AU710458B2

AU710458B2 - Tyre vulcanization with venting capability

Info

Publication number: AU710458B2
Application number: AU71784/96A
Authority: AU
Inventors: Klaus Heimbuchner; Heinz-Jurgen Hollander; Heinz Kohler; Arthur Friedrich Noll; Detlef Pleger
Original assignee: Continental AG
Current assignee: Continental Reifen Deutschland GmbH
Priority date: 1995-11-20
Filing date: 1996-11-15
Publication date: 1999-09-23
Anticipated expiration: 2016-11-15
Also published as: TR199600886A2; EP0774333A3; RU2189311C2; PT774333E; AU7178496A; TW362061B; CA2190720A1; JPH09141660A; CZ291837B6; KR970025900A; MX9605708A; HU9602172D0; MY117718A; HUP9602172A3; HUP9602172A2; KR100484002B1; DE59606405D1; ZA967689B; CN1154291A; CZ230896A3

Abstract

This vulcanisation mould (1) for tyre (14) mfr. has 600-3,000 air release holes (2). Each has a valve (3) so configured, that it is closed by the approaching tyre blank surface, to re-open again after vulcanisation, during tyre extraction. Pref. in each of the air release holes (2) is a valve (3)with moving insert (4), comprising valve rod (5) with an attached plate (6). The plate presents a frustrated conical section (7) towards the insert internal cavity. On the tyre surface side there is a plane surface (8). The conical surface mates with a valve seat surface (9) in the valve casing or in the surface of the mould (1) segment (10).

Description

TIRE VULCANIZATION MOLD WITH VENTING CAPABILITY Background of the Invention The present invention relates to a vulcanization mold for the manufacture of pneumatic vehicle tires with a plurality of venting bores in the range of 1,000 to 3,000 individual bores.

It is known that any tire vulcanization mold must be vented so that the green tire during blowing from the interior can come into contact with the shaping tools of the vulcanization mold.

During this process the exterior of the green tire pushes the air radially outwardly. When this air cannot be vented, it is compressed to a pressure just below the applied blowing pressure. Despite the fact that the pressure application results in an increase of air absorption capability within the rubber, the air

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absorption capability remains extremely low. The remaining air which is neither vented nor dissolved in the rubber material, forms localized cushions between the inner contour of the vulcanization mold and the outer contour of the green tire. The missing contact at these locations between the vulcanization mold and the green tire not only results in a depression being formed within the green tire at such location but also results in a reduced heating due to the substantially reduced heat transmission coefficient of air 1Arelative to the metal of the vulcanization mold. This may result in an insufficient sulfur-based curing of the rubber and subsequent material failure during operation.

Therefore, all tire manufacturers pay great attention to the venting of vulcanization molds.

Tire tread patterns are, in general, very detailed comprising longitudinal and transverse grooves as well as a plurality of cuts, sometimes even meandering cuts, which define different positive V portions such as tread blocks and stays. With regard to the pneumatic behavior, the plurality of projections of the vulcanization mold that define the negative portions of the tire tread divide, in general, radially inwardly the air volume to be dissipated into numerous isolated chambers each requiring the removal or venting of the air volume therein so that each one requires at least one venting channel.

According to the oldest and still prevailing technology a plurality of thin bores which extend approximately perpendicularly to the surface to be formed are used for venting the vulcanization mold. The bores are arranged in the shaping tools such that they open into venting channels of the outer components of the vulcanization mold. These bores have a diameter of -2approximately 0.7 to 1.5 mm depending on the required bore depth and the tire size. A typical passenger car tire vulcanization mold has approximately 1,500 venting bores; a typical mud and snow tire vulcanization form has more than 2,500 venting bores.

These bores present a minimal flow resistance to the air to be vented. However, the flow resistance is also minimal for the viscous rubber so that, after the blowing pressure has been generated, until a sufficient cross linking (curing) prevents a further flowing of the rubber material, a substantial amount of rubber flows into the venting bores. In general, it is possible, by adjusting the vulcanization speed, selecting the course of the temperature over time, the dosage of accelerators and of sulfur, the diameter of the venting bores, and the breaking stability of the vulcanized bristle-like excess rubber on the tread, to prevent that the excess rubber knobs during removal of the tire from the mold breaks off. If the excess rubber broke off, the bristle-like projections would remain within the respective venting bore and would thus impede a correct venting of the vulcanization mold during vulcanization of a further tire to be vulcanized.

However, especially for tires within the upper price range, many customers do not like the bristle-like appearance of the -3produced tire. Therefore, in many cases the bristles are removed before distributing the tires to the tire dealers. For this purpose, various techniques are known which are similar to a shaving process, a planing process or a grinding process. It is also known to super-cool the bristles in order to produce clean cut edges at the tire tread. However, all of these techniques require a considerable expenditure.

Therefore, it has been an object for a long period of time to provide devices and/or methods which produce a tire free of bristle-like excess rubber without requiring a post vulcanization treatment step. For solving this object a plurality of suggestions

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are known in the prior art.

From U.S. Patent 3,377,662 it is known to introduce into each of the venting bores a pin which in cross-section is substantially star-shaped whereby the outer envelope of the star is slightly greater than the inner diameter of the venting bore so that each pin can be secured in the respective venting bore by press-fitting. Thus, the venting bore which initially has a relatively large cross-sectional area is thus divided into a plurality of smaller channels having a smaller cross-sectional area. The sum of the cross-sectional areas of the resulting individual channels is -4approximately 1/10 of the cross-sectional area of the thus throttled venting bore whereby the individual cross-sectional areas of each individual channel is approximately 100th of the initial crosssectional area. This solution is based on the knowledge that a drilling tool cannot surpass a certain limit with regard to the ratio of tool length to the diameter to be drilled because upon surpassing this limit the drill bit would break. Thus, the diameter ~of a venting bore cannot be selected to be as small as desired.

