Traditional extruder technology bottleneck
Traditional plastic extruders are heated by heating devices outside the barrel. During the whole work process, the pressure inside the barrel of the extruder is very low, and the geometric compression ratio is generally less than 5 times, otherwise chemical materials will be produced. Self-heating, resulting in excessive temperature of the extruder, resulting in degradation of polymer materials, especially materials with poor thermal stability such as PVC. Therefore, the extrusion processing can be carried out only by prolonging the melt plasticization time in a low pressure state.
From the 65-cone double equipment of organotin American profiles processed by the Suzhou Huasu Plastic Co., Ltd. profile factory, the processed chemical materials are usually extruded from the feeding port to the die mouth for more than 8 minutes. Even with the most advanced twin-screw extruder in the world, when processing PVC materials, the degree of refining of the original micro-nucleus of PVC can only be less than 65%, and in order to curb the decomposition of HCL, it is also necessary to add in the formula. A large number of heat stabilizers have seriously affected the quality of PVC products.
In addition, in order to improve the shearing and kneading effect under low pressure, a very demanding requirement is put forward for the design and manufacture of the extruder: the gap between the two screws of the twin-screw extruder should be controlled to about 0.2 mm. These requirements have made the extruder difficult to manufacture and the cost has risen sharply. Since the structure of the twin-screw extruder has determined the wear between the screw and the barrel, this creates a contradiction with the 0.2 mm gap between the two screws. Because as long as the production is after a period of time, due to the wear between the screw and the barrel, the gap between the two screws will inevitably increase. To ensure the quality of the product, the screw and the barrel must be repaired or replaced, which not only increases the Maintenance costs, but also the difficulty of stabilizing the quality of chemical building materials.
Chemical building materials are a kind of renewable resources with a wide range of uses. At the same time, the production and extrusion technology of chemical building materials is obviously backward. The promotion and use of PVC plastic doors and windows fully illustrates this problem. On the effect of heat preservation and energy saving, PVC plastic window is the first choice for energy-saving buildings, but the aging deformation phenomenon of PVC plastic doors and windows sometimes occurs, and the current extrusion technology is still difficult to solve these problems.
Ultra high pressure extruder working principle
Now, an ultra-high pressure single-screw extruder has been developed on the market: the heating device outside the barrel is removed, a cooling device is placed on the barrel and screw of the extruder, and the specific characteristics of the chemical material being extruded are determined. The geometric compression ratio of the extruder is designed to be at a high magnification of 10-120. According to the friction temperature of the barrel, screw and chemical material, a suitable screw speed of 30-1500 rpm is set.
The heating device outside the barrel of the extruder is removed, and a cooling device is arranged on the barrel and the screw of the extruder to eliminate the temperature exceeding the normal value generated by the chemical material under the high-pressure friction on the barrel and the screw, and the cooling amount is controlled. The temperature is controlled within the normal operating range, and the extruded chemical material is between the barrel and the screw to form an ultra-high pressure solid conveying plug. At this time, between the chemical material and the screw, between the chemical material and the barrel In the state of ultra-high pressure between chemical materials and chemical materials, friction is generated to generate heat, forcing the chemical materials to melt and plasticize in a short time, and effective shearing and kneading under ultra-high pressure.
Advantages of ultra high pressure extruder
The ultra-high pressure single-screw extruder does not need heating at all during normal operation. The mechanical energy rotated by the screw is transferred by the solid material with high rate of solidity, which creates pressure between the screw and the barrel, forcing the material to be under ultra-high pressure. Rubbing, shearing, mixing, and melt plasticizing in a short period of time. When the ultra-high pressure single-screw extruder is used for mixing and granulating, the time of the chemical material in the high temperature zone is only about 0.1 second; when it is used for extrusion molding, the time of the chemical material in the high temperature zone is about 20 seconds. Chemicals with poor heat sensitivity are extremely advantageous.
