WO2001004364A1

WO2001004364A1 - Device and method for treating molten metal with calcium

Info

Publication number: WO2001004364A1
Application number: PCT/US2000/040364
Authority: WO
Inventors: Patsie C. Campana, Jr.
Original assignee: P. C. Campana, Inc.
Priority date: 1999-07-12
Filing date: 2000-07-12
Publication date: 2001-01-18
Also published as: AU6954700A

Abstract

Calcium powder (14) is introduced into a molten metal bath by a multi-layered tubular device (10). The tubular device (10) has an inner tubular member (12) enclosing the calcium powder (14) and an outer tubular member (16) disposed about the surface of the inner tubular member (12) thereby defining a space (22) between the outer surface of the inner tubular member (12) and inner surface of the outer tubular member (16). The space (22) is filled with ha gas, an additive material, and mixtures thereof. A method for inserting calcium powder (14) into a molten metal bath using the device (10) is also disclosed.

Description

DEVICE AND METHOD FOR TREATING MOLTEN METAL WITH CALCIUM

Cross References to Related Applications

This application is based upon and claims priority from U.S Provisional Application Serial No. 60/143,346, filed July 12, 1999. This application is also based upon and claims priority from U.S. Provisional Application Serial No. 60/155,453, filed September 22, 1999.

Background of the Invention

In the production of steel, it is well known to add calcium to a hot molten ferrous bath as a refining agent for oxide inclusion flotation, oxide inclusion morphology modification, desulfurization, etc. Unfortunately, the low density (relative to steel), volatility, and reactivity of calcium severely complicates the task of providing a satisfactory process for its addition to molten material, such as in a ladle.

A variety of techniques have been employed for the addition of calcium to molten material in a steelmaking ladle. Simple bulk addition of calcium-containing particulate materials is unsatisfactory because these materials rapidly rise to the surface of the bath without spending a sufficient residence time within the melt. Efforts to increase residence time by pouring the particulate material directly into the tapping stream from the furnace give rise to excessive reaction of the calcium-containing materials and are complicated, expensive, and time-consuming procedures.

In an attempt to overcome the above-mentioned problems, calcium has also been added to melts in steelmaking ladles in the form of a calcium metal-containing wire (clad or unclad) continuously fed through the upper surface of the melt A major advantage of wire feeding is that large flows of gas are not needed, as in powder injection, to propel the calcium-containing material into the molten ferrous material. However, the high volatility of calcium hinders the attainment of an efficient utilization of the calcium added in surface wire feeding If the wire does not penetrate to a sufficient depth below the surface before the calcium in the wire desohdifies, a low residence time and poor utilization of the calcium results along with a non-uniform treatment of the melt It is particularly important that most or all of the input calcium remain unreacted until it descends below the depth at which the ferrostatic pressure is equal to the vapor pressure of calcium This goal is difficult to achieve, even when a clad calcium metal- containing wire is employed When calcium desohdifies at ferrostatic pressures lower than its vapor pressure, large calcium gas bubbles are formed that rise rapidly to the surface of the melt The result is an inefficient non-uniform treatment of the molten ferrous material and the generation of a large amount of turbulence at the surface of the melt

The present invention seeks to overcome the above problems found in currently known calcium additive systems

Summary of the Invention

The present invention is directed to an improved device and method for the addition of calcium to a hot molten metal system The device is a tubular device comprising an inner tubular member having calcium powder The tubular device also comprises an outer tubular member disposed about the inner tubular member having a predetermined space between the outer surface of the inner tubular member and the inner surface of the outer tubular member One or more gaseous materials are contained between the inner tubular member and the outer tubular member

In an alternative embodiment, the tubular device compπses an inner tubular member filled with calcium powder An outer tubular member is disposed about the inner tubular member The outer tubular member is radially spaced apart from the inner tubular member, preferably at a predetermined distance The space between the inner tubular member and outer tubular member is filled with an additive material Optionally, the space between the inner tubular member and the outer tubular member is additionally filled with one or more gases The present invention is also directed to a method for treating hot molten metal with calcium powder Particularly, the method is directed to inserting a tubular device comprising an inner tubular member filled with calcium powder and an outer tubular member disposed about the inner tubular member at a predetermined space from the inner tubular member, wherein the space comprises a gas, additive material, or mixture thereof, into a hot molten metal bath As the tubular device enters the hot molten metal bath, the gas additive material, or mixture thereof from the space is directed into the hot molten metal bath The device, containing the inner tubular member filled with calcium, is directed into the hot molten metal bath and the inner and outer tubular members and calcium powder melt and/or are released in the bath Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter It should however, be understood that the detailed description and specific examples while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art