For the desired venting function the flow cross-sections however could be substantially smaller than those that can be produced with a drilling tool. Thus the bristle-shaped forced-out rubber material would be a lot smaller in diameter. The basic idea of this patent is that bores with a relatively large diameter, produced with conventional drilling tools, is subsequently reduced in its cross-sectional area by dividing into a plurality of narrow channels. European patent 0 518 899 suggest substantially the same solution.

European patent application 0 311 550 teaches that into a known venting bore a substantially circular pin is to be inserted which has a somewhat smaller outer diameter than the inner diameter of the venting bore at the side of the vulcanization mold which shapes the tire. In a radially outwardly located area the venting channel is provided with projections which secure the respective pin by press fitting.

This patent application thus also deals with a retrofitting solution for narrowing the channels of a large cross-sectional area, in this case by insertion of a pin. This application differs from the previously discussed U.S. patent in that the remaining flow crosssection of the venting bore is not divided into a plurality of small gaps arranged in a circular fashion but that a continuous, narrow annular gap is formed. While the star-shaped outer profile of the inserts according to the U.S. Patent 3,377,662 can be inexpensively produced by drawing a wire with corresponding dies, the spline bore hub-type inner profiling of the venting channels according to the European application 0 311 550 requires more expensive cutting operations.

European patent application 0 591 745 suggests to use a porous material at the vulcanization mold that comes into contact with the tire. The pores should have a pore size of less than 0.05 mm. This porosity should be large enough in order to provide for a sufficiently fast air removal but small enough in order to prevent penetration of rubber into the pores, thus causing clogging of the -6pores.

Experiments in this regard, however, have shown that already after a small number of vulcanization cycles many pores are clogged. Pore cleaning, however, is impossible.

From European patent application 0 440 040 it is known to divide the mold segments into partial segments along planes which connect locations where venting is required. Again, this is based on the principle that the venting channels must be made more narrow so that the thus resulting flow resistance allows only a very shallow penetration of rubber into the channels.

In contrast to the prior art solutions discussed before, this 0 solution allows for cleaning of the venting gaps by dismantling the respective mold segment into its partial segments. However, such molds, due to the great number of contact surfaces which, for most modern tire tread designs, can no longer be planar but must be curved corresponding to the course of the transverse grooves of the finished tire, would be very expensive.

From German Offenlegungsschrift 39 14 649 a special arrangement of such venting gaps, indicated with reference numeral 18 in this publication, is known which are arranged directly at the bottom of the ribs (see column 2, line 43).

-7- The European patent application 0 451 832 teaches also an arrangement of venting gaps with a puzzle-like fine division of the mold segments. The German Offenlegungsschrift 19 33 816 (claim Japanese application 76 91 423, Japanese application 51 119776, and U.S. patent 4,691,431 as well as U.S. Patent 4,708,609 are all based on the same concept.

It has also been suggested repeatedly to generate a vacuum within the tire vulcanization mold before shaping of the tire tread. For this purpose, a substantially smaller number of venting channels would be sufficient; for a satisfactory time allowance for evacuating the mold, one single venting channel might even be sufficient.

The tires produced in such molds are substantially free of any projecting excess rubber, and there is no need for cleaning the mold.

However, it is disadvantages that with respect to the size and the numerous dividing planes of tire vulcanization molds a vacuum below 0.1 bar can be achieved only with extreme expenditure. With a vacuum of 0.1 bar, however, there remains a residual amount of air which surpasses the solution absorption capacity of the rubber for air. Thus, venting channels cannot be -8omitted completely. Similar suggestions are proposed in U.S.

patents 4,573,894, 4,597,929, 4,881,881, and 5,283,022 as well as in German Offenlegungsschrift 22 10 099 and European patent application 0 458 154. European patent application 0 414 630 also relates to such a solution and teaches also to perform the opposite, in order to removed the finished vulcanized tire, gas is blown into the vulcanization mold through the venting channels.

This latter process, without previous vacuum application, is known from U.S. patent 4,812,2 8 1.

German Offenlegungsschrift 22 00 314 and 25 24 538 as well as 31 42 288 disclose devices for manufacturing injection molded parts free of lateral flow. One single venting channel is concentrically arranged relative to the rotational axis of the cavity and opens into an evacuating device which, before beginning the injection molding process of the polymer mixture, produces substantially a full vacuum in the mold. The residual air pressure can be so small because only one single sealing surface with a very short arc length is present. Shortly after the injection molding process begins, before complete filling of the cavity with the polymer mixture, the venting channel is closed off with a valve having a conical valve plate.

-9- The valve closure is caused directly (German Offenlegungsschrift 22 00 314 and German offenlegungsschrift 31 42 288) by impacting of the polymer mixture flow onto the surface of the valve plate at the side of the cavity or (German Offenlegungsschrift 25 24 538) indirectly by deformation of a plate caused by the unilaterally acting conveying pressure which is then transmitted with a displacement mechanism onto the valve plate.

The very early closure of the valve ensures that no amount of polymer mixture can enter into the gap between the seating surface and the conical surface of the valve plate facing away from the cavity. This allows for a complete prevention of lateral flow, and sticking problems of the valves are avoided from the beginning. Therefore, it is sufficient to provide a weak coil spring for opening the valve upon removing of the finish-vulcanized part, especially rubber seals and gaskets.

