With the increase of people's needs, the life of many types of plastic materials, screw barrel shorter and shorter, in the final analysis: screw barrel corrosion and heat damage to the resin is good because there is no choice of suitable material produced screw and barrel and did not establish a good preventive maintenance program.
First, corrosive, abrasive and high temperature resins may damage the screw and barrel unconsciously. For example, part of the project materials, thermoplastic elastomers and bio-polymer materials, sometimes forming a corrosive environment. In addition, the reinforcing material (such as glass fibers, glass beads, etc.), some filler and an additive are abrasive. To avoid affecting production efficiency and product quality, processors must be closely monitored hazards of these materials may have caused the device. To maintain high processing standards, the establishment of a preventive maintenance program (hereinafter referred to as "PM program") is necessary. When needed, the screw and barrel should be checked and measured, and the screw pull out and re-installation or replacement, because of wear will be minimal impact on product quality.
Protect your device from damage corrosive and abrasive resins, the best way is to choose the right material to manufacture screw and barrel. In response to corrosive, abrasive and high temperature melt and manufacturing barrel and screw wear resistance, which cost more than the standard polyolefin processing screw about 3 to 4 times. This is because the wear and tear-resistant alloys are expensive and difficult to process. But they can provide a longer service life and maintenance intervals can be longer.
Second, in the process, when the metal oxide coating can be dissolved by the acidic liquid (or gas) attack occurs corrosive wear, such as point-barrel and screw surface corrosion. Highly corrosive polymers, including polyvinyl chloride produces hydrochloric acid, formic acid to produce acetal and generating fluoropolymer hydrofluoric acid, and other corrosive melt generally contains a flame retardant and a blowing agent. Composite steel, nitrided steel or standard barrel made of tool steel, can be a fluoropolymer serious damage in a very short period of time.
Typically, the resin manufacturers to provide some suggestions for improving the processing equipment. DuPont noted that when the processing Teflon fluoropolymer extrusion equipment all come into contact with the melt member must use a special corrosion-resistant material, the material can be selected from acid on nickel-based alloy.
Third, the bimetallic cylinder liner wear-resistant alloy may provide protection in a variety of wear, and provide a range of cost / performance options, in terms of corrosion resistance, the best performance is used for injection molding and extrusion hot isostatic press cylinder (hereinafter referred to as "HIP barrel"). Even fluoropolymers are no threat to the class barrel. A layer of nickel-rich boron alloy protective layer such barrel, while in the protective layer, and containing molybdenum and boron carbide substrate.
Allegedly, when using corrosion-resistant screw, HIP barrel greatly reduced the number of iron particles from the barrel cavity absorption. Of course, this level of protection required higher prices. As long as the discharge end of the barrel with a chromium / nickel / iron alloy (hereinafter referred to as "Inconel") casting and the transducer surface energy hole and the flange is also manufactured by Inconel, you can use a nickel / chromium and tungsten alloy manufacturing barrel. At the same time, these low prices than HIP barrel barrel price.
Fourth, preventive maintenance
1, excessive wear processors will bring very serious losses. Excessive clearance between the screw flight and barrel surface will affect the machine's performance, efficiency and energy consumption. In extrusion, the wear may cause the occurrence of extrusion lower amount, requiring a higher screw speed and energy usage. Also, this is usually accompanied by a higher melting temperature and more quality problems.
Through good PM program, key screw / barrel gap careful testing to ensure maximum processing extrusion rate, while there will be no unplanned downtime. When the production of high quality parts requirements, PM plan becomes more important, for example for the production of medical catheters and components of medical devices.
2, the detection process, the screw pull out and thoroughly cleaned while hot check the thread outer diameter (OD) and barrel inner diameter (ID). Plastic material on the screw and barrel surfaces, you can use a wire brush and a copper mesh removed. Wear precision measuring instrument can achieve accurate measurements and easy to use, and there are a variety of sizes and features to choose from.
First, the clear plastic barrel, then an electronic meter aperture is inserted into the cylinder, read ID data at each measurement location. Screw thread diameter and depth can be measured by a micrometer screw, while the digital test model provides an LCD readout, data is recorded into a computer.
To be able to predict when a screw or cylinder will need to be replaced or repaired, and the stop arranged in a favorable time, the need for periodic measurements. A size of a new pair of screw and barrel of 5.08cm, the recommended gap in the range of 0.01016 ~ 0.01524cm.
3, there is a rule of thumb is, the screw with a reasonable gap and barrel are generally the size of 1/1000. When the gap exceeds the maximum allowed, should be re-assembled screw. With respect to the complete replacement and repair services at a lower cost of the wear parts back into service. Further, part of the injection molding machine barrel wear, can replace the bushings, and the extruder barrel is typically replace the entire bushing, so maintenance costs are more expensive, and thus not cost-effective.
Once the screw is worn at some point, a melt will return to the thread, screw and barrel wear leading to further accelerate. Severe wear can cause a lot of wasted resin, and reduced productivity. However, through regular PM detection can prevent the occurrence of serious wear and tear. The best maintenance strategy is to make the screw / barrel gap has remained within a reasonable range.