Castable urethanes are made by mixing and pouring together two liquids, a prepolymer and a curative. These two liquids are blended either by hand mixing or through a processing machine, poured into a mold and allowed to cure into a final shape. The major characteristic of these materials is that they have extraordinary physical properties. They are actually engineering materials and are chose for use on the basis of these properties.
Why use them ? Why use castables versus some other kind of material ?
There are really two main reasons: Performance and Cost Effectiveness
In some cases, performance characteristics of these materials allows them to be used in applications where other material simply cannot be used satisfactorily at all due to the tough environment. In other cases, urethanes are selected because they can outperform other materials by a large margin. This is usually a result of their particular properties, abrasion resistance and toughness, that is, resistance to breakage on impact or in rough handling, very high tear resistance, and high load-bearing ability. These four properties, although certainly not the only outstanding properties of urethanes, are the ones that usually make them stand out far above other materials in many applications.
The second reason is cost effectiveness. Even though polyurethanes are often more expensive than other materials, including various rubbers, the extra cost is often justified in terms of less downtime in actual operation. This is particularly critical, for instance, in mining and paper mills. Downtime in these operations is very expensive. If a mining operation has to be shut down for replacement of a part that has failed or worn out, the cost can run to thousands of dollars per hour. The somewhat higher initial cost of a urethane part which will last two, four or even ten times as long as a part made from another material is clearly more than justified.
Another area where urethane’s cost effectiveness is of interest is in the cost of tooling and equipment. Tooling for urethanes is not expensive because molds can easily be made out of plastic, metal, urethane itself or fiberglass-reinforced epoxy, in short, almost anything that does not hold moisture and can take the rather modest heat of casting operations. Tooling for rubber molding, on the other hand, is relatively expensive because it has to withstand the high pressures developed in compression molding operations and the high heat of curing.
Therefore, even though the cost of the materials in small production runs with urethane may be more expensive, the cost of setting up to do the job may in fact easily offset that cost.
What are some of the materials that urethanes compete against ?
In general, urethane competes in various applications with metals, plastics and rubbers.
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