Author: Site Editor Publish Time: 2022-04-25 Origin: Site
Screw for extrusion blow molding machine
In the extrusion blow molding machine, the screw is the heart of the plastic extrusion blow molding machine and an important part for compressing the plastic in the plastic extrusion blow molding machine. It is an important part for mixing and pressurizing the plastic for extrusion. The screw obtains the compression effect by gradually reducing the volume of the screw groove by equidistant and unequal depth, equal depth and unequal distance, and unequal depth and unequal distance.
It can be seen from the extrusion process that the screw works under high temperature, certain corrosion, strong wear and high torque. Therefore, the screw material must meet the following conditions:
1) High temperature resistance, no deformation under high temperature;
2) Wear resistance, Long life;
3) Corrosion resistance, material is corrosive;
4) High strength, can withstand large torque, high speed;
5) Good cutting performance;
6) After heat treatment, the residual stress is small, and the thermal deformation is small. Through practical experience and continuous improvement research, our current commonly used screw material is 38CrMOAlA, double alloy.
1) 38CrMoAIA is a nitrided steel with high strength, excellent comprehensive properties and wide application. Generally, the nitride layer is 0.4-0.6 mm.
2) Double alloy material is superior to other materials, with high temperature resistance, corrosion resistance and wear resistance, and is suitable for raw materials with relatively high hardness.
In addition, the main parameters of the screw structure are composed of the length-diameter ratio of the screw, the compression ratio of the screw, the pitch of the screw, the barrier section of the screw, and the mixing section.
We often say the length-diameter ratio L/D, and the screw diameter D refers to the outer diameter of the screw thread. The effective length L of the screw refers to the length of the working part of the screw. Effective length and total screw length are different. The aspect ratio is the ratio of the effective length of the screw to the diameter. Increasing the aspect ratio has the following advantages: 1. The screw is fully pressurized, and the physical and mechanical properties of the product can be improved. 2. The material is plasticized well, and the appearance quality of the product is good. 3. The extrusion volume is increased by 20-40%. At the same time, the slope of the characteristic curve of the screw with a large aspect ratio is small, relatively flat, and the extrusion volume is stable. 4. It is beneficial to powder molding, such as extrusion of PVC powder. However, increasing the aspect ratio makes the manufacture of the screw and the assembly of the screw and the barrel difficult. Therefore, the aspect ratio cannot be increased indefinitely.
There are many types of plastics for extrusion molding of plastic extruders, and it is impossible to form all plastics with one screw. The screw should be designed according to the characteristics of the raw materials and consider the commonality of various raw materials as much as possible, so that one screw can extrude several plastics at the same time, which is economically meaningful in industrial production.