Air venting belt for retreading tyres

Abstract: An air venting belt for use between an outer surface of a tyre and an inner surface of an envelope when a retread tyre is vulcanised, comprising a base cloth (2) made of woven cloth which is expansible at least in the longitudinal direction of the belt.

Description: The present invention relates to an air venting belt used in curing a retread tyre by the precured retreading method in which a worn-out tread is removed from a used tyre by buffing, a sheet-like unvulcanised cushion rubber is applied thereon, a belt-like precured tread is applied thereon, and the cushion rubber is vulcanised, thereby integrating the buffed tyre and the precured tread. Heretofore, an air venting belt has been used in the method which comprises a heat resistant and non-expansible nylon cloth. In general such a process for retreading a tyre, as shown in Figure 12, is as follows. A belt-like precured tread b is applied over the crown of a buffed tyre c (the tyre to be re-treaded from which the worn-out tread has been buffed) which has been covered with a non-vulcanised sheet-like cushion rubber d . Thereafter, the assembly is covered with an envelope e (a rubber cover) which protects the outer surface of the tyre from direct contact with the curing steam. The overall appearance of the envelope e is like a doughnut having a "U"-shaped cross section open inwardly. At this time, strips of air venting belt a made of nylon cloth are laid between the tread and the rubber cover at prescribed intervals in the circumferential direction. Thus a prepared tyre g is then loaded with others into a vulcanising vessel with seal plates f laid between the tyres and heated steam, the pressure of which is several kg/cm², is supplied to both the tread and sidewall zones as shown by arrows P. At this time, since the above-mentioned belts a are laid between the tread b and the envelope e , air between the tyre and the envelope vents through the mesh or open weave of the cloths as shown by arrows A. However, as mentioned above, since a non-expansible belt a is used in the conventional method, the tyre grooves h are unusually deformed, as shown in Figure 13. That is to say, the non-expansible belt a prevents the envelope from stretching and fitting itself to the inner surface of the tyre grooves h . Therefore, the force shown by arrows F operates on the end faces of the tread b , and a stress concentration happens in a narrow or thin portion i located at the bottom of the tyres grooves h , and deformation happens. For example the width of the groove becomes extremely narrowed (see the tyre groove h in the upper side of Figure 13), or even the groove takes a "W"-shaped bottom face because of the association to a bend of the cushion rubber (see the tyre grooves h in the lower side of Figure 13). As mentioned above, the conventional air venting belt thus causes a bad appearance for the tyre grooves h and reduces the value and quality of the tyre. Further, since several tyres g are loaded for vulcanisation, pressed together as shown in Figure 14, in the portion where the belt is positioned marking from the fabric may occur and cause a bad appearance. According to the present invention there is provided an air venting belt comprising a strip for use in a retread tyre vulcanisation process between an outer surface of a tyre and an inner surface of an envelope in the sidewall and tread regions of the tyre characterised in that the air venting belt comprises a base cloth made of woven cloth which is expansible in at least the longitudinal direction of the air venting belt corresponding to the radial direction of the tyre and the end regions of the strip, which areas contact the sidewall regions of the tyre, have a smooth film laminated onto the base cloth. The expansible woven cloth preferably comprises a rubber yarn arranged in the longitudinal direction of the belt corresponding to the radial direction of the tyre. Alternatively both sides of the end regions of the strip may be covered by smooth film. The base cloth and the smooth film may be seamed together to integrate and laminate them such that the base cloth is fully adhered to or sandwiched between the smooth film or films. Further, according to the present invention, there is provided an envelope laminated with air venting belt made of expansible woven cloth. The envelope laminated with such air venting belt cloth comprises an envelope made of rubber and air venting belts fixed integrally to the inner surface of the envelope. Hereinafter, the use of the belt of the present invention will be explained. When steam pressure is applied to the tread, the belts fitted around the tyre assembly are deformed together with the rubber envelope and closely contact the tyre tread including the sidewalls of the tyre grooves, since the belt is stretchable. Thus stress concentration does not occur in the thin portion (referring to i of Figure 13 in the conventional example) located at a bottom of the tyre