US3504794A - Method and apparatus for controlling operation of a centrifugal - Google Patents

Description

Apnl 7, 1970 D. M. THOLL ET AL 3,504,794

METHOD AND APPARATUS FOR CONTROLLING OPERATION OF A CENTRIFUGAL Filed Feb. 12, 1968 5 Sheets-Sheet 1 Daarzid 772 -TirozZ Ezzaecif J 2%,

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p 1970 D. M. THOLL E L 3,504,794

METHOD AND APPARATUS FOR CONTROLLING OPERATION OF A CENTRIFUGAL 1 Filed Feb. 12, 1968 5 Sheets-Sheet 5 April 7, 1970 THOLL ET AL 3,504,794

METHOD AND APPARATUS FOR CONTROLLING OPERATION OF A CENTRIFUGAL 5 Sheets-Sheet 4 353 M E RH QMV Aprll 7, 1970 M, THOLL ET Al. 3,504,794

METHOD AND APPARATUS FOR CONTROLLING OPERATION OF A CENTRIFUGAL Filed Feb. 12, 1968 5 Sheets-Sheet 5 Ea mi) Jaime,

United States Patent C) 3,504,794 METHOD AND APPARATUS FOR CONTROLLING OPERATION OF A CENTRIFUGAL David M. Tholl, Cumberland, R.I., and Ernest J. Zltke, Brockton, Mass., assignors, by mesne assignments, to The De Laval Separator Company, Poughkeepsie, N.Y., a corporation of New Jersey Filed Feb. 12, 1968, Ser. No. 704,808

Int. Cl. B04b 13/00 US. Cl. 210-78 Claims ABSTRACT OF THE DISCLOSURE A rotatable centrifuging basket apparatus having variable speed power driving means is regulated by a speed sensing apparatus arranged to continuously sense changes in rotative speed of the basket. The sensing apparatus is particularly designed to operate at relatively low rotative speeds at which the basket is driven when moved into engagement with a scraper blade or plow for removing caked material from the inner peripheral surface of the basket at the end of a centrifuging cycle. The sensing device controls speed stabilizing means for adjusting the power driving means in response to change in basket speed within a specific range to increase power driving forces and maintain the basket at a proper rotative speed for carrying out the plowing operation without danger of stalling or causing excessive wear of the equipment.

This invention relates in general to centrifugals and, more particularly, to a method and apparatus for controlling the operation of a variable speed centrifugal. Machines of the variable speed class indicated include a curb, a basket rotatably supported in the curb, and power driving means for driving the basket at selected speeds, including a loading speed, a relatively high spin or centrifuging speed, and a relatively low plow speed for enabling a scraper blade or plow to remove caked material collected on the inner peripheral surface of the basket during removal of the liquid material.

In dealing with some mixtures which are required to be centrifuged, displacement of liquid material through the perforated basket of the centrifugal is accompanied by the accumulation of a layer or cake of solid material in the mixture. This cake may become quite firmly packed against the inner peripheral surface of the basket. An adjustable scraper or plow member is commonly used to remove the cake at the end of the centrifuging cycle and must be used with the basket slowed to a relatively low plowing speed.

The resistance of the cake to displacement by the plow may vary and, in many instances, may build up rapidly to exert sudden torque forces on the power driving means for the basket. Such torque forces can induce excessive wear and in some cases may cause slowing down of the basket toa point where it becomes stalled, thus resulting in loss of time and lowered efficiency.

Operation of centrifugals may also be of a somewhat hazardous nature when explosive mixtures are being processed. As is frequently the case this imposes limitations on the use of some forms of electrical controls where the danger of accidental sparks may be present.

It is, in general, a chief object of the invention to improve operation of variable speed centrifugals. The invention is also concerned with the problems indicated in connection with operating a centrifugal at relatively low plowing speeds to remove caked mate-rial.

Another specific object of the invention is to devise a speed stabilizing control apparatus which can be used to regulate the speed of a basket during plowing operations so that a sudden build-up in torque load will not unduly reduce speed of the basket or cause it to become stalled.

Still another specific object of the invention is to provide speed stabilizing control apparatus which can be safely used in processing explosive mixtures and which is capable of operating automatically and which can be conveniently and quickly installed on standard types of Centrifugals.

