US2796834A - Short interval delay blasting device - Google Patents

Description

June 25, 1957 F. H. G. MCCAFFREY ETAL 2,796,834

SHORT INTERVAL DELAY BLASTING DEVICE Filed March 9, 1956 5 Sheets-Sheet 1 INVEN TOR S FmN/s H. G. M5 CAFFREY, WILLIAM E. HAMILTON B 5, 4 4% a 6M;

. June 25, 1957 F. H. G. MCCAFFREY ET AL 2,796,334

SHORT INTERVAL DELAY BLASTING DEVICE Filed March 9, 1956 3 Sheets-Sheet 2 IN VEAZTORS FRANCIS ma. Ms CAI-FEEY, WILLIAM E. HAMILTON.

fiM/MQA/ AGENT 7a POPUL ,4 770/V 70 opuuv/o/v June 25, 1957 F. H. cs. MOCAFFREY ET AL 2,796,834

SHORT INTERVAL DELAY BLASTING DEVICE Filed March 9, 1956 3 Sheets-Sheet 3 ATTORNE'Y SHORT INTERVAL DELAY BLAS'I'ING DEVICE Francis Hamnet GarlandMcC'afirey and William Edgar Hamilton, Brownsburg, Quebec," (Ianada, assignors to Canadian'Industries Limited, Montreal, Quebec, Canada, a corporation of Canada Application'March 9, 1956; Serial No. 570,490

3 Claims. (Ch '102 27) The j present invention relates 'toshbrt "interval delay blasting devices and more particularly, toshort interval delay connectors I commonly 1 known as detonatingf relays whichare'used to introduce a shortinter-val delay into a 'trainof 'detonating fuse.

This application is a-continuation-impart ofouncepending application SerialNo. 432,545; filed on-May 26,

1954, nW abandoned.

Detonating fuse is well-known" as the'type-offuse which consists of a high explosive core-such as pentae'ry'thritol -"--tetranitrate, for example, contained within a wat'erproof lsheath-overlaid by reinforcing coverings. This fuse has a "very high velocity of detonation bfiappr'oximat'ely -2l000 feet per second. 1 Its explosive 'forceis' such that i1 it may be-u's'ed to detonatehigh explosives adjacenttoit in I borehole or the like.

I As in= other methods of detonating explosivesfishort 'i'nterval delays are desirable when using the detonating fuse method in order to enjoy the'benefits of successive shots separated by very short periods of time.

When using the detonating fuse method of detonating ="explosives, the short interval delay has been obtained in the past by using short delay electric blasting caps to i'ni-.

" tiate-separate lines of detonating fuse, each'linebeing connected to one'or more charges 'of explosives. Delay- *ing the detonation of the successive blasting caps by known methbds'resulted in the delay being transmitted-to the detonating fuse and thus to the separate explosive charges. The complexity of such methods is not desirable in the -field.

Devices have also been proposed which are designed 'tobe inserted in a length of detonating fuse itself to act as delay mechanisms whereby the progress of the-detonation wave along a line of fuse is interrupted for a short, definite and predetermined timeinterval. #These'devices are commonly known as detonating relays.

One proposed type of detonat-ing relay has'the" great practical disadvantage of being uni-directional. That is, the detonation wave" must enter the device at=only one end for it to be delayed and re-initiated in the remaining d'etonating fuse. An error in directional orientation while setting up a blast in the field will-result in a misfire with this type of detonating relay.

.A nother proposed type employs an air gap within a metallic tube assembly as a delay'd'evice. 'The chance "of misfire is relativelyhigh with this typeuand' two or :three relays must be connected inparallel to assure proper d'etcnation transmission.

-In 'Fren'ch Patent No. 1,069,960 issued to-Dynamit-' Actien-Gesellschaft a detonating-relay is describ'ed which is bi-directional in the sense that the delay will 'be obtained regardless of the direction from which the detonationwave enters the device. Howeven'because'ofthe "form of'thedelay element'contained therein, this device si'i'fie'rs from large deviations from the desired definite,

predetermined delay interval, as will" be shown herein- H 2,796,834 "Patented June- 25, 1957 short intervaldelay blasting.

It is an object of the present invention to provide an improvedshort interval delaydevice for use with'detonating fuse. 7

- A further object of'this invention is to provide a waterproof, reliable short interval delay device whichmay be .-quickly and conveniently attached to twoiends of detonating fuse in the field without regard to thedirection of propagation of 'the detonation wave.

