Method for producing ingot mold stools

Cast iron ingot mold stools having exceptionally smooth flat surfaces and a longer average life are produced by casting such stools in a mold, the inside of which is formed by rigid thermal insulative boards.

BACKGROUND OF THE INVENTION 
Ingot molds used in the production of steel ingots usually consist of 
upright cast iron, box-like shells open at both ends. To close the bottom 
for casting steel therein, the mold is placed upright on a thick cast iron 
mold stool. Hence, an ingot mold cavity is formed by the mold stool on the 
bottom and the interior side-walls of the ingot mold thereover. A 
reasonably close fit between the mold and stool should be assured to 
prevent leakage of molten steel therebetween. 
Ingot molds and mold stools are usually manufactured in accordance with 
established sand-mold foundry techniques. While molding techniques for the 
manufacture of ingot molds has undergone some refinements, such as chill 
casting procedures, mold stools are still usually produced by conventional 
age-old foundry practices. Specifically, a rectangular molding flask is 
placed over and clamped to a rigid molding plate to form an open-topped 
box-like structure. Molding sand is then spread over the inside bottom to 
a depth of several inches, and then compacted to form a flat sand surface. 
A rectangular pattern, usually made of wood, is then placed on the flat 
sand surface such that there is several inches of clearance between the 
sides of the pattern and the flask walls. Molding sand is then compacted 
into that space. The pattern is then carefully removed to leave a 
rectangular cavity in the molding sand. A pouring gate must also be 
provided in the molding sand adjacent to the cavity to funnel molten cast 
iron to the bottom of the cavity. After the mold stool has been cast in 
the cavity and solidified, the cast metal is removed from the sand mold, 
the gate broken-off and the surfaces cleaned. Surface cleaning is usually 
performed by hand, using a pneumatic chipper to scrape-off the molding 
sand adhering to the as-cast surface. 
SUMMARY OF THE INVENTION 
This invention is predicated upon my development of a new and improved 
method for producing ingot mold stools which utilizes thermal insulative 
boards instead of molding sand to shape the mold, thereby greatly 
simplifies the mold-making procedure, the casting conditions and surface 
cleaning; and which produces a superior casting having smoother and 
flatter surfaces and a longer service-life span; and finally provides a 
healthier foundry environment by eliminating dust and dirt conditions 
associated with conventional sand casting.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to FIG. 1, the ingot mold stool of this invention is formed 
by first providing a smooth flat surface 10 upon which the rest of the 
mold is constructed. For example, a thick metallic plate 12 of suitable 
dimensions may be laid flat on a horizontal heat resistant surface such as 
the foundry floor. Thereafter, a rectangular thermal insulative board 14 
is placed on top of surface 10. A rectangular molding flask 16 is then 
placed on top of insulative board 14. Insulative board 14 should be 
suitably sized so that it extends at least to the outer perimeter of 
molding flask 16 so that the weight of flask 16 will readily hold 
insulative board 14 in place and provide as much of a seal therebetween as 
possible. Four thermal insulative boards 18 (only two are shown) are then 
secured to the inside surfaces of molding flask 16. Although any suitable 
means may be used to secure insulative boards 18 to the inside face of 
flask 16, I have preferred to use a commercially available nailing system 
wherein a nail is driven through the molding board 18 and into the molding 
flask 16 to hold the insulative boards 18 in place. 
Although it is possible to cast the molten iron directly into the 
open-topped mold as shown in FIG. 1, I have preferred to provide a gate, 
as shown in FIG. 2, so that the smooth flat surface of the insulative 
board 14 is not disturbed or damaged by the pour stream. The gate is 
formed by providing a small rectangular extension 20 on one wall of flask 
16 (FIG. 3) sufficient to receive a preshaped and baked sand gate 22 
having a pouring gate 24 therethrough. 
In a preferred practice of this invention, I have found it most helpful to 
place an insulative cover over molding flask 16 before the metal is cast. 
Normally, I have used an 8-inch cast iron plate, which serves three very 
useful functions: one, the added weight on flask 16 serves to better seal 
the interface between insulative board 14 and flask 16; two, the heavy 
plate further thermally insulates the casting to slow the cooling rate as 
necessary to effect the desired microstructure; and three, the plate will 
shield the foundry workers from radiant heat. As an alternative, a loose 
particulate insulative material, such as vermiculite, has been used by 
spreading it over the cast metal. While this alternative insulates the 
casting and shields the workers from radiant heat, it does not provide 
added weight to better seal the mold. 
When the mold is completed as shown in the drawings, molten iron is cast 
into gate 28 filling the mold cavity defined by insulative boards 14 and 
18, and the molten metal therein is allowed to solidify, When solidified, 
the casting is removed and the gate metal broken-off. The resulting 
casting, i.e. those surfaces formed against insulative boards 14 and 8 are 
exceptionally smooth and flat. Since no sand was used to form any of the 
stool surfaces, no chipping or surface conditioning is necessary. All that 
may be necessary is that portions of the insulative boards may have to be 
scraped-off. 
In the above-described process, it is essential that insulative boards 14 
and 18 have good thermal-insulative properties so that the stool casting 
will cool and solidify slowly, at least as slow as in conventional sand 
molds, and preferably even more slowly. Such slow cooling rates will 
promote a microstructure having large graphite flakes, which serve to 
enhance the stools' life span as discussed below. To this end, I have 
utilized rigid boards 1/4-inch thick consisting of compressed fibrous 
silica-alumina which are commercially available from Norman F. Tisdale & 
Associates, Inc., Gibsonia, Pennsylvania. Such boards have a density of 24 
pounds per cubic foot and have excellent thermal-insulative properties. In 
combination with the good thermal insulative characteristics of boards 14 
and 18, the thick metal plate 12, the foundry floor upon which plate 12 
rests and the optional cover, further serve to insulate the casting to 
promote slow cooling. 
The procedure as described above not only eliminated the use of molding 
sand (except for the optional gate) but it also significantly reduces the 
manpower necessary to produce the mold and to condition the casting, and 
it also produces a cast stool of greatly improved quality. The quality 
improvements are not only physical in that the surfaces are smoother and 
flatter as compared to stools produced in sand molds, but also such stools 
have been shown to have a longer average life. For example, the first mold 
stool produced according to the above-described embodiment was used in 
excess of 100 pours, whereas prior art stools are scrapped after about 50 
pours on an average. After the above-described practice was established as 
the standard practice for producing mold stools in one foundry, the stool 
condemnation rate dropped over a period of eight months from 18 lbs/ton to 
14 lbs/ton. The condemnation rate is the pounds of stool scrapped per ton 
of steel poured thereon. The improved rate of 14 lbs/ton noted above does 
not fully reflect the advantages of this invention as it is the rate of 
all stool on hand including those produced pursuant to prior art 
practices. Hence, the improved rate of from 18 lbs/tons to 14 lbs/ton 
reflects a gradual improvement in condemnation rate as the stools produced 
by this inventive method gradually increase in number and in proportion to 
the prior art stools. 
As noted above, this inventive process provides the added advantage of 
providing a healthier foundry environment. While this advantage has been 
appreciated since the first actual reduction to practice, its significance 
has become even more important in more recent months. Specifically, new 
OSHA standards have set maximum limits on silica contents in foundry 
atmospheres in order to minimize the risk of silicosis to foundry workers. 
Some steel mill foundries which produce only ingot mold stools have been 
threatened with a complete close-down due to their inability to meet these 
new standards. In utilizing this inventive process, however, at least one 
such foundry to date has been able to easily meet the new silica standards 
to stay in operation and also reap the other advantages produced by this 
process.