US3048507A - Matchhead igniters and compositions and method for their manufacture - Google Patents

Description

Aug. 7, 1962 D. T. ZEBREE 3,048,507 MATCHHEAD IGNITERS AND COMPOSITIONS AND METHOD FOR THEIR MANUFACTURE Filed Dec. 51, 1956 2 Sheets-Sheet 1 FLASH QUALITIES OF MATCHHEADS WITH SNOW FLOSS DIAZODINITROPHENOL /KC I0 /Mg./SNOW FLOSS /NITROCELLULOSE 26.0/47] HOS/2% FIG.| FIG. 2

FLASH QUALITIES OF MATCHHEADS WITHOUT SNOW FLO-SS DIAZODINTROPHENOL KC I0 Mg/ NITROCELLULOSE FIG. 4 FIG.5

DAVID T ZEBREE INVENTOR.

AGENT Aug. 7, 1962 D, T. ZEBREE 3,048,507

MATCHHEAD IGNITERS AND COMPOSITIONS AND METHOD FOR THEIR MANUFACTURE Filed Dec. 31, 1956 2 Sheets-Sheet 2 FIG? DAVID T ZEBREE INVENTOR.

BY W AGENT United States Patent MATCHHEAD XGNITERS AND COMPOSETIQNS AlQD METHOD FDR THEIR MANUFACTURE David Thomas Zebree, Kingston, N.Y., assignor to Hercules Powder Company, Wilmington, Del., a corporation of Delaware Filed Dec. 31, 1956, Ser. No. 631,032 Claims. (Cl. 149-64) This invention relates to new ignition compositions. In one aspect this invention relates to ignition compositions of the matchhead type, containing a siliceous material, for use in electric initiators. In another aspect this invention relates to matchheads exhibiting improved regularity of flashing and improved sensitivity to ignition by virtue of a siliceous material contained therein. In still another aspect this invention relates to a single dip method for making matchhead igniters employing a siliceous material in the dip solution to facilitate uniform pickup in the formation of matchheads of uniform size and strength on the ignition element. In still another aspect this invention relates to the utilization of siliceous materials as agents for facilitating manufacture of matchhead dipped bridges and as components which impart marked improvement to the dipped bridge so produced.

Blasting cap charges comprise generally a base charge of a detonating explosive such as pentaerythritol tetranitrate, a heat-sensitive primer charge such as diazodinitrophenol superposed on the base charge and a readily ignitable ignition charge capable of firing the primer charge by the flame generated. In the case of delay caps an additional slow-burning composition or delay fuse is generally included between the ignition and primer charges and exhibits such a predetermined rate of burning that the specified time interval elapses between the application of the firing current and the explosion of the primer charge.

Matchhead igniter charges have been used in the art for some time. As is well known, a matchhead-type igniter comprises a charge of a mixture of a flash material, an oxygen supplier and a binder therefor in direct fixed contact with an ignition element, generally a resistance or bridge wire and functions to produce a hot flame to initiate a suitable heat-sensitive material such as a primer in a blasting cap.

Matchhead igniters characteristically present field problems with reference to irregularity of flash, inconsistency in lighting the delay fuse and erratic sensitivity to ignition by the bridgewire and are for that reason often undesirable as igniters in delay caps. Further, manufacture of matchhead-type igniters exhibiting constant uniformity of strength and size has always presented a problem.

This invention is concerned with new matchhead-type compositions which have overcome problems heretofore precluding their broader use as igniters in delay caps, and with a method by which they can be manufactured to exhibit uniformity in size and strength.

An object of this invention is to provide new compositions of the matchhead type. Another object is to provide matchhead compositions exhibiting improved characteristics making them especially suitable as igniters in delay blasting caps. Another object is to provide improved matchhead-type igniters. Another object is to provide -a method for manufacture of matchhead-type igniters exhibiting greater uniformity of size and strength than heretofore. Another object is to provide for the utilization of siliceous materials in the manufacture of matchhead-type igniters and as a component of improved igniters so produced. Other aspects and objects will be apparent from the accompanying disclosure and the appended claims.

