3,223,599 United States Patent Office Patented Dec. 14, 1965

2 A still further object of the invention is to provide an 3,223,599 improved fixture for holding a plurality of detonator plugs HOLDING PLATE FOR ELECTROPLATING A during the finishing steps of grinding and electroplating. DETONATOR PLUG A still further object of the invention is to provide a Daniel Dwight Taylor, Altadena, Calif., assignor to Beck detonator plug of a novel structure which facilitates the man Instruments, Inc., a corporation of California finishing operations. These and other objects and ad Filed Apr. 15, 1963, Ser. No. 273,198 vantages of the invention will become more apparent in 4 Clains. (C. 204-15) the following detailed description of a preferred practice This invention relates to electrical detonators and more of the invention and as illustrated in the accompanying specifically to the manufacture of detonator plugs and to O drawing. an improved structure. In the drawing: In one manner of manufacture of detonator plugs, a FIG. 1 is a sectional view of a detonator plug of the plug disc of very small dimension is drilled to accept a invention following application of swaging force to neck plastic coated wire or stem. The drilled hole is some down an electrode wire placed in the hole of the plug what oversized. A typical procedure is described in co 5 disc the view illustrating an intermediate stage of fabri pending patent application Serial No. 147,354, now Patent cation; No. 3,155,553, filed October 24, 1961. Taylor and FIG. 2 is a fragmentary sectional view showing two Brawner. As a result of the drilling step, a burr appears detonator plugs held within a fixture of the invention; by one face of the plug disc about the drilled hole. The FIG. 3 is a sectional view illustrating the detonator burr is preferably not removed at this time because of the 20 plug in an advanced stage of fabrication, following grind possibility of returning part of the burr inside of the hole ing of the head and prior to electroplating; where it would interfere with assembly. Following the FIG. 4 is a plan view of the head of the detonator plug drilling of the hole in the plug disc; a slightly undersized of FIG. 3; plastic coated wire or stem is positioned within the hole F.G. 5 is a sectional view of a finished detonator plug of the plug disc. The plastic coating is capable of with 25 following gold-plating; and standing fracture upon the subsequent application of high FEG. 6 is a plan view of the detonator plug of FIG. 5. swaging force to the plug disc. The detonator plug, i.e., The detonator plug 10 of the invention comprises a the plug disc with the coated wire therein, is positioned plug disc 2 which is swaged about a wire or stem 14. within a suitable bushing fixture which closely controls The plug disc 12 is preferably a punched slug of Type the outside diameter and finish of the completed plug 30 302 stainless steel which is drilled to accept the wire 14. upon application of a high Swaging force, generally in the The wire 14 has a plastic coating 16 which is capable range of 3,000 to 5,000 pounds, to the end of the plug. of withstanding fracture upon application of high swaging In a subsequent operation, the burr and the wire or stem force. The drilled hole of the plug disc 2 is oversized adjoining the burr are ground off to provide a substan and it will be seen that a burr 18 appears on one face of tially smooth head for the detonator plug. This grind 35 the plug disc (see FIG. 1). Following the drilling of ing operation removes a thin oxide film which is charac the hole in the plug disc 12, the slightly undersized coated teristic of stainless steel out of which the plug is desir wire 14 is positioned within the hole of the plug disc. In ably made. The detonator plug at this time is placed di the practice of the invention, one end of the wire 14 has rectly in a gold-plating bath and a thin gold coating is been threaded. For a detonator plug employing a wire formed on the recently ground head. The gold coating 40 stem of 0.062 inch diameter, 80 threads per inch have been forestalls the formation of an invisible oxidation film on found to be suitable. the head which would interfere with firing of the deto The plug disc 12 with the coated wire 14 therein is nator. positioned within a suitable bushing fixture which limits It is conventional practice during the finishing opera the outside diameter and imparts a finish to the completed tions of grinding and gold-plating the face to hold a large 45 disc plug upon application of a high swaging force. The number of detonator plugs in a fixture. Heretofore, the swaging force is applied through a doughnut-shaped die to method of holding the detonator plugs or buttons, as they the end of the plug opposite the burr 18. This high swag are sometimes called, involved inserting the stem or wire ing force brings about an inward flow of metal toward of the detonator plug in a hole of the fixture and then the hole of the plug disc 12, resulting in the necking down pouring a low-melting alloy around the wire which on 50 of the wire 14 which as seen in FIG. 1 secures the wire freezing held the detonator