US3610773A

US3610773A - Metallurgical stirrer construction

Info

Publication number: US3610773A
Application number: US817057A
Authority: US
Inventors: Hubert Polomsky
Original assignee: Demag AG
Current assignee: Mannesmann Demag AG
Priority date: 1968-04-20
Filing date: 1969-04-17
Publication date: 1971-10-05
Anticipated expiration: 1988-10-05
Also published as: DE1758194B1; FR2006599A7; DE1758194C2

Abstract

A stirrer for metallurgical purposes particularly for the treatment of pig iron, steel or cast iron melts during desulfurization desilication, carbonization or addition of other metallurgical reactants, includes a rotatable tubular element or body preferably having at least two radially extending delivery conduits which communicate centrally with a central suction passage. The body is provided on its inside with a reinforcement and on its outside with a heat resistant material and advantageously includes axial and transverse intersecting tubular elements formed of high silicon steel alloyed with aluminum and chromium and having a coating of synthetic slag.

Description

Inventor Hubert Polomsky Duisburg-Buchholz, Germany Appl. No. 817,057

Filed Apr. 17, 1969 Patented 0ct.'5, 1971 Assignee Demag Aktiengesellschaft Duisburg, Germany Priority Apr. 20, 1968 Germany P 17 58 194.1

METALLURGICAL STIRRER CONSTRUCTION 8 Claims, 3 Drawing Figs.

416/224, 416/241 Int. Cl B011 9/12 Field of Search 416/91,

[56] References Cited UNITED STATES PATENTS 3,326,534 6/1967 Pryde 416/241 X FOREIGN PATENTS 85,394 7/1958 Denmark 416/91 29,737 11/1958 Finland I 416/91 143,372 11/1963 U.S.S.R. 416/241 Primary Examiner-Everette A. PowellJr. Attorney-McGIew and Toren ABSTRACT: A stirrer for metallurgical purposes particularly for the treatment of pig iron, steel or cast iron melts during desulfurization desilication, carbonization or addition of other metallurgical reactants, includes a rotatable tubular element or body preferably having at least two radially extending delivery conduits which communicate centrally with a central suction passage. The body is provided on its inside with a reinforcement and on its outside with a heat resistant material and advantageously includes axial and transverse intersecting tubular elements formed of high silicon steel alloyed with aluminum and chromium and having a coating of synthetic slag.

PATENTED UB1 5 I97! SHEET 1 [IF 2 Inventor hIJEPT p 1,, x,

PATENTED OCT 5 97 SHEET 2 [IF 2 Inventor H0850) Relay METALLURGICAL STIRRER CONSTRUCTION SUMMARY OF THE INVENTION This invention relates, in general, to metallurgical devices and, in particular, to' a new and useful stirrer for metallurgical purposes particularly for the treatment of pig iron, steel or cast iron melts during desulphurization, desilication, carbonization or addition of reactants and which is provided with a reinforcement on its inside and an outside coating of a heat resistant material.

It is known to design metallurgical stirrers as beam stirrers having a full cross section or to provide a pumplike body which consists of a tubular part for the suction and one or more tubular parts radially arranged for outward centrifugal discharge. in all cases, the molded part of refractory material is provided with a steel reinforcement which is rigidly connected with the drive shaft and thus capable of transmitting the torque. The inner reinforcement can also be air cooled by using tubes as reinforcing rods so that no critical influences can be formed which will influence the strength of the device.

A stirrer which is formed of refractory material is exposed to the direct heat of a molten bath of up to l,500 C. and even more, and it is also subject to additional greater stresses. According to the literature, for example, Journal Giesserei of Mar. 28, 1968, only the manufacturing method and the durability of the stirrers are the determinant factors for the profitability of such stirring methods. Giesserei mentions that it has been found in practice that one of the most important factors of wear is the stress under sudden changes of temperature (Giesserei 1966 No. 23, pages 816 and 818). The stirrer is dipped without preheating directly into the liquid iron and brought against the ambient air after use without any special precautions and such a rough treatment leads to small cracks in the surface of the ceramic material.

