US2723753A - Gyratory sifter - Google Patents

Description

Nov. 15, 1955 E. B. COOK GYRATORY SIFTER Filed Oct. 29, 1952 United States Patent GYRATORY SIFTER Eugene B. Cook, Hales Corners, Wis., assignor to Allis- Chalmers Manufacturing Company, Milwaukee, Wis.

Application October 29, 1952, Serial No. 317,517

Claims. (Cl. 209-332) The present invention relates generally to an improved apparatus and balancing means for agitating devices and more specifically to an improved apparatus and balancing means for gyratory screens and sifters.

Agitating motions have heretofore been imparted to prior art mechanisms such as screens and sifters by gyrating the part to be agitated about an axis. However, the part in moving along its gyratory path generates a centrifugal force which acts at right angles to the axis and produces a turning moment tending to tip theaxis. If this turning moment is not balanced tipping forces are transmitted through the frame of the mechanism to the supporting structure to which it is attached causing the structure, if not a rigid'one, to heave and roll as the mechanism gyrates.

It has heretofore been proposed to compensate for the centrifugal force by incorporating in the mechanism certain other masses mounted for the purpose of generating centrifugal forces to counterbalance the centrifugal force generated by the gyrating part. The nature of thepresent invention resides in the provision of an improved arrangement of sifter parts and additional masses so chosen and positioned along the axis that the sum of the turning moments due to all of the forces present are equated to zero to thereby effectively eliminate the tipping forces.

It is therefore an object of the present invention to provide an improved gyratory sifter in which the gyrating part is statically and dynamically balanced so that the summation of the turning moments of all centrifugal forces equals zero.

Another object of the invention is to provide an improved gyratory device in which high inertia stresses on the bearings, supporting rods and the supporting surface due to unbalanced forces,'are substantially reduced or eliminated.

, Another object of the invention is to provide an improved gyratory sifter which substantially eliminates heaving and rolling of the structure supporting the sifter.

Another object of the invention-is to provide an improved gyratory sifter which is steadier and quieter in operation than prior art gyratory sifters.

Another object of this invention is to profide an improved gyratory sifter with motor driven gyrating means in which the motor may be automatically deenergized in response to unbalanced loading of the gyratory part.

Another object of the invention is to provide an improved gyratory sifter which is cleaner in operation and easier to clean than prior art gyratory sifters.

Objects and advantages other than those set forth will be apparent from the following description when read together with the accompanying drawings, in which:

Fig. 1 is a view in elevation and partly in section of a gyratory sifter embodying the invention;

Fig. 2 is a force diagram showing masses M1, M2 and M3, centrifugal forces F1, F2 and F3 and their general direction, R1, R2 and R3 that represent the distances the masses are located from an axis of rotation A-A, and X1 and X3 represent the distances that the masses M1 "ice 2 and M3 are located axially from the center of bearings 49; and

Fig. 3 is a side view of an alternative embodiment of the invention.

The gyratory sifter shown in Fig. 1 comprises generally three subassemblies identified, respectively, (in vertically ascending order from the bottom) as a base frame 1, a vertically extending crank shaft assembly 2 rotatably journaled in the frame 1, and a gyratable sieve assembly 3 journaled in the crank shaft assembly 2.

The base frame 1 comprises a plurality of sill members 4 which may be angle struts. The sill members 4 are rigidly attached as by bolts 5 to a supporting surface or foundation identified by the line 6. Bridging the gap between the sill members 4 and rigidly fastened thereto, as by welding, is a transverse structure 7 which is preferably dished upward to provide a space beneath.

The transverse structure 7 is provided with a vertical bore at its center for receiving therein a bearing housing 8 which is made fast to the structure 7 by any suitable fastening means, such as bolts 11. Secured in the housing 8 by any suitable means is a bearing 12 of the self-aligning antifriction type. The bearing has an inner race 13 adapted to grip, as by a shrink fit, a downward extending journal 14 of the crank shaft 2. Lubricant is fed to the bearing 12 by means of a lubrication fitting 15 mounted in the housing 8.

The crank shaft journal 14 extends upward from the bearing 12 and terminates in a disk 16 radially oifset from the axis of rotation of the journal 14. Fastened rigidly to a flange 17 of the disk 16, as by bolts 18, is an eccentric throw shown as an upward extending tubular member 21 equipped with flanges 22 at both its ends. The tubular member 21 forms a bearing housing for a bearing means preferably comprising a pair of vertically spaced antifriction bearings 23 mounted in general register therein and held in place by means of snap rings 24. Lubrication is supplied to the bearings by any suitable means such as a lubricating fitting 25 mounted in the flange 17 and communicating with the interior of the bearing housing.

Each of the pair of bearings 23 have inner races 26 adapted to grip a stub shaft 27. The upper end of the stub shaft terminates in a disk 23 having a flange 31. The sieve assembly 3 is mounted on top of the flange 31 and attached thereto by any suitable means, such as bolts 32.

