Countrose offers an additional service to other manufacturers in the fact that we offer two different types of elastomeric lined bearings, polyurethane and nitrile rubber.
Polyurethane is a very tough, highly abrasion resistant elastomeric material. Its excellent physical properties allow it to operate at loads beyond that of other elastomers, whilst its high resilience and abrasion resistance make it ideally suited to the toughest working environments. Polyurethane is slightly absorbent and, when immersed in water, it will swell a small amount until equilibrium is reached. The bearings supplied by Countrose are designed with initial clearances to cater for the dimensional movements caused by changes in temperature and water content.
Nitrile rubber is softer and has slightly lower physical properties than polyurethane. Generally, nitrile has a lower load capacity and is less abrasion resistant. It is resistant to grease and oil and is dimensionally stable in water, allowing tighter clearances.
Under most normal conditions polyurethane and nitrile rubber lined bearings have been found to perform equally well, displaying the same wear rates and giving a similar co-efficient of friction under lubrication. However, where the vessel is operating in abrasive conditions, for example in shallow water containing sand or grit, polyurethane has proven to far outlast nitrile. In contrast, where vibration may occur in the shaft caused by misalignment, nitrile has proven to have superior noise dampening properties than polyurethane, because it is a softer material.
Countrose bearings are generally produced with straight flutes as, in most applications, the greater open flow area reduces the incidence of blockage. However, we can also offer non-standard bearings with special flute designs to suit the criteria of different applications, including where spiral flutes, either right or left hand start, are required.