EPS foam equipment - processing and application of expandable polystyrene

　　Processing

　　The processing of expandable PS is divided into two steps. The first step is pre foaming or simple foaming to set the density of the final product. In this process, the polymer particles containing foaming agent soften under heating conditions and the foaming agent volatilizes. As a result, expansion occurs in each bead and many bubbles are formed. The number of pores (ultimate density) is controlled by heating temperature and heating time. In this process, the beads must remain dispersed and free to move. In industrial production, the foaming process is carried out by directly placing the expandable PS in steam. Generally, the reaction is completed by the continuous mixing of beads and steam in the stirred tank. The reaction equipment is open under normal pressure to maintain the external pressure and make the foamed beads overflow from the top. Some manufacturers use batch reactors to ensure more balanced residence time or when some expandable DPS requires relatively high temperature. After foaming, the beads should be cured to gradually mix air into the cell.

　　Thermoforming is the second step of EPS foaming. First, put the matured pre foam beads into a mold with a specific cavity. For small and complex products, venturi action equipment shall be used during molding. Beads shall be blown into the mold cavity with the help of air flow. Large products can fill the mold cavity according to their own gravity. The mold cavity filled with pellets is sealed and heated, and the beads are softened by heating to expand the pores. The beads expand to fill the gaps between them and form a uniform foam. At this point, the foam is still soft and bears the pressure of the hot gas in the bubble. Before taking out the product from the mold, negative gas must seep out of the bubble and reduce the temperature to stabilize the shape of the product. This is generally the method of spraying water on the inner wall of the mold.

　　Because the forming mold is double walled, the forming of foamed PS is called "steam chamber forming". The dimension of the inner wall of the die is the size of the actual product. There are holes on the inner wall of the die so that steam can pass through the foam and spread the heat. The space between the double walls forms a steam chamber in which steam for heating beads is introduced. For most products, the molding pressure of foamed PS is lower than 276kpa. The mold is made of aluminum and cast into a certain shape according to the product requirements. The molding of foamed PS is an economic production method because of its low molding pressure and low cost of molding equipment.

　　Apply

　　The main purpose of foamed PS is to exhaust thermal materials, disposable appliances and anti-seismic protective packaging materials in the construction industry.

　　EPS is used for thermal insulation products because it has constant low thermal conductivity, low density and low processing cost. EPS tea cup is because EPS is easy to foam into thin products and has thermal insulation. The shock absorption, low cost and formability of the foam make EPS a choice of protective packaging materials.

　　Foam polyolefin products absorb more impact energy per unit thickness, so it can be used as packaging for more fragile items and shock absorbers for shock absorbing components, such as some new types of automobiles.