US3915440A

US3915440A - Apparatus for controlling the cooling rate of metallic bodies

Info

Publication number: US3915440A
Application number: US443597A
Authority: US
Inventors: John T Watson; Raymond B Palmer
Original assignee: Airco Inc
Current assignee: Airco Inc
Priority date: 1974-02-19
Filing date: 1974-02-19
Publication date: 1975-10-28
Anticipated expiration: 1992-10-28

Abstract

An apparatus is disclosed for controlling the cooling rate of as-cast metallic bodies. The as-cast body is removed from a casting station and placed within the apparatus. The apparatus comprises a detachable insulated upper portion and an insulated base portion. The base portion contains a socket member for retaining cast bodies of various cross-sections in a vertical plane.

Description

United States Patent 1 1 Watson et al.

[ Oct. 28, 1975 1221 1 Filed:

[ 1 APPARATUS FOR CONTROLLING THE COOLING RATE OF METALLIC BODIES [75] Inventors: John T. Watson, Walnut Creek;

' Raymond B. Palmer, Berkeley, both of Calif.

[73] Assignee: Airco, lnc., Montvale, NJ.

Feb. 19, 1974 21 Appl, No.: 443,597

52 "U.S. C1. 266/2; 220/9 R; 220/10; 432/254 51 Im. cm c210 1/02 ['58] Field (if Search 220/9 R, 9 A, 10; 432/254,

I 432/256, 258; 266/2 R, 1 R, 5 C; 248/308, 310, 314, 346; 269/287, 270

[56] I References Cited UNITED STATES PATENTS 303,092 I I 8/1884 Wilkes 432/254 955,733 4/1910 Winter 220/9 R 9/1928 Green 432/254 2,043,456 6/1936 Watrous, Jr 266/2 R X 2,174,642 10/1939 Toll 266/5 R 2,310,991 2/1943 Pierce 266/2 R 2,775,441 12/1956 Campbell et al..... 266/2 R X 3,071,500 l/1963 Corbett et a1 266/5 C FOREIGN PATENTS OR APPLICATIONS 976,198 11/1964 United Kingdom 220/9 A Primary ExaminerRoy Lake Assistant Examiner-Paul A. Bell Attorney, Agent, or FirmLarry R. Cassett; Edmund W. Bopp; H. Hume Mathews [5 7] ABSTRACT An apparatus is disclosed for controlling the cooling rate of as-cast metallic bodies. The as-cast body is removed from a casting station and placed within the apparatus. The apparatus comprises a detachable insulated upper portion and an insulated base portion. The base portion contains a socket member for retaining cast bodies of various cross-sections in a vertical plane.

12 Claims, 9 Drawing Figures ullllbllllllllll Sheet 1 of 2 i fffilllllllllll 46 US. Patent 0a. 28, 1975 U.S. Patent 'Oct. 28, 1975 Sheet 2 of2 3,915,440

WV/A/M APPARATUS FOR CONTROLLING THE COOLING RATE OF METALLIC BODIES BACKGROUND OF THE INVENTION less steel slabs, blooms and ingots.

2. Description of Prior Art Heat removal, after casting large metallic bodies such as ingots, billets or slabs, is a conventional step practiced in metal founding. Before the development of continuous casting, an ingot represented the typical product of a refined melt. Following completion of the refining operation, in an appropriate refining furnace, a melt is poured from the furnace into a ladle. From the ladle the melt is teemed into a plurality; of ingot molds. The liquid metal is allowed to solidify and the solidified ingots are then stripped from the mold. In normal practice the ingots are thereafter placed into soaking pits and slowly heated to a uniform temperature throughout and then passed to a heavy primary rolling mill for conversion into slabs, blooms or billets. The amount of care exercised in controlling heat removal after casting and placing the ingots into soaking pits is not generally critical.

The development of continuous casting has eliminated the use of ingot molds, stripping facilities and soaking pits. The continuous cast product is essentially equivalent to the primary mill product.

In continuous casting, a refined melt is tapped into a ladle, passed into a pouring box or tundish and poured into a mold so that the required slab, bloom or billet section is solidified continuously in the mold, and in a series of sprays beneath it, as it is withdrawn downwards from the mold by means of withdrawal rolls. The product thus obtained is one that is directly converted from liquid steel into semi-finished rolled sections.