This venting technology, however, has the problem that the residual amount of air in the vulcanization mold cannot be vented after the early onset of closure of the valve but is instead compressed. This disadvantage can be tolerated in high quality injection molds, because very small residual amounts of air can be achieved by evacuation. Furthermore, the extruders, depending on the type, for conveying the polymer mixture can reach a pressure of 100 to 400 bar, usually approximately 300 bar.

Accordingly, the minimal amount of residual air within the injection mold can be compressed to an extreme extent so that at the end of the filling process the residual amount of air is practically zero.

Furthermore, the high pressure also increases the amount of air that can dissolve in the rubber material.

Since such small amounts of residual air are not possible within tire vulcanization molds due to the greater volume (approximately greater by three powers of 10) and the numerous abutting sealing surfaces of very great arc length and since the blowing pressure for the manufacture of passenger car and motorcycle tires are only approximately 10 bar, for heavy duty truck tires approximately 15 bar, this prior art injection molding process which is free of lateral flow is not transferable onto the manufacture of pneumatic vehicle tires.

From German Offenlegungsschhrift 36 22 598 the arrangement of venting bores in a shaping tool for multicomponent plastics on a manually displaceable push rod is known.

In summarizing the review of the prior art, it is noted that some of the aforementioned suggestions have brought small 11 12 improvements, but that to this date no completely satisfactory solution for venting of vehicle tyre vulcanization moulds has been suggested which is evidenced most clearly by the fact that to this date most tyres after removal from the vulcanization mould still exhibit the undesirable bristle-like lateral flow projections.

SUMMARY OF THE INVENTION The present invention provides a vulcanization mould for manufacturing tyres, the vulcanization mould including: mould walls having 600 to 3,000 vent bores; a valve inserted into each of the vent bores;

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each valve having a moveable valve member including o S 15 a valve shaft and a valve plate connected to the valve shaft, each valve plate having a substantially planar surface facing the interior of the mould; and each valve further having a wire helical spring which is compressed when said valve is closed, said 20 helical spring being arranged concentrically around said o valve shaft and extending substantially to said valve •coo plate; wherein each valve is arranged such that, in use, an advancing surface of a green tyre, inserted into the mould to be vulcanized, bears against said valve plate to close said valve and, said helical spring opens said valve upon removal of the tyre from the mould.

Preferably, each valve plate has the shape of a j ~truncated cone with the substantially planar surface 13 facing the interior of the vulcanization mould, the conical surface of the valve plate faces away from the interior of the vulcanization mould, and the valve has a matching counter surface for the conical surface.

Preferably, the matching counter surface is provided in the mould walls.

The valve preferably comprises a housing to which the valve member and the return spring are securely connected.

The housing is preferably cylindrical.

Advantageously, the counter surface is provided at the housing.

Preferably, the housing has an outer diameter between 2 and 6 mm, the outer diameter being greater than 15 the inner diameter of the vent bore before mounting of the housing in the vent bore.

1 4771A700 Preferably, the valve comprises a stroke limiter, connected to the end of the valve facing away from the interior of the vulcanization mold for limiting the stroke of the valve member in a direction toward the open position to less than 2 mm.

Preferably, the stroke limiter is detachably mounted to the valve shaft so as to be detachable for demounting the valve member.

Advantageously, for demounting the valve member the stroke limiter is in the form of a releasable snap connection for connecting the valve member with play within the valve so as to allow for an opening and closing stroke of the valve member.

Advantageously, the valve comprises a housing with an inner chamber in which the valve member and the return spring o are positioned, wherein the inner chamber of the housing has a first groove at an end of the housing facing away from the interior of the vulcanization mold, the first groove positioned in a plane extending perpendicularly to a longitudinal axis of the valve housing and having a first width wI5 in a direction of the longitudinal axis of the valve housing, the stroke limiter comprising a retainer spring of a thickness w16 positioned in the first groove the stroke limiter further comprising a second groove having a 14second width w17 provided at the valve shaft, the retainer spring engaging the second groove, wherein at least one of the first and second widths are greater than the thickness of the retainer spring by such an amount that the play P, defined by the equation P w17 w15 2 x w16, is at least as great as the stroke of the valve member.

Preferably, the retainer spring in a plan view has a Cshaped main portion and has free ends connected to the main portion and bent outwardly relative to the main portion. The free ends engage the first groove.

Advantageously, the retainer spring in another embodiment has in a plan view a C-shaped main portion and free ends connected to the main portion and bent inwardly relative to the main portion. The free ends engage the second groove.

Advantageously, the valve shaft has a first end facing away from the interior of the vulcanization mold, the first end having a collar, wherein the collar has an abutment surface facing the interior of the vulcanization mold for limiting the stroke of the valve member toward the open position, the first end having at least one slot in order to allow a compression of the diameter of the collar so that by compressing the collar the valve member is removable from the valve.

The abutment surface preferably has a truncated cone shape so that a pulling action toward the interior of the vulcanization mold causes an automatic compression of the collar for removing the valve member.

Advantageously, a surface of the collar opposite the abutment surface has a truncated cone shape and the vent bore has a conically inwardly tapering inlet facing the interior of the vulcanization mold so that by pushing the valve member from the interior of the vulcanization mold into the vent bore, the collar is automatically compressed for insertion of the valve member into the vent bore.

Preferably, the valve comprises a housing with an inner chamber in which the valve member and the return spring are positioned, the housing having a conically inwardly tapering inlet facing the interior of the vulcanization mold when mounted, wherein the surface of the collar opposite the abutment surface has a truncated cone shape so that by pushing the valve member into the conically inwardly tapering inlet the collar is automatically compressed for insertion of the valve member into the housing.

