US 3278295 A
Description (OCR text may contain errors)
Oct. 11, 1966 JAN-ERIK OSTBERG ETAL 3,278,295
METHOD OF STIRRING DISPERSING OR HOMOGENIZING METAL OR SLAG CHARGES HAVING A TEMPERATURE OF AT LEAST 800C Filed Aug. 10, 1964 INVENTORS JAN-ERIK OSTBERG SVEN GYNT LARS GYNT AKE SAHLBERG United States Patent 3,278,295 METHOD OF STIRRING DISPERSING 0R HOMOG- ENIZING METAL 0R SLAG CHARGES HAVING A TEMPERATURE OF AT LEAST 800 C. Jan-Erik Ostberg, Bettua, Sven Gynt and Lars Gynt, Vasteras, and Ake Sahlberg, Halsingborg, Sweden Filed Aug. 10, 1964, Ser. No. 388,397 (Ilaims priority, application Sweden, July 7, 1960, 6,627/60 1 Claim. (Cl. 7561) This application is a continuation-in-part of our application Serial No. 119,548, filed June 26, 1961, now abandoned.
The present invention relates to a method for stirring, dispersing or hornogenising metal or slag charges having a temperature of at least 800 C. with one or several phases to which is possibly added material in solid, liquid or gaseous form and in which a physical process is desired either within one of the phases or between these. The invention also relates to a mechanical device for performing the said method.
A problem which often arises within this technique concerns homogenizing a fluid or combining two or several fluids with each other. This is especially so in the metallurgical industry. The precautions taken with raw products or semi-finished products are very often marked by the fact that they immediately influence only one part of the system or the batch of material being treated. The actual process, therefore, would completely or partially fail if the effect could not be successfully spread over the whole quantity of material.
This can be illustrated by some practical examples. When vacuum treating a metal charge only a very insignificant outer layer is influenced, which is in direct contact with the evacuated space. charge would completely escape the influence of the low pressure if it were not successfully transported up to the surface just mentioned. This circumstance is connected with the heating. Only that part of the metal charge which is directly subject to the influence of an arc, flame or heat radiating surface, is heated immediately. In order that the actual process may take place sufficiently rapidly, it is often a condition that the heat, by means of stirring or some other type of forced convection, is transported further to other parts of the charge. Another typical problem of this type arises when the percentage of some alloying material is to be increased by means of a suitable addition to a charge of alloying material in solid form. While the solid alloying material melts and dissolves, only that part of the charge is influenced which is in direct contact with the alloying material. Finally, as an example of homogenizing it should be established that, in such metallurgical reactions which consist of an exchange of material between a metal charge and a slag, it is generally a very small part of the whole system which is directly influenced by the reaction. Particularly when it is a question of a demand for high reaction speed and reaching relatively completely equal thermodynamic equalizations, it is necessary to equalize the compositions and temperature dissimilarities which are the result of the material conversion which takes place at the boundary layers where the different phases meet.
When such problems arise on a small scale it may be suflicient to take some simple manual steps such as shaking or agitating or utilizing some simple hand tool. On the other hand, when it is a question of work on a large scale, when a certain pattern of movement is aimed at, when it is desired to maintain clear phase boundaries and when it is desired to screen off the space above the charge in order to maintain a vacuum there or a particular type of atmosphere, a mechanical device must be used. The
The main part of the "ice stirring, dispersing and homogenizing operations outlined above are of course of a transitory nature, but they all have in common that their completion cannot be brought about effectively without a rapid movement being created in the charge, the movement including the whole or the greater part of the charge and being preformed with a minimum of turbulence.
The problem in this connection might also be expressed as a desire to obtain a closed pumping circuit or streaming circuit in which the streaming occurs regularly and according to a certain pre-determined movement, and in which acceleration power is introduced in the charge according to a part or along the whole length of the circuit. Good results have been obtained with the so-called electro-dynamic stirrer, but this solution is relatively expensive, as is the so-called vibratory ladle also. In .both these cases, the forces which set the charge in motion automatically guide them in regular streaming circuits.
