US2437694A

US2437694A - Method for blending powder grains

Info

Publication number: US2437694A
Application number: US669765A
Authority: US
Inventors: Clarence N Hickman
Original assignee: National Aeronautics and Space Administration NASA
Current assignee: National Aeronautics and Space Administration NASA
Priority date: 1946-05-15
Filing date: 1946-05-15
Publication date: 1948-03-16
Anticipated expiration: 1965-03-16

Description

March 16, 1948. c. N. HICKMAN 2,437,694

' METHOD FOR BLENDING POWDER GRAINS Filed May 15, 1946 2 Sheets-Sheet 1 a l7 l2 I Blur Bil Ll: e N- H-i cum-an M r 16, 1948. c. N. HICKM'AN I 2,437,694

METHOD FOR BLENDING POWDER GRAINS Filed May 15, 1946 2 Sheets-Sheet 2 1 P i 51. EL.

awe/WM Blur an; e N. HiuKm-nn- Patented Mar. 16, 1948 UNI TE-D -:STAT ES PATENT OFF-ICE -M-ETHGD FOR, BLENDING POWDER GRAINS *Cia'r'ence" N. Hickman, Jackson Heigh ta'Y N. Y,

*assignor to U nite'dstatcs' 'ofjfA'iiiri'oa, as represented by the Secretary of War Application May 15, 1946, Serial No.-669,765

(Granted under the act 'of March 3, 1883, as

4 "Claims.

operation in powder manufacturing, Without which uniformity l'in b'allistic performance could not be obtainedbe'cause it --is impossible to "accurately control the chemical manufacturing processes so'tha't each batch of powder will have exactly the same pr'eperties. n powder indexer lot, 1 as made up for service useeonsi'stspf 50,000 pounds or more of owder and-in order' to make up such a lot it-i'sinece'ss'ary' to use dried-grains .fromralnumber of difierent powder-batches. The

:grain's'lirom the different powder batches mudt be thoroughly mixed or hlendedto g-ive uniformity throughoutthe lot. g

The blending of pwder, as a-cco ished by the prior art, isica'rriedout in blend-1 g' towers.

One type of blending" tower consists foi 'a series of .bins arranged in horizontal groups; the groups being positioned in vertical relation-toeachother. The bins of each groupmay be in polygonal re lation, each bin having a trapbrgatevalve rac ing toward'the center of the group. In blending, the top group of fthe bins is 'cha'rgeti with the required amount of powder from'eachof theselected batches. The trap or gate valves are opened simultaneously and-the powder from all f the bins falls to the'nextgroup in a single stream which divides about equally into the 'bins of the next group. This operation is continued from group to group and the powderis finally=draiwn ofi through arhopperlatthe bottom'of the "blending. tower. In 1 other blending towers the powder in the first blending bin is released .-to fall over a distribution-cone before enteringthe nextlower group of bins. This distribution cone improves the blending of the powder. If a' highdegree of uniformity is desired, however, it is necessary to run the powder through the blending tower at number of times. One characteristic disadvan tage of this prior art blending process is the hazard involved due to the development of static electricity. Although apparatus has'be'endesigned to remove the electric charge from the parts of the system, the addition of this apparatus rather complicates the structure and is not entirely satisfactory. a

amended April 30, 1928; 370 O. 'G. 757) In one type of rocket motor, as many as 30 individual grains, each about 5 inches'in length andabout V8 inch-in diameter, are used; Different loading performances have been found, traceable only to'noh uniformity in the powder mtg-from which'theloadihgs weremade, i. e., to inadequate blending of the powder. Because of the tremendous hazards involved, it has not been possible to blend powders of this larger grain size with the -Iiie'chanical means known to the prior-art, hence, it is an object of this invention to provide 'a inetho'd and apparatus for blending powders of /8 inch 'grainsize or larger which is non-hazardous and which produces a higher degree of uniformity in blending than has been obtainable heretofore by any of the methods known to the prior art.

The specific-natiire of the invention as well as other objects and advantages thereof will clearly appear froma description ofa preferred embodimerit as shown in the accompanying drawings in which:

Fig. '1 is a vertical -section through the blend ing apparatus is described.

Fig. 2 shows an alternate arrangement for the recirculating system.

This invention consists essentially of a method of and an apparatus for mixing powder grains by means of the circulation of an electrolytic mixing medium of lower specific gravity than the powder through a 'vat containing the powder grains, at a sufic'ient velocity to displace them with respect to each other, the preferred medium for this application being water which has been saturated with nitro-glycerine ito prevent any of the nitro-glycerine content of the powder from being absorbed by the water. The powder grains to be mixed are placed in avat, the liquid mixing medium 'is added until it rises considerably above the top of the grains and then a jet of the liquid is ejectedupwar'dly through the bottom of the vat at sufliciently high velocity to break through the surfaceof the liquid and fan out in a fountain-like manner, The grains located in the path ofthe jet are carried upwardly and out wardly along with the jet dropping back in a haphazard manner, thus being very thoroughly dispersed or mixed.

The apparatus consists of a base i on which is mounted a vat 3 in the form of an ellipsoid generated by revolution of an ellipse about its conjugate axis, the axis being disposed, vertically. The vat 3 contains water saturated with nitroglycerine. charging door 5 is provided in the upper part of the Vet 3' and-a discharging door 1 near the bottom. A recirculating system is provided, the system consisting of an outlet pipe ll, a pump II and an inlet pipe l2 terminating in a nozzle l3 adjacent the bottom of and in the vertical axis of the vat through which a water jet I6 is forced by the pump ll. Outlet pipe i is covered by a baflle l4 and a screen l5 which prevents powder grains 24 from gathering around or passing into the outlet line I!) of the recirculating system.

