US2377731A

US2377731A - Surface chilling means for castings

Info

Publication number: US2377731A
Application number: US531326A
Authority: US
Inventors: Edwin A Walcher
Original assignee: OHIO STEEL FOUNDRY CO
Current assignee: OHIO STEEL FOUNDRY CO
Priority date: 1944-04-17
Filing date: 1944-04-17
Publication date: 1945-06-05
Anticipated expiration: 1962-06-05

Description

'June 5, 1945- A. wALcHER 2,377,731

SURFACE CHILLING MEANS FOR CASTINGS y l Filed April 17, 1944 2 Sheetsfsheet 1 `June 5, 1945.

E. ApwALcHER Y SURFACE CHILLING MEANS FOR CASTINGS Filed April -17, 1944 2 sheets-sheet 2 EDI/FINA. ML :HER

AT Tw TIE-'5- Patented `June 5, 1945 UNITED 'STATE s PATENT "o A `z`v,371,731

FFIC a SURFCE CHILLING MEANS FOR CASTINGS .Edwin Walcher, Lima, Ohio, assignor `to The Ohio Steel Foundry Company, Lima, Ohio, a

corporation o! 0h10 Application April 17, 1944, Serial No. 531,326

2 Claims.

This invention relates to foundry practice`and `particularly to the surface chilling of castings-of largeeodies, such as steel rolls, is that the molten metaL which is subjected Itochlll, solidifles by large volume, such as'iron and steel-rolls of the type used in rolling mills.

It is generally believed that in a mold consistving of sand rammed into a steel flask, the process of solidlflcation of a. steel casting formed therein proceeds as follows: as the molten metal comes in contact with the mold wall, which has a temforming an elongated crystalline structure; that these primary crystals undoubtedly form very rapidly and tendto push any non-crystallineand lower melting eutectic substances in the molten metal in toward the center of the casting; that the portion of the roll which.l solidifies` in thisv manner `is the best part of the roll for mill usage due to the uniformity of its,crystalline structure, andthat therefore it is important to drive these substances of lower melting point as deeplyinto Vthe roll structure as possible.4 It is known that inside of the chilled rim portion of a roll casting,

` in the zone of equiaxial crystals. defects such as segregation 1ines,.softness and lack ofQ-density will appear, and'that the presence of theseldefects not only shorten the usable lifeof a roll for instance, of a roll mold poured vertically with a gate in the bottomr endof the mold, sothat the molten metalV as it rises in the'mold swirls iny side of a very thin casing of metal.V In an ordi. nary mold, such as commonly used for the making of large mill rolls, this transfer of heat from the molten 'metal to the mold causesa certain but frequently renders arollunsuitable for mill use when it is initiallyv dressed down from :its

original diameter. s l i Many attempts have been madeto accelerate the cooling ratev forthe'working surfaces `of roll amount of expansion in the mold itself. Because the outer portion of the mold retains its lower temperature for a time after pouring, the expansion of the mold must be inwardly until all of the mold walls have become substantially uniformly heated byl conduction yof` heat from the molten metal.' When this has occurred, the heat is removed from the exterior walls of the flask by transference to the surrounding atmosphere. By the time the mold and flask have become heated probably reached a temperature somewhere near that of the contacting metal which has become solid` around the outer surface portion of the casting. As soon. as the sand mold and iiask have vbecome heated throughout, outward expansion of the mold begins so that an air space forms between the casting and the interior mold wall, which space becomes a very effectiveinsulating area against heat conduction. tlonsequently,l the only chilling action on metal poured' into an oru Ydinary sand mold is that which. obtained in the short period which is required to'hrlng the inner surface of the mold up to ahlmximately the same temperature as the outer surface of the casting, which action must taheplace before the mold is heated throughout. crbefore an `insu cent to its inner wall; inthoseareas for which' better Wearing qualities are desired in the roll castings sofas to-overcome theseobjectionsfbut, so far as I am aware,y withoutentire success. One

method employs chill ringsofymetal, usually iron or'steel, placed in arsand moldyatortclosely adj acasting. This methodis .generally usedin the ,casting of sweptout pass'.rolls,rthe metalrings being made in shapes tocorrespond tothe designs of thepasses. These chill rings with iiat` surfaces are also frequently used along` the `entire length of `the body in thercasting of plain body throughout, the interior surface ofV the mold has rolls. With this method, the extent or depth of `transfer of heat from the casting proceeds in a `similar manner to that for simple sand` molds.

l Therefore, while this method is anirnprovement lating air space can form between the mold wall 1 and the surface of the casting.

Another recognized factor in the casting of over-,the sample form in which-.sand alone is used, it hasfvery definite limitations.

Another method consists in the use l? a metal instead of asand wall-mold to effect more rapid' the rim portion of the roll casting overI thatef- .fectecl bythe use of sand molds. While..this method# is an improvement.; over the` sand 4vroll casting method in that the initial absorption of vheat by the metal mold is carried on at a very rapid rate which quickly solldies -a. heavy skin of metal on the rou casting, this method is umited to the size of the mold walls and can only be used in the production of plain body rolls.

