WO1995035477A1

WO1995035477A1 - Tin and tin alloy liners and sheaths for explosive, deflagrating and pyrotechnic products

Info

Publication number: WO1995035477A1
Application number: PCT/US1995/007469
Authority: WO
Inventors: John A. Graham; William C. Hadden; Ernest Tarca, Jr.
Original assignee: The Ensign-Bickford Company
Priority date: 1994-06-20
Filing date: 1995-06-13
Publication date: 1995-12-28
Also published as: AU2825195A

Abstract

The liner (16) and, optionally, the tamper (12) of a shaped charge and the sheathing of mild detonating cord, ignition cord, delay cord, etc., are advantageously made of a tin-based alloy that is preferably substantially lead-free and generally comprises about 86 to 99.5 percent tin, 0.5 to 14 percent antimony and, in some embodiments, 0.25 to 6 percent copper. In some embodiments, the alloy may contain 95 to 99 percent tin; balance antimony. Suitable alloys include commercially pure tin (e.g., about 99.5 percent tin and 0.5 percent antimony) and antimonial tin (e.g., about 95 percent tin and 5 percent antimony) and modern pewter, (e.g., about 90 to 98 percent tin, about 1 to 8 percent antimony and 0.25 to 3 percent copper). Modern pewter is preferred as it is found to provide superior working characteristics. Modern pewter also provides superior performance relative to aluminum liners for shaped charges.

Description

TIN AND TIN ALLOY LINERS AND SHEATHS FOR EXPLOSIVE, DEFLAGRATING AND PYROTECHNIC PRODUCTS

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to tin and tin alloy liners and sheaths for explosive and pyrotechnic materials and in particular, to tin alloys used for liners for both conical and linear shaped charges and for sheaths for linear ex¬ plosives and pyrotechnics generally.

Shaped charges generally comprise a concave tamper which receives explosive material and a metallic liner 5 that holds the explosive material in place and which de¬ fines and maintains the explosive material in a concave configuration to focus the energy of detonation. Upon detonation, the liner forms a penetrating jet which is di¬ rected towards a target material. Thus, a conical shaped _Q charge can be used to perforate an oil well casing or to perforate armor plating, and a linear shaped charge can be used for cutting a target material or structure. The ma¬ terials used for the liner are chosen to be sufficiently malleable to facilitate manufacture of the shaped charge 5 and to provide adequate performance with respect to the target. Conventionally, linear explosive (including de¬ flagration material) and pyrotechnic products, such as mild detonating cord and ignition cord, are contained

0

5 within an outer sheath made of a malleable metal such as tin, lead or their respective alloys. Liners for shaped charges have conventionally been made of lead, aluminum, copper, silver and their respective alloys.

Related Art

U.S. Patent 3,128,701 to Rinehart et al, dated April 14, 1964, discloses a variety of alloys for use as liners in shaped charges, including an alloy comprising 91 per- cent tin, 8 percent antimony and 0.6 percent nickel.

German patent document 29 01 500 discloses a shaped charge liner alloy comprising 95 percent tin and 5 percent bismuth.

U.S. Patent 3,112,700 to Gehring, Jr., dated December 3, 1963, discloses a shaped charge liner alloy comprising 61.9 percent tin and 38 percent lead.

U.S. Patent 3,147,707 to Caldwell, dated September 8, 1964, discloses lead-based liner alloys comprising tin, antimony and copper. U.S. Patents 1,923,761 to Snelling et al, dated

August 22, 1993, and 2,982,210 to Andrew et al, dated May 2, 1961, broadly teach the use of tin or tin alloys (or lead) as sheathing material for detonating cord.

U.S. Patent 3,903,800 to Kilmer, dated September 9, 1975, discloses that detonating cord sheath may be made

"of tin, lead or other suitable metal or alloy" (column 1, lines 15-18).

U.S. Patent 3,657,500 to Gawlick et al, dated April 18, 1972, discloses the use of tin alloyed with 1 to 3 percent by weight antimony for use as non-corroding elec¬ trical contacts in percussion or vibrating fuses used in grenades and the like.