A stil1" further object of :the inventionis-to provide a short interval delay device whichmay be constructed to have adefinite predetermined delay interval with'devi- I ations from the desired delay interval which are negligible for the purpose of short intervaldelayblasting-techniques. According to the: present invention; a short interval delay blasting device-adapted-to be inserted between two ilengths of detonating fuse-is provided-which comprises in combination a tubulan I casing, t-woimpervious-recep tacles adapted to receive-the ends of said length of detonating fuse partially encased and supported-in symmetrical opposing relationship byithe tubular-casing-at the ends thereof, two-explosivechargesabutting the closed ends "of 'said -receptacles externally "thereof and-a metallic element 'lyingintermediate-said two explosive charges; said element being solid except for a core-of highly compressed 'gasless :delay composition having a helicalshape and said element being produced by charging and compacting' the "delay: compo'sitioninto aductile; malleable-:metal tube until the tube isfilled, swa'ging the endsbf thetube to seal the compesition therein; drawing said t'ube'down" to a predetermined diameter,- winding'said drawn tube around a mandrel' toj'produce a regular helix, removing said mandrel'and filling the void left in the centre of said helix with a ductile; malleable metal wire, 'encasing said helix 'in'a second -ductile, 'malleable metal tube, swaging 'the ends of said second tube to' seal the helixther ein; draw- 'ing' said second tube down to a diametersuitable for insertion into said tubular casing and'cutting' from said second drawntube a section having the desired length for said element.

The tubular casing and impervious' receptacles are preferably constructedof a copper or aluminum-based alloy.

The explosive-abutting the ends of the receptacles may be 'anysuitable composition having suflicient explosive force to initiate"detonating'fuse and of sufficient sensitivity to be ignited by'theburningdelay composition such as lead az'ide, for example. If desired' the explosive charge can be comprised of two separate explosives, i. e. lead'azide which is sensitive to the burning delay composition may be placed next to the delay'element and pentaerythritol tetr-anitrate may be placed-between the lead azi-de' and the impervious receptacles.

The metallic element lying between the two' explosive charges is preferably of lead or a lead alloy'and theif'gasless delay composition containeditherein is preferably-of the lead oxide/silicon'metal mixture type.

The delay element when produced is seated in the tubular casing in a conventionalmanner. The=subsequent assembly of the delay device is also carried-out by conventional methods.

The invention will be-morereadily understood through reference to the accompanying drawings wherein:

Figure 1 represents a cut-away section lengthwise through a typicaldelay device embodied bythe scope of the invention;

Figures 2 to 6 represent various steps-inthemanufacture of the .delay element used in thedevice of the invention;

Figure 7 is a distribution diagram illustrating' thedevianating fuse held in the cup-shaped receptacle 2 which is.

in turn held by the tubular casing 3. 4 represents an explosive charge next to the element 5 carrying the spiral of gasless delay composition 6, while 7 indicates a circular crimp employed to position the element 5 during assembly and prior to the seating operation.

The method of manufacturing the delay element 5 for the short interval delay device of this invention is hereinafter described with particular reference to Figures 2 to 6 and with reference to a delay element of a specific size.

A tube of lead or lead alloy of about 1 inch outside and 0.5 inch inside diameter and about 16 inches long is swaged shut at one end. About 125 to 150 grams of delay composition is tamped into the tube and the open end of the tube is swaged shut. The sealed tube is then drawn down from 1 inch to approximately 0.25 inch outside diameter. Figure 2 illustrates the drawn tube 8 containing the delay composition 6.

A section of the drawn tube 8 containing the delay composition is subsequently wound tightly around a wire mandrel 9, as shown in Figure 3, to form a regular helix approximately 8 inches long and approximately 0.5 inch in outside diameter.

Then, as shown in Figure 4, the helix is removed from the mandrel and the void left in the helix by the removal of the mandrel is filled with a lead or lead alloy Wire 10. The helix and the lead or lead alloy wire 10 are placed in a second lead or lead alloy tube 11 swaged shut at one end. This second tube is about 1 inch outside diameter and of length and inside diameter just sufficient to receive the 8 inch length of helix. The open end of the tube 11 is then swaged shut and the tube is drawn down to a diameter such that sections of it may be readily inserted in the tubular casing 3 of the delay device.

The second drawing operation causes the helix to be drawn out and the delay composition core becomes very small in cross-section and extremely dense. The delay composition core is now in the form of a drawn out regular helix, each convolution of which requires about 3 inches of tube length. The drawing also causes all of the voids between the turns of the helix, between the helix and the lead wire filling 10, and between the helix and the second tube 11 to be completely filled and all the lead components become essentially solid lead.

Figure 5 illustrates a plan View of a section of the second lead tube 11 and its contents after the second drawing operation. 12 represents the compacted lead components while 6 represents the delay composition core contained therein.

