---
title: "Why Does Injection Molded Parts Develop Discoloration During Production?"
description: "Batch molded parts with brown streaks and yellowing create quality hold risk. Separate resin degradation, contamination, and mold surface staining with process, tooling, and inspection checks to restore stable color."
url: "https://www.hyneu.com/questions/why-injection-molded-parts-discoloration-production.html"
language: "en"
type: "Q&A"
category: "Injection Molding Q&A"
datePublished: "2026-11-03"
dateModified: "2026-11-03"
brand: "HYNEU"
manufacturer: "HYNEU"
answerCount: 8
---

# Why Does Injection Molded Parts Develop Discoloration During Production?

## Question

 I am currently holding a batch of black ABS control panel housings because of intermittent discoloration on the cosmetic side. The parts show brownish streaks near the gate, and some cavities have yellow-brown patches around venting areas after roughly four hours of continuous production. Dimensional checks are still inside tolerance, but the appearance is not acceptable under normal customer inspection. Our shift team has already adjusted barrel temperature and purged several times, but the discoloration keeps returning. I need to understand why injection mold discoloration occurs, not just read a generic defect list. There is also visible brown deposit on the mold surface near the hot runner gate and along some venting channels. I am not sure whether the deposit is transferring to the part, or whether the material is degrading inside the hot runner and then staining the tool. The most confusing point is that the defect is not on every cavity and not on every shot. Some shots look clean, then a run of parts shows a light yellow streak in the same area. I have to decide tonight whether we can continue running with increased visual inspection, rework the affected parts, or stop the tool for cleaning and maintenance. What specific checks should I do first? What process settings, tooling measurements, or material tests would help me separate resin degradation, contamination, and mold surface staining before we commit to a correction? If we block only the affected cavities, what evidence do I need to support that decision? 

## Answers
                            
### Answer 1 — Best Answer

The first issue to clarify is that “injection mold discoloration” can mean two different conditions: color shift on the molded part, or staining/discoloration on the mold surface itself. In your case, both are present. Brownish streaks near the gate and yellow-brown patches around venting areas are usually not a uniform resin color change. They point to local material degradation, gas venting, or tool surface contamination. **Separate whether the discoloration is occurring in the melt or on the tool surface.** The decision path is different for each one.

Start by mapping the defect. Record cavity number, shot count, time after startup, hot runner drop, and whether the mark appears consistently or randomly. If discoloration appears in all cavities, especially after a short idle period, focus on barrel temperature, residence time, hot runner temperature, and material lot. If it appears only in specific cavities near the gate or vent, focus on tool surface condition, vent depth, gate insert wear, and local flow restriction. The fact that some shots look clean and then a run of parts shows a light yellow streak in the same area often means degraded material is being released intermittently from a dead spot or a contaminated gate detail.

Material degradation is the most common cause of brown or yellow streaks. Check the barrel temperature profile against the resin datasheet, but do not rely only on set values. An infrared probe or manual melt check may show actual melt temperature is higher than the controller indicates. Long residence time is often hidden: if shot weight is only a small fraction of barrel capacity, material sits in the barrel too long. High screw rotation speed, high back pressure, or a worn screw can also add shear heat. Degraded polymer, additives, or colorant will produce yellow to brown or black streaks. If the hot runner manifold has a dead zone, material can degrade there and release later, producing intermittent marks. Corrective actions include lowering the front zone temperature by 5–10°C, reducing back pressure, setting screw rpm within the resin supplier’s range, and purging with a commercial purging compound until the purge is clean and stable.

Contamination should be checked next. Residue from a previous material, colorant, or purge compound can remain in the hopper, feed throat, screw channels, check ring, nozzle, or hot runner. Moisture in ABS or colorant can cause hydrolysis and yellowish discoloration during processing. Check dryer dew point, drying time, and material lot variation. If the product is black ABS using masterbatch, confirm that the carrier resin is compatible with ABS and that the let-down ratio is within the supplier’s limit. Regrind above roughly 15–20%, especially if material has already seen multiple heat cycles, can increase yellowing. A temporary trial with 100% virgin material is one way to separate material-related causes from mold-related causes.

