Arc Welder
SIZE: Amperage range: 30 to 250
MATERIAL: Various
ACCESSORIES: Welding rods
USE: To join metal by fusion of the workpiece
Arc welding joins metal to metal by heating the material to melting point with an intense electrical discharge in the form of an arc. The arc is produced by passing an electric current, regulated by a transformer, across an air gap between an electrode and the work. The electrode also melts, adding more molten metal to the weld, filling up any vacant space and reinforcing the joint.
The outside of the electrode is covered with a flux-like coating. During the welding process some of the coating is burnt off, forming a gaseous screen to protect the molten metal from oxidation. The remaining material combines with impurities in the molten metal floating to the surface to form a coating of "slag" which is broken off when the weld finally "freezes".
Preparing to weld
Protect yourself against the intense light produced by arc welding, as well as the inevitable shower of sparks. Use special dark glass goggles or a face mask to view the work whenever the welder is used.
Wear heavy duty leather gloves preferably with gauntlets. A 'leather apron stops any sparks falling on your clothes, which should be dark to avoid reflected light from the arc.
Make sure that the area surrounding the welding bench is free from inflammable material. If possible, cover the bench 1/4 in. sheet steel.
Setting up the equipment
The ground connection must be connected to the work, or to a metal bench top if the work is in contact with it. Insert a welding rod in the electrode holder and select the appropriate amperage recommended for the rod. The smaller transformers available to the home user will handle electrode sizes from 16 to 10 swg. Mild steel electrodes are the most common, although many alloys are used for different materials.
Clamp or wire together the workpieces to secure the joint.
Striking an arc
When the electrode is brought into contact with work and quickly lifted 1/8in. from the surface, a spark is produced. Either strike the work with the tip of the rod letting it bounce the required amount, or swing the tip against the work rather like striking a match, lifting it from the work as it comes into contact. If the electrode is not lifted quickly enough, the end of the rod will stick to the work producing a short circuit. Dislodge a sticking electrode as quickly as possible by moving the rod from side to side pulling it from the work.
An electrode held the correct distance from the work will crackle evenly. If held too far away, it will sound uneven and snap out completely at a certain distance from the work. At the end of the weld, lift die electrode quickly from the work to snap out the spark.
Laying a bead
The process of applying molten metal to the weld is known as "laying a bead". Hold the electrode 15° in the direction of the weld. Strike an arc and move the rod at a steady rate, maintaining the correct angle and length of arc. Move the rod as the back end of the crater fills up with the molten metal called the "puddle".
If you move it too slowly, the slag will flow in front of the molten metal and contaminate the weld, producing gas pockets. When the weld has frozen, chip off the slag with a cold chisel or a "chipping hammer", which has a cross peen and a pointed end.
Getting the bead right
A good weld will produce an evenly rippled bead which is uniform in width. Current which is too low will not penetrate the metal very far, leaving a high bead on the surface of the work. The arc will also be intermittent.
If the current is set too high, it will penetrate well, but the bead itself will be thin leaving undercuts. The arc will hiss.
If the weld is too slow, a wide bead will form, which does not fuse well at the sides. The job will also be overheated, encouraging distortion.
If the weld is too fast, it will not deposit enough metal, so an irregular narrow bead with undercuts will form.
If the arc is too long, it will produce a rough weld, splattering globules of metal along the bead. If you have any trouble maintaining an arc, even with the electrode held at the recommended distance from the work, check that the ground connection is satisfactory. Alternatively, you may need to increase the current to suit the size of the welding rod.
GOOD WELD
Types of joint
Practice all the various joints and techniques on scrap material before attempting to weld an actual job. Always tack-weld a job with beads about 1/4 to 3/8in. long at strategic positions along the joint to hold the work securely while you lay the main bead.
For thin gauge metal, 16 swg, for example, butt the edges together and tack-weld the joint. Raise the work above the bench on pieces of scrap metal, and lay a bead along the joint. If the current is too high or the rate of travel is too slow you may burn through thin sheet metal.
Set the transformer at 30 to 50 amps for this thickness of metal and use a 14 swg rod. For thicker sheets, say 18 swg metal, leave a 1/16in. gap at the joint and tack-weld both side? before laying a bead on one side to penetrate halfway through the metal. Turn the work over and lay a second bead.
WELD SHEET METAL
BACK UP SHEET
Preventing burn-through
Back up the joint with a strip of copper to absorb some of the heat of the arc. It will also leave a perfectly flat joint on the underside.
Butt jointing thick metal
On metal up to 3/8in. thick, bevel the edges of the plate. If the plates can be welded from both sides, bevel the underside also. Make a pass to lay a bead in the centre of the joint. Clean off the slag and lay two more beads. Finally, lay a reinforcing bead. You will need to weave the electrode from side to side as you move along the joint to achieve a wide enough bead.
Reinforcing bead
Make four passes to butt joint really thick metal. The first pass (top) deposits the bead in the centre of the joint. It must penetrate to form a small bead on the other side. Make the second and third passes side by side to fill the gap. Finish the joint with a reinforcing bead, (bottom).
Corner weld To join on the outside of a corner, fill the right angle gap between the two edges. For thin metal lay one bead down the centre, or fill the gap with weld as for a beveled butt joint.
Edge weld
Weave a bead across the two edges for a side by side join.
Lay a bead in each corner of the lap joint. Try to fill the right angle with an even bead. Do not melt too much of the top corner.
Fillet or right angle weld
Lay a single bead down the centre of the joint, keeping the electrode centreed between the two halves of the joint. The thickness of the bead should be approximately that of the metal, and the surface of the bead should be nearly flat with the edges slightly curved where they meet the metal. If necessary, lay more than one bead.
Position welding
The easiest way of welding a joint is to lay it flat on the bench. Welding in this position is known as "flat welding'. It is not always possible to work on the bench and it may be necessary to weld a joint in situ.
Vertical welding
The most difficult part of welding a vertical joint is keeping the molten metal from falling out of the puddle. The arc must be kept short and the puddle kept small to encourage the weld to freeze quickly.
For welding sheet metal over 1/8in. thick use the vertical up method. Use 8 or 10 swg rods.
Lay wider beads for a large fillet or beveled joint by weaving the rod from side to side.
Vertical up welding
Point the electrode up slightly and strike an arc depositing a small amount of metal at the base of the joint. Quickly raise the tip with a wrist movement, which lengthens the arc before depositing more metal on that previously laid. Continue with this "whipping" motion up the entire joint.
Vertical down welding
For sheet metal up to 1/8in. thick work from top to bottom. Hold the electrode centrally on the joint pointing upward and lay a bead at a steady rate. Large diameter rods are difficult to control so use as small a rod as will do the job.
Horizontal and overhead welding
To prevent the bead sagging, the movement of the electrode must be slightly faster than for other positions. Insure that falling sparks or molten metal cannot get inside your collar or gauntlets.
