US3911993A

US3911993A - Method and apparatus for adding treating agents to molten metal

Info

Publication number: US3911993A
Application number: US487934A
Authority: US
Inventors: Maurice L Caudill; Steven C Cochran; Donald C Loebach
Original assignee: Caterpillar Tractor Co
Current assignee: Caterpillar Inc
Priority date: 1974-07-12
Filing date: 1974-07-12
Publication date: 1975-10-14
Anticipated expiration: 1992-10-14
Also published as: DE2531571B2; JPS5132432A; GB1504769A; DE2531571A1; FR2277900A1; FR2277900B1

Abstract

A method and apparatus for adding treating agents to molten metal in which the agent, in wire-form is fed through a passage provided in an internally cooled stopper rod, thereby introducing the treating agent directly into the nozzle and to a stream of molten metal as it is discharged therethrough. The method is particularly applicable for adding treating agents to steel for completely deoxidizing same with agents such as aluminum, titanium or zirconium. The stopper rod is adapted to seat into the entrance of the nozzle as a valve seat, with the stopper rod constructed in hollow form with a centrally disposed passage extending axially therethrough for feeding the wire completely through the stopper to the bottom of the ladle. The treating agent is protected from excessive heat by cooling it by means of a special stopper rod construction, in which means are provided for circulating cool air in surrounding relation to the treating agent within the stopper rod, and the rod itself is constructed of an insulating outer wall.

Description

United States Patent Caudill et al.

[ METHOD AND APPARATUS FOR ADDING TREATING AGENTS TO MOLTEN lVlETAL [75] Inventors: Maurice L. Caudill, Peoria, 111.;

Steven C. Cochran, Louisville, Ky.; Donald C. Loebach, East Peoria, Ill.

[73] Assignee: Caterpillar Tractor Company,

Peoria, Ill.

[22] Filed: July 12, 1974 [21] App]. No.: 487,934

United Kingdom 164/57 Primary ExaminerFrancis S. Husar Assistant Examiner-John E. Roethel Attorney, Agent, or Firm-Phillips, Moore, Weissenberger Lempio & Strabala Oct. 14, 1975 [57] ABSTRACT A method and apparatus for adding treating agents to molten metal in which the agent, in wire-form is fed through a passage provided in an internally cooled stopper rod, thereby introducing the treating agent directly into the nozzle and to a stream of molten metal as it is discharged therethrough. The method is particularly applicable for adding treating agents to steel for completely deoxidizing same with agents such as aluminum, titanium or zirconium. The stopper rod is adapted to seat into the entrance of the nozzle as a valve seat, with the stopper rod constructed in hollow form with a centrally disposed passage extending axially therethrough for feeding the wire completely through the stopper to the bottom of the ladle. The treating agent is protected from excessive heat by cooling it by means of a special stopper rod construction, in which means are provided for circulating cool air in surrounding relation 'to the treating agent within the stopper rod, and the rod itself is constructed of an insulating outer wall.

12 Claims, 3 briwing Figures I\ i9 67\ r U.S. Patent Oct. 14, 1975 7 1 METHOD AND APPARATUS FOR ADDING TREATING AGENTS TO MOLTEN METAL BACKGROUND OF THE INVENTION The present invention relates to amethod and apparatus for adding treating agents to molten metal, and more particularly to a method and apparatus for adding deoxidants to steel just prior to the casting thereof.

lt is well known that certain treating agents should be added to the molten metal to be cast soon prior to the casting thereof in order to prevent the advantageous characteristics of the additive from unduly fading prior to the set-up of the casting in the mold. This is particularly true when it is desired to make fully killed steel castings by the additions of deoxidants thereto. For instance, even though sufficient deoxiding agents may be added to fully deoxidize the steel in the ladle, unless the melt is protected from an inert atmosphere reoxidation will occur during the subsequent stirring, holding and pouring operations of the molten metal. It is therefore advantageous to add treating agents which have a time limited effectiveness as late in the pouring process as possible.

Heretofore it has frequently been necessary to add excess amounts of treating agents to compensate for the above described limitations. Not only has this practice been costly, but it should be remembered that the addition of any agent will influence the alloy content of the finished casting. Since melt chemistry must be closely controlled to assure that the desired physical properties are present in the finished casting, treating agents cannot be added indiscriminately. It is therefore desirable to make the most efficacious use of any materials which are added.

