US2416639A - Slow-burning powder composition - Google Patents

Description

Patented Feb. 25, 1947 SLOW-BURNING POWDER COMPOSITION David E. Pearsall, Avon, Conn., assignor to The Ensign-Bickiord Company, corporation of Connecticut Slmsburg, Conn, a

No Drawing. Application July 8, 1944, Serial No. 544,134

11 Claims. (CL 52--2) The present invention relates to combustible materials and more particularly to a novel composition for such materials, including a new and peculiarly useful ingredient which may be incorporated into such compositions to produce certain desired and heretofore unobtainable results. The present invention is based upon discoveries made in the course of certain studies in connection with slow burning combustible mixtures.

The prior art has produced combustible having slow burning characteristics or reduced velocities by several methods, such as:

1. The addition thereto of inert materials, especially those having high specific heats and small particle size; for example, titanium dioxide and barium sulphate, as disclosed in my prior United States Patents Nos. 2,072,719 and 2,072,- 720. a

2. The addition oi increased amounts of oxidizers or fuels to the mixture, which produces unbalanced powders, i. e., those that have an excess of positive or negative elements or so-called positive or negative oxygen balances.

3. A change in the type of combustible fuel, this also tending in some respects to unbalance the powder.

4. The addition of cooling agents, such as salts containing water of crystallization.

5. The addition of combustible materials which give oil gases, such as carbon dioxide, nitrogen, etc.

All these known means of producing slow burning or low velocity compositions of the prior art, while possessing certain advantages, usually possess disadvantages in that many of them tend to produce powders that are irregular and unpredictable in velocity or burning time and may even cease burning particularly if extreme slowness is desired. This is often due to the unpredictable physical and/or chemical characteristics of the slowing materials used which frequently render the explosive unsuitable 'for certain purposes including, e. g., ordnance material. Furthermore, it has also been found that practically all of the combustible powders slowed by way of the prior art have increased volumns, compared with the unslowed powders, so that they are not adaptable for certain ordnance uses wherein but a small space can be devoted to the slow burning material and where definite and relatively long time delays are desired or necessary. All of these disadvantages are overcome by the powders of my invention.

I have discovered that the substance polyvinyl alcohol when added to and suitably compounded with combustible and explosive materials will impart particularly desirable slowing effects and that it possesses the advantages of prior art slowing materials-without their disadvantages-and, in addition, it possesses unique advantages of its own. As an extreme case I have discovered, e. g., that substantially twice the slowing time can be attained in burning compositions by the use of this material as compared to materials which have been used in the prior art for this purpose. I have further determined that this material, which is synthetically prepared as hereinafter set forth, and hence is controllable as to its chemical and physical characteristics, makes possible the production of combustible and explosive materials which are regular and predictable in their effects and not subject to the difllculties encountered in using certain prior art materials due to their irregularity.

The providing of combustible materials, including as an essential ingredient, polyvinyl alcohol. for slowin the combustion rate is therefore a principal object of the present invention.

I have also discovered that by the use of this novel material, I am able to produce combustible elements, such, for example, as delay elements, flares, pyrotechnics, etc., which are slowed to a desired extent, including a much greater extent than was attainable with prior art materials, wherein the slowing is definite, regular and predictable, and wherein the volume of the combustible composition produced is relatively small as compared to that of prior art materials producing the same or similar results.

In the course of the research upon which the present invention is based, I have also discovered a second highly useful property of polyvinyl alcohol, namely that it can serve as a binding agent to bind together the other solid or liquid ingredient or ingredients of a combustible composition into a substantially self-sustaining mass,

which may be grained powder wherein each grain includes all the ingredients used and wherein the grains have no particular shape, but are all of a general desired size range. Such ingredient materials may also be bound by the polyvinyl alcohol into pellets, which may be of any desired predetermined size and shape and which are substantially self-sustaining, so as to be usable without any external wrapping or container and which may have a waterproofing coating such as that disclosed in my prior U. S. Patent No. 1,917,540. This desirable characteristic of polyvinyl alcohol makes it possible to dispense with a desired part or all the binding agents heretofore required by the prior art for forming grained and pelleted materials for combustion purposes.

Polyvinyl alcohol is a combustible material which burns-with the addition of oxygen-to form carbon dioxide and water and as such may be considered as a fuel, so that its characteristic as a fuel should be taken into account in any composition in which it is included. As such it may be used insubstitution for a part or all the fuels otherwise necessary in a combustible composition. It will be understood that one or more oxidizing agents for furnishing the oxygen to burn the fuel present will always be used therewith in accordance with my present invention.

