US 3265778 A
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Aug. 9, 1968 G. L. GRIFFITH METHOD FOR EXTRUDING EXPLOSIVES Filed Feb. 10, 1964 3,255,773 Patented August 9, 1966 3,265,778 METHOD FOR EXTRUDING EXPLOSIVES George L. Gritfith, Coopersburg, Pa., assignor to T'Z'Ojfil'l Powder Company, Allentown, Pa., a corporation of New York Filed Feb. 10, 1964, Ser. No. 343,844 Claims. (Cl. 264-3) This invention relates to a method and apparatus for the extruding of explosives, and, more particularly, to a process .for extruding a column of explosive composition for packaging, and to apparatus for carrying out this process.
Recently, machinery has been made available which preforms an explosive composition, and this is then wrapped automatically in paper and crimped at both ends, to produce a completed shell rather quickly, as compared to the conventional procedure. This is an operation which produces shells of a fixed length. Due to certain mechanical restrictions, as well as the investment cost of the machine, it is-not feasible to manufacture finished shells having a length in excess of sixteen inches. Furthermore, the production rate of the machine is rather low.
The packaging of ammonium nitrate explosives presents a particularly severe problem, from the standpoint of economics. Ammonium nitrate is a cheap raw explosive material, which can be sensitized rather inexpensively with fuel oil or some other form of carbon or carbonaceous material to form what are termed the nitrocarbonitrates, which have explosive properties. Such mixtures can be brought in bulk to the explosive site where they can be filled directly into small diameter bore holes having a diameter of as low as one inch, and then shot. This technique poses a particularly difficult packaging problem, since, using conventional explosive packaging procedures, it has been practically impossible to package an inexpensive product in long lengths in a practical manner at a price sufliciently low to be competitive with the ammonium nitrate-fuel oil bulk compositions which can be blown directly into the holes without packaging.
A further problem created by individual packaging of explosive compositions arises from the necessity of propagating the charge from one cartridge to another in the train. It has always been necessary to use an explosive composition in the package of such sensitivity that it is capable of shooting through a discontinuous column of explosive, the discontinuity being brought about by the fact that for practical purposes explosives. are loaded normally in lengths of less than 24 inches, and usually in lengths of 4 to 8 inches. Thus, an explosive column in a small diameter hole of great length usually consists of four to twelve sticks of powder, and the composition must necessarily have sufiicient sensitivity so that the detonating -wave will not die out as it travels through the discontinuous column of a plurality of sticks. Furthermore, a discontinuous column has less water resistance, since the point where two shells butt together is the first point at which water desensitizes the composition, presenting a zone through which the shock wave often fails to pass from one cartridge to the next. Obviously, if it were possible to prepare an explosive column of great length, so that a continuous column could be loaded in the hole in place of a discontinuous one, composed of a plurality of sticks in close juxtaposition, it would be possible to use an explosive composition of less sensitivity, since there would be no need to propagate the explosive wave from one cartridge to another. Such a column would also have greater water resistance than the discontinuous one, since there would be no point at which water could enter between one portion of the explosive and another.
The packaging of gelled explosives has also presented a problem. These are diflicult to package in an efiicient manner so that they can be sold at a price which is competitive to ammonium nitrate-fuel oil compositions. These difiiculties basically are due to the lack of a method for packing long continuous tubes in an economical manner.
Casings of any desired length can be fabricated from plastic materials, such as regenerated cellulose, polypropylene, and the like. These are extruded in the desired diameter, and then filled by means of a long loading tube or nozzle through which the filling material is extruded into the casing. This method has been used for many years in the manufacture of sausages in the meat industry. However, it is not adapted for explosive compositions.
In the first place, explosive compositions of a consistency desirable for such packages are virtually impossible to extrude. If the explosive is fluid, it extrudes and packages easily, but the package isflimsy and limp. If the explosive is semi-solid or solid, the packages are selfsupporting, but such consistencies can be extruded only at rather high pressures, at which the composition may be unsafe to handle, due to the pressures and heat generated, and which increase as the extruded column increases in length. As a practical matter, the limiting extrusion pres sure at which semi-solid explosives are safe to handle is rather low, of the order of 40 psi, so that it is impossible to extrude more than rather short columns, not much longer than normal length cartridges. This prevents reali zation of the real advantage of extrusion: the preparation of explosive packages of practically unlimited length.
