GB2032356A

GB2032356A - Making pneumatic tyres

Info

Publication number: GB2032356A
Application number: GB7928095A
Authority: GB
Original assignee: Continental Gummi Werke AG
Current assignee: Continental AG
Priority date: 1978-08-14
Filing date: 1979-08-13
Publication date: 1980-05-08
Also published as: DE2835586C2; IT7924819A0; DE2835586A1; IT1122381B; AT380201B; FR2433411B1; FR2433411A1; GB2032356B; ATA453479A

Abstract

In a method of producing a belted tyre, in which the belt 1 is built up on a drum 8 and is then removed and joined to a carcase 10 which is subsequently inserted in a vulcanizing mould, Fig. 5, for moulding the tread surface profile, an increase in diameter of the belt occurs in the mould, and the belt diameter is reduced before joining the belt to the carcase in order to render the belt expansible by an amount which corresponds at least substantially to the diameter increase which occurs in the mould. The illustrated belt comprises two plies 2, 3 with circumferential cords and a ply 5 with cords at 10 DEG -30 DEG to the circumferential. <IMAGE>

Description

SPECIFICATION Method of producing belted tyres The present invention relates to a method for producing belted tyres, the belt being built up individuaily and, after being joined to the carcase for insertion in a vulcanizing mould, has its diameter enlarged for moulding the tread surface profile.

So-called belted tyres are distinguished by a belt which is tension-resistant in the circumferential direction of the tyre transversely cross-braced and producing the lateral stabilisation ofthe pneumatic tyre, resulting in a favourable travelling behaviour.

Difficulties are caused, however, during the manufacture of the tyre insofar as generally a belt bracing cannot be increased in diameter when the rubber enveloping the reinforcing members is still unvulcanized. For these reasons, normally so-called "radially divided" moulds with radially displaceable segments are used for vulcanization, whereby the tyre blank substantially fixed in diameter has imparted thereto the tread surface profiling by radially inward displacement of the segments.

These vulcanizing moulds are not only costly to obtain, but are also prone to breakdown in comparison to "centrally-divided" vulcanizing mounds which are comprised only of two rigid, namely an upper and a lower, rings, which at their outer circumference each have half the tread surface profile.

The object of the present invention is to provide a method of production of belted tyres having tension resistant belts in the circumferential direction of the tyre, that permits the use of the so-called centrallydivided, thus not radially-divided, vulcanizing moulds.

According to the present invention there is provided a method for producing belted tyres, whereby the belt is bulit-up individually and, after being joined to the carcase and inserted in the vulcanizing mould for moulding the tread surface profile, is increased in diameter, in which the belt diameter is reduced before joining the belt to the carcase by circumferential overfeeding by an amount which corresponds at least substantially to the diameter increase (residual elevation) necessary for moulding the tread strip profile.

On account of this proposal, the belt is first, in conventional manner, built up on a drum; then the belt diameter is reduced which may be effected by a drum diameter reduction under use of a vacuum.

This belt, artificially reduced in diameter, and the reinforcing plies of which extend substantially in a circumferential direction, are overfed in themselves, is then in conventional manner combined with a carcase and then inserted in a vulcanizing mould rigid in outer circumference, thus a mould not enlarge able in diameter at the outer circumference. Then, by using the internal pressure, the diameter of the tyre blank is increased in that the overfeeding is cancel led, whereby it is understood that the extent of overfeeding is such that same is cancelled when the tyre blank is moulded, thus is provided with its final profile on the outer circumference. The invention includes such proposals which permit a deformation of the tyre blank, if during the tyre production the tyre belt or the tyre blank are not subjected to any tension.For these reasons the overfeeding caused at the beginning of the tyre production is practised to such an extent that the diameter increase occurring during the production of belted tyres (until the blank is inserted in the vulcanizing mould) is automatically compensated. What is important, is that the above diameter increase is still possible, and thus to such an extent still possible as is necessary for moulding in the initially mentioned simple vulcanizing mou Ids.