Thus a combustible powder or material as these terms are used herein and in the appended claims is one in which the oxygen necessary for the combustion of the fuel ingredients is substantially all provided by some one or-more oxidizing ingredients, i. e., the composition must contain both fuels and oxidizing ingredients.

The. combustible materials of my present invention are useful, (1) for the burning medium of safety fuses which are used for the controlled and delayed firing of explosives for commercial blasting purposes; and (2) for producing delayed or prolonged burning in the fields of blasting, ordnance, pyrotechnic and elsewhere. Other uses for these novel materials include signal flares, combustible material for actuating various mechanisms by means of heat and/or gas and for cooking where portable heat units are desired.

, A further and more specific object of the present invention is to provide combustible powders in bulk, grained or pelleted form, which will burn longer than those of the prior art, without unduly adding to the volume or bulk of the powder. For example, delay elements for blasting caps have been made by prior art methods which will produce time intervals up to 13 seconds duration as a result of the burning of about 0.5" of material. Also the prior art highway and railroad flares represent near the extreme in slow burning compositions now available, such devices burning at rates of about 1 to 2 minutes per inch. Flares of this type which have a burning time of to minutes are at least 10 inches in length and about one inch in diameter. By using powders of the present invention, the desired 10 to 20 minute burning time can be Obtained using flares 4 to 5 inches in length and if desired, only one-half inch in diameter. Similarly, the blasting cap delay elements can, by the use of the present invention, be reduced from 0.5" to 0.25" or less in length. Thus it is apparent that I have effected a saving in space which is highly important in design and as respects the storage and transportation of devices employing powders of the present invention and is important ecnomically. Such novel delay burning elements constructed as herein taught may also be included in or as a part of relatively small mechanisms or articles of manufacture which are useful, particularly in various ordnance and chemical warfare devices or material.

The combustible powder compositions of my present invention consist essentially of polyvinyl alcohol, one or more oxidizing agents, and usually, but not always, one or more other reducing agents or fuels. However, other materials may be added to such compositions for effecting particular results for example: (1) lowering the ignition temperature, (2) regulating the density, (3)

adding to the water-resistance, and ('1) for lubricating purposes.

As herelnabove set forth, the polyvinyl alcohol of the present invention is to be considered as a fuel. I contemplate, however, that usually, but not always, this will not be the only fuel mate- 5 rial present, but that some other material classifled as a fuel will be present in the final composition. Such other fuels may include organic materials such as a form of carbon, including charcoal and graphite, hydrocarbons, carbohydrates (or other combinations of carbon, hydrogen and oxygen) and inorganic materials including nonmetals such a sulphur and silicon, metals such as aluminum, magnesium, zirconium, zinc, copper and iron, and metallic alloys such as the alloys of silicon with iron, aluminum, calcium or barium.

oxidizing agents, one or more of which is an essential ingredient in the combustible powder compositions of my invention, may include the nitrates, chlorates, perchlorates, peroxides, permanganates and chromates of the alkali metals, sodium and potassium, the alkaline earth metals, barium, calcium and strontium and of other metals, such as lead, zinc, aluminum and magnesium. All such materials are known to the prior art as being useful oxidizing agents. In addition to the inorganic salts listed, such organic peroxides as benzoyl peroxide and urea peroxide may be used in certain amounts as oxidizing agents. Other materials may also be considered in this class, such as red lead, as will appear more specifically hereinafter.

Examples of some of the materials, which may optionally be used to effect the characteristics in the resultant combustible powder composition, include as density regulators, i. e., to control the porosity or conversely the compactness of the powders, such materials as wood flour, carbon (charcoal), etc. It is noted that carbon has been mentioned above as a fuel and partake-s of that 40 function as well. As hereinafter set forth, a form of carbon, 1. e., graphite, further has a-lubricating action as is well known in the art. Lubricating materials which may be added to the powder if desired include such materials as graphite and aluminum stearate. Such materials are useful in powders which are to be pelleted in that they facilitate the removal of the compressed powders from the molds wherein they are formed into desired shapes. The ignition temperature of the powder may be lowered by the addition of known materials for this purpose, such, for example, as sulphur. Here again sulphur has a dual function in that it serves as a fuel and also assists to some extent in binding the powders together. For increasing the water resistance of a combustible powder in accordance with the present invention, I contemplate the addition of such materials as suitable waxes and/or graphite or sulphur. the last two materials also having other functions as herein explained.