Brief Description of the Drawings

FIG 1 is a cross-section of a preferred embodiment tubular device of the present invention, and

FIG 2 is a cross-section of an alternate preferred embodiment of the tubular device of the present invention

Detailed Description of the Preferred Embodiments

The present invention provides a novel device and method for providing hot molten metal with calcium powder Referring to FIG 1 the present invention is a tubular device 10 comprising a hollow inner tubular member 12 filled with calcium powder 14 and an outer tubular member 16 generally disposed about the inner tubular member 12 Preferably, the outer tubular member 16 is concentrically disposed about the inner tubular member 12 thereby defining an annular space 18 between the inner tubular member 12 and outer tubular member 16 The inner tubular member and outer tubular member can be formed from a variety of materials The choice of materials for forming the inner and outer tubular members is generally dictated by the particular application of the device and the type of molten metal(s) to receive the device Mateπals used in forming the inner tubular member and outer tubular member may be metallic or non-metallic Also, the inner tubular member and outer tubular member may be formed from the same or different materials

The outer tubular member has a diameter greater than the inner tubular member The larger diameter of the outer tubular member gives the tubular device greater rigidity and allows for better penetration through the slag line Preferably, the outer tubular member has an outer diameter of about 21 mm and the inner tubular member has an outer diameter of about 13 mm

The inner tubular member and outer tubular member of the tubular device can be formed to have a variety of cross-sectional shapes The inner tubular member and outer tubular member can have a circular cross-section or any geometric shape as desired Preferably, the inner tubular member and outer tubular member have the same cross-sectional shape Most preferably the inner and outer tubular members both have a circular cross-sectional shape The annular space 18 between the inner tubular member 12 and outer tubular member 16 can be filled with a gas, additive material, or mixture thereof Gases which may be contained within the space between the inner and outer tubular members include, but are not limited to inert gases, such as helium neon, argon, krypton, xenon, and radon Additionally, other gases, including nitrogen and air, may be used in the space Preferably, argon is disposed within the space 18

When the space between the inner and outer tubular members in accordance with a preferred method of the present invention, is filled with one or more gases, flow of the gas through the tubular device is initiated prior to during or subsequent to insertion of the device into a molten bath The gas flow can be produced by any desirable means Preferably the gas flow is produced by a conventional system that supplies a source of gas in the space at a desired pressure In an alternate embodiment, FIG 2 shows a tubular device 20 having an inner tubular member 12 filled with calcium powder 14 The inner and outer tubular members 12 and 16, and their arrangement and shapes, are preferably as previously described An outer tubular member 16 is disposed about the inner tubular member at a generally uniform radial distance or space 22 between the inner tubular member 12 and outer tubular member 16 The space 22 can be filled with additives or slag forming materials Additives or slag forming materials include but are not limited to calcium, aluminum silicon, vanadium, magnesium, sodium, and mixtures thereof This additive or slag forming material can be in elemental form or as an inorganic compound

In addition to filling the space 22 with an additive or slag forming material, the space can also be filled with a gas, such as a inert gas or other gases such as nitrogen and air In a preferred form, passageways are formed within the additive or slag forming material between the inner and outer tubular members for the passage of gas through the space filled with additive or slag forming material

The present invention tubular device may have one or more intermediate tubular members disposed between the outer tubular member and inner tubular member When one intermediate tubular member is disposed between the inner tubular member and outer tubular member, two annular spaces or regions are formed one space or region between the inner tubular member and intermediate tubular member and another space or region between the intermediate tubular member and outer tubular member Either or both of the two spaces are filled with gas, additive or slag material, or mixtures thereof The present invention tubular device is preferably formed by providing or forming an inner tubular member and filling its interior, i e the region between its inner walls, with calcium powder An outer tubular member is disposed, preferably concentrically disposed, about the inner tubular member, thereby creating a space or region between the inner tubular member and outer tubular member The space is filled with a gas, additive or slug forming material or mixture thereof, in order to insulate and reduce the rate of melting of the inner tubular member upon introduction into molten material The larger diameter of the outer tubular member disposed about the smaller inner tubular member gives the tubular device greater rigidity and thus allows better penetration through a slag line of a molten ferrous metal bath The double layer tubular device allows for better yields of calcium, and, if desired, additive or slug forming material being introduced into molten metals

