CURING RECIPES AND SETTINGS
The curing recipe determines the settings to be used for the curing process. The curing recipe contains: Information Information on the mould, bladder, flanges as well as the tyre markings that vary by type (ply rating, LI, DOT etc.) Press settings (press type, bushing etc.) Shaping information (loading heights, shaping time) Curing program Shaping time Bladder steam / hot water filling time Bladder steam / hot water circulation time Pressure and time of dome steam applied Release time Cooling time Press opening The operator follows a checklist to make sure all changes have been made and settings changed, and with his signature acknowledges that the setting procedure has been been completed. The markings and dimensions dimensions are checked on the first tyre completed from each production series so as to get the final affirmation of the correctness of the settings. Cur in g Time of a Tyre Tyre
Curing time = State of cure definition + Safety factor + Pressure release time + Press opening time Saf ety Factor F actor
Deviations in compound (reaction time) Deviations in tyre thickness
Deviations in temperatures Steam temperature Hot water temperature Variation of the temperature of the green tyre Mould temperature Deviations in bladder thickness Post curi ng in fl ation
The post curing inflation stage involves mounting the green tyre on the flanges, inflating it and cooling it according to a predetermined and preselected procedure. Conditions for Post Curi ng I nf lation
Immediately after release from the press, the green tyre is mounted on the flanges either automatically or manually. The post curing inflation pressure has to be about 20-35 % higher than what the normal inflation pressure of the tyre would be. The inflation time has to be long enough (at least one curing cycle) depending on the size of the tyre (thickness of materials). The distance between the flanges needs to be same as the width of the recommended rim for the tyre. Pur pose of Post Curi ng I nf lati on
Stabilize the shape of the tyre. Post curing inflation will help eliminate the influence of hot shrinkage on the tyre -> the tyre dimensions will not increase under actual operating conditions. Post curing inflation is recommended especially tyres of nylon carcass construction.
Di f ferences in the cur in g of r adial and cross ply tyres Cr oss Ply Tyr es
Cylindrical bladder is used.
Green tyres are preshaped in a press.
Before curing, the inside of the tyre carcass is painted - or alternatively the bladder may be processed or painted - which helps the tyre carcass slide well against the bladder during shaping. Considerable deformation of green tyres is possible during curing.
Radial Tyres
Loading requirements are more precise than with cross ply tyres.
A so called B-type bladder is used.
Deformation during curing is small.
Th e most common cur i ng fau lts accordi ng to the F M EA analysis
Tread bareness
Damaged tread
Shoulder blisters
Sidewall bareness
Sidewall blisters
Sidewall damage (steam or water leak)
Toe cuts
Inside bareness
Bladder break
Wrong green tyre
Undervulcanized tyre
Curing failures
Dirty mould
Damaged mould
Distorted stretch
Defective mould equipment
Mould extraction split
DOT missing/wrong
Wrong post inflation pressure
MAIN PHASES OF THE CURING PROCESS FOR CROSS PLY TYRES
The curing process can be divided into:
preshaping
loading the green tyre onto the press
shaping: the shaping bladder is stretched evenly inside the green tyre
curing and cooling
offloading the tyre from the press
post curing inflation (if needed)
Cur in g press
The tyre is vulcanized in a curing press, which receives the energy required for the vulcanization process through the dome and bladder. The steam building up within the dome transmits the energy through the mould. Energy is transmitted from the hot water circulating in the shaping bladder through the bladder into the tyre carcass. The pressure of hot water forces the tyre carcass against the mould, which process causes the tyre tread impression to be moulded into the surface of the tyre and determines the final shape of the tyre.
The press requires four types of motive power:
electricity (control commands, press motion open/closed) compressed air (lubricators, confirmation of the control commands, other compressed air powered equipment) Hydraulic pressure (tyre loading/offloading equipment, bladder motion etc.) dome steam and hot water (vulcanization energy)
Cur in g Press Types
1. Bag-O-Matic, BOM type, the most commonly used curing method 2. AF-type press 3. Autoclave curing method
Common press sizes are 36", 40", 55", 60", 63,5", 75", 85", 88", 91", 104" and 114".
