GB2067939A - Making ingots by centrifugal casting with bottom-pausing - Google Patents

Abstract

Molten metal is poured into a substantially cylindrical mould (21) from its bottom while the mould is being rotated about its vertical center axis I, to produce an ingot having a good surface and a uniform internal structure. The mould is supported on a spacing slab (24, 26) with a vertical pouring channel (33) communicating with a runner (28) provided in the spacing slab. A metal receiver (41) communicates with the top of the pouring channel (33), and the mould and spacing slab are supported on a rotatory table (13, 14). The metal receiver, which rotates with the mould, is arranged to receive molten metal continuously from a stationary ladle. Several suitable arrangements are disclosed. In some embodiments the pouring channel or channels is/are integral with a sidewall of the mould and the metal receiver is combined with a hot-top, as in Fig. 7 for example. <IMAGE>

Description

SPECIFICATION Method and apparatus for making ingots This invention relates to a method and apparatus for making castings called ingots, especially cylindrical ones.

It is well-known that there are two ways of casting molten metal top pouring and bottom pouring. Top pouring is a method that has been in use from olden times. One of the shortcomings of top pouring is that liquid metal flows out of a ladle at high speed because of the high static pressure in the ladle. But as it enters a mould, the metal strikes the stool at the bottom of the mould violently, scattering in the form of splashes. Part of the poured metal splashes adheres to the inner walls of the mould and causes deterioration of surface quality of the resulting ingot.Other parts of the stream of poured metal bounce off the inner walls of the mould and drop into the pool of liquid metal, but this repelled splashed metal becomes atmospherically oxidized so that the iron oxide at the surface of the splashes and the carbon in the molten metal react with each other to evolve gases which, in turn, form blowholes. To keep the liquid metal hot, a heat-retaining agent or the like is added into the mould. Such additives are often incorporated into the pouring stream, giving rise to slag inclusions and other similar defects. For these reasons, splash-preventing stools, cylinders or other devices are used, but none of them is completely satisfactory.

Bottom pouring is one of the methods in increasing use to overcome the disadvantages of top pouring. In bottom pouring, the flow energy of the stream of metal which enters the mould is reduced by the resistance offered by the fountain and runner which connect the ladle and the mould. The molten metal enters through an inlet at the bottom of the mould and rises very steadily and quietly in the mould, without causing splashing. The result is a good ingot surface.

There are also a variety of conventional methods of more specialised kind which are used to make clean ingots of uniform structure. Rotary ingot-making is one example. In this method, liquid metal is poured into a mould that is turned around on a rotating plate, the rotation being continued until the metal solidifies to a desired thickness. Accordingly, non-metallic inclusions of low specific gravity move toward the centre of the molten metal and float upwards so that they are more readily removed. With unwanted nonmetallic inclusions thus eliminated, ingots with good internal cleanliness result. But conventional rotary ingot making has been conducted on the top pouring principle (as disclosed in Japanese Patent Publication Nos. 11113 of 1961 and 39597 of 1971).When operating in this way, the surface of the molten metal in the rotating mould becomes parabolic, under the effect of centrifugal force, rising toward the mould walls and dipping in the centre. As a result, more violent splashing occurs than when a stationary top-poured mould is used, damaging the ingot quality to a greater extent. It has been suggested that a splash preventing cylinder should be inserted into the mould to prevent such vigorous splashing, but fully satisfactory results are not obtained when this expedient is adopted. We have devised a method and apparatus which can make ingots having a good cast surface with few surface defects and containing little non-metallic inclusions by rotary ingot-making on the bottom pouring principle.

According to this invention, a substantially cylindrical mould is placed on a rotatable base, with a spacing slab therebetween, so that the central axis of the mould is substantially aligned with the axis of rotation of the base. A pouring channel rotatable with the mould and spacing slab communicates, between at its upper end, a metal receiver which preferably coincides with the axis of rotation of the base and, at its lower, end a runner formed in the spacing slab. In this way molten metal may be supplied into the mould from the bottom as the mould is rotated.

This splash-free bottom pouring produces smooth-surfaced ingots with few surface defects.