Furthermore, the chilling of the primary crystalline structure cannot extend to any substantial portion in depth of the cross-section of the roll. For instance, in a roll thirty inches in diameter. which is cast at approximately thirty-one inches to allow some stock for finish, the depth of the primary crystalline structure is probably not more than two inches to three inches on a side, thus when it becomes necessary to remove the outer half inch of stock on each side during machining, it is seen that there will be only -about one and one-half inches of good metal forming a rim around the roll casting, and that'below this rim defects such as Seregation lines, softness and lack of density will appear.

After practicing the above-noted methods, and recognizing the fact that chilling by such methods depended upon the transfer of heatto the outer atmosphere, and realizing that the rate of this transfer was somewhat slower than necessary to provide the desired results, as indicated by the fact that the interior surface of'a chill mold remained quite hot, the idea of spraying the'outside surface of a mold with water to expedite the transfer of heat was experimented with and some degree of success obtained. Out of this practice, which was unsuitable for very close control, developed the idea of providing molds with circulating water chills. This method, however, as hereto increase the chilling action of the casting and consequent conduction of heat therefrom over' the methods heretofore employed, whereby to increase the depth of uniformity of crystalline structure in the roll body from the working surface inward and to consequently increasethe life and wear characteristics of the roll.

Further objects and advantagesof the invention will be apparent from the following detailed description and from the laccompanying drawingsillustrating two embodiments of the inventionI and in which- Figure 1 is a fragmentary perspective view of one-half of a mold embodying the water chill feature of the invention looking at the drag end of the chill, with a part in section and with the inner thin sandcoating over the -chill partly broken away: Fig. 2 is an enlarged perspective of a corner portion of a water chill unit, with a part broken away to disclose the communicating opening between the inlet header and a tube: Fig. 3 is an inner plan view of a water chill unit section, with parts broken awayrm. 4 is an inlet end view of such chill unit section: Fla. 5 is a fragmentary vertical section of a mold including the combined water chill and ring lchill features of the invention with a formed casting. parts of which are broken away, and Fig. 8 is a cross-sectional view on the line i-l in Fig. 5, with a part of the sand wall of the mold broken away.

The invention assumes two forms. one in which a water circulating means of improved construction is imbedded in the mold wall and produces increased and highly beneficial chilling results on the roll casting over those heretofore obtained,

while the other form combines both the water circulating and the ring chill methods to obtain such results and is used particularly in connection with the casting of swept out pass rolls, but is not restricted to such use.

In the ilrst form of the invention, which is illustrated particularly in Figs. l to 4, the structure which carries and controls the movement of the cooling fluid (usually water, and hereinafter referred to as such) within the mold wall in close relation to its interior wall is composed of a plurality of spaced parallel tubes i0, preferably e'xtending lengthwise of the mold and connected at theirr lower and upper, or drag and cope, ends by v body ofthe casting, and, in the case oi a roll, the

working portion-thereof, which is desired to be dense and free of streaks and segregation.

The tubes i0, in the present instance, are square in cross-section, instead of round as has heretofore been the custom in connection with chills of this character, and each presents a substantially flat side longitudinal and tangential to a circle struck from the axis of the roll forming cavity of the mold, with a radial line thereof, which is normal to such side, intersecting the side at its center, as indicated at a in Fig. 4. This presents a fairly broad face to the roll surface and causes a-more uniform spacing of a tube throughout/its Width from such surface than is the case with a round tube, thus resulting in a more uniform and deeper chilling of the roll metal.

'I'he spacing of the tubes I0 from each other is preferably substantially equal to the width of the tubes, and the tubes are preferably imbedded in the -sand wall of the mold an extent to provide a thin sand covering for the inner side of the tubes so that the tubes will not have direct contact with the roll metal. It has been deter.

mined in practice that by chilling a roll by the use of tubes of this character, the lower melting eutectics, such for instance as sulphur, metallic sulphides, phosphides, etc., in the casting metal, are driven more deeply into the roll so as t0 provide a-greater depth of uniform grain structure from the outer surface inwardly of a roll than is necting passages endwise of the tubes.

This disposition of the headers relative to the tubes I0 is to lessen the,ol 1illing action on the casting metal of the cooling water at the inlet header end where the water is the coldest and to increase the chilling tction thereof on the casting metal at the outer header end where the water is the hottest. These headers, however, are usually positioned at the neck ends of a roll casting beyond its body ends, so that they are more remotely spaced from the casting metal than the tubes i0 and therefore, in such case, their positions with respect to the tubes are not of such great importance. although desirable. In practice, two inch square pipes have been used forthe headers while one and. one-quarter inch square pipes have been used for the lengthwise tubes. It is not intended, however, to restrict the headers and tubes to any particular sizes.

