US2687553A - Apparatus for manufacturing fuses - Google Patents

Description

Aug. 3l, 1954 R. coLoMBo APPARATUS FoR MANUFACTURING FUsEs Filed Feb. 19, 1948 FIG; 1

Ill l 7\ A m w. W

Patented Aug. 31, 1954 UNITED STATES PATENT OFFICE Roberto Colombo, Turin,

Italy, assignor to Lavorazione Materie Plastiche (L. M. P.) di M. I. Colombo & C.Societa in Accomandita Semplice, Turin, Italy Application February 19 In Italy Octob Section 1, Public Law Patent expires 0 2 Claims.

This invention relates to apparatus for manufacturing matches or fuses for all civilian uses in which explosives are employed, such as blasting or road building, mining, demolition and the like.

It is known that matches or fuses for such purposes generally consist of gunpowder or special explosive mixtures, enclosed in a tubular casing formed by helical wound textile threads. As a rule, a plurality of helical windings are made with alternately right-handed and left-handed thread. Between the textile layers gums or solutions thereof or other materials are interposed in order to hold together the threads of the various layers and form a sheath withstanding bending or slight tensile stresses. The solution of gum or other material further tends within certain limits to protect the 'match or fuse against moisture, but this result is in practice hardly satisfactory, for an exposure of matches or fuses of this type to moisture makes them useless or, at least, seriously impairs their eiiiciency. Moreover, with a coating of this kind the matches or fuses treated with gums or other special mixtures tend to expand when the matches or fuses are subjected to small radius curves or frequent bending in course of laying, which often makes the match or fuse inoperative. Finally, the coating requires a lengthy operation, as gums, paints or the like should be allowed to dry after the formation of each helical layer before the next layer is begun.

A further coating in use for matches or fuses consists of a sheath of soft lead, within which the explosive material is compressed. This coating also has various disadvantages in practice, among which the most serious is certainly the low resistance to frequent bending, more particularly at acute angles. In this case, on account of the material of which it is constituted the coating tends to crack and operation of the match or fuse is generally impaired. If the coating is well made the match or fuse is safely protected against moisture, but it can only be manufactured to limited lengths, which are in many cases insuiiicient for practical use. The manufacture of this match or fuse is carried out by successive drawing of sections of tubes of lead or lead alloys, in which a certain quantity of gunpowder has previously been filled. Successive drawing operations of lead with the explosive therein, while 50 1948, Serial No. 9,584 er 4, 1944 690, August 8, 1946 ctober 4, 1964 they gradually reduce the inner diameter of the tube and its thickness accordingly, also eiect a certain compression of the gunpowder packing the latter. Frequent drawing operations are, however, necessary and, apart from the considerable unavoidable waste, the production of tube sections of considerable length is not possible.

A further known match or fuse coating consists of interwoven threads, instead of threads helically wound about the blasting charge. The interwoven layer is coated with a waterproof paint which protects, to a certain extent only, against moisture. The chief drawback of this coating is that on close bending the hose may be strangled, the match or fuse interrupted so that the unit becomes inoperative, for the material composing the outer hose is not elastic.

A considerable improvement over the above types of matches and fuses is a fuse having a coating of synthetic substances. Said synthetic substances are preferably thermoplastic materials, for instance products of polymerisation and mixed polymerisation of vinyl compounds, polycondensation products, such as polyamides or polyurethanes, and polymerisation products of acryl, styrol compounds, and the like, or softened cellulose acetate or ethylcellulose compounds.

Since thermoplastic materials are generally slightly elastic, which might result in objectionable discontinuties under considerable tensile streses of the inner explosive lling of the match or fuse, the coating is reinforced by means of strong longitudinal threads, for instance of natural or articial silk or, better, of polycondensed resins of the amino group such as nylon.

The advantages of the fuse having an outer coating of thermoplastic material, reinforced by means of longitudinal threads, are as follows:

(1) The fuse is absolutely water-proof even if steeped in water or other liquids;

(2) The coating is protected against acids, bases, oils, fats, saline solutions, sea water, etc.;

(3) The fuse can be bent even to a loop without any danger of damaging either the coating or the explosive charge contained therein;

(4) The reinforced coating provides a high resistance against tensile stresses and small elongation;

(5) The fuse can be permanently colored, using colored matter mixed with the synthetic substances forming the outer layer.

The invention relates to an apparatus for manufacturing fuse having an oute-r layer of thermoplastic material provided with reinforcing threads of high tensile strength. The apparatus according to the invention affords the possibility of manufacturing said fuse in one operation and of any desired length. The thermoplastic material is processed in any known manner, but preferably by means of extrusion. machines of the screw press type, and the hardness and flexibility of the coating can be varied 'by` suitably admixing the raw material with particular substances of various types, such as plasticizers or softening agents.

The apparatus is described with reference to accompanying drawings, in which Figures 1 and 2 show a part axial section and cross section of the fuse, Figure 2 shows the bored head for manufacturing the reinforced fuse and- Figur-,elfi isa diagrammatical View of the apparatus.

The fuse, Figures 1 and 2, comprise a core l of explosive material enclosed in a sheath 2 of synthetic material in whichstrong threads 3 (for instancenylon) of low elongation areembedded in a` longitudinal direction.

