US2104906A - Means for casting rolls - Google Patents

Description

Jan. 11, 1938. H. MUELLER ET AL MEANS FOR CASTING ROLLS Filed April 6, 1935 2 Sheets-Sheet l WITNESSES ATTORNEYS.

Jan. 11, 1938. I H. MUELLER r AL 2,104,906

I MEANS FOR CASTING ROLLS Filed April 6, 195 5 2 Sheets-Sheet 2 4 "62 FIG. 30

INVENTORY M I WITNESSES BY Wib/W 66%. M *7M 6 0% I ATTORNEY.

Patented in. ii, 193a MEANs ron CASTING ROLLS Pennsylvania Application April 6, .1935, Serial No. 15,028

5 Claims.

This invention relates to the manufacture of castings from metal which shrinks upon solidiiying, and is more particularly concerned with apparatus for casting rolls for use in rolling mills. In the casting of rolling mill rolls and the like, K it is necessary to produce rolls free from blowholes, piping, segregations, pockets and other casting faults. Likewise it is of paramount importance to reduce the machining requisite after casting to a minimum to save material and labor costs. 1

However, in vertically casting, substantially to form and size, a roll having a heavy central body portion and reduced bearing necks on either end, the metal in the neck portions solidifies before the metal in the heavy middle portion of the roll. This results in the formation of a pocket or fissure just where the upper neck portion joins the middle portion of the roll. Thus the strength of the casting is greatly reduced just at the point where the most strength is needed, and as a result roll failure has often occurred at these points of weakness which has led to the scrapping of poorly cast rolls.

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of considerably greater diameter than the diameter of the bearing neck after machining and as used on the roll. In this practice the bearing neck may even be cast the same diameter as the body portion of the roll. Methods of this character may improve the strength and solidness of the casting, but much more metal is required and subsequent removal of this excess material, to bring the bearing necks to size, necessitates lengthy and expensive machining operations so that roll cost is high.

Extra-long or high risers have also been sug gested but their use entails extra material in the casting which must be sheared or machined ofi andscrapped and moreover difficulty in the formation of pockets and fissures is still encountered.

,It is the object of our invention to avoid and overcome the foregoing and other difliculties of,

45 prior practices and to provide improved commercially feasible apparatus for casting rolls free of casting faults and requiring little machining. I

Our invention is predicated on our discovery that a roll with reduced bearing necks can be 50 cast substantially to form in a sand mold without the formation of casting faults so long as the heat is bled or removed in a controlled manner from the lower bearing neck and large central portion of the roll while insuring that the 55 heat will be retained in the upper bearing neck It has been proposed to eliminate the pocket or fissure by casting the roll with bearing necks,

to keep itg liquid until the lower bearing neck and the central portion of the casting freeze.

In the practice of our invention we provide a molding flask having substantially only heat insulating material defining a molding cavity positioned so the axis of the cast roll is substantially vertical. The heat insulating means adjacent the upper neck portion of the casting has a relatively high resistance'to the passage of heat and is substantially thick so that it func- 0 tions to maintain the upper roll neck molten for a considerable period after casting. The heat insulating, means adjacent the remaining portions of the casting have a. medium resistance. to the passage of heat and are relatively thin and have high heat conductive means positioned directly behind them to absorb and conduct away. in a rapid manner but without chilling, the heat of the lower bearing neck and the enlarged central portion of the roll casting. Thus these portions will freeze in the order named and before the upper bearing neck to produce asound cast ing and one which will necessitate little machining and scrap, and which will have a very solid and sound connection between the upper bearing neck and the central portion of the roll.

Apparatus which may..be and has been'used in the practice of our invention as just explained is illustrated in the accompanying drawings, 01' which Fig. 1 is a. vertical cross-sectional view of 30 a. molding flask and casting constructed in accordance with the principles of the invention; Fig. 2 is a fragmentary cross-sectional view of a portion of Fig: l, but illustrating a. modification of the construction thereof; and Fig. 3 is a vertical cross-sectional view similar to Fig. 1, but illustrating another embodiment of the invention. Referring to the particular embodiment of our invention seen in Fig. 1 of the drawings, the numeral lfl indicates generally a flask, which may be of any standard type, but which preferably comprises a plurality of endless-ring portions l2, M, l6 and I8 secured one on top 01. another in any suitable way as by the usual flask clamps (not shown).

