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Sept. 24, 1946? 2,408,124 H. J. ROLFES MEANS FOR SAFEGUARDING ELECTRIC'IGNITERS OF BLASTING ' DETONATORS AGAINST ACCIDENTAL FIRING. Filed Aug. 18, 1942 I? 2 Sheets-Sheet l ??/ 1?? 22 \ 25w 2r I24. ' p 2 11\ 20? -/12 ~10 9?;v ? ~\\16 7 4 - g6 0 ?57 [� 14! 55 36 59 .55 52 5Q . 9 , 30 5 Sept 24, 1946. H. J. ROLFES �8,124 MEANS FOR SAFEGUARDING ELECTRIC IGNITERS OF BLASTING 'DETONATORS AGAINST ACCIDENTAL FIRING Filed Aug. 18, 1942 2 Sheets-Sheet 2 65 __Fi51-" 75 76 .s/ 82 79 73 )/%0 ' F510 Patented Sept. 24, 1946 also STATES 2,408,124 MEANS FOR SAFEG'UARDING ELEGTRIG IGNITERS OF BLASTING DETONATORS AGAINST ACCIDENTAL FIRING Hans Jay Rolfes, Melrose, Johannesburg, Transvaal, Union of South Africa Application August 18, 1942, Serial No. 455,235. In the Union of South Africa September 11, 1941 4 Claims. (Cl. 102-28) 2 I This invention relates to means for safeguard ing the electric igniters of blasting detonators against accidental ?ring by electric currents or spark discharges produced respectively in, or in the vicinity of, the ?ring means of the igniter by atmospheric electricity. More speci?cally, the invention consists in means for safeguarding as aforesaid electric ig niters which includes a plug of material which is grounded through the shell of the igniter or detonator or otherwise and which comprises mi It is obvious that a possible solution to this nute metal or other electrically conductive par ticles which in the mass are non-conductive to problem is to surround the two electric leads of voltages of the magnitude used for intentionally the igniter at a position a safe distance from the ?ring the detonator and which in the mass be come instantly conductive through coherer action to currents or electric discharges at voltages of ?ring means thereof by a grounded mass of a material, which may be termed the ideal mate rial, and which will exhibit a high resistance at voltages of the magnitude used for intentionally ?ring the igniter and a low resistance at volt ages of the magnitude of the electrostatic charges which produce the currents and spark discharges aforesaid. One means of obtaining a solution of the prob lem has already been proposed, the means con sisting broadly in employing for the purposes of the material surrounding the leads any material which has the characteristic that its resistance to electric currents or discharges is an inverse the magnitude resulting from atmospheric elec tricity along a locally con?ned path from the lead or leads to ground. The grounded mass may surround the electric leads, e. g. igniter wires or wires of the blasting circuit, at parts located inside and/or outside the igniter, these parts being bared; or the igniter wires or blasting circuit wires may be tapped by insulated conductors having bared parts sur rounded by the grounded mass. The invention will now be described by way of example with reference to the annexed draw function of the voltage applied thereto. Amongst materials having this property are, for example, ings, in which: galena, stibnite, carborundum, yellow crystalline instantaneous electric detonator embodying the invention. Fig. 1 is a sectional view in elevation of an iron pyrites and zincite. This application is a continuation in part of Fig. 2 is a sectional view in elevation of an my copending application No. 422,452. instantaneous electric detonator, enclosed in an The object of the present invention is to pro 30 inert body or so-called wax primer, embodying vide another means of solving the problem stated the invention._ which will render available as the ideal material Figs. 3 and 4 are sectional views in elevation a class of materials other than those of which of electric igniters for delay-action detonators, the resistance is an inverse function of the ap embodying the invention. plied voltage as aforesaid, and which will afford 35 Fig. 5 is a diagrammatic view of an alternative a particularly e?ective safeguard against cur means for associating the igniter leads indirectly rents or spark discharges produced in, or in the with each other through a coherer mass. vicinity of the ?ring means of the igniter by elec Figs. 6 and '7 are diagrammatic views of two trostatic charges caused by lightning or atmos embodiments of this alternative means applied pheric electricity in general. 