Today, industrial parts manufacturers utilize a variety of heat treatment processes to alter the surface of steel alloys. One of the most popular ways to harden the exteriors of metal work pieces involves induction hardening.
A manufacturer may position a steel work piece within a coil carrying an electrical current to help create an alternating magnetic field within the steel. As the work piece undergoes heat induction, its surface temperature rises above a critical point. The manufacturer then (after a designated interval) quenches the work piece, typically in an oil bath. This protocol creates hardened exterior surfaces cost-effectively.
The History of Induction Hardening
Scientist Michael Faraday, widely known for his work with gas laws, revealed the discovery of magnetic induction in 1831. His work helped form a basis for later investigations into electrical currents and magnetic fields by other researchers, such as Thomas Edison and Nikola Tesla.
By the 1920s, metal parts manufacturers began using induction heating in mass-production fabrication settings. Interest in the process grew. In the early 1950s, many companies in the USA implemented systems for the induction hardening of high volume production runs of metal components.
The Induction Hardening Process
The induction hardening process in commercial environments usually occurs with the assistance of water-cooled copper coils. The metal comprising the induction coil must carry an electrical charge sufficient to help generate an alternating magnetic field within a carefully-positioned steel work piece. Significantly, the induction coil and the steel work piece never need to come into direct physical contact with one another. A single induction coil may help heat a succession of work pieces.
An induction heater contains at least three essential mechanical elements: the inductor coil (capable of carrying an electrical charge); a power unit (used to generate the electrical charge); and the work-head (an interface between the coil and the power unit). Engineers have developed a wide array of different induction heater units for use in industrial and metal parts fabrication environments.
The Induction Heating Process
Induction heating to a level above an alloy's critical temperature will cause the surface of the work piece to begin melting. When followed with quenching in an oil bath, a source of available carbon, this heat treatment helps harden the steel's exterior, causing it to become more brittle and better able to resist scratching and other abrasions. The surface displays important structural changes at a microscopic level sometimes referred to as "martensitic" due to the inclusion of interstitial atoms of carbon across the surface of the metal.
By causing a work piece to undergo induction hardening, a manufacturer may enhance the ability of a resulting metal component to withstand daily wear and tear. Ultimately, induction hardening contributes to longer effective lifespans for many machine parts.
Frequency and Induction Heating
Some manufacturers use specialized inducting heating units which generate electrical currents in induction coils at specific controlled frequency ranges. Both the hardness of a metal alloy undergoing surface hardening and the depth of the desired hardening influence the selection of currents. These tools typically fall into four categories:
High Frequency Hardening Current
Abbreviated as HFC machines, these units employ electrical currents in high frequencies. They perform an especially prominent role in contemporary induction hardening in mass production environments.
Mid-Frequency Hardening Current
Abbreviated as MFC, these units typically operate within a range between 500 Hertz and 10 Kilo Hertz. Since they operate at lower frequencies, they may contribute to selective hardening at somewhat deeper levels of a metal component.
Dual Frequency Hardening Current
HFC/MFC machines can alternate between high frequency and mid-frequency electrical currents. This type of unit offers manufacturing flexibility.
High Frequency Impulse Hardening Current
Specialized induction hardening units generate high frequency electrical currents flowing in controlled impulses.
Induction Hardening: Materials and Applications
Induction hardening environments today rely on a variety of useful materials and applications:
Materials required for induction hardening include access to electricity and a suitable induction heating manufacturing device, such as a specialized induction heater unit. Parts manufacturers typically also require quenching technology, such as oil or water baths.
Since the process of induction hardening holds potentially widespread applications in numerous industries, manufacturers have developed a myriad of applications for this technology. Some of the products frequently generated with the assistance of induction hardening include: oilfield drilling pipes, pinions, gear shifts, metal treads and springs.
As a heat treatment, induction hardening offers some important advantages for manufacturers.
- This process occurs rapidly. A metal parts fabrication facility seeking to harden metal work pieces in high volumes quickly can utilize specialized automated induction heating technology effectively to help meet production goals.
- The process furnishes the ability to attain selective hardening of the exterior without modifying the core of a metal part. Like many other forms of surface hardening, heat induction hardening potentially enhances corrosion resistance and brittleness.
- This form of surface hardening won't require extensive finishing afterwards to remove scale or decarburize. In this sense, heat induction hardening technology promotes environmentally-friendly, cost-efficient manufacturing.
- The use of automated induction hardening equipment does not require steep personnel learning curves. Although manufacturers must ensure employees adhere to health and safety protocols, plants do not need to utilize cyanide salts or other caustic chemicals to accomplish this process.
- Induction hardening may enhance the long term value of metal parts by significantly improving wear resistance and durability. In this respect, it may offer a way to produce higher quality components cost-effectively.