Patent Application
20110011502
The present disclosure relates to priming mixes or priming compounds, and in particular to priming mixes with improved sensitivity.
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Priming mixes or priming compositions are used in ammunition cartridges, including both center fire and rim fire, shot shells, and loads for power tools and power actuated devices to initiate the combustion of the propellant in the cartridge or shell. The priming mix is disposed in a priming cup at the back of the cartridge or shell. Ignition of the primer is initiated by the impact of a weapon's firing pin on the cup. This mechanical energy deforms the cup, compressing the priming mix and generating heat, causing the priming mix to ignite. The combustion products from the burning priming mix are directed (e.g., by flash holes in the base of the cartridge or shell) to the propellant in the cartridge or shell.
It is of course desirable that the priming mix be sensitive to impact so that it can initiate the combustion of the propellant, however, sensitivity in the context of priming mixes is more than mere reactivity, rather it means more consistent performance for a given impact. Merely increasing the reactivity of the priming mix is neither sufficient nor desirable, because it could increase the incidence of accidental firing of the cartridge or shell. Instead, improved sensitivity of priming mixes is measured by the compression of the range of heights from 100% fire to 100% misfire while maintaining the later at an established safe level, in a industry standard test called drop test, wherein the test was done by dropping weight on the composition from standard heights, and recording the number of times that the priming mix ignites versus the number of times the priming mix does not at each height. What improves a priming mix versus what merely makes the priming mix more reactive is neither readily apparent, nor predictable.
A typical modern priming mix contains a primary explosive—a chemical compound which is impact sensitive. This primary explosive in almost all cases must be modified because it is too powerful or its velocity of detonation is too high. The modification is accomplished by the addition of other chemical ingredients which may be fuels, oxidizers, propellants, sensitizers, and other agents.
For example, since World War II it has been common to base priming mixes on lead styphnate, with various modifiers including secondary explosives, such as TNT, TNR, sensitizers, such as tetrazene, fines, such as double based propellant and PETN, fuels, such as aluminum, calcium, silicide and antimony sulfide, and oxidizers, such as barium nitrate and potassium nitrate. More recently, efforts have been made to reduce the use of lead and other heavy metals in priming mixes, and thus priming mixes based upon alternative primary explosives, such as diazodinitrophenol (dinol or DDNP) or potassium dinitrobenzofuroxan (KDNBF), are increasingly common.
There is a continuing search for improved priming mixes with an improved balance sensitivity, stability, and other desirable properties.
Generally, embodiments of the present invention provide a priming mix with improved sensitivity. In accordance with a preferred embodiment, an improved priming mix of the type including an initiator, fuel, and oxidizer, and pyrotechnic component is provided. The improvement being that the composition comprises between about 3% and about 20% propellant superfines, and more preferably, between about 5% and about 8% superfines. It is believed that the superfines act as a fast fuel that bridges the reaction between the primary explosive and the pyrotechnic mixture (i.e. the fuel and oxidizers) more reliably than the conventional fines due to its larger surface area. These superfines are preferably through −140 mesh, and more preferably through −250 mesh. Preferably all of the particles have a diameter less than about 100 μm, and preferably at least 80% of the particles have diameters less than about 80 μm, and at least 50% of the particles have diameters less than about 40 μm. In one embodiment, these superfines have a median diameter of between about 23 μm and about 28 μm.
In another aspect, the superfines have a surface area of at least 2000 cm2 per cm3 of bulk material, and more preferably at least 3500 cm2 per cm3 of bulk material. Preferably at least 10% and more preferably at least 50% of the total surface area of the superfines is from particles of 26 μm or less, and at least 80% and more preferably 90% of the total surface area of the superfines is from particles of 40 μm or less.
In at least some embodiments, the average aspect ratio (longest dimension/shortest dimension) of the particles comprising the superfines is less than 2.
The superfines can be a single-base propellant, a double-base propellant, a triple-base propellant, or a mixture or composite of single-base, double-base, and/or triple-base propellants.