plug for the subsequent opera within the disc plug. Simultaneously with the inward tions of grinding and gold-plating. The later removal flow of metal there is an outward flow of metal to give of the detonator plug from the grip of the alloy presents the diametrical dimension and finished surface of the serious problems. If the alloy is melted and allowed to completed plug. The detonator plug of FIG. 1 illustrates run away from the wire, it is not possible to obtain a 55 the disc plug 12 immediately subsequent to the Swaging clean surface and the residue of the alloy has to be picked operation. The plug is then ejected from the fixture off with a needle by hand. This, it will be appreciated, bushing by a plunger. The tough plastic coating of the is a very tedious task and it has also proven difficult to accomplish without damage to the plastic coating. An wire plug, which is preferably made from the plastic alternative procedure involves gripping the edges of a 60 “Formvar,' transmits the high pressure without fracturing. finished detonator plug between the jaws of cutting pliers In the practice of the invention, the detonator plug 10 and pulling the detonator plug out of the solid alloy. at the stage of manufacture illustrated in FIG. 1 is then With this method of removal unknown damage may be held to a holding plate 22 of a fixture 20 by an elongated imparted to the plug, especially at the swaged joint. The nut 24. In actual practice the fixture 2.0 is usually de invisible damage will become known only when an at 65 signed to contain 100 detonator plugs 10. The fixture 29 tempt is made to fire the detonator employing the plug. with the several detonator plugs 10 fastened thereto is It is a object of this invention to provide an improved conveniently presented to an abrasive wheel to grind off method of manufacturing a detonator plug. the burrs 18 and protruding portions 28 (see FIG. 1) of 3,223,599 3 4. the wires 14. Ordinarily a series of abrasive papers will chor the plugs in place. With a detonating plug having be used in the grinding operation with the last grinding a disc plug diameter of approximately .175 inch diam being achieved with a 600-grade Carborundum. This eter, it has been found that a torque of 5 to 7 oz./in. is grinding operation also removes a thin surface film which best employed for seating the nut within the second Sec is characteristic of stainless steel. In order to avoid or tion 38 of the transverse hole and in drawing the plug forestall the formation of an invisible oxide film which disc 2 tight against the face of the fixture 20. would present an electrical resistance, the recently ground Although exemplary embodiments of the invention face 30 of the disc plug 2 is desirably provided with a have been disclosed herein for purposes of illustration, it gold-plated face 43. It has been found that stainless will be understood that various changes, modifications, steel plugs allowed to stand for several hours in air before and substitutions may be incorporated in such embodi assembly without the gold-plated face often produce un 0 ment without departing from the spirit of the invention satisfactory firings. Since the holding plate 22 of the as defined by the claims which follow: fixture 20 is desirably made of steel or copper, it may be 1. In combination: used as one of the terminals of an electroplating bath. a metal holding plate having a transverse hole includ There is an additional advantage in the use of the fix 15 ing a first section of smaller diameter and a second ture 20 of the invention as one of the terminals of the section of larger diameter; electroplating bath. Heretofore, when a fixture having a detonating plug structure comprising a conductive the detonating plugs held thereto by a low-melting alloy plug disc and a conductive stem securely held within was used, oftentimes there would occur a “poisoning' of a central hole of the disc and extending outwardly the gold-plating bath by the low-melting alloy, resulting 20 from one face of said disc, said stem being insulated in an unduly short life for the plating bath. from the plug disc and provided with threads along The metal holding plate 22 of the fixture 20 has a plu at least a part of its external length; rality of transverse holes 34, each comprising a first sec a nut having an outside diameter somewhat less than tion 36 of smaller diameter in alignment with a second the diameter of the second section of the hole of the Section 38 of larger diameter. The end wall 40 of the 25 holding plate; and larger second section 38, which is located at the juncture said plug structure being held to the holding plate with of the second section with the first section, has desirably a face of the plug disc engaging the holding plate a conical shape. The elongated nut 24 has a rounded about the transverse hole and with the stem extend or ball-shaped end 44, which on engagement with the ing through the first section and into the second sec conical end wall 40 presents a circular line contact rather 30 tion of the hole, said nut engaging threads of the than a surface contact which would occur with comple stem to draw the