The difference between thermoplastic and hot-cast polyurethanes lies in the greater elasticity of the latter as well as its superior physical and chemical properties. Hot-cast polyurethanes, in fact, perform better in terms of resistance to abrasion, resistance to torsion and elongation at fracture.
Both thermoplastic and hot-cast polyurethanes are defined as compact polyurethanes.
The difference between thermoplastic and hot-cast polyurethanes is also linked to the production process.
Thermoplastic polyurethane demonstrates a reversible modification of its physical state depending on temperature. At 120° C, it goes from a solid to a liquid state allowing the production of numerous plastic products by means of extensive systems such as RIM (Reaction Injection Mould).
Despite its very high degree of viscosity, thermoplastic polyurethane can be injected into a mould using dedicated machines capable of working at very high temperatures.
By cooling the inside of the moulds, the thermoplastic polyurethane is able to take on any shape.
The disadvantage of thermoplastic polyurethane lies in its mediocre physical and chemical properties when compared to hot-cast polyurethane, especially with regard to the “elasticity” factor.
Hot-cast polyurethane is produced using machines that work at low pressure and is poured into dedicated moulds heated to a temperature of around 100° C.
Products made with hot-cast technology irreversibly go from a liquid to a solid state during the polymerisation process, thus guaranteeing maximum mechanical performance with respect to thermoplastic polyurethane.
Products made using the hot-cast system can also take on any shape but their reliability and superior strength are ensured thanks to the process adopted.
The ideal use of hot-cast polyurethane lies in the replacement of some types of rubber, steel and different kinds of plastic materials.
A reduction in hardness and mechanical properties, also called “pseudo-thermoplasticity”, can also occur with products manufactured using some hot-cast polyurethanes.
This not necessarily a disadvantage, however, if the temperature threshold at which the phenomenon occurs is lower than the temperature inside the plant where the piece is going to be installed. Despite its high degree of viscosity, thermoplastic polyurethane can be injected into a mould using dedicated machines capable of working at very high temperatures.
In reality, each hot-cast polyurethane has its own intrinsic thermoplasticicity. Good quality polyurethanes usually show a slight reduction in physical properties at around 120°C, while at over 150°C hardness and various mechanical properties drop dramatically.
In cases where a product has to work constantly at temperatures of around 150° C, special polyurethanes with exceptional dynamic properties, formulated using exclusive and very expensive raw materials, are employed.
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