Rotating the mould brings non-metallic inclusions and gases to the centre of the metal surface, which are then removed easily through the hot top surface of the metal. As a result, the molten metal solidifies to form a clean ingot with a uniform internal structure.

The metal receiver is shaped like a body of rotation formed by rotating a curve having an opening at the top in a vertical plane about the axis of rotation of the base. With this arrangement, the opening of the metal receiver remains in a single position to receive the liquid metal from the ladle or the like even when the metal receiver is rotating with the mould. This permits bottom pouring to be carried out continuously without interruption. The supply of liquid metal from the ladle to the mould can be accomplished without providing any special joint to the pouring channel, etc. So the apparatus can be of very simple structure.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows, in cross-section, a mould spacing slab, a vertical pouring channel or fountain, and part of a ladle which make up a conventional bottom-pouring ingot-making apparatus; Figure 2 is a vertical cross-section showing an ingot-making apparatus according to this invention; Figures 3a, 3b and 3c comprise three plan views of ingot-making apparatus according to this invention, showing arrangements with one, two and three fountains, respectively; Figure 4 is a vertical cross-section showing another embodiment of the metal receiver according to this invention, along with the mould and part of the fountain; Figure 5 is a cross-sectional view of an embodiment in which the fountain is provided in the mould wall;; Figure 6 comprises two plan views of moulds having the fountain in the wall thereof; Figure 6a shows a mould with one fountain, and Figure 6b shows a mould with three fountains; Figure 7 is a cross-section showing an assembly of a mould having an internal fountain, hot top, and metal receiver; the left half of the view is taken along the line AC of Figure 8 and the right half along the line BC; Figure 8 is a plan view similar to Figure 7; Figure 9 comprises four plan views showing part of a mould having an attached fountain; Figures 9a and 9b show embodiments in which the fountain is fitted in a dovetail groove formed in the mould, and Figures 9c and 9d show embodiments in which the fountain is bolted to the outside of the mould; Figure 10 is a cross-section showing an assembly of a fountain-attached mould, hot top, and metal receiver; the left half of the view is taken along the line DF of Figure 11 and the right half along the line EF; and Figure 11 is a plan view of the arrangement shown in Figure 10.

Figure 1 shows a conventional bottom-pouring ingot-making apparatus in popular use. A mould 1 is placed on a spacing slab 3 mounted on a working floor 2. The spacing slab 3 is formed with a runner 4, and a downwardly directed metal delivery tube or "fountain" 5 is communicatingly attached to the runner 4. At the top of the fountain 5 is provided a pouring funnel 6.

Before starting casting, the mould 1, stool 3 and fountain 5 are set up as illustrated. Molten metal M is poured from the nozzle 9 of a ladle 8 into the pouring funnel 6. The molten metal M then passes through the fountain 5 and runner 4, and enters the mould 1 from the bottom thereof.

When the molten metal M has solidified completely in the mould 1, the mould 1, stool 3 and fountain 5 are disassembled to strip the formed ingot out of the mould 1. But such a bottom-pouring practice has not permitted combination with a rotary ingot-making method because of the following difficulties: (1) Because the fountain 5 is stationary, a joint to connect with the rotating mould 1 must be provided somewhere along the way down to the mould bottom. But no satisfactory joint is available that is safe and leaks no molten metal in a system under the arduous conditions employed which involve high-speed rotation and high pressure; (2) If the joint were made integral, the fountain 5 too would rotate about the axis of rotation of the mould 1, making it impossible to pour the molten metal from the stationary ladle 8.Thus, bottompoured rotary ingot-making has hitherto been absolutely impracticable.

By the present invention bottom-poured rotary ingot-making is possible without having to provide a joint between rotating and non-rotating parts that has constituted the greatest difficulty of the conventional practice. It is a feature of this invention that such a joint is eliminated by combining the metal receiver, fountain and runner with the mould and spacing slab so that the whole assembly is rotatable in one piece. A further feature of this invention is that the metal receiver is located coincident with the axis of rotation of the mold.

Figure 2 shows an apparatus with which the ingot-making method of this invention is implemented.

