1. Modification process
The main production equipment of modified plastics is a twin-screw extruder, and the common production process is: ingredients, mixing, extrusion, k-strand, cooling, all pellets, and packaging.
The quality problems of modified plastic products can be divided into appearance defects and unqualified performances. The appearance defects are discussed here. Most of the appearance defects are related to factors such as production process, raw material quality, production equipment, production environment and other factors. Common defects include long strips, continuous grains, black spots, discoloration, poor vacuum, iron filings, poor plasticization, carbonization, etc. The article starts with the production process, analyzes the common quality problems of modified plastics and proposes countermeasures.
2. Common defects
1. Long strip
The length of more than 2 times the normal particle is regarded as a long strip. The main reasons for this are as follows: power-on pull or break, the direction of the material is not straight, the cutter of the pelletizer is worn or notched, etc.
1) During normal production, adjust the direction of the strip entering the pelletizer and adjust the length of the water;
2) Strictly covering the broken strips during production requires adjustment and processing;
3) Pay attention to the apricot inspection of the cutting motorized knife, and replace the damaged moving knife in time;
4) Use a suitable vibrating screen for the emergence of Chojomachi, and sieving treatment.
2. Continuous grain
Two or more particles connected side by side are called continuous particles. The main reasons for cattle production are bar breakage when pulling bars and insufficient water length.
1) When extruding the strip, use a guide wheel with a suitable width to separate the connected strips;
2) Adjust the appropriate cooling water length, that is, reduce the continuous grain;
3) For the emergence of contiguous granules, a vibrating screen with appropriate sieve openings can be used for sieving.
3. Black spots
There are black speckled particles on or inside the particles. The main reasons for black spots are: cleaning machine is not clean; there are black spots in the raw materials; screw carbonization: environmental pollution.
1) If it is not cleaned up during the process of changing production and cleaning, just clean the machine again;
2) Strengthen the inspection of incoming materials, especially the black spots and impurities are more likely to appear in the filled mineral powder or flame retardant;
3) Pay attention to control and adjust the temperature of the barrel and the residence time of the material in the barrel to prevent the processing temperature from being too high;
4) Pay attention to the surrounding environmental hygiene, and it is necessary to do a good job of isolation and protection between the machines that produce products of different colors.
It is manifested as a sudden change in the color of the product during the production process, resulting in obvious color difference. The main causes of discoloration are uneven mixing; unclean cleaning; temperature is too high; shear is too strong.
1) Strictly follow the mixing process to ensure the uniformity of the mixing;
2) After the cleaning is completed, an annual inspection will be conducted to ensure that the cleaning is clean;
3) Control the extrusion temperature to prevent the toner from decomposing when the temperature is too high;
4) Choose a suitable screw combination to avoid too strong shear.
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