US1575717A - Process and apparatus for disintegrating dry powders - Google Patents

Description

March 9 1926.. 1,575,717

H. PLAUSON PROCESS AND APPARATUS FOR DISINTEGRA TING DRY PRODUCTS Filed Nov. 5, 1922 2 Sheets-Sheet 1 March 9 1926. 1,575,717

H. PLAUSON PROCESS AND APPARATUS FOR DISINTEGRATING DRY PRODUCTS .Filed Nov. 5, 1922 2 Sheets-She et 2 possible;

Patented Mar. 9, 1926.

HERMANN PLAUSON, or HAMBURG, GERMANY.

PROCESS AND APPARATUS FOR DISINTEQRATING DRY POWDERS.

Application filed November 3, 1922. Serial No. 598,827.

To all whom it may ooncerm Be it known that I, HERMANN PLAUsoN, a citizen of the Republic of Esthonia, residing in Hamburg, Germany, have invented certain new and useful Improvements in Processes and Apparatus for Disintegrating Dry Powders, of which the following is a specification. I

This invention relates to a process and apparatus for disintegrating dry powders and it is the object of the invention to providemeans whereby a dry powder can be obtained whose particles are less than .008 mm. in diameter (less than 8 microns). A

further object of the present invention is to j provide a process and apparatus by which dry particles of colloidal or almost colloidal size can be obtained by mechanical disintegration. Further objects'of the invention are to accelerate the process of dry disintegration of solids and to provide an apparatus in which solids can beefiectively disintegrated by impact at high velocity in a more eflicient manner than has hitherto been Hitherto dry disintegration on a commercial scale has produced powders in which'a very small fraction of the product is in the form of particlesare .less than .008 in diameter and even on extremely prolonged grinding, a very small proportion of particles is obtained'having a diameter-of the order of magnitude of .008 to .001 mm. If the process is further continued, 'such enormous quantities of energy are necessary that theiprocess is impracticableon a commercial sca e.

My copending application No. 437117 describes a process and apparatus by which it is possible to disintegrate solids to colloidal fineness by the use of a large amount of liquid-under the conditions therein recited. The present invention is aresult of an extensive series of experiments performed on materials in the dry state as a result of which it has been discovered that when air isused as the dispersion medium, inthe ordinary way, it is .not possible to obtain commercial disintegration below theorder of magnitudeof .008 mm, but that very suc-.

cessful results can be obtained by complying with the first of the following requirement's, and preferably with the furtherrequirements specified. My'experiments-show that the best results are obtained as folows:

1. The use of a vacuum or'reduced pres- 1s)ure 1n. the grmdmg or disintegrating 0 amer. use of a fairly highvacuum, but I, use the words reduced pressure to denote any pressure which is substantially below atmospheric pressure.

, 2. An extremely intensive disintegration or grinding action is essential. The disintegrator should have a peripheral speed of at least 1,000 metres per minute and should revolve at not less than 1,000 revolutions per minute and better results are obtained I employing much higher velocities, though in apparatus of the grindin heavy pressures may be use using higher velocities.

,3. It has been discovered that the disintegration of dry substances can be matetype very instehd of rially-accelerated by the addition of small quantities of foreign substances which appear to act as catalysts for the mechanical disintegration. These solid or liquid substances will be termed dispersators and examples of suitable substances will be recited hereafter.

The best results. are obtained by the 4. Means should be provided continuously be maintainedbut is impermeable to particles of a diameter of .008 to .001 mm., e. g. an ultra-filter It is largely for the lack of such an ultra-filter that grinding in vacuo is impossible in mills of the ordinary type.

A millv according to the present invention must however be provided with an eflicientstufiing-box orpacking round its shaft.

" The benefits of the present invention can be obtained to a certain extent by using ordinary mills if they'a're made vacuum tight, connected with a-vacuum pump and then rotated at high speed, butsuitable dispersators should be added. It has also been found that ordinary ballmills and. edge runners will give a better result byoperation in vacuo asabove described and that on very prolonged grinding much finer-particles can be obtainedthan has hitherto been possible. Still better results are obtained by using high speed mills of various kinds which are adapted to be operated in vacuo as above described, but I have found that the grinding effect increases much more rapidly than the increase in the number of revolutions in the rotary disintegrator and the best results according to the present invention have been obtained by using grinding mills havingaperipheral speed of 1,000 to 3,000 metres per minute and disintegrators of the beater type having a peripheral speed up to 12,000 metres per minute, but as above mentioned, grinding mills of known type can be rotated at known speed by utilizing the other conditions hereafter specified and better results will be obtained than has hithertobeen possible.

In the preferred form of the present invention, it is possible to obtain particles of.

colloidal size towards the order of magnitude of .0001 mm. diameter (one tenth of :1. micron). A

The invention will be understood more clearly by a description of the following diagrammatic drawings in which Fig. 1 represents a vertical section; Fig. 2 is an elevation of a slightly modified device. Fig. 1 illustrates a mill consisting of. an inner casing 2 and an outer casing 1 between which a coo ing or heating fluid may be passed. The casing 1 is secured to a suitable foundation by the bed-plate 2. 4 is an eccentrically mounted rotary shaft carrying a plufixed beater bars 6 and 6 rality of beater bars 5 which cooperate with The bars 6 are secured bybolts 7 to the bottom of the easing and the bars 6 are secured by bolts 7 to a central member 8 which is crescent shaped in cross-section so as to provide an annular path to the other side of the disintegrator. The clearance between bars 5 and bars 6 and 6" is very small.

The material to be disintegrated is supplied through the hopper 12 provided with a lid 13 secured by a crescent device 14. Valves 10 and 11 are mounted within the annular pipe 9 and these valves are coupled by the wheels 15 and 16. The wheels are drlven by the belt 19 through a suitable source of power not shown and it will be seen that one valve is closed while the other 1s open so that the material is fed into the mill without allowing too much air to enter.

