US2394156A - Method of producing rolls - Google Patents

Description

Feb. 5, 1946. F. c. T. DANIELS 2,394,156

METHQD OF PRdDUCING ROLLS Z 4 Filed May 3, 1945 2 Sheets-Sheet 1 INVENTOR fired GTDanz'eZs arm a 86 N rway Feb. 5, 1946. C. DANIELE;- 2,394,156

METHOD OF PRODUCING ROLLS Filed May 5, 1945 2 Sheets-Sheet 2 A E -If; 2513 1 INVENTOR Fred Cfflaniels a Wm 29% Patented Feb. 5, 1946 t NT OFF'lCE METHOD OF PRODUCING ROLLS Fred C. .T. Daniels,

Bridgeville, Pa; assignor to Mackintosh-Hemphill Company, Pittsburgh, Pa., a corporatlon'of Delaware Application May 3, 1945, Serial No. 591,812

4 Claims.

This invention relates to the casting of rolls and particularly to a method of roll producing to increase the useful life of chilled rolls.

It is the object of the invention to provide a method whereby a particularly enduring quality is imparted to the surfaceof chilled rolls without detriment to the softness and toughness of the roll necks and wobblers; and without detriment to the toughness and strength of the interior structure of the roll bodies. That is, it is the object of my invention to provide a method of casting rolls, the chilled surfaces of which are of increased hardness without imparting the property of brittleness to the interior of the roll bodies or the necks and wobblers f the rolls.

It has been observed previously that the moisture content of air brought into contact with a furnace melt either by way of the combustion air of the furnace, or by bubbling the air through the metal, has an effect upon castings produced from the melt. In previou laboratory experiments in which air of high moisture content has been brought into contact with molten casting iron, it has been noted that as such iron is cast in small sections and in metal molds the effect of hydrogen introduced by a high moisture content of the air is a negative graphitizing effect leading to the formation of white cast iron. It' was to be anticipated that in actual practice this phenomenon of carbide retentivity attendant upon a high moisture content of air brought into contact with the iron would be undesirable and uncontrollable as applied to rolls. Any undue extension of the depth of achill consisting primarily of white iron would tend to weaken the roll bodies and particularly would be detrimental to the necks and wobblers of the rolls. It is accepted in the art that the brittleness' resulting from any substantial content of White iron in the necks and wobblers of a roll renders the roll unserviceable. In practice the depth of chill .U limited to maintain the strength of the roll body, and the strength and shock resisting properties of the neck and wobblers also must respond to specifications.

I have, however, discovered that I am able to produce rolls of superior quality by regulating the moisture content of the combustion air in an air furnace above a prescribed minimum, and desirably within the range of 4 to 8 grains of water per cubic foot of combustion air if the cast iron so prepared be cast in the large section and under the normal conditions for the casting of chilled rolls. Also I have discovered that these particularly desirable results are obtained in rolls cast from metal having a high carbon content of from about 2.80 to 3.75, and with a normal silicon and the casting of chilled relative volumes of g with standard practice in furnaces ofthis type,

the apportionment manganese content. That is, in rolls cast from melts responding to compositions accepted as suitable for chilled rolls. 1

In normal furnace practice combustion air contains the normal atmospheric moisture content as of the particular time at which the furnace is operated. In cupola melting there has been in some instances an effort to reduce the moisture content of the air to provide uniformity of product and some economy of operation. The same s true of blast furnace operation for the production of pig iron. It will be understood, of course, that in the operation of furnaces of those types, as well as air furnaces, the normal moisture content of the atmospheric air varies very widely from day to day leading to variation in the properties of the melted iron. Also to some extent the air blasts of cupolas have been saturated with water for the purpose of oxidizing metalloids by oxygen liberated within the furnace by decomposition of the water introduced by the blast. All these last named propasals have ignored the effect of the moisture upon the physical qualties of the iron, and has not previously been suggested to utilize a uniformly highcontent of water in the combustion air of an air furnace.

In accordance with the method of my invention I utilize a furnace of the forced fuel feed type, such as reverberatory furnaces fired by fuel introduced in an air blast or some other suitable form of air furnace. Accurate control of the atmosphere in contact with the charge may be accomplished in such furnace by regulating the fuel and air. In accordance of fuel and air is such as to minimize in the furnace atmosphere free oxygen introduced as air or produced by decomposition of moisture in the air.

