Title:
REPAIRED BASE PLATE FOR INGOT MOLD
United States Patent 3874628
Abstract:
Eroded base members of ingot molds may be repaired by attaching to the eroded cavities thereof at least two irregularly-shaped anchor bars. After attaching the anchor bars the eroded mold cavity is filled with a thermally-resistant plastic refractory composition which is subsequently cured. Improved ingot molds may be produced by using the above described technique. Improved molds may be prepared with a preformed cavity into which the irregularly-shaped metal anchor bars and refractory composition are placed.
US Patent References:
Method of repairing furnace linings
Anderson - June 1930 - 1765558
Lightweight aggregate furnace patch lining and process of applying
Gibson - September 1959 - 2903778
Hot patching of refractory structures
Lentz - January 1961 - 2968083
Refractory brick and preparation thereof
McDonald - August 1961 - 2997402
Coated chimney
D'Asto - October 1966 - 3281308
Method of repairing furnace linings
Anderson - June 1930 - 1765558
Lightweight aggregate furnace patch lining and process of applying
Gibson - September 1959 - 2903778
Hot patching of refractory structures
Lentz - January 1961 - 2968083
Refractory brick and preparation thereof
McDonald - August 1961 - 2997402
Coated chimney
D'Asto - October 1966 - 3281308
Inventors:
Jarron, Robert C. (Burlington, Ontario, CA)
Petersen, Peter L. (Hamilton, Ontario, CA)
Petersen, Peter L. (Hamilton, Ontario, CA)
Application Number:
05/447601
Publication Date:
04/01/1975
Filing Date:
03/04/1974
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
29/402.150, 164/121
International Classes:
B22D7/06; B22D7/00; B22D35/04
Field of Search:
249/204 266/1R,43 264/30 29/402 164/121
US Patent References:
Primary Examiner:
Husar, Francis S.
Assistant Examiner:
Brown, John S.
Attorney, Agent or Firm:
Premo, John Lambe James G. F.
Parent Case Data:
This application is a divisional of our earlier filed application Ser. No. 356,697 filed May 18, 1973, which is a continuation-in-part of our earlier filed application Ser. No. 143,345 filed May 14, 1971, now abandoned.
Claims:
We claim
1. A repaired base member for a two part ingot mold comprising a cast iron base for a separate and detachable vertically positioned hollow mold, said base having formed within its top surface a cavity, said cavity having attached to its surface by mechanical means at least two irregularly-shaped metal anchor bars and said cavity being completely filled with a cured thermally resistant refractory composition which contains at least 40 percent by weight of alumina.
2. The improved base member of claim 1 wherein the thermally-resistant refractory composition is a cured alumina ramming mix which contains at least 60 percent by weight of alumina.
3. The repaired base member for a two part ingot mold of claim 1 wherein the refractory composition is a plastic refractory composition.
4. The repaired base member for a two part ingot mold of claim 1 wherein the irregularly-shaped metal anchor bars are in the shape of a "Z".
5. The repaired base member for a two part ingot mold of claim 3 wherein the thermally resistant refractory composition comprises:
1. A repaired base member for a two part ingot mold comprising a cast iron base for a separate and detachable vertically positioned hollow mold, said base having formed within its top surface a cavity, said cavity having attached to its surface by mechanical means at least two irregularly-shaped metal anchor bars and said cavity being completely filled with a cured thermally resistant refractory composition which contains at least 40 percent by weight of alumina.
2. The improved base member of claim 1 wherein the thermally-resistant refractory composition is a cured alumina ramming mix which contains at least 60 percent by weight of alumina.
3. The repaired base member for a two part ingot mold of claim 1 wherein the refractory composition is a plastic refractory composition.
4. The repaired base member for a two part ingot mold of claim 1 wherein the irregularly-shaped metal anchor bars are in the shape of a "Z".
5. The repaired base member for a two part ingot mold of claim 3 wherein the thermally resistant refractory composition comprises:
Description:
INTRODUCTION
All metal ingots are cast from molds. One popular type is a "big end down" mold. These molds rest on bases commonly known as "stools." The stools are merely large, normally rectangular, flat slabs of metal, commonly made of cast iron, which are used as support for the mold sides and also, of course, form the bottom portion of the mold. The mold sides generally taper up in diameter from bottom to top. Another type of mold is known as the "big end up" mold. These are ladle-like receivers for the molten metal, the bottom portion of which molds are integral, non-removable parts of the entire mold.
