polyurethane foam, its properties and characteristics
The basis of foam are prepolymers, synthesized from polyol and isocyanate. In addition, inside the container is a propellant comprising a mixture of liquefied propane, butane and isobutane. It performs the propellant for polyurethane foam function foam by pushing it under pressure from the cylinder to the outside.
At the exit from the cylinder of its contents comes in contact with air and turns to foam, which is repeatedly increasing, fills all the free space. This process is called the primary extension. For home foam the degree of initial expansion is from 20 to 60%, professional foam this percentage is much higher and reaches a value of 300%.
Entering into chemical reaction with moisture contained in the air, since the foam hardens, becoming chemically stable polyurethane. Usually the curing of the foam takes about 24 hours. Wetting a processed surface, this time can be reduced significantly. Throughout the process of solidification, there is a secondary expansion of the foam, its quality construction material can reach 25-30%.
The cured foam is a solid having a porous structure, resistant to moisture, with excellent insulation properties polyurethane. In addition to the primary and secondary expansion can occur and the reverse process – the shrinkage of the foam. Its importance for quality of foam should not exceed 3-4%.
The cylinders for domestic and professional foam easy to discern by visual inspection. Household foam does not require special tools for application, and therefore is a cylinder with a valve on the end on which is screwed an adapter in the form of a lever and a plastic tube.
It is quite another thing – professional foam. To work with it you need a special device – mounting the gun. Before you start working with container remove the protective cap and screw the cylinder with foam on the gun. After repeated vigorous shaking of the container the device is ready for application of the foam.
In addition to the way to use, professional foam differs from domestic its technical characteristics. It has a higher ratio of primary extension of the structure is smaller, and the elasticity is higher.
The scope of domestic structural foam is limited to filling in small cracks and holes. Using the same professional foam not limited to almost nothing, the only requirement to the work surface – it should not be inert, because the value of adhesion of the polyurethane foam in contact with polyethylene, Teflon, graphite and some other materials has a value close to zero.
Summer and winter
Polyurethane foam is divided into types depending on the temperature of its use. Summer foam is used to perform work at air temperature from +5 up to +400 C. In the case of use in sub-zero temperatures of the air leaving the cylinder is greatly reduced, and the stated degree of expansion is markedly reduced.
To perform work at air temperature from -10 to +400 With the right winter construction foam. There are all-season foam, but it is essentially winter.
Volume of cylinder
How to choose the volume of the cylinder? When you install the standard window size 1.5 m by 1.2 for foaming the box it will require from 15 to 20 liters of foam. To obtain such amount of foam mixture will be enough of the cylinder of foam with a capacity of 300 ml.
To froth up the door frame measuring 2.0 by 0.8 m will need approximately 30 liters of foam. This amount of foam will produce a cylinder with capacity 500 ml.
There are cylinders with a volume of 750 ml, which results in an output of 50-60 l of foam. As it is easy to calculate, this amount of mounting you have enough material for door foaming two boxes or three boxes for Windows.Remember that polyurethane foam has the property of being degraded by exposure to UV rays. Therefore, after final solidification of the foam do its protection, Shtukaturov treated foam surface.
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