As an example of a combustible powder composition made up in accordance with the present invention, I may use polyvinyl alcohol as a slowing agent; potassium nitrate and red lead as oxidizers; sulphur, ferro-silicon and ferro-aluminum alloys as the reducing fuels: and as additional ingredients, wood flour as a density regulator and fuel and graphite or aluminum stearate to impart lubricating properties to the mix.

When the polyvinyl alcohol or my present invention is to be employed as a slowing agent, i. e., to impart a definite predetermined slowing action to the powder composition, I contemplate that it should be present in amounts of from 7 about 5 to 55% of the total powder ingredients.

These limits are not critical, however, as it will be understood that the slowing action is more or less progressive and is dependent in amount upon the amount of the polyvinyl alcohol used.

6 above 65 (1. (149 F). Both type B and type A polyvinyl alcohols are produced commercially in several grades which, are known as low, medium and high viscosityv grades, 1. e., they derive their As a further and somewhat; more specific ex- 5 names from the viscosities of their water soluample of powders made up in accordance with tions. The increases in viscosities result from the resent invention, I may use a composition higher degrees'of polymerization during manucomprising polyvinyl alcohol 5%55% and the facture with the consequent increases in molecubalance of the powder to be chosen from the lar weights of the alcohols. For the purposes of following in the listed proportions: 10 my invention, the alcohols polymerized to pro- Per cent gllllce mledtilum or high visgossity sloligtitinsglheu use a are po ymerize 0 re a vey g er A :33 1 to 12 molecular weightsare most satisfactory. Sulphur to 50 The degree of fineness of the polyvinyl alcohol wood a; 1 to 25 15 is also importantand the material finely ground Graphite 05 to 10 to about the consistency of flour. is preferred to and as &; the more coarsely ground and more fibrous grades. Potassium nitrate 10 to 60 The process of preparing my novel materials and 2o gar use istamlithler titmfiortartiit object fiat this inveigon, par icu ar y a por on o e process Red lead (nummum pbzo) to 75 cluding the baking of pelleted materials tolm- It will be understood that powders in accordpart strength thereto. ance with the present invention may be com- The slow burning powder compositions of my pounded in view of the desired use and will vary invention may be made by mixing the various in characteristics according to the raw materials ingredients together in a ball-mill or other types used so as to be adaptable for special purposes. of equipment known in the art to be suitable to For example for low gas producing powders, I impart an intimate mixing and grinding action. prefer to use relatively large amounts of red lead The powders so produced can be grained in the and the silicon alloys, while for high gas producmanners similar to the. graining of black powder ing powders, the red lead and silicon alloys are and smokeless powder. However the powders may replaced in whole or in part by such materials also be used ungrained.

as potassium nitrate and sulphur, respectively. Pellets may be made from the mixed powders It will be understood, however, that in all these by pressing them in hydraulic molding presses powder compositions polyvinyl alcohol will be or by the use of the so-called tablet or pellet an ingredient. presses. The densities of the molded or pelleted The following specific examples are given illuspowders depend upon their composition, the detrating various different combustible powder gree of fineness of the components, the degree compositions in accordance with the present inof moisture present and the pressure and time of vention and the burning time attained from pelpressing. The purposes for which the pellets are lets made therefrom, the latter being expressed produced determine the pressures at which they in minutes of burning time per inch. will be pressed. However, these pressures usual- 2 Powder compositions Pellet l i "ti-li KNO; Pbtol cmcnon). s X51? FeSi SiAl min iii.

32 2s 21 15 4 1.0 21 30 1s 24 4 2 1 a0 22 24 20 as 1 3 1 as l s 55 7 14 s 8 8.8 i as e 14 6 a l as From the aboveit will be apparent that a wide range of burning times per unit of length can be obtained by the use of powders of the present invention with a range thereof exceeding in slowness that which can be attained from any known prior art powder.

