US2681769A

US2681769A - Machine for densifying powders and for transferring them from one atmosphere to another

Info

Publication number: US2681769A
Application number: US338942A
Authority: US
Inventors: Louis O Simenson
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1953-02-26
Filing date: 1953-02-26
Publication date: 1954-06-22
Anticipated expiration: 1971-06-22

Description

L. O. SIMENSON FYING 2,681, 769 ING MACHINE FOR DENSI POWDERS AND FOR TRANSFERR THEM FROM ONE ATMOSPHERE TO ANOTHER Filed Feb. 26. 1953 June 22, 1954 INVENTOR. Lau/s' 0. S/rmsrnson ATTORNEYS Patented June 22 1954 MACHINE FOR DENSIFYING POWDERS AND FOR TRANSFERRING THEM FROM IONE ATMOSPHERE TO ANOTHER Louis 0. Simenson, Berkeley, Calif., assignor to The Dow Chemical Company, Midland, Mich., a corporation of Delaware Application February 26, 1953, Serial No. 338,942

2 Claims. 1

This invention relates to a pump for moving powdered or dusty materials from one atmosphere to another without significant leakage of the one atmosphere to the other.

Many industries are troubled by the necessity for handling finely divided powders or dusts in large quantities. These may be pyrophoric, or they may present explosion hazards when mixed with air. For these and other reasons, such dusts are commonly transferred, as produced, to an inert atmosphere, or they are discharged from one medium to another with the exercise of rigid safety precautions. It is commonly observed that, at the point of discharge, using the available equipment, the new atmosphere leaks back into the old one, and the old atmosphere leaks into the new one. This is objectionable and costly, either because of newly created hazards, or because of loss of expensive materials, or because of the added load on pumps required to maintain either atmosphere in a preselected condition of pressure or concentration of constituents. One such problem arises in the manufacture of alkali metal alkyl xanthates which are produced in fine powder form in a flammable reaction medium and are pyrophoric when freed from that medium until they are pelletized. It is necessary to prevent leakage of flammable vapors from the reaction vessel, and to protect the fine powder from ignition. Other dusts or powders which present other but equally aggravating problems are found in many industries, and include powdered caustic alkalies, wood flours, resin dusts, and many others.

The objects of the present invention include the provision of apparatus for transferring dusts or fine powders from one atmosphere to another without interchange between those atmospheres and the provision of such apparatus capable of so densifying powders as to reduce or eliminate the hazards incident to their original dusty condition. A particular object is the provision of such apparatus capable of automatic repetitive operation.

The apparatus of the invention comprises a vertical cylinder connected through a chute with a source of supply of the dust to be transferred, a disk capable of forming a mechanical seal over the lower end of the cylinder, a piston within the cylinder for compressing a charge of powder therein, means above the cylinder for advancing and retracting the piston, means below the cylinder for holding the disk firmly while the load in the cylinder is being compacted and for retracting the disk and rotating it to abrade the lower end of the compacted dust plug and convert the same into a coarser and denser powder, and auxiliary control means for moving each of the working parts in its proper sequence.

The apparatus will be described more fully with reference to the annexed drawing, the single figure of which is a vertical section through the principal elements of the dust pump, and a diagrammatic representation of one satisfactory set of controls therefor.

A source or supply ll! of fine powder is connected through chute H with a vertically disposed compression chamber, such as cylinder l2. Piston l3, having a close sliding fit in cylinder I2, is carried at the lower end of rod 14, the upper portion of which passes through hydraulic cylinder l5 and carries a second piston I 6, dividing cylinder [5 into separate lower chamber l1 and upper chamber l8. A disk l9, coaxial with the lower end of cylinder I 2, and shaped to make a tight mechanical closure over the end of said cylinder, is carried at the upper extremity of shaft 20 which extends downwardly through another hydraulic cylinder 2l which is divided into lower chamber 22 and upper chamber 23 by piston 24 carried on shaft 20. Shaft 2|] extends below cylinder 20 and its lower extremity forms the axis of a positive displacement gear motor 25. A source (not shown) of hydraulic fluid is connected through a header 26 and lines 21, 28,

29, 3D and 3! to chambers l8, l1 and 23 and-to motor 25, respectively. Chamber 22 is connected through line 32 with pressure accumulator 33 and the source (not shown) of hydraulic fluid. The several lines are valved and the valves are connected with and actuated by electrical circuits, as will be described later. The electrical circuits contain

switches

34, 35, 36 and 31, the first of which is actuated in response to a preselected pressure condition in chamber l8 and the others of which are tripped by

arms

38 and 39 mounted on shafts i4 and 26, respectively.

