There are many components with in a tyre that we manufacture separately and brought together in a built process. Each of the component has a dedicated function.
- Raw Material: Latex
- Raw Material: Chemical
- Raw Material: Steel
- Tread Manufacturing
- Belt/Ply Manufacturing
- Bead Manufacturing
- Green Tyre
- Curing and Inspection Process
Begining of the Tyre Manufacturing Process
The Tyre manufacturing process begins in the rubber tree plantation of South East Asia, where a sloping cut is made in the bark of the tree from which the latex bleeds and is collected.
Materials added to the rubber during this process
There are many chemicals added to the rubber to improve its strength and rigidity. Of the key chemical components carbon black is the largest, followed by sulphur, zinc stearate, wax, accelerator and antioxidants.
Carbon balck makes up about 30% of the tyre.
Rubber reinforced with carbon black is much more abrasion – resistant, stronger, slower wearing and is easier to process than rubber alone. Carbon black also helps protect rubber against ultraviolet (UV) light from the sun.
The sulphur is a very important vulcanizing agent, which strengthens the rubber and gives qualities of strength and elasticity that one associates with tyres.
Small amount of zinc stearate and waxes can help control the cure rate and make rubber a bit easier to process. They also help prevent oxidation.
The accelerators help control the speed of the cure, so everything ends up fully cured, without having to spend excessive time in the mould.
The steel makes up around a fifth of the tyre’s weight and is essential component, especially for the ‘ Three Bs,’ Beads, Belts and Body. Just as the carbon black acts as a sort of ‘rebar’ for the ‘concrete of the rubber, the steel cord in a radial tyre acts a bit like the steel frame of a modern building.
The steel must first be treated with a special coating to help it adhere to the rubber in the tyre. The coating is tightly bonded to the wire, and in turn, bonds tightly to the rubber during processing.
THE FIRST STEP IN BRINGING THESE MATERIALS TOGETHER TO FORM A TYRE
First of all the rubber compound must be prepared for use on different tyre specification and for the different tyre components. All of the materials (natural/synthetic rubber, carbon black, sulphur and other chemical agents) are mixed together and pressed to form rubber sheets. This is done in a mill, which is commonly called a ‘Banbury mixer’, after the name of its inventor. The rubber sheets are then cooled and loaded into pallets delivered to the manufacturing process of the different tyre components.
Types of processes to shape Rubber sheet to form different components
There are two different processes to shape the rubber into the individual components of the tyre:
Calendering for the inner liner, body ply and belts, and extrusion for the tread, bead, fillers, and sidewalls.
Calendering means “pressing the rubber compounds between large rollers”. The calender is machine equipped with three or more steel rollers which revolve in opposite directions, forcing the rubber compound to adhere to the cords.
Extrusion means “forcing the rubber compound through a die”. The die is metal mould in the shape of the tyre component to be manufactured. This distributes the rubber volume into the appropriate final shape and dimensions.
THE TREAD EXTRUDING PROCESS
After heating the rubber to soften it, the tread is extruded to create a cross sectional shape. The extruded tread is completely cooled and cut into lengths suited for individual tyres.
In the case of belt and body ply, the steel cord is sandwiched between the rubber sheets and cut into length with given angles for individual tyres
The bead core is made of steel and is rubber coated by extrusion. The bead filler is also extruded an applied to the bead and they are placed on a rack ready for assembly.
HOW ARE THESE COMPONENTS ASSEMBLED TO FORM THE TYRE
The inner liner, body ply, bead with bead filler, sidewalls, belts and tread are assembled in sequence to form the ‘green’ tyre.
The tyre is built on a Tyre Assembly Machine (TAM).It is the “workbench” on which the tyre builder will assemble all the parts that make up the green tyre. Essentially this is a big, horizontal drum with a diameter the same size as the final “hole” in tyre.
The tyres are built inside out, starting with the inner liner. The tyre builder wraps this on the drum and then applies the body ply.
The body ply is then turned around the preassembled bead/filler, and wire and nylon chafers are added, depending on the specification of the tyres.The sidewall rubber is then added.
We have been wrapping flat components around a drum whose size is closer to that of the wheel. However, the circumference of the belt and tread is a lot greater than that of a wheel. Thus we have to change the shape of the tyre to receive the belts and tread. A rubber bladder inflates the layer we have already put on and at the same time, the drum shortens itself-pushing the wheel edges of the various layers together to form a shape of a green tyre.
Once the belt a tread are placed, the drum TAM starts spinning and as it does, rollers come in and press all of the various parts together. This is called stitching and the pressure squeezes out any air that might be trapped between the layers.
At this point what we call the green tyre is ready. Note that there is no pattern on the tread at this point of time.
The green tyre must be vulcanized, or cured, by applying heart and pressure in special machines to produce the finished tyre.
During vulcanization, the soft green-tyre is transformed into the tough road-worthy tyre. The green tyre is placed in a curing mould and is subjected to intense pressure and adequate heart internally and externally for a specified period of time.
The long hydrocarbon chains of natural rubber and randomly intertwined with one another but have no molecular links between them. By mixing, sulphur with the natural rubber and heating the mixture, sulphur cross-links, are formed between the rubber molecules. This hardens the rubber and gives it the qualities of strength and elasticity that one associates with rubber tyres.
Simultaneously, the tread pattern and sidewall information in moulded on the exterior of the tread and sidewall.
Every Bridgestone tyre has to undergo a strict quality check on a variety of inspection machines an at the hands of a skilled human inspector. Only those tyres that pass these strict inspections can be sold to a customer.