Encon in Foundaries

8/19/2019 Encon in Foundaries

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Draft Copy Only

SEMINAR ON ENERGY

CONSERVATION

IN IRON

CASTING INDUSTRY

UNIDO

Sponsored by

United Nations Industrial DevelopentOr!ani"ation #UNIDO$

and

Ministry o% International

Trade and Industry #M$&

Hosted by

Ministry of Industry Socialist Republic of Viet Nam

Organized by The Energy

conseration !enter" #apan $E!!%

'(()

*anoi


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PREFACE

The conservation of energy is an essential step we can all take toward

overcoming the mounting problems of the worldwide energy crisis and

environmental degradation. Although developing countries and countries with

economies in transition are very much interested in addressing the issues

related to the inefficient power generation and energy usage in their countries,

only a minimum amount of information on the rational use of energy is available

to them. Therefore, distributing the available information on modern energy

saving techniques and technologies to government and industrial managers, and

to engineers and operators at the plant level in these countries is essential.

In December 1!", #$ID% organi&ed a regionalmeeting on energy consumptionand an e'pert groupmeeting on energy conservation in small( andmedium(scale

industries for Asian countries. The outcome of these promotional activities

prompted #$ID% to initiate a new regional programme designed to increase the

awareness and knowledge of government officials and industrial users on

appropriate energy saving processes and technologies. In 11, the first

pro)ect, *rogramme for +ational use of nergy -aving Technologies in Iron and

-teel and Te'tile Industries in Indonesia and alaysia /#-0+A-00234, was

approved and financed by the 5overnment of 6apan.

The successful completion of this pro)ect prompted #$ID% to request the

financial support of the 5overnment of 6apan to carry out similar pro)ects

under this programme in other Asian countries. -ince 17, under continuous

support of the 5overnment of 6apan, three other pro)ects have successfully

been completed8 +ational #se of nergy -aving Technologies in *ulp and *aper

and 5lass Industries in the *hilippines and Thailand /#-0+A-070"34 9 in

:eramic and :ement Industries in ;angladesh and -ri 0>>4 .

This year #$ID% is carrying out the programme in :hina and ?ietnam,

targeting two energy intensive industrial sub(sectors8 iron casting andrubber

industries.

Iron casting industry consumes a substantial amount of energy. 'cessive

use of energy is usually associated with many industrial plants worldwide,

and iron casting plants are no e'ception. normous potential e'ists for


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cost-effective improvements in the existing energy-using equipment. Also,

application of good housekeeping measures could result in appreciable savings

in energy. Therefore, it is imperative to introduce anddistribute information

on modern energy-saving techniques and technologies among the parties

concerned in government and especially, at plant level, in industries.

To achieve the objectives of this programme, U!"# has adopted the

follo$ing strategy%

&. 'onduct plant surveys to characteri(e energy use and to identify measures

to improve energy conservation at the plants.

). *repare handy manuals on energy management and on applicable energy

conservation techniques and technologies.

+. #rgani(e seminars to discuss the content of the handy manuals and the

findings of the plant surveys $ith government officials, representatives

of industries, plant managers and engineers.

. "istribute the handy manuals to other developing countries and countries

$ith economies in transition for their proper use by the targeted

industrial sectors.

U!"# prepared this handy manual for the iron casting industry, $ith the

cooperation of experts from the nergy 'onservation 'enter, apan /''0, on

energy saving technologies in the frame$ork of this U!"# programme. !t is

designed to provide an overvie$ of the main processes involved in iron casting,

and to present a concise outline of the applicable energy saving measures.

Appreciationis expressed to the follo$ing institutions for their valuable

contribution to the successful preparation and publication of this manual%

The 1tate conomic and Trade 'ommission of the *eople2s 3epublic of 'hina4

The 5inistry of !ndustry of the 1ocialist 3epublic of 6iet am4 The

5inistry of !nternational Trade and !ndustry of apan4 and The nergy

'onservation 'enter, apan.


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Contents

1. anufacturing of castings and energy ............................ 1

7. *roduction of cast iron and energy consumption .................. 7

7.1 :ast iron ...................................................... 7

7.7 The production of cast iron and energy consumption rate ...... "

7." The yield of products and the energy consumption rate ......... >

7.> :ast iron melting and energy conservation ................... @

". :upola melting ....................................................

".1 =unctions of cupola ..........................................

".7 -tructure of cupola ........................................

"." elting operation of cupola ................................. 1@

".> =oundry coke .................................................. 1

>. nergy conservation of cupola ................................. 77

>.1 eat efficiency of cupola ................................... 77

>.7 :alculation of heat input ................................... 7"

>." :alculation of heat output ................................ 73

>.> eat balance diagrams and heat efficiency of a cupola ........ 73

3. Improving the heat efficiency of a cupola ...................... 72

3.1 ot blast cupola .............................................. 72

3.7 %'ygen enriching cupola ..................................... 7

3." umidity control cupola ..................................... "1

3.> ulti(stage air blasting cupola ........................... ""

3.3 Bater cool cupola ........................................... "@


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3.@ Improvement of heat efficiency by synergetic effect

of air blast conditions .................................... "

3.2 'amples of improvement in properties of molten metal

by measurement control of a cupola ......................... >1

@. $atural gas cupola .......................................... >@

@.1 The structure of a natural gas cupola ...................... >@

@.7 :omparison of melting energy................................. >

@." :omparison of e'haust gas in melting ........................ 3

@.> Advantages of a natural gas cupola......................... 31

2. Induction melting furnace................................... 3"

2.1 =eatures of induction melting furnace ..................... 3"

2.7 eat balance of induction furnace......................... 3"

2." nergy saving measures for induction furnaces ............... 3@

!. Arc furnace melting.......................................... @!

!.1 elting energy ........................................... @!

!.7 nergy saving measures for arc melting furnace .............. @


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Energy Conservation in Cast Iron Foundry

1. Manufacturing of castings and energy

The foundry sector is well recogni&ed as one of the supporting industries

for the machinery and assembling industry. Bith a recent remarkable economic

development in Asia, the production of castings, as apart of process materials

in every engineering industry, has been increased9 that of the Asian area is

the highest in the world. owever, the production of castings per capita is

only !. 7 kg, which is lower than world average of 1 " . @ kg. This fact shows

that the production of castings will be sure to increase along with an economic

growth not only in the Asian area, but also in developing countries.

=rom another point of view on the economic development, an increase in

the amount of energy consumption has become as a great problem for mankind.

nergy problems such as limited fossil fuels, global warming caused by carbon

dio'ide generated by combustion, air pollution caused by other o'ides,

destruction of plants and world heritage buildings caused by acid rain generated

by sulphur o'ides, radioactive wastes from nuclear power plants, etc. to be

continued on the 71st century, are important problems inevitable for the

survival of mankind.

-ince a large amount of energy is consumed in melting metals at high

temperatures, the foundry sector has to be a source of various kinds of

pollution9 on the other hand, it plays a role in recycling a large amount of

metal scraps occurring in a modern society. Thus, the production of castings

has a lot of global environmental problems to be solved in the future. The

development of an earth(friendly casting production process is the highest

on the list in the foundry industry.

( 1 (


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2. Production of cast iron and energy consumption

2.1 Cast iron

The term C:ast ironC is a general term for Cgray iron castingsC and

Cspheroidal graphite cast iron castingsC. -ince cast iron is easy to

manufacture and its manufacturing cost is low, and, besides, it has various

physical and chemical properties, it is used in the largest amount among

metal products in almost all area of industries including the automobile

in the beginning. The annual production of cast iron castings in the world

is over 3 million tons.

5ray iron castings are distinguished by good castability, abrasion

resistance, damping capacity, corrosionresistance, machinability, etc.9 they

have been used for a long time and are produced in the largest amount among

all sorts of castings. It forms about 23 of the total production of cast

iron.

-pheroidal graphite cast iron is superior to gray cast iron in mechanical

properties, especially in ductility. Though only a half century has passed

since the invention of spheroidal graphite cast iron, its production has

been increasing year by year since its utili&ation technology was

established9 it reaches 1" million tons, which is 73 of whole cast iron

and the further increase will be e'pected also in the future. The 71st century

may be called as the age of spheroidal graphite cast iron.

Thoughmalleable iron castings are a parity of cast iron, statistically

it is usually e'cluded from cast iron. -ince malleable cast iron has to be

heattreated in the process of its manufacturing for long hours at high

temperature in order to improve its mechanical properties, a large amount

of energy has to be consumed9 the rate of energy consumption per ton of

malleable cast iron is four or more times of cast iron. Therefore malleable

cast iron is replaced with spheroidal graphite cast iron and its production

has remarkably decreased.


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2.2 The production of cast iron and energy consumption rate

The process of manufacturing iron castings is mainly divided into the

melting process where metal is melted at high temperature over 1>E: and

the molding process where a mold is prepared into which molten iron is poured.

It is obvious that of these two processes the melting process consumes most

of cast iron manufacturing energy. Though iron castings are mainly used as

cast for final products having necessary properties. -ome of them may be

sub)ected to heat treatment to get necessary properties. The amount of energy

consumed varies depending on the materials and it is said that 3 to

of whole energy for the production of iron castings is consumed in melting

process.