Aluminum is economically favored as a deoxidizing or killing agent for steel, but it cannot be used in sufficient amounts to fully kill steel when added by any of the present methods heretofore in use. For example, one of the methods now in use is to add the treating agent to the ladle so that sufficient mixing will occur and the steel will be killed throughout the entire composition. However, deoxidants such as aluminum, after combining with oxygen, tend to precipitate out of the molten solution and build up at the ladle or tundish nozzle and cause excessive clogging thereof.

Accordingly, it has been a common practice to employ an oversized nozzle and stopper rod so that as precipitate buildup at the nozzle increases, the stopper rod must be increasingly raised to partially compensate for the reduced nozzle flow area. However, such practice is only minimally effective, as the buildup will continue until the nozzle is completed plugged. This makes it necessary to replace the nozzle frequently. Additionally, the buildup of material at the nozzle makes it difficult to closely regulate the metal flow rate so that such processes are not easily adaptable for automation.

Similar problems have been encountered when using silicone, manganese, titanium, zirconium and similar materials which combine with oxygen to form high melting point compositions. The melting point of such compositions, which are loosely classified as ceramic or refractory compounds, is substantially higher than the normal molten steel solution temperature. Also, the temperature of the pouring nozzle, particularly early in the pour, may be substantially lower than the molten metal temperature in the ladle. This encourages more rapid precipitation of higher melting point compositions out of solution at the nozzle surfaces.

SUMMARY OF THE INVENTION From the foregoing discussion, it is seen that the primary object of the invention is to provide a method and apparatus for adding treating agents into a molten metal about to be cast, in which the treated molten metal is protected from recontamination from atmospheric contact, and in which substantially complete mixing and treatment of the molten metal occurs prior to the metal setting up in cast form.

Another object of the invention is to provide a method and apparatus for adding deoxidizing agents to steel in which the deoxidizing agent is added to a closed stream of metal moving from a ladle or like reservoir to the casting mold.

A further object of the invention is to provide a method and apparatus of the character described in which high melting oxides produced by certain treating agents do not build up in restricted areas and impede normal continued operation of the process and apparatus.

Yet still another object of the invention is to provide a method and apparatus of the character described in which the process may be carefully controlled, is suitable for automation, and in which maximum use of the treating agents is obtained.

Further objects and advantages of the invention will become more apparent as the specification progresses.

In accordance with the apparatus form of the invention, an apparatus is provided for adding treating agents to molten metal as it flows from a supply reservoir or ladle into a mold. The apparatus comprises a nozzle formed in the bottom of said reservoir or ladle adapted to deliver molten metal to a mold, a valve seat formed at the inlet end of said nozzle, a stopper rod formed to move into and out of fitting relation with said valve seat for controlling the flow of metal through said nozzle, said stopper rod being formed with a hollow interior in surrounding relation to a central passage, means for supplying a wire-like treating agent through said central passage, and means for circulating cooling fluid through said hollow interior.

Thus, it is seen that the, apparatus provides a ladle having a nozzle and a stopper rod adapted to allow molten metal to flow through said nozzle in a controlled stream. The nozzle and valve seat are constructed so that the maximum velocity of the molten metal flow will occur through the valving and nozzle and no reverse flow of molten metal occurs. The wire-like treating agent is moved down into the nozzle past the valved portion of flow of the molten metal so as to prevent the formation of oxides at the valve seat that would interfere with the operation thereof. In addition, the treating agent is added at the central portion of the nozzle where velocity flow is at a high rate so that it is quickly carried on through the nozzle in the narrow stream where intimate mixing occurs and provides a melt adapted to be immediately molded. I

The wire-like feeding means is provided with a direct drive motor so that the quantity of treating agent may be accurately metered and the apparatus is designed to use wire-like treating agents now available on the market. In addition, the stopper rod is adapted for controlled opening and closing so that the pouring of metal through the nozzle and the addition of treating agent may be accurately coordinated. Since these operations are mechanized, it is seen that the apparatus is well adapted for automation, if desired.