Preferably, the collar in a plan view deviates from a circular -16shape such that the diameter of the collar remote from the at least one slot is greater than the diameter of the collar in the vicinity of the at least one slot.

According to the present invention, each one of the vent bores comprises a valve that is designed such that it is closed by the advancing surface of the green tire during blowing and upon removal of the tire is opened so that the imprinting process of the green tire to be subsequently molded and vulcanized takes place :again with open valves. Preferably, each one of the valves inventively arranged within the vent bores comprises a movable valve member with a valve shaft and a valve plate arranged thereat which at the side facing away from the interior of the :vulcanization mold is shaped as a truncated cone and at the side facing the interior of the vulcanization mold is provided with a substantially planar surface. The truncated cone surface of the valve plate cooperates with a matching surface of the corresponding segment of the vulcanization mold, respectively, of a valve housing.

Each one of the valves is moved into the closed position upon impacting of the polymer mixture during the imprinting step of the green tire, which is preferably a pneumatic vehicle tire.

-17- However, with a weak spring each valve is forced into the open position upon removal of the finished (vulcanized) tire.

While in the prior art injection mold, which is evacuated with a single valve that is substantially 2 to 3 times as large as the inventive valves, the evacuation valve closes too early, in the suggested inventive solution, which preferably operates without evacuation, the plurality of tiny valves close substantially more precisely with respect to correct timing. Especially, they do not close too early, which is very important with respect to safety considerations, because they are arranged at the end of a polymer flow branch and not in the vicinity of its beginning. It is accepted that for a 100 percent prevention of lateral flow some of the valves will close too late. The thus resulting circular lateral flow projections have an annular diameter of 2.8 mm, a ring width of approximately 0.3 mm, and a ring height of approximately 0.25 mm. The lateral flow projections are thus so small that at least for most tire market segments a post treatment for removal of lateral flow projections is obsolete.

The resulting savings with respect to manufacturing time, space requirements, and waste rubber that is expensive to dispose of are beneficial. These savings surpass the monetary -18investments for the vulcanization molds with respect to the valve costs. Especially the savings with respect to man hours have surprised in house critics of the invention which first feared that the saved man hours at the conventional grinding machines would be more than outweighed the maintenance requirements for the enormous number of valves within the vulcanization mold.

However, surprisingly, the first experimental vulcanization mold has required no maintenance at any of the approximately 1600 small valves.

The remaining lateral flow projections which with respect to the predominantly nail-shaped (bristle-shaped) lateral flow projections of the prior art are substantially reduced in size, correspond in their appearance to those disclosed in European patent application 0 311 550, discussed supra.

In contrast to many prior art suggestions in regard to narrow or rigid venting gaps, no rubber accumulations or burned (carbonized) rubber residues are observed with the inventive device. The surprisingly clean operation of the cooperating valve seat and valve plate surfaces appears to be based in the fact that, on the one hand, the rubber amount penetrating into the valve gap results in a fast and almost complete sealing relative to further -19rubber flow, because of the valve closure so that the amount of rubber introduced per gap length is much smaller than in previous suggestions for venting via rigid gaps and, on the other hand, due to the fact, however, that the projections, which due to their tenderness have first been viewed as being prone to rupture, do not break off because the opening of the valve, best effected by a spring, after vulcanization will not clamp any portion of the projection. Especially, there is no after effect of the rubber compression resulting from the blow pressure which conventionally i would cause the generally observed clamping effect.

In order to improve the clean operation of the two cooperating, preferably conically shaped, surfaces at the valve seat and the valve plate, it is possible to coat these surfaces with an antiadhesive material. As an antiadhesive material .polytetrafluoroethylene or polydimethylsiloxane are suggested which are, in general, known from German Offenlegungsschrift 39 03 899 and European patent application 0 228 652.

Instead of the forced opening with a spring this refers to a valve drive instead of pulling the valve member with the adhesion between the finished tire and the valve plate, it is also possible to use a pneumatic drive as an equivalent to the spring by injecting air into the venting channels. However, this solution appears to be more expensive. Even though European Patent Application 0 414 630 and U.S. patent 4,812,281 already show air injection for the purpose of removing the tire, there are no valves present in these devices and therefore there is no valve drive and also no pneumatic drive support disclosed.

For an economic manufacture of the inventive vulcanization molds and for the purpose of a simple valve exchange, in the case that a valve might fail, it is suggested that each valve has its own, preferably cylindrical, housing at which all movable components of the valve are connected so as to be "non-loosable". The term non-loosable in this connection means that no individual parts during transport from the valve manufacture or during mounting or removal can be lost or fall out. This does not mean that the valve cannot be dismantled. At least during the experimental stages it has been shown to be advantageous that the valve plate for a regular inspection can be easily demounted, for example, with a snap connection (no valve failure was observed). Two such embodiments are disclosed herein.

Preferably, the valve housing (12) has an outer diameter of between 2.0 and 6.0 mm for passenger car tires, preferably -21 between 2.0 and 4.5 mm, and for heavy truck tires preferably between 3.0 and 6.0 mm.

Since demounting of the valves will occur only very infrequently, it is suggested to use instead of a threaded connection a press-fit for securing the valves within the mold segments. For this purpose, in the demounted state of the valve the outer diameter of the valve housing is greater than the inner diameter of the corresponding vent bore in the mold wall mold segment. For a housing diameter of 3.5 mm the oversize relative to the bore should be 50 to 150 pm. For greater housing diameters it should be correspondingly greater and for smaller housing diameters it should be correspondingly smaller. These o. versizes relate to a material pairing of steel for the valve housing and aluminum for the segments of the mold with the receiving bores. It is known to a person skilled in the art that for stiffer material pairings, for example, steel/steel, the oversize can be selected correspondingly smaller.

