Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 1

Technical basics and applications of induction furnaces

Prof. Dr.-Ing. Egbert Baake Institute of Electrotechnology

Leibniz University of Hanover (Germany)

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 2

  Introduction   Fundamentals and application of the induction

crucible furnace   Fundamentals and application of the induction

channel furnace   Other industrial induction melting applications

Outline

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 3

Industrial process requirements for melting in induction furnaces

Mixing and homogenisation of the entire melt Homogenisation of the temperature, avoiding of local overheating , but realizing of sufficient superheating of the entire melt Intensive stirring at the melt surface (melting of small-sized scrap, carburization process) Avoiding of erosion and clogging of the ceramic lining Avoiding of melt instabilities, splashing or pinching Intensive stirring for cleaning of the melt (zinc removing)

Optimisation of the heat and mass exchange in the melt

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 4

magnetic field - distribution of power - electromagn. forces geometry of melt

velocity field homogenisation of melt

temperature field

meniscus shape

- overheating - heat flow

skull formation liquid-solid-interface

Physical correlations in induction furnaces

alloy composition melt components

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 5

Induction furnaces for melting

Induction crucible furnace Induction channel furnace

Used mainly for melting Medium high efficiency Operating frequency: 50 ... 1000 Hz

Used mainly for holding and pouring High efficiency Operating frequency: 50 Hz, 60 Hz

Source: RWE-Information Prozesstechnik

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 6

Construction of induction crucible furnace

melt

steel- construction

concrete-ring

meniscus

melt flow

crucible

induction coil

magnetic yoke

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 7

Meniscus shape and melt flow of the crucible induction furnace

Magnetic field: B

Inductor current: J1

Induced current density in the melt:J2

Electromagnetic force density:

F = J2 x B

Melt flow pattern

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 8

Example: Induction crucible furnace

melt

steel- construction

concrete-ring

meniscus

melt flow

crucible

induction coil

magnetic yoke

Height of meniscus is proportional to:

Velocity v of the melt is proportional to the inductor current I: v ! I

Velocity v of the melt is proportional to:

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 9

Spec. kinetic energy of turbulence:

k = ½ (v´x12 + v´x2

2 + v´x32)

local melt flow velocity in dependence on time

Shared in:

1. Time averaged flow velocity   convective heat and mass transfer

2.  Instationary fluctuations and oscillations

  turbulent heat and mass transfer

Characteristics of turbulent flow in induction furnaces

Vmax ≈ 20 cm/s

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 10

3D hydrodynamic model of an industrial induction crucible furnace

P = 4540 KW

Hind = 1.33 m

Rcr = 0.49 m

Filling level 90 %

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 11

Calculation of the melt flow velocity in the ICF: (3D transient LES)

symmetric state unsymmetric state

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 12

Calculation of the melt flow velocity in the ICF: Melt surface (3D transient LES)

calculated time: 5 sec calculated time: 40 sec

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 13

Example of medium frequency induction crucible furnace: 12 t/9,3 MW/250 Hz

source: ABB Industrietechnik AG

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 14

MF-ICF-melting installation with two furnaces: 12 t, 9,3 MW/250 Hz

Source: ABB

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 15

Induction crucible furnace installation for melting of grey cast iron

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 16

Induction craucible furnace during pouring

Medium frequency-ICF

Capacity: - 6 t grey cast iron

Power: - 3300 kW/250 Hz

Quelle: ABB Industrietechnik AG, Dortmund

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 17

Induction crucible furnace: capacity 8 t grey cast iron with charging vehicle

Source: ABB Industrietechnik AG

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 18

Back tilt position of an ICF for 8 t grey cast iron during slag cleaning process

Source: ABB Industrietechnik AG

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 19

Induction crucible furnace (ICF): Advantages in comparison with competitive processes

Homogenisation of the melt due to stirring of the melt

Less oxidation losses (dross) because no local overheating

High accurate alloying process

Well defined melt temperature

Simple automatic process control

High quality of the melt even with cheap charge material (scrap)

High throughput because fast melting and fast heating up of the melt

High furnace efficiency

Simple handling of the furnace and the process

Well defined controlling of the power input

Good working conditions for the workers at the furnace

Environmental friendly (small dust emission, no exhaust gas)

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 20

Induction crucible furnaces melting material, capacities, power rates, frequencies

Material Capacities [t]

Power rates [MW]

Frequencies [Hz]

LF-furnaces:

Cast iron, steel 1,3 ... 100 0,5 ... 21 50 ... 60

Light metal 0,5 ... 15 0,2 ... 4 50 ... 60

Heavy metal 1,5 ... 40 0,5 ... 7 50 ... 60

MF-furnaces:

Cast iron, steel 0,25 ... 30 0,3 ... 16 150 ... 1000

Light metal 0,1 ... 8 0,2 ... 4 90 ... 1000

Heavy metal 0,3 ... 70 0,3 ... 16 65 ... 1000

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 21

Charging of line-frequency induction crucible furnace

heal starting blocks

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 22

Energy supply of induction crucible furnaces

a) LF-Energy supply via switching transformer b) MF-Energy supply via converter

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 23

Energy flow diagramm of a MF induction crucible

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 24

Parallel operation of two ICF

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 25

Design of a melt processor control system

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 26

Melt processor with operator

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 27

Melt processor main menu

-  sintern

-  starting with

cold crucible

-  melting

-  overheating

-  holding

- crucible wear

detection

Operation modes:

