PROCESS OF CASTING AN INGOT AND STRIPPING MOLD VERY SHORTLY THEREAFTER
United States Patent 3672433
The disclosure relates to a process for the treatment of metal ingots in which ingot molds are intended to be stripped from ingots very shortly after filling and to a device for carrying out said process. A heat-insulating and/or exothermic lining is fixed prior to casting on the internal surface of the ingot mold in the vicinity of the upper portions thereof, in order that said lining should remain attached to the ingot at the time of stripping of the mold; the bottom portion of the lining is applied with zero clearance against the internal wall of the ingot mold along an impervious contact surface, whereas a narrow peripheral gap is formed above said mold impervious contact surface between the internal wall of the ingot mold and the lateral surface of the lining; said peripheral gap is further adapted to communicate on its top portion with the atmosphere and also to communicate with the space inside the lining through lateral openings, which permit filling of said peripheral gap with molten metal at the latest when the cast metal bath has reached its top level within the ingot mold.
US Patent References:
Ingot casting mold
Gombosh - October 1952 - 2612667
Method of producing sound ingots of fully killed steel in big-end-down molds
Shields - March 1956 - 2737696
Insulating cover
Urmetz - October 1958 - 2856657
Hot tops, feeders or sinking head boxes
Vallak - February 1959 - 2873492
/1262718.html
Walker - April 1918 - 1262718
Ingot casting mold
Gombosh - October 1952 - 2612667
Method of producing sound ingots of fully killed steel in big-end-down molds
Shields - March 1956 - 2737696
Insulating cover
Urmetz - October 1958 - 2856657
Hot tops, feeders or sinking head boxes
Vallak - February 1959 - 2873492
/1262718.html
Walker - April 1918 - 1262718
Application Number:
05/040187
Publication Date:
06/27/1972
Filing Date:
05/25/1970
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
249/106, 164/131
International Classes:
B22D7/10; B22D7/00; B22D29/00; B22D7/10
Field of Search:
249/106,197-201,204,202 164/53,33,120,131,123
Primary Examiner:
Baldwin, Robert D.
Claims:
I claim
1. A process for treating a metal ingot in a mold which is stripped from the ingot very shortly after casting metal into the mold to form the ingot, comprising securing to an upper portion of the internal surface of the mold a heat-insulating lining having a lower portion applied with zero clearance against said internal surface along a contact zone impervious to the cast metal and an upper portion spaced from said internal surface and having at least one lateral opening therethrough spaced a substantial distance above said contact zone thereby to establish communication between the space inside the lining and the space between the lining and said internal surface only at least one level substantially above said contact zone and with an upper portion of said space between said lining and said internal surface communicating with the atmosphere, casting molten metal into the ingot mold until the upper surface of the cast metal reaches a level above the level of said lateral opening but below the top of the lining whereby molten metal flows through said lateral opening and flows downwardly into the space between said lining and said interior surface thereby progressively to fill the last-named space while air and gases within the last-named space pass out to the atmosphere, and stripping said mold from the resulting ingot when the portions of cast metal which are in contact with said lining have solidified.
2. A process as claimed in claim 1, and applying to the upper surface of the cast metal an insulating powder prior to completion of the casting step.
3. A process as claimed in claim 1, and covering the upper surface of the cast metal in the mold before stripping the mold, and thereafter stripping the mold from the resulting ingot when the sides and bottom of the resulting ingot have solidifed but while the interior of the resulting ingot is still liquid.
1. A process for treating a metal ingot in a mold which is stripped from the ingot very shortly after casting metal into the mold to form the ingot, comprising securing to an upper portion of the internal surface of the mold a heat-insulating lining having a lower portion applied with zero clearance against said internal surface along a contact zone impervious to the cast metal and an upper portion spaced from said internal surface and having at least one lateral opening therethrough spaced a substantial distance above said contact zone thereby to establish communication between the space inside the lining and the space between the lining and said internal surface only at least one level substantially above said contact zone and with an upper portion of said space between said lining and said internal surface communicating with the atmosphere, casting molten metal into the ingot mold until the upper surface of the cast metal reaches a level above the level of said lateral opening but below the top of the lining whereby molten metal flows through said lateral opening and flows downwardly into the space between said lining and said interior surface thereby progressively to fill the last-named space while air and gases within the last-named space pass out to the atmosphere, and stripping said mold from the resulting ingot when the portions of cast metal which are in contact with said lining have solidified.
2. A process as claimed in claim 1, and applying to the upper surface of the cast metal an insulating powder prior to completion of the casting step.
3. A process as claimed in claim 1, and covering the upper surface of the cast metal in the mold before stripping the mold, and thereafter stripping the mold from the resulting ingot when the sides and bottom of the resulting ingot have solidifed but while the interior of the resulting ingot is still liquid.
Description:
This invention relates to a process for the treatment of metal ingots in which ingot molds or casting molds of similar types are intended to be stripped from ingots without any stationary period, that is to say in which stripping is performed very shortly after filling of the molds. The invention is also concerned with a device for carrying out said process.
