US2388232A - Stemming device for explosive charges - Google Patents

Description

Oct c. o. TAPPAN 2,388,232

STEMMING DEVICE FOR EXPLOSIVE CHARGES Filed May 8, 1941 2 Sheets-Sheet 1 ATTORNEY.

Oct. 30, 1945. c, O TAPPAN 2,388,232

STEMMING DEVICE FOR EXPLOSIVE CHARGES Filed May 8, 1941 2 Sheets-Sheet 2 INVENTOR; Cfiaries 0. 70? an.

Patented Get. 30, 1945 STS STElVIll/IING DEVICE FOR EXPLOSIVE CHARGES East Hartford, Conn.

Application May 8, 1941, Serial No. 392,468

8 Claims.

The present invention relates to an improvement in blasting plugs and has for its principal object an improved means for stemming explosive charges, in blasting work, in rocks, coal, and similar materials.

In current practice'it is well known to drill holes, in the blasting of rock, coal and the like and in charging the said holes, the blasting charge being usually detonated by an electric current, this being the usual practice. It is also current practice to increase the explosive force of the blasting charge by stemming the charged hole with a tamping means, usually comprised of earth, clay or sand, or a combination of these and thus the explosive force exerted when the charge is fired, is greatly enhanced, in proportion to the tightness of the stemming means in the charged bore or drill.

With the usual practice, stemming such explosive charges, when tamping with sand or other similar means, consumes considerable time to accomplish, prior to the firing of the explosive charge.

In current stemming practice, the plug sometimes lets go and the explosive force exerted in the rock is partially lost. It has been found that if a stemming means is provided that does not let go upon explosion, the explosive forces created in the blasting hole is very greatly amplified.

Accordingly, as in the present stemming device, if the said means applied to the charged hole is positively engaged in the hole, and does not let go at the instant of explosion, a greater mass of rock or coal may be disrupted with a minimum quantity of explosive material.

It is usually customary, when the high explosive material used is dynamite, which is extremely active and extremely powerful, to fire the explosive charge by means of a controlled detonator, which is buried at the bottom of the charged hole.

It is amongst the features of advantage of my present invention to provide a simple stemming means of a mechanical expanding type, that may easily and quickly be applied, with a minimum of time and effort, the said device being unitary, and

which. at the instant of explosion automatically increases its expansive resistance to let down at the instant of explosion. The present tampin device is simple in construction and easy to apply and it only takes a short time to install the same over the explosive charge, as it requires only a few seconds to place in charge stemming position.

One of the outstanding advantages in addition to the above noted, is the provision of a blasting plug of the expanding mandrel type wherein the few assembled parts, which are separate, are held together in operative and applying position by a simple, flexible and resilient parts retaining means.

Another feature of advantage is that due to the construction of the present blasting plug, it may be tamped very easily without any danger of prematurely exploding the blasting charge.

Another feature of advantage in the present blasting plug is that; in the case of a misfire, i. e. the non-firing of the detonator, which sometimes occurs, a secondary charge of explosive may be placed in the hole over the first plug inserted, with another detonator, and a second plug tamped over the secondary charge, which upon firing of said second detonator it causes the original explosive charge to explode. This latter desirable function is possible due to the construction of the blasting plug. This practice obviously does away with the necessity of removing the original explosive charge, to replace the defective detonator with a new one, and then reloading the hole. In other words the present plug obviates a number of time consuming steps both in the stemming of the original firing charge and restemming to explode the original misfired charge by the secondary charge.

The foregoing and other advantages will be apprehended as the herein description proceeds and it will be obvious that modifications may be made in the construction'herein, and the methods involved, without departing from the spirit hereof, or the scope of the appended claims.

