US2996232A - End closures - Google Patents

Description

Aug. 15, 1961 s. E. WALKER END CLOSURES Filed Sept. 14, 1956 INVENTOR SAMUEL E. WALKER BY 66 Q AiiiNEY Unite The present invention relates to end closures for tubular shells of the type used in the manufacture of blasting cartridges. More particularly, the present invention relates to a closure of this type having improved strength and sealing characteristics in comparison with closures which have heretofore been known in this art.

In the manufacture of blasting cartridges, it has long been the practice to form tubular shells of a spiral paper column which is severed into individual tubes of desired lengths. One end of the tube is then crimped closed by means of a cooperating mandrel and crimping head, with or Without the addition of a reinforcing disc. Glue is customarily applied on appropriate areas to provide a firm and effective crimp closure. A suitable apparatus for the formation of crimp closures of this type is described in copending application Serial No. 552,851 filed December 13, 1955, in the name of U. P. Jennings and E. F. Lewis, corresponding to U.S. Patent No. 2,769,377 issued November 6, 1956.

Upon formation of this closure, which may be called the bottom crimp, the cartridge is filled with powder or other blasting agent and the filled shell is customarily closed on the top with a similar crimp closure.

Experience has shown that the bottom crimp which is formed on the empty tube generally provides a strong and effective closure since a mandrel may be used to back up the crimping head thus making possible the application of extreme pressures in the crimping operation. Also, the components of the bottom crimp can be glued before the shell is waxed. Wax is usually applied to paper cartridges of this type to enhance the water resistance of the finished cartridge and to resist penetration of nitroglycerin in those cases where nitroglycerin is a component of the explosive. In the case of a top crimp closure, however, it is not possible to use a mandrel and the only back up to the crimping head is the powder column which is somewhat compressible. In addition, glue will not adhere very well to shells to which wax has been applied. It is, therefore, not possible to provide filled cartridges with crimp closures on their top ends that are consistent in appearance and quality.

Top end crimp closures have several main disadvantages. They are non-uniform in configuration and appearance. They are non-siftproof, i.e. small amounts of the explosive contents of the cartridge can leak through the crimp. This necessitates a separate liner for the box in which the cartridges are stored and shipped. They have poor resistance to popping. The latter occurs when the crimp actually opens or unfolds outwardly and is caused by the natural resistance of paper to folding. When a crimp has popped, the cartridge has lost most of its strength at that end; heavy sifting occurs, and any rough handling in subsequent operations may cause spillage. Not only is sifting and spillage dangerous because of the obvious hazard of loose explosive material, but an additional problem is encountered in the case of nitroglycerin-containing explosives because of the headaches which result when people are directly exposed to nitroglycerin fumes, as is well-known in the art.

In addition, cartridges provided with crimp closures at the top end easily become out-of-round due to sideto-side compression if the shells are stored in a vertical stack several rows high. This is a. serious problem with blasting cartridges. Cartridges on the bottom of such a stack having top end crimp closures are frequently deformed to an oval shape. For example, many instances have been noted in which 6-inch diameter shells have been deformed out-of-round by as much as 2 inches at the top end. Out-of-roundness is objectionable in appearance, causes difficulties in loading boreholes, and increases the tendency of the cartridge to pop and the contents to sift or spill.

It is an object of the present invention to provide an end closure for filled tubular shells which has better strength and sealing characteristics than the crimp closures which have heretofore been used. It is a further object of the present invention to provide an end closure which is safe, convenient, and easy to install. Other and additional objects will become apparent from a consideration of the ensuing specification and claims.

My superior end closure employs an entirely separate unit which is inserted into the open upper end of the filled cartridge. For this reason I call my novel closure an insert closure, as compared with the crimp closures of the prior art which are integral, at least in part, with the wall of the shell. My insert closure consists essentially of a shallow cup having a flat disc pressed into its base and a heavy-duty reinforcing ring atop the disc. The insert closure is placed as a unit into the open upper end of the filled cartridge, as will be more particularly hereinafter described. The insert closure may be glued in position or it may simply be held in position by tight frictional engagement with the inner wall of the shell.

To illustrate the insert closure of my invention reference is made to the accompanying drawing in which FIG- URE 1 represents a cross-sectional view of an insert closure, FIGURE 2 illustrates the closure of FIGURE 1 secured in position in the mouth of a filled shell.