To control the water content of the furnace air I may use any suitable methods and apparatus for supplying moisture. Probably the simplest and most eflicient control is effected by saturating with water air that previously has been brought to such temperature that its water content when the air is water saturated lies within the range of from 4 to 8 grains of water per cubic foot of air. Alternatively the air may be heated .to a temperature highervthan that necessary to carry the specified weight of water, and water may be added by a suitable evaporator capable of regulation to vaporize water at a rate suitably to as applied to actual practice it.

supply the air. The regulation may be accomplished by means of a wet and dry bulb thermometer arranged to actuate a control apparatus in accordance with well known practice in moisture controlling installations.

My experience has shown that in the operation of an air furnace the maximum effective moisture content, hydrogen from the decomposition of which acts effectively on the physical properties of theiron of the furnace melt, is 8 grains of water per cubic foot of air. Increase of the moisture content beyond that point shows no substantial progressive increase in the effect of hydrogen on the iron. Ihave, therefore, found it unnecessary to employ means for removing structure of a roll cast in accordance with the method of my invention, the roll shown being of the clear chill type.

- Fig. 11 is a vertical sectional view roughly illustrating the structure of a roll of the indefinite chill type as cast in a similar mold in accordance with the method of my invention. I

In practice the cast iron, which has been prepared in an air furnace the combustion air of which contains from 4 to 8 grains of water per cubic foot of air, is run into a mold which is provided with means for chilling the roll body The illustration of Fig. I is of a roll of the clear chill type. As therein shown, the chilled white iron structure of moderate depth in the roll body is designated by letter of reference A. There is a fairly definite line of demarcation between that chill structure and an intermediate zone B of mottled iron; and there is an inner structure or core C of gray iron which also has a fairlydefinite line of demarcation with the mottled iron zone. The necks D and wobblers E of the roll, which are cast in the sand molds ,la and 2a are composed wholly of gray iron. No perceptible variation from this conventional structural arrangement of a roll so cast, and which is of a composition to give a clear chill, can be observed with variation in the moisture content of the furnace air in the presence of which the roll iron is prepared.

' The performance of rolls of that sort cast in accordance with my method may be illustrated by several examples comparatively with rolls the casting metal for which is prepared in the presonce of combustion air having a much lower moisture content. In a specific example of the effect of the high moisture content of the furnace air upon the cast roll, comparison was made between chilled cast iron alloy rolls of identical size and substantially identical composition, used in identical service and cast from iron molded under conditions substantially identical except as to the water content of the combustion air su plied to the furnace. The metal for the rolls was melted in the same reverberatory furnace which was, fired by automatically controlled pulverized coal burners. I The composition of the respective rolls, the moisture content of th air fed to the furnace, and the hardness of the rolls were as follows:

Table No. 1

sch Grains Roll Si Mn s P 0 Or Ni M0 hardf f air a. 24 o. 54 a. 05 o. 22 69/71 0. 639 3. 32 54 2. 96 25 68/70 596 3. 26 52 2. 94 25 71/73 539 3. 21 56 2. 98 25 73/75 7. 4H) 3. 15 58 2. 87 25 72/74 4. 476

l The principal substance of the rolls is iron.

and. with means, for causing slow cooling of the roll necks and wobblers. embodiment of such mold, having upper and lower flasks l and 2, with heat retaining dry sand molds la and 2a therein, and a central wholly metal, or chill, portion 3. As cast ina mold of this general sort the roll, which is of substantial cross-section throughout, does not on solidification develop any greater depth of chill in the body portion of the roll than is formed in rolls cast from metal prepared under such conditions that the moisture content of the air is below 4 grains per cubic foot. The body of the roll has a surface chill and the core of the roll body is definitely gray iron. 'In the necks and.

wobblers of the roll cast in the sand molds the entire structure is gray iron.

Under these circumstances the effect of high moisture content in the combustion air of the furnace in which the iron is prepared results in a definite improvement in the chill structure of the roll without detracting from the softness and toughness of the roll core and the necks and wobblers.

The drawings show one The rolls weretwenty-two inch diameter work rolls for a four-high hot strip mill, a severe service requiring a high quality roll. Although the rolls were of identical composition, variations in analysis being within the limits of error in chemical analysis of the metal, and were used in identica1 service of the same strip mill, th two pairs of rolls listed as 4 and 5 far exceeded the other three pairs of rolls in tonnage produced,

and gave no evidence of fire cracking or spelling.

