By W m . Y. Buchanan (Associate Member)
A lthough the possible practical application of results of the w ork done has always been kept in m ind, it is thought th a t the subject o f this Paper m ay form a suitable basis fo r discussion and, further, though the subject is still in a prelim inary stage, it is hoped that its presenta
tion will result in some definite lines being indicated along which additional w orth-while investigations m ay be pursued. T he Paper, however, is intended m ainly to prom ote dis
cussion. The subject is rather difficult to approach owing to the m any experim ental diffi
culties, and the procedure adopted should receive due consideration initially. T he many variables entering into ordinary cupola melting m ake the direct application of this research to the cupola in everyday practice lengthy and sometimes confusing.
Apparatus Used
In order to im prove the conditions of the tests a new ladle was m ade and drilled all over the sides and bottom with |- in . diam eter holes to facilitate the escape o f steam during the drying of the lining. A block pattern was made to form the lining 1 in. thick all over the bottom and sides and used for ram m ing up. P rior to this, there was a tendency to m ake the bottom o f the old ladle too thick and the sides too thin, and any variation in thickness of the refractory altered the cooling rate of the metal. This cooling rate was always checked by plotting a tim e-tem perature graph for each test. W ith the new system a very smooth, even lining was obtained and this was dried very thoroughly with the “ A urora ” burner used for lighting the cupola, by apply
ing the heat to the outside as well as the inside of the ladle. The ladle was knocked out after each day’s tests and m ade up afresh before the next in order to ensure reasonably identical conditions; no black-wash was used on the sur
face of the lining.
The burette with the two-way glass stopcock, as illustrated in the previous Paper,* was found unsatisfactory when very high rates of evolu
tion were encountered as the bore o f the
stop-* See page 227.
cock gave a “ wire ” effect which hindered the registration of sudden increases in rate, and at the sam e time 50 ml. capacity was in some cases found to be inadequate. A burette was therefore constructed from glass tubing of 15-mm. bore and 42-in. length, having a capacity of 200 ml. w ithout running out and reading in in., equivalent to 0.5 ml. Care was taken to keep the inlet at the bottom end as large as possible, and by this means sudden fluctuations in gas evolution were easily re
corded. One particular increase in evolution appears to coincide with some change, such as perhaps the separation of prim ary graphite.
This point, although interesting, is evidently not of much practical im portance.
It is interesting to note that the introduction of cold m aterial appears to liberate large q uan
tities of gas from liquid cast iron. This is shown in the case of steel additions referred to later in the Paper. The use of the bell which constitutes a cold addition may have the same effect. This would explain why the large evo
lution takes place imm ediately on placing the bell in position in the surface o f the metal, irrespective, within limits, of the initial tem perature.
The Measurement o f Temperature It is said that molten cast iron varies in its emissivity, and that this gives conflicting results where the variable is m easured against tem perature change, as for exam ple in the study of fluidity by casting tests. Different m ethods of melting are said to give different emissivity values for the same tem perature. The emissivity is also held by some w orkers to change even from furnace to ladle. W ith tem peratures taken by optical pyrom eter in the open-hearth o r elec
tric furnaces, where (1) the angle of the tele
scope o f the pyrom eter to the m etal surface is very oblique; (2) the surface is covered with slag of a glassy or sm ooth type with highly reflecting surface; (3) the furnace gases are lum inous and continually changing;
(4) the atm osphere contains fine lim estone dust at high tem perature, or (5) on tapping, a very heavy fum e (red o r white) covers the launder,
67 f 2
the emissivity, as recorded by the optical p yro
m eter, m ust be subject to great and constantly varying errors. T he substitution o f th erm o couples fo r optical pyrom eters is the obvious solution, and it is said to have been the m eans of turning a rath e r dou b tfu l set o f results into a highly successful piece o f research. The m easurem ent o f tem perature by optical p y ro m eters is, however, no t necessarily always wrong, an d has m uch to recom m end it owing to its relative freedom from trouble when m aking large num bers o f daily readings. T he im m ersion o f therm ocouples usually results in rapid w ear
ing o f the therm ocouple wires, bu t couples of suitable m aterials fo r use on steel and cast iron are said to have been developed a num ber of years ago, although these have not become generally available as yet.
Ladle additions are said to change the em issivity value, considerable errors m entioned in this connection being o f the order o f 190 deg. C., although this is rath e r difficult to accept w ithout substantial proof. T he emissivity value for m olten m etal is likely, o r perhaps certain, to be entirely dependent on the type of surface film. This film is usually an oxidation pro d u ct diluted by non-m etallic inclusions separating from the m olten metal. The addi
tions can and do m odify the film radically, and so also the emissivity, as, fo r example, in the case o f traces o f soda-ash slag and sim ilar fluxes.
