GB2341339A

GB2341339A - Improvements to tyre moulds

Info

Publication number: GB2341339A
Application number: GB9819455A
Authority: GB
Inventors: Robert Arthur Price; Leslie Whitworth
Original assignee: Dunlop Tyres Ltd
Current assignee: Dunlop Tyres Ltd
Priority date: 1998-09-08
Filing date: 1998-09-08
Publication date: 2000-03-15
Also published as: GB9819455D0

Abstract

A tyre mould comprises two annular sideplates 1,2 separated by an annular tread ring 3. Interior surfaces 1i,2i and 3i of the respective plates and ring together define the exterior profile of respectively the sidewalls and tread of the tyre. The mould is characterised in that at least one of the sideplates 20 (see figure 3) has a concentric annular groove 21 formed in its interior surface 20i, and having two sidewalls GS1,GS2 and, at its bottom GB, at least one vent hole 23 extending through the sideplate to its exterior surface 20e. An annular insert ring 22 is fitted into the annular groove 21. The ring 22 comprises two insert ring side faces RS1,RS2, being a non-interference fit between the groove sidewalls GS1,GS2 and, between the two ring side faces RS1,RS2, an interior face 22i defining part of the tyre sidewall profile such that an air-escape path is provided between the annular insert ring 22 and the annular groove 21 and thereafter via the vent hole 23 to the exterior of the mould.

Description

2341339 IMPROVEMENTS TO TYRE MOULDS This invention relates to tyre moulds

and particularly to the venting of such moulds.

A problem which commonly arises in the moulding of elastomeric articles such as tyres is the trapping of air between the surfaces of the article and the moul d. Such trapped air prevents the elastomeric article from contacting the mould surface and thus locally reduces conductive heat transfer and spoils the finished surface appearance. In the tyre art such resultant blemishes are termed "bareness-".

Such bareness may be prone to occur in the region of component joints such as sidewall joints where the overlapping of tapering ends may result in a localised increase in rubber thickness.

To help prevent bareness on tyres, moulds are commonly vented by means of holes of very small diameter provided through the mould wall. In practice vent holes of between 0. 6 mm and 1. 0 m -are commonly used. Such vent holes allow trapped air to escape but suffer the disadvantage that rubber can 2 also flow into the hole resulting in bristle-like projections or 'spue- pips' covering the surface of the moulded tyre.

Such spue-pips detract from the visual appearance of the tyre and are normally removed by rotating the tyre against a trimming knife held to the tyre surface. However such removal of spue-pips presents a particular problem because of the potential damage which can be done to the salient features of the tyre surface.

For example a particular problem which has been encountered concerns bareness which occurs in the lower sidewall region of the tyre. In this area of the sidewall, tyres are normally provided with several small annularly extending ridges known as clinch ribs. The provision of venting in the vicinity of these clinch ribs is a problem since their shape and size renders them vulnerable to trimming damage.

Accordingly it is an object of the present invention to provide a tyre mould which, in the region forming 3 the sidewall of the tyre, is provided with venting not requiring trimming.

According to the present invention there is provided a tyre mould comprising two annular sideplates separated by an annular tread ring each having an interior surface which surfaces together define the exterior profile of respectively the sidewalls and tread of the tyre, characterised in that at least one of the sideplates has a concentric annular groove formed in its interior surface, the grooves comprising two groove sidewalls and having at its bottom at least one vent hole extending through the sideplate to its exterior surface, and an annular insert ring fitted into the annular groove the insert ring comprising two insert ring side faces being a non-interference fit between the groove sidewalls and between the two ring side faces an interior face defining part of the tyre sidewall profile such that an air-escape path is provided between the annular insert ring and the annular groove and thereafter via the vent hole to the exterior of the mould.

4 The insert ring may be a parallel fit in the annular groove or it may be a taper fit. An included taper angle of 30' is preferable.

Also preferably the side faces of the annular insert ring on the annular groove sidewalls are finely grooved, preferably in the form of knurling.

Further aspect of the invention will become apparent from the following description by way of example only of embodiments of the invention in conjunction with the following drawings in which:

Figure 1 shows a general schematic sectional view of a ty-re mould; Figure 2 is a schematic drawing of a mould sideplate according to a first embodiment of the invention; Figures 3 and 4 show further details of the embodiments of Figure 2; Fiaure 5 shows another embodiment of the invention; and Figures 6 and -7 show further features of the embodiment of Figure S.

Shown in Figure 1 is a sectional schematic view of a conventional tyre mould comprising two annular sideplates 1 and 2 separated by a tread ring 3. The interior surfaces li, 2i and 3i respectively of the sideplates and tread ring together define the moulding profile of the sidewalls and tread of a tyre.