In accordance with this invention is provided a bound mass of a solid heat-sensitive material capable of flash combustion upon being heated, in admixture with a solid material capable of supplying oxygen for said combustion and a suffioient amount of a siliceous material of the group of natural occurring, and synthetic, silicas and silicates having a particle size within the range of 0.02. to 4 microns, to impart improved regularity to said flash. Also in accordance with this invention a method is pro vided for the manufacture of a matchhead-type igniter which comprises contacting a heating element with a volatile organic liquid suspension of a heat-sensitive material and an oxygen supplier, as an igniter powder, together with an amount of a siliceous material of the group of natural occurring, and synthetic, silicas and silicates having a particle size within the range of 0.020 to 4 microns, sufficient to maintain said suspension, and a binder material in amount sufl'icient to bind the said suspended material as a solid mass when said solvent is evaporated therefrom; withdrawing said element from said suspension with suspended materials adhered thereto; and drying the resulting adhered material. Still in accordance with this invention a matchhead igniter in each of a plurality of electric delay blasting caps is fired while maintaining a siliceous material of the group of natural occurring, and synthetic, silicas and silicates having a particle size in the range of 0.020 to 4 microns in each igniter, in an amount sufficient to impart improved regularity of flash thereto.

Exemplary of suitable composition components of this invention are p-phenylenediamine dipicrate, diazodinitrophenol, mercury fulminate, lead mono nitro resorcinate, lead styphnate and the like, as heat-sensitive materials; potassium chlorate, potassium perchlorate, potassiumnitrate, potassium permanganate, sodium nitrate, lead chromate, barium peromde, oxides of lead and the like, as oxidizers; nitrostarch, nitrocellulose and the like, as binders; and celite, kieselguhr, synthetic hydrated silicas, mica, complex natural silicates, diatomaceous materials, metal salts of silicic acid, synthetic silicas and the like, all finely divided to a particle size in the range of 0.020 to 4 microns, as siliceous components.

A fuel element such as magnesium, aluminum, iron, chromium, lead, boron, sulfur and the like can be included in the suspension when desired to facilitate combustion to produce additional heat during the flash combustion.

Siliceous material components of the matchhead compositions of this invention provide for a marked reduction in irregularities in flashing and erratic sensitivity to ignition by the bridgewire. The siliceous material also provide during the manufacturing process of this inven tion for a markedly improved uniformity in matchhead size and physical strength. These advantages will be more apparent in light of the accompanying disclosure.

Celite, above referred to, is a soft earthy formation of siliceous skeletons of microscopic aquatic plants called diatoms. Snow Floss is a trade name given to such a material in a highly purifiedstate such as to be substantially white. Snow Floss is a now preferred siliceous component of the matchheads of this invention, and several embodiments are therefore described in terms of Snow Floss. Of course, celite, in a brown and less purified form, and other siliceous materials, are also highly suitable as a siliceous material component of the matchhead compositions of this invention. All such siliceous materials referred to herein are of particle size of from 0.020 to 4 microns.

In accordance with a specific embodiment of the method of manufacture of this invention, the matchhead composition ingredients including a siliceous material, preferably Snow Floss, are prepared as a suspension in a suitable volatile organic solvent, and a bridgewire is 'ice then dipped into the suspension during which time materials in suspension adhere to the bridgewire. The wire, with resulting adhered material, is then withdrawn, and the adhered material is dried to form a dry matchhead composition strongly adhered to the wire. The proportions of oxidizer, flash material, and binder are any such proportions known in the art as suitable for formmga matchhead composition. The Snow Floss is present 1n an amount sufiicient to maintain the resulting suspension at least for a time to enable representative proportions of the suspended materials, including the Snow Floss to contact the bridgewire. The preferred suspension contains the ingredients in a concentration such that a significant settling of ingredient can occur only after there has been time for a number of dips, i.e., for dipping a plurality of elements. Thus the need for continuous stirring or agitation is eliminated, whereby the suspended materials are substantially static and adhere to the bridgewire in a matter of a few seconds. The suspension into which the bridgewire is dipped generally contains on a weight basis from about 11 to 65 percent heat-sensitive material, 15 to 70 percent oxygen-supplying salt, 2 to 48 percent siliceous material, and from 16 to 55 percent binder solution. Appropriate amounts of extra fuel, e.g., finely divided magnesium, are also included, when desired.

