Because it is a unique engineering material that gives you the power to design in properties impossible to capture with other materials. Plus the power to improve cost performance and find novel solutions to thousands of difficult engineering problems. Overall, products made with polyurethane are stronger, tougher, and more durable than products made with conventional elastomers and plastic.
Harder Than Bone or Softer Than a Rubber Band
Polyurethane elastomers can be formulated to create products with a hardness range from 10 Shore A which is softer than a gum eraser, to over 90 Shore D which is harder than a golf ball. As you can see in the comparison chart below, polyurethane has a hardness range far wider than conventional rubbers.
Resistant to Abrasion
Where severe wear is a problem, polyurethane often outperforms rubber, plastic, and metals. In many applications, this abrasion resistance allows users to fabricate polyurethane products with less material than other elastomers would require. Other benefits include lighter weight, longer life, reduced maintenance and lower replacement costs. Since abrasion resistance is a complex property that can very with a number of factors, it is best to rely on our experience in selecting compounds for a given application.
More Load Bearing Capacity at a Given Hardness
Compared to other elastomers of equal hardness, polyurethanes have greater load bearing capacity in both compression and shear. This is an important advantage in many designsú such as stripper springs and press on solid tires. In other cases, this greater load-bearing capacity is what makes some designs possible at all.
Highly Resistant to Impact
While conventional plastic materials tend to become brittle as they become harder, polyurethanes remain elastic and resist fracture even in very hard formulations. This great toughness makes polyurethanes ideal for parts that have to stand up to high impact or repeated impingement.
Wide Resilience Range
Unlike rubbers, polyurethanes don't have to be made soft to make them resilient. Hard polyurethanes can be as resilient as much softer materials. For shock absorbing applications, polyurethanes can be formulated with rebound values as low as 10% to 25%. For quicker recovery, or where high-frequency vibrations are a factor, they can be formulated with rebound values up to 40% to 70%.
Suitable for High-Flex Applications
Under repeated flexing, polyurethanes resist cracking as well as most other elastomers. However, since cracking in any elastomers can be reduced by making the part thinner, polyurethanes offer an important advantage: they can be used in very thin sections because of their great strength and toughness.
Flexible at Low Temperatures
Depending on the formulations, polyurethanes remain quite flexible even in arctic-like temperatures. In addition, polyurethanes have proven remarkably resistant to thermal shock, and withstand sudden and drastic temperature drops without cracking.
Stable up to 200°C (390°F)
In special formulations, polyurethanes can withstand continuous use at 200°C (390°F) or higher. In standard formulations, polyurethanes are suitable for continuous use up to about 90°C (194°F), although they can withstand temperatures as high as 200°C for short periods in certain applications. For advice on high-temperature applications, ask UPP.
Won't Swell or Deteriorate in Water
Polyurethanes remain stable even when immersed in water as warm as 50°C (122°F) for very long periods. (They are not recommended for continuous use in water hotter than about 70°C (158°F).) They absorb practically no water -barely 0.3% to 1 % by weight and show negligible swell in volume even after prolonged immersion. In fact, polyurethanes are used successfully in water-lubricated bearings, where a slight increase in volume would cause seizing.
Wide Resistance. to Oil, Grease, and Chemicals
While many rubbers and plastics show excellent resistance to certain solvents, oils, and chemicals, polyurethanes will resist a much wider range of substances. Polyurethanes are therefore more suitable for products or parts that could come in contact with a number of different substances. As with any material, we recommend that polyurethane be tested for the specific resistance in actual use, or at least on a test that simulates actual use as closely as possible.
High and Low Friction Formulation
Polyurethanes resemble most plastics and other elastomers in that friction against non-lubricated surfaces generally decreases with harder formulations. Polyurethanes can be formulated with very low coefficients of friction for products like bushings, bearings and wear strips. The wear of shafts and mating surfaces is minimal with polyurethane, and usually much less than with conventional plastics. Additives can be used to further reduce friction. Softer formulations are used where more friction and traction are required, as in solid industrial tires, feed rollers, and drive rollers.
Of all elastomers, polyurethanes are considered to have the best resistance to gamma ray radiation. After exposure, they retain virtually all of their original flexibility and toughness.
Most polyurethanes are excellent insulators. They are used extensively in potting and encapsulating applications, and other areas where electrical isolation is important.
Bonds to Wood, Metals, and Most Plastics
During the molding process, and under controlled conditions, polyurethanes can be bonded to a wide variety of materials. Bond strengths are often stronger than the polyurethane itself, and are usually several times stronger than a similar rubber-to-substrate bond. With special techniques, cured polyurethanes can be bonded to many materials.
Low Mold and Tool Costs
The tools and molds used for creating polyurethane products can often be produced inexpensively. Polyurethane itself is frequently used on short runs and for manufacturing special items on short notice. A further advantage of low-pressure liquid casting process is the ability to produce large parts in limited quantities economically.
Yes, Polyurethanes Do Have Their Limitations
Like other engineering materials, polyurethanes cannot do everything. The very characteristic that makes them ideal for some applications may make them less suitable for others. And if selected, formulated, or applied improperly they may not perform as expected. To obtain optimum performance from polyurethanes UPP recommends the following:
- Provide us with specific, precise dimensions in your drawings, and let us work with you to optimize design to take best advantage of the polyurethane properties.
- Give UPP as much information as possible on how the part will be used, what you expect it to do, and under what conditions. (Such as flex, tension, temperature, compression, chemical contact, etc.).
Versatile, Cost-Effective, Dependable
Polyurethane elastomers are unique design and construction materials that combine many of the advantages of rigid plastics, metals, and ceramics with the flexibility and resilience of rubber. Chemically, they are polymers containing urethane groups (-NH-CQ-Q-), created by reacting isocyanates with polyols and chain extenders. By varying the nature of these three components, UPP can create literally thousands of different combinations of properties. Because of this versatility, polyurethanes can be custom-tailored to suit a wide variety of applications. The nature of the casting process can result in lower costs compared to other materials. Low-pressure, liquid casting means low cost tooling economical low-volume production, and great design flexibility. Furthermore, thanks to superior performance characteristics, polyurethane products are also more cost effective.