Direct extrusion foam molding
DATE：2021/12/22 9:05:44 / READ： / SOURCE：This station
Direct extrusion foam molding
Using high molecular weight crystalline polystyrene resin and liquid alkane foaming agent, a single-screw extruder unit or a two-stage single-screw extruder unit is used to produce polystyrene foamed sheets. When a two-stage single-screw extruder unit is used for production, the liquid foaming agent is continuously and quantitatively injected into the resin melt from the middle decompression section of the first extruder, and then enters the second extruder to be further plasticized and pressurized. The gas generated by the heating of the blowing agent is uniformly dispersed in the resin melt. When the melt is extruded from the die, the pressure drops sharply and the gas expands to foam the melt. After cooling, shaping, traction, and cutting, the polystyrene foamed sheet is obtained.
The plane layout of the double-stage single-screw extrusion foaming unit for styrene foam sheet is shown in Figure 410. The first extruder screw of the two-stage single-screw extrusion foaming unit has a smaller diameter and a relatively large length and diameter; the second extruder has a larger screw diameter and a relatively small length and diameter. The difference from the ordinary single-screw extruder is that the homogenization section of the first extruder (near the pressure section) of the extrusion foaming unit is equipped with a liquid foaming agent intermediate injection system.
The technical requirements of the direct extrusion foaming unit are as follows.
Compression ratio of the screw-like exiting machine is 2～3 to maintain a high extrusion pressure.
The depth of the screw groove in the homogenization section should not be too shallow to prevent the material from being over-sheared. In the transition zone (ie joint) between the start of foaming and molding, the material should flow uniformly into the molding part without causing excessive flow resistance. However, the part should have sufficient cooling capacity.
The contact part of the traction device and the foamed product should have a larger coefficient of friction, but the driving pressure should not be too high.
The temperature and pressure of the extrusion process must be precisely controlled to make the cell ruler pair and the density of the foam sheet meet the requirements. The extruded foam sheet should be cooled slowly to prevent large internal stress.
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