It is a known practice to make use of heat-insulating and/or exothermic lining which is placed prior to casting of a metal such as a ferrous metal on the internal surface of an ingot mold or casting mold and at the top of said surface or within the interior of a raised section or so-called hot top. Said lining remains bonded to the ingot or casting at the moment of stripping of the mold and is intended to maintain the top part of the cast metal bath in the liquid state during solidification for a sufficient period of time to ensure that the pipes or cavities formed in the ingot as a result of shrinkage of this latter are filled by the metal which has remained in the liquid state at the top portion of the mold.
It is also known to complete the action of the side lining mentioned above by means of a heat-insulating and/or exothermic powder referred-to as a covering powder which is spread over the surface of the molten metal bath during filling of the ingot mold or casting mold or immediately after the filling operation.
In the case of known processes, it is necessary after filling of ingot molds or other metal molds to hold these latter in a stationary position in the casting area until the metal contained therein has solidified to a sufficient extent to ensure that stripping and displacement of stripped ingots can take place without any attendant hazards. Such hazards are related to the quality of the ingot or casting and above all to the safety of persons who are in charge of operations involved in stripping and removal from the casting area and who are exposed to projections of metal which has not yet solidified.
In practice, in the case of ingots whose weight varies between 2 tons and 100 tons, the time during which said ingots remain stationary and which is a function of many factors is usually between 2 hours and 6 hours. Up to the present time, it has never proved possible to reduce this delay to a period of less than 1 hour in spite of precautionary measures taken during the casting operation. This has resulted in considerable capital expenditure, not only by reason of the "standing" of ingot molds (or, in other words, of keeping them in a stationary position) but also as a result of the heat which is dissipated during standing and which must be restored by means of heating furnaces such as ingot reheating furnaces, hereafter called pits.
This invention is intended to reduce standing times to a minimum as well as corresponding losses of heat while obtaining better behavior of ingots or castings during solidification of these latter.
In accordance with the invention, the process in which metal ingots are subjected to treatment in molds intended to be stripped from said ingots very shortly after filling and in which a heat-insulating and/or exothermic lining is fixed prior to casting on the internal surface of the ingot mold and/or the raised top section of said mold in the vicinity of the upper portions thereof in order that said lining should remain attached to the ingot at the time of stripping of the mold is essentially characterized by the fact that the bottom portion of the lining is applied with zero clearance against the internal wall of the ingot mold and/or the raised top section thereof along an impervious contact surface, that a narrow peripheral gap is formed above said impervious contact surface between the internal wall of the ingot mold and/or the raised top section thereof and the lateral surface of the lining and that said peripheral gap is adapted to communicate on its top portion with the atmosphere and also to communicate with the space formed internally of the lining through at least one lateral opening which is located above the impervious contact surface and permits filling of the peripheral gap with molten metal at the latest when the cast metal bath has reached its top level within the ingot mold and/or within the raised top section thereof.
After filling the peripheral gap, the molten metal solidifies very rapidly in contact with the internal wall of the ingot mold and/or top section in order to form around the lining a band which ensures lateral protection of said lining at the moment of stripping and during the following operations.
In a preferred form of execution of the process according to the invention, a heat-insulating and/or exothermic covering powder is spread over the surface of the cast metal bath during filling of the ingot mold and/or top section and at the latest when the cast metal bath has reached the top level thereof, the downward motion of the surface of the cast metal bath being accompanied by said covering powder progressively as the shrinkage of the ingot mold and the filling of the peripheral gap take place so that both processes are facilitated.
In an advantageous embodiment of said process, a cover is placed on top of the cast metal bath and is bonded to the metal as solidification takes place progressively in the zone adjacent to the lining, stripping and transporting of the ingot away from the location provided for casting in ingot molds being carried out as soon as the still-unsolidified central portion of the ingot is completely isolated from the exterior, especially under the protective action of the cover and of the metal which has solidified within the peripheral gap after filling of said gap.
The combination of means consisting in protecting the top portion of the ingot or casting by surrounding said casting both with a peripheral band of metal and with a cover which is securely attached to the ingot therefore provides a complete solution to the problem which consists in substantially avoiding any standing of ingots after filling of the molds without entailing any danger of projections of liquid metal during displacement of the ingots.
In accordance with this invention, the device for carrying out the process hereinabove defined is characterized by the fact that the external surface of the heat-insulating and/or exothermic lining comprises a bottom portion which permits of impervious contact with the ingot mold and/or the raised top section thereof, said bottom portion being followed by a slightly narrowed portion having at least one opening for establishing a communication between the peripheral gap and the interior of the ingot mold.
In an advantageous embodiment of the device, the cover is prefabricated and comprises means such as anchoring rods for ensuring attachment to the metal during solidification.
In a preferred embodiment, the cover is formed within the ingot mold itself and in contact with the cast metal bath by means of a product which is spread over the surface of said bath.