The operation of the apparatus is repetitive,

and, for ease of understanding may be deemed to begin with piston 13 raised to a position above the opening of chute ll into cylinder l2. Power is admitted to cylinder l2 from the supply I10 while disk I9 is in the illustrated position closing the lower end of cylinder i2. Hydraulic fluid is sup plied through line 2! and control valve 4|] to upper chamber IS in hydraulic cylinder l5. Full pressure is not attained immediately in chamber l8, due to pressure drop in the lines and to the initial yielding of the body of powder in cylinder I2. As piston I3 is forced downward by the hydraulic pressure in chamber I8, the pressure increases and the powder is compacted. Pressure switch 34 is actuated when the pressure in chamber I8 reached a value which has been found sufficient to give the desired density to the plug M of compacted powder. Switch 34 opens valve 42 in line 29 which supplies hydraulic fluid to lines 39 and 3| to lower shaft 20 and its supported disk I9 away from cylinder I2 and to drive motor 25, thereby rotating disk I 9. The pressure in chamber 22 is held constant by accumulator 33, and, until this pressure is overcome by the combination of the forces transmitted through the powder plug 4| by piston I3 and the pressure in chamber 23, disk I9 is held securely in place against cylinder I2 and motor 25 cannot turn. When disk I9 is freed, hydraulic fluid passes through motor 25, causing disk I9 to rotate and abrade a relatively coarse and dense powder from the plug 4| being forced out of cylinder I2. This powder may be collected in a suitable hopper 43 andfed to further processing apparatus or to packaging equipment.

As hydraulic fluid moves through motor 25, the resulting pressure drop draws additional fluid from chamber 23 through line 39, reducing the pressure therein. The constant pressure in accumulator 33 and in chamber 22 then causes shaft 20 and disk I9 to rise until disk I9 is held securely against cylinder I2. Thereupon, motor is no longer free to rotate.

In the course of the downward movement of piston I3, and before the plug 4| of compacted powder has been worn too thin by the action of rotating disk I9 to maintain an effective seal against intrusion of air into cylinder i2, switch 36 is actuated'by arm 38 carried on rod I4. This closes valve 49. When disk I9 approaches its seatedposition beneath cylinder I2, arm 39 actuates switch 37.

Switches

36 and 31 are interlocked so that when both areclosed they close valve 42 which, however, allows excess fluid from chamber 23 to be forced back into line 26. Valves 44 and 45 are openedwhen valve 42 is closed. Valve 44 admits hydraulic fluid to chamber I1 and valve 45 releases the fiuid'from chamber I8. These conditions favor a rapid upward stroke of piston I3 to :admit more power from chute II to cylinder I2. At the upper end of the stroke of piston I3, arm 38 actuates switch 35 which resets pressure switch 34, closes valve 45, opens valve49 and thus puts the apparatus in condition to start another cycle. The described sequence is repeated as long as desired.

The forces which act to discharge the compacted plug 4| of powder from cylinder I2 are the hydraulic pressures in chambers l8 and 23. Those which act to hold the powder in cylinder I2 :are the friction generated in compacting the powder and the hydraulic pressure in chamber 22 which is supplied by accumulator 33. Variations in the nature of the powder being handled, which result indifierences in its tendency to jam in the compressing cylinder, are compensated for by adjustment of the operating pressure of accumulator 33, which is supplied independently of the other pressures in the system. If the powder being acted on is free-flowing, it must be compacted tightly before it will form the required seal against blow outs, and a relatively highpressure must be maintained in the accumulator. If, however, the powder is sticky or has a tendency to form a coherent mass, a relatively low pressure is required in the accumulator, to form the desired plug and to preventjamming.

by the setting of control volve 49.

