INSPECTION

The first step involves selecting suitable casings from old and worn-out tyres for retreading. Each casing undergoes a meticulous visual inspection to identify and mark any punctures, ruptured cords, separations, or other defects. Casings that fail the inspection are rejected.

Pre-inspection requirements:

• Ensure the casing is clean and dry.
• Tyre grooves and channels must be well-cleansed.
• Conduct inspections in proper lighting conditions.
• Use appropriate tools such as a hammer, poker, crayon, or cloth.
•  

INSPECTION PROCESS:

1. Use a hammer to tap the shoulder and crown areas to detect separations by the change in sound. Mark and reject tyres with separations.
2. Check for bulges at the bead area by running your palm over it. Reject if found.
3. Use a poker to examine cuts on the crown. If the cuts are large or irreparable, reject the casing.

VENTING

Venting is essential to release trapped air from the casing before curing. This involves using an air tool to prick the bead and shoulder areas, a process recommended only for bias tyres. Skipping venting can lead to tread separation during use.

BUFFING

Buffing removes the worn-out tread from the casing’s crown, creating a smooth, uniform surface for the new tread. Proper buffing ensures accurate tread placement and bonding during curing. Casings are inflated to their recommended size and pressure for precise results.

Note: Inconsistent buffing due to inadequate machinery or skills may lead to bonding failure. Ensure high-quality tools and methods are used.

SKIVING

This process addresses damage or injuries on the casing’s crown. Loose or damaged material is removed to prepare the casing for retreading. Skiving ensures a clean surface, critical for successful bonding.

CEMENTING

The buffed surface is coated with a rubber solvent (Universal Spray Cement) to prevent oxidation, which can reduce bonding strength. Cementing must be done within two hours of buffing and skiving.

REPAIR AND FILLING

Damaged casings are repaired based on the severity and location of the damage:

1. Spot Repair: Repairs damage affecting up to 25% of the ply.
2. Reinforced Repair: For damage affecting 25–75% of the ply, a reinforced patch is applied.
3. Sectional Repair: For damage exceeding 75% of the ply or deep cuts, sectional patches are used.

The repaired areas are filled with vulcanizing rubber to restore the casing’s integrity.

TREAD PREPARATION

The pre-cured tread rubber is cut to the required length and coated with bonding gum (URSG) to eliminate air gaps. The edges of the tread are sealed with URSG, ensuring proper adhesion.

BUILDING

In this step, the tread is applied to the prepared casing. The casing is inflated and mounted on a tyre-building machine. The tread is stretched and adhered to the casing with precision to avoid air entrapment, ensuring strong bonding.

CURING

Curing is the final step in forming the retreaded tyre. The tyre is wrapped in a rubber envelope to ensure uniform pressure, and a thin perforated poly film

facilitates air release during curing. The tyre is then placed in a pressurized, temperature-controlled chamber where bonding gum cures, chemically binding the tread to the casing.

KEY PARAMETRES

1. Maintain a differential pressure of 25 PSI (chamber pressure: 85 PSI, tube pressure: 110 PSI).
2. Adhere to the set time, temperature, and pressure.

FINAL INSPECTION

Each retreaded tyre undergoes a detailed inspection to ensure it meets quality standards. Polishing the tyre enhances its appearance, making it resemble a new tyre.
This comprehensive process ensures a durable and reliable retreaded tyre, ready for use.