Electric detonator with milled and unmilled DBX-1

Abstract

Lead free microdet electric detonators comprising a bridgewire having milled DBX-1 as a spot charge and unmilled DBX-1 as the intermediate material. Such improved microdet electric detonator is free of lead azide and lead styphnate, but with comparable stability, power and sensitivity to current lead-based M100 electric detonators.

Claims

1. An electric detonator comprising: a metal bridgewire having a spot charge composition disposed thereon wherein said spot charge composition comprises milled DBX-1; an intermediate charge comprising unmilled DBX-1; and output charge.

2. The electric detonator of claim 1, wherein the particle size of the milled DBX-1 is about 1 μm to about 28 μm.

3. The electric detonator of claim 1, wherein the particle size of the milled DBX-1 is about 5 μm to about 1 μm.

4. The electric detonator of claim 1, wherein the spot charge composition further comprises nitrocellulose and lacquer.

5. The electric detonator of claim 1, wherein said spot charge composition is a slurry.

6. The spot charge composition of claim 1, wherein the milled DBX-1 is a single spot charge at about 0.27 mg to about 0.38 mg per header.

7. The electric detonator of claim 1, wherein the metal bridgewire is selected from the group consisting of nickel chrome, platinum, tungsten, and platinum-iridium.

8. The electric detonator of claim 1, wherein the bridgewire is nickel chrome.

9. The bridgewire of claim 8 wherein the diameter of said nickel chrome bridgewire is about 0.00023 inches.

10. The electric detonator of claim 1, wherein the unmilled DBX-1 is about 12 mg.

11. The electric detonator of claim 1, wherein the unmilled DBX-1 is loaded at a consolidation pressure of about 8 Kpsi to about 10 Kpsi and the height of the loaded unmilled DBX-1 is about 0.090 to about 0.060 inches.

12. The electric detonator of claim 1, wherein the output charge is HMX or CL-20.

13. The electric detonator of claim 1, wherein the output charge is HMX.

14. The electric detonator of claim 1, wherein the HMX is about 12 mg and loaded at a consolidation pressure of about 12 to about 14 Kpsi and about 0.100 inches to about 0.130 inches in height.

15. An electric detonator comprising: a nickel chrome bridgewire having a spot charge composition disposed thereon and wherein said spot charge composition comprises milled DBX-1, nitrocellulose and lacquer and wherein said spot charge composition is a slurry; an intermediate charge comprising unmilled DBX-1; and HMX.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further features and advantages of the present invention may be understood from the drawings.

(2) FIG. 1 is a representative standard stab detonator

(3) FIG. 2 is a representative standard microdet electric detonator

(4) FIG. 3 is a representative standard M100 military electric detonator

DETAILED DESCRIPTION

(5) A typical electric detonator is composed of three main components: a bridgewire, an intermediate charge and an output explosive charge. The bridgewire acts to transmit electrical impulses to the intermediate charge creating a cascade of subsequent chemical reactions to detonate the main explosive. Both LA and LS have been widely adopted by the military as the two most common primary explosives acting in concert to detonate the main explosive charge. For many measurable explosive properties, LA and LS behave similarly, possessing comparable sensitivity to impact and friction, detonation velocity, thermal stability, and power (as determined by Trauzl Pb block tests). Where they differ is in brisance, or shattering capability, with LA measured to be 39% TNT and LS found to only be 27% TNT. At least partially as a result, LA possesses much higher “initiating efficiency” for triggering secondary explosives such as RDX, HMX, and TNT; whereas LS is generally not capable of directly initiating secondary explosives with the exception of uncompressed PETN; instead, it is largely only capable of initiating other primary explosives or propellants. Further, LS tends to be much more sensitive to electrostatic discharge and to initiation by heat/flame. These qualities help to make LS much more reliable to initiate an intermediate explosive.

(6) As a result of these key differences, LA and LS tend to be used for different initiation applications. Because of its much greater brisance and initiating efficiency, LA is the main explosive used in detonators and blasting caps acting as the intermediate charge to directly initiate secondary explosives. Whereas LS, with its higher sensitivity/reliability, fills the role of receiving the triggering stimulus (e.g. hot-wire or firing pin impact) and subsequently triggering another primary explosive, such as LA, or a propellant. Therefore, in general, many detonators require both LA and LS acting in concert to function properly as the triggering explosive and intermediate explosive; LA gives the ability to initiate secondary explosives, while LS gives the ability to initiate LA reliably.