The mold surface itself can create or transfer discoloration. Brown deposits near the gate and venting channels are often baked-on gas residue, degraded material, or corrosion. Gas burns occur when air or volatile gas is compressed in a blind pocket, and the resulting heat oxidizes the polymer. Vent depth and land length should be checked with a feeler gauge, and the depth must match the material supplier’s recommendation. ABS may call for a relatively shallow vent, but if the vent is too shallow, worn, or blocked, local burning and discoloration will continue. Inspect the gate insert under magnification. A pitted, rough, or worn gate detail can hold material, create local shear, and cause brown streaking. Clean the mold with an approved mold cleaner and brass or copper tools only. Steel scrapers can damage plating, polished surfaces, and vent edges, making the problem worse.

For tonight’s decision, collect evidence before changing everything. Take labeled samples of good and defective parts by cavity and shot sequence. Photograph the defects and the corresponding mold areas. Check the actual temperature profile, shot size, cushion, cycle time, material lot, dryer dew point, and regrind percentage. Inspect each vent and gate with a flashlight and magnification. If the defect is cavity-specific, clean those cavities and run 20–30 short cycles. If the stain returns quickly, the tooling needs vent re-machining or gate insert repair, not just wiping. If the defect appears in all cavities, stop and correct the process or material before making more suspect stock.

Use a simple containment decision. **Residence time, local venting, and gate condition** are the three factors that most often explain intermittent near-gate discoloration. If all cavities are affected, do not continue production. If only one or two cavities are affected and the remaining cavities are stable, you may block those cavities temporarily, but only after documenting the cavity number, cleaning the tool, and verifying that the remaining cavities produce acceptable parts. Affected parts should be quarantined. Do not ship them as first quality without a formal deviation, and do not assume that polishing will restore a textured cosmetic surface.

After the immediate issue is controlled, correct the root condition. Re-machine or clean vents to the correct depth, repair or replace worn gate inserts, and verify vent land length and surface finish. Rebalance the hot runner if needed. Set a repeatable process window based on actual melt temperature, shot size, and screw speed. Validate the correction with a startup sequence and at least 30–50 consecutive shots. Long term, implement a material changeover checklist, a regrind ratio limit, periodic vent inspection after a fixed number of shots, and a mold cleaning interval. Record the correction so the next batch does not repeat the same troubleshooting loop.

**status:** accepted
**Author:** Leo Shen
**Date:** 2026-11-03

### Answer 2

The tool should be evaluated before any further process adjustment is made. Check the gate insert and vent surfaces under magnification, because brown deposits around those areas often indicate gas burning, material sticking, or plating wear.

Measure vent depth with feeler gauges at several points across each cavity and record the values. A cavity that combines a shallower vent, a rough vent land, and discolored parts is a strong local root cause.

Clean the deposit with a brass or copper tool and an approved mold cleaner. Do not use a steel scraper on polished steel, chrome plating, or textured surfaces, because even light scratching can create a new adhesion point for degraded resin.

After cleaning, run a short trial and compare early shots with later shots. If the stain returns in the same cavity, the issue is not simply residue. Plan vent re-machining or gate insert replacement instead of repeated on-press wiping.

Also check insert seating, parting line contact, and ejector clearance, because small clearance changes can alter gas escape and shift a defect from one cavity to another. Cavity-specific discoloration is usually a tooling and gas venting problem, and barrel temperature changes alone will not correct it.

**status:** suggested
**Author:** Victor Luo
**Date:** 2026-11-03

### Answer 3

Check whether the material lot changed at the same time the defect appeared. ABS can vary between lots in thermal stability, moisture level, or additive package, especially with flame-retardant or high-flow grades.

If this tool and process produced good parts before, do not assume the material is innocent. Pull the certificate of analysis, compare melt flow rate and moisture specification, and check pellet color under consistent light.

Regrind ratio should also be confirmed. Repeated heat history above roughly 15–20% can lower thermal stability and produce yellow or brown tones.

The colorant system matters as much as the base resin. Verify the masterbatch carrier is compatible with ABS, the let-down ratio is within supplier limits, and the colorant has enough heat resistance for the actual melt temperature. A temporary run with 100% virgin material and no regrind can separate material sensitivity from tooling or process causes.

Also check dryer dew point; wet base resin or colorant can hydrolyze and yellow during processing. If the discoloration disappears under lower melt temperature and correct moisture, the correction is material and process related rather than mold repair.

**status:** suggested
**Author:** Grace Sun
**Date:** 2026-11-03

### Answer 4

Before making a process or tooling change, define how the defect relates to the customer’s surface specification. For black ABS housings, a brown streak on an exposed A surface is usually rejectable, but the same mark on a hidden rib or inside face may be acceptable under an appearance class.

