Heat Load Calculation for Mold Temperature Control Units
Left: Sentra Series mold temperature control unit. Right: Regal Series hot oil temperature control unit.
Mold temperature control units, such as the Advantage Sentra and Regal Series units, must achieve three objectives:
Initially elevate mold up to operating temperature
Maintain the temperature during operation
Compensate for heat losses due to absorption and radiation
To achieve these objectives, the mold temperature control unit's heater must be sized correctly. The formula for calculating the process heat load requirements
for mold temperature control units is discussed in this document.
Heaters are selected by Kilowatt rating. That is, the amount of heat energy introduced into the system, expressed in thousands of watts per hour.
Common ratings are 4.5KW, 9KW and 12KW. Advantage offers heaters from 4.5KW to 36KW in standard units. Larger heaters are available on a custom option basis.
To determine the process heat requirements, the following formula is presented:
1. Determine the mold's weight. Do this by multiplying the outside dimensions to compute total cubic inches. Multiply this by the particular weight of the mold
material.
2. Determine the mold's temperature rise. this is the difference between the non-operating (ambient) temperature and the setpoint temperature. It can be assumed the
average ambient temperature is 70°F.
3. Determine the mold's specific heat value. The standard value for steel is .12 and for aluminum is .24. Other values are listed on Advantage FYI #108.
KW Per Hour is the kilowatts required to bring the mold up to temperature within one hour. Select the nearest "standard" KW rating for the heat
load. Example: a 7.5KW load would require a 9KW standard heater.
If a faster heat-up time is required, then the heater must be sized accordingly. For example, a 6KW load for one hour becomes a 12KW load for a half hour.
Furthermore, a 4KW load for one hour becomes a 16KW load for 15 minutes.
45 minute heat-up : divide KW per hour by .75
30 minute heat-up : divide KW per hour by .50
15 minute heat-up : divide KW per hour by .25
The KW required to maintain the setpoint, once achieved, is only a fraction of what is needed initially. Therefore, a heater sized for the initial heat-up is
typically sufficient for maintaining the setpoint and compensating for any minute radiation or absorption loss. (See FYI #009 for more information.)
For more information about calculating the heat load for mold temperature control circuits call the Advantage Sales Department at 317-887-0729.