For example, the processing temperature of unplasticized PVC material is between 180-220 Â°C, and the decomposition of HCL of PVC material starts above 120 Â°C. When it reaches 160 Â°C, HCL begins to decompose a lot, but the decomposition amount of HCL is made of PVC. The length of time the material is in the high temperature zone is determined. Practice has proved that PVC is kept at 280 Â° C for 1 minute or at 220 Â° C for 2 minutes, and the amount of HCL decomposition is within the normal range, which indicates that the product of unplasticized PVC material is produced by an ultrahigh pressure single screw extruder. The time of the material in the high temperature zone is only 20 seconds, and the decomposition amount of HCL is negligibly small, which can fundamentally solve many difficult problems caused by the extremely narrow processing area of â€‹â€‹PVC materials, and also greatly improve the PVC products. Weather resistance.
At the same time, due to the high extrusion pressure of the ultra-high pressure single-screw extruder, the friction, shearing and mixing effect of the PVC material under the ultra-high pressure is good, so that the original micro-nuclear nucleation degree of the PVC material is as high as 95% or more. Improving the mechanical strength of PVC products plays a crucial role.
It is precisely because of the above characteristics of the ultra-high pressure single-screw extruder, it is particularly suitable for processing chemical materials with particularly high viscosity and particularly high molecular weight, such as CPVC resin. The processing viscosity of CPVC resin is at least twice that of PVC resin, and the processing difficulty is particularly large. However, the use temperature, chemical stability, aging resistance and flame retardant smoke resistance of CPVC products are more than PVC, and can be used for chemical temperature resistance. Corrosion-resistant pipes, hot water pipes, etc., are currently in the development stage internationally, and it will become a new trend in the development of the plastics industry, and the prospects are immeasurable. The ultra-high pressure single-screw extruder is easy to handle and is insensitive to chemical materials with a particularly high viscosity.
In addition, the shearing and mixing plasticizing effect of the ultra-high pressure single-screw extruder is particularly good. The chemical building materials produced have high density, the mechanical strength is doubled, the surface finish can reach 90 or so, and the surface of the chemical building materials is bright as a mirror, any The dirt is infiltrated and cleaned after rubbing, which not only improves the mechanical properties of the chemical building materials, but also improves the product grade.
The ultra-high pressure single-screw extruder can plasticize and shape chemical materials in a short period of time, effectively suppressing the thermal degradation of chemical materials during high-temperature processing, thereby greatly improving the weather resistance of chemical building materials. Production of colored chemical building materials. Due to the very short production time, the temperature is less harmful to the coloring pigment. Due to the high extrusion pressure, the inorganic pigments (such as carbon black, iron oxide red, etc.) with particularly poor fluidity are not added to the formula. The pressure requirements are so special, so that the color chemical building materials in the extrusion can be ensured without fading.
The ultra-high pressure single-screw extruder only needs 30% of the traditional formula to prevent the decomposition of HCL. It can even be used. Because of the low or no heat stabilizer, it reduces or eliminates lead and cadmium pollution in chemical building materials. Building materials are truly green.
The ultra-high pressure single-screw extruder has good self-cleaning performance. Due to the high extrusion pressure, even if the ultra-high molecular weight resin with particularly high viscosity is produced, there will be no phenomenon that the chemical material sticks to the barrel and sticks to the screw. For example, our factory produces PVC plastic window profiles, which can only be used with relatively low molecular weight. Five types of PVC resin, but the use of ultra-high-pressure single-screw extruder can use ultra-high molecular weight S-1300 resin, so that all technical indicators of PVC plastic window profiles can be greatly improved. The higher the molecular weight of the PVC resin, the higher the glass transition temperature, mechanical properties, cold resistance, and heat stability of the product, and the lower the solubility in the solvent. This shows that the use of high molecular weight chemical materials is the basis for improving the technical indicators of chemical building materials, but the ability to produce high molecular weight chemical materials depends on the advanced level of production equipment. The quality of the chemical building materials produced by the ultra-high pressure single-screw extruder is highly stable, and the quality of the products produced at the time of starting up and the quality of the products continuously switched on for several days can be highly consistent, and the product yield rate is as high as 95% or more.
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Perforated Metal Mesh
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