More specifically, a heat-sensitive material, say flash grade diazodinitrophenol, an oxidizer such as potassium perchlorate, and Snow Floss are admixed, in a suitable solvent, as butyl acetate, employing any suitable method such as ball milling. The wet milled mixture is then sized to say about 1 to 70 microns, the preferred range being in the order of about 1 to 20 microns. The excess solvent in the mixture is removed by decantation and the resulting admixture is then admixed with a suitable binder such as a 30 percent solution of nitrocellulose in ethyl acetate in an amount to form the desired suspension. Due to evaporation, ethyl acetate is added periodically to maintain the desired consistency of the ingredients. A plasticizer can be used, if desired, in the binder solution to maintain desired flexibility during the dipped bridge manufacture. A bridgewire affixed to the terminal ends of a set of leg wires is then dipped or swept through the suspension to permit the suspended ingredients to adhere to the bridge so that when the solvent is initially evaporated from the adhered material, the residue is uniformly deposited on the wire. The adhered material is then completely dryed to permit evaporation of the remaining solvent and formation of the matchhead igniter. The size and uniformity of the matchhead composition is controlled by the manner in which the wire is pulled through the wet mixture and by the viscosity of the suspension. When employing nitrocellulose as a binder, and Snow Floss, the matchhead often has a size say for example about 0.14 inch by 0.09 inch by 0.08 inch. However, other sizes can be made, a larger size being for example 0.15 inch by 0.12 inch by 0.10 inch. In some instances when forming a relatively large matchhead size, a second dip may be advantageously employed.

Prior to dipping it is preferable that the terminal leg wires be associated in the ignition plug to be inserted in the cap so that after the dipped bridge is formed, the plug, with terminal wires and dipped bridge, can be directly pressed into the cap. An air space is permitted between the plug and the top of the priming explosive or fuse as the case may be. An exemplary air space has a length from about to /2 inch, a space in the order of about inch being often advantageously employed.

The dip method involves dipping the bridgewire into the ingredient suspension to a predetermined depth and then allowing the matchhead material to form completely around the bridgewire. Therefore, it is important that the composition of the suspension be maintained constant and that the depth of immersion of the bridge- Wire be without substantial variance and that the removal of the wire be at a uniform rate in a uniform direction. The faster the bridgewire is removed, the larger the bead size.

In the matchhead composition the function of the heat-sensitive material is to provide the flash, and the function of the oxidizer is to supply sufficient oxygen to support flash burning. In those instances wherein a fuse in a delay assembly requires a large amount of heat for its ignition, a fuel such as magnesium, aluminum, or the like is included in the matchhead for supplying such heat. The siliceous material component regulates the burning speed of the matchhead mixture and accordingly controls the flashing qualities of the matchhead. When substantial quantities of the siliceous material are utilized, the flame produced by the burning heat-sensitive powder is sustained for longer periods and as a result makes it possible to use little or no extra fuel.

I have found that without the siliceous component ingredient, the pickup features of the matchhead mixture are not satisfactory. That is to say, without the presence of say Snow Floss, there is .a marked settling of the ingredients in the solution so that there is a nonuniform distribution of the materials in the suspension which causes an inconsistency in matchhead product composition, i.e., from dip to dip. Furthermore, the siliceous component, by virtue of imparting improved pickup features and distribution of ingredients in the suspension provides for a matchhead or bead of constant predetermined size dependent upon the rate at which the assembly is withdrawn from the suspension.

Nitrocellulose is advantageously employed in the suspension or lacquer, not only as an ultimate binder material, but it also facilitates suspension of the composition ingredients and aids in control of the flash properties of the matchhead.

In the preparation of the suspension, about parts of the wet mixture of ingredients are mixed with about 30 parts of the lacquer, say nitrocellulose/butyl acetate, in about 20/80 Weight proportions.