To ensure energy conservation in cast iron foundry, it is necessary to

grasp the amount of energy consumed in them and to recordthe kinds andamounts

of energy used in the foundry every month and every year. -ince the amount

of energy used is e'pressedusing different energy consumption rate for each

kind of energy, the total consumption of heat is obtainedby summing up every

kind of energy consumed /kcal4 after calculating the amount of energy consumed

using the respective heat consumption rate.

$aturally, this total amount of heat varies depending on the change in

the production volume, and it is impossible to evaluate the state of energy

conservation only by the total amount of heat. The value obtained by dividing

this total amount of heat by the weight of production /in tons4 is called

the unit reguirement for converting the amount of heat of energy /kcal0ton4

and is used as an evaluation standard.


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+,- T.e yield o% produ/ts and t.e ener!y /onsuption rate

The energy consumption rate is a value obtained by dividing the total

consumption of energy by the production volume by ton, and the yield of

products, that is, the ratio of the $eight of final products to that of ra$

materials used has a great influence on the energy consumption rate. !t is

indispensable for reducing the unit requirement to improve the yield of

products, $hich results from the foundry technology accumulated in each

process of manufacturing of castings.

#a$ T.e yield o% eltin!

The yield of melting is defined as the percentage of the $eight of

molten metal cast in the mold against that of ra$ materials charged in the

melting furnace. The yield of melting becomes $orse because of metal loss

due to oxidation in the melting process, metal adhesion to the furnace$all,

ladle, etc., molten metal disposal due to improper chemical compositions

and temperature, failure by poor pouring into the mold, residual molten

metal due to rough estimation of $eight, etc.

#b$ T.e yield o% /astin!

The cast shape against its final shape is planned prior to patternmaking,

some surpluses are needed for sound castings such as, machining allo$ances,

pattern draft. *adding for better directional solidification, $all

thickness allo$ances covering dimensional fluctuation, and etc. 7ased on

the above shape, risers and gating system are designed, that is, proper risers

to compensate the shrinkage of molten metal through solidification and gating

system to prevent any damage on castings by controlling speed of molten flo$

and to avoid any slag inclusions into castings.

The yield of casting is defined as the percentage of the $eight of deliver

castings against cast $eight including $hole surpluses of the avobe.


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The yield of casting is reduced by the deformation of the mold during

molding caused by pattern such as loosening, low accuracy, insufficient

strength, obsolescence, insufficient draft angle, etc., by unnecessary

large risers and gating system, by e'pansion of the mold due to weakness

of molding sand, by lifting of the cope and leaking of molten metal due

to clamping of the mold and an insufficient weight, etc. Adversely, the

yield can be improved by using a cylindrical sleeve ensuring heat insulation

of the riser, a heat generating sleeve actively heating the riser by

e'othermic reaction, or a chiller for thick parts to reduce the si&e of

the feeding head, etc.

c! The percent defective of castings

-ome castings are )udged to be re)ected according to the inspecting

standard in the finishing and inspection process before shipment.

Defective castings show their defects in various forms andcauses of defects

are not simply connectedwith defective phenomena. *ractical information

on all the processes of manufacturing of castings and a lot of e'perience

ensuring correct evaluation are necessary for taking measures against

defects. Taking measures against defects in casting correctly found may

sometimes lead to lowering of the yield, but it is sure to be increased

on the whole by the reduction in the percent defective. Also in melting,

the quality of cast iron obtained can vary subtlely depending on the raw

materials and melting conditions. -hrinkage cavities and chills can be

caused frequently in castings even with the same chemical compositions of

molten metal. This is e'plained by o'idation and melting of the cupola.

It is the accepted view that high temperature melting over 133E: is

necessary to prevent the above phenomenon. +aising tapping temperature

will lead to consumption of e'cessive energy, but energy conservation can

be reali&ed by lowering the percent defective of castings.

( 3 (


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+,0 Cast iron eltin! and ener!y /onservation

+,0 ,' Cast iron eltin! %urna/e

8ig.l sho$s the kinds of cast i ron melt ing furnace. Today the

percentage of cupolas and induction furnaces used for cast iron melt ing

is obscure due to lack of proper statistics. 1ystems $ith a cupola used

for primary melting formedabout 9:; in &s, but it $as remarkably reduced

to ?+; around &, and after that cupolas may be used at a percentage of

:>to ?>;.

'ast iron

@

inelti(ig furnace2

7last furnace /"irect pouring0

7aby cupola

1haft kiln

/'ontinuous tapping0 Btlpola

Cffliiiary eu11o1a

Mast

7atch type furnace

/8ixed capacity0

2 Cru/ible %urna/e

@ 3otary furnace &

3everberatory furnace

D Eo$-frequency

furnace ?'?:.,,.-:~-

3*i!.4%te5ueri/y

furnace. .

Fig." C"assification of cast iron me"ting furnaces

The cupola is a shaft furnace for continuous melting of cast iron with

new pig iron, return scrap iron, and steel scrap used as raw materials and

coke used as a fuel. A cupola has not only an economic advantage of low

eguipment cost, but also refining and self(purifying capability, which

makes it possible to get e'cellent molten metal even from inferior(guality

raw materials and has been widely used.

owever, the e'haust gas from cupola, containing not only carbon

r


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dio'ide from coke combustion, but also smoke and dust generated coak ash,

$%, and -%,, causes pollution in air and working environment.

The use of a solid fuel makes it difficult to manage and control

operation, making it difficult to cope with mechani&ation, personnel saving,

especially lack of skilled workers.

The induction furnace is of electric heating type, whichmakes it easy

to handle and to control temperature and to ad)ust chemical compositions

has an advantage over cupola in capability to improve the quality of material

and ensure the reliability of quality. In addition, since air is not used

for heating, o'idation loss of metal is low, the amount of carbon dio'ide

and smoke and dust generated is less, which can improve working environment9

and is useful for the protection of global environment. owever, high

equipment cost, comparatively high power rates, etc. make the induction

furnace have to share the ma)or part of cast iron melting with the cupola.

The arc furnace has developed mainly as a steel melting furnace. In

6apan some people say that there are technical problems inmelting of gray

cast iron, and only " to 3 of whole melting process are seemed to be arc

furnace including the use as a dual melting furnace with a cupola.

2 . # . 2 Energy conservation in me"ting

Independently of the kind of melting furnace, the following

considerations are necessary for energy conservation in the melting

process8

/14 improvement of melting operation9

/74 reduction of heat input9

/"4 reduction of heat loss.

Items characteristic of each sort of melting furnace will be described

in details later9 the following are common ones8


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1! Improvement of me"ting operation

a! Remova" of rust$ sand and oi" stain on charged scrap

They form slag which need more heat input9 they shall be removed

by shot blast before charging. In addition, attention shall be paid

to the scrap storage to prevent rusting.

%! Reduction in ana"ysis time

To reduce melting time, analysis time shall be reduced as far as

possible. To reali&e this, it is necessary to put the melting furnace

and analysis test place as near as possible and attention shall be paid

for rapid and e'act communication of the analysis result.

c! Reduction &aste time for mo"ding and crane to furnace

Attention shall be paid not to hold molten metal uselessly by

mismanaging the tapping timing with mold preparations or by waiting

a crane, etc.

d! Reduction in residua" mo"ten meta"

The weight of metal cast shall be estimated properly to reduce the

amount of residual molten metal.

2! Reduction of heat input

a! 'o&ering of temperature of mo"ten meta"

To avoid raising of tapping temperature in consideration of

temperature loss during pouring and keeping a proper pouring temperature,

attention shall be paid to perform preheating of the ladle, to prevent

heat radiation using the lid of the ladle, to locate themelting furnace

and pouring place as near as possible, and to reduce moving time, etc.

(! Reduction of heat "oss

Details will be described in each sort of furnace.


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(. Cupo"a me"ting

(.1 Functions of cupo"a

A cupola is intended to economically obtain molten metal ensuring

castings with few defects, that is,

/14 to produce hot and clean molten metal9

/74 to produce molten metal with high fluidity9

/"4 to produce molten metal with proper chemical compositions

/>4 to ensure economical and constant operation and easiness of repair.

To fulfil these functions, the following are necessary8

/14 to design the cupola with proper structure9

/74 to select and use proper charge materials9

/"4 to establish and manage proper operating conditions9

/>4 to control the inter(process quality properly.

