Curing is the process of applying pressure to the green tyre in a mould. This gives it its final shape. There is heat energy applied to stimulate a chemical reaction between the rubber compounds and other materials.
In curing process, you will observe (a video) that the green tyre is transferred onto the lower mold bead seat, a rubber bladder is inserted into the green tire, and the mold closes while the bladder inflates. As the mold closes and is locked the bladder pressure increases so as to make the green tire flow into the mold, taking on the tread pattern and sidewall lettering engraved into the mold.
The bladder is filled with a circulating heat transfer medium (such as steam, hot water, or inert gas). At the end of cure the pressure is bled down, the mold opened, and the tire stripped out of the mold.
Various suppliers manufacture curing bladders to fit to the different curing press types viz. Bag-o-Matic (BOM), Autoform and Hydraulic (Bagwell).
A bladder curing press cure bladders. Sizes vary because there are radial and bias type curing bladders for the passenger car, light truck, OTR (Off-The-Road), agricultural, bicycle, and motorcycle tyres. You will also find curing bladders for tire retreading and air spring production.
Here’s a structure of a compact mechanical bladder curing press.
Additionally, you would also find this L&T newsletter informative on technical aspects.
A good curing bladder has following key features
- It is made of a sustainable and flexible compound
- The bladder contour is optimized to tire contour
- A good surface structure to prevent trapped air
- Durable and simple to use during service
If the bladder contour and venting system are not optimized, the tyre plants experience higher level of trapped air and blisters. This is predominant in motorcycle tyres when compared to other tyre segments.
A good bladder has minimum inner-liner consumption. It also facilitates a smooth and simple final inspection of the tyre due to its constant surface structure. Imperfections, if any, can be easily detected which in turn gives you extra ordinary final finish.
So choose your bladder curing press wisely and operate it smartly to produce the best curing bladder for your customers.
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