Further properties of the invention will become apparent from the description given hereinafter, reference being made to the accompanying drawings which are given by way of non-limitative example and show a number of different forms of execution of the invention, and in which :
FIG. 1 is a view in elevation and in cross-section taken along line I--I of FIG. 2 and showing a first form of construction of the lining which is placed in the top portion of an ingot mold ;
FIG. 2 is a corresponding plan view taken in cross-section along line II--II of FIG. 1 ;
FIG. 3 is a partial view derived from FIG. 1 but drawn on a larger scale after addition of a prefabricated cover to the lining ;
FIG. 4 is a view which is similar to FIG. 1 and shown after a cover which is formed in contact with the molten metal bath has been added to the lining ;
FIG. 5 is a view in elevation and in cross-section taken along line V--V of FIG. 6 and showing a second form of construction of the lining ;
FIG. 6 is a corresponding plan view taken in cross-section along line VI--VI of FIG. 5 ;
FIG. 7 is a view in elevation and in cross-section taken along line VII--VII of FIG. 8 and showing a third form of construction of the lining ;
FIG. 8 is a corresponding plan view.
Referring now to FIGS. 1 and 2 of the accompanying drawings, there is shown an ingot mold A having a substantially square horizontal cross-section with rounded corners. A lining which is constructed in accordance with a first form of execution of the invention and designated by the general reference B is placed within the interior of the ingot mold. Said lining, the top end face 2 of which is located at a lower level than that of the top end face 1 of the ingot mold, is constituted by four plates which are symmetrical in pairs, namely the plates 4a and 4c on the one hand and the plates 4b and 4d on the other hand. These plates are in contact with each other along edges 5 and 5a, said edges being inclined symmetrically with respect to a vertical plane which passes through the longitudinal axis Y--Y of the ingot mold A ; in addition, the edges 5 and 5a are oblique with respect to the walls of the ingot mold. By virtue of this arrangement, the plates 4b and 4d behave with respect to the plates 4a and 4c in much the same manner as wedges, the downward displacement of which makes it possible to obtain a very tight fit of the lining within the interior of the ingot mold.
It should be pointed out that the ingot mold A as illustrated in the figures has an internal wall 3 whose generator-lines are parallel to the longitudinal axis Y--Y. In general, in order to facilitate stripping of the mold from the ingot, said generator-lines are inclined at an angle which is referred-to as a "draw-taper" and accordingly converge either towards the top or towards the bottom. But this arrangement does not have any incidence on the invention which is equally applicable to the case in which the generator-lines converge towards the top and to the case in which they converge towards the bottom. It is by reason of this lack of distinction that the ingot molds are shown in the figures without any draw-taper.
Consideration being now given to a vertical cross-section of the lining B, it is seen from FIG. 1 that said lining is provided from the bottom upwards with three zones, namely a bottom zone having an external wall 6 which is applied in intimate contact with the internal wall 3 of the ingot mold A and with zero clearance around its entire periphery ; a central zone whose external wall 7 is set back relative to the wall 6 so that a peripheral gap C is accordingly formed between said wall 7 and the internal wall 3 of the ingot mold ; a top zone whose external wall 8 is in contact with the internal wall 3 of the ingot mold only over a portion of its periphery, vents 10 being formed at intervals between the wall 8 and the wall 3. The vents 10 are four in number in the example shown in FIG. 2 and serve to connect the peripheral gap C to the atmosphere. In addition, the central zone of the lining is traversed by lateral openings 9 which provide a communication between the peripheral gap C and the space formed within the interior of the lining B ; said openings 9 are 12 in number in FIG. 2 and have the shape of outwardly inclined ducts, the lower portion of which is located in the external wall 7.
There is also shown in FIG. 1 the molten metal M with which the ingot mold is filled and on the free surface of which is placed a layer consisting of a heat-insulating and/or exothermic covering powder P, the function of which will be explained below.
In FIG. 3, there is also shown a sheet metal cover 13 which is placed over the molten metal M and the covering powder P and is fitted with four anchoring rods, only two rods having been shown in this figure, namely the rods 14 and 14a ; said rods are intended to penetrate into the molten metal M at an oblique angle.
The process which makes use of the device as hereinabove described takes place as follows :
1. Prior to casting, the assembly which consists of the four plates 4a, 4b, 4c, 4d and forms the lining B is placed on the internal wall 3 of the ingot mold A so that the top end face 2 of said lining is located slightly below the top end face 1 of the ingot mold A. As has been explained earlier, the wedging action resulting from the inclination of the edges 5 and 5a along which the plates 4a, 4b, 4c, 4d are applied in contact with each other ensures on the one hand that the lining B is maintained at a fixed height within the ingot mold A and on the other hand that a contact with zero clearance is maintained between the external wall 6 of the bottom zone of the lining B and the internal wall 3 of the ingot mold A.
2. The molten metal M is then poured into the ingot mold A and this operation can be carried out at will either "downhill" (from the top of the ingot mold) or "uphill" (from the bottom of the mold). This pouring operation is continued until the free surface of the molten metal bath reaches the level designated by N--N on the left-hand side of FIGS. 1 and 3. This level N--N must be located below the top end face 2 of the lining and slightly above the lateral openings 9. The molten metal M penetrates through said lateral openings into the peripheral gap C and fills this latter progressively while driving out the air which is contained therein and which is discharged to the atmosphere through the vents 10 together with the gases which are given off by the molten metal.