The apparatus is evacuated by pipe 20 which leads into the settling pipe 21, continuous pipe 21 and the settling vessel 25 and the pipe 32 which is connected to a suitable vacuum pump 50. The settling pipe 21 may be provided with a sieve 22 which allows fine particles to pass through it but holds back coarse particles. This sieve may not be necessary if a vacuum of over 40 cm. of mercury is employed. The sieve is a itated by an eccentric 23 which is rotated y suitable means not shown.

29 mounted on the shaft 28 and rotated by the pulley 30.

In operation the mill is disintegrated by the beater bars and the very coarsest material is carried round in the annular space by centrifugal force. The material of intermediate coarseness is either separated out in the upwardly flaring pipe 21 or held back by the coarse sieve 22. The fine material settles in chamber 25 and is prevented from passing to the pump by the ultra-filter 31.

The ultra filter is an extremely important feature of the apparatus according to the present invention and it is preferred to employ a metal structure which may consist of.

superimposed slotted plates wherein the slots of adjacent plates are at an angle from one another. After a certain time the dust particles themselves fill up the zig-zag or devious paths within the plates and dust particles therefore form the filtering medium themselves. But metal structures can be employed in which the pores are constricted by a material set therein such as porous colloidal materials, cellulose esters, rubber, or in some cases cement may be sufficient. It is preferable to employ mechanical means such as the above described brushes to keep the surface of the sieves clear.

Metal sieves covered with finer wire or yarn are preferably used to separate the dust of intermediate coarseness and to allow the fine dust to pass through.

The sedimentation of the dust of intermediate fineness in the passage 21 can be effected by adjusting or predominating the height of the vacuum and in some cases it is possible to obtain sufficient separation of the coarse dust and dust of intermediate fineness from the fine dust without using a special filter 22.

It will be apparent that a further vacuum pipe may be connected direct to the mill if desired if a suitable filter or ultra-filter is interposed.

' Fig. 2 shows an installation of the same type in which more effectual means are employed to maintain the vacuum. Hopper 1s vacuum-tight and can be closed after being filled with a substantial amount of the coarse material. Hopper 33 is connected with the vacuum pump by valve 43 and pipe 44. The collecting vessel '25 is provided with a three-way valve 34 so that the material can be discharged either through pipe 35 to vessel 36 or through pipe 37 to vessel 38.

These vessels are provided with discharge valves 39 and 40 and are connected with the vacuum pipe 44 through valves-41 and 42. Thus material can be charged into the mill and removed from vessel 25 without breaking the vacuum.

As regards the dispersators which are employed, it has been found experimentally that these substances not only increase the degree of fineness of the powder, but they decrease the. quantity of energy necessary to operate the mill. The theory of their action remains obscure at present. Satisfactory results can be obtained by adding to a solid substance a sn'iall quantity, e. g. 1-5% of certain liquids such as water or a 33% .solution of waterglassor of sulphite cellulose liquor or other colloids. But small quantities of a tanning agent or a protein or aqueous solutions thereof appear to exert a slmllar actlon 1n considerably acceleratmg the high speed disintegration of solid substances although the material is not wetted thereby. Such materials do not therefore act in the same way as the tannin which is used asa deflocculating agent in the slow grinding of a moist paste of graphite or other substances in which the phenomenon of peptization appears to play a predominating part.

The' best results according to the present invention are obtained by observing the four conditions already recited and by using a disintegrator which is adapted'to rotate at the maximum practicable speed, e. g. the dislntegrator may be cdnnected direct with a steam turbine, but as already explained the .invention includes processes in which exist ing mills are adapted so asto operate in such manner as will obtain some but not all of the benefits of the preferred form of the invention. I

It may be, added that the products obtained, according -to the invention are in many cases of colloidal fineness, but it must not necessarily be assumed that they will all" be of colloidal size by mere admixture with water unless dispersators or protective colloids are added during disintegration. If

this is 'not the case, certain conditions are necessary after grmdmg. For example, talc,

oxide of iron,'alumina, rock phosphate and the like may be treated-with 1-5% of a 33% solution of waterglass. Certain colours of the mineral type can be treated with alkali, aluminates. Known protective colloids may be added to the dispersion.

The fineness of grinding may be tested by mixing the comminuted material with water and a small quantity of a protective colloid; if the material consists of particles of 0.1 to 0.02 mm. diameter the sol cannot be obtained as a rule, whereas products can be obtained accordin to the present invention in the form 0 ,a colloidal sol .which exhibits Brownian movement, the

phenomemm of the Tyndall cone and can be precipitated or coagulated by the addition of acids or 'other electrolytes in the same manner as other colloidal solutions.

I declare that what I claim is 1. The process of disintegrating dry material by impact against moving parts in which (a) the moving parts are rotated at a relative velocity of at least 1000 revolutions per minute and in which the peripheral speed is at least 1000 metres per minute and (b) the operation is performed in vacuo.

2. The process of disintegrating dry material by impact against rotary parts in which (a) the rotary parts are rotated at a relative speed of at least 1000 revolutions per minute and at a peripheral speed of at least 1000 metres per minute, (6) the operation is preformed in vacuo and (0) the sufficiently finely ground material is con- 6. An installation for grinding dry material comprising a high speed disintegrator, a hopper, valves between said hopp r and said disintegrator, a plurality of c leeting vessels, a valve between said collecting vesselsand said disintegrator and means to maintain a vacuum in said hopper, mill and collecting vessels.

In witness whereof, .I have hereunto signed my name-this 10th day of October 1922. 1

- HERMANN PLAUSON. [1,. s.]

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