Polyurethane rubber products are made up of complex molecular chains that, when formed, tend to maintain their resilience, flexibility, and shape under compression, tension, or stress. Due to urethane products’ ability to be manipulated into practically any size, shape, and hardness, it is a highly versatile material.
Here’s some key information about polyurethane rubber and how Uniflex Inc. makes sure you get the finest quality components.
Durometer (Hardness)
The “durometer” scale is used to measure the hardness of polyurethane (PU) in terms of its elasticity. A diamond-tipped hammer inside a graduated glass tube is made to fall from a certain height on the product being tested. The harder the polyurethane, the higher the rebound – the hardness number is calculated based on the height to which the hammer rebounds.
“Hardness” essentially measures the resistance of PU to indentation by three-spring-loaded indenter. The higher the durometer number, the greater the resistance.
The Rockwell hardness test or Shore durometer test are the most common ways to test the hardness of polyurethane rubber. Both tests measure its resistance toward indentation, and both provide a verifiable hardness value that doesn’t correspond to fundamental characteristics or other properties.
Durometer hardness, using either the Shore D or Shore A scale, is the widely accepted method for elastomers. The Shore D scale is used for harder polyurethanes while Shore A is used for softer ones.
The relative hardness of elastic materials like PU tends to be the Shore A hardness. If the indenter doesn’t penetrate the sample at all, a reading of 100 is obtained, and if it is able to penetrate the sample completely, the durometer reads 0.
Durometer Scales
Shore A (most common scale): Used for the majority of rubbers and elastomers
Shore OO: Used for exceptionally soft materials.
Shore D: Used for rigid plastics and other harder materials.
While a durometer is a commonly used, industry-wide indicator of other physical properties, it by no means displays the remarkable versatility of polyurethane. Depending on your unique needs, physical properties such as stretchability, flex strength, water/chemical resistance, temperature resistance, shock absorption, and rebound may be more important than hardness.
Uniflex Inc. will be happy to custom formulate your product so it has the ideal physical characteristics you want.
Typical Properties of Polyurethane Rubber Formulas: Shore A
| (ASTM D2240) Durometer | 40A | 50A | 60A | 70A | 80A | 90A |
| (ASTM D412) Tensile Modulus, PSI | ||||||
| 300% | 259 | 381 | 430 | 470 | 1120 | 2640 |
| 200% | 202 | 297 | ||||
| 100% | 142 | 216 | 285 | 370 | 375 | 1436 |
| (ASTM D412) Elongation at Break % | 692 | 573 | 760 | 700 | 585 | 440 |
| (ASTM D412) Tensile Strength, PSI | 4691 | 6206 | 4320 | 5450 | 4500 | 6382 |
| (ASTM D624) Die C | 140 | 159 | 195 | 260 | 345 | 514 |
| Tear Resistance (lb/in.) | ||||||
| (ASTM D395B) Compression Set % | 16 | 17 | 51 | 36 | 35 | 29 |
| Split Tear (ASTM D470) | 22 | 28 | 42 | 70 | 100 | 222 |
| (ASTM D2632) Resilience (Rebound %) | 22 | 4 | 32 | 21 | 56 |
Typical Properties of Polyurethane Rubber Formulas: Shore OO
| (ASTM D2240) Durometer | 25-OO | 40-OO | 50-OO |
| (ASTM D412) Tensile Modulus, PSI | |||
| 300% | 14.2 | 22.7 | 35.5 |
| 200% | 7.33 | 15.8 | 24.2 |
| 100% | 3.05 | 9.06 | 14.6 |
| (ASTM D412) Elongation at Break % | 865 | 763 | 706 |
| (ASTM D412) Tensile Strength, PSI | 86.5 | 167 | 273 |
| Die C (ASTM D624) | 8.87 | 17.3 | 21.4 |
| Tear Resistance (lb/in.) | |||
| (ASTM D2632) Resilience (Rebound %) | 25 | 30 | 39 |
| (ASTM D395B) Compression Set % | 0.00 | 0.00 | 0.00 |
Typical Properties of Polyurethane Rubber Formulas: Shore D
| (ASTM D2240) Durometer | 50D | 60D | 70D |
| (ASTM D412) Tensile Modulus, PSI | |||
| 300% | 4400 | ||
| 200% | 3977 | 5677 | |
| 100% | 2100 | 3340 | 4342 |
| (ASTM D412) Elongation at Break % | 329 | 262 | |
| (ASTM D412) Tensile Strength, PSI | 6800 | 6346 | 7391 |
| (ASTM D624) Die C | 785 | 754 | 983 |
| Tear Resistance (lb/in.) | |||
| (ASTM D395B) Compression Set % | 28 | 41 | 45 |
| (ASTM D470) Split Tear | 120 | ||
| (ASTM D2632) Resilience (Rebound %) | 42 | 45 | 42 |
| (ASTM D1938) Trouser | 314 | 295 |
Other Properties of Polyurethane (PU) Elastomers
#1. Compression
In addition to high load-bearing properties in both compression and tension, PU materials have a high load-bearing capacity in shear.
#2. Abrasion
Polyurethanes are known to outperform metals, plastics, and rubber in applications where severe wear is a problem. This often means that a component made from PU can be made with lower cost, reduced maintenance, and less material.
#3. Mechanical Properties
Almost all elastomeric materials tend to bend under impact at lower hardness levels. They are compounded up to a higher degree of hardness so they end up losing their elasticity, which leads to cracks. But even at their highest hardness levels, polyurethanes have substantially better impact resistance than most plastics.
#4. Resilience
PU can be formulated in a wide range of resiliencies. If your application requires quick recovery, it can be made with rebound values from 40–70%, or it can be manufactured with rebound values of 10–25% for extreme shock-absorbing uses.
#5. Flexibility
Polyurethane rubber elastomers do not crack under continual flexing. By decreasing the thickness of the component, any cracking under heavy flexing may be reduced, which allows PU to be used even in incredibly thin sections.
#6. Temperature
Most polyurethane elastomers maintain their flexibility at very low temperatures and display excellent resistance to thermal shock. This is why PU is widely used in many applications in arctic conditions.
Polyurethanes are able to endure dramatic and sudden changes in temperature without cracking. They can also easily withstand consistent rise up to 194 F (90 C).
#7. Friction Coefficients
PU can be made with coefficients of friction ranging from really low (for parts like wear strips, bearings, and bushings) to really high (for parts like rollers and tires).
#8. Water
Polyurethanes that are polyether-based maintain their stability in water as warm as 122 F (50 C) for prolonged periods. Water absorption is extremely low at 0.3% to 1% by weight and any swell in volume is negligible. In water-lubricated applications, this allows operation at tight tolerance.
Contact Uniflex Inc. For Superior Polyurethane Rubber Products
Since 1979, through our own independent research in the polyurethane industry, Uniflex Inc. has stayed on the leading edge of molded rubber and elastomers technology. In fact, we were one of the very first manufacturers in the Midwest to set standard thickness tolerance of precision sheets at +/-.005″.
If you are looking for a partner that can meet your strict specifications in terms of versatility, durability, toughness, and strength of polyurethane parts, get in touch with us today. You can call us at 248-486-6000 or write to us online.