In FIGURES 1 and 2, C represents in its entirety an insert closure of my invention consisting of a shallow cup 1 which has a disc 2 pressed into its base and a heavyduty reinforcing ring 3 superimposed upon the disc. The cup 1 consists of a base member 11 having a unitary peripheral lip '12 integral therewith at right angles to the base member. The outer rim 13 of the lip 12 lies directly adjacent to reinforcing ring 3 at right angles thereto and provides a sharp-cornered ledge which, when within the confines of tubular shell 4 (FIGURE 2), tends to infix itself securely into the inner surface of the shell to prevent expulsion of the closure unit C.

FIGURE 2 illustrates the insert closure C in position at the top end of a shell 4 containing a blasting agent or explosive composition 5. The base of the shell has previously been provided with a tapered crimp closure 6 while the shell was still empty, as described above. Glue may be applied on any one or more of the surfaces 7, 8, 9, and 10 to provide a stronger and more effective closure. If the shell is waxed, as is common in the art, it will not be feasible to use glue on surface 8, and the closure must be retained in position solely by means of its tight frictional engagement with the inner wall of the shell 4. In the normal case the outer end of the reinforcing is flush with the top end of the shell, as depicted in the drawing.

The cup 1, the disc 2 and the heavy-duty reinforcing ring 3 may be formed of a wide variety of commonly available materials provided only that the reinforcing ring is considerably stronger and more difficult to crush, deform or compress than the other two elements. For example, the cup 1 may be formed of cardboard, fiberboard, kraft paper, thin plastic sheeting or the like. The disc 2 may be cut or stamped from similar materials as well as from thin wood. The reinforcing ring 3 may be of extremely heavy-duty kraft paper or chipboard, or multiply heavy-duty cardboard, or it may be formed of wood or plastic or metal. In the normal case, for reasons of economy, the cup and disc will be made of light-duty kraft paper, paperboard, cardboard or fiberboard while the reinforcing ring will be made of extra heavy-duty chipboard or kraft. In such cases the crosssectional thickness of the reinforcing ring will normally be at least about 2 /2 to 3 times that of either the cup or the disc.

The length of the reinforcing ring may vary widely except that experience has demonstrated that resistance to abuse is increased in direct relation to the length of the ring. Also shallow inserts tend to tilt or cock in the shell. Reinforcing rings having a length 2 to 3 times that of the lip of the cup 1 have proven especially satisfactory in all respects.

As noted above the insert closure of my invention may be fixed firmly in position by the application of glue to surface 8 except where the shell is provided with a Wax coating in which case the closure is retained firmly in position by frictional engagement with the shell. For this purpose the outer diameter of the cup 1 is made slightly larger than the inner diameter of the shell 4. Satisfactory closures have been prepared with cups having an outer diameter as large as 0.040 inch greater than the inner diameter of the shell, but in the normal case this overage will be restricted to about 0.015 inch for ease of insertion. This slightly oversized cup will actually cause a mild bulge in the wall of the shell, as indicated at 12 in FIGURE 2, and insures a snug frictional fit of the closure.

The closure of the present invention may be inserted manually or with hand tools without difiiculty. For reasons of economy, however, the insert closure will normally be placed into position, with or without glue, by a suitable automatic inserting apparatus (not shown) of any appropriate design. With such an apparatus, the insert closure of the present invention is readily adaptable to mass-production manufacturing techniques which is extremely important from an industrial standpoint.

The insert closure of my invention is advantageous in numerous respects over the crimp closures which have heretofore been used in the art at the top end of a cartridge. With the insert closure, a considerably smaller mass of paper rests atop the powder than is the case with the crimp closure and there is thus less interference with the propagation of the explosion from cartridge to adjacent cartridge in a column. Furthermore, the tapered crimp 6 at the bottom of a next adjacent cartridge will generally nestle into the central cavity formed by the reinforcing ring 3 thus tending to provide a continuous column of explosive cartridges in the borehole.

The insert closures of my invention are considerably stronger and more resistant to popping than the crimp closures heretofore used and are likewise considerably more resistant to deformation by dropping and to out-ofround deformation by side-to-side compression. These numerous advantages are all obtained with little or no sacrifice in cost or case in manufacture.

