13.2
CHARGE CALCULATIONS CALCULATIONS
It is very important in the foundry to know the final composition of the metal being obtained, so as to control it properly. properly. The elements in the final analysis are essentially the sum total of what is contained in each of the charge ingredients, with some losses or pickup in the cupola. Out of the various elements, the ones that are relevant are carbon, silicon, manganese and sulphur. As the charge comes through the coke bed, some amount of carbon is picked up by the metal depending on the temperature and the time when the metal is in contact with the coke. However, it may be reasonable to assume a pick up of the order of 0.!" carbon. #ilicon is likely to get o$idi%ed in the cupola and therefore, a loss of 0 " of total silicon contained in the charge is normal. &nder the worst conditions, it may go as high as '0 ". If the silicon content in the charge is not high, e$tra silicon can be added by inoculating the metal in the ladle with ferro( silicon. )anganese is also likely to be lost in the melting process. The loss could be of the order of ! to *0 ". +oss of manganese in the final analysis, can be made up by the addition of ferro manganese. #imilar to carbon, sulphur is also likely to be picked up from coke during melting. The pick up depends on the sulphur content of the coke, but a reasonable estimate could be 0.0' to 0.0! ". $amples are presented below for estimating the final analysis of the melt. EXAMPLE 13.1
stimate the final composition of the cast iron produced with the following charge compositions and proportions. -arbon #ilicon )anganese #ulphur hosphorous " ig iron '.!0 *.!0 0./0 0.0 0./0 /0 ig iron * '.*0 .!0 .00 0.0* 0.0 '! -I scrap '.*0 .*0 0.!0 0.0 0./0 *! +et us now now analyse analyse the the total amount amount of element elementss present in ton ton 1 000 000 kg 2 of charge, charge, assuming assuming carbon carbon pick up as ! ", ", sulphur sulphur pick up as 0.0! 0.0! ", silicon silicon loss as 0 " and manganese loss as *0 ".
ig iron ig iron * -I scrap Total -hange " -hange in cupola 7inal analysis
-harge mass, 1kg2 /00 '!0 *!0 000
" '.!0 '.*0 '.*0
kg / .* 4 ''.* '.'* 50.! './3
#i " *.!0 .!0 .*0
kg 0 !.*! ' 4.*! .4*! 60.4' ./*
)n " 0./0 .00 0.!0
kg " .0 0.0 '.!0 0.0* .*! 0.0 .'! 0.'! 60.*3 0.!04
# kg 0.0/ 0.03 0.*! 0.' 0.0' 50.0!0 0.04
The foundry engineer can actually control his final analysis by actually trying with various mi$es of charge materials available in his foundry to obtain an economical melt. The following e$ample presents one such case. EXAMPLE 13.2
In a foun foundr dry y, it was was re8u re8uir ired ed to obta obtain in a cast cast meta metall with with the the foll follow owin ing g
composition9 carbon '.*0 to '.0": silicon *.'0 to *.0": manganese 0.0 to 0.40": sulphur 0.04" ma$imum: and phosphorous 0./0 to 0.0". If the following raw materials are available, estimate the best charge proportions. #i )n # ig iron '.!0 '.00 .00 0.0* 0./0 ig iron * '.*0 .!0 0.!0 0.0 0.40 ig iron ' '.!0 *.!0 0.40 0.0* 0.!0 #crap '.!0 .40 0.0 0.04 0.!0 #crap * '.*0 .*0 0.0 0.0 0./0 7erro silicon !0.00 +ooking at the raw materials available, pig iron * has got very low silicon content, and therefore it should not be used. #imilarly the scrap * which has low silicon and high sulphur may also be eliminated. #o the final choices are the pig iron and ' and scrap . +et the charge be of /0" of scrap with the pig irons in e8ual proportions of '0" each. +et us do the analysis for 000 kg with the carbon pick up assumed as 0.!", sulphur as 0.0!", the o$idation losses of silicon as 0" and that of manganese as *0".
ig iron ig iron ' #crap Total -hange " -hange in cupola 7inal analysis
-harge mass, 1kg2 '00 '00 /00 000
" '.!0 '.!0 '.!0
kg 0.! 0.! /.0 '!.0 '.!0 50.! '.! '.* to '.
#i " '.00 *.!0 .40
kg ;.00 3.!0 3.*0 *'.30 *.'3 60.*'3 *.'' *.' to *.