Various problems commonly occur in use of these molds and particularly with respect to the surface of their base portions. First, the unprotected metal surface quickly erodes and pits in the presence of molten metals which are cascaded upon their surface. Large gouges in the base portions are produced due to the force and high temperature developed by the flowing molten metal which contacts the surface of the stool. Since many molds are generally approximately 5-10 feet in height, the metal must be poured from a height at least equal to that distance and quite often is poured from even greater heights. A considerable pressure head is thereby developed. Thus, the hot molten metal easily gouges gaping depressions in the base members under such force and at a temperature of at least the liquefaction temperature of the molten metal. Moreover, the problem of creation of pits or gouges in the base portions of the molds, caused by the above factors is aggravated due to the fact that the molten metal, especially near the bottom of the mold, remains in its erosive hot liquid states for a considerable amount of time subsequent to pouring.
The molten metal upon solidification to an ingot thereby has a bottom form conforming to the undesirable eroded surface configuration of the stool or base member of the mold. Thus, a considerable amount of the ingot, when withdrawn from the mold and subsequently processed into slabs or blooms, is lost through a cropping of the irregularly formed end of the slab. This, of course, is highly undesirable, since it results in undue loss of usable metal and increase in scrap, which must be subsequently reprocessed.
Another extremely serious and costly problem results after the ingot in the mold has solidified to a point where it can be removed from both the mold sides and its base platform member or stool. In many cases, if the surface of the stool is unprotected, or inadequately protected, and erosion occurs as described above, the ingot has a greater tendency to remain tightly adherent to the stool. Thus, after the mold sides are removed from around the ingot, which process can normally be efficiently achieved with a minimal film of coating selected from a variety of coating agents, the ingot must be forcibly removed from the stool. This is normally achieved by raising both ingot and adherent stool, and thrusting them against some other larger object whereby the ingot is jarred loose. In many cases the stool and ingot are merely dropped on the floor from some suitable height. In such a situation, the stool is often broken into two or more smaller pieces and cannot be subsequently reused in casting other ingots. Again, replacement cost of these stools is high, making this aspect of the overall casting process somewhat disadvantageous. The same problem exists with respect to big end up molds wherein sticking exists with respect to big end up molds wherein sticking of ingots particularly occurs at their base portion. New molds of this type are especially vulnerable to sticking due to their smooth surface unprotected by any layers of metal oxides or scale. A tight metal-to-metal bond between mold bottoms and ingots then occurs.
Cracking of molds and particularly their base portions due to the above discussed rough handling occasioned by "stickers" between the base portions and ingots is also enhanced by thermal shock during ingot formation. Unprotected or inadequately protected bottom surfaces of mold are especially susceptible to such destructive shock.
Many solutions to alleviating the above described problems in connection with the erosion of base members of ingot molds have been proposed by the prior art. A number of refractory coatings have been suggested but these are not entirely satisfactory. An early solution to the erosion of ingot mold stools resided in the suggestion that refractory inserts could be placed into the bottom of the mold, which refractory would tend to minimize erosion. Ceramic inserts have not met with any degree of commercial success. Their main drawback is that in use the molten metal works its way into the space between the insert and mold itself due to capillary action and tends to force the ceramic insert from its cavity. When this occurs the ceramic insert is above the top surface of the stool and tends to become entrained into the ingot. This entrainment produces metallic inclusions in the ingot which necessitates the expensive operation known as "butt cropping."
If it were possible to produce improved base members of ingot molds or to repair eroded stools whereby improved life could be achieved a substantial advance to the art would be afforded.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to provide an improved method for repairing eroded base members of ingot molds.
Another object is to provide improved base members of ingot molds which are less subject to erosion than the problems associated therewith. Other objects will appear hereinafter.
THE DRAWINGS
FIG. I is a horizontal cross-sectional side view of an eroded mold which has been repaired by the method of the invention.
FIG. II is a top view of an eroded base member of an ingot mold.
FIG. III is a horizontal view of a cavity showing Z-shaped metal anchor bars fitted within the cavity.
With more specific reference to the drawings wherein like parts have like numbers, there is shown a base member of an ingot mold 10 of substantially rectangular dimension. This base member or stool is normally of large dimension and is constructed of cast iron. Typically such stools can have a thickness of 12 inches or more and a length of 4 to 6 feet. Badly eroded stools can be eroded to a diameter of as much as 3 feet and to a depth of as great as 10 inches. When such erosion occurs these stools are normally discarded as being unfit for service.
As shown to the best advantage in FIGs. I and II the stool 10 has a cavity 12 which is formed in the top of the stool 14.