(7) In the M100 detonator (FIG. 3), the LS is typically applied as a spot charge on the bridgewire 200. LS 100 is initiated when the wire is electrically heated, which in turn initiates the LA 300 intermediate charge, which subsequently initiates the HMX output charge 400. The LS works well in the M100 because it has a very low hot wire ignition point. LA is not used as a spot charge because its hot wire ignition point is too high and fails to produce satisfactory results under normal firing energy pulses.

(8) U.S. Pat. No. 7,833,330 to Fronabarger et al, discloses the use of copper (I) nitrotetrazolate (DBX-1) as a potentially useful lead free substitute for lead azide. DBX-1 has properties similar to lead azide such as friction sensitivity, impact sensitivity, and strong confinement/dent block testing. Accordingly, it has also been reported that the physical and chemical characteristics of DBX-1 would make it an ideal candidate as a drop-in replacement for LA. Conversely, DBX-1 would not be considered interchangeable with LS because its initiation and explosive properties is significantly different from LS. Consequently, it was presumed that DBX-1 has too high an ignition point and would therefore fail as an initiating explosive.

(9) Table 1 below summarizes the differences between LA, LS and DBX-1

(10) TABLE-US-00001 TABLE 1 Lead Styphnate (normal) Lead Azide DBX-1 Poor explosive initiating Good explosive initiating Comparable initiating efficiency (only adequate efficiency (can initiate most efficiency to LA (can initiate for other primary explosives secondary explosives: RDX, secondary explosives such as and PETN) HMX, etc.); RDX, HMX, etc.) Most abundant primary Most abundant primary Prior reports investigate explosive component found explosive component found DBX-1 as LA replacement, in primers (e.g. percussion in detonators and blasting not LS primers for small arms) caps Generally employed in Generally employed as a Employed as a neat material mixtures with other neat material (notable ingredients (e.g. primer exception: formulation formulations, NOL-130 stab ingredient in NOL-130 stab mix) mix) High sensitivity to flame (2 Relatively low sensitivity to Flame test data not available ms to reach 100% flame (11 ms to reach 100% probability of initiation) probability of initiation).sup.|4|

(11) Given that DBX-1 would not be a replacement for LS, it has unexpectedly been discovered that electrical detonators comprising the combination of milled DBX-1 as a spot charge and unmilled DBX-1 as an intermediate charge, and HMX results in comparable function and output over current detonators, but without the toxic lead-based products found in current electrical detonators.

(12) The present milled DBX-1 composition is prepared by mixing milled DBX-1 into a slurry comprising of nitrocellulose lacquer, binder, carrier and solvent. The various components are all commercially available. Milled DBX-1 can be obtained from Pacific Scientific Energetic Materials Company (PSEMC). Preferably, the particle size of the milled DBX-1 is about 1 μm to about 28 μm, more preferably about 3 μm to about 12 μm and even more preferably about 5 μm to about 11 μm.

(13) The milled DBX-1 slurry composition may be applied to the header of a metal bridgewire using techniques well known in the art. The slurry containing milled DBX-1 may be placed onto a bridgewire as a single spot. The amount of the milled DBX-1 can be applied in the range of about 0.27 mg to about 0.38 mg per header.

(14) Typical bridgewire materials contemplated by the present invention are composed of metal. Preferred metals are nickel-chrome, platinum, tungsten, and platinum-irridium. Typical diameters of the bridgewire may be about 0.0005″ to about 0.0002″, preferably 0.00023″.

(15) The dimensions of the microdet electric detonators useful for the present invention have an outer diameter of 0.100″ with an inner diameter of 0.075″, an explosive column height of about 0.250″, which includes the header and an explosive column length of about 0.190″.

Example 1

(16) An M100 microdet detonator comprising milled DBX-1 as the initiating charge, unmilled DBX-1 as the intermediate charge, and HMX as the output charge was prepared having a nickel-chrome bridgewire with a diameter of 0.00023″. For the initiating charge, about 11 μm milled DBX-1 slurry composition was applied as a single spot charge to the bridgewire. The milled DBX-1 slurry composition comprises of a mixed ratio of clear lacquer adjusted to yield a 3.5% lacquer solids content depending on the amount of DBX-1 to be mixed into slurry and the percent of solids in the clear lacquer. The composition of clear lacquer comprises: camphor 9.8%, nitrocellulose (½ second) 26.2%, nitrocellulose (60 to 80 second) 14%, n-amyl alcohol 12.4%, and butyl acetate 37.6%. In one embodiment, 0.5 g milled DBX-1 (5 um) Lot# EL4X104B, 3.5% solids, and 0.15 cc lacquer were mixed together. Lacquer thinner (n-amyl alcohol 75% and toluene 25%) may be added for consistency. In another embodiment, 0.78 g milled DBX-1 (5 um) Lot# EL4X104B, was mixed with 3.4% solids and 0.22 cc lacquer. Lacquer thinner may be further added for consistency.