Review the drawing, texture standard, gloss level, and any cosmetic boundary samples. If the part will be painted, plated, or laser marked, the stained surface may also affect adhesion, hiding, or mark contrast, so the decision cannot be based on color alone.

If dimensional results are still in tolerance, this is largely an appearance and field-acceptance risk rather than an immediate fit or function failure. Still, unauthorized surface degradation near the gate may indicate overheated material and could create local brittleness over time.

For containment, sort parts by cavity and visible area, keep retain samples, and define clear pass/fail inspection under the same lighting the customer will use. Do not rework textured cosmetic surfaces by polishing. If only hidden areas are affected, request a temporary deviation in writing before shipping; otherwise, quarantine the suspect stock.

**status:** suggested
**Author:** Nathan Guo
**Date:** 2026-11-03

### Answer 5

Local discoloration near the gate and vent area is often related to the machined condition of the mold. Vent depth may look acceptable but can be uneven because of tool wear, hand polishing, or chatter during machining. Measure the vent land with a pin gauge at multiple points rather than checking only at the edge.

A shallow section can compress gas and create a hot spot that oxidizes the polymer and leaves a brown stain. The gate land surface finish also matters: rough machine marks can trap degraded material and make the problem reappear quickly.

If the mold was repaired or re-machined recently, compare the actual gate diameter, land length, and vent depth against the tool drawing. Re-cutting the vents to the correct depth and angle may resolve a cavity-specific stain without changing the molding process.

Any modification should be followed by a full cavity-by-cavity first article check, including part weight and dimensions, because changing gate geometry or venting can affect fill balance and part size. Do not polish out the defect unless you can preserve the required surface texture and verify the dimensional result.

**status:** suggested
**Author:** Irene Tang
**Date:** 2026-11-03

### Answer 6

This problem needs structured data collection before more trial and error. Create a simple log for 50 consecutive shots recording cavity number, time, shot count, defect location, and pass/fail.

Plot the results by cavity and by time. A time-related pattern after startup or idle points to residence time or hot runner buildup.

A stable cavity-specific pattern points to venting, gate condition, or fill imbalance. Without this separation, the team will keep changing both process and tooling and not know which change worked.

After the data identifies the pattern, use containment by sorting suspect lots and labeling each box with machine, time, cavity, and inspector. A Pareto chart will usually show whether two or three cavities create most of the loss. From there, change one major variable at a time, such as front zone temperature or screw speed, and define a pass criterion before the trial.

Update the control plan and PFMEA with the verified process window, purge procedure, regrind limit, and vent inspection frequency. Long-term yield improvement comes from locking the correction into standard work, not from relying on operator memory.

**status:** suggested
**Author:** Evan Qian
**Date:** 2026-11-03

### Answer 7

Look at actual melt temperature and material residence time. Setpoint is not the same as actual melt temperature, especially with shear heating from high screw speed or high back pressure. If the shot weight is small compared with barrel capacity, the material may sit too long and degrade even at a normal barrel setting.

Reduce the front zone by 5–10°C, lower screw rpm to the supplier range, and reduce back pressure to limit shear heat. Maintain a consistent cushion in the 3–6 mm range, and check that excessive decompression is not pulling air into the melt, which can oxidize material and create yellow streaks.

Hot runner temperature should be checked separately from the barrel. A hot nozzle or manifold zone can degrade material locally and release discolored material intermittently, which matches the pattern of some good shots followed by defective ones.

If the defect appears after idle, purge until the purge is clean and stable before making good parts. Also check injection velocity through the gate.

An undersized gate with high velocity can cause diesel-effect burning and brown marks near the gate. Slow the fill through the gate while monitoring pressure, then restore a controlled process window after the correction.

**status:** suggested
**Author:** Claire Ren
**Date:** 2026-11-03

### Answer 8

From a design-for-manufacture view, the near-gate brown streaks should trigger a review of gate size, gate type, and wall thickness transition. A gate that is too small for the material and shot weight creates high shear and local temperature rise, degrading the polymer or colorant exactly where the discoloration appears.

Calculate shear rate and compare it with the material supplier’s maximum recommendation. A thin wall section feeding into a thicker area can also create flow hesitation and stagnation, which lets material degrade and release later as brown streaks.

If the tool is already built, use short shots and cavity pressure data to confirm fill balance before changing gate geometry. Widening the gate or adding a radius at the gate entrance can reduce local degradation, but it may also change gate vestige, packing, and part dimensions.

