Jan; 16, 1940. F. c. T. DANIELS' 2,187,415
METHOD OF MAKING ROLLS Filed May 13, 1939 A\\. 'll/111111111111111 INVENTOR mold; in the mold to percolate upward through the unsolidied portion of the initial body of metal to mix homogeneously therewith. The -rate at which the inoculant metal is added I make so slow that there is no bodily displacement of any portion of the metal initially contained in the mold, but on the contrary as the level of the total metal in the mold slowly rises, the softer inoculant metal ,with great rapidity spreads through the body of initial metal, the concentration of the softer metal, rather than its distribution, becoming greater as the inoculation slowly proceeds. It is thus the inoculated metal, and not the initial hard metal, which rises to flll the mold cavity for the upper roll neck.
As inoculation proceeds, and the total volume of metal in the mold increases, the level of the metal rises upwardly beyond the upper mold space for one of the roll necks, and into the adjacent hot top of the mold. By appropriate proportioning of the total mold cavity and the level (about the body cavity of the mold) to which the mold initially is filled, I may add inoculant metal in a proportion of from 15% to 25% the total weight of the roll without displacing any metal from the mold.
The slow addition of the inoculant metal is a feature of my method which should be emphasized since. such slow addition results in homogeneity in the composition of the metal in al1 regions of the roll, save the chilled surface of the body. This is resultant from the fact that the quiet inoculation renders it possible to avoid any such thrust of the inoculant metal as bodily to displace any of the still liquid metal already contained in the mold. This is in accordance with my discovery, above noted, that inoculation seems to proceed so rapidly throughout the body of initial metal in the mold that is stillin the liquid state (i.,e., that metal that has not been congealed by the bodyvchill mold). I have found that, depending upon the conditions of the rollcasting operation, I may vary the time of pouring the inoculant from 4 to 20 minutes; but in any case it is added slowly, and either continuously or in very small closely timed increments.
It will be readily understood that my method of quiet inoculation avoids all the disadvantageous effects incident to relatively violent displacement of metal from the mold. By heat transfer through the body of metal in the mold, it tends to preserve uniformity of temperature in the entire metal of the casting, and ter/ids wholly to eliminate gases from the metal during the relatively extended period in which the inoculant metal is added. Tests have shown the rapidity with which thet metal in the upper region of the mold becomes uniform in composition with that in the lower mold regions, and that the progress of. inoculation after the first introduction of the `inoculant metal consists chiefly in progressive concentration 'of the inoculant. This is shown by the approximately complete homogeneity in character of the metal in the necks and body interior of each inoculated roll.
` The method of ,my invention provides a practical process for making rollsfin which it is desired to combine strengthwith a desirably high surface hardness and hardness penetration. I have found that the advantages of my method of roll casting are realized in the casting of metalworking rolls up to an 85 scleroscope hardness and with a chilled depth in the approximate proportion of from 1 to 2 inches for a 12 to 18 inch diameter roll, and of from 2 to 4 inches for a 20 given as follows:
3. 28 3. 20 3. 46 51 95 96 24 46 43 4. 2l 1. 04 4. 49 32 68 96 l. 95 M0 26 45 In each formula the percentages of alloying ingredients are given, as is usual, by weight, and in each the remainder of the composition is iron,
except for small quantities of the usual impurities.
In practicing my method it is advantageous that the hard, initially cast, metal should be one of those ferrous compositions, or alloys, which do not tend rapidly to thicken when poured into the mold. The propriety of utilizing an initial metalwhich tends to retain fluidity will be clear in view of the manner in which I perform the inoculation stepgadding the inoculant metal slowly, and avoiding bodily displacement of any substantial portion of the initial metal. If the initial metal be of a sort which tends rapidly to thicken, inoculant may in substantial quantity be nonetheless added. The proportion of inoc ulant which may homogeneously be distributed through the body of metal initially in the mold is, however, limited by the decreased time available for the inoculation due to obstruction to its spreading presented by the thickening of the metal initially in the mold.
Usually it is desirable that the softer inoculant metal be of such composition that it develops to a great extent a graphitizing tendency, so that it may serve adequately to soften and strengthenI the initially hard metal which it inoculates. A generally advantageous formula for the inoculant metal maybe given as follows:
Formula No. 1
The remainder iron and small quantities of the 5 usual impurities.
Formula No. 2
Per cent Carbon 4.00 Silicon 2.10 Manganese 1.00
The remainder iron and small quantities of vthe usual impurities.
In connection with the duration of the period of quiet inoculation, given above as from about 4 to about 20 minutes, I prefer to employ as much time in inoculation as the teeming temperature and composition of the metals will permit. Thus, if the initially cast metal be teemed at high temperature, and be of a composition capable of retaining a condition of high iuidity for a rela.- tively long time (the inoculant metal similarly meeting those requirements) I prefer to teem so slowly that as much as ten minutes is usually taken for conducting the quiet inoculation step, in making rolls of average size. If on the contrary the conditions are such that a lesser order of fluidity of the initial metal is to be expected, the time during which the inoculant is added should be shortened.
In relating the time during which the inoculant metal is added to the size of the roll which is cast by my quiet inoculation method, and the relative proportions of the metals desirably poured in the several stages of casting, I give the following illustrative information. A roll requiring 10,000 lbs. of total metal, I have cast with 7500 lbs. of metal in the initial pouring, and have then inoculated it with 2500 lbs. of the inoculant metal, taking about minutes :for the inoculation step. I have cast a 30,000 lb. roll, using 21,000 lbs. of metal in the initial pouring, and adding 9000 lbs. of the inoculant metal during an inoculation period of minutes. I have cast a 71,000 lb. roll, using 40,000 lbs. of metal during an inoculation period of about 10 minutes. The roll last noted represents approximately the maxiniurn weight oi rolls commonly cast. It is to be understood, however, that if even heavier rolls are being cast, the inoculation period may well be extended beyond minutes. In each noted instance the initial metal was poured at a temperature in the neighborhood of 2500" F. and the inoculant was poured at a temperature `in the neighborhood of 2400" Ii.