The diameter increase necessary for moulding the tread strip profile is designated by the term "residual elevation"; such term being used in the particular description hereinafter.

The present invention will be further illustrated, by way of example, with reference to the accompanying drawings, in which: Fig. lisa radial part section of a tyre belt building drum having a belt blank located thereon; Fig. 2 is a side view of the belt according to Fig. 1; Fig. 3 is a radial part section through the belt building drum in accordance with Fig. 1, including a tread strip blank; Fig. 4 is a fragmentary section of the tyre blank prepared for insertion in the vulcanizing mould; Fig. 5 shows the blank in accordance with Fig. 4 inserted in a vulcanizing mould; and Fig. 6 shows the mould in accordance with Fig. 5 but after termination of the moulding and vulcanizing operation.

Belt 1, comprised of rubberised cord fabric plies has an inner ply 2 and an outer ply 3, each having tension resistant reinforcing members intheform of wires 4, made for example of steel and extending parallel to one another in the circumferential direction of the tyre. Between the two plies 2,3 there is a rubberised ply 5, the filamentary reinforcing members of which also extend parallel to one another and which may extend substantially transversely to the belt thus, for example, at an angle of from 10 to 30".

In accordance with Fig. 2, the wires 4 are not endless but are open ended; however, the overlapping points 6 of both plies 2, 3 necessary to produce firm interlocking, for reasons of compensating centrifugal force are located at diametrically opposite positions.

To explain the term "residual elevation" reference is made to Fig. 6.

The neutral plane 7, which is substantially determined by the centre of the ply 5, is the finished diameter after moulding and vulcanization of the belt 1. The associated diameter D is a diameter which no longer requires any diameter increase and hence residual elevation. Smaller diameters which are required during manufacture are related to the diameter D and the difference thereto is quoted as residual elevation, in percent, of the diameter D.

The belt building drum S has a variable diameter which may be varied by means of segments, not shown in detail, which accordingly have to be radially adjusted. Induction air connections which permeate the segments are also an expedient with which the belt 1 can be non-displaceably retained on the outer surface of the belt building drum 8.

For reasons of manufacturing tolerance and accu racy the drum in accordance with Fig. 1 is so adjusted that, having regard to the plane 7 of the belt in accordance with Fig. 1, a residual elevation of between 0.3-and 0.6% results (i.e. a diameter increase of from 0.3 to 0.6% of the diameter relative to diameter D is necessary to attain the end diameter D in accordance with Fig. 6.) With this residual elevation of 0.3 to 0.6%, preferably 0.4%, and fixedly adjusted belt drum 8, the plies 2,3 and 5 are placed in position in a conventional manner taut and free of bubbles in accordance with Fig. 2. Then, in accordance with Fig. 3 a diameter reduction of the belt building drum 8 occurs by a dimension which corresponds to a residual elevation of from 5 to 12%.

The belt 1 herewith is overfed in itself, whereby the mutual spacing of the reinforcing members of ply 5 is reduced, the reinforcing members 4 of plies 2 and 3, however, being longitudinally overfed. After this diameter reduction the tread strip 9, still in a crude state, is placed in position.

In order to permit the belt 1 so overfed in itself, and enclosed by the tread strip 9, to be joined together with a radial carcase 10, the belt 1 and the tread strip 9 have to be removed from the drum 8.

During and subsequent to such removal, the tread strip 9 exerts a bandage effect, however it is not possible to prevent the overfeeding stress introduced into the belt 1, from causing a diameter increase of the belt 1. A diameter increase will also occur in that, for attaining a cover rigidity of the carcase 10, internal pressure has to be introduced therein so as fo permit a secure, bubble-free abutment of the belt against the carcase 10, and rolling on of the tread strip 9 has to be carried out. Thus, if the tyre blank so made together with the carcase 10 is now drawn off the associated apparatus, then in accordance with Fig. 5, it will just about have to fit into the vulcanizing mould without having to damage the tread strip 9.The residual elevation should still be possible under these conditions, and thus by a dimension of from 4 to 6% so that when introducking the internal pressure into the tyre blank in accordance with Fig. 5, the over feeding of the belt 1 is cancelled out, the tread surface profile is moulded on and finally, the terminal state attained asin Fig. 6.

