US3244102A

US3244102A - Secondary blasting unit

Info

Publication number: US3244102A
Application number: US381439A
Authority: US
Inventors: Iii George Thomas Wofford; James E Darrough; Mcferrin William Don
Original assignee: Individual
Current assignee: Individual
Priority date: 1964-07-09
Filing date: 1964-07-09
Publication date: 1966-04-05
Anticipated expiration: 1983-04-05

Description

April 1966 G. T. WOFFORD m, ETAL 3,244,102

SECONDARY BLASTING UNIT Filed July 9, 1964 m D l ROW T Fm O 5 RA W A O T A O E V E N AM E J L G H W W E G 3 2 2 2 ATTORNEYS United States Patent 3,244,102 SECONDARY BLASTING UNIT George Thomas Wofford III, James E. Darrough, and William Don McFerrin, all of 1560 Idlewild Drive, Reno, Nev.

Filed July 9, 1964, Ser. No. 381,439 Claims. (Cl. 10224) The invention relates to the movement of rocks, earth comparable material by explosive techniques and is especially concerned with a device for use after an initial blast has broken up the terrain for reducing large rocks, boulders and the like into fragments which can be more readily handled.

When an explosive charge is detonated to blow down a rock wall or to dislodge comparable materials from their original place, there is a good deal of shattering and fragmentation of the material, but in some formations and under many conditions there still result bodies of rock or integral material too large to be readily handled and requiring further breaking down.

It is a particular object of the invention to provide a portable secondary blasing unit which can be hand carried and can be placed on a large body of such material and which when detonated will cause fragmentation of the body into pieces which are readily handled and will in effect cause the body to be reduced to small fragments.

Another object of the invention is to provide a sec ondary blasting unit which can be utilized with safety, yet which is effective to produce the result desired.

Another object of the invention is to provide a sec ondary blasting unit so arranged as to utilize the capabilities of a shaped explosive charge so as to concentrate the effect of an explosion onto a particular body to be fragmented and in a particular path.

Another object of the invention is to provide a sec ondary blasting unit which can easily and cheaply be manufactured and which is reliable in its operation.

Another object of the invention is to provide a secondary blasting unit so constructed as to be usable not only in the atmosphere under ordinary circumstances, but also to be usable subaqueously when occasions require.

Another object of the invention is in general to improve secondary blasting units.

Other objects together with the foregoing are attained in the form of the invention described in the accompanying description and illustrated in the accompanying drawings, in which:

FIGURE 1 is a plan of one form of secondary blasting unit constructed pursuant to the invention;

FIGURE 2 is a bottom plan view of the structure shown in FIG. 1;

FIGURE 3 is a transverse vertical cross section, the plane of which is indicated by the line 3-3 of FIGURE 1; and

FIGURE 4 is an enlarged, fragmentary, side elevational view of the radial boss showing the arrangement of the exterior-opening detonating cap cavity and, in outline, the interior opening recesses containing the two ends of the primer cord.

A practical embodiment of our secondary blasting unit, one which has served to illustrate and carry out the principles of the invention includes a casing 6. This is conveniently fabricated with a substantially uniform wall. A suitable material is a plastic that can be readily molded into an approximately or substantially dome shape. The dome is planar in the upper central portion 7 and has curved Walls 8 surrounding the central portion. The entire dome is preferably symmetrical about a central axis 9 except for minor deviations. The dome terminates in a peripheral rim 11 and encloses a central chamber 12.

3,244,102 -Patented Apr. 5, 1966 Conveniently the rim 11 is extended in one area to afford a carrying handle 13.

Designed to fit on and cooperate with the dome casing in enclosing the cavity 12 is a cover 16. This is likewise symmetrical about the central axis 9 when in position and is coterminous with the rim 11. To secure the cover 16 on the casing both parts are formed with appropriate mating portions. Upstanding around the edge of the cover is a contoured rib 17 substantially like an arrowhead in cross section. This is received in a corresponding groove 18 within the rim 11. When the cover 16 is forced upon the casing, the parts snap together and are permanently retained during normal storage and transport. The cover also is provided near or on its rim with three feet 19 conveniently quite sharp.

The cover 16 is not fiat, but has a particular configuration in order to take advantage of the characteristics of a shaped charge of explosives. Preferably the cover 16 is of a shallow or relatively flat conical configuration for the most part symmetrical about the axis 9. Also, the cover is contoured to define a semi-toroidal concavity 20 opening outwardly and terminating on the conical portion of the cover so that the cone of action 21 of the toroidal portion, as illustrated by the

lines

22 and 23, is symmetrical with the axis 9 and converges downwardly away from the chamber 12.

Within the chamber 12 a charge 25 of an explosive is situated. Disposed in juxtaposition to the explosive charge and arranged symmetrically in an annular channel 26 forming part of the casing 6 is a cord primer 27 effective when ignited to ignite the charge 25. The cord primer 27 is referred to as Primacord in the trade. It terminates in a pair of ends each received in one of a pair of interiorly opening

recesses

31 and 32 formed in a radial boss 33 projecting outwardly from the channel 26 and from the curved portion 8 of the dome 6. The ends of the Primacord are substantially parallel to each other and are firmly secured by frictional fit within their individual recesses.

Particularly in accordance with the invention, the ends of the Primacord 31 and 32 are not exposed exteriorly of the blasting unit, but rather are protected from the outside by the closed ends of the recesses. The boss 33 is additionally provided with an exterior opening cavity 34 which does not communicate with the chamber 12 but does extend alongside of and close to the

recesses

31 and 32, leaving therebetween relatively thin,

plastic walls

36 and 37. The thickness and resistance of the

walls

36 and 37 is such that a detonating cap disposed within the cavity 34 and exploded is effective to shatter the

frangible walls

36 and 37 and to ignite the Primacord which sets off the charge 25.

In the preferred manner of use of the device, it is placed fully charged and provided with a detonating cap on the object to be fragmented. This is often a boulder or large rock and the legs or feet 19, being relatively sharp or pointed, engage into recesses or concavities in the rock so that the blasting unit is firmly and easily put into position. The direction of the expected blast is arranged to correspond generally to the direction of the central axis 9. By utilizing the handle 13 and otherwise orienting the casing of the unit, it can be positioned so that the blast direction is as desired. The placement can be in the atmosphere or under water since the entire charge and the Primacord are completely protected from the atmosphere and deleterious external influences by the tightly engaged cover and casing.

Once the secondary blasting unit has been appropriately positioned, the detonating cap is appropriately set off and the Primacord is ignited through the so-fractured, intervening

frangible walls

36 and 37. The ignited Primacord, being arranged in a nearly closed loop and acting very quickly, in turn sets otf the charge 25 by almost simultaneous ignition of a top, ring-like portion substantially above the concavity 2t). This affords what we call ring ignition and is productive of improved detonation of the explosive charge and accentuates the efiect of the toroidal blast. The force of the explosion is directed not only by the curved walls 8. the planar wall 7 and the conical wall 16, but particularly is directed and channeled by the configuration of the toroidal portion 20 so that a concentrated, convergent blast is directed downwardly along the central axis 9.

In practice it has been found that rocks or boulders of several cubic feet in content can be shattered to crusher size by the use of a secondary blasting unit of the configuration and characteristics described herein.

What is claimed is:

1. A secondary blasting unit comprising:

(a) a casing of substantially dome shape terminating in a lower circular rim and being substantially concentric with a central axis;

(b) a radial boss on the upper portion of said casing,

said boss being formed with an exterior-opening cavity to receive a detonating cap, said boss also including a pair of interior-opening recesses alongside said cavity and separated therefrom by frangible walls;

(c) a bottom cover mounted on and extending across said lower circular rim of said casing, said cover including a downwardly opening, semi-toroidal concavity concentric with said central axis;

(d) an explosive charge in said casing; and,

(e) a primer cord in said casing in contact with said charge, said cord being annularly disposed substantially concentric with said central axis and with a diameter substantially equal to the mean diameter of said semi-toroidal concavity, the ends of said primer cord terminating in said recesses.