In according with the instant invention, apparatus is provided for extruding explosive compositions that permits extrusion of practically endless columns of explosive under moderate and safe extrusion pressures below that at which detonation of the explosive would occur with a minimum of heat generation. It thus is possible to package semi-solid and plastic or gelled explosive compositions of extrudable consistency in packages of any desired length and configuration.
The extrusion apparatus of the invention comprises an extruder block having a lubricating means fitted therein to supply a film of lubricant between the explosive column being extruded and the walls of the extruder block. The term extruder block is used generically herein to refer to the extruder nozzle, die, barrel, tube or other means for confining and shaping the material during extrusion. Such means can take the form of a porous bearing or wall, a perforated plate, a wick or brush applicator, or a seep opening or plurality of openings arranged to distribute lubricant over the column, preferably uniformly. Other means will be apparent from this description. The porosity and pore size will conform to the viscosity of the lubricant and the volume thereof to be applied to the explosive column for the desired lubricating effect.
The lubricating means can be made of any material, preferably-long wearing, such as metal, for instance, stainless steel, brass, bronze, iron, steel or plastic, for instance, polyamide, polytetrafiuoroethylene, polyethylene, polypropylene, polystyrene, polyvinyl chloride, ureaformaldehyde or phenol-formaldehyde resin, or porcelain or ceramic material, or glass.
The lubricant can be applied by fluid pressure, as by a pump, or by gas pressure, or by a sufficient head of fluid pressure. Usually, the liquid is applied under a pressure at least equal to the extrusion pressure and preferably at a pressure of from to 50 p.s.i. greater than the extrusion pressure, to ensure a continuous film formation at the interface.
Uniform and steady application of lubricant is best assured by maintaining a feed flow of lubricant to and past the lubricating means, in contrast to a feed which dead-ends at the applicator. It is quite difficult in the latter case to maintain a head of pressure adequate to ensure a steady and uniform lubricant flow without an occasional break through, as when extrusion pressure diminishes, for some reason, or when fluid pressure builds up too high. A flow through, however, in the manner, for instance, shown in FIGURES 1 and 2, makes it possible to maintain a constant head of pressure adequate to ensure a slow feed of lubricant over the normal range of extrusion pressure variations encountered in operation.
The application means selected will have a pore size and flow capacity appropriate to deliver the required amount of lubricant to maintain a safe, low, extrusion pressure, below about 60 p.s.i., and this will depend upon the friction developed bet-ween the explosive and the nozzle wall, the size of the column, the length of the nozzle, and the length of the column, as well as the type and viscosity of the lubricant.
The apparatus of the invention is useful for filling completed explosive packages of any size and length, such as conventional cartridge containers, as well as stuffing or filling tubes of unlimited length, in the manner of stufiing sausage casing, for which use the apparatus is of especial advantage. The extruded column is inserted into the enclosing wrapper shortly after leaving the extruder, and is then sealed therein to close the package when a suitable length is filled. The container or package can be made of any desired material, such as paper or plastic, for example, polyvinyl chloride, polyethylene, or polypropylene.
Any type of extrusion equipment can be employed. The choice will depend upon the characteristics of the explosive composition being extruded. Conventional extruders comprising a feeding device and forming tube or die, otherwise referred to as an extrusion nozzle or barrel, of the desired configuration for shaping the explosive column, are satisfactory. Such equipment will be provided with the lubricating means in accordance with the invention for delivering the selected lubricant to the explosive.
The lubricant can be any appropriate liquid, and preferably a solvent for the explosive but inert to the material of which the extruder is made. Water is the preferred lubricant, but lubricating oil, petroleum derivatives such as kerosene and fuel oil and hrydrocarbons of all kinds, silicone oils, dilute 0.5 to aqueous solutions of natural gums, such as guar-gum and karaya gum, and alkylene glycols such as ethylene glycol, propylene glycol, and polyethylene glycol, and glycerine, are also exemplary. Preferably, the lubricant does not upset the oxygen balance of the composition, or else the lubricant is taken into account, if necessary, in formulating oxygen balance.