3. While the metal M is being poured into the mold A and at the latest when the molten metal bath has reached its top level N--N, the covering powder P is spread over the surface of the metal bath. Said powder has the property of forming in contact with the metal bath a soft crust which closely follows the shrinkage profile of the surface of the bath. The shrinkage which is caused both by release of the gases contained in the molten metal M and by filling of the peripheral gap C with said metal results in the formation of a concave recess at the surface of the bath along the line shown at Na--Na on the right-hand side of FIGS. 1 and 3.
4. While a cavity is being formed at the surface of the cast metal bath, the molten metal M begins to solidify in that portion which is in contact with the lining B, namely firstly in the portion which fills the peripheral gap C and which forms a layer of small thickness between the ingot mold A and the lining B ; on the right-hand side of FIGS. 1 and 3, the solidified metal is represented by oblique hatchings whereas the metal which is still in the liquid state is represented by horizontal hatchings.
5. As soon as the cast metal bath has reached the level N--N and the covering powder P has been completely spread over the surface, the prefabricated cover 13 is placed in position as rapidly as possible. Said cover becomes attached at its periphery to the metal which is located in the vicinity of the lining B and which begins to solidify, with the result that the cover is rapidly bonded to the ingot. In order to make this bond even more secure, the cover can be fitted with anchoring means such as the rods 14 and 14a which are shown in FIG. 3 and are intended to penetrate to a substantial depth into that portion of the cast metal bath which first begins to solidify.
6. Once these operations have been carried out, the metal ingot M can be removed from the mold by the usual means without waiting for the central portion located in the vicinity of the longitudinal axis Y--Y to solidify up to the top. In fact, the metal which has remained in the liquid state is surrounded by the cover 13 after this latter has been securely fixed to the peripheral zone which has already solidified and by the lining B which is in turn securely maintained in contact with the ingot by means of the metallic band produced by the metal which has solidified from the outset within the peripheral gap C. It will then be possible to displace the ingot without entailing the need for any stationary period or standing time after casting and without any risk of consequent danger to operating personnel.
7. After removal from the mold, the ingot is conveyed to the pits in which the solidification process is completed under the most advantageous conditions of cost and quality by eliminating standing time and resultant heat losses. If this transfer to the ingot pits is not carried out immediately for any reason, the ingots can in any case be brought to an intermediate waiting station so that the casting pit or any other working site employed for filling ingot molds may thus be freed for the following operation.
FIG. 4 shows another method for covering the top of the cast metal bath in which a prefabricated cover is no longer employed but in which the cover is formed within the ingot mold itself and in contact with the cast metal bath by means of a product P 1 which is spread over the surface of the bath after the exothermic powder P. Said product P 1 is a covering powder and by virtue of the heat given off by the metal bath and by the exothermic powder P, said powder has the property of forming a hard crust which rapidly attains a sufficient degree of strength so that said crust itself constitutes a suitable cover for protecting the top portion of the ingot ; a natural or synthetic binder may be employed in the composition of said cover.
The product P 1 is shown on the left-hand side of FIG. 4 at the moment when said product has just been spread in the powdered state over the exothermic powder P. The right-hand portion of the same figure shows the product P 1 when this latter has solidified so as to form a cover above the cast metal bath. It can be noted from said right-hand portion :
1. That the cover formed by the product P 1 is in contact neither with the metal bath M nor with the exothermic powder P which is placed on said bath. In fact, as soon as the cover P 1 has acquired a sufficient degree of strength to be self-supporting, said cover no longer follows the shrinkage of the cast metal bath, the top surface of which moves away from said cover.
2. That the cover P 1 is not flat but has a slightly concave top surface by reason of the fact that shrinkage of the cast metal bath has already commenced at the moment at which solidification of said cover takes place.
3. That the cover P 1 is made integral with the band formed around the lining by the metal which has solidified within the peripheral gap C by virtue of the fact that the lateral openings 9 have been filled with the same metal prior to solidification of this latter.
It can also be observed from both portions of FIG. 4 that the lateral openings 9 are located at two different levels in the central zone of the lining. In this design which represents an alternative to FIG. 1, there is no necessary relationship with the difference in the cover structure between the embodiment of FIG. 1 and the embodiment of FIG. 4.
In FIGS. 5 and 6, there is shown a lining B 1 which is constructed according to a second form of execution of the invention. In this example, the top edge or end face 2 of the lining is located at a higher level than the top end face 1 of the ingot mold A, which makes it possible to fill said mold with the metal M up to the level of said end face 1. In addition, the plates 11a, 11b, 11c, 11d which constitute the four side walls of the lining are provided with shouldered portions 12a, 12b, 12c, 12d which bear on the top end face 1 of the ingot mold.
