The Working Principles and Operating Variables of Flame Hardening

28 September 2022

One common way of processing metal materials is through heat treatment. While metals already possess high-quality properties, they should still undergo heat treatment processes to further enhance their overall characteristics. 

Heat treatment helps improve the qualities of metals as it heats the materials without reaching their molten phase. After heating them for a specific amount of time, the metals are subsequently cooled in a controlled way to achieve their desired mechanical properties. Some metals end up getting stronger, while others become more ductile. Heat-treated metals can also become more malleable and more resistant to abrasion.

Different heat treatment techniques can be carried out to process metals. One of these techniques is flame hardening.

Flame Hardening and Its Working Principles

Flame hardening is a surface-hardening process wherein a thin surface section of metal is heated rapidly. The heating application of the material is done by the direct application of the flame, boasting a temperature that is above the metal’s upper critical temperature. After exposing it to the said temperature, the metal is quickly quenched in oil or water. The quenching process turns austenite to martensite without affecting the core’s original soft state.   

The high-temperature flame used in this process comes from the combustion of a fuel gas with air or oxygen. The hardened depth of the material may range between 0.8 and 6 mm, which would mostly depend on the fuel gas, air or oxygen, flame head design, heating duration, quenching medium, quenching method, and the hardenability of the metal.

Operating Variables for Flame Hardening

One of the operating variables for flame hardening is the distance between the flame’s inner cone and the surface of the material or component. The travel speed of the flame head or the component can also affect the success of the said heat treatment technique. 

Other operating variables for flame hardening are oxygen to fuel gas ratio in the mixture, type and angle of the quench, and flame velocities.

All these variables should be controlled optimally by the professionals assigned to conducting this heat treatment technique. 

Understanding Flame Hardening Methods

Various flame hardening methods can be carried out by heat treatment experts. These methods would normally have to consider the shape, size, and composition of the metal. They would also have to consider the area to be hardened, the desired depth of the hardened case, and the number of materials that will be hardened.

One of these methods is manual hardening. This method is done with the help of a welding torch, with the flame head boasting either a single orifice or multiple orifices. The spinning method is another flame hardening method that can be perfect for components like wheels, gears, and cams, which boast round or semi-round structures. 

Progressive hardening is then used for components that cannot be hardened by the manual method. Shafts, rolls, and other long parts can, ultimately, take advantage of progressive spin hardening. This method combines spin hardening and progressive hardening. 

Flame hardening, in general, can be useful for materials with any shape. It can also be used for numerous types of steels, large forgings, and castings without requiring expensive equipment pieces. To know more about this process, you can contact us at Alpha Detroit Heat Treatment.

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