The author learned from a screw repair manufacturer that the abrasive wear between the screw barrels of the injection molding machine occurs in such a way that when a relatively soft base member of a part is corroded or worn, the remaining harder particles (for example, various The carbides are exposed on the surface of the metal. These hard particles plan to shave and scratch the softer surface, or strongly rubbing the surface of their relative motion like a grinding wheel. When these hard particles fall off the substrate, not only Pits and projections are formed on the surface of the screw barrel, and the falling hard particles, like the abrasive used in grinding, produce an improved grinding action between the screw and the barrel, accelerating the damage of the screw barrel.

Obviously, if the plastic is originally mixed with a lot of high hardness inorganic filler, then the above-mentioned grinding effect must be greatly accelerated, for example, when processing nylon material mixed with magic fiber, a 30-ton nitride steel screw barrel is used for 1250 hours. It was later ground to 12-4.

Some studies have shown that the size and hardness of abrasives have a great influence on the abrasive wear. When the size of hard particles (carbides, nitrides, etc.) is greater than 100 microns, the abrasive wear will be strong when the hardness is greater than 50% of the substrate hardness. Therefore, if the size of hard particles (such as calcium carbonate in calcium plastics) can be reduced to less than 100 microns and they are well dispersed, this will reduce the wear.

In general, the ability to resist abrasive wear can be improved by increasing the surface hardness of the screw barrel of the injection molding machine. There are two ways to increase the surface hardness of the screw and barrel of an injection molding machine when surface hardening is not considered. First, the surface of hard alloy is used instead of heat treatment. Abrasion tests show that high surface hardness does not mean high wear resistance. For example, the nitriding steel nitride hardness reaches HRC=66-70, while the Xaloy800 alloy has HRC=50-64, but the latter has much higher wear resistance than the former.

This is due to the fact that these alloys have high inter-atomicity and strength and have a high elastic modulus. Because of this, if various hard alloys are smelted with iron with alloying elements such as chromium, boron, calcium, molybdenum, and titanium, the presence of various carbides in these alloys will greatly improve the wear resistance of the parent metal. Corrosion and grinding of these carbides requires very high pressures and temperatures. The various alloys of Table 12-1 and Table 12-4 were produced based on these principles.

On the other hand, since the process of spraying or overlaying these alloys onto the surface of the screw of the injection molding machine is not yet mature, the method of increasing the surface hardness by heat treatment is still widely used.