insert 4' and the spring member 19 can be removed from the valve sleeve 3 through the opening at the first of the valve sleeve 3. Thereafter, the valve insert of different type, e.g. the valve insert shown 4 in figs. 1 -3, is inserted into and detachably attached to the valve sleeve 3. The retainer member 8 of the valve insert 4 abuts the edge of the opening 12 of the second end of the valve sleeve 3 and is elastically compressed and deformed such that the retainer member 8 can be brought through the opening 12. Finally, the valve disk 7 abuts the seat surface 9 of the valve sleeve. The retainer member 8 is against the edge of the opening 12 of the valve sleeve, thus retaining the valve insert 4 stationary in the valve sleeve 3. When the necessary number of valve inserts 4' has been replaced, the vulcanizing mould 1 can be operated again. With the valve inserts shown in figs. 1 -3 sticking of the valve insert does not occur. When the problems causing the sticking of the valve insert has been solved, the valve insert 4 can be replaced with the valve insert of a different type, e.g. with the valve insert 4' and spring member 19 shown in fig. 4.