While propellant fines have been used in priming mixes in the past (see, e.g., U.S. Pat. Nos. 4,963,201, 5,466,315, 5,417,160, 5,547,528, 5,610,367, and 5,831,208), these fines have typically been finely divided propellant made up of nitrocellulose and nitroglycerin (e.g. 60% nitrocellulose and 40% nitroglycerin). However these “fines” have typically been an order of magnitude coarser that the superfines used in accordance with the principles of this invention. Conventional fines range in small particle sizes from about from 0.011 inch to 0.018 inch (280 μm to 460 μm) in contrast with the superfines, which the inventor has discovered improved the sensitivity of priming mixes without adversely affecting reactivity.
Embodiments of the priming mix thus provide improved sensitivity while maintaining shelf life, reactivity, and safety.
Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.
The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.
Embodiments of the present invention provide improved priming mixes of the type including an initiator, a fuel, an oxidizer, and a pyrotechnic component. According to the principles of this invention, the improvement comprises between about 3% and about 20%, and more preferably between about 5% and about 8%, propellant superfines in the priming mix. These superfines are particles of a propellant that are preferably less than 100 μm or −140 mesh.
In accordance with one aspect of the invention, the particles comprising the superfines have a median diameter of between about 20 μm and about 30 μm, and more preferably between about 23 μm and about 28 μm.
In accordance with another aspect of the invention, the superfines have a surface area of at least 2000 cm2 per cm3 of bulk material, and more preferably at least 3500 cm2 per cm3 of bulk material.
In accordance with another aspect of this invention, wherein at least 10% and more preferably at least 50% of the total surface area of the superfines is from particles of 26 μm or less, and at least 80% and more preferably 90% of the total surface area of the superfines is from particles of 40 μm or less.
In accordance with another aspect of this invention, the particles comprising the superfines have an average aspect ratio (greatest dimension/smallest dimension) of less than 2. This is different from fines conventionally in use which were often elongate and stringy.
In accordance with another aspect of this invention, the superfines comprise particles less than about 100 μm, at least at least 80% of the particles are less than about 80 μm; and at least 50% of the particles are less than about 40 μm.
The particle size distribution of the superfines is illustrated in
The superfines can be of a single-base propellant, a double base propellant, or a composite of single base and double base propellants.
In a first preferred embodiment, a priming mix is made with from 30% to 40% lead styphenate, 2% to 6% tetrazene, 0% to 6% PETN, 3% to 8% superfines; 2% to 5% aluminum, and 35% to 55% Ba(NO3)2. More specifically, an exemplary priming mix was made with about 35% lead styphenate, about 5% tetrazene, about 3% PETN, about 5% propellant superfines, about 3% aluminum, and about 50% Ba(NO3)2.
More specifically, an exemplary composition of a priming mix and a control of the compositions shown in Table 1 were prepared, and tested in three sets of steel die drop tests. The results of which are reported in Table 2.
As shown in Table 2, the performance of the exemplary composition is superior at 5″, where there was at least one misfire out of fifty for the control in each set compared to no misfire for the exemplary composition; at 4″, where there was at least eight and as many as eighteen misfires out of fifty for the control in each set, compared to a maximum of four misfires out of fifty for the exemplary composition; and at 3″, where the control had between 38 and 40 misfires out of fifty, compared to between 23 and 28 misfires out of fifty for the exemplary composition. However, the exemplary composition still maintained an adequate safe level of sensitivity with no more than 2 fires out of 50 at 2″ and no fire out of 50 at 1″. The exemplary composition also demonstrated better performance in the 10″ off-center firing pin strike with equal or less misfires than control,
In other preferred embodiments, primer compositions can comprise between about 30% and about 45%, and more preferably between about 35% and about 42%, of a dinitrobenzofuroxan salt, such potassium dinitrobenzofuroxan (KDNBF); between about 4% and about 6% tetrazene; between about 5% and 15% superfines; between about 7% and 15% fuel, such as boron (B) or iron sulfide (ferrous sulfide) (FeS) or antimony sulfide (Sb2S3); and 30% to 41% of an oxidizer, such as potassium nitrate (KNO3), barium nitrate Ba(NO3)2; or manganese peroxide MnO2.
A primer composition was prepared with the following composition:
A primer composition was prepared with the following composition:
A primer composition was prepared with the following composition:
A primer composition was prepared with the following composition:
A primer composition was prepared with the following composition:
This application claims priority to prior provisional application Ser. No. 61/226,496, filed Jul. 17, 2009, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61226496 | Jul 2009 | US |