In the drawings,

Fig. 1 is a longitudinal sectional view with parts in elevation the section being taken along the line l-l of Fig. 2 and showing the general construction of the present improved blasting plug;

Fig. 2 is an outer-end elevation of the plug;

Fig. 3 is a sectional View, partially enlarged, of an explosion bore, as drilled in the material to be blasted, showing the mode of operation of the blasting plug, including the manner of lockin-s the same in the hole to prevent its outward movement at the instant of explosion;

Fig. 4 is a view similar to thatof Fig. 3 being in longitudinal section showing theaction of the device at the instant of explosion;

Fig. 5 is a sectional view of the hole showing the mode of retamping or restemming and the secondary explosion of a misfired charge, due to the failure of the original detonator;

Fig. 6 is an inner-end elevation of the plug;

Fig. '7 is a fragmental longitudinal sectional the inner ends 5 ofthe. said segments. rangement is for the purpose permitting inward view partly in elevation showing another form of the invention;

Fig. 8 shows a section on the line 8-8 of Fig. 7, looking in the direction of the arrows of said line;

' Fig. 9 is a longitudinal sectional view showing another form of the invention;

Fig. 10 is a view similar to Fig. 7, showing a similar form of the invention;

Fig. 11 show an exaggerated transversevsection of a plug much expanded;

Fig. 12 is a side elevation,.partly, in section,

showing a plug showing a passage space between plug sections; and

Fig. 13 is a side elevation, partly in section, showing another form of plug in which the passage space between plug sections is closed by other plug sections.

In Fig. 1 there is shown a preferred form of stemming? device and. it. comprises a centrally located; tapered; mandrel or plug, t, preierabl-ycylindrical in cross-section the. inner larger'end, which is inserted into the drill hole foremost, being provided: with an' extending cylindrical flanged. head 2, the plural. surrounding expandible members; 3-3'-33 of which are. operated upon b z-"inward or outward movement oi the tapering: mandrel: land; said members.- comprise plural segmental' sections 3,, as shown: in Fig. 2, the. external surfaces ofthese joint segmental sections forming a;v cylinder, which is. slightly smaller diameter than the bore into which the plug is tnv be introduced. The.-,centralv apertures: of" the combinedsegments form. a. cylindrical. bore, the; said borebeingtapered to fit upon and cooperate with the tapering plug; portion I when the segments are assembled as in Figs. 1 and 2'; While themandrclt anda'the se ments It may be made of any-desired material, they may be. made preferably" of a suitable wood, such as ash, hickory; birchpr-the like.

The segments are held-in. engaged position as shown inFigs- I; and 2byr mean of an outer, preferably cylindrical rubber casing or contoun ing' tube 4, the said'casing holding: the segments in position on the tapered plug I.

The assembly; as: shownin Fig. 1, shows: the inner mandrel I its end: flange? spaced at considerable distance from the inner" ends 5- of the-sectors. 3:; and the casingkis extended from the sectors to also embrace a portion-0t the outer diameter of the flange 2; thus to hold the mandrel and flange a certain spaced distance: from This arl'ongitudinal movement of the segments to cause expansion thereof;v As thus described the rubber shield or tube holds the plugin. assembled bore applying condition.

The flanged end 2 of the plug is. provided with a;v diagonal vent. bore (i which is locatedangul'arly to the said flange 2. and emergesatthe inner space 1 between the inner face of..the flange 2 and the inner faces il oilthe. sectors 3'.

The inner faces 5 of thesectors3 are provided witha resilientwasher 8,,the purpose of which will be describedlater, in detail.

In the assembly above described the. outer diameter of the blasting plug; as exemplified by the rubber shield 4 issm'aller in diameter than the drill bore into which the plug is to be introduced, to. permit of. easy manual introduction of the plug within the bore.

In the use of thepresent device, as shown in Fig. 3, after the explosive charge G and the detonator, not shown, have been introduced into the drill bore B, the assembled blasting plug is introduced into the bore B until the outer face of the mandrel flange 2 meets the outer end of the charge G, and then a tamping rod T is introduced intothe outer end. of" the bore B, and moved orpushed gently in the direction of the arrow t, and the segments 3 are then pushed inwardly towards theexplosive charge G in the direction oi the arrow F thus causing the segments 3 to expand outwardly in the direction of the arrows H, shown in Fig. 3. This action causes the segments to expand in the bore B and to firmly engagethe inner surface of the bore B alliroundthereby causing the blasting plug segments to firmly engage in the bore B.

limtampingthe blasting plug as above described it isobvious that the mandrel flange 2 which is in contact with the explosive charge G cannot be moved. forwardly and. that. the segments. are therefore caused to-ride onthe mandrelplug l. andthereby cause their expansion as above described- It is understood that the detonator. for the charge: hasalready beenv placed. in the. bottom of the. hole or bore. 13. Afterwards the explosive charge is placed therein, and. obviously the. detonator itself is. attached to the usual. conducting wires. W which have. current. conductive terminalson the exterior ends. thereof; at. the outer ends. external of the bore. Bl whichhave. to pass by the blasting plug and. this is. accomplished without. abrasionof the. conductin wires. W" to the detonator when the. plug isinserted by reason of, the resilient retaining casing 4 asthedetonator wires W- sink into the. soft. rubbercasing. without deterioration or short circuiting abrasion.

