The Flame Cutting Process

Flame cutting of steel is performed by preheating the material to its ignition temperature, which is normally 1600-1800 degrees Farenheit, and then adding a high purity oxygen jet. The introduction of high purity oxygne, commonly referred to as the "cutting jet", chemically combines with the steel to form oxides of iron with a resultant liberation of a tremendous amount of energy in the form of heat. It is the combination of the oxidation of the steel and the liberation of heat which performs the actual cutting of the steel.

 

There are basically four main functions performed by the preheat flame:

1. Preheat the steel to the ignition temperature.

2. Maintain a protective envelope around the center jet oxygen, and also preheat the oxygen jet.

3. Maintain the reaction temperature of the new material constantly being presented to the center jet oxygen.

4. Penetrate any foreign substance on the surface of the steel such as rust, scale, dirt, etc.

 

The preheating functions can be obtained from any fuel gas, in combination with oxygen, which has the following properties.

 

1. Sufficient heat content to repidly heat the surface of the steel to combustion temperature.

2. High flame temperature to concentrate the heat transfer to a small area.

 

The only function performed by the cutting oxygen is that it performs all of the work during the cutting operation. Combination of oxygen with steel at the combustion temperature is a pure chemical reaction and the rate at which the reaction proceeds is governed by several distinct factors.

 

1. PURITY OF OXYGEN

Oxygen must be 99.5% pure or higher. Every 1% decrease in the purity will decrease cutting speed by 25%. At about 95% purity, all cutting action stops and is replaced by a melt and wash action.

 

2. CHEMICAL ANALYSIS OF THE STEEL

Elements such as chromium, nickel, molybdenum and carbon reduce the reaction rates as their conten tin the steel increases. At varying limits, 7% nickel, 5% chromium, etc. The reaction with oxygen stops with the standard cutting process.

 

3. CENTER JET OXYGEN TIP DESIGN

High speed tips of convergent - divergent design will force the reaction rate to maximum. The design introduces the maximum amount of oxygen per unit time to the steel at the combustion temperature. At the same time, the cutting jet stream remains coherent which produces a square, smooth, straight cut edge.