Rolls ofpairs 1 to 3 produced only mediocre tonnages andshowed a distinct tendency to spell. It is to be understood that the rolls analyzed above are of such composition as to give in the cast roll a clear chill and a structural arrangement of the sort shown in Fig. I of the drawings.

With rolls of such composition as to give an indefinite chill the same comparative results are found. Thus Fig. II shows a roll cast of a composition to give an indefinite chill in a mold organization identical with that shown in Fig. I. In the roll so cast the roll body has an indefinite chill designated by letter of reference F, in which the entire chill structure is i 'work rolls the metal for thesame reverberatory furnace under conditions the white iron merges indefinitely with gray iron nace above a minimum of 4 grains of water per throughout a very considerable depth of the chill cubic foot of air advantageously aflected the structure. There is no definite 'zone of gray iron, and the demarcation betwe the effects of chilling and the gray iron core C of the roll body is not clean cut as in the roll shown in Fig. I. Asin that first described roll, the roll necks D- and wobblers E are composed wholly of gray iron. This is the type, and there isno perceptible va iation from this structural arrangement with variation in the moisture content of the combustion air supplied to the furnace in which the iron wa In the following table the composition of the rolls are such that an indefinite chill of the sort shown in Fig. II of the drawings was formed in the roll bodies. That is, in the chill region of the roll there is between the white chill structure and an underlying zone of mottled iron, but on the contrary ndefinite in the sense that it is partially mottled and merges with the gray iron structure interiorly of the roll body. All the rolls of the table, were twenty-two inch which was melted in which were identical except as to the moisture content of the air supplied to the furnace. The composition of the several rolls of the table obviously varies but little for the several pairs analyzed. The table give pairs of rolls showing the moisture content of the combustion air in the presence of which the melt for casting them is prepared, together with the number of tons rolled by each before failure. It is to be understood that each enumerated pair of rolls was used as the work rolls of a fouren the zone showing conventional structure for an iron roll of the indefinite chillv nace atmosphere proportionally is s prepared.

no definite line of demarcation s an analysis of several high continuous strip mill under identical conwearing properties of the rolls, by regulating the amount of free hydrogen present in the atmosphere contacting the iron and consequently controlling the amount of hydrogen absorbed by the iron. The removal of metalloids by oxidation is not a part of the process, and during the normal operation of a furnace of this type fuel substantially to consume free oxygen of the furintroduced. Theoretically it appears that the hydrogen content in the iron acts as a metallurgical component and serves as a hardening agent, not only increasing the hardness of the surface chill of the roll body but render g it more resistant to fire cracking, spalling and other destructive effects. It has been my observation that within the range of a water content of 4-150 8 grains of water per cubic foot of combustion air, increase from a minimum of 4 grains does not show correspondingly improved results, a determined water content of 4 grains being in most instances sufiicient. As above noted, increase in the moisture content of the combustion air above 8 grains of water per cubic foot of combustion air has a negligible influence on the properties'of-the rolls.

In the light of prior practical experience and laboratory experiments it is surprising that'the effect of high moisture content in the combustion air of an air furnace on the rolling properties of a rollcast from the metal melted-in the furnace is wholly beneficial. That is, the hardening effect of hydrogen released by the moisture in the furnace air does not lead to the formation of white iron in the roll necks and wobblers when the metal is cast in a sand chill mold, nor does it cause a dangerously inditions of service, -40 creased depth of white iron chill structure in Table 2 ,1

(Tags sch T 'We r ons Roll perm. Si 8 P Mn 0 N1 Or 131::- toned ft.air

1 The principal substance of the rolls is iron.

It will be noted that the stated hardness of these rolls bears no relation to the hydrogen absorption of their metal during the process of melting and casting. This is because all of the rolls were temper drawn to a uniform scleroscope hardness after casting. In this table it will-be noted that the pairs of Nos. 6, 7, 8 and 9 were all cast from metal which in the melting operation was having a determined substantial moisture content. The pairs of rolls designated by Nos. 10, 11, 12 and 13 were cast without such regulation at a time when the moisture content of the atmosphere was low. As appears in the table the rolls cast from metal having a substantial determined hydrogen absorption showed a useful life approximately longer than that of the other rolls.