Any gate or runner change should be reviewed as an engineering change, followed by dimensional validation and a cosmetic boundary sample run. Air traps predicted near the vent areas should be compared with the actual defect locations, because adding a vent or improving an existing vent may be a lower-risk fix than changing the process.

**status:** suggested
**Author:** Owen Jiang
**Date:** 2026-11-03

## Related Resources

- [Injection Molding Q&A](https://www.hyneu.com/questions/injection-molding/)
- [Plastic Injection Molding](https://www.hyneu.com/capabilities/injection-molding/)
- [Injection Molding Buying Guides](https://www.hyneu.com/buying-guides/injection-molding/)
- [Injection Molding Guide](https://www.hyneu.com/guides/injection-molding/)
- [Custom Manufacturing](https://www.hyneu.com/custom-manufacturing/)
- [Products](https://www.hyneu.com/products/)
- [Manufacturing Defects](https://www.hyneu.com/knowledge/manufacturing-defects/)
- [Mold & Tooling](https://www.hyneu.com/knowledge/mold-tooling/)

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        "text": "I am currently holding a batch of black ABS control panel housings because of intermittent discoloration on the cosmetic side. The parts show brownish streaks near the gate, and some cavities have yellow-brown patches around venting areas after roughly four hours of continuous production. Dimensional checks are still inside tolerance, but the appearance is not acceptable under normal customer inspection. Our shift team has already adjusted barrel temperature and purged several times, but the discoloration keeps returning. I need to understand why injection mold discoloration occurs, not just read a generic defect list. There is also visible brown deposit on the mold surface near the hot runner gate and along some venting channels. I am not sure whether the deposit is transferring to the part, or whether the material is degrading inside the hot runner and then staining the tool. The most confusing point is that the defect is not on every cavity and not on every shot. Some shots look clean, then a run of parts shows a light yellow streak in the same area. I have to decide tonight whether we can continue running with increased visual inspection, rework the affected parts, or stop the tool for cleaning and maintenance. What specific checks should I do first? What process settings, tooling measurements, or material tests would help me separate resin degradation, contamination, and mold surface staining before we commit to a correction? If we block only the affected cavities, what evidence do I need to support that decision?",
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            "text": "The first issue to clarify is that “injection mold discoloration” can mean two different conditions: color shift on the molded part, or staining/discoloration on the mold surface itself. In your case, both are present. Brownish streaks near the gate and yellow-brown patches around venting areas are usually not a uniform resin color change. They point to local material degradation, gas venting, or tool surface contamination. Separate whether the discoloration is occurring in the melt or on the tool surface. The decision path is different for each one. Start by mapping the defect. Record cavity number, shot count, time after startup, hot runner drop, and whether the mark appears consistently or randomly. If discoloration appears in all cavities, especially after a short idle period, focus on barrel temperature, residence time, hot runner temperature, and material lot. If it appears only in specific cavities near the gate or vent, focus on tool surface condition, vent depth, gate insert wear, and local flow restriction. The fact that some shots look clean and then a run of parts shows a light yellow streak in the same area often means degraded material is being released intermittently from a dead spot or a contaminated gate detail. Material degradation is the most common cause of brown or yellow streaks. Check the barrel temperature profile against the resin datasheet, but do not rely only on set values. An infrared probe or manual melt check may show actual melt temperature is higher than the controller indicates. Long residence time is often hidden: if shot weight is only a small fraction of barrel capacity, material sits in the barrel too long. High screw rotation speed, high back pressure, or a worn screw can also add shear heat. Degraded polymer, additives, or colorant will produce yellow to brown or black streaks. If the hot runner manifold has a dead zone, material can degrade there and release later, producing intermittent marks. Corrective actions include lowering the front zone temperature by 5–10°C, reducing back pressure, setting screw rpm within the resin supplier’s range, and purging with a commercial purging compound until the purge is clean and stable. Contamination should be checked next. Residue from a previous material, colorant, or purge compound can remain in the hopper, feed throat, screw channels, check ring, nozzle, or hot runner. Moisture in ABS or colorant can cause hydrolysis and yellowish discoloration during processing. Check dryer dew point, drying time, and material lot variation. If the product is black ABS using masterbatch, confirm that the carrier resin is compatible with ABS and that the let-down ratio is within the supplier’s limit. Regrind above roughly 15–20%, especially if material has already seen multiple heat cycles, can increase yellowing. A temporary trial with 100% virgin material is one way to separate material-related causes from mold-related causes. The mold surface itself can create or transfer discoloration. Brown deposits near the gate and venting channels are often baked-on gas residue, degraded material, or corrosion. Gas burns occur when air or volatile gas is compressed in a blind pocket, and the resulting