Why Injection Molded Parts Degrade

Plastic degradation is a common headache in the 사출 성형 industry. Whether it appears as burn marks, discoloration, or brittleness, degraded plastic compromises the quality and strength of your final product.

But what exactly causes this issue? Usually, the culprits fall into three categories: The Machine, The Mold, 또는 The Material.

In this guide, we break down the root causes of plastic degradation and provide actionable solutions to help you optimize your production process.

Often, degradation happens because the plastic is subjected to excessive heat or stays in the barrel for too long. Here is how to troubleshoot machine-related problems:

A. Excessive Heating in the Barrel

The Problem: The plastic melt temperature is set too high, causing the polymer chains to break down.
The Solution: Lower the melt temperature settings. Ensure the temperature profile matches the specific requirements of the resin you are using.

B. Malfunctioning Temperature Controllers

The Problem: The temperature controller may be reading incorrectly or failing to regulate the heat properly.
The Solution: Verify that the controller is monitoring the correct zone of the barrel. Recalibrate the temperature controller and inspect the heating bands for stuck relays or loose connections.

C. Incorrect Thermocouple Type

The Problem: Using a thermocouple type (e.g., J-type vs. K-type) that does not match the controller's configuration leads to false temperature readings.
The Solution: Check that the installed thermocouples match the type specified by the controller manufacturer (e.g., FECON). Test all thermocouples to ensure they are functioning accurately.

D. Excessive Residence Time

The Problem: If the shot weight is too small for the machine size, plastic sits in the barrel too long and degrades.
The Solution: Check your shot weight. If it is less than 25% of the machine's maximum injection capacity, move the mold to a smaller machine.
- 참고: If a smaller machine is unavailable, reduce the barrel temperatures to the minimum viable limit to produce acceptable parts.

E. Material Stagnation During Stops

The Problem: Leaving plastic inside the barrel during production pauses or shutdowns allows it to bake and degrade.
The Solution: Always purge and clean the barrel before stopping production. Leave the screw in the forward position to prevent material from sitting in the heating zones.

F. Material "Hang-ups" in the Barrel

The Problem: Plastic can get trapped in scratches or damaged areas inside the barrel (often near the non-return valve), eventually degrading and breaking off into the shot.
The Solution: Inspect the barrel interior thoroughly. Remove any residue or buildup on the mating surfaces and check for mechanical damage.

While less common, mold specifications can indirectly contribute to degradation issues.

A. Mold Capacity Mismatch

The Problem: Similar to the machine issue, if the mold requires a shot size that is too small for the available machine, it leads to long residence times.
The Solution: Relocate the mold to an injection molding machine with a smaller shot capacity that better matches the part weight.

Sometimes the defect starts before the plastic even enters the machine.

A. Excessive Moisture Content

The Problem: Many engineering plastics (like Nylon, PET, PC) are hygroscopic. High moisture content causes hydrolysis, leading to degradation and splay marks.
The Solution: Implement a strict drying regimen. Use the correct hopper dryer settings (temperature and time) recommended by the material supplier.

B. Poor Quality or Contaminated Regrind

The Problem: Using regrind (recycled scrap) that contains dust, metal contaminants, or has been heat-damaged previously will ruin the new batch.
The Solution: Strictly separate and inspect regrind materials. Filter out impurities and limit the percentage of regrind mixed with virgin material.

Summary Checklist

To prevent plastic degradation, remember these key takeaways:

Monitor Temperatures: Ensure controllers and thermocouples are accurate.
Match Machine to Part: Avoid running small parts on massive machines.
Cleanliness is Key: Purge the barrel when stopping and keep regrind clean.
Dry Your Material: Never skip the drying process for hygroscopic resins.

By systematically checking these areas, you can eliminate degradation defects and improve your overall yield.

저자 소개

Alex Yu

아이디얼 프로 매뉴팩처링

알렉스는 Ideal Pro의 공동 창립자이지만, 주요 프로젝트를 총괄하거나 기술 팀을 이끌지 않을 때는 장거리 자전거 타기를 즐기거나, 동네에서 가장 맛있는 커피를 찾아다니거나, 다음 여행 계획을 세우는 모습을 볼 수 있습니다. 국제 무역 영업과 프로젝트 관리 분야에서 20년 이상의 경력을 쌓아온 그는 촉박한 마감 기한부터 까다로운 엔지니어링 문제까지, 그 사이의 모든 상황을 다 겪어보았습니다. 그는 훌륭한 성과는 충분한 휴식을 취한 마음과 맛있는 커피에서 나온다고 믿으며, 맡은 모든 프로젝트에 그와 같은 호기심과 세심한 주의를 기울입니다. 사무실에 있지 않을 때는 대개 야외 어딘가에서 새로운 장소를 탐험하며, 나중에 나눌 이야기를 수집하곤 합니다.