The invention and its other objects and novel features will be more fully understood and appreciated from the following description of preferred embodiments selected for purposes of illustration and shown in the accompanying drawings in which:

FIGURE 1 is a plan view of a centrifugal with which is associated a hydraulic motor and a separately located hydraulic pump apparatus for actuating the hydraulic motor, together with electrical control devices;

FIGURE 2 is a cross section taken on the line 22. of FIGURE 1;

FIGURE 3 is a diagrammatic view further illustrating the apparatus shown in FIGURE 1 and more particularly indicating electric control means in suitably connected relationship;

FIGURE 4 is a wiring diagram for air control means for the centrifugal apparatus shown in FIGURE 1; and

FIGURE 5 is a diagrammatic view illustrating a modified form of electric control apparatus.

From a consideration of the torque problem described above, we have devised a novel method for realizing the objectives outlined by utilizing metered changes in rpm. in the motor means employed to drive the basket of a centrifugal during the period when a plowing operation is in progress. The invention in one preferred embodiment therefore will be described with reference to measuring changes in the -r.p.m. of a hydraulic motor operated by a hydraulic pump and suitable control valve apparatus for the pump.

In a typical centrifuging operation using a hydraulic system of this class the hydraulic motor may drive the basket at a load speed of, for example 600 rpm. When loading is completed, the rotative speed of the basket is increased to a spin speed of 1100 rpm. for instance and run until the product is satisfactorily centrifuged. Thereafter the basket is slowed to a plow speed of approximately 50 rpm.

In one preferred embodiment the method and apparatus of the invention is particularly concerned with stabilizing the plowing speed and, in particular, with preventing any appreciable drop in plow speed below 50 rpm. during the period of operation in which plowing is required to be carried out. It will, however, be understood that the invention is not limited to this or any other particular operating speed or variation thereon.

Considering in further detail the method of stabilizing plow speed to maintain approximately 50 rpm. during period when excessive torque loads may be anticipated in removing cake from a centrifugal basket we may employ, for example, a centrifugal of well-known construction including a curb 2 having a bottom 3 solidly supported on a base of suitable nature. The bottom of the curb is formed with a discharge opening 4. At its upperside the curb 2 is constructed with a top section 6 bolted as at 8 and having a central section through which is rotatably mounted a vertical driving shaft mechanism 10 in a suitable bearing means 12.

Secured around the driving shaft 10 is a basket 14 constructed in the usual manner with perforations as 16 through which liquid material introduced into the basket may pass and drop down through the opening 4 of curb 2. The driving shaft 10 is powered by a. hydraulic motor 18 in a bearing mount 20'.

Also located through the top section 6 of the curb at one side of the drive shaft 10 is a pivoting plow apparatus including a scraper blade or shoe 22 supported on a shaft 24 which is adjustable about a vertical axis by means of a pneumatic cylinder 26. The cylinder 26 when engaged operates to swing the shoe 22 into and out of engagement with the inner peripheral surface of the basket 14.

A tachometer 28 is provided at the upper side of the hydraulic motor 18 in the conventional manner to measure rotative speed of the motor 18 and electrically connected to the tachometer is a speed or meter indicator 30 which is indicated diagrammatically in FIGURE 3.

At a point removed from the curb 2 is located a hydraulic pump 32 also shown in FIGURE 3 and driven by electric motor 33. The pump 32 is connected to hydraulic motor 18 by conduits 34 and 36. These conduits conduct hydraulic fluid into and out of the hydraulic motor from a hydraulic fluid supply 40. The hydraulic pump 32 is regulated by means of a spring-loaded pneumatically operated actuator or throttle device 42 which is connected to a source of compressed air 44 (FIGURE 3) through a series of control valves. Other forms of positioning devices may also be employed.

As indicated diagrammatically in FIGURE 4, the control valves are operated by solenoid devices electrically connected to operate in a predetermined sequence under the control of electrical relay control means as indicated diagrammatically at the upper right hand side of FIG- URE 4.

In a typical machine operation a pressure range of from 3 psi. to psi. may be supplied from a source of compressed air 44 (FIGURE 3), and this source of compressed air is connected by suitable conduit means through the solenoid control valves shown in FIGURES 3 and 4 to regulate the speed of hydraulic pump 32.

In starting a centrifuging operation the electrical motor 33 (FIGURE 3) is energized and drives pump 32 in turn delivering hydraulic fluid to hydraulic motor 18 at some desired rate controlled by the setting of valve means as determined by the electrical relay control means referred to above, and shown at the upper right hand side of FIG- URE 4.

