US3679782A

US3679782A - Manufacture of globular powder

Info

Publication number: US3679782A
Application number: US878269A
Authority: US
Inventors: Eugene A Andrew; Henry J Halverson
Original assignee: Olin Corp
Current assignee: Olin Corp
Priority date: 1969-11-20
Filing date: 1969-11-20
Publication date: 1972-07-25
Anticipated expiration: 1989-07-25
Also published as: FR2070718B1; TR18537A; DE2055338A1; CA963264A; DE2055338B2; DE2055338C3; SE425084B; FR2070718A1; JPS496643B1; BE759229A; ES383945A1; GB1287346A

Abstract

A method of preparing globular propellant powder wherein presized lacquer particles are entrained in a liquor suspending medium and forced to flow through a long section of tubing until the propellant grains are dewatered and rounded into spherical shape. The spherically shaped powder globules are then passed into a flash evaporator having a pressure lower than that in the dewatering and shaping conduit so that a portion of the solvent within the globules volatilizes. The remaining solvent is removed by passing the slurry through a final hardener consisting of several chambers. Each of these chambers are individually heated to increase the temperature of the slurry of powder granules as it moves through the column. The temperature gradient between adjacent chambers in the latter stages may be increased.

Description

United States Patent Andrew et a1.

[ July 25, 1972 [54] MANUFACTURE OF GLOBULAR POWDER [73] Assignee: Olin Corporation [22] Filed: Nov. 20, 1969 [21] Appl. No.: 878,269

[56] References Cited UNITED STATES PATENTS 2,740,705 4/1956 ONeill ..264/3 E 3,014,246 12/1961 Cook et al. ....264/3 E Primary Examiner-Benjamin R. Padgett Attorney-Donald R. Motsko. H. Samuel Kieser and William W. Jones 57] ABSTRACT A method of preparing globular propellant powder wherein presized lacquer particles are entrained in a liquor suspending medium and forced to flow through a long section of tubing until the propellant grains are dewatered and rounded into spherical shape. The spherically shaped powder globules are then passed into a flash evaporator having a pressure lower than that in the dewatering and shaping conduit so that a portion of the solvent within the globules volatilizes. The remain ing solvent is removed by passing the slurry through a final hardener consisting of several chambers. Each of these chambers are individually heated to increase the temperature of the slurry of powder granules as it moves through the column. The temperature gradient between adjacent chambers in the latter stages may be increased.

10 Claims, 1 Drawing Figure PATENFEEJMS I972 h 3,679,782

INVENTORS EUGENE A. ANDREW HENRY S. HALVERSON BY WK 1% I hr/ .5 4r

ATTORNEY BACKGROUND OF THE INVENTION This invention relates generally to the manufacture of propellant powder. More particularly, this invention relates to the manufacture of globular granules of smokeless powder.

US. Pat. No. 2,027,114, granted Jan. 7, 1936, discloses a process of manufacturing smokeless powder wherein a lacquer, comprising a smokeless powder base in a solvent is formed into globules and solidified while suspended in a nonsolvent medium. Many variations have been added to this basic process to control the size and density of the resulting powder particles which are of a spherical or near-spherical shape. This process for manufacturing propellant powder has come to be known to those skilled in the art as the globular powder process.

The globular powder" process as heretofore known is essentially a batch process. Being a batch process, it suffers from the disadvantage that it is relatively slow with the result that a large amount of equipment is tied up at a given time. In addition, there is some variance in the final product from one batch to another.

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide an improved process for the manufacture of spherical or nearspherical grains of propellant powder base.

It is another object of the present invention to provide an improved method of presizing and shaping particles of propellant powder to produce spherical or near-spherical grains.

Yet another object of the present invention is to provide an improved process for hardening globules of a lacquer of a powder base and solvent to produce spherical or near-spherical particles of propellant powder.

Still another object of the present invention is to provide a continuous process for making spherical or near-spherical grains of propellant particles.

A further object of the present invention is to provide an improved process for making spherical or near-spherical grains of propellant powder having a relatively high density.

A still further object of this invention is to provide an improved process for making spherical or near-spherical powder grains in which the processing time is materially reduced.