After the plughas been tamped. in position as described in Fig; 3 the plug will occupy a position in whichit is firmly grippedin the bore B the surface of which is usually rough, and thus upon firing of the explosive charge in bore B asindicated at G, Fig. 4-, the instant explosive expansion of the. charge G causes two things to happen to the blasting plug which are as follows:

Uponv explosion of the charge G,- li-ig. 4, the fiangedtapering mandrel l2 is pushed inwardly into the bore engaged segments-3'; in thedirection of the arrow by the. force. of the. explosion. and this further. expands the segments Sin the. bore. B and. causesa very mucharnplified grip ofthesegmentsfi against-the. internalwall of the bore B and at the same time someof the explosive force enters. into thevent hole 5. and expansion is'created-"inthe space I causing the shield 4- at the explosion. end to further firmly engage the wall otthebo-re B as indicated by the arrows'in the. space 6., Fig. 4. Simultaneously with the explosive action. of charge G of Fig. 4-, some of, the explosion-- forces-react on.- top and against the l-ip-y, Fig. 4-,. andas-she-wnby the arrows f -j in said. figure, saidlip y. is. forced down upon thetop of the mandrel flange 2 and seals the plug, against. outward explosion loss. At the same: instant, the-mandrel t, isiorced towards. the faces 5 of the segments 3 to fmther increase the expansive grip. of the segments 3 to the bcreB,-. as previously described. The. resilient washer 8, further prevents-back flow of the cxplos'rveforces, at the instant of. explosion-.-

It isobviousirom the description. of the temping of the plug in the bore-B as shown and. dcscribed for Fig. 3: that itreduires alight pressure of the tamping rod'I to cause the segments to primarily expand in the bore B sufficiently for initially stemming the explosive charge G, and that thereafter the explosionof charge G causes a secondary, immediate expansion of the plug in sit-u.

In Fig. 5 there is shown a furtheradvantageous use of the present blasting plug, there being two shown in the said Fig. 5 one of which is shown in partial section, and due to the fact that the initial charge G has misfired, the charge G remains unexploded and thus it becomes necessary to devise a modification for causing the explosion of the unexploded charge G, without its removal, and this is accomplished by the following steps:

A secondary explosive charge G is placed at the outer end of the initial blasting plug, this explosive charge G being also provided with a detonator, such as g, and the wires 10 of the detonator pass externally of the bore B after which a second plug P is forced on to the secondary explosion charge G and the secondary plug P is then tamped in position over the secondary charge G and the secondary charge is exploded and upon explosion of the secondary charge a flame therefrom is passed in the direction of the arrows A between the faces of the expanded segments 3 and the flame continues to pass on in the direction of the arrows A-a--h causing an expansion of the inner end of the flexible sleeve 4, such flame passing into the unfired original charge G. Some of the flame also passes through the vent hole E5, to the unexploded charge G and the action of this flame conduction from the secondary charge causes the explosion of the initial charge GJ It will be noted in this action that the resilient washer K is thrown over from its seat to permit the passing of the flame from the secondary charge into the primary unexploded charge G.

The tube or sleeve 4 may be of rubber or other elastic material. and the price of rubber is high, the sleeve may be made thinner in order to save expense, as shown by the sleeve 4' of Fig. 9, and a thick elastic band 4a maybe added, for filling the space between the segments 3 and the wall B of the bore.

The sleeve 6 or i may be omitted entirely as shown in Figs. 10 to 13, or may be replaced by thin paper 4b around the bands do, the bands providing the proper elastic filling around the plug-sections. Thus the thick band may be used around the sleeve or tube d of Fig. 1 and with or without the sleeves 4, 4 or 42).

Fig. 11 is an enlarged transverse section across a plug with the proportions exaggerated to show that when the plug is over expanded as when used in an oversized bore, the thick band do will compensate for the lack of roundness of the plug.