40 to groups of detonators connected in series. Figs. 8 and 9 are respectively a sectional ele According to this invention, means for safe guarding electric igniters of blasting detonators vation, and a sectional plan, of a convenient prac against accidental ?ring by electric currents or tical form of the alternative means. spark discharges produced respectively in, or in Figs. 10 and 11 are respectively a sectional ele the vicinity of, the ?ring means of the igniter 45 vation and sectional plan of an improvement in by atmospheric electricity, comprises a grounded the alternative means. mass of a material which offers a complete or Referring to Figs. 1 to 4: In Fig. 1, the insulated electric leads Ia, Ib pass through a rubber plug 2 crimped in the mouth of substantially complete resistance to voltages of the magnitude used for intentionally ?ring the igniter and which, on its being subjected to volt ages of the magnitude of electrostatic charges caused by atmospheric electricity, becomes locally conductive through coherer action along a path or paths permitting the passage therethrough of the high voltage charge. the copper or other conductive shell 4 of the detonator. In the usual manner the detonator shell 4 contains a fuze-head 5, a primary charge 6 and secondary charge ?I. The fuze-head 5 has a bridge-wire 8 within the igniter composition or bead thereof, and the one end of the bridge-wire 2,408,124 3 4 3 is connected to a bridge-pole 9 and the other end to a bridge-pole I3. These poles 9, H! are connected at soldering points M, �to the re voltage charge from the leads Ia, lb, or either of them, into the coherer plug l5. When the detonator is ?red, the ?ring current spective leads Ia, lb. passes in the normal manner through the one Parts i3, M of theleads la, lb respectively are bared, as shown in the? drawings, and these parts pass in spaced relationship through a plug I 5 provided within the detonator shell 4 between the rubber plug 2 and the insulating sleeve or lead, say la, across the bridge-wire S, and out body 55 of the fuze-head 5. . The plug l5, hereinafter referred to as the through the other lead I?, the bridge-wire being heated to incandescence and ?ring the igniter bead of the fuze-head 5. In other words, to the voltage of the magnitude used for the ?ring cur 10 rent, the coherer plug I5 reacts as an insulator. If, on the other hand, an electrostatic charge of high potential is induced in the ?ring circuit con sisting of the leads la, lb and bridge-wire 8, or if this circuit is struck by a lightning discharge, the ductive to Voltages of the magnitude used for in tentionally ?ring the detonator and which in the 15 ?nely divided aluminium of the coherer plug I5 ?coherer plug,? consists of ?nely divided alumin ium particles which in the mass are non-con mass become conductive through coherer action to currents or electric discharges at voltages of becomes at once locally conductive through co tricity. herer action along outward radial paths from the teeth I1, E8 to the wall of the detonator shell 4, permitting the passage through these paths of that ?nely divided aluminium used in the paint trade is a particularly suitable material for the coherer plug. Such aluminium appears to be in the form of minute ?akes which have a ?lm of charges its high potential to ground without any flow of current being produced in the bridge-wire 8, or spark discharges being produced in the vi the magnitude resulting from atmospheric elec It has been discovered as a result of experiment 20 the high Voltage charge from the ?ring circuit to ground. In this manner the ?ring circuit dis grease or oxide over them, which may account 25 cinity of the fu'ze-head 5, such as would cause in for their exceptional non-conductivity in the mass to normal voltages. Preferably the aluminium powder is mixed with oil to form a paste, or with candescence of the bridge-wire or premature ig nition of the fuze-head. ,By using the teeth IE, it or similar discharge points, an effective safeguard is provided against lique?ed paraffin wax to form a melt or heat plas tic mass, so that the requisite amount may be 30 the consequences of a high voltage electric surge which may arise in one lead only of the deto squirted as a plug into the igniter shell. The alu nator. The discharge teeth (say the teeth I?! if the surge arises in the lead'l?) elfect complete discharge of that surge direct to the detonator tic materials, and, in any case, be used to replace shell 4, without any residual surge passing on to 35 the rubber plug or sealing means at the mouth of the bridge-wire 8. In this case also, therefore, a detonator, or alternatively it may be used in there is no flow of current through the bridge place of the insulation mass commonly employed wire such as might cause incandescence and pre for the leads or for part of the wires in the blast mature ?ring of the fuze-head 5. ingcircuit. .Other substances displaying coherer action are ?nely powdered silver, nickel, iron, 40 The coherer mass may be used not only in the minium ' powder may, on the other hand, be mixed