Tyres

The life of tyre curing bladders can be increased through the application of a curing bladder treatment, which helps to protect the bladder against chemical and abrasion attack throughout its service life. This type of attack is prevalent at the surface of the curing bladders that contacts with the beads of the tyres being cured. Coatings can significantly help increase average bladder life. The choice of inside tyre paint can also have a positive impact on the service life of curing bladders.

Most products for the tyre industry are developed for application to green tyres using any of the following systems:

• Spray gun, either automated, e.g. Ilmberger or Plummer units etc., or hand-held spray guns
• Paint brush
• Sponge or swab

The actual application technique(s) chosen by any given tyre plant depends primarily on the equipment available and the logistics of the particular plant. Experienced release agent suppliers should be able to provide recommendations to improve and optimize application techniques where desired.

Most inside tyre paints (filled and unfilled) are sprayed fully automatically. Semi-permanent products are often applied semi-automatically or manually using a sponge, because this process requires less tyre spraying.

Generally speaking the optimum coating of inside paint is one that is evenly spread across the entyre inner face of the of tyre reaching across the tyre from bead to bead. For outside paint the coverage should be a thin even film applied to the areas of the tyre that benefit most from the use of an outside paint, typically this would be the tyre sidewall areas and perhaps an area around the external shoulders. The tread area is often not coated with an outside paint.

Once the optimum coverage is obtained, using the visual guidelines mentioned above then the actual coat weight may be determined. This may be achieved by either measuring the shot weight or using pre-weighed patches adhered to the inside or outside of the tyre, the so called “patch-test”. The shot weight may be determined by using pre-weighed polythene bags placed over the spray gun heads to capture the amount emerging from the spray gun head when it is activated. The “patch-test” involves applying pre-weighed patches applied to the inner-liner or outer face of the tyre, depending whether one is measuring the volume of inside or outside paint being applied. In the case of the plastic bag technique it is usually best to measure an average of five to six activations of the spray gun to simulate the spraying of five to six tyres, and then calculating the average amount in order to obtain better accuracy. In the case of the “patch test” it is better to apply three patches spread around the inside or outside of the tyre to help determine the distribution of the film around the tyre. In both cases the measured coat weight is obtained from calculating the differences between the pre-weighed empty bags or pre-weighed clean patch, and the weight after the tyre is sprayed or the spray cycles simulated, depending on which technique is being used. An experienced release agent supplier should be able to provide support in this process.

Inside tyre paints are applied to the inner-liner of uncured tyres to provide the necessary slip required to allow the curing bladder (membrane) to locate easily inside the uncured tyre during the shaping process of the curing cycle. High slip at this point of the process aids the bladder to conform to the contour of the inside of the tyre, thus ensuring a well-centered tyre. These paints also assist in the elimination of trapped air. Their use is important in ensuring minimal curing defect levels and optimum tyre uniformity. At the end of the curing cycle inside tyre paints provide the effective release needed to remove the tyre from the bladder.

This is a difficult question to answer to provide a definitive answer to because it depends on the type of tyres being cured, the equipment they are being cured on and the application equipment available. The best product can only be determined by a thorough assessment and is best answered in consultation with an experienced release agent supplier.

A single release inside tyre release agent is applied to the inside of each tyre prior to it being cured. A durable inside tyre paint is applied to the inside of one tyre prior to it being cured; the film is designed to transfer from the treated tyre to the surface of the curing bladder during its curing cycle. The transferred film forms a layer on the bladder that has sufficient slip and release to permit the curing of several tyres before the film requires replenishment via the curing of another coated tyre.

A single release inside tyre paint is particularly useful when curing tyres with complicated contours like ultra-high performance tyres, where the low profile and square shoulders create the likelihood of trapped air. In these cases a specialist filled inside tyre paint applied to each tyre is required. Durable inside tyre paints are preferred with tyres having less complex contours and in regions where labor costs are high.