A rotatory frame 13 is mounted on a support 11 , with a bearing 12 therebetween, so as to be rotatable about a vertical central axis. To the centre of a bottom plate 14 of the rotatory frame 1 3 is attached a rotating shaft 1 5 extending downward. The intermediate part of the rotating shaft 15 is supported by a bearing 16 held by the support 11, with a bevel gear 1 7 fastened to the lowesi end thereof. A reductior;-gear-attached motor 18 is provided under the support 11, and a bevel gear 19 adapted to mesh with said bevel gear 1 7 is fastened to the output shaft of the motor 18.

A mould 21 is substantially cylindrical in shape, and slightly tapered to facilitate ingot stripping.

The mould 21 is placed on the bottom plate 14 of the rotatory frame 13, with a spacing slab 23 therebetween, so that the central axis of the mould 21 is substantially aligned with the vertical rotational axis I. A hot top 31 is placed on top of the mould 21.

The spacing slab 23 consists of an upper board 24 and a lower board 26. The upper board 24 has a central inverted frustoconical outlet 25. The lower board 26 has a groove 27 that extends from near one edge to the centre thereof, opening upward at both ends. A runner 28 made of refractory brick is fitted in this groove 27. The upper board 24 and lower board 26 are placed, one above the other, on the bottom plate 14 of the rotatory frame 1 3 so that the outlet 25 and the exit end of the runner 28 are positioned on the vertical centre axis I. With the spacing slab 23 thus set up, the upper board 24 presses the runner 28 against the lower board 26.

A vertical fountain 33 is fastened with bolts 34 to the lower board 26 so as to communicate with the inlet end of the runner 28. The fountain 33 is lined with foundry sand or refractories. The intermediate part of the fountain 33 is supported by the rotating frame 1 3 by way ef a metal holder 35 so as to withstand high-speed rotation. Elbows 37 and 38 are fastened with bolts 39 to the top of the fountain 33. The elbow 37 extends horizontally over the mould 21 so that the inlet end thereof opens upwardly on the vertical centre axis I. A metal receiver 41 is attached to the inlet end of the elbow 38 with bolts 42.

In order to cast an ingot using the above apparatus the integral assembly of the mould 21 and other units is rotated at a predetermined speed (e.g., 30-100 rpm) by the motor 18 through the shaft 1 5. Then, molten metal is poured into the metal receiver 41 by opening a stopper (not shown) of a ladle.

The stream of liquid metal passes through the fountain 33 and runner 28, and then emerges into the bottom of the mould 21 through the outlet 25 in the upper board 24, to form a pool of metal of steadily increasing volume in the bottom of the mould. Because it is bottom-poured, the molten metal emerges quietly from the outlet 25, causing little splashing. Because of centrifugal force, the poured liquid metal is pushed against the wall of the mould 21 so that its surface defines a paraboloid of revolution. As a consequence, unwanted non-metallic inclusions and gases move to the centre of the mould 21, and then, as casting proceeds, move into the hot top 31. When the molten metal has filled the mould 21 and hot top 31, pouring is discontinued and the stopper is closed to complete pouring.Rotation is continued for an appropriate period after completion of pouring, and the mould 21 is then brought to a standstill to complete one cycle of the ingot casting operation.

In the above-described example, the mould reaches its full rotational speed before the start of the metal pouring. But it is possible to start metal pouring before the mould has reached its full speed and then to increase the rotational speed gradually. Or, the mould may initially be held at rest and then made to start rotation as a pool of liquid metal collects.

When the metal has completely solidified in the mould 21, the fountain 33 is detached from the spacing slab 23 after which the mould 21 , still holding the ingot, and the spacing slab 23 are taken out of the rotatory frame 13. Then, the ingot is stripped from the mould 21.

Figure 3 comprises three plan views showing the arrangement of the fountain. Figure 3a is similar to the embodiment shown in Figure 2, in which a single fountain 33 is provided.

If the need arises to control the casting rate as well as to withstand the vibration and maintain the balance of centrifugal force, both resulting from the high speed rotation, two or more fountains may be used. To provide adequate vibration resistance, use of two or three fountains, as shown in Figures 3b and 3c, is preferable. In Figure 3b, two fountains 51 are spaced at angular intervals of 1 80 degrees around the mould 21.