It is clear that regulation of the water content of the air supplied to the reverberatory furrolls designated the roll body. In the relatively large cross-section of a roll body and with the slow cooling of the sand molds, a roll cast in accordance with my method therefore has increased life, being without inducedv weakness in any portion thereof and having improved properties in the chilled body structure of the roll.

It is to be above noted that the method of my invention has its utility in the casting of chilled iron rolls which have the high carbon content which is normal for rolls of that sort, and a normal content of silicon and manganese. In accordance normal carbon content for chilled rolls is from about 2.80 to 3.75, as a range including both rolls having chill structure of the clear chill type and of the indefinite chill type. In accordance, with standard practice the normal silicon content is about .30 to .75, and the manganese content about .10 to .30 for clear chill rolls; and for with standard practice the rolls having an indefinite chill the normal silicon content is about .50 to 1.50, and the manganese content about .30 to 1.50. Thus my method fundamentally is practiced in casting rolls having the above noted carbon content of about 2.80 to 3.75, a silicon content of from about .30 to 1.50, and a manganese content of from about .10 to 1.50. It is to be understood, however, that there may be reasonable deviation at both ends of these standard ranges without going beyondwhat is to be considered in chilled rolls a normal content of carbon, silicon and manganese; and corresponding latitude may be taken in compounding the cast alloy iron used in practicing themethod of my'invention without impairing the beneflcial effect obtained from that practice. Itis also to be understood that the non-ferrous content other than carbon,.silicon and manganese included in the rolls listed in rolls; High moisture content in the atmosphere of the melting furnace does not render them critical. v a

The application herein is a continuation-inpart of my application Serial No. 481,291, filed March 31, 1943, for an Improvement in furnace atmosphere control.

I claim as my invention:

1. The herein described method of producing rolls by melting an iron having a normal content of carbon, silicon and manganese for chilled rolls in a forced fuel feed furnace while regulating the moisture of the combustion air fed to the furnace to constitute at least 4 grains of water per cubic foot of air, supplying to the heating flame fuel adequate to prevent substantial oxidation of the charge, and casting the said alloy iron into the form of a roll of substantial cross-section with chilling of the body portion of the roll and slow cooling of the end portions of the roll, to give a cast roll having a chilled body surface of superior wearing qualities and an interior body region and end portions possessing the retained toughness of the normal unchilled gray iron of the roll composition.

2. The hereindescribed method of producing rolls by melting an iron having a normal content of carbon, silicon. and manganese for chilled rolls in a forced fuel feed furnace while regulating the moisture of the combustion air fed to the furnace to constitute from 4 to 8 grains of water per cubic foot of air, supplying to the heating flame fuel adequate to prevent substantial oxidation of the charge, and casting the said alloy iron into the form of a roll of substantial cross-section with chilling of the body portion of the roll and slow cooling of the end portions of the roll, to give a cast roll having a chilled body surface of superior wearing qualities and an interior body region and end portions possessing the retained toughness of the normal unchilled gray iron of the roll composition.

3. The herein described method of producing rolls by melting an iron comprising from 2.80 to 3.75% carbon, from .30 to 1.50 silicon, and from .10 to 1.50 manganese in a forced fuel feed furnace while regulating the moisture of the combustion air fed to the furnace to constitute at least'4 grains of water per cubic foot of air, supplying to the heating flame fuel adequate to prevent substantial oxidation of the charge, and casting the said alloy iron intothe form of a roll of substantial cross=section with chilling of the body portion of the roll and slow cooling of the end portions of the roll, to give a cast roll having a chilled body surface of superior wearing qualities and an interior body region and end portions possessing the retained'toughness of the normal unchilled gray iron of the roll composition.

4. The herein described method of producing rolls by melting an iron comprising from 2.80 to 3.75% carbon, from .30 to 1.50 silicon, and from .10 to 1.50 manganese in a forced fuel feed furnace while regulating the moisture of the combustion air fed to the furnace to constitute from 4 to 8 grains of water per cubic foot of air, supplying to the heating flame fuel adequate to prevent substantial oxidation of the charge, and casting the said alioyiron into the form of a roll of substantial cross-section with chilling of the body portion of the rolland slow cooling of the end portions of the roll, to give a cast roll having a chilled body surface of superior wearing qualities and an interior body region and end portions possessing the retained toughness of the normal unchilled gray iron of the -roll composition.

FRED c. '1'. ohms.

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