A p a rt from the question o f degree o f
emissivity, the condition and appearance of the surface film seem to be an indication o f the m etal conditions, and it m ay have som e relation to the quantity and character of dissolved gases.
T here are, how ever, some difficulties in record
ing the appearance o f the film in any system atic investigation ow ing to the state of constant m otion in the m etal surface. T he surface films were constantly u nder observation, b ut no detailed record was m ade in the course o f the investigations described here. H ow ever, in the case of cast iron, unless the oxide film is modified radically by ladle additions, the emissivity is n o t likely to vary as m uch as the cases quoted. In all the gas experim ents for this research, the surface o f the m etal was con
stantly being raked over to expose a fresh surface for tem perature m easurem ent by optical pyrom eter. T here seems no reason w hy a thickening m edium cannot be used to assist in raking off this film unless it interferes w ith the norm al m easurem ent o f tem perature. T here is, however, no d o u b t th a t a study o f this question of tem perature m easurem ent is highly desirable and perhaps long overdue. T he use o f the im m ersion therm ocouple pyrom eter as a check w ould no d o u b t be helpful in ord in ary foundry conditions, w here the optical pyrom eter is regu
larly used.
Gas Analysis
On first considering the type o f gas app aratu s required for the analysis o f sm all volum es of gas collected from liquid cast iron, several points had to be considered. F o r exam ple, the volum e o f gas collected m ay be extrem ely small, especially if an attem pt is m ade to separate fractions o f the volum e given off, and to allow o f repeat tests the ap p a ratu s m ust be capable of handling sm all samples accurately. T he use o f m ercury seemed advisable and so the various form s o f the O rsat type were ruled out.
T he cost o f types like the Bone and W heeler was deem ed prohibitive, and the apparatus selected and described here is designed by A m bler. T he arrangem ent and sim ple design show an intim ate knowledge o f the subject by the designer and considerable practical experi
ence in gas analysis. T he ap p aratu s which is shown in Fig. 1 consists o f : —
A.— A com bined explosion and absorption pipette o f ab o u t 25 ml. capacity.
B .—A m easuring vessel consisting o f three bulbs o f volum es 1, 3, and 6 ml. respectively, w hich allows the use o f sam ples from 0.25 ml.
to 15 ml. at N .T.P.
C.— A w ater jacket and therm om eter E for m easuring the tem perature of the sample.
R, and R 2.—-Reservoirs fo r applying o r reduc
ing pressure.
G .— A barom eter for taking readings required tubing, and all rubber connections are eliminated from the m ain p art of the apparatus. three following consecutive percentage analyses of the same sam ple o f town gas: —
Some difficulty is encountered in determ ining the actual weight o f w ater in the atm osphere.
The wet- and dry-bulb hygrom eter is well known, and there are m any similar instrum ents in attractive bakelite m ountings for general indoor use. These are, however, supplied with a table giving the percentage hum idity at the observed tem perature, and sometimes this scale is built into the instrum ent case and operated in small suitably-ventilated cupboard on a post situated in the open where the readings were
Ta b l eI .— D a ily V ariations in Atm ospheric M oisture
Thura. 4 9 .0 109 Overcast— R aining
Fri. 3 7 .3 55 Overcast— R aining suggestions fo r drying blast.
1869.— T he D uke o f D evonshire, a t the
U.S.A. with a view to drying by refrigeration; calcium chloride, the regeneration was carried ou t in a low er drum and the regenerated cal
1907-9.— R efrigerating plant was installed at D owlais-Cardiff plant and a considerable saving quoted. T he H arb o rd process using calcium
1909.—-Experiments were undertaken at Clarence Ironw orks to determ ine the effect of uniform ity of m oisture. It was shown that considerable quantities of steam could be added to the blast to attain regularity w ithout m aterially increasing the coke consum ption.