heat oxidizes the polymer. Vent depth and land length should be checked with a feeler gauge, and the depth must match the material supplier’s recommendation. ABS may call for a relatively shallow vent, but if the vent is too shallow, worn, or blocked, local burning and discoloration will continue. Inspect the gate insert under magnification. A pitted, rough, or worn gate detail can hold material, create local shear, and cause brown streaking. Clean the mold with an approved mold cleaner and brass or copper tools only. Steel scrapers can damage plating, polished surfaces, and vent edges, making the problem worse. For tonight’s decision, collect evidence before changing everything. Take labeled samples of good and defective parts by cavity and shot sequence. Photograph the defects and the corresponding mold areas. Check the actual temperature profile, shot size, cushion, cycle time, material lot, dryer dew point, and regrind percentage. Inspect each vent and gate with a flashlight and magnification. If the defect is cavity-specific, clean those cavities and run 20–30 short cycles. If the stain returns quickly, the tooling needs vent re-machining or gate insert repair, not just wiping. If the defect appears in all cavities, stop and correct the process or material before making more suspect stock. Use a simple containment decision. Residence time, local venting, and gate condition are the three factors that most often explain intermittent near-gate discoloration. If all cavities are affected, do not continue production. If only one or two cavities are affected and the remaining cavities are stable, you may block those cavities temporarily, but only after documenting the cavity number, cleaning the tool, and verifying that the remaining cavities produce acceptable parts. Affected parts should be quarantined. Do not ship them as first quality without a formal deviation, and do not assume that polishing will restore a textured cosmetic surface. After the immediate issue is controlled, correct the root condition. Re-machine or clean vents to the correct depth, repair or replace worn gate inserts, and verify vent land length and surface finish. Rebalance the hot runner if needed. Set a repeatable process window based on actual melt temperature, shot size, and screw speed. Validate the correction with a startup sequence and at least 30–50 consecutive shots. 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            "text": "The tool should be evaluated before any further process adjustment is made. Check the gate insert and vent surfaces under magnification, because brown deposits around those areas often indicate gas burning, material sticking, or plating wear. Measure vent depth with feeler gauges at several points across each cavity and record the values. A cavity that combines a shallower vent, a rough vent land, and discolored parts is a strong local root cause. Clean the deposit with a brass or copper tool and an approved mold cleaner. Do not use a steel scraper on polished steel, chrome plating, or textured surfaces, because even light scratching can create a new adhesion point for degraded resin. After cleaning, run a short trial and compare early shots with later shots. If the stain returns in the same cavity, the issue is not simply residue. Plan vent re-machining or gate insert replacement instead of repeated on-press wiping. Also check insert seating, parting line contact, and ejector clearance, because small clearance changes can alter gas escape and shift a defect from one cavity to another. Cavity-specific discoloration is usually a tooling and gas venting problem, and barrel temperature changes alone will not correct it.",
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            "text": "Check whether the material lot changed at the same time the defect appeared. ABS can vary between lots in thermal stability, moisture level, or additive package, especially with flame-retardant or high-flow grades. If this tool and process produced good parts before, do not assume the material is innocent. Pull the certificate of analysis, compare melt flow rate and moisture specification, and check pellet color under consistent light. Regrind ratio should also be confirmed. Repeated heat history above roughly 15–20% can lower thermal stability and produce yellow or brown tones. The colorant system matters as much as the base resin. Verify the masterbatch carrier is compatible with ABS, the let-down ratio is within supplier limits, and the colorant has enough heat resistance for the actual melt temperature. A temporary run with 100% virgin material and no regrind can separate material sensitivity from tooling or process causes. Also check dryer dew point; wet base resin or colorant can hydrolyze and yellow during processing. If the discoloration disappears under lower melt temperature and correct moisture, the correction is material and process related rather than mold repair.",
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            "text": "Before making a process or tooling change, define how the defect relates to the customer’s surface specification. For black ABS housings, a brown streak on an exposed A surface is usually rejectable, but the same mark on a hidden rib or inside face may be acceptable under an appearance class. Review the drawing, texture standard, gloss level, and any cosmetic boundary samples. If the part will be painted, plated, or laser marked, the stained surface may also affect adhesion, hiding, or mark contrast, so the decision cannot be based on color alone. If dimensional results are still in tolerance, this is largely an appearance and field-acceptance risk rather than an immediate fit or function failure. Still, unauthorized surface degradation near the gate may indicate overheated material and could create local brittleness over time. For containment, sort parts by cavity and visible area, keep retain samples, and define clear pass/fail inspection under the same lighting the customer will use. Do not rework textured cosmetic surfaces by polishing. If only hidden areas are affected, request a temporary deviation in writing before shipping; otherwise, quarantine the suspect stock.",
