US3851701A - Gas venting in the manufacture of chilled rolls - Google Patents

Abstract

In the casting of iron base rolls wherein multiple chiller sections are employed for effecting a hard roll surface; as the molten metal rises in the mold, combustion gases and air are entrapped between the rising metal and the chiller surface. These gases are vented by use of an inexpensive, thin, spacer element between the interfaces of the chiller sections. The spacer element may take the form of a continuous permeable material or of discreet spacers. In the latter instance, it is not necessary that the spacers be composed of permeable material and may, for example, be made of metal.

Description

States net [191 Souers 1 Dec. 3, 1974 [54] GAS VE TI I TH M U U OF 1,921,729 8/1933 Charman 249/201 2,133,829 10/1938 Ogden CHILLED ROLLS 2,431,879 12/1947 Mebs [75] In entor: G rg uers, Min ral City,'0 2,453,643 11/1948 Schmertz 164/412 x [73] Assignee: United States Steel Corporation,

Pittsburgh, Pa. Primary ExaminerAndrew R. Juhasz Assistant Examiner-John S. Brown v [22] Filed 1972 Attorney, Agent, or FirmArthur J. Greif [21] Appl. No.: 310,722

Related US. Application Data ABSTRACT Continuation of 141,863. y 1971, In the casting of iron base rolls wherein multiple abandonedchiller sections are employed for effecting a hard roll surface; as the molten metal rises in the mold, com- [52] US. Cl. 164/127, 164/355 bustion gases and air are entrapped between the rising [51] Il lt. Cl 322d 15/00 metal d the chiller surface These gases are vented [58] Field of Search 249/80, 111, 197, 201, by use of an inexpensive, thin Spacer element 249/202; 164/122 133, tween the interfaces of the chiller sections. The spacer 412 element may take the form of a continuous permeable material or of discreet spacers. In the latter instance, it [56] References and is not necessary that the spacers be composed of per- UNITED STATES PATENTS meable material and may, for example, be made of 233,315 10/1880 Barr .1 164/373 metal- I 795,643 7/1905 Newingham 164/373 933,996 9/1909 Lewis 164/373 3 Chums 5 Drawmg Flgures GAS VENTING IN THE MANUFAC F CHHLLED ROLLS This is a continuation, of application Ser. No. 141,863, filed May 10, .971 and now abandoned.

This invention relates to an improved method forventing gases during the casting of iron rolls.

Of all the steel ingots produced today, greater than 99 percent are processed further by being passed through either cast iron or cast steel rolls. Iron base rolls differ from steel base rolls principally in their carbon content, the steel roll containing up to about 2.5 percent carbon, whereas the iron roll contains carbon in greater amounts. Both types of rolls are produced by the bottom pour swirl method, with the mold in the vertical position. The hot metal enters at the bottom of the dragneck through a gate which is placed tangentially to the periphery of the neck. This placement imparts a vigorous spin or swirl to the metal as it enters the mold. The spinning action throws the denser, purer metal to the surface, thus ensuring a cleaner working face. The less dense, dirtier metal is concentrated in the center of the rising metal and is subsequently carried to the top of the sinkhead. Iron base rolls are cast in a chill type mold, in which the neck is cast in sand but the body of the roll is formed by a heavy-walled cast iron cylinder called a chill. The chill, as its name implies, serves to cool the molten iron quickly, thereby producing a hard surface containing a minimum of graphite. Chill molds are of two types: the one piece chiller, with body lengths of up to feet; and the multiple chill cylinder, in which a body of similar length is built up of chill sections, sometimes only a few inches long. These chill sections are bored to a smooth finish and prior to casting are coated with a thin refractory dressing to avoid burn on of the hot metal. In the process of pouring the hot metal into the mold, gases are produced, both as a result of chemical reaction with the refractory dressing and as a result of evolution from the molten metal itself. These gases and the air entrapped by the rising liquid metal, must be efficiently vented to avoid surface defects in the casting. Previous attempts at venting such gases have taken the form of finely machined saw cuts, either in the chill mold face or at the interface between the various chill sections. In the former instance, these saw cuts are coated over by the refractory dressing which is permeable, and thus serves as channels for the gas to escape. This method has been found to be unsatisfactory in a number of instances, since the rapidly poured molten metal tends to dislodge the dressing and enter the saw cut channel, thus producing a fin of metal at the surface, which in turn will cause a tear" or crack in the casting during the contraction stage of the solidifying process. Similarly formed fins also result when the saw cut channels are employed in the interface between chill sections. In addition to the expense and difiiculty in making such saw cuts, both methods suffer from additional problems in that hot spots are formed at the air gap or at the thicker refractory layer, where the hot liquid metal is not in virtually direct contact with the metal chill. This invention is therefore directed to a method for overcoming these difficulties, and eliminating the need for such critical machining with its corresponding excessive expense, by placing an inexpensive and expendable, thin spacer element between the various chill sec-- tions.

The objects and advantages of, the invention will be better understood by reference to the following description and drawings in which:

FIG. 1 is a cross-section of a roll mold; and

FIGS. 2 through 5 are sectional views of the top of a chill, depicting various types of spacer elements which may be employed.