The flask l0 carries molding sand 20, or other similar material, which defines the contour of the mold and shapes the roll, indicated generally at 28. The mill roll 28 comprises an enlarged central portion 30 with reduced neck bearing portions 32.and 34. The neck portion 34 is extended vertically to provide a riser or head 36 inaccordance with the usualpractice. The dotted lines 40 indicate the contour to which the casting 28 is preferably machined. a

' tion in the nature of a' true chill, to form the cast- It will be seen from the drawings that the ring N5 of the flask I is made in the form of a heavy chill which has substantially the same volume of metal as the heavy central portion 30 of the roll casting 28. This heav'y chill ring l6 does not funcing '28 with a hardened surface, as the chilling action is definitely prevented by the layer of sand 20a coatingthe surface of the chillring l6. By

avoidingthe true chilling action and having instead heat bleeding operation as hereafter explaine I .able because of'necessity for heavy machining and danger of roll failure from the cracks and at the same timev provide means whereby the amount of heat removed from the casting can be predetermined and controlled.

The resistance of the layer of sand-20w to the passage of heat is very carefully determined, either by actual experiment, by calculation, or by both, to reach a conclusion as to its proper thickness. In all events the thickness is such that the heat from the thickened portion 30 of the roll casting 28 will be drawn to the chill ring I in an even steady flow which will cause the solidification of the central enlarged portion .30 shortly after We have found that when casting a roll having a centrally enlarged portion from about two to about five feet in diameter the sand layer 20a should be about three-quarters of an inch. thick for the smaller size rolls and should increase in thickness proportionallyfor the larger size rolls the solidification of the lower bearing neck with the sand being about one and one-half inches thick for the largest rolls. The sand, or other molding material, formingthe layer 20a should tween the chills and the casting, andpermits a have a. thermal conductivity of "approximately three B. t. u. when used in the thicknesses described just above. (Thermal conductivity is the number of British thermal units passing through a one-inch thick layer of the material 'one foot square with a one degree Fahrenheit temperature 4 difference on opposite sides of the layer.) This compares with a thermal conductivity of over three hundred B. t. u. for steeL,

"The lower bearing neck 32 of the casting "28 is adapted to be solidified first in the freezing of the casting, and this is accomplished in the embodiment of the invention illustrated by the provision of chill rings 44 and 48 adjacent to the portion 32.

As will be seen from the drawings the chill rings.

44 and 46 are not placed directly in contact with the surface of the casting which would chill and harden the casting surface, but'they are spaced from the casting by a covering layer 2llbof molding sand.v This molding sand layer 20b functions similarly to the layer 20a above described in that it servesas a refractoryor insulating layer bestantially equal the volume of the. associated neck we prevent the formation of surface cracks on the cast roll which are very umdesirportions. We have found that chill rings of approximately the character described give the best results. However, it possible to increase the size of the chills 44 and 46 and even to make them part ofring I8 so long as the bleeding of heat from the lower bearing 32 follows the teachings of our invention. The chillor heat withdrawing rings I6, 44 and 46 are preferably of cast iron or other material having a thermal conductivity of at least two hundred B. t. u.

The upper neck portion 34 of the casting 28 is adapted to be kept in a molten condition until after the solidification in turn of thebearing neck 32 and the main central portion 30 of the casting 28. This is achieved by providing a relatively thick refractory layer 50 at the upper end of the mold, which refractory may comprise any suitable heat insulating material having a thermal conductivity of not over approximately two and preferably about three-quarters B. t. u, By way of example, we employ a calcined semirefractory type of diatomaceous silica. This ma- I terial as mined is substantially of the composition which we employ. However, to assist in the molding thereof, we preferably grind the material and mix it with fire clay which functions as a binder.

