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When Does Uneven Mould Temperature Require a Different Control Configuration?

2023/04/27 By Topstar

When Does Uneven Mould Temperature Require a Different Control Configuration

A stable reading on the mould temperature controller does not necessarily indicate that the mould temperature is uniform. The screen value reflects the temperature at a specific sensor location, while conditions inside the mould depend on circuit flow rate, runner layout, localised heat loads, and heat transfer performance. Consequently, even if the circulating medium temperature remains close to the setpoint, temperature variations may still occur across different parts of the mould. Before adjusting the temperature settings, a more prudent approach is to verify the measurement data, inspect each circuit and address the root causes of the uneven mould temperature.

What causes uneven mould temperature during production?

Mould temperature control involves both regulating the circulating medium and transferring heat through the mould (tooling). Various issues may arise between these two stages. First, distinguish between ‘the values measured by the controller’ and ‘the actual conditions inside the mould’, then investigate why thermal control effectiveness varies across different areas.

What causes uneven mould temperature during production

Why do stable readings from the mould temperature controller not prove that the mould temperature is uniform?

The controller regulates the temperature based on signals fed back from sensors. Depending on the equipment type, the sensor may monitor the temperature of the supply water, return water, or an external measurement point. Before interpreting the displayed values, confirm the sensor’s specific location.

Sensor readings cannot reflect the specific conditions within every cavity, core or on the mould surface. Heat must transfer between the circulating medium and the mould; the distance between the cooling channels and areas with high heat loads directly affects the local temperature in those areas.

For example, suppose the mould temperature controller maintains the water temperature at a stable 80°C, but a local blockage in the cooling channel for a particular cavity reduces flow at that point. In this case, the controller’s screen may show a stable value, yet that cavity’s heat dissipation efficiency has already decreased. The setpoint alone cannot detect such a blockage in the cooling channel.

‘Temperature control accuracy’ and ‘mould temperature uniformity’ are two distinct performance indicators. You must check both aspects simultaneously before concluding that the thermal processing is stable.

How does uneven flow in the circuit affect mould temperature control?

In a parallel circuit, the flow rate in each circuit does not automatically remain equal. Differences in channel length, diameter, fittings, valve positions, and internal conditions can create varying resistance in each circuit. When a branch becomes obstructed, the circulating water may be redistributed towards other branches with lower resistance. Consequently, although the total flow rate may appear normal, a specific circuit may still have insufficient flow.

Please check the filters, hoses, fittings and mould runners for blockages or obstructions. Trapped gas may impede circulation, while deposits may narrow the channels, reducing heat-transfer efficiency. After replacing a mould, it is essential to check all connections; particular care must be taken if the supply and return hoses look similar, to avoid confusion.

A mould temperature controller cannot fully compensate for the shortcomings caused by an ill-designed runner layout. If the root cause is not identified, simply increasing the pump output or adjusting the set temperature will not only fail to resolve the issue of the hottest areas but may also lead to temperature deviations in other areas.

How does uneven flow in the circuit affect mould temperature control

How can one identify and correct issues of unevenness?

Adopt a repeatable inspection procedure rather than making multiple adjustments simultaneously. Record thermal conditions and cycle status, identify where deviations occur, and test each corrective measure individually. This helps to distinguish between ‘maintenance issues’ and ‘problems caused by the inherent limitations of the equipment or the mould itself’.

How can one identify and correct issues of unevenness

Which measurement parameters help diagnose problems with mould temperature controllers?

Start measurements only after the process has reached a repeatable operating state. Ensure the material, cycle settings, cooling water supply, and measurement timing remain consistent to ensure comparative results are meaningful.

Take temperature measurements at fixed points on the mould and at the same stage of the process cycle. If using infrared measurement instruments, account for surface reflection and measurement settings; inconsistent operating techniques can produce misleading variations in the data.

Analyse temperature differentials alongside flow rates. A significant temperature difference between the supply and return water may indicate high heat exchange, insufficient flow, or both. Conversely, a small temperature difference does not directly prove that cooling is effective. As an initial check, compare current readings with data from previous production runs where performance was satisfactory. Subsequently, inspect any abnormal circuits, rectify connection issues or clear blockages in the pipework, and repeat the measurements.

Which measurement parameters help diagnose problems with mould temperature controllers

Addressing Non-Uniformity Through Targeted Adjustments

If you can restore normal performance by ensuring correct connections, cleaning the runners, and improving venting, you don’t need to replace the mould temperature controller. If the problem persists, assess whether the pump performance matches the circuit resistance and verify that the cooling capacity meets the actual thermal load requirements. Generally, you cannot achieve both maximum flow rate and maximum pressure simultaneously. When different areas of the mould require different temperature settings, independent zone control may be helpful; however, this approach cannot resolve issues such as blocked runners or an inefficient runner layout.

Topstar’s mould temperature control technology includes flow rate monitoring and gas-liquid separation and offers single-zone or dual-zone configurations, depending on the model. Before selecting a model, please provide the operating temperature, circuit layout, required flow rate, cooling water conditions and specific issues encountered during production. To resolve uneven mould temperature, one should first verify the measurement data and circulation conditions; subsequent configuration adjustments should be optimised to address the limitations identified during these checks.

 

 

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