Cooling channels, molds

Production molds are usually made from steel for pressure molding that requires heating or cooling channels, strength to resist the forming forces, and/or wear resistance to withstand the wear due to plastic melts, particularly that which has glass and other abrasive fillers. However most blow molds are cast or machined from aluminum, beryllium copper, zinc, or Kirksite due to their fast heat transfer characteristics. But where they require extra performances steel is used. 

The simplest molds consist of two parts one fixed and one moveable. We use such molds to fabricate items, such as disposable stadium cups, compact disks, and coat hangers, which have simple designs with no undercuts. As the complexity of the product increases, so must the complexity of the mold. The molds used to produce large items, such as dishwasher tubs and automobile bumpers, may consist of multiple moveable components and weigh several tons. Even apparently simple items, such as screw tops for bottles, require a complex ejection system that unscrews the product from part of the mold. In order to facilitate cooling, virtually all molds are designed with liquid cooling channels. 

The best molds are made of aluminum with water-cooling channels cut into them. Tooling costs are low, and heat transfer is high. The formed plastic sheet must be held against the mold surface until it is cooled to the solid state. This is often judged by the heat deflection temperature at 455 kPa (66 psi). 

The injection mold is a series of steel plates, which when assembled produces the cavity that deflnes the shape of the molded part. Conventional molds consist of the mold frame, components, runners, cooling channels, and ejector system. The mold frame is a collection of steel plates that contain mold components and runners, cooling and ejection systems. Components are parts inserted into either bored holes or cutout pockets in the mold frame. The polymer melt enters into the mold cavity or cavities through the runners, which are passages cut into the mold frame. The hot polymer material in the mold... 

The mold for thermoplastics receives the molten plastic in its cavity and cools it to solidity to the point of ejection. The most is provided with cooling channels. The mold temperature is controlled by regulating the temperature of the cooling fluid and its rate of flow through the channels. Proper cooling or coolant circulation is essential for uniform repetitive mold cycling. 

Zinc alloy (kirksite) high-quality molds can be made from cast zinc alloys, offering good non-porous surfaces but are relatively heavy, with lower heat conductivity than aluminum, requiring closely spaced cooling channels. 

Rocker bottoms Blowing air not vented before mold opens Insufficient cooling Increase air exhaust time Clean mold cooling channels Increase blow time... 

In mold design, the core is (1) a channel in a mold for circulation of heat transfer media or (2) a part of a complex mold that molds undercut parts. In the latter case the cores are usually withdrawn to one side before the main sections of the mold open (also called a core pin). Cores are usually withdrawn before the main sections of the mold are opened. A core drill is a device for making cooling channels in the mold. 

The mold may consist of regions where circuits are not feasible. Additional cooling channels such as baffles, bubblers, or thermal pins may be used to divert the coolant flow into these regions. Shoemaker (2006) has shown some examples. 

The mold boundary T is comprised of the cavity surface the cooling channel surface F, and the external surface F. The boundary conditions are as follows ... 

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