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A simple fact in plastic molding is that heat from the molten plastic must be removed from the mold cavity in order for the part to solidify. Metals being relatively good conductors of heat are able to carry heat away from the mold cavity by simple conduction. Some metals are better conductors of heat that others, which often lead to the use of such materials as beryllium-copper and aluminum-bronze in the mold cavity. This heat is often removed from the metallic components by water flowing through them. Cold, flowing water has excellent heat extraction capabilities, but can only remove heat where it is in contact with the mold components. This means that heat must first travel from the plastic through the metallic components before it can be transferred to the water. The type of metal, the temperature and the type of plastic and the distance the heat must travel to get to the water cooling all have a factor in the heat equation that controls the molding cycle. .

The conventional method of supplying cooling water within molding components is to drill connecting holes to make a series of straight channels. This method can get water closer to the mold cavity, but is limited by the ability to produce straight channels only. If the part to be molded is of complex geometry, straight cooling channels will be at varying distances from the mold cavity. This will have the effect of providing effective cooling where the channels are close to the mold cavity, and potentially poor cooling where they are further away. This uneven cooling can produce molding problems, but more importantly, does not provide optimum cooling performance. If water-cooled channels were to conform to the geometry of the part, more even and effective cooling can be realized. The problem is how to make these curved channels.

Fused Metals Inc. has served the plastics industry for over 25 years with plating, coatings, vacuum heat-treating and vacuum brazing. It is this last one that allows for the creation of engineered cooling channels that conform to part geometry. Brazing is simply the joining of two or more parts into a single component by the addition of a filler metal. In the plastic molding industry, the parts are common items such as cores, cavities, stripper rings, poppet’s, inserts and gate pads made from tool steel. The difference with these parts is that they are made from more that one piece which will be brazed together to enclose a designed cooling pathway. A simple example would be to envision one of these components split into two halves. A water channel of conforming geometry can now be milled onto the exposed face of each half, and the two parts brazed together to enclose the cooling channel. The tool steel is heat-treated at the same time that brazing takes place, so an additional operation is not necessary.