Appropriate proportions in the mixture of polyurethane components

In other articles, we have already analyzed how polyurethane is formed and used as an insulation system or to manufacture some parts, among other applications. The mixture of the two components, polyol and isocyanate, which are liquids at room temperature, produces a chemical reaction that results in a solid, uniform and highly resistant structure.

If the heat released by the reaction is used to evaporate an inflating agent, a rigid product with a cellular structure is obtained, with a volume much higher than that occupied by the liquid products. This is what we call rigid polyurethane foam or PU.

The rigid polyurethane foam applied in situ by spray, that is to say, the sprayed polyurethane foam, is obtained by means of a simultaneous pulverization of the two previously mentioned components.

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Polyurethane manufacturing processes

There are two manufacturing systems that lead to two differentiated products:

• Rigid polyurethane foam (spray foam) applied on site is obtained by spraying the two components simultaneously to the substrate.”
• Rigid polyurethane foam applied in situ by casting, or injected polyurethane, in which the two components are agitated and introduced into a cavity where the expansion is carried out.

Proportions of polyurethane components

In these processes of polyurethane foam formation, is there an appropriate proportion for each of the two components? The answer is yes: each polyurethane system, specifically designed for spray or injection into different substrates or moulds, has a defined proportion in their respective technical data sheets.

Analyzing the polyurethane systems of Synthesia Technology, we find the following examples:

• Polyuretan Spray S-35RGB/ECO: like the other Polyuretan Spray systems, they are sprayed with high-pressure, heated equipment. The mixing ratio should be 1:1 in volume.
• Phono Spray I-905: like the other systems in the Phono Spray range, the ratio between polyol and isocyanate is 1:1 in volume.

The conclusion we reached is that the polyurethane base mixture tends to have the same proportion of its two components. If you want to achieve extra performance such as some colour shade, you can add the necessary components to the foam forming process according to the manufacturer's regulations. It is also very important to take into account the ambient temperature and the substrate where the polyurethane will be applied.

For these additional performances, it is important to read carefully the technical data sheets of the polyurethane systems, since they specify all the characteristics of the product as well as their recommendations for safety.