In accordance with this invention, these and other objects are accomplished, generally speaking, by passing a lacquer comprising a powder base in a solvent through a mechanical grainer which presizes the lacquer into particles of generally cylindrical shape. The presized lacquer particles are immediately suspended in a liquor solution which is a non-solvent for the powder base and substantially immiscible with the lacquer solvent. The liquor/lacquer slurry is then forced to flow through a long section of tubing until the cylindrical grains are dewatered (by the presence of a dewatering salt in the liquor) and rounded into spheres due to the inner molecular and interfacial forces acting on the grain caused by elevated temperatures in the tubing line. Turbulance within the shaping line also assists in the shaping of the grain and aids in preventing adhesion between individual grains.

To harden the lacquer globules in accordance with this invention, the liquor/lacquer slurry is maintained under pressure during the dewatering and shaping operation. The pressure is necessary in order to prevent solvent vaporization since the temperature in the line is above the boiling point of the solvent of the lacquer. The slurry is continuously passed from the dewatering and shaping line into a flash evaporator which is maintained at a temperature approximately the same as that of the incoming slurry and at a pressure lower than that in the dewatering and shaping line. As the slurry enters the evaporator, the reduced pressure causes the solvent within the globules to rapidly migrate from the globules and volatilize. At this point, the grain becomes hard and resists further deformation. Although over half of the solvent in the grain is removed in this operation, some solvent still remains. To remove the remaining solvent in an expeditious manner, the slurry is further processed through a final hardener which consists of a second evaporator having a plurality of chambers. Each of the chambers are individually heated to increase the temperature of the slurry as it moves through the column. This reduces the amount of time required to remove the solvent without causing deformation of the individual globules. If desired, the temperature gradient between adjacent chambers in the later stages may be increased.

DETAILED DESCRIPTION In order that the invention may be further clarified, reference may be had to the drawing which diagrammatically illustrates the steps of the process and to the following detailed description. Unless otherwise indicated, all the proportions of the materials used are given in parts by weight of the resulting mixture.

The lacquer is prepared by mixing together the smokeless powder base and a solvent in a mixing unit 2 equipped with an agitator 4. The smokeless powder base is preferably nitrocellulose which may be in the form of ground and extracted FNl-I (flashless non-hydroscopic) powder which is wholly or partly purified or any water wet nitrocellulose. The only requirement for the solvent is that it be a solvent for the smokeless powder base and be substantially immiscible with the suspending medium. In the case where nitrocellulose is the smokeless powder base and the suspending medium or liquor is an aqueous solution, such solvent may include ethyl acetate, isopropyl acetate, butyl acetate, ethyl formate, methyl ethyl ketone, methyl isopropyl ketone, diethyl ketone and mixtures thereof and the like. A stabilizer for nitrocellulose such as diphenylamine may be added to the vat 2 in a. small amount of about 0.2 to 0.7 percent. a

The viscosity of the lacquer should be controlled to provide uniform extrusion and permit hardening of the grains without distortion. Generally, the viscosity may range from about 6 seconds to 17 seconds as measured by the falling rod method. The falling rod method entails utilizing a 0.314 inch diameter stainless steel rod weighing 60 grams and dropping it from the lacquer surface into the lacquer for a distance of 2.31 inches. The time required for the rod to move this distance is the viscosity in seconds. If the viscosity is too low, the shape of the resulting grains will be distorted. If the viscosity is too high, the particles will not assume a rounded shape and will not have the required density as they will be difficult to dewater. Although a viscosity of 6 to 17 seconds may be used, 12 to 15 seconds is the preferred range for making grains having a final size of 0.020 to 0.030 inch.

The ingredients in mixing unit 2 are agitated and brought to a temperature between about 60 to about 70 C. The agitation of the mixture should continue until the lacquer becomes homogeneous.

Concurrently with the preparation of the lacquer, a liquor which forms the suspending medium is prepared by mixing together in a separate tank 6 which is provided with an agitator 8, the proper suspending vehicle, a protective colloid and a dewatering salt. As has been stated above, the suspending vehicle should be a non-solvent with respect to the smokeless powder base and also immiscible with the lacquer. For reasons of economy, such vehicle is usually water. The protective colloid may be selected from any one of the following materials: cornstarch, gum arabic, animal bone glue, dextrine, bentonite or the like.

The dewatering salt is preferably selected from a water soluble metal salt such as sodium sulfate, magnesium sulfate, aluminum sulfate, barium nitrate, sodium chloride, sodium nitrate and mixtures thereof. However, any substance which actually dissolves in the non-solvent medium and which will alter the physical properties of the liquor with respect to water in the lacquer so that the water will migrate from the lacquer particles into the suspending medium may be used.

