Polyurethane begins as prepolymers which are high viscosity liquids. Most polyurethanes are a 2-part system consisting of the prepolymer for a specific grade and hardness of polyurethane and as a catalyst.

  • The prepolymer and the catalysis are stored in separate heated vessels inside the casting machine,
  • The raw materials are kept under high vacuum to extract any gasses in the polymer.
  • These gently stirred inside the vessel to maintain an even heat distribution.
  • Once the raw materials are degassed and heated to desired casting temperature, it’s time to cast.

Our 10 step casting process

  1. We program a specific material volume to be cast and the machine pumps the specified volume and ratio of prepolymer and catalyst through heated pumps and hoses to the mixing head which will mix the prepolymer and the catalysis together. For more complex parts we then use a hose to fill open cast moulds or produce parts via low pressure injection.
  2. All moulds are preheated to the same temperature as the liquid polyurethanes so we control the heat of the process to ensure even polymerisation occurs.
  3. Once a batch of polyurethane moulds are cast or poured, the catalysis will slowly begin to react with the prepolymer and begin polymerisation.
  4. After 3-10 minutes the polymerisation has begun to solidify the polyurethane part which is now in a semi-cured stage referred to as a green casting.
  5. Once they have tempered we have produced a high quality completely homogeneous stress-free polyurethane part.
  6. The green casting is now solid and no longer a liquid but lacks its final strength. The green casting is then transferred into an industrial oven.
  7. Depending on the material grade and size of the polyurethane parts, heat is used to accelerate the cross linking of polymer chains to complete the polymerisation process
  8. They will need between 9 to 16 hours in an industrial oven to fully cure and achieve full strength.
  9. After the required time period the oven is turned off to allow the polyurethane castings to slowly temper to room temperature.
  10. These finished parts generally require some cleaning and packaging before being shipped to customers. In the case of a wheel or roller, these are typically turned on a lathe to guarantee a perfect final tyre diameter and concentric alignment with the wheel centre.

 

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