c. D. PRATT sfm. 2,413,516 SHBATHIHG HATERIAL Filed April 20. 1944 Cam. pawn Jm-aes vA. FARR INVENTORS ATTORNEY "2,1351 Patented Dec. 31, 1946 2,413,516 SHEATHING MATERIAL Carl D. Pratt and James A. Farr,’ Tamaqua,‘ Pa., assignors to Atlas Powder Company, Wilming ton, Del., a corporation of Delaware cApplication April 20, 1944,,S‘erial No. 531,888 10 Claims. (01. 102-24) _ . 2 . ' an improved sheath for an explosive cartridge. Another object of the invention is the pro or about ‘1/1" and therebetween in thickness have usually been found most desirable. Since thesheath dimensions are not readily varied, sheath weight is 'most e?ectively altered by means of change in sheath density. Many following description. sirable that the sheaths be‘ readily susceptible The present application relates to sheathing for explosives. An object of the invention is the provision of sheathing compositions heretofore proposed vision of an improved sheathing composition for have not been susceptible for preparation of an explosive cartridge. sheaths of suf?ciently varying densities. A further object of the invention is the pro The sheaths prepared according to the present vision of an improved sheathed explosive. Still another object ‘of the invention is the 10 invention are characterized by extraordinary ?exibility of density control. provision of a sheath for an explosive cartridge, Usually it is desired that sheaths be prepared which sheath has improved volume and weight . as self-sustaining units which will hold their characteristics. . shape before they are placed around explosive 'A still further object of the invention is the provision of a sheath for an explosive cartridge, 15 cartridges. It is then important that the sheaths be sui'?ciently strong and rigid to withstand which sheath is sturdy and yet can be cut easily. > rough handling. At the same‘ time, it is de Other objects will become apparent from the . to cutting without crumbling when part car Most explosives, when ?red, produce .a hot ?ame. In gaseous ,and dusty locations, this 20 tridges' are to be used. ?ame is a source of danger; for it may initiate . _ an explosion in the surrounding atmosphere. It has been known for some time that this Many of the sheathing compositions prepared prior to the present invention haverequired the inclusion of undesirable bonding agents. Some have employed adhesive organic materials which danger may be reduced if explosive cartridges are sheathed in compositions containing ?ame 25 are troublesome to use and which produce sticky compositions giving considerable difficulty in suppressing chemicals. The ?ame suppressing loading. Other bonding materials which have chemicals employed operate, it is believed, to re been necessary in prior compositions have caused duce the ?ame temperature ‘or to prevent the the compositions to set up into brittle sheaths ?ame from reaching mine dust or gases. Prob; 30 which cannot be readily cut; and, in some cases, ably both of these effects occur. such sheaths have been so-hard that the force Many materials which decompose with’the of the explosion, instead of disintegrating the absorption of heat or which have high speci?c heats have been used as flame suppressing chem ' icals in sheathing materials. Such materials as hydrated salts such as hydrated magnesium sul phate, borax, and gypsum, iron ?lings, alkali halides, such as sodium ?uoride, sodium chlo ride, and potassium chloride, magnesium car bonate, and sodium bicarbonate have been em ployed. , sheaths into a powder so that the flame sup pressing chemical may act, has merely broken 35 them into large pieces which ?y off uselessly. Sheaths bonded in other ways have permitted passage of a knife but have crumbled away on cutting. , Sheaths of the present invention when com 40 pressed, as by ordinary tamping, during forma tion‘may be made upwithout the inclusion of bonding agents and yet form entirely satisfac~ positions usually require di?erent weights of tory sturdy sheaths. When sheaths of this in sheathing composition and often'these weights vention are prepared with looser packing pro should be within rather narrow limits, if op 45 cedures, firm. and strong sheaths which may be timum e?ects are to be obtained. If the- sheaths readily out without crumbling may be prepared are too heavy, the explosive eiliciency is unduly with the inclusion of inorganic binding agents lowered while if they are too light there is in such as are described hereinafter. sufficient‘ ?ame suppression. For best results, Some sheaths suggested prior to this invention however, sheaths should be made co-extensivef 50 have contained organic substances, as filler ma in length with the sheathed cartridges and 1 terials for example. Such substances being com usually it is preferred to avoid a wide variety of bustible have, to the extent of their presence, desheath wall thicknesses both from a point of view feated the ?ame suppressing function of the Explosive cartridges of di?erent sizes and com; of ease of manufacture and from a consideration. oi’ convenience of use. sheaths. - sheaths of this invention may be pre Sheath walls about %" 55 pared Without the inclusion of organic materials. 2,413,516 3 . 