The device for manufacturingthe reinforced fuse isshown diagrammatically in Figure 3 and comprises an extrusion head I formed withan axial bore l, and witha pressure die of Iannular form ,5 concentrcwithfthe bore l andan inner annular chamber i ,to which `the synthetic materialadapted to form the sheathZ is fed bythe s crew press 5I (Figure 3) nxed at ,The chamber Yl has conveniently mounted therein a bush for distributing the material fed by the press. The sheath materialis forced under pressureto- Wards the pressure die 5. rAt the same time through holes t arranged in a circular row inthe rearlportion of the extrusionheadr Il) along a circle equal in diameter to thezmiddle diameterof the pressure die, nylon threads 5, adaptedto :form the armature for the matchor-fuse sheath, zare conveyedinto the chamber ,6 towards the pressure die. The material is extruded through the `annular ,pressure die incorporating the .nylon threads therein,v said nylon threads unwinding from spools 55 on thebutercasingof -the1ex trusionhead lf3. Atthesame time theexplosive chargezis Afed to the device lpthroughthecentral hole ,l in the extrusion head iii. The synthetic: material issues .throughthe extrusion head I-Eliin cylindrical form whichis drawn either by virtue of its own weight or by otherzmeans. The traction of the still hot materialissung from. the pressure die causesthe hose to contract and4 come thereby .into contact with the core of explosive materialissuing from the axial bore l in theiextrusion head llt-form the coating whichy exerts a slight pressure on the explosive. A short distance from the pressure'die, as the coating has cooled down,'the-match orfuse is denitely'formedits manufacture being lobviously continuous and very rapid.

The explosive material may be introduced into therhole -1 either through a-hopper or bylmeans of a screw press or a cylinder and piston device. The latter preferably consists of a pairof cylinders and pistons to ensure a continuous feed, If the explosive material is in powder, grain, flake or plateform or the like,'itwill be possible to employ a binding agent adapted to hold the particles together and preventthe explosive from slipping 4 out when the match or fuse is cut. 'Ihe binding agent may likewise be a synthetic material.

In certain cases it may be preferable to employ instead of a continuous explosive core, preformed 5 blocksI or cylinders of explosive of small length conveniently threaded on a thread for instance of polyamide resin. These blocks, connected together by the thread, are introduced through the hole 1, kcaught by :the coating and carried along l thereby as they are incorporated therewith.

When the operation is completed, the resin thread 1 connecting the blocks may be removed.

-In-most cases, however, the explosive is in power or grain form, and it 1s then preferable to l lemploytwo extrusion presses, one of which compresses the, explosive material. A compression of the powder'is in any case necessary for avoiding `the above mentioned drawback that the powder may pourout ofthe. coating when the match or yfuse is cut to length. When compression of the powder is insufcient, a binding agent as mentioned above is admixed thereto for holding together the granules of which it is made. Syntheticrresins as binding agents may be admixed with the powder. v

Inother cases it 1 is possible :to 4employpJ :paste of explosive powder :which can'bewell. compressed in the extrusion press.

What I claim is:

1. Apparatus for manufacturing fuses havingya sheath of thermoplastic Vmaterial Vcomprising Lin combination an annular chamber, means fori feeding thermoplastic material to'said annularrchamber, an annular extrusion die coaxial .with-said annular chamber, means .for feeding threads :of

synthetic material to saidannular chamber to,be embedded in the thermoplastic material, means for .extruding a pipe Vof thermoplastic :material havingdncorporated A.therein the threads 'of'syn- 40 thetic material arranged.parallelftoithesaxisfof the Vextruded pipe, Van inner extrusion die .co` axial with said, annular chamber,-means:5for; feed-` ing an explosive charge to saidfinn-er extrusion die, .the cross-sectional iarea ,of vthe linner ex, 5 trusiondiebeing. smaller than thercross+sectional area of :the ,annularfextrusion die, the fpipepof,

thermoplastic material coming; into contact withA the continuous ooreof explosive charge,.andeex.

erting a slightpressureon it byqefectofwa trav. tion exerted` on said pipe when-hot. 2. Apparatus for manufacturingzfuses l'raving-a sheath of `thermoplastic material comprising Yin combination an annular. chamber; meansfforfeedingthermoplastic material to said: annular'chamber, yanannular extrusion die coaxial withisaid: annularchamber, means for feeding threads of synthetic material yto.` said annular chamberxto'be embedded `in the A.thermoplastic imaterial, :meansA for `extruding fa gpipe of thermoplastic :material from said extrusion die v.having incorporated, therein the threads of synthetic material arranged parallelrtoy the axis of .the extrudedpipefand.y along the edgesof a regularprism, an inner .cylindrical extrusion die coaxial with Ithefsaid. annulanchamf ber, means for: feeding anI explosive charge, tosaid inner extrusion die, means for extrudingva cnn tinuous core of explosive `material `from ,said zinner extrusion die, .thecrossfsectional area of .the

inner extrusion diebeingsmaller thanthe crosssectional Aarea Vof the. annular extrusion die, Ythe pipe of .thermoplastic material .coming into ,con-

tact with the,continuouscoreofexplosive chargel and'exertinga slightpressure ,on itbyeffectfof a traction exerted on said .pipe whenhot.

Y.@References :on fo'llowing page) References Cited in the file of this patent Number UNITED STATES PATENTS Name Date 5 Mignon Feb. 14, 1882 Hamon Nov. 20, 1883 Webb Jan. 14, 1908 Sutton July 26, 1921 Bond Apr. 18, 1933 lo Short Mar. 18, 1941 Wiley et al. Aug. 4, 1942 Caldwell Nov. 28, 1944 Number Number Name Date Imber Aug. 14, 1945 Johnson Oct. 1, 1946 Slaughter Nov. 2, 1948 Selvidge Feb. 21, 1950 Prendergast Mar. 28, 1950 FOREIGN PATENTS Country Date Great Britain Aug. 7, 1928 Great Britain July 1, 1949 France Mar. 6, 1944

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