ESAB Knowledge center.
What is Flame Cutting?
June 2, 2013
A process known by many names
The process often called Flame Cutting is known by many names, such as Oxy Acetylene Cutting, Oxy Fuel Gas Cutting, Oxygen Burning, Steel Burning and other terms too numerous to mention. The process is now about 111-112 years old as it was patented in 1901 by Thomas Fletcher. One of the first commercial applications was what the British referred to as “an unauthorized bank entry”, or a “safe cracking”.
How does it work?
The process is a Thermo-Chemical Process requiring a source of intense heat, referred to as “Preheat”, and pure oxygen. The pure oxygen requirement is of a 99.5% minimum purity, which is the minimum purity typically provided in cylinders and bulk systems. A reduction in purity of .1% will reduce cutting speed about 10%, so one can see the necessity for the purity.
While the source of the Oxygen may be pure, improper connections, bad hoses, or leaks of any sort can allow impurities in the system thereby reducing the cutting speed. The high purity of the Oxygen presents a very dangerous situation and requires extreme care in the selection of equipment and the design of piping systems for its use. There are numerous documents available to assist with these safety issues. Federal Law (OSHA) presents numerous requirements for the equipment to be used, as well as the procedures to be followed.
The process can be used for cutting/severing many different materials with the basic requirement that the oxide formed must have a lower melting point than the base material to be cut. A good example of a material one cannot cut is Aluminum whose melting point is in the order of 1,200-1,300 degrees F but whose oxide is in the range of 5,000+ degrees F. Stainless steel has additives such as Chromium and Nickel added for “Oxidization Resistance” and this is the process (Oxidization) one is trying to promote, i.e. this type material is not cut without some assistance.
What thickness material can be cut?
The process can cut from sheet metal thicknesses to 100 inch material. Prior to 1958, when Plasma was introduced, all thicknesses were flame cut. Today metal thinner than 3/8-1/2 are typically only cut by plasma or laser, as thin materials are very challenging to flame cut. Thin material requires a very intense preheat as the cutting speed required for a good quality cut is very high, therefore a high temperature high velocity preheat is desired.
The process for all thicknesses is the same and that is the material must be “preheated” to a temperature of 1,600-1,800 degrees F, then the pure Oxygen is discharged into the preheated area and the steel is then oxidized or burned, hence the term “burning”. (The term “burner” is often used for the operator.) The quality of the final cut surface can be quite excellent with a sharp top edge, square/flat cut surface, and a sharp slag- free lower edge.
What are the Parameters that control Flame Cutting?
Cut quality is dependent on a number of parameters, the primary one being the competency of the burner/operator. A brief, but not complete list of items/parameters that control cut quality includes:
- Proper cutting tip selection
- Proper cutting oxygen pressure selection
- Proper preheat (a function of the cutting tip and the operator) this includes quantity of preheat as well as ratio of Oxygen to the fuel gas
- Proper cutting speed
- Proper tip to work
- Proper selection of the fuel gas
- A gas supply system (both fuel gas and Oxygen) that is sufficient to supply the quantity of gas required at the pressure required.
Most of these parameters may vary depending on the material and surface condition of the plate to be cut. All of these items are controlled by the operator and emphasize the importance of a well trained operator as well as a proper and well maintained machine.