(.2 )tructure of cupo"a

=ig." shows the basic structure of a cupola and Table 1 ( the standard

dimensions of principal parts of conventional cupola. The function of a

cupola depends on the part lower than the charging door, which is divided

into the preheating &one, the melting &one, the superheating &one, and the

well from a functional point of view.

etal charged through the charging door is first heated in the preheating

&one by combustion gas heat of coke, and then melted in the melting &one

followed by being sub)ected to superheating and tapped from the tapping hole

through the trough. In favorable operation, as shown in =ig.7, the furnace

temperature is said to be 3 to 1E: in the preheating &one, 17 to 13E:

in the melting &one, and 1@ to 1!E: in the superheating &one9 it is

desirable that the tapping temperature be 13 to 133E:. The melting &one

and the superheating &one are classified into the deo'idation &one and the

o'idation &one from the viewpoint of combustion reaction. in cupola melting,


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the positions of these deoxidation (one and oxidation are important4 they

have a great influence on the properties of molten metal. Fhen the oxidation

(one is expanded to the top of furnace or solid metal is put in a strong

oxidi(ing atmosphere because of lo$ering of the metal melt-do$n position,

oxidation of molten metal is accelerated, the melting loss of 1i is increased,

$hich may cause the abnormal of graphite form and defect such as shrinkage

cavity, etc.

1! Effective height

The height from the tuyere /lower tuyere in case of a multistage

tuyere4 to the lower end of the charging door is called Ceffective heightC,

which is the most important part from a functional point of view. This

part, which is a preheating &one where metal and coke are preheated by

heat of combustion gas blown up form below and moisture of coke is

evaporated, needs enough height, while e'cessive height may increase

blast resistance and cause crushing of coke at the time of charging9 it

is desirable that it be ".3 to @ . times as large as the inside diameter

of the cupola.

#+$ Tuyeres

They are blastingports for combustion air4 this is an important part

affecting the combustion of coke. Uneven pressure or quantity of air

supplied from each tuyere $ill lead to uneven combustion and heat

generation of coke at the tuyere, causing oxidation melting in lo$-

temperature parts, thus generally lo$ering the temperature of molten

metal. There are many researches and patents related to egui-blast such

as the form of the tuyere, $indbox, buffer plate, etc. The ratio of the

total cross section of tuyeres to the cross section of the furnace /tuyere

ratio0 is : to < for a small furnace and &> to &: for a large furnace.

- & > -


16/86

This is because in the case of a large furnace it is necessary to increase

wind speed so that wind will reach the inner part of the furnace. The

number of tuyeres shall be increased so that there are no dead points

where combustion is insufficient9 it shall be @ in the case of a small

furnace and be increasedwith an increase of the si&e of furnace9 tuyeres

shall be arranged hori&ontally on a plane at equal intervals, surrounding

the furnace.

(! *ind%o+

The windbo' is intended to convert the kinetic pressure of air to

static pressure to make equi(blasting from each tuyere into the furnace .

The windbo' shall be designed so that the velocity head of air passing

through the air blast tube will be as small as possible to supply an equal

quantity of air to each tuyere.

Mo"ten iron

Preheating

,one

Me"ting

,one

-io+idation$ .,o.ne )uper heating,one +idation

,one

/00 1$000 1$/00 *e"" ,one Reaction ofT coe and

Furnace temperature$ Me"ting furnace

C c ondition gas

0 10 20

Amount of gas

Fig.2 Com%ustion reaction and gas distri%ution in cupo"a

( 1 1 (

,one


17/86

8ig.+ 1tructure of cupola and functional (ones

- & ) -

118 ffective height

;8 eight of bed coke

h8 Depth of pool for molten metal5iarging door.

Biarging

coki4

5aterial /im4tal0D

!%ire brick

AEr blast tuba

*reheating &oqe

#iu'Fu6alion&one

ind l'4'

1lagging u f 4 GHvI

1lag /Tluating0

5olten motal


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Ta%"e 1 )tandard dimensions of principa" parts of cupo"a

Insidediameteroffurnace/mm4 D

:rosssection

offurnace/m74 A

TuyereratioA0a

ffectiveheightratio0D

ffectiveheight/mm4

Bell depth/mm4

Dimensions of verticalsection of wind bo' /mm4 Thickness

of liningof superheating&one /mm4

Thicknessof bottom

sand/mm4

eltingspeed

/t0h4 =ront

slagging =i'ed

receiver oli&ontal ?ertical > .17@ > ( 2 @. 7,> > "3 1> 3@ 17 1 .! >3 .13 > ( 2 @. 7,2 > "3 13 @ 17 1" 1.1 3 .1@ > ( 2 @.

", >73

"3

1@

@>

17

1@

1.>

33 .7"2 3 ( ! 3.! ",1 >73 "3 1! 27 1 1! 1.2 @ .7!" 3 ( ! 3.@ ","@ >3 "23 7 ! 1 7 7.1 @3 .""7 3 ( ! 3.> ",37 >3 "23 713 !@ 1 7 7.3 2 ."!3 @ ( 3.7 ",@> >23 "23 7" 7 7> 77 7. 23 .>>7 @ ( 3. ",23 >23 > 73 1 7> 77 ".> ! .37 @ ( >. ",7 3 > 72 1! 7> 77 ". !3 .3@2 2 ( 1 >.! >,! 3 > 7!3 11> "1 7> >.> .@"@ 2 ( 1 >.2 >,7" 373 >73 " 17 "1 7> 3.

3 .2! 2 ( 1 >.@ >,"2 373 >73 "7 17! "1 7> 3.@

1, .2!3 ! ( 1 1 >.3 >,3 33 >73 "> 1"@ "@ 7@ @.7 1,3 .!@3 ! ( 1 1 >.> >,@7 33 >3 "33 1>7 "@ 7@ @. 1,1 .3 ! ( 1 1 >." >,2" 323 >3 "2 1>! "@ 7@ 2.@ 1,13 1."! ( 1 7 >.7 >,!" 323 >3 " 13@ "@ 7@ !."

1,7 1.1" ( 1 7 >.1 >,7 @ >23 >1 1@> >" " .1 1,73 1.772 1 ( 1" >. 3, @ >23 >" 127 >" " . 1," 1."72 1 ( 1" ". 3,2 @73 >23 >3 1! >" " 1.!

1,"3 1.>"1 11 ( 1> ".! 3,1" @73 3 >2 1!! >" " 11.2 1, > 1.3" 11 ( 1> ".2 3,1! @3 3 > 1@ >" " 17.@ 1,>3 1.@3 17 ( 13 ".@ 3,77 @3 3 31 7> >" " 1".@ 1,3 1.2@@ 17 ( 13 ".3 3,73 @23 3 3" 717 >" " 1>.2


19/86

#! 3"ast vo"ume and pressure

The blast volume and pressure are important to ensure proper operation

of a cupola. In Table 7 are given some e'amples of relationship between

capacity of a cupola, blast volume and pressure. The blast volume shall

be large enough to supply sufficient o'ygen to hold proper combustion

andensure complete combustion of carbon content in coke e'cept that picked

up to iron. ;ut too large blast volume will lower the furnace temperature,

leading to o'idation melting, to which attention shall be paid. The

theoretical air quantity is 2.23 $m?min per 1 kg of coke.

-hown in =ig.> is the mesh diagram of the relationship between blast

volume, carbon ratio, tapping temperature and melting speed. ost

effective blast volume is shown by the dotted curve plottedby connecting

the highest points of tapping temperature for each carbon ratio. =ig. 3

shows the relationshipbetween blast volume and o'idation loss of molten

metal. As seen from the figure, o'idation proceeds rapidly when blast

volume e'ceeds certain value and o'idation loss increases more sharply

according as coke ratio is lowered.

;last pressure shows resistance by charges in the furnace9 pressure

shall be changed by the height of the coke bed and particle si&e of coke,

and operation trouble such as hanging and clogging of a tuyere with shall

be watched slag by means of wind pressure.

( 1 > (


20/86

1" 13 12 1 71 7" 73 72

Inside diameter of cupola

8 3mm Acid,

water(cooled

operation *article

si&e of coke

8 ! to 1mm

6last volue& NVinI I I I i

40 ! 1 110 17 1"

6last volue& NVin4+

Fig. / +idation "oss$ %"ast vo"ume and coe ratio

(.( Me"ting operation of cupo"a

1! Ignition

After repaired and dried cupola, firewood for igniting coke is put

on the bottom and ignited. After ignition, bed coke is charged to a

specified height followed by burning it sufficiently by natural draft.

2! Fore %"o&ing

As soon as flames reach above the bed coke, the tuyere peep holes

are closed and conduct fore blowing for " to 3 minutes is allowed, then

the height of the bed coke shall be ad)usted using a chain, a steel bar,

etc. from the charging port. The proper height of the bed coke is 1.3

to 1 .! times as large as the furnace diameter for small furnace up to

2 mm in diameter, and 17 to 1" mm for larger furnace.

( 1 @ (

2.0

7.

1.3to c in7 HI l,UO 8049

U %

Go


21/86

(! Charging of materia"s

etallic materials such as pig iron, scrap iron, steel scrap,

ferro(alloys are mi'ed in accordance with the pre(determined table and

charged into furnace. It is desirable that a batch of metal charge is

about 101 of the guantity of molten metal tapped per hour. Then a fi'ed

amount of coke /charging coke4 to compensate the loss of bed coke and

lime stone of " to > of metal to increase the fluidity of slag generated

during melting. :harging shall be done in order of coke, limestone then

metallic materials and shall be up to )ust below the charging port. Too

large chargedmaterials increase the speed of passage of combustion gas,

lowering preheating effect. They may cause hanging sometime. %n the

other hand, too small materials prevent ventilation in the furnace,

causing incomplete combustion or lowering melting speed. It is

recommended that materials charged have the following dimensions.

