US3900293A - Controlling admixture of aqueous liquid to ball rolling of powdery iron ore - Google Patents

Abstract

A method of and a device for controlling admission of material consistency adjusting liquid to a powdery moist material to be shaped into balls by treatment in a ball rolling machine comprising an open ended ball rolling drum having an entrance end for the supply of said material and an exit end. A sieve is provided for separating balls of a prescribed size and the rest of material leaving the drum at the exit end thereof, a conveyor for conveying material passing through the sieve as return material back to the entrance end of the drum, means for supply of water to material charged into the drum at the entrance end thereof, means for controlling said supply of said material consistency adjusting liquid, and means for measuring the rate at which said return material is conveyed to the entrance end of the drum. A rate sensing governor senses variations in said rate of return material and provides an indication whether amplitude of oscillations in said rate is above or below a predetermined amplitude limit, the governor being arranged to in dependence of indication whether amplitudes are above or below said predetermined limit actuate a servomotor to adjust to liquid supply control means so as to increase or decrease, respectively, the supply of liquid.

Description

United States Patent Sjoberg et a1.

1 1 Aug. 19, 1975 1 CONTROLLING ADMIXTURE OF AQUEOUS LIQUID TO BALL ROLLING OF POWDERY IRON ORE Sweden [73] Assignee: Luossavaara-Kiirumavaara AB.,

Stockholm, Sweden [22] Filed: Dec. 29, 1972 [21] Appl. No.: 319,467

[30] Foreign Application Priority Data Dec. 30, 1971 Sweden 16944/71 [52] US. Cl. 23/313; 264/117; 425/222; 75/3 [51] Int. Cl. C2lb l/08; C2lb l/24; BOlj 2/12 [58] Field of Search 23/313, 314; 264/117; 425/222; 75/3 [56] References Cited UNITED STATES PATENTS 2,699,381 l/l955 King 23/314 2,800,399 7/1957 King 23/314 2,867,513 l/l959 Bayer 23/314 2,872,300 2/1959 Pollock... 23/314 2,948,918 8/1960 Austin 23/314 3,017,662 1/1962 Marsh 23/314 3.036737 5/1962 King..." 23/314 3,293,003 12/1966 Jones 23/314 3,390,424 7/1968 Fortune 23/314 FOREIGN PATENTS OR APPLICATIONS 845,041 8/1960 United Kingdom 23/314 PEQHITTED LQWER LIMIT UANTITY RETURN MATERIAL 688,776 3/1953 United Kingdom 23/314 Primary ExaminerA. Louis Monacell Assistant Examiner-S. .I. Emery Attorney, Agent, or FirmWa1ters, Schwartz & Nissen [57] ABSTRACT A method of and a device for controlling admission of material consistency adjusting liquid to a powdery moist material to be shaped into balls by treatment in a ball rolling machine comprising an open ended ball rolling drum having an entrance end for the supply of said material and an exit end. A sieve is provided for separating balls of a prescribed size and the rest of material leaving the drum at the exit end thereof, a conveyor for conveying material passing through the sieve as return material back to the entrance end of the drum, means for supply of water to material charged into the drum at the entrance end thereof, means for controlling said supply of said material consistency adjusting liquid, and means for measuring the rate at which said return material is conveyed to the entrance end of the drum. A rate sensing governor senses variations in said rate of return material and provides an indication whether amplitude of oscillations in said rate is above or below a predetermined amplitude limit, the governor being arranged to in dependence of indication whether amplitudes are above or below said predetermined limit actuate a servomotor to adjust to liquid supply control means so as to increase or decrease, respectively, the supply of liquid.

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CONTROLLING ADMIXTURE ()F AQUEOUS LIQUID TO BALL ROLLING OF POWDERY IRON ORE When rolling a moist granulous or powdery material to balls which are then to be further treated by sintering to provide sintered balls, such as ore ball sinter, it is, to obtain high quality ball sinter, of importance that the raw balls fed to the sintering oven have a sufficient strength. It is a prerequisite for a high production that the raw balls have, amongst other properties, a liquid content within extremely narrow limits, plastic or wet or otherwise too weak balls preventing the processing air during the subsequent sintering to uniformly flow through the ball bed consisting of balls located side by side and on top of each other during sintering. Further, ball sintering machines, irrespective of type, are to be fed with an even flow of raw balls, wherefore the rather high variations in feeding rate which in the present practice arise by so called pulsing" in the delivery of raw balls from a ball rolling machine is very inconvenient.