plug disc against the holding plate mentary Surfaces. It has been found that a line engage and to bottom the nut against the end wall of the ment of the end wall 40 and nut 24 allows for some non second section at the juncture of the second section perpendicularity of wire 14 as to the plug 10 and still with the first section of said transverse hole. assures the holding of the inside face of the plug 10 flush 35 2. A combination in accordance with claim 1 wherein against the fixture holding plate 22. the inner end of the nut is rounded to form a line en Where the manner of manufacture consistently pro gagement with the end wall of the second section which duces the detonator plugs 10 with the wires 14 normal end wall has a conical shape. to the disc 12, the end wall 40 of the larger second sec 3. In a method for the electroplating of a conductive tion 38 may have a rounded surface which is comple 40 detonator plug comprising a plug disc and a stem of mentary to the ball-shaped end 44 of the elongated nut smaller diameter extending outwardly from one face 24. In another form, the end wall 40 of the second thereof along the axis of said plug disc, the step com Section 38 and end 44 of the nut may be provided with prising: conical complementary surfaces. In the latter two forms, providing as one terminal of an electroplating bath a the contact between the hole and nut is a surface contact, 45 metal holding plate having a transverse hole of two in contrast to the line contact illustrated in FIG. 2. succeeding diameters, holding the detonator plug to It will be seen that the nut 24 has an outside diameter the holding plate with a face of the plug disc engag Somewhat less than the diameter of the second section ing the holding plate about the transverse hole and 38 of the transverse hole 34 of the holding plate 22. with the stem extending through the smaller diameter The nut is provided with a wrench-receiving head 46, usu 5) length of the hole into the larger diameter length of ally hexagonal in configuration, at the end opposite the said hole, engaging an elongated nut to the threads rounded or ball-shaped end 44. The nut is internally of the plug stem, drawing the plug disc against the threaded along its longitudinal axis. holding plate and bottoming the nut against the wall The detonator plug 10 is held to the holding plate 22 at the juncture of the two diameter lengths of the with the face of the plug disc 12 engaging the holding 55 transverse hole, placing the plate in an electroplating plate about the transverse hole 34 and with the stem 14 bath and electroplating the exposed portions of said of the plug extending through the first section 36 into plug. the second section 38 of the hole. The portion of the 4. In a method for electroplating a conductive deto elongated nut 24 within the second section 38 engages the nator plug comprising a plug disc and a stem of smaller threads of the plug stem 14 to draw the plug disc 12 60 diameter extending outwardly from one face thereof along against the holding plate 22, thereby bringing about bot the axis of said plug disc, the step comprising: toming of the ball-shaped end 44 of the nut 24 against providing as one terminal of an electroplating bath a the conical end wall 40 of the second section 38 of the metal holding plate having a transverse hole of two transverse hole. The provision of the conical end wall succeeding diameters, holding the detonator plug to 40 and the ball-shaped end of the elongated nut 24 as 65 the holding plate with the face of the plug disc en sures proper alignment of the detonating plug within the gaging the holding plate about the transverse hole fixture 20. and with the stem extending through the smaller di The gold-plated detonator plug 10 of the invention is ameter length of the hole into the larger diameter illustrated in FIGS. 5 and 6. It will be seen that the very length of said hole, engaging an elongated nut having thin gold-plate 43 does not form on the exposed surface 70 a portion of its length exposed outside of the holding of the plastic coating 16, thus maintaining the insulation plate and being provided on said exposed section between the wire 4 and the disc 2. with a wrench receiving head to threads of the plug With the fixture of the invention it is possible to mount stem, drawing the plug disc against the holding plate considerably more detonating plugs 10 than was formerly and bottoming a rounded end of the nut against a possible with a fixture using a low-melting alloy to an conical end wall at the juncture of the two diameter 8,223,599 5 6 lengths of the transverse hole, placing the plate in 2,789,457 4/1957 Allen ------85-32 an electroplating bath and electroplating the exposed 2,816,066 12/1957 Russell ------204-46 portions of said plug. 2,820,757 1/1958 Belke ------204297 2,994,244 8/1961 Hay ------86-1 References Cited by the Examiner 3,018,322 1/1962 Goellner ------174-15 UNITED STATES PATENTS 3,077,515 2/1963 Divers ------174-15 1,721,414 7/1929 Robe ------204-297 2,366,885 1/1945 Van Tuyl ------86-1 BENJAMIN A. BORCHELT, Primary Examiner. 2,761,349 9/1956 Heller ------85-32 SAMUEL W. ENGLE, Examiner.