The distance below cylinder I2 to which disk I9 drops and at which it operates is controlled This valve controls the rate at which hydraulic fluid is supplied to chamber I8, and hence the rate at which piston I3 is caused to descend, forcing downward plug 4| and disk I 9. Valve 42 similarly controls the lag between the depression of disk l9 and the beginning of rotation of motor 25. Thus, the settings of

valves

40 and 42 affect the rate of attrition of plug 4| .by disk I9.

In the compaction of pyrophoric alkali metal alkyl xanthate powders, the herein-described apparatus accepts a fluffy powdered feed having a bulk density of about 20 pounds or less per cubic foot and compresses it to a plug from which the abrader disk grinds a non-pyrophoric powder having a bulk density of 40 to pounds per cubic foot. This is done withan available hydraulic pressure to header 29 of about 1500 pounds per square inch, and pressure switch 34 is set to operate at about 600 pounds per square inch. The independently maintained pressure in accumulator 33 is about 1200 pounds per square inch; Having described the new machine and its mode of operation, the selection of suitable pressure conditions for use with other powders is within the skill of the art.

I claim:

1. In a machine for densifying powders and for transferring them from one atmosphere to another, the combination of a vertical compression cylinder; 2. piston therein; an externally and coaxially supported disk closure .over the" end of the cylinder opposing said piston; means for supplying a compressible powder intermittently to the cylinder between said piston andisaid.

disk; external pressure means for advancing the piston to compress powder against said disk; a constant pressure means associatedwith said disk for holding it in engagement with the cylinder until said constant pressure is overcome by that applied to the piston; means associated with said disk for causing it to rotate in abrading .relationship to the compacted powder forced from the cylinder when the disk is disengagedfrom the end of the compr ssion cylinder; means associated with the'piston and responsive to a predetermined penetration thereof into the compression cylinder: (a) to reverse the direction of said external pressure means and thereby to return the piston to its original position, and (b) to restore control of said disk to said constant pressure means, thereby to return said disk toengagement with said cylinder and to immobilize said disk; and, means responsive to the reengagement of the disk with the cylinder to reactivate said external pressure means for advancing the piston;

2. In a machine for densifying powders and for transferring them from one atmosphere to another, the combination of a vertical compression cylinder; a piston therein; an externally andco axially supported disk closure over the end of the cylinder opposing said piston; means for supplying a compressible powder intermittently to the cylinder between said piston and said disk; a two-way hydraulic cylinder mounted coaxially about an external extension of the piston rod; a similar two-way hydraulic cylinder mounted co axially on the support for said disk; 21. motor mounted on the end of the shaft supporting .said disk; means for supplying hydraulic fluid under pressure to the outer end of the first said hydraulic cylinder to advance the piston to compress powder against said disk; pressure sensitive means, responsive to the attainment of a predetermined pressure in the outer end of said first hydraulic cylinder for supplying hydraulic fluid to the inner end of said second hydraulic cylinder; means for maintaining a constant hydraulic pressure in th outer end of the second said hydraulic cylinder for holding the disk in engagement with the compression cylinder until said constant pressure is overcome by the pressure applied to the piston in combination with that exerted in the inner chamber of the second hydraulic cylinder; means for driving the motor and for rotating the disk in abrading relationship to the compacted powder forced from the cylinder when the disk is disengaged from the compression cylinder; means associated with the piston and responsive to a predetermined penetration thereof into the compression cylinder: (a) to admit hydraulic fluid under pressure to the inner end of the first said hydraulic cylinder and to release the fluid from the outer end thereof, and (b) to release hydraulic fluid from the inner end of the second said hydraulic cylinder and thereby to restore control of said disk to said constant hydraulic pressure means, to return the disk to engagement with the compression cylinder and to immobilize said disk; and, means responsive to the reengagement of the disk with. the compression cylinder to reactivate the means for supplying hydraulic fluid to the outer end of the first said hydraulic cylinder and for releasing hydraulic fluid from the inner end of said cylinder.

No references cited