US2374904A - Core structure for casting hollow rolls or the like - Google Patents

Description

y 1945. E. A. WALCHER 2,374,904

CORE STRUCTURE FOR CASTING HO LLOW ROLLS OR THE LIKE Filed Jan. 4, 1944 2 Sheets-Sheet 1 IE-l- Hug .. 3MW EDWZNAWZILFHEE.

.May 1, 1945. E. A. WALCHER CORE STRUCTURE FOR CASTING HOLLOW ROLLS OR THE LIKE Filed Jan. 4, 1944 2 Sheets-Sheet 2 EDWIN AWFUL EH51;

Patented May 1, 1945 CORE STRUCTURE FOR GASTIN G HOLLO ROLLS OR THE LIKE Edwin A. Walcher, Lima, Ohio, assignor to The Ohio Steel Foundry Company, Lima, Ohio, a

corporation of Ohio Application January 4, 1944, Serial No. 516,934 1 Claim. (Cl. 22-165) This invention relates primarily to improvements in apparatus for casting hollow rolls of the character used in rolling mills, and particularly to the core structures of such apparatus.

In the casting of hollow mill rolls wherein a roll body of large volume is present, it has been heretofore quite generally considered in foundry practice that the core structure used in the casting of such rolls should have an internal chilling action on the metal of the roll so that solidification of the roll metal would not only be infiuenced inwardly from the mold wall but also outwardly from the core means.

It has been found that for the most eflicient results this theory is erroneous and that the core structure'should be such that the chilling action of the cooling fluid flowing therethrough is insulated from the roll metal and only used to preserve the core structure against the destructive action of the heat .from the enveloping molten metal'of the casting? Therefore, the only proper purpose in practice of the core structure in the production of hollow mill rolls, or other similar bodies, is to form the hollowsv in the castings, and, for ideal conditions, such structures should not be employed as internal chill means nor should they act to effect any such chill.

The core structure which heretofore has been preferably used in this work includes an interior pipe through which water is flowed for cooling purposes, and a surrounding protecting sleeve of baked clay, or other suitable refractory material, in direct contact with the molten metal of the casting and composed of a plurality of short builtup tile-like sections in end-to-end abutment. It is found in practice that this type'of core is not entirely satisfactory not only by reason of its cooling action on the cast metal but also due to difficulty in handling during mold construction. in maintaining proper alignment during'handling or the mold and while pouring, in removal of the core from the casting, the danger of collapsing of the sleeve and pipe under the action and compressive force of the molten metal, and the liabilit of leakage of molten metal through the sleeve joints at the abutting ends of the sections and into contact with the water pipe. Such leakage of metal forms irregularities and projections on the inner wall of a roll, and produces points of stress which could lead to roll failures.

In the use of a combination tile and water pipe core, it has been found in actual practice that difficulty has been experienced in removal of the water pipe and surrounding tile sleeve from the casting due to leakage of the molten metal through imperfect joints between the ends of the tile sections or through collapsed portions of the sleeve whereby the casting metal contacts the water pipe and tends to produce solid portions at such points and to render the removal of the core parts extremely diflicult.

It has also been found very difiicult, particularly with long rolls, to maintain a proper alignment of the tile sleeve both during handling and during pouring due to the inherent flexibilityof the sectional structure, as any deflection of the tile sleeve will effect the straightness of the hole through the roll and will cause a breaking of joints at the bending points and the consequent admission of the molten metal to the interior of the sleeve to produce stress raisers.

The primary object of the present invention is the provision of a core for use in casting hollow rolls or the like of the character described, which core can be cheaply fabricated and easily handled, will maintain a proper alignment during handling of the mold and while pouring, is effectively resistant to injury by the compressive force of the mold during pouring and until the interior metal of the roll has solidified, will reduce to a minimum internal chilling of the casting metal, and, insofar as the parts intended for removal are concerned, is capable of easy and ready removal from a casting, thus avoiding or overcoming, at least to a very large extent, the troubles incident to the use and handling of the refractory sleeve and enclosed water pipe type of core heretofore described.