:oke 103 to 10! of the inside diameter of

furnace

etal 10" or less of the inside diameter of

furnace and 10@ or less of the cross

section of furnace

*ig iron, scrap iron 13 kg or less0pc.

-teel scrap Thickness 73 mm or less

#! )tart of %"asting

After charged materials, hold them for 13 to 7 minutes to preheat

them followed by starting air blast through the blast tube, windbo', and

tuyeres with the use of the air blower to start melting. aterials on

the bed coke are preheated by combustion gas, then melting starts. In

" to 3 minutes molten metal can be seen through tuyere dropping in the

bed coke. If it takes less than 7 minutes the bed coke is too low, and

- 1 1 -


22/86

if it takes more than @ minutes the bed coke is too high.

In 13 to 7 min after starting air blast the tapping hole shall be

open. olten metal is heated in the superheating &one and accumulated

in the well followed by being tapped through the tapping hole and trough.

The temperature of the first molten metal is generally low and is apt

to fluctuate in chemical compositions9 it is recommended that initial

tap shall not be used for qualitatively important products. To get the

high temperature molten metal form the beginning, it is necessary to

increase slightly the height of the bed coke and to blast e'cessive air

at initial stage, to add 7 of calciumcarbide to the first charging coke,

or to perform air blasting with o'ygen enriched.

/! Tapping

-ince materials charged in the furnace begin to fall after air

blasting is started, coke, metal, etc. shall be supplied continuously

at constant intervals so that the furnace will always be filled with raw

materials up to )ust under the charging door. The change in this height

will lead to a change in blast pressure, affecting the furnace condition,

to which attention shall be paid. ven when operation is conducted with

a proper blast volume and proper coke ratio, the bed coke inevitably lowers

due to errosion of the furnace wall in the melting &one after longtime

operation. To compensate this, it is necessary to add about one charge

of coke every 1 to 1 . 3 hours after operation is started.Bhen the cupola is working satisfactorily,

14 the color of a flame of combustiongas in the charging door is light

purple or light pink. A yellowish(red flame shows an o'idi&ing

atmosphere9

74 each tuyere is uniformly bright9

"4 slag is of good fluidity, glossy, andglassy, light green or whitish,

( 1


23/86

and light9 at the time of o'idai&ing melting, the =e% content is

increased in slag and its color becomes blackish, its specific

gravity becomes higher, and it loses gloss9,

>4 molten metal is hot /13"E: or higher4 and the break surface figure

of molten metal does not appear for awhile after poured into ladle.

(.# Foundry coe

=oundry coke has two roles an energy source for melting and carbon pick

up agent to iron. Attention shall be paid to the following items when

selecting foundry coke8

1! Partic"e si,e

The si&e of coke is recommended to be 103 to 10! of the inside diameter

of the cupola. The coke particle si&e has a great influence on ventilation

resistance and combustion in the furnace. Bhen the particle si&e is small,

the surface area becomes larger and the o'idation &one )ust above tuyeres

becomes shorter and hotter, accelerating deo'idation reaction, thus

lowering furnace temperature. In addition, the position of the metal

melting &one is also lowered, causing lowering of melting temperature.

%n the other hand, when the particle si&e is large, the o'idation &one

is e'panded, making :7 deo'idation reaction insufficient, thus

generating an atmosphere with a lot of :7 in the upper part and causing

o'idi&ing melting.

( 1 (


24/86

56Temperature 7as

/a4 -mall(si&e

8 Temperature 7as

/b4 edium(si&e

8Temperature 7as 8


25/86

increases carbon pickup to molten metal, raising tapping temperature.

Therefore, in case of small cold blast cupola operation, low ash content

coke is often used, while a hot blast cupola, high ash content coke is

used from an economical point of view, because blast temperature is high

and influence of ash is reduced.

/! )u"fur content

-ulfur in coke, when molten metal comes in contact with red(hot coke,

the sulfur pickup to molten iron should occur and badly effect. -ulfur

content of foundry coke should be as low as possible.

9! Moisture

oisture in coke is heated and evaporated in the preheating &one of

cupola, so it is said to have little influence on molten metal. owever,

the change of moisture content affects the weighing accuracy of charged

coke, making proper melting difficult. Therefore, when storing coke,

attention shall be paid so that a roof will be provided to prevent

penetration of rain, the floor will be inclined slightly to prevent

formation of puddles, and good ventilation will be ensured for natural

drying.

( 7 1 (


26/86

#. Energy conservation of cupo"a

#.1 :eat efficiency of cupo"a

The energy conservation of cupola is evaluated by its heat efficiency.

That is,

eat efficiency /eat content of molten metal0Total heat input4 ' 1.

The heat efficiency is calculated by using the above formula after

calculating heat balance by using heat input and heat output obtained for

each item per ton of molten metal. Table " shows main items of heat input

and heat output. eat balance is intended for e'amining heat output in detail

to take measures for reducing heat loss, but it is difficult to reali&e it

only by the foundry from the viewpoint of measuring eguipment and technology.

The heat efficiency alone can be calculated from the four factors of heat

input and sensible heat carried away by molten metal.

Ta%"e ( Factors of heat %a"ance of cupo"a

=actors +emarks >(J"ac

G>(J K#

4

1.1 :ombustion heat of coke


27/86

0,+ Cal/ulation o% .eat input

#'$ Cobustion .eat o% /o:e

To obtain correct combustion heat of coke is difficult, because

inter-reaction of fixed carbon, volatile materials, sulfur, moisture,

etc. in coke is complex, and a lo$er heating value, heat of condensation

of $ater vapor reduced from higher heating value, is used as combustion

heat of coke.

Eo$er heating value /J K Jh - ? x /< x h L $0 /kcalMkg0 ,

Jigher heating value /Jh0 K 1ix ' L +> x /h->M90 L ): x 1 /kcalMkg0,

$here

h8 Actual hydrogen content in coke /4

w8 Actual whole moisture at usage in coke /4

:8 =i'ed carbon of coke /4

8 %'ygen of coke /4

-8 -ulfur of coke /4 .

-ince in a cupola, coke is consumed not only for combustion, but also

carbon pickup, the amount of coke practically burned is obtained by

subtracting the amount of coke consumed for picking up from the total

amount of coke used.

The amount /B4 of coke burned per It of molten metal is8 B

/B) ( B74 0T,

where

B)i Total amount of coke used /kg4

B78 Amount of coke consumed for carbon pickup /kg4

T 8 Total amount of molten metal /t4

The heating value /M6 of coke per It of molten metal is8

MiB ' I.

(7"(


28/86

2! )ensi%"e heat in air %"ast

The sensible heat /M74 in air blast per ton of molten metal is8

;+ Cair > #Tair 2 Tr$ &

where

Bsup ' -#p or M>


29/86

0,- Cal/ulation o% .eat output

#'$ *eat /ontent /arried a?ay by olten etal

The heat content of moltenmetal is calculatedbased on the material

and temperature. The heat capacity of each element in Table is

calculated from the temperature follo$ed by integrating them according

to their percentage in the material.

Table 0 *eat /apa/ity per ton o% ea/. eleent

/xample0 Bray cast iron' +.+;1i &..?;

1 >.>=;

8e N' can becalculat ed in the follo$ing $ay% C K/:9>.: L =.+ x :> M &>>0 x >.>++

L /= :& .? L ):.9 x :> M &>>0 x >.>&<L / + + ) . > L &< .> x :> M &>>0 x >.>>?

L /) + < . < L &= .) x :> M &>>0 x >.>>>=

L /+&:.? L &=.) x :> M &>>0 x >.+0

8rom the description above, the heat efficiency of a cupola is

expressed as follo$s%

Jeat efficiency K /Jeat content carried a$ay by molten metalMTotal

heat input0 x &>> K /CmM/Ci L C)

L C+ L C0O x &>>,

0 , 0 *eat balan/e dia!ras and .eat e%%i/ien/y o% a /upola

8ig. = sho$s examples of heat balance of cold blast operation and +>> N'

and ?>> N' hot blast operation of a cupola $ith an inside diameter of ?:> mm.

The heat efficiencies are +).;, :&.9;, and ?>.>;, respectively.

- 2 5 -

etal

element

eat capacity /kcal0t ' 1"4

1>E: 13E: per 1E:

: b"".7 bb%.b >2."

n "1". ""7. 1.

$i-

73!.777.2

72>."7".

1@."