In accordance with the method form of the invention, a method is provided for adding treating agents to a molten metal stream as it is provided from a nozzle in a ladle or the like and delivered directly into a mold. Specifically, the method comprises the steps of adding said treating agent to the molten stream substantially within the nozzle in an amount SUfflClCI'lt to treat the metal being cast. Preferably, the wire-like treating agent is added to the central portion of the stream and is retained at near outside ambient temperature prior to entrance into the molten stream. In addition, the method provides for a residence time of treating agent in the nozzle to be very low with a high velocity stream of metal being provided through the nozzle so that the treating agent is immediately carried therethrough as it is added. Thus, deposition of oxides at the forward end of the nozzle and within the nozzle itself is positively prevented.

BRIEF DESCRIPTION OF THE DRAWING A preferred form of the invention is illustrated in the accompanying drawings forming a part of this description, in which:

FIG. 1 is an elevational view of an apparatus constructed according to the invention together with a fragmentary cross-sectional portion of a ladle in which it is installed;

FIG. 2 is an enlarged fragmentary view partly in section illustrating the area marked by circle 2 of FIG. 1; and

FIG. 3 is an enlarged fragmentary, cross-sectional view of the apparatus taken in the area indicated by circle 3 of FIG. 1. t While only the preferred form of the invention is shown, it should be understood that various changes or modifications may be made within the scope of the claims attached hereto without departing from the spirit of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring more particularly to the drawings, there is shown in FIG. 1, an apparatus 11 for adding treating agents 12 in wire-like form to molten metal as it flows from a supply reservior or ladle 13 into a mold (not shown) formed for easing metals. The ladle includes a side refractory lining l4 and a bottom refractory lining 16 disposed within a suitable-housing 17. A nozzle 18 is fit into the bottom of the ladle in a manner making replacement of the nozzle relatively easy. Thus, the nozzle 18 is constructed of a suitable ceramic or refractory material 19 and has a vertically extending cylindri-' cal bore 21 communicating at its upper end with a conical valve seat 22. The nozzle is fit into a suitable bore in the bottom of ladle 13 for providing avalve seat and nozzle passage at and through the bottom. The nozzle is secured as shown by a plate 23 attached to housing 17.

A stopper rod assembly 24 is mounted on the ladle housing and comprises a stopper rod 26 having a curved lower end 27 formed to move into and out of fitting relation with the valve seat 22, and means 28 for axially moving the stopper rod 26. Stopper rod 26 is formed with a cylindrical ceramic wall 29 fitting against end 27, which is also composed of ceramic material. These parts define a hollow interior 31 in which is fit a tubular member 32. The tubular member 32 has a hollow central area through which the wire-like treating agent 12 is moved.

Referring more particularly to FIGS. 2 and 3, it is seen that the tubular member 32 is composed of metal and has threads 33 at its upper end, with the member being threaded through a gooseneck 34 and secured in threaded position by

nuts

36 and 37. The hollow interior 31 between the tubular member 32 and the ceramic wall 29 is further divided into an inner annular chamber 38 and an outer annular chamber-39 by a tubular baffle 41 which has its upper end welded to or otherwise secured to a plate 42. The plate 42 has an inlet tube 43 for communicating compressed air or like cooling fluid to the internal chamber 38 and an outlet 44 to provide for egress of such fluid from the outer annular chamber 39.

The stopper rod assembly is assembled and held together as follows. First, the ceramic wall 29 is provided with a threaded ceramic bushing 46 (see FIG. 3), which is fit in place, and then tubular member 32 is fit within the hollow interior. The member 32 has a flanged lower end 47, which is fit in abutting relation against bushing 46. The plate 42 and its associated baffle 41 is then fit over the tubular member, and a nut 48 is threaded over threaded portion 33 of tubular member 32 against the upper portion of plate 42, so as to clampingly cooperate with flange 47 of the tubular member and hold the assembly together. The lower end 27 of the stopper rod is then threaded over bushing 46, nut. 37 screwed into position, and the tubular member threaded through gooseneck 34. Then nut 36 is screwed on and

nuts

36 and 37 tightened in place with the gooseneck positioned as desired. The wire feeding means 12 is then threaded down through the interior 49 of tubular member 32, and the interior 51 of end 27.