The most delicate operation in the continuous casting process is the cooling of the skin or thin shell that surrounds the descending mass. The control of solidification is indeed critical, faulty cooling in the mold will result in the bleeding or sticking of the strand. Aside from insuring a transition from the molten state to the solid state, that is from the ladle through the mold, heat removal during casting is the most critical factor affecting the quality of the continuous cast product.

There are three principal zones of heat removal; in the mold, secondary cooling zone and soaking zone.

In the mold sufficient heat is removed to form a thin shell which contains the remaining liquid steel.

The secondary cooling zone is where most of the total heat is removed from the partially solidified product. Under normal conditions the product is completely solidified upon exit from this zone. Precise control is required in this zone. High cooling rates from high spray water flow rates, result in large temperature gradients in the cast section. These in turn can cause high stresses, resulting in, internal cracks and/or brittle cast structures.

The soaking zone is located between the exit from the secondary cooling zone and the entry to the top of a pair of pinch rolls. Heat removal is very low in this zone.

The prevention of the formation of internal and external cracks in stainless steel slabs is a very important phase of the continuous casting process. The absence of transformation stresses is of considerable advantage in casting austenitic stainless steel and fully ferritic alloys. Cooling stresses do exist and can present very serious problems.

Cracks that can occur upon cooling can be grouped into external cracks, corner cracks and cracks on the wide slab face and internal cracks, sub-surface cracks, cracks perpendicular to the small faces and/or wide faces and diagonal cracks running on the interface of two solidification planes. The incidence of cracks can be minimized by varying or changing the configuration of the cast shape, i.e. round corners.

The formation of internal cracks in stainless steel slabs can be fully eliminated by setting the proper cooling conditions. These conditions are such that the temperature gradient between the center of the slab and the slab surface must not exceed a critical value. If this limit is exceeded the tensile stresses arising from the shrinkage of the slab will exceed the hot tensile properties of the steel and hot ruptures will develop.

In the case where the outer shell reaches a very low temperature rather rapidly, little further shrinkage will take place, in the meantime the very hot center will have to pass through the whole shrinkage process unaccompanied by the outer sections, and the stresses will cause internal rupturing or hot tears.

Cooling rate is also manifested in the metallurgical structure of the cast product. It is known that stainless steels show a great tendency for columnar crystallization. Structures generally consist of columnar grains which have grown from the perimeter inward. The length and size of these grains vary with the quality of the metal cast. Crack sensitivity is definitely increased by the cast grain size. The grain boundaries of the large columnar grains reduce the actual strength of the metal and any hot tears or internal cracks propagated will follow the boundaries of the columnar crystals.

In the cooling of continuously cast stainless steel product forms proper cooling conditions can be established after obtaining experience with various crosssection designs. If, however, the product is cast within a vacuum chamber, employing hot-topping capabilities, the heretofore described techniques available for controlling heat removal are no longer available. For instance, the cooling sprays which are utilized in the secondary cooling zones to obtain rapid and precise heat removal cannot be employed.

To obtain a satisfactory cooling rate for product continuously cast in a vacuum environment and prevent the formation of the hereinbefore described defects, the product was cooled in the following manner. After the cast product was removed from the casting station it was held in a vertical position for a sufficient length of time to make sure it was entirely solidified; the product was then horizontally placed in a bin-like structure and covered with granular insulating materials such as vermiculite or basalite. The product thereafter slowly cooled down to ambient temperature.

Athough this procedure of covering the cast product with an insulating material controlled heat removal, it presented several deficiencies. First of all, this procedure posed a health and safety hazard. vermiculite particles are tiny leafy scales of mica and tend to rise andfloat into the atmosphere thereby creating a dusty and dirty work environment. Visibility is decreased obstructing the observation of moving equipment normally found in a steel mill. The light, scaly particles can enter workers eyes or be inhaled, creating a health problem unless protective safety equipment is worn. An equipment maintenance problem also develops because equipment is contaminated by these fine, dusty particles. This procedure initially required the placement of the product to be cooled in a vertical position for a length of time to insure that solidification was complete. This meant that for a period of time, up to several hours, the cast product was cooling in air at a rate that could create internal thermal stresses.

