Comparing Induction Hardening, Case Hardening

What Is Induction Heating?

Induction Hardening relies on the existence of eddy currents discovered by Léon Foucault in 1855. Briefly, when a changing magnetic field passes through any conductive object, current flow is induced in the object. That current flow creates a secondary electric field in the conductor. The secondary electric field, in turn, produces another flow of current which is known as the eddy current, so named because it flows in a circular pattern, much like water can swirl in a slow-moving stream when it encounters an obstacle. The push-pull between these fields—literally, the kinetic energy caused by electrons being shuttled back and forth—produces heat in the conductor.

Induction Heating Applications

Induction heating is used to manufacture end items as diverse as bulldozers, spacecraft, faucets and sealing plastic lids on pharmaceutical bottles. The fundamental design of an induction heating device uses a coil of wire and an AC current to induce a changing magnetic field in the item to be heated—the work piece. The coil can measure only a few centimeters in diameter, or any other dimension suited to the job at hand.

The work piece is placed inside the magnetic field generated by the coil, but not in contact with it, then heated to the desired level by the eddy currents. Depending upon the material being heated, temperatures as high as 2,200° F (1,200° C) can be achieved.

Induction heating is clean, requiring no fossil fuels. Parts exposed to induction heating simply heat up, so there's no cleanup afterward and no worry about contamination of the work piece. It's also fast. For example, manufacturers of pipes and tubular channels use induction heating to weld a seam along the longitudinal dimension of pipes passing by at high speed on a conveyor.

A few other processes that use induction heating include:

• ·      Induction hardening and tempering, which alters the physical characteristics of materials to meet the needs of various applications.
• ·       Induction melting can be used to melt any ferrous or non-ferrous metal, including nuclear material and various alloys used in medicine and dentistry.
• ·     Metal and carbon fiber materials can be bonded together by heating them, thereby curing adhesives placed between two surfaces.
• ·     Soldering, brazing and welding are all natural applications for induction heating where precise temperature control and accurately confining heat to the desired area is important in air cooler oil cooler.

Induction Heating Solves Real Problems

The so-called Tylenol Murders took place in Chicago during 1982 when someone, never identified, laced Tylenol bottles with cyanide. The subsequent events led to a nationwide recall of Tylenol products. The poisoning also forced the entire over-the-counter pharmaceutical industry to package their products in tamper-proof containers.

The aluminum foil that's commonly used to seal OTC drugs is part of the industry's solution, and it uses induction heating. The process begins by placing the foil, which is electrically conductive, into the cap. The cap is screwed down, and then the entire package is placed inside an induction heating coil. As the foil heats up, adhesives around its edge adhere it to the lip of the bottle.

Designers of induction cap sealing equipment must take several factors into account. The induction heater's physical dimensions need to be tailored to the containers to be sealed. The electromagnetic field needs a depth suitable for heating the foil. The heating should take place as quickly as possible for productivity reasons. The efficiency of the induction heater needs to achieve a specific performance level.

These and other design constraints can be reduced dramatically when the wire used to make the coil is custom-manufactured. New England Wire Technology, a long-time supplier to the induction heating market, provides wire specially made to solve such design problems in Induction Hardening Faridabad.

For instance, NEWT can supply round, square and rectangular conductors. Their exact size can be tailored specifically for the AC current and frequency to be used. And, because the efficiency can be optimized in the wire itself, the induction cap sealer design engineer has much greater flexibility in choosing the spacing, shape and size of the sealing head. In fact, that same flexibility benefits designers of any induction heating device.

Case Hardening

Heat-treatment processes such as case hardening are used to prolong the service life by increasing the surface hardness and vibration resistance while maintaining a ductile, elastic microstructure at the core. Steels suitable for case hardening have a carbon content of approximately 0.1-0.3% weight percent. For a high surface hardness – for example, 60 HRC – a carbon content of 0.1-0.3% is not sufficient. The part has to be carburized.

Carburization takes place by diffusion of the carbon into the work piece surface. A mixture of carrier gas and additive gas forms the basis for the carburization atmosphere in the furnace. Crucial factors for the right choice of the carburization process are the material-specific parameters, hardening demands in conjunction with the gas composition and a continuous, homogeneous furnace atmosphere.

Hardening is achieved by heating to austenitizing temperature with a sufficiently long holding time and subsequent quenching process. What is crucial here is that the carbon in the austenite is brought into solution. The amount of carbon is dependent on the material composition and the state of the initial microstructure. Excessive holding times or excessive temperatures during the austenitizing process can have a negative impact on the grain growth and material microstructure.

The hardening process can be followed by a low-temperature cooling process or direct tempering process. Both processes result in a reduction of the residual austenite and of the hardness and distortion properties.

Tempering is performed in different temperature ranges. The tempering temperature of parts made of low-alloy or unalloyed steels generally lie between 180-250°C (356-482°F). A higher temperature leads to a greater drop in hardness.