Foam rubber, soft rubber is an elastic material subdivided into several types depending on its base(rubbers EPDM, SBR, NBR, CR - polychloroprene) and pores (closed, interconnected and mixed).Foam rubber properties depend on the inherent properties of the polymer base and on the density,compositions and structure of pores.
Pore size varies from about 0.4 μm, and rubber with pores up to 0.4 μm is referred to asmicrocellular. The volume of pores in the total composition of rubber may vary from 20% to 80%depending on the rubber type.
Foam rubber has a number of advantages compared to the solid one. For example, it has improvedelasticity, softness, good damping, sound and vibration-proof properties.
Soft rubber is successfully used both in tropical and moderate climates. EPDM rubber and Neoprene CR can be used even in the far north regions.
Foam rubber can be named differently: foam rubber, soft rubber, sponge rubber, porous rubberplate, cellular rubber. Several types of the material produced are as follows:
The essence of the process is in softening rubber and adding all ingredients included in the formula.
The only exception is foaming agents. These substances are introduced into the overall stock of components at the last step.
As a rule, rubber constitutes 80% of the resultant mixture. Plasticity of this component determines quality of foam rubber. Usually producers tend to use natural rubber, because when replaced with synthetic rubbers, for example, acrylonitrile-based butadiene copolymers or butadiene polymers the low-strength vulcanizers will be the outcome. In order to avoid it producers add technical carbon to synthetic rubbers.
Foaming agents are substances which decompose at the temperature lower than the curing temperature and release gases. Foam rubber type depends both on the sort of foaming agents and
quantity of organic or nonorganic foaming substances which may constitute from 2 to 30%.
Foaming agents are added to the mixture of ingredients at 40-60 °С.
After the foaming agents are added, the resultant mixture is processed on an extrusion machine or a colander. It is done at a lower temperature.
Curing is carried out under constant and alternating temperatures. The temperature regime and curing process duration depend on the thickness of an item, composition of foam rubber, accelerators and types of foaming agents.
Modern technologies providing possibilities to modify chemical composition of the mixture, rubber plasticity and curing, offer the potential to obtain foam rubber with various properties. It can be soft
and hard, with various pore diameters, etc.
Foam is cured in special molds, and after washing the foam rubber is subjected to drying and processing.