In order to feed the wire-like treating agents 12, feeding means 52 is provided for supplying the treating agent through the central interior passages 51 and 49 and down into a central location within bore 21 of nozzle 18. Feeding means 52 comprises a plurality of drive rollers 53 mounted for rotation on a bracket 54, which in turn is secured to the gooseneck 34. The drive rollers are driven by a suitable electric motor (not shown) mounted at the rear of the bracket, and formed with appropriate drive means or control means whereby the driving velocity of drive rollers 53 may be accurately adjusted.

The means 28 for moving the stopper rod 26 up and down in an axial direction comprises a barrel housing 56 attached to the ladle housing 17 by a support bracket 57, and a slide 58 slidably positioned within the barrel housing. The slide is vertically adjusted with respect to the barrel housing by means of an adjustment crank 59 which is rotatably mounted on the ladle housing. The adjustment crank has a plurality of pinion teeth 61 which engage threads provided on a rack portion (not shown) of the slide to raise or lower the slide. The slide is rotatably positioned by means of a control lever 62 pivotally attached to the lower end of the slide. The slide may be locked in fixed axial and rotational position by clamp assembly 63 mounted on the barrel housing and actuated by a lever arm 64. The slide 58 is connected at its upper end to the gooseneck 34 which in turn is connected to the stopper rod 26 as described above.

In operation, the ladle is filled and the nozzle positioned to deliver molten metal to a mold. In addition, the wire-like treating agent 12 is positioned so that it extends just down through the end of the stopper rod. The stopper rod is then lifted by operation of crank 59, and the wire-like treating agent is simultaneously threaded down through the stopper rod by operation of the feeding means 52. By accurately matching the flow I rate, which can be determined by calibration, with the rate of feed of the wire treating agent 12, an accurate addition of treating agent may be provided into the nozzle where the moving molten stream immediately melts and mixes the treating agent throughout.

Thus, in its method aspect, the invention provides a method of adding treating agents to a molten metal stream provided from a nozzle in a ladle or the like and delivered directly into a mold comprising the steps of adding said treating agent to the molten stream substantially within the nozzle in an amount sufficient to treat the metal being cast. In addition, provision is made for adding the wire-like treating agent to the central portion of the stream. Moreover, cooling means are provided to retain the wire feeding means at a relatively low temperature prior to entrance of the treating material into the metal stream. This temperature control is made possible by the addition of compressed air or like cooling fluid through tube 43 which maintains a relatively cool atmosphere surrounding the tubular member 32 which is metal and tends to transfer its heat easily to the air. The partially heated air then travels around the baffle and continues to cool by cooling the inner surface of the ceramic wall 29. The ceramic wall 29 serves as an insulator between the interior of the stopper rod and the molten metal. carried on the outside thereof, and this construction allows excellent protection for the treating agent. It is also noted that the residence time of the metal added to the nozzle is very low because of the comparatively high velocity of the molten stream passing through the nozzle and therefore deposition of oxides at the valve seat is positively prevented and deposition within the nozzle is substantially prevented.

It should be noted that as the stream of molten metal exits from the nozzle, it has a vortex or swirl flow characteristic, in addition to the vertical flow velocity, which serves to mix the treating agent into the molten solution for effective treatment throughout all of the molten metal. Further mixing, although not necessarily required, also occurs within the sprue, gating system, and casting cavity of the mold.

The present invention also permits unusual flexibility in controlling the amount and rate of additions to the molten metal. The wire feed rate may be automatically determined for a given nozzle opening or pour rate, or the rate may be manually controlled by the ladle operator. The wire composition may be selected to provide a single treatment, such as deoxidation, or a plurality of treatments such as inoculation, grain refinement and alloy addition in addition to or in lieu of deoxidation.

By way of example, the wire-like treating agent 12, as shown in FIG. 3, has an aluminum core 66 circumscribed by a steel sheath 67 to provide rigidity at high temperatures and protection against premature melting of the aluminum core. With such construction, it will be appreciated that other treating agents may be carried, in adidtion to, or instead of, aluminum in the core area. With the stopper nozzle constructed according to the invention, and cooling provided, it is thus seen that comparatively volatile agents may be added to the molten metal, if desired, since protection is provided'for such agents until they reach the point of use.

The amount of deoxidant required will generally exceed the amount they may be conveniently added through the wire feeders. In such cases, it is preferred to partially kill the steel in the process somewhere in advance of the nozzle, and then fully kill the steel at the nozzle in accordance with the invention.

