BASICS OF TEXTILES USED IN TYRE MANUFACTURE

Textiles are reinforcing materials which give strength and dimensional stability to the tyre. It is like the bones of the human body. Cotton was the first textile material to be used in tyres. Then slowly, cotton was replaced by rayon. Now eventhough rayon is used in very negligible amounts, NYLON is the widely used fabric in tyre manufacture. Textiles are used for carcass, breaker, flipper and chafer.


The manufacturing sequence of a tyre cord is as follows

· Filaments are drawn out from spinnarets
· Group of filaments (without twist) Yarn
· Yarn in twisted form Ply
· Two or more plies twisted together Cord
· Knitted, or woven cords Fabric


The nylon fabric comes in different deniers like 840/2, 1260/2, 1680/2, and 1260/3. The nomenclature can be explained by taking an example. If we take 1260/2, it means that two plies make one cord (represented by the digit 2 in the denominator) and 9,000 meters of one yarn will weigh 1260 grams.


Nylon is costlier than rayon, but it is preferred over nylon because it has higher strength and lower moisture regain. The moisture regain of nylon is about 4.5%. The breaking strength of various deniers of nylon are as follows.

840/2 13.2 kg (minimum)

1260/2 21.0 kg (minimum)

1680/2 27.7 kg (minimum)

1260/3 32.0 kg (minimum)


The required cord for a particular tyre is selected based on the principle that the force exerted on the cord in service should be only one-third of the breaking load. Since this is the force exerted in service, the possible elongation of the nylon cord is tested at this level (at one-third of the breaking load)

PLY TWIST

The plies are twisted on itself and with another ply before it is formed into a cord. The ply twisting directions are denoted by “Z” and “S”. If the direction of twist is from right to left, then it is called “Z” twist and if the direction of twist is from left to right, then it is called “S” twist. Usually, the individual ply is twisted in the “z” direction and two plies are twisted together in “s” direction to form a cord.


Normally all fabric will have a balanced twist which means that S and Z twists will be equal.

The usually given twists in turns per meter are

840/2 ---- 472 TPM (turns per metre)

1260/2 --- 394 TPM

1680/2 -- 335 TPM


By twisting, we lose tensile strength but gain flex fatigue resistance. Hence the twist factor must by decided by striking a compromise between tensile strength and flex fatigue resistance. By twisting, the cord acts as a single unit, and gains good abrasion resistance.


The following are the tests done on the fabric:
Elongation at break, twist, intermediate elongation, denier and moisture regain percentage.


Finish oil estimation is done to determine the amount of finish oil present on the surface of the cord. Finish oil is applied during twisting to avoid inter filament abrasion. Excessive finish oil will affect adhesion and also increase fumes in the department.

Hot water extract test is done to find out if there is any monomer left in the polymer

DIPPING PROCESS

The grey fabric as such has very poor adhesion to rubber. Hence it is treated with RFL (Resourcinol – Formaldehyde – Latex) solution which acts as a bonding agent between fabric and rubber. The amount of dip pick up is determined by finding the difference in weight between the grey roll and dipped roll. Chemical estimation of dip pick up is more accurate. This is the process in which the fabric is dissolved in a solvent where the dip pickup does not dissolve and the amount of dip deposit is weighed. The dipped fabric has to be kept properly covered always since it can absorb moisture and moisture is very dangerous in a tyre.


Fabric is hot stretched to reduce the effect of thermal shrinkage. This process is called heat setting. In this process, the fabric is heated nearly to its melting point and stretched.
Nylon’s unusual property of shrinkage when heated, warrants post cure inflation so that the tyre is cooled in the inflated condition under pressure.


Coding of different deniers of fabric is done as follows

840/2 fabric is indicated by the code number 4

1260/2 fabric is indicated by the code numner 5

1680/2 fabric is indicated by the code number 8

1260/3 fabric is indicated by the code number 6

1890/3 fabric is indicated by the code number 7