12.7

=e 7!.> "13.@ 12.7


30/86

"7.>8 eatused for melting

1@."8+adiation from cupola.!8:ooling water7.18;last air.78oisture1.@8:alcining of lime stone>.8-lag fromation

( 18TotalNOOCheatinput*-------2.78(((:ombustionheat GNGNGof coke

+?.);% Eatent heat in stack gas

?.; i 1ensible heat in stack gas).9;% #mdation of

elements

/a0 'old blast operation

/b0 Jot blast operation =.:;% Air blast tube

/+>>N'0

"(18

+adiation from cupola

1.8 :ooling water

".38;last air

.>8oisture

@.78 -lag formation

C; 13.!8 -ensible heatF of

air blasting

PnnPf- t E* e r a t iE n /@ :4

.;% 3adiation from cupola

>.=?;%'ooling $ate(

).>);%7iast air >.>:;%5oisture

). >=;% 'alcining of limestone4

=.>;% slag formation

:&.9;% Jeat usedfor melting

)?.?;% Eatent heat instack gas

:.+;% 1ensible heat in

stack gas

&>>;% Jeat input

99.=;% 'ombustibi

GQheat of coke+.


31/86

!.8


32/86

/. Improving the heat efficiency of a cupo"a

/.1 :ot %"ast cupo"a

/ . 1 . 1 The purpose of hot %"asting

The temperature of e'haust gas of a cupola is as high as !E:, making

it possible to preheat blast air up to as high as >E: by heat e'change.

Inaddition, both the sensible and latent heat of e'haust gas can be recycled

for preheating blast air by combustion of :% gas included in e'haust gas.

Bhen blast air is preheated to "E: or higher, the sensible heat of

blast air is added to heat input, activating combustion of coke, leading

to the rise in combustion temperature /=ig. ! Q , thus improving heat

efficiency and economy owing to the reduction in the coke ratio andincrease

in melting speed. oreover, in the upper part of the combustion &one, : 7

gas due to coke is deo'idi&ed by high temperature, reali&ing a highly

reductive atmosphere, thus decreasing the o'idation loss of metal. In cold

blast operation, combustion is hindered around tuyeres by cold air, while

in hot blast operation, the ma'imum temperature &one comes down )ust above

tuyeres /=ig.4.

C.ar!in!door

2000 I

Cold blast

:G &9>> *ot a

l

a

s

t

&?>>

0 100 200 (00 #00 /00 900

:ot air temperature :ot air temperature and coe

f"ame temperature

Fig. ? Furnace temperature

distri%ution in co"d %"ast and

hot %"ast operation


33/86

(72(


34/86

ot blast

i4 reduces the coke ratio, improving the heat efficiency /-ee

=ig.249 ii4 raises tapping temperature, improving the

quality of molten

metal9

iii4 increases melting speed, increasing melting capacity9 iv4

increases the percentage of steel scrap in chargemetals due

to the increase in carbon pickup and : value, improving

quality of the material and reducing the material cost9

v4 ensures little loss of -i and n in molten metal in a

reductive atmosphere, saving ferro(alloysF cost, vi4

reduces sulfur pick up to iron, improving the quality of

material9 vii4 lowers the temperature of e'haust gas,

reducing the

equipment and power cost due to miniaturi&ation of a dust

collector.

/ . 1 . 2 :ot %"ast e@uipment

/14 =urnace wall heat recovery type8 ;last air is preheated by the sensible

heat of e'haust gas by double wall of the furnace or using a sleeve.

This is often used in a small cupola even today.

/74 -tack gas heat e'change type8 *reheating blast air is performed by

using the sensible heat of e'haust gas of the stack./"4 #tili&ation of the latent and sensible heat of e'haust gas8 'haust

gas is sucked )ust below the material charging port to utili&e both

the latent and sensible heat of e'haust gas. 'haust gas is taken

out of several suction ports, led into the combustion chamber followed

by mi'ing with air and ignited. Then the burnt gas is controlled to

a set temperature of about 1E:, led to heat e'changer. -table hot

( 7


35/86

air with a temperature of > to @E: can be obtained with 1 or

more of :% gas content in stack gas.

/.2 +ygen enriching cupo"a

/ . 2 . 1 The purpose of o+ygen enrichment

%'ygen necessary for combustion of coke is no more than 71 of air9

nitrogen occupying 2 of air absorbs heat in the furnace and carries away

a lot of heat as stack gas.

%'ygen enrichment is intended to increase the concentration of o'ygen

during air blasting to raise tapping temperature easily at the beginning

of operation or at any melting condition and to increase melting speed.

Table 3 shows some e'ample of o'ygen enrichment. The following are

advantages of o'ygen enrichment8 i4 +aise tapping temperature,

improving the quality. ii4 Increase melting speed and melting capacity,

iii4 Decrease blast volume and save

power, iv4 +educe coke ratio and

improve heat

efficiency.

v4 Increase steel scrap in charge and

improve the quality of material and

reduce the material cost, vi4 Improve

the yield of -i and n, and

reduce fello(alloys.

vii4 +educe - pickup to iron, andensure

1"#71R7"

(((((((((((((((((((((((((((((((((((((((((((((((((73( 72R7(("102 during air %"asting !

easy treatment of molten metal

such as inoculation. Fig. 10 Amount of o+ygen and

tapping temperature

(7(

T e m p e r a t u r e o f m o l t e n m

e t a l R N ' S / o p t i c a l p y r o m e t e r 0

.

J ! - J - 2 U - i U - @ j #

@ Q @ @ Q Q @ Q U @ G f H Q Q @

o @ - V c o t n - D W I o

+ # # # # #

i S o-

G

[

1

1


36/86

Ta%"e / Effects of o+ygen enrichment

Inside diameterof cupola

%'ygen enrichmentmethod

elting speed /t0h4 :oke ratio / 4

inch /mm4 /amount of o'ygeSadded, 4

i ;efore After ;efore After

> /1,1>4 nrichment /7.34 @ ! 1> 17 "@ / 174 nrichment /".4 > 3 13 1

>@ /1,1@@4 nrichment />.4 1 17 17.3 .>

>! /1,71@4 In)ection /".4 2 2 17.3 .>

"7 / !114 nrichment /7.4 7.3 7.3 12 1>

/.2.2 +ygen enriching e@uipment

Though a method using an o'ygen enrichment membrane has also been

developed recently, generally pure o'ygen produced by evaporating liquid

o'ygen is added through inserting duct in the air blast tube. %'ygen is

diluted with blast air and enriched uniformly to 77 to 73 blasted through

tuyeres. The lattermethod is common and easy ad)ustable, it is used both

continuously or intermittently. In addition, there is also in)ection

procedure blowing o'ygen into the furnace through ducts installed in

tuyeres.

/.2.( :igh8efficiency cupo"a &ith high8rate o+ygen enrichment

The amount of o'ygen enrichment is generally up to >, and it is said

that enrichment e'ceeding this value can cause o'idation of molten metal.

owever, high rate o'ygen enrichment can increase the heat efficiency of

a cupola up to "3 to >, which has beendifficult for a small cupola, making

it possible to produce a cupola ensuring high(quality molten metal by

high(temperature tapping and capable of varying the melting speed in the

range @ to 7 of a rated value. This cupola ensuring both energy

conservation and fle'ible operation was commended as e'cellent energy

saving equipment by 6apan achinery =ederation. This cupola can be

("1(


37/86

produced both newly and by modifying an e'isting one.

/.( :umidity contro" cupo"a

/ . ( . 1 The purpose of humidity contro" of %"ast air

igh moisture content of the blast air in cupola melting comes in

contact with coke, causing the following reaction. 7 L : :% L 7 (

17" k60mol 77 L : :7 L 77 ( !1.1 k60mol

The upper reactionprogresses at a temperature of 1E: or higher and

the lower reaction ( at a temperature below 1E:. ;oth of them are

endothermic, and the temperature ad)acent to the tuyere fall down. The

condition of combustion and heating in the furnace becomes worse. The

e'periment has shown that tapping temperature sharply lowers at an absolute

humidity of 13g0m" or more, the material and becomes inferiormelting speed

reduces.

=urthermore, moisture in blast air increases o'idi&ing metal in the

furnace, causing adverse influence such as lowering of carbon pickup, and

yield of silicon, etc. To cope with cupola operation in a high humidity

period, the height of the bed coke is generally increased or the coke ratio

is increased in amounts of 1. 3 to 7 . . ;ut this is not desirable from

the viewpoint of energy conservation. ;y controlling humidity8 i4

reduction in the amount of coke used, ensuring energy

conservation9

ii4 easy guality control for molten metal by keeping stable air low

humidity in blast all the year round, reducing defective ratio

of castings9

iii4 reduction in the material cost due to increase in the percentage

of steel scrap in charge9

( " 1 (


38/86

iv4 rise in the temperature of the first tap molten metal and increase

in tapping temperature, etc.

;ut in 6apan with a remarkable fluctuation of humidity in a year, the

absolute humidity in the dry season is > to @ g0m ", while in the wet season

it is 1! to 7> g0m", that is, the difference between them is no less than

7 g0m". In a cupola /about "t0h4 operation with blast volume of @m"0min,

water in blast air changes at a rate of as high as 1 . 7 litre0min. Though

the improvement of the heat efficiency is an effective achievement, stable

quality is the greatest energy conservation effect of humidity control

operation.

