Most LSR Injection Molding Defects do not have a single cause. Flash may point to a shutoff, contamination, clamp condition, or excessive cavity pressure. A short shot may be related to flow resistance, venting, material delivery, or an incorrect cure window. The fastest way to improve a part is to classify the symptom before changing several settings at once.
This troubleshooting guide is organized by visible symptom and confirmation step. It assumes a controlled project using 液状シリコーンゴム（LSR）成形, but the actual corrective action must be verified against the selected grade, mold design, and approved process window.
Use a four-question triage
- Where is the defect? Gate, end of fill, parting line, insert interface, or random location?
- When did it start? After a material change, cleaning, tool adjustment, or long production run?
- Is it cavity-specific? One cavity suggests balance, venting, insert, or local shutoff issues.
- Does the defect move with the process? A repeatable response to one controlled change is valuable evidence.
Keep the machine, material lot, mold temperature, fill profile, and handling condition stable while checking one factor. Otherwise the team may remove one symptom while creating a second problem that is harder to trace.
Flash: check sealing before reducing flow
Flash usually appears at the parting line, vent, insert interface, or ejector-related feature. Begin with a clean inspection of the sealing land. Silicone residue, a damaged edge, incomplete mold closure, thermal distortion, or a displaced insert can create a leak path. If the flash is cavity-specific, compare that cavity’s shutoff and insert seating with a good cavity.
| Pattern | Likely areas to check | First confirmation |
|---|---|---|
| All cavities, same edge | Parting strategy or common closure condition | Clean and inspect the shared land |
| One cavity only | Local shutoff, insert, or balance | Compare cavity measurements |
| At vent only | Vent geometry or air escape path | Check vent land and residue |
Short shots and knit lines: follow the flow front
A short shot can result from insufficient delivered volume, an overly restrictive gate, an unfavorable flow path, premature cure, or trapped air. A knit line may be expected in a complex geometry, but its position and strength depend on how the flow fronts meet. Map the defect to the fill sequence before increasing injection speed.
- Confirm both material components are metering and mixing correctly.
- Check for a blocked gate, runner, or cold section.
- Inspect the end-of-fill vent and any hidden pocket.
- Compare mold temperature and cure timing with the approved window.
- Revisit gate location if the weld line sits on a functional feature.
If faster filling improves a short shot but creates bubbles or flash, the original issue may be venting or balance rather than speed. Record both outcomes so the team does not optimize one defect in isolation.
Bubbles, burns, and void-like marks: investigate air
Bubbles and burn marks often appear where air cannot escape as the cavity fills. Look behind ribs, near pins, around inserts, at the last-fill region, and where multiple flow fronts meet. Check whether vents are open, clean, correctly connected, and still suited to the current gate layout. A material-delivery problem can also introduce bubbles, so inspect the component containers, mixer, and purge condition.
Do not enlarge a vent without considering flash. A safer approach is to confirm the location, clean the feature, evaluate the flow sequence, and adjust the vent or gate in a controlled trial. If the part is used in a fluid or medical context, define how internal air defects are detected and what size or position is unacceptable.
Incomplete cure, tack, or color variation
A tacky surface, inconsistent release, or color shift can point to cure, material, contamination, or temperature variation. Confirm the grade and lot, storage condition, component ratio, mold-temperature uniformity, and cure time. Some contaminants or substrate treatments can inhibit cure locally. If only one area is affected, compare the local insert, cavity surface, and thermal path instead of changing the entire cycle.
For color work, treat pigment concentration and material lot as process inputs. Visual comparison should use a defined sample and lighting condition. A general visual judgment is not enough when color is a functional or brand requirement.
Tear, distortion, or release damage: inspect the exit path
A molded part can be fully cured and still be damaged during release. Check undercuts, draft, sharp steel transitions, stripper action, air assistance, operator handling, and the position of any gate or trim feature. Compare the defect before and after changing the release sequence. If the part stretches out of tolerance and later relaxes, define the measurement time and fixture condition.
の quality-control process should record defects by cavity, location, lot, and disposition. That evidence helps separate a random handling event from a repeating design or process problem.
Close the loop with a controlled corrective action
A good corrective-action record states the defect, suspected cause, evidence, change made, result, and follow-up control. Avoid changing injection speed, temperature, cure time, and tool geometry simultaneously. When the root cause is confirmed, update the work instruction, inspection method, or maintenance checklist so the same issue does not return on the next lot.