One-Shot Cast Elastomers
The majority of all polyurethane products are manufactured using the so-called "one-shot" process. This includes flexible and rigid foams, reaction injection-molded elastomers and solid elastomers. In the one-shot process, the components (raw materials) of the elastomer formulation are metered and mixed simultaneously and then poured into the mold.
One-shot cast elastomers have found wide acceptance due to the ability to employ low-temperature processing, the potential to use lower-cost raw materials (such as polymeric MDI), and the possibility of producing thermoset polyurethanes with very high heat distortion temperatures.
Another advantage is the use of low-pressure gear pumps in processing one-shot cast elastomers. The ratio of the reactants often can be adjusted from approximately 1:1 to 1:2 by volume, which results in more forgiving metering accuracy when compared to hot-cast elastomers with ratios of approximately 9:1.
One-shot polyurethane cast elastomers, based on either liquefied MDI or liquid PMDI allow processing at ambient temperature using a combination of polyols and glycols on the B-side at mix ratios of 1:2 or 1:1. At these ratios, slight deviations do not have a dramatic effect on the elastomer's properties, which results in more robust polyurethane systems. At these ratios, slight deviations do not have a dramatic effect on the elastomer's properties, which results in more robust polyurethane systems. The overall properties of the resulting polyurethane elastomers are suitable for many applications, though these properties are not as robust as those produced with the prepolymer or hot-cast elastomer process.
One-shot cast elastomers are found in a wide variety of applications, including gaskets and squeegees, binders for rubber granules in the construction of sports tracks, concrete molds and stamps, joint sealants for concrete, automotive applications, bowling balls, and endcaps for oil and water filters.
One-shot cast elastomers have been particularly successful in electrical encapsulation for cables and transformers. In Europe, these elastomers have almost completely displaced other materials in the encapsulation of power, signal and telephone cables.