Structural alloy steel is generally used, and cemented carbide is spray welded on the top of the screw teeth.
Restricted by structural alloy steel, the base metal of the screw has extremely poor corrosion resistance and wear resistance; as shown in the figure above, the base metal has been severely corroded and fractured
The alloy layer has the risk of cracking and falling off; the screw cannot be thoroughly cleaned during production and refueling, and Kotler does not recommend using it
Affected by cost factors, domestic injection molding machines still widely use fully covered screws
After heat treatment, the surface of the screw is melted with cemented carbide
Affected by alloys and processes, wear and corrosion resistance still cannot meet the life requirements of acid plastics
Under the action of large torque, the alloy is easily cracked and separated, and Kotler does not recommend it.
Affected by technology, cost, life, etc., less sintered screws are used
Mainly used in the production of halogen-free plastics, with extremely high anti-wear and anti-corrosion properties, which solves the shortcoming of screw life. will be the main research direction in the next few years
Sintering technologies include: Spark Plasma Sintering (SPS), Microwave Sintering, Electric Field Activated Sintering (FAST), Metal Powder Selective Laser Sintering (SLS), Thermal Oscillation Activated Sintering (HSAS), Hot Isostatic Pressing (HIP), etc.
PS: Halogen-free plastics are halogen-free by adding halogen-free flame retardants to the raw materials. Generally, halogen-free flame retardants for plastics include the following: phosphorus-nitrogen intumescent flame retardants (IFR), phosphorus-based flame retardants, inorganic flame retardants Burning agent magnesium hydroxide, aluminum hydroxide, zinc borate, etc. At high temperature, super acid gas will be produced, which will cause serious corrosion to the screw.