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How can I prevent material degradation by adjusting the molding machine barrel temperature?

2025/10/24 By le zhan

Improve Your Injection Molding Process with Barrel Temperature Shift Mode

Every year, many manufacturers waste 5-10% of their raw materials due to degradation, equivalent to significant resource losses for a medium-sized enterprise operating 24/7. Worse still, these manufacturers fail to realize that degradation is the root cause of part defects. As an injection molding machine manufacturer, I’ve found that 70% of degradation cases are due to a single, controllable factor: incorrect molding machine barrel temperature. Thermoplastics such as PP, PC, and ABS have a narrow “safe zone” within which they melt uniformly without decomposition. Even temperatures exceeding this range by 10°C can cause degradation, requiring precise temperature control to eliminate this risk.

What is Material Degradation? The Importance of Molding Machine Barrel Temperature

Material degradation refers to the molecular breakdown of thermoplastics during the injection molding process. This can result in discoloration, yellowing (common in PP or ABS), or black specks. It can also cause brittleness, resulting in easily broken parts, poor melt flow, and uneven viscosity, which can lead to short shots or flash. These issues are often caused by barrel temperatures that are too high or too low. Thermoplastics have a strict “processing window,” a temperature range within which they can fully melt without degrading. For example: PP: 170°C–220°C; PC: 260°C–320°C; ABS: 220°C–280°C.

Above these temperature ranges, heat breaks down the plastic’s molecular bonds. Below these temperatures, the plastic doesn’t fully melt and therefore remains in the barrel longer, subjecting it to heat for longer than expected. Topstar injection molding machines allow you to target this temperature range precisely, but you first need to determine the specific temperature range for your material.

What is Material Degradation

Step 1: Determine Your Material’s Processing Temperature

The first rule for preventing material degradation is to know your material’s processing temperature before you start molding. Guessing at the right temperature leads to waste. Here’s how to do this, and how Topstar molding machines simplify the process:

Check the material datasheet: Every resin supplier provides a “processing temperature range” for their product. Highlight the middle 50% of this range (e.g., for PP’s 170°C–220°C window, focus on 190°C–200°C) to avoid extremes.

Using Topstar Molding Machines: Topstar injection molding machines come with a built-in database of over 500 common thermoplastics (PP, PC, ABS, etc.) pre-loaded with processing temperatures. Select your material, and the molding machine automatically sets the starting barrel temperature, eliminating manual guesswork.

Small-batch test: Run 10-20 parts at a preset temperature. Inspect for signs of degradation. If the parts appear clean, maintain the range. If not, adjust in 5°C increments.

One packaging customer using a Topstar injection molding machine to produce PP lids initially skipped this step and set the temperature to 225°C. They discovered a 12% scrap rate due to the yellowing of the lids. After loading Topstar’s PP at the preset temperature (195°C) and testing, the scrap rate dropped to 1.5%.

Step 2: Zone-by-Zone Barrel Temperature Adjustment

The barrel of molding machines doesn’t have a single temperature zone. Instead, it’s divided into three to five zones (feed zone, compression zone, metering zone, and sometimes a nozzle zone), each requiring a different temperature to prevent degradation. Topstar’s injection molding machines allow you to adjust each zone independently, a key feature that’s lacking in cheaper machines. The settings for each zone are as follows:

  1. Feed Zone: Cooling to prevent “bridging”
    Goal: Keep the resin solid before entering the compression zone. Excessive heat here can cause premature melting, adhesion to the barrel, and degradation.
    Setting: 10°C to 20°C below the metering zone temperature.
  2. Compression Zone: Gradual Heating
    Goal: Evenly melt the resin and avoid overheating and sudden temperature jumps.
    Setting: 5°C to 10°C below the metering zone temperature.
  3. Metering Zone (near the nozzle): Peak Temperature
    Goal: Completely melt the resin and achieve smooth flow. This is the only area where the material’s processing limits are reached.
    Setting: The middle value of the material’s processing window.
  4. Nozzle Zone: Sync with Metering Temperature
    Goal: Prevent “drooling” and maintain a stable melt temperature. Too high a temperature will cause the resin to degrade in the nozzle; too low a temperature will cause the resin to solidify.
    Setting: Same as the metering temperature (195°C) or 5°C lower (190°C).
Injection molding machine barrel

Step 3: Monitor Material Dwell Time in the Barrel

Even with ideal zone temperatures, excessive dwell time in the barrel can lead to material degradation. This is common during production pauses or when the shot size is small relative to the barrel capacity. Here’s how to manage this with a Topstar injection molding machine:

Calculate Maximum Dwell Time: Check the “Maximum Allowable Dwell Time” on the material datasheet; for example, 8 minutes for ABS and 10 minutes for PP.

Set a Topstar Dwell Time Alarm: The injection molding machine tracks the dwell time, or the time the material remains in the barrel. If a set limit (e.g., 8 minutes) is exceeded, an audible/visual alarm sounds, and a small amount of resin is automatically purged to refresh the barrel.

Purge on Demand: If the dwell time exceeds the limit, purge 1-2 shots of resin to remove degraded material. Never leave old resin in the barrel.

Step 4: Calibrate the Molding Machine’s Temperature Sensor

Even the best regional settings can be ineffective if the molding machine’s temperature sensor is inaccurate. Over time, the sensor drifts due to heat and vibration, so the machine may report a temperature of 195°C when the barrel is actually 205°C. The Topstar injection molding machine addresses this issue with a built-in calibration tool:

Access the calibration menu: Navigate to “Tools > Temperature Calibration” on the machine’s touchscreen.

Use a certified thermocouple: Connect a handheld, NIST-certified thermocouple to the barrel to measure the actual temperature.

Adjust the sensor offset: If the machine reading is 5°C higher than the thermocouple, set a -5°C offset in the menu. Topstar saves this calibration value for future runs. We recommend calibrating your sensors every three months. A quick calibration, which takes just 15 minutes, can prevent costly performance degradation.

Molding Machine 9

Injection Molding Machine Temperature Regulation: The Top Solution for Material Degradation

Material degradation isn’t a costly factor in the injection molding process. By determining material temperature, precisely adjusting barrel zones, monitoring dwell time, and calibrating sensors, you can reduce scrap and save thousands of dollars annually. All Topstar injection molding machines are designed to simplify these steps—with material presets, independent zone control, dwell time alarms, and built-in calibration tools—you can spend less time troubleshooting and more time producing high-quality parts.

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