Another object of the invention is that the outer metallic casing member of the core not only presents a smooth exterior surface to the cast metal, thus avoiding stress points, but also becomes a fused integral part of the casting and forms a hole or hollow therein which has a smooth wall and requires ver little if any subsequent dressing. This feature is important as it obviates the time and work necessary to dress a casting hole and to remov the core parts therefrom incident, so far as I am aware, to the use of the core structures heretofore employed.

Other objects and advantages of the invention will be apparent from the following description and from the accompanying drawings, in which Figure 1 illustrates the application of my improved core structure to a molding flask and shows the flask, the hollow roll and the core structure in central longitudinal section, with parts in full and parts broken away; Fig. 2 is a fragmentary top plan view thereof, and Fig. 3 is a fragmentary cross-section on the line 3-3 in Fi 1.

Referring to the drawings, l designates a flask of the usual form having a mold cavity therein that is formed by molding sand l2, as well understood in the art. Molten metal may be supplied to the mold cavity through the customary feed gate or gates, shown in dotted lines, to form the roll or other casting M. The cope end of the casting includes the usual feed head portion l5 that is cut off after the casting has been removed from the mold. The rolls M are usually large, frequently being 200 inches or more in length overall, not including the head portion, and 45 inches or more in diameter at the body, thus subjecting the core structure to very considerable compressive forces and to the high heat, over quite a long period, of a large body of molten metal, and producing conditions and problems which for efficient work must be taken into consideration in the construction and use of the core. The invention has been practiced in casting. rolls as small as inches in diameter. It will be understood, however, that its use is not restricted to rolls within any particular limits as to size.

The core structure which I have found to best meet the noted conditions and problems includes an outer tubular metallic casing 18, preferably of steel and smooth or devoid of irregularities externally and interiorly, an inner metallic tube I9 spaced from the casing l8 and concentric thereto and through which a cooling medium, such, for instance, as water, can becirculated, and a thermal insulating material 20 disposed between said casing and the tube. The insulating material 20 serves to control but not to entirely prevent the transfer of heat from the roll metal to the cooling medium in the tube l9. Irregularities on either or both surfaces of the casing it become points of stress which may lead to roll failures and should, therefore, be avoided.

In practice, the insulating material 20, mainly to facilitate handling, is in the form of a sleeve that is held slightly spaced, as at 2i, from both the casing and the tube, and while any suitable material for the purpose can be used, it has been found that silica sand bound together in sleeveform by any suitable binder produces very good results. Any sand binder commonly used in foundries can be used, an example of one such binder being oil, a cereal binder and water. The insulator sleeve mixture after forming is, of

course, dried to facilitate handling. The spaces 2| are for venting any gases which may be evolved when the sand sleeve is subjected to the pouring temperature of the molten metal. The thermal insulating characteristic of the material 20 should be such as to permit transfer of heat from the sleeve Hi to the cooling medium sufficiently fast to prevent destruction of the sleeve by the heat and the ferrostatic and compressive pressures of the contacting body of metal while at the same time permitting a melting or softening and consequent fusing of the outer surface of the sleeve to the roll metal so that the sleeve becomes an integral part of the roll.

While it is not desired to restrict the invention to any particular dimension of parts, it has been found that good results in the casting of rolls of various sizes are obtained by using an ordinary metal water pipe I 9 of approximately one inch inside diameter, an approximately three inch steel pipe casing l8 having a wall thickness of approximately A; inch, and an insulating sleeve 20 of approximately inch wall thickness with a inch space 2| between it and the water pipe I9 at its inner side and the casing l8 at its outer side.

When a core structure has been assembled and mounted in a mold preparator to pouring, the water pipe l9, in the illustrated embodiment, has a lower inlet connection 26, with the former preferably mounted in the bottom of the mold flask, and with the upper end of the pipe held centered with the mold by a top cross frame 21 mounted on the flask. The insulating sleeve 20 rests at its lower end on the inlet connection 26 in spaced centered relation to the pipe l9 and its upper end has a yielding down-pressure applied thereto by a coiled compression spring 28, which seats at its lower end against a washer 29 on the sleev and has its upper end-thrust against the cross frame 21. This frame is tied to the upper end of the flask ID by bolts 30. The metal casing IB also rests at its lower end on the connection 26 through the medium of a washer 3| and its upper end is held by a pressure spider 32. To permit expansion of the casing I 8 under varying temperature conditions, a yielding down-pressure is applied to the spider 32 by a series of coiled expansion springs 33 which are connected to the upper end of the flask by bolts 34.

