Retread Process | Concepts of cold retreading:


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.

Retreading Process

Initial Inspection

 

Each tyre received in a retread plant is subjected to a rigorous visual inspection. Inspectors are assisted by the use of non-destructive sophisticated inspection equipment.
We also purchase a new machine (Inspection Spreader).This Inspection Spreader designed to detect pinholes, nail holes, cuts, cracks, porosity,etc,Automatic tyre rotation stop when penetration detected with sparks.

Buffing

 

The tyre’s old tread is mechanically removed on high speed buffers. Today’s buffers are extremely accurate and will remove the proper amount of old rubber while turning the tyre to an exact specified diameter and radius.

Skiving & Repairing

 

With advances in state-of-the-art repair materials and repair methods, many of these tyres can be routinely repaired and in most cases can be retreaded when the original tread is worn off. The repair station is where any surface injury is treated using effective material and tools for grinding and patching.

Cementing & Filling

 

Even in small injuries it is critical that the injury is cleaned and filled. If this is not done, severe rust, separation and steel cable looseness could take tyre out of service. The injury should be inspected, and then cleaned out with a carbide cutter. After cementing the injury, a vulcanizing rubber stem should be applied to “fill” the injury. This would create a permanent repair that maximizes tyre life.

Building

 

In the pre-cure system, the tread rubber has already been vulcanized with the new tread pattern design. The buffed tyre needs a thin layer of cushion gum to be wrapped around its crown area. The pre-cured tread rubber is then applied with the building machine. This is called the building process.

Enveloping, Rim Mounting & Double Envelope System

  

a) The built tyres are then mounted with envelops and rims to prepare them for curing.
b) For enveloping, tyres are first fitted an outer envelope at the envelope-mounting table before the inner envelope is fitted into them. The enveloped tyres are then vacuumed out for preparation prior to curing. Modern plants have their casings hoisted by monorail systems.

Curing by Chamber (Precure)


 

The Precure Tread system is a process by which a tread pattern is fully cured or vulcanized into the tread by using a press. The tread is then vulcanized onto a tire casing using a bonding layer of uncured natural rubber. The tyre is vulcanized with heat, time and pressure in a curing chamber that bonds the tread to the casing. This thin layer called precure cushion or bonding gum. Cold retreading was then a term used to describe a process in which the final curing of retread is done at temperature lower than 115c.

Hot Process (Hotcure)

This system is similar to the technology of new tyre manufacturing.
Hot retreading is the term used to describe the retreading process in which the curing of retread is done at a temperature of above 140c. It employs a steel or aluminum mold with a tread design cast or machined into it.

Final Inspection (Presure Test) & Painting



  • Tyre inflation pre-set at 2, 4 & 8 bar (max) for a better QC inspection.
  • Enclosed by steel cage as safety protection.
  • Testing cycle ended automatically to reduce supervision work.
  • Well lighted within the cage for better visual inspection.
The retreaded tyre is subjected to a final inspection. This inspection insures that only tyres that meet industry quality standards are allowed to leave the retread plant.
All retreaded tyres are encouraged to be returned with the sidewalls painted using a light coat of black tyre paint.