The drawings show affixed to the side walls 16 of the cavity 12 two or more irregularly-shaped anchor bars 18, which are shown in the drawing in their preferred form as being of a Z-shaped configuration. The Z-bars shown in the drawing are anchored to the side walls 16 of the cavity 12 by means of threaded studs 20, which are shown in greater detail in FIG. III. A convenient method of anchoring irregularly-shaped Z-bars resides in the use of a cartridge actuated nail-driving impact tool, which allows for rapid anchoring of the Z-bars into the cavity.
While the metal anchor bars are shown to be in the shape of a Z, it will be understood that other irregularly-shaped configurations of a general serpentine nature may be used. Thus, cork screw shapes, L-shapes, V-shapes, and the like may be used.
It is preferred that in anchoring the irregularly-shaped anchor bars that the base portion thereof which contacts the cavity of the stool be in the same plane as the surface rather than being perpendicular. Expressed in other words, threaded studs wherein a pointed end is affixed into a base member is not desirable since the end of the stud forms a heat transmission foci which would cause a hot spot or burning effect when the top portion of such a stud were contacted with molten metal. As seen in the drawings the base portion of the Z-bar contacts the cavity wall, thereby providing a greater heat transfer surface to minimize localized hot spotting of the mold.
After the irregularly-shaped metal anchor bars 18 are positioned in the mold cavity, the cavity is then filled with a ceramic material which is designated by the numeral 22. This plastic refractory material should be heat resistant and curable to provide a dense ceramic surface which is capable of receiving teemed molten metal such as liquid steel.
SPECIFIC DESCRIPTION OF THE INVENTION
The invention has been described thus far with respect to the drawings and shows a method for repairing eroded base members of metal molds. Thus it is evident that the method of this invention for repairing eroded base members of metal ingot molds which have their top surfaces worn into a cavity comprises the steps of attaching into the cavity at least two irregularly-shaped metal anchor bars, filling the cavity with a thermally-resistant plastic refractory composition and heat-curing said plastic refractory composition.
As indicated, the irregularly-shaped metal anchor bars are preferably in the form of a Z. They may be positioned inside of the cavity in a variety of configurations. They should be sufficient in number to allow a good anchoring effect to be achieved between the surfaces of the cavity and the plastic refractory composition.
THE PLASTIC REFRACTORY COMPOSITIONS
The plastic refractory compositions that have given outstanding results in the practice of the invention are composed predominantly of alumina and may contain other ingredients such as inorganic phosphates, minor amounts of water, clay and the like. The compositions should contain at least 40 percent by weight of alumina and preferably 60 percent by weight. These so-called high alumina ramming mixes are discussed and described in U.S. Pat. No. 3,547,664, including certain of the references cited thereagainst. This patent and certain of its references are incorporated herein by reference. A preferred ramming mix of the type described in this patent has the following composition:
Tabular alumina (6 mesh) 60 Calcined alumina (-325 mesh) 28 Kyanite (48 mesh) 5 Kaolin clay 3 Phosphoric acid (85%) H 3 PO 4 4 Ceramic fiber 0.12 Water 4
Compositions of the above type are rammed by pneumatic means or the like into the mold cavity which has been previously fitted with the irregularly-shaped metal anchor bars. In addition to using ceramics of the type described, the invention contemplates using other ceramic materials as long as they are thermally resistant to contact with molten metal.
After the cavity has been filled the plastic refractory composition is thermally treated to bond the refractory into a unified shape. Molds thus treated have been put back into service and have exhibited a useful life which in many instances is far in excess of that achieved by the use of new cast iron stools.
PREPARATION OF NEW STOOLS
It becomes apparent that the techniques thus described for repairing eroding stools may be adapted to the preparation of new stools. When it is desired to produce new stools, a cast iron stool is produced which has formed in its top a suitable cavity. Into the cavity is affixed the irregularly-shaped metal anchor bars and the plastic refractory composition is then placed into the cavity. If suitable casting facilities are available the preformed cavity may have incorporated therewith the irregularly-shaped metal anchor bars by means of the initial casting process rather than the use of a subsequent anchoring procedure.
EVALUATION OF THE INVENTION
An eroded stool cavity had placed therein four Z-bars having the following dimensions: 21/2 × 3 × 21/2 inches. They were positioned as shown in FIG. I of the drawing, then packing therein the specific ramming mix described herein. This composition was heat cured with a gas torch. The stool was placed in service and lasted for over 15 campaigns of steel pouring.
All metal ingots are cast from molds. One popular type is a "big end down" mold. These molds rest on bases commonly known as "stools." The stools are merely large, normally rectangular, flat slabs of metal, commonly made of cast iron, which are used as support for the mold sides and also, of course, form the bottom portion of the mold. The mold sides generally taper up in diameter from bottom to top. Another type of mold is known as the "big end up" mold. These are ladle-like receivers for the molten metal, the bottom portion of which molds are integral, non-removable parts of the entire mold.
