US2315083A - Attrition mill and method - Google Patents

Description

March 30, 1943. 1, CHESLER ATTRITION MILL AND METHOD Filed Jan. 15, 1940 ATTORNEYS INVENTOR lsiaof' C/zesler Patented Mar. 30, 1943 ATTRITION MILL AND METHOD Isidor Chesler, Oceanport, N. J., assignor to Eagle Pencil Company, New York, N. Y., a corporation of Delaware Application January 15, 1940, Serial Nb. 313,876 16 Claims. (01.8346) The present invention relates to the art of pulverizing granular material such as graphite, clay, coal, sandstone, cinder, cement, ore and the like.

It is an object of the invention to provide a simple method and correspondingly simple apparatus for expeditiously pulverizing material of the above character to substantially any selected degrees of fineness, even to the utmost fineness required in the industrial arts.

Another object is to provide an efficient pulverizing mill which is devoid of swinging hammers, blades, paddles, rotors or other impacting or moving parts.

Another object is to provide a mill of the above type, in which the material is comminuted by attrition without waste or dust, without adulteration thereof by particles gouged out of the wall of the mill and with substantial elimination of wear on the latter.

Another object is to provide a mill of the above type, which may be operated without the need for expert care or attention and in which, as long as a sufficient supply of raw material is available, feed to the machine at the rate at which it can best operate is inherently maintained throughout.

According to the invention, the raw material to be comminuted is passed by pneumatic propulsion, through an elongated column, desirably a metal pipe of uniform cross-section, suction being applied for such propulsion at the outlet end of the pipe, which is vented at its inlet end. The venting is desirably accomplished through an ejector communicating with a sourceof supply of the material to be comminuted. The suction is desirably applied through a second ejector at the outlet end of the. attrition pipe. The ejector at the inlet end thus draws upon the source of supply of the stock, usually granular material, while the ejector at the outlet end draws upon the pipe contents and blows ejected material outwardly therefrom, desirably into an expansion chamber, where the pneumatic energy is dissipated in a whirling action, permitting the heavier particles blown out therewith from the pipe to drop by gravity, desirably back to the source of supply, and the lighter particles to be levitated.

for further separation and collection. The ejectors are desirably constructed or set to aliord a larger jet at the outlet than at the inlet, which results in maintaining sub-atmospheric pressure within the attrition pipe, which therefore becomes and remains filled at all times from the source of supply with material. The column of material in the attrition pipe as such, advances under the applied suction but that near the axis moves faster than that contacting the'wall of the pipe. Apparently, the attrition takes place as the result of this difl'erential movement. As a consequence, the discharge from the pipe consists of a mixture of finely comminuted particles with a proportion of coarser particles, the coarser particles returning to the source of supply in the 4 expansion operation referred to, for repeated cycles of operation through the attrition pipe, all of which occurs automatically in the normal operation of the installation.

There is no positive feed of stock from the source of supply into the attrition pipe, the inlet ejector serving as a vent and drawing only enough material from the source of supply to make up for the comminuted material which has been removed from the attrition circuit by levitation.

Preferably the granular-material from the supply hopper discharges by gravity through a small port near the bottom of the expansion chamber, so that feed from the hopper is blocked as long as that small port is covered by granular material in the bottom of the expansion chamber and the hopper automatically resumes its feed in the operation of the mill, when the discharge port is uncovered, until the port is again closed by passage therethrough of sufficient granular material.

In the accompanying drawing, in which is shown one of various possible embodiments of the .several features of the invention:

Fig. 1 is a diagrammatic view tion,

Fig. 2 is a cross-sectional view of a detail taken on line 22 of Fig. i,

Fig. 3 is a view in longitudinal cross-section on a larger scale, through the inlet ejector,

Fig. 4 is a similar View of the discharge ejector,

of the installa- Fig. 5 is a view in longitudinal section and on -may be of inner diameter of approximately 1 or 2 inches and be of a length hundreds of times its periphery, and desirably in excess of feet. In one practical embodiment being used at the present time for pulverizing graphite for lead pencil manufacture, a pipe of about 200 feet in length is employed. This pipe is mounted in any i desired or convenient location about the walls of a-large factory room, desirably near the ceiling, where it is out of the way. The inlet end ll of the pipe is desirably connected to the lower end of a downwardly tapering expansion chamber l2 and the outlet end ll of said pipe nearer the upper end of said chamber l2 at a cylindrical part I! thereof. The attrition pipe C has a supply run it and a return run ll. Preferably the angle-turns I 8 by which the two runs are connected are large diameter arcs to avoid turbulence, excessive wear or pocketing that might occur if sharp turns were used.

