At this stage the operator is assessing the condition of the tire casing, mechanical damages on the casing and suitability for retreading. With the help of special equipment visual assessment of the inner layer of the tire, of the boards, of the shoulders and of the crown of the tire is done. All the identified damages are marked, the individual tracking card of the tire is filled and the serial production number is offered to each tire.
The main goal is to remove the residual layer of the tread from the tire carcass and thus provide an initial profile and the necessary structure for imposing the prepared tread. The removal of the residual layer of the tread is done on a special computerized Buffing Machine. After the buffing process the casing is no longer placed on the floor. It is hanged on a hook on a special monorail on which the tire is moved from one technological step to another thus being protected from dirt and dust.
During its exploitation the layers of the tire get damaged by foreign objects which penetrated into the tire resulting a faster process of oxidation and rusting of the cords. While repairing the tire it is necessary to identify each such damage, to trim it and whenever necessary to apply special patches.
At this stage a thin layer of special solution (cement) is sprayed and applied over the buffed surface of the tire. After the application and drying a sticky rubber foil is formed which holds the tire casing, cushion gum and the new tread.
This action constitutes a process of filling all the trimmed and repaired damages on the surface of the tire with raw rubber. The raw rubber is applied by a special hand extruder.
The main goal is to impose the new tread rubber over the existing casing which passed through all of the preparation stages. Compulsory, the newly prepared tread should be similar to the original size of the tire, both in width and circumference. The application of the tread rubber is done on a special computerized Builder Machine.
The prepared casing with applied new tread is place in an outer rubber envelope. An inner rubber envelope is placed inside the casing. After that, both envelopes are vacuumed (all the air is pumped out), a tight fit of the tread to the casing occurs and the tire is ready for vulcanization.
This operation takes place in a special autoclave under strict ratio of time, temperature and pressure. All necessary parameters are introduced by the operator and controlled by a special soft. Prepared “enveloped” casings are loaded through the monorail into the autoclave and connected to the vacuum pump. A high pressure (up to 6 bar) is raised inside the “barrel” of the autoclave. Due to this the tread is pressed into the casing, and the optimum temperature enhances the effect of chemical coupling. The row rubber is vulcanized. The casing becomes one with new tread.
The tires are unloaded from the autoclave. A new load of prepared tires is placed into the autoclave. The unloaded vulcanized tires, still in the envelopes are moved for dismantling of the envelopes through the monorail.
The process of final inspection is to assess the final product. Until the tire is hot the final visual inspection is carried out. If there are any unidentified defects, omissions of retreading all of that can be easily seen at this stage. After the final inspection the shoulders and sides of the tire are painted.