(17) Lead-based standard detonators and lead-free detonator compositions of the present invention were loaded into M100 detonators as follows. The maximum column height for an M100 detonator is generally about 0.190″. Thus, the standard loading parameters for HMX is about 15 mg, about 0.150″ to about 0.160″ column height and a consolidation pressure of about 12 Kpsi to about 14 Kpsi (Test number 1). The lead azide intermediate charge in the typical lead based M100 detonator is loaded at about 0.030″ to about 0.040″ column height and about 12 Kpsi to about 14 Kpsi (Test number 1). In contrast, the lead free detonators of the present invention can be loaded with less HMX at about 12 mg and about 0.100″ to about 0.130″ column height and under the same consolidation pressure as the standard lead-based HMX compositions (Test number 6 and 7 compared to Test number 1). The unmilled DBX-1 can be loaded at about 0.060″ to about 0.090″ column height with less consolidation pressure at about 8 Kpsi to about 10 Kpsi (Test number 6 and 7). The spot charge for each composition is applied according to Table 2.

(18) A witness plate dent test was used to determine whether the lead free detonators of the present invention performed under high order or low order when fired at 1.6V at 100 μF. If the dent is 0.005″ or higher, the charge is assumed to have gone “high order” meaning that the output charge in the detonator is functioning at or near its maximum detonation velocity. If the dent is less than 0.005″ then it is a “low order” failure meaning the tested charge does not fully detonate and/or detonates at a much lower velocity.

(19) Table 2 compares the results of the present inventive lead free detonator composition as described in Example 1 against detonators with LS or LA compositions fired at 1.6V at 100 μF capacitor.

(20) TABLE-US-00002 TABLE 2 Intermediate Results Spot Charge Weight (g) HMX Average Test Charge Consol. P (kpsi) Consol. P (kpsi) Dent Number Weight (g) Height (inches) Height (inches) (inches) Performance 1 Lead Lead Azide 15 mg 0.010″- High Order Styphnate 10 mg 14 Kpsi 0.016″ 14 Kpsi 0.160″ Height: 0.030″ 2 Lead Unmilled DBX-1 Varied Poor Low Order Styphnate Varied Varied Varied 3 2X Lead Unmilled DBX-1 16 mg Poor 7/14 High Order Styphnate 8 mg 12 Kpsi 6/14 Low Order- 8 Kpsi 0.133″ ± 0.002″ no dent 0.056″ ± 0.002″ 1/14-untested 4 Colloidal Unmilled DBX-1 16 mg Poor Low Order Lead Azide 8 mg 12 Kpsi 8 Kpsi 0.133″ ± 0.002″ 0.056 ± 0.002″ 5 Lead Milled DBX-1 16 mg Poor 4/13 High Order Styphnate 8 Kpsi 12 Kpsi 9/13 Low Order- 0.056 ± 0.002″ 0.133″ ± 0.002″ no dent 6 Milled DBX- Unmilled DBX-1 12 mg 0.01294″ High Order 1 12 mg 12 Kpsi (Unsealed) 11.71 μm 10 Kpsi 0.100″ ± 0.002″ 0.093 ± 0.002″ 7 Milled DBX- Unmilled DBX-1 12 mg 0.01372″ High Order 1 12 mg 12 Kpsi (Sealed) 11.71 μm 10 Kpsi 0.100″ ± 0.002″ 0.093 ± 0.002″

(21) The results indicate that the lead-free milled DBX-1 in combination with unmilled DBX-1 and HMX performed under the same performance standards as the standard lead-based detonator composition containing LS and LA.

(22) The weight and volume of the HMX output charge was less in the lead-free milled DBX-1 composition compared to the standard LS and LA based M100 composition. It may be expected that reducing the weight and column height of the loaded HMX output charge would reduce the output dent, however, it was unexpectedly discovered that increasing the loading volume of unmilled DBX-1 and lowering its consolidation pressure provides the same performance results under standard firing conditions of 1.6V at 100 μF capacitor (Test numbers 6-7).

(23) While the invention has been described with reference to certain embodiments, changes, alterations and modifications to the described embodiments are possible without departing from the spirit and scope of the invention as defined in the appended claims, and equivalents thereof.