Some ignition cord manufactured for use in automotive air bag inflators are known to comprise tin-based alloy tubes that contain a core of explosive material. Such ig¬ nition cords are used to initiate a surrounding charge of explosive material such as sodium azide which, upon such initiation, generates gases that inflate the air bag. As is understood in the art, the tube of an ignition cord is designed to shatter radially, as well as to propagate lin¬ early, to allow the hot gases and particles produced by the explosive core material to eject radially into the surrounding explosive material. Detonating cord is de¬ signed to propagate a reaction linearly along the cord but may also be designed to explode radially. On the other hand, the function of a liner for a linear or conical shaped charge is to develop cutting or penetrating action by using the explosive force to form from the liner a mol¬ ten high-velocity jet and propel it towards a target.

SUMMARY OF THE INVENTION In accordance with the present invention there is provided a reactive product comprising a sheath at least partially encasing a reactive material selected from the group consisting of explosive material, deflagrating mate¬ rial, pyrotechnic material and mixtures of two or more thereof, and the sheath is comprised of from about 86 to about 99.5 percent tin and from about 0.5 to about 14 per¬ cent antimony.

Another aspect of the present invention provides that the reactive material is in the form of a linear core and the sheath is in the form of a linear sheath radially sur- rounding the core.

Other aspects of the present invention provide that the sheath may have any of the following compositions: (a) from about 86 to about 99.5 percent tin, from about 0.5 to about 14 percent antimony and about 0.25 to about 6 per- cent copper; (b) a metal alloy selected from the group consisting of modern pewter, commercially pure tin and an- timonial tin; (c) from about 90 to about 98 percent tin, from about 1 to about 8 percent antimony and from about 0.25 to about 3 percent copper; (d) from about 95 to about 97 percent tin, from about 1 to about 3 percent antimony and from about 1 to about 2 percent copper; (e) from about 94 to about 96 percent tin and from about 4 to 6 percent antimony; (f) about 96.5 percent tin, about 2 percent an- timony and about 1.5 percent copper; (g) about 97.3 per¬ cent tin, about 1.1 percent antimony, and about 1.2 per¬ cent copper; (h) any of the above compositions wherein the sheath is substantially free of lead; and (i) wherein the sheath comprises modern pewter.

Another aspect of the present invention provides that the sheath may comprise the liner of a shaped charge, either a conical shaped charge or a linear shaped charge. In a related aspect, the present invention provides that the reactive product may comprise a shaped charge in¬ cluding a tamper and a shaped explosive material having a concave surface, the explosive material being disposed against the tamper with the concave surface of the explo¬ sive material facing away from the tamper. In this as- pect, the sheath comprises a liner which is attached to the tamper and lines the concave surface of the explosive material to cooperate with the tamper to surround the ex¬ plosive material between the tamper and the liner.

Other aspects of the present invention provide that the reactive product may comprise mild detonating cord, ignition cord or delay cord.

According to various other aspects of the invention, the liner or sheath may be substantially free of nickel; and in the case of a shaped charge the tamper of the shaped charge may comprise the same or a different mate¬ rial as the liner.

As used herein and in the claims, the following terms have the stated meanings.

The term "concave", as used to describe the config- uration of a surface, is intended to include the interior surface of a linear angled strip, i.e., the non-reflex angled surface, as well as the interior of a generally conical, pyramidal or hemispherical shaped surface.

The term "reactive material" means an explosive mate- rial, a deflagrating material, a pyrotechnic material, or a mixture of two or more such materials.

The term "reactive product" means a product contain¬ ing a reactive material and therefore includes, by way of illustration and not limitation, detonating cord, ignition cord, linear shaped charges and conical shaped charges.

The term "sheath" means a liner, cover or casing of a reactive product, which liner, cover or casing surrounds, or at least partly covers, a core of reactive material.

The term "modern pewter" or "modern pewter alloy" shall mean a tin alloy containing from about 90 to 98 per¬ cent tin, from about 1 to 8 percent antimony and from about 0.2 to 3 percent copper. Throughout the description of the invention and the appended claims, the stated percentages of components in an alloy or metal indicate percentages by weight of the total weight of the alloy or metal.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic, partly cross-sectional per¬ spective view of a linear shaped charge including a liner, in accordance with one embodiment of the present inven¬ tion; Figure 2 is a schematic cross-sectional view of a conical shaped charge including a liner, in accordance with another embodiment of the present invention; and

Figure 3 is a schematic perspective view of a linear reactive device including a sheath, in accordance with a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS THEREOF The present invention relates to the use of commer- cially pure tin or tin-based alloys not previously used in shaped charges or for sheaths for linear reactive devices. (For economy of expression, unless the context requires otherwise, reference herein to the tin alloys used in ac¬ cordance with the present invention should be deemed to include commercially pure tin. ) The present invention al¬ so addresses a need in the art to avoid the use of heavy metals, particularly lead and lead-based alloys, for such uses. Such heavy metals are disfavored because of the health and environmental hazards they pose.

