JPS60145262A - Method and device for minimizing formation of bubble during free falling of molten metal into mold, trough or other vessel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for controlling the melting of molten metal during its injection into a mold or similar container, or during the free fall of molten metal from a furnace to a gutter, or during the cascading fall of molten metal from a gutter to a gutter. TECHNICAL FIELD The present invention relates to a method of minimizing bubble formation on top surfaces of metals.

During injection or free fall of molten metal, such as zinc, a significant amount of metal foam forms on the top surface of the molten metal. This foam is usually skimmed off the molten metal surface by hand. This operation is laborious, requires operator access to the molten metal, and produces significant amounts of foam metal that must be recycled.

Experiments conducted by the inventor during pouring of molten zinc into a mold have shown that the formation of bubbles is due to the entrainment of air by the falling flow of the molten metal. Air is thus transported below the surface of the molten metal forming air bubbles within the molten metal. Due to oxidation, a thin but tough film of zinc oxide forms on the inner surface of the bubble. These bubbles rise to the surface, and when they appear on the surface, the outer surface of the bubbles is also oxidized, and large bubbles (about 1/2 in diameter)
It is observed that in the case of 1.5 inch) the upper film part of the bubble solidifies immediately, but the metal puddle below it remains liquid for several minutes longer.

Having found that the bubbles that form on the top surface of molten metal are due to the formation of a zinc oxide film on the surface of the bubbles, the inventors have determined whether to release the bubbles or prevent their formation. I researched several ways to bond by doing one or the other. As a result of such research, the inventors of the present invention have provided a method for maintaining molten metal in a substantially non-oxidizing atmosphere while it fills a mold or while it freely falls into a gutter or other container. , the falling flow causes enough oxygen to form an excessive amount of bubbles that have a strong oxide film and that, if suspended on the molten metal surface, would not collapse but rather produce undesirable bubbles on the surface. It has been found that bubble formation can be minimized by preventing entrainment into the molten metal.

Preferably, the non-oxidizing atmosphere is provided by an inert gas such as nitrogen. The non-oxidizing atmosphere can also contain small amounts of oxygen, for example up to 2%, without creating excessive amounts of bubbles.

The method disclosed above includes placing a cover on top of a molten metal container, an opening for passing the molten metal into the container, and means for introducing a non-oxidizing gas under the cover. This can be done by providing.

The present invention also provides a continuous slab casting machine consisting of closely spaced rows of open in-fit moldings mounted on an enveloping conveyor chain, with a hood over the casting machine at the filling table, This can also be done by introducing a non-oxidizing gas underneath. Seals are required at the inlet and outlet as well as the sides of the hood to prevent excessive loss of the non-oxidizing gas. The tool V, of course, requires a sealed opening through one of its walls for the introduction of molten metal.

Preferably, the method is carried out in a continuous caster with equipment that does not require the use of any seals. Such a device is disposed a predetermined distance above a number of containers or invite molds and has an opening therein;
The openings consist of cover plates for casting molten metal into each container as the containers pass under the opening.

the cover plate extends a predetermined distance before and after the opening and has a predetermined number of holes therein for supplying non-oxidizing gas through the cover plate; gradually develops a non-oxidizing atmosphere within the vessel as it approaches the opening in the cover plate, and maintains the atmosphere in the vessel as the nuclear vessel passes through the opening.

The inlet length of the cover plate before the mold fill opening is necessary to progressively develop the required non-oxidizing atmosphere, while the outlet length of the cover plate is necessary to maintain the required non-oxidizing atmosphere. is necessary. The inlet length is determined by the linear velocity of the conveyor, the volume of the container and the gap between the container and the cover, and the effect of these factors on the volume of purge gas required to achieve the desired atmosphere.

The outlet length is determined by the air resistance required to prevent backflow of air into the filled container.

Using a plate with a length equal to the width of the five molds (three before and two after the mold fill opening) with a conveyor line speed of 2 inches/second and a 56 bond ingot mold; 3 inch gap and 20,0
It has been found that oxygen levels of less than 0.5% can be achieved with gas flow rates of less than 0.05 CFH.

The invention is disclosed by way of example with reference to the drawings.

In FIG. 1, laboratory equipment t2 includes a bottom casting tundish (sump) 10.