groove. The expansible cloth of the belt can be produced easily by using rubber yarns in the longitudinal direction which is used in the radial direction of the tyre. Further, when smooth films are on the surface which directly contacts the sidewalls of the tyre impressed patterns (referring to j of Figure 14) are not left. Further, when smooth films are used for not only the front face but also the reverse face of the cloth and the base cloths and the smooth films are seamed together such that the base cloth is sandwiched between smooth films, the smooth films can be integrated tightly and easily with the cloth. Further, if the expansible cloths are integrally laminated with an inner face of the envelope, there is no need to separately arrange the air venting belt or belts in the vulcanising operation for a retread tyre. Therefore, the efficiency of the work will be improved. Hereinafter, on the basis of the accompanying drawings, several embodiments of air venting belt of the present invention are explained in detail. The drawings comprise: Figure 1 is a perspective view showing one embodiment of air venting belt; Figure 2 is a cross section of the air venting belt of Figure 1; Figure 3 is a cross section of another air venting belt; Figures 4a and 4b are cross sections illustrating the use of the air venting belt; Figure 5 is a plan view illustrating the use of the air venting belt; Figure 6 is a perspective view showing an envelope with the air venting belt of the present invention; Figure 7 is a cross section showing the process producing the envelope of Figure 6; Figure 8 is an enlarged cross sectional view showing a vulcanising step in which the air venting belt of Figure 1 is used; Figure 9 is a perspective view showing an example of a tyre to be retreaded; Figure 10 is a perspective view showing components of a retread tyre before retreading process; Figure 11 is an enlarged cross sectional view illustrating an example of a vulcanising step; Figure 12 is a sectional view showing an example of conventional vulcanisation step; Figure 13 is an enlarged sectional view showing the drawbacks of the conventional vulcanisation step; and Figure 14 is a plan view showing a conventionally retreaded tyre. In the embodiment shown in Figures 1 and 2, an air venting belt 1 comprises a base cloth 2 made of a Strip of expansible woven cloth and rectangular end regions 3 covered by smooth film. The film regions 3 are laminated and integrated onto both end portions of the base cloth 2. The base cloth 2 and the smooth film regions 3 are made of heat resistant materials. For example, the base cloth 2 comprises rubber yarn (warp) in the longitudinal direction (i.e. the radial direction of a tyre when the tyre is covered with this belt as shown in Figure 4 or Figure 5) and any kind of heat resistant yarn (weft) such as cotton, synthetic resin or the like in the width direction. For the film region 3, rubber or synthetic resin material can be used. Both the base cloth 2 and the film are integrated with each other by bonding with adhesive or by seaming. When used, as clearly shown in Figures 4 and 5, the above-mentioned air venting belt 1 is arranged with a "U"-like shape extending in the radial direction of the tyre 5. The tyre is then covered with an envelope 6 by expanding and opening one sidewall of the envelope 6 as shown by phantom lines in Figure 4a. Thus the smooth film regions 3 are placed at positions corresponding to the sidewall portions 7 of the tyre 5 and is mounted on the tyre 5. Next, Figure 3 shows another embodiment of the present invention. In both tyre sidewall contacting portions of the base cloth 2 of the air venting belt of Figure 3, the smooth films are put on not only the front faces but also on the reverse faces. Further, the base cloth 2 and the smooth films are seamed with each other by means of stretchable yarns such as rubber threads to integrate and laminate them such that the base cloth 2 is sandwiched between the smooth films 3. Therefore, there is an advantage that the air venting belt can be mounted on the tyre 5 as shown in Figure 4 without the need to take special care which face is the front. Further, Figure 6 shows another embodiment of an envelope laminated with air venting belt of the present invention. The circular-shaped envelope 6 of substantially "U"-shape has an inner surface 6a. A plurality of air venting belts 1, for example those shown in Figures 1, 2 or 3 and so on are integratedly fixed on the inner surface 6a of the envelope 6 so as to cross with the circumferential direction. A preferable method for fitting the air venting belts into the envelope will be explained with reference to Figure 7. Before raw rubber material is vulcanised and formed to form the envelope by means of an upper die 10, a middle die 9, and a lower die 11, the above-mentioned belt 1 made of woven cloth is stuck on the middle die 9. Then the upper die 10 and the lower die 11 are assembled, raw rubber material is supplied to the cavity