Respective percentages of the various ingredients constituting the liquor may be: the suspending vehicle between about 85 and about 95 percent, the protective colloid between about 0.5 and 1.5 percent, and the dewatering salt between about 3.5 and 6 percent.

in addition, a solvent, usually the solvent employed in the preparation of the lacquer, may be added to the liquor in an amount of between about 3 and about 6 percent to prevent migration of the solvent from the lacquer globules during the presizing, shaping and dewatering operation. The solvent may be added to the tank 6 or it may be metered into the liquor line.

The ingredients in the tank 6 are mixed together by means of the agitator 8 and heated to about 50 to about 65 C. The liquor is pumped by means of a pump 10 to the downstream 7 side of the presizing plate of presizing unit 12.

The presizing unit 12 comprises a presizing extrusion plate 14 having a plurality of orifices therein and a rotating knife 16 to cut the extrudate into cylindrical particles having a diameter-to-length ratio of approximately 1 to l. The lacquer is pumped by means of pump 18 through the extrusion plate 14 and is cut into the appropriate size particles by the knife 16. The liquor is pumped into the presizing unit at a point immediately above the extrusion plate 14. As soon as the lacquer is cut into cylindrical particles, the particles are immediately immersed and suspended in the liquor to form a slurry. The slurry of lacquer particles and liquor is then forced through a dewatering and shaping line 20.

The dewatering and shaping line 20 may be a long section of tubing provided with suitable means to raise and maintain the temperature of the slurry to between about 75 to 85 C. Such means may be in the form ofa water bath in which the section of pipe or tubing is immersed, or by means of a coaxial tube, the inner one of which provides the path for the slurry and the outer one 22 provides a path for steam or other fluid of proper temperature to pass in heat exchange relationship. A nozzle or construction 24 is provided in the outlet end of the line 20 so that the slurry up to this point is maintained between a pressure slightly above atmospheric and a pressure of three atmospheres. As the slurry travels through line 20, the dewatering salt present in the liquor causes migration of water from the lacquer globules resulting in a less porous particle of higher specific gravity. In addition, the cylindrical particles of lacquer tend to assume a spherical or near-spherical shape due to the molecular and interfacial forces acting on the grain as well as the turbulance within the line.

After the slurry passes through constriction 24 it enters a flash chamber or evaporator 26 which is provided with a suitable agitator 28. The flash chamber 26 is maintained at a temperature approximately equal to the temperature of the incoming slurry or slightly greater if desired. The pressure within the evaporator is less than the pressure within the dewatering and shaping line 20 so that the exposure of the slurry to the reduced pressure will cause the solvent to rapidly migrate from the grain surface and volatilize. The volatilized solvent may be withdrawn through outlet 30 by suitable means and recovered by condensation. The length of time a particular grain stays in the flash chamber depends basically upon the level of the slurry contained therein and may be anywhere from to 60 minutes. During the process, about 60 to 80 percent of the solvent in the globule is removed and the grain becomes relatively hard and resistant to further deformation.

After the appropriate interval of time, the slurry is passed to a final hardener 32 which consists of a column comprising from about three to six chambers 34-44 which are individually heated. Some or all of them may have a progressively higher temperature so that the temperature of the slurry is increased as it moves through the column. The remaining solvent is extracted from the grain during this operation and is volatilized and recovered by condensation. The temperature gradiant between adjacent chambers may be increased in the final stages of the hardener.

If desired in the event ofa six chamber evaporator, the first three chambers may all be at the same temperature which may be about 2 to 4 C. above that of the incoming slurry. The fourth chamber may be 2 to 4 C. above the previous chamber, the fifth chamber 4 to 6 C. above the fourth, and the temperature raised about 8 or 9 C. in the final chamber. The important consideration being that the temperature gradient between adjacent chambers should be about the same in the beginning and then may be increased in the later stages. If the temperature is raised too quickly and too great an amount, the grains may become thermally shocked and distorted. The retention time of the grains within the final hardener is between about 10 and 40 minutes depending upon the process conditions.

As the slurry passes from the column, it enters a catch box 46 wherein the hardened spherical powder is separated from the liquor by means of a suitable screen 48. The hardened powder is now ready for further processing such as nitroglycerine impregnation, deterrent coating and the like to provide a finished product. The liquor is cooled, reprocessed and cycled back to the graining chamber and the condensed solvent is reused to make lacquer.

In order to further illustrate the invention, the following is a detailed description of a preferred embodiment of the entire process. All proportions are expressed by weight unless otherwise indicated.

