Connection and sealing of injection molding cooling water channels
The connection and sealing of injection molding cooling channels are critical to ensuring the proper functioning of the cooling system, directly impacting the flow and pressure of the cooling medium and the lifespan of the mold. Improper connections or seal failures can lead to cooling medium leakage, reducing cooling efficiency and even damaging the mold and injection molding equipment, increasing production costs. Therefore, during mold design and assembly, it is crucial to employ appropriate connection methods and sealing structures to ensure secure cooling channel connections, reliable sealing, and ease of installation, maintenance, and cleaning.
The connection method for cooling channels should be selected based on the mold structure and cooling system layout. Common connection methods include threaded connections, quick-connect fittings, and flange connections. Threaded connections are the most common method. Internal threads (such as G1/8 and G1/4 pipe threads) are machined into the mold channel interface, which then connects to externally threaded pipes or fittings. This method is simple, low-cost, and suitable for most small and medium-sized molds. To enhance the connection’s security, threaded connections are often wrapped with raw tape or coated with thread sealant (such as PTFE) to prevent leakage. Quick-connect fittings are suitable for applications where frequent mold disassembly is required. They utilize elastic retaining rings or O-rings for quick connection and sealing, offering easy installation and disassembly, excellent sealing performance, but are relatively costly. They are therefore suitable for automated production lines or large molds. Flange connections are suitable for large-diameter cooling channels (>20mm). Using flanges and bolts, the pipe connects to the mold, providing a secure connection and reliable sealing. However, they are bulky and are therefore suitable for applications with high cooling medium flow rates.
The design and material selection of the sealing structure are crucial to preventing coolant leakage. Common sealing structures include O-rings, gaskets, and taper seals. O-rings are the most common method. They are typically made of water-, oil-, and high-temperature-resistant rubber materials (such as nitrile rubber and fluororubber). They are installed in the sealing groove of the waterway joint. When the joint is tightened, the O-ring is compressed and elastically deforms, filling the gap between the sealing surfaces and achieving a seal. The cross-sectional diameter of the O-ring is determined by the size of the waterway joint, generally ranging from 1.5 to 5 mm. The depth of the sealing groove should be 70% to 80% of the O-ring diameter to ensure sufficient compression (usually 20% to 30%). Gasket seals are suitable for flange connections or flat joints. Gasket materials can include rubber, copper, and aluminum. The preload of the bolts causes the gasket to plastically deform, blocking the tiny gaps in the sealing surface. They are suitable for high-pressure cooling systems (pressures > 10 bar). Conical seals achieve sealing through close fit between the conical surfaces of the joint and the mold interface. The fit angle is usually 60° or 90°. It is suitable for high-pressure and high-temperature applications, but has high machining accuracy requirements. The surface roughness of the conical surface must reach Ra≤1.6μm.
The installation process for connections and seals directly impacts the sealing effect and joint strength. Before installation, clean the surfaces of the waterway interfaces and connectors to remove impurities such as oil, rust, and burrs. Ensure the sealing surfaces are smooth and flat. Failure to do so will result in a poor seal. For threaded connections, tighten the connector to the specified torque. Excessive torque may cause thread stripping or seal damage, while insufficient torque may prevent a seal. The tightening torque for G1/4 threads is generally 15-20 N · m , and for G1/2 threads it is 30-40 N · m . When installing O -rings, inspect them for defects such as damage and aging. Avoid scratching the O – rings during installation . A small amount of lubricant can be applied to the O -ring surface to facilitate installation. For quick-connect fittings, ensure the pipe is inserted to the specified depth. After insertion, gently pull the pipe to check for a secure connection. After installation, perform a pressure test. Typically, a coolant (such as tap water) at 1.5-2 times the operating pressure is passed through the connector. Maintain the pressure for 30 minutes and observe for leaks. If leaks are detected, recheck the connection and sealing structure and troubleshoot.
Common cooling water channel connection and sealing issues and their solutions are crucial to ensuring long-term, stable system operation. Common problems include leakage, blockage, and loose joints. Leakage is often caused by damaged seals, poor thread machining accuracy, or insufficient installation torque. Solutions include replacing damaged seals, re-threading (ensuring thread accuracy of 6g/6H), or re-torquing the joints to the specified torque. Blockages are often caused by impurities from the cooling medium (such as sand and rust) deposited in the joints, or by loose seal fragments that block the water channels. These can be prevented by disassembling the joints to remove impurities and installing filters (with a filter accuracy of ≥50μm) at the cooling system inlet. Loose joints are often caused by vibration during mold opening and closing. Locknuts or applying lock glue (such as Loctite 243) to the threads can prevent loosening. Furthermore, when using hot water or hot oil as the cooling medium, consider the impact of thermal expansion on connections and seals. Select high-temperature-resistant sealing materials (such as fluororubber) and appropriately reduce installation torque to avoid excessive compression of the seals due to contraction during cooling.
Connection and sealing designs for special applications require targeted optimization based on actual operating conditions. For cooling channels in deep-cavity molds or core-pulling mechanisms, conventional connections are difficult to install due to limited space. Instead, rotary joints can be used. These facilitate cooling medium transfer between relatively moving parts while ensuring a tight seal. These sealing structures typically utilize mechanical or combined seals, making them suitable for applications with larger core-pulling distances. For high-temperature cooling systems (media temperatures > 100°C), high-temperature-resistant connectors and sealing materials are required, such as stainless steel connectors with fluororubber O-rings, to prevent material degradation and seal failure caused by high temperatures. For industries requiring high cleanliness, such as food and medical, cooling channel connectors and sealing materials must meet food-grade standards (e.g., 304 stainless steel connectors and silicone seals), and joints must be regularly disinfected and cleaned to prevent contamination. Furthermore, when operating in cold regions or during winter, antifreeze should be added to the cooling system to prevent freezing of the water channels and cracking of the connections. Low-temperature-resistant sealing materials (e.g., EPDM) should be used to ensure sealing performance even at low temperatures.
