Urethane

Urethane is widely used in applications requiring high strength and resistance to impact. It has outstanding abrasion resistance and a reputation for toughness and durability. Urethane's combination of high load bearing strength, resistance to impact, abrasion and compression set make it the ideal material on many applications where rubber will not hold up.

HARDNESS AND RESILIENCE
The hardness of urethane ranges between 25A and 75D. The D scale is typically used to measure hardness greater than 95A. Urethane bridges the gap between rubber and structural plastics. No other type of elastomers offers unique properties over this hardness range.

Special formulations can be prepared with resilience (bayshore rebound) values as low as 15 percent or as high as 80 percent. Urethane can maintain its resilience with changes in temperatures (far greater than rubber) from 10°C to 107°C (-50°F to 225°F).

(Urethane durometer key chains are available at Parkway Products Inc. Call for a free sample #513-851-5550)

CASTABILITY

Because Urethane has the ability to be poured, it can be cast into simple molds. Parkway Products is a leader in molding Urethane assembly pallets and nest where quantities are generally under 500 pcs. Epoxy, aluminum and rubber molds are typically used for casting urethane.

ABRASION RESISTANCE Urethane has outstanding abrasion resistance, which has led to many important applications where severe wear is a problem such as roller blades wheels, snow truck blades, sand-blast mask, and coatings on aircraft engine blades. Urethane is considered to have excellent sliding and abrasion resistance and has out worn conventional rubber and plastics often by a factor as much as 8 to 1.

IMPACT RESISTANCE
Urethane has better impact resistance than structural plastics. Most standard compounds of urethane have excellent low temperature impact resistance and low brittle points. Although the coefficient of friction decreases drastically with temperature, its properties still enable it to be used on applications for snowmobile rollers and ski boots.

The impact or shock resistance of a material is measured in foot-pounds, with a swinging pendulum (hammer). As you see in the drawing, urethane will flex and bend on many applications where metal and/or plastic fracture. This has lead to urethane being used as front grills on tractors and automobiles.

SHEAR

Mounting and suspension assemblies generally require the loading in shear. Elastomers deflect more under a given load in shear than in compression. Since shear is a combination of tensile and compression forces acting at right angles to each other, the stress strain curve for anelastomer in shear is similar to the tensile and compression stress strain curves. Urethane's combination of properties (specifically in the higher hardness range) make it the ideal material for high impact / shear applications.

FLEX PROPERTIES
Urethane resists cracking under repeated flexure time after time, as evident by its successful use in dynamic applications such as forklift tires and boots used in earth compactor devices. Urethane is superior to rubber on almost all accounts, as long as, the part is designed properly. When subject to flexing, rubber products frequently fail due to the development and propagation of cracks. Urethane's high cut and tear resistance, usually surpasses the life of a rubber part by four times.

As with all elastomers, its rate of cut growth under flexing may be reduced by decreasing the thickness of the part. Unlike other elastomers, urethane can be practically utilized in very thin sections because of its exceptional strength and toughness. Design of the part to reduce localized concentration of the stress or heat build up will improve flex life to obtain the ultimate in flex life with urethanes, careful attention must be paid to part design. Urethane has a wide hysteresis loop and thus absorbs more energy (heat) then other elastomers. Parts undergoing high frequent flexing should be designed to eliminate as much bulk as possible. Premature failure of Urethane parts most often occurs due to heat (generated by working the material). A simple method of determining this failure mode is to feel the part. If it is hot to the touch the design needs to be altered. Contact Parkway Products for design and engineering assistance.

ADHESION
Urethane can be adhered to metals, elastomers, and plastics. The adhesive strength often exceeds the cohesive strength of the urethane itself. The hardness and rigidity of urethane make it practical to apply to rollers and wheels. Parkway has roll-grinding equipment up to 8ft. Long.

PHYSICAL PROPERTIES

Hardness,durometer value	80A	90A	95A	75D
Specific gravity	1.07	1.10	1.13	1.21
Tensile strength, Mpa (psi)	20.7 (3,000)	31.0 (4,500)	34.5 (5,000)	62.0 (9,000)
Impact resistance, Izod notched J/m (ft.-lb./in.) 24°C (75°F) -40°C (-40°F)	Flexed ---	Flexed ---	Flexed ---	800.7 (15) 58.7 (1.1)
Tear strength split, kN/m (pli.)	12.2 (70)	13.1 (75)	26.2 (150)	19.2 (110)

(The above data is supplied by Uniroyal Chemical Company. See Parkway's home page for more information)

PROCESSING
Adiprene urethane can be modified to provide greater strength, maximum ultraviolet resistance, specific hardness, or various other elastomeric characteristics. However, modifying urethane to enhance one property can result in sacrificing another property. Therefore, choosing the right molder & supplier is very critical. Parkway Products, Inc. is a leading molder of urethane in Northern America. Parkway has the technical competence, state of the art facilities, equipment and knowledge to engineer your complete design, material selection, mold making and secondary machining. See Parkways home page for more information.

Urethane Tray molded by Parkway Products Inc.

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