A lacquer was prepared by adding 140 pounds of ethyl acetate, one pound of diphenylamine and 15 pounds of benzene to a mixer equipped with an agitator. The mixture was agitated and brought to a temperature of 65 C. FNH smokeless powder was added to the agitated mixture in the amount of 70 pounds on a dry basis. The powder contained water in the amount of 7 percent by weight of the nitrocellulose. The agitation was continued and the lacquer brought to a temperature of 60 C. Agitation of the lacquer was continued for about 1 hour until it reached a relative viscosity of 15 seconds as measured by the falling rod method. The specific gravity was approximately 1.03. The solvent ratio, i.e., the ratio of the ethyl acetate to the dry nitrocellulose, was 2.2/1.

Concurrently with the preparation of the lacquer, a liquor was prepared by adding 896 pounds of water to a vat or tank equipped with an agitator. The water was agitated and 15 pounds of a protective colloid and about 0.04% of silicon antifoam B were added to the water over the period of 3 to 4 minutes. The colloid and water were mixed for 15 minutes and the temperature thereof elevated to 60 C. Fifty pounds of sodium sulfate was added over a period of l to 2 minutes. The liquor was pumped to a presizing unit at the rate of 9.90 pounds per minute. in addition, ethyl acetate in the amount of 3 to 6 percent was metered into the liquor line prior to the grainer to complete the preparation of the liquor.

The lacquer was pumped through the extrusion plate at the rate of 2.85 pounds per minute where it was cut into cylinders having a length and a diameter of 0.022 inch. The cylinders of lacquer were immediately entrained in the liquor and passed into the dewatering and shaping line which comprised a pipe having an internal diameter of approximately inch and a length of 300 feet. The temperature of the liquor/lacquer mixture was 60 C. as it entered the dewatering line and was heated to C prior to leaving and the pressure was maintained at about 20 psig.

The liquor/lacquer mixture was passed through the dewatering and shaping line at a rate such that a given lacquer particle remained in the dewatering line between about 5 and 10 minutes. At the end of this time, the lacquer particle had been rounded into a substantially spherical shape.

The mixture of liquor and spherical lacquer particles entered an evaporator which was maintained at atmospheric pressure and about 80 C. The mixture was kept under constant agitation whereby the solvent was condensed and removed at the rate of about pounds per hour along with a portion of the water. The mixture remained in this evaporator for about 15 minutes.

The spherical particles along with the liquor passed into the first chamber of the final hardening unit. The final hardening unit consisted of six chambers with the mixture in the first three chambers being maintained at 83 C., the mixture in the fourth chamber being maintained at 86 C., the fifth chamber 91 C., and the final chamber 99 C. The mixture was passed through the final hardener at the rate of l 1.0 pounds per minute and had a residence time of 30 minutes. After the final hardening treatment, substantially all of the solvent had been removed from the spherical powder particles and the particles were hardened. The mixture may then be passed through a screen to separate the hardened spherical powders from the remainder ofthe liquor.

The hardened powder grains resulting from this process had an average size of 0.0235 inch and were all between the range of 0.016 inch to to 0.028 inch with 95 percent of the particles being between 0.020 inch to 0.025 inch. The average specific gravity of the powder grains was 1.55 with all the grains having a specific gravity between 1.54 and 1.56.

It will be appreciated that one of the advantages of the present invention is the fact that by the use of a dewatering and shaping line, an individual particle can be shaped into a substantially spherical body in the order of 3 to minutes. In accordance with previous processes, at least three hours was required to form the spherical particles and dewater the grain. In addition, the use of a flash chamber wherein only a portion of the solvent is removed in combination with a final hardening unit having a plurality of chambers which are maintained at increasing temperatures reduces the time required to harden the spherical particles from about 5 hours to 1% hours. Moreover, the combining of the various steps of the present process permits a truly continuous powder making operation resulting in a higher rate of production of powder for a given amount of equipment.

What is claimed is:

1. In the art of making powder grains wherein discrete particles of a lacquer of a smokeless powder base and a solvent therefor are formed and shaped into substantially spherical particles while entrained in a liquor suspending medium which is a non-solvent for said powder base and substantially immiscible with said solvent, the method comprising placing the shaped lacquer particles and said suspending medium under a pressure and temperature which prevents vaporization of the solvent, passing said shaped lacquer particles while entrained in said suspending medium through a first evaporator which is maintained at a temperature above the boiling point of said solvent and at a pressure below the pressure to remove a por tion of said solvent from said shaped lacquer particles and thereafter passing said lacquer particles and said suspending medium through a series of hating zones, at least some of said zones having a higher temperature than the zone immediately before it.