It has been found that tin-antimony and tin-antimony- copper alloys function well as liner materials for shaped charges and as sheaths for linear reactive products. Such alloys generally comprise from about 86 percent to about 99.25 percent tin, from about 0.5 to about 14 percent an¬ timony and, optionally, may also include from about 0.25 to about 6 percent copper. Alloys comprising tin, anti¬ mony and copper in these proportions have melting points in the range of about 430° to about 480°F. Encompassed within these alloys is the known tin alloy usually refer¬ red to as modern pewter, which is generally recognized as comprising from about 90 to 98 percent tin, from about 1 to 8 percent antimony and from about 0.25 to 3 percent copper, and which has a melting point of about 471°F. The known modern pewter in particular was found to possess the mechanical properties required to facilitate the drawing, swaging and rolling operations used in connection with the manufacture of linear shaped charges and linear reactive products generally. Modern pewter was found to yield shaped charges that perform as well as, and in some in¬ stances better than, comparative lead and aluminum liners for shaped charges.

The known commercially pure tin comprising about 99.5 percent tin and about 0.5 percent antimony has been found by the applicants to also possess the physical properties required for the production of shaped charges. Commer¬ cially pure tin could also be used as sheathing material for linear reactive products. However, commercially pure tin has a tendency to work-soften, and so is preferably used in reactive products that can be manufactured with a minimum of stress and strain to the material, e.g., in the manufacture of liners for conical shaped charges.

Based on the successful use of the tin-antimony-cop- per alloys, such as modern pewter as described above, the alloy sometimes referred to as antimonial tin, which may comprise about 94 to 96 percent, e.g., about 95 percent tin, and about 4 to 6 percent, e.g., about 5 percent. antimony, should also perform satisfactorily as a liner for a shaped charge and as a sheath for linear reactive products. This is based on the fact that the physical properties of antimonial tin, e.g., its melting point and percent elongation, are close to those of modern pewter. In contrast to the tin-based liner alloy described in U.S. 3,128,701 (discussed above), antimonial tin does not com¬ prise a significant quantity of nickel.

Since one of the advantages of the tin-based liners and sheaths of the present invention is their lack of sub¬ stantial quantities of lead or other heavy metals, the al¬ loys of the present invention may optionally be described as consisting essentially of the stated amounts of tin, antimony and, where present, copper. However, the use of the "consisting essentially" terminology should not be construed to require the exclusion of trace quantities of lead or other metals that are commonly present in commer¬ cially produced tin-based alloys of the type described herein. Accordingly, a quantity of lead or arsenic, e.g., up to about 0.05 percent each, may be present as impuri¬ ties in a normally lead-free (and arsenic-free) pewter, in an alloy consisting essentially of, e.g., tin, antimony and, optionally, copper, in a lead-free antimonial tin, or in a lead-free commercially pure tin used in the present invention. Up to about 0.015 percent iron and up to about 0.005 percent zinc may also be present in such tin alloys as trace impurities and these and any other trace impuri¬ ties are not considered to be alloying constituents.

For example, the ASTM Standard Specification for Mod- ern Pewter Alloys (ASTM Designation B-560-79, Reapproved

1989) provides in Table 1 at page 420 thereof, the follow¬ ing chemical requirements for modern pewter alloy. Table

Composition, %

Type 1 Casting Type 2 Sheet Type 3 Special

Element Alloy* Alloy⁸ Purpoise Alloys

Tin 90-93 90-93 95-98

Antimony 6-8 5-7.5 1.0-3.0

Copper 0.25-2.0 1.5-3.0 1.0-2.0

Lead, max. 0.05 0.05 0.05

Arsenic, max, 0.05 0.05 0.05

Iron, max. 0.015 0.015 0.015

Zinc, max. 0.005 0.005 0.005

^A Nominal Type 1 alloy composition: 92 Sn., 7.5 Sb., and 0.5 Cu.

Nominal Type 1 alloy composition; 91 Sn., 7 Sb., and 2 Cu.

It will be noted that the definition of modern pewter alloy given above at the end of the section entitled Sum¬ mary Of The Invention, is an overlapping composite of the ranges of the three alloys in the above Table.

Tin-based alloys as described herein can be used ad¬ vantageously for liner or sheath material in high radia- tion environments, since they do not readily absorb ther¬ mal neutrons which cause a heating effect in other com¬ monly used liner or sheath materials. In addition, linear shaped charges and linear reactive products in accordance with the present invention lend themselves to inspection for manufacturing defects by using radiographic X-ray, a technique that is obviously less effective or not possible with shaped charges or sheathed reactive products compris¬ ing lead-based liners or sheaths.

Conical and linear shaped charges and linear reactive products comprising tin or tin alloy, preferably modern pewter alloy, in accordance with the present invention, may be produced using conventional techniques well-known to those skilled in the art. For example, in those em- bodiments in which the tamper and the liner of a shaped charge are made of the same material, a chevron-shaped tube made of a tin alloy in accordance with the present invention may be co-extruded with explosive material. Al- ternatively, the linear shaped charge 10 shown in Figure 1 may be formed from a tube made of, e.g., modern pewter, and packed with explosive material. The packed tube can be swaged into a cross-sectional chevron configuration, to form an angled tamper 12 and a liner 16 between which the explosive material 14 is enclosed.

Whether rolled, drawn, spun, swaged or co-extruded, the tamper and the liner of a shaped charge may be made from the same material and constitute a continuous struc¬ ture, i.e., the tamper 12 and liner 16 are portions of a continuous sheath that surrounds the explosive core. Fig¬ ure 1 shows shaped charge 10 supported (by means not shown) at a stand-off distance 18 from a target 20, to illustrate one test configuration used in the trials dis¬ cussed below. For the manufacture of shaped charges, the relative thickness of the tamper and liner and the amount of ex¬ plosive material disposed therein are chosen to best suit the use intended for a particular shaped charge. In some applications, as when a shaped charge is used for an air- craft pilot ejection device, it is advantageous for the tamper and the liner to be substantially the same pewter composition and thickness, so that when the shaped charge detonates, the tamper disintegrates substantially without producing shrapnel, which could severely injure the eject- ing pilot.

In other shaped charge embodiments, the tamper may be physically and compositionally distinct from the liner, and the two may be secured together. One example of such a shaped charge is the conical shaped charge 21 shown schematically in Figure 2, wherein a generally conical modern pewter liner 22 is secured to tamper 24 with explo¬ sive material 26 in a generally concavo-convex configura¬ tion therebetween. A detonating charge 28 is situated at the apex of explosive material 26, beneath a detonator cap housing 30. Housing 30 is secured onto tamper 24 and com¬ prises a bore 32 dimensioned and configured to receive therein a detonator cap (not shown) that is secured to an initiating signal transmission line (not shown) by which an initiation signal is sent to the detonator cap. Initi¬ ation of the detonator cap detonates the detonating charge 28 to fire the shaped charge. In such a configuration, the tamper 24 may comprise a material other than pewter, e.g., copper, which may be chosen over modern pewter due to the differences in their performance characteristics, e.g., for the different types of back blast they produce.

Example 1 Several linear shaped charges in accordance with the present invention were prepared having liners comprising an alloy comprising about 96.5 percent tin, 2 percent an¬ timony 1.5 percent copper, and several others were pre¬ pared that had liners that comprised about 97.3 percent tin, 1.1 percent antimony and 1.2 percent copper. Thus, both types of liners constituted Type III modern pewter, as defined in ASTM B 560-79, which defines Type III modern pewter as comprising about 95 to 98 percent tin, 1 to 3 percent antimony and 1 to 2 percent copper. The linear shaped charges contained explosive core loads ranging from 10 to 25 grains of explosive material per linear foot. The explosive material used was PBXN-5, but those skilled in the art will understand that there are numerous other explosive materials that work well in shaped charges. Comparative linear shaped charges comprising commercially pure aluminum liners and lead liners were also prepared. All of the charges used in the following tests were of the contiguous tamper-and-liner types, i.e., they were formed from tubing that was drawn and rolled to comparable shaped configurations.

Example 2

In penetration tests against a 6061-T6 aluminum tar- get, the linear shaped charges of Example 1 made in ac¬ cordance with an embodiment of the present invention pen¬ etrated the target, on average, 45 percent more deeply than a comparative linear shaped charge comprising an alu- minum liner and having the same loading of the same explo¬ sive material. The linear shaped charges in accordance with the invention penetrated the aluminum target 80 per¬ cent more deeply than a linear shaped charge comprising a lead liner and otherwise identical to the linear shaped charge of the invention. When tested for penetration into 304 stainless steel, the linear shaped charges in accord¬ ance with the present invention achieved 60 percent deeper penetration than otherwise identical linear shaped charges comprising an aluminum liner, and 100 percent deeper than an otherwise identical linear shaped charges comprising a lead liner. These tests show that for at least these tar¬ get materials, shaped charges comprising Type III modern pewter liners according to the present invention provide superior target penetration than comparable prior art lin- ear shaped charges.

Example 3

A cutting test was performed against a graphite com¬ posite-type target which an aluminum linear shaped charge comprising 12.5 grains per foot of the explosive material was not capable of cutting. Another cutting test was per¬ formed using (1) a Type III modern pewter linear shaped charge in accordance with the present invention comprising 10 grains per foot of explosive material identical to that of the aluminum linear shaped charge, and (2) a compara¬ tive aluminum linear shaped charge comprising 15 grains per foot of the identical explosive material. It was found that to obtain optimum cutting performance from the comparative aluminum shaped charge, it was necessary to dispose the charge at a stand-off distance (item 18 in

Figure 1) from the graphite composite target. The modern pewter linear shaped charge according to an embodiment of the present invention provided comparable optimum cutting performance without a stand-off, i.e., when the linear shaped charge was placed in direct contact with the tar¬ get. Such direct-contact placement is advantageous be¬ cause the omission of a standoff leads to simple installa- tion of the charge on a target, and allows the charge to be used in tighter spaces than it otherwise could. Both the aluminum linear shaped charge (with its optimum stand¬ off) and the modern pewter shaped charge (in contrast with the target) cut the target even though the modern pewter linear shaped charge comprised less explosive material (10 grains per foot) than the comparative aluminum linear shaped charge (15 grains per foot).

The pulse pressure produced in each charge upon de¬ tonation was measured by a high frequency pressure trans- ducer placed in close proximity to the shaped charge. It was found that the shaped charge in accordance with the present invention produced only 60 percent of the pressure developed by the aluminum shaped charge due to the lower loading of explosive in the shaped charge according to the present invention. This is advantageous because of the corresponding reduction in the risk of injury or damage to persons or objects other than the target, and due to the reduction in the noise produced upon detonation.

The alloy compositions disclosed above for use in the manufacture of shaped charges may also be employed as a sheath for linear reactive products such as mild detonat¬ ing cord, ignition cord and delay cord. Such detonating cord, ignition cord and delay cord may be manufactured in the known manner by multiple-step swaging or drawing oper- ations, using one of the tin alloys, such as antimonial tin or modern pewter, as the sheath material in accordance with the present invention. For example, a tube made of modern pewter or antimonial tin and about one inch in out¬ side diameter and one-half inch in inside diameter may be filled with a suitable reactive material (e.g, explosive, deflagrating or pyrotechnic material) and then repeatedly drawn to reduce its outside diameter, e.g., to one-fifth to one-tenth or less, of the original outside diameter to compress the reactive composition within the reduced dia¬ meter tube and provide a mild detonating cord, an ignition cord or a delay cord. For example, as is well-known in the art, if the tube is filled with a suitable explosive, detonating cord may be produced by the described method. For another example, if the tube is filled with a known type of delay composition, i.e., a pyrotechnic material, a delay cord or fuse is produced. The delay cord may be di¬ mensioned and configured to be cut into segments sized to fit within a detonator cap as part of the detonator cap firing train, in order to provide one or more delay ele¬ ments to establish the delay period of the cap. Such de¬ lay elements are of course well-known in the art but con¬ ventionally employ a lead sheath. Thus, Figure 3 shows a linear reactive product 34, which may be a detonating cord or ignition cord and comprises a core 36 of reactive mate¬ rial, such as an explosive or deflagrating material or a pyrotechnic material. Suitable explosive, deflagrating and/or pyrotechnic materials will be selected for core 36 depending on its intended use, as is well-known to those skilled in the art. The core 36 is surrounded by a sheath 38 which, in accordance with the present invention, com¬ prises a tin alloy as disclosed herein, preferably, modern pewter alloy.

Example 4 An eight-foot length of tubing made of Type III mod¬ ern pewter having an outside diameter of 0.750 inch and an inside diameter of 0.450 inch was filled with a mixture of equal parts by weight of an igniter mix and RDX explosive, both in powder form. The igniter mix comprised equal parts by weight of titanium powder (specification MIL-T- 13405E, Type II) and potassium nitrate (specification MIL- P-156B, Class 2). The ends of the filled tube were capped and the tube rolled and swaged to an outside diameter of

0.110 inch, to provide a coil of ignition cord. The igni¬ tion cord was test fired and operated successfully. An average velocity of detonation rate of 6,864 meters per second was exhibited by test samples.

While the invention has been described in detail with reference to particular preferred embodiments thereof, it will be appreciated by those skilled in the art that vari¬ ous alterations may be made to the invention as described, without departing from the intent and spirit of the inven¬ tion, and it is intended to include such alterations with¬ in the scope of the invention and the appended claims.

Claims

THE CLAIMSWhat is claimed is:

1. A reactive product comprising a sheath at least partially encasing a reactive material selected from the group consisting of explosive material, deflagrating ma¬ terial, pyrotechnic material and mixtures of two or more thereof, the sheath being comprised of from about 86 to about 99.5 percent tin and from about 0.5 to about 14 per¬ cent antimony.

2. The reactive product of claim 1 wherein the reac¬ tive material is in the form of a linear core and the sheath is in the form of a linear sheath radially sur¬ rounding the core.

3. The reactive product of claim 1 or 2 wherein the sheath further comprises from about 0.25 to about 6 per¬ cent copper.

4. The reactive product of claim 1 or claim 2 wherein the sheath comprises a metal alloy selected from the group consisting of modern pewter, commercially pure tin and antimonial tin.

5. The reactive product of claim 1 or claim 2 wherein the sheath comprises modern pewter.

6. The reactive product of claim 1 or claim 2 wherein the sheath comprises from about 90 to about 98 percent tin, from about 1 to about 8 percent antimony and from about 0.25 to about 3 percent copper.

7. The reactive product of claim 1 or claim 2 wherein the sheath comprises from about 95 to about 97 percent tin, from about 1 to about 3 percent antimony and from about 1 to about 2 percent copper.

8. The reactive product of claim 1 or claim 2 wherein the sheath comprises from about 94 to 96 percent tin and from about 4 to 6 percent antimony.

9. The reactive product of claim 1 or claim 2 wherein the sheath comprises about 96.5 percent tin, about 2 percent antimony and about 1.5 percent copper.

10. The reactive product of claim 1 or claim 2 wherein the sheath comprises about 97.3 percent tin, about 1.1 percent antimony, and about 1.2 percent copper.

11. The reactive product of claim 1 or claim 2 wherein the sheath comprises the liner of a shaped charge.

12. The reactive product of claim 1 comprising a shaped charge including a tamper and a shaped explosive material having a concave surface, the explosive material being disposed against the tamper with the concave surface of the explosive material facing away from the tamper, and wherein the sheath comprises a liner attached to the tam¬ per and lining the concave surface of the explosive mate¬ rial and cooperating with the tamper to surround the ex¬ plosive material between the tamper and the liner.

13. The reactive product of claim 2 comprising mild detonating cord.

14. The reactive product of claim 2 comprising igni¬ tion cord.

15. The reactive product of claim 2 comprising delay cord.

16. The reactive product of claim 12, claim 13, claim 14 or claim 15 wherein the sheath is comprised of a metal alloy selected for the group consisting of modern pewter, commercially pure tin and antimonial tin.