Why Is Polyurethane A Good Seal Material?

When formulated appropriately, Polyurethane yields an impressive set of material properties that make it an ideal material for sealing products.
It can be flexible; which allows seals to be assembled into closed grooves, resist large deformation and make them robust enough to survive without damage. In this respect it outperforms PTFE and is at least on a par with rubber.

It has excellent elastic behaviour, recovering almost instantly from deformation; again outperforming PTFE (no springs or rubber energisers needed here to give the initial sealing contact stress) and matching rubber materials. However, unlike rubber it has a lower coefficient of friction, with very high abrasion resistance, tensile strength and stiffness. These properties mean it can often be used without anti-extrusion/back-up rings at considerably higher pressures than even a 90 durometer elastomer o-ring would be capable of.

In abrasion tests, Polyurethane has a quarter of the wear rates shown by typical rubber sealing materials such as NBR (and considerably lower than even filled grades of PTFE). Its tensile and tear strengths are typically 3-5 times higher than rubber seal materials, and although it lacks the chemical resistance and temperature capability of PTFE, it is compatible with mineral oils.

Polyurethane seal materials typically have a general operating temperature range of around -35°C to +110°C, although more specialist grades can remain flexible down to -50°C, and other grades can push the upper limit to around 130°C.

Because it can be injection moulded as well as machined from tubes, it lends itself to production of seals in both high and low quantities, which allows commercial flexibility at both prototype and production stages of a project.