The dipped bridge compositions, of the invention, by virtue of the presence of the siliceous material component, exhibit markedly improved regularity in flashing characteristics, as illustrated with reference to the photos of FIGS. 1, 2, 3, 4, 5 and 6, showing a comparison in flashing qualities between a matchhead containing Snow Floss and without Snow Floss, i.e., containing no siliceous material. The photos show the great uniformity in flashing which is directly attributable to the siliceous ingredient.

Instantaneous shots in delay caps are those which result from abnormal flash to transfer heat through the delay fuse to the primary explosive before there has been time for the delay fuse to burn. Such occurrences are substantially eliminated in the practice of this invention in view of the regularity of flash that is achieved. However, to further assure against any such occurrence, it is advantageous to maintain a suitable interference between the shell and fuse, say in the order of from about 0.001 to 0.005 inch.

With reference to FIG. 7 is further illustrated utilization of a matchhead composition of this invention as an igniter in a delay blasting cap. Referring to FIG. 7, metal shell 31 is flared at central portion 32 to provide upper portion a having an inside diameter in the order of about 0.259 inch and a lower portion b having a smaller inside diameter than portion a, namely in the order of about 0.0256 inch. The length of portion b is about inch; portion a will vary with the length of the shell as desired, usually between /2 and 6 inches. A suitable base charge 34 such as pentaerythritol tetranitrate containing about 2 percent graphite is placed in the bottom of shell 31 with priming charge 36 such as straight diazodinitrophenol superposed on charge 34. Delay fuse 37 comprises a lead tube 0 containing a core "(1 of suitable delay powder, as, for example, a barium peroxide/ selenium delay fuse and is superposed on primer 36. Space 38 is disposed above fuse 37 into which pin wires 39 extend. A dipped bridge 41 of this invention, connecting the terminated ends of pin wires 39 in space 38, provides a matchhead-type igniter in accordance with the invention. Pins 39 extend upwardly from the bridge into upper portion a through semiconductive plug 40, which can be an aluminum/candelilla wax composition, preferably spaced from the shell wall, and then through a phenolic-type ignition plug 44 superposed on the semiconducti've plug 40- and joined in any suitable manner with leg wires 42 extending from the exterior into the upper portion a of the cap through the top sulfur seal 43 and waterproofing material 46, the connection being preferably a solder joint 45 the waterproofing plug. The bridgewire of dipped bridge 41 is advantageously a plain or gold-plated nichrome wire on about 0.1 inch center and is say about 0.00175 inch in diameter.

A preferred matchhead composition of dipped bridge 41 is a milled diazonitrophenol/potassium perchlorate/ Snow Floss/ nitrocellulose, in relative weight proportions of 22./52.8/18.9/5.7.

The following data exemplify firing time obtained in a delay cap discussed above employing a dipped bridge of this invention. Firing time data, obtained when firing a loose lead-selenium ignition mixture, as a control, is included.

1 Control. Loose Pb-Se (0.7 gm) in stoichiometric proportions employed as the ignition mixture in lieu of a matchhead igniter.

In carrying out these shots the inside diameter of lower section b was 0.254 inch, the upper section diameter being 0.259 inch, the length of flared cap (the taper) extending over about 17/32 inch of the shell length, the shell being 2.5 inches long. The dipped bridge was a mixture of flash grade diazodinitrophenol/potassium perchlorate/ Snow Floss ball milled in respective 24/56/20 ratios. The ball milling was done in 2.4 percent nitrostarch97.6 percent butyl acetate solution for 4 hours. The excess butyl acetate was siphoned subsequent to settling for about 12 hours. The resulting wet mixture was then blended with a solution of nitrocellulose in ethyl acetate in a respective weight ratio of 100/ 30. On a dry basis the milled mixture contained diazodinitrophenol/ potassium perchlorate/ Snow 'Floss/ and lacquer in relative weight proportions of 22.6/52.8/18.9/5.6. The

BaO /Se(7525 /PbSn was respectfully 80/20 standard fuse powder, the PbSn being about 85/ 15. An air space between the top of the delay fuse and the face of the semiconductive plug was inch. The distance between the top of the fuse and the bottom of the dip bridge was inch.