The tubular device is utilized by inserting one end of a predetermined length thereof from a spool or coil into a molten ferrous metal bath The desired length of the tubular device depends upon the desired amount of calcium to be added Generally, the amount of calcium to be added is dictated by the amount or volume of the molten bath When the space between the inner and outer tubular members is filled with gas the gas is blown or directed through the tubular device into the hot molten bath to prevent upflow of the hot molten bath into the device The gas can be delivered to the device and blown or directed in the space or region between the inner and outer tubular members by any known method in the art

As the gas is blown through the space into the molten metal bath, the inner tubular member filled with calcium powder is delivered into the bath Preferably, the inner and outer tubular members and calcium powder melt and generally dissolve in the bath It will be appreciated that the present invention tubular device can be used to introduce a wide array of other additives besides, or in addition to, calcium Furthermore, it will be understood that the present invention can be used in conjunction with other molten metals besides ferrous based systems Additional details of typical additive introduction systems and molten metal processes are described in U S Patent Nos 4,481 ,032, 4,308,056, 4,200,456 and 4,154,604, all of which are hereby incorporated by reference

The invention has been described with reference to the preferred embodiment Obviously, modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description It is intended that the invention be construed as including all such alterations and modifications insofar as they come within the scope of the appended claims or the equivalence thereof

Claims

Having thus described the invention, it is claimed

1 A tubular device for introducing an additive to molten metal, the tubular device comprising an inner tubular member having an inner surface and an outer surface, the inner surface of the inner tubular member defining an interior cavity, the inner tubular member comprising an additive for addition to molten metal, the additive being disposed within the interior cavity, and an outer tubular member having an inner surface and an outer surface, the outer tubular member being disposed about the inner tubular member, thereby defining a space between the outer surface of the inner tubular member and the inner surface of the outer tubular member wherein a gas is disposed within the space

2 A tubular device according to claim 1 , wherein the gas is an inert gas selected from the group consisting of helium, neon, argon, krypton, xenon, radon, and mixtures thereof

3 A tubular device according to claim 2, wherein the gas is argon

4 A tubular device according to claim 1 , wherein the additive is calcium

5 A tubular device according to claim 1 , wherein the outer tubular member is concentrically disposed about the inner tubular member

6 A tubular device according to claim 1 , the tubular device further comprising an intermediate tubular member disposed between the outer surface of the inner tubular member and the inner surface of the outer tubular member

7 A tubular device for use in a molten ferrous metal bath comprising an inner tubular member containing calcium powder, an outer tubular member disposed about the inner tubular member and thereby defining a region between the inner tubular member and the outer tubular member, and additive material disposed within the region, for subsequent addition to a molten ferrous metal bath

8 A tubular device according to claim 7, the tubular device further comprising an inert gas selected from the group consisting of helium, neon, argon, krypton, xenon, radon, and mixtures thereof, disposed in the region defined between the inner tubular member and the outer tubular member

9 A tubular device according to claim 8, wherein the gas is argon gas

10 A tubular device according to claim 7, wherein the additive material is selected from the group consisting of calcium, aluminum, silicon, vanadium magnesium, sodium, and mixtures thereof

11 A tubular device according to claim 7, the tubular device further comprising at least one tubular member disposed between the inner tubular member and the outer tubular member

12 A method for treating molten metal with calcium, comprising the steps of providing a tubular device having an inner tubular member containing calcium and an outer tubular member disposed about the inner tubular member thereby defining a region between the outer wall of the inner tubular member and the inner wall of the outer tubular member, filling the region with at least one of a gas, an additive material, and a mixture thereof, and introducing the tubular device into a molten metal bath 13 A method according to claim 12, wherein the region contains a gas, the method further comprises flowing the gas through the region from the tubular device into the molten metal

14 A method according to claim 12 further comprising adding a predetermined length of the tubular device into the molten metal bath