Material Properties

Polyurethanes are probably the single most versatile material available to the industrial world. Physical test results do not do justice to the array of real world properties that polyurethanes provide. Polyurethanes were originally developed as an alternative material to natural rubber. They have grown far beyond this combining many attributes of metals, plastics and rubber into one unique material.

V-THane polyurethane offers the following service properties:

Hardness
V-THane polyurethane is supplied in a range of hardnesses from 25° Shore A which is softer than a pencil rubber or an elastic band to 84° Shore D which is harder than a golf ball.The table below gives some guidance as to these hardness ranges.

Compression
When load is applied to a V-THane polyurethane it deflects but unrestrained surfaces bulge in sympathy. This is because polyurethane is incompressible and acts like a fluid capable of changing its shape to the limit of its strength under load. Strictly speaking this is not compression but nevertheless it is the term used in elastomer technology. V-THane has a higher load bearing capacity than that of more conventional elastomers for the same hardness. This characteristic permits greater design choices and usually allows the use of smaller components. HPE can offer guidance on polymer selection and provide indicative load and deflection figures for most compression applications.

Tension
Tensile strength and associated elongation are usually measured as part of material and process control regimes. It is rare that polyurethane elastomers are used in tension and then only at a small fractlon of thelr ultimate strength. Even so V-THane has much higher tensile strengths than conventional elastomers.

Resilience
While resilience is generally a function of hardness in conventional elastomers, this is not true of V-THane polyurethanes. V-THane can be formulated to give a wide range of resilience values. An added benefit is that the resilience changes very little between 10°C and 100°C giving more consistent performance in a variable environment.

Abrasion
When compared to rubber, plastics and metals V-THane offers outstanding resistance to wear giving many times the life span of these conventional materials. V-THane can be tailored to suit sliding and impingement abrasion and has a well deserved reputation for its durability.

Temperature
V-THane will provide excellent service in cold stores and Arctic conditions. Physical properties change little down to -15°C, and while further reductions in temperature result in a gradual stiffening, V-THane is still quite serviceable at -70°C. At higher temperatures V-THane will provide good service up to 90°C and is suitable for intermittent use at 120°C. Beyond these temperatures, specially formulated materials are needed.

Radiation
V-THane polyurethanes offer superb resistance to gamma ray radiation. Products exposed to 1 x 10 Roentgens continue to give satisfactory service and are resistant to stress cracking.

Water Resistance
Selected grades of V-THane polyurethane are suitable for use in water at up to 50°C. Water absorption is very low and volume swell is negligible. This means that precise components (eg polyurethane seals and polyurethane tubes) can be used safely in water without fear of size changes affecting performance. High humidity has little effect on V-THane and a secondary benefit is that these elastomers do not support fungus growth and are generally resistant to such attack. This makes V-THane mouldings particularly suitable for tropical environments.

Ozone and Oxygen
V-THane polyurethane is highly resistant to ozone and oxygen attack. Tests conducted at 2.1 Map oxygen pressure for 4 weeks show little change to physical properties. The same result is obtained when tests are conducted at 3 ppm ozone for 500 hours. There is no measurable deterioration of the V-THane and past experience indicates that materials which resist these concentrations are virtually immune from atmospheric attack of ozone and oxygen.

Mechanical Properties
At low hardnesses all elastomers, V-THane included, merely bend under impact. As hardness rises elastomers and plastics demonstrate a tendency to brittleness and crack under impact. V-THane has significantly better impact resistance than any material of comparable hardness. V-THane will resist cracking under repeated flexing. Selection of the appropriate grade will allow extremely high life spans, with tests proving that in excess of 1,000,000 cycles is common place. V-THane will also show excellent resistance to cut propagation and can be used in very thin sections because of its exceptional strength and toughness.

Friction
V-THane resembles most other elastomers in that friction decreases as hardness rises. The coefficient of friction against non-Iubricated surfaces ranges from 0.2 (hard polymers) to 0.6 (soft polymers).

Machineability
It is possible to machine most grades of V-THane polyurethane. The harder grades can be processed on most conventional machine tools, while softer compounds need to be ground or cut with very sharp tools.

Electrical Properties
V-THane generally has very good insulating properties and can be used for potting and encapsulation. It is also an excellent material for mounting conductive rails, particularly outside, where it not only provides good insulation but also does not deteriorate.

Noise
The combination of compressive and flex characteristics make V-THane ideal for breaking noise transmission paths. It makes superb heavy duty machine mounts and can be utilised in fixing systems to provide a non-metallic barrier.

At HPE, we specialise in moulding high performance polyurethane components tailor made to customer requirements providing a solution to a wide range of application problems. We provide in-house development functions and can often produce representative samples for customer trials. We are able to identify a wide range of materials and can match samples where the original specification or source is long forgotten.

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