The dipped bridge compositions of this invention by the presence of a siliceous material as exemplified by Snow Floss exhibit markedly improved voltage breakdown characteristics. Thus in one series of tests the composition of the dipped bridge material was diazodinitrophenol/potassium perchlorate/Snow Floss/and nitrocellulose in respective weight ratios of 22.6/52.8/ 18.9/ 5.7 except that the Snow Floss was omitted from one composition. In determination of breakdown voltage based on 25 shots for each composition, the lowest breakdown voltage encountered in the presence of Snow Floss was 3000 volts,

6 whereas in the absence of Snow Floss the lowest value was 1100 volts.

Other tests have shown the advantages of the dipped bridge composition of this invention to series firing. Thus 5 a composition of flash diazodinitrophenol/potassium perchlorate, 24/56 was found to have a cirtical firing current of 1 amp. The same composition, except that it contains about 19 percent Snow Ross, is characterized by a critical firing current of 0.8 amp. These results were obtained "by firing 30 caps in series, each at 110 volts and measuring the minimum current required for firing.

Although a proportion of siliceous material in the matchhead in a range of say 3 to 55 percent can be employed, I prefer generally to employ a proportion in the range of say from 10 to 25 weight percent, 18 to 20 percent being optimum in many instances. This latter range (18 to 20 percent) particularly as applied to Snow Floss, gives especially smooth flashing and generally the most desirable electric firing properties.

The amount of extra fuel component, when employed, depends upon the specific heat requirements. Generally, however, from about 5 to 40 weight percent of extra fuel is suflicient. In utilizing a metal, as extra fuel, having an atomic weight below about that of iron, from about 5 to weight percent is generally sufficient, heavier metals being most advantageously employed within a range of about 10 to weight percent.

The following tabulation sets forth preferred ranges Auxiliary flash compositions, not sensitive to an ignition wire, can be employed when desired in form of loose powder mixture intermediate the matchhead and delay fuse, when the fuse powder is somewhat more difficult than usual to light. Exemplary auxiliary compositions are barium peroxide-tellurium, barium peroxideselenium and other gasless mixtures.

As will be evident to those skilled in the art, various modifications can be made or followed, in the light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims.

55 What I claim and desire to protect by Letters Patent .1. In an electric blasting cap assembly containing a bound ignition mixture, as a matchhead, around the bridgewire, the improvement comprising, on a weight basis, as said matchhead, from 9-70 percent of a primary initiating explosive capable of flash combustion in response to heat developed by passage of electric current through said bridgewire, from 10-75 percent of an inorganic solid oxidizer capable of decomposition to liberate free oxygen for support of said flash combustion in response to said heat developed as above described, from 1.5-15 percent of a binder material and from 3-55 percent of a siliceous material selected from the group consisting of natural occurring, and synthetic, silicas and silicates, having a particle size within the range of 0020-4 microns.

2. A blasting cap assembly of claim 1 wherein said siliceous material is a diatomaceous earth.

3. A blasting cap assembly of claim 2 wherein said diatomaceous earth comprises siliceous skeletons of microscopic aquatic plants and is of sufliciently purified state as to be substantially white.

4. A blasting cap assembly of claim 3 wherein said primary initiating explosive is at least one of the group consisting of diazodinitrophenol and phenylenediamine dipicrate, and wherein said oxidizer is at least one of the group consisting of potassium chlorate and potassium perchlorate.