The lower end of the expansion chamber tapers to a small elbow pipe ll communicating with an ejector I to which gas desirably compressed air, from a compressor is supplied by way of pipe 2|. The ejector thus blows longitudinally into the attrition pipe C and at .the same time exerts aspiration upon the lower reduced end of the expansion chamber i2, where there is a supply 8 of material to be comminuted. Supply S is introduced through a conduit 2| discharging through small port 22, a feed hopper 23 de livering into the upper end of conduit II.

The ejector which taken by itself is not my invention, may comprise a cast metal chamber having a bulb structure 24 and a reduced neck 25 to provide a Venturi eilect. Pipe 28 is threaded into the base end- 21 of the bulb and is adjustablymounted and fixed in position by lock nut 28. The compressed air enters the chamber 2! through the lateral pipe 20 and discharges through the ring jet 29 formed between the wall of the chamber 24 and the beveled end 30 of pipe 28. The air issuing from the ring jet creates a partial vacum in pipe l8 which tends to draw into attrition pipeC fromthe supply S.

A discharge ejector structure D similar to intake ejector I is afiixed at the outlet end I 3 of the attrition pipe C, but in reverse relation to the intake ejector, so that it exerts suction upon and draws stock from the attrition pipe C. The

discharge ejector may be of the same construcconstruction, but the nozzles are differently set,

the inlet ejectordesirably having a very small ring jet 29 in the order of .019 square inch in area and the discharge ejector D having ring jet 29' in the order of 0.195 square inch, i. e. ten times as great. This settingwhile preferred for comminuting graphite for lead pencil manufacture is by no means critical, for the relative areas of the ports maybe varied to change the proportions of fine and coarse material.

A curved tube 32 connects the outlet of discharge ejector D to the expansion chamber II. the reversely bent end 32' of said tube feeding tangentially into said chamber. The end of pipe 32 is telescoped over a corresponding tangential stud ll on the wall of the expansion chamber I! for that purpose.

The expansion chamber includes a downturned duct -34 which discharges into a collector 35, the lower funnel end 36 of which discharges into a collecting barrel 31. A duct 38 extends axially downward through the top of said collector and has a horizontal-run 29 which feeds horizontally and tangentially into the upper end of a second and larger collector 40 the lower end ll of which in turn discharges into a second receiving barrel 42. Similarly larger duct l3, the inlet end of which extends axially downward into collector 4i feeds at 44 into a further collector 45 to take the finest particles. Collector 15 has an inner muslin sleeve 46 and feeds through a funnel end 41 to a third receiving barrel 48.

The pressure fluid, usually a gas or a vapor may be superheated steam but is desirably air preferably at a temperature of about 650 F. and a pressure in the order of 100 pounds per square inch. Desirably the compressed fiuid is supplied to inlet ejector I and discharge ejector D by a compressor (not shown) connected to their respective pipes 20 and 20'.

The hopper 23 is charged and desirably kept filled with the stock or material, preferably in dry and granular form not larger than four mesh. Without further attention the mill will perform automatically to collect the finest material in barrel it somewhat coarser material in barrel 42 and the coarsest though yet a relatively fine grade in barrel 31. 4

The mode of operation briefly stated is as follows:

Air, gas or steam is drawn through the length of attrition pipe C by the suction action of the ring jet 29' of the discharge ejector D at the outlet end of said pipe. This action takes place constantly since the pipe C is vented through the inlet ejector I by air or gas blown in through the minute circular jet 2!. As a consequence the attrition pipe becomes rapidly filled by flow of granular materialsfrom the supply S drawn inward through pipes i8 and 26 by the aspirating action of the ring jet 29.

