The third type of material competing with urethanes is rubber.
The main advantage of urethanes versus rubbers are the higher abrasion resistance compared to most rubbers combined with their high cut and tear resistance.
In addition, most cast urethanes are available in grades from either completely clear to opaque white or amber in color. Their ready acceptance of a wide variety of pigments and dyes also permits coloring from black up to brilliant fluorescent oranges, reds, or greens.
This is especially useful in color-coding of parts. A good example are parts used in computers and printing machinery where rolls and belts can be color coded so that correct replacement can be easily made. Rubber also tends to be subject to ozone cracking, particularly around electrical equipment where ozone concentrations can be rather high.
Polyurethanes have no ozone cracking problems.
The fact that urethanes are pourable and castable, which was mentioned earlier, makes for cheaper tooling and makes possible the fabrication of complicated parts. Moreover, most rubber compounds when they are compounded up to 90A or 95A durometer, have sacrificed a good deal of their physical properties.
On the other hand, polyurethanes in the 80A to 95A durometer range are approaching the peak of their properties and give extremely good performance at these hardnesses. So far we have discussed the advantages of polyurethanes compared to other materials.
Naturally, as with anything, there have to be some disadvantages as well.
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