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Overhead Welding

These welds should be made as for welds in the flat position ‑ with due allowance for gravity! Obviously large pools of molten metal are not manageable in this position and wide weaves are rarely acceptable. Fast narrow beads are the easiest with 4.Omm being a maximum size usually employed. Use slightly lower than normal currents but travel faster. Again an overhead pad is the best way of practicing control. Use a 3.2mm Austarc 12P or 13S at 120 amps, maintaining a short arc length. Two hands may assist steadiness. The electrode should be kept at right angles to the plate width, pointing back some 5° ‑ 10° on to the molten pool In subsequent pad runs the electrode can be slanted at an angle on to the toe of the preceding bead. To achieve a comfortable welding position it may be desirable to bend the electrode at the holder with some types of holders. When proficient, try a fillet weld with the sequence and angles indicated in Fig. 24.

A slight weave can be attempted to help smooth out the bead shape and if this is used a drop in amperage may assist in controlling the molten pool.

General Notes on Fillet and Butt Welds

Larger electrodes using higher amperages put down more metal faster. While this is important in industry, the use of one or two electrodes of smaller gauge in a small shop may reduce outlay, make for greater skill and better welds. Consider 4mm as the maximum size out of position ‑ a 3.2mm gauge in the vertical may often prove easier to handle for the beginner and occasional welder.

Always place a cover pass on the reverse side of a simple vee butt weld (if no backing plate) and generally have both sides of a T fillet welded for full strength in all directions.

Lap joints should be secured wherever practicable with welds on both sides of the joint. Certainly welds in tanks should never be carried out with only one weld externally where corrosion can take plate in the open inner seam. Always lap the plates to the extent of at least five times the thickness of the thinner plate.

Lap and corner welds should be watched to ensure full throat thickness being achieved without melting of the edges of the plates, which would result in reduced effective plate thickness.

Two pass fillet welds can be considered as acceptable providing care is taken to ensure penetration to the root of the joint.

 The bottom leg is made longer than the vertical leg and the second pass brings the vertical leg to size.

A fillet size is nominated by the leg length. Thus a six millimeters fillet has leg lengths of 6mm. Usually fillet size is equal to plate thickness of the smaller plate, e.g.. for welding 12mm plate to 6mm plate, a 6mm fillet is selected.

Some reinforcement of fillet and butt welds is acceptable, but excessive reinforcement is undesirable from both a strength and economy point of view.

Concave welds are more prone to cracking problems than convex welds. A flat weld is the ideal from most points of view.

Undercut‑sections of the parent metal where the material has been scarfed away by arc action and not replaced with weld metal is particularly undesirable in items subjected to reversal stress or flexing, such as shafts, beams, etc.

Excessive currents tend to overheat electrodes and add little to their penetration.

Care in joint preparation is more than amply repaid in reduced welding time, quality of workmanship and joint soundness.

Moisture in electrodes increases spatter, fiery running, impairs general appearance, properties, and slag removal. Take care to ensure your electrodes are stored correctly and dry.

Summarising

In the preceding sections we have suggested practical welding in almost only one size and type of electrode for purposes of easy tuition. The welder has been gradually led into trying other types, sizes and currents and we should perhaps summarise these important aspects at this point.

Electrode Size

Electrode size is nominated by diameter of core wire.

Electrodes are available from 2.Omm to 6mm diameter, and this permits economic industrial welding of a wide range thickness of material. The small user rarely has the need or the equipment to warrant stocking of this full range.

Within limits, larger electrodes permit more economical welding on heavy jobs, but with correct techniques the maintenance welder need rarely exceed 4mm a to achieve sound welds. Similarly, a suitable 2.5mm electrode with appropriate technique can weld down to 1.5mm material, although on the flat a 2.Omm size may be desirable. Size of course determines the amperage used and so

the heat input into the job. Generally, the bigger the joint the bigger the electrode desirable. It will be found how, by use of special techniques the effective heat input and penetration can be reduced in light material by coming down and increased in heavy material by going up, with the flat giving average rates of heat input and penetration. Thus a 3.2mm electrode can be used to weld 1.5mm

sheet vertically down and 15mm thick section vertically up but would be considered as inappropriate for either on the flat.

Welding Current

Each packet of electrodes indicates a suitable range of usable welding currents. Generally normal currents are above the average of the upper and lower limits and welders will experience less trouble when keeping to this more efficient upper range.

The upper limit is usually determined by the ability of the electrode to run out its full length without deterioration of its running characteristics or weld metal properties. On lighter material, currents may be reduced to reduce penetration or overheating of the base material.

Electrode Selection

A wide and to some extent confusing range is available to the user. From the point of view of economical stocking, perfection of technique with one GP type makes sense. Because the many little peculiarities which may warrant a different special electrode in a particular type of high production application are not present in the all round jobbing shop, the user will do well to restrict his range to several lines with wide applications.

The Table on page 16 shows the major lines recommended for this class of rural jobbing application. Some more specialised Austarc electrodes are available and may be used where the volume of work or its nature is such that their use is warranted.
 

 

 

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