2. In the art of making powder grains, the method comprising continuously passing a lacquer ofa smokeless powder base and a solvent therefor through at least one extrusion orifice, cutting said lacquer into discrete particles after it passes through said orifice, entraining said discrete particles in a liquor suspending medium which is a non-solvent for said powder base and substantially immiscible with said solvent to form a slurry, continuously passing said slurry through conduit means of a predetermined length and at a predetermined rate to shape said particles into spherical or near spherical shape, passing the resulting slurry of suspending medium and shaped lacquer particles through a first heating zone having a lower pressure than said line and a temperature above the boiling point of said solvent and thereafter continuously passing the remaining slurry through a series of heating zones at east some of which have a higher temperature than the preceding zone.

3. The method of clam 2 wherein the lacquer is cut into cylinders having a length to diameter ratio of about 1 to l t form said discrete particles.

4. The method of claim 2 wherein. the temperature of said conduit means is maintained at a temperature above the boiling point of the solvent and under a pressure sufficient to prevent vaporization of the solvent.

5. The method of claim 2 wherein at least half of the solvent is removed from the shaped lacquer particles during the passage thereof through said first zone.

6. The method of claim 2 wherein said suspending medium contains a dewatering salt to cause migration of any aqueous medium from said lacquer articles as said particles pass through said conduit means.

7. The method of claim 6 wherein said suspending medium is an aqueous medium.

8. In the art of making powder grains from a lacquer of a nitrocellulose based powder and a solvent therefor, the method comprising passing said lacquer through an extrusion plate, cutting said extruded lacquer into discrete particles, entraining said lacquer particles in a liquor suspending medium which is a non-solvent for said powder base and substantially immiscible with said lacquer to form a slurry, passing said slurry through conduit means for a time and temperature sufficient to shape said lacquer articles into a substantially spherical shape while maintaining said slurry at a pressure above atmospheric, passing the resulting slurry of shaped lacquer particles and suspending medium through a first evaporator at at mospheric pressure and at a temperature above the boiling point of the solvent, and thereafter passing said slurry through a series of heating zones all maintained at atmospheric pressure, at least some of said zones having a higher temperature than the zone immediately preceding it, and thereafter separating said hardened powder grains fro said suspending medium.

9. In the art of making powder grains, the method comprising preparing a lacquer of smokeless powder base and a solvent therefor, preparing a liquor of an aqueous medium, a protective colloid and a dewatering salt, extruding said lacquer through an extrusion plate having at least one opening of predetermined size, cutting the extruded lacquer into lengths such that the length to diameter ratio of the resulting particles is about 1 to I, immediately entraining said particles in said liquor to form a slurry and passing said slurry through a conduit for a time sufficient to cause migration of any aqueous medium from said lacquer particles and to permit said particles to assume a substantially spherical shape, passing said slurry through an evaporator at atmospheric pressure and at a temperature above the boiling point of said solvent, and thereafter passing said slurry through a series of heating zones all having a temperature higher than said evaporator and at least some of said zones having a temperature greater than the temperature of the zone immediately preceding it 10. The method of claim 14 wherein a first group of heating zones of said series of zones is maintained at a temperature about 2 to 4 C. above that of said first zone, the next zone is maintained about 2 to 4 C. above said evaporator, the next zone about 4 to 6 C. above that of the previous zone, and the final zone about 8 to 9 C. above the previous zone.

UNITED STATES PATENT @TTTCT QEIIFICAEE We CQRECIIQN Patent No. 3 ,679 ,782 Dated July 25 1972 Inventor(s) Eugene A. Andrew and Henry J. Halverson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In Column 5, line 50, "hating" should read as --heating-.

In Column 5, line 16, please delete 'to" the second occurence.

In Column 6, line 3, "east" should read as --least-.

In Column 6, line 5 "clam" should read as --claim--.

In Column 6, line 6, "t" should read as --to--.

In Column 6, line 17, "articles" should read "particles".

In Column 6, line 29, "articles" should read --particles-.

In Column 6, line 38, "fro" should read -from-.

In Column 6, line 58, "14" should read "9".

Signed and sealed this 30th day of January 1973.

