HOME / NEWS / Industry News / Several Questions About Lost Foam Casting——foam Molding Of EPS Foam

Expandable polystyrene resin (ExpandablepolyStyrene) is a liquid foaming agent with a low boiling point added to polystyrene beads. Under the condition of heating and pressure, it penetrates into the polystyrene beads to make them swell. Into expandable polystyrene resin (beads).

Molding process

1. The bubble core formation stage of the foam: when the synthetic resin is added with chemical blowing agent or gas, when the temperature is increased or the pressure is reduced, gas will be generated to form a foam, and the gas will be formed when the gas exceeds its saturation limit in the melt or solution. When the solution is saturated, the gas will escape from the melt and form bubbles. At a certain temperature and pressure, the decrease of the solubility coefficient will cause the dissolved gas concentration to decrease, and the released excess gas will form bubbles.   

2. Bubble core growth of foam: In the foaming process, the cell growth rate is determined by the growth rate of the internal pressure of the cell and the deformation ability of the cell rate. After the bubble is formed, since the pressure of the gas in the bubble is inversely proportional to the radius, the smaller the bubble, the higher the internal pressure, and increase the number of bubbles through nucleation, and the expansion of the bubble expands the growth of the bubble. The main factors that promote foam growth are the increase of dissolved gas, the increase of temperature, the expansion of gas and the merging of bubbles.

3. Stable solidification of the foam: If the cell growth process is not interrupted at a certain stage, some cells can grow to a very large size, so that the material forming the cell wall reaches the material rupture limit, and finally all the cells will be connected in series. , The entire foam structure collapses, or all the gas slowly diffuses from the cells to the atmosphere, the pressure of the gas in the foam gradually attenuates, then the cells will gradually become smaller and disappear.

Therefore, it is important to control the growth rate and stability of pores in foam formation. This can be accomplished by causing the polymer matrix to suddenly solidify or gradually reducing the deformability of the matrix. Many methods to stabilize the foam can reduce its surface tension, reduce gas diffusion, and stabilize the foam. For example, in the foaming process, the viscosity of the plastic liquid can be increased by cooling the material or cross-linking the resin to achieve the purpose of stabilizing the foam.

According to the heating method or heating medium, the foam molding of foam can be divided into: high frequency heating molding, hot water molding, steam cylinder foam molding and press foam molding. Due to the high cost of high frequency heating, it has not been widely used in production. Hot water molding also has many shortcomings, such as the inability to produce foam patterns with a wall thickness greater than 50mm, the core is prone to defects such as poor adhesion of beads, and high energy consumption. It has also been phased out.

Compressor air chamber foaming molding is to fill pre-expanded beads into a foaming mold with air chambers. The molds are installed on the upper and lower or left and right pressure plates of the press with a mechanical clamping device, one of which is Movable, the superheated steam enters the mold through the air chamber through the pores on the mold, so that the beads are foamed; then the cooling water is passed through the same channel to cool the mold and the foam, and the desired foam pattern can be obtained .

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