The invention relates to a method producing both an effective and economic solution to the above mentioned problem and is characterised in that the charge (temperature at least 800 C.) completely or for the most part is given a streaming movement by means of a mechanical device at least partly lowered in the charge, whereby the said device while rotating with respect to a surrounding vessel containing the charge with a speed of at the most 500 r.p.m. guides the streaming of the charge partly along a substantially horizontal, partly along a substantially vertical path of movement, the total path of movement within the device per streaming revolution for each stirred part of the charge being at least 15% of the sum of the average height and the average diameter for the whole charge. At the same time a good stirring is obtained according to the above mentioned requirements. The invention also includes a mechanical device for performing this stirring. This mechanical device is characterized in that it is formed of a substantially vertical tube and one or more side tubes placed at an angle and communicating with the upper part thereof, in which the total length of the vertical tube from outlet opening to longitudinal axis of a connecting tube and the length from this tube from the longitudinal axis of the vertical tube to the outflow opening is at least 15 of the total maximum average fluid height and maximum average fluid diameter in the ladle or the vessel in which the device is intended to be lowered.
The advantages of this device, as also certain further advantages with the above indicated method according to the invention will be seen more clearly from the follow ing description taken together with the accompanying drawings which form a part thereof.
In the drawings:
FIG. 1 shows a ladle with the stirrer in section according to the invention.
FIG. 2 is a cross-section on the line 2-2 of FIG. 1;
FIGS. 3, 4 and 5 show modified stirrers in vertical cross-section.
In the vessel of FIGS. 1 and 2, which constitutes a ladle 1, is a charge (temperature over 800 C.) covered by slag. Into the charge is lowered a stirring device 2. This device consists of a cross-bar fixed in a vertical shaft 3 which is driven by the gear 4 of the motor 5. The motor and gear are parts of a single construction which in its turn is held by a lid 6 placed on the vessel 1. The lid is provided with sealings at 7 and 8. As is clear from the figures, the stirring device is formed of a vertical pipe section, and on this are rigidly fixed one of several horizontal tube connections or lateral pipes 9, usually shorter than the part of the vertical tube below each horizontal lateral pipe, the interiors of which communicate directly with the interior of the tube section. The vertical pipe section is closed at the top.
The laterally extending pipes are angularly spaced apart and thus have lateral side walls 11 which exert a stirring action on the charge.
As mentioned, the stirrer should rotate with a speed of at the most 500 r.p.m. and the sum of the length b of the vertical pipe section below the longitudinal axis of the lateral pipes and the distance a from the outer end of the horizontal tube part to the longitudinal axis of the vertical part should be at the most 15% of the sum of the maximum average fluid diameter d and the maximum average fluid height h of the charge. These limitations are of importance in order to achieve the required stirring and at the same time limit the wear on the stirrer. The provision may also be made that, with relatively insignificant horizontal guiding, at least 25% of the maximum average liquid height should be guided vertically and at least 25% of the maximum average fluid diameter should be guided horizontally with relatively short vertical guidance. Furthermore, the distance b should be at least twice, and preferably at least three times, the internal diameter e of the pipe section 2.
A vacuum can be produced within the ladle by pump P.
One of the many advantages with the present stirrer is that the pump (the stirrer) as such rotates, but relative movement between the pump device and the guiding device is avoided since both these devices are instead constructed as a unit. The pump is further built on the principal known per se of operating the pump by allowing the fluid to accelerate in a tube arranged at an angle to the rotating shaft. The guiding is obtained by giving the tube the required length. Characteristic of the invention is further that the pump, by rotating, places that pump nearest the surrounding charge in rotating movement. Since the pump is made large in comparison with the surrounding fluid, it can be constructed for moderate rotation movements. Even with moderate speeds of rotation such great centrifugal speeds are reached in the outlet of the horizontal tube connections that the device will operate as an effective pump which draws in fluid at the inlet of the vertical tube and pumps it out of the mouthpieces of the horizontal tubes; The stirring takes place partly on account of pump action, partly on account of moving parts of the charge by the action of the side walls of the protruding side hook arms.
