Heat Load Calculation for Mold Temperature Control Units
- 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:
- 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.
- 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.
- 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.
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