Preferably the controls are first set to bring the machine up to a loading speed of approximately 600 rpm. by operating solenoid 48. When the machine reaches this loading speed the valve mechanism furnishes a pressure of approximately 7 p.s.i. to the throttle device 42 of the hydraulic pump 32 and a relay opens a feed valve for introducing material into the basket 14. Loading of material into the basket then continues until a predetermined depth of material is reached at which point loading is interrupted by suitable switch limit means. Thereupon valve 48 is opened and valve 50 is closed to provide a spin speed of some desired value. As a result of the valve being energized by the spin speed solenoid indicated a pressure of approximately 15 psi. is exerted through the throttle device 42 providing, for example, a spin speed of about 1,100 rpm.

The electrical control means continues to time the duration of the spin operation and at a desired point the spin speed solenoid and valve 50 are operated and an exhaust solenoid opens the exhaust valve 53. When the machine reaches a speed of a predetermined lesser rpm. the electrical control means operates a relay for re-energizing the exhaust solenoid 53 and also energizes the plowing speed solenoids and valves 46 and 47 to furnish a pressure of approximately four p.S.i. This produces a plow speed in motor 18 of about 50 to 60 rpm.

The present invention, as earlier indicated, combines with the conventional operations described a method and means for stabilizing plow speeds in a range of from 50 to 60 rpm. In carrying out this procedure we continuously regulate the position of the throttle device 42 in response to changes in speed of motor 18 within the selected range of plow speeds of from 50 to 60 rpm. This is accomplished by interposing in the compressed air lines, which is selectively set to deliver a pressure of 4 p.s.i. to throttle device 42, an adjustable air valve of the flapper type which is indicated in FIGURE 3 diagrammatically by numeral 66 and which can be opened to increase the pumping pressure in pump 32 whenever a drop in r.p.m. at the motor 18 occurs.

In carrying out this procedure in one preferred embodiment of the invention, there is combined with the speed regulating apparatus already described an adjustable shunt potentiometer which, as shown in FIGURE 3, is electrically connected into the conductor wires leading to the speed indicator 30 so as to sense changes in voltage across the speed indicator.

Sensed changes in voltage modified by the potentiometer 60 are led into a converter device 62 of a type suitable for changing electromotive forces to current. The resulting output of current from member 62 is electrically connected to a transducer device 64 for changing electrical energy into mechanical movement. This mechanical movement is applied through a pivoting linkage 65 (FIG- URE 3) to adjustably close the position of a flapper valve 66 located in the plow speed air conduit leading to member 42 in a slightly opened position so as to increase pressure up to approximately seven pounds at the pump thereby producing a speed of about 50 r.p.m.

In operating this stabilizing control apparatus, the plow 22 starts to move into contact with caked material at the inside of the basket 14 and the basket at this point is being driven by a hydraulic motor 18 at a range of speeds of from 50 to 60 rpm. As soon as the plow engages against a cake of suflicient resistance to cause the machine to slow down appreciably, the potentiometer 60, which is in series with the rpm. meter 30, sends an electrical signal to the transducer which adjustably closes the flapper valve 66 and provides for increasing the pressure to the pump 32 with the resultant increase in speed of hydraulic motor 18. Immediately upon the hydraulic motor regaining its desired speed of from 50' to 60 rpm. the flapper valve 66 adjustably opens to a prior slightly opened position and operation continues as before. A similar cycling takes place thereafter whenever the machine slows down appreciably as indicated by the meter output.

It will be apparent that we may also use additional valve means to control or maintain suitable load and spin speeds when an unusually heavy load resistance may suddenly develop in response to an appreciable change in rpm. above or below a desired predetermined range for either of such speeds. In addition, we may desire to vary the location and type of the adjustable flapper valve 66.

In still another desirable modification of the invention, we may employ an apparatus of the class described in FIGURE 5 in which a variable speed electric motor 72 is employed to drive a basket 70. As noted in FIGURE 5, the basket 70 is suspended below the driving motor 72 which is contained in an explosion proof housing and electrically connected to an electrical control circuit consisting of a silicon control rectifier 74 located at a removed point at an opposite side of a shield barrier 76. This revents any possible occurrence of sparks coming into contact with an explosive mixture in the basket. The member 74 is operated under the control of a firing circuit device 78 of conventional nature responsive in turn to change in electrical signals from a transducer 80, also externally located with respect to barrier 76. This transducer 80 includes a pneumatically displaced element connected to an air line 82 and this air line 82 has connected therein a flapper valve 84 which is arranged to regulate flow of compressed air through the line in response to changes in speed of motor 72 as regulated by a pneumatic tachometer 86.

