What is Cast Polyurethane?

Cast polyurethanes are a diverse and versatile group of materials that are known for abrasion resistance, chemical resistivity, stability in water, ease of processing and relative low cost. Cast polyurethanes are found in almost every industry. Molds for cast urethanes are relatively inexpensive and can be made from a variety of materials.

Cast polyurethanes are a good substitute for a number of materials where improved performance is required. Urethanes can be made as soft as gum rubber or as hard as a golf ball. In fact, most golf balls are polyurethane!

Cast polyurethanes are elastomers and are created by the reaction of a prepolymer which contains reactive isocyanate groups and a curative which contains hydroxyl or amine groups. In their simplest form, these two components, the prepolymer and curative are the only chemicals in the mix. The mixture is then poured into a heated mold where the components react to form a solid elastomeric piece.

The majority of prepolymers have one of two different molecular reactive groups, Toluenediisocates (TDI) and methyldiisocyanates (MDI). The curative systems for these materials can differ, and very different physical properties can be achieved. Prepolymers are further broken down into polyester and polyether backbone chemistries, again varying the possible physical properties.

Unlike injection molded materials which are thermoplastic, cast polyurethanes are thermosets. Thermoset materials are chemically different than the chemicals that were initially mixed together before the part was finished. (i.e. Chemical A + Chemical B = Chemical C), unlike thermoplastic materials ( Chemical A is heated and pressured into a mold = Chemical A in a different shape) which can be chopped up, mixed with virgin materials and then remolded. Thermoset materials are reacted once and are then unable to be remolded.

Because of the homogeneous and reactive properties of cast polyurethane, they form a great matrix for specialty additives which can impart different characteristics to the finished part.

For example, Armorglide^TM cast polyurethanes offer the cut and tear resistance of urethane and the lubricity and sliding wear resistance of UHMW polyethylene. Other additives can make urethanes that are bouncy or dead, slippery or sticky, or stretchy or rigid.

There are literally thousands of possible material combinations, each with special physical properties. Let us know what you need your cast urethane part to do and we help to develop the optimal formulation.