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Why Do Thick-walled Parts Need Higher Mold Water Flow?

2026/09/07 By le zhan

Why Do Thick-walled Parts Need Higher Mold Water Flow

For thick-walled parts, mold temperature control is more than reaching a set temperature. Rather, it involves removing and redistributing large amounts of heat while keeping the mold surface uniformly temperature throughout each molding cycle.

Compared to thin-walled parts, thick-walled plastic products contain more molten material per unit area. As a result, more heat accumulates in the core areas, and solidification takes longer. If the mold water flow rate is insufficient, the cooling water rapidly absorbs heat as it flows through the runner, increasing the inlet-to-outlet temperature difference. This causes different areas of the mold to operate at different temperatures, thereby prolonging cooling time and increasing the risk of shrinkage, sink marks, warpage, or dimensional inconsistencies. For this reason, high-flow mold temperature controllers are required for mold temperature control in automotive parts and other thick-walled injection molding applications.

Thick-walled parts require higher mold water flow rates to continuously remove more heat

The main reason thick-walled parts require higher water flow rates is that more material means more accumulated heat must be removed before the part can be safely demolded.

During the injection molding cycle, the temperature of the molten polymer entering the cavity is much higher than the mold temperature. Heat then transfers from the plastic to the mold steel, and then from the mold to the circulating water.

From a simple heat balance perspective:

Heat removed = mass flow rate of water × specific heat capacity × temperature rise of water.

This relationship explains the importance of water flow rate. If the mold has a high heat load but the water flow rate is low, each unit of circulating water must absorb more heat. Consequently, the water’s temperature rise as it flows through the mold increases, leading to a corresponding increase in the temperature difference between the incoming and returning water. Increasing the flow rate means more water flows through the mold in the same amount of time. Under the same heat load, this typically reduces the temperature rise per unit of water and brings the cooling-channel temperature closer to the set target value.

Thick-walled parts require higher mold water flow rates to continuously remove more heat

Thick-walled parts accumulate heat deep within the component

Thin-walled parts dissipate heat relatively quickly because the distance between the material center and the mold surface is short. In thick-walled parts, the center is farther from the cooling cavity wall. Even after the outer layer begins to solidify, the center may remain hot for an extended period.

This creates the following temperature gradient:

Hot center → Solidifying intermediate layer → Cooler mold surface → Circulating cooling water

Even if the part’s surface appears solidified, the cooling system must continue removing heat. If the water circulation cannot handle this sustained heat load, the mold temperature will gradually rise. In this situation, the manufacturer may have to extend the cooling time before demolding.

Increasing the mold cooling water flow rate helps the mold temperature controller remove heat continuously, preventing it from accumulating inside the mold.

Thick-walled parts accumulate heat deep within the component

Thick-walled parts require high flow rates to reduce mold temperature differences

Cooling capacity alone is not enough; you must also consider temperature distribution.
Consider a long mold cooling circuit: the cooling water entering the runner is relatively cool and continuously absorbs heat as it flows through the mold. If the flow rate is too low, the outlet water temperature may be significantly higher than the inlet temperature.

This temperature difference leads to uneven mold temperatures. One part of the cavity may cool faster, while another remains hotter. For thick-walled parts, this unevenness has a significant impact, as the cooling phase accounts for a large proportion of the molding cycle.

The resulting effects include:

  • Uneven shrinkage;
  • Sink marks;
  • Warping;
  • Extended demolding time;
  • Dimensional deviations.

Increasing the flow rate can reduce the temperature difference as cooling water flows through the circuit, helping maintain a more uniform mould temperature. Therefore, increasing the mold water flow rate is not merely about increasing cooling-water volume; it is about establishing stronger, more uniform heat-transfer conditions throughout the entire mold.

Reducing Cooling Bottlenecks in the Production of Thick-Walled Parts

For many thick-walled parts, injection molding and mold movements are not the most time-consuming stages of the production cycle; instead, cooling is often the bottleneck that affects production efficiency.