with rubber, or rubber-like or other plas brass and cop-per and these substances can also be used for the coherer plug, being preferably mixed for this purpose with paraf?n wax or-other fusible, powdered or liquid dielectric. Another material which has been found suitable for the coherer plug is graphite, preferably in de?occulated state, mixed with a viscous neutral hydrocarbon such as light lubricating oil to form a paste. ?Through varying the amount of oil admixed with the vgraphite, and by adding other inert materials which may in?uence the physical properties vof the paste, it is possible to vary to a large extent the resistance to the ?ring current without im pairing the coherer action with respect to the high voltage" discharges. . Teeth, projections, edges or other means may be formed or provided on the igniter leads, at their bared parts surrounded by the coherer mass, and/or on the interior of the casing con taining the said mass, or otherwise so as to con stitute discharge points which promote the dis charge of the high voltage charge from the leads form of a plug enclosed within the igniter or detonator shell, but also in the form of a plug or layer surrounding the leads at a place outside the igniter or detonator. Fig. 2 shows an applica tion of this to a detonator enclosed in an inert body or so-called wax primerZO. Reference nu merals used in this ?gure similar to those used in Fig. 1 refer to similar parts. In this embodi ment, the coherer mass 2| is made in the form of a layer interposed between the inert or wax body 20 and a top inert or wax layer 22, The leads la, lb are bared and formed with outwardly directed discharge teeth at 23 and 24 respectively, where they pass through the coherer layer 2|. In function, the embodiment shown in Fig. 2 is similar to that already described with reference to Fig. 1, and, as shown in Fig. 2, the toothed and bared parts 23, 24 of the leads Ia, I10 are prefer ably spaced outwardly from each other in the coherer layer 2| so as to afford high voltage dis charges a 'readier path to ground, 1. e. to the rock or side of the borehole in which the wax primer is inserted. In Fig. 3, similar numerals again denote similar or either of them into the said mass, as described 65 parts. The embodiment shown in this ?gure is an electric igniter having a copper or other con in my co-pending patent application No. 422,452. The bared parts l3, I4 of the leads la, 1'? are formed, in the particular example shown in Fig. 1, with pointed teeth ll, l8 respectively directed diametrically outwards towards the wall of the ductive cylindrical shell 30 into the lower open end of which there is crimped a ?exible delay fuze 3!, of which the other end (not shown) is crimped in known manner in the mouth of a detonator. A coherer plug 32 is in' this instance inserted in the igniter shell 30 so as to surround detonator shell 5. Any projections, edges or other means adapted to constitute the discharge points may be employed in lieu of the particular teeth the solder points H, 12, the adjacent parts of [1, I8 illustrated, so long as they ful?ll the pur the bridge-poles 9, l0, and the bared lower ends pose aforesaid of promoting discharge of a high 75 33, 34 of the leads la, lb. The upper end of the 2,408,124 ?'5 to a group of series-connected detonators 6|. The insulated conductors 53, 5'41 are in this in stance led from the positive and negative wires ' to a delay-action detonator of the Eschbach type. The construction of this detonator is similar to that of the instantaneous detonator shown in Fig. 1, with the exception that, between the fuze head 5 and the primary charge 6, a delay compo sition 3 is (e. g. antimony and potassium per manganate) contained in a lead body 3!?) is pro vided. Otherwise, similar reference numerals in the two ?gures denote similar parts. In any of the embodiments of the invention, 6 the detonator shell in preference to the casing 58. Fig. 6 shows the application of the same means igniter shell 30 is closed by a rubber plug 35 crimped therein. Fig. 4 Shows the application of the invention 50??, 5|EL of the blasting cable, and the grounded casing 58 is connected by separate conductors 59a, 59b and sleeves 60a, 60b to the ?rst and last detonators of the series respectively. Otherwise 10 the arrangement is similar to that described with reference to Fig. 5. " Fig. 7 shows another application of the said means to a similar group of series-connected detonators 62. The insulated conductors 53a, 54a more than one grounded coherer plug or mass may be used in association with the one detonator or igniter. One form of this modi?cation is are led from the blasting wires 58%, 5M and their bared ends 55a, 56*1 inserted into