OTR Retreading Process

OTR Retreading Process | Retread Process

Concepts of cold retreading:

        The low temperature is against the high hot retread temperature.Generally, 120℃ is the denatured point of rubber, over called hot retreading, blow called cold retreading. And more advanced technology allows the temperature below 100℃. Because of the high temperature produce a negative effect to the tyre, the cold  retreading is more and more popular.

        Precure Retreading means the tread should be precured by the high-pressure vulcanizing machine

separately, while the hot retreading means the tread and casing are made up with non-vulcanized rubber, so the tread pressure is far below than the cold retread technology. Therefore, wear resistance, mileage of cold retread tyre can be comparable to the new tires, And flat mould can make tread with kinds of patterns, help

the users to choose the more suitable patterns. However, it will be a big expense if you change tread patterns with hot retreading technology.

1.Cleaness and dry of casing

        Before retreading, outer and inner surface should be cleaned for good adhesion strength. Drying is also

essential because the water in casing would affect the retreading quality.

2.Tyre inspection

        Not all the used tyres can be retreaded. Different standard for different conditions. Some defects can be

found directly by the experienced operator, but some inner ones can only depend on the inspection of equipment and devices.

3.Buffing

        Obtained tire surface with a certain profile and adhesion after buffering. It should be stressed that this is a

crucial process, because unqualified tire size, roughness, or roundness would affect the quality of retread tires.

4.Skiving

        Buffer can not grind the pattern grooves and the concave parts caused by using, so can only use hand-held

pneumatic or power tools with special grinding wheel. In addition, the uncertain damage can be confirmed exactly and remarked.

5.Cement

        In order to prevent the grinding tread surface to be oxidated in the long-time exposure, and to provide

operating viscosity to  next adhesion step, the operator paint a thin cement layer on the polished surface. Spray

cement has been eliminated in some advanced plant, because the wet cement would affect the adhesive property and has flammable risk.

6.Repairs

        Cuts repair, fill, paste patch liner depend upon complete tools in this station. By scientific design, high

strength, light weight, resistance to flex, the patch liner can be prefabricated into a variety of models. Right

models with correct operation lead to reliable quality. And it should be noted that all the work is operated  manually, so need the operator have proficient skills and responsibility

7.Extruding

        Using soften rubber fill tire grooves and surface pits. The traditional way is to fill the pits by hand, one by

one, using the extruding gun with heating function. But advanced larger factories use cold feed extruder reshaping

the adhesive to a certain width and thickness, and then extrude onto the prepared casing surface. Compared with

manual filling, the latter tire has smooth surface, reduced air probability when bonding, more efficient, and even eliminates the spraying cement operations.

8.Tread builder

        If not use a larger cold feed extruder, it needs to paste adhesive (the cushion gum) before laminating tread.

Now there are two traditional methods. One way is to install a pair of rubber roller on a rectangle table, and then

press the adhesive onto the tread. Another way is to laminate the adhesive onto the cassing surface directly. The  former is better than the latter.

        First method: after tread surface inspection, cover the adhesive, which has plastic film, on the tread by hand.

Be noted that the hand is in close contact with the film cover, not the bonding surface, reducing the chance of

contamination. Several finished products can be prepared for the next step for high efficiency. Also note that the

adhesive has the same length with tread rubber, no splice.

        The second method: need a operation to laminate adhesive onto the tread innner surface, so occupy the work

time. Of course the first method need to add a machine. Apply the new tread onto casing surface consolidately in

high gas-pressurized state, ensure it is straight, centered on the casing, and the end splices match. Now traditional

practices still use manual operation, But advanced factories have adopted automatic tension control and laser

positioning tread laminating machine, with high precision and efficiency.

9..Curing assembly

Encase the uncured, built tire in an elastic envelope in preparation for curing. The envelope is a flexible rubber

mold. Under pressure, the envelope can adapt itself to the tire shape, so there is no internal stress. While hot

retreading use rigid mold. But the used tyres are so different that they can not match with the rigid mold

completely, and produce a pressure. Therefore the use of envelope is better than rigid mold.

        Assembly methods

        Traditional method is wrapped envelope, inner tube assembly and curing rims. Now the bias tires still use

above method. With the development of radial tires, ARC Central and dual-packet envelope methods are more

and more popular as they are more efficiently, saving time and energy.

10.vulcanization
        An curing chamber applies heat and pressure, and over time, causing the bonding layer to cure, permanently

adhering the new tread to the prepared casing. If there are any problems in vulcanizing, it will make the retreading

tyres to gap. The tyres for truck need several hours to vulcanize, need the experienced and responsible operators.

Now the advanced plants adopt the curing chamber auto controlled by computer, which can complete vulcanize

automatically and exactly.

11.Final inspection

        A final inspection is performed to ensure the tire in perfect operating condition depending visual, hands-on

inspection. In some countries and regions, the finished product must be checked in high gas-pressurized state,

but special protective equipment is necessary to reduce the operation risk. Laser non-destructive checking

equipment has been used in some advanced plants. By spraying paint, the qualified production can be put into use  after 24 hours.