Since the tubular member 21 is otfset from the axis of rotation of the journal 14, the longitudinal axis of the shaft 27 will also be offset from the axis of rotation of the journal 14.

The sieve assembly 3 comprises a plurality of detachable sieves 33 in vertically stacked relation, the bottom sieve resting upon a base 39 for the sieve assembly. The sieves 33 may be held in place by any suitable means such as a plurality of threaded rods 34 anchored in the base 39 of the sieve assembly and extending upward through respective corners of the sieves. A wing nut 35 cooperates, respectively, with each rod 34 to retain the stack of sieves 33 in place.

Each sieve 33 comprises a screen through which the material fed to the sifter may be sized.

The sieve assembly 3 is supported on the base frame 1 and prevented from rotating about the longitudinal axis of shaft 27 by a combined supporting and antirotational constraining means comprising a plurality of parallel rods 36 interposed in resilient relation between the sieve assembly 3 and the sills 4. Each rod 36 is respectively connected with a corner of the base 39 of the sieve assembly 3 by a resilient mounting means comprising a detachable mounting plate 37 (through which the rod extends) bolted to the base of the sieve assembly 3. The mounting plate 37. is sandwiched between a pair of resilient pads 38 which are held in an adjustable position relative to the rod 36 by means of oppositely spaced retaining nuts 41 threaded to the rod. Lock nuts 42 prevent the retaining nuts from turning once the position of the resilient means relative to the rod is determined. A similar type of resilient mounting means fastens the lower end of each rod 36 to a respective end portion of the sill members 4. By adjusting the respective nuts 41, the sieve assembly 3 may be leveled.

In order to rotate the crank shaft assembly 2 and gyrate the sieve assembly 3 about the axis of rotation of the journal 14, a sheave 43 is fastened to the lower end of the journal 14 in the space beneath the transverse structure 7 by means of a key 44 and pin 45. The sheave 43 is caused to rotate by means of an endless belt 46 interconnecting the sheave 43 with a driving sheave 47 mounted on the shaft of a motor 48. The motor 48, which is preferably electrically driven, is mounted on the base frame 1.

The gyratory sifter operates in the following manner:

When the motor 48 is energized, it imparts a rotary motion to the driven sheave 43 which in turn rotates the journal 14 in its bearing 12. As the journal rotates, the tubular member 21 is caused to rotate about the axis of rotation of the journal 14. The sieve assembly 3 which is constrained by the supporting rods 36 from turning about its own axis, is thereby gyrated about the axis of rotation of the journal 14.

Referring now to Fig. 2, as the sieve assembly 3 gyrates, its mass M1 produces a centrifugal force F1 in accordance with the formula F1' l.227M1gR1N where M1 is in slugs, R1 in in inches, N is in revolutions per second, and g is the acceleration due to gravity of 32.174 feet per second squared. Since the sifter is generally operated at a constant speed, the constants 1.227 and g may be grouped with N as a single constant k. The formula then becomes F1=kM1R1. Given the value of the mass M1 and the perpendicular distance R1 that the mass M1 is located from the axis of rotation A-A of the journal 14, it is possible to compute the centrifugal force F1. Having determined the centrifugal force F1 produced by the gyrating sieve assembly and knowing distance X1 which represents the distance this mass M1 is vertically spaced from the midpoint 49 of the bearing structure 23, it is possible to compute a turning moment Z1 produced by the sieve assembly 3 about the midpoint 49 of the bearings 23 in accordance with the formula Z1=F 1X 1.

A counterweight wheel 51 having an annular web 52 and depending flanges S3, to protect the bearings 23 from foreign matter such as dirt and dust etc., is secured by means such as cap screws 54 to the upper flange 22 of the tubular member 21. The wheel 51 has a variable mass M2 secured to the underside of the annular web 52. The center of mass M2 is spaced a perpendicular distance R2 from the axis of rotation AA of the journal 14 and is in a horizontal plane through the midpoint 49 of the bearings 23. The mass M2 produces a centrifugal force F2 upon rotation of the wheel 51 in accordance with the formula F2=kM2R2. A turning moment Z2 may be considered as being produced by the mass M2 about the midpoint 49 of the bearings 23 in accordance with the formula Z2=kM2R2X2. Since M2 and the midpoint 49 lie in the same horizontal plane, the distance X2 which represents the vertical distance between M2 and the midpoint 49 is equal to zero and the turning moment Z2 is therefore zero.

