US2636437A - Closure assembly for the discharge end of blasting devices - Google Patents

Description

April 28, 1953 F. A. LOVING, JR 2,636,437

CLOSURE ASSEMBLY FOR THE DISCHARGE END OF BLASTING DEVICES Filed Feb. 29, 1952 III/III,

IN VEN TOR.

Fran/ 6A .Lomlgfi Mu Patented Apr. 28, 1953 UNITED STATES CLOSURE ASSEMBLY FOR THE DISCHARGE END F BLASTING DEVICES Application February 29, 1952, Serial No. 274,254

4 Claims.

The present invention relates to an improvement in blasting devices. More specifically, the present invention relates to an improved closure assembly adapted to be used in a reusable, pressure-resistant blasting tube.

It has been found that coal can be safely and economically broken down by the sudden release of gas under high pressure when this gas is properly directed. To accomplish blasting operations utilizing this finding, a blasting cartridge has been developed which consists essentially of a strong, pressure-resistant tube which is inserted in the borehole and which has a release mechanism at the end inserted. In one form of operation of this device, compressed air is forced into the pressure-resistant tube in the borehole until a predetermined pressure is reached which serves to operate the release mechanism. In another variety of blasting cartridge, independent of a compressed-air line, one end of the strong, pressure-resistant metal tube is closed with a so-called electrical firing head, and the other end is closed with a discharge head including the release mechanism. Two main types of charges are used in this variety of blasting cartridge to produce the high-pressure gas; those wherein the material is charged under pressure outside of the mine, and, after insertion of the tube in the borehole, increased pressure is produced by the application of heat, e. g., carbon dioxide, and those wherein the gases are produced by the chemical decomposition of a solid, e. g., ammonium nitrate.

In a copending application filed by Davis, Glogau, Loving, and Swed, Serial No. 174,818, an improvement in the latter type of charge is disclosed. According to this application, the charge is packaged in a cylindrical container of lesser diameter than the inside diameter of the tube, thereby avoiding packing of the composition in any portion of the tube, and thus permitting a more even development of pressure.

Regardless of the type of charge used, it is important that the blasting tube be securely sealed against pressure loss until the actual blast occurs. The most commonly used closure device is that wherein the aperture from the tube body to the discharge head is blocked by a disc, usually of metal, which will rupture at some predetermined pressure, such as, for example, 18,000 to 24,000 pounds per square inch. The disc is positioned between the shoulders formed at the threaded connections of the tube body and the discharge head. In order to effectuate a tight closure, it has become customary to provide a gasket on one or both sides of the disc, and to tighten the discharge head severely while the tube body is clamped to prevent rotation. The tightening is performed with heavy wrenches and the same equipment is required to remove the discharge head in order to replace the disc after a blast.

Even though high torques are applied to the threaded closing parts. the seal has not been completely satisfactory. In many cases, the disc, which is usually stamped from sheet metal, is neither exactly fiat nor free from minor pits and depressions. Small particles of foreign matter on the shoulder of the tube-body or the discharge head may interfere with the seal. The nad ertent omission of a gasket will render the seal imperfect. Regardless of the cause, an inadequate closure may produce serious damage to the device because of the erosive properties of the gas under high pressure, or may result in a misfire where confinement is required in order for the decomposition of a solid to be self-sustaining.

It is an object of the present invention to provide a closure assembly wherein the probability of leakage is reduced. A further object of the present invention is to provide a closure assembly wherein severe tightening of the elements is not required. A still further object of the present invention is to provide a closure assembly capable of repeated use without replacement of gaskets or other parts. Additional objects will become apparent as the invention is further described.

I have found that a highly satisfactory closure may be obtained without requiring severe tightening when I provide a movable sleeve at the high pressure side of the discharge orifice, said sleeve containing at least one sealing element about the periphery thereof and at least one sealing element at the end adjacent to the rupture disc.

In order to describe the invention more completely, reference is made to the accompanying drawings, in which:

Figure 1 represents a partial view of a blasting tube, showing one embodiment of the closure assembly of the present invention;

Figure 2 represents a detail view of a sleeve separated from the blasting device; and

Figure 3 represents a second embodiment of the present invention.