An ideal when producing raw balls would be a production of raw balls in such a manner that the quantity of raw balls produced per time unit and fed to the sintering machine remains substantially constant at a desired level, an ideal situation which can at present not be reached to a desired degree for the following reasons:

The pulsing in the delivery of raw balls which are ready for being transported to the sintering machine is dependent of a large number of facts. Important such facts are, for instance, variations in the grain size distribution and moisture content of the slick which is fed to the ball rolling machine, the slope and rotational speed of the ball rolling drum, etc. Further, the so called rolling circuit is individual to each ball rolling machine due to possibly different drum length of the machine, different rotational speed, different circulation time in the rolling circuit, wear of sieve bars, and the like, to the effect that characteristics of one rolling circuit can not be immediately adapted to another one.

It appears to be a difficult task, for each individual rolling circuit to chart the influence of the different factors on the quality of the obtained raw balls and in this manner to optimize the ball rolling process, this in particular due to the face that, in practice, the properties of the slick fed to the rolling machine is continuously varying and it is, at present, not possible to continuously and with a satisfactory accuracy as to all details of importance to measure these properties in such a manner that the ball rolling procedure can be univocally foreseen.

The rolling circuit of a ball rolling machine broadly appears from the following:

At one end, the upper one, of a sloping ball rolling drum a slick is fed to the drum, said slick having a content of granulate or powdery material and liquid which by experience is considered as suitable for the rolling, and material which has already passed the rotating drum but which has as yet not got the size of raw balls ready to be passed on to the sintering oven. A sieve comprising parallel rods or bars is arranged at the other, lower, end of the drum, this sieve letting such material, which after having passed the drum has as yet not obtained a prescribed size, to pass through the sieve, while balls which have obtained the prescribed size do not pass through the sieve, but are instead conveyed to a machine for sintering the balls. The material passing the sieve and representing balls which have as yet not reached a prescribed size, fragments of crushed and other material passing the sieve is returned by means of a conveyor to the upper end of the drum and fed into the drum to again pass through the drum together with fresh slick.

Hitherto it has been common practice to control the ball rolling process by aid of observation by the operator of the ball rolling machine, the operator by guidance of such observations controlling the rolling process by varying the rate of addition of liquid to the rolling drum according to the following pattern:

a. When oscillations or pulsing in the rate of goods returned in the rolling circuit from the sieve to the drum inlet show a tendance of increasing in amplitude, the addition of liquid, mostly water, adjacent the inlet port of the rolling drum is successively increased by the operator of the machine, the rate of change being chosen, with great carefulness based on experience, until the oscillations cease or are hardly noticeable. After the lapse of some time, the raw balls will, as a rule, then on the contrary prove to contain too much liquid, manifested by the balls adopting a plastic consistency and too low strength properties, the consistency and strength of the balls being continuously checked by the operator by means of a so called knocking test" (KH45).

b. When plastic or wet balls, which are too weak and deformable to carry the load to which they are exposed in the sintering oven, are observed, the rate of supply of liquid adjacent the inlet port of the rolling drum is successively decreased. After some time this will usually lead to a situation in which the rate of added liquid is too low, in consequence whereof oscillation or pulsing in the quantity of return goods will usually again increase so as to necessitate a return to the control procedure mentioned under (a).

In this connection it is also to be mentioned that the difference between too small" and too large addition of liquid for a particular one slick is so minute that the difference in rate of addition is in practice measurable only with difficulty. The difference between too small and too large as well as the total quantity of liquid required for a particular ore slick to obtain an optimal result varies from time to time with variations of properties of the solids of the slick, all this making the control of the rolling procedure rather hazardous.

The highest quality raw balls are obtained during an intermediary state in which a small pulsing in the feed rate of return goods is present and the amplitude of the variations is still small as compared with the average feed rate of return goods. Obtaining such a state of running the rolling machine is however in practice considered as strokes of luck, this with respect to the fact that a systematic adaption to a pulsing amplitude at which the ball quality is at an optimum can not be made by guidance of information obtained simply by observing the rolling process.