Despite the fact that the attrition pipe is of uniform diameter throughout its length without restriction or obstruction and applied air or steam moves rapidly therethrough, the granular material is yet so greatly retarded in its advance through the attrition pipe as to be subjected to the attritionaction therein for a period of time sufilcientiy long to reduce. a considerable proportion of it to the desired degree of fineness in a single pass.

The slow advance of the column of granular material filling the attrition pipe is due to frictional retardation. That retardation is greatest where the material contacts the wall of the pipe,

- the material in the axial'region of the pipe advancing less slowly. It is as a result of this differential movement that marked mutual attrition occurs by the rubbing of the more slowly moving particles with respect to those more rapidly moving in the filled pipe. As a result the material escaping through the discharge ejector is not uniformly comminuted. It includes a proportion of very fine particles mixed with others that are considerably coarser,

Automatic separation of the fine particles, occurs as a result of the blowing from the discharge ejector D through the pipe 32 tangentially into the expansion chamber or separator ll. The gas or air with the entrained particlesv rapidly moves in a whirl to dissipate its energy, the finer or lighter particles being levitated through the pipe '34 for removal from the attrition circuit and separation as hereinafter set forth.

The heavier particles are returned by gravity back to the source of supply S for re-circulation through the attrition circuit, separation of the fine particles'and return for further treatment of the coarser particles occurring in each traverse through the attrition pi e.

As comminuted material is removed from the attrition cycle and as quickly as it is removed, it

is automatically replaced by granular material from the source of supply S. Such ire'sh supply is drawn in automatically under the suction maintained upon pipe 26 and It by ring jet 29.

Accordingly, the attrition pipe is at all times maintained filled, so that the effective attrition operation set forth is kept up. Fresh material passes through port 22 to supply S only at the rate at which comminuted material is removed from the attrition cycle, for much of the material that is expelled from the attrition pipe C returns by gravity to the supply S as previously pointed out. The level of the latter is kept substantially constant at all times, just to cover the port 22. There is thus a simple automatic control action by which material is drawn in to the attrition pipe only as fast as comminuted product is removed from the cycle. By thus, keeping the attrition pipe full at all times, the greatest efliciency of attrition action is attained. Were the pipe only partly filled, the attrition action would be greatly reduced, as particles might move past each other without rubbing. On the other hand, were the pipe packed or forcefully clogged the system might stall, and the intake ejector might backfire through the source of supply S. Uniformity of action is assured according to the present invention since the filled pipe is replenished as fast and only as fast 'as it can digest" the load, and there is no forceful feeding,

In operation the interior of the attrition pipe is at all times maintained under sub-atmospheric pressure, the strong suction applied at the outlet end being practically maintained even at the inlet end. At no time can pressure build up in said system. Where the system is operated under the particular conditions set forth, the material advances in the attrition pipe at slow rate, the average rate of only about two feet per second, the complete circuit taking about two minutes. It is understood that when the equipment is of difierent size or operated under different conditions there would be variations in the rate of propulsion of the stock through the attrition pipe but such rate will always be of the order of that set forth. This is sharply to be contrasted with the action of impact pulverizers in which the material is hurled at terrific speeds.

The expanding gas from the pipe 34 above referred to delivers to the first dust collector 35 where the heavier particles will drop into the barrel 3! and the lighter particles be levitated through the pipe 38, 39 into the second and larger dust collector 46, where a similar separating action takes place. the coarser residual particles dropping into barrel 42 and the finest residue capable of being levitated by the same, travelling on through duct 43 into the final dust collector 45 to drop into the barrel 48.

In the operation of the particular installation above illustratively described, more than half of the particles collected in the'last barrel 4B are of diameter of around 2 microns and practically all of the rest is between 2 and 8 microns. In the intermediate barrel 42, fully 86% of the par-, ticles are found to be below 8 microns and the remainder between 8 and 30 microns. while the product collected in the first barrel 31 includes 40% below 9 microns and about 60% between 9 and 31 microns.

