You are here:Home / Blogs / How to choose injection molding machine screw?
How to choose injection molding machine screw?
Views: 65 Author: Site Editor Publish Time: 2022-07-14 Origin: Site
The screw is the main core component of the injection molding machine, and the quality of the screw determines the quality of the product. The plasticizing screw of the injection molding machine has the functions of conveying, melting, mixing, compressing, metering and exhausting, which are the key factors affecting the plasticizing quality.
This article will introduce the material classification, parameter description, and how to choose the injection molding machine screw for you.
Classification of screw materials of injection molding machines
HPT fully hardened powder alloy screw
Tungsten-cobalt powder alloy tool steel is used, and it is formed by a special process of overall hardening treatment. The internal and external overall hardness of the screw is the same, reaching about HRC65°. It is suitable for processing various transparent products, precision products and special high temperature and high corrosive plastics such as LCP, PPS, PES, PPA with added fibers.
Double alloy screw
Using SACM645 and 38CrMoAlA as the base material, and then ion spray welding tungsten carbide nickel-based alloy on the tooth top or screw groove, the surface hardness of the screw is about HRC60°. It is suitable for processing various transparent products and engineering materials such as PA6 and PA66 with added fibers.
Using SACM645 and 38CrMoAlA as the base material, after forming, the outer surface is electroplated with a layer of hard chromium, nickel, titanium and other elements. The hardness is around HRC60°. Suitable for processing PC, PMMA, PET transparent material and corrosive plastic U-PVC material.
Stainless steel screw
The material is 9Cr18MoV special stainless tool steel, which adopts overall quenching and overall hardening treatment, and the overall hardness is about HRC55°.
Ordinary nitrided screw
Using SACM645 and 38CrMoAlA as the base material, it is formed by special processing, the depth of the nitride layer is 0.5-0.8mm, and the overall hardness is HV980~1080°. Suitable for processing common plastics, such as PP, ABS, PS, AS, PVC and other common plastics.
Generally speaking, the screw of injection molding machine can be divided into feeding section, compression section and homogenization section. Different screw three sections have different ratios, different screw groove depths, and different screw bottom diameter transition forms.
Injection molding machine screw feeding section
This section of the screw groove has a fixed depth, and its function is to be responsible for preheating and plastic solid conveying and pushing. It must be ensured that the plastic begins to melt at the end of the feed section.
This section is the depth of the screw groove of the tapered screw, and its function is to melt, knead, shear and compress the plastic raw materials and pressurize the exhaust. The plastic will be completely dissolved in this section, the volume will be reduced, and the design of the compression ratio is very important.
This section is the depth of the screw groove fixed groove. Its main functions are mixing, melt conveying, and metering. It must also provide enough pressure to maintain a uniform temperature of the melt and stabilize the flow of molten plastic.
How to choose injection molding machine screw
Related to the required injection volume, the injection volume=1/4×π×D↑2×S (injection stroke)×0.85. Inversely proportional to the highest injection pressure and proportional to the plasticizing capacity.
It is responsible for the transportation, pushing and preheating of the plastic, and it should be preheated to the melting point. Crystalline plastics should be longer (such as POM, PA); amorphous materials are next (such as PS, PU, ABS); thermal sensitivity is the shortest (such as PVC).
It is responsible for the mixing, compression and pressurized exhaust of the plastic. Almost all the raw materials passing through this section are melted, but they may not be uniformly mixed. In this area, the plastic is gradually melted, and the volume of the screw groove must decrease accordingly to correspond to the decrease in the geometric volume of the plastic, otherwise the material will not be compacted, the heat transfer will be slow, and the exhaust will be poor.
The compression section generally accounts for more than 25% of the working length of the screw, but this section of the nylon screw accounts for about 15%, the plastic screw with high viscosity, fire resistance, low conductivity and high additives accounts for about 40%, and the PVC screw can account for 100%, so as to avoid intense shear heat.
Generally account for 20%/25% of the working length of the screw to ensure that the plastic is fully melted and the temperature is uniform, and the mixing is uniform. If the metering section is long, the mixing effect is good, but if it is too long, it is easy to make the melt stay too long and cause thermal decomposition, and if it is too short, it is easy to make the temperature uneven. Heat-sensitive plastics such as PVC should not stay for too long to avoid thermal decomposition, and a shorter metering section or no metering section can be used.
Thread groove depth
The deeper the depth of the feeding groove, the greater the conveying volume, but the strength of the screw of the injection molding machine needs to be considered. The shallower the depth of the metering screw groove, the higher the plasticizing heat and the mixing performance index. However, if the depth of the metering screw groove is too shallow, the shear heat will increase, the self-generated heat will increase, and the temperature rise will be too high, which will cause discoloration or burning of the plastic, which is especially unfavorable for heat sensitive plastic.
Lianzhong Industry Co., Limited is one of the biggest manufacturers of bimetallic screw&barrel and twin screw&barrel in China. The occupied area is more than 14000 m2. Integration of “Science and technology, production, sales”, introducing into the high and new technology, w dedicate to research and develop Cobalt-based Tungsten carbide super hard bimetallic screw and barrel with high wearing resistance, high corrosion resistance, high hardness which lies in the top place in the world now.
We have a unique view of processing technology of special bimetallic barrel screw barrel in Halogen-free flame-retardant plastic, high fiberglass plastic, magnetic plastic, high calcium powder plastic, Bakelite plastic, XPS, etc in engineering plastics. If you are looking for reliable Chinese extruder screw barrel manufacturer, please contact us, we are happy to provide you with help and service!
Lianzhong Industry Co.,Limited is one of the biggest supplier of bimetallic screw&barrel and twin screw&barrel in China. The occupied area is more than 14000 ㎡. Integration of “Science and technology, production, sales”, introducing into the high and new technology, w dedicate to research and develop Cobalt-based Tungsten carbide super hard bimetallic screw and barrel with high wearing resistance, high corrosion resistance, high hardness which lies in the top place in the world now.