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            "text": "Local discoloration near the gate and vent area is often related to the machined condition of the mold. Vent depth may look acceptable but can be uneven because of tool wear, hand polishing, or chatter during machining. Measure the vent land with a pin gauge at multiple points rather than checking only at the edge. A shallow section can compress gas and create a hot spot that oxidizes the polymer and leaves a brown stain. The gate land surface finish also matters: rough machine marks can trap degraded material and make the problem reappear quickly. If the mold was repaired or re-machined recently, compare the actual gate diameter, land length, and vent depth against the tool drawing. Re-cutting the vents to the correct depth and angle may resolve a cavity-specific stain without changing the molding process. Any modification should be followed by a full cavity-by-cavity first article check, including part weight and dimensions, because changing gate geometry or venting can affect fill balance and part size. Do not polish out the defect unless you can preserve the required surface texture and verify the dimensional result.",
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          ,          {
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            "text": "This problem needs structured data collection before more trial and error. Create a simple log for 50 consecutive shots recording cavity number, time, shot count, defect location, and pass/fail. Plot the results by cavity and by time. A time-related pattern after startup or idle points to residence time or hot runner buildup. A stable cavity-specific pattern points to venting, gate condition, or fill imbalance. Without this separation, the team will keep changing both process and tooling and not know which change worked. After the data identifies the pattern, use containment by sorting suspect lots and labeling each box with machine, time, cavity, and inspector. A Pareto chart will usually show whether two or three cavities create most of the loss. From there, change one major variable at a time, such as front zone temperature or screw speed, and define a pass criterion before the trial. Update the control plan and PFMEA with the verified process window, purge procedure, regrind limit, and vent inspection frequency. Long-term yield improvement comes from locking the correction into standard work, not from relying on operator memory.",
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          ,          {
            "@type": "Answer",
            "text": "Look at actual melt temperature and material residence time. Setpoint is not the same as actual melt temperature, especially with shear heating from high screw speed or high back pressure. If the shot weight is small compared with barrel capacity, the material may sit too long and degrade even at a normal barrel setting. Reduce the front zone by 5–10°C, lower screw rpm to the supplier range, and reduce back pressure to limit shear heat. Maintain a consistent cushion in the 3–6 mm range, and check that excessive decompression is not pulling air into the melt, which can oxidize material and create yellow streaks. Hot runner temperature should be checked separately from the barrel. A hot nozzle or manifold zone can degrade material locally and release discolored material intermittently, which matches the pattern of some good shots followed by defective ones. If the defect appears after idle, purge until the purge is clean and stable before making good parts. Also check injection velocity through the gate. An undersized gate with high velocity can cause diesel-effect burning and brown marks near the gate. Slow the fill through the gate while monitoring pressure, then restore a controlled process window after the correction.",
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          ,          {
            "@type": "Answer",
            "text": "From a design-for-manufacture view, the near-gate brown streaks should trigger a review of gate size, gate type, and wall thickness transition. A gate that is too small for the material and shot weight creates high shear and local temperature rise, degrading the polymer or colorant exactly where the discoloration appears. Calculate shear rate and compare it with the material supplier’s maximum recommendation. A thin wall section feeding into a thicker area can also create flow hesitation and stagnation, which lets material degrade and release later as brown streaks. If the tool is already built, use short shots and cavity pressure data to confirm fill balance before changing gate geometry. Widening the gate or adding a radius at the gate entrance can reduce local degradation, but it may also change gate vestige, packing, and part dimensions. Any gate or runner change should be reviewed as an engineering change, followed by dimensional validation and a cosmetic boundary sample run. Air traps predicted near the vent areas should be compared with the actual defect locations, because adding a vent or improving an existing vent may be a lower-risk fix than changing the process.",
            "upvoteCount": 0,
            "url": "https://www.hyneu.com/questions/why-injection-molded-parts-discoloration-production.html#suggestedAnswer-8",
            "datePublished": "2026-11-03T15:31:36Z",
            "author": {"@type": "Person","name": "Owen Jiang","url": "https://www.hyneu.com/team/owen-jiang.html"}          }
                  ]
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