The particular installation above set forth as applied to the comminution of graphite for lead pencil manufacture, produces in the final barrel $8 a product sufilciently fine for the very highest quality of drafting pencil which retails for 10 or more. In the intermediate barrel 2 the product is sumciently fine for the best quality of writing pencil, while the product in the first barrel 3'! is superior in fineness to that used in many lead pencils that retail at 5 or more. With the systemset forth, about 88'pounds of comminuted product is collected per hour, of whichflO pounds is in the first barrel 31, 10 pounds in the second barrel 2 and 8 pounds'in the third barrel 8.

While as set forth, the arrangement of the attrition pipe C in a single loop is advantageous and ordinarily preferred, it will be understood that it is within the scope of the invention to arrange such pipe in the form of a helix or of a single loop and that pipe of any cross section other than that set forth may be used.

The expansion chamber I1 is desirably provided in addition to the stud 33 with one or more further studs at diiferent levels illustratively two studs 49 and 50 which are normally closed by caps 5|. Depending on the stud to which the pipe 32 is connected, the proportion of finely ground material to be collected may be adjusted. For example, if a larger proportion of finer material is required, the discharge from ejector 3! may be moved to lower opening 49 Similarly a smaller proportion of fine particles would result if the connection were made to the upper inlet stud 50. Other methods for varying the proportion of fine and coarse material may be employed, for example by enlarging th chamber II which results in. a greater proportion of fines. or reducing its diameter for a larger proportion of coarser particles.

Thus, depending on the setting, the granular material may be comminuted even to finer particles than in the illustrative installation above specifically set forth, as for instance for the finest grade of powder used for cosmetic purposes, or for lens polishing. For the comminution of coal it is rarely necessary to grind the particles to dimensions much below 60 microns. The installation when adjusted for that degree of coarseness would have an output of close to ten times that above set forth, and especially so since coal is more friable than crystalline graphite and therefore grinds more readily.

I As manychanges could be made in the above construction and method and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it. is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, what I clagin as new and desire to secure by Letters Paten s:

I 1. The method of pulverizing which consists in propelling stock to be comminuted through an elongated confined course of length hundreds of times its transverse periphery at slow rate, by feeding the material thereinto and simultaneously sucking thematerial therefrom while maintainmg the relative eifectiveness of feed and suction such as to maintain the elongated course substantially filled with stock at all times.

2. The method of pulverizing which consists in sucking stock to be comminuted into an elongated confined course of length hundreds of times its transverse periphery, and, simultaneously therewith applying more powerful suction at the other extremity of said course, whereby said course remains substantially filled with stock, fresh material enteringat one extremity as comminuted material is withdrawn at slow rate through the other extremity.

3. Th method of pulverizing which consists in propelling stockby suction applied at the end of an elongated confined course of length-hundreds of times its transverse periphery for comminution therein, while drawing by aspiration upon a source of supply of the stock which is maintained'under gravity head near the begin ning of said confined course, while maintaining the suction and aspiration at such relative intensity as to cause the stock substantially to fill and to advance slowly through said course.

4. The method of p'ulverizing which consists in passing stock to be comminuted through a cycle including an elongated confined attrition course of length hundreds of times its transverse periphery vented at its inlet, by aspirating upon the stock to such extent as substantially to fill the attrition course and slowly to advance the stock therethrough, blowing the product drawn from-said course in a circular'path and thereby dissipating the pneumatic energy while directing the heavier ejected particles to return to the source of supply for repeated attrition cycles.

5. The method of pulverizing which consists in introducing gas through one end of a greatly elongated confined course of length hundreds of 'times its transverse periphery in communication with a source of stockto be comminuted and simultaneously applying suction near the other end of said course of intensity such as to maintain the confined course under sub-atmospheric pressure and to effect propulsion of the stock through said course at slow rate, with resultant outflow from the discharge end of said course, and automatic intake of further stock from said source to maintain said course filled.

