Properties of Polyurethane:
Polyurethane can be adapted to comprise a wide range of unique properties, which is a key factor of its versatility.
- Abrasion resistance
- Toughness – Tensile strength
- High load bearing ability
- High tear resistance
- Mechanical properties
- Resistance to water, oil, grease
- Electrical properties
- Corrosion resistance
- Colour range
- Cost effectiveness (when long service life of PU parts are taken into account
Due to its remarkable impact and abrasion resistance, parts made from polyurethane elastomers will often outwear rubber, plastic, and metal by margins of 20 to 1.
Other important characteristics include extremely high flex life, cut resistance, load bearing capacity and outstanding resistance to weather, ozone, oxygen, and radiation. It performs well from -50°C to 90°C and has excellent resistance to oil, gasoline, and most solvents.
Costly down-time and maintenance expense can be avoided by substituting polyurethane for materials that are not performing to satisfaction. Urethane typically offers a longer service life compared to plastics or conventional rubber.
A key advantage of cast polyurethane is its ability to be easily bonded to other materials, such as many types of metal, composites, and to both reinforced and unreinforced plastics. These other components, commonly called inserts, can include bearings, wheel hubs, threaded fasteners, injection moulded parts, castings, etc. With correct preparation, the bond strength may exceed the high tear strength of the polyurethane.
Castable urethane raw materials are liquid, mixed and poured under very precise control of temperature and component proportions. They enter moulds as a hot liquid and are cured at an elevated temperature. This unique characteristic allows us to mould very large urethane parts with thick cross-sections which are completely uniform throughout.
Tooling for casting polyurethane parts is very economical, costing significantly less than molds for rubber or plastic. Polyurethane parts typically provide a substantial increase in product life over other materials, which translates to a better overall value.
Where severe wear becomes an issue, polyurethanes often outperform rubber, plastic, or even metals. This means that a part made from polyurethane can have a lower overall cost because it can be made with less material and therefore have a reduced weight, and work longer meaning reduced maintenance costs.
Urethane display high load-bearing properties in compression, tension and shear. Even at their highest hardness levels urethanes tend to have significantly better impact resistance than most other plastics. Polyurethane has excellent load bearing capacity which makes it great for many applications.
Polyurethanes can be formulated with high-resistance to stresses and they tend to maintain their shape and properties after repeated exposure to stress. Generally, polyurethane exhibits a high tensile strength when compared to other elastomers.
Polyurethanes resist cracking under repeated flexing.
Polyether-based polyurethanes can remain stable in water enabling operation at close tolerance in water lubricated applications. Polyurethanes can be formulated to resist the absorption of water. Weight and swell are practically negligible even after prolonged exposure. This makes polyurethane an excellent choice for applications in which tight tolerances must be maintained in wet conditions.
Most polyurethanes have very good insulating properties and are used in many electrical or encapsulating applications.
Oxygen and Ozone
Polyurethanes are nearly completely resistant to oxygen and ozone and will show no noticeable degradation even after hundreds of hours of exposure. In addition, polyurethanes do not support the growth of fungus, mould or mildew caused by prolonged exposure in humid climates. Polyurethanes are pigmented to be highly resistant to sunlight and weather. This makes them highly successful when used outside without hardening or cracking.
Polyurethanes can be machined with traditional tools, making polyurethane an economical choice for low production runs or prototype parts.
Through proper treatment of the bonding surface, a high strength bond can be achieved to metals, polyurethanes and other substrates. In some cases the bond strength can exceed the tear strength of the polyurethane itself.
Range of Hardness
Durometer is the measurement of a material's hardness. Polyurethanes range from 10 Shore A, about as soft as a rubber band, to 80 Shore D, about as hard as a bowling ball.
Polyurethanes operate within a wide temperature range. Some elastomer formulations can retain their flexibility at temperatures below -50°C while others can operate continually at temperatures in excess of 90°C.
Polyurethanes display excellent resistance to oil, grease and a wide range of chemicals; however, prolonged exposure to caustic acids, solvents and other heavy corrosives should be avoided. Simulated environmental testing should be performed to ensure part life.
Plastic Craft stock a range of polyether and polycaprolactone based raw materials in the hardness range of 60 Shore A to 75 Shore D. We use plasticizers or alternative hardeners to achieve hardnesses as low as 40 Shore A. We have also made products from optically clear materials, with vacuum degassing enabling a bubble free finish.
Polyethers are recommended for applications were parts undergo dynamic stress. ie. They incur lower heat build-up. They also have advantages in resilience, low temperature performance and resistance to water attack (hydrolysis).
Polyester based urethanes have superior cut, tear, abrasion, oil and solvent resistance, but finished parts are susceptible to hydrolysis. Polyesters can be sourced on request.
Urethane vs Rubber:
- High Abrasion Resistance
- High Cut & Tear Resistance
- Superior Load Bearing Capacity.
- Versatility in Hardness: we can provide 40 shore "A" (soft) to 75 shore "D" (hard)
- Environmental Resistance; Resistant to Sunlight, Weather, Oil, Ozone, Radiation
- Colour range: available in grades that are completely clear, but also accepts a wide variety of pigments making it easy to color-code your components
- Castable nature; lower cost tooling
Polyurethane vs Plastics:
- Elastic Memory: Polyurethane will return to its original shape when stretched
- Higher Impact Resistance: Polyurethane won't crack and break under impact and shock like other plastics
- Resilience: Urethane has outstanding wear, abrasion, and impact properties allowing for longer life
- Versatility in Hardness: Urethane is available in a wide range of durometers
- Thick Section Molding
- Lower Cost Tooling.
- Low Temperature Resistance: Polyurethane retains properties in temperatures as low as -50°C
- Resistance to Compression Set (or Cold Flow)
- Radiation Resistance