Purpose:
- To give a brief introduction to engineering students about metal arc welding.
- To give a real life experience of metal arc welding to engineering students.
- To teach the student about the safety in working in welding workshop.
Equipment:
Welding Machine.
There are 2 types of welding machine:
a) Alternating Current-AC
This machine is good for use in workshop and farm workshop. It is
specially designed for small voltage work for example 37.5 amps. It is needed for welding
work in all places no matter the voltage is small or large. This machine is cheap, easy to
be taken care of and do not produce a lot of noise. It is mobile but it can only use
limited amount of electrode. It does not have moving parts and cannot be used on aluminum
electrode. It uses only one level of electricity.
b) Direct Current-DC
This machine is so costly and it uses three level of
electricity and the generator provides it. The use of electrode is not limited, produce a
lot of noise when used, difficult to maintain, can be use in places where there is no
electricity available and good for thin metal. High-powered DC machines usually uses air
or gasoline cooling system. The machine amps limit is between 180 –200 amps. All
welding machine have their own degree of heat so that it can be used to weld work metal
and electrode of different sizes. It should be kept in a safe and dry. If it is stored in
damp and cold places, the transformer and the generator will be damaged.
Cables.
There are two cables that bring electricity from welding machine
to work metal and back to welding machine and earth cable. These cables are made from
small copper wire coated with strong rubber so that you can hold it. Every cable has it
own size. Size No. 2 means that the cable will be able to withstand welding electricity up
to 200 amps. These cables are connected to the welding machine through its copper end.
Electrode Holder.
It is used to electricity from welding machine to work metal. It is
also used to hold the electrode during the welding process. It has a spring as its parts
so that it can hold and let go off the electrode easily. Electrode holder must be
lightweight, have good rubber coating and easy to handle for quite along time. It has its
own size for the amount of electric current that it carries.
Earth Holder.
It is connected to the earth cable and clipped to the work metal
or to work table. It has a spring so that is can be easily clipped and unclipped. Without
this equipment, welding work will certainly cannot be done.
Shield.
It is made from fireproof material. In the middle of the shield
there is a bright glass coated with dark colored glass. It is used to protect you from
fire-bolt and harmful rays. There are two types of shield, one is the helmet type and the
other one is the hand held type. It has the size of No. 10 and No. 11.
Chipping Hammer.
It is made from an old punch, chisel or spring metal. Shape like
a chisel at one end and has a sharpened end at the other one. Its holder is made from
welded soft metal. It is used commonly to break off slag excess stringer from the surface
of the work metal.
Wire Brush.
It is used to clean the surface of the stringer bead after the
slag is chipped away and to remove dirt from the surface of work metal before welding can
be done.
Glove.
It must be made from high quality leather. Use to protect your
hand from fire-bolt and hot metal welding.
Tongs.
Use to hold hot work metal after welding process.
Procedure:
- Connect the electrode cable and the earth cable to the Direct Current Welding Machine.
- Clip the earth cable using its holder to the working table.
- Put an electrode onto the holder. Make sure that the flux is not in contact with the
holder.
- Set the dial to 90 amps and turn on the machine.
- Before you start welding, put on your gloves and shield.
- Take a piece of scrap metal and put it on the working table.
- Hole the electrode 90o above the scrap metal. Tilt the electrode 20o-25o
degrees to the right or left depending on which hand do you use from the work metal.
- Scratch the front end of the electrode onto the work metal to start the burning After
the electrode has started burning, hold it at 10mm above the work metal. Do not touch the
metal during the welding process because the electrode might be stuck onto it.
- Repeat the welding process for several times until you get a straight and firm stringer
bead line when you weld onto the work metal.
- Get a cubic-shape metal block from your instructor.
- Weld onto one side of the block to increase its thickness.
- You must weld onto the block line by line. When you finish welding a line, use chipping
hammer to chipped off the slag and brush it off using a wire brush.
- Stop when you have finished welding the side in three layers.
Safety Precautions.
Always protect your eyes from arc rays.
Protect your face and body from heat radiation and molten metal.
Make sure that your working place is clean and tidy.
Move all the flammable material off the working place or cover it up using fireproof
material.
Make sure that all electric connection is tight, clean and dry.
Make sure that all line holder, earth clip and connection placed on good place.
Do not ever scratch arc on top of gas cylinder.
Avoid welding cable from be in contact with hot metal, water, oil and grease.
Avoid pulling the cable on top or near sharp things.
Turn off the welding machine when not in use.
Wear all safety clothing when welding.
All equipment such as hammer, chisel, brush and others must be well taken care of.
A welder should not try to install or repair a welding machine.
Make sure that the welding machine is earthen.
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