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How to prevent overheating with proper mould temperature controller settings?

2025/06/06 By Topstar

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When overheating occurs in injection moulding, it affects part quality and shortens equipment life. Mould temperature controller are the central system that regulates mould temperature during the injection cycle. By maintaining a precisely controlled thermal state, they ensure consistent part dimensions, avoid defects, and optimise cycle times. When mould overheating occurs, it is usually due to incorrect temperature setpoints, insufficient coolant flow, or improper control loop adjustment. As a result, the mould will be thermally unbalanced, causing the plastic to solidify too quickly to form hot spots. These hot spots not only reduce the surface finish of the part but also increase internal stress, causing premature wear and even damage to the mould.

Risk of overheating in mould temperature controller

Overheating usually comes from setpoints that are too high, improper coolant flow, or delayed control response. Additionally, fast cycle times and high injection pressures cause the heat generated in the mould to exceed the cooling system’s ability to dissipate it.

First, the injection moulding parameters will have a certain impact on the mould temperature, and the cooling channels must dissipate heat more quickly as the melt temperature increases. If the setpoint of the mould temperature controller is too close to or above the optimal solidification range of the polymer, the controller may struggle to maintain stability. As a result, the actual mould surface temperature may exceed the expected level, resulting in hot spots and local over-solidification. To avoid this, choose a mould temperature controller setpoint that reflects the polymer’s recommended processing window, typically 5-10°C below the material’s melting point, to ensure adequate heat dissipation without thermal stress.

Second, uneven temperature distribution can occur due to insufficient or inconsistent flow, which partially closed valves may cause, blocked cooling channels, or improperly sized pumps. As a result, some areas of the mould may not receive adequate cooling, prompting the mould temperature controller to increase the heater output to compensate, which in turn exacerbates overheating in other areas.

Optimal Mould Temperature Controller Temperature Settings

The mould temperature controller setpoint must be consistent with the processing requirements of the specific polymer, the thermal conductivity of the mould material, and the required cycle time. A temperature setting that is too low will prevent the polymer from filling properly, resulting in insufficient injection or premature solidification. Conversely, a temperature setpoint that is too high may cause the mould to overheat, resulting in flashing and other issues. Therefore, it is necessary to understand the range of polymer processing temperatures, for example, 20-40°C for crystalline materials, such as polypropylene, and 80-120°C for amorphous materials, such as ABS.

You should generally set the set point of the mould temperature controller near the middle of this range, as this ensures adequate flow for proper mould filling while preventing overheating. Second, consider the mould material and thickness. Steel moulds absorb and conduct heat more effectively than aluminium moulds. If using steel moulds with high thermal conductivity, you can set the temperature 5-10°C higher than the recommended minimum. Conversely, aluminium moulds tend to heat up and cool down faster; in this case, you can set the temperature a few degrees below the polymer’s midpoint to avoid local hot spots.

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Flow and coolant considerations

After setting the temperature point, ensure adequate coolant flow. Even if you set the mould temperature controller accurately, insufficient or uneven coolant circulation can still cause hot spots. First, use an in-line flow meter to measure the actual flow and pressure drop of the mould coolant circuit. Compare these measurements with the design requirements of the mould. If the flow rate is below the recommended threshold, the mould temperature controller may have difficulty maintaining a uniform temperature. In this case, you should consider installing a dedicated coolant pump with adjustable speed control so you can precisely adjust the flow rate to meet the unique needs of each mould.

Second, minimise air entrapment in the coolant circuit. Air pockets can significantly disrupt the flow and create localised temperature zones. To prevent this, the piping layout should be designed with a gentle slope and a high-quality vent valve installed at the highest point in the loop. Before production begins, open the vent valve to exhaust air from the system until the coolant flows steadily out. It is also necessary to ensure that there is no air in the coolant loop, which allows the mould temperature controller to maintain consistent temperature readings and avoid erratic heating caused by local temperature differences caused by air.

PID parameter optimisation to ensure temperature stability

The PID control loop in the mould temperature controller minimises temperature overshoot and ensures rapid recovery from thermal disturbances. Suppose the PID settings are not appropriately adjusted. In that case, it will cause oscillation, where the mould temperature repeatedly exceeds and falls below the set point, or it will be sluggish to respond and unable to offset rapidly changing heat loads.

To optimise the PID settings on the mould temperature controller, first, observe the mould at ambient temperature, apply the necessary changes, and then increase the set point moderately. Observe how quickly and accurately the temperature approaches the new set point. At the same time, increase P until the temperature response shows slight oscillations, and then reduce P by 10% to 20% to achieve a stable, slightly underdamped response. Next, the integral time can be gradually increased to minimise the steady-state error. If the temperature reaches saturation with no oscillations when it is slightly above or below the setpoint, the integral term is close to the optimum value. The last step is to introduce a small derivative time to dampen any rapid changes. You can repeat the above steps to fine-tune P, I, and D until the response becomes smooth.

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Take advantage of advanced control features

Topstar’s range of mould temperature controllers is equipped with a range of advanced features designed to prevent overheating further. In addition to basic PID control, these units often include features such as preheat scheduling, adaptive damping, automatic over-temperature alarms and remote monitoring.

Many moulds require a preheating phase before injection to ensure a uniform temperature distribution, especially for complex moulds or those with multiple materials. By programming a timed start-up preheating schedule directly into the mould temperature controller, heated coolant circulates through the mould at a low flow rate, gradually heating the tool. Ramping progressively up to the production set point minimises thermal shock and allows for uniform expansion of the metal.

Topstar equips its mould temperature controllers with an over-temperature alarm function to prevent uncontrolled temperature increases. When the temperature sensor in the mould detects a deviation exceeding a predetermined safety threshold, the controller triggers an audible and visual alarm on the machine interface to signal the injection moulding machine. This prevents the mould from reaching dangerously high temperatures. At the same time, under a unified control system, the mould temperature controller can be interconnected with the equipment, allowing for the remote monitoring of mould temperature in real-time. This enables the prevention of mould overheating and ensures production continuity.

Make appropriate settings to prevent overheating

Overheating poses a significant threat to injection moulding efficiency, part quality and mould life. Select set points based on polymer properties, mould materials, and geometric complexity. Ensure sufficient coolant pump capacity, adjust the PID, and utilise advanced functions to achieve robust and reliable thermal management. This approach prevents mould overheating, reduces scrap rates, and produces consistent, high-quality parts.

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