©
COPYRIGHT 1999 THE ESAB GROUP, INC. LESSON
I, PART B
compensated
for by the characteristics of this process. To understand this, keep in
mind that with
the proper voltage setting, amperage setting, and arc length, the rate that the
wire melts is
dependent upon the amperage. If the amperage decreases, this melt-off rate
decreases and if the amperage increases,
so does the melt-off rate. 1.9.2.2
In Figure 21, we see that condition
#2 produces the desired arc length, voltage, and
amperage. If the arc length is increased as in #1, the voltage increases
slightly; the amperage
decreases considerably, and therefore, the melt-off rate of the wire decreases.
The wire is now feeding faster than
it is melting off.
This condition will advance the end of the wire
towards the work piece until the proper arc length
is reached where again, the melt-off rate equals
the feeding rate. If the arc length is decreased
as in #3, the voltage drops off slightly,
the amperage is increased considerably,
and the melt-off rate of the wire increases.
Since the wire is now melting off faster
than it is being fed, it melts back to the proper
arc length where the melt-off rate equals
the feeding rate. This is often referred to
as a self-adjusting arc. These automatic corrections
take place in fractions of a second, and
usually without the operator being aware of
them. 1.9.2.3
There are a variety of different welding
machines, each with its own unique internal
design. Our purpose is not to detail the function of each part of the machine,
but to emphasize
that their main difference is in the way they control the voltage and amperage
output. 1.9.3
Types
of Welding Power Sources - A great variety of
welding power sources are
being built today for electric arc welding and we shall mention some of the major
types briefly.
Welding power sources can be divided into two main categories: static
types and rotating
types. 1.9.3.1
Static
Types - Static type power sources are all of those
that use commercially generated
electrical power to energize a transformer that, in turn, steps the line voltage
down to useable welding voltages. The
two major categories of static power sources are the
transformer type and the rectifier type. 1
2
3 V
O L
T S
40 30
20 10
100 200
300
400 AMPERES
VOLT / AMPERE CURVE - CONSTANT VOLTAGE
FIGURE 21