The present invention, which is based on the experience explained above, that the raw ball quality has an initimate, although secondary, connection with oscillation or pulsing of the rate at which material leaving the rolling drum passes the sieve and is returned to the inlet of the drum relates to a method of controlling addition of liquid in a ball rolling device, said method having characteristics as appearing from the appended claims.

Further, the invention is in respect ofa device to execute the method, said device having characteristics as appearing from appended claims in respect ofa device.

Thus, the invention is based on the rather peculiar and not yet explained fact that the quantity of return material varies not only with the ball quality or liquid content of the slick (which is, as such, obvious), but that as well the quantity of return material is exposed to oscillation or pulsing having an amplitude which is intimately associated with the ball quality and which is small or none when the balls contain too much liquid and large when the balls contain too little liquid.

On the other hand, the period of the oscillations is, as far as have been hitherto stated, substantially individual of a particular ball rolling device and independent of the amplitude of the variations in quantity of the returned material. Thus, for a particular ball rolling machine, the quantity of return material continuously varies with the frequency one-seventh period per minute irrespective of the amplitude, while for a second particular rolling machine the frequency was oneeighth period per minute.

The average rate of recirculated return material has, in these measurements, been between 150 and 200 percent of the rate of slick fed to the rolling machine. With both of the said machines, the amplitudes of the variations of return goods during the oscillations superimposed on the average feed rate was about percent of the rate at which the ore slick is fed into the rollingdrum when the produced balls have shown the desired quality (that is, the added quantity liquid has been the correct one for the actually treated slick material), while the amplitudes during periods with too large ad dition of water (leading to wet plastic balls) have been less than fi percent about the average level. When the addition of water was too low to provide for balls with optimal strength properties, the oscillations have had amplitudes considerably above the said 1': 10 percent, as far as up to i 70 percent of entering quantity of ore slick, the average level of quantity of circulating goods above a certain lowest amplitude (high content of liquid) increasing with increasing amplitude,

Due to the fact that variations of the order 2 10 percent of the rate of fresh slick fed into the machine, thus corresponding to about 7 percent of the average rate of return material, said variations having the frequency of the order mentioned above, has no inconvenient influence on the operation of the oven to which the ready balls are fed to be sintered, the amplitudes in the rate of transport of the return material can, according to the invention, be utilized for a fully automatic control of the ball rolling, aiming at a high and invariable quality of the raw balls delivered by the rolling machine, such quality of the balls being, as described above, being a condition for obtaining a high-qualitative ball sinter product.

The invention will become more readily apparent from the following exemplary description and the accompanying drawings wherein:

FIG. 1 is a schematic plan of the rolling circuit of a ball rolling machine,

FIG. 2 is a schematic control circuit diagram ofa circuit for controlling addition of liquid to the slick mate rial to be treated in the rotatable drum of the ball rolling machine, and

FIG. 3 is a diagram showing. by way of example, the variations in the rate of return material as a function of time.

Referring to FIG. I, it shows, as a skeleton sketch, a ball rolling machine having a rotational rolling drum 1 to one of the ends of which, the inlet end 2, a slick, such as iron ore slick, containing a quantity of liquid calculated to be substantially adapted for the proper ball rolling, being, as represented by arrow 3, supplied by means of a conveyor of arbitrary construction suitable for the purpose as well known to the art. The rotational axis of the drum is sloping downwardly towards the exit end 4 of the drum, at which ready made rolled balls, balls not yet ready for sintering, and remaining slick material leaves the drum to pass a sieve 5, usually consisting of bars extending in the axial direction of the drum. Balls ready for being sintered roll over the sieve onto a conveyor 6 by which, as indicated by arrow 7, the finished balls are conveyed for further treatment in a sintering oven (not shown). Material passing through the sieve 5, said material thus consisting of balls which have as yet not reached a prescribed size, fragments of crushed balls and remaining loose slick material, is conveyed by a conveyor 8 as indicated by arrow 9 to a return material conveyor 10, by which the material passing through the sieve is returned to the entrance of the drum for being treated anew in the drum.

