◆Sprue material (runner sprue) sticking to the mold and solutions
Excessive noise during plasticizing and its solutions：
Plasticizing noise refers to the "squeaking" or "crunching" friction sound produced inside the barrel during injection molding when the screw rotates and plasticizes the material (this noise is more pronounced when plasticizing high-viscosity PMMA and PC materials).
Excessive noise during plasticizing is mainly caused by excessive screw rotational resistance, leading to strong dry friction between the screw and the plastic material in the compression and feeding sections. The causes and solutions for this phenomenon are shown in the table below.
Causes and solutions for excessive noise during plasticizing
| Causes Analysis | Solutions |
|---|---|
| ① Excessive back pressure | ① Reduce back pressure |
| ② Screw speed too high | ② Reduce screw speed |
| ③ Barrel (compression section) temperature too low | ③ Increase temperature of the compression section |
| ④ Plastic viscosity too high (poor flowability) | ④ Switch to a plastic with better flowability |
| ⑤ Poor self-lubricating property of the resin | ⑤ Add lubricant (e.g., stearic acid, talc) to the raw material |
| ⑥ Screw compression ratio too small | ⑥ Replace with a screw having a larger compression ratio |
Screw slippage and solutions
During injection molding, the phenomenon where the screw fails to plasticize the raw material and only spins without moving is called screw slippage. When screw slippage occurs, the screw only rotates and does not retract. The causes and solutions for this phenomenon are shown in the table below.
Causes and solutions for screw slippage
| Causes Analysis | Solutions |
|---|---|
| ① High temperature at the rear of the barrel, material melts and concludes (not fully melted) | ① Cool the feed throat with cooling water; lower rear barrel temperature |
| ② Dry the material insufficiently | ② Dry the material thoroughly and add lubricant if appropriate |
| ③ Excessive back pressure, screw speed too high (screw slips) | ③ Reduce back pressure and lower screw speed |
| ④ High resin viscosity inside the barrel (material not fully melted) | ④ Repair/replace barrel heating system; replace with new material |
| ⑤ Excessive recycled material ratio in feed port, causing "bridging" phenomenon | ⑤ Increase the size of the feed port hopper; re-pulverize the recycled material |
| ⑥ Material shortage inside the barrel | ⑥ Feed material in time and add material continuously |
| ⑦ Severe wear on barrel wall and screw | ⑦ Inspect and replace the barrel/screw |
Nozzle clogging and solutions
During injection molding, the phenomenon where the melt cannot enter the mold runner is called nozzle blockage. The causes and solutions for this phenomenon are shown in the table below.
Causes and solutions for nozzle clogging
| Causes Analysis | Solutions |
|---|---|
| ① Presence of metals or other non-meltable foreign matter in the nozzle | ① Dismantle and clean the nozzle; remove foreign matter inside the nozzle |
| ② Mixed metal particles in the feed port | ② Inspect/clean metal particles from the hopper; replace feed material (use centrifugal material sorting if necessary) |
| ③ Insufficient drying of material in the feed port | ③ Dry the material in the hopper thoroughly before feeding |
| ④ High melting point plastic mixed in the hopper | ④ Remove high melting point plastic from the hopper |
| ⑤ Crystallizing resins (e.g., PA, PBT) with high moisture sensitivity | ⑤ Increase drying temperature |
| ⑥ Damaged or torn heating bands on the nozzle | ⑥ Replace damaged/torn nozzle heating bands |
| ⑦ Too few nozzle heating zones | ⑦ Increase the number of nozzle heating zones |
| ⑧ Nozzle not installed with magnetic filter | ⑧ Install magnetic filter on the nozzle |
Nozzle drooling and solutions
The phenomenon of melt flowing out of the nozzle during plasticizing is called nozzle drooling. In contact injection molding, if nozzle drooling occurs, the melt flows into the main runner, and the cooled plastic can affect the smooth progress of injection molding (clogging the gate or runner) or cause appearance defects on the surface of the plastic part (such as cold spots, shrinkage, shortness of material, etc.). This is especially true for plastics with good flow properties, such as PA materials, which are very prone to nozzle drooling. The causes and solutions for nozzle drooling are shown in the table below.
Causes and solutions for drooling
| Causes Analysis | Solutions |
|---|---|
| ① Material temperature or barrel temperature too high | ① Lower overall barrel temperature and nozzle temperature |
| ② Excessive back pressure or screw speed too high | ② Reduce back pressure or lower screw speed |
| ③ Insufficient shot volume (material stays too long in barrel) | ③ Increase shot volume (shorten residence time) |
| ④ Excessive nozzle temperature or uneven nozzle heating | ④ Use smaller-diameter nozzle or replace with self-cleaning nozzle |
| ⑤ Excessive screw speed | ⑤ Reduce screw speed |
| ⑥ Excessive back pressure setting | ⑥ Change to multi-stage back pressure or lower back pressure |
Nozzle glue leakage and solutions
During injection molding, the phenomenon of hot molten plastic flowing out from the nozzle head or the connection between the nozzle thread and the barrel is called nozzle leakage. Nozzle leakage can affect the normal operation of injection molding. In minor cases, it can cause inconsistencies in product weight or quality; in severe cases, it can lead to shrinkage, material shortages, and burnt heating coils, thus affecting the product's appearance. The causes and solutions for nozzle leakage are shown in the table below.
Causes and solutions for nozzle glue leakage
| Causes Analysis | Solutions |
|---|---|
| ① Poor fusion between melt fronts from nozzle and mold | ① Use nozzle and mold accessories with better compatibility |
| ② Melt fracture or flow marks caused by the nozzle | ② Replace the nozzle or change to a different nozzle type |
| ③ Excessive back pressure or screw speed too high | ③ Reduce back pressure or lower screw speed |
| ④ Barrel temperature or nozzle temperature too low (low fluidity) | ④ Lower back pressure and increase temperature |
| ⑤ Slow injection speed | ⑤ Use multi-stage injection and increase speed |
| ⑥ Excessive screw forward time (FMI holding pressure too high) | ⑥ Use multi-stage holding pressure or reduce holding pressure |
Product sticking to the mold and solutions
Causes and solutions for products sticking to the front mold
| Causes Analysis | Solutions |
|---|---|
| ① Low clamping force (mold not fully closed, poor rigidity, or deformation inside the mold cavity) | ① Increase clamping force |
| ② Excessive injection pressure or holding pressure | ② Reduce injection pressure or holding pressure |
| ③ Too long holding time | ③ Shorten holding time |
| ④ Too fast end-stage injection speed | ④ Reduce end-stage injection speed |
| ⑤ Insufficient material temperature or cooling time | ⑤ Lower material temperature or extend cooling time |
| ⑥ Melt temperature too high or too low | ⑥ Adjust melt temperature and reduce temperature fluctuation |
| ⑦ Uneven or excessive feed amount per cycle | ⑦ Change gate position or reduce gate size |
| ⑧ Molding conditions with front mold temperature higher than rear mold temperature | ⑧ Inspect and repair mold; clear trapped air |
| ⑨ Poor precision or burrs on the mold parting surface | ⑨ Repair mold or polish/repair parting surface |
| ⑩ Poor front/rear mold surface finish or presence of scratches | ⑩ Polish mold or re-coat mold surface |
| ⑪ Too large or too small mold venting gap | ⑪ Increase exhaust gap thickness |
| ⑫ Excessive mold temperature vacuum (strong suction) | ⑫ Extend cooling time or change cooling method |
| ⑬ Fast mold opening speed at start | ⑬ Reduce initial mold opening speed |