The driven sheave 43 which is shown in Fig. 1 as having an annular web 55 and a depending flange 56, to greatly eliminate dust catching, and is also provided with a counterbalancing mass Ma secured to the underside of the web of sheave 43. The center of the mass M3 is spaced a perpendicular distance R3 (see also Fig. 2) from the axis of rotation of the journal 14 and axially spaced a distance X3 which represents the distance mass M3 is vertically spaced from the midpoint of the bearingsv 23. The mass M3 generates a centrifugal force F3=M3Ra and produces a turning moment Z3 about the midpoint of the bearings 23 in accordance with the formula Z3=kMaRsXa.

In order to dynamically balance the sieve assembly 3 the summation of the centrifugal forces generated by the masses about the center of the bearing 23 must equal zero, or stated in another way (see Fig. 2), it is necessary to select and position M2 and M3 in the same vertical plane with M1, so that the combined turning moments Z2+Za about the center of the bearings 23 are equal to the turning moment Z1 produced by the sieve assembly 3 about the same point, or in formula form:

This formula may be rewritten in the following form: (c) kM1R1X1=kM2R2X2+kM3R3X3 Since X2 is equal to zero by design, the formula (0) reduces to:

The values of M1, R1, X1, R3 and X3 are measurable values determined by the design of the sifter and it is therefore possible to compute from formula (d) the value of M3. R3 being measurable and M3 now being known, the centrifugal force Fa generated by mass M3, may then be determined by:

Since M1 and R1 are measurable, the centrifugal force F1 generated by the mass M1 of the sieve assembly 3, may be determined by:

i Fl=kM1R1 Having computed the values of F1 and F3, in order for the system to be balanced along the vertical axis, F2 must equal the sum of F1 and F3 or F2=F1+F3 Having computed F2 from formula (g) and R2 being measurable the mass M2 needed to place the system in dynamic balance is computed by the formula:

(h) F 2=kM2R2 which may be rewritten as Since the turning moment Z2 produced by M2 is in opposition to the moments produced by M1 and M3, the formula (j) is actually:

to M

Since one of the conditions for establishing dynamic balance is expressed in formula (g) F2=F1+F3, formula (g) may be rewritten as:

and since the k is common to both sides of the equation, it may be canceled out so that:

which fulfills the necessary condition for static equilibrium expressed by formula (I).

The system now is statically and dynamically balanced for the given mass M1 of the sieve assembly 3. However, it may happen that in continually loading the sieve 33 with material to be sifted (the sifter being adapted for a continuous sifting process rather than a batch process) the mass of the sieve assembly 3 may at times be greater or less than the predetermined'value M1 so that the summation of the turning moments about the midpoint 49 of the bearings 23 is no longer equal to zero. When such is the case, the sifter becomes dynamically unbalanced and some of the unbalancing force is absorbed in allowing the crank shaft assembly.2 and sheave 43 to gyrate about the bearing 12 in a conical path. If this gyration should become excessive, damage to the hearing 12 may result. To obviate this difficulty, a normally closed limit switch 57 is mounted on transverse structure 7 of the base frame 1 adjacent the bearing housing 8 and has an actuator 58 adapted to be operated by the sheave 43 in response to a predetermined gyratory motion of the sheave. The limit switch 57 is operably interposed between the motors source of energy. (not shown) and the motor 48 to'disconnect the motor from its source of energy.

In the modified embodiment of the invention shown in Fig. 3, the sifter instead of being mounted above a supporting structure as shown in Fig. 1 is suspended from a supporting element 59. e

In Fig. 1, the counterweight wheel 51 and sheave 4 have flange portions 53 and 56 on their peripheries that cooperate with the remainder of the wheel and sheave to form cavities that open away from the sieves 33. In Fig. 3, flange portions 60 and 61 are reversed so that the cavities formed open downwardly toward the sieves 33 forming a cover for protecting the bearings from dirt or any other foreign matter. An upwardly dished disk 62 is attached to the sieve assembly to catch grease or oil leakage from the machine parts which would otherwise contaminate the flour.

The foregoing analysis prescribed a method for properly balancing a gyrator statically'and dynamically so that it will fulfill the stated objects of the invention.

Although only two embodiments of the present invention have been illustrated and described herein, it will be apparent to one skilled in the art that various changes or modifications, singly or collectively, may be made therein without departing from the essence of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In a gyratory sifter, the combination of a stationary structure including a frame; a self-aligning bearing mounted in said frame; a generally vertically extending gyratable and rotatable crank shaft assembly journaled in said bearing, said crank shaft assembly including a sheave fastened to one end thereof; a sieve assembly rotatably connected to the other end of said crank shaft assembly; a plurality of supporting members connecting said sieve assembly to said frame for constraining movement of said sieve assembly to translatory movement upon gyration of said sieve assembly; driving motor means, said motor means being drivingly connected to said sheave to impart rotation to said crank shaft assembly; and electric circuit means including a switch connecting said motor to a power source, said switch being mounted on said stationary structure and having an actuable member operably engageable by one of said assemblies to open said switch and disconnect said motor from said power source in response to gyration of said crank shaft assembly in said bearing beyond a predetermined amount.

