The invention relates to a method for retread¬ ing a tyre, comprising placing a tyre to be retreaded between press parts in a vulcanizing press, and form¬ ing a tread pattern by means of matrix blocks, where¬ by the placing of the tyre in the vulcanizing press is further carried out under the guidance of a di¬ visible rim member attached to the opposite parts of the vulcanizing press, the matrix blocks, a displac¬ ing means and its counterpart, or to one or more of the above-mentioned parts, whereby the rim member aligns the tyre to be retreaded, and whereby com¬ pressed air or the like is fed into the tyre and a tight pressure space is formed in a space between the tyre and the rim sections.

It is a common practice to provide tyre bodies with a new tread pattern to recycle used tyre bodies. The retreading takes place by covering the surface of the body by a vulcanizable rubber substance and by placing the tyre in a vulcanizing press, in which a desired tread pattern is pressed in the rubber substance by a matrix mould or the like at a prevail¬ ing temperature. It is previously known to utilize baking inner tyres in the retreading process, which are placed within the tyre body before the tyre is placed in the vulcanizing press. The purpose of the baking inner tyre is to protect the inner surface of the tyre itself and to form a supporting structure for the tyre during the retreading process, thus enabling the retreading material to be bonded evenly to the sur¬ face of the tyre body.

It is also previously known to use vulcanizing bellows to support and protect the tyre, the bellows

being filled with compressed air, water or steam, similarly as the baking inner tyre, whereby the vul¬ canizing bellows slide to the inside of the tyre body and is shaped so as to support the structure of the tyre during the vulcanization.

Further, it is known in the retreading of the tyres of heavy vehicle equipment, such as earth moving machinery, to use a method in which the tyre to be retreaded is placed on a rim consisting of two or three sections, whereby the combination of the rim and the tyre corresponds to the combination of a normal vehicle rim and tyre. At the following step, the tyre to be retreaded together with its rim is lifted into a vulcanizing press, in which air is fed through the rim via a single valve so as to seal the rim and the tyre against each other. This solution is disclosed in US Patent 3,690,794.

The prior art has many drawbacks and weak¬ nesses. The methods utilizing a baking inner tyre are slow to carry out and involves unnecessary extra work for the operator of the vulcanizing press.

The baking inner tyre as such forms part of the retreading process, being a cost item in itself. The service life of the baking inner tyre is also restricted as rubber is continuously ulcanizable, wherefore the baking inner tyre becomes harder and harder in connection with every retreading procedure.

The apparatus arrangements required for the method utilizing vulcanizing bellows are un- necessarily complicated and expensive to realize and use.

The prior art method utilizing the rim is dif¬ ficult, slow and includes unnecessary work stages as it requires that the multiple-part rim be placed separately by hands on the tyre, whereafter the tyre

with the rim is placed in the vulcanizing press. After vulcanization, the rim again has to be removed from the middle of the tyre by laborious measures.

A vulcanizing press comprising a rim member has also been used in other retreading methods or apparatus arrangements in which the pressurization of the inner space of the tyre takes place by the intro¬ duction of compressed air. US Patent 2,854,692 dis¬ closes a vulcanizing press in which the pressuriza- tion is carried out through a feed pipe for com¬ pressed air. The feed pipe extends directly from above, being tangent to the side of the inner periphery of the tyre. This solution comprises narrow upper and lower rim sections, and the space between the sections is closed by the feed pipe. This structure is unnecessarily complicated in view of the formation of a closed pressure space and difficult to use, as the halves of the rim member, that is, the rim sections are not pressed directly against each other, and so the formation of the pressure space and the pressurization requires various other measures and unnecessary apparatus arrangements for the rim member and the press. In addition, the apparatus dis¬ closed in the above-mentioned patent document is such that its rim sections do not approach each other by parallel motion but the second rim section screws itself upon the first rim section like a lid. More¬ over, the operation of this apparatus requires that the rim sections should be tightened against each other, usually manually, by means of various insertion pieces or other such means separate from the rim member halves.

US Patent 3,135,996 discloses an annular mould in which compressed air is fed through a separate cylindrical wall. This structure is still unnecessar-

ily difficult to use, as the rim member sections are joined by a separate wall.

US Patent 4,238,174 also discloses a structure similar to those described above, in which the halves of the rim member are not in direct contact with each other, and so the pressurization of the inner space of the tyre is difficult to carry out.

DE Patent Specification 2 047 074 discloses a structure in which the matrix block of the press is heated.

The object of the present invention is to provide a method which avoids the above-mentioned disadvantages and enables the tyre retreading process to take place in a purposeful and efficient way. This object is achieved by means of a method according to the invention which is characterized in that the feeding of compressed air or the like takes place through the periphery of the rim via the periphery of one or more rim sections of the rim member pressed directly together in the vulcanizing press.