Another drawback to this procedure of cooling was increased product handling with a resultant loss in production. After casting, the product had to be moved from the casting station to a location where it could cool vertically and then moved to a second location whereupon it was placed in a horizontal position for final cooling.

The present invention eliminates the health, safety and material handling problems of the prior art. Furthermore, the product is not exposed to atmospheric cooling after removal from the casting station.

After casting, the product is removed from the casting station and placed vertically into the apparatus of this invention. Slow and controlled cooling commences immediately after placement into the apparatus; and the disadvantages associated with handling tiny, fine, loose particles are also eliminated.

SUMMARY OF INVENTION In accordance with the teachings of the present invention, a tower is provided for controlling the cooling rate of metallic bodies. The tower consists of a detachable insulated upper portion and an insulated base portion. The upper portion contains a pair of concentric cylindrical wall members with an annular space defined therebetween. A pair of spaced covers is placed on top of this portion. Insulation is distributed into the annular space and the area between the spaced covers thereby providing an insulated detachable member.

The lower base portion contains a centrally disposed socket member for receiving vertically, metallic bodies. Insulation can also be provided in the space between the socket member and the outer wall. The socket member is designed in such a manner so as to accommodate metallic bodies of square, rectangular or round cross-sections.

To employ the apparatus of this invention the upper portion is detached from the base portion whereupon a cast product is placed into the base portion socket member. The insulated upper portion is then replaced and the product remains within the apparatus until a predetermined temperature is reached. Thermocouples can be provided at various locations within the apparatus in order to monitor the temperature of the product.

It is an object of this invention to provide an apparatus for controlling the cooling rate of continuously cast metallic bodies.

It is a further object of this invention to provide an apparatus for controlling the cooling rate of cast bodies of different cross-sections.

Still a further object of this invention is to provide an apparatus for cooling cast bodies that are free from internal defects.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of the apparatus of this invention showing the upper portion in place on the lower base position.

FIG. 2 is a vertical sectional view showing in detail the construction of the detachable upper portion of the apparatus of FIG. 1.

FIG. 2A is an enlarged sectional view showing in detail the peripheral construction of the top of the detach'able upper portion.

FIG. 3 is a sectional view of the lower base portion.

FIG. 4 is a perspective view partially cut-away, showing the placement of a cast slab within the base portion socket member, with guide means removed.

FIG. 5 is a sectional view of the upper portion taken along plane 5-5 of FIG. 2.

FIG. 6 is a sectional view of the base portion taken along plane 66 of FIG. 3 showing in detail the construction of the socket member.

FIG. 7 is a sectional view similar to FIG. 6 showing the socket member accommodating a rectangular cast product.

FIG. 8 is a sectional similar to FIG. 6 showing the socket member accommodating a round cast product.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1, controlled cooling tower 1 comprises a detachable upper portion 2 and a fixed lower stationary base portion 3.

Referring now to FIGS. 2, 2A, and 5, there is shown in detail the construction of upper portion 2. These views show that this portion comprises an outer cylindrical wall 4 and disposed within this wall in a generally concentric manner is inner cylindrical wall 6. Defined between

walls

4 and 6 is annular space 8. The size of this space is significant and will be described hereinafter in more detail.

Space 8 contains vertical connecting rods 10. These rods extend from top inner junction 12 of annular rim members 32 to an annular bottom plate 14. The latter has an inside diameter 15 which is equal to the inside diameter of the inner wall 6. The upper portion of each of rods 10 contains an angular bent section 16. The extremity 18 of this section terminates and may be fastened, as by welding, at top inner junction 12. Four flat steel plates 20, each containing a central bore (not shown), are disposed within annular space 8, at symmetrically spaced positions so that the rods 10 pass through their respective central bores and terminate at junction 12 as previously described. These plates function to maintain the annular space 8 between

concentric members

4 and 6 and also to stabilize the upper ends of rods 10. The lower ends of rods 10 are fastened to annular bottom plate 14 at 21 as by welding.

Sealing the upper end of inner wall 6 is a circular plate 22, the diameter of which is substantially equal to the inner wall diameter. Fastened, for example as by welding, to the top exterior surface of upper portion 2 are lifting lugs 24 containing passages (not shown) for engaging hooks to facilitate movement of the upper portion as will be described hereinafter in more detail.