Based on the above explained experience as regards the connection between ball quality and amplitude of oscillations in the quantity of return material per time unit, the ball rolling apparatus is, according to the invention, provided with a control equipment, by means of which the amplitude of oscillations in the quantity per time unit of return material returned to the drum is being kept at or adjacent a level, with which the quality of the finished balls, that is, the balls delivered by the sieve 5 to the conveyor 6, have adopted a strength desired and required for the following treatment thereof in a sintering machine. Said control equipment comprises a conveyor weighing machine 1 1, a governor 12 controlled by weight information received from the conveyor weighing machine, said governor 12 in the embodiment described below having two measuring limits for an input signal received from the weighing machine 11, said measuring limits representing values of rate of return material, that is, quantity per time unit, on both sides of the average value of the rate of return material, said two values representing amplitudes in the vicinity of which the largest and smallest quantity of return material during the oscillations in said quantity are to be to obtain balls with the desired properties during rolling.

Thus, governor 12 constitutes a feeler which states whether the oscillations are between two predetermined limits which are located such a distance from on both sides of the average rate of return material that the total amplitude between the limits corresponds to the optimal ball quality. As shown in FIG. 2, the governor 12 has three output terminals, namely one, 15, by which a signal is delivered to a time relay 16 when the regulator senses a rate of return material above the higher limit. an output terminal 17 delivering a signal to a time relay 18 when the rate of return material is between the two predetermined limits, and an output terminal 19 for a signal to a time relay 20 when the rate of return material is lower than the lowest predetermined limit.

The time relays 16, 18, and are such that after a period, duly selected with respect to the period of the oscillations in the rate of return material, they emit a pulse exciting a predetermined stepwise change of rate of addition of water to the slick treated in the rolling drum, the rate of change being a predetermined one based on experience. The stepwise change of rate of added liquid is provided for by means of a servomotor 21, controlled by excitation pulses from one of the relays 16, 18, 20, the servomotor actuating a valve 22 to control the quantity of water added to adjust the liquid content of the slick by means ofa conduit 23, by which the water is fed to the slick in a manner as such well known to the art for controlling the moisture content of the material treated in the rolling drum.

In the embodiment illustrated by FIG. 2, the governor is, as intimated by contacts 13 and 14, made so as to actuate relay 16 when the amplitude of the oscillations in the rate of return material increases above the highest limit and to actuate relay 20 when the amplitude decreases below the lowest limit, the time relay 16 or 20 after said predetermined delay and if then the rate of return material has not returned to within the limits generating a signal for the stepwise increase of addition of water to the servomotor 21. Time relay 18, which is activated when the oscillations during a predetermined sampling period has not reached anyone of the predetermined limits, then emits a signal to the servomotor 21 causing a decrease of the rate of added water, that is, a stepwise closing of valve 22.

It is obvious that a corresponding result in accordance with the method which is subject of this inven' tion can be attained by other means, well understandable to the man skilled in the art, the important feature being that an increase of rate of added water is provided when the amplitudes increase above a limit and that the addition of water is decreased when the amplitudes are below said limit. Generally speaking the control may be provided for by use of one single limit. With a device in which two limits are used, an upper and a lower limit, the additional possibility of obtaining a supervision of the position of the control range relative to an average of the rate of return material during a plu rality of variation periods is obtained.

FIG. 3 shows a typical control scheme when using the devices illustrated by FIGS. 1 and 2. Curve represents quantity of return material per time unit as mea sured by the weighing machine 11. In practice, the period of the oscillation may be in the order of 7 to 8 minutes. Lines 31 and 32 represent the upper and the lower limit, respectively, of the amplitude of the oscillations to obtain a desired quality of the balls. In the area 33 the position of governor 12 in dependence of the input signal from the weighing machine 11 is shown, the marking of the surfaces during sampling and valve action being indicated in the figure. The rate of water added under the control of valve 22 of FIGS. 1 and 2 is illustrated by the lowermost curve 34 (drawn in an enlarged ordinate scale as compared with the ordinate scale of curve 30).