In this second form of execution, the plates are provided with lateral openings 9 and vents 10 as in the first form of construction. However, the lateral edges of said plates are not juxtaposed and are separated by four wedge-shaped members 16a, 16b, 16c, 16d which are in contact with the rounded corners of the ingot mold A and the downward displacement of which serves to form a tight joint between the internal wall 3 of the ingot mold and the external wall 6 of the bottom portion of the lining B 1 . The wedge-shaped members 16a, 16b, 16c, 16d are provided at mid-height in the same manner as the plates 11a, 11b, 11c, 11d with a central zone, the external wall of which is set back with respect to the wall of the bottom zone and is traversed by lateral openings 9 for the passage of liquid metal. The metallic band which is formed around the lining B 1 as a result of solidification of the metal within the peripheral gap C is therefore continuous as in the first form of execution of the invention.
FIGS. 7 and 8 show a lining B 2 which is constructed in accordance with a third form of execution of the invention. As in the previous case, the top end face 2 of the lining is located at a higher level than the top end face 1 of the ingot mold A. But in this example, the lining B 2 is in fact formed in one piece or at least the top portion of said lining has a wall in which there are no joints. By virtue of this arrangement, the liquid metal can be poured up to a level N 2 --N 2 which is higher than that of the top end face of the ingot mold. This permits a further increase in the quantity of metal which can be cast into the same ingot mold A as in the previous embodiment while the lining B 2 constitutes at the same time a hot top or raised top section of the ingot mold.
There can again be seen in the lining B 2 the same lateral openings 9 and the same vents 10 as in the linings B and B 1 . However, the top portion of the lining has a double wall, namely : an inner wall 17 which forms an upward extension of the central zone and an outer wall 18 in the form of a sleeve which is in contact with the internal wall 3 of the ingot mold A. The walls 17 and 18 are joined together at the level of the top end face of the lining by means of a ring-shaped connecting member 19 in which are formed the vents 10. The ring 19 can be made up of a number of elements which are joined to the walls 17 and 18 in known manner ; however, said ring can also be cast in one piece with said walls so as to form a single-unit assembly.
It is apparent that the invention is not limited to the embodiments herein described and that many alternative forms may accordingly be contemplated. However, the following main advantages are again met with in all cases :
1. A higher degree of safety of operating personnel.
2. Shorter periods of standing of ingot molds.
3. Economy of heating in pits.
4. Better quality of ingots : in fact, since the lining is jacketed with the solidified metal in the peripheral gap and the temperature of the pits is substantially lower than the melting temperature of the metal, the action of the exothermic covering powders can be continued until complete solidification of the ingot and there still remains a quantity of liquid metal for the purpose of filling the cavities of the ingot until the period during which this latter remains in the pits.
It is a known practice to make use of heat-insulating and/or exothermic lining which is placed prior to casting of a metal such as a ferrous metal on the internal surface of an ingot mold or casting mold and at the top of said surface or within the interior of a raised section or so-called hot top. Said lining remains bonded to the ingot or casting at the moment of stripping of the mold and is intended to maintain the top part of the cast metal bath in the liquid state during solidification for a sufficient period of time to ensure that the pipes or cavities formed in the ingot as a result of shrinkage of this latter are filled by the metal which has remained in the liquid state at the top portion of the mold.
It is also known to complete the action of the side lining mentioned above by means of a heat-insulating and/or exothermic powder referred-to as a covering powder which is spread over the surface of the molten metal bath during filling of the ingot mold or casting mold or immediately after the filling operation.
In the case of known processes, it is necessary after filling of ingot molds or other metal molds to hold these latter in a stationary position in the casting area until the metal contained therein has solidified to a sufficient extent to ensure that stripping and displacement of stripped ingots can take place without any attendant hazards. Such hazards are related to the quality of the ingot or casting and above all to the safety of persons who are in charge of operations involved in stripping and removal from the casting area and who are exposed to projections of metal which has not yet solidified.
In practice, in the case of ingots whose weight varies between 2 tons and 100 tons, the time during which said ingots remain stationary and which is a function of many factors is usually between 2 hours and 6 hours. Up to the present time, it has never proved possible to reduce this delay to a period of less than 1 hour in spite of precautionary measures taken during the casting operation. This has resulted in considerable capital expenditure, not only by reason of the "standing" of ingot molds (or, in other words, of keeping them in a stationary position) but also as a result of the heat which is dissipated during standing and which must be restored by means of heating furnaces such as ingot reheating furnaces, hereafter called pits.
This invention is intended to reduce standing times to a minimum as well as corresponding losses of heat while obtaining better behavior of ingots or castings during solidification of these latter.
In accordance with the invention, the process in which metal ingots are subjected to treatment in molds intended to be stripped from said ingots very shortly after filling and in which a heat-insulating and/or exothermic lining is fixed prior to casting on the internal surface of the ingot mold and/or the raised top section of said mold in the vicinity of the upper portions thereof in order that said lining should remain attached to the ingot at the time of stripping of the mold is essentially characterized by the fact that the bottom portion of the lining is applied with zero clearance against the internal wall of the ingot mold and/or the raised top section thereof along an impervious contact surface, that a narrow peripheral gap is formed above said impervious contact surface between the internal wall of the ingot mold and/or the raised top section thereof and the lateral surface of the lining and that said peripheral gap is adapted to communicate on its top portion with the atmosphere and also to communicate with the space formed internally of the lining through at least one lateral opening which is located above the impervious contact surface and permits filling of the peripheral gap with molten metal at the latest when the cast metal bath has reached its top level within the ingot mold and/or within the raised top section thereof.
