Page 168 - Electromechanical Devices and Components Illustrated Sourcebook

130 Electromechanical Devices & Components Illustrated Sourcebook

Resistive Heating Drive Motors
Arc Carbon
Resistively heating a part is using the part itself as the heating Electrodes
element. Generally, the component to be heated is connected + −
to a high-current power supply, as shown in Figure 7-8. When
the power supply is turned on, the component will be heated Pinch Rollers
between the two terminals.
The most common use for resistive heating is to thaw
frozen water pipes, as shown in Figure 7-9. In this case, a
small AC arc welder is connected to either end of the exposed
Feed
pipe and then switched on. The pipe slowly warms, and the Controller
internal ice melts. AC Ignition Supply
Current Transformer
+ −
DC Power Supply
Heat-Affected Zone Figure 7-10 Carbon Arc Schematic

Component to
be Heated
Figure 7-10 shows a schematic representation of a carbon
arc heater. The arc is fed with a high-current DC power sup-
ply. The AC ignition supply is used to generate a spark to start
the arc. The electrodes are mounted into roll feeders that auto-
matically compensate for their loss due to erosion. The feed-
High-Current Power Supply ers are controlled by monitoring the current that the arc is
Figure 7-8 Resistive Heating Schematic drawing.

Arc Gouging

Arc gouging is a process that is used extensively in the steel
Water Pipe Exposed to fabrication industries. In this process a carbon electrode is
Freezing Temperatures used to produce an arc to the base metal. The arc generates an
intensely high temperature zone that locally melts the steel.
The electrode holder carries two air jets that are connected to
Small AC Rod Holder a compressed air source. As the metal melts, the air jets blow
Arc Welder the molten material clear of the workpiece. Figure 7-11 shows
Ground a typical arc gouging operation.
Clamp

Welding Cable Removed Material

Carbon Electrode
Figure 7-9 Thawing Pipes with Resistive Heating

Electrode Holder
Air Orifice
Arc Heating Steel Plate
Air Jet
Kerf
For extreme heating applications, electric arcs are deployed.
An electric arc will produce very high temperatures and are
commonly used for melting and alloying metals. Most of the
recycled steel made in the world is melted with electric arc Direction of Cut
furnaces. Figure 7-11 Carbon Arc Gouging