Oxy/Fuel Cutting-An Introduction
With oxy/fuel cutting, an oxygen/fuel gas flame preheats the steel to its ignition temperature. A high-power oxygen jet is then directed at the metal, creating a chemical reaction between the oxygen and the metal to form iron oxide-also known as slag. The high-power oxygen jet removes the slag from the kerf. Cut quality, preheating times, and thicknesses can be influenced by the type of fuel gas used. Oxy/fuel cutting is used for ferrous (iron-containing), mild, and low-alloy steels in thicknesses up to 24 inches.
With a fuel tank, oxygen tank, and a torch, you can cut steel anywhere-except for non-ferrous metals such as aluminum and stainless steel. Oxy/fuel cutting allows metalworkers to cut extremely thick metals with ease-and a variety of torch options allow users to braze, solder, fusion weld, gauge, preheat, and bend metals as needed.
Other Methods-An Overview
This article, while focusing on hand-held oxy/fuel and plasma cutting, would be remiss if it did not make brief mention of other methods of cutting metal and steel. Bandsaws are extremely effective in accurately and efficiently cutting tube and pipe. Lasers, along with mechanized plasma and oxy/fuel, are frequently used in large-production applications such as the manufacturing of construction equipment and shipbuilding to cut massive, intricate sheets of steel-eliminating operator error and operator fatigue-but are only necessary for certain high-flow work applications. Other more antiquated and labor-intensive tools, such as shears and hacksaws (with the appropriate blade), are used in some applications, but are hardly efficient given the lowering costs and overabundance of power tools to do the job.
Making The Selection: Plasma Or Oxy/Fuel?
The two key questions that need to be asked before choosing plasma or oxy/fuel cutting tools are:What do you cut on a day-to-day basis?What is the thickest metal, within reason, that you'll ever cut?The answer to these two questions will point you in the right direction.
The Argument For Plasma
Plasma cutting has been praised for its ability to cut thin metals (less than 3/8 inch) quickly, neatly, and with a minimal heat-affected zone-minimizing distortion and warpage. It is also typically a very clean cut, with minimal cleanup, as any dross is blown clear of the work piece. This method continues to gain market share in the metal cutting industry as equipment becomes less expensive, units become smaller due to inverter-based technology, and it continues to prove itself as a viable cutting option. Plasma cutting cuts all electrically conductive metals, including aluminum and stainless steel. These two metals cannot be cut by oxy/fuel cutting systems due to an oxide layer that prevents oxidation from occurring. If your day-to-day business involves cutting aluminum and stainless steel, a plasma cutting system is the right tool for you. Equally as important as the type of alloy, however, is the thickness
Each plasma cutter features a rated output and a rated cut-the higher the amperage (output), the thicker the cut. For instance, a plasma cutter with a rated output of 40 amps at 140 volts DC at 50 percent duty cycle features a rated cut of 1/2 inch, a maximum quality cut of 5/8 inch, and the ability to sever steel as thick a 7/8 inch. Compare that to a plasma cutter with a rated output of 100 amps at 120 volts DC at 80 percent duty cycle, and the capabilities increase: a rated cut of 1 1/4 inches, a maximum quality cut of 1 1/2 inches, and a sever rating of 1 3/4 inches.
The three cutting ability ratings tell you how quickly you can cut with a given plasma cutter. A "rated" cut represents a machine's ability to cut steel at a rate of 10 inches per minute (IPM). A "maximum quality" cut represents 7 IPM at the given thickness, while the "sever" rating simply points out the thickest metal the machine can cut-it does not have the amperage to adequately blast the arc through steel any thicker.