Alternative cooling devices

For areas in the mold where it is not possible to use normal drilled cooling channels, alternative methods must be employed to ensure these areas are uniformly cooled with the rest of the part. The methods employed usually include baffles, bubblers, or thermal pins.

Baffles and bubblers are sections of cooling lines that divert the coolant flow into areas that would normally lack cooling, e.g. cores. A baffle is actually a cooling channel drilled perpendicular to a main cooling line, with a blade that separates one cooling passage into two semi-circular channels. The coolant flows in one side of the blade from the main cooling line, turns around the tip to the other side of the baffle, and then flows back to the main cooling line.

Example of core cooling by means of baffles: less effective heat discharge at core top.

This method provides maximum cross sections for the coolant, but it is difficult to mount the divider exactly in the center. The cooling effect and with it the temperature distribution on one side of the core may differ from that on the other side and this is the main disadvantage. The use of a helix baffle will solve the problem by conveying the coolant to the tip and back in the form of a helix. It is useful for diameters of 12 to 50 mm, and makes for a very homogeneous temperature distribution. Another logical development of baffles are single or double-flight spiral cores.

Single or double flight spiral cores.

A bubbler is similar to a baffle except that the blade is replaced with a small tube. The coolant flows into the bottom of the tube and "bubbles" out of the top, like a fountain. The coolant then flows down around the outside of the tube to continue its flow through the cooling channels.

For slender cores this is the most effective form of cooling. The inner and outer diameters must be adjusted so that the flow resistance in both cross sections is equal. The condition for this is: Inner Diameter / Outer Diameter = 0.7

Example of core cooling (tube with flange): good heat discharge at core top.

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. The heat transfer efficiency of a thermal pin is almost ten times as greater than a copper tube. For good heat conduction, avoid an air gap between the thermal pin and the, or fill it with a highly conductive sealant.

Cooling of 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. This design weakens the core significantly.

Cooling of large cores.

Cooling of slender core
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. The wall thickness of the core should be at least 3 mm in this case.

Cooling of slender core.

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 opening or flows through a central hole from inside. This procedure, of course, does not permit maintaining an exact temperature.

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. 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.

Cooling of slender core with inserts.