The method of the invention is based on the idea that compressed air or the like is fed through the periphery of the rim member connected to the vul- canizing press or its parts into a space defined between the tyre and the rim sections pressed together directly and by parallel motion in parallel directions in the vulcanizing press. The rim member utilized in the method preferably comprises two rim member sections positioned opposite to each other in the press. The tyre is first placed upon or around the first, preferably the lower rim member section or half. The rim member sections or halves are pressed directly against each other by causing them to approach each other evenly by parallel motion. The

first and the second rim section or half are thus pressed directly and tightly together. More precise¬ ly, the peripheries of the rim member sections are sealed directly against each other. The pressuriza- tion of the tyre is then carried out through the periphery of the rim member into a space between the tyre and the rim member. The pressurization is carried out either through the periphery of one rim section or half or through the periphery of both halves. The operability of the method is considerably improved as compared with the known solutions. The structure of the rim member may also be such that one rim section comprises most of the periphery of the rim member while the other rim section is mainly a counterpart. In the method according to the inven¬ tion, the rim member halves are pressed directly against each other, and so a closed pressure space is formed easily and reliably between the tyre and the rim sections pressed together. The rim sections are attached to the press or to the mould halves or to the displacing means of the rim sections or to other parts positioned in the press blocks. The sections of the rim member may be connected to one or more of the above-mentioned structural parts.

In the press apparatus the tyre to be retreaded can be placed on one rim section, whereafter the sections of the divisible rim member are pressed directly tightly against each other by the press apparatus, i.e. the vulcanizing press, by substan¬ tially parallel motion, and the pressurization of the space between the rim and the tyre is started through the periphery of the rim. As the pressurization is carried out in the vulcanizing press directly through the periphery of the rim member sections pressed

directly together, the operation of the method is extremely reliable and easy.

The method is notably rapid to carry out, as it does not comprise any unnecessary intermediate stages. In the press, the halves of the rim member are pressed directly against each other by parallel motion.

As distinct from certain prior art solutions, the method avoids handling separate baking inner tyres or rim sections. When using the method accord¬ ing to the invention, the alignment of the ^* tyre can also be carried out as the rim member sections are attached to the press parts or to the mould halves.

The invention is also concerned with a tyre retreading apparatus for realizing the method, the apparatus comprising a divisible rim member for supporting a tyre placed in a vulcanizing press and for creating an internal pressure, whereby rim member sections are attached apart from each other by fastening means to press parts, matrix blocks, a dis¬ placing means and its counterpart, or to one or more of the above-mentioned parts, and the rim member com¬ prises means for feeding compressed air into a space between the rim sections pressed together and the tyre to be retreaded. The apparatus according to the invention is characterized in that the pressure feed is arranged to take place through several through- openings formed in the periphery of one or more rim sections of the rim member formed by the rim sections pressed directly together by means of the vulcanizing press.

On the apparatus level, the method according to the invention is of the greatest possible benefit due to the introduction of compressed air or the like through the periphery of the divisible rim member,

that is, through the periphery of the rim, which is attached to the matrix blocks or to the opposite press parts or to the displacing means and its counterpart, or to several of the above-mentioned structural parts. The apparatus is simple in struc¬ ture and, as distinct from the known solutions, does not require any significant measures to be performed on the rim member. The introduction of compressed air or the like according to the invention in the pres- surization through the periphery of the rim member sections pressed together enables unnecessary stages and parts to be omitted from the retreading process.

In the following the invention will be described by means of the attached drawings, in which Figure 1 shows a vulcanizing press which is the operating milieu of the method and apparatus accord¬ ing to the invention;

Figure 2 shows rim member halves to be posi¬ tioned against each other; Figure 3 shows a stage at which a tyre to be retreaded has been placed on the lower rim member section attached to a matrix block;

Figure 4 shows a rim member comprising two halves; Figure 5 shows a rim member and a. tyre to be retreaded;

Figure 6 is a simplified general view illustrating the air feed openings of the rim member. The operating milieu of the method and the apparatus is an apparatus similar to the vulcanizing press shown in Figure 1, although the method and the apparatus are equally applicable in vulcanizing presses with transversely divisible or radial matrices. In the press 1 shown in Figure 1, com- prising a transversely divisible matrix, an upper

press block part 2 movable by a displacing mechanism 6 and 7 is provided around a frame structure 8, which press block part can be moved towards a lower press block part 3 comprising a matrix pattern 4, the upper block 2 similarly comprising a matrix pattern 5.