A cover 26 seals the interior between the walls of the upper portion 2 including the annular space 8 and the shallow cylindrical space 27 between circular plate 22 and cover 26 above inner wall 6. Into the space 27 and the annular space 8 are placed insulating materials thereby establishing upper portion 2 as a sealed insulated unit.

Cover 26 is provided with a lifting lug 28 which contains a passage (not shown) for the engagement of a lifting hook to facilitate placement. Fastened to the cover plate bottom surface 30 are members 32 which aid in aligning the cover when it is placed onto upper portion 2 and serve to seal space 27 so that insulation cannot escape and contaminate the work area. Annular rim members 32 also improve the insulating qualities of the unit. After placing the cover 26 into position it is then fastened to members 32 by fasteners 35.

Referring to FIGS. 3, 4 and 6 there is shown in detail the construction of lower base portion 3. These views show that this portion comprises an outer cylindrical wall 34, a base support section 36, guide means 37 and a socket section 38. Fastened to the outer wall are aligning means 40. (see FIG. 4) These aligning means permit rapid placement of the upper portion 2 onto the stationary base portion 3.

The base support section 36 contains a pair of square plates 42 and 42'. These plates are slightly larger than the diameter of outer wall 34. A course of refractory bricks 44 are placed between said plates. The bricks serve to dissipate the heat emitted by slabs, ingots or blooms as they cool and cushion the impact of these sections when they are placed into the socket. Supporting this section are

support rails

46 and 46. (see FIG. 3) This construction can withstand the compressive and thermal stresses imposed by the cooling of large extremely hot metallic bodies.

Guide means 37 (FIGS. 3 and 8) permit easy and rapid entry of hot as-cast metallic bodies into socket section 38.

Placed within said cylindrical wall 34 is socket section 38. This member serves to support in a free standing vertical manner an as-cast product. (see FIG. 4) The socket member is so designed that it can accommodate products of rectangular, square or round crosssections.

As shown in FIG. 6 socket section 38 comprises two pair of opposed elements. A pair of

opposed channel members

48 and 48 are designed to receive rectangular slab sections and opposed angle members 50 and 50' are designed to receive square or round sections.

Channel members

48 and 48 comprise base portions 52 and 52 and welded perpendicular to said base portions are

side portions

54, 54', 56 and 56'. As indicated in FIGS. 6 and 7, the distance t between

portions

54 and 56 and 54 and 56' is slightly larger than the slab thicknesses that can be accommodated by said channel members. Furthermore the maximum slab width is defined by the distance I.

Spaced between said channel members are opposed angle members 50 and 50'. These members each comprise a pair of

plate sections

60 and 62 and 60' and 62. The adjacent edges of the respective plate sections are welded together, at right angles, at 64 and 64; and thereafter their remote edges are respectively Welded to channel

member side portions

54, 54, 56 and 56'. As shown in FIG. 8, the distance d is equal to the 'diameter of a round ingot or the size of a square section that can be accommodated between said angles.

Interposed between the socket section 38 and the cylindrical wall 34 are four symmetrically spaced, inwardly directed

stiffeners

66, 67, 68 and 69; as shown in FIG. 6, these stiffeners serve to maintain the socket section in a fixed spaced relationship within the cylindrical wall and to provide a platform for supporting upper portion 2.

Stiffeners

66, 67, 68 and 69 are fastened at their respective opposite ends to the wall 34 34, and to the socket 38 in any conventional manner, as by welding. Furthermore the aforesaid stiffeners now define

interior spaces

70, 71, 72 and 73. Insulation may be placed into these spaces thereby creating an insulated lower unit. To further cushion the impact of the placement of a cast section loose insulation 45 may be provided on the bottom of the socket section. (see FIG. 3

FIG. 4 shows a cast slab 74 placed into socket section 38 shortly after discharge from a casting station.

FIG. '7 shows a rectangular section 76 retained within socket section 38.

FIG. 8 shows a round section 78 retained within socket section 38.