The particular type of mould depicted in Figure 1 is a 'two-phase' mould in which the annular tread ring comprises a plurality of sector elements. To load the tyre for moulding the upper sideplate 1 is moved upward in the direction of arrow A whilst the individual sector elements of the tread ring are moved radially outward in the direction shown by arrow B. In other types of mould the tread ring may be formed in one complete ring or two half-rings being split along or near to its circumferential centreline.

However since the present invention concerns a modification to the mould sideplate it is applicable to all tyre moulds.

6 Shown in Figures 2-4 is a sectional view of a modified mould sideplate in accordance with a first embodiment of the present invention.

According to the invention the sideplate 20 on its interior surface 20i in the region corresponding to the lower sidewall of the tyre had an annular groove 21, which is concentric with the annular sideplate, into which is fitted an annular insert ring 22. The insert ring is held within the annular groove 21 by one or more bolts (not shown) extending through a hole or holes from the exterior surface 20e of the sideplate. In its fitted position the interior surface 22i of the insert ring forms part of the moulding profile.

In this first embodiment the two sidewalls GS1 and GS2 of the annular groove and the two side faces RS1 and RS2 are mutually parallel. The fit of the ring 22 within the groove 21 is a noninterference and preferably a sliding fit with minimum tolerance so to provide an airescape path to the bottom GB of the annular groove 21. The groove bottom GB is provided with one or more drilled holes 23 extending to the exterior surface 20e of the sideplate so as 7 to complete the air-escape path from the interior to the exterior of the mould.

As can be seen in this particular embodiment the annular ring 22 fits to the bottom GB of the annular groove and thus the bottom edges 26,27 of the ring are chamfered to allow passage of escaping air into the drilled holes which are provided at the axial outer edges of the groove bottom.

As mentioned previously the lower sidewall region of the tyre may have small ridges known as clinch ribs which of course correspond to small grooves provided in the mould surface. As can be seen from Figures 2-4 the annular groove 21 may be disposed between two such small grooves such that the adjacent radiused profiled edges of the groove 21 and the ring 22 form the shallow groove 24,25.

Whilst the two sidewalls GSI and GS2 of the annular groove and the two side faces RS1 and RS2 of the annular ring may be plain they may also be grooved such as knurled to assist in air-escape. Preferably for ease of manufacture the side faces RS1 and R52 8 of the annular ring are knurled, such knurling preferably having a depth of 0.2 mm or less.

In a second embodiment of the invention shown in Figures 5-7, the annular insert ring 51 has a tapering configuration which is form-matched with tapering sidewall portions of the annular groove 52. Thus as shown the annular ring has tapering side faces TS1 and TS2 set at angles of 01 and 02 respectively to a direction perpendicular to the annular plane of the side plate. When positioned in the annular groove these tapering side faces are matched to similarly tapered portions GST1 and GST2 of the groove sidewalls. In a preferred embodiment the ring side faces are knurled and both they and the groove sidewall taper portions GST1 and GST2 are each set at a taper angle E) of 15', i.e. at an included angle of 30'.

A tyre mould constructed as described above has demonstrated improved trimless venting in the sidewall region of the tyre profile, particularly in the local region of overlapping sidewall rubber joints.

3. A tyre mould according to claim 1, wherein the annular insert ring is a taper fit in the annular groove.

4. A tyre mould according to any of claims 1 to 3, wherein the annular insert ring side faces are finely grooved.

5. A tyre mould according to any of claims 1 to 3, wherein the annular groove sidewalls are finely grooved.

6. A tyre mould according to either of claims 4 or 5, wherein the fine grooves comprise knurling.

7. A tyre mould according to claim 6, wherein the knurling has a depth of 0.2 mm or less.

8. A tyre mould according to claim 3, wherein the included taper angle is 300.

9. A tyre mould according to any of claims 1 to 8, wherein the interior face of the annular insert ring defines a part of the tyre sidewall profile between two adjacent concentric profile ribs.

10. A tyre mould substantially as herein described and depicted in Figures 1 to 7.

9

Claims

CIAIMS

1. A tyre mould comprising two annular sideplates separated by an annular tread ring each having an interior surface which surfaces together define the exterior profile of respectively the sidewalls and tread of the tyre, characterised in that at least one of the sideplates has a concentric annular groove formed in its interior surface, the grooves comprising two groove sidewalls and having at its bottom at least one vent hole extending through the sideplate to its exterior surface, and an annular insert ring fitted into the annular groove the insert ring comprising two insert ring side faces being a non-interference fit between the groove sidewalls and between the two ring side faces an interior face defining part of the tyre sidewall profile such that an air-escape path is provided between the annular insert ring and the annular groove and thereafter via the vent hole to the exterior of the mould.

2. A tyre mould according to claim 1, wherein the annular groove sidewalls and the insert ring side faces are mutually parallel.