A fine filament hangs from the tip after opening and needs manual removal; severe cases wrap around the part.4 directions · 3 directly solved
Injection defect troubleshooting encyclopedia
Thirty-nine injection defects, checked in six-link order and judged by cause direction
Each defect is broken down by cause direction: which direction gate temperature control can solve, and which must go back to material, machine, structure, flow analysis or mold. Capability is stated only for the specific direction, not as a blanket promise for the whole defect.
This guide covers engineering plastics and heat-sensitive materials across the nineteen grades listed in the brochure; commodity grades are outside its scope.
Scope first: manifold and its runners, nozzles and tips, heaters and thermocouples, constant-temperature and fast-heat-fast-cool controllers, sequence controllers, valve-pin drive interfaces and harnesses are all supplied and owned by us. Cavity and core, mold base, ejection, cooling circuits, venting and gate-bush machining belong to the mold maker; gate bore and fit are agreed by us during joint review.
Three temperatures are accounted for separately: melt temperature belongs to the molder, mold temperature to the mold maker, and hot runner temperature to us. Hot runner heating cannot replace mold temperature; raising the gate when the mold is too cold only turns a cold slug into stringing.
Material
Material and drying
Machine
Injection unit and screw
Structure
Part structure and flow ratio
Flow
Flow analysis
Mold
Venting · water · mold temperature
Hot runner
Hot runner system
The order cannot be reversed: until the first five links are cleared, adjusting gate temperature is blind tuning. A good result has no known cause, and a bad one has no traceable cause.
First locate the link
Causes sit in six places. The customer describes a symptom; the engineer has to place it. Once the place is fixed, who should check and who should change becomes clear.
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The same defect appears at different frequencies by resin. Select a material to keep its high-frequency defects; leave unselected for all.
Thirty-nine defects
Open a defect to read its cause directions. Each direction is judged separately: directly solved, can improve, joint fix, first five links, or external condition. Judgement follows responsibility, not a technical weakness; directly solved covers four key structural features supported by 7 filed patent applications and five gate dynamic temperature bases, not temperature alone.
Current group：Gate and hot runner interface
11 items · 31 directions directly solved
The contact interface between the nozzle tip and the mold gate. Start here for defects that appear at this interface.
A film or droplet forms at the gate, leaving an extra thin flap at the part edge.4 directions · 2 directly solved
Shot volume falls cycle by cycle or a cavity shorts; dismantling shows a blocked gate passage, with the blockage shape depending on gate design.6 directions · 3 directly solved
A dark carbon layer builds on the gate wall, thickens cycle by cycle and makes flow unstable with black specks.5 directions · 3 directly solved
Melt freezes early at the gate, causing a short at the end or a cold-slug mark on the part.4 directions · 2 directly solved
Valve-pin sticking and incomplete closing: causes and fixes
The valve pin moves late or does not reach its seat, leaving residue or stringing at the gate or shorting one cavity.4 directions · 3 directly solvedLCPPA9TPPSPC+ABS
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Melt seeps at the nozzle-to-manifold joint, leaving a film on the mold face or flash-like overflow on the part.4 directions · 3 directly solved
Measured temperature stays away from setpoint, cycles periodically, or zones interfere with each other.4 directions · 3 directly solved
A white stress mark or haze appears around the gate and rejects cosmetic parts.4 directions · 3 directly solved
A bump, residual tab or visible shear mark remains at the gate and affects assembly or appearance.4 directions · 3 directly solved
The tip or gate bush shows wear, erosion or rust; the bore grows and flow and freeze-off drift.4 directions · 3 directly solved
Check criteria by link
The six links follow the group order above. When the problem is already placed in the first five links, check that link item by item instead of starting at the gate. Criteria come from measurements and drawings, not setpoints.
Material and drying
Grade, moisture, drying curve, regrind ratio
Injection unit and screw
Actual peak injection pressure curve, injection speed, L/D and compression ratio
Part structure and flow ratio
Thinnest rib, flow length and material flow limit
Flow analysis
Filling, front velocity, weld lines and biaxial shrinkage
Venting, water and mold temperature
Vent location and depth, circuit flow, measured mold-face temperature
Gate and hot runner
Gate type and material fit, tip-to-mold temperature difference, residence time
Bring the part and run the six links
Send the part, material grade, current process settings and defect photos. We give a conclusion link by link through material, machine, structure, flow, mold and gate, and state for each direction which can be solved by gate temperature control and which must go back to the mold or machine.
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