between the middle die 9 and the upper and lower dies 10,11. Then the material is heated and pressurised between the upper and lower dies 10,11. Thus the air venting belt is integrated and laminated on the inner surface 6a of the envelope 6. The above-mentioned air venting belt is used in retreading a tyre as shown in Figure 8. It is laid between the outer surface of the tyre 5 and the inner surface 6a of the envelope 6 when the rubber cushion 14 is vulcanised, for the purpose of venting air in the direction of arrow A between the outer surface of the tyre 5 and the inner surface 6a of the envelope 6. Preparation of a worn tyre before this is briefly explained as follows. A used tyre 12 for retreading is smoothly finished as shown in Figure 10 by buffing to remove the worn tread, and is laminated with a precured tread having a belt-like shape and a vulcanisable cushion rubber sandwiched between the tyre carcass and the belt-like tread. The tyre 5 assembled as mentioned above is then covered with the envelope 6, as shown in Figures 4 and 5 with the air venting belts 1 laid between them. Further a tube 19 and a flap 20 are fitted, and a rim 21 is attached, and then the tube 19 is pressurised such that the inner pressure in the tube is nearly equal to that of a running tyre. Further several retread tyres each prepared in this way are loaded together with seal plates 15 laid between the tyres into a vulcanising chamber. The space 16 located outside the tyre is filled with steam having a temperature of 105 to 160°C and a pressure P of 4 to 6 kg/cm². The envelope 6 protects the outer surface of the tyre from direct contact by steam. The above-mentioned vulcanisable sheet-like cushion rubber 14 (see Figure 10) is vulcanised, and then the precured tread 13 is integrated tightly to the tyre casing 12. During this operation, as shown in Figure 8, the belt 1 and the envelope 6 are elastically deformed and lie along the inner surfaces of the tyre grooves 17 due to the steam pressure P, since the air venting belt is expansible. Therefore, the above-mentioned pressure p is applied to the surfaces of the tyre grooves 17, and stress concentration does not occur in the thin portion 18 located in the bottom of the tyre groove 17. Therefore, the tread 13 can retain the normal shape thereof, and, of course, the normal shape of the tyre grooves can be kept, and the vulcanisation successfully finished. Further as is clearly shown in Figure 8, the smooth films 3 touching directly the sidewall portions of the tyre 5 prevent the cloth of the belt from leaving a mark on the sidewalls in the pressurised region located under the seal plate 15. The points "S" in Figures 8 and 11 show the seal portion where the seal plate 15 is in tight contact with the envelope 6. The pressure of the space 16 of the vulcanising vessel is retained by means of these seal portions. The present invention which has the above-mentioned construction obtains technical effects as follows: 1. Deformation shown in Figure 13 does not happen in the tyre grooves and a normal shape of the tyre grooves is obtained so that a tyre having a superior appearance is given. 2. Because a rubber yarn is arranged in the radial direction of the tyre, the air venting belt can be produced cheaply and easily. 3. When the air venting belt has the smooth film ends it avoids marking the tyre. 4. If the air venting belt is laminated with the envelope, covering and removing work is easier.

Claims: An air venting belt (1) comprising a strip for use in a retread tyre vulcanisation process between an outer surface of a tyre (5) and an inner surface of an envelope (6) in the sidewall and tread regions of the tyre (5) characterised in that the air venting belt (1) comprises a base cloth (2) made of woven cloth which is expansible in at least the longitudinal direction of the air venting belt (1) corresponding to the radial direction of the tyre (5) and the end regions of the strip, which areas contact the sidewall regions of the tyre (5), have a smooth film (3) laminated onto the base cloth (2). The air venting belt of claim 1, characterised in that the said expansible woven cloth comprises a rubber yarn extending in the longitudinal direction of the belt. The air venting belt of claim 1 or 2 characterised in that the tyre sidewall contacting areas of said belt are laminated on the base cloth (2) with smooth films at both sides thereof. An envelope for capping a tyre tread when a cushion rubber is to be vulcanised to make a retread tyre, comprised by an envelope (6) made of rubber and air venting belts (7) integrally fixed on the inner surface of the envelope, said air venting belts (7) being made of expansible woven cloth according to any one of claims 1 to 3.

Inventors: YAMAMOTO KOUZOU SUMITOMO RUBBE, YAMAMOTO, KOUZOU, SUMITOMO RUBBER KOBU DORMITORY
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LIMITED
Application year: 1990
Main classification: B29D30
IPC codes: D03D15, G09F3, B29D30, B29C37, D03D1, B29C43, B29C35