After filling the peripheral gap, the molten metal solidifies very rapidly in contact with the internal wall of the ingot mold and/or top section in order to form around the lining a band which ensures lateral protection of said lining at the moment of stripping and during the following operations.
In a preferred form of execution of the process according to the invention, a heat-insulating and/or exothermic covering powder is spread over the surface of the cast metal bath during filling of the ingot mold and/or top section and at the latest when the cast metal bath has reached the top level thereof, the downward motion of the surface of the cast metal bath being accompanied by said covering powder progressively as the shrinkage of the ingot mold and the filling of the peripheral gap take place so that both processes are facilitated.
In an advantageous embodiment of said process, a cover is placed on top of the cast metal bath and is bonded to the metal as solidification takes place progressively in the zone adjacent to the lining, stripping and transporting of the ingot away from the location provided for casting in ingot molds being carried out as soon as the still-unsolidified central portion of the ingot is completely isolated from the exterior, especially under the protective action of the cover and of the metal which has solidified within the peripheral gap after filling of said gap.
The combination of means consisting in protecting the top portion of the ingot or casting by surrounding said casting both with a peripheral band of metal and with a cover which is securely attached to the ingot therefore provides a complete solution to the problem which consists in substantially avoiding any standing of ingots after filling of the molds without entailing any danger of projections of liquid metal during displacement of the ingots.
In accordance with this invention, the device for carrying out the process hereinabove defined is characterized by the fact that the external surface of the heat-insulating and/or exothermic lining comprises a bottom portion which permits of impervious contact with the ingot mold and/or the raised top section thereof, said bottom portion being followed by a slightly narrowed portion having at least one opening for establishing a communication between the peripheral gap and the interior of the ingot mold.
In an advantageous embodiment of the device, the cover is prefabricated and comprises means such as anchoring rods for ensuring attachment to the metal during solidification.
In a preferred embodiment, the cover is formed within the ingot mold itself and in contact with the cast metal bath by means of a product which is spread over the surface of said bath.
Further properties of the invention will become apparent from the description given hereinafter, reference being made to the accompanying drawings which are given by way of non-limitative example and show a number of different forms of execution of the invention, and in which :
FIG. 1 is a view in elevation and in cross-section taken along line I--I of FIG. 2 and showing a first form of construction of the lining which is placed in the top portion of an ingot mold ;
FIG. 2 is a corresponding plan view taken in cross-section along line II--II of FIG. 1 ;
FIG. 3 is a partial view derived from FIG. 1 but drawn on a larger scale after addition of a prefabricated cover to the lining ;
FIG. 4 is a view which is similar to FIG. 1 and shown after a cover which is formed in contact with the molten metal bath has been added to the lining ;
FIG. 5 is a view in elevation and in cross-section taken along line V--V of FIG. 6 and showing a second form of construction of the lining ;
FIG. 6 is a corresponding plan view taken in cross-section along line VI--VI of FIG. 5 ;
FIG. 7 is a view in elevation and in cross-section taken along line VII--VII of FIG. 8 and showing a third form of construction of the lining ;
FIG. 8 is a corresponding plan view.
Referring now to FIGS. 1 and 2 of the accompanying drawings, there is shown an ingot mold A having a substantially square horizontal cross-section with rounded corners. A lining which is constructed in accordance with a first form of execution of the invention and designated by the general reference B is placed within the interior of the ingot mold. Said lining, the top end face 2 of which is located at a lower level than that of the top end face 1 of the ingot mold, is constituted by four plates which are symmetrical in pairs, namely the plates 4a and 4c on the one hand and the plates 4b and 4d on the other hand. These plates are in contact with each other along edges 5 and 5a, said edges being inclined symmetrically with respect to a vertical plane which passes through the longitudinal axis Y--Y of the ingot mold A ; in addition, the edges 5 and 5a are oblique with respect to the walls of the ingot mold. By virtue of this arrangement, the plates 4b and 4d behave with respect to the plates 4a and 4c in much the same manner as wedges, the downward displacement of which makes it possible to obtain a very tight fit of the lining within the interior of the ingot mold.
It should be pointed out that the ingot mold A as illustrated in the figures has an internal wall 3 whose generator-lines are parallel to the longitudinal axis Y--Y. In general, in order to facilitate stripping of the mold from the ingot, said generator-lines are inclined at an angle which is referred-to as a "draw-taper" and accordingly converge either towards the top or towards the bottom. But this arrangement does not have any incidence on the invention which is equally applicable to the case in which the generator-lines converge towards the top and to the case in which they converge towards the bottom. It is by reason of this lack of distinction that the ingot molds are shown in the figures without any draw-taper.