This bottom pour tundish is used to supply molten zinc to the slab mold 12 through a cover 14 covering the top of the mold. The bottom of the tundish is provided with an opening in register with a corresponding opening in the cover 14 and sealed thereto by any suitable means, such as welding. The opening in the bottom of the tundish is closed by a plug valve 16, which can be opened when it is desired to inject molten metal into the mold. The cuffs are sealed to the mold by an O-ring 18. A metered nitrogen inlet 20 and exhaust valve 22 are provided through the cover to maintain a suitable non-oxidizing atmosphere at the top of the mold.

A preliminary experimental procedure was performed that included filling the tie dish with molten zinc and then opening the valve to fill the mold. A significant amount of bubbles formed on the top of the molten metal. The same procedure was repeated except that the covered mold was purged with nitrogen before opening the valve and filling the mold. Immediately after filling and before solidification, the mold cover was removed and the metal was allowed to spread in air and solidify. No bubbles were observed on the top surface of the molten metal.

A series of casting tests were conducted while varying the metal casting temperature and the oxygen concentration in the nitrogen. Normal zinc casting temperature range 440°
The effect of varying the metal casting temperature between 530°C and 530°C was observed. Purging was performed with a nitrogen atmosphere ranging from industrial purity to a concentration of 2% oxygen for 1 minute at a gas flow rate of 20 J/min. Oxygen concentrations varying from 0% to about 2% in nitrogen resulted in a bubble-free surface on the slab ingot. It has also been observed that temperature and oxygen effects interact as far as the generation of the receiving slab surface is concerned. The conditions that produce an acceptable surface on the Nurap Inuit are summarized below: (a) An atmosphere of industrial purity nitrogen at a temperature below 450°C. These conditions produce bright crystal surfaces that are visible through the sufficiently transparent oxide film.

At temperatures above 450°C, the color ranges from straw yellow to dark purple.
A phenomenon called coloration J was observed.

(b) about 2% at temperatures in the range 450-475°C.
oxygen concentration. These conditions produce a smooth scissor-shaped oxide film on the surface of the inbit.

The present invention also provides for a five-hepparade having a large number of molds mounted on an endless conveyor chain.
) can also be carried out in a continuous slab casting machine, such as a casting machine. For such machines, a non-oxidizing atmosphere can be provided by a hood surrounding the casting machine at the filling table. As the mold moves past the filling table, molten metal is fed from the furnace to a pouring ladle located inside the V and from the pouring ladle to the mold. A metered nitrogen inlet and exhaust valve is provided through the V to provide a non-oxidizing atmosphere within the hood. The nitrogen atmosphere within the hood must be maintained at a slightly positive pressure so that the environmental oxidizing atmosphere outside the hood cannot enter the hood through the mold inlet and outlet holes. However, cooling is required at the hood inlet and outlet to prevent excessive loss of nitrogen gas.

In FIG. 2, an open input monitor 3 rests on an endless conveyor chain 32 moving in the direction indicated by arrow A at a linear velocity of approximately 2 inches/second.
A closely spaced column of 0 is shown. All of the in situ molds have flat top surfaces. Fixed cover plate 3
4 are attached close to the upper surface of the molds but at intervals of a predetermined distance to cover a predetermined number of molds in front and behind a metal casting table attached to the top of the cover plate. The metal casting stand has a trough 3 used to feed molten metal into the ladle 40.
It is a conventional design consisting of a gutter 36 ending in 8. A ladle 40 is intermittently pivoted to continuously inject metal into each mold through pouring 5 lots 42 in the cover plate.6 A trap 44 is placed at the end of the trough to allow melting. Capture the dress (d) that may float on the surface of the metal.

As shown in FIG. 3, cover plate 34 is provided with a predetermined number of gas inlet holes 46 into which inert gas is supplied through front manifold 48 and main manifold 50. Inert gas is supplied through three gas inlet holes to the front mold entering under the plate to quickly purge the mold, and one to the remaining molds under the plate.
The oxygen level in the casting bed is gradually reduced by feeding through the rows of holes and kept below a predetermined value. An auxiliary manifold 52 is also provided to supply inert gas to the ladle container 54 and the seed container 56. A cover strip 58 is placed in the gap between the molds to prevent excessive leakage of gas through the gap.

As shown in FIG. 4, the width of the plate 34 is equal to the width of the casting W30. The inert gas enters the mold at gas hole 46;
It flows out through the gaps at the sides and ends of the cover plate. The width of the cover in relation to the carrier of the container as well as the width of the container are related to the air resistance required to prevent air from flowing back into the mold.

