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Measures to the Modified Plastics Appearance Defect

Views:11     Author:Vera     Publish Time: 2017-09-27      Origin:Site

Measures to the Modified Plastics Appearance Defect


The main production equipment of modified plastics is twin screw extruder, and the common production process is as follows: formula-mixture-extrusion-die-cooling-pelletizing-Packaging. Appearance defects is a quality problem of modified plastic products, mostly related to production process, raw material quality, production equipment, production environment and other factors. Common problems are strand, granules adhesion, black spots, discoloration, bad vacuum exhausting, poor plasticization, carbonation and so on.

 

Long strand

The length twice times longer than the normal pellet is considered as strand. The main reasons may be broken strand, wrong direction of the strand, wear or north of the pelletizer and so on.

 

Resolution measures

▍ Adjust the direction of the strand into the pelletizer; adjust the length of the water bath.

▍ Pay attention to check the pelletizer knife, the timely replacement of damaged knife;

▍ Sieve the long strand with suitable vibrating screen.

 

Pellets adhesion

It means two or more pellets tied together. The main reasons may be strand broken while extruding, or the length of the water bath is not long enough.

 

Resolution measures

▍ Select guide wheel with appropriate width while extruding, in order to separate the adhesive material.

▍ Adjust the lenght of cooling water to reduce the adhesive pellets;

▍ The adhesive pellets can be screened by suitable vibrating sieve.

 

Black spots

There are black spots on the surface or inside of the pellets. The main reasons include: The plastic extruder machine is not clean up; there are black spots in raw materials; screw carbonization; environmental pollution.

 

Resolution measures

▍ Clean up the extruder machine carefully;

▍ strengthen the inspection of raw material, especially the filling powder or flame retardants, which is easy to have black spots and impurities .

▍ pay attention to control the temperature of the screw barrel and the stay time of material in the screw barrel, to prevent too high processing temperature;

▍ pay attention to the surrounding sanitation, do a good job to the isolation and protection between the machines for producing different color product is necessary.

 

Discoloration

In the production process, the product color suddenly changes, showing obvious chromatic aberration. The main causes of discoloration are uneven mixed material, dirty machine, the temperature is too high or the shearing is too strong.

 

Resolution measures

▍ in strict accordance with the mixing process, to ensure the homogeneity of the mixture;

▍ Clean up the extruder machine carefully;

▍ Control the extrusion temperature, prevent color powder decomposition by the high temperature ;

▍ Select the appropriate screw combination to avoid too strong shear.

 

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