WATLOW ELECTRIC MANUFACTURING COMPANY
Installation & Maintenance Manual for MULTICELL
TM
Heaters
I&M MANUAL No: 316-42-21-1
Page: 8
Date: 3/15/2017
Rev: 5.00
WATLOW ELECTRIC MANUFACTURING COMPANY - 6 INDUSTRIAL LOOP RD.
– HANNIBAL, MO 63401 - PHONE 573-221-2816
Original Instructions (English)
The use of proportioning temperature controls and SCR power controls is recommended to
assure maximum possible heater life and adequate temperature control. On/off type electro-
mechanical controls are discouraged, and should not be used for heaters operating at process
temperatures above 982°C (1800°F).
For high temperature applications, longer heater life can be achieved by controlling the heater
temperature ramp rates as follows:
Initial Start Up Ramping to Operating Temperature:
The recommended temperature ramp up
rate from room temperature to operating temperature is 38°C (100°F) per hour.
Production Idling:
Whenever possible, installed heaters should remain energized at an
intermediate temperature to prevent moisture accumulation. The recommended production idle
platen temperature is 260°C (500°F) minimum.
Production Idling to Operating Temperature:
The recommended temperature ramp up rate
from idle temperature to operating temperature is 38°C (100°F) per hour.
Cool Down from Production Temperature to Idle Temperature or Room Temperature:
The
recommended cooling rate is 38°C (100°F) per hour. Note: Specific slow cool down rates are
recommended to reduce the probability of creating differential thermal stresses that could break
mounting fasteners, shorten heater life, warp the platen, etc. The cool down rate will vary with
each press design.
Ramping to Operating Temperature After Maintenance:
Scheduled maintenance periods
could necessitate cooling the press to room temperature. The decrease in temperature creates
the possibility of moisture absorption in the Multicell heaters. Significant downtime could result in
the need to follow the “Initial Start Up Ramping to Operating Temperature” procedure, if the press
is below 100°C (212°F) for more than approximately 4 hours. Always check and ensure that
insulation resistance is greater than 50 Megohm prior to restarting the heater. A faster ramp up
time of up to 94°C (200°F) is acceptable when the press has been cooled to room temperature
for time periods that do not allow for significant moisture absorption by the magnesium oxide.
If a shorter ramp up time is necessary the following is acceptable. Overtemperature sensor(s)
and controls must be in operation at all times. Set overtemperature at 950°C (1850°F) for SPF
presses designed to operate up to 899°C (1650°F). Consult factory if high temperature control
tripping occurs.
Ramp from room temp to 120°C (250°F) in 1 hour.
Soak at 120°C (250°F) for 1/2 hour
Ramp to 370°C (700°F) in 1 hour
Soak at 370°C (700°F) for 1/2 hour
Ramp to operating temperature at 177°C (300°F) per hour.