1. Maintaining a desired inert gas atmosphere below the water channel 42 by adjusting the length of the cover plate 34, the number and arrangement of gas discharge holes, the gas flow rate, and the gap between the mold and the cover plate. However, it has been found that this can be done without the need to use contact seals. To facilitate the study of gas inlet hole spacing, gap size, and inert gas (nitrogen) flow rate, an apparatus was designed in the laboratory to simulate a conventional casting machine. The number of gas introduction holes in the cover plate is determined so that a minimum of three gas holes and a maximum of four gas holes are always present on the passing mold. The length of the cover plate was such that five molds (three before and two after the water channel 22) were always located under the cover plate.

Tests were conducted by establishing a predetermined flow rate of nitrogen through the cover plate and then moving the mold across the cover plate at the same speed as a conventional caster conveyor (2 inches/second). Each mold was purged with salt water as it went under the cover crate. When the mold approached the water groove, a sample of the mold atmosphere was collected at the center of the mold by sucking up the sample with a pump and subjected to oxygen analysis.

Experiments were conducted to measure the oxygen concentration in the mold atmosphere (a) at varying mold and constant nitrogen flow rate with respect to cover gap size, and (b) at varying nitrogen flow rate and constant gap size. The results of these tests are shown in FIGS. 5 and 6. The front manifold flow rate in the test shown in Figure 5 was approximately 20,080 FH, and the main manifold flow rate was approximately 15
It was 005CFH.

In the test shown in Figure 6, the flow rate in the front manifold was set to approximately 2
0 O5CFH and the main manifold flow rate to 500-3
It was changed to 00080FH.

The results of the tests in FIG. 5 showed that the oxygen level increased very quickly for gap sizes larger than 0.25 inches. More importantly, this curve is 0.
It has been shown that oxygen levels below 0.5% can be achieved with economically reasonable gas consumption (~2000 SCFH) by using gaps up to 3 inches. The effect of varying nitrogen consumption with respect to the oxygen level in the mold atmosphere is shown in the sixth section.
Two different gap sizes are illustrated in the figures: 0.10 inch and 0.125 inch. These curves show that no gain is achieved by increasing the atmosphere usage above 20.005 CFH, and that it is very low (100 CFH).
05CFH) It is clear that acceptable oxygen levels are readily achieved with gas consumption.

The 0, 10 inch and 0.0 inches employed in these tests.
A gap height of 125 inches is a practical value that can be achieved and maintained in current casting machines. Tighter tolerances to aim for when designing future casting machines may be less than 0.1% oxygen with economical use.

Following the completion of the above pilot plant trial, the equipment shown in Figure 2 was installed at Canadian Electrolytic Zinc Limited, Barryfield, Quebec, Canada.
It has been demonstrated under plant production conditions that slabs containing no skimming (dross) can be produced by casting liquid zinc under a nitrogen atmosphere by installing it in a slab ingot casting machine at a company (IC Zi, NC Lim1ted). .

First, an atmospheric test was conducted with the casting machine in operation but without casting liquid metal. These tests showed that oxygen levels could be maintained within the range of 0.3-0.5% at the pour table and that no gains could be achieved by increasing the nitrogen flow rate above 20005 CFHu.

The liquid zinc was then started with a preheated flame on the gutter and ladle. First, nitrogen was added to the front manifold at 2505CFH.
and 1' to the main manifold of the cover plate at 5005CFH and then to the ladle vessel and vertical trough vessel at 2508CFH. The oxygen level maintained in the casting bed was within the range of 0.35-0.45%.

A major reduction in airborne bubbles on the cast slab was observed even before the start-up procedure was completed. The total absence of foam was achieved upon completion of sealing and purging of the ladle vessel and trough vessel.

The surface of the slab ingot appeared to be shiny and free of dross. 0.2 in laboratory tests
A clear oxide film identical to that obtained using oxygen levels in the range of 0.5% was observed on the slab.

Figures 7.8 and 9 illustrate improvements to reduce gas losses between molds and thus reduce gas flow requirements. In FIG. 7, the edges of the mold are thicker than those shown in FIG.
increases the resistance of gas flow at zero. In FIG. 8, the edges of the mold are designed so that gaps 62 are horizontal to prevent direct flow of gas from the holes in the cover. This design is approximately equivalent to the cover strip 58 of FIG. 2, but is more abrasion resistant and resistant to pull-off. FIG. 9 shows another method of reducing gas flow, which uses a seal 64 between the molds. It includes using. This variation is possible because the seal is non-rubbing.

