What Should We Pay Attention To in The Underwater Pelletizing Process of ABS?

Regarding the production process of ABS resin, in industrial applications, the underwater strand pelletizing process is more common and more mature. However, the pelletizing system is not closed and there may be some uncertain factors that may lead to product contamination, such as the die plate of the industrial extruder, the water bath, etc.

The process and principle of underwater strand pelletizing

The main equipment of the underwater strand pelletizing system includes die head, guide trough, cutting chamber, post-cooling section, dryer, vibrating screen, and water system. The length of the guide trough is generally designed to be 3m in the applications of SAN pelletizing and ABS pelletizing.

The working principle of underwater strand pelletizing is that the molten material passes through the die head and enters the guide groove in the shape of a strip for cooling. The process water is generally around 40-60°C. When the strip is cooled to a certain temperature, it is fed into the cutting chamber through the upper and lower feeding rollers of the cutting chamber, and cut into particles by the moving knife. After the particles are cooled in the post-cooling section, they are sent to the dryer for drying, screened by the vibrating screen, and finally the qualified materials are sent to the silo to prepare for downstream processing.

The structure of underwater strand pelletizing

The products produced by underwater strand pelletizing are cylindrical particles. During the production process, the material strips need to be cooled to a certain hardness before they can be cut. Otherwise, the internal temperature is too high and the viscosity is low, which may cause the knife to entangle. The continuous pellets or material strips that cannot be cut are prone to adhesion. The layout of the pelletizer occupies a large area, with a guide trough of 3m, a spiral length of 3 to 5m in the post-cooling section, and a total area of about 12 to 15m for the dryer and vibrating screen. The particles have a certain hardness when cut, and the cylindrical particles have chamfers/edges. The contact between particles is point-to-face, face-to-face and other contact methods, and the content of continuous or irregular particles is high.

During the drying and particle cooling process, particles come into contact with pipeline equipment and dryers, and dust is easily generated at the edges and corners. Toothpick material and fine particles may appear in the die hole of the material strip. The specific surface area of cylindrical particles is relatively small, and monomer suction equipment needs to be installed at the particle die to ensure that there is no monomer volatilization and environmental pollution. When replacing the die, it is necessary to stop the machine, and when replacing the cutter, fixed knife, and upper and lower feeding rollers, it is necessary to discharge waste. The replacement time takes 15 to 20 minutes.

Application of ABS resin underwater strand pelletizing

In the underwater strand pelletizing system, the ABS molten material is extruded through the extruder and die head to become strands, then pelletized by the underwater strand pelletizer, dried by the dryer, and finally sieved on the particle screen. In daily production, most of the ABS particles will enter the finished product silo through the particle screen, but particles of unqualified size will be separated out, generally in the form of long strips, sticky materials, and oblique cut materials. Once these unqualified products are mixed with qualified products, they will cause complaints from downstream customers and have a negative impact on the company's brand.

In order to reduce the production of defective products, most production equipment will regularly replace the pelletizer roller and cutter, and replace the extruder die plate. These operations require the production line to be stopped. The cost of each start-up and shutdown is also very high, and a lot of start-up materials are generated, which also increases the labor intensity of the operators, thereby increasing production costs. In addition, when the extrusion line is just started, the strips on both sides of the die plate will also carry paste. If not handled properly, it will contaminate the finished product silo, causing trouble for monitoring product quality.

For newly built ABS resin production companies, how to optimize production process technology, make good equipment selection, and reduce the workload of operators are favorable guarantees for improving product quality and increasing market share.

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