Consideration being now given to a vertical cross-section of the lining B, it is seen from FIG. 1 that said lining is provided from the bottom upwards with three zones, namely a bottom zone having an external wall 6 which is applied in intimate contact with the internal wall 3 of the ingot mold A and with zero clearance around its entire periphery ; a central zone whose external wall 7 is set back relative to the wall 6 so that a peripheral gap C is accordingly formed between said wall 7 and the internal wall 3 of the ingot mold ; a top zone whose external wall 8 is in contact with the internal wall 3 of the ingot mold only over a portion of its periphery, vents 10 being formed at intervals between the wall 8 and the wall 3. The vents 10 are four in number in the example shown in FIG. 2 and serve to connect the peripheral gap C to the atmosphere. In addition, the central zone of the lining is traversed by lateral openings 9 which provide a communication between the peripheral gap C and the space formed within the interior of the lining B ; said openings 9 are 12 in number in FIG. 2 and have the shape of outwardly inclined ducts, the lower portion of which is located in the external wall 7.
There is also shown in FIG. 1 the molten metal M with which the ingot mold is filled and on the free surface of which is placed a layer consisting of a heat-insulating and/or exothermic covering powder P, the function of which will be explained below.
In FIG. 3, there is also shown a sheet metal cover 13 which is placed over the molten metal M and the covering powder P and is fitted with four anchoring rods, only two rods having been shown in this figure, namely the rods 14 and 14a ; said rods are intended to penetrate into the molten metal M at an oblique angle.
The process which makes use of the device as hereinabove described takes place as follows :
1. Prior to casting, the assembly which consists of the four plates 4a, 4b, 4c, 4d and forms the lining B is placed on the internal wall 3 of the ingot mold A so that the top end face 2 of said lining is located slightly below the top end face 1 of the ingot mold A. As has been explained earlier, the wedging action resulting from the inclination of the edges 5 and 5a along which the plates 4a, 4b, 4c, 4d are applied in contact with each other ensures on the one hand that the lining B is maintained at a fixed height within the ingot mold A and on the other hand that a contact with zero clearance is maintained between the external wall 6 of the bottom zone of the lining B and the internal wall 3 of the ingot mold A.
2. The molten metal M is then poured into the ingot mold A and this operation can be carried out at will either "downhill" (from the top of the ingot mold) or "uphill" (from the bottom of the mold). This pouring operation is continued until the free surface of the molten metal bath reaches the level designated by N--N on the left-hand side of FIGS. 1 and 3. This level N--N must be located below the top end face 2 of the lining and slightly above the lateral openings 9. The molten metal M penetrates through said lateral openings into the peripheral gap C and fills this latter progressively while driving out the air which is contained therein and which is discharged to the atmosphere through the vents 10 together with the gases which are given off by the molten metal.
3. While the metal M is being poured into the mold A and at the latest when the molten metal bath has reached its top level N--N, the covering powder P is spread over the surface of the metal bath. Said powder has the property of forming in contact with the metal bath a soft crust which closely follows the shrinkage profile of the surface of the bath. The shrinkage which is caused both by release of the gases contained in the molten metal M and by filling of the peripheral gap C with said metal results in the formation of a concave recess at the surface of the bath along the line shown at Na--Na on the right-hand side of FIGS. 1 and 3.
4. While a cavity is being formed at the surface of the cast metal bath, the molten metal M begins to solidify in that portion which is in contact with the lining B, namely firstly in the portion which fills the peripheral gap C and which forms a layer of small thickness between the ingot mold A and the lining B ; on the right-hand side of FIGS. 1 and 3, the solidified metal is represented by oblique hatchings whereas the metal which is still in the liquid state is represented by horizontal hatchings.
5. As soon as the cast metal bath has reached the level N--N and the covering powder P has been completely spread over the surface, the prefabricated cover 13 is placed in position as rapidly as possible. Said cover becomes attached at its periphery to the metal which is located in the vicinity of the lining B and which begins to solidify, with the result that the cover is rapidly bonded to the ingot. In order to make this bond even more secure, the cover can be fitted with anchoring means such as the rods 14 and 14a which are shown in FIG. 3 and are intended to penetrate to a substantial depth into that portion of the cast metal bath which first begins to solidify.
6. Once these operations have been carried out, the metal ingot M can be removed from the mold by the usual means without waiting for the central portion located in the vicinity of the longitudinal axis Y--Y to solidify up to the top. In fact, the metal which has remained in the liquid state is surrounded by the cover 13 after this latter has been securely fixed to the peripheral zone which has already solidified and by the lining B which is in turn securely maintained in contact with the ingot by means of the metallic band produced by the metal which has solidified from the outset within the peripheral gap C. It will then be possible to displace the ingot without entailing the need for any stationary period or standing time after casting and without any risk of consequent danger to operating personnel.
7. After removal from the mold, the ingot is conveyed to the pits in which the solidification process is completed under the most advantageous conditions of cost and quality by eliminating standing time and resultant heat losses. If this transfer to the ingot pits is not carried out immediately for any reason, the ingots can in any case be brought to an intermediate waiting station so that the casting pit or any other working site employed for filling ingot molds may thus be freed for the following operation.