In a typical run, the base metal is melted and refined in an arc or induction melting furnace. The metal is brought up to tap temperature and tapped into the receiving ladle while final alloy adjustments are shoveled into tap stream. At this time, vacuum degassing is conveniently effected.

Assuming a 10 ton ladle with 52 inches of metal and a 2 inch diameter nozzle, the initial volume flow should be about 157 pounds per second and should reduce to about 86 pounds per second in the bottom 12 inches of the ladle. The wire feed rate is matched with the volume flow of metal by feeding the weight plus other factors to a computer input, which constantly adjusts the feed rate. Alternatively, the wire feeders are programmable to the extent that with a known ingot size, the wire feeder can be indexed after each ingot.

As used herein, the term treating agent should be broadly construed and will include any alloying or treating agent having an effect on the composition or form of the final casting. By way of further illustration, the following applications may be advantageously carried out while utilizing the invention:

1. Different alloys such as chromium, molybdenum, vanadium and titanium may be added to selected castings so that the heat can be split several ways.

2. Controlled rimming action may be effected in the ingot molds by measuring the oxygen content in each ingot poured and feeding more or less aluminum wire to tailor the oxygen content.

3. Adding an alloy that is known to fade while holding in a ladle; for example, boron steel may be made'by deoxidizing the steel during the tap and/or vacuum degassing and then adding the nitrogen fixing agents (titanium and zirconium) and the boron through the wire feeder at the nozzle.

4. Use in a continuous casting operation where'aluminum deoxidized steel causes nozzle plugging, add aluminum and/or grain refiners in the continous cast mold while allowing only semi-killed steel to contact the tundish nozzle, thereby avoiding the aluminumoxide dross problem associated with adding aluminumv wire.

5. In gray iron applications, alloy and inoculating agents may be added at the mold so that one base iron may be used to make castings of different specifications.

is provided. It is also seen that the invention .is particularly applicable to the addition of deoxidizing agents for providing fully killed steel. 1

What is claimed is: 1. A method of adding a treating agent to a molten metal stream provided from a nozzle carried in a bottom of a molten metal filled ladle or the like and delivered directly from said nozzle into a mold, comprising: feeding said treating agent in a wire-like form through a central passage of a tubular metal member within a stopper rod which passes through said molten metal and provides access to said molten stream substantially within the said nozzle; and

concurrently with said feeding, passing a coolant fluid through the interior of said stopper rod in contact with the exterior of said tubular metal member while preventing said fluid from contacting said treating agent.

2. A method as in claim 1 wherein said passing comprises:

introducing a cool incoming stream of said coolant fluid at the top of said stopper rod against the exterior of said tubular metal member;

flowing said incoming stream downwardly against the exterior of said tubular metal member from the top of said stopper rod to adjacent the bottom thereof, thereby cooling said tubular metal member and the treating agent passing therethrough while concurrently heating said incoming stream of coolant fluid; and thereafter directly the heated stream adjacent the bottom of said stopper rod radially away from said tubular metal member and about a tubular baffle surrounding said tubular metal member and therefrom upwardly to the top of said stopper rod and out an outlet provided thereat.

3. A method as in claim 2, including providing a sheath about said treating agent to provide added rigidity thereto and protection against premature melting thereof.

4. A method of adding treating agents to a molten metal stream as defined in claim 1, in which the treating agent is added to the central portion of the metal stream within the nozzle.

5. A method of adding treating agents to a molten metal stream as defined in claim 4, in which the velocity of molten metal moving through the nozzle and past the treating agent is relatively high, whereby the treating agent is almost immediately dissolved in the metal stream and swept on through the nozzle.

6. A method of adding treating agents to a molten metal stream as defined in claim 5, in which the treating agents contain deoxidants selectedfrom the class consisting of aluminum, titanium and zirconium.

7. An apparatus for adding treating agents to molten metal as it flows from a molten metal containing supply reservoir orladle into a mold, comprising:

a nozzle formed in the bottom of said ladle adapted to deliver molten metal to a mold,

a valve seat formed at the inlet end of said nozzle,

a stopper rod formed to pass through said molten metal containing ladle and to move into and out of fitting relation with said valve seat for controlling the flow of metal through said nozzle,

means for supplying a wire-like treating agent through said stopper rod and into the nozzle; said stopper rod being formed with a hollow interior in surrounding relation to a tubular metal member with the wire-like treating agent being supplied through a central passage in said tubular metal member, and

means for circulating coolant fluid through said hollow interior and into contact with the exterior of said tubular metal member.