1910.— D aubine and Roy described calcium-
"303 CO O N t'ON ON tOOOlOiOOOOCKNlCCOH
>>
Temp. range during sampling. 1160-1110 1130-1110 1140-1110 1140-1110 1220-1170 1190-1160 1180-1120 1160-1130 1160-1110 1170-1110 1170-1090 1190-1130 1180-1120 1180-1110 1200-1150 No record No record 1210-1150
© IO LO lO 1C VO VO
D ifferdange were o u t o f operation and reported
In Scottish blast-furnace practice, the weight of air used per ton of pig-iron is ab o u t lO cw ts.
lected at varying tem peratures. T he sam e re
m arks apply to variations in pressure o f blast which can be taken to indicate large variations in volum e o f blast going through the cupola although not necessarily through the fusion zone of the cupola. analysis, m oisture content, blast pressure, tem perature range. In all the cases graphs were
This experim ent showed th a t the presence adversely affected by high m oisture conditions owing to the high concentration o f the blast
This experim ent represents a well-heated coke bed receiving a w ater addition o f relatively short made from cupola-direct-arc electric furnace iron “ the incidence o f porosity was checked up against hum idity o f the atm osphere, and although the curves w ere n o t qualitatively analogous, there was some quantitative analogy between the curves.”
M etal analysis. Transverse test.
1 .2 in. dia.
control the am o u n t o f w ater going in with the always been associated w ith oxidation, sulphur pick-up, and heavy lining wear. This applies m ore particularly to thin steel scrap w hich pre
sents large surface area. T he introduction of steel as a ladle addition is free from the excessive oxidation, sulphur pick-up and lining w ear taking place in the cupola, and on th a t account has cutting bars produce small curled-up cuttings less than | in. diam eter, which can be shovelled corresponding percentage o f these valuable alloys m ay be introduced in a relatively econo
w hat effect, if any, this had on the volum e an d analysis o f the dissolved gases. T he p ro cedure used was to take a ladle o f m etal direct from the furnace for gas volum e m easurem ent an d then, for com parison, place steel turnings in the b ottom of the next ladle an d tap the metal on this, an d after this was dissolved to m ake a volum e m easurem ent. In order to elim inate any variables from one day to the other a n um ber o f volum e m easurem ents was m ade on the sam e day and alternately w ith the steel additions an d “ as tapped ” whilst record
ing the blast pressure in the wind belt. T he last reading o f this pressure set ou t in T able V shows that a larger volum e was being taken by the cupola, and this m ight tend to increase the q u a n tity o f dissolved gases. G raphs o f tem perature an d tim e an d tem perature and rate o f evolution were m ade as in all other cases, an d these show very clearly the considerable reduction in gas content b rought ab o u t by the steel addition; but these graphs are n o t reproduced, as a large n u m ber o f graphs w ould overload the printed Paper.
The figures included in T able V , however, prove the case clearly.
T he conclusion is th a t the gas content is reduced, in the case o f low initial content, by ab o u t 30 per cent., and in the case of high initial gas content by 54 per cent., as show n in the examples.
T he effect o f steel-turning additions on the com position o f the gas in solution is show n in the exam ples in T able V I and seems to confirm the conclusion already reached, nam ely, that no very definite chem ical selection takes place in the rem oval process. T he solution o f steel in cast iron probably disturbs gas equilibrium conditions, resulting in the liberation o f a quantity of gas of m ixed com position.
T he fractional boiling off, th a t is the separa
tion o f one gas before the other, has no t been observed so far, but the point m ight require
m ore careful and extended tests. W hether 01 no t it w ould lead to any useful conclusions, or have any bearing on the elim ination o f gas de
fects in practice, is doubtful.
A n addition o f steel w ould be expected to alter the physical properties of the iron and p robably to som e extent the m icrostructure (Table VII). Som e transverse bars cast from m etal w ith and w ithout steel addition show, w here the analyses before and after are substan
tially the same, an increase in strength o f ab o u t 5 per cent, fo r a 4 per cent, addition o f steel to an iron o f the com position show n in T able V II. It is uncertain w hether the gas elim ination has co ntributed to the change in strength, a n d it m ust be understood th a t small variations o f elements such as silicon, sulphur and m anganese m ay produce variations in strength o f sufficient m agnitude to m ask the effects being m easured.
It has been suggested that a certain quantity o f dissolved gas m ight retard o r control the shrinkage o f cast iron. In order to test this p o int a num ber o f casting tests were m ade on a stan d ard pattern to cast blocks 8 in. by 4 in.
by 4 in. w ith a cut in the gate at one end and a riser taken off through a cut gate at the other end. N o risers were used for the purpose of feeding the casting. These blocks were cut through the centre an d polished for Brinell m easurem ents diagonally across the centre section.
T able V III gives the results o f tests m ade on blocks cast as tapped, and degasified by scale addition. As is show n in the table, the tendency to porosity is n o t increased by degasification and from sim ilar experim ents there is no reason to support the idea th at dissolved gas in anv way influences porosity o r shrinkage.
T h e author wishes to thank Jo h n L ang & Sons for perm ission to place the results o f these in vestigations before the Institute.
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