Source: ABB Industrietechnik AG

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 28

Induction channel furnace (one loop design)

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 29

Channel inductor (ABP): -  single loop -  P = 250 kW -  symmetrical channel

Design of a single loop induction channel furnace

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 30

Dopple loop induction channel furnace

Source: ABB Industrietechnik GmbH Dortmund

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 31

Melting in the induction channel furnace

Homogenisation of the entire melt

Sufficient overheating of the entire melt

Avoiding of overheating of the melt in the channel

Efficient heat and mass exchange between the channel and the furnace vessel is the key point

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 32

Melt flow in a model single loop induction channel furnace (measurements)

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 33

3D-Simulation model for electromagnetic calculation of the channel inductor

(power density and electromagnetic force density)

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 34

Channel inductor: distribution of power density in the melt

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 35

Channel inductor: distribution of electromagnetic force density

Parameters:

P = 60 kW I = 850 A

Melt: Wood-metal

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 36

Channel inductor: distribution of elektromagnetic force density

Parameters: P = 60 kW I = 850 A

Measured Melt flow distribution

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 37

Line frequency induction channel furnace used for storing, holding and pouring of cast iron

Quelle: ABB Industrietechnik AG

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 38

CIF used in non-ferrous metal industry (aluminium foundry)

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 39

CIF used in non-ferrous metal industry (aluminium foundry)

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 40

Source: ABB Industrietechnik AG

CIF installation used in non-ferrous metal industry (aluminium foundry)

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 41

Channel inductor for melting of copper and brass

•  power: 2400 kW

•  frequency50...70 Hz

•  mass:15 t

Quelle: ABB Industrietechnik GmbH Dortmund

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 42

Induction channel furnace melting material, capacities, power rates, frequencies

Melting materials Capacities [t]

Power rates [MW]

Frequencies [Hz]

Cast iron 10 ... 135 0,1 ... 3 50 ... 60

Aluminium, Al-alloys 5 ... 70 0,1 ... 6 50 ... 60

Copper, Co-alloys 5 ... 160 0,5 ... 10 50 ... 60

Zinc, Zinc-alloys 10 ... 100 0,2 ... 10 50 ... 60

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 43

Energy flow diagram of an induction channel furnace

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 44

Comparison: induction crucible vs. induction channel furnace

Crucible furnace Channel furnace

application melting, holding, all metal materials

Holding, melting, all metal materials

Melting rate (power) high (MF) medium

Meltíng process heal, scrap pieces Heal

Furnace volume medium big

Lining live time good vessel very good, Channel sufficient

Efficiency sufficient high

Operating frequencies 50 ... 1000 Hz 50 ... 60 Hz (60 ... 120 Hz)

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 45

Design of a pressure controlled pouring installation with induction heating

1 pressure vessel with melt 5 output valve 2 channel inductor 6 melt level controlling 3 input spout 7 main frame with rolls 4 output spout 8 casting mould

Source: RWE-Information Prozesstechnik

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 46

Induction pouring installation 10 t, 500 kW

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 47

Induction pouring installation Presspour®, 2,5 t, 130 kW

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 48

Holding processor for channel furnaces

Quelle: ABB Industrietechnik AG

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 49

Clogging, erosion and infiltration of the ceramic lining of the channel inductor influenced by e.g.:

Heat transfer and temperature distribution in the channel

Mass transfer in the channel and in the vessel

Type of alloy (purity)

Type of ceramic lining

and many others …

Clogging and erosion of a channel inductor used for holding of grey cast iron

Practical problems: induction channel furnace

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 50

Holding processor for channel furnaces Inductor-diagram

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 51

Crucible inductor furnace

Industrial applications: Comparison with induction channel furnace: •  holding and casting of grey cast iron + flexible operation,energy saving, easier to clean •  melting and holding of non-ferrous metal due to complete emptying •  reduction process in steel industry – but: lower efficiency

Experimental furnace Industrial furnace for casting of grey cast iron

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 52

melt with meniscus shape

crucible segment

inductor

bottom

slit

skull

current

melt flow

EM-forces

heat conduction

radiation

(water cooled)

(water cooled)

(water cooled)

Features of the Induction Furnace with Cold Crucible

  slitted crucible to realize efficient electromagnetic transparency

  free melt surface and intensive melt stirring, based on electromagnetic forces

  water cooled bottom and crucible segments leads to solid layer (skull)

  heat losses by radiation and conduction depending on the meniscus shape

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 53

Melting in the Induction Furnace with Cold Crucible

  high reactive and high purity materials, e.g. TiAl

  melting, alloying, over- heating and casting in one process

  no pre-alloys necessary, using of scrap material

  good homogenisation of the melt due to intensive electromagnetic stirring

Prof. Dr.-Ing. E. Baake / Institute of Electrotechnology, Leibniz University of Hannover 54

Cold crucible induction skull melting process

inductor

crucible

vacuum chamber

  High reactive and high purity materials, e.g. TiAl

  Melting, alloying, over- heating and casting in one process