Though the danger of cracking could be reduced by suitable measures, for reducing stress under sudden changes in temperatures, other inconveniences could not be eliminated. The properties of the ceramic material and the substances of the reaction carriers are such that they produce deposits on the stirrer during the metallurgical process and even to a greater extent during the cooling of the stirrer. This increases not only the weight of the stirrer, but also its capacity for forming a desired flow. Cleaning the ceramic body shortly after stirring cannot be carried out by the operators because of the great heat, and, only after the stirrer is cooled, is it possible to remove the slag which adheres thereto and becomes hard enough to require this use of special removing tools. The mechanical removal of the melt and slag residues is costly and risky. There is a great danger that the stirrer will be damaged, that is, that parts of its circumference will be removed. Stirrers encrusted with slag cannot be kept completely hot apart from the fact that a considerable amount of heat must be considered as lost.

The known stirrers do not meet the requirements of modern manufacturing methods and their construction is not satisfactory. The ceramic material which is used to form a stirrer requires a mold and any reinforcements for the material must be inserted with accuracy in order to form a core which permits the body of the ceramic material to be applied in the liquid or pasty form around the core. In the solidified state, the body reaches the final state after a prolonged burning process. Such a manufacturing method requires very large apparatus even for simple stirrers and they are not available for every metallurgical plant. For hollow stirrers, which yield special results, the expenditures increase because of the special cores which are required. Charge durability values which have already been obtained and the results of the degree of purity achieved show that it may be advisable to use more complicated stirrers in order to achieve better metallurgical results. Thus, for example, it is preferable that the stirrer be capable of circulating the entire melt of the reactive slag composition in the shortest period of time and not merely to mix this composition. lt was found that this was far more economical because the durability of the lining material increases with low slag costs and good circulation of the molten bath. The lining of the reaction vessel is destroyed very rapidly with a simplestirring tool and with highly aggressive slags and they are also more expensive.

in accordance with the present invention, there is provided a stirrer of simple construction which is better for the particular metallurgical operative use than the known stirrers and which is durable and capable of long operation. The invention provides a metal body forming the contour of the stirrer which is bonded together with a heat resistant coating. With such a construction, the resistance to mechanical treatment of the stirrer structure is great so that slag residues or similar deposits can be removed, for example, by chilling the body in a medium of much lower temperature. Mechanical treatment can also be completely avoided by cooling the stirrer from its operating temperature of over l,000 C. in a water bath or an air current of very much lower temperature so that the abrupt cooling will cause the slag to break off. In the preferred form, the stirrer is made up of a plurality of tubular bodies, for example, a central tubular body comprising the suction portion and one or more radially extending tubular bodies which are joined to the central portion such as by welding. A heat-resistant coating is then produced over the body, for example, by dipping the body. The coating which is formed may be either detachable or undetachable, and, in the case of an undetachable coating, a particularly thin layer is used. If the coating is to be removed later, it can be formed as a simple ring which may be inserted or attached around the stirrer body.

A particular advantage of the construction is that, even if the outer coating deteriorates or wears off, the interior body may be recoated.

In accordance with one embodiment of the invention, a stirrer is provided which is suitable for stresses which are produced by sudden temperature changes and caused by frequent cooling and reheating. In this case, the body cornprises a high silicon steel alloyed with aluminum and chromium and the coating comprises a synthetic slag. The inventive construction utilizes the characteristic of the higher melting point of the synthetic slag with respect to the lower temperature of the operation of steel baths.

in accordance with another feature of the invention, the stirrer construction is formed of a plurality of tubular elements which are provided both on the inside with liners of ceramic material which are removable. With such a construction, the liners may be readily replaced after long operating periods, if necessary. Thus, both the manufacture and the replacement of such stirrers are greatly facilitated. It should be appreciated that during operation as well as under continuous alternating stresses, within very wide temperature ranges, the stirrer can perform its function only when there is a good bond between the body and the coating. In addition, the mechanical removal of the slag provides a further stressing of the bond between these parts. It is therefore desirable that the surfaces of the body are made uneven in order to provide a greater anchoring of the coating. The stirrer is advantageously made of a plurality of individual parts which may be fitted together and the ceramic inserts may be inserted into the parts after they are fitted together or the parts may be dipped in a coating bath to apply a light coating thereto.

