Method for foaming polyvinyl chloride with chemical foaming agent
I squeezed out two different streams of water.
This * * * extrusion method is also called Lai Venhaus process (Reifenh? Users), invented by German company Lefenhauser. This * * * extrusion foaming method (as shown in figure 1) is formed by * * extruding dense external hollow profile and internal foaming core material. The product has a uniform and smooth appearance. During extrusion, the foamed material flows into the core of the profile, regardless of the cross section of the die, and the complete combination of dense material and foamed material can be realized without unified structure, correct formula and technology. This process realizes the combination of two different types of plastics.
Figure 1 le Venhaus process
Figure 2 Card insertion process
2. Extrusion of foam solid profile and hollow profile
This method is called crust foaming method, also known as controlled foaming method, also known as CELUKA process. At present, it is widely used by the French company Genet cullmann. It is one of the first patented extrusion foaming methods (as shown in Figure 2). The principle of Seruka method is that the skin of the melt is compressed and cooled in the solidification device directly connected with the die, while the core die in the die cavity ensures that there are spaces inside the extrudate when it leaves the die, and these spaces are filled by the free foaming of the melt in the solidification die. The cooling intensity, the size of the core die and the extrusion speed will affect the density of the foam core layer and the thickness of the skin.
Fig. 3 Improvement process of card insertion method
Fig. 4 Incomplete Lucca Process
Wood.
Incomplete Seluka process (as shown in Figure 4), which is an example of the combination of controllable foaming process and free foaming process. The dense skin is only formed in the part flush with the die opening in the setting device, and its total cross section is larger than the die opening, and the rest of the whole cross section is filled with foaming melt, while the surface layer adjacent to the cell structure is only in a proper position and is smooth and closed.
There are also two different types of plastic extruded hollow profiles (as shown in Figure 5). This method is a combination of Seluka method and Lefenhausen method. This method is also used to shape profiles with dense outside and foaming in the middle.
Hollow profiles extruded from different types of plastics.
Fig. 6 Amzel method
3. Extrusion of foam wall tube
This foaming process is called Amzel method, which was invented by sociètè Armosic company (as shown in Figure 6). Through correct runner design, sufficient pressure is built in the mold cavity to prevent the melt containing foaming agent from foaming in advance, and the annular gap begins to shrink into a cone, and then becomes annular on a certain length of parallel section. The extruded tube blank is foamed in the direction of diameter and wall thickness immediately after flowing out of the tube die, and then enters the setting device at a suitable position. By selecting a suitable ratio, the foamed tube with smooth inner and outer surfaces can be produced.
Fourthly, the wood-like sheet of the material flow is extruded.
This foaming process is called "wood-like" molding method, which was invented by Sekisui kaseihin kogyo Company to produce foamed board with wood-like structure. As shown in fig. 7, the melt containing foaming agent is extruded from the die through the splitter plate. Due to the high resistance of the external eyelet, the single steel wire will fuse together immediately when it reaches the setting device. Each steel wire has a high-density cortex and a low-density inner layer, and the product looks like wood.
Figure 7 "Imitation Wood" Forming Method
Fig. 8 Solid Profile Extrusion with Split Flow
5. Extrusion of solid profile with material distribution flow
This process was invented and developed by scherer Trier (as shown in Figure 8). With this method, the mold cavity design can divide the foaming melt into at least two strands, thus producing foamed products with different densities and cross-sectional areas, and the outer layer material flow forming the product shell is extruded at a given temperature. A smooth and non-porous surface is produced by the connected qualitative device. The melt flowing into the inner layer is heated to a higher temperature, and then flows out of the die core to foam freely, thus forming a profile in which the foamed core layer and the shell are firmly fused to the shell.
Six, BASF foaming method
BASF foaming process (as shown in Figure 9) uses an extruder to introduce the melt containing foaming agent into a pressure vessel, and then the melt is released from the vessel for foaming.
Fig. 9 BASF foaming process
Figure 10 Direct Inflatable Twin Screw Extrusion Foaming Process
Method for using physical foaming agent
The foaming process of PVC products usually adopts chemical foaming agent. For the extrusion of PVC physical foaming agent, only special fluorinated hydrocarbon foaming agent is used, and the foaming agent is continuously added to the melt under pressure by direct aeration method. After the foaming agent and the melt are homogenized, the raw materials are cooled to the extrusion process temperature with appropriate foaming viscosity to extrude the product. Direct inflatable foaming extrusion molding (as shown in figure 10).
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