Thermal pins
A thermal pin is an alternative to baffles and bubblers. It is a sealed cylinder filled with a fluid. The fluid vaporizes as it draws heat from the tool steel and condenses as it releases the heat to the coolant, as shown in Figure 4. The heat transfer efficiency of a thermal pin is almost ten times as great as a copper tube. For good heat conduction, avoid an air gap between the thermal pin and the mold, or fill it with a highly conductive sealant.
FIGURE 4. Thermal pin heat transfer efficiency
Cooling slender cores
If the diameter or width is very small (less than 3 mm), only air cooling is feasible. Air is blown at the cores from the outside during mold opening or flows through a central hole from inside, as shown in Figure 5. This procedure, of course, does not permit maintaining an exact mold temperature.
FIGURE 5. Air cooling of a slender core
Better cooling of slender cores (those measuring less than 5 mm) is accomplished by using inserts made of materials with high thermal conductivity, such as copper or beryllium-copper materials. This technique is illustrated in Figure 6 below. Such inserts are press-fitted into the core and extend with their base, which has a cross section as large as is feasible, into a cooling channel.
FIGURE 6. Using high thermal conductivity material to cool a slender core
Cooling large cores
For large core diameters (40 mm and larger), a positive transport of coolant must be ensured. This can be done with inserts in which the coolant reaches the tip of the core through a central bore and is led through a spiral to its circumference, and between core and insert helically to the outlet, as shown in Figure 7. This design weakens the core significantly.
FIGURE 7. Use of helical baffle to cool large core
Cooling cylinder cores
Cooling of cylinder cores and other round parts should be done with a double helix, as shown below. The coolant flows to the core tip in one helix and returns in another helix. For design reasons, the wall thickness of the core should be at least 3 mm in this case.
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