Preferably, each valve of the inventive vulcanization mold is provided with a stroke limiter at the side of the valve shaft facing away from the interior of the vulcanization mold. This stroke limiter limits the stroke of the valve member into the open -22-

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position, preferably, for valves in passenger car tire molds, to a stroke of between 0.3 and 1.2 mm and for molds for heavy duty truck tires to a stroke between 0.5 and 2.0 mm. The stroke to which the valve opening movement is limited, will be named valve stroke in the following. With this movement limitation it is possible, in cooperation with a tension-free spring length that is greater than the mounting length of the spring in the widest open 9*eo position, that the spring at its force introduction surfaces is always ""under pull or pressure load. This avoids in a simple and effective 9 manner rattling of the spring which would otherwise occur for a spring connection with play. Furthermore, for a valve stroke that is too long, the valve closure will occur delayed and will cause a large excess rubber projection between the cooperating, preferably conically shaped, sealing surfaces.

Despite the fact that in all of the conducted heating I experiments all of the valves functioned properly, it is nevertheless advisable to provide for inspection and exchange possibilities for the valve members. Accordingly, the valve member should be removable from the valve housing, respectively, for an arrangement of the valve member without housing directly within the respective mold segment, from the mold segment even when -23a stroke limiter for limiting the valve stroke is provided. Especially such a stroke limiter, however, usually impedes a demounting of the valve member in the direction toward the interior of the vulcanization mold.

As one solution to this problem it is suggested to design the connection of the stroke limiter (abutment) at the valve shaft in a detachable manner, for example, with a matching thread. For this purpose, the end of the valve shaft facing away from the interior Sof the vulcanization mold, could be provided with an external thread. The abutment in the form of a disk could be provided with a throughbore to be received by the external thread and could be subsequently secured thereat with a nut. For reducing the number of parts, it is also possible to provide the throughbore of the abutment disk with a matching inner thread for the external thread of the valve shaft.

For a faster manipulation it is suggested to provide the stroke limiter in the form of a snap connection having play between the valve shaft and the valve housing, respectively, the respective mold segment. Thus, all valve members can be demounted without loosening hundreds of threaded connections.

The snap connection of each valve member should be designed -24such that a forceful pulling in the direction toward the interior of the vulcanization mold results in demounting, and a forceful pressing in the opposite direction results in mounting thereof.

Brief Description of the Drawings The object and advantages of the present invention will appear more clearly from the following specification in conjunction with the accompanying drawings, in which: Fig. la shows in longitudinal section the left half of a mold segment in the area with which the tread portion of the tire is to be molded, within a valve is positioned in each vent bore of the mold wall and the green tire does not abut the mold; Fig. 1b shows in longitudinal section the same half of the mold segment but with the green tire abutting so that all venting valves are in the :0 closed position; Fig. 2 shows in the same cross-sectional plane in a scale of 20:1 an individual venting valve with a threaded abutment at the side facing the interior of the vulcanization mold for limiting the opening stroke of the valve; Fig. 3 shows in the same cross-sectional plane in a scale of 20:1 an individual venting valve with a stroke limiter of the valve stroke with defined play, the stroke limiter embodied as a snap connection comprising a retainer spring as a separate component; Fig. 4a shows in the same scale in a plan view the retainer spring of Fig. 3 after removal; Fig. 4b shows in an analogous representation another embodiment of the retainer spring of Fig. 3; and eo Fig. 5 shows in an analogous representation to Fig.

3 a single valve with a stroke limiter of the valve stroke with the defined play embodied as a snap connection whereby the spring action required for the snap connection is not achieved by bending a separate retainer spring but by bending the lower slotted end of the valve shaft.

Description of Preferred Embodiments -26- The present invention will now be described in detail with the aid of several specific embodiments utilizing Figures 1 through Fig. la shows in longitudinal section the left half of a mold segment 10 of the inventive vulcanization mold 1. The vulcanization mold 1 in this embodiment is, as is conventional but not required for the present invention, radially divided in the tread portion so that the mold segments 10 are radially movable. The shown mold segment 10 is part of the tread-forming area for the tire. Conventionally, radially divided molds have 7 to 13 mold segments 10 within the tread area, whereby tire molds for passenger car tires have usually 7 or 9, for light truck tires have usually 9 or 11 and for heavy duty truck tires have usually 11 or 13 mold segments.

In contrast to the functional position of the finished tire with horizontal position of the axis of rotation, the vulcanization molds are in general arranged in a horizontal arrangement with vertical position of the axis of rotation. The green tires are easier to insert ":000" in this manner and the vulcanized tires can be more easily removed in this manner. The two lateral parts of the mold are therefore called top mold portion and bottom mold portion.

-27- A need for venting is present for the radially movable mold segments 10 as well as for the non-represented lateral parts. The number of required vent openings 2 per surface area however is smaller at the lateral parts than within the mold segments because the shape being imparted to the tire is not as complicated at the lateral parts. Preferably, the venting in the axially movable lateral mold parts 10 is performed with the same valves 3 that are also positioned in the radially movable mold segments 10. Since, with exception of the less tight arrangement of the venting openings 2, no difference exists between the venting of the radially movable mold segments and the axially movable lateral parts 10, the reference numeral 10 is used for both mold part •types.

It is important to note that in each venting bore 2 a valve 3 is arranged. The mold segment 10 in Fig. la is represented without a green tire inserted therein. Therefore, all venting valves 3, biased by a weak pressure spring 11, which is represented in more detail in Fig. 2, are open. The valve plates 6, as can be seen in Fig. 2, extend therefore radially inwardly into the interior of the vulcanization mold.