Each of them communicates with a metal receiver 53 through an elbow 52. In Figure 3c, three fountains 55 are spaced at angular intervals of 120 degrees around the mould 21, and each of them communicates with a metal receiver 57 through an elbow 56. Where a plurality of fountains is provided, they should be regularly spaced around the mould in order to minimize the resultant force and moment derived from the rotation-induced force of inertia.

In the above described embodiment, the metal receiver 41 was shaped like a funnel. But the metal receiver 41 may also be shaped like a doughnut, containing the axis of rotation, or any other suitable shape, so long as the poured liquid metal can be properly received. In other words, any shape is acceptable as long as the metal receiver has a top opening that, when the mould is rotated about its vertical centre axis I, is always so positioned as to receive the stream of molten metal poured from the ladle above. Figure 4 shows another embodiment of the metal receiver.

This metal receiver 61 consists of an annular trough 62 that is supported by two or three fountains 63 so as to be positioned over the mould 21. The metal receiver 61 is disposed so that the centre line thereof is substantially aligned with the vertical centre axis I. A nozzle 65 of the ladle is positioned over the metal receiver 62.

Therefore, the metal receiver 62 can always receive the liquid metal from the nozzle 65, even while being rotated about the vertical centre axis I.

The ingot-making method of this invention has the most beneficial effects on larger ingots rotated at higher speeds. There is no need to limit the fastening method and shape of the rotatory frame, provided that the fountain and metal receiver can well withstand the centrifugal force and vibration imposed thereon. The ingots manufactured according to the method of this invention exhibit the same smooth surface free from pitting and other surface defects as those cast by the stationary bottom-pouring method. The interior is satisfactorily clean, with a uniform structure typical of the rotary ingot-casting method. In a word, the resulting ingot proved sound and satisfactory, both inside and outside.As will be understood from the above, the ingot-making method of this invention is applicable to the manufacture of ordinary steel ingots, but it is of particular value for such ingots to be supplied to the rolls of a rolling-mill where high internal cleanliness and uniform fine-grained structure are required.

In the foregoing embodiments, the pouring channel takes the form of a fountain pipe provided away from the mould. In the following embodiments, the pouring channel is provided integrally within the mould. As shown in Figure 5, part of the wall 72 of a mould 71 is made thicker, and a vertical opening 74 is formed which passes through the thick-walled part 73. As will be described later, this vertical opening 74 is lined with refractory bricks 75, which are fixed in position by dry sand filled therearound, thus forming a pouring channel 76. This does away with the separate fountain and means for supporting and fixing it.

Figure 6 shows two moulds of the abovedescribed type in plan view. Figure 6a shows an embodiment having a single pouring channel 82 in the wail of the mould 81, while Figure 6b shows another embodiment having three pouring channels 84 in the wall of the mould 83, and disposed equi-angularly about the central axis.

From the viewpoint of dynamic balance, providing two or three pouring channels is preferable. To reduce the mould wall thickness variation and attain uniform cooling rate, the cross-sectional shape of the pouring channel 84 may be made elliptical or slot-like, as shown in Figure 6b.

The pouring channel 76 in the mould 71 and the runner 78 in the upper board 77 can be set without difficulty by adapting the mould bottom 79 to be fitted in the upper board projection 80 like a faucet joint, as shown in Figure 5. This permits a rough preliminary positioning, both sideways and circumferentially, after which exact alignment can easily be achieved irrespective of the number of the pouring channel 76.

Figures 7 and 8 show a mould having pouring channels in the wall thereof and a metal receiver assembly to supply liquid metal thereto. As shown, three vertical openings 87 are provided in the mould wall 86, spaced at angular intervals of 120 degrees. Into each of these openings 87, a number of cylindrical refractory bricks 88 are set to form a pouring channel 89. The space between the surface of the vertical opening 87 and the external surface of the refractory bricks 88 is filled with foundary sand 90, thereby securing the refractory bricks 88 in position in the vertical opening 87. A hot top 91 to be placed on top of a mould 85 has an annular frame 92 whose diameter is substantially equal to that of the top of the mould 85. The annular frame 92 has an inwardly projecting sand mould 93.The sand mould 93 has a surface lining of heat-insulating material 94 and a vertical opening 95, in which is fitted a cylindrical refractory brick 96. The hot top 91 is placed on top of the mould 85 so that the opening 97 of the refractory brick 96 communicates with the pouring channel 89 provided in the mould 85.