The ellipsoidal form of vat is especially advantageous for this application since the tendency therein of the grains to slide toward the center without excessive crowding is uniform in all directions; however, any form of vat having a declivitous fioor sloping toward a low point at which the nozzle can be located may be used.

A drain pipe IT with a valve [8 is provided for draining water from the vat 3 into a storage reservoir (not shown). A screen I9 covers drain pipe I! to prevent egress of powder grains 24.

For some applications it may be desirable to make use of gravity feed of the water, thereby maintaining a constant head and as a result, constant pressure at the nozzle l3 and uniform fountain effect in the vat. This construction is illustrated schematically in Fig. 2 in which a standpipe 30 would provide the necessary head. A feed line 3| leads from standpipe 30 to nozzle l3 with a valve 32 inserted to control the flow. An overflow line 33 and a drain line 34 with a shutoff 35, lead from vat 3 to a storage tank 36.

, Standpipe 30 is also provided with an overflow line 31 leading to storage tank 36. A pump 38 supplies water to standpipe 30 through a feed line 39.

In operation, a lot of powder, consisting of a predetermined quantity of powder from each of the batches to be blended is placed in the vat and sufficient water, saturated with nitro-glycerine, is added to fill the vat to a point well above the top of the powder grains and the outlet I0. Charging door 5 is then closed and pump Ii started, forcing a jet of water from the nozzle l3 to rise vertically upward from the bottom of the vat breaking through the surface of the water and fanning out in a fountain-like manner before falling back. As the grains in the middle of the vat 3, i. e., in the path of the jet l6, are carried upward and spread out on top, the mass settles toward the center so that eventually all grains are recirculated or redistributed, hence a high degree of dispersion is attained with a consequent uniformity of blend. By using an electrolytic liquid such as water as a circulating medium, the dangers resulting from static charges developed in blending towers are avoided and by saturating this water with nitro-glycerine, the nitro-glycerine content of the powder grains is maintained undiminished.

In the manufacture of service smokeless powder, particularly single-base service smokeless powder, the drying operation may be carried out by circulating warm waterrather than air through the powder grains. It may be desirable to continue the drying process for the removal of volatiles in the nitro-cellulose powder, utilizing the blending process of this invention, thus combining steps in manufacture. However, notwithstanding this possible combination of operations, the superior blending obtained by this process would warrant the substitution of this step in manufacture for the conventional blending process as carried out in towers, particularly in view of the fact that blending towers now utilized are inadequate for blending powder grains of a size necessary for some rocket propellent applications. A heating coil as indicated at 2| could be used to warm the mixing medium when desired.

While the preferred embodiment as above described is especially adapted for this application, modifications such as would occur to anyone skilled in the art may be made without departing from the spirit of the invention.

. It is apparent from the description and drawrings that this invention provides a method and apparatus whereby very large size grains of smokeless powder can be safely and thoroughly .mixed, resulting in an improved blending of various batches of powder into a final uniform :index or lot.

I claim:

1. A method of blending powder grains includ- .ing the steps of placing the powder grains to be blended in a vat, adding a liquid of lower specific gravity than the powder grains in quantity sufficient to rise to a substantial height above the grains, said liquid being substantially a non- :solvent with respect to said grains, and circulating said liquid, including projecting a jet of the liquid upwardly from the bottom of the vat among the grains whereby the grains in the path of the jet are propelled upwardly into changed relation with respect to the other grains in the vat.

2. A method of blending smokeless powder grains including the steps of placing the powder grains to be blended in a vat, adding water saturated with nitroglycerine, said water being added in quantity sufiicient to rise to a substantial height above the grains, and circulating said water by withdrawing it from the vat and projecting it upwardly through the bottom of the vat with sumcient velocity to break through the surface and fan out in a fountain-like manner, whereby the grains in the path of the jet are propelled upwardly above the surface of the liquid to fall back in a haphazard manner on top of the other grains therein.

3. A method of mixing and drying particles of solid material containing a volatile constituent,

including the steps of placing the solid particles in a vat, adding enough liquid of lower specific gravity than the solid particles in quantity sufiicient to rise to a substantial height above the solid particles, said liquid being substantially a non-solvent with respect to the particles, maintaining said liquid at a temperature capable of volatilizing the volatile constituents thereof and projecting a jet of the liquid upwardly from the bottom of the vat among the particles whereby the particles in the path of said jet are moved into changed relation with respect to the other particles in the vat.

4. The method of blending propellent powder grains which comprises placing in a vat the said propellent powder grains and a liquid of lower specific gravity than the powder grains, said liquid being substantially a non-solvent for the constituents of the powder grains and present in sufiicient quantity to rise above said grains; and circulating said liquid by withdrawing a portion thereof from the vat and injecting said portion in the form of a high velocity stream vertically upwards through powder grains and liquid in said vat, the velocity of said stream being sufficient to thoroughly mix the said grains.

CLARENCE N. HICKMAN.

(Iteferences on following page) Pontoppidan "Feb. 8, 1927 1 537,408

Name Date Kelly Mar. 26, 1929 Bloom Dec. 15, 1931 Soderholm Jan. 19, 1937 Alexander June 26, 1945 FOREIGN PATENTS Country Date Germany Nov. 11, 1933 Great Britain June 20, 1941