It is of course unnecessary for the rotating shaft to be completely vertical. The movement can also be altered in a number of other ways. The inlet can thus be placed in the upper section of the vertical tube. The pump can be placed more or less eccentrically in the vessel. Finally, the horizontal tube connections can be made shorter or longer. They could be directed somewhat upwards or downwards and of course be placed at different heights in the vessel.
The apparatus also has the advantage that additions in solid, liquid or gaseous form can be made to the streaming fluid. The additon can be made in such a way that only the immediately pumped fluid is influenced and can easily be modified so that the walls of the pump are not influenced.
The pump which is shown in the figures is constructed for use with an iron ladle, for example of a type containing tons. It operates with a speed of rotation of approximately one revolution per minute and, with an inner tube diameter of 150 mm., gives such a great capacity that the complete iron content passes through the vertical aird horizontal tubes of the pump. On this movement is superimposed a horizontal rotation brought about by the si-defaces of the horizontal branch tubes. Despite the fact that the pump operates with very low speeds, so that the mechanical stresses on it will be very low, a rapid mixing is thus obtained in accordance with one pattern of movement, which can be varied within wide limits.
These circumstances are important if the problem is to be solved by means of a mechanical aid in surroundings where stresses of temperature, temperature shocks and chemical actions are severe. Without such a simple construction that the thickness of the material does not fall below 10 mm. at any position and that neither do any radii fall below this measurement, the stirrer cannot be sufiiciently stable for work in metal charges or slagsv For the same reason the speed of rotation, as mentioned above, should not exceed 500 r.p.m. and the speed of the fluid 5 m. per second.
The tube is manufactured according to any known method and of any material which is durable in the specific conditions. With crude iron, graphite is often the best solution. If the carbon percentage is too low or with steel, schamotte may be chosen instead which at high temperatures may be replaced by special schamotte or sillimannit. If the dimensions and speeds are kept within the specified limits the choice of material will not be difficult.
In the modification of FIG. 3, a single lateral or side tube 9a is shown.
In FIG. 4, lateral pipes 9b are arranged at the bottom, and pipe section 2 has openings 10 at its upper end. The flow direction is the reverse of that shown in FIG. 1.
As shown in FIG. 5, lateral openings 100 instead of a downward opening may be provided for pipe section 2.
The stirrer according to the invention and the method of stirring, etc., likewise according to the invention may be varied in many ways within the scope of the following claim.
A method of stirring charges of a temperature of at least 800 C. with at least one phase in a vessel, in which materials are added to the charge in order to obtain physical processes in at least one phase, which comprises immersing into said vessel, and at least partly into said charge, a mechanical stirring device comprising a depending driving member having at its lower end a vertical pipe section and at least one lateral pipe extending out from said pipe section and having exposed side walls so that one side wall exerts a stirring action upon rotation of the stirrer, the interior of the lateral pipe communicating directly at its inner end with the interior of the pipe section, said pipe section having an opening therein remote from said pipe and being otherwise closed, said pipe section and lateral pipe together forming a vertical and outward flow path; the length of vertical pipe section between said opening and the point of communication of the lateral pipe being at least twice the internal diameter of the vertical pipe section revolving said stirring device at a speed of not more than 500 r.p.m. in relation to the vessel to cause streaming movement in at least the greater portion of said charge, the path of movement of each stirred portion of the charge in its passage through the vertical pipe section and lateral pipe being at least 15% of the sum of the mean height and mean diameter of the whole charge.
References Cited by the Examiner UNITED STATES PATENTS 1,311,964 8/1919 Grosvenor. 2,397,737 4/1946 Heuer -55 2,660,525 11/1953 Foster 75--77 3,893,860 7/1959 Lorenz 7549 OTHER REFERENCES The Iron Age, Nov. 2, 1939, p. 55.
BENJAMIN HENKIN, Primary Examiner.