Flame Hardening Methods and Applications

02 May 2019

Flame hardening technology uses a heat treatment methodology that’s reminiscent of old blacksmithing procedures. Instead of electrically powered induction coils, an oxy-fuel gas flame takes care of the workpiece hardening work. Capable of applying a focused heat source, this is a process that’s used to target reduced geometrical outlines. It’s also a heat treatment technique that’s available in two different forms.

The Spin Flame Hardening Technique

A stationary oxyfuel flame burns its focused heat source while the workpiece to be heat treated spins in place. The spin rate is adjustable. For example, the process can vary in radial velocity to accommodate the circumference of a gear. As the spur wheel spins at a predetermined velocity, the teeth segments absorb thermal energy and harden. Because of the speed and mass limitations imposed by the technology, this heat treatment method is best suited as a moderate-to-large gear hardening solution.

Applying the Tooth-To-Tooth Process

This time around, the shape of the flame head alters. A single cone-shaped flame sinks deep into each tooth and root. Hardening depths go deeper and are applied more uniformly when this newly configured setup is used. Alternatively, two flames are lined up, one on either side of the tooth ramp. With this dual-flame configuration applied, each tooth is treated faster and that hardened case is laid down more uniformly. Of most note here, this progressive scanning technique incorporates a separate quench mechanism. Scanning with the flame, the head then switches to its quench function.

Alternative Flame Hardened Applications

So, why are there at least three flame treatment techniques in use? Well, as mentioned previously, the spin flame method works better on moderately sized gears, and it can sometimes be used on larger parts, too. Small vehicle parts and medium-sized crane gears receive attention from as many as 8 stationary but perfectly focused oxyfuel heat sources. As far as tooth-by-tooth heat treatment goes, the scanning flame and quenching assembly work together to process very large gear teeth. Large crane assemblies, locomotive gears, massive truck parts, all of these massive power transmission systems have much to gain when their teeth and root sections are individually flame-scanned and quenched.

There’s a flip side to the heat treatment coin, as it were. On one side, the oxy-acetylene heat sources harden specific parts areas. That’s a perfectly adequate feature for a gear hardening equipment rig. However, the temperatures and case hardening depth must be weighed against a number of opposing forces. Worst of those, the parts distortion effect cannot be allowed to impact teeth geometry. Highly reputable heat treatment facilities find the point of equilibrium, which exists between a high-tolerance, case hardened end-line-product and one that’s on the verge of distorting.

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