Figure 2 shows how sections 9 and 10 of the divisible rim member are positioned directly against each other. The rim member preferably comprises two sections fastened substantially in alignment opposite to each other so that the sections 9 and 10 can be pressed tightly and directly against each other by the pressing movement of the press 1. The movement of the press is preferably parallel, that is, different points in the rim sections approach each other even- ly. The rim sections or halves are pressed in the press directly together without any special auxiliary means such as separate walls or other such structural parts. The sections of the divisible rim member are attached to the press parts 2 and 3, to the matrix blocks 4 and 5, or to actuating means connected to the above-mentioned parts, such as a means 29 dis¬ placing the rim member sections and its counterpart (not shown), by means of which the rim member section 10 placed on the lower press part 3 can be lifted and lowered.

Figure 3 shows how a rubber-covered tyre to be retreaded is placed on the lower rim section 10. The press apparatus 1 presses the press parts 2 and 3 closer to each other, and so the opposite rim halves are sealed directly against each other, whereafter compressed air or the like is fed through a valve 15 or the like means through the periphery of the rim, whereby the pressure between the rim member 9, 10 and the tyre 14 to be retreaded rises and the compressed air is introduced at such a high power that the

amount of air flowing in is considerably greater than the amount of air escaping from between the rim 9, 10 and the tyre. The tyre is thereby pressed tightly against the rim 9, 10, thus creating an internal pressure in the tyre 14 to be retreaded and support¬ ing the structure of the tyre 14 during the retread¬ ing process.

Figure 5 shows the attachment of the tyre 14 to the divisible sections pressed together. Compressed air or the like fed through the periphery of the rim passes through peripheral openings 11, 12 (the other openings are not shown in the figure) into a space defined between the rim 9, 10 and the tyre 14, whereby a bead 18 of the tyre 14 is pressed strongly against a plane A of the rim section 9 under the influence of the compressed air, and forms a seal face C; correspondingly, another bead 19 of the tyre 14 is pressed against a plane B of the other rim section 10, and forms a seal face D. The rim member section 10 is attached through a fastening means 17 to the lower press part 3, the matrix block 5, or to an associated means, such as a means 29 (not shown) intended to displace the rim section 10. Correspondingly, the other rim member section 9 is attached through a fastening means 16 to the press part 2, the matrix block 5 or to an associated means, such as a means (not shown) intended to displace the rim section 9. The rim section 9 may be attached to one or more of the above-mentioned structural parts.

Compressed air is fed through the periphery of the rim through one or more rim sections 9, 10. Through the valve or the like means 15, compressed air is fed into the space defined between the rim and the tyre 14 through a number of feed openings 11 to

13, 24 to 28 formed in the rim section, whereby the pressure is caused to be distributed evenly and rapidly and thus the beads 18, 19 of the tyre 14 are pressed tightly against the edges of the rim. The feed openings 11 to 13, 24 to 28 are preferably posi¬ tioned uniformly along the periphery of the rim.

In one embodiment of the invention, compressed air is fed into the feed openings 11 to 13, 24 to 28 through a tunnel-like conduit 23 positioned on the arch of the rim. The conduit 23 also acts as an intermediate storage for compressed air, by means of which the creation of pressure between the rim and the tyre can be carried out rapidly. The conduit can be formed on the surface of the arch of the rim, as shown in Figures 3 and 4. The tunnel-like conduit may also be formed within the structure of the rim.

The feed openings 11 to 13, 24 to 28 for compressed air are formed on the arch of the rim preferably substantially in the radial direction of the rim 9, 10, whereby the supplied compressed air is directed substantially perpendicularly towards the inner surface of the tyre 14 and thus less air escapes from between the rim 9, 10 and the beads 18, 19 of the tyre 14 at the initial stage of the pressure feed.

The divisible rim member preferably comprises two sections 9 and 10, which are pressed directly against each other by the press apparatus 1. The halves 9, 10 of the rim member can be joined in several different ways. The halves 9, 10 of the rim member can be positioned so as to overlap, thus form¬ ing a sliding seal face. The rim member sections can be positioned in abutment with each other or they are shaped so that a wedge-shaped seal face (not shown) is formed between the halves 9, 10.

After the rim sections have been pressed together, compressed air is fed through the periphery of the rim member into the space between the rim 9, 10 and the tyre 14 to be retreaded, and after the desired pressure has been obtained, the matrix blocks are pressed against the surface of the rubber-covered tyre.

After a predetermined period of time, the re- treaded tyre can be removed from the vulcanizing press, before which stage the internal pressure of the tyre 14 is released.

The drawings and the description related to them are only intended to illustrate the idea of the invention. In their details, the method and the apparatus according to the invention may vary within the scope of the attached claims.