Thermocouples, indicated by

numerals

29, 31 and 33, (see FIGS. 2 and 3) are used to monitor the temperature of the cast product as it cools down. These devices are situated in various locations on tower 1 in order to monitor the temperature of the entire body. As shown in FIG. 2

thermocouples

29 and 31 are interposed in a radial direction into the insulation in upper portion 2 and thereby provide temperature monitoring of the upper portion of a cast product such as slab 74 shown in FIG. 4. In a like manner, FIG. 3 shows that base portion 3 is provided with thermocouple 33 interposed radially into the insulation for monitoring the temperature of that portion of the cast product retained by the base.

An important feature in the construction of the apparatus of this invention is the annular space 8 provided between outer wall 4 and inner wall 6. This space significantly controls cooling rate. In order to prevent the formation of stresses in metallic bodies of a particular size and reduce the incidence of internal crack formation a cooling rate in excess of 25F per hour but less than the rate in still air should be employed. The size of space 8 can be varied depending upon the composition of the cast product. The cooling rates of nonferrous materials and other ferrous products are not the same; therefore different sized annular spaces can be used.

By placing insulation into annular space 8 and shallow cylindrical space 27 an entirely insulated unit can be constructed. Two types of insulation have been employed, viz. vermiculite and basalite.

Vermiculite is a hydrated mineral of the mica group and is generally of a platelet type crystalline structure. Basalite is a derivate of basalt, an igneous rock without olivine. Vermiculite has the unique property of expanding 6-20 times the volume of the unexpanded material when heated to about 2000F and for this reason is the preferred insulating material.

Cast metallic bodies that will employ the apparatus of this invention are generally obtained in the following manner.

Molten steel is poured into a water cooled copper mold having a moveable water cooled bottom. By carefully controlling the casting rate a skin of sufficient thickness, to maintain a molten central mass, is formed. As the skin starts to form themoveable bottom portion is gradually lowered. As previously discussed, heat removal during casting is the most critical factor affecting quality of the continuously cast product. The most effective cooling technique is high pressure water sprays. This technique cannot be used because casting is conducted under a hard vacuum. A hard vacuum is necessary because the top surface of the casting is hot topped. Hot topping is accomplished by keeping the top surface of the casting molten by directing electron beams onto the surface. Lowering the vacuum level or using water sprays would prevent this form of hot topping. By correlating pouring rate and the heat removal capacity of the mold a satisfactory skin formation can be achieved.

Since water cooling cannot be employed heat removal after casting is very critical because the cast product is substantially hotter than a conventionally continuously cast product. To achieve uniform heat removal and a metallurgically sound product the casting is placed into the apparatus of this invention.

SPECIFIC EXAMPLE :1. Pouring rate at continuous casting station is adjusted to about 4.5 tons per hour in order to cast an 18 X 40 inches slab of a ferritic stainless steel containing about 26% Cr into a water cooled copper mold.

b. Cast for about 145 minutes in order to obtain a slab 116 inches long and 21,700 lbs.

c. Hot top with electron beam bombardment on slab top surface for /:z to /1 hour.

d. Allow hot top to solidify and feed into body of slab.

e. Strip slab from copper mold. Elapsed time from start of cast to removal from casting station is approximately 3 4 hours.

f. Remove slab from casting area, transport to cooling area and lower slab into socket member. Slab temperature is about 1800F at top and about 800 900F at bottom.

g. Place insulated upper portion 2 onto base portion 3.

h. Monitor slab temperature to about 500F, remove upper portion 2 and allow slab to air cool to ambient temperature.

We claim:

1. Apparatus for controlling the cooling rate of cast metallic bodies comprising:

a detachable insulated upper chamber;

an insulated base portion which is adapted to receive said upper chamber; and

means disposed within said base portion for vertically supporting said metallic bodies, said means comprising: i

a pair of opposed channel means; and

a pair of opposed angle means disposed between said channel means.

2. Apparatus as recited in claim 1 wherein each of said opposed channel means further comprises:

a vertical base member and a pair of opposed vertical side members.

3. Apparatus as recited in claim 2 wherein the width and thickness of a metallic body of rectangular section that can be accommodated by said means for vertically supporting said metallic bodies are respectively defined by the distance between the two side members of each of said channel means, and the distance between the base members of opposite channel means;

and wherein the diameter ofa metallic body of round section that can be accommodated by said means for vertically supporting said metallic bodies is defined by the distance between opposite faces of said opposed angle means.

