page_title: Tire manufacturing
section_title: Curing
hierarchical_section_title: Tire manufacturing / Manufacturing process / Curing
caption_attribution_description: English: Cleaning a rubber mold
context_page_description: Pneumatic tires are manufactured according to relatively standardized processes and machinery, in around 455 tire factories in the world. With over 1 billion tires manufactured worldwide annually, the tire industry is a major consumer of natural rubber. Tire factories start with bulk raw materials such as synthetic rubber, carbon black, and chemicals and produce numerous specialized components that are assembled and cured.
  The tire is an assembly of numerous components that are built up on a drum and then cured in a press under heat and pressure. Heat facilitates a polymerization reaction that crosslinks rubber monomers to create long elastic molecules.
context_section_description: Curing is the process of applying pressure to the green tire in a mold in order to give it its final shape, and applying heat energy to stimulate the chemical reaction between the rubber and other materials. In this process the green tire is automatically 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 recirculating heat transfer medium, such as steam, hot water, or inert gas. Temperatures are in the area of 350 degrees Fahrenheit with pressures around 350 PSI.  Passenger tires cure in approximately 16 minutes. At the end of cure the pressure is bled down, the mold opened, and the tire stripped out of the mold. The tire may be placed on a PCI, or post-cure inflator, that will hold the tire fully inflated while it cools.  There are two generic curing press types, mechanical and hydraulic.  Mechanical presses hold the mold closed via toggle linkages, while hydraulic presses use hydraulic oil as the prime mover for machine motion, and lock the mold with a breech-lock mechanism. Hydraulic presses have emerged as the most cost-effective because the press structure does not have to withstand the mold-opening pressure and can therefore be relatively lightweight. There are two generic mold types, two-piece molds and segmental molds.
  Large off-road tires are often cured in ovens with cure times approaching 24 hours.
caption: An opened tire mold being cleaned.  The deflated rubber bladder is on the central post.
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