The return spring 11 for reaching the open position should -28be as weak as possible but as strong as needed, taking into consideration the weight, friction and manufacturing tolerances.

In order to reliably reach the open position, it is sufficient, according to conducted experiments, when the prestress, more precise the precompression of the return spring, is 1.5 times the sum of the own weight of the valve member and half the spring weight.

Into the mold, shown in Fig. 1a, with open vent channels 2, due to the valves 3 being in the open position, a green tire 14 is to be inserted in a manner known per se.

Fig. lb shows in an analogous representation to Fig. 1 the moment where, at the end of the residual raising, the green tire to be imprinted and vulcanized just comes into contact with the groove bottoms of the mold 1 which mold the projecting portions (lugs, ribs) of the resulting tire tread. Most of the venting channels 2 open into the groove bottoms at the interior of the mold. The contact of the rubber material which has already a certain dimensioned stability thus forces the valves 3 into the closed position (as represented) against the weak resistance of the respective pressure spring 11.

The term residual raising in the tire technology refers to the -29remaining portion of the total raising of the green tire. The raising within the vulcanization mold is achieved by blowing and results in the molding of the tread pattern or, for very deep treads and/or very pull-resistant reinforcements, the completion of the molding process.

Fig. 2 shows in the same cross-sectional plane as Fig. 1 at a scale of 20:1 an individual venting valve 3 with a valve member 4. The valve member 4 comprises one valve plate 6 and a valve shaft 5. At a step of the valve plate 6 the return spring 11 is centered. For limiting the valve opening stroke, a stroke limiter or abutment 13 with inner thread is threaded onto the outer thread of the respective end of the valve shaft 5 facing away from the interior of the vulcanization mold.

The valve plate 6 comprises a substantially planar end face 8 which matches the shape of the interior of the mold. The green tire will come to rest at this end face 8 during residual raising.

The valve plate 6 is otherwise embodied as a truncated cone 7 matching with its diameter and with the cone angle the inner conical surface 9. The cone angle defined relative to the dashdotted line indicating the longitudinal axis of the valve member should be between 15° and 60". Especially suitable is the shown angle of 22°.

For improved logistics with respect to the mold manufacture, for example, with respect to outsourcing of the entire valve manufacture to a valve producer, it is suggested, as shown here, to provide each valve member 4 in a separate substantially cylindrical housing 12. Together with the pressure (return) spring 11 and the abutment 13 a constructive unit results which combines all individual parts of the valve 3 such that they cannot be lost. Such a valve 3 can be completely mounted by the valve manufacturer and can be inserted by the mold manufacturer into correspondingly prepared vent bores from the interior of the vulcanization mold.

49* The insertion is carried out preferably by pounding the valve into a narrow bore. This results in a press fit. In order to provide, on the one hand, a sufficiently secure hold and, on the other hand, a demounting possibility that will not destroy the mold segment, it has been proven successful in practice to provide for an outer housing diameter D of 3.5 mm an inner bore diameter D (see Fig.

1a) of the 3.35 mm. In order to facilitate the pounding action, the housing 12 has advantageously a tapered portion at the end facing away from the interior of the mold. The return spring 11 is -31 preferably in the form of a coil spring with approximately 10 free windings and with one extra abutting winding each positioned at either end. By providing a greater pitch of the spring windings, it seems possible to achieve for each opening and closing stroke a small rotation of the valve member about the dash-dotted longitudinal axis. Thus, it would be possible to provide for an extended period of time an especially uniform closing action over the entire valve plate circumference.

When in a variant to Fig. 2 the valve 3 is without housing, the inner conical surface 9 is then directly provided at the corresponding location of the wall of the mold segment by drilling or cutting.

Fig. 3 shows in the same cross-sectional plane as Fig. 2 and in the same scale 20:1 an individual venting valve 3 with a valve limitater in the form of a snap connection for limiting the valve stroke h by a defined play. The valve limiter comprises as a separate component a retainer spring 16. In the widest open position of the valve shown in the drawing, the valve shaft 5 with o the truncated cone surface 18.1 of the collar 18 facing the interior of the mold comes into contact with the end face 16.3 of the inwardly oriented free ends 16.1 of the retainer spring 16 This inwardly oriented free ends 16.1 of the retainer spring 16. This 32end face 16.3 faces away from the interior of the mold. The collar 18 is connected to the end of the valve shaft 5 which faces away from the interior of the mold.

Fig. 4a shows this retainer spring 16 in detail in the same scale in a plan view with outwardly positioned C-shaped main portion 16.2 which can be compressed to such an extent that the spring 16 can be inserted from the side facing away from the interior of the mold, in Fig. 3 from below, into the interior of the housing where it snaps into the groove 15 provided at the inner side of the valve housing 12, respectively, for a design without housing, in the vent bore within the mold segment in a plane that extends perpendicularly to the longitudinal axis of the valve 3. The retainer spring 16 has inwardly oriented elastically deformable free ends 16.1 that are designed such that after being released they engage the groove 16 of the valve shaft 5 shown in Fig. 3. The free ends 16.1 are close enough to one another that, after the surface 16.3 of the spring 16 facing away from the interior of the mold contacts the surface 18.1 of the collar 18 facing the interior of the mold a resistance against further removal of the valve member 4 is present. Preferably, the free ends 16.1, on the other hand, should be spaced far enough apart that the -33valve member 4 can move without jamming along its dash-dotted longitudinal axis between the abutments 18.1 and 17.1.

