Exothermic Electrode Cutting Techniques
The 1/4-inch exothermic cutting electrode may be used to cut steel up to 1/2 inch in thickness. The 1/4 inch electrode leaves a narrow kerf and is preferable for fine cutting. When visibility is poor or when cutting heavier steel, the 3/8-inch electrode is more efficient. The following techniques are recommended:
Insert the electrode into the collet opening until it bottoms out on the washer. Tighten the collet nut. When ready to start the cut, hold the oxygen trigger down to get a steady flow of oxygen. Release the trigger slightly. Hold the electrode at an angle of 45o to 90o to the surface to be cut, depending on material thickness (see Figure 2-7). Call for SWITCH ON. Draw the tip of the electrode across the work and strike an arc. As soon as the arc is established, squeeze the trigger full open. Hold the tip of the electrode in the molten pool and drag the electrode along the line of cut. Apply a downward pressure until the electrode penetrates the full thickness of the material to be cut.
Before beginning the cut, the diver should visually check the oxygen flow while holding the electrode in a horizontal position. Holding the oxygen trigger down for approximately 20 seconds allows time enough for cutting-gas pressure to build up along the full length of the hose. To ensure a clean cut, a 6-inch (minimum) oxygen emission should be maintained at the electrode tip.
Technique for Cutting Steel Using Exothermic Electrodes
To advance the cut, apply slight pressure to maintain electrode/work contact. Hold the electrode with the free hand as if holding a pool que, approximately 4 inches from the tip for a more stable cut. Move slowly at first, maintaining full penetration. Lack of penetration will be evident by back-spray, increased cutting noise and slag build-up. In such cases, stop advancement and go back and wash out all hangers to complete the cut. It is important to keep the electrode against the work while cutting and keep the tip of the electrode in the puddle. Do NOT try to hold an arc. CAUTION Burning the electrode shorter than the 3-inch minimum can damage the torch interior.
When the electrode has burned down to within 3 inches of the collet nut, break the contact, release the oxygen trigger and call for SWITCH OFF. When the phone talker has confirmed SWITCH OFF, tap the electrode twice to make sure the switch is off. Loosen the collet nut 1/2-turn and blow the cutting stub from the torch by squeezing the trigger. Insert a new electrode and repeat the starting procedure outlined in 2-3.6a. above.
For cutting material thicker than 1/2-inch, use a 3/8-inch electrode. A sawing motion often works well on thicker materials.
For materials several inches thick, a saw and wedge cutting technique similar to chopping
a tree with an axe may be necessary to widen the cutting path.