Polyvinyl alcohol is made by hydrolyzing polyvinyl acetate, which in turn is made by polymerizing the reaction product of acetylene and acetic acid. There are two types of polyvinyl alcohol commercially available, one of which is the completely hydrolyzed material, while the other one contains small amounts of the unhydrolyzed polyvinyl acetate. Although either grade may be used, I prefer the completely hydrolyzed polyvinyl alcohol which is known commercially as "type E." Type B alcohols may be differentiated from type A alcohols, since they soften and swell in water at ordinary temperatures, but do not dissolve unless the mix is heated to 70 C. (158 F.) or above: the type A alcohols are soluble in water at ordinary temperatures and have decreased solubility ly range from 5,000 to 20,000 lbs. per square 5 inch, the higher pressures producing the harder Pellets.

The powders may also be pressed into metal, paper, or composition tubes or containers and the elements so produced, used in place of the unsupported and uncovered pellets. For many purposes, however, the unsupported pellets are preferable.

The powders when grained may be used as the burning medium for safety fuses, pyrotechnic fuses and the like, which fuses consist of a central powder train surrounded by various textile and insulating media.

The combustible powder pellets produced by compression as aforesaid can be made to have increased water resistance and to have greater physical strength if they are baked in an oven. I have found that baking at a temperature of about 300 F. for one to three hours gives good results depending upon the degree of hardness and'strength that is desired. Neither the time nor the temperature is particularly critical provided the temperature is high enough to soften the polyvinyl alcohol and not so high as to cause undue loss or damage to any constituent material. However, at higher temperatures, a shorter time is required to obtain the same or similar results. This is probably due in part at least to the thermoplastic character of polyvinyl alcohol, which tends permanently to bind the other ingredients together upon cooling after the baking as aforesaid.

While I have disclosed my invention as to the general principles involved in the utilization thereof and given various specific examples of compositions made up in accordance therewith, it will be understood that this invention is not limited to the specific examples given herein, but is defined solely by the scope of the appended claims, which are to be given the broadest valid construction which the state of the prior art permits.

What is claimed is:

1. A slow burning powder composition, comprising polyvinyl alcohol, and an oxidizing agent, wherein the polyvinyl alcohol is present in amounts between approximately 5% and 55% of the total powder ingredients.

2. A slow burning powder composition in accordance with claim 1, including, as an added ingredient, a material for lowering the ignition a temperature thereof.

3. A slow burning powder composition in accordance with claim 1, including, as an added ingredient, a material for regulating the density thereof.

4. A slow burning powder composition in accordance with claim 1, including, as an added ingredient, a material for increasing the waterresistance thereof.

5. A slow'burning powder composition in accordance with claim 1, including. as an added ingredient, a lubricating material.

6. A slow burning powder composition producing relatively little gas, comprising a fuel including a substantial proportion of a powdered metal, an oxidizing agent including a substantial proportion of powdered metallic oxide material, and from about to about 55% of polyvinyl alcohol.

7. A delay element for use with ordnance ma- 50 2,001,212

8 terial and blasting caps consisting of a combustible powder containing from about 5% to about 55% of polyvinyl alcohol, an oxidizing agent, and a fuel.

8. A slow burning pelleted combustible material, consisting of a combustible powder composition, including from about 5% to about 55% of polyvinyl alcohol, said composition being compressed to a predetermined form and then subjected to heat to impart a predetermined degree of hardness and strength thereto.

9. A slow burning powder composition, consisting ofpolyvinyl alcohol approximately 5% to 55%, a metallic alloy of silicon approximately 1% to 12%, an oxidizing agent approximately 10% to 75%, wood flour approximately 1% to 25%, sulphur approximately 5% to and graphite approximately 0.5% to 10%.

10. The process of producing a slow burning combustible pelleted material, which comprises the steps of mixing about 5% to about of polyvinyl alcohol in substantially powdered form with the remaining percentage of ingredients of the combustible material including an oxidizing agent, pressing the mixture to a predetermined shape and size to form pellets, and baking the pellets thus produced at a temperature of about 300 F. for approximately one to three hours.

11. A slow burning powder composition producing a relatively large amount of gas, comprising from about 5% to about 55% polyvinyl alcohol, a fuel which upon combustion produces gaseous products of such combustion, and an oxidizing agent comprising at least one inorganic oxidizing salt.

DAVID E. PEARSAIL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,341,262 Brun Feb. 8, 1944 1,438,759 Gray Dec. 12, 1922 1,971,502 Piccard Aug. 28, 1934 1,833,573 Hill Nov. 24, 1931 1,382,563 Snelling June 21, 1921 Olsen May 14, 1935