Figure 6 shows in cross-section a section of the tube shown in Figure 5 which issuitable for use as a delay element 5 in the inventive device.

The tube of Figure 5 is cut into sections as shown in Figure 6 which are suitable for insertion in the delay device and which will give definite, predetermined delay intervals.

The following examples serve to illustrate the invention without thereby limiting its scope andrto differentiate over the prior art.

Example I Detonatingrelays of a nominal 50 millisecond delay were prepared according to the above-mentioned method using a red lead/ silicon delay composition. The explosive charges used were composed of lead azide and pentaerytly the ends of the delay element and P. E. T. N. charges between the lead azide charges and the respective impervious receptacles.

A random sampling of the relays so produced were fired and the delay times obtained were recorded. The

results of this test are shown graphically in Figure 7 which is a distribution diagram showing the distribution of the delay times obtained. The population, or number or relays, fired was 129. These relays as mentioned above were selected at random from production over a period of time. 5 l

Example 11 A number of relays as described and shown in French Patent No. 1,069,960 were obtainedfrom the patentee, Dynamit-Actien-Gesellschaft (DAG). These relays were of nominal 50 millisecond delay time and were constructed according to the said patent.

About 395 of the DAG relays were fired as in Example I and the delay times obtained were recorded. The results of this test are shown graphically in Figure 8 which is a distribution diagram showing the distribution of the delay times obtained.

' ritol tetranitrate. Lead azide charges were placed against Inspecting these diagrams, it can be seen that the relay of the present invention has a unimodal (i. e. singlepeaked) distribution, while the DAG relay is clearly :bimodal (i. e. double peaked). Hence, it is quite clear that the delay times obtained with the relay of the present invention are quite difierently distributed than those of the DAG relay. Whereas the relay of the present inventi-on has delay times clustered about one value, the DAG relay has delay times which fall roughly into two overlapping groups. I This indicates a difference in construction and/or functioning between the two relays.

It can also be seen that'the DAG relay is much more variable than the relay of the present invention with regard to delay times. It can be shown that the distribution of delay times for the relay of the present invention approximates very closely the theoretical normal distribution which is obviously not the case for the -DAG relay.

if the arithmetic mean and the standard deviation ofthe theoretical normal distribution are known, the distribution is completely defined and the percentage of all observations which would be expected to lie within certain values of the variable can be predicted. T-he arithmetic mean and the standard deviation of the observed delay times of the relays of Example I were found to be 51.8 and 4.39 milliseconds, respectively. Using these values and assuming a theoretical normal distribution, it was found that of the delay times should lie within :7.2 milliseconds of the arithmetic mean and 99% of the delay times should lie within i113 milliseconds of the arithmetic mean. From the test results of Example I and taking the 90% and 99% limits to be 7 and 11 milliseconds, respectively, it was found that in practice 91.5% of the observed delay times lie within :7 milliseconds of the mean and 99.2% of the observed delay times lie within :11 milliseconds of the mean. Thus, for the relay of the invention, theory and practice are in close agreement.

if these same tolerances: -7 and :11 milliseconds from the mean, are applied to the observed delay times of the DAG relay, it is found that only 45.3% and 70.6% respectively, of the observed delay times lie within these limits as compared wit-h 91.5 and 99.2%, respectively, for the relay of this invention.

In Figure 7, the limits of i7 and :11 milliseconds are shown by lines bb and a-a', respectively. These same limits when carried over to the distribution for the DAG relay are shown in Figure 8 again as lines b-b' and aa', respectively.

The DAG relay was found to have an arithmetic mean delay time of 54.6 milliseconds. However, since the dis- .tribution is bimodal, it can be seen by inspection from Hence, with the relay .of the invention as shown in Example I it can be predicted that in practice the delay time will be, in over 99% of the cases, within :11 milliseconds of the mean. On the other hand, with the DAG relay it can be roughly said that to make such a predic tion with the same degree of assurance, the limits would have to be extended to about :25 milliseconds as can be seen from Figure 8.

It is believed that the advantages of the present invention are due to the use in the delay element of a highly compressed gasless delay composition core having a helical shape. Since the core is a section of a helix, it, of necessity, is oil-centre in the delay element and does not follow a straight path through the element.

With certain straight delay composition core elements, it has been found that when they are subjected to the blast pressure from the detonated detonating fuse, the composition is blown through or from the element. This results in large deviations from the desired delay interval or in instantaneous firing of the detonating fuse on the other end of the relay.