These free ends 16.1, as can be seen in Fig. 3, are spread apart upon mounting of the valve shaft 5 from the direction of the interior of the mold by the leading conical surface 18.2 of the collar 18 which surface is arranged at the end of the collar 18 facing away from the interior of the mold. The collar 18 is connected to the end of the valve shaft 5 end facing away from the interior of the mold. After overcoming the thickest portion of the collar 18, the free ends 16.1 come together again while gliding along the inversely oriented conical surface 18.1 such that the ""valve shaft 5 can be removed only with great force expenditure in the reverse direction toward the interior of the mold (especially with a greater force than that of the spring 11). In order to secure i the spring 16 more reliably against removal from the groove when mounting the valve member 4, it is possible to press or screw a sleeve from the side facing away from the interior of the mold against the spring.

The inwardly facing free ends 16.1 engage a groove 17 of the valve shaft 5. The groove 17 is delimited to the side facing away from the interior of the mold by the conical surface 18.1 and -34to the side facing the interior of the mold by a preferably planar surface 17.1. The groove width w17 of the grove 17 is greater by a certain amount than the thickness of the spring 16. This amount is somewhat greater than the valve stroke h so that in the closed position of the valve 3 the end face of the groove 17.1 which follows the closing movement, does not advance to the end face 16.4 of the spring 16 facing the interior of the mold. Thereby an over definition in the limitation of the valve stroke is avoided and an easy introduction of the outer conical surface 7 of the valve plate 6 into the inner conical surface 9 is possible. This effects a perfect closure of the valve 3 and eliminates displacement between the end surface 8 of the valve plate 6 and the surrounding surface of the interior of the mold. This could theoretically also be achieved with a smaller groove width w17 when the groove width w15 is correspondingly greater according to the following equation: w17 w15 2w16 h.

o o However, then the main portion 16.2 would have to be displaceable relative to the housing 12 which would result in additional play also in the radial direction of the valve and in a tendency to canting with correspondingly fluctuating coefficients of friction. Thus, it is preferred to have w16 only slightly smaller than so that the required play of approximately 20 pm required for the insertion is provided. The aforementioned equation then is simplified as follows: w17 w16 >h.

Fig. 4b shows in an analogous representation to Fig. 4a such a variant of the retainer spring 16 in which the C-shaped main portion, identified as 16.5, is provided with free ends that do not extend inwardly but outwardly and which are identified at 16.6.

The free ends 16.6 are designed to engage the groove 15 at the housing and the C-shaped main portion 16.5 is designed to engage the groove 17 of the valve shaft Fig. 5 shows in an analogous representation to Fig. 3 a single venting valve 3 with a stroke limiter in the form of a snap connection with defined play whereby the required elastic compression for the snap connection is also achieved by bending, .:"however, not as bending of a separate retainer spring but as bending of the slotted end of the valve shaft 5 facing away from the interior of the mold and represented at the bottom of the drawing.

In order to save manufacturing costs the slotting is -36preferably achieved by a single slot 19, as shown. In this embodiment, the slot 19 must be of a substantial width in order to allow for a sufficient compression stroke of the two remaining tongues in the shown longitudinal section plane for insertion and removal of the valve shaft 5 through the opening 12.1 of the housing 12 facing away from the interior of the mold and also in the longitudinal section plane of the valve 3 extending perpendicular thereto. (The latter cross-sectional plane would be a cross-sectional plane for the entire mold However, a more narrowly slotted embodiment would be possible when the collar 18 in the vicinity of the slot were flatter, would project less from the remaining surface of the shaft 5 or when instead of the single slot 19 two crossing slots would be provided at the end of the shaft 5 facing away from the interior of the mold.

The collar 18 at the end of the valve shaft 5 facing away from the interior of the mold has a limiting surface 18.1 facing the interior of the mold. This limiting surface serves as an abutment surface for limiting the valve opening stroke and is positioned such that in the desired open position, which for a valve plate diameter of approximately 2.8 mm and a cone angle to the longitudinal axis of 220 should require a valve stroke of approximately 0.5 mm, as -37shown, abuts the surface of the housing 12 facing away from the interior of the mold, or an equivalent surface for an embodiment without housing. With this abutment surface the opening stroke is limited.

The reverse movement, the closing movement, is not limited in any way by the collar 18. The stroke limitation is exclusively achieved by the outer conical surface 7 of the valve plate 6 contacting the inner conical surface 9.

For demounting of such a valve member 4 a forceful pulling at the valve plate 6 in the direction of the interior of the mold is sufficient for the shown and preferred conical embodiment of the abutment surface 18.1. Otherwise, it would be required to elastically compress with the other hand the tongues of the valve shaft 5 to such an extent that the opening 12.1 of the housing 12 can be passed.

For mounting, a conical embodiment of the other limiting surface 18.2 of the collar 18 is expedient in an analogous manner.

Then, a forceful pressing is sufficient.

The depth of the slot 19, respectively, of the slots at the end of the shaft 5 facing away from the interior of the mold is small enough in order to provide a sufficient resistance against 38accidental removal of the valve member in cooperation with the resulting tongue stiffness, but is, on the other hand, great enough in order to make the tongues elastic enough that a demounting can be performed easily.

The detailed embodiments are designed to provide a person skilled in the art with comprehensive knowledge of the invention. The desired protection however is not to be limited by the details provided. The gist of the invention is simply that in each of the hundreds of venting bores of a tire vulcanization mold a valve is to be inserted whereby each valve is closed by the advancing surface of the green tire and is opened upon removal of the vulcanized tire.

The present invention is, of course, in no way restricted to the specific disclosure of the specification and drawings, but also encompasses any modifications within the scope of the appended claims.

