less effective. Oxides of the alloying elements have a higher melting point than the alloying elements themselves and are refractory in nature. (Remember that oxides of iron have melting points lower than the melting point of iron so they become fluid and they readily leave the kerf as molten slag.) Unlike iron oxides, an alloy’s oxides do not readily run out of the kerf to expose new iron to oxygen to keep the burning process going, and cutting becomes more difficult.
By what means can OFC be extended to metals and alloys not readily cut?
•Torch Oscillation
•Waster Plate
•Wire Feed
•Metal Powder Cutting
•Flux Cutting
How does torch oscillation work?
By torch manipulation the entire starting edge of the cut is brought to a bright red color before beginning the cut. This technique is usually used in conjunction with one of the other four cutting enhancement methods on low-alloy stainless steel up to 4 inches thick and on resistant cast iron.
How does a waster plate work?
A low-carbon steel waster plate is secured to the top of the stainless steel to be cut, and the cutting action begun on the waster plate. The heat released from the waster plate’s burning provides additional heat to the cutting action in the stainless below. Hot slag from the waster plate tends to flush the kerf of the stainless steel’s refractory oxides. Waster plate disadvantages are the extra cost of the waster plate, additional set-up time, slow cutting speeds, and rough cut.
How does wire feed cutting work?
A small diameter carbon steel wire is fed into the torch preheat flame just ahead of the cut and melts onto the surface of the alloy steel. The additional carbon steel works just like a waster plate to enhance cutting action. A motor feed and wire guides are needed as accessories.
How does metal powder cutting work?
Powder metal cutting (AWS abbreviation is POC) uses iron-rich powder that is dropped into the kerf or injected into the cutting oxygen stream to add heat. Some powders also chemically combine with the alloying oxides to increase their fluidity and increase the ability of the oxygen jet to wash them out of the kerf. Frequently, cutting speed of POC in high-alloy steels can match OFC in mild steel of the same thickness.
How does flux cutting work?
Flux cutting uses a granular flux introduced into the oxygen cutting stream. The flux combines with the alloying metals’ oxides to lower their melting temperatures to near those of iron oxides and get them to flow out of the kerf. Flux cutting can eliminate torch oscillation and can increase cutting speeds in stainless to that of carbon steel of the same thickness.
Tips, Techniques, and Helpful Accessories
Why is it important to keep the torch tip face clean and flat and to clean out the orifices with tip cleaners regularly?
A damaged tip face or plugged tip orifice can cause an unsymmetrical flame. Such a flame will produce irregular rough edges, and slow cutting action. Dirt inside the torch tip may cause flashbacks.
What are the two best ways of marking the line of cut?
•With welder’s soapstone.
•By a series of center punch marks along the line of cut.
What readily available material may be used to improve the quality of some cutting tasks?
Angle-iron may be used as a straight edge guide, or as a bevel guide. See Figure 2–10.
Figure 2–10Angle iron used as a straight edge (left) and bevel guide (right)
What are two mechanical aids that can be attached to a cutting torch?
•Wheels to keep the torch tip at a constant height above the work and reduce operator fatigue. See Figure 2–11.
Figure 2–11Torch wheels
•Compass attachment to make nearly perfect circles easily. See Figure 2–12.
Figure 2–12Compass attachment
Name the four main types of electrical or electronic aids to guide a cutting torch to increase the accuracy and quality of cutting.
•The motorized cutting head is the most primitive improvement over a handheld torch. Its wheel is motor-driven to maintain optimum cutting speed; the wheel also keeps the torch-to-work distance constant. However, the welder must still guide the motorized head manually. The small wheel in the rear of the unit is useful for cutting accurate bevels. See Figure 2–13.
Figure 2–13A motorized cutting head
•A portable track cutting machine travels along a pair of steel rails driven by a 120 VAC motor. It can make 90° bevel angle and chamfer cuts. It also cuts circles from 4 to 96 inches (0.1 to 2.4 m) diameter. With a second torch, it makes two parallel cuts simultaneously to produce a strip of metal with two parallel edges. It is especially useful in cutting accurate bevels and chamfers for proper fit up. See Figure 2–14 and 2–15.
Figure 2–14Portable track cutting machine
Figure 2–15Two-torch strip cutting attachment for portable cutting machine
•A pattern tracer is the next level of improvement. A stylus follows the edge of a metal pattern, or a photoelectric eye follows the lines on paper and a torch (or could be multiple torches) is directly connected to the pattern tracing mechanism, permitting the torch to reproduce the pattern shape in steel. These systems require heavy cutting operator involvement and supervision.
•Computer driven cutting machines produce the most accurate and best quality cuts. These machines store the path of the cutting torch in their memories. Advanced machines control torch-to-work distance, adjust the torch speed on curves and around corners, adjust the pre-heat and cutting flame to starting and ending cuts. The most sophisticated