4 strength was good. The dry sheath was ?rm and When sheathing materials are loaded to form coherent sheaths they are usually mixed with water to permit proper sheath formation. The strong, readily cut, and weighed 100 grams. Example 3 water is later dried out so that the sheaths may be su?iciently ?rm and strong. Many sheathing Another sheath was prepared as in Example 1 . except that in this'case a coarser grade of per lite, 90% of which passed a U. S. Standard No. 8 sieve and 98% was held on all. 8. Standard No. compositions have required so much water dur ing formation that they have become obiectiona- _ bly wet and have had insu?icient wet strength, while other compositions have, on loading, tended 45 sieve. This sheathing mixture also possessed to ball up or to become lumpy and consequently 10 good wet strength. It was slightly more di?icult have been di?icult to pack. I to load than the composition of Example 1, but ~ not objectionably so. It produced a good ?rm sheath easily cut. weighing 105 grams on drying. The sheathing compositions of the present in vention on the other hand take up water in suf ficient quantities to provide cohesive. self-sus taining sheaths of good wet strength without be coming di?icult to load. ‘ ' Example 4 A sheath was prepared having the proportions 15 > used in Example 2 and by the method of Example These sheathing materials of the present inven 2. but the coarser expanded perlite was used. The dried sheath weighed 101 grams and had proper Expanded perlite, a commercially available .20 ties slightly better than those of the sheath of tion are prepared with combinations of a flame suppressing chemical and expanded perlite. Example 3. material, is the mineral perlite, a volcanic glass composed largely of an alkali aluminum silicate, ' ' It is found that sheaths may be strengthened if some binding agent such as Epsom salts (mag which has been put through a heating process so nesium sulphate) is added to the mix. . that it is expanded into an extremely light cellu The addition of some ?brous material improves lar form. 25 the ?exibility of the sheaths. Short ?bered as The invention will be described in comiection bestos is particularly desirable for this purpose. with the drawing, which is a view, partly in sec The next two examples show di?erent formu tion, of a sheathed explosive cartridge. lations, using Epsom salts and short ?bered As shown in the drawing, II' is a cylindrical ’ paper shell inside which lies sheathing compo 30 asbestos. which have produced valuable sheaths. In. each of these examples, the ?ne expanded sition 13. The ends of shell I l are closed by end perlite was used and the proportion of water wads l5 and I1. Lying inside sheathing I8 is an given is based on the total weight of the other explosive cartridge made up of paper shell [9, in ingredients. In each case, the Epsom salts were closing explosive charge 2|. dissolved in the water which was mixed with A sheathed explosive such as that shown in the the remaining ingredients as in the examples drawing may be prepared by placing shell it over above. The sheaths of each of thé following ex ' a solid mandrel which is about the size of the ex- ' amples, however, instead of being tamped, were plosive cartridge to be sheathed. The sheathing packed by vibration packing. ‘The mandrel was composition is then packed between the shell and the mandrel. Thevmandrel is removed and the 40 ?xed in an upright position on a vibrating table. The paper shell was placed around the mandrel sheath is dried. Then the cartridge of explosive ' and the sheathing composition was poured in as‘ is inserted in the sheath and the end wads are the table vibrated. These sheaths all showed ex fastened in place to produce the ?nished sheathed explosive. cellent wet strength and loading characteristics _ and all shells produced were found on drying to Sheathing materials of the present invention have good ?exibility and to be ?rm, strong sheaths are also particularly adapted for use in the prep aration of preformed sheaths, such as are dis closed in the application of Daniel D. Huy'ett and Frank S. Pollock, Ser, No. 315,094, ?led January /. 22, 1940 for "Sheathing tori explosive." which were easily cut. Example 5 . 50 10 Expanded perlite ________________________ __ 20 .Short ?bered asbestos ___________________ __ 20% of fine expanded perlite, 99% of which Dried sheaths prepared according to this form ulation weighed 65 to 70 grams. » Example 6 60 " Y 1 ' Per cent Sodium bicarbonate ____________________ __,_ 80 Epsom salts _________ __'_________________ __ eter and 8%" long around a mandrel 11's" in diameter. The material loaded into the shell eas ily and had good wet strength, as was shown by the absence of crumbling on removal of the man Expanded perlite ________ -_- ______________ __ could be easily cut, and weighed 108 grams. 5 10 it into an 8 gram heavy paper shell 13/4" in diam ' drel. After the mandrel was removed, the‘ sheath » was dried at 65° C. It was then ?rm and.strong,_ 65 Epsom salts __________ _.-. ____ _.... _________ __ 55 Water passed a U. S. Standard'No. 12 sieve, was mixed with 80% of pulverized sodium bicarbonate. The ‘composition was then thoroughly mixed with an‘ amount of water amounting to 10% of the dry. ingredients. The mixture was loaded by tamping Per cent Sodium bicarbonate _____________________ __ ‘The following examples illustrate speci?c em bodiments of the invