Induction Heating – Operation, Applications and Case Studies - Presentation Slides

Baskar Vairamohan

Project Manager

Industrial Center of Excellence

December 17, 2014

Energy Savings with Induction Process Heating

Overview, Applications and Case Studies

2 © 2014 Electric Power Research Institute, Inc. All rights reserved.

Agenda

• Heat Transfer Modes

• Induction Fundamentals

–Heating

–Melting

• Applications

• Case Studies

•Benefits of Electrotechnologies

• Summary


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Collaborative

Nonprofit

Introduction to EPRI

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Objective, scientifically based

results address reliability,

efficiency, affordability, health,

safety and the environment

Nonprofit

Chartered to serve the public

benefit

Collaborative

Bring together scientists,

engineers, academic

researchers, industry experts


Facility HVAC

4.2%

Process Cooling

and Refrigeration

1.5%

Electrochemical

Processes

1.3%

CHP and/or

Cogeneration

8.5%

Conventional

Boiler Use

9.9%

Machine Drive

10.6%

Process Heating

21.0%

Other

3.9%

End Use Not

Reported

39.1%

Facility HVAC

4.2%

Process Cooling

and Refrigeration

1.5%

Electrochemical

Processes

1.3%

CHP and/or

Cogeneration

8.5%

Conventional

Boiler Use

9.9%

Machine Drive

10.6%

Process Heating

21.0%

Other

3.9%

End Use Not

Reported

39.1%

Break-down of All Energy Use in Industries

• Process heating accounts for

– 21% of total industrial energy use

– 2 to 15% of total industrial production cost

• Process temperature range: 300 – 5,000+oF

Source: Energy Information Administration, 2010 Manufacturing Energy Consumption Survey


Other

6.6%

Process

Heating

12.1%

Facility HVAC

9.3%

Electro-

Chemical

Processes

7.2%

Facility

Lighting

6.9% Process

Cooling and

Refrigeration

7.2%

Machine Drive

50.6%

Other

6.6%

Process

Heating

12.1%

Facility HVAC

9.3%

Electro-

Chemical

Processes

7.2%

Facility

Lighting

6.9% Process

Cooling and

Refrigeration

7.2%

Machine Drive

50.6%

Industrial Net Electricity Consumption (End

Use)

• Process Heating uses 12.1% of total net electricity in manufacturing

• Total Industrial Net Electricity Consumption

= 2,850 Trillion Btu (= 835 Billion kWh) • Source: Energy Information Administration, 2010 Manufacturing Energy Consumption Survey

~100 Billion

kWh

http://www.eia.gov/consumption/manufacturing/




Process Heating - Electricity Use by Industry

Sector

Primary Metal Manufacturing

– Largest electricity user

(39.4 billion KWh)


Heat Transfer Modes

• Heat transfer happens in three ways:

– Conduction

• Heat transfer occur when adjacent atoms vibrate against one another

– Convection

• Transfer of heat vis mass flow (transfer).dominant form of heat transfer in liquids (also molten metals) and gases.

– Radiation

• Transfer of heat energy by means of photons in electromagnetic waves

Source: https://www.nsa.gov/research/tnw/tnw202/article4.shtml

https://www.nsa.gov/research/tnw/tnw202/article4.shtml




Induction Heating

• Induction heating makes use of I2R

losses, the same as the elements in

a resistance furnace or toaster.

• The difference is that the current is

“induced” with magnetic flux field,

rather than “applied” through

physical contact.

Network 60 Hz Frequency converter Filters

Chiller

Water cooling circuit

Inductor

and heated

piece

Transformer

Image Courtesy: Electricity de France (EDF)


Induction Heating

• Used for heating directly, heat

treating or melting conductive

materials, typically metals.

• Similar to the operation of

transformer

• Plastics and other nonconductive

materials (e.g., chemicals) often

can be heated by first heating a

conductive material that transfers

heat to the nonconductive material.

• Generates heat within the

workpiece

Workpiece

Induction

coil


Induction Heating Types

• Direct induction heating:

– It occurs when the material to be heated is in

the direct alternating magnetic field.

– The frequency of the electromagnetic field and

the electric properties of the material determine

the penetration depth of the field, thus enabling

the localized, near-surface heating of the

material.

– Comparably high power densities and high

heating rates can be achieved.

– Direct induction heating is primarily used in the

metals industry for melting, heating, and heat

treatment (hardening, tempering, and

annealing).

Examples of

Induction

Coils


Induction Heating Types

• Indirect induction heating:

– a strong electromagnetic field generated by

a water cooled coil induces an eddy

current into an electrically conducting

material (susceptor), which is in contact

with the material to be treated.

