Tyre Reinforcement Materials

Reinforcement materials are the cords used in the carcass and belts and bead wires. The requirements for them are

• good strength-to-weight ratio
• flexibility
• dimensional stability
• good chemical and thermal resistance
• good fatigue resistance.

Generally in agricultural tyres textile cords are used in the carcass and textile or steel cords in the belts.

As textile cords is usually used Nylon (polyamide), Rayon and Polyester. Textile cord characteristics are the following:

Nylon is the strongest of these materials. It is generally used as carcass material especially in big earthmoving tyres. The Nylon 6.6 is more common nowadays. It is more stabile than older Nylon 6. The problem is that nylon changes by the action of temperature. The cord shrinks after curing, which may cause separations in use. Shrinkage can be compensated by post curing inflation. Nylon is not suitable for highway tyres, because when the tyre gets cool, it may result in a flat spot.

Rayon is the most stabile of these materials. It is used primarily in the agricultural tyre belts. As regards to strength, it is better than polyester. High price is the only problem.

Polyester is more stabile than Nylon. It is used both in cross ply and radial tyre carcass. It suits well for driving on a highway, because the flat spotting is not characteristic to it. New types of Polyester have been developed lately and they have partly displaced rayon.

Steel cords are used as the belt material of the radial earthmoving tyres and fortification of the forestry tyres. Truck tyres have monoply construction (All steel). Different cord constructions are used for different purposes. For example truck carcass is required to be fatigue resistant. The belt cord is required to be stiff. The fortification needs to have strength and good elongation (HE).

The most important property of the bead wire is strength. Typical wire diameter is 0,9-1,5. Bead wire may also have a stronger core wire. Socalled HT quality is also used. In truck tyres may be used square shaped wire.