On completion of the vulcanization, the belt 1 is substantially free of tension it has transversely orientated reinforcing members, as well as reinforcing members which extend in the circumferential or substantially the circumferential direction of the tyre.

It is to be noted that the overlap points in accordance with Fig. 5 to permit minor diameter increases; however, the invention does not provide a diameter increase by way of strip reduction, but by way of an artifical overfeeding which is cancelled out the vulcanizing mould, namely by taking into consideration the inevitable diameter increase occurring during manufacture which is caused by the elastic components still contained in the unvulcanized rub ber.

The invention does not exclude that, after building the belt and after its diameter reduction, diameter increases can be prevented in that the belt or the blank treated strip already located thereon being provided with a bandage so as to stop diameter increases. The use of these bandages may also occur after the belt is connected to its carcase, e.g. in case the completed tyre blank cannot be directly supplied to the vulcanizing mould.

Filament angles for the tyre belt in question are such which permit overfeeding of the reinforcing members in a longitudinal direction. It is therefore preferable to select filament angles of up to about 20 with reference to the circumferential direction of the tyre. It is, however, understood that the overfeeding effect is still greater the smaller the filament angle- measured with reference to the circumferential direction of the tyre.

The invention is also not restricted to certain materials for the belt. Other materials than those specifically mentioned are possible, as well as different reinforcing member designs which permit overfeeding in the longitudinal direction of the reinforcing members. It is understood moreover, that the invention is not bound by a definite number of plies, although the belt development reproduced in the specific embodiment illustrated in the drawings, comprised of three plies, is advantageous.

Claims

1. A method for producing belted tyres, whereby the belt is built up individually and, after being joined to the carcase and inserted in the vulcanizing mould for moulding the tread surface profile, is increased in diameter, in which the belt diameter is reduced before joining the belt to the carcase by circumferential overfeeding by an amount which corresponds at least substantially to the diameter increase (residual elevation) necessaryformoulding the tread strip profile.

2. A method as claimed in claim 1, in which the belt is overfed by an amount which is s úbstantially greates than the diameter increase necessary to obtain the residual elevation.

3. A method as claimed in claim 1 or2, in which during the overfeeding a diameter reduction occurs which is about twice the size of the diameter increase necessary for attaining the residual elevation in the vulcanizing mould.

4. A method as claimed in claim 1, in which the belt is overfed to such an extent that, on completion of the residual elevation in the vulcanizing mould, the reinforcing members extending in or substantially in the circumferential direction of the tyre are either substantially stress-free or, in this state, the overfeeding has just been cancelled out.

5. A method as claimed in claim 1, in which the build up of the belt having a drum diameter occurs in such a mannerthatthe medial diameter of the belt blank is smaller by about 0.4 to 0.6% than the end diameter of the completed tyre.

6. A method as claimed in claim 1, in which after building up the belt and its diameter reduction by circumferential overfeeding, the blank tread strip is placed securely in a bracing or bandage-like manner around the belt.

7. A method as claimed in claim 1, in which after building up the belt and its diameter reduction, and possibly after its combination with the tread strip and the carcase, a diameter increase of the belt is prevented by a detachable bandage being placed externally in position.

8. A method as claimed in any preceding claim, in which the filament-like reinforcing members of the belt blank which extend substantially in the circumferential direction of the tyre are laid in known manner in an extended condition.

9. A method as claimed in any preceding claim, in which the belt encloses reinforcing members extending substantially in the circumferential direction of the tyre, mutually parallel, reinforcing members being located in a cord ply and which extend substantially transversely, preferably at an angle of about 10 to 30 , relative to the circumferential direction of the tyre.

10. A method for producing belted tyres, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.