Castable Urethane ELASTOMERS are materials which can be stretched and will recover instantaneously on release. They are thermosetting, as are natural and synthetic rubbers. In simple terms, an Elastomer is a material which can be stretched at room temperature to twice its own length, held for five minutes, and upon release, will return to within 10% of its original length over a period of time.
Once cured these materials are not re-formable and can not be liquefied by the application of heat, like thermoplastics.
The main significant properties of Castable Elastomers
There are basically two types of Castable Urethane Elastomers. They are based on either POLYETHERS and/or POLYESTERS. Both Polyether and Polyester based elastomers have excellent physical properties, including abrasion resistance, load bearing characteristics and many other useful properties like tensile strength and tear resistance. These are tough durable materials that offer unique advantages over other materials. The cured properties of these products bridge the gap between rubber, plastics and and those available using metals. The properties include outstanding abrasion, tear and flex resistance, good tensile strength and excellent impact resistance. These products excel in application where severe wear is a problem and will withstand pounding, abrasion, cutting and general abuse only to come back for more. Indeed, there are many applications where the parts will never wear out.
Since these Urethanes are processed in liquid form, the required moulding pressures are low, therefore the tooling does not have to be extremely strong, heavy or expensive. Moulds can be manufactured from variety of materials like steel, aluminum, wood, urethane or epoxy. With proper techniques, moulds can be made using an original part as the model. There is virtually no limit to the size of the part that can be cast. As with other forms of Urethanes, the Castable liquids are supplied as both Polyether and Polyester based systems. Polyester Urethanes are excellent for printing applications where organic solvents are present. They are excellent in both dry and moist environments.
Physical Properties
One of the important advantages of Cast Urethanes is the extremely wide hardness range within which parts can be moulded. The typical range is from a low hardness of 5-10 Shore "A" which is softer than gum eraser to about 85 on the "D" scale which is perhaps harder than a bowling ball.
The next most visible property is probably the wide range of available resilience (bounce). Urethanes can be formulated to a low of 10% rebound (Bayshore) to a very lively 65%. The most important characteristics are physical strength, resistance to abrasion and tear resistance.