Views: 0 Author: Site Editor Publish Time: 2025-08-13 Origin: Site
When the wall thickness of the product is large, the outer surface cools faster than the center. As cooling progresses, the plastic resin in the center shrinks while expanding towards the surface, causing insufficient filling in the center. This is known as vacuum bubbles. Main solutions include:
a. Determine a reasonable gate and runner size based on wall thickness. Generally, the gate height should be 50% to 60% of the product wall thickness.
b. Maintain a certain amount of holding pressure material until gate seal-off.
c. The injection time should be slightly longer than the gate seal-off time.
d. Reduce injection speed and increase injection pressure.
e. Use a material with a higher melt viscosity grade.
Solutions mainly include:
a. Ensure thorough pre-drying of the material.
b. Reduce resin temperature to avoid generating decomposition gases.
Can be solved by increasing resin and mold temperatures and increasing injection speed.
Cooling time is too short; the sprue has not solidified.
Insufficient draft angle on the sprue; increase its draft angle.
Improper fit dimensions between the sprue bushing and nozzle causing leakage.
Rough sprue surface; no cooling well in the sprue.
Nozzle temperature is too low; increase the temperature.
High plastic temperature and mold temperature lead to long cooling times.
Long plasticizing time; reduce back pressure, minimize use of regrind to prevent bridging, ensure sufficient cooling in the feed zone.
Slow machine movements; adjust hydraulic and electrical circuits to speed up appropriately.
Mold design should facilitate demolding; design for full automatic operation where possible.
Excessive part wall thickness causes excessively long cooling times.
Nozzle drooling hinders normal production; use a self-sealing nozzle or reduce nozzle temperature.
Insufficient heating capacity of the barrel; use a machine with larger plasticizing capacity or enhance material preheating.
Inconsistent plasticizing capacity or heating power of the machine; select a machine with sufficient plasticizing capacity and heating power.
Wear on the screw, barrel, or check ring causing material leakage back, resulting in insufficient actual filling volume.
Malfunction in heating systems (thermocouples, heating rings, etc.) causing the actual barrel temperature to be too low.
Wear in injection cylinder seals causing oil leakage or backflow, preventing the required injection pressure from being reached.
Nozzle orifice too small or nozzle misalignment causing excessive resistance and pressure loss.
a. Local or overall mold temperature too low causing difficulty in material flow; appropriately increase mold temperature.
b. Unbalanced cavity layout or excessively thin part walls causing significant pressure loss and poor filling. Increase the wall thickness of the entire part or the specific area, or set up auxiliary runners or gates near the underfilled area.
c. Runners too small causing pressure loss; too large causing weak injection force; excessive surface roughness causing short shots. Appropriately size runners. Apply suitable radii to transitions (e.g., between sprue and runners, gates) and bends within the runners themselves.
d. Poor mold venting. Material entering the cavity is blocked by gas pressure that cannot escape quickly enough, causing incomplete filling. Utilize screw decompression for venting, reduce clamping force to vent along the parting line, or if necessary, add vent slots or vent pins.