The lubricating effect is enhanced if the lubricant is applied hot, preferably at above 50 C., and optimally at a temperature at which the surface of the explosive is softened or melted.
FIGURE 1 is a longitudinal section through an extruder feed and nozzle of the invention, showing an annular porous sintered metal bearing ring for lubricating the column of explosive being extruded.
FIGURE 2 is a cross-sectional view of the extruder of 4 FIGURE 1, taken along the line 22 and looking in the direction of the arrows.
The extruder of FIGURES 1 and 2 comprises a housing 1 made of stainless steel wit-h a rubber liner 2. A screw conveyor also of stainless steel 3 is provided to feed explosive composition 7 to the stain-less steel extruder nozzle 4, where it is brought to the shape of a column 5.
The extruder nozzle 4 is provided at a point near housing 1 with a lubricating means in the form of an annular porous sintered metal bearing 10, made of, say, stainless steel, Monel, bronze, ceramic or polyte-trafiuoroethylene, and extending all the way around the inner wall of the extruder nozzle. The bearing is press-fitted into the top of a stepped recess or groove 11 in the wall, where it rests against the step 9, defining a space 12 between it and the base of the recess 11. Two circumferential grooves 17 and 18 extending all the way around the bearing receive O-rings 19 and 20 to ensure a leak-tight seal between bearing 10 and the step 9. A pair of ducts 13 and 14 provide access to space 12 from the exterior of the extruder. It will be seen from FIGURES 1 and-2 that the bearing '10 is thus spaced away from the base of the recess 11 throughout its periphery. Two fittings 15 and 16 are welded to the outside wall of the extruder, and serve as a means for attachment of a supply connection for delivery of lubricating fluid to the duct 13 and thence into the space 12, and withdrawal of excess lubricant via duct 14 and fitting 16. In this manner, lubricating fluid is conveyed to all portions of the bearing 10, whence it can be expressed in the form of a film of lubricating fluid, enveloping therein the extruded column 5 of explosive 7 passing through the nozzle, and lubricating its movement along the inner wall of the extruder. The arrows show the course of lubricating fluid from the fitting 14 to the column .16 of extruded explosive in the extruder nozzle 4.
In operation, the explosive material 7, which is of a semi-solid consistency, is poured into the hopper l, whence it is forced by the screw conveyor 3 into the extruder nozzle 4. The rubber lining 2 on the walls of the hopper 1 provides a desirable resiliency, to avoid shock to the ex plosive under the force of the impeller 3.
The explosive 7 acquires the columnar configuration of the nozzle 4 as soon as it enter the nozzle, filling it completely and forming a column 5. As the column 5 is forced through the nozzle, under a pressure of say 20 p.s.i., by the impeller 3, it passes the bearing 10, and there acquires a film of lubricant liquid such as water fed through the bearing 10 under a pressure of say 30 to 40 p.s.i. applied by a fluid pump (not shown) in the line supplying fluid to the fitting 15. Surplus water is withdrawn via duct 14 and fitting 16. The explosive column 5 is now coated with a very thin film of lubricant liquid at the interface between the explosive and the inner wall of the extruder 4. This film is extremely thin, of the order of 0.0001 inch to 0.05 inch. As a result of application of the lubricating film, the pressure of extrusion of the column 5 is greatly reduced, and the column length extrudable thereby at a given extrusion pressure correspondingly increased. Whereas a column length of approximately 12 inches, for example, may be the limit of which the extruder is capable, at 60 p.s.i., without development of excessive extrusion pressures and heat generation, due to friction between the wall of the extruder and the explosive composition, the presence of the bearing 10 and the lubricating film (water) can increase the length extrudable at from A to A; of the I pressure needed to extrude 12 inches with no lubrication to from to inches and more. Thus, the lubricating film makes it possible to avoid high extrusion pressures, and to keep extrusion pressure below the detonation limit of the explosive composition.
The following examples, in the opinion of the inventors, represent the best embodiments of their invention.
