BOC Smootharc MMA 170, Руководство по эксплуатации, Страница: 7 / 36

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2.1 Introduction
Arc welding, although in the past principally
the tool of tradesmen and fabricators, has
in recent years found increasing usage with
small workshops, farmers, handyman-hobbyists
amongst others. This has been brought about
by the introduction of low-cost portable arc
welding machines and the ready availability
of small diameter electrodes and thinner
section construction materials. Provided the
operator is familiar with the basic principles and
techniques, arc welding can be a fast, efficient
and safe method of joining metals.
The main purpose of this manual is to help
the welder with limited experience to obtain
a better understanding of the process, and to
acquire a reasonable degree of proficiency in
the least possible time. Even welders with some
experience will benefit from the information in
this manual.
2.2 Process
Manual Metal Arc welding is the process of
joining metals where an electric arc is struck
between the metal to be welded (parent metal)
and a flux-coated filler wire (the electrode).
The heat of the arc melts the parent metal and
the electrode which mix together to form, on
cooling, a continuous solid mass.
Weld Metal
Slag
Core Wire
Flux Covering
Arc
Weld Pool
Workpiece
Before arc welding can be carried out, a suitable
power source is required. Two types of power
sources may be used for arc welding, direct
current (DC) or alternating current (AC).
The essential difference between these two
power sources is that, in the case of DC, the
current remains constant in magnitude and
flows in the same direction. Similarly, the voltage
in the circuit remains constant in magnitude and
polarity (i.e. positive or negative).
In the case of AC however, the current flows
first in one direction and then the other.
Similarly, the voltage in the circuit changes from
positive to negative with changes in direction
of current flow. This complete reversal is called
a ‘half cycle’ and repeats as long as the current
flows. The rate of change of direction of current
flow is known as the ‘frequency’ of the supply
and is measured by the number of cycles
completed per second. The standard frequency
of the AC supply in Australia is 50 Hz (Hertz).
2.3 Welding Machine
The most important consideration when
contemplating the use of arc welding for
the first time is the purchase of a suitable
welding machine.
BOC supplies a popular range of arc welding
machines. Machines range from small portable
welders that operate from standard 240 Volt
household power to heavy-duty welders used
by the largest steel fabricators.
2.0 Manual Metal Arc Welding
Process (MMAW)