Background of the Invention It is well known in the prior art the retreading system, according to which a new tread, which is previously formed and vulcanized in the form of strips, is incorporated to the abraded, clean and degreased external surface of a worn tire carcass, by means of an intermediate connecting film to be vulcanized to both the carcass and the new tread.

For achieving the vulcanization of the film and the consequent incorporation of the new tread to the carcass, the assemblies, usually in a number from 10 to about 20 and being formed, each one, by a carcass, a connecting film and a new tread usually defined in multiple complementary circumferential extensions, are placed inside an autoclave, so that the connecting film and the adjacent and confronting surfaces of both the carcass and the tread be heated at a determined temperature, generally higher than 90°C, and so maintained by a certain time, in order to promote the vulcanization of the connecting film and the consequent fixation of the tread to the carcass.

In these known systems, the heating required to vulcanize the connecting film is provided by induction, by increasing the temperature of the whole environment of the autoclave from heat sources defined by electrical resistances or steam coils, operating jointly with forced air circulation provided inside the autoclave, with the aid of a turbine or a fan and respective hot air conducting tubes.

While they operate satisfactorily regarding the vulcanization of the connecting film, these known heating systems by induction lead to an enormous and unnecessary consumption of energy and operational time. Due to the utilization of induction heating, these prior art systems promote heating of the whole mass associated with each tire inside the autoclave, including the carcass, the connecting film, the tread, the external envelope and, in some cases, the inner wheel used to lock the envelope. The heated air, which is circulated inside the autoclave, heats the whole mass therein, until the connecting film, which is pressed between the carcass and the tread, is taken to a temperature usually higher than 90°C, remaining in this condition for a certain time, until the complete vulcanization has been achieved.

Besides the loss of the energy used to heat the whole mass associated to each tire, which mass may reach about 100 kg, the time required for the heating thereof is also relatively long, usually about 4 hours for the autoclaves containing a load of about 10 to 20 tires.

Considering the high production rates, the retreading companies are obliged to have multiple autoclaves operating by turns.

Disclosure of the Invention It is a general object of the present invention to provide a device for retreading worn tire carcasses, with previously formed and vulcanized treads, by means of a relatively simple construction and with a great reduction in both the energy consumption and the time required to complete the operation.

It is a further object of the invention to provide a process for achieving the retreading considered above.

The device of the present invention is employed for

retreading tires, each tire being formed by a carcass with an abraded and clean peripheral surface, onto which is seated a vulcanizable connecting film, which is externally covered by a previously formed and vulcanized tread.

According to the invention, the device comprises a reactor defining a heating chamber, which is dimensioned to receive a plurality of tires to be retreaded, and which is internally provided with a plurality of microwave emitters, which are designed to operatively actuate on the connecting film through the thickness of the respective tread, said microwave emitters being operatively associated with a control unit for regulating the operational time and the power.

The device defined above in general terms allows the connecting film, not yet vulcanized, to have its molecular structure submitted to the effect of the microwaves long before and more effectively than the circumjacent structures, such as the carcass, the tread and the envelope, with the reduced mass of said connecting film being heated more rapidly, allowing to achieve the desired vulcanization in a time of about up to 1/8 the time usually required for the same operation of the prior art devices.

Brief Description of the Drawings The invention will be described below, with reference to the attached drawings, in which: Figure 1 is a cross-sectional view of a worn tire carcass, already abraded and covered by a vulcanizable connecting film and by a previously formed and vulcanized tread placed inside the heating chamber of a reactor (autoclave); and Figure 2 is a partial cross-sectional view of the assembly of figure 1, said view being taken according

to line II-II in the previous figure.

Best Mode of Carrying Out the Invention According to the illustration, the invention is applied to the retreading of tires, each tire being defined by a carcass 10 with its external surface already abraded, clean and degreased, onto which is applied a connecting film 20 in a vulcanizable material, such as a rubber compound compatible with the material of the carcass and with that of a tread 30, which has been previously formed and vulcanized and which is placed on the connecting film 20. The tire thus formed is mounted in an adequate envelope 40, such as for example, that contemplated in the patent application PI9604105 of the same applicant, and then conducted to the inside of the heating chamber 51 of a reactor 50 that may be formed by the shell of an autoclave of the type normally used for retreading said tires by means of induction heating and which is dimensioned to receive, therewithin, about 10-20 tires to be retreaded, which are arranged side by side according to an alignment generally coaxial to the heating chamber 51.

According to the invention, the heating chamber 51 of the reactor 50 is provided with a plurality of microwave emitters 52, for example having an individual power of about 800 watts, which are adequately placed in the internal face of the reactor, in order to emit the microwaves in the radial direction, towards the connecting film 20, through the tread 30.

Due to the fact that the connecting film 20 has a molecular structure that is less cohered than that of the carcass 10, of the tread 30, and of the envelope 40, and is formed of a non-vulcanized rubber compound, submitting the assembly to the molecular agitation by

the microwaves will heat the connecting film 20 much more rapidly, making the latter reach the vulcanization temperature, which is maintained for the necessary time, with a minimum energetic consumption for heating the tire.

In order to maintain the microwave emitters 52 refrigerated during operation, ducts 53 containing a circulating refrigerant liquid, such as water or forced circulation air, may be provided. In case the reactor has its structure defined by a known autoclave, the ducts 53 for the circulation of liquid may be those employed for the circulation of hot air in the autoclave.