JPH0259406B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved float for accurately sensing the liquid level at the surface of a molten metal. This float is especially suitable for vertical DC (direct mold) casting and vertical EM casting of metals such as aluminum, magnesium and their alloys.
Suitable for molten metal level control device for (electromagnetic) casting.

DC casting generally consists of introducing molten metal into the feed end of a water-cooled, open-ended tubular mold and removing the solidified or partially solidified metal from the discharge end of the mold. A coolant, usually water, is directed to the surface of the metal emerging from the discharge end of the mold, and most of the solidification is performed by this coolant. At the start of casting, when the molten metal is first introduced into the mold, the discharge end of the mold is closed by a downwardly movable bottom block, which supports the ingot or billet as it descends during casting. I'm starting to do that.

In EM casting, instead of the shape of the molten metal being controlled by a mold until it solidifies, the shape of the molten metal is controlled by pressure created by an electromagnetic field generated by an annular inductor surrounding the molten metal. is DC
It is very similar to casting. In EM casting, substantially all solidification is accomplished by applying a coolant to the surface of the metal at the discharge end of the inductor.

Whether the metal forming equipment is a mold or an electromagnetic field, controlling the liquid level within it is very important in vertical continuous casting. To precisely control the head of the molten metal, a float operatively connected to a level sensor such as a linear displacement transducer as described in U.S. Pat. No. 4,498,521, issued February 12, 1985 is used. It has been found to be most advantageous to use a device. In the method described in that patent, signals from a transducer are used to regulate the flow of molten metal into a mold or inductor, thereby controlling the level of the molten metal.

However, heretofore it has been difficult to accurately position the float due to the variability of the molten metal meniscus. For example, when a float is pushed down into molten metal, even if you remove the applied thrust and allow the float to rise by its natural buoyancy, it often does not return to the same exact position as before; When using a float to sense the molten metal level, it has been difficult to accurately control the molten metal level because it cannot return to the same position each time. This is particularly important when performing EM casting, since small changes in the molten metal head can result in appreciable changes in the dimensions of the ingot or billet being cast. Changes in the surface tension of the molten metal due to changes in temperature, composition, etc. further exacerbate this problem.

The present invention was developed with this background in mind.

The present invention relates to an improved molten metal float which, when positioned above the molten metal surface, always has the same relative position with respect to the molten metal surface.

According to the invention, said float has an upper part having a substantially flat lower surface adapted to float above the surface of the molten metal, and a stepped element comprising an element projecting into the body of the molten metal from the flat surface of the upper part of the float. It has a lower portion. Thus, if a float is used that has an upper part with a flat lower surface and a stepped lower part, the molten metal meniscus (which always presents a slightly convex surface) will, by its own viscosity, It will adhere only to the corner portion formed between the lower surface and the vertical surface of the stepped lower portion and only in one predictable direction. Therefore, the above-mentioned difficulty caused by the inability of the float to return to the same position each time is eliminated. The area of the flat surface of the upper part in contact with the melt should be at least 10% of the area of the float facing the surface of the melt. This "at least 10%" limitation is established in relation to both the float's deslagination capacity and the minimum surface area required to limit the depth of the float's submersion into the melt. If the area is 10
If it is less than %, the float will sink too deeply into the molten metal and will no longer be able to act as a sludge removal device and/or a liquid level sensor. For best results, ie to ensure that the float acts as an effective level sensor as well as a sludge remover, the area should be at least 25%. Said element projecting into the molten metal displaces a quantity of molten metal having a weight substantially equal to the total weight of the float and the force applied to the float by the float's attachments.

In a preferred embodiment, the float is used as a slag device to prevent oxides or dross from becoming mixed with the metal being cast. In this case, the float is entirely annular or ring-shaped, and the float removes oxides present on the surface when the molten metal is introduced into the inner part of the float, or which rise to the surface during casting. and become trapped. In this preferred embodiment, the element protruding into the molten metal prevents oxides or dross from escaping from the float during casting. For slag removal to be effective, the stepped lower portion should project at least 0.5 inches into the melt, preferably at least 1 inch. Although the shape of the element protruding into the melt is not critical, excessive protrusion, eg, three inches or more into the melt, is undesirable.

