Shape of the water-passing end of the spacer
The water-passing end of the spacer is a key component for controlling the flow state of the coolant in the mold cooling system. Its shape directly affects the cooling efficiency, water flow resistance and mold temperature uniformity. In the cooling water channel of the injection mold, spacers are usually used to separate the coolant in different areas, or to guide the water flow to form turbulence to enhance the heat exchange effect. Common shapes of the water-passing end of the spacer include straight, wedge-shaped, arc-shaped and sawtooth-shaped, and each shape is suitable for different cooling needs and water channel structures. For example, straight spacers are suitable for occasions requiring stable water flow, while wedge-shaped spacers can significantly increase the turbulence intensity and are suitable for high heat load areas. The shape design of the water-passing end of the spacer needs to be combined with the water channel diameter, flow rate and cooling target. By optimizing the water flow path to reduce dead corners, ensure that the temperature deviation of each area of the mold is controlled within ±2°C, and provide guarantees for the stable quality of plastic parts.
The straight baffle is the most basic structural form. Its characteristic feature is a flat surface parallel to the inner wall of the water channel, allowing water to flow in a straight line with minimal resistance. This shape is suitable for cooling systems with low flow rates (1-2 m/s) or for precision molds requiring high water flow stability. For example, in the narrow water channels (6-8 mm in diameter) of small electronic component molds, straight baffles can avoid local temperature fluctuations caused by water flow disturbances. Straight baffles are simple to manufacture and can be formed by wire cutting or milling, resulting in low cost and ease of mass production. However, due to the predominantly laminar flow, heat transfer efficiency is relatively low, making them unsuitable for cooling high-heat-load plastic parts (such as thick-walled products). In practical applications, the width of the straight baffle is typically 1/3-1/2 the water channel diameter. For example, a 10 mm diameter water channel paired with a 3-5 mm wide straight baffle ensures smooth water flow while also providing some diversion.
The wedge-shaped spacer’s sloped surface at the water channel guides the water flow, creating localized turbulence and significantly improving heat transfer efficiency. The wedge’s slope is typically 15°-30°, and the water channel tapers gradually from one side to the other. This creates a velocity gradient due to the change in cross-section, forming swirling vortices and increasing the contact frequency between the coolant and the channel wall. For example, in the thick-walled areas of an automobile bumper mold (5-8mm thick), using a 20° wedge-shaped spacer increased cooling speed by 25% compared to a straight spacer, and shortened the molding cycle by 10%. The slope length of the wedge-shaped spacer must match the channel diameter, typically 1.5-2 times the diameter, to ensure sufficient vortex formation while avoiding pressure loss caused by excessive resistance. This shape is suitable for cooling systems with medium to high flow rates (2-3m/s), and is particularly effective in areas requiring rapid cooling (such as near the gate). However, it is slightly more difficult to manufacture than a straight shape, requiring precise control of the slope angle using a CNC milling machine.
The smooth curve of the curved spacer’s water-passing end reduces flow resistance and promotes even water distribution, making it suitable for complex water channels or cavities requiring all-around cooling. The arc radius is typically 1/2 to 1 times the water channel diameter. The water-passing end curves from the center outward, guiding the water flow along a curved path and avoiding eddy currents caused by right-angle turns. For example, in the conformal water channels of curved plastic molds, curved spacers keep the water flow close to the cavity surface, improving cooling uniformity. Compared to wedge-shaped spacers, curved spacers offer 30% lower pressure loss, making them more suitable for cooling systems with long water channels (lengths > 500mm), such as those in large appliance housing molds. Curved spacers must be machined using wire cutting or grinding to ensure a smooth surface (roughness Ra 0.8μm or less) to avoid localized eddy currents and scaling caused by surface roughness. In practical applications, arc-shaped spacers are often used in combination with other shapes. For example, an arc-shaped transition is used at the waterway inlet, and a wedge-shaped middle section is used to enhance turbulence, achieving both low resistance and high heat transfer efficiency.
Serrated diaphragms disrupt laminar flow boundaries with their serrated edges at the water-passing end, generating intense turbulence and making them ideal for areas with high heat loads. The number of serrations is typically 3-6, with a tooth height of 1/5-1/4 the waterway diameter and equal spacing between the teeth. As water flows through, numerous small vortices are formed between the teeth, significantly increasing the turbulence at the liquid-solid interface and improving heat transfer efficiency by over 50% compared to straight diaphragms. For example, in the gate area of a PC transparent plastic mold (where temperatures reach up to 300°C), serrated diaphragms can reduce cooling time from 20 seconds to 12 seconds, effectively reducing sink marks near the gate. However, serrated diaphragms present significant flow resistance and require a high-powered pump (head >10m). They are suitable for high-pressure cooling systems with flow rates of 3-4m/s. During processing, ensure the serrated edges are sharp (burr-free), otherwise localized vortices will cause scale deposits. Cleaning and maintenance are recommended every 10,000 molds. The application of serrated diaphragms requires balancing heat transfer efficiency and energy consumption, and finding the optimal solution between high heat load and energy consumption constraints. It is usually used in production scenarios with large batches and high cooling speed requirements.
