A characteristic feature of the production technology of foam bespressovyj method is two-stage foaming process.

During the initial foaming granules are formed uniformly distributed cells, filled with pairs of isopentane, having the form of polyhedra. The cell size of 50 to 150 microns. The wall thickness of the cells does not exceed a few microns, which is comparable with the size of the molecules of polystyrene, in which the walls of the cells are oriented in the state of forming an anisotropic film, which increases the dimensional stability of the foamed pellets. Primary foaming is characterized by the pre-expansion coefficient, which is determined by the ratio of the volume of foam and the original granules. The value of K is chosen in each case so as to ensure filling of foamed granules of the total volume of the form and obtain a foam of a given volumetric weight. The value of K depends on the molecular weight, particle size distribution and content of pentane in polystyrene suspension, as well as the temperature and duration of its foaming.

Original granules suspension of polystyrene have a bulk density of 450 — 550 kg/m3.

After pre-foaming mass of 15 — 100 kg/m3.

For each batch of polystyrene that there is an optimum time of foaming at a certain temperature at which an equilibrium between the partial pressure inside the granules and external pressure. Longer foaming leads to the destruction of the granules, the formation of a porous structure and increase volumetric weight. The pellets expand when heated due to the vapor pressure of isopentane only in the initial period, and then the foaming is greatly influenced by the diffusion of water vapor in the resulting cell.

Water vapor have significant permeability through films of polystyrene: for example, at normal temperature the permeability of water vapour in 4100 times greater than the permeability of nitrogen. When the temperature increases, the permeability decreases slightly, but remains substantial. Therefore, compared with the vapor diffusion of pentane from the cell, the penetration of steam into the cells more rapidly.

The purpose of a preliminary foaming is to reduce the amount in polystyrene isopentane. Studies have shown that in order to create the desired gas pressure and obtain immature product with a bulk density of 20-30 kg/m3 10 — 12% of isopentane. In fact, in the granules of polystyrene contains 4-4,5% isopentane. Required gas pressure in the final shaping of the foam is achieved in that during the exposure (6-24 h) dried granules after pre-expansion, the atmospheric air is sucked into pellets, in which a vacuum was formed in the condensation of isopentane.

Preliminary foaming are using hot water, steam, air or high frequency currents by heating the polystyrene bead to a temperature of 90-120 OS. The volume of the granules is increased by 30 to 50 times, depending on the properties of the feedstock.

For this operation use different types of foaming agents periodic and continuous action with different coolants. The choice of coolant and design of the expander is determined by the volume of production of the foam.

When small amounts more efficiently prior to foaming in the periodic blowing agents using hot water or steam. When foaming the hot air, there is no need of drying and soaking of pellets, but the low heat transfer coefficient complicates the efficient conduct of the process that leads to uneven expansion of granules.

When large volumes of EPS production is most advantageous to use steam which allows you to automate the process of pre-expansion. In this case the granules are moistened slightly and the need of drying them out. This method is most popular. The pre-expansion process is accelerated in a field of high frequency currents. The disadvantage of this method is the low value of the loss tangent of dry granules of polystyrene. Therefore, the need of hydration of the granules and subsequent drying makes this method impractical.

The granules are maintained at temperatures no higher than +22…+28°C, because the diffusion of isopentane from cell pellets accelerated by increasing temperature. The dwell time depends on the volume of the bulk weight of the granules and is at 20-30 kg/mg for about 6-24 hours The decrease in bulk density causes an increase in the length of exposure. The maximum duration of exposure of the expanded granules is not more than 14 days: if more time keeping the pentane evaporates and the ability of the granules to foaming is reduced.

For molding foamed pellets hurt in a form where they occupy 60-70% of its volume. The rest falls on Microline space. When the secondary heating polystyrene again is softened and becomes viscous-fluid state In the cell pellet is created, the partial vapor pressure of isopentane, water and air, causing the granules increase in volume. The increase in the volume of granules leads to a complete filling of the volume form. Pellets, compressed, deformed and transformed into polyhedra. In places of contact of individual granules are welded (fused), resulting in a nearly solid product.

During the secondary expansion of the mold wall under pressure, the value of which depends mainly on the volumetric weight of the foam.

Curve pressure foaming mass of granules in the mold wall, depending on time of the secondary foaming has a pronounced maximum. Upon reaching this maximum pressure is possible to fix the end time of the molding process.

It should be noted that timely completion of the molding process has a decisive influence on the quality. When premature termination of pellets not enough froth and therefore poorly fused. If excessive time forming cells of the granules are destroyed and there are concrete shrinkage. In both cases there is a sharp decrease in mechanical properties and quality of the product.

Upon cooling of the foam after the final foaming in the cell pellets, as well as during cooling after pre-expansion, a vacuum is created. The skeleton of the foam should resist the pressure difference in the cell as long as the air fills the cells. Therefore derived from Delia from Styrofoam gradually cooled in molds to a temperature of 40-50 C, then remove them.

The product is preferably dried so as laced the vacuum in the cell pellet moisture will increase the weight and reduce the thermal conductivity of the material. To obtain products of polystyrene foam with a volumetric weight of over 10 kg/m3 can one-step method, since the vapor pressure of isopentane and water is sufficient for filling the entire volume of the form, sealing and gluing. Technology provoste foam is organized according to the technological scheme, which provides two-stage heat treatment suspension of polystyrene (double foam). Organization of production of various enterprises in different designs of equipment used. Equipment selection is mainly determined by the desired configuration and bulk density of the products obtained from Styrofoam.