– Indirect induction heating is often used to

melt non-ferrous materials in crucibles

such as gold and precious metals.

– Plastics and other nonconductive materials

(e.g., chemicals) often can be heated by

indirect induction heating

Single/Double Push-

Out Furnaces

Courtesy: Inductotherm


What is Heat-treating?

• Heat treating as a technology can be very broadly defined as any process involving controlled heating and/or cooling of a work piece for the purpose of developing a given set of physical and mechanical properties.

• In general, this means:

– heating the work piece to a specific temperature—well above room temperature—at which the desired metallurgical transformations occur, then

– holding it at that temperature for a period of time sufficient for the transformations to occur through the work piece.

– followed by cooling at a prescribed rate to either develop additional transformed structures, or maintain the structure developed at the higher temperature.


What is Annealing?

• Annealing is a treatment that consists of:

– heating a work piece and holding it at a suitable temperature

– followed by cooling at an appropriate rate.

• E.g. A steel work piece is heated to 1600oF (871oC) and held at this temperature.

– Approximate time needed is one hour per 1 inch (2.54 cm) of section thickness.

– The work piece is then slowly cooled to room temperature.


What is Quenching?

• Quenching is the process of rapidly cooling the work piece

from the austenitizing (or, in the case of aluminum or stainless

steels, solutionizing) temperature in order to harden the

workpiece.

• The quenching usually takes place in a water, oil or polymer

bath. Gaseous quenchants are also used.

• Quenching medium depends on the ability of the work piece

material to be hardened (called hardenability), the section

thickness and shape of the part, and the cooling rates

required to develop the desired microstructure.

• Liquid quenchants include: Oil, Water, Aqueous polymer

solutions, Water containing salt or caustic additives

• Gaseous quenchants: helium, argon and nitrogen


What is Tempering?

• Tempering is defined as a process in which a previously hardened (quenched) or normalized steel is heated to a temperature below the lower critical temperature and then cooled at a rate that will increase ductility, toughness and grain size.

• Tempering can be performed in a wide variety of equipment:

– Convection furnaces

– Salt bath furnaces

– Oil bath furnaces

– Molten metal baths

– Induction equipment


Induction Hardening

• Involves heating the work piece into the austenitic range by

placing the part in the magnetic field generated by high-

frequency alternating current flowing through an inductor.

• The part is then quenched with liquid.

• The process is extremely versatile and can be used for

uniform surface hardening, localized surface hardening,

tempering and thorough hardening.

• The depth of heating is inversely proportional to the

frequency, consequently very precise case thickness can

be developed.

Dp is Current penetration depth, material electrical resistivity (ρ), magnetic permeability (μ) and coil current frequency (f):

𝑫𝑷 = 𝟑𝟏𝟔𝟎𝝆

𝝁𝒇 inch


Power Density for Various Metal Heating

Technologies

• Productivity increases are often synonymous with

increases in power density.

• Table below shows the transmitted power density range for

the rapid metal heating process technologies.

Process Power Density

(W/cm2)

Power Density

(kW/m2)

Gas 1-10 10-100

Infrared 1-30 10-300

Induction 5-5,000 50-50,000

Direct

Resistance

10-10,000 100-100,000

Plasma 100-105 1000-106

Electron Beam 1,000 -109 10,000 -1010

Laser Beam 10,000 -1015 100,000 -1016 Source: EPRI


Induction Heating Applications


Other Applications of Induction Technology

• Hot Metal Working - forging,

forming, rolling, extrusion, and

upsetting.

• Melting - ferrous and non-ferrous

materials for sand, permanent mold,

and investment casting.

• Heat Treatment - hardening,

tempering, annealing, normalizing,

and stress relieving.


Applications of Induction Heating

Source: Induction Heating Study 2003, BNP Market Research


Dual Frequency Gear

Induction Hardening

Parts

• Dual frequency systems are used

more for surface hardening parts with

varying contours, such as gear teeth.

• The gear is induction-heated by:

– medium frequency to the deep

region for several seconds and

– reheated by high frequency for a

short period (taking advantage of

the surface skin effect of high

frequencies)

– followed by quenching by water

spray.


Dual Frequency Gear

Induction Hardening

Parts

Inductor Coils

Example:

• For instance, a conventional induction heat

treatment might use a single frequency of

25kHz for 2.8 seconds.

• A dual frequency induction system might

use:

– 3kHz frequency for 1.8 sec in

preheating

– 150 kHz for 0.18 sec during final

heating.

• This new technique produces the desired

thin-surface hardening with little distortion

and high compressive residual stresses.