8. An apparatus for adding treating agents to molten metals as defined in claim 7, in which the exterior portion of the stopper rod is composed of a ceramic material, and baffle means are provided within the hollow interior for directing cooling fluid downwardly within the stopper rod first against the exterior of said tubular metal member containing the treating agent, and thence outwardly radially from said tubular. metal member, around said baffle and upwardly adjacent the ceramic exterior portion to an outlet.

9. An apparatus as in claim 8, wherein said valve seat is conically shaped and an end of said stopper rod which is formed to move into and out of fitting relation with said valve seat is rounded whereby said end contacts said valve seat over only a part of the area thereof.

10. An apparatus for adding treating agents to molten .metal as defined in claim 9, in which controlled drive means are provided for driving the wire-like treating agent at a controlled rate through the stopper rod and into the metal.

1 1. An apparatus for adding treating agents to molten metal as defined in claim 10', in which means are provided for positioning the stopper rod in open and closed position with respect to the valve seat.

12. An apparatus as in claim 11, wherein said stopper rod is disassembleable into said tubular metal member,

said baffle and said exterior ceramic material portion.

Claims

1. A method of adding a treating agent to a molten metal stream provided from a nozzle carried in a bottom of a molten metal filled ladle or the like and delivered directly from said nozzle into a mold, comprising: feeding said treating agent in a wire-like form through a central passage of a tubular metal member within a stopper rod which passes through said molten metal and provides access to said molten stream substantially within the said nozzle; and concurrently with said feeding, passing a coolant fluid through the interior of said stopper rod in contact with the exterior of said tubular metal member while preventing said fluid from contacting said treating agent.

2. A method as in claim 1 wherein said passing comprises: introducing a cool incoming stream of said coolant fluid at the top of said stopper rod against the exterior of said tubular metal member; flowing said incoming stream downwardly against the exterior of said tubular metal member from the top of said stopper rod to adjacent the bottom thereof, thereby cooling said tubular metal member and the treating agent passing therethrough while concurrently heating said incoming stream of coolant fluid; and thereafter directly the heated stream adjacent the bottom of said stopper rod radially away from said tubular metal member and about a tubular baffle surrounding said tubular metal member and therefrom upwardly to the top of said stopper rod and out an outlet provided thereat.

6. A method of adding treating agents to a molten metal stream as defined in claim 5, in which the treating agents contain deoxidants selected from the class consisting of aluminum, titanium and zirconium.

7. An apparatus for adding treating agents to molten metal as it flows from a molten metal containing supply reservoir or ladle into a mold, comprising: a nozzle formed in the bottom of said ladle adapted to deliver molten metal to a mold, a valve seat formed at the inlet end of said nozzle, a stopper rod formed to pass through said molten metal containing ladle and to move into and out of fitting relation with said valve seat for controlling the flow of metal through said nozzle, means for supplying a wire-like treating agent through said stopper rod and into the nozzle; said stopper rod being formed with a hollow interior in surrounding relation to a tubular metal member with the wire-like treating agent being supplied through a central passage in said tubular metal member, and means for circulating coolant fluid through said hollow interior and into contact with the exterior of said tubular metal member.

8. An apparatus for adding treating agents to molten metals as defined in claim 7, in which the exterior portion of the stopper rod is composed of a ceramic material, and baffle means are provided within the hollow interior for directing cooling fluid downwardly within the stopper rod first against the exterior of said tubular metal member containing the treating agent, and thence outwardly radially from said tubular metal member, around said baffle and upwardly adjacent the ceramic exterior portion to an outlet.

10. An apparatus for adding treating agents to molten metal as defined in claim 9, in which controlled drive means are provided for driving the wire-like treating agent at a controlled rate through the stopper rod and into the metal.

11. An apparatus for adding treating agents to molten metal as defined in claim 10, in which means are provided for positioning the stopper rod in open and closed position with respect to the valve seat.

12. An apparatus as in claim 11, wherein said stopper rod is disassembleable into said tubular metal member, said baffle and said exterior ceramic material portion.