/.(.2 -ehumidification e@uipments

i0 "ehumidification $ith equipment hygroscopic materials

This type equipment is using as moisture adsorbents silica gel,

activated alumina, calcium chloride or lithium chloride. quipment is

necessary for drying by heating and reclaiming absorbent materials $hen

lost their po$er in longtime use. ii0 3efrigeration

This type equipment removes excess moisture by cooling air under a

de$ point to condense. 'ooled air is heated by a reheater and supplied

to the cupola. The refrigerator type has become popular today by the

improvement of the capacity of a refrigerator and measuring and

controlling technology to keep humidity constant.

@,-,- E%%e/ts o% .uidity /ontrol

!nhumidity control operation of cupola, tapping temperature rises and

the coke ratio is reduced. 8ig.&& sho$s a refrigerator type dehumidifier

capable of keeping the absolute humidity at about ?.:gMm+ all the year round.

8ig.&) sho$s ho$ the coke ratio $as reduced by this operation.

- 3 2 -


39/86

en

a<

10

&:

&

!nput absolute jhumidity HM =

X

M M X fHYGGY20 7efore dehumidificationVJJJtfa After dehumidification

H X X

Q

& &+fl0

9 &)

>

H

/ / /

/ / /

@Q@G H

i i k X x Fx 6

xxxxxW

p- -

j2 Z 1 PPP

PPPPPPPP

p

@

P P P P P P P

P

mr

M \ X '-Y

Y : *

- f - r -

H2

'l K \ -'--*

& #utputhumidit abs

c@y

pe

Wlut

I-atr

]

G & ) + : ? = 9 < &> && &) I + - 0 %& %i & ) ( ' II '+

Ca"endar months

Fig.11 Effects of refrigerator type Fig.12 Reduction of coe ratio %y

dehumidifier humidity contro"

dehumidification

/.# Mu"ti8stage air %"asting cupo"a

/ . # . 1 Purposes of mu"ti8stage air %"asting cupo"a

There are two points of view as shown below8 -econdary air blast is

provided above the main tuyere to burn :% gas coming up in the deo'idation

&one and to use the combustion heat for9

/14 metal preheating in the preheating &one is enhanced9 or

/74 themelting &one is e'panded, the melting position is raised a


40/86

little,

the falling distance of molten drops is increa sed, and furnace

temperature is raised to increase melting and superheating effect.

$owadays upper tuyeres are often provided in the coke bed for the latter

purpose.

- 3 3 -


41/86

/.#.2 Mu"ti8stage air %"asting type

In a multi(stage blasting cupola the position of the upper tuyere and

ratio of blast volume of the upper and lower tuyeres are to be determined

according to the purposes.

/14 Bhen preheating solid metal, upper tuyeres shall be provided in

places

at a distance of 7 to " times the furnace diameter from lower ones,

and the blast volume of them may be 13 of the total volume, when

the amount of :% gas in flowing gas in the preheating &one is estimated

to be 1" to 13.

/74 Bhen e'panding the melting &one and ensure sufficient

superheating

of molten drops, upper tuyeres shall also be provided in the coke

bed9 they shall be at a height of 1 . to 1 . 7 times the furnace diameter

from level of lower tuyeres. The blast volume through upper tuyeres

is considered adequate to be equal as lower ones.

/.#.( Effects of mu"ti8stage %"asting

=ig.1" shows heat balances for a large hot blast water cooled no lining

cupola with the inside diameter 7" mm where the upper tuyeres are provided

whose total area is half of the main tuyere and at a height of 23 mm above

the lower tuyeres. It is reported that the percentage of steel scrap in

charge and the yield of :, -i are increased, while the heat efficiency isimproved only by 1.> though.

=ig.1> is a diagram illustrating the effect of multi(stage blasting

cupola by ;ritish castings association. The reduction in the coke ratio

and the increase in melting speed to obtain the same tapping temperature

are compared for ordinary operation and dual stage blasting. This figure

shows remarkable energy conservation and improvement of productivity.


42/86

(">(


43/86

Eine stone decomposition heat

l,BCD

Jeat carried a$ay by 7lag

1ensible heat of reiidual coke%

, ( F <

-ensible heat of oisturein e'haust gasi .1N

#rdinary blasting "ual blasting

8ig.&+ 'omparison of heat balance for ordinary and dual blasting

133

13

1>

elting speed

@ 2

!1

1 1 1 7 1 " 1 > I - 1 @:oke ratio S

!nside diameter of

cupola%=?>mm Total amount of

air blasted%+m=min 7last

volume ratio of dual tuyeres%

&%&

8ig.& 'hange in /o:e consumption and melting speed for dual

blasting operation

:ombustion heat of cokei !!."

Total heat input8 1N


44/86

- 3 5 -


45/86

/./ *ater coo" cupo"a

/ . / . 1 Purposes of &ater coo"ing of furnace &a""

As increasing in the si&e of cupola, the number of no(lining hot blast

water cool cupolas having only a outer casing made of steel plate without

lining in the melting and superheating &ones and water shower cooling and

preheating hot blast combined has been increasing, which ensures longtime

continuous operation.

i4


46/86

@ , @ , + EGaples o% iproveent o% .eat e%%i/ien/y due to lon!tie /ontinuous

operation #Ener!y /onservation /ase report& '((' edition$

#'$ Reasons %or ta:in! easures

At this plant melting $as performed in a lo$-frequency induction

furnace, but the galvani(ed (inc steel plates for automobiles is increased

in steel scraps, $hich cause $orse $orking environment and ^n content

exceeds the allo$able limit of > . > ? ; in molten metal > . > ? ; for induction

furnace, increasing the amount of expensive pig iron and the cost of charge.

To cope $ith this situation, a cupola $as introduced to improve the heat

efficiency. 8ig.&: sho$s the state of energy use before taking measures.

#+$ Measures ta:en

a! Tapping ho"e patent pending!

The life of refractories of a cupola depends on the abrasion of

the tapping hole. A method of replacing this from outside the furnace

in hot condition was established, achieving longtime continuous

operation for 7 weeks9 until then bottom drop down had been performed

after > day operation for repair. The energy efficiency has been

improved by 1.3.

("2(


47/86

Conventional /upola =o? %re5uen/y indu/tion

%urna/e

Meltin! ener!y Co:es Ele/tri/ po?er

*eat balan/e ,>H, Coolin! ?ater' %t F* H ' J K?rnt/e eLia% 6 * )S@ 'J4ALL3lndlallaL ( 6last air $L %O Ot.ers + pre.ealin!4NBIl S P 3.6otto drop

Operation loss I (((((((( tH&teo B+ ' ' Q,KniLe/1@/,BJ ))* 'f(bol ndialM #' J ' J(Ele/tri/ity '

Ele/tri/ loss

A Coolin! ?ater

ViH%W Co:e /obuslionPil QBed /o:es MetaloidationX !! 4BlH +

*eat e%%i/ien/y --

Consuption rate in

/rude Rear:s Oil4

e5uivalent A,A( :lVt A,'@ :lVt

CA+ !eneratin!

5uantity 'AU/ :!Vt 'A-/ :!Vt

Fig.1/ Comparison %et&een conventiona" cupo"a and "o&8fre@uency

induction furnace

%! Improvement of heat e+changer$ others

The hot blast temperature is raised from >3E: to @E: by improving

the material and construction of the e'haust gas heat e'changer. The

heat efficiency has been improved by ". Air blast dehumidificationwas also performed and warm water was utili&ed for heating.

(! Effects of measures

Ta%"e 9 )ummari,ed resu"ts of measures taen

heat efficiency

Eo$- frequency

furnace

'onventional

cupola

'upola after

taking measures

5eltingefficiency /;0

?? +9 /++0 ? /++ &>? 9:

( "


48/86

Kurna/e /uin! beat radiation

N )

Olben '

100% 1 w

Bottomdro|

Coke combustion

!!! "3# !!$$!

edcokei

! 1% !&!

^ ^

Fig.19 :eat %a"ance of cupo"a after taing measures

/.9 Improvement of heat efficiency %y synergetic effect of air %"ast

conditions

/.9.1 3acground of e+periment

:upola operating techniques have been developed one after another and

it is difficult to correctly )udge the synergetic effect of combinations

of these techniques. In this operation e'periment the effect of

combinations of a cupola with air blast conditions was checked. Inparticular, there is few operation e'periments for a small cupola. These

will be a guideline of energy conservation and improve properties of molten

metal of cupola for medium and small foundry.

/.9.2 The contents of e+periments

'periments were performedby using a 7T0 cupola under the following

five conditions8

/14 :old blast L $on(dehumidification

/74 :old blast L Dehumidification

/"4 ot blast L Dehumidification

/>4 %'ygen enrichment L Dehumidification

/3 4 ot blast L %'ygen enrichment L Dehumidification

( " (

*e ?ater used -

,Coolin! ?ater lost )6lulairpr/bealins

'+

Metal oidation

0


49/86

Air blasting conditions are8

umidity conditions 8 7 g0$m" RN 1 g0$nr

ot air temperature 8 "3E:

%'ygen enrichment 8 L> /734

/ . 9 . ( E+periment resu"ts

It was possible for a small cupola to remarkably improve the heat

efficiency by reducing the coke ratio and improving the melting speed

through humidity control, o'ygen enrichment and hot blast or combinations

of them. In addition, advantages of increasing carbon pickup in molten

metal were also confirmed such as reduction in the percentage of pig iron

in charge, improvement in the yield of material melted, rise in tapping

temperature, etc.

