Field of technology

This invention relates to a method for retreading tires for heavy-duty vehicles, of the “hot retreading” type, which will find application in the transport industry and in particular in retreading the tires of various types of vehicles.

Background of the invention

Retreading is a method of restoring used tires in which, after the addition of new material, the tire returns to its original purpose, thus prolonging its life.

In most cases, the part of the tire that wears out is the tread, leaving the carcass intact. Because the tire carcass is designed to last longer, the ability to extend tire use by replacing the tread is economically and environmentally advantageous. Usually light tires are retreaded only once, cargo tires two or three times, and aircraft tires many times. In the “hot retreading”, the tread is made directly on the pre-treated carcass, thus ensuring a good connection between the individual parts of the retreaded tire.

A method for retreading heavy-duty vehicle tires is known in the art, which includes the following operations:

- checking and control of internal separations of the worn tire on a TheadReader scanner to establish its suitability for regeneration;

- removal by scraping the rest of the worn tread and on the side of the retreadable tires by rotating cutting heads of a scraping machine;

- treatment of deep injuries on the base and on all risk areas of the scraped tire by a straight hand sander; - if necessary, applying a patch to the damaged area of the treated scraped rubber;

- application of an adhesive providing a connection between the carcass and the applied rubber for the formation of the new tread, the operation being performed in a syringe cabin, providing drying of the adhesive when the tire stays in it for 15 minutes;

- placing the dried tire in an extruder, the head of which is heated to 90 °C to heat unvulcanized rubber applied in the form of strips on the carcass;

- application on the scraped sides of the carcass of a unvulcanized rubber layer, used to form a new side, the operation being performed on a machine for side tape;

- inflation of the diaphragm inside the tire, the diaphragm being inflated to a pressure of 15 bar;

- firing of the tire and molding of the tread is performed in molding presses, heated by steam with a pressure of 5.7 bar at 155 °C for 90 minutes at a press pressure of 16 - 18 bar;

- removing the tire from the molding press and removing the rubber extrusions;

- visual inspection of the retreaded tire.

In the described known method for retreading heavy-duty tires, it has been found that air remains between the diaphragm, whose function is to provide maximum pressure of the tire to the molds, and the inner side of the tire. This air forms air pockets that counteract the diaphragm and it takes on an irregular shape, which also affects the shape of the tire, which is under mechanical pressure from the molds. As a result, the diaphragm wears out faster due to bending or swelling and thinning in certain places. As a result, its life is shortened to 40-50 bums, which requires more frequent replacement with a new one, which makes the production of retreaded tires more expensive. The remaining air expands during the firing process and this leads to its penetration into the carcass through micro cracks and makes the tire unusable. In addition, in the case of tires on which patches are applied, the poorly located diaphragm does not provide optimal compression at the point of adhesion, as a result of which the patches are not completely vulcanized and fail during the operation of the tire.

In the known method, it is difficult to determine the exact amount of raw material to be placed on the carcass, because due to the deformation of the carcass in some places more material is concentrated, and in others it is lacking. This causes visible defects on the side and tread of the tire due to both the skew of the carcass and the uneven pressure from the diaphragm. The result is a different thickness between the tread grooves, which leads to vibration and imbalance of the retreaded tire and disrupts its normal operation.

Technical essence of the invention

The invention object is to provide a method for retreading tires for heavy-duty vehicles, which provides both retreading of tires, in which the newly formed tread is without any deformations, and quality vulcanization of the applied patches over their entire area.

The problem was solved by creating a method for retreading tires for heavy-duty vehicles, including the following operations:

- checking and control of internal separations of the worn tire on a TheadReader scanner to establish its suitability for regeneration;

- removal by scraping the rest of the worn tread and on the side of the retreadable tires by rotating cutting heads of a scraping machine; - treatment of deep injuries on the base and on all risk areas of the scraped tire by a straight hand sander;

- if necessary, applying a patch to the damaged area of the treated scraped rubber; application of an adhesive providing a connection between the carcass and the applied rubber for the formation of the new tread, the operation being performed in a syringe cabin, providing drying of the adhesive when the tire stays in it for 15 minutes;

- placing the dried tire in an extruder, the head of which is heated to 90 °C to heat unvulcanized rubber applied in the form of strips on the carcass;

- application on the scraped sides of the carcass of a unvulcanized rubber layer, used to form a new side, the operation being performed on a machine for side tape;

- inflation of the diaphragm inside the tire, the diaphragm being inflated to a pressure of 15 bar;

- firing of the tire and molding of the tread is performed in molding presses, heated by steam with a pressure of 5.7 bar at 155 °C for 90 minutes at a press pressure of 16 - 18 bar;

- removing the tire from the molding press and removing the rubber extrusions;

- visual inspection of the retreaded tire.