separate coherer masses 5'53, 5111 contained in separate grounded casings 58a, 58?). This is a specially effective safe guard against short-circuiting of the ?ring cur rent, e. g. between the bared ends 56, 56 (Fig. 6) of the conductors 53, 53 through the coherer shown incorporated in the embodiment illustrat ed in Fig. 3 where, in addition to the coherer plug 32 surrounding the bared parts 33, 34 of the leads within the igniter shell 30, a second coherer plug 35 is contained in a separate copper or other conductive sleeve or shell 31 which is crimped on rubber plugs 38, 33 as an independent unit mass 51. The outside arrangement of the coherer plug shown in the preceding Figs. 5 to '7 necessitates that the construction of the plug should be ro bust, in order to withstand rough handling. In particular, the internal spacing of the bared ends or mass is thus used, discharge of high voltage of the conductors and the grounded casing must charges from the ?ring circuit to ground may not be disturbed during the charging operations. take place through either one or other or both of easily made assembly is illustrated the said plugs or masses. In carrying out the in 30 A rigid in Figs. 3 and 9. In this assembly, the bared vention. steps may, if necessary, be taken to en ends of the conductors 53, 54 are constituted by sure that high voltage discharges should they oc two strips 63, 64 of metal foil secured by an ad cur, will not take place through the coherer mass hesive to the opposite sides of an. I shaped piece from one lead of the igniter or detonator across to the other. A safeguard against this happening is 35 65 of cardboard or like insulating material, which is a neat ?t into the metal casing 65. This in the provision. of discharge points hereinbefore re sulating piece 65 serves to position, and to main ferred to, Should these points not be employed, tain in position, the strips 63, 64 with respect to as for example in the embodiment illustrated in the wall of the casing 65, which is, itself closed Fig. 3, a preventive against the occurrence of dis at its top and bottom ends by sealing means 61, 68 charges between the leads, and consequent short held in place by crimpings 69, ?H3. In the con circuiting of firing current, is obtained by, for struction shown in Figs. 8 and 9 a copper wire example, either spacing the leads I 1?, l?D apart in ?ll is soldered at one end to the casing 66 and at the coherer mass (as in Fig. 2) a distance which its other end to a, copper ring or sleeve 12, for is substantially greater than the distances be connection to the detonator casing (as already tween the respective leads and the detonator shell described with reference to Fig. 5). or ground, or inserting between the leads within Although the bared ends of the conductors in the coherer mass (as in the case of the upper around bared parts 48, 4| of the leads la, lb out side the igniter shell 38. When more than one grounded coherer plug coherer plug 36 in Fig. 3) a paper sheet 42 or Figs. 5 to 9 have been shown as of ?attened and 52 are shown within the discharge plug, these points may be outside the said plug and insulated from each other and from the igniter shell by being surrounded by a rubber or similar plug. Referring to Figs. 5 to 11: the said ends and/or the casing or grounding means may be provided with discharge points as straight-edged shape, it will be understood that other insulating element. While, in the drawings, the soldering points H 50 these ends may be of ordinary round section or described in our co-pending patent application aforesaid. Under practical tests, my coherer protected detonators have invariably been found capable of being ?red, that is, intentionaly ?red, after they have been subjected to a discharge of high voltage In these ?gures, an alternative means of asso ciating the igniter leads with each other is shown, such means comprising a coherer mass or masses static electricity either through one lead only, or which does not, or do not, surround the igniter leads directly, but which is or are contained in a grounded casing or casings and surrounds or sur round the bared ends of insulated conductors led from the respective igniter leads. Fig. 5 shows the application of this indirect means to a single detonator. The leads 5!), 5| of I the detonator 52 are respectively tapped by in sulated conductors 53, 54, the ends 55, 55 of which are bared and surrounded by a coherer mass 51 contained in a grounded metal casing 53. De sirably, but not necessarily, the casing 58 is elec trically connected to the detonator 52 by a con ductor 59 and conductive sleeve 60. This en sures that the detonator casing is not at a lower through both leads simultaneously. In the latter