Tire Curing Process --Pre and Post Cure Operations

Green Tire Preparation

To obtain good quality moulding and for the smooth laying of bladder
inside the green tire , it has to be subjected to the following operations
• Tread splice jamming
• lubing
• Awling

Tread Splice Jamming

· To avoid opening of tread splice during shaping process
· Pneumatic pressing device used
· 60 psi pressing pressure for truck and 40 psi for others

Inside lubing

Inner lube is applied
· To ensure smooth laying of bladder
· To ensure bleeding of air trapped between tire and bladder
· For easy removal of cured tire from bladder



Outside lubing

Outer lube is applied

· To facilitate proper flow of compound in mould
· To prevent air entrapment
· To avoid tire outside blemishes

Awling

• Awling is done by pneumatic drill as well as at auto awlingmachine
• This is to remove entrapped air
• It is important to awl at tread splice location

Tire curing Curing Methods

Dome Steam, Bladder Steam

Usually used in production of small tires like passenger car tires,
bicycle tires and smaller agricultural tires.

Dome Steam, Hot Water in Bladder

This is the most common method in production of big tires.

Often is used also circulation of cooling water in the end of the curing
phase to cool the tire before release (temperature 25-50 oC).

Nitrogen Curing
Rather new curing method. Steam or hot water in the bladder is
replaced by nitrogen.
With nitrogen curing, the curing time can be shortened and problems
caused by water or steam can be eliminated.
This method decreases energy consumption in curing compared to hot
water or steam curing.

Vulcanization of Tires Using Presses


· Tires are introduced into molds, so that the compound does not come into
contact with neither the thermal agent, nor the atmosphere.
· The vulcanization presses are built under various forms, which differ each
other by size, number of working sites, operating system (mechanic, hydraulic,
pneumatic, electromechanical) or heating system (steam, overheated water,
electrical resistances).
· In the design and construction of molds, the nature and the thermal
characteristics of the compound, the allowed pressure and the vulcanisate
shrinkage are taken into account. The vulcanisate shrinkage is empirically
correlated with compound hardness or density

Main Phases of the Curing Process

• Loading The Green Tire Onto The Press
• Pre-shaping
• Shaping: Bladder Is Stretched Evenly Inside The Green Tire
• Closing Delay
• Sequence Of Valve Operation
• Curing And Cooling
• Offloading The Tire From The Press
• Post-curing Inflation

Post Cure Inflation’

The post curing inflation stage involves mounting the tire on the flanges,
inflating it and cooling it according to a predetermined and pre-selected
procedure.

Conditions for Post Curing Inflation

• Immediately after release from the press, the tire is mounted on the flanges
either automatically or manually
• The postcuring inflation pressure has to be about 20-35 % higher than what
the normal inflation pressure of the tire would be.
• The inflation time has to be long enough (at least one curing cycle) depending
on the size of the tire (thickness of materials).
• The distance between the flanges needs to be same as the width of the
recommended rim for the tire.

Purpose of Post Curing Inflation

• Stabilize the shape of the tire.
• Postcuring inflation will help eliminate the influence of hot shrinkage
on the tire.
• The tire dimensions will not increase under actual operating
conditions.
• Postcuring inflation is recommended especially for tires of nylon
carcass construction.