Induction heating

Induction Heating

BY-Anuj A. Umare

WHAT IS INDUCTION HEATING?

• Induction Heating is a Contactless Heating Method of bodies, which absorb energy from an Alternating Magnetic Field, generated by

Induction Coil (Inductor).

OR

• heating of material by means of an electric current that is caused to flow through the material or its container by electromagnetic

induction.

Principles of Induction Heating :-

Chain of phenomena:-1.Power supply delivers current (I1) to induction coil.

2.Coil currents (ampere-turns) generate magnetic field. Lines of field are always closed and each line goes around the current source – coil turns and work piece.

3.Alternating magnetic field flowing through the part cross-section (coupled to the part) induces voltage in the part.

4. Induced voltage creates eddy currents (I2) in the part flowing in direction opposite to the coil current where possible.

5.Eddy currents generate heat in the part.

Magnetic Flux lines

Power Supplying Circuitry

Specific Features of Induction Heating:-

• Heating is contactless.• Heat generation occurs inside the part. • Method can provide very high power densities.• Heating may be highly selective in the depth and along the surface. • Any processing atmosphere (air, vacuum).• Very high temperature may be created.• Stand-by losses of equipment are very low. • Fast start-up.• Heating may be easily programmed and automated.• No pollution of surrounding space.• Compare to safe gas heating.

Design(Temporary):-

job

heating plat Structure Electronic & Digital Display

Base

Parts of an Induction Heating System:-

An induction heating system comprises a tank circuit, a power supply, and a work coil. In industrial applications, there is sufficient current passing via the coil to need water cooling; therefore a basic installation contains a water cooling unit. The alternating current from the AC line is converted through a power supply to an alternating current that is in line with the combination of coil inductance, work head capacitance, and component resistivity.

There are two mechanisms of energy absorption:-Eddy Current & Hysteresis

• Eddy current heating occurs in all conductive materials (magnetic or non-magnetic steels, copper, aluminum, graphite, molten glass or oxide etc.) when they are placed in an alternating magnetic field. Eddy currents always flow in a closed loop and for effective heating there must be a good path for current to flow in the part to be heated. For example, it is easy to heat a wire loop but almost impossible to heat a thin wire then the loop is open.

• Hysteresis heating is zero in non-magnetic materials (aluminum, copper, hot steels) or responsible for a small percentage of heat generation in compact magnetic bodies (mainly steels at low or middle temperatures). However, in magnetic materials composed of particulates (including magnetic flux concentrators) hysteresis may be the major source of heat generation. Each particle is heated individually and the workpiece may have any shape and size (massive bodies, strips, films, wires).

Operating Frequency:-

EX-a 20mm steel bar can be stress-relieved by heating it to 540°C (1000°F) using a 3kHz induction system. However, a 10 kHz system will be needed to harden the same bar by heating it to 870°C (1600°F). Hence it can be said that higher operating frequencies, mostly more than 50kHz, can be used to heat smaller parts with induction and lower operating frequencies can be used to heat larger parts more efficiently.In the case of advanced solid-state induction power supplies with embedded microprocessor control systems, consistent and effective heating techniques are achievable based on the fact that all parts are placed at a consistent location within the coil.

Approximate smallest diameter for efficient heating at different induction frequencies

Material Temperature 1 kHz 3 kHz 10 kHz 30 kHz

Steel below curie

540 °C(1000 °F)

8.89 mm(0.35 in)

5.08 mm(0.20 in)

2.79 mm(0.11 in)

1.27 mm(0.05 in)

Steel above curie

870 °C(1600 °F)

68.58 mm(2.7 in)

38.10 mm(1.5 in)

21.59 mm(0.85 in)

9.65 mm(0.38 in)

Advantages of Induction Heating:-

• Short heating cycles and high production rates.

• Better metallurgical results due to fast and clean heating.

• Energy savings due to selectivity and high efficiency.

• Good control and repeatability.

• Minimal or no surface oxidation and decarburization.

• Lower distortions.

• Favorable for industrial environment (in-line heating, no pollution, “push button” performance).

• Some processes may not be accomplished other than by induction.

• Safer surrounding environment.

Major Applications of Induction Heating:-

• Melting

• Forging & Forming

• Heat Treatment

• Welding

• Brazing & Soldering

• Shrink-fitting

• Bonding

• Inductively Coupled Plasma

• Crystal Growth

THANK YOU