By means of this arrangement it will be apparent that the speed of the electric motor 72 may be regulated in accordance with a change in r.p.rn. resulting from engagement of a plow member with caked material in the basket apparatus 70 and any drop in r.p.m. of appreciable nature will result in the wiring circuit acting through the silicon control rectifier 74 increasing the motor speed and overcoming caked resistance almost instantly. It will also be evident that by means of the method and apparatus of the invention a more efficient centrifuging operation may be carried out, particularly with respect to the removal of cake. By compensating for torque load in the manner described, a greatly simplified discharger shoe operation may be carried out with one discharger blade making a single cut into the caked material instead of having to be utilized to make a number of cuts at progressively lower levels as is now the practice in many cases.

We claim:

1. In a method of centrifuging the steps which include containing a mixture of liquid and solid material in a perforated basket which is mounted for rotative movement in a curb member and actuated by variable speed power driving means, subjecting the mixture to centrifugal forces exerted at relatively high rotative speed of the basket whereby the liquid component is centrifugally displaced through the perforated basket and solid material is collected on the inner peripheral surface of the basket in the form of a hard layer of cake, reducing the rotative speed of the basket to a redetermined value by controlling the said power driving means, then engaging the inner periphery of the relatively slowly rotating basket and the said layer of caked material against a cake displacing plow whereby the caked material is displaced with torque forces being induced tending to slow down the rotating basket, sensing changes in basket speed, and continuously regulating the power driving means in response to sensed changes in rotative speed of the basket by said torque forces to maintain the basket in rotative operation while the caked material is being removed.

2. A method according to claim 1 in which change in rotative speed of the basket induced by said torque forces is electrically sensed and the power driving means is regulated in accordance with the electrically sensed changes.

3. A method according to claim 2 in which the power driving means consists of a hydraulic motor and said electrically sensed changes in basket speed control the rate of flow of hydraulic fluid supplied to the hydraulic motor.

4. A method according to claim 2 in which the power driving means consists of an electrical motor and the electrical sensing changes in basket speed are automatically transmitted to the said electrical motor.

5. A method according to claim 1 in which the change in rotative speed of the basket is mechanically sensed and the power driving means is regulated in accordance with the mechanically sensing changes.

6. Apparatus for centrifuging a mixture of liquid and solid material comprising a curb, a perforated basket mounted for rotative movement in the crub, a plow in the basket, means mounting the plow for movements to and from an operating position in which the plow is engageable with solid material caked on the inner periphery of the basket, for plowing the caked material from said inner periphery, variable speed power driving means for rotating the basket at a range of speeds including a centrifuging speed and a relatively low speed at which said plowing is effected, means for sensing a reduction in said relatively low speed of the basket during the plowing, and means responsive to said sensing means for increasing power driving forces exerted on the basket to counteract said sensed reduction of the plowing speed.

7. A structure according to claim 6 in which the power driving means consists of a hydraulic motor and the sensing means consists of an electrically operated mechanism for regulating the speed of the hydraulic motor.

8. A structure according to claim 7 in which the electrically operated mechanism includes a meter for electrically measuring speed of the hydraulic motor and means for converting electrical measurements into mechanical movement for regulating flow of hydraulic fluid into the hydraulic motor.

9. A structure according to claim 6 in which the means responsive to the sensing means for increasing power driving forces consist in a pump, a pressure-regulated valve for controlling the pump and a pneumatic valve device operable to change the setting of the pump valve, said pneumatic valve device being responsive to sensed changes in rotative speed of the basket.

10. A structure according to claim 6 in which the means responsive to the sensing means for increasing power driving forces consist in a pump, a pressureregulated valve for controlling the pump and a pneumatic valve device operable to change the setting of the pump valve, said pneumatic valve device being responsive to sensed changes in rotative speed of the basket, and said means for sensing a change in rotative speed of the basket including an electrically operated meter for indicating electrical voltage changes and means for converting said voltage changes into current changes.

References Cited UNITED STATES PATENTS 2,461,764 2/1949 Olcott 210- 2,667,974 2/1954 Hertrich 210l45 3,152,462 lO/1964 Elliott et al. 210143 X 3,262,569 7/1966 Wade et a1. 210-144 I. L. DE CESARE, Primary Examiner U.S. Cl. X.R.

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