Spray polyurethane foam insulation parameters

What is spray polyurethane rigid foam?

Today thermal insulation is the biggest factor for the energy saving. At this point, rigid polyurethane foam which has closed cell structure is the material having the lowest heat transfer coefficient (0.018-0.022 W/mK) in the world. This type of polyurethane foam can be applied easily by spraying on the surface on which the thermal insulation is necessary. Polyurethane adheres and expands on the surface and forms a foam layer of 20-40 kg/m3 density enabling an effective thermal insulation.

How is spray polyurethane foam applied?

A spray machine is needed to apply this type of polyurethane foam. This machine withdraws polyol and isocyanate components from their drums, heats them up to 35-45℃ and pumps them to their hoses with high pressure. The hoses are also heated to the same temperature to prevent cooling of components. After 15-30 m length, polyol and isocyanate component’s hoses are combined in the mixing chamber of the pistol. When the trigger of the pistol is pulled, the components coming to the pistol are mixed and sprayed on the surface with the help of the pressurized air fed to the pistol. Polyol and isocyanate components react with each other when they are mixed and they expand when they reach the surface and form the polyurethane foam structure. In seconds, the expanded polyurethane foam comprises an effective thermal insulation layer.

Thermal insulation of spray polyurethane foam

Spray polyurethane foams are expanded by both chemical blowing agents (water) and physical blowing agents (low boiling point hydrocarbons). Since this type of foams have closed cells majorly, the gases generated from those blowing agents (carbondioxide and hydrocarbon gases) are trapped inside the cellular structure of the foam. At this point the thermal conductivity of the foam, which is the inverse of the thermal insulation, is affected by the three parameters below.

●  The thermal conductivity of the polyurethane solid.

●  The therma conductivity of the entrapped gased,

●  The density and the cell size of the foam.

The thermal conductivities of some materials at the room temperature that can be used in the polyurethane foam structure are given in the table below

Thermal conductivity of the Materials in the Foam