Tyre Curing methods

a) Dome Steam, Bladder Steam

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

b) Dome Steam, Hot Water in Bladder

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

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

c) 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.

Curing Temperatures

Generally the bladder steam or hot water temperature is standardized. Instead, the dome steam temperature is changed according to the product. By stopping the circulation of hot water it is possible to regulate the energy that comes through the bladder.

Temperature levels in a curing process are determined by the vulcanization properties of the compound. Typically the dome steam is lower, 120-170 ^oC. Hot water in the bladder is 150-220 ^oC.

Mould Materials

• Full Aluminium
• Full cast iron

Frame / Tread segment

Steel / All cast

Steel / Steel cast

Steel / Cast iron

Steel / Steel engraved

Essential Properties

• surface quality
• mould strength
• thermal conductivity
• ventilation holes
• possible to take the tyre off the mould without pattern breaks

Mould Maintenance

The precuring mould maintenance procedure includes:

• cleaning the mould (cleaning by sandblasting)
• opening the ventilation holes
• setting the equipment to meet the requirements of the tyre to be cured:
• changing the date of manufacture (DOT)
• checking or changing the LI and plyrating markings
• checking that the other markings needed correspond with the production formula for the tyre in question
• with 2-piece moulds controlling the accuracy of the alignment key so as to avoid the mould pieces becoming indented
• visual inspection of the condition of the mould before taking it to curing.

Curing bladders

• Dimensioning of the following characteristics is required:

height/width

shape

grooving (density/shape)

thickness

• Tight bead area
• Homogeneity of the material:

porosity

cuts

hardness

The Criteria for Choosing a Bladder

The dimensions and geometry of the tyre to be cured determine the bladder to be chosen for the job. Stretching occurs during the curing process both as far as the diameter and the height of the bladder are concerned. The stretching ratio of the bladder should be kept in balance. Too big an elongation not only shortens the service life of the bladder, but it may also lead to an irregular elongation of the tyre, which may cause the tyre to become asymmetric in shape. Too small an elongation may cause wrinkles to the bladder, which in turn will cause damage in the inner surface of the tyre.

The service life of a bladder depends on the elongation, bladder material, curing temperature and pressure used. The bladders are made of butyl rubber.