Thermoset Compression Mold HEATING

A uniform mold temperature means that the temperature of each half of the mold is the same (within ±3°C (5°F)) for all locations when the mold is heated by oil or steam. Molds that are

heated with electric cartridge heaters can vary by as much as 6°C (10°F). A mold with a uniform temperature will fill easier and produce parts with less warpage, improved dimensional

stability and a uniform surface appearance. Achieving a uniform mold temperature is dependent
on your method of mold heating.
A mold that is heated by steam or oil will have a uniform mold temperature because the heat
source maintains a constant temperature. However, oil as a heat source is only about half as
efficient as steam. Therefore, when using oil to heat a mold, it is necessary to set the oil
temperature higher than the desired mold temperature.
Electrically heated molds are more difficult to maintain at a uniform temperature because the
cartridge heaters are constantly cycling on and off. When they are on, they generate a great deal
of heat at the source but this heat must be dispersed throughout the mold in a way that produces a
uniform mold temperature.
To determine the amount of wattage needed to heat a mold, the use of the following formula
might be helpful: 1¼ kilowatts for every 45 kg (100 pounds) of mold steel. Note: This
formula normally will allow the mold to be heated to molding temperatures in 1 to 2 hours.