case, theoreticallyat least, a circuit permanently conductive to the ?ring current is created from one lead outwardly through the coherer mass to the metal casing, thence round the wall of the casing and inwardly through the coherer mass to the other lead. That such a detonator was found on test nevertheless to be capable of being ?red is clearly due to the fact that the (perma nently reduced) resistance of the (outward) dis 70 charge paths in the coherer mass was still high 7 enough to divert a current through the fuze head sumciently strong to ?re the same. A means of positively ensuring that the coherer detonator may be ?red after simultaneous high potential potential than the casing 58 and that therefore discharges on both leads is shown in Figs. 10 and 75 discharge to ground will not take place through 2,408, 124 7 11. In these ?gures, the'said means is shown applied to an outside coherer plug (as used, e. g., in the constructions shown in Figs. 5 to 9), but it may equally well be applied to an interior coherer plug as shown in Figs. 1 to 4. The means comprises an insulating casing 13 which is closed at the top by sealing means '13a and which con 8 by atmospheric electricity, comprising a coherer mass which is in electrical cooperation with insu lated conductive branches connected with each lead of the igniter, said branches having bared ? parts surrounded by the coherer mass, a conduc tive grounded casing conductively connected to a conductive shell of the igniter, the coherer mass including a metal powder offering a substantially tains the coherer mass 14 in which the bared parts 15, 76 of the leads 11, 18 are inserted as complete resistance to voltages of the magnitude usual. At the portions of the casing 13 directly 10 used for ?ring the igniter and which, on being adjacent to the bared parts 15, 16, interior con subjected to voltages substantially higher than ductors 79, 80 are disposed parallel to the said said ?ring voltages, becomes locally conductive parts and are respectively formed integral with through coherer action along a path permitting or conductively connected to exterior conductors the passage of the high voltage charge. BI, 82. With these separate conductors, even the 15 2. An electric igniter of a blasting detonator permanent reduction in resistance of the dis in combination with means by which it is safe charge paths created by discharge from both guarded against accidental ?ring by electric cur igniter leads simultaneously cannot result in a rents or spark discharges produced respectively short circuit of the ?ring current occurring be in, or in the vicinity of, the ?ring means of the tween the bared parts of the leads via the casing 20 igniter by atmospheric electricity including leads containing the coherer mass. for the igniter common to a group of two or more A5 is the case with coherer materials in general, detonators, insulated branches tapped from said the part or parts of the grounded plug or mass leads and having bared parts, said bared parts which has or have had its or their resistance re being surrounded by a coherer mass which is in duced by the coherer action caused by a high 25 electrical cooperation with each lead through the voltage discharge may have the resistance thereof insulated branches, said mass including a metal restored to its normal high value by the plug or powder offering a substantially complete resist mass being lightly shaken. ance to voltages of the magnitude used for ?ring With the present invention, an electric deto the igniter and which on being subjected to volt nator is obtained which is substantially safe ages substantially higher than said ?ring volt against stray currents and which, in addition, is ages, becomes locally conductive through a co equally applicable to series, as to parallel, blasting. herer action along a path permitting the passage In the appended claims, the term ?electric of the high voltage current, and a conductive leads? is to be understood as including the wires casing enclosing said mass and connected elec of the igniter and/or the Wires of a blasting cir 35 trically to the ?rst and last of the detonators of cuit, and/or conductors led from these wires. the group when the groups are connected in series. I claim: . 1. An electric igniter of a blasting detonator in a combination with means by Which it is safe guarded against accidental ?ring by electric shock or spark discharges produced respectively in, or in the vicinity of, the ?ring means of the igniter 3. A construction as de?ned in claim 1, wherein the mass is common to both leads of the igniter. 4. A construction as de?ned in claim 2, wherein the mass is composed of ?nely divided aluminum ?akes. ' HANS? JAY ROLFES.