The Properties of Polyurethane
The open casting of Polyurethane compounds allows for an economical flexibility in processing that can be altered, depending on the properties needed for specific applications. This can be accomplished by making modifications to the Polyurethane compounds that will allow improved product performances in a variety of environments. For applications involving exposure to water, the parts can be cast using polyether-based resins. for applications requiring urethane with strong abrasion resistant properties for heavy wear applications, polyester-based resins can be used. As shown below, polyurethane offers the engineer a remarkable range of properties and hardness's that enable them to outperform wood, metals, rubber or plastics in many applications
Harder Than Bone...or Softer Than a Rubber Band
Polyurethane elastomers can be formulated to create products with a hardness ranging from 10-15 Shore A (durometer), which is softer than a gum eraser, to over 90 Shore D (durometer), which is much harder than a golf ball. As you can see on the comparison chart on the next page, polyurethane offers a hardness range far wider than conventional rubbers.
Resistant to Abrasion
Where severe wear is a problem, polyurethane often outperforms rubber, plastics, 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, and reduced maintenance and replacement costs.
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%.
Flexible at Low Temperatures
Depending on the formulation, 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 120° C (248° F)
In special formulations, polyurethanes can withstand continuous use at 120°C (248°F) or higher. In standard formulations, polyurethanes are suitable for continuous use up to about 90°C (194°F).
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.
Most polyurethanes are excellent insulators. They are used extensively in potting and encapsulating applications, and other areas where electrical isolation is important.
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. As with any material, we recommend that polyurethane be tested for the specific resistance in actual use, or at least in a test that simulates actual use as closely as possible.
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.
Can be Made Flame Resistant
By incorporating flame-retardants into the formulation it is possible to produce polyurethane materials that meet several self-extinguishing or non-burning specifications.
Won't Support Mold, Mildew, or Fungus Growth
Suitably compounded polyurethane elastomers will not support fungus growth, and are generally resistant to such attack, making them suitable for tropical or high-humidity environments.
High and Low Friction Formulations
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. Additives can be used to further reduce friction.
Softer polyurethane formulations are used where more friction and traction are required, as in solid industrial tires, feed rollers, and drive rollers. Special designs can be employed via the casting process to improve traction.
FOR APPLICATIONS REQUIRING THE ABRASION RESISTANCE OF POLYURETHANE AND THE LUBRICITY OF UHMW:
ARMORGLIDE™ is a series of modified urethanes offering increased abrasion and tear resistance and a reduced coefficient of friction when compared to traditional urethanes.
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.
Formulations Available - Special polyurethane formulations are available for sound-deadening and anti-vibration applications. These generally have low resilience.
Low Mold and Tooling Costs
The tools and molds used for creating polyurethane products can often be produced inexpensively. Polyurethane is frequently chosen for short production runs and for manufacturing special items on short notice. A further advantage of the low-pressure liquid casting process is the ability to produce very large parts in limited quantities economically.
Yes, Polyurethanes Do Have Limitations
Like other engineering materials, polyurethanes cannot do everything. The very characteristics that make 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. Remember, it may be more difficult to machine or mold polyurethane to the very fine tolerances possible with machined metals.
Along with other Engineering materials, Polyurethanes are available in films, sheet, rod, and tubing.