When metallurgical deposits form on the stirrer during operation, they not only increase the weight of the stirrer and make the power requirements for rotating the stirrer higher, they also present a disadvantage because they must be kept hot when the stirrer is removed from the melt. The inventive construction permits the easy detachment of the adhering residues and enhances the flow conditions accordingly. To this end, the inner and/or outer parts of the body are made conical in the form of a diffuser. An inner conicity enhances the detachment of the metallurgical slag regardless of whether it is accomplished by mechanical means or by shrinkage. Such a design of the flow ducts, however, provides a considerable influence on the velocity and pressure conditions.

In metallurgical processes, it can be expected that molten metals of any type will carry slag parts which will float on the melt or be suspended inside the bath depending of the phase of the stirring process. When hollow stirrers are employed, the slag pieces can produce clogging of the stirrer. It is also possible that such semisolid melt parts of slag will be pressed into the interior when the stirrer is dipped into the molten bath which is covered with the solid reactants. In order to avoid such difficulties, the inventive construction provides a stirrer with teeth which operate during the rotation of the stirrer to crush the slag parts. Particularly for a hollow stirrer, it is preferable according to the invention, that the inlet of the suction pipe be provided with ducts which are opened at the bottom and which widen in a radial or circumferential direction. The portion on each side of the ducts form teeth and the arrangement of the slots or ducts therebetween produces a whirling of the melt and the forcing of the melt to the outside without getting immediately into the circulation proper at the time that it is introduced. As a rule, only liquid material will therefore rise in the stirrer itself so that deposits which could have been formed by separation from the melt will have no opportunity to deposit on the walls of the stirrer.

Accordingly, it is an object of the invention to provide an improved stirrer construction which includes a body made of a rigid material such as ametal and having a coating of a slag material.

A further object of the invention is to provide a rotatable stirrer which comprises a plurality of tubular portions including a central or axially extending tubular portion forming a suction tube and one or more radially extending tubular portions forming centrifugal discharges and wherein a coating of a slag material is applied over the body either in the form of a coating or a separate jacket and also wherein the passages formed in the tubular elements are advantageously made conical and the inlet to the passages, particularly the suction inlet, is provided with teeth elements defining inflow passages therebetween.

A further object of the invention is to provide a stirrer which is simple in design, rugged in construction and economical to manufacture.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings FIG. 1 is a sectional view of a stirrer constructed in accordance with the invention;

FIG. 2 is a partial perspective view of the suction end of a stirrer of another embodiment of the invention; and

FIG. 3 is a view similar to FIG. 1 of another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, in particular, the invention embodied therein in FIG. I comprises a stirrer generally designated 50 which includes a metallic body or core 1 having a corrugated or wavy exterior and interior surface 2. A coating 3 of a synthetic slag material is applied over both the interior and exterior surfaces, for example, by dipping and the corrugations ensure that the coating is retained. In the embodiment of FIG. I, the stirrer 50 includes a vertical suction pipe portion 4 and laterally and radially arranged ejection pipes or

discharge pipes

5 and 6 which, in the embodiment shown,extend-outwardly in respectiveopposite directions. The body 1 is in form locking and force-locking connection to a drive shaft 7 which is rotated by means (not shown).

The suction tube 4 includes an inlet or suction 8 which may be of the configuration indicated in FIG. 1, or may be provided with a plurality of circumferentially spaced teeth 9 as indicated by the suction 8' in FIG. 2. The teeth 9 are formed as axial or radial projections. The gaps between the teeth 9 form ducts 10 which are formed to the general configuration of a centrifugal pump impeller in order to effect an acceleration of the material radially to the outside.

In FIG. 2, the ducts 10 have a curved configuration, but they can be made with simple straight walls, if desired. The ducts 10 are advantageously worked into the body portion comparable to the body 1 of FIG. 1 so that the subsequent methods for coating with synthetic slag or similar heat resistant coating materials will enclose only the preshaped body form.