According to the invention, the method also includes an operation performed before the operation to inflate the diaphragm inside the tire, namely:

- placing two diametrically opposite textile strips between the diaphragm and the tire; and

- the textile strips remain between the diaphragm and the tire during the operation of firing the tire and forming the tread to remove the remaining air between them and to constantly press the diaphragm to the inner part of the tire.

The advantage of the created method is the provided possibility for complete removal of the air caused by the temperature expansions between the diaphragm and the tire, thanks to the ensured presence of the textile strips during the firing of the tire. The absence of air, which expands when heated, also protects the carcass from damage. In addition, the life of the diaphragms used is extended to 100 tire bums. Another advantage of the method is the provided constant pressing of the diaphragm to the inner side of the tire and the patch quality adhesion, which is vulcanized over its entire area without the presence of bubbles at their edges. Raw material is saved, because due to the lack of deformations the exact required amount is calculated and there are no unnecessary extmsions. There are no visible defects on the side and tread, neither uniform mbber residues in between the grip grooves, which prevents vibration and imbalance in the operation of the finished tire.

The main advantage of the created method is the impossibility to deform the carcass, which ensures uniformity and control of the outgoing extmsions.

Examples of the invention embodiment

The developed method for retreading tires for heavy-duty vehicles, such as buses, tracks, agro-tires and industrial tires by hot retreading, includes the following operations:

- checking and control of internal separations of the worn tire on a TheadReader scanner to establish its suitability for regeneration. This inspection allows the removal of unfit for retreading tires that are discarded; - removal by scraping the rest of the worn tread and on the side of the retreadable tires by rotating cutting heads of a scraping machine. Removing the rest of the worn tread is to a level that guarantees a smooth installation of a new tread. In the case of “hot retreading”, the scraped side is also restored. This allows tires with larger damage to be retreaded;

- the scraped tire on a monorail is moved for treatment of deep injuries on the base and on all risk areas. The operation for scraping the tire is performed by a straight hand sander;

- if necessary, applying a patch to the damaged area of the treated scraped rubber;

- application of an adhesive providing a connection between the carcass and the applied rubber to form the new tread, the operation being performed in a syringe cabin equipped with aspiration, ensuring even drying of the adhesive when the tire stays in it for 15 minutes. This guarantees quality bonding of the new tread;

- placing the dried tire in an extruder, the head of which is heated to 90 °C to heat unvulcanized rubber applied in the form of strips on the carcass;

- application on the scraped sides of the carcass of a unvulcanized rubber layer, used to form a new side, the operation being performed on a machine for side tape;

- before the diaphragm is inflated, two diametrically opposed textile strips are placed between the diaphragm and the tire, thus ensuring sufficient conductivity to remove the remaining air between them;

- inflation of the diaphragm inside the tire, the diaphragm being inflated to a pressure of 15 bar;

- the textile strips remain between the diaphragm and the tire during the operation of firing the tire and forming the tread to remove the remaining air between them and to constantly press the diaphragm to the inner part of the tire;

- the tire is fired and the tread is molded in molding presses heated by steam at a pressure of 5.7 bar at 155 °C for 90 minutes at a press pressure of 16 to 18 bar. The presses are heated by steam supplied by a steam plant. The new tread is formed by molds divided into six segments, which are mechanically pressed against the tire placed in the press;

- removing the tire from the molding press and removing the rubber extrusions;

- visual inspection of the retreaded tire.

The created method achieves a significant increase in the quality of retreaded tires, which guarantees their trouble-free operation and significant savings in time and resources. After applying the method, there is no need to revise and replace the patches before the tires are made available for use. Material is saved and excellent quality of the finished product is guaranteed.