Welding course notes

The following are some notes taken from a night course I did on welding:

Stick welding

• Welders with a ‘hot start’ feature temporarily raise amperage when the arc is first formed to help warm up the material.
• Clean flux from weld between runs.
• Weld pool should be about two times the electrode diameter.
• The greater the distance the electrode is from the weld pool, the wider the weld pool becomes and you get more splatter.
• The lead angle of the electrode should be about 20° in the direction of the run.

• Larger electrodes are used for thicker materials.
• Rutile or general purpose rods have a wide range of applications.
• Electrode storage in the tropics is pretty important. Wet season humidity can destroy a pack of electrodes in an afternoon.
• Electrodes can sometimes restored by cooking them in an oven for 150°C for an hour or two.
• An old sealed fridge, fitted with an always-on incandescent bulb can be used to store the electrodes. Otherwise you are looking at about $200 for an electrode storage oven.

• Welding galvanised metal gives off toxic fumes.
• Wear a respirator fitted with activated charcol filter.
• And/or remove 5mm of galvinsation around the weld with a grinder.
• Store respirator filters in a zip-lock bag when not in use (they absorb moisture and lose effectiveness).

TIG welding

• Electrode made out of tungsten, has a melting point of 3000°C and is not consumed.
• Need to avoid contaminating the electrode by touching the weld pool or filler wire.
• Mild and Stainless steel requires a sharp fine point to the tungsten electrode.
• If the Tungsten becomes contaminated, you will need to grind it back. When grinding, keep the grains lengthwise. Otherwise the arc will wander.
• Argon is used as a shielding gas to prevent the weld from oxidizing while it is hot.
• Keep the gas flowing for 1 second per 10 amps after the arc is extinguished. (Post flow).
• TIG welding machines have three modes:
  1. DCSP - not good for aluminium. The electrode is negative.
  2. DCRP - need large electrode, limited applications. The electrode is positive.
  3. AC - Use a square wave arc that is extinguished for shorter periods. (Good for aluminium).
• Different types of tungsten electodes are available:
  1. Thoriated tungsten is good for stainless steels and copper. Used in DCSP mode (electrode is negative). This is not suited for aluminium.
  2. Zirconiated tungsten is good for aluminium, used in AC mode.
  3. Ceriated tungsten is good for all metals in AC & DC modes.
• Aluminium melts at 600°C and gomes in different grades:
  1. 1000 series is the lowest.
  2. 5000 and 6000 series is marine grade (most common)
  3. 7000 series is aviation grade and becomes brittle when welded.
• Filler wire needs to match material.
• Grinding tungsten on a grinder shared with steel may contaminate the electrode with steel particles.
• Use a stainless steel brush to clean any aluminium surfaces. A steel brush will contaminate the surface.

 

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August 16, 2017