8#08


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g 1.900 IA.>4(!

|3 1.500

T (1.773)

+,

@

+,

60

V

Co"d %"ast$ Bon8

dehumidificationCo"d %"ast$ dehumidification

:ot %"ast$ dehumidification

+ygen enrichment$

dehumidification

:ot %"ast$ o+ygen

enrichment$

dehumidification

Fig. 14 Resu"ts of operation of high8efficiency sma"" cupo"a

/ . 4 E+amp"es of improvement in properties of mo"ten meta" %y measurement

contro" of a cupo"a / . 4 . 1

3acground of taing measures

olten metal of malleable cast iron is made by means of dual melting

a 13 T0 hot blast cupola and a low(frequency induction furnace. A cupola

has an advantage of low melting cost, but has a lot of factors affecting

themelting condition, and its operationrequires great skill. Themelting

1.5501.823

40 5

V


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( > 1 (


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condition was measured to ensure stable properties of molten metal and

energy conservation.

/ . 4 . 2 Measures taen

1! 'eve"ing of the height of charging materia"

#neven height of charging material causes uneven blast air resistance,

that is, it prevents equi(blasting, adversely affecting properties of

molten metal. Attention was paid to the correlation between the ambient

temperature of the preheating &one of a cupola and the difference in height

of charging material. Temperature was measured in @ places around the

preheating &one as shown in =ig.1! to minimi&e the difference in height

of charging material.

At the time of starting of measurement, the difference in ambient

temperature was no less than 73E: and the difference in height of charging

material was > mm. To cope with this situation, charging equipment

and were improved as shown in =ig.1.

(>7(


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condition, which was effective in estimating the height of bed coke.

It is possible to grasp the change of the furnace condition earlier

than the melting operator )udges it by tapping temperature, ensuring

stable operation.

Time series change of vertica" temperaturein the preheating ,oneIncrease Increase

3 @ C F ( ( (

(.0 D

I

2.0

Fig.20 Time series change of vertica" temperature in the

preheating ,one

/ . 4 . ( Effects of measures taen

/14 The fluctuation of tapping temperature has become smaller and tapping

temperature increased by 3E: on average, remarkably reducing the

power consumption rate of a low(frequency induction furnace.

/74 The fluctuation of molten metal chemical compositions has become

smaller and the amount of residual o'ides such as -i 7, n%, etc.

in molten metal has become smaller, reducing casting defects as shown

in =ig.71.

(>>(

• \ • Vv

((231

800

Verti/al teperature in t.e pre.eatin! "one CO500 700


55/86


56/86

9. Batura" gas cupo"a

9.1 The structure of a natura" gas cupo"a

An e'ample of a cokeless cupola which uses natural gas as an alternative

fuel of coke is introduced. This is a shaft furnace having a cylindrical

steel plate lined with refractory same as a coke cupola. It has no tuyeres,

but instead has a grate of water cooled pipes in the middle stage and natural

gas burners under it. =ig.77 shows a schematic structure of a shaft furnace

using natural gas.

1! Me"ting capacityK 9tLhr Furnace inside diameterK 1000 mm

2! Preheating ,one

The furnace has an effective height ratio of > . ! 9 which has enough

capacity for store and preheat charging material sufficient for about

one hour melting, considering effective use of heat.

(! :eat regenerative materia" %ed and &ater coo"ed grate

The bed consists of ceramic balls with a diameter of about 13 mm

laid in 7 to " layers.

Theseballs are made of refractorymaterials having high(temperature

strength capable of standing the melting loss against slag at high

temperatures and the impact and weight of falling of charging material.

A water cooled grate of steel pipe welded construction is used to support

the weight of this bed and melting material and the impact load of falling

of charged material.

#! Com%ustion ,one

Three natural gas burners with each capacity of 1.3 million kcal are

installed at intervals of 17E to achieve a melting efficiency of 33.

( > @ (


57/86

To ensure a balanced amount and pressure of combustion air supplied to

each burner, a $indbox having a sufficient sectional area is provided.

#xygen enrichment is also possible. 8urnace temperature in the

combustion (one reaches &?>> to &?:>N'4 combustion gas heats ceramic balls,

melting and superheating ra$ materials. Fater cooling is performed by

sho$er to cool refractories of the furnace $all. 8ig.)+ sho$s an

operation scheme.

/! *e""

The well located under the combustion chamber has a tapping hole

diameter of as large as 13 to 13 mm to prevent the tapping hole from

being clogged with ceramic balls worn and dropped through the grate.

9! 'o&8fre@uency induction furnace

Bith operation cost taken into account, molten metal tapped at low

temperature of 1"3E: is sub)ect to ad)ust carbon and other element content

and to superheat in a low(frequency induction furnaces. There are two

low(freguency induction furnaces provided, each of which has a capacity

of " kg and an input of @ kB(l%%%?. Their temperature raising

capacity from 1"3E: to 13E: is !.3 t0h /21 kBh0t4.

(>2(


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)"ag ho"e

Iron tap ho"e

Fig.2(peration scheme of natura" gas cupo"a

9.2 Comparison of me"ting energy

Table 2 shows a heat balance of a natural gas cupola in a steady state.

In the case of this furnace, preheating is performed before melting in a

steady state9 the longer the continuous melting time in relation to the

preheatingtime, the higher the heat efficiency. Bhen preheating and melting

are performed for 27 minutes and hours, respectively, the heat efficiency

will be 31 to 37.

Ta%"e 4 :eat %a"ance ta%"e of natura" gas cupo"a !

5ascombustion

*otential heatof molten metal

*otential heatof e'haust gas

*otential heatof cooling water

*otentialheat of slag

%thers

1 3@." 13. 1>.! >. .

Tables ! and show heat balances including electric power of low(

frequency induction furnace for superheating and ad)ustment and electric

power used for motive power of cupola. -tandard e'amples of a coke cupola

(>(

Air %"ast

Refractory %edrefractory %a""!

*ater coo"ed grate

*ater sho&er coo"ing

Fue"

"i@uid natura" aas!3urner Com%ustioncham%er


60/86

and a low(frequency electric induction furnace are shown for reference. =rom

the viewpoint of energy consumption, the natural gas cupola is the most

earth(friendly of these three melting methods.

Ta%"e > Energy used in each me"ting furnace and their heat

efficiency E"ectric po&erK direct"y input!

Zind of energy #nit eating

value

/kcal4

5as cupola :oke cupola lectric inductionfurnace

nergy

consumption

0ton

nergy

/kcal0ton4 nergy

consumption

0ton

nergy

/kcal0ton4 nergy

consumption

0ton

nergy

/kcal0ton4

$atural gas $m" , 3 @ 32,

:oke kg 2,7 133 1,11@, lectric power kBh !@ ! @!,! @3 33,

;lower kBh !@ 3 >," 1 !,@

Dust collector kBh !@ @ 3,1@ 7 12,7 @ 3,1@

Total @23,7@ 1,1>1,! 3@>,1@

eat efficiency 32 "" @!

Ta%"e ? Energy used in each me"ting furnace and their heat

efficiency E"ectric po&erK indirect"y input!

Zind of energy #nit eating

value

/kcal4

5as cupola :oke cupola lectric inductionfurnace

nergyconsumption0ton

nergy/kcal0ton4

nergyconsumption0ton

nergy/kcal0ton

nergy8onsumption0ton

nergy

/kcal0ton4

$atural gas $m" ,3 @ 32,

:oke kg 2,7 133 1,11@, :

lectric power kBh 7,73 ! 1!, @3 1,>@7,3

;lower kBh 7,73 3 11,73 1 77,3

Dust collector kBh 7,73 @ 1",3 7 >3, @ 1",3:

Total !1,23 1,1!",3 1,>2@, %%: eat efficiency >! "7 7N

9.( Comparison of e+haust gas in me"ting

'haust gas of a conventional coke cupola and a natural gas cupola can

be calculated from their fuel compositions and consumption.

( 3 (


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Ta%"e 10 Composition and com%ustion product of foundry coe

'omponents /$t;0 Eo$-level

heating value

/kcalMkg0

'ombustion product /m+ Mkg0

' J > 1 J)> Ash '>) J)> ) 1>)

9:.: >.)= >.>? >.? >.)? &).? ?,+ &.?& >.>+ ?.>

Ta%"e 11 Composition and com%ustion product of natura" gas

'omponents /$t;0 Eo$-level

heating value

/kcalMkg0

'ombustion product /m+ Mkg0

'J ')J? '+J9 ',Jio '#) J)> ) 1>)

99 ? )


62/86

(! Recyc"ing automo%i"e scraps

Though in melting in an induction furnace, there are problems of

worsening of working environment duringmelting, lowering of the quality

of castings, shortening of life of refractories, etc. due to [n galvani&ed

steel plates of automobile scraps which are e'pected to increase in the

future, the refining effect of a cupola makes it possible to recycle them.

armful elements such as *b, -n, Al, etc. can be collected as o'ides with

a dust collector in the cupola.