A metal receiver assembly 98 consisting of an annularframe 99, a metal receiver 101 and a communication channel 103, rests on the hot top 91. The annular frame 99 is placed on the annular frame 92 of the hot top 91 that has the same diameter. The metal receiver 101 is an annular trough made of refractory brick and is mounted on the same mould 93 together with the communication channel 103 which is lined with refractory brick and is positioned on the same mould 93 so as to connect the opening 97 in the hot top 91 with the lower part of the metal receiver 101. Foundry sand 104 fills the space between the annular frame 99 and metal receiver 101 and surrounds the communication channel 103.

The hot top 91 and the metal receiver assembly 98 are fastened on top of the mould 85 by means of a turn buckle 109 which engages the projections 106 and 107 on the mould 85 and annular frame 99. The mould 85, hot top 91 and metal receiver assembly 98 thus put together are placed on a rotating table (not shown), with a spacing slab (not shown) therebetween, as in the embodiment of Figure 2. Liquid metal supplied to the metal receiver 101 passes through the communication channel 103, the opening 97 in the hot top 91, the pouring channel 89 and the runner (not shown) into the mould 85.

Figure 9 shows other embodiments, in which the mould and fountain are assembled into one piece by fitting together the groove, projection and/or fastening face correspondingly formed thereon or by use of bolts and the like. In an embodiment shown in Figure 9a, a fountain 111 is fastened to a mould 11 3 by fitting a dovetail 112 on the fountain 111 tightly in a corresponding vertical dovetail groove 11 5 provided in the mould wall 114. In an embodiment shown in Figure 9b, a dovetail 11 8 on a fountain 11 7 has a projection 119, and a corresponding dovetail groove 122, having a recess to receive the projection 11 9 of the dovetail 118, is cut in the mould wall 121. The fountain 117 of this embodiment is more securely fastened to the mould 120 than the one in Figure 9a.The fountains of the foregoing two embodiments are fitted in the respective dovetail grooves in the following manner. The moulds 11 3 and 120 are placed on a flat table (not shown), and the fountains 111 and 11 7 are raised, and then lowered into the dovetail grooves 11 5 and 122 cut in the mould walls 1 and 121, respectively.

In an embodiment shown in Figure 9c, fastening faces 127 are formed on both mould 125 and fountain 126, which are fastened together with bolts 1 28 or by other means such as welding. In an embodiment shown in Figure 9d, a dovetail groove 131 is cut in the mould wall 130, in which a fountain 1 32 having a dovetail 133 is fitted. Then, the fountain 132 is fastened to a mould 129 with bolts 134.

Figures 10 and 11 show in detail an embodiment in which the fountain and mould are integrally formed by the above-described methods. As shown, three vertical grooves 143 are provided around a mould 141, spaced at angular intervals of 120 degrees. A fountain channel 145 is fitted into each groove 143, and fastened to the mould 141 with a bolt 146. As in the foregoing embodiment, cylindrical refractory bricks 147 are fitted in the fountain channel 145 to define the fountain. Foundry sand 148 fills the space between the fountain channel 145 and refractory bricks 147 to hold the bricks in place.

A hot top 151 to be placed on the mould 141 has an annular frame 1 52 whose diameter is substantially equal to that of the top of the mould 141. The hot top 151 has an inwardly projecting annular metal mould 1 54 whose vertical position.

is adjustable. The surface of the metal mould 1 54 is lined with a heat-insulating material 1 55. The annular frame 152 has a vertical opening 153, in which the top of the fountain 145 can be inserted.

