Eliminating thermal stress from metal.

Almost anything that is made from metal is harboring unseen stress. It is invisible until the part prematurely fails, cracks or distorts. All of us are affected. Something fails on a piece of farm equipment for no apparent reason. Or a weld cracks shortly after repair. There is a reason for these events and it is called thermal stress.

Metal can unintentionally shelter two different stresses: mechanical and thermal. Mechanical stress is induced when metal is bent, formed or stamped. The metal is forced into a different shape. Thermal stress is created when metal is cut, welded, cast, drilled or quenched. It is induced by a sharp temperature drop. For example, when welding a natural air quench occurs as you move traversely away from the line of work. This is known as the heat affected zone (HAZ). During this sharp temperature drop both the weld metal and HAZ are impacted. This results in potential cracking or distortion over time. Between the two, thermal stress is the most destructive.

Thermal stress is found in every engine, transmission, tillage implement, planter, sprayer, combine, clutch, brake rotor and anything else that experienced a sharp temperature drop either in use or during manufacturing. We all unknowingly pay the price for thermal stress but there is a way to eliminate it.

Good vibrations

Bonal Technologies Inc. developed a procedure to remove thermal stress from metal even from assembled engines, transmissions, and implements, up to 40,000 pounds. It works via induced vibrations. It is identified as sub-harmonic vibrational stress relief. The patented process is called Meta-Lax. What is exciting is the unit being stress relieved does not need to be disassembled and there is no detriment to the part —- just the removal of thermal stress.

This technology has been used by a multitude of industries including NASA. As the author, I have experience with Meta-Lax processing since I owned a unit when I had my engine shop and can attest to its effectiveness.

The Meta-Lax system consists of a control console, a transducer to read the amplitude and a forced inducer that creates the vibration. The forced inducer and transducer are mounted on the piece to be stressed relieved. Depending on the metal alloy, weight, and thermal stress, the complete job will take approximately one hour.

Without getting mired in physics, the basis of the process resides in a component of Young’s Modulus of Elasticity. In simpler terms this is what happens.

Vibration is induced at an increasing rate while amplitude is monitored.  At some frequency, amplitude will reach a high point (harmonic peak) — the greatest rate of molecular excitement. An amplitude corresponding to the lower one-third of the harmonic peak amplitude is then maintained for up to one hour. During this time the molecules will properly realign, eliminating thermal stress and restoring strength and dimensional stability.

Unlike heat treating that cannot be done to complete machines, Meta-Lax is the only method that can confirm the elimination of thermal stress.

This is done by first identifying the harmonic peak frequency. Then periodically monitor the harmonic peak to observe a shift in frequency. When the harmonic peak frequency repeats within 0.8 hertz as read on the console, the process is complete.

An additional feature of Meta-Lax processing is that sub-harmonic vibrations can be applied while welding. The most desired benefit for farm equipment is longer service life after welding, sometimes as much as triple. Other benefits include less distortion and less blow-through. Weld metal is “pulled” into the joint making the weld easier to start. In addition, thermal stress is removed throughout the welding.

Metallurgically, the weld metal will have significantly higher ductility and impact values, up to 400% and 75% respectively, which are indications of a crack resistant weld.

As with any new tool, fixturing the forced inducer and transducer is awkward until you become familiar with it.

The entry level Meta-Lax Model 2001 starts at $19,000 and the top-of-the-line Model 2401 sells for $24,965. You can spend almost that much on a high-end tool box these days! Bonal offers low cost leasing plans along with a one-day training class at their Michigan facility.

With today’s advanced farm equipment and engines, it is unacceptable to allow them to harbor thermal stress and the issues it causes. It is prudent to get the most service life from your farm machinery investment. Thermal stress steals that service life from you. When it comes to repairs even though you may be an expert welder, you cannot do anything about the HAZ without the use of a Meta-Lax.

The modern and progressive farm operation should consider this technology and stress relieve every piece of equipment, engine and transmission. It is a one-time process. Since the unit is easily transported and is usually not needed on a daily basis, a pooled investment between friends or neighbors is easily doable to dramatically lower the cost.

For more information than we could provide here please visit www.bonal.com or call Tom Hebel (248-582-0900). Tell him that The Hot Rod Farmer said you should let the stress out!