When the sections are rammed far inwardly on the mandrel to take care of a large or oversized bore B", the plug becomes not an exact cylinder, but has larger diameters, as at d, at the longitudinal mid-line of the section periphery, and smaller diameters d,

section peripheries. In such cases. the thick elastic bands 4a are compressed to be thinner at 5 40, but remains thickest at 4d, so that the space between the peripheries of the segments and the bore is everywhere filled,'and the plug is held firmly in place.

In the form of the invention of Figs. 7 and 8, two thick elastic bands do disposed around the sections 3 hold the sections together, and the whole is enclosed by a sleeve of thin paper disposed around the bands and plug, in which form the plug may be used, shipped and sold. A cup- If the sleeve is made of rubber a r with the single thick sleeve at the side edges of shaped disk Ill, I l of fiber or thick paper or other suitable material has its body part It disposed against the ends of the segments to fill the spaces therebetween, and provided with a central opening It received on'the mandrel. Said disk includes a flange ll extending inwardly substan: tially against the wall of the bore B and adapted to be forced valve-like against the bore to render the plug gas tight against outgoing gases during explosions and adapted to allow hot gases to move inward between flange H and the bore wall during the firing of an unexploded inner charge as a a result of a misfire as described of Fig. 5.

The body part it of said disk has a small opening l2 (Fig. 8) alined with a space 13 between the segments and adapted to receive a rubber tube disposed longitudinally in said space H! and through the opening it and projecting beyond both ends of the plug and adapted to receive and protect the detonator wires W The flange ll may be provided with a slit communicating with the opening i2, through which the tube I3 may be moved laterally into the opening, if desired.

In the form of invention of Fig. 9, a thin elastic tube i and a surrounding thick elastic band to, hold the sections 3 together and provide a cushioning gripping surface to engage the wall of the bore. In order always to protect the sleeve lip 4 and the band 4a from any chance of being burnt or disabled by the heat of the explosion of the charge, I may provide a thin disk I0", M (Fig. 9) of flexible asbestos or other suitable heat-resistant material having its middle part 10" disposed against the head 2 and its margins H" folded back over the end lip 4" of the sleeve to protect the latter.

This disk ID", H" may be effectively used 4, or thin sleeve l with or without the band 4a.

In the form of invention of Fig. 13, I provide an outer set 311 and an inner set 3b of segmental plug sections, each section having an inner face having a taper slidably received on and substantially corresponding to the taper of the mandrel I, as in Fig. 1, the peripheral faces of the sections of both sets 3a and 3b togetherforming an approximately cylindrical plug, as shown. Thick elastic bands 4a are disposed around the sections of each set, the sleeves 4 or may also be used.

The end faces of one set ofv sections 3a or St meet the end faces of the other set in a plane perpendicular to the axis of the plug, the sections of one set being alined with the spaces l3 between the sections of the other set, thereby to close said spaces l3 to render the plug substantially gas-tight during the explosion.

The invention claimed is:

1. A blasting plug including a taper mandrel disposable coaxially of the explosive-charge-receiving hole and provided at its larger end with an inner flanged head; plug sections each having an inner tapered face slidable on the mandrel, the sections and mandrel together forming an approximately cylindrical plug; a resilient tube around the sections and said head; the sections being movable inwardly on the mandrel to compress the tube against the wall of the hole leaving a chamber between the sections and said head, the inner end lip of the tube lying against the peripheral face of the head; a resilient washer disposed around the inner end of the mandrel and closing the spaces between the sections; saidhead being provided with an aperture between the chamber and the face of said head at the charge; pressure of the explosive gases pressing said lip onto the head to confine and force the gases against the head to force outwardly the mandrel to further expand the sections; said washer and lip serving as a check valve to prevent outward passage of gas during the explosion, and serving to admit the inward passage of flame through said spaces and aperture and around the head, when a secondary charge is exploded at the outer end of the plug, to explode an inner charge that has misfired.

