At present, the commonly used screw materials in China are 45 steel, 40Cr, ammoniated steel, 38CrMoAl, high temperature alloy, etc.
1) No. 45 steel is cheap and has good processing function, but its wear resistance, corrosion resistance and aging resistance are poor.
Heat treatment: Quenched and tempered hb220-270, high frequency quenching hrc45-48.
2) The function of 40Cr is better than that of 45 steel, but it often needs to be plated with a layer of chromium to improve its ability of corrosion and wear resistance. But the requirement of chromium plating layer is higher, the plating layer is too thin and easy to wear, too thick, it is easy to fall off, but after falling off, it accelerates corrosion, which has been less used.
Heat treatment: tempered hb220-270, hard chrome plated HRC > 55
3) Nitriding steel and 38CrMoAl have excellent comprehensive functions and are widely used. Generally, the nitriding layer is 0.4-0.6mm. But this kind of data can resist the corrosion of hydrogen chloride with low ability and high price.
4) the superalloy data is superior to other data. The data need not be plated. Most of them are used in the raw halogen-free screw of injection molding machine. The data have high anti-oxidation, anti-corrosion and anti-aging functions, and heat treatment hra55`60.
Injection screw is operated under high temperature, high pressure, high mechanical torque and high friction environment for a long time. The first few elements are required by the process conditions, and the losses due to friction are inevitable. Generally, the screw has been surface-nitrided to improve the surface hardness, that is, to improve the wear resistance. However, if the cause of wear is neglected, if the wear is not reduced as much as possible, the operating life of the screw will be greatly reduced.
The following explains the causes of screw wear and ways to reduce wear
1. Each plastic has an aspiration plasticizing processing temperature scale. The barrel processing temperature should be controlled to be close to this temperature scale. The granular plastic enters the feed barrel from the hopper, and it will first reach the feed section, which will inevitably exhibit dry friction. When these plastics are lack of heat and the melting is uneven, it is easy to form the inner wall of the barrel and the external wear of the screw. Similarly, in the tightening section and the homogenizing section, if the melting state of the plastic is disordered, it will also form increased wear.
2. The speed should be adjusted properly. Because some plastics are added with reinforcing agents, such as fiberglass, minerals or other fillers. The friction of these materials on metal raw materials is often much greater than that of molten plastics. In the injection of these plastics, if the high speed is used, the improvement of the shear force on the plastic will also strengthen the correspondingly more shredded fibers. The shredded fibers have sharp ends and wear Powerful addition. When inorganic minerals glide at high speed on the surface of metal, their scraping effect is not small. Therefore, the speed should not be adjusted too high.
Post time: Jun-03-2020