Material Drying
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Defects Caused by Insufficient Drying of Polypropylene Before Processing
Problem Phenomenon
Silver streaks, bubbles, and surface roughness appear on the product surface, and the mechanical properties decline.
The consequences of insufficient drying cover many types of defects and are a common problem in plastic processing.
Cause Analysis
(1) The raw material absorbs moisture (although polypropylene has low water absorption, it will still absorb water when exposed for a long time)
(2) The drying temperature is too low or the drying time is insufficient
(3) The drying equipment fails or the dehumidification capacity is insufficient
(4) The dried raw material is placed in a humid environment for too long and absorbs moisture again
(5) The regrind is not dried or is insufficiently dried
Solution
(1) Use a dehumidifying dryer, with a drying temperature of 60-80°C and a time of 2-4h
(2) Control the moisture content after drying to below 0.02% (polypropylene)
(3) Store the dried raw material sealed, cover the hopper, and expose it to air for no more than 2h
(4) Dry the regrind the same as the new material
(5) Control the workshop ambient humidity below 60%
Key Takeaway
Insufficient drying is a common root of processing defects, and a sound drying system and moisture content inspection system need to be established.
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