Monday, August 16, 2010

POST CURE INFLATION

1. What is post cure inflation ?

Post cure inflation is the process of cooling the tyre under pressure immediately after it has been cured. This is done by inflating the tyre using specified air pressure after mounting the tyre on the specified rim. This is done for one or two cycles (one cycle is equal to the time taken for one curing cycle) depending on the specification which is arrived at by considering the time taken for the tyre to cool down to room temperature.

2. Why are tyres subjected to post cure inflaltion ?

Nylon has a unique property of shrinking while it is heated. Since nylon is used in the carcass of tyres (which forms the skeleton of the tyre) there is a tendency for nylon to shrink when the tyre is heated to vulcanise it. But when the tyre is inside the press, it is not possible for nylon cords to shrink because there is high pressure inside the tyre which keeps the nylon cords in the stretched condition. But when the curing process is over and the pressure inside the bladder is released, the nylon cords tend to shrink since the tyre is still hot.

Hence in order to avoid thermal shrinkage, we are trying to cool the tyre under pressure. If this is not done, the tyres may lose shape, may get distorted or can be subjected to small changes in dimensions.

3. What happens if PI is delayed ?

If the tyre is not post inflated as soon as possible after the pressure has been released then the nylon cords may shrink and lead to distortion in tyre shape, and changes in dimensions. When PI is delayed, the damage would be caused and it will be irreversible damage.

4. How will PI delay affect the customer and the company ?

If a customer is given a tyre which was affected by PI delay, then the dimensions of the tyre will be slightly different from normal tyres. This can lead to problems like uneven wear, problems to the axle and bearings of the vehicle etc.
The distortion in shape can lead to problems of uniformity. Tyre uniformity is a very important factor considering the high levels of comfort and performance levels expected of tyres in the highly advanced vehicles.
A tyre which is distroted can also lead to safety problems.
If a tyre is affected by any of the above factors, it can have a very negative impact on the company’s image and consequently the market. It can have far reaching economic and legal implications to the company

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