There are some fairly common characteristics among tread materials offered on industrial casters, for example 95A shore hardness is pretty much a standard offering from all manufacturers. A softer 85A shore hardness offering is also common, as is a harder poly, usually a 70D shore hardness. Shore hardness is a very common attribute that polyurethane is identified by, but there is so much more to polyurethane than its level of hardness.
Their are common characteristics that define polyurethane tread material. These characteristics are defined by the American Society for Testing and Materials (ASTM), which is an internationally recognized standards setting organization. The characteristics that they test for are:
• Hardness – as measured by Durometer according to the Shore Hardness Scale.(ASTM D-2240-81)
• Resistance to Abrasion – resistance to scuffing, scratching wearing down etc. measured by how much mass is lost after abrasion. (ASTM D-1044-78)
• Rebound (Resilience) – Measures the vertical rebound of dropped mass. (ASTM D-2632-81)
• Tear Strength – Determines the amount of force necessary to propagate a tear in material. (ASTM D-1938-67)
• Tensile Strength – A tension test measuring how much force must be applied until failure is caused. (ASTM D-412-80)
• Compression Set – The permanent deformation remaining when a force that was applied consistently is removed. (ASTM D-395)
Each of the above mentioned characteristics has certain benefits, but is often countered by a reduction in another characteristic. For example, it is almost impossible to have a high rebound with a hard wheel. Most high rebound wheels have an 85A Shore hardness level. The same is true for other characteristics, therefore a trade off is usually made.
Here at Caster Concepts, we mix and pour our own polyurethane, and have formulated premium tread materials that achieve unique benefits, these premium polyurethanes are:
ErgoTread – Reduces the amount of energy exerted to keep rolling, this formulation returns energy
T/R 95 – A harder tread material with a resistance to many chemicals and high level of tear resistance, and more elasticity than other 95A hard wheels
T/R 85 – A softer version of our tear resistant poly, it is easier on flooring and quieter than the 95 version
HPPT – Designed to resist heat build up, this is the ideal poly for use on powered applications like Tuggers and AGV’s
Of course we also offer a standard 95A shore hardness poly that is economical, as well as a 70D Shore hardness poly that is extremely hard for very heavy loads.