Referring to FIG. 1, hot liquid metal is poured through the spout 1 and into gate 2, which is set tangential to the periphery of neck 3. The metal is poured rapidly so as to set up the vigorous spin referred to above and to avoid steep thermal gradients in different parts of the roll, thereby preventing hot tears at such gradient points. The hot metal rises through the mold and contacts the chills 4 and 5, promoting a hard, refined outer skin at the contact areas. The metal thereafter rises through neck 6 and into the sinkhead area 7.

If machined channels are employed in the mold face, the gases will penetrate the refractory dressing covering the channels and exit through the permeable sand at 8. On the other hand, if channels are cut in the interface between the chills (illustrated by heavy, dotted line at 9), the gases will be vented at those points. In both instances, the machining required to effect the critical depth of cuts is expensive and tedious. Small deviations in the depth of these cuts, result in either insufficient venting or in the production of fins and hot spots. Thus, if the channel is too shallow, the gases will not have a sufficient area for escape; whereas if the channel is too deep, hot metal will either enter the channel and produce a fin, or will not be chilled sufficiently (due to lack of contact with the metal chill) and produce a soft spot on the roll surface, due to the precipitation of graphitic carbon. Equally important, the sharp edges of the saw cuts provide areas for excessive build-up of the refractory wash, thus providing additional surface defects.

The instant method overcomes these various difficulties by interposition of an inexpensive, expendable spacer element between the chill interfaces 9. FIGS. 2 through 5 show the top of a chill interface, depicting, in section, a few of the embodiments which may be employed within the scope of the instant invention. In a preferred embodiment, as shown in FIG. 2, thin wires 10 are interposed between the chills to provide a large venting area with a small gap, thus considerably reducing the possibility of intrusion of molten metal into the vent areas (shown by arrows). It should be understood that for purposes of this invention, the term wire is not limited to strand material of circular cross-section, but refers to any such material of various polygonal cross-sections.

In a specific application, soft copper wires, 0.030 inches in diameter were placed radially (as shown) at a distance of about six inches apart. The weight of the top chill and the top portion of the flask was sufficient to compress the wires to a gap of about 0.01 inches. An additional benefit may be derived in the use of an easily compressible material, such as soft metal, in that the compression exerted by the top portions of the flask provides a positive, equal venting around the entire circumference of the chill, thus overcoming any possible misfit in the interface between the chills. Thus, if the interface fit between the chills is not perfectly flat (as is generally the case) the more contiguous portions would tend to compress the wires to a greater extent than those interface portions in which some misalignment exists.

FIG. 3 shows the use of sheet material 11 to effect the desired venting and FIG. 4 shows the use of a continuous porous gasket material 12. FIG. 5 illustrates the use of labyrinth type spacer element, which provides a more indirect venting capability, thereby further inhibiting the introduction of molten metal into the venting areas. Any refractory type material such as metals or ceramics may be employed in the gaskets. In all instances, it is desirable to employ a material with sufficient yield qualities to provide a more uniform vent gap spacing, by accommodation to irregularities in the chill mold surfaces in contact with the spacer element. To provide adequate venting and avoid the occurrence of finning, the final vent gap, after compression of the spacer element should preferably be between about 0.01 and 0.02 inches.

I claim:

I. In the casting of iron base rolls wherein the molten metal which forms the roll body is poured through a gate set tangential to the periphery of the neck portion of the roll, said metal being poured rapidly to achieve a vigorous spin and thereby avoid steep thermal gradients in different parts of the roll, wherein said molten metal is contacted with a heavy-walled cast iron chill which serves to quickly cool said molten metal, thereby producing a uniformly hard roll surface containing a minimum of graphite, said chill comprising at least two separate, cylindrical, vertically aligned chiller sections, thereby resulting in the production and entrapment of gases which are deleterious to the production of a smooth roll surface, the improvement which comprises, interposing discrete, removable spacer elements around the circumference of said roll body, between the horizontal interfaces of said chiller sections to effect a gap therebetween for effectively venting said deleterious gases; said gap being small enough to substantially prevent the ingress of molten metal, said spacer elements being of a dimension thicker than the desired gap opening and composed of a material which is suffciently yieldable to provide the desired gap opening on being compressed during the set up of the mold.

2. The method of claim 1 wherein said yieldable material is a metal in the form of a wire.

3. The method of claim 1 wherein said desired gap is from about 0.01 to about 0.02 inches.

Claims (3)

1. In the casting of iron base rolls wherein the molten metal which forms the roll body is poured through a gate set tangential to the periphery of the neck portion of the roll, said metal being poured rapidly to achieve a vigorous spin and thereby avoid steep thermal gradients in different parts of the roll, wherein said molten metal is contacted with a heavy-walled cast iron chill which serves to quickly cool said molten metal, thereby producing a uniformly hard roll surface containing a minimum of graphite, said chill comprising at least two separate, cylindrical, vertically aligned chiller sections, thereby resulting in the production and entrapment of gases which are deleterious to the production of a smooth roll surface, the improvement which comprises, interposing discrete, removable spacer elements around the circumference of said roll body, between the horizontal interfaces of said chiller sections to effect a gap therebetween for effectively venting said deleterious gases; said gap being small enough to substantially prevent the ingress of molten metal, said spacer elements being of a dimension thicker than the desired gap opening and composed of a material which is sufficiently yieldable to provide the desired gap opening on being compressed during the set up of the mold.

2. The method of claim 1 wherein said yieldable material is a metal in the form of a wire.

3. The method of claim 1 wherein said desired gap is from about 0.01 to about 0.02 inches.

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