From a first time 1 on and during a sampling time t, to the rate of return material remains within the limits 31 and 32, the increasecontacts l3 and 14 (or corresponding means) of the governor 12 are not actuated. The period of time [T1] represents a sampling time at the expiry of which relay 18 emits a decreasepulse to the servomotor 21, the servomotor then clos- -A signal is emitted by the governor 12 to the time relay 16, the time relay however, in the same way as relays l6 and 20, being such that it reacts only when the signal has reached a predetermined lowest duration. Consequently, the valve is not actuated. Neither the valve is actuated for reason that the oscillation in the rate of return material during the time period I to 1 increases above the upper limit, and neither the time relay 20 is actuated for reason that the rate of return material decreases below the lower limit during the period to I However, due to the fact that the limits have been reached, the decreased-signal which, as a principle, is in readiness to be passed onto the decrease-relay l8 whenthe rate remains between the limits, is inhibited. The period t to 1 during which the rate of return material thereafter increases above the upper limit is, however, so long that relay 16 is activated and provides an increase"-signal to the servomotor 21, the servomotor then opening the valve 22 a corresponding step. The valve motions are, in the area 33 of FIG. 3, indicated by black rectangels provided with an arrow indicating a valve motion decrease and increase, respectively. During the following oscillations in the rate of return material, between the times t and t the rate of return material increases above and decreases below, respectively, the respective limits during a time sufficient to cause actuation of the servomotor and correspondingly a valve motion for each period. Due to the increase of rate of water addition the oscillations slowly decrease, to finally, after the time adopt a value for which further increase-signals to the servomotor are not generated. After the time r the oscillations are so small that the rate of return material does not reach either the upper or the lower limit, wherefore an inhibition of decrease-signal from the relay 18 to the servomotor does not appear, so that relay 18 is actuated at the end of sampling periods I and so on until the oscillations again increase in amplitude so that the limits are reached.

It is to be observed that the rate of added water to keep the oscillations at a selected amplitude may be different at different occasions, this due to the fact that the water content of the fresh slick supplied to the rolling machine is continuously varying. Further, it is to be observed that the difference in water content of balls which are too wet and balls which are too dry is, relatively seen, extremely minute and hardly measurable with means usable in practice.

Obviously, a control of the water content of the slick may, as a principle, as well be provided for by other means than the ones described] by reference to FIGS. 1 and 2, as, for instance, by aid of electronic or other integration apparatus which during predetermined sampling times, the length of which are, obviously, to be selected with due respect to the period of the oscillations and larger than this period, measured time during which the oscillations are above or below a predetermined limit, or establish that they do not do so, and in dependence of the result provides for an increase of rate of added water, a decrease of said rate. or maintains the rate uneffected.

in dependence of the way within the scope of the invention in which it is stated that the variation amplitude is within, at or outside a predetermined limit, calling for a decrease, maintaining or increase, respectively, of the addition of water, the device has a number of obvious auxiliary means which may be necessary for obtaining the desired result.

Thus, in the embodiment described with reference to FIGS. 1 and 2, a clock signal generator 24 is present, providing for clock signals with a periodicity selected with respect to the periodicity of the rate variations and the circulating time for the material in the rolling circuit. The clock pulse generator 24 generates a signal applied to governor l2 and defining the above mentioned sampling time at the end of which an increasesignal is sent to the servomotor, should the amplitude not touch a predetermined limit during the sampling period. Further, it may be a convenient measure, in particular when the device is such that a control signal is supplied to the servomotor with a predetermined to prevent a valve motion caused by occasional variations in the rate of return material independently of the water content of the slick and the balls, to provide for a back signal indicating the completion of a control motion of the servomotor 21 or valve 22, respectively, said signal being applied to the governor 12 via a back signal conductor 25 to zero-positioning it, this to obtain that the state present prior to the control motion of servomotor or valve does not, due to the time constant valid for the rolling circuit, gives rise to a control signal for a control in the same direction and before the control already provided for has been stated by observation of a change in the oscillation amplitude of the return material.

Finally, it is to be observed that the average quantity per time unit of the return material measured by the measuring machine 11 has, according to experience, a determined relation to the quantity of fresh material supplied to the rolling machine for a particular ball rolling circulation circuit, to the effect that an adjustment or change of amplitude limits in the governor 12 may be provided for by guidance of a weighing machine 26 which provides for a signal indicating rate of fresh material supplied to the machine. Normally, such a weighing machine 26 is present in the equipment of conventional ball rolling machines of the kind.

