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Home / Guide to PID control Mold temperature controller: Fix Low-Temperature Dead Zones in Cold Runner Injection Molding

Guide to PID control Mold temperature controller: Fix Low-Temperature Dead Zones in Cold Runner Injection Molding

2025/12/10 By le zhan

Low temperature dead zone in injection molding 2

A car interior parts manufacturer was struggling with problems with cold-runner injection molds. Their products suffered from defects such as shrinkage marks, short shots, and uneven wall thickness, all stemming from “low-temperature dead zones” in the runner system, where the temperature is 15-20 degrees Fahrenheit below the set value. Their traditional on/off mold temperature controllers were simply ineffective, often leading to overheating to repair cold spots, followed by overheating and new defects.Topstar’s PID control mold temperature controller effectively solved this problem. Within two weeks of installation, the dead zone disappeared. The scrap rate plummeted to 3%, and the controller reduced energy consumption by 10% by precisely regulating heat output, eliminating waste caused by overheating. Therefore, we will explain in detail how the PID control mold temperature controller eliminates dead zones, improves efficiency by 10%, and ensures temperature stability.

What are low-temperature dead zones in injection molding, and why do they damage parts?

Before addressing low-temperature dead zone problems, you need to understand what they are and why traditional mold temperature controllers cannot handle them. In cold-runner injection molding, the runner is the network of channels that convey molten plastic into the mold cavity. To ensure proper part molding, the runner temperature must be maintained within a strict set temperature range, typically ±1°F. A low-temperature dead zone is an isolated area in the runner that cools below the set temperature range, even if the rest of the system remains warm.

These dead zones are primarily caused by three factors:

  1. Poor heat distribution: Cold runners often have complex geometries, such as sharp bends, thin walls, or areas far from heating elements.
  2. Ambient temperature fluctuations: Temperatures in a factory workshop can vary by 10-15°F between shifts, causing exposed parts of the runner system to cool down.
  3. Ineffective temperature control: Traditional “on/off” mold temperature controllers work like a household oven—they heat rapidly to the set temperature, then shut off completely. By the time they are restarted, a cold spot has formed.

How does the PID algorithm in a mold temperature controller eliminate dead zones?

PID stands for Proportional, Integral, and Derivative—the controller uses these three mathematical “tools” to maintain a stable temperature. Unlike on/off controllers that operate in extreme conditions, PID-controlled mold temperature controllers progressively adjust heating output based on real-time data. This precision eliminates dead zones and reduces energy waste by 10%—here’s how each component works:

  1. Proportional (P): Corrects Current Temperature Error

The “P” component adjusts the heating output based on the difference between the actual and set temperatures. If the runner temperature is 5°F lower, the controller increases the heating power—but only enough to compensate for the temperature difference, not at full power. For example, if the set temperature is 350°F and the dead zone temperature drops to 340°F, the PID controller will increase the output by 10%, rather than jumping directly to 100% as an on/off controller would.

  1. Integral (I): Eliminates Persistent Cold Spots

Some dead zone temperatures are “stubborn,” remaining low even with minor heating adjustments. The “I” component tracks the duration of the error and slowly increases heating until the dead zone temperature rises. If the temperature at the runner bend remains below 2°F for 60 seconds, the PID controller will gradually increase heating until the temperature stabilizes.

  1. Derivative (D): Preventing Overheating

The “D” component predicts future temperature changes by observing the rate of temperature change. If the dead zone temperature rises from 340°F to 348°F within 5 seconds, the controller will reduce heating power prematurely, thus avoiding temperature overshoot problems common in switching systems. This not only maintains temperature stability but also reduces energy consumption.

PID control mold temperature controller

Step-by-Step Setup to Address Cold Runner Dead Zone Issues

First, determine the location of the dead zone by scanning the runner during mold operation, looking for areas where the temperature is more than 5°F below the set value—these are the target temperatures. Mount one RTD sensor on the mold’s heating element and a second sensor directly on the dead zone. For hard-to-reach locations, use a flexible sensor probe. Avoid placing sensors near cooling pipes, as this can lead to inaccurate readings.

Then turn on the PID control mold temperature controller and enter your set value (e.g., 350°F). Press the “Auto-Tune” button—the controller will run a 5-10 minute test, gradually heating and cooling to learn the mold’s characteristics. Once complete, it will display the optimal P, I, and D values. For cold runners, the P value is expected to be between 5 and 10, the I value between 60 and 120 seconds, and the D value between 5 and 15 seconds. Then run the mold for 30 minutes using the new settings. Recheck the thermal imager; the dead zone temperature should be within ±1°F of the set temperature. If a region is still too cold, adjust the I value (increase it by 20 seconds) so the controller continues heating for a longer period. If overheating occurs, increase the D value (increase by 5 seconds) to predict temperature peaks earlier.

Real-world Application Cases of Cold Runner Molding Processes

While data is essential, real-world case studies from manufacturers better demonstrate how PID control mold temperature controllers are revolutionizing cold runner molding processes. Below are three case studies from Topstar customers, covering the automotive, medical, and consumer goods industries:

Case 1: Automotive Components

Problem: Cold-runner dead zones resulted in 15% scrap; to compensate, production cycles increased by 8%. Solution: Topstar PID-controlled mold temperature controller. Results: Scrap rate reduced to 3%; production cycles returned to normal; energy savings of 10%. Case 2: Syringe Housing

Challenge: FDA rejection due to inconsistent wall thickness (caused by ±2°F temperature fluctuations); traditional controllers could not maintain uniformity. Solution: Use a mold temperature controller with data logging capabilities. Result: Temperature uniformity improved to ±0.5°F; FDA rejection rate decreased from 7% to 0.3%.

Case 3: Toy Components

Challenge: Seasonal production stoppages; scrap rate as high as 12% in the fourth quarter. Solution: Use a mold temperature controller with adaptive tuning and ambient temperature compensation. Result: Annual scrap rate remained below 2%; no need to adjust setpoints between seasons.

Injection molded automotive parts 1-1

PID Control Mold Temperature Controller Better Solve Cold Runner Dead Zones

Low-temperature dead zones in cold-runner injection molding not only affect product quality but also cause financial losses. Traditional on/off mold temperature controllers cannot meet the complex temperature requirements of cold runners, leading to increased scrap rates, longer production cycles, and energy waste. PID control mold temperature controllers use precise predictive technology to eliminate dead zones, improving efficiency by 10% and completely solving this problem.

 

 

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