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How to choose the screw of injection molding machine?

2022-09-13 Hits: 2 views

The “screw plasticizing component” of the injection molding machine is the main core unit of the injection molding machine, which directly reflects the performance of the injection molding machine. The screw, known as the “heart”, is a vital part, and its performance determines the quality and efficiency of the processed products.Our products, for example, are inseparable from screw,for example,the led mould,injection container molds,washing machine panel mold,industrial precision mould,etc.
With the rapid development of plastic industry, injection molding equipment has become mature. As designers and users of injection molding equipment, it is necessary to know clearly which screws are suitable for processing which materials. Especially in today’s multifarious materials, the types of screws in the market are also varied day by day, but the actual use is rather confusing. Users often use one screw to process plastics with inappropriate physical properties. In this paper, several commonly used screws with main structure are briefly introduced, so as to provide some reference for processing products.
(1) Characteristics of polycarbonate:
1. Amorphous plastic with no obvious melting point, glass transition temperature of 140℃-160℃, melting temperature of 215℃-225℃ and molding temperature of 230℃-320℃;
2. The viscosity is high, the processing temperature is high, the range is narrow, and it is easy to decompose. Avoid overheating when selecting the screw;
3. Sensitive to moisture, the resin is easy to hydrolyze at high temperature, and the drying temperature is 120℃-130℃ for about 4 hours.
Parameters selected:
1. l/d for its good thermal stability and high viscosity, try to choose a large length-diameter ratio to improve plasticizing effect;
2. Because of its wide melting temperature range, long feeding section, short homogenizing section and moderate compression ratio, barrier rubber head can be selected to increase plasticizing effect;
3. If you add flame retardant or glass fiber reinforced PC material, you can choose to use corrosion-resistant and wear-resistant high-quality stainless tool steel screw and three small pieces.
(2) PMMA features:
1. The glass transition temperature is 105℃, the melting temperature is higher than 160℃, the decomposition temperature is 270℃, and the molding temperature range is 180-250℃;
2. The viscosity is high, the fluidity is poor, and it is sensitive to shear rate, so the temperature should be strictly controlled during processing;
3. The temperature of the barrel is 240℃-250℃, and the retention time is less than 8 minutes when it exceeds 260℃;
4. Strong water absorption, drying temperature 80℃-90℃, time more than 3 hours.
Parameters selected:
1. the l/d ratio is 20-22, and the gradual screw generally takes L1=35-45% and L2 = 35-40%;
2. The compression ratio ε is generally 2.3-2.6;
3. In view of its hydrophilicity, a mixing head structure is adopted at the front end of the screw.
(3) PA, PA6, PA66 characteristics:
1. There are many kinds of crystalline plastics, with different melting points and narrow upper melting point range. Generally, PA66 has a melting point of 260℃-270℃;
2. Low viscosity, good fluidity, obvious melting point and poor thermal stability;
3. High water absorption rate, dryer temperature 80℃, no more than 120℃, time 16 hours. If the raw materials are exposed to air for 8 hours, a vacuum oven should be used at about 105℃ for 12 hours.
Parameters selected:
1.L/D select a mutant screw with a length ratio of 18-20;
2. Generally, the compression ratio is 2.5-3.5, in which H3: 0.067-0.089D to prevent overheating decomposition;
3. Because of its low viscosity, the clearance between apron and barrel should be as small as possible about 0.05-0.08, and the clearance between screw and barrel should be 0.08-0.12;
4. The nozzle can be equipped with a spring self-locking nozzle.
(4) PET
1. The melting point is 250℃-260℃, the molding temperature of blow-molded PET is wide, about 255℃-290℃, and the reinforced GF-PET can reach 290℃-315℃.
2. High melting point, low viscosity, strong adhesion with metal and easy hydrolysis;
3. Hydrophilicity, the adhesive is sensitive to water at high temperature, and the drying temperature is 150℃-160℃ for more than 4 hours.
Parameter selection:
1. generally, l/d is 20-22, with three-segment distribution L1=50-60% and L2 = 20-30%;
2. Screw with low shear and low compression ratio has compression ratio ε=1.8-2.2, which leads to discoloration or opacity H3 = 0.09-0.10d due to shear overheating;
3. When using recycled materials (chips), increase the conveying capacity of the feeding section and adopt the forced feeding plasticizing system.
We have a wide range of injection moulds, such as precision mold,TV remote controller mold,industrial part injection mold,etc.If you need to contact the manufacturer.

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