The Model DBW-15 is a resistance-type butt welder. The
two clamping jaws of the welder hold the butted band ends together.
When the welding switch lever is pressed, an electric current is in-
duced through the butted band ends, creating enough heat to soften and
Pressing the welding lever also releases a spring which causes the
jaws to force the band ends together. The electrical current is shut
off before the movable jaw completes its movement. Final upset or
"forging" occurs when the band is still hot, but is no longer being
heated by its electrical energy source.
JAW GAP AND UPSET FORCE CONTROLS
The initial gap between the welder jaws and the spring upset force
must both be adjusted in proportion to the cross-sectional area of
the band being welded. A greater jaw gap will allow a wider or thicker
band to reach its proper welding temperature. A greater upset force
produces the same unit pressure in welding a wider or thicker band.
A jaw upset force selector is used to provide a variable control of
upsetting force. Initial jaw gap is set by adjusting the position of the
weld lever before making the weld.
When the band is heated in the butt welding process, the steel at the
point of weld air-hardens and becomes brittle. The annealing push
button is used to anneal the weld by reheating it. This returns the
band to an approximation of its original condition. A selector switch
is provided for choosing the correct annealing heat, depending upon
the width of the saw blade.
The grinding wheel is used to prepare the blade for welding and to remove
fIash from the weld. Flash on both sides of the weld must be ground off
to blade's thickness. The gage at the top of the wheel guard is used to
check for complete removal of the flash. After grinding, the weld should
pass freely through this gage.
Since it may be difficult to see if the grinding wheel is rotating, a pilot
light is provided as a safety feature. T h i s l i g h t i s o n w h e n t h e g r i n d -
ing motor is running.