4. Apparatus as recited in claim 1 wherein said detachable upper chamber further comprises:

an outer cylindrical wall;

an inner cylindrical wall of lesser height than said outer wall forming an annular cylindrical space between said outer and inner walls;

a first cover means for said inner wall, said means being substantially equal in diameter to the diameter of said inner wall; and

a second cover means for said outer wall, said means being substantially equal in diameter to the diameter of said outer wall whereby an upper shallow cylindrical space is formed between said first cover means and said second cover means.

5. Apparatus as recited in claim 4 wherein mineral type insulation capable of expanding upon exposure to heat is placed into said annular cylindrical space formed between said inner and outer walls and said shallow cylindrical space formed between said cover means.

6. Apparatus as recited in claim 5 wherein said insulation is vermiculite.

7. Apparatus as recited in Claim 5 wherein said insulated space is of a specific predetermined cross-section so as to provide a predetermined cooling rate.

8. Apparatus as recited in claim 7 wherein said insulated space provides a coolingrate less than exposure of said metallic body to still air but more than 25F per hour.

9. Apparatus as recited in claim 4 wherein said second cover means further comprises means fastened to the bottom surface of said cover means for aligning said cover means with said outer wall and sealing said upper shallow cylindrical space.

10. Apparatus as recited in claim 1 wherein said insulated base portion further comprises:

an outer cylindrical wall; aligning means fastened to the upper end of said outerwall for facilitating placement of said upper chamber onto said base portion; and base support means disposed at the lower end of said outer wall. 11. Apparatus as recited in claim 10 wherein said base support means further comprises:

an upper plate and a lower plate, said plates spaced a predetermined distance apart, the width of said plates being substantially equal to the diameter of said outer cylindrical wall; a course of refractory bricks placed into the space between said plates; and vertical support means fastened to the bottom surface of said lower plate. 12. Apparatus as recited in claim 1 wherein said means disposed within said base portion can accommodate rectangular and circular cross-sections.

Claims

1. Apparatus for controlling the cooling rate of cast metallic bodies comprising: a detachable insulated upper chamber; an insulated base portion which is adapted to receive said upper chamber; and means disposed within said base portion for vertically supporting said metallic bodies, said means comprising: a pair of opposed channel means; and a pair of opposed angle means disposed between said channel means.

2. Apparatus as recited in claim 1 wherein each of said opposed channel means further comprises: a vertical base member and a pair of opposed vertical side members.

3. Apparatus as recited in claim 2 wherein the width and thickness of a metallic body of rectangular section that can be accommodated by said means for vertically supporting said metallic bodies are respectively defined by the distance between the two side members of each of said channel means, and the distance between the base members of opposite channel means; and wherein the diameter of a metallic body of round section that can be accommodated by said means for vertically supporting said metallic bodies is defined by the distance between opposite faces of said opposed angle means.

4. Apparatus as recited in claim 1 wherein said detachable upper chamber further comprises: an outer cylindrical wall; an inner cylindrical wall of lesser height than said outer wall forming an annular cylindrical space between said outer and inner walls; a first cover means for said inner wall, said means being substantially equal in diameter to the diameter of said inner wall; and a second cover means for said outer wall, said means being substantially equal in diameter to the diameter of said outer wall whereby an upper shallow cylindrical space is formed between said first cover means and said second cover means.

6. Apparatus as recited in claim 5 wherein said insulation is vermiculite.

8. Apparatus as recited in claim 7 wherein said insulated space provides a cooling rate less than exposure of said metallic body to still air but more than 25*F per hour.

10. Apparatus as recited in claim 1 wherein said insulated base portion further comprises: an outer cylindrical wall; aligning means fastened to the upper end of said outer wall for facilitating placement of said upper chamber onto said base portion; and base support means disposed at the lower end of said outer wall.

11. Apparatus as recited in claim 10 wherein said base support means further comprises: an upper plate and a lower plate, said plates spaced a predetermined distance apart, the width of said plates being substantially equal to the diameter of said outer cylindrical wall; a course of refractory bricks placed into the space between said plates; and vertical support means fastened to the bottom surface of said lower plate.

12. Apparatus as recited in claim 1 wherein said means disposed within said base portion can accommodate rectangular and circular cross-sections.