US2830885A - Delay compositions - Google Patents

Description

April 15, 1958 H. M. KERR ETAL 2,830,885

DELAY COMPOSITIONS Filed March 29, 1956 2 sneaks-sheet 1 //V VE/VTORS 1100/1 MOWAT/(ERR (iv/won rowzu Y 5 1 April 15, 1958 H. M. KERR ET AL DELAY COMPOSITIONS 2 Sheets-Sheet 2 Filed' March 29, 1956 m w 0 w 0 C COMPOSITION-2 kwzmroks 1 HUG/l Mon 4r KERR GORDO/V TOWfZL United States. Patent DELAY COMPOSITIONS Hugh M. Kerr, Cartierville, Quebec, and Gordon Towell, Brownsburg, Quebec, Canada, assignors to Canadian Industries Limited, Montreal, Quebec, Canada, acorp'oration ofCanada Application March 29, 1956, SerialNo. 574,653

priority, application Canada August 3, 1955 4 Claims. (Cl. 52'2) This invention relates to substantially gasless, slow burning delay compositions for use in delay fuses of various types and more particularly for use in the delay fuses for ventless delay electric blasting caps.

The prior art delay compositions are either of the gas-generating or gasless class. Those of the gas generating class evolve a large volume of gas when burning ng'charges through the medium of which the detonating charge is fired after a predetermined delayinterval. The delay element is, customarily reuse of such length compbsitionas will afford the desired delay interval between "firing" of "the ignition and detonatin'g charges.

Delay electric blasting caps which are commercially available are generally of three types: the short interval ventless delay type which uses relatively fast burning gasless delay compositions and which has delay intervals 1 ran'girig ffrorn a few'milliseconds to approximately one second; theveuted slow delay type which commonly uses gas-generating delay compositions such as black powderand which has delay intervals ranging from about /2 second to seconds and longer; and the ventless slow delay typewhich commonly .uses gaslessldelay composi-.

tions and ,Which has delay intervals of the same order as the vented slow delay type.

p In the vented slowdelay type of electric blasting cap, the 'igas generating delay composition produces a large volumeofigas when'bur'ning. Therefore, the-cap casing isfvented to permit the free escape ofthe gases which, if release'd wouldcause increase in the burning ra "oflthe delaycomp'osition because, of the pressure generated, 'andh'ence would: produce irregularities in the delay interval of the cap. In the extreme case the pres- {build-up might resultfin the delay comp'osition explodin thus causing an almost instantaneous detonation ofth mainexplosive charge.

Y ted capsfhave a number of serious disadvantages. Alth h "the vent in' the cap is usually sealed with a 111' urblemembrane to prevent the entrance ofmoishire, 't li e'se caps haveb'een found to be much more susceptible to wa-ter penetration than comparable caps with a; casing Furthermore, flashes from the burning de y compositionmay escape through the vent and may cfausefpremature burning'of the primed explosive charge. Ther'eis also'a serioushistory of this type of cap misfifingiir-We t ground where the shock from charges fired by vented delay caps of relatively short delayintervals threes water through theiv'entsof neighbouring vented de y of relatively longer delayintervals, thus wetringers duenchingtheir burnin'g delay trains. "Should 2,830,885 Patented An 195g 2 the vent hole inadvertently be blocked up or improperly aligned, a. pressure build-up may also occur within the casing when the delay composition is ignited, with a resultant irregular burning of the fuse and, hence, an irregular delay interval.

Both the slow delay and short interval delay ventless caps need 'not be vented since they use gasless delay compositions. Thus, they avoid the disadvantages of the vented delay caps. However, despite their useful properties, the gasless delay compositions of the prior art suffer from serious practical disadvantages when used in delay electric blasting caps with delay intervals ofthe order of the vented slow delay caps. These prior art compositions either burn at a rate such that the length of delay element required to produce the long delay intervals desired necessitates a cap casing which isinconveniently long for priming explosive cartridges, or they are so. sensitive to moisture that extreme care must be taken to-exclude moisture from the cap and its component parts and compositions.