In using the apparatus just described in the manufacture of a mill roll, the mold is first made .up in the usual manner with the axis of the mold .substantially vertical. The steel is then cast in the mold, by any well-known way, as for example, by bottom pouring with the aid of tangentially extending gates (not shown) connected to the bottom of the molding cavity. When the casting is completely poured, the heat withdrawing or chill rings 44 and 4S first cause the neck portion 32 of the casting to freeze with freezing extending gradually upwardly as occasioned by the heat withdrawing or chill ring is. The refractory and heat insulating layer 50 prevent the premature freezing of the neck portion 34 as the casting solidifies from the bottom 'upwardly, and impurities, inclusions andthe like are carried to the very top of the riser or head- 36 with the forma tion of only arelatively short pipe. The formation of a fissure or pocket at the junction of the upper bearing neck and the central portion of the roll is completely avoided.

In the modification of the invention illustrated in Fig. 2, the thickness of the sand layer 20a of Fig. 1 has been changed so that the layer, indicated by the numeral 20m in Fig. 2, gradually increases in thickness upwardly of the mold.

This still further insures freezing of the casting from the bottom gradually up to the top in that themost heat will be withdrawn from the casting at and near its bottom with the ,heat bleeding control layer of sand 20la getting thicker upwardly of the casting and finally becoming a distinct insulating layer and merging into the heat insulating refractory 5M at the juncture of the upper bearing neck and the roll body. The chill ring I6| associated with the tapered-thickness sand layer 20la is appropriately tapered also. The chill ring adjacent the lower bearing neck is numbered 441, and the flask and sand are iden tifled as I, IN and ZOIQrespectively.

Now referring to the embodiment of the invention illustrated in Fig. 3, the numeral indicates generally a vertically positioned cylindrical flask filled with molding sand 62 which carries and supports cooling rings 64, 66 and 68. These cooling rings are preferably made of welded steel,

. tions ,to carry the cooling fluid from the rings.

Vanes it are-preferably formed in conjunction with the cooling rings to prevent the collapse of the walls thereof and to assist in distributing the water or other cooling fluid around the cooling rings. The thermal conductivity of the coolingringswill be quite high" and obviously well in excess of two hundred B. t. u. dependent upon the flow of cooling fluid therethrough. 1

Positioned at the top of the cooling rings is a cylindrical, relatively thick layer 80 of heat insulating material which is held in the flask with the aid of the surrounding molding sand 62, or if desired, gaggers 82, or other similar means, can

be secured in the insulating body 80 to extend into the molding sand to assist in holding the insulating body inthe mold. The composition, dimensions, and function of the insulating layer 80 are similar to those above described in conjunction with the heat insulating layer shown in Fig. 1.

The numeral 86 indicates generally a steel casting having an enlarged central portion 88, a reduced lower bearing neck 89 and a reduced upper bearing neck 90 which extends into a riser or head 92 of the casting. a The dotted lines 94 indicate generally the contour of the machined roll obtained from the casting 86.

Positioned between the cooling rings 64, B6 and I 68 and the casting 86 are layers 62a and 62b of,

molding sand which'prevent direct contact and chilling of the metal of the casting against the "cooling rings. The thickness of the sand layers 62a and 62b is such that they permit the controlled withdrawing of heat from the casting portions. The composition, thickness and function of the layers 62a andliZb are similar to those described above for layers 20a and 20b. The casting may be poured in any suitable manner, but preferably is bottom poured with the aid of one or more gates 96 positioned tangentially of the molding surface of the neck portion 8,9. The size of the flask can be increased at one corner,'for example, to permit the in-" clusion of a vertical passage from the gates 96 to the top of the flask. This has not been illustrated in the drawings as bottom pouring is old and Well known. l v

'The modification of the invention shown 'in Fig. 2 and relating to the tapered thickness of the sand or insulating layer between the casting and the heat withdrawing means, may be applied also to the apparatus of Fig. 3 as will be understood. v

In practicing our invention with the apparatus just described, the mold is made up in the standard manner and in the form set forth, and the casting is poured in-accordance with the usual procedure. We then begin ,to pass cooling fluid to and throughthe cooling chambers 64, 66 and 68 after the castingha's been completely poured.

Therefore anypossible danger is prevented which might result if the water were in the cooling,

rings during the pouring with the-water leaking through into contact with the molten metal. It

will be appreciated that the cooling rings are very carefully manufactured -,and tested under high pressures so that chances for. escape of water and contact with the molten metal can safely be said to be eliminated.

As indicated in the drawings the arrows,

cooling fluid passing through the rings 64, 66,

and 68 is introduced into the bottom ring (it by means of-conduit 10, passes through the lower the riser 92 and together with thecooling rings insures that the upper neck portion is the last to freeze in the casting. In this manner all slag, blow-holes and the like are carried upwardly and finally form a small pipe at the top of the riser as is illustrated. The casting, and particularly the joinder of the upper bearing neck and the central portion of the roll, is very solid and free of air pockets, impurities, segregations, blowholes and the like and when machined down tothe dotted lines 94 provides a very high-grade mill roll. I

From the foregoing description it will be apparent that improved apparatus for casting metals, such as steel, which shrink on cooling, has been provided, and that more particularly improved apparatus for the manufacture of mill. rolls is provided. The disadvantages and unde sirable features of prior known practices have been avoided. Moreover, the apparatus is relatively inexpensive and requires no complicated heating structures and is readily incorporated in standard molding flasks.

While we have illustrated only certain particular'embodim'ents of the invention, it will be appreciated that the invention is not limitedthereto or thereby but is defined in the appended. claims.

We claim:

1'. Apparatus for casting mill rolls or the like,

including a flask, heat insulating means completely defining a molding cavity in the flask,

the cavity being positioned so the axis of the cast roll is substantially vertical, said heat insulating means surrounding the upper neck portion of the casting being substantially thick and adapted to maintain the surrounded portion of the casting molten, the heat insulating means adjacent substantially all the remaining portions of the casting being less resistant to the passage of heat, and

also relatively thin, and high heat conductive means positioned directly behind the last referred to heat insulating means for readily absorbing and conducting away heat passing therethrough.

J 2. Apparatus for casting mill rolls or the like including heat insulating means defining a molding cavity positioned so the axis of the cast roll is substantially vertical, the heat insulating means adjacent the upper neck-portion of the casting being substantially thick and adapted to maintain the surrounded portion of the casting 'molten, the heat insulating means adjacent the remaining portions of the casting being less resistantto the passage of heat and also relatively thin, and high heat conductive means positioned directly behind the last referred toheat insulating means for. readily absorbing and conducting away heat passing therethrough, said ream)? ductive means including metal jackets with cooling fluid circulated therethrough.

3. Apparatus .for casting mill rolls or the like including afiask, heat insulating means defining a molding cavity positioned so the axis ofthe cast roll is substantially vertical, said heat insulating means surrounding the upper neck portion of the casting having a thermal conductivity of approximately three-quarters B. t. u. and being substantially thick and adapted to maintain the surrounded portion of the casting molten, the heat insulating means'adjacent the remaining portions of the casting having a thermal conducume of the casting.

4. Apparatus for casting mill rolls or the like including a flask, heat insulating means defining a molding cavity positionedso' the axis of the cast roll is substantially vertical, said heat insulating means adjacent the upper neck por.

tion of the casting having a thermal conductivity of approximately three-quarters B. t. u. and

' being substantially thick and adapted to maintain the surrounded portion of the casting molten,

the heat insulating means adjacent the reining portions of the casting having a thel conductivity of approximately three B. t. u., and being between three-quarters and one and one half inches thick, and high heat conductive means, having a thermal conductivity of at least approximately two hundred B. t. u., positioned directly behind the last referred to heat insulat= ing means 'for readily absorbing and conducting away heat passing therethrough.

5. In a mold for casting mill rolls and like articles in a vertical position, heat removing means adjacent the casting-for cooling the casting, and insulating means of increasing thickness upwardly oi the casting positioned between the heat removing means and the casting for reducing and controlling the flow of heat to the removing means.

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