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Furthermore virtually any shape and configuration are possible which would allow the application of this product
to a wide variety of industries and furnace designs. As we have the unlimited ability with this high temperature
element we welcome all opportunities to apply this product to the most difficult
environments.
The laminated construction allows for maximum hot face radiation and high temperature stability while backup
insulation optimizes efficiency.
Electric control of these modules as well as individual elements requires an intimate understanding of the
characteristics of the Molydisiliside element material composition. The material exhibits a sharp resistance
increase between room temperature and maximum operating temperature of approximately 15 times. The
material also is very brittle below temperatures of 800° C. For this reason full voltage should not be applied to a
cold element due to severe electromagnetic forces which could fracture the element.
The design to the power supply for this material must be comprehensive of these points. The use of a current
limiting, phase angle fired SCR is highly recommended. This is essential in limiting the current until the element
heats to a higher temperature and subsequently a higher resistance, which then will allow the voltage to increase
closer to a nominal operating value. Listed below are the maximum values for common element diameters.
- 3/6 75 amperes max.
- 6/12 200 amperes max.
- 9/18 350 amperes max.
The basic control components are a phase angle fired , current limiting SCR, and a step down transformer. The
SCR unit controls the amount of power delivered to the element. The transformer serves to match the line
voltage to the design voltage of the specific element. In the case where several elements are wired in series line
voltage may eventually be matched in which case the transformer can be eliminated.
In order for these components to work properly the SCR must be supplied with a ramp turn on function and
RMS current limit option. This insures the appropriate current during startup and reheat. Generally this feature is
adjustable within the SCR.
A temperature controller is also an important device to include. This device reads the element or furnace
temperature and instructs the SCR to Increase or decrease the current to the element system which then
maintains the temperature set point.
The finishing touches to a good power supply package would be output current and voltage meters to enable the
operator a device status reading. The use of a contactor could offer the possibility of remote control from a
control room setting. Circuit breakers, on/off power switch and a NEMA rated electrical
enclosure are also practical when designing high power equipment.
The above electrical considerations will offer an automatic control system, which will allow the element and
furnace system years of uninterrupted performance. Furnace Concepts offers custom designed and built power
systems for use with all elements and furnace systems.
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