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TYPES OF HEAT SOURCES
Depending on the application, a wide variety of heat sources can be used. Gas fired units can be direct fired where atmosphere control is not important. Radiant tubes are used on gas fired units where atmosphere must be controlled. Electric furnaces can feature coiled, ribbon or rod type elements or can have elements enclosed in radiant tubes. Top to bottom zoning is possible with some types of elements.
CERAMIC FIBER INSULATION FEATURES FAST HEAT UP AND COOL DOWN
The entire furnace, except for portions of the hearth, is insulated with ceramic fiber and mineral wool. The total insulation thickness is typically 8.” 2600F (1425C) fiber is used for 2200F (1200C) furnaces and 2300F (1260C) fiber is used for 2000F (1095C) or below. The bottom, where typically a fan is located, normally has castable refractory for erosion resistance. No asbestos is used.
HEAVY DUTY CASE
The case is typically made of strongly reinforced 3/16 thick steel. It is primed with 800F silicon paint and finished in machine enamel. Larger units are fabricated in more than one section for shipping purposes and erected on site.
DOOR AND SEAL
The typical door seal is a wide pad of ceramic fiber. This seals against a rigid ceramic fiber board attached to the case. Controlled atmosphere furnaces can also feature sand seals. The most common door is a counterbalanced lift and swing door.
FANS
Most of these furnaces feature bottom mounted fans for recirculation of the furnace atmosphere. These are typically water cooled fans that mount as a plug unit. Recirculation baffles are typically used also.
ATMOSPHERE CONTROL SYSTEMS
These furnaces can be designed for controlled atmosphere. Atmosphere can be inert, endothermic, slightly carburizing, exothermic, etc. See the separate MPN, MPH, NM and EN Series Bulletins for information concerning L&L’s atmosphere control panels.
DIGITAL PID CONTROL AND HIGH LIMIT SYSTEM
The standard control is a Honeywell UDC 2300 digital PID 3 mode tuning control. All fuses, transformers, contactors, and controls are housed in a floor standing NEMA 12 panel with a fused disconnect switch. Quiet, long life mercury contactors are standard, although SCR power control is a common option. Thermocouples are inconel sheathed Type K. Thermocouple break protection is included. A Honeywell UDC 2000 digital high limit back up control with manual reset, back up contactors and separate thermocouple is provided. A NEMA 13 lighted On/Off switch and NEMA 13 door power cut off switch are included. Control voltage is transformed to 120 volts. The control circuit and each power branch circuit are fully fused. Single point power connection. Meets National Electrical Code.
TESTING AND INSTRUCTIONS
The furnace is power tested to insure proper watt ratings. A complete instruction manual includes easy start up instructions, theory of operation, maintenance instructions, parts list, general dimension drawing, general assembly and subassembly drawings where required, and a detailed trouble shooting guide. A ladder logic diagram and panel layout are prepared on CAD for easy readability.
START UP SERVICE
L&L will check out and leak test the atmosphere system, inspect the customer’s assembly of the furnace, repair any refractory cracks, check tightness of elements, start up equipment, tune controller, adjust SCR, instruct customer’s personnel in how to do this, train operator in the use of the control systems, review the furnace manual, test for proper operation of all components and systems and start, watch and run the bakeout cycle.
WARRANTY
The furnace is warranted for one year except for elements and thermocouples (warranted for 6 months.)
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