Although the method of the present invention has been disclosed with respect to particular equipment, it is understood that the method can be carried out with other equipment, including various types of continuous casters, and that the method can be carried out using the disclosed apparatus in accordance with the present invention. It should be understood that it is not limited to implementing.

[Brief explanation of drawings]

FIG. 1 shows the equipment used to perform the fixed slab mold practice. FIG. 2 is an example of equipment used to pour molten metal into individual molds on a continuous in-pit molding machine. FIG. 6 is a diagram drawn along line 6-3 in FIG. FIG. 4 is a diagram drawn along the line A δ of 44 in FIG. 2. FIG. 5 is a graph illustrating the effect of varying gap size on the oxygen level trap in the mold atmosphere at a fixed nitrogen consumption. FIG. 6 is a graph illustrating the effect of varying oxygen consumption on the oxygen level in the mold atmosphere at two different gap sizes. Figures 7 and 8 illustrate improvements to the mold to reduce gas flow requirements. FIG. 9 shows another possible improvement that reduces gas flow but includes a frictionless seal. Agent Akira Asamura Continuation of page 1 0 Inventor George Deep Power/Toda Country Sex 9R 1M 2. Quebec, Pouin-Clair, Frince Lepere Avenue 104 Procedural Amendment (Method) April 1980, President of the Patent Office 1, Indication of the Case Patent Application No. 252500 of 1988 3, Relationship with the Amendment Person Case Patent Application Person 4, Agent 5, Date of amendment order March 27, 1980 8, Contents of amendment as attached.

Claims (1)

Claims: (1) To eliminate the need for skimming the formation of bubbles on the surface of molten metal that forms bubbles during the free fall of the molten metal into a mold, trough or other container. In a method of minimizing the molten metal, during its free fall, an excess of bubbles that have a tough oxide film and do not collapse when suspended on the molten metal surface, but rather create undesirable bubbles on the surface. said method characterized in that the atmosphere is maintained under a substantially non-oxidizing atmosphere so as to prevent sufficient oxygen from being entrained into said molten metal by said falling stream to form a quantity of oxygen. (2) The method according to claim (1), wherein the non-oxidizing atmosphere is an inert gas atmosphere. (3) Claim No. (2) in which the inert gas is nitrogen
. The method described in section. (4) The method according to claim (1), (2) or (3), wherein the non-oxidizing atmosphere contains a small amount of oxygen. (5) The method according to claim (1), (2) or (3), wherein the molten metal is zinc. (6) Apparatus for minimizing the formation of bubbles on the surface of molten metal that forms bubbles during the free fall of the molten metal into a mold, gutter, or other container, so as to eliminate the need for skimming. , the molten metal during its free fall,
The falling stream carries enough oxygen to form an excess of bubbles that have a tough oxide film and that do not collapse when floating on the molten metal surface, but rather produce undesirable bubbles on said surface. Apparatus as described above, characterized in that it includes means for maintaining a substantially non-oxidizing atmosphere to prevent entrainment into the molten metal. (7) The means for maintaining the molten metal under a non-oxidizing atmosphere is a cover closing the top of the container for the molten metal, the cover having an opening for the passage of the molten metal and a non-oxidizing gas. and means for introduction under the cover. f8) Endless Equipment used in continuous casting machines comprising a row of closely spaced open vessels mounted on a conveyor chain, in which means are provided for maintaining the molten metal under a non-oxidizing atmosphere. It is a hood,
The hood accommodates a plurality of containers and has an opening for introducing molten metal through one wall of the hood and a non-oxidizing gas below the hood to fill the containers. An apparatus according to claim (6), comprising means. (9) Placed on an endless conveyor chain,
a vessel used in a continuous casting machine comprising a row of closely spaced open vessels, wherein means for maintaining the molten metal under a non-oxidizing atmosphere are predetermined on a plurality of said vessels; a cover plate disposed at a distance therebetween and having an aperture for casting molten metal into each of the containers as the containers pass under the aperture; extend a predetermined distance forward and rearward of the opening, and the cover plate supplies non-oxidizing gas through the cover plate to prevent the container from approaching the opening in the cover plate. said cover plate having a predetermined number of holes for progressively developing a non-oxidizing atmosphere within said container and maintaining said atmosphere within said container as said container passes said opening; No. (6th
)Changing equipment. (1υ) The apparatus according to claim (9), wherein the atmosphere is an inert atmosphere.