Consider a thick-walled automotive component: if it requires a long cooling time before demolding to ensure sufficient rigidity, increasing injection speed will have little effect on shortening the total production cycle. A high-flow mold temperature controller helps the mold return to the required temperature more quickly after each injection. When mould cooling becomes more efficient and uniform, you can reduce unnecessary cooling time while ensuring product quality.

Design of Topstar’s Ultra-High-Flow Mold Temperature Controllers

Because thick-walled products generate higher and longer-lasting thermal loads, traditional mold temperature controllers often struggle to meet the circulation flow rates required for large molds or demanding automotive manufacturing applications.

Topstar’s high-flow mold temperature controllers emphasize high-flow water circulation technology rather than relying solely on increased heating or cooling power. Their technical configuration focuses primarily on three key areas: high-flow circulation, rapid cooling water replacement, and protection of electrical components. (Click here for specific mold temperature controller technology details.)

Vertical Multistage Centrifugal Pumps Provide a Stable, High-Flow Water Stream for Thick-Walled Product Molding

A core component of a high-flow mould temperature controller is a vertical multistage centrifugal pump. Its primary function is to deliver a stable, high-flow water stream to the mold’s cooling channels. For large molds, this is critical for two reasons:

First, cooling channels generate flow resistance. Long flow paths, pipe fittings, manifolds, and multiple mold cooling channels all increase the pressure the pump must overcome.

Second, thick-walled product applications require sufficient actual flow within the mold—not merely the theoretically high flow rates measured without accounting for system resistance.

Multistage centrifugal pumps provide the pressure needed to ensure continuous water circulation through complex cooling channels while maintaining high flow rates. This enables ultra-high-flow mold temperature controllers to deliver the following benefits:

  • Maintain robust circulation within large molds;
  • Achieve more uniform mold temperatures;
  • Accelerate heat removal;
  • Enhance thermal stability between production cycles.
Vertical Multistage Centrifugal Pumps Provide a Stable, High-Flow Water Stream for Thick-Walled Product Molding

Accelerating Cooling of Thick-Walled Products with a 20 mm Large-Diameter Cooling Circuit

If the cooling water supply channel becomes a bottleneck, the benefits of high flow rates in the mold circuit will be very limited.

Therefore, our high-flow mold temperature controllers incorporate a large-diameter cooling circuit equipped with a 20 mm cooling solenoid valve. The larger flow cross-section enables faster cooling and supports more robust temperature control. It also allows for greater cooling water flow when cooling demands increase.

For thick-walled products, this design is particularly effective when significant heat builds up during continuous molding cycles or when using large molds with substantial thermal mass.

The combined solution of a “vertical multistage centrifugal pump + large-diameter cooling circuit” thus addresses two key requirements: it ensures a greater volume of cooling water flows through the mold while enabling the temperature control system to rapidly dissipate heat when needed.

Accelerating Cooling of Thick-Walled Products with a 20 mm Large-Diameter Cooling Circuit

Maintaining Reliable Operation Under High Thermal Load Conditions

Topstar physically separates the electrical control cabinet from the main unit’s high-temperature areas. Although this design does not directly increase water flow, it effectively addresses a challenge in high-heat-load applications: the impact of heat on electrical components. In an integrated enclosure design, heat from piping, pumps, heaters, and the circulating medium can raise the temperature around electrical components. Topstar’s separated enclosure structure isolates these components from high-temperature heat sources, thereby protecting the electrical system.

Maintaining Reliable Operation Under High Thermal Load Conditions

Manage heat by controlling water flow

Thick-walled parts require a higher mold water flow rate because, compared to thin-walled parts, they store more heat and dissipate it more slowly. Insufficient circulation can lead to uneven cooling-water temperature and mold-temperature distribution, which in turn prolongs cooling time and causes issues such as shrinkage, warpage, sink marks, and dimensional deviations.

Increasing the mold water flow rate removes more heat from the mold, reduces temperature rise in the cooling circuit, improves heat-transfer uniformity, and helps the mold recover faster between molding cycles. When water circulation capacity limits cooling time and mold temperature uniformity, increasing the actual mold water flow rate—rather than simply lowering the set water temperature—is often a more effective solution.

 

 

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