Energy Savings Opportunities for Induction

Heat Treatment • Instant On/ Off: When not in use, the induction power supply can be

turned off thus saving energy. No pre-heating required.

• Rapid Heating of Parts: Induction heating rapidly heats the parts or part

sections. Because high electrical currents are induced into the part, the

resistance to this current flow causes very rapid heating in the area of the

induced current flow.

• Scale/ Scrap and Remelting: Shorter heating times - characteristic of

induction heating - result in considerably less scale (25% less than gas

furnace).

– Scrap losses due to improper heating are higher in gas-fired furnaces

– Remelting of scrap consumes lot of energy

• Lower energy costs achieved by localized workpiece heating and no off-

cycle heating losses.


Induction Heating – Non-Energy Benefits

• Ease of automation: Many manufacturers have

completely automated their induction heating equipment.

• Compact footprint: Induction heating installations are

generally much smaller than conventional gas fired heating

furnaces for equivalent throughput.

• Precise heat location

• Easier process control and monitoring: It is easier to

control repeatability and monitor the process on a part-by-

part basis since it is not a batch process.

• No On-site emissions with induction heat treatment.

Especially beneficial in non-attainment areas.

Source: Induction Heat Treating Marketing Kit –

A Sales and Marketing Support Guide- TR-111818-Final Report, February 1999

Induction Melting


Induction Melting – Operating Principle

• An induction furnace operates on a similar

principle to a transformer.

• The induction coil acts as a primary coil, having

many turns, and the charge acts a secondary

coil, with only a single turn.

• When an alternating current is applied to the

induction coil of a furnace, a significantly larger

current is induced in the metallic charge

materials.

• The resistance to the passage of the induced

current within the furnace charge causes the

charge to heat up until it eventually melts.

• Once the metal is molten the magnetic field

generated creates a stirring action in the bath,

producing both homogenization of the chemical

composition and assimilation of any bath

additions.

• Two major types: Coreless & Channel Furnace

Coreless Melting Furnace


Coreless Induction Furnaces

• Has refractory shell surrounded by the coil. Further

classified as:

• Line: 60Hz

• Medium: 200-1200Hz

• High: Over 1200 Hz

• Variable Frequency Units

• Best suited for melting turnings or clippings & for simple

charging and pouring operations

• Advantages:

– Furnace can be completely emptied to change an

alloy

– Can be sized to meet melting needs

– Very efficient – 55-80% compared to fossil-fuel (7-

50%)

• Disadvantages:

– Refractory cracks can cause premature lining failure Source: Melting technologies for Aluminum and other Non-ferrous metals – EPRI Technical Commentary –Product Id:1001025, 2000

Image courtesy: Good Practice Guide 50 – Efficient Melting in Coreless Induction Furnaces


Channel Induction Furnace

• Inductor consists of water-cooled coil embedded in the refractory

• Channel is formed in the refractory through the coil and this channel forms a continuous loop with the metal in the main part of the furnace

• Hot metal in the channel circulates into the main body of the metal in the furnace and is replaced by colder metal

• Advantages:

– Higher efficiency than coreless and natural gas furnace

– Extremely effective at mixing to have homogeneous temperature

– Typically used for holding molten metal

Source: Melting technologies for Aluminum and other Non-ferrous metals – EPRI Technical Commentary –Product Id:1001025, 2000

http://www.fomet.com/P/24/INDUCTION-FURNACE/POURING-INDUCTION-FURNACE---PR---PRV.html













Energy Efficiency Improvements with

Induction Melting

Electric

Induction

Melting

Source: Melting technologies for Aluminum and other Non-ferrous metals – EPRI Technical Commentary –Product Id:1001025, 2000


Energy (kWh) Required to Melt Per Ton of

Metal (Approximate Values)


Energy Savings Opportunities with Induction

Melting

• Energy efficient: Induction furnaces are energy-efficient.

The overall efficiency normally ranges from 55 to 75

percent, which is significantly better than combustion

processes.

• No preheating of furnace required – as in the case of

natural gas furnace – thus saving energy as well as wasted

heat

• Natural mixing (stirring) action eliminates stratification

– Results in uniform melting


Energy Efficiency Improvements in Induction

Melting Systems

Power Supplies used in Induction Melting Systems

Latest Generation Induction Melting Systems

Source: Inductotherm


Non-Energy Benefits of Induction Melting

• Higher yield: Due to the absence of combustion sources, induction furnaces reduce oxidation losses that can be significant in the melting process.

• Faster startup: Induction furnaces can take up to full power instantaneously, thus reducing the time to reach working temperature. Melting batch time from metal charging to molten metal tapping can be reduced to one to two hours.