(37(


63/86

4. Induction me"ting furnace

4.1 Features of induction me"ting furnace

In metallic material placed in magnetic field generated by the current

in induction coil of the furnace, electromotive force is induced by the actionof electromagnetic induction, and induced current flows to heat up the

material by its 6ouleFs heat. :ompared to other types of melting furnace,

induction furnace has the following features8

/14 Its heat efficiency is high because the material is directly

heated

by electromagnetic induction.

/74 $o carbon dio'ide is produced and little smoke and soot are

emitted

because cokes are not used as fuel.

/"4 etal loss by o'idation is little, thus little contamination

of in

metal because of heating without air.

/>4 Temperature control is simple, uniform composition of metal

product

is attained by agitation effect and alloyed cast iron is easily

produced.

/34 Induction melting is suitable for high temperature melting

because

of its energy concentration, and installing space is reduced as

compared with other types of melting furnace.

Induction furnace is classified into the following types according

to its structure and frequency applied8

Induction R

furnace

R :rucible type

R :hannel type

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4 . 2 . 1 Tota" efficiency of induction furnace

fficiency of induction furnace is e'pressed as a total, deducting

( 3 " (


65/86

electrical and heat transfer losses. eat balance diagram of crucible type

induction furnace is shown in =ig.7>.

lectrical losses consist in transformer, frequency converter,

condenser, wiring, cable, coil, etc. (

Input

'AANr8ed e

ater8coo"ed ca%"e 1./!

s%orer#'$

s arn enser

sformer

1!

conduction(!

ota"iciency

94

radiation2!

eat conduction4!

eat radiation#./!


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frequency conversion.

Ta%"e 12 :eat %a"ance of induction furnaces at continuous

operation

Type of furnace 2".7 @1. @@.>

eat loss 1S 7".@ 1". 2.3 3.2 >.3 7.1 7.7 1."

lectrical loss 1S ". 7.! 7!.7 1!. 73.7 13.> 71.1 1!.3

Biring loss 1S "." 7.! "." 7. ".7 7.2 7.! 7.@

-econdary power loss S 1." . 1." 1. 7.7 7.1 7.! 7.

*rimary power loss 1S 1.@ 1.3 1.@ 1.3 >.3 >.3 2.1 !."

elting power rate kBh0tS ( ( @33 3"> @7! 37 @77 327

eating power rate kBh0tS "@ " >1 "> > "" "! "@

+emark8 elting power rate is given up to 13Ct and heating power rate is shown by 1E:.

4 . 2 . 2 Po&er consumption rate

=ig.73 shows the relationship

between furnace capacity and the power

consumption rate, i.e. electric energy

required for melting each ton of metal.

*ower consumption rate is lowered as the

furnace capacity is increased

appro'imately upto 17 to 13 tons,

thereafter consumption rate remains

unchanged at about @1 kBh0t. *ower

consumption rate of small(si&ed furnace

about 1 to " tons e'ceeds 2 kBh0t.

Dotted line with CHC marks in the figure

> 12 19 20 2# 2>

Furnace capacity$ t

RemarsK 3roen "ine &ith mars =+=

sho&s standard rated va"ues.

Mared &ith are given for

high8fre@uency furnace$ and

mared &ith =H = are given for

me"ting in t&o furnaces.

Fig.2/ Furnace capacity and

specific po&er

consumption.

8 //


67/86

shows the power consumption rate at standard rating of the furnace with

remaining 107 melt in the furnace, which is calculated about kBh0t lower

than actual consumption. This rated value doesnFt include the electric

energy required for holding molten metal, slag removing, tapping and other

related operations. This difference in theoretical and practical values

indicate possibility for decreasing the power consumption rate.

4.( Energy saving measures for induction furnaces

4 . ( . 1 Improved heat efficiency %y improvement of furnace

nergy efficiency at power source side, such as frequency convertion

efficiency, power(factor improving capacitor, etc., includingproper coil

design, can not be ad)usted by userFs side. %n introducing the induction

furnace, specific features of the furnace must be understood fully to make

proper decision about kind of material, si&e and shape of charging materials

to be melted, melting amount, connection with pouring line and layout of

the melting shop.

1! E@uipment "ayout

Induction furnace equipment should be melted with minimum distance

between each equipment to reduce wiring losses. To reduce the wiring

losses remarkably, it is essential to shorten the distance between furnace

body and power(factor improving capacitor as very large current flows

between them.

2! Fre@uency

/a0 1kin effect% !nduction current flo$s concentratedly in the surface

of material to be melted. This concentration of current becomes more

remarkable as the frequency becomes higher, resulting in better

heating efficiency.

- 5 ) -


68/86

"iameter or thickness of material to be melted in the furnace may

be decreased according as the frequency becomes higher. Fhen cast

iron is melted in high-frequency induction furnace, there is

practically no limitation in its si(e, but in lo$-frequency furnace

$hen starting $ith cold metal, melting has to be started only by the

use of starting block. 'ontinuous melting is to be performed $ith

residual molten metal.

/b0 ffect of agitation% As molten metal is excited by current opposite

to current flo$ing in induction coil, molten metal is agitated to

raise its surface in the center. 1urface of molten metal is risen

higher as frequency becomes lo$er, i .e. agitation of molten metal

occurs stronger in lo$-frequency furnace than in high-frequency

furnace. This effect of agitation makes it possible to ensure uniform

temperature of molten metal and its uniform quality as $ell as to

promote entrapment of material charged and fusion of chemical

composition adjusting agents, specially carbon addition. #n the

other hand, excessive agitation may cause such troubles as oxidative

$earing of molten metal and fusing out of refractories or danger of

spattering of molten metal. !n this respect, as compared $ith lo$-

frequency furnace, high-frequency furnace can be charged $ith larger

electric po$er at the same agitation degree, $hich $ill speed up the

melting and improve the furnace heat efficiency because high-

frequency furnace can be operated $ith po$er density about three times

larger than that of lo$-frequency furnace.

,- , + Iproveent o% .eat e%%i/ien/y in operation #'$

Iproveent o% .eat e%%i/ien/y a$ Tappin! teperature

s.ould be as lo? as possible,

Jeat capacity of molten metal increases $ith increasing the tapping

- 5 * -


69/86

temperature, and furnace heat loss is fully proportional to melting

temperature. eat capacity of gray iron increases about 7 kBh0t as

its temperature rises per 1E:. eat conduction loss /Mc4 and radiation

loss /M6 are calculated as follows8

M: I T(t G io( "

+

Mc 8 :onduction loss /kB4 t8 :ooling water

temperature /EZ4 T8 olten metal temperature

/EZ4 +8 eat resistance of furnace wall

/kB0EZ4

M+ 3.@2 G 1O" G A G @ G /T014>(C /74

M+ 9 +adiation loss /kB4 e 8 missivity

A8 -urface area of molten metal /m74

=rom the abovementioned eguations it follows that conduction loss

and radiation loss of high(frequency furnace with It, 3 & and

kB at tapping temperature of 13E: come to 3 kB and "3 kB respectively,

and these losses can be reduced appro'imately by 1 kB each at tapping

temperature of 1>E:.

To keep the tapping temperature lower, it is necessary to take

carefully thought out measures in practice, for e'ample inoculation,

laddie traveling distance, preheating and covering of laddie, etc.

%! Furnace cover shou"d %e c"osed as far as possi%"e.

As calculated by the abovementioned equation / 7 4 , heat radiation

loss from molten metal surface is proportioned to the forth power of

temperature. This heat loss at temperature about 13 E: comes to @

( 3


70/86

( 2 kB0m7, which is ma'imum loss in melting. In practice of furnace

operation, especially in case of small(si&ed furnace, furnace cover

sometimes remains open carelessly. It is important to train personnel

and make necessary preparation so as to charge materials and ad)usting

agents regulator as quick as possible.

As the effect of furnace cover against radiation loss reduced by

half, if even a small opening e'ists in covering, any erosion of

refractory by e'pansion or dropping at the top of crucible and0or furnace

cover have to be repaired deligently.

c! Mo"ten meta" shou"d %e he"d at "o& temperature and in short time.

olten metal should be held, when required, at low temperature,

or turn off power supply. +ated power should be turned on to heat up

again. :hemical analysis of molten, preliminary furnace test and

temperature measurement should be performed quickly. *reparatory

operations should certainly be performed so that there is no unmatching

with mold assembly or waiting for crane.

d! -ust co""ecting hood

Dust collecting degree and time should be controlled according to

furnace running conditions.

e! C"eaning of sand$ rust and other dirts

-and or rust /=e7", =e%4 adhered to cast iron or steel scrap may

react with furnace refractory to form slags. If slags are formed about

1 in melting of " tons iron, power loss at 13E: is about 1 kBh0t.

2! Ma+imum po&er supp"y

It is proper to increase power input for improvement of heat

efficiency of the furnace. a'imum capacity of the furnace can be

attained and power consumption rate can be reduced when operating the

fu

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