Tips for Resolving Unstable Plasticizing and Melt Shot Size Deviations in Injection Molding Machines

Issues such as raw material moisture, excessive dust, and uneven particle size cause fluctuating feed rates, leading to instability in melt metering. To address this, materials must be thoroughly dried to standard specifications, regrind must be screened to remove fines and ensure uniform particle size, and a vibration device should be installed on the hopper to prevent bridging and material flow interruption

If the temperature at the feed inlet of the barrel is too high, the raw material melts and clumps prematurely, clogging the feed channel and causing intermittent under-feeding. Moderately lower the temperature in the feed zone and, if necessary, install a cooling water jacket at the feed inlet.

Fluctuations in the material level within the hopper cause variations in material pressure, which affect the discharge rate. Maintain a stable material inventory in the silo to avoid massive, one-time replenishments after the silo has emptied.

Melt pressure and flow rate sensors exhibit drift, servo output feedback is inaccurate, and deviations occur in the plasticizing stroke. Regularly calibrate pressure sensors and position transducers to ensure accurate signal feedback.

Clogged hydraulic oil filter elements and degraded oil containing impurities can cause intermittent oil supply to the plasticizing motor and inconsistent material accumulation speeds. Replace filter elements and hydraulic oil according to the maintenance schedule, and clear impurities from the oil lines.

Internal leakage in the plasticizing motor and wear on seals result in unstable output torque and inconsistent material accumulation strokes per cycle. Check the motor's pressure-holding capability and replace worn components as necessary.

Wear on the screw non-return ring leads to increased clearance, causing melt backflow during the injection phase and a continuous reduction in the actual plasticized volume. Disassemble and inspect the non-return ring and the sealing surfaces; replace the entire non-return assembly if wear is found.

Excessive clearance between the screw and the barrel causes backflow of the molten material, resulting in an insufficient effective melt volume; carbonized material buildup on the screw surface impedes material transport and causes fluctuations in metering. Regularly clean the machine and polish the screw, and replace the screw and barrel if the clearance exceeds specifications.

Screw bearing wear and excessive transmission backlash are causing slippage during plasticizing rotation and unstable metering during material accumulation; inspect and service the transmission bearings and couplings.

If the melt back pressure is set too low, melt mixing is uneven and metering stability is poor; conversely, excessively high back pressure can easily cause screw slippage. Set a moderate back pressure based on the material's characteristics and pair it with a stable screw rotation speed.

The melt plasticization speed fluctuates, resulting in significant shear variations and inconsistent melt density. Adopt a constant-speed, multi-stage plasticization process to minimize drastic changes in rotational speed.

The injection delay time is inconsistent, leading to varying dwell times after plasticization and differences in the degree of melt backflow; standardize the interval between the completion of plasticization and the start of injection for each cycle.

The cushioning setting for the end of the material charging phase is insufficient, causing backflow due to impact when the screw stops; fine-tune the deceleration range for plasticizing to reduce backflow caused by the sudden stop of the screw.

Periodically clean carbon deposits from the barrel and screw to prevent material buildup from affecting material conveyance; ensure proper heat dissipation for the servo control cabinet to prevent drive overheating and resulting output anomalies; and verify the plasticizing stroke value after every mold change, promptly investigating any significant deviations.