Polyurethanes were invented to offer an alternative material to natural rubber. The first Polyurethanes were manufactured as millable gums and so could be processed on normal rubber manufacturing equipment. From this relatively simple start Polyurethanes have expanded to embrace a bewildering array of products.
The name Polyurethane refers to any polymer that uses urethane linkages to join up bits of the material. This is why the name Polyurethane is used to describe materials and products encountered in all walks of life be it the varnish on laminate flooring or the roller coaster wheel in every theme park.
Not all polyurethanes are the same
At Hallam Polymer Engineering we specialise in producing high performance Polyurethane components from the very best of thermoset elastomers. These are high molecular weight materials formulated to exacting standards yielding consistent and repeatable processability. The end result is a family of materials with extraordinary physical properties in a material that can be as soft as a pencil rubber or harder than a golf ball. This family of materials is known collectively as V-THane Polyurethane.
There are many inferior polyurethanes on the market but parts made from V-THane will perform better and last many times longer.
The range and depth of properties that are fulfilled by V-THane polyurethane is almost too good to be true.
A very common application is a moulded tyre as seen on a roller coaster or a fork truck. These are usually made in the same grade of material, nominally a 90/95°A.
If the polyurethane properties for all the different hardnesses could be plotted on the same graph, this grade would be the intersect point and offers the best combination of physical and dynamic performance.
Using these tyres as examples these are the expected performance attributes.
The hardness could be increased upwards improve load capacity or downwards to soften the ride or indeed improve grip for a cold store environment.
The excellent abrasion resistance will allow a typical coaster wheel to last for at least two seasons whilst a fork-truck tyre can last almost indefinitely in a warehouse environment. A fork-truck tyre working in an engineering workshop is still likely to give a life measured in years. The mechanical aspects of the wheel are the usual failure mode.
A coaster tyre sees a lot of load at the bottom of the first big dip. The tyre absorbs the load by deflecting or deforming (as the material is incompressible) and then the polyurethane elastomer recovers it’s shape. In exactly the same fashion, the fork-truck tyre forms a larger flatspot at the bottom of the tyre when picking up very heavy loads. This flatspot disappears as the load is discharged.
Resilience is a measure of a materials ability to spring back into shape. The excellent resilience that polyurethane’s have explains why the loaded tyre recovers it’s shape. The same property also eliminates cyclic vibration caused by a rough or rippled running surface.
Polyurethane also resists cracking under repeated flexing and is part of the reason for the life span of heavily loaded wheels.