2. The device of claim 1 further characterized by at least two legs extending downwardly from said cover, said legs having a height not greater than one-fifth the height of said casing.

3. The device of claim 1 wherein said casing is provided with a handle extending from said rim.

4. A secondary blasting unit comprising:

(a) a dome-shaped casting substantially concentric with 1 a central, vertical axis, said casting terminating in a substantially circular lower rim;

(b) a bottom cover substantially circular in outline mounted on said lower rim and entirely enclosing the bottom of said casing, said cover having formed therein a downwardly opening semi-toroidal concavity substantially concentric with said central vertical axis;

(0) a radial boss on the upper portion of said casing,

said boss being formed with an exterior-opening cavity to receive a detonating cap, and a pair of interioropcning recesses alongside said cavity and separated therefrom by frangible walls;

(d) an explosive charge in said casing;

(e) an annular channel on the upper portion of said casing substantially concentric with said central axis, said channel being in communication at its opposite ends with said pair of recesses and open at the bottom to said explosive charge; and,

(f) a primer cord formed into a loop within said annular channel, the ends of said cord terminating in said pair of recesses and being ignitable by a detonating cap detonated, within said cavity, said cap being capable of shattering said frangible walls separating said cavity from said pair of recesses.

5. A secondary blasting unit as in claim 4 in which said cover is provided with legs and in which said casing is provided with a handle.

References Cited by the Examiner UNITED STATES PATENTS 2,513,233 6/1950 Byers 10224 2,839,997 6/1958 Church et al 10224 2,984,307 5/1961 Barnes 10224 2,988,994 6/1961 Fleischer et al. 10224 3,117,518 1/1964 Porter et al. 10224 3,119,178 1/1964 Owen et a1 102-24 FOREIGN PATENTS 1,092,563 11/1954 France. 1,051,708 2/1959 Germany.

90,705 12/1957 Norway.

ENJAMIN A. BORCHELT, Primary Examiner.

Claims

1. A SECONDARY BLASTING UNIT COMPRISING: (A) A CASING OF SUBSTANTIALLY DOME SHAPE TERMINATING IN A LOWER CIRCULAR RIM AND BEING SUBSTANTIALLY CONCENTRIC WITH A CENTRAL AXIS; (B) A RADIAL BOSS ON THE UPPER PORTION SAID CASING, SAIDBOSS BEING FORMED WITH AN EXTERIOR-OPENING CAVITY TO RECEIVE A DETONATING CAP, SAID BOSS ALSO INCLUDING A PAIR OF INTERIOR-OPENING RECESSES ALONG SIDE SAID CAVITY AND SEPARATED THEREFROM BY FRANGIBLE WALLS; (C) A BOTTOM COVER MOUNTE ON SAID EXTEDNING ACROSS SAID LOWER CIRCULAR RIM OF SAID CASING, SAID COVER INCLUDING A DOWNWARDLY OPENING, SEMI-TOROIDAL CONCAVITY CONCENTRIC WITH SAID CENTRAL AXIS; (D) AN EXPLOSIVE CHARGE IN SAID CASING; AND, (E) A PRIMER CORD IN SAID CASING IN CONTACT WITH SAID CHARGE, SAID CORD BEING ANNULARLY DISPOSED SUBSTANTIALLY CONCENTRIC WITH SAID CENTRAL AXIS AND WITH A DIAMETER SUBSTANTIALLY EQUAL TO THE MEANS DIAMETER OF SAID SEMI-TOROIDAL CONCAVITY, THE ENDS OF SAID PRIMER CORD TERMINATING IN SAID RECESSES.