6. The method of pulverizing which consists in propelling gas in communication with a source of stock to be comminuted into a greatly elongated confined course of length hundreds of times I it transverse periphery, applying suction to the opposite end of said course of intensity such as to maintain the confined course under subat mospheric pressure and to effect propulsion of the stock through said course at slow rate, permitting the heavier comminuted discharge resulting from said operation to drop back to the sourceof supply, whilelevitating the lighter par'-" ticles of the discharge by the expanded gas delivered from said course.

'7. An attrition mill, including an elongated conduit of length hundreds of times its transverse periphery having an inlet at one end for the stock to be comminuted and an outlet at the other end,

a source of the stock. a source of gas connected to blow through said conduit and in aspirating relation with the source of stock, and means for applying strong suction to said conduit near the outlet end thereof thereby to cause the stock to advance through said elongated conduit and to escape therefrom at'slow rate while said conduit is at all times maintained substantially filled with stock. a

a 8. An attrition mill, comprising a pipe of length hundreds of times its transverse periphery, a gas 2,31aoss 9. An attrition mill, including an expansion chamber, an elongated pipe of length hundreds of times its transversefperiphery communicating at its opposite ends with said expansion chamber, a source of stock to be comminuted, means for feeding said stock into an end of said expansion chamber, a gas jet delivering into said pipe, and having aspiratingcommunication with said end of'said expansion chamber, and-a second gas jet drawing from said pipe and delivering into said expansion chamber and so correlated with said gas jet as to cause the stock substantially to fill the pipe and to be slowly advanced therethrough.

10. An attrition mill, including an expansion chamber, an elongated pipe of untform diameter and of length hundreds of times its transverse periphery, communicating at its inlet end with said expansion chamber, a source of stock to be comminuted, means for feeding said stock into the lower end of said expansion chamber, a gas jet delivering into said pipe and having aspirating communication with said end of said expansion chamber, and a suction device connected todraw upon said pipe at the outlet end thereof and to blow into said expansion chamber and so correlated with said gas jet as to cause the stock substantially to fill the pipe and to be slowly advanced therethrough.

11; An attrition mill, comprising an attrition pipe of length hundreds of times its transverse periphery, having an intake ejector at one end,

to blow thereinto, a source of supply of stock to be comminuted, said ejector having a jet of small cross-sectional area in aspirating relation with respect to said source of supply, a discharge ejector at the opposite end of said pipe having a jet in aspirating relation with respectto the contents of said attrition pipe, the jet of said discharge ejector being of cross-sectional area. several times as large as that of said inlet ejector.

12. The combination recited in claim 11 in which the attrition pipe is of inner diameter in the order of 2 inches and of length in the order of 200 feet, in which the inlet ejector has a circular jet of area in the order of .02 square inch and the outlet ejector has a circular jet in the order of 0.2 square inch.

13. An attrition mill, comprising an expansion chamber circular in cross-section and reduced at its lower end, an ejector connected to draw therefrom a container for the stock to be comminuted, with which said ejector is in aspirating relation, an attrition pipe into which said ejector delivers, a source of gas under pressure feeding into said ejector, said attrition pipe having a length in excess of one hundred feet and extending in a continuous reversely bent line back to a higher part of the expansion chamber, and an ejector at the outlet end of said attrition pipe to draw from said outlet end and deliver tangentially into said expansion chamber said outlet ejector being so correlated with the inlet ejector as to cause the stock substantially to fill the attrition pipe and to be which the expansion chamber has a plurality of alternative connections at different elevations for the delivery from the outlet ejector for controlling the fineness of comminuted product collected by levitation from the expansion chamber.

15. The combination recited in claim 13, in which the material to be comminuted is lodged in a hopper feeding by gravity into the lower end of the expansion chamber, whereby the feed is arrested as long as the inlet to the expansion chamsion chamber and drawing from said pipe, said latter ejector delivering tangentially into said expansion chamber to eflfect return of heavier particles to the inlet end of-the attrition pipe and levitation of lighter particles for separation, said attrition pipe extending from the expansion chamber in a plurality of rectangular runs back to the expansion chamber, said rectangular runs being connected by bends of relatively large 10 curvature.

ISIDOR CHESLER.

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