In general I may say that I prefer to inoculate as slowly as the several conditions oi the casting process will permit; and in this connection may note that (other conditions being equal) it is possible, and desirable, to inoculate a large roll casting proportionally more slowly than a small roll casting, because of the greater total heat content of the larger body of metal. One skilled in the art of roll casting will, with these general guides, be enabled, without experiment, and using merely reasonable care, properly to time the length oi the inoculation period. Y
hy the simple method above described, I have made rolls having in the roll body a scleroscope i hardness of from 00 to 85; and in which test pieces taken from the necks, and the interior of the roll body show (uniformly for each individual roll) a tensile strength of from 32,000 lbs. per su. in. to 40,000 lbs. per sq. in.
It has .been indicated above that nay/quiet inoculation methodNis not limited to procedure which provides a definite, or clean chill structure. Illustration of that fact is given in the formulae for the initially poured metal of the roll. Of these formulae, 1, 2, and 3 give a substantial depth of deiinite, or clear chill structure, while formulae 4 and 5 give a roll having a hardened surface, but without a sharply dehned, or clear chillstructure. These latter rolls are, therefore, to be considered .to be of the grain type, rather than of the chilled type.
It may be that an initial metal which, because oi its chill, will have a suiilcientiy hard surface,
. may, because of its composition and the slow rate of cooling in the sand portions of the mold, give necks which, although they contain a relatively high proportion of graphite, have their graphite in large platey structure, and are for that reason weak. In such case an inoculant metal though it be inherently "harder than the unchiiled portion of the initial metal, may so improve the form and distribution of the graphite structures in the necks, so to increase the strength of the necks. Whereas 'throughout the specification the initial .metal has been spoken of as hard metal, and the inoculant metal as soft metal (as is usually the case) it is thus apparent that the procedure of my method is consistent with the use of an inoculant inherently no softer than the initial metal. It must, however, be of strengthincreasing character. Thus the inoculant metal will have strength-increasing qualities, though not necessarily softer but. even harder than the initial metal, if it be within 'the ranges of the commonly known high-test cast irons. A proportioning of alloys in the initial metal and the inoculant also may cause the inoculant to impart the desired strengthening effect without being inherently softer than the initial metal.
I claim as my invention:
1. In making cast-iron rolls having a hardened body surface and relatively soft and strong body and necks those steps which consist in initially iilling a mold contoured for the casting of rol1s\ to a level slightly above the body cavity of the mold, surface chilling the body portion of the roll to form a cylindrical shell of solidified metal, and inoculating all the initial metal of the roll other than that contained in the chilled surface of the roll body by slowly introducing at the bottom of the mold a strength-increasing different metal while permitting the level of the total metal to rise in the mold.
2. In making cast-iron rolls having a hardened body surface and relatively soft and strong body and necks those steps which consist in initially hlling a mold contoured for the casting of rolls to a level slightly above the central body cavity ci the mold with a metal of relatively high iiuidity, surface chilling the body portion of the roll to form' a cylindrical shell of solidied metal, and during the continuance of the fluidity of the said metal initially in the mold inoculating all the said initial metal of the roll other than that in the chilled surface of the roll body by slowly and quietly introducing at the bottom of the mold an inoculant strength-increasing metal different from the initial metal, while permitting the level ofthe total metal to rise in the mold.
3. In making cast-iron rolls having a hardened body surface and relatively soft and strong body and necks those steps which consist in initially filling a mold contoured for the casting of rolls to aAlevel slightly above the central cavity of the mold, surface chilling the body portion of the roll to form a cylindrical shell of solidified metal, and quietly inoculating substantially the entire body of the metal initially in the mold other than that contained in the chilled surface of the roll body by adding as slowly as the per- .sistence of fluidity in the said initial metal will permit strength-increasing dierent inoculant metal introduced at the bottom of the mold, while permitting the level of the total metal in the mold to rise.
4. In making cast-iron rolls having a hardened body surface and relatively soft and strong body and necks those steps which consist in initially filling a mold contoured for the casting of rolls 'to a level slightly above the central body cavity of the mold, surface chilling the body' portion of the roll to form a cylindrical shell of solidied metal, and effecting quiet inoculation of all the initial roll metal other than that comprised in the chilled surface of the roll body by slowly introduoing at the bottom of the mold an inoculant metal softer than that rst introduced into the mold, while permitting the level of the total metal to rise in the mold.
5. In` making composite cast-iron rolls having a hardened body surface of one composition and a body interior and necks of a different composi. tion the steps of pouring into a mold contoured for the casting of rolls metal to be included in the hardened body surface of the roll to a level above the body cavity in the mold, forming a solidified shell on the body region of the initially 6. In making composite cast-iron rolls having a hardened body surface and a body interior and necks of a softer and stronger composition than that included in the hardened body surface of the roll, the steps of pouring into a mold contoured for the casting of rolls metal to be included in the hardened body surface of the roll to a level above the body cavity in the mold, forming a solidied shell on the body portion of the initially poured metal in the body cavity of the mold, then while retaining in the mold substantially the total initially poured metal mixing a molten strength-increasing and softening metal with the still-liquid portion of the total initially poured metal standing in the mold.
FRED C. DANIELS.