Urethane Casting
Urethane casting, technically referred to as polyurethane (or PU), is an elastic polymer, or elastomer, containing urethane carbamate links. From a molten liquid state, polyurethane may be fabricated or molded into low-density flexible foam, low-density rigid foam, soft solid elastomers (gel) and hard solid plastics. Valued primarily for its uses in rigid and flexible "memory" foams, polyurethane is extremely useful in solid plastic form as well. Urethane casting combines many of the desirable qualities of plastic, rubber and metal with longer service life than plastics, higher impact resistance than rubber, elastic memory, noise reduction, heat and chemical resistance, and many other properties. Cast urethane products include wide variety of pneumatic seals, press tool blocks, conveyor bushings, bumpers, bowling balls and parts for a broad spectrum of industries such as construction, automotive, food processing and athletic equipment.
The raw materials of polyurethane exist in a liquid state, which allows for easy mixing and measuring in preparation for molding, which may be open casting or closed casting. Raw materials react with one another to form a pre-polymer, then during the urethane molding process, a curative is introduced to the pre-polymer in order to complete the polymeric transition. Accelerated by heat and/or pressure, the mixture is poured into a mold cavity and cured to form the final polymer. During open urethane casting, the pre-polymer and curative are heated and mixed together, poured into an open cavity and cured without the application of pressure. During closed urethane casting processes such as injection molding, the pre-polymer and curative are heated and mixed together, then injected into the closed cavity through small holes. An example of a type of urethane casting would be compression urethane casting, which is commonly used to make small polyurethane parts such as gears.
Although all elastomers maintain strength and versatility in many industrial applications, polyurethane elastomers possess several advantages over other elastomers and materials. Urethane has higher abrasion, cut, tear, oil, ozone and radiation resistance, greater load bearing ability, broader hardness range and better colorability than rubber. Polyurethane also has thick section molding and low pressure tooling capabilities and a castable nature. As compared to metal, urethane has better noise reduction and resilience, greater abrasion, corrosion and impact resistance, more flexibility and is less costly to fabricate. Polyurethane is also lightweight, easily moldable, non-conductive and non-sparking. Urethane serves better than regular plastic in many applications, as it has higher impact, low temperature, cold flow, radiation and abrasion resistance, better elastic memory and noise reduction capabilities, greater resilience and provides lower cost tooling. The cost of urethane casting is on par with the cost of rubber and typical polymer molding, giving urethane an economic advantage as well.