Next, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a perspective view, partially in section, of a preferred float 10 comprising an upper portion or collar 11 having a substantially planar lower surface 12 and a stepped lower portion or projecting element 13. ing. The volume of the projecting element 13 is equal to the volume of the molten metal that it displaces, so that the flat surface 12 of the collar 11 floats on the surface of the molten metal. The weight of metal displaced by the element 13 is equal to the weight of the float and the force exerted on it by the attachments to the float. The area of the flat surface 12 should be at least 10%, preferably at least 25%, of the total area of the float projecting downwardly relative to the melt surface.

FIG. 2 shows a preferred float 10 associated with an EM casting apparatus 20, which includes an inductor 2.
1. It consists of a water jacket 22 and a refractory down pipe 23, which is adapted to feed molten metal into the inside of the annular inductor 21. A bottom block 24 is also associated with the apparatus 20 and is positioned within the inductor at the start of casting to provide vertical support for the molten metal therein, and is electromagnetically guided relative to the molten metal. The pressure controls the lateral spread of the melt until it solidifies into its final shape. The inductor 21 is provided with a number of holes or conduits 25 through which water from the water jacket is applied to the ingot or billet emerging from the discharge end of the inductor. The float 10 is equipped with rods 26 and 27, which support the float during non-casting when no molten metal is present in the inductor 20. Preferably one of the rods 26 or 27 is connected to the float 10
is operatively connected to a linear displacement transducer (not shown) or equivalent device which generates a signal representative of the level 28 of the molten metal in which it is floating. The signal from the transducer can be used to control the flow of molten metal from a source such as a gutter through the refractory lined downspout 23. (See the aforementioned U.S. Pat. No. 4,498,521 for such use.) Figures 3 and 4 show a modified float design, in this example a collar 11 with a flat bottom and a protruding Element 13 differs from the embodiment shown in FIG.

Next, the effects of the present invention will be specifically explained with reference to FIG. For example, the conventional float F, which is cylindrical and has been used in aluminum casting, is sensitive to a molten metal meniscus that forms when the molten metal adheres to the float. That is, the cylindrical float F carefully placed on top of the molten metal is
As shown in Figure a, it is easy to form a molten metal meniscus and adhere to the float F below the buoyancy level. Once the float F is submerged into the molten metal by some mechanical or wave action, the meniscus readily changes its shape to that shown in FIG. 5b. In any case, in actual use of Float F, there is no way to predict the behavior of its meniscus, and as a result, accurate control of the molten metal level has been impossible.

On the other hand, if the configuration of the float 10 with a stepped lower portion is adopted in accordance with the present invention, the meniscus will always be slightly convex and will only be present at the corner portions 14 of the float 10, as shown in FIG. 5c. Moreover, it will adhere only in one predictable direction. Therefore, the drawback associated with conventional floats, such as the inability to accurately control the molten metal level, is eliminated.

The float is made of a material that has a specific gravity much lower than that of the molten metal and is sufficiently resistant to the molten metal and the surrounding harsh environment to provide a fairly long service life. Suitable materials of construction include lightweight refractories such as fibrous magnesium silicate, glass rock foam, spongy refractories, and the like. A preferred material is fibrous magnesium silicate, sold under the trademark Marinite®.

The present invention can be modified in various ways without departing from the scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional perspective view of a preferred float according to the invention; FIG. 2 is a sectional view of a float according to the invention installed in an electromagnetic casting machine; FIGS. A sectional view showing another embodiment; FIG. 5 is a sectional view illustrating the function and effect of the float according to the present invention. 10: float, 11: upper part, 12: flat lower surface, 13: protruding element, 21: inductor,
24: Bottom block.

Claims (1)

[Scope of Claims] 1. A molten metal float for sensing the liquid level of molten metal, comprising an upper portion having a substantially flat lower surface that floats above the surface of the molten metal, and an upper portion that is submerged below the liquid level of the molten metal. a stepped lower portion of the float submerged below the level of the molten metal; A float characterized in that the volume of the stepped lower portion is adapted to displace a volume of molten metal of a weight substantially equal to the weight of the float and the normal force applied to the float by an attachment to the float. 2. The float of claim 1, wherein the area of said flat surface is at least 25% of the area of said downwardly projected image. 3. The float according to claim 1, which is made of a light refractory material. 4. The float of claim 1, wherein the stepped lower portion is in the molten metal at least 12.7 mm (0.5 inch), but 76.2 mm (3 inches) from the flat surface of the upper portion.
A float that protrudes as shown below. 5. The float of claim 4, wherein the stepped lower portion projects at least 1 inch from the flat underside of the upper portion.