-39- 40

CLAIMS:

i. A vulcanization mould for manufacturing tyres, the vulcanization mould including: mould walls having 600 to 3,000 vent bores; a valve inserted into each of the vent bores; each valve having a moveable valve member including a valve shaft and a valve plate connected to the valve shaft, each valve plate having a substantially planar surface facing the interior of the mould; and each valve further having a wire helical spring which is compressed when said valve is closed, said helical spring being arranged concentrically around said valve shaft and extending substantially to said valve plate; wherein each valve is arranged such that, in use, an advancing surface of a green tyre, inserted into the mould to be vulcanized, bears against said valve plate to close said valve and, said helical spring opens said valve upon removal of the tyre from the mould.

20 2. A vulcanization mould as claimed in claim 1 wherein each valve plate has the shape of a truncated cone, the conical surface of each valve plate faces away from the interior of the mould, and each valve further has a matching counter surface for said conical surface.

25 3. A vulcanization mould as claimed in claim 2 0e "wherein said matching counter surface is provided in said mould walls.

4. A vulcanization mould as claimed in claim 2 *000 wherein each valve includes a housing to which said valve member and said spring are securely connected.

A vulcanization mould as claimed in claim 4 wherein said housing is cylindrical.

6. A vulcanization mould as claimed in claim 4 wherein said counter surface is provided at said housing.

7. A vulcanization mould as claimed in claim 4 wherein said housing has an outer diameter between 2 and 6 mm, said outer diameter being greater than the inner

Claims

8. A vulcanization mould as claimed in claim 1 wherein said valve includes a stroke limiter, connected to an end of said valve facing away from the interior of said vulcanization mould, for limiting the stroke of said valve member in a direction toward the open position to less than 2 mm.
9. A vulcanization mould as claimed in claim 8 wherein said stroke limiter is detachably mounted to said valve shaft so as to be detachable for demounting said valve member. A vulcanization mould as claimed in claim 8 wherein for demounting said valve member said stroke limiter is in the form of a releasable snap connection for connecting said valve member with play within said valve so as to allow for an opening and closing stroke of :said valve member.
11. A vulcanization mould as claimed in claim 20 wherein said valve includes a housing with an inner chamber in which said valve member and said return spring are positioned, wherein said inner chamber of said housing has a first groove at an end of said housing facing away from said interior of said vulcanization 25 mould, said first groove positioned in a plane extending -perpendicularly to a longitudinal axis of said valve eoea housing and having a first width w15 in a direction of eeo. said longitudinal axis of said valve housing, said stroke limiter comprising a retainer spring of a thickness w16 positioned in said first groove, said stroke limiter further comprising a second groove having a second width w17 provided at said valve shaft, said retainer spring engaging said second groove, wherein at least one of said first and second widths w15, w17 is greater than said thickness w16 of said retainer spring by such an amount that said play P, defined by the equation P w17 w15 2 x w16, is at least as great as the stroke of said valve member. 42
12. A vulcanization mould as claimed in claim 11 wherein said retainer spring in a plan view has a C- shaped main portion and has free ends connected to said main portion and bent outwardly relative to said main portion, said free ends engaging said first groove.
13. A vulcanization mould as claimed in claim 11 wherein said retainer spring in a plan view has a C- shaped main portion and has free ends connected to said main portion and bent inwardly relative to said main portion, said free ends engaging said second groove.
14. A vulcanization mould as claimed in claim wherein said valve shaft has a first end facing away from said interior of said vulcanization mould, said first end having a collar, wherein said collar has an abutment surface facing said interior of said vulcanization mould for limiting said stroke of said valve member toward the open position, said first end having at least one slot in order to allow a compression of the diameter of said collar so that by compressing said collar said valve 20 member is removable from said valve. V* 15. A vulcanization mould as claimed in claim 14 wherein said abutment surface has a truncated cone shape so that a pulling action toward said interior of said vulcanization mould causes an automatic compression of 25 said collar for removing said valve member.
16. A vulcanization mould as claimed in claim 14 wherein a surface of said collar opposite said abutment surface has a truncated cone shape and wherein said vent bore has a conically inwardly tapering inlet facing said interior of said vulcanization mould so that by pushing said valve member from said interior of said vulcanization mould into said vent bore said collar is automatically compressed for insertion of said valve member into said vent bore.
17. A vulcanization mould as claimed in claim 14 wherein said housing has a conically inwardly tapering inlet facing said interior of said vulcanization mould when mounted, wherein a surface of said collar opposite 771AZ/700 43 said abutment surface has a truncated cone shape so that by pushing said valve member into said conically inwardly tapering inlet said collar is automatically compressed for insertion of said valve member into said housing.
18. A vulcanization mould as claimed in claim 14 wherein said collar in a plan view deviates from a circular shape such that a diameter of said collar remote from said at least one slot is greater than a diameter of said collar in the vicinity of said at a least one slot.
19. A vulcanization mould for manufacturing tyres substantially as herein described with reference to the accompanying drawings. DATED this 15th day of July 1999 9 a a. a. CONTINENTAL AKTIENGESELLSCHAFT 15 By its Patent Attorney GRIFFITH HACK a. a. a. a. a. a S. r a. a a ao* a 04771AZ/700 4 4 Abstract of the Disclosure A vulcanization mold for manufacturing tires has mold walls with 600 to 3,000 vent bores. A valve is inserted into each one of the vent bores. The valve is designed such that an advancing surface of the green tire, inserted into the vulcanization mold for vulcanization, closes the valve and that the valve is opened when the vulcanized tire is removed after vulcanization. 0..0 so&: 0 0609p SS 0