The annular frame 1 52 and adjustable metal mould 154 are placed on the mould 141 with an annular spacer 1 56 therebetween. A metal receiver assembly 161, consisting of an annular frame 162, a metal receiver 167 and a communication channel 169, rests on the hot top 1 51. The annular frame 1 62 possesses a metal receiver support 1 64 that has three radially extending bridges 1 65 disposed at angular intervals of 120 degrees. One end of the three bridges 1 65 each is attached to the lower flange 1 63 of the annular frame 1 62, while the opposite ends thereof meet at the centre where a cylindrical support member 166 is provided. A cup-shaped metal receiver 1 67 of refractory brick is inserted in the support member 16.The communication channel 1 69 is of refractory brick and is mounted on the bridge 1 65 so that it connects the metal receiver 1 67 with the fountain 145. The inside of the annular frar..e 162 is filled with foundry sand 1 70 in order to fix the metal receiver 1 67 and communication channel 1 69 in position. The assembled hot top 151 and metal receiver assembly 1 61 are fastened to the mould 141 by means ofaturnbuckle 172.

The fountain can also be fastened to the mould by other methods, such as shrink fit. Any usual fastening method will do, so long as adequate stre ígth to withstand the great centrifugal force is obtainable. Likewise, there is no limitation as to the shape of the fastening parts provided that they are strong enough. Preferably, however, the corresponding part of the mould wall should be made thicker. In the foregoing embodiments, a groove is formed in the mould and a projection is formed on the fountain. The same result can be obtained from the reversed combination too; i.e., the projection on the mould and the groove in the fountain. Where the fountain is separate from the mould wall there is the advantage of less variation in the metal cooling rate than where the fountain is formed within the mould wall.But where a separate fountain is done away with and a vertical runner is formed within the mould wall, or where the fountain is fastened to the mould by fitting dovetail bolting or a combination of the two, there are the alternative advantages of easy fabrication, and tight, high-strength fastening which enables the entire mould to be rotated at high speed without fracturing. Compared with the conventional apparatus in which the fountain is separately held in the upright position, the radius of rotation is smaller, which removes the need for a large fountain supporter. The result is a reduction in apparatus size and weight. Also, dynamic balance can be controlled easily to reduce vibration.

Thus, this invention offers a great commercial advantage through a sharp reduction in mould assembling time resulting from the practical eiimination of fountain supporting means, saving of power consumption due to a decrease in apparatus weight, and stabilization of product quality because of vibration reduction.

Claims (8)

1. A method of making ingots which comprises placing a substantially cylindrical mould on a spacing slab, connecting a vertical pouring channel to a runner formed in the spacing slab, and supplying molten metal through the pouring channel and runner into the mould from the bottom thereof, the molten metal being introduced into the mould while the mould spacing slab and pouring channel are rotating through an entrance disposed substantially above the vertical central axis of the mould.

2. An apparatus for making ingots which comprises a substantially cylindrical mould, a spacing slab on which the mould is placed and provided with a runner through which molten metal can be introduced into the bottom of the mould, a vertical pouring channel connected to the runner in the spacing slab, and a metal receiver communicating with the top of the pouring channel, a rotary table on which the spacing slab is supported, the rotary table being rotatable about a vertical axis, for introducing molten metal into the vertical channel, said receiver having a top opening and being disposed with its centre substantially coincident with the vertical axis of rotation of the rotary table so that the molten metal can be poured into the receiver from a fixed outlet as the table rotates.

3. Apparatus according to Claim 2, wherein the metal receiver is funnel-shaped and is attached to a horizontal elbow connected to the top of the pouring channel.

4. Apparatus according to Claim 2, in which the metal receiver consists of an annular trough.

5. An ingot-making apparatus according to Claim 2 or 3, in which the pouring channel is within the wall of the mould.

6. Apparatus according to Claim 2 or 3, in which the pouring channel consists of a pipe that is attached to the external wall of the mould.

7. An ingot-making apparatus according to Claim 5 or 6, further comprising a hot top adapted to be mounted on the mould, the hot top having a vertical opening communicating with the pouring channel provided within or attached to the mould, and an assembly comprising an annular frame placed on the hot top, a metal receiver and a communication channel fitted in the annular frame so as to connect the metal receiver and the vertical opening.

8. Apparatus for making ingots substantially as hereinbefore described with reference to and as illustrated in Figure 2; or Figures 3a, 3b or 3c; or Figure 4; or Figure 5; or Figure 6a or Figure 6b, or Figures 7 and 8; or Figure 9; or Figures 10 and 11 of the accompanying drawings.