The water chills, comprised by the tubes I and headers Il and l2 with their connections, are

preferably fabricated in two half circular sections, as shown so that they may be set in the two halves comprising the standard steel roll flask. In order to 'provide substantially uniform distribution of the water to the inlet header, the supply pipe I3 therefore has a three-way connection Il therewith, with the connections substantialiy uniformly distributed throughout the length of the header section. Standard molding practice provides that, when used, these chills should be covered at the casting side of a mold wall with a layer of sand, the thickness of which depends upon the amount of chilling desired for the roll or other casting and upon the chemical analysis of that casting. As is well known in the casting industry, metals of high nickel and chrome content cannot be subjected to as drastic a chilling action as plain low carbon steels.

Where the castings to be made are of the swept order to alleviate the drastic eiect of this abrupt out pass roll type, it is found that a hardened Y surface structure, improved both as to depth of hardness and uniformity of crystal, can be obtained over that produced by the use of the usual chill rings if a water chill is used in combination ,therewith in surroundingcontacting relation to the rings. It is also found that these results are improved if a water chill having square or iiat surfaced tubes as distinguished from round tubes is used.

Such.a combination is illustrated in Figs. 5 I

and 6 in which the chill rings, designated IB,

change in chilling conditions, a sectional chill ring composed of Van annular series of spaced metal chill members 2| is used on the cope shoullder section of the mold; These chill members are vspaced apart and are of decreasing thickness from ,their outer ends inwardly so as to distribute the chilling action at the end of the roll chill over a considerable portion of the roll neck by abstracting a gradually decreasing amount of heat from the roll neck as the size of the neck becomes smaller and transferring this heat to the water chill. `Groodresults have been obtained by makingthese chill members about two inches wideA with about two inch spaces therebetween, as indicated in Fig. 5. These dimensions, however, are merely illustrative and not in limitation of the invention.` It is necessary to use a heavy cast chill 22 of ring-formy at the drag shoulder of the mold, which, resting upon the water chill, be-

` comes an effective heat removing agent sothat directional solidiiication upwards is obtained in the casting at the adjacent neck shoulder, which is a highly desirable feature.

I wish it understood that my invention is not limited to any specific construction, arrange,-

are set in the passes I9 of the roll, and the water chill sections, designated 2U, are of the same square type tube construction as described in connection with Figs. 1 to 4. The water chill sections 2l! are disposed within the mold wall around the chill rings I8, and both the water chills and the ring chills are usually spaced from the casting by a thin wall of sand as described in connection with the water chill alone. The rings I8 are usually quarter sectioned to facilitate assembly.

The chill rings I8, which usually are of cast s steel9 are placed in direct contact with the water chill sections so that the heat abstracted from the molten casting is readily transferred through the rings to the water which is kept circulating under a pressure of approximately seventy-live pounds in the water chill piping. The constant flow of the water or other coolantl under this pressure means that the heat is continually abstract-V ed from the chill rings, and th eect of this chilling goes on until the entire roll casting has become solid. This action is facilitated by the flat contact of the chill pipes with Ithe chill rings. 'I'he chill rings when used alone, as Vhas heretofore been the practice, are not always a satisfactory medium for extracting the heat and controlling the grain structure of a casting, and particularly roll castings of large volume, because the rings 'are liable to become distorted under contraction and expansion. Also, rthe extent of ment or form of the parts, as'vit is capable of numerous modifications and changes withoutdeparting from the spirit of the claims, andalso that while lit has been more particularly described for use in casting mill type rolls, it is intended for use in connection with the making of any. castings of considerable volume and for whichI it maybe adapted.

Having thus described my invention, what I claim as new, and desire to secure by United StatesLetters Patent, is: 4

1. In a sand mold having a cavity for casting large swept out pass rolls, the combination with one or more ring chills inthe mold wall to suit the roll passes, of a water chill set into the mold wall without. said ring chills and having 4a plurality of transversely spaced parallel water circulating tubes disposed lengthwise of the mold with their inwardly facing sides substantially nat and in heat conducting contact with the outer sides of the. ring chills, whereby the radial conduction of heat from the roll metal within the moldw to the tubes is substantially uniform throughout the width of each tube at any cross- `the chilling action of theserings is dependent upon the size of the rings, and this size can never be very great. as has heretofore been pointed out. Also when these metal chills become saturated with heat they have'little further chilling action,

unless used in combination with cooling pipes containing a circulating coolant under pressure.

sectional edge thereof.

2.. In a sand mold having a cavity'for casting a large iron or steel roll having a reduced diameter .cope end neck portion', the combination with a water chillin the mold wall, of a sectional chill set into the mold wall around said neck portion in close relation to its inner surface and in heat transfer contact at its inner side with said water chill, said sectional chill comprising an annular series of narrow spaced apart chill members following the contour of the neck forming portion of the mold from the roll body in a radial direction and gradually decreasing in thickness inwardly from its water chill contact;

ing surface end.

- EDWIN A. WALCHER.