The traditional low-voltage Electrical Resistance Local heat-treating method uses Flexible Ceramic Heaters connected to a control unit by use of Secondary Cables. A thermocouple is used to monitor the material temperature and provide feedback to the control unit and temperature recording system. The control unit can come in 3 different forms:
1) Twin Heat Module that is powered by a welding machine
2) Heat Treatment Console that can be powered by a 3 phase supply
3) Heat Treatment Rig, a fully self-contained unit with a Generator
These heaters have been called Chicklets, FCPs (Flexible Ceramic Pads), CMHs (Ceramic Mat Heaters) and CPs (Ceramic Pads). Regardless of the name used, they all provide the same function.
The industry standard for North America has been an 85 Volt heater that covers approximately 120 square inches. The heater’s design specifies 45 amps at 85 Volts, generating 3600 watts(3.6kw) of power when connected in a standard parallel circuit.
The heaters are constructed by hand with a 20′ high-resistance Nickel Chrome wire providing the heater’s body. This Ni-Cr wire is then tig welded on both ends to 9″ lower resistance to create “cold tails.” We weld the wire through die-pressed ceramic beads, with 90 amp cam lock connectors on each end. Ceramic beads are widely available in various chemical compositions and grades of quality. Typically the higher quality beads have a higher percentage of sintered alumina.
Secondary cables often referred to as Triple Cable Sets (TCS) consist of 2 power carrying cables, and 1 type K compensating cable.
The standard construction for a 3 – heater TCS would use two welding cables (#2) and a shielded 20 gauge solid wire Type K compensating lead. We bundle these cables together using a high-quality filament tape to prevent separation. Some lower-quality cable constructions use electrical tape, which tends to fall apart quickly, or use a smaller gauge wire that is susceptible to overheating. TCS can be any length, with 50′ and 100′ being most common. 3 – heater TCS terminate with 300 Amp Male Camlocks and Type K Male Thermocouple Plugs on one end.
We use 3-Way Splitters with 3 – heater TCS to allow heaters connection in a parallel circuit. Their construction is with 3 x #6 welding cables approximately 4-feet long with 1 x 300 amp male camlock and 3 x 90 amp female camlocks.
Smaller single heater TCS use a #6 welding cable, and construction is the same as the 3 – heater TCS using 90 amp camlock in place of the larger ones.
This control unit consists of 2 controlled outputs designed to power a maximum of 3 heaters per output. The THM needs 110 volts to run the control system and a welding machine power supply with a minimum of 300 amp @ 100% Duty Cycle. We do not recommend inverter welding machines for use with the THM, where PWHT is required without a test run. The lower Open Circuit Voltage of Inverter type welding reduces the heaters’ output and may not provide sufficient heat for PWHT applications.
The Twin Heat Module is available with or without a built-in Temperature Recorder. The THM is a favorite among portable welding operations to provide Welding Pre-heat for Heavy Equipment Repair.
The Heat Treatment Console control unit typically has six controlled outputs and a 65-70kva power supply. With a 3 Phase 600-550 / 480-440 power supply, the console will step down the voltage to 85VAC and increase the available amperage to 135 amps on each output, giving the console enough power to run 18 heaters at 100% duty cycle.
While consoles typically come as 6-ways, there are also 9-ways, 12-ways, 18-ways, and 24-ways versions. Consoles can be a custom build with any # of output, but for the use of 3-phase power and to avoid concerns with phase balancing, they usually have outputs in multiples of 3.
These “Rigs” are sometimes trailer-mounted or on a 5-Ton Truck Unit. Similar to the Console, they usually have outputs in multiples of 3. 12-way, 18-way and 24-ways are the most common configurations, but they can be custom-built as well.
The primary difference is that these Rigs come with a self-contained Gen-Set. The rigs can have transformers to step down the voltage like consoles, or sometimes less efficiently, the gen-set itself lowers the voltage by using a single phase 110 Volts with a voltage reducing regulator. The rigs without transformers generally lose 15-25% of its total KVA potential.
Truck-mounted rigs have control rooms for the technicians to monitor and control the Field Heat Treatment process. Trailer Rigs may or may not have a control room.
For more information regarding our electrical resistance local heat treating methods, contact us today.