• Better product: Induction furnaces allow precise control, resulting in dependable and consistent quality. Exact control of power input ensures that the optimum temperature is maintained throughout processing. Medium frequency magnetic fields give a strong stirring effect, resulting in a homogeneous melt.


Non-Energy Benefits of Induction Melting

• Flexibility: Induction furnaces require no molten metal as the starting batch. This facilitates repeated cold starting and frequent alloy changes.

• Automatic operation: Precise automatic control of power reduces furnace operation manpower to that required only for charging, tapping and metallurgical measurements.

• Compact installation: High melting rates can be obtained from small induction furnaces. No space is required for fuel storage and handling.

• Better working environment: Induction furnaces are much quieter than gas furnaces, arc furnaces, or cupolas. No combustion gas is presented and waste heat is minimized.


Energy Savings and Productivity Increase in a

Metal Heat Treatment Plant for Railroad Bearing

• Challenge: Increasing production demand for

railroad bearings required additional heating

capability. Excessive energy and maintenance

cost were associated with the initial gas fired

furnace operation.

• New Method:

– Induction heating systems from Pillar/ Ajax

Tocco were considered as an alternative to

conventional gas fired furnace.

– The new installation requirement is

evaluated to determine cost/performance

savings opportunities via use of induction

heating systems.

– Five new 2500 kW - 60/200 Hz induction

heating systems were installed.


Metal Heat Treatment for Railroad Bearing

Payback and Other Benefits

1. Overall cost savings/ton was 25% to 30%, providing a payback period that ranged from 0.9 years to 1.25 years

2. Scale loss reduced by 75%

– Removal of scales results in wasted products that cannot be remelted or reused

3. Scrap reduced by 75%

– Reduction of scrap resulted in reduction of energy, otherwise spent on remelting of scrap

4. Operating labor reduced by 50%

5. Maintenance reduced by 50%

6. Cost: Total installed system cost was $600,000

Photo Source: www.freefoto.com

http://www.freefoto.com/


References

1. Industrial Process Heating: Current and Emerging Applications of Electrotechnologies.

EPRI, Palo Alto, CA: 2010. 1020133.

2. Rapid Metal Heating: Reducing Energy Consumption and Increasing Productivity in

the Thermal Processing of Metals, EPRI, Palo Alto, CA: 2000. TR-114864.

3. Energy Efficiency Improvement and Cost Saving Opportunities for the Vehicle

Assembly Industry, Christina Galitsky and Ernst Worrell Energy Analysis Department,

Lawrence Berkeley National Laboratory, March 2008

4. Development of a Performance-Based Industrial Energy Efficiency Indicator for

Automobile Assembly Plants, Boyd, Gale A., Argonne National Laboratory, ANL/DIS-

05-3, 2005.

5. Electric Process Heating, Maurice Orfeuil, 1987 (Battelle Press) - Book

6. Electrotechnology Update, Induction Heating. EPRI, TB-110221

7. Electrotechnologies in Metal Heat Treating Systems—Marketing Kit, EPRI, Palo Alto,

CA: 2000.1000136

8. ENERGY STAR:

http://www.energystar.gov/index.cfm?c=in_focus.bus_motorveh_manuf_focus

9. DOE – Process Heating Source Book For the Industry:

http://www1.eere.energy.gov/manufacturing/tech_deployment/pdfs/process_heating_s

ourcebook2.pdf

http://www.energystar.gov/index.cfm?c=in_focus.bus_motorveh_manuf_focus

http://www1.eere.energy.gov/manufacturing/tech_deployment/pdfs/process_heating_sourcebook2.pdf

http://www1.eere.energy.gov/manufacturing/tech_deployment/pdfs/process_heating_sourcebook2.pdf


References

• Induction Melting:

– Melting technologies for Aluminum and other Non-ferrous metals

– EPRI Technical Commentary –Product Id:1001205, 2000

– Induction and Cupola Melting: A cost comparison model: CR-

108697, CMP – Report No 89-4, 1989

– Efficient Electric Technologies for Industrial Heating, product Id

– 1014000, 2007

– Good Practice Guide 50 – Efficient Melting in Coreless Induction

Furnaces, 2000

– Ind Heat WS Code - Cost Comparison Worksheet for Induction

Heating, Version 1.0, EPRI Product Id: 1001500, May 2001

– http://www.fomet.com/P/24/INDUCTION-FURNACE/POURING-

INDUCTION-FURNACE---PR---PRV.html













Questions


Contact

Baskar Vairamohan

Project Manager, EPRI

Ph: 865-218-8189

[email protected]

mailto:[email protected]


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