Various problems commonly occur in use of these molds and particularly with respect to the surface of their base portions. First, the unprotected metal surface quickly erodes and pits in the presence of molten metals which are cascaded upon their surface. Large gouges in the base portions are produced due to the force and high temperature developed by the flowing molten metal which contacts the surface of the stool. Since many molds are generally approximately 5-10 feet in height, the metal must be poured from a height at least equal to that distance and quite often is poured from even greater heights. A considerable pressure head is thereby developed. Thus, the hot molten metal easily gouges gaping depressions in the base members under such force and at a temperature of at least the liquefaction temperature of the molten metal. Moreover, the problem of creation of pits or gouges in the base portions of the molds, caused by the above factors is aggravated due to the fact that the molten metal, especially near the bottom of the mold, remains in its erosive hot liquid states for a considerable amount of time subsequent to pouring.
The molten metal upon solidification to an ingot thereby has a bottom form conforming to the undesirable eroded surface configuration of the stool or base member of the mold. Thus, a considerable amount of the ingot, when withdrawn from the mold and subsequently processed into slabs or blooms, is lost through a cropping of the irregularly formed end of the slab. This, of course, is highly undesirable, since it results in undue loss of usable metal and increase in scrap, which must be subsequently reprocessed.
Another extremely serious and costly problem results after the ingot in the mold has solidified to a point where it can be removed from both the mold sides and its base platform member or stool. In many cases, if the surface of the stool is unprotected, or inadequately protected, and erosion occurs as described above, the ingot has a greater tendency to remain tightly adherent to the stool. Thus, after the mold sides are removed from around the ingot, which process can normally be efficiently achieved with a minimal film of coating selected from a variety of coating agents, the ingot must be forcibly removed from the stool. This is normally achieved by raising both ingot and adherent stool, and thrusting them against some other larger object whereby the ingot is jarred loose. In many cases the stool and ingot are merely dropped on the floor from some suitable height. In such a situation, the stool is often broken into two or more smaller pieces and cannot be subsequently reused in casting other ingots. Again, replacement cost of these stools is high, making this aspect of the overall casting process somewhat disadvantageous. The same problem exists with respect to big end up molds wherein sticking exists with respect to big end up molds wherein sticking of ingots particularly occurs at their base portion. New molds of this type are especially vulnerable to sticking due to their smooth surface unprotected by any layers of metal oxides or scale. A tight metal-to-metal bond between mold bottoms and ingots then occurs.
Cracking of molds and particularly their base portions due to the above discussed rough handling occasioned by "stickers" between the base portions and ingots is also enhanced by thermal shock during ingot formation. Unprotected or inadequately protected bottom surfaces of mold are especially susceptible to such destructive shock.
Many solutions to alleviating the above described problems in connection with the erosion of base members of ingot molds have been proposed by the prior art. A number of refractory coatings have been suggested but these are not entirely satisfactory. An early solution to the erosion of ingot mold stools resided in the suggestion that refractory inserts could be placed into the bottom of the mold, which refractory would tend to minimize erosion. Ceramic inserts have not met with any degree of commercial success. Their main drawback is that in use the molten metal works its way into the space between the insert and mold itself due to capillary action and tends to force the ceramic insert from its cavity. When this occurs the ceramic insert is above the top surface of the stool and tends to become entrained into the ingot. This entrainment produces metallic inclusions in the ingot which necessitates the expensive operation known as "butt cropping."
If it were possible to produce improved base members of ingot molds or to repair eroded stools whereby improved life could be achieved a substantial advance to the art would be afforded.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to provide an improved method for repairing eroded base members of ingot molds.
Another object is to provide improved base members of ingot molds which are less subject to erosion than the problems associated therewith. Other objects will appear hereinafter.
THE DRAWINGS
FIG. I is a horizontal cross-sectional side view of an eroded mold which has been repaired by the method of the invention.
FIG. II is a top view of an eroded base member of an ingot mold.
FIG. III is a horizontal view of a cavity showing Z-shaped metal anchor bars fitted within the cavity.
With more specific reference to the drawings wherein like parts have like numbers, there is shown a base member of an ingot mold 10 of substantially rectangular dimension. This base member or stool is normally of large dimension and is constructed of cast iron. Typically such stools can have a thickness of 12 inches or more and a length of 4 to 6 feet. Badly eroded stools can be eroded to a diameter of as much as 3 feet and to a depth of as great as 10 inches. When such erosion occurs these stools are normally discarded as being unfit for service.