5. An assembly of claim 2 containing from 10-25 percent of said diatomaceous earth.

6. An assembly of claim 3 containing from 18-20 percent of said siliceous skeletons.

7. In an electric blasting cap assembly containing a bridgewire, a matchhead around the said bridgewire and lead wires from said bridgewire to the outside of said cap, a detonatable base charge spaced from said matchhead, a primer charge intermediate said detonatable charge and said matchhead and a delay fuse intermediate said primer and said matchhead, the said matchhead being ignitable in response to heat developed by passage of electric current through said bridgewire via said lead wires, the said delay fuse being ignitable by heat from ignition of said matchhead and, when burned, being in operative relation with said primer to cause detonation of said primer, and the said detonatable charge being detonatable in response to detonation of said primer, the improvement comprising as said matchhead, on a weight basis, from 9-70 percent of a primary initiating explosive capable of flash combustion in response to heat developed by passage of electric current through said bridgewire, from 10-75 percent of a solid inorganic oxidizer capable of decomposition to liberate free oxygen for support of said flash combustion in response to said heat developed as above described, from 1.5 to 15 percent of a binder material and from 3-55 percent of a siliceous material selected from the group consisting of natural occurring, and synthetic, silicas and silicates, having a particle size within the range of 0.020-4 microns.

8. An assembly of claim 7 wherein said siliceous material is a diatomaceous earth.

9. An assembly of claim 8 wherein said diatomaceous earth comprises siliceous skeletons of microscopic aquatic plants and is of sufliciently purified state as to be substantially white.

10. An assembly of claim 7 wherein said primary explosive is at least one of the group consisting of diazodinitrophenol and phenylenediamine dipicrate, and wherein said oxidizer is at least one of the group consisting of potassium chlorate and potassium perchlorate.

11. An assembly of claim 7 wherein said binder material is selected from the group consisting of nitrocellulose and nitrostarch.

12. An assembly of claim 7 wherein said matchhead contains from 9-55 percent of said primary explosive, from 15-65 percent of said oxidizer, and from '5-55 percent of said siliceous material.

.13. In an assembly of claim 7, a supplemental ignition mixture intermediate said matchhead and said fuse and ignitable by heat developed from combustion of said primary explosive to thereby supply additional heat for ignition of said fuse.

14. A blasting cap assembly of claim 7 wherein said matchhead also contains from 5-40 weight percent of a fuel material selected from the group consisting of magnesium, aluminum, iron, chromium, lead, boron, and sulphur, the said material being combustible in response to said flash combustion of said primary explosive so as to thereby provide additional heat for ignition of said fuse.

15. In an assembly of claim 14, magnesium as said fuel.

References Cited in the file of this patent UNITED STATES PATENTS 1,240,549 Du Pont Sept. 18, 1917 1,852,054 Kaiser Apr. 5, 1932 1,916,078 Schless June 27, 1933 2,175,249 Burrows et al Oct. 10, 1939 2,287,093 Ellis June 23, 1942 2,440,579 Frazer et al. Apr. 27, 1948 2,473,405 Zebree June '14, 1949 2,478,501 Patterson Aug. 9, .1949 2,607,672 Spaeth et al Aug. 19, 1952

Claims (1)

1. IN AN ELECTRIC BLASTING CAP ASSEMBLY CONTAINING A BOUND IGNITION MIXTURE, AS A MATCHHEAD, AROUND THE BRIDGEWIRE, THE IMPROVEMENT COMPRISING, ON A WEIGHT BASIS, AS SAID MATCHHEAD, FROM 9-70 PERCENT OF A PRIMARY INITIATING EXPLOSIVE CAPABLE OF FLASH COMBUSTION IN RESPONSE TO HEAT DEVELOPED BY PASSAGE OF ELECTRIC CURRENT THROUGH SAID BRIDGEWIRE, FROM 10-75 PERCENT OF AN INORGANIC SOLID OXIDIZER CAPABLE OF DECOMPOSITION TO LIBERATE FREE OXYGEN FOR SUPPORT OF SAID FLASH COMBUSTION IN RESPONSE TO SAID HEAT DEVELOPED AS ABOVE DESCRIBED, FROM 1.5-15 PERCENT OF A BINDER MATERIAL AND FROM 3-55 PERCENT OF A SILICEOUS MATERIAL SELECTED FROM THE GROUP CONSISTING OF NATURAL OCCURING, AND SYNTHETIC, SILICAS AND SILICATES, HAVING A PARTICLE SIZE WITHIN THE RANGE OF 0.020-4 MICRONS.

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