2. A blasting plug for stemming explosive charges in holes drilled in rock, coal or other material, said plug including a taper mandrel of wood or other suitable material disposable coaxially of the hole and provided at its larger end With a flanged head large in diameter than said larger end but smaller in diameter than the hole and having a flat end face disposable fiat against the explosive charge in the inner part of the hole; a plurality of segmental plug sections of wood or other suitabl material, each having an inner face having a taper received on and substantially corresponding to the taper of the mandrel, the outer faces of the sections together forming an approximately cylindrical plug of slightly less diameter than the hole; a cylindrical rubber contouring tube disposed around the sections and said head; the sections being adapted to be simultaneously rammed rearwardly on the mandrel with a tamping rod, to uniformly expand the sections against the contouring tube and compress the latter against the wall of the hole to grip the latter, leaving an annular chamber between the inner ends of the sections and said head, the inner end lip of the tube lying against the peripheral face of the head and yieldably closing said chamber; a flat resilient washer disposed around the inner end of the mandrel and flat against the inner ends of the sections to close the spaces between the sections; said head being provided with an aperture between said chamber and the face of said head at the charge.

3. A blasting plug for stemmin explosive charges in holes drilled in rock, coal or other structure, said plug comprising a taper mandrel; a plurality of segmental plug sections, each having an inner face having a taper slidably received on and substantially corresponding to the taper of the mandrel, the peripheral faces of the sections together forming an approximately cylindrical plug; one or more thick elastic bands disposed around the sections; a cup-shaped disk of fiber or thick paper or other suitable material having its body part disposed against the ends of the segments to fill the spaces therebetween, and provided with a central opening received on the mandrel, and with a flange extending inwardly substantially against the wall of the bore and adapted to be forced valve-like against the bore during explosion.

4. In a plug as in claim 3 the body part of said disk having a small opening alined with a space between the segments; and a rubber tube disposed longitudinally in said space and through the Opening, and projecting beyond both ends of the plug and adapted to receive and protect the" detonator wires.

5. A blasting plug for stemming explosive charges in holes drilled in rock, coal or other structure, said plug comprising a taper mandrel; an outer and an inner set of segmental plug sec-, tions slidably received on the mandrel; end faces of one set meeting the end faces of the other set in a plane perpendicular to the axis of the plug; the sections of one set being alined with the spaces between the sections of the other set.

6. A blasting plug including a taper mandrel disposable coaxially of the explosive-charge-receiving hole and provided at its larger end with an inner flanged head; plug sections each having an inner tapered face slidable on the mandrel, the section and mandrel together forming an approx imately cylindrical plug; a resilient tube around the sections and said head; the sections being movable inwardly on the mandrel to compress the tube against the wall of the hole leaving a chamber between the sections and said head, the inner end lip of the tube lying against the peripheral face of the head; and means movable relative to the mandrel forming a transverse arcuate bridge at the inner end faces of the sections and spanning the spaces therebetween to prevent passage of gases between the plug sections when the sections are separated by the mandrel.

7. A blasting plug disposable coaxially of an explosive-charge-receiving hole comprising a tapered mandrel having on its larger end a flanged head disposable against an explosive in the hole; longitudinal plug sections on and around the mandrel and each section having an inner tapered face slidable on the mandrel, the sections and mandrel together forming an approximately cylindrical plug; a stretchable band around the sections to hold the sections and mandrel together; the sections being movable toward said head on the mandrel to compress theband against the wall of the hole; and means movable relative to the mandrel forming a transverse arcuate bridge at the inner end faces of the sections and spanning the spaces therebetween to prevent passage of gases between the plug sections when the sections are separated by the mandrel.

8. A blasting plug disposable coaxially of an explosive-charge-receiving hole comprising a tapered mandrel having on its larger end a flanged head disposable against an explosive in the hole; longitudinal plug sections on and around the mandrel and each section to be enga ed against an explosive charge; plug sections, each having an inner tapered longitudinal face in straight line contact with and slidable on the mandrel and an end face at right angles to the axis of the mandrel to form a shoulder, the sections and mandrel together forming an approximately cylindrical plug the sections terminating at their outer end in a common substantially transverse plane; stretchable binding means around the sections; the sections being longitudinally movable on the mandrel toward the head thereof to compress the means against the wall of the hole; and arcuate means movable relative to the mandrel forming a transverse arcuate bridge at the inner end faces of the sections engaging said shoulders and spanning the spaces therebetween, whereby impact of a tamping rod on the outer end of the plug, will cause longitudinal movement of the sections relative to the mandrel and toward the head and said shoulders will force the arcuate means along the mandrel and prevent the means from being caught concentrically between the tapered faces of the sections and mandrel.

CHARLES O. TAPPAN.

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