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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.