A number of tests have conclusively demonstrated the superior strength characteristics of my novel insert closure. A series of several drop tests were performed in which loaded cartridges having crimp closures on both ends were dropped repeatedly until an end closure fractured or failed. The results of these drop tests were compared against similar tests wherein the loaded cartridge had a bottom end crimp closure but an insert closure on the top end. For one of these drop tests, the cartridge /8 inch diameter) was suspended in each instance at a 45 degree angle with its lowermost portion 4 feet above a concrete floor. The cartridge was released and allowed to fall to the concrete. The cartridge was then elevated to the same suspended position, but 180 degrees out of phase (i.e., the end which was farthest from the floor at the prior drop is now closest), and dropped again. With 4 l unwaxed shells, the cartridges having frictionally engaged top end insert closures generally required 50% more drops before failure occurred than did a series of shells having a variety of top end crimp closures. Insert closures (unwaxed shells) which were glued in, on the other hand, withstood better than twice the number of drops than the top end crimp closures did before they failed. With cartridges having waxed shells, friction fit top end insert closures were only slightly better than top end crimp closures, but glued top end insert closures sustained ahnost 2 /2 times as many drops before failing as did the crimp closures. Similar tests were run holding the cartridge parallel to the concrete floor before dropping rather than at an angle, and the results were very much the same.

In order to study the resistance of various end closures to side-to-side compression, a series of shells were placed under compression in a Tinius-Olson Compression Tester and the forces required to compress the closure a given distance were observed. For these tests, 3-inch long sections of a 4-inch diameter shell, closed at one end, were used. On the average, insert closures required 2 to 5 times as much compressive force to deform the closure inwardly by A of an inch than did the crimp closures. Complete failure by out-of-round deformation was determined visually as being that point at which the closure was so badly deformed that its inherent resilience could not be relied upon to return it to a serviceable condition. Here again, complete failure of the insert closures required forces on the average of about 2 to 5 times greater than did complete failure of a variety of crimp closures.

It is possible in some instances, depending upon the size of the cartridge and the nature of the charge, to eliminate the disc 2 from the insert closure if the cup 1 is made from heavier material than is normally required. Such a closure would be somewhat inferior (though operable) in a number of respects to the insert closure depicted in FIGURE 1 and the latter represents by far the preferred form of the invention.

My invention has been described clearly in the foregoing specification. It will be understood, however, that many variations in details of material, shape, and configuration of components and the assembly thereof may be made without departing from the scope of the invention. I, therefore, intend to be limited only by the following claims.

I claim:

1. An end closure for the tubular shell of a blasting cartridge comprising a shallow cylindrical cup having a unitary lip at right angles to a base member, said cup being disposed entirely within the confines of one end of the said shell such that the base member closes said end of said shell and the open side of the cup faces outwardly with the unitary lip in snug contact with the inner tubular surface of said shell, said shell completely covering and encompassing the said lip, the outer diameter of said lip being greater than the inner diameter of said shell by an amount up to about 0.04 inch, a circular disc having a diameter substantially equal to the inner diameter of the peripheral lip of the cup and positioned within the cup flat against the outward face of the base thereof, and a reinforcing ring having an outer diameter substantially equal to that of the disc positioned within the cup atop the disc and extending at least a short distance out of the cup past the outer end of the lip of the cup, said reinforcing ring being formed of heavy-duty material relative to the material of which the cup and disc are formed, the continuous outer rim of the unitary peripheral lip of the cup which lies at right angles to the adjacent reinforcing ring constituting a continuous ledge which infixes itself securely into the inner surface of the tubular shell to prevent expulsion of the end closure.

2. An end closure as in claim 1 in which the crosssectional thickness of the heavy-duty reinforcing ring is at least about 2 /2 times as great as that of either the cup or th c.

3. An end closure as in claim 1 in which the cup, the disc, and the reinforcing ring are secured into a uniform closure assembly by means of glue.

4. An end closure as in claim 1 wherein the unitary insert closure is fixed in said tubular shell by frictional engagement of the oversized lip of the cup with the inner wall of the shell.

5. An end closure as in claim 1 in which the unitary insert closure is secured in said shell by means of glue on the outer face of the lip of the cup.

References Cited in the file of this patent UNITED STATES PATENTS Jenkins Sept. 28, 1909 Koontz May 29, 1917 Saucier Feb. 27, 1923 Chapman et a1. Mar. 20, 1945 Simmons June 19, 1951 Hall et a1 May 4, 1954 Gibbs Dec. 25, 1956

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