The barrel is a cylindrical cavity, and the compression, melting, mixing, metering and suction of the pellets are generated in the cylinder due to the rotation of the screw with the main part of the screw. The polymer in the barrel was fed at a temperature of 20 ° C and 100 KPa. The pressure solid pellets become a molten resin having a temperature of about 325 ° C and a temperature of about 325 ° C and a pressure of up to 35,000 kPa. The barrel is made of thick-walled high-strength steel advanced alloy to withstand high temperatures and pressures. To ensure safety, a safety factor is added to the calculation. Most manufacturers generally follow
The temperature is 290 ° C with a pressure of 70,000 kPa to calculate or design the barrel, the safety factor is 1. Therefore, in a typical coating and compounding condition with a pressure of 14000 - 21000 kPa, the theoretical safety factor is 3.0-5.0.
The inner cavity of the barrel is rubbed into the cylinder due to the screw spiral, and it is required to withstand the wear (in the solid material compression and melting zone), and sometimes it is also corrosive. On a good centering extruder, the screw helix will actually be in the center of the barrel while suspended on the polymer film "lubricant" between the helix and the barrel. Friction-type abrasion can be solved by hardening the inner surface of the barrel. By subjecting the heated nitridable steel (generally an aluminum alloy containing aluminum and chromium) to nitriding or surface hardening in nitrogen, a chromium oxide and iron nitride having a Rockwell hardness of 70.125 mm deep is formed, which is a An ancient technology that is cheaper but is rarely used today. The bimetallic surface is formed by centrifugal casting to form a layer of alloy material in the steel cylinder. The cylinder is rotated at a high speed (horizontal or vertical) in a high temperature furnace, and the alloy is melted and uniformly distributed until the thickness reaches 5 mm, eventually reaching 58-65 Rockwell hardness. Some bimetallic alloy linings also provide corrosion resistance.
Most bimetallic cylinder manufacturers produce three common alloy materials. The first type is an iron-boron alloy of 58-65 Rockwell hardness for general corrosion resistance applications. The second type is a nickel-chromium alloy of 48-54 Rockwell hardness for corrosive materials such as vinyl chloride. The third is a highly corrosive use of 67-70 Rockwell hardness metal solids embedded with various carbides. For the general corrosion resistance of the lining, the cost is increased by about 10%, and the lining of the extremely strong corrosion resistance is increased by as much as 80%-100%. The double metal lining is bored and polished to a concentricity of about 0.05 mm, a straightness of 0.085 mm/m, and a smoothness of 8 to 12 RMS after finishing.
Coating a composite extruder barrel is to make the hard surface directly cast into the cylinder without replacing the liner, mainly because the general lining can not adapt to this harsh condition on many extruders only 5 -- 20 years of life. The short life of the bimetallic lining is probably due to poor bonding with the base metal, cracking or cracks caused by metal debris (or foreign matter). The true surface abrasion is gradually occurring, it does not have a The exact life span. The original radial gap between a typical screw helix and the barrel lumen is 0.001 mm / nominal screw diameter mm. As the barrel cavity wears, the gap increases while the extruder output is reduced because the amount of leakage of polymer over the spiral gap increases. The output of the extruder is very slow and can only be clarified when the actual output is compared to the theoretical output.
The total length of the barrel of a composite extruder has increased over the years due to the need to increase mixing zones, smoother transitions, and longer metering zones. It is very common to use a 30:1 extruder for the current length to outside diameter ratio (L/D). By lengthening the components of these screws, it is possible to obtain a 24:1 or 28:1 (L/D) ratio than the old one. The extruder has a higher quality and higher output.
Click here to view Previous or Next