2. In a gyratory sifter, the combination of a stationary structure including a frame; a self-aligning bearing mounted in said frame; a generally vertically extending gyratable and rotatable crank shaft assembly journaled in said bearing, said crank shaft assembly including a sheave fastened to one end thereof; a sieve assembly rotatably connected to the other end of said crank shaft assembly; a plurality of supporting members connecting said sieve assembly to said frame for constraining movement of said sieve assembly to translatory movement upon gyration of said sieve assembly; driving motor means, said motor being connected to said sheave to impart rotation to said crank shaft assembly; and electric circuit means including a switch connecting said motor to a power source, said switch being mounted on said stationary structure andhaving an actuable member operably engageable by said crank shaft assembly to open said switch and disconnect said motor from said power source in response to gyration of said crank shaft assembly in said bearing beyond a predetermined amount.

3. In a gyratory sifter, the combination of: a frame; a, self-aligning bearing mounted in said frame; a generally vertically extending gyratable and rotatable crank shaft assembly journaled in said bearing, said crank shaft assembly including a sheave fastened to one end thereof; a sieve assembly rotatably connected to the other end of said crank shaft assembly; a plurality of supporting members connecting said sieve assembly to said frame for constraining movement of said sieve assembly to translatory movement upon gyration of said sieve assembly; driving motor means, said motor being connected to said sheave to impart rotation to said crank shaft assembly; and electric means including a switch connecting said motor to a power source, said switch being mounted on said frame and having an actuable member operably engageable by said sheave to open said switch and disconnect said motor from said power source in response to gyration of said crank shaft assembly in said bearing beyond a predetermined amount.

4. A gyratory sifter comprising: a frame, a first selfaligning bearing mounted in said frame; a first shaft journaled in said first bearing for combined rotary and gyratory movement relative to said frame, said gyratory movement being about a vertical axis; a tubular member mounted on one end of said first shaft in eccentric relation thereto and for rotation and gyration therewith; a wheel mounted on said member having an annular first web and a peripheral depending flange, said first web and said flange cooperating to define a first cavity; a first detachable weight positioned in said first cavity and secured to said wheel; a second bearing journaled in said member; a sieve assembly having a base; a second shaft mounted on said base, said second shaft being journaled in said second bearing of said member for rotation relative tosaid tubular member and for gyratory movement about said vertical axis; a plurality of supporting members connecting said base of said sieve assembly to said frame for constraining movement of said sieve assembly to translatory movement upon gyration of said sieve assembly; a sheave attached to the other end of said first shaft, said sheave having an annular second web and a peripheral depending flange, said second web and said flange cooperating to define a second cavity; a second detachable weight positioned in said second cavity and secured to said sheave, said first and second detachable weights being selected to effect dynamic balance of the sifter; a motor mounted on said frame, said motor being connected to said sheave to impart rotation to said first shaft whereby a translatory gyrating motion is imparted to said sieve assembly.

5. A gyratory sifter comprising: a frame, a first selfaligning bearing mounted in said frame; a first shaft journaled in said first bearing for combined rotary and gyratory movement relative to said frame, said gyratory movement being about a vertical axis; a tubular member mounted on one end of said first shaft above said first bearing in eccentric relation to said shaft and for rotation and gyration therewith; a wheel mounted on said member having an annular first web and a pcripheral depending flange, said first web and said flange cooperating to define a first cavity; a first detachable weight positioned in said first cavity and secured to said wheel; two second bearings in vertical register journaled in said member; a sieve assembly having a base; a sec- 0nd shaft mounted on said base, said second shaft being journaled in said second bearings of said member for rotation relative to said tubular member and for gyratory movement about said vertical axis; a plurality of detachable sieves stacked in vertical register on said base; a plurality of rods having one end fixed to said base and the other end cooperating with one of said sieves for retaining said sieves on said base; a plurality of supporting members connecting said base of said sieve assembly to said frame for constraining movement of said sieve assembly to translatory movement upon gyration of said sieve assembly; a sheave attached to the other end of said first shaft below said first bearing, said sheave having an annular second web and a pcripheral depending flange, said second web and said flange cooperating to define a second cavity; a second detachable Weight positioned in said second cavity and secured to said sheave, said first and second detachable weights being selected to effect dynamic balance of the sifter; a motor mounted on said frame, said motor being connected to said sheave to impart rotation to said first shaft whereby a translatory gyrating motion is imparted to said sieve assembly, and electric circuit means including a switch connecting said motor to a power source, said switch being mounted on said frame and having an actuable member operably engageable by said sheave to open said switch and disconnect said motor from said power source in response to gyration of said first shaft in said first bearing beyond a predetermined amount.

References Cited in the file of this patent UNITED STATES PATENTS (Addition to No. 335,435)

Images