Foreign matter and black spot defects in injection molding refer to a defective phenomenon in which foreign matter or black spots appear on the surface or inside of a product. This is an important quality control issue because it adversely affects the appearance and function of the product.
At first glance, it may look like gas burning, but the cause of occurrence is different, and it does not always occur in a specific location.
Examples of foreign matter and black spot defects
Foreign matter:
Foreign matter refers to undesirable substances that are mixed into the product. These include metal, dust, rubber, fibers, and other resin fragments.
Black spot:
Black spots are small black specks that appear on the surface or inside of a product. They are primarily caused by burnt or contaminated resin.
Main causes of foreign matter and black spot defects
Contamination of raw materials:
When dust or foreign matter is mixed in during storage of raw materials, or when the raw materials themselves contain foreign matter.
Contamination of machinery and equipment:
Foreign matter or deteriorated material adhering to the barrel, screw, hopper, or mold of the molding machine.
High temperature decomposition:
When resin is processed outside of the proper temperature range and decomposes, causing scorching and black spots.
Mold contamination or wear:
Dirt or degradation on the mold surface that is transferred to the molded product.
Residue from color change:
When the previous color material is not completely removed during a color change and is mixed with the new material.
Contamination of the work environment:
Insufficient cleaning of the work area or failure to maintain an appropriate clean room environment.
Countermeasures for foreign matter and black spot defects
Control of raw materials:
Select high quality raw materials and remove foreign matter with filters or magnets before use.
Store raw materials properly to prevent moisture and dust contamination.
Cleaning and maintenance of machinery and equipment:
Regular cleaning and maintenance of barrels, screws, hoppers, molds, etc. are performed to prevent foreign matter from adhering to them.
Thoroughly clean the inside of the machine, especially during material changes and after the end of production.
Thorough temperature control:
Properly control resin processing temperatures to prevent decomposition due to high temperatures.
Periodic inspection and calibration of temperature sensors and control devices.
Mold maintenance:
Perform periodic maintenance and cleaning of molds to prevent contamination and wear.
Special coatings are applied to the mold surfaces to prevent the adhesion of dirt.
Cleaning during color change:
When performing a color change, the screws and barrels are thoroughly purged to completely remove the previous color material.
Thorough cleaning with a purging material is also effective.
Cleaning and management of the work environment:
Keep the work environment clean by installing a clean room or clean booth.
Ensure that workers wear appropriate clothing and gloves to prevent contamination by foreign matter.
By taking these measures, foreign matter and black spot defects in injection molding can be reduced and product quality can be improved. Continuous control and improvement are important.
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