Detailed introduction





What is the purpose of the alloy screw?



  alloy screwWhat is the purpose?

In recent years, due to the increase of screw speed and barrel pressure, especially due to the addition of a large amount of filler in the extrusion process, the wear resistance of the screw and barrel made of nitride steel is quite insufficient. So, what is the purpose of the alloy screw?

What is the purpose of the alloy screw?

Used in plastic molding equipment, such as plastic profile extruders, injection molding machines, etc. Screw and barrel are the core components of plastic molding equipment. It is the part that is heated, extruded and plasticized. Is the core of plastic machinery. Lead screws are widely used in machining centers, CNC machine tools, CNC lathes, injection molding machines, wire cutting, grinding machines, milling machines, wire cutting, high-speed wire cutting, PCB drilling machines, engraving machines, engraving and milling machines, EDM machines, tooth biting machines, Planer, large vertical lathe gantry milling, etc.

What are the commonly used materials of alloy screw?

1. No. 45 steel is cheap and has good processing performance, but it has poor wear resistance and corrosion resistance. Heat treatment: quenching and tempering HB 220-270, high frequency quenching HRC45-48.

2. The performance of 40Cr is better than that of 45# steel, but it is often plated with a layer of chromium to improve its corrosion resistance and wear resistance. But the chromium plating layer requires high, the coating is too thin and easy to wear, too thick and easy to peel off. Accelerated corrosion after peeling, has been used less. Heat treatment: quenching and tempering HB 220-270, hard chromium plating HRC55

3. Nitrided steel and 38CrMoAl have excellent comprehensive properties and are widely used. Typically, the nitride layer is 0.4-0.6mm. The price is high.

High temperature alloy materials are better than other materials. This material does not require a coating and is mainly used for halogen-free screws in injection molding machines. This material has high oxidation resistance and corrosion resistance, and has undergone heat treatment HRA55'60.

common screw andalloy screwWhat's the difference?

1. Hard chrome plating

This is an ancient chemical treatment. The screws may be made of 40Cr or 45 steel. The hard chrome-plated screw has good surface finish, strong corrosion resistance and good wear resistance. However, this method has high requirements for the chromium plating process; the coating is too thin, the microstructure is loose, too thick, and it is easy to peel off. Currently the general 0.05 is -0.1mm. The combination of the coating and the metal substrate should be firm, and the peeling pits will form the two poles of the chemical battery with the chromium layer, causing the screw to corrode.

2. Surface flame hardening or high frequency brittle hardening

Case hardening is an inexpensive and convenient treatment. After hardening, the hardness can reach HRC55, and the quenching depth can reach 23mm. When flame quenching is used, 40Cr or 45 steel can be used as the screw material, so it is very economical for large screws. The surface hardening can be performed by heating the screw to 815 with acetylene, propane, nitrogen, water gas, or the like. as fuel. If high-frequency quenching is used, the quenching frequency should be greater than 4000Hz, and then hardened with a water bath or spray. alloy screw

3. Surface treatment

Surfacing can be performed on the screw by arc welding, plasma welding, etc. The hardfacing alloy can be a cobalt-based alloy strip (CoCrWMo alloy, such as Reiloyp48 alloy) or a nickel alloy electrode. The former can reach a hardness of HRC36-54, and the latter can reach a hardness of HRC52-58. When higher hardness is required, tungsten carbide can be directly surfacing. This process can be used to repair worn screws. According to our country's experience, surfacing can reach about 3mm, and the cost of repair is 35p% of the new screw. alloy screw

4. Surface spraying

This is a method that is currently being intensively studied. The screw can be made of nitrided steel, and then a layer of 0.5-0.8mm special alloy material is sprayed on the screw ribs and even the surface of all screws. In order to further improve the wear resistance, tungsten carbide can also be added to the material.

In order to increase the bonding force between the alloy material and the screw matrix, the screw was sandblasted with Al2O3 before spraying. In the spraying process, the dispersed alloy powder is in a state of complete melting or surface melting, and is sprayed to the surface of the screw in a 1750 oxyacetylene flame. When using boron-containing materials, because the melting point is only 1050-1070, it can be further sintered after spraying., Such a screw can bear an important load. When the process of sintering after spraying is adopted, the base metal of the screw cannot be chromium steel with a tendency of cold air hardening, because this steel is easy to cause cracks in the nominal sprayed alloy during cooling.