The oil-centre characteristic of the delay core of the relay delay element of the present invention is believed to reduce the possibility of blow-through or to reduce its eifects since the core is not subjected to the higher pressure at the centre of the blast wave. The fact that the delay core does not follow a straight path and that its cross-sectional area is exceedingly small in comparison with the cross-sectional area of delay cores in the delay elements of relays previously known is believed also to reduce the possibility or effect of blow-through.

Furthermore, the compression of the delay composition due to the two drawing operations results in a delay composition core which is extremely dense. This also is believed to offer exceptional resistance to the blast pressure, thus further reducing the danger of full or partial blow-through.

It is believed that one or more of these features combine to produce the superior delay time characteristics of the present invention.

Helical shaped delay elements have heretofore been known in the blasting art, as witnessed by United States "Patent No. 1,493,881 issued to Jones et al., May 13, 1924. Jones et al. describe a delay element for a safety igniter comprising a tubular helix containing a rapidly combustible material, the tubular helix being imbedded in an easily fusible material.

It should be noted in the first place that delay elements for safety igniters or blasting caps are not necessarily successful or operative in detonating relays. The delay elements of safety igniters or blasting caps are only subjected to a flame before ignition, whereas the delay elements of detonating relays are subjected to the full force of the blast pressures generated by the detonating fuse.

Furthermore, the deficiency of helical shaped delay elements different from the element of this invention can be readily shown. A delay element somewhat similar to the Jones et a1. element was prepared according to the procedure of United States Patent No. 2,757,566 dated August 7, 1956. It was found to be impossible to produce such a delay element which would, when installed in a relay such as that of the present invention, give a delay interval of the same order, i. e. 50 milliseconds, as in Examples I and H without a very large number of misfires. An attempt was made to produce such delay elements which would give a delay interval of the order of 200 milliseconds. One hundred such delay elements were produced and installed in relays according to the present invention. When fired it was found that 94 of these relays had an average delay time of 191 milliseconds with 6 complete misfires. The actual observed delay times ranged from to 275 milliseconds.

What we claim is:

1. A short interval delay blasting device adapted to be inserted between two lengths of detonating fuse which comprises in combination a tubular casing, two impervious receptacles adapted to receive the ends of said lengths of detonating fuse partially encased and supported in symmetrical opposing relation-ship by the tubular casing at the ends thereof, two explosive charges abutting the closed ends of said receptacles externally thereof and a metallic element lying intermediate said two explosive charges, said element being solid except for a core of highly compressed gasless delay composition having a helical shape and said element being produced by charging and compacting the delay composition into a ductile, malleable metal tube until the tube is filled, swaging the ends of the tube to seal the composition therein, drawing said tube down to a predetermined diameter, winding said drawn tube around a mandrel to produce a regular helix, removing said mandrel and filling the void left in the centre of said helix with a ductile, malleable metal wire, encasing said helix in a second ductile, malleable metal tube, swaging the ends of said second tube to seal the helix therein, drawing said second tube down to a diameter suitable for insertion into said tubular casing and cutting from said second drawn tube a section having the desired length for said element.

2. A short interval delay blasting device as claimed in claim 1 in which said tubes are of material selected from the group consisting of lead and lead alloys.

3. A short interval delay blasting device adapted to be inserted between two lengths of detonating fuse which comprises in combination a tubular casing, two impervious receptacles adapted to receive the ends of said lengths of detonating fuse partially encased and supported in symmetrical opposing relationship by the tubular casing at the ends thereof, two explosive charges abutting the closed ends of said receptacles externally thereof and a metallic element lying intermediate said two explosive charges, said element being solid except for a core of highly compressed gasless delay composition having a helical shape and said element being produced by charging and com pacting the delay composition into a tube until the tube is filled, said tube being of material selected from the group consisting of lead and lead alloys and having outside and inside diameters of about 1 and 0.5 inch, respectively, swaging the ends of the tube to seal the composition therein, drawing said tube down to about 0.25 inch outside diameter, winding said drawn tube tightly around a wire mandrel to produce a regular helix the convolutions of which are in contact with each other, removing said mandrel and filling the void left in the centre of said helix with a lead or lead alloy wire, encasing said helix in a second tube, said second tube being of material selected from the group consisting of lead and lead alloys, of outside diameter about 1 inch and inside diameter such as will just receive said helix, swaging the ends of said second tube to seal the helix therein, drawing said second tube down to a diameter suitable for insertion into said tubular casing and cutting from said second drawn tube a section having the desired length for said element.

References Cited in the file of this patent UNITED STATES PATENTS 1,493,881 Jones et a1. May 13, 1924 FOREIGN PATENTS 1,069,960 France Feb. 17, 1954

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