Cooling channel configuration

In general, the cooling system will be roughly drilled or milled. Rough inner surfaces enhance turbulent flow of coolant, thus providing better heat exchange.  Turbulant flow achieves 3 to 5 times as much heat transfer as does non turbulant flow. Cooling channels should be placed close to the mold cavity surface with equal center distances in between (see figures below). The mechanical strength of the mold steel should be considered when designing the cooling system. Basic principle of cooling channels.

Position of cooling channels.

Some thermoplastics may require mold temperatures of 100°C or higher for optimal processing and properties. Effective mold insulation is advised to minimize heat loss between the mold and the machine mounting platens. Insulation boards with low thermal conductivity and relatively high compressive strength are commercially available. Care is required in the correct placing of seals; they may be damaged by the sharp edges of the pocket when the mold insert is mounted (see figure below). Seals or O-rings should be resistant to elevated temperatures and oils. Sealing and cooling channel lay-out.

Guidelines for optimal mold temperature control Independent symmetrical cooling circuits around the mold cavities. Cores need effective cooling (see baffles, bubblers & thermal pins). Short cooling channels to ensure temperature differences between in- and outlet do not exceed 5°C. Parallel circuits are preferred over serial cooling as shown in figure below. Avoid dead spots and/or air bubbles in cooling circuits. Heat exchange between mold and machine should be minimized. Differences in flow resistance of cooling channels, caused by diameter changes, should be avoided. Mold parts that are excessively heated, like sprue bushings and areas near the gates, must be cooled intensively. Rapid and even cooling is enhanced by the use of highly conductive metals, such as beryllium-copper. These metals are used to full advantage in places where it is impossible to place sufficient cooling channels. Beryllium copper transfers twice as much heat as carbon steel and four times as much heat as stainless steel. This does not mean beryllium copper molds will run 4 times faster tan a stainless steel mold but they will run some thin walled parts significantly faster. Beryllium copper is not recommended for materials that require high mold temperatures as they allow so much heat transfer that it is difficult to maintain adequate heat economically. Cooling of the mold.