FIG. 4 shows another method for covering the top of the cast metal bath in which a prefabricated cover is no longer employed but in which the cover is formed within the ingot mold itself and in contact with the cast metal bath by means of a product P 1 which is spread over the surface of the bath after the exothermic powder P. Said product P 1 is a covering powder and by virtue of the heat given off by the metal bath and by the exothermic powder P, said powder has the property of forming a hard crust which rapidly attains a sufficient degree of strength so that said crust itself constitutes a suitable cover for protecting the top portion of the ingot ; a natural or synthetic binder may be employed in the composition of said cover.
The product P 1 is shown on the left-hand side of FIG. 4 at the moment when said product has just been spread in the powdered state over the exothermic powder P. The right-hand portion of the same figure shows the product P 1 when this latter has solidified so as to form a cover above the cast metal bath. It can be noted from said right-hand portion :
1. That the cover formed by the product P 1 is in contact neither with the metal bath M nor with the exothermic powder P which is placed on said bath. In fact, as soon as the cover P 1 has acquired a sufficient degree of strength to be self-supporting, said cover no longer follows the shrinkage of the cast metal bath, the top surface of which moves away from said cover.
2. That the cover P 1 is not flat but has a slightly concave top surface by reason of the fact that shrinkage of the cast metal bath has already commenced at the moment at which solidification of said cover takes place.
3. That the cover P 1 is made integral with the band formed around the lining by the metal which has solidified within the peripheral gap C by virtue of the fact that the lateral openings 9 have been filled with the same metal prior to solidification of this latter.
It can also be observed from both portions of FIG. 4 that the lateral openings 9 are located at two different levels in the central zone of the lining. In this design which represents an alternative to FIG. 1, there is no necessary relationship with the difference in the cover structure between the embodiment of FIG. 1 and the embodiment of FIG. 4.
In FIGS. 5 and 6, there is shown a lining B 1 which is constructed according to a second form of execution of the invention. In this example, the top edge or end face 2 of the lining is located at a higher level than the top end face 1 of the ingot mold A, which makes it possible to fill said mold with the metal M up to the level of said end face 1. In addition, the plates 11a, 11b, 11c, 11d which constitute the four side walls of the lining are provided with shouldered portions 12a, 12b, 12c, 12d which bear on the top end face 1 of the ingot mold.
In this second form of execution, the plates are provided with lateral openings 9 and vents 10 as in the first form of construction. However, the lateral edges of said plates are not juxtaposed and are separated by four wedge-shaped members 16a, 16b, 16c, 16d which are in contact with the rounded corners of the ingot mold A and the downward displacement of which serves to form a tight joint between the internal wall 3 of the ingot mold and the external wall 6 of the bottom portion of the lining B 1 . The wedge-shaped members 16a, 16b, 16c, 16d are provided at mid-height in the same manner as the plates 11a, 11b, 11c, 11d with a central zone, the external wall of which is set back with respect to the wall of the bottom zone and is traversed by lateral openings 9 for the passage of liquid metal. The metallic band which is formed around the lining B 1 as a result of solidification of the metal within the peripheral gap C is therefore continuous as in the first form of execution of the invention.
FIGS. 7 and 8 show a lining B 2 which is constructed in accordance with a third form of execution of the invention. As in the previous case, the top end face 2 of the lining is located at a higher level than the top end face 1 of the ingot mold A. But in this example, the lining B 2 is in fact formed in one piece or at least the top portion of said lining has a wall in which there are no joints. By virtue of this arrangement, the liquid metal can be poured up to a level N 2 --N 2 which is higher than that of the top end face of the ingot mold. This permits a further increase in the quantity of metal which can be cast into the same ingot mold A as in the previous embodiment while the lining B 2 constitutes at the same time a hot top or raised top section of the ingot mold.
There can again be seen in the lining B 2 the same lateral openings 9 and the same vents 10 as in the linings B and B 1 . However, the top portion of the lining has a double wall, namely : an inner wall 17 which forms an upward extension of the central zone and an outer wall 18 in the form of a sleeve which is in contact with the internal wall 3 of the ingot mold A. The walls 17 and 18 are joined together at the level of the top end face of the lining by means of a ring-shaped connecting member 19 in which are formed the vents 10. The ring 19 can be made up of a number of elements which are joined to the walls 17 and 18 in known manner ; however, said ring can also be cast in one piece with said walls so as to form a single-unit assembly.
It is apparent that the invention is not limited to the embodiments herein described and that many alternative forms may accordingly be contemplated. However, the following main advantages are again met with in all cases :
1. A higher degree of safety of operating personnel.
2. Shorter periods of standing of ingot molds.
3. Economy of heating in pits.
4. Better quality of ingots : in fact, since the lining is jacketed with the solidified metal in the peripheral gap and the temperature of the pits is substantially lower than the melting temperature of the metal, the action of the exothermic covering powders can be continued until complete solidification of the ingot and there still remains a quantity of liquid metal for the purpose of filling the cavities of the ingot until the period during which this latter remains in the pits.