What we claim is:

l. A method of controlling a supply of liquid to a material composition adapted to be formed into balls for sintering, said composition being constituted of a slick consisting of a mixture of powdery iron ore material and aqueous liquid in a ball rolling machine comprising an open ended rotary ball rolling drum to an entrance end of which is supplied a supply of fresh slick and a supply of said ore material which has already passed through the rotary drum and which after having left the drum at an exit end remote from said entrance end, has passed through a sieve separating material which upon passing the drum is below a size of balls of a prescribed size to be passed on as a final product of the machine, said separated smaller-sized material passing through the sieve being reconveyed from said exit end back to said entrance end of the drum at a rate corresponding substantially to the rate of which said reconveyed material passes through the sieve, the liquid content of the material being treated in the drum being adjusted by varying a supply of aqueous liquid being added to the material so as to change the consistency of the material, measuring amplitudes of variations in the rate at which said material is reconveyed from said exit end to said entrance end of the drum, ascertaining whether said amplitudes increase above or decrease below a predetermined variation amplitude, increasing said rate of supply of said consistency adjusting aqueous liquid when said amplitudes increase above said predetermined amplitude and decreasing said rate of supply of said consistency adjusting aqueous liquid when said amplitudes decrease below said predetermined amplitude.

2. A method according to claim 1, characterized by increasing said supply of material consistency adjusting liquid when said amplitudes increase above a first predetermined limit and that said supply of material consistency adjusting liquid is decreased when said amplitudes decrease below a second predetermined limit, said second predetermined limit representing smaller amplitudes than said first predetermined limit.

Claims (2)

1. A METHOD OF CONTROLLING A SUPPLY OF LIQUID TO A MATERIAL COMPOSITION ADAPTED TO BE FORMED INTO BALLS FOR SINTERING, SAID COMPOSITION BEING CONSTITUTED OF A SLICK CONSISTING OF A MIXTURE OF POWDERY IRON ORE MATERIAL AND AQUEPUS LIQUID IN A BALL ROLLING MACHINE COMPRISING AN OPEN ENDED ROTARY BALL ROLLING DRUM TO AN ENTRANCE END OF WHICH IS SUPPLIED A SUPPLY OF FRESH SLICK AND A SUPPLY OF SAID ORE MATERIAL WHICH HAS ALREADY PASSED THROUGH THE ROTARY DRUM AND WHICH AFTER HAVING LEFT THE DRUM AT AN EXIT END REMOTE FROM SAID ENTRANCE END, HAS PASSED THROUGH A SIEVE SEPARATING MATERIAL WHICH UPON PASSING THE DRUM IS BELOW A SIZE OF BALLS OF A PRESCRIBED SIZE TO BE PASSED ON AS A FINAL PRODUCT OF THE MACHINE, SAID SEPARATED SMALLERSIZED MATERIAL PASSING THROUGH THE SIEVE BEING RECONVEYED FROM SAID EXIT END BACK TO SAID ENTRANCE END OF THE DRUM AT A RATE CORRESPONDING SUBSTANTIALLY TO THE RATE OF WHICH SAID RECONVEYED MATERIAL PASSES THROUGH THE SIEVE, THE LIQUID CONTENT OF THE MATERIAL BEING TREATED IN THE DRUM BEING ADJUSTED BY VARYING A SUPPLY OF AQUEOUS LIQUID BEING ADDED TO THE MATERIAL SO AS TO CHANGE THE CONSISTENCY OF THE MATERIAL, MEASURING AMPLITUDES OF VARIATIONS IN THE RATE AT WHICH SAID MATERIAL IS RECONVEYED FROM SAID EXIT END TO SAID ENTRANCE END OF THE DRUM, ASCERTAINING WHETHER SAID AMPLITUDES INCREASE ABOVE OR DECREASE BELOW A PREDETERMINED VARIATION AMPLITUDE, INCREASING SAID RATE OF SUPPLY OF SAID CONSISTENCY ADJUSTING AQUEOUS LIQUID WHEN SAID AMPLITUDES INCREASE ABOVE SAID PREDETERMINED AMPLITUDE AND DECREASING SAID RATE OF SUPPLY OF SAID CONSISTENCY ADJUSTING AQUEOUS LIQUID WHEN SAID AMPLITUDES DECREASE BELOW SAID PREDETERMINED AMPLITUDE.

2. A method according to claim 1, characterized by increasing said supply of material consistency adjusting liquid when said amplitudes increase aBove a first predetermined limit and that said supply of material consistency adjusting liquid is decreased when said amplitudes decrease below a second predetermined limit, said second predetermined limit representing smaller amplitudes than said first predetermined limit.

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