EXAMPLE 1 An explosive mixture of semi-solid consistency was prepared using dry milled nitrostarch, fine grained ammonium nitrate, fine-grained sodium nitrate, flake aluminum, and the additional ingredients noted in the table below. The nitrostarch and mixed nitrates were thoroughly blended, and there was then added the zinc oxide, flake aluminum, guar gum, and then the oil and water. The proportions of the final explosive composition were as follows:
Percent Nitrostarch 27.00 Grained ammonium nitrate 47.25 Grained sodium nitrate 10.75 Flake aluminum 2.50 Guar gum 2.50 Oil No. 5 1.00 Zinc oxide 1.00 Water 8.00
This composition was quite stiff, and was easily extruded through long 1% inch diameter extrusion nozzles of the type shown in FIGURES 1 and 2 at an extrusion pressure of 25 p.s.i. using water as the lubricant under a pressure of 35 p.s.i., into a tubular casing ten feet long and two inches in diameter, made of polyethylene film, which was rolled up as it was filled.
EXAMPLE 2 An explosive mixture of semi-solid consistency was formulated using milled nitrostarch, ammonium nitrate, and sodium nitrate. The ammonium nitrate and sodium nitrate were both fine-grained. These material were mixed thoroughly and there were then added zinc oxide,
flake aluminum, guar gum, sodium carboxymethyl cellulose, and wood flour, after which the water was added. The proportions of the final explosive mixture were as follows:
This mixture had the consistency of a gelled-oil, and was easily extruded through long 1 inch diameter nozzles of the type shown in FIGURES 1 and 2 at an extrusion pressure of 25 p.s.i. using water as the lubricant under a pressure of 35 p.s.i., into a polyethylene tubular casing 1% inches in diameter and twenty feet long, which was rolled up as it was filled.
EXAMPLES 3 TO 5 Three explosive mixtures of semi-solid consistency were prepared using as the sensitizer pentaerythritol tetranitrate or trimethyloltrinitrate, with mill ammonium nitrate, mill sodium nitrate, flake aluminum, and the additional ingredients noted in the table below. The sensitizer and mixed nitrates were thoroughly blended, and there were then added the zinc oxide, flake aluminum, guar gum, sodium carboxymethyl cellulose and wood flour, and then the water. The proportions of the final explosive composition were as follows:
Example Number Ingredient Percent Percent Pcrcrnt 'Irimethylolethnne trinitmte. .6 Pentaerythritol tetrnnitrnto 24. (l 12. l) Ammonium nitrate, mill 48. 4 61. 9 72. 5 Mill sodium nitrate 13. 5 Flake aluminum. 2.0 2.0 '2. 0 Jaguar guar gum 1.0 1.0 1.0 Sodium carboxymethyl cellulo O. 6 0. 6 0. (1 Wood flour 1.5 1.5 1. 5 Zinc oxide 1.0 1.0 1.0 Water 7. 4 7. 4 7. 4
100. 0 100.0 100.0 Density 1. 53 1. 23 1. 26
These compositions were quite stiff, and were easily extruded through long one inch diameter extrusion nozzles of the type shown in FIGURES 1 and 2 at an extrusion pressure of 25 p.s.i. using ethylene glycol as the lubricant under a pressure of 35 p.s.i., into cartridges 48 inches long and 1% inches in diameter, made of heavy cardboard, 0.082 inch in thickness, and the cartridges were then covered with cardboard caps.
EXAMPLES 6 AND 7 Example Number Ingredient Composition B Ball powder (Olin WC 820) Mill ammonium nitrate. Mill sodium nitrate 1 Flake aluminum Jaguar 100 guar gum Sodium carboxymethyl cellulose Loading density... Sensitivity in 1% pipe 1 Pellets averaging about 1.25 mm. in diameter.
I Double base nitrocellulose powder. 9 3 gm. PETN.
These mixtures had the consistency of a gelled oil, and were easily extruded through long one inch diameter nozzles of the type shown in FIGURES l and 2 at an extrusion pressure of 25 p.s.i. using water as the lubricant under a pressure of 35 p.s.i., into open-ended cardboard cartridges 1% inches in diameter and two feet long. The cartridges then were closed with cardboard covers.