As shown to the best advantage in FIGs. I and II the stool 10 has a cavity 12 which is formed in the top of the stool 14.
The drawings show affixed to the side walls 16 of the cavity 12 two or more irregularly-shaped anchor bars 18, which are shown in the drawing in their preferred form as being of a Z-shaped configuration. The Z-bars shown in the drawing are anchored to the side walls 16 of the cavity 12 by means of threaded studs 20, which are shown in greater detail in FIG. III. A convenient method of anchoring irregularly-shaped Z-bars resides in the use of a cartridge actuated nail-driving impact tool, which allows for rapid anchoring of the Z-bars into the cavity.
While the metal anchor bars are shown to be in the shape of a Z, it will be understood that other irregularly-shaped configurations of a general serpentine nature may be used. Thus, cork screw shapes, L-shapes, V-shapes, and the like may be used.
It is preferred that in anchoring the irregularly-shaped anchor bars that the base portion thereof which contacts the cavity of the stool be in the same plane as the surface rather than being perpendicular. Expressed in other words, threaded studs wherein a pointed end is affixed into a base member is not desirable since the end of the stud forms a heat transmission foci which would cause a hot spot or burning effect when the top portion of such a stud were contacted with molten metal. As seen in the drawings the base portion of the Z-bar contacts the cavity wall, thereby providing a greater heat transfer surface to minimize localized hot spotting of the mold.
After the irregularly-shaped metal anchor bars 18 are positioned in the mold cavity, the cavity is then filled with a ceramic material which is designated by the numeral 22. This plastic refractory material should be heat resistant and curable to provide a dense ceramic surface which is capable of receiving teemed molten metal such as liquid steel.
SPECIFIC DESCRIPTION OF THE INVENTION
The invention has been described thus far with respect to the drawings and shows a method for repairing eroded base members of metal molds. Thus it is evident that the method of this invention for repairing eroded base members of metal ingot molds which have their top surfaces worn into a cavity comprises the steps of attaching into the cavity at least two irregularly-shaped metal anchor bars, filling the cavity with a thermally-resistant plastic refractory composition and heat-curing said plastic refractory composition.
As indicated, the irregularly-shaped metal anchor bars are preferably in the form of a Z. They may be positioned inside of the cavity in a variety of configurations. They should be sufficient in number to allow a good anchoring effect to be achieved between the surfaces of the cavity and the plastic refractory composition.
THE PLASTIC REFRACTORY COMPOSITIONS
The plastic refractory compositions that have given outstanding results in the practice of the invention are composed predominantly of alumina and may contain other ingredients such as inorganic phosphates, minor amounts of water, clay and the like. The compositions should contain at least 40 percent by weight of alumina and preferably 60 percent by weight. These so-called high alumina ramming mixes are discussed and described in U.S. Pat. No. 3,547,664, including certain of the references cited thereagainst. This patent and certain of its references are incorporated herein by reference. A preferred ramming mix of the type described in this patent has the following composition:
Tabular alumina (6 mesh) 60 Calcined alumina (-325 mesh) 28 Kyanite (48 mesh) 5 Kaolin clay 3 Phosphoric acid (85%) H 3 PO 4 4 Ceramic fiber 0.12 Water 4
Compositions of the above type are rammed by pneumatic means or the like into the mold cavity which has been previously fitted with the irregularly-shaped metal anchor bars. In addition to using ceramics of the type described, the invention contemplates using other ceramic materials as long as they are thermally resistant to contact with molten metal.
After the cavity has been filled the plastic refractory composition is thermally treated to bond the refractory into a unified shape. Molds thus treated have been put back into service and have exhibited a useful life which in many instances is far in excess of that achieved by the use of new cast iron stools.
PREPARATION OF NEW STOOLS
It becomes apparent that the techniques thus described for repairing eroding stools may be adapted to the preparation of new stools. When it is desired to produce new stools, a cast iron stool is produced which has formed in its top a suitable cavity. Into the cavity is affixed the irregularly-shaped metal anchor bars and the plastic refractory composition is then placed into the cavity. If suitable casting facilities are available the preformed cavity may have incorporated therewith the irregularly-shaped metal anchor bars by means of the initial casting process rather than the use of a subsequent anchoring procedure.
EVALUATION OF THE INVENTION
An eroded stool cavity had placed therein four Z-bars having the following dimensions: 21/2 × 3 × 21/2 inches. They were positioned as shown in FIG. I of the drawing, then packing therein the specific ramming mix described herein. This composition was heat cured with a gas torch. The stool was placed in service and lasted for over 15 campaigns of steel pouring.