In accordance with the embodiment of the stirrer 50, indicated in FIG. 3, there is provided a body generally designated 1 made of a metal or similar material which is formed of a plurality of separate conical tubes or pipes including suction tube 4' and discharge or ejection tubes 5' and 6'. A conical interior configuration 16 helps to permit the entrance of a large amount of metal material during operation. The flow is accelerated to the interior of the stirrer through the suction duct 4' and accelerated and transformed into pressure energy as it issues from the ejection tubes 5 and 6'. This produces a particularly intensive contact of the bath particles with the slag materials. It also provides means for breaking of the slag at the inlet and at the outlet ports of the suction tube 4' and the outlet tubes 5' and 6' in the cold state of the stirrer.

In the embodiment of FIG. 3, the body portion 1' includes an upper tubular part 15 which is secured to a shaft 7' for rotation therewith and this is assembled to the ejection tubes 5' and 6, such as by welding or bolting together at the

conical surfaces

13 and 14 of these tubes to the suction tube 4. The assembled boy 1' is then provided with a coating 3 of a heat resistant material which is effected by dipping it into a bath, for example, of a material such as a synthetic slag.

I claim:

1. A stirrer for metallurgical purposes particularly for treatment of pig iron, steel or cast iron melts during desulphurization, desilication, carbonization or addition of other reactants, comprising a rigid tubular stirrer body which is adapted to be rotated and including at least one transversely extending portion inclined upwardly toward each end from its center and an axial tubular portion extending downwardly from the center of said transversely extending portion and having an interior communicating with the interior of said transversely extending portion, and being of a length longer than the length of the transversely extending portion which extends from its center to either end thereof, and a reinforcement coating on the inside and outside of said body of a heat resistant synthetic slag material, said tubular stirrer body being made of a high silicone steel alloy with aluminum and chromium.

2. A stirrer according to claim 1, wherein said body is covered on the inside and outside with rings of ceramic coating material.

3. A stirrer according to claim 1, wherein said axial tubular portion comprises a separate conical portion forming a suction passage communicating at the center with transversely extending portion.

4. A stirrer for metallurgical purposes, particularly for the treatment of pig iron, steel or cast iron melts during desulphurization desilication, carbonization or addition of other reactants, comprising a rigid tubular stirrer body which is adapted to be rotated, and a reinforcement coating on the inside and outside of said body of a heat-resistant material, said body being formed with corrugations on the exterior and interior surface thereof to facilitate adherence of the coating thereto.

5.. A stirrer, according to claim I, wherein said coating comprises several layers.

' 6. A stirrer, according to claim 1, wherein said coating comprises aceramic insert located within said tubular portion.

7. A stirrer, according to claim 1, wherein said body portion includes a suction portion of conical configuration and at least one transverse discharge portion of conical configuration.

8. A stirrer, according to claim 1, wherein said and tubular

Claims

2. A stirrer according to claim 1, wherein said body is covered on the inside and outside with rings of ceramic coating material.
3. A stirrer according to claim 1, wherein said axial tubular portion comprises a separate conical portion forming a suction passage communicating at the center with transversely extending portion.
4. A stirrer for metallurgical purposes, particularly for the treatment of pig iron, steel or cast iron melts during desulphurization desilication, carbonization or addition of other reactants, comprising a rigid tubular stirrer body which is adapted to be rotated, and a reinforcement coating on the inside and outside of said body of a heat-resistant material, said body being formed with corrugations on the exterior and interior surface thereof to facilitate adherence of the coating thereto.
5. A stirrer, according to claim 1, wherein said coating comprises several layers.
6. A stirrer, according to claim 1, wherein said coating comprises a ceramic insert located within said tubular portion.
7. A stirrer, according to claim 1, wherein said body portion includes a suction portion of conical configuration and at least one transverse discharge portion of conical configuration.
8. A stirrer, according to claim 1, wherein said and tubular portion is arranged along the axis of rotation and forms a suction conduit, said axial tubular portion having an inlet formed by a plurality of circumferentially spaced teeth defining inlet passages therebetween.