EXAMPLES 8 TO 10 Three explosive mixtures of semi-solid consistency were prepared using trinitrotoluene and ethylene glycol dinitrate as sensitizers, mill ammonium nitrate, mill sodium nitrate, flake aluminum, and the additional ingredients noted in the table below. The trinitrotoluene. and/or ethylene glycol dinitrate and mixed nitrates were thoroughly blended, and there were then added the zinc oxide, flake aluminum, guar gum, sodium carboxymethyl 7 cellulose, wood flour, and then the water. The proportions of the final explosive composition were as follows:
- Example Number Ingredient Perce Percent Percent Trinitrotoluene, 35 mesh 24. 6 20. 14. 1 Ethylene glycol dinitrate 10. 6 Mill ammonium nitrate 13.0 48. 0 41. 0 Mill sodium nitrate..- 4B. 9 20.0 20. 9 Flake aluminum 2. 0 2. 0 2. 0 Jaguar 100 gunr gum 1. 0 1. 0 1. 0 Sodium carboxymetliyl cellul 0. 6 0.6 0. 6 Wood flour 1.5 1. 1.5 Zinc oxide 1.0 1.0 1.0 Water 7. 4 7. 4 7. 4
' 100. 0 100. 0 100.0 Loading density 1. 44 1. 34 1. 53
Sensitivity in 1% pipe 1 N o. 8 cap. These compositions were quite stiff, and were easily extruded through long one inch diameter extrusion nozzles of the type shown in FIGURES l and 2 at an extrusion pressure of 25 p.s.i. using water as the lubricant under a pressure of 35 p.s.i., into polypropylene film casings feet long and 1% inches in diameter. The open ends of the casings were sealed, and the filled lengths rolled up.
EXAMPLES 11 TO '15 Five explosive mixtures of semi-solid consistency were formulated using dry milled nitrostarch, ammonium nitrate, and sodium nitrate. The ammonium nitrate and sodium nitrate were both fine-grained. These materials were mixed thoroughly, and there were then added zinc oxide, flake aluminum, guar gum, sodium carboxymethyl cellulose, and wood flour, after which the water was added. The proportions of the final explosive mixture were as follows:
These mixtures had the consistency of a gelled oil, and were easily extruded through long one inch diameter nozzles of the type shown in FIGURES l and 2 at an extrusion pressure of 25 p.s.i. using water as the lubricant under a pressure of p.s.i., into open-ended cardboard cartridges 1% inches in diameter and two feet long.
The following is claimed:
1. A process for extruding an explosive composition of extrudable consistency, comprising a primary explosive and sensitive to detonation at pressures in excess of about p.s.i., and at elevated temperatures, in order to minimize pressure and heat-generation during extrusion, comprising confining said explosive compos-itior within a passage of relatively small diameter to form an explosive column of substantial length therein, and moving the explosive column along the passage by application of a pressure below about 60 p.s.i. to one end thereof, while applying a film of liquid lubricant at a pressure within the range from the extrusion pressure to 50 p.s.i. greater than the extrusion pressure, between the surface of the explosive column and the wall of the passage, whereby the explosive composition is extruded safely at a pressure and temperature below that at which detonation of the explosive occurs.
2. A process in accordance with claim 1 in which the liquid lubricant is water.
3. A process in accordance with claim 1 in which the liquid lubricant is ethylene glycol.
4. A process in accordance with claim 1 in which the liquid lubricant is applied at a temperature of at least 50 C.
-5. A process in accordance with claim 1 in which the liquid lubricant is a solvent for the explosive composition being extruded.
Example N umber Ingredient Percent Percent Percent Percent Percent Nitrostarch r 40. 0 Pentnerythritol tetranitrat G. 0 9. 0 12. 0 40. O Mill ammonium nitrute 79.0 74. 5 57. 0 24. 0 35.0 Mill sodium nitrate 7. 5 15. 0 15. 0 Flake aluminum 5.0 1.0 0. 5 1.0 0. 5 Jaguar guar gum 1.0 1.0 3. 5 3. 6 0. 1. 5 1. 5 0 5. 0 l. 0 0. 5 .0 1. 0 1.0 1. 0 5 12. 0 12. 0 8. 5
2 g. PETN. 10 g. PETN. 111-21) g. PEIN. 4 No. 2 cap. 5 No. 8 cap.
References Cited by the Examiner UNITED STATES PATENTS LEON D. ROSDOL, Primary Examiner. L. DEWAYNE RUTDEDGE, REUBEN EPSTEIN,
Citations de brevets