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One of the fundamentals is the use of the correct electrode angles. For
fillet and groove welds, correct electrode angles are vital for preventing undercut
and inadequate fill. When depositing a fillet weld, the electrode should be held so
that it bisects the angle between the plates and is perpendicular to the line of the
weld. On groove weld, the technique is much the same; although varying slightly with
multiple pass welding. There are two tearns to specify electrode angles. These are
travel angle and work angle.
The travel angle applies to the position the electrode makes with a reference
perpendicular to the axis of the weld in plane of the weld axis. It can be either a
drag angle or a push angle. A drag angle is when the electrode is pointing
backward, which means, the welder's hand and electrode holder precede the puddle.
A push angle is when electrode is pointing just the opposite of the drag.
The work angle is the position the electrode makes with reference to the
surface of the plate on a plane perpendicular to the weld axis. On butt joints, the work
angle is usually 90 degrees to the surface of the plate.
To some degree, you can correct for an improper condition by varying the
essential variables. It is better though to have all conditions as correct as possible.
trude
Manipulatia-
Respuestas
Respuesta:
1) CORRECT ELECTRODE SIZE
The correct choice of electrode size involves consideration of a variety of factors, such as the type, position, and preparation of the joint, the ability of the electrode to carry high current values without injury to the weld metal or loss of deposition efficiency, the mass of work metal and its ability to maintain its original properties after welding, the characteristics of the assembly with reference to effect of stresses set up by heat application, the practicability of heat treatment before and/or after welding, the specific requirements as to welding quality and the cost of achieving the desired results.
2) CORRECT CURRENT
If current on equipment is too high or too low, you are certain to be disappointed in your weld. If too high, the electrode melts too fast and your molten pool is large and irregular. If too low, there is not enough heat to melt the base metal and your molten pool will be too small, will pile up, and look irregular.
3) CORRECT ARC LENGTH or VOLTAGE
If the arc is too long or voltage too high the metal melts off the electrode in large globules which wobble from side to side as the arc wavers, giving a wide, spattered and irregular bead-with poor fusion between original metal and deposited metal. If arc is too short, or voltage too low, there is not enough heat to melt the base metal properly and the electrode quite often stick to the work, giving a high, uneven bead, having irregular ripples with poor fusion.
4) CORRECT TRAVEL SPEED
When your speed is too fast your pool does not last long enough, impurities and gas are locked in. the bead is narrow and ripples pointed. When speed is too slow the metal piles up, the bead is high and wide, with a rather straight ripple.
5) CORRECT ELECTRODE ANGLE
The electrode angle is of particular importance in fillet welding and deep groove welding. Generally speaking, when making a fillet weld, the electrode should be held so that it bisects the angle between the plates and is perpendicular to the line of weld. If undercut occurs in the vertical member, lower the angle of the arc and direct the arc toward the vertical member.
8 FACTORS to consider in selecting arc welding electrodes
Base metal strength properties
Base metal composition
Welding position
Welding current
Joint design and fit-up
Thickness and shape of base metal
Service condition and/or specifications
Production efficiency and job conditions
1) BASE METAL STRENGTH PROPERTIES
Know and match mechanical properties. Mild steel-generally E-60XX or E-70XX electrodes match base metal. Low alloy steel-select electrodes that match base metal properties.
2) BASE METAL COMPOSITION
Know and match composition. Mild steel –any E-60XX or E-70XX electrode is satisfactory. Low alloy steel – select electrode that most closely matches base metal composition.
3) WELDING POSITION
Match electrode to welding position encountered.
4) WELDING CURRENT
Match power supply available. Some electrodes are designed for direct current (DC); other, alternating current (AC); some, either. Observe correct polarity.
5) JOINT DESIGN AND FIT UP
Select for penetration characteristic- digging, medium, or light. No beveling of tight fit- up – use digging. Thin material or wide root opening – light, soft arc.
6) THICKNESS AND SHAPE OF BASE METAL
To avoid weld cracking on thick and heavy material of complicated design, select electrode with maximum ductility. Low hydrogen processes or electrodes are recommended.
7) SERVICE CONDITION AND/ OR SPECIFICATIONS
Determine service conditions – low temperature, high temperature, shock loading – match base metal composition, ductility and impact resistance. Use low hydrogen process. Also, check welding procedure or specification for electrode type.
8) PRODUCTION EFFICIENCY AND JOB CONDITIONS
For high deposition and most efficient production under flat position requirements, select high iron powder type of large diameter wires; for other conditions, you may need to experiment with various electrodes and sizes.
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