For previous reading, please refer to How to accurately determine whether plasticization quality has reached a "good" state duri.

1. Melt temperature:
Measurement: Use a calibrated needle thermometer to measure actual temperature of air-shot melt (the most reliable method), or check temperature settings and actual feedback of each section of barrel and nozzle on machine (pay attention to sensor position and accuracy).
Good state: Measured melt temperature is within recommended range of material and has a small stable fluctuation (usually within ±3-5℃). Temperature settings of each section of barrel are reasonable to form a stable temperature gradient (usually low in feeding section, high in homogenization/metering section, and slightly low or flat in nozzle section).

 

Bad state: Measured melt temperature is much lower or higher than recommended range.
Melt temperature fluctuates too much (> ±10℃).
Barrel temperature setting is unreasonable (such as temperature of homogenization section is too low).
Nozzle temperature is abnormally high (nozzle heating ring may fail or friction heat is too large).
2. Screw rotation parameters:
Speed: Under premise of ensuring that plasticizing time is less than cooling time, speed should not be too fast. Too high a speed will cause excessive shear heat, which may cause local overheating and degradation; it may also cause plasticizing stroke to be too short and uneven melting.
Back pressure:
Function: compact melt, increase shear, increase melt density and uniformity, promote exhaust (push gas toward hopper), and improve color mixing.
Good state: Back pressure is set reasonably (usually 5%-20% of injection pressure, depending on material and effect). Improvement of back pressure on gloss and density (material strips) of melt can be observed.
Bad state: Back pressure is too low: melt is loose, contains many bubbles, mixing effect is poor, and plasticizing amount is unstable.
Back pressure is too high: increase unnecessary shear heat, which may cause melt temperature to rise or even degrade; increase load on screw and drive system; and extend plasticizing time. You may see melt change color or smoke due to overheating.
Plasticizing time/screw reset time: should be stable and less than cooling time. If time is too short, plasticization may be insufficient; if time is too long, melt may be retained and degraded.
3. Stability of plasticizing amount (shot amount):
Monitoring: Observe repeatability of screw reset position (V-P switching point) on machine display.
Good state: Screw reset position is very stable (with a small fluctuation range, usually within ±0.2mm), indicating that volume and density of melt plasticized each time are consistent.
Bad state: Reset position fluctuates greatly, indicating that plasticization is unstable (such as uneven feeding, insufficient back pressure, large temperature fluctuations, screw/check ring wear causing backflow), which directly affects injection stability and is a key indicator for judging whether plasticization quality is stable.

1. Screw and barrel:
Wear: Gap between screw and barrel is too large due to severe wear, resulting in low plasticizing efficiency, insufficient shear, increased reflux (unstable plasticizing amount), and uneven melt temperature. Regular inspection is required.
Design: Is length-to-diameter ratio (L/D), compression ratio, and length of each section of screw suitable for material being processed? An unmatched screw will seriously affect plasticizing quality.
2. Check ring:
Worn or failed check rings will cause melt reflux during injection, reduce injection pressure and speed stability, indirectly affect filling and holding pressure effects, and sometimes affect stability of plasticizing amount.
3. Drying system:
For hygroscopic materials (such as PA, PET, PC, ABS, etc.), insufficient drying of raw materials is one of the most common causes of water vapor, silver streaks, and bubbles. It is necessary to ensure that drying temperature, time, and air volume meet requirements, raw materials in drying hopper do not agglomerate, and dew point is low enough (usually <-40℃).
4. Cooling water:
Insufficient cooling in rear section of barrel (feeding section) may cause premature softening and agglomeration ("bridging") of raw materials in throat, affecting feeding and plasticization stability.

1. Raw material drying: As mentioned above, it is critical for hygroscopic materials.
2. Raw material batch/source: Materials from different batches or sources may have differences in melt index, additives, moisture content, etc., which affect plasticization behavior. Pay special attention to plasticization state when changing batch numbers.
3. Recycled material ratio and status: Use ratio, cleanliness, crushing particle size, drying degree, and thermal history (degradation degree) of recycled materials will significantly affect plasticization quality and melt uniformity. Excessive recycled material ratio or poor recycled material is a common cause of poor plasticization (particles, moire, degradation, brittleness).
How to comprehensively judge plasticization quality as "good"?
1. "Three-No" material bar: There are no visible unmelted particles, bubbles/voids, discoloration/burnt particles on the surface and inside of empty shot material bar. This is the most intuitive and important passing line.
2. "Two-Even" Appearance: Color of material bar is uniform and surface gloss is uniform (in line with material characteristics).
3. "One Stable" Parameter: Screw reset position is stable (with minimal fluctuations).
4. "One Suitable" Temperature: Measured melt temperature is moderate and stable (within recommended range of material, with small fluctuations).
5. "Smooth" Injection: Injection action is smooth, melt flows out continuously and smoothly without abnormal spraying or smoke.