In practice the molten metal of the casting, as it enters and fills the mold cavity, has intimate contact with the exposed exterior surface of the core casing l8 and fuses thereto so that the casing becomes an integral part of the casting structure. Utilizing the outer casing of the core as the lining for the casting hole is highly important, as it not only forms a permanent smooth inner surface lining for the hole but permits an easy and rapid removal of the inner pipe l9 and insulating material 20, or what is left of it, from the casing, inasmuch as the casing has substantially retained its original form and no molten metal has been admitted to the interior thereof to form projections therein or to fuse to the center pipe l9. This is an extremely important factor in avoiding internal stresses in the casting. It has been found in practice that if irregularities or projections are present in the wall of the center hole of a roll, such, for instance, as occurs at the joints between tile sections having direct contact with the roll metal, these irregularities or projections become points of stress which might lead to roll failures. The provision of a metallic casing I8 for the core is also important in preventing flexing of the core structure under pressure of the molten metal, and in enabling it, due to its increased rigidity, to have its diameter decreased over the tile casings heretofore used, thereby permitting casting of a roll with a smaller center hole, which is frequently desirable.

The provision of the insulating sleeve 20 between the pipe 19 and casing I8 protects the pipe l9 from the injurious action of the casing metal heat and prevents heating of the casing I8 to such an extent that it will collapse or become distorted. The insulating action of the sleeve 20 should be so gauged, however, that While serving to protect the casing l8 from the injurious action of the molten metal heat of the casting, it will at the same time so reduce the cooling effect of the core as to have very little chilling action on the casting metal. This latter is important as it has been found that the presence in a castto occur at a greater depth in the casting or more remote from its outer or working surface if there is little interior chilling of the casting metal through the core. In other words, contraryto previous belief, experiments and tests have shown that too drastic cooling at center of roll is an undesirable feature and that, therefore, the construction and cooling action of a core in producing castings of this character should be only suflicient to protect the core parts against the molten metal heat. In this connection recent studies of defective rolls have tended to show that too drastic center chilling of the rolls has probably been a contributing factor of cracked cope necks and other defects.

Another disadvantage resulting from the too drastic roll chilling action of a core is that the metal in the feed head portion of the casting,

where longest liquidity of the metal should be maintained to take care of shrinkage feed conditions, is internally chilled by the core and externally chilled by the mold wall so that the feeding efliciency of the metal in the head is reduced. The internal chilling of the head metal through a core of the present construction is reduced substantially to a minimum so that the chilling action of the central portion of the feed metal is materially reduced.

The sleeve 20, particularly if of sand, is powdered by the heat of the molten metal at the pouring temperature, and consequently after a roll has become solid can be readily removed, together with the water pipe, from the casing ,ll,

which is then an integral part or the roll structure. This feature has meant a reduction of several hours time necessary for core removal on even the very smallest sizes of rolls where cores having sectional refractory tile casings are em- The hollow, steel roll and method of making same disclosed herein are claimed in a co-pending application.

I wish it understood that my invention is not limited to any specific construction, arrangement or form of the parts, as it is capable of numerous modifications and changes without departing from the spirit of the claim.

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

In an apparatus for casting hollow steel rolls or similar articles and in' combination with a mold body, a core structure therefor consisting of a tubular steel casing which fuses to the casting when formed and provides an integral lining for a hole formed through the casting by the core, a metallic pipe for a circulating cooling fluid extending centrally through said casing, a

, thermal insulating sleeve of sand disposed between said casing and pipe in slightly spaced relation to each and serving to maintain said casing chilled to a point where it will resist injury thereto by the action of the molten casting metal in contact therewith and also reducing the chilling action of the circulating fluid on the adjacent casting metal so as to have very little chilling action thereon.

EDWIN A. WALCHER.

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