In the figures, the tube body I is connected to the discharge head 2 by means of threads 3. The discharge head 2 is hollow and contains thermo-plas'tic .physical properties. In the drawings, the sealing venting ports :1 and aperture 5, the latter being present to facilitate removal of the sheared disc after firing. Extending beyond the threads 3 is the shoulder 6 of the discharge head 2. :Positioned within the tube body 1 is the sleeve 7 containing the sealing elements 8 and 9. Rupture disc I0 is secured between the shoulder 6 and the sleeve i. To prevent sleeve 1 from slid ing toward the electrical firing head end -(not shown) of tube body I, a portion of the tube body I is upset to form shoulder I I In assembling the closure unit of the present invention, sealing elements 8 and 9, for example O-rings, are placed in the proper channels of sleeve 7, and the sleeve I is pressed into the tube body l until stopped by shoulder H. The disc 10 is then inserted, and discharge head 2 screwed on and hand-tightened When the blasting tube is charged or initiated, the pressure increase tends to force sleeve 1 into tighter engagement with disc I0, and to force the sealing elements a and 9 towards the edge of disc i0 facing the tube body I. Since movement of the sealing elements ll and 9 is restricted by the channels in the sleeve 1, they form a highly eificient seal.

After the tube has been discharged, and pressure is no longer acting on sleeve 1, the discharge head is easily unscrewed, and the remaining portion of the rupture disc removed. Only a simple visualinspection is required to determine whether sealing element 9 has been damaged or can be reused. If damaged, it is simply replaced. Damage to scaling element 8 is less likely, but if it occurs, it can generally be noted without removal of sleeve 7 because portions of the seal will have been extruded to the disc area. Reassembly is then made as previously described.

With a closure assembly as described herein, it is possible to use roughly fabricated rupture discs, and to eliminate the need for clamps and heavy wrenches, and the time-consuming efiorts to tighten and loosen the dischargehead previously required. At the same time, the seal obtained is excellent, and the parts required are simple and-inexpensive. In the event a leak does occur, most of the scoring damage will be on the sleeve, thus making the repair a simple matter.

Formy sealing element, I prefer to use a synthetic rubberihaving a high-resistance to oil, thus permitting :heavy oiling of the threads. How-- ever, any resilient, rubber-like material may be use. Obfiously, the sealing material must'be both compressible and resilient to form a good seal and to be reusable. As suitable materials, I might use natural rubber, synthetic rubber, and the polymers having rubber-like elements are shown in the form of O-rings, and theseare preferred. However, ,itis not'essential that the sealing element be circular in cross-sec- 4 tion, nor that the channel in the sleeve be squared. The sealing element will preferably have a thickness equal to about ten percent (10%) more than the depth of the groove.

The diameter and thickness of the sleeve depends primarily on the diameter of the tube and the required orifice size. The sleeve should fit very closely, so that the sealing element will not be extruded past the channel under high pressure. The length of the sleeve is entirely a matter of choice, with the minimum length being that just sufiicient to provide the required channels. A typical sleeve made in accordance with the present invention has an outer diameter of 1.748 in., an inner diameter of 11 g in., a length of 1 in., andthe channels are 0.113 in. in depth. The O-ring has a cross-section diameter of A; in., and the inner diameter of the tube at the portion adapted to retain the sleeve is 1.750 in.

While I have illustrated a tube having a shoulder to limit the inward travel of the sleeve, other means may be used, or, if the sleeve fits very tightly within the tube, the limiting element may be omitted.

The sleeve may be made of any rigid material, steel being preferred. Many other modifications may be made without departure from the spirit of the present invention. Therefore, I intend to be bound only by the following claims.

Iclaim: v

1. A closure assembly for the discharge end-of a reusable pressure resistant blasting tube of the type wherein the said discharge end is internally threaded which comprises a,h0llow :discharge head in threaded engagement with said tube, a shear-disc adjacent to the interior end of said discharge head and of larger diameter than the inner diameter of said discharge head, and a sleeve within said tube adjacent the .said shear-disc on the side opposite the said discharge head, said sleeve being of slightly smaller diameter than that portion of said tube and having an annular groove at the end adjacent to said disc and at least one peripheral groove, each of said grooves containing a resilient sealing element of greater thickness than the depth of said groove.

2. ,An assembly as claimed in claim 1,-wherein the resilient sealing elements are of rubb ri material.

'3. An assembly :as claimed in claim 11, wherein the resilient sealing element isgsynthetic rubber in the form of an O-ring.

4. .An assembly as claimed in ,claim .1, wherein the thickness of the sealing -:element:is equalito about ten percent 10%) more than the depth-pf the groove.

FRANK A Ja.

vNo referencescited.

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