456A SMAW Stick — Questions and Answers
Question 1: What does the 'E7018' electrode designation mean according to CSA/AWS classification?
- E = electrode, 70 = cost in dollars, 18 = length in inches
- E = electrode, 70 = minimum tensile strength (70,000 psi / 480 MPa), 1 = all-position capability, 8 = low-hydrogen iron powder coating with AC/DCEP (Correct answer)
- E = electric, 70 = amperage, 18 = rod diameter
- E = electrode, 7018 = catalogue number
Correct answer: E = electrode, 70 = minimum tensile strength (70,000 psi / 480 MPa), 1 = all-position capability, 8 = low-hydrogen iron powder coating with AC/DCEP
In the AWS/CSA designation: E = electrode, 70 = minimum tensile strength in ksi (70,000 psi or 480 MPa), 1 = usable in all positions (flat, horizontal, vertical, overhead), 8 = low-hydrogen iron powder coating suitable for AC and DCEP. The E7018 is the most widely used structural electrode in Canadian construction.
Question 2: What is the purpose of the flux coating on a SMAW electrode?
- To make the electrode easier to grip
- To shield the weld pool from atmospheric contamination, stabilize the arc, add alloying elements, and form a protective slag over the cooling weld (Correct answer)
- To increase the electrical resistance of the electrode
- To colour-code the electrode for identification
Correct answer: To shield the weld pool from atmospheric contamination, stabilize the arc, add alloying elements, and form a protective slag over the cooling weld
The flux coating serves multiple critical functions: it decomposes in the arc to create a shielding gas that protects the molten weld pool from nitrogen and oxygen contamination, forms a slag that protects the cooling weld, stabilizes the arc, adds deoxidizers and alloying elements, and controls the weld bead profile.
Question 3: Why must low-hydrogen electrodes (E7018) be stored in a heated oven or opened from vacuum-sealed packaging?
- To keep them warm for easier striking
- To prevent moisture absorption by the flux coating, which can introduce hydrogen into the weld and cause hydrogen-induced cracking (Correct answer)
- To make the flux coating harder
- To prevent the electrodes from sticking together
Correct answer: To prevent moisture absorption by the flux coating, which can introduce hydrogen into the weld and cause hydrogen-induced cracking
Low-hydrogen electrode coatings readily absorb atmospheric moisture. If used wet, the moisture decomposes in the arc, introducing hydrogen into the weld. Dissolved hydrogen can cause delayed cracking (hydrogen-induced cracking or cold cracking) in the heat-affected zone. CSA W59 requires storage at 120°C to 150°C in a rod oven after opening.
Question 4: What polarity is typically used for E7018 electrodes and why?
- AC only, for better arc stability
- DCEP (DC Electrode Positive / Reverse Polarity) for deeper penetration and a smoother, more stable arc; AC is also acceptable (Correct answer)
- DCEN (DC Electrode Negative / Straight Polarity) for less heat input
- Polarity does not matter for SMAW
Correct answer: DCEP (DC Electrode Positive / Reverse Polarity) for deeper penetration and a smoother, more stable arc; AC is also acceptable
E7018 electrodes perform best on DCEP (reverse polarity) where the electrode is positive and the workpiece is negative. DCEP concentrates about two-thirds of the arc heat at the electrode tip, promoting deeper penetration and better arc characteristics. E7018 is also designed to run on AC, making it versatile for field conditions.
Question 5: What is arc blow in SMAW welding and how can it be corrected?
- A loud noise from the arc; corrected by wearing hearing protection
- An uncontrolled deflection of the welding arc caused by magnetic fields; corrected by changing ground clamp position, welding toward the ground, using shorter arc length, or switching to AC (Correct answer)
- An explosion of the electrode; corrected by reducing amperage
- Excessive spatter; corrected by cleaning the base metal
Correct answer: An uncontrolled deflection of the welding arc caused by magnetic fields; corrected by changing ground clamp position, welding toward the ground, using shorter arc length, or switching to AC
Arc blow is the deflection of the welding arc by magnetic fields created by the DC welding current flowing through the workpiece. Corrections include: repositioning the work lead (ground clamp), welding toward the ground connection, using a shorter arc length, wrapping the work lead around the workpiece, or switching from DC to AC power.
Question 6: What is the correct technique for striking an arc with a SMAW electrode?
- Stab the electrode straight down onto the workpiece
- Use either a scratching motion (like striking a match) or a tapping motion, then establish the correct arc length (Correct answer)
- Hold the electrode close to the workpiece without touching it
- Touch the electrode to the workpiece and hold it in contact for 5 seconds
Correct answer: Use either a scratching motion (like striking a match) or a tapping motion, then establish the correct arc length
Two common arc-striking techniques are: the scratch method (drag the electrode tip across the workpiece in a scratching motion, then lift to establish arc length) and the tap method (touch the electrode tip lightly to the workpiece and quickly lift). Both establish the arc, which is then maintained at the correct arc length (approximately equal to the electrode core wire diameter).
456A SMAW Stick
What does the 'E7018' electrode designation mean according to CSA/AWS classification?