)n
#
" .00 0.40 0.0
kg " kg '.00 0.0* 0.0 *./0 0.0* 0.0 *./0 0.04 0.'* 3.40 0.// 0.34 0.0// 60.! 50.0! 0.*/ 0.;/ 0. to 0.4 0.04 ma$
=ith the chosen charge composition, the final analysis differs from the re8uired one with carbon, silicon and sulphur percentages. To reduce the carbon and sulphur percentages, we may have to use pig iron * which may reduce the silicon percentage but that can be made up by adding suitable amount of ferro silicon. The reduction in sulphur that could be achieved by the addition of kg of pig iron * for scrap is 0.04 − 0.0 = 0.0003 kg 00 The reduction in carbon that could be achieved by the addition of kg of pig iron * for scrap is '.!0 − '.*0 = 0.00' kg 00 The e$cess sulphur present in 000 kg is 000 × 10.0;/ − 0.0402
= 0./ kg 00 The e$cess carbon present in 000 kg is 000 × 1'.! − '.02 = 0.! kg 00 To reduce the sulphur to the desirable limit, the amount of pig iron * to be substituted is 0./ = *00 kg 0.0003
To reduce the carbon to the desired limit, the amount of pig iron * to be substituted is 0.!0 = 3 kg 0.00' Hence, substitution of *00 kg of pig iron would be sufficient to give the desired analysis. To confirm this let us do a fresh analysis.
ig iron ig iron * ig iron ' #crap Total -hange " -hange in cupola 7inal >esired
-harge mass, 1kg2 '00 *00 '00 *00 000
" '.!0 '.*0 '.!0 '.!0
kg 0.! ./ 0.! 3.0 '/./ '.// 50.! '.!; '.* 6 '.
#i " '.00 .!0 *.!0 .40
kg ;.00 '.00 3.!0 '.0 *'.0 *.' 60.*' *.03; *.' 6 *.
)n
#
" .00 0.!0 0.40 0.0
kg " kg '.00 0.0* 0.0 .00 0.0 0.0* *./0 0.0* 0.0 .*0 0.04 0. 3.0 0.'0 0.3 0.0' 60.!*! 50.0! 0.04 0.04 0. 6 0.4 0.04 ma$
It is not possible to increase silicon any further, and therefore, the only way out is to add ferro silicon of re8uisite amount to make up the short fall. Amount of silicon to be added for 000 kg is 000 × 1*.'00 − *.03;2 = *.* kg 00 This can be made up by adding ! kg of ferro silicon in place of scrap . ! × 1!0.0 − .402 = *./ kg $tra silicon added ? 00 #o, the final mi$ of the charge is ig iron ? '00 kg ? '0 " ig iron * ? *00 kg ? *0 " ig iron ' ? '00 kg ? '0 " #crap ? ;! kg ? ;.! " 7erro silicon ? ! kg ? 0.! " In the previous e$ample, we have proceeded with a trial and error method and have not considered the cost of various constituents of the charge. A more appropriate analysis would be to take into account the cost of each of the constituents of the charge and the chemical compositions. This can be done by formulating the linear programming problem and solving it by the simple$ method. PROBLEMS
'.
On a particular day, an iron foundry prepared the charge for cupola as *0" pig iron , *!" pig iron *, and !!" scrap iron. 7ind the final composition of the produced melt, given the following compositions for the charge elements. Assume suitable losses or gains in the cupola. -arbon #ilicon )anganese #ulphur " " " " ig iron '.*0 .30 0.40 0.0' ig iron * '.!0 *./0 0.0 0.0 #crap iron '.*! *.'0 0.! 0.04
'.*
A foundry engineer is re8uired to produce castings with '.0 to '.!0" carbon, *.00 to *./0" silicon, 0.0 to .00" manganese and a ma$imum of 0.04"
sulphur. The pickup in cupola is appro$imately9 carbon 0.!" and sulphur 0.0/". The losses in cupola are 0" silicon and *0" manganese. If he has the following raw materials at his disposal, what should be the best charge composition@ -arbon #ilicon )anganese #ulphur " " " " ig iron '.*0 .30 0.40 0.0' ig iron * '.*0 .4! 0.0 0.0 ig iron ' '.!0 *.0 0.30 0.0* #crap '.*! *.'0 0.! 0.04 #crap * '.'0 *.0 0.40 0.0 7erro silicon !0.00 '.'
pecify the composition of the charge to be used for producing 4 metric tons of the following grey iron9 '.*0 to '.0" carbon, *.* to *." silicon, and a ma$imum of 0.04" sulphur. Thae available raw materials and their compositions are given below9 -arbon #ilicon #ulphur " " " ig iron '.*! *.3! 0.0! ig iron * '.!0 *./0 0.0 ig iron ' './! *.!0 0.0 Iron scrap '.00 *.00 0.04 7erro silicon !0.00
'./
A grey iron foundry produced 3!00 kg of good castings in a day. The charge consisted of *!" pig iron , *!" pig iron * and !0" iron scrap. The composition of the charge was found to be as follows9 -arbon #ilicon #ulphur " " " ig iron '.!0 '.*! 0.0' ig iron * '.*! *.3! 0.0! Iron scrap '.00 *.00 0.04 The castings were found to contain *.*!" silicon and 0.00*" sulphur. 7ind the percentage gain or loss of silicon and sulphur during melting.