(SEAL) Attest:

EDWARD M. FLETCIIER,JR., ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-1050 (10-69) USCOMM-DC 60376-P69 a US, GOVERNMENT PRINTING OFFICE: I969 0-366-834 Patent No. 3,679,782 Dated July 25, 1972 Inventor(s) Eugene A. Andrew and Henry J. Halverson It is certified that error appears in the above-identified pat ent and that said Letters Patent are hereby corrected as. shown below:

In Column 5, line 50, "hating" should read as --heating--.

In Column 5 line 16, please delete "to" the second occurence.

In Column 6, line 3, "east" should read as --least--.

In Column 6, line 5 "clam" should read as --claim--.

In Column 6, line 6, "t" should read as --to--.

In Column 6, line 17, "articles" should read --particles--.

In Column 6, line 29, "articles" should read --particles--.

In Column 6, line 38, "fro" should read --from--.

In Column 6, line 58, "14" should read --9--.

Signed and sealed this 30th day of January 1973.

(SEAL) Attest:

EDWARD P I.FLETCIIER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM USCOMM-DC 60376-P69 .5. GOVERNMENT FRlNTlNG OFFICE I 1969 0-356-335

Claims

2. In the art of making powder grains, the method comprising continuously passing a lacquer of a smokeless powder base and a solvent therefor through at least one extrusion orifice, cutting said lacquer into discrete particles after it passes through said orifice, entraining said discrete particles in a liquor suspending medium which is a non-solvent for said powder base and substantially immiscible with said solvent to form a slurry, continuously passing said slurry through conduit means of a predetermined length and at a predetermined rate to shape said particles into spherical or near spherical shape, passing the resulting slurry of suspending medium and shaped lacquer particles through a first heating zone having a lower pressure than said line and a temperature above the boiling point of said solvent and thereafter continuously passing the remaining slurry through a series of heating zones at east some of which have a higher temperature than the preceding zone.
3. The method of clam 2 wherein the lacquer is cut into cylinders having a length to diameter ratio of about 1 to 1 t form said discrete particles.
4. The method of claim 2 wherein the temperature of said conduit means is maintained at a temperature above the boiling point of the solvent and under a pressure sufficient to prevent vaporization of the solvent.
5. The method of claim 2 wherein at least half of the solvent is removed from the shaped lacquer particles during the passage thereof through said first zone.
6. The method of claim 2 wherein said suspending medium contains a dewatering salt to cause migration of any aqueous medium from said lacquer articles as said particles pass through said conduit means.
7. The method of claim 6 wherein said suspending medium is an aqueous medium.
8. In the art of making powder grains from a lacquer of a nitrocellulose based powder and a solvent therefor, the method comprising passing said lacquer through an extrusion plate, cutting said extruded lacquer into discrete particles, entraining said lacquer particles in a liquor suspending medium which is a non-solvent for said powder base and substantially immiscible with said lacquer to form a slurry, passing said slurry through conduit means for a time and temperature sufficient to shape said lacquer articles into a substantially spherical shape while maintaining said slurry at a pressure above atmospheric, passing the resulting slurry of shaped lacquer particles and suspending medium through a first evaporator at Atmospheric pressure and at a temperature above the boiling point of the solvent, and thereafter passing said slurry through a series of heating zones all maintained at atmospheric pressure, at least some of said zones having a higher temperature than the zone immediately preceding it, and thereafter separating said hardened powder grains fro said suspending medium.
9. In the art of making powder grains, the method comprising preparing a lacquer of smokeless powder base and a solvent therefor, preparing a liquor of an aqueous medium, a protective colloid and a dewatering salt, extruding said lacquer through an extrusion plate having at least one opening of predetermined size, cutting the extruded lacquer into lengths such that the length to diameter ratio of the resulting particles is about 1 to 1, immediately entraining said particles in said liquor to form a slurry and passing said slurry through a conduit for a time sufficient to cause migration of any aqueous medium from said lacquer particles and to permit said particles to assume a substantially spherical shape, passing said slurry through an evaporator at atmospheric pressure and at a temperature above the boiling point of said solvent, and thereafter passing said slurry through a series of heating zones all having a temperature higher than said evaporator and at least some of said zones having a temperature greater than the temperature of the zone immediately preceding it
10. The method of claim 14 wherein a first group of heating zones of said series of zones is maintained at a temperature about 2* to 4* C. above that of said first zone, the next zone is maintained about 2* to 4* C. above said evaporator, the next zone about 4* to 6* C. above that of the previous zone, and the final zone about 8* to 9* C. above the previous zone.