Gasless delay compositions generally comprise a mixture of oxidising and fuel materials. The materials are selected and proportioned such that, upon ignitiomthe decomposition products of the oxidising materials are solids and gases, which gases react with the fuel material to form other solid products. Thus, all products of combustion are solids and essentially no residual gases are produced; The materials must" also be so selected and proportioned that the burning temperature of the composition after ignition is sufficiently high to generate the heat'required to sustain combustion throughout the length of the delay element and to subsequently initiate the explosive charge.

The burning speed ofthe prior art gasless delayhcompositions may be reduced by the judicious selection and proportioning of the ingredients and by the additioncf inert materials which retard oxidation and, hence, slow down combustion. Attempts have been made to produce slow-burning, gasless delay compositions by these and other means but all such compositions produced have had one or more serious disadvantages. Some are difiicult to ignite-and some generate .-ins|ifficient heat tosustain combustionzthr oughoutthe length of the delay element, thus causing misfires in the delay caps in which they are used;

Others are'chemically unstable and deteriorate, particu-v andfto substantially initiate the explosive charge, and.

which is also readily'ignited. A further object is to pro vide such a'gasless delay composition which is chemically stable and whichis not markedly affected by changes'in moisture content such as would be expected in a capas sembly. A still further object of the invention is to pro vide a gasless delay composition burning at a slow, even rate which makes' possible the fabrication of:a precise and accuratelytimed series of ventless delay capshaving delay intervals of large fractions of a second and longer and lamp shells substantially shorter than most other" known slow delay ventless' caps.

The essentially gasless, slow-burning delay composition of-this invention comprises, as essential ingredients,

silicon, solid non-metallic material selectedfromdlie groupconsisting of selenium and tellurium, and oxidising material selected from the group consisting of leadloxides and water-insoluble metallic chromates.

The preferred oxidising agents for use in the composition of the invention are lead peroxide, red lead, barium chromate and lead chromate.

It is possible to formulate a series of delay compositions of the aforesaid type with varying burning rates by the judicious proportioning of the ingredients. However, since a main object of the invention is the provision of a slow-burning delay composition which will make possible the fabrication of a precise and accurately-timed series of ventless delay caps having delay intervals of large fractions of a second and longer and in cap shells substantially shorter than most of .those of comparable delay heretofore known, it is preferable to limit the proportion of silicon in the delay compositions generally and also the ratio of silicon to selenium and/or tellurium in the fuel.

It is thus preferable generally to use not more than 65% of silicon, by weight of the delay composition and when the oxidising material is comprised solely of chromates, not more than 40% of silicon by weight of the delay composition. For the same reason, it is preferable to have at least a minimum proportion of silicon in the fuels of the delay compositions, as shown in the table of preferred compositions below, in which all parts and percentages are by weight and the fuel ingredients are silicon, selenium and/ or tellurium.

The compositions of the invention also include all compositions which may be produced by combining compositions B and C shown in the above table in all proportions.

The gasless delay compositions of the invention are readily prepared by means well known to the art. It ispreferable to use particularly finely ground fuels and oxidising material in the compositions, the particle sizes of which are much smaller than the largest particles which will pass through a 250-mesh Tyler screen. After grinding and screen, if necessary, the ingredients are throughly mixed by well known methods.

The application of the invention in ventless delay electric blasting caps may be more readily understood by reference to Figure l in the accompanying drawings which shows a longitudinal sectional view of a preferred form of ventless delay electric blasting cap.

Figure 1 shows a ventless delay electric blasting cap' in which 1 is a solid drawn cylindrical metal shell in the base of which is pressed a suitable detonating charge 2 such as, for example, tetryl or pentaerythritol tetranitrate. Directly above the detonating charge is pressed a' suitable priming charge 3 on top of which is pressed a delay element 4 containing the gasless delay composition 5. The priming charge 3 may be, for example, a mixture of lead azide and lead styphnate or the like, while the delay element comprises a lead tube containing the gasless delay composition 5 which is seated at such a pressure that a gastight seal is made with the shell wall 1. The bridge wire 6 is soldered or welded to the terminals of the two leg wires 7 and 8. A rubber plug 9 carries and supports the two leg wires 7 and 8 and seals off the open end of the cap shell 1. An essentially gasless loose charge ignition composition 10 such as, for example, a corned mixture of 98% by weight of red lead and 2% by weight of boron, surrounds the bridge wire 6 and substantially fills the space between the rubber plug 9 and the delay element 4.

The delay fuse may be prepared by tamping the delay composition into a large diameter lead tube closed at one end which, when full, is closed at the open end and sized down by rolling, drawing or rotary swaging to any desired diameter. It is preferable to select a lead tube of such external and internal diameters that when it is subsequently sized down into a delay fuse with an external diameter of about 0.25 inch it will contain a delay composition train about 0.125 inch in diameter. The delay elements are prepared by cutting the delay fuse into segments of such length that when used in delay caps, the desired delay intervals are obtained.

Example 1 Two preferred compositions illustrative of the invention were prepared having the following compositions:

These compositions were prepared and compressed into delay elements by methods described above .and were used in the heretofore-described ventless delay electric blasting caps. The following table illustrates a series of these caps wherein the delay elements were of difierent lengths.

' TABLE Element Mean No. of Composition Length Delay Gaps in inches interval, Tested Secs.

The experimental data are graphically illustrated in Figure 2 of the accompanying drawings. Figure 2 is a graphical plot of the mean delay intervals obtained in the tests illustrated in the above table against the length of delay element used in the caps. The solid lines represent the curves obtained from the tests while the dotted lines are extrapolations of these curves.

The straight-line relationship which exists between'the element length and mean delay interval when delay compositions of the invention are used is clearly illustrated:

by Figure 2. It has been found that the curve based on experimental data can be extrapolated and used to predict the delayintervals of caps usingelements of greater length than those for which data are available. For example, using the graph of Figure 2, it can be predicted with a reasonable degree of accuracy that a ventless delay electric blasting cap, as heretofore described,,

' art gasless delay compositions is that their burning rates are too high for efiicient use in slow delay electric blasting caps. When used in delay elements ofventless delay electric blasting caps such as heretofore described, they result in inordinately long caps when delay intervals of large fractions of a second and longer are desired. For example, most commercially available slow delay gasless electric blasting caps range in length up to inches or greater. Caps of this length are undesirable because when used to prime standard explosive cartridges of say 8 inches in length, they must penetrate very nearly the whole length of the cartridge. If the explosive material in the cartridge is stiff due to'material characteristics or weather conditions, this becomes a difficult and timeconsuming operation. Also, ,if extreme care is not taken, the cap may be inserted at a slight angle which might result in it protruding'throughthe side of the cartridge. Thus, when loading a borehole, there would be a danger of premature detonation due to a protruding cap striking the side of the borehole or of an unexploded charge if the cap fires properly but dissipates its power outside the charge.

To obviate these difiiculties those skilled in the blasting art prefer to use caps of a maximum length of about 4 inches. Using the delay compositions of the invention, it is possible to manufacture caps with a maximum length of about 4 inches which have delay intervals up to seconds or greater. For example, the components of the cap illustrated in Figure 1, other than the delay element, consume about 1% inches of the total cap shell length. Therefore, there is available within a cap shell 4 inches in length, a space of about 2% inches to house the delay element. Referring to Figure 2, it can be seen. that a delay interval of about 16 seconds can be obtained by using about 2.4 inch lengths of delay element containing compositions 1 or 2 in such a cap. The selection of even slower burning compositions of the invention would result in'4 inch caps with delay intervals even greater than 16 seconds.

Example 2 I The following table illustrates two further compositions of the invention in which selenium and tellurium are interchanged. These compositions were prepared and used in caps as heretofore described. The delay elements were 0.75 inch in length. i

i It is to be understood that the foregoing examples and details are for the purpose of illustration only and that the invention is not limited thereto but may be moditied and embodied in various other forms without departing from its intended scope. A particular modification which is desirable when using the slower burning composition of the invention in the delay elements of ventless delay electric blasing caps is the use of a delay element priming charge comprising a faster burning composition of the invention, said delay element priming charge being pressed on top of the delay element.

It will be further understood that the invention is not limited to the preferred compositions described herein, nor to the particular cap structure illustrated. In the foregoing description of the invention, only its application in ventless delay electric blasting caps has been shown. It is apparent, however, that the invention has many other important applications such as for example in delay fuses required in various types of military explosive devices and in the delay elements for detonating fuse delay connectors.

What we claim is:

1. A substantially gasless, slow-burning delay composition consisting essentially, per 100 parts by weight of said composition, of 6.5 to 50 parts of fuel and 93.5 to 50 parts of oxidising material, said fuel consisting essentially of a mixture of not less than 60% by weight of silicon and not more than 40% by weight of solid, nonmetallic material selected from the group consisting of selenium and tellurium, and said oxidising material comprising a mixture of lead oxides and water-insoluble metallic chromates containing not less than 30% by weight of lead oxides.

2. A substantially gasless, slow-burning delay composition consisting essentially, per 100 parts by weight ofsaid composition, of 7 to parts of fuel and 93 to 35 parts of oxidising material, said fuel consisting essentially of a mixture of not less than 17% by weight of silicon and not more than 83% by weight of solid, non-metallic material selected from the group consisting of selenium and tellurium, and said oxidising material being selected from the group consisting of lead peroxide and red lead.

3. A substantially gasless, slow-burning delay composition consisting essentially, per 100 parts by weight of said composition, of 10 to 40 parts of fuel and to 60 parts of oxidising material, said fuel consisting essentially of a mixture of not less than 80% by weight of silicon and not more than 20% by weight of solid, non-metallic material selected from the group consisting of selenium and tellurium, and said oxidising material being selected from the group consisting of barium chromate and lead chromate.

4. A substantially gasless, slow-burning delay composition consisting essentially, per parts by weight of said composition, of 1.6 to 1.7 parts of selenium, 6.1 to 6.2 parts of silicon, 36.0 parts of red lead, 35.9 parts of lead chromate and 20.3 parts of barium chromate;

References Cited in the file of this patent UNITED STATES PATENTS 2,562,928 Lewis Aug. 7, 1951 2,586,959 Kerr Feb. 26, 1952 2,726,943 Heiskell Dec. 13, 1955 2,740,703 Mulqueeny Apr. 3, 1956 2,749,226 Lewis June 5, 1956

Claims (1)

1. A SUBSTANTIALLY GASLESS, SLOW-BURNING DELAY COMPOSITION CONSISTING ESSENTIALLY, PER 100 PARTS BY WEIGHT OF SAID COMPOSITION, OF 6.5 TO 50 PARTS OF FUEL AND 93.5 TO 50 PARTS OF OXIDISING MATERIAL, SAID FUEL CONSISTING ESSENTIALLY OF A MIXTURE OF NOT LESS THAN 60% BY WEIGHT OF SILICON AND NOT MORE THAN 40% BY WEIGHT OF SOLID, NONMETALLIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF SELENIUM AND TELLURIUM, AND SAID OXIDISING MATERIAL COMPRISING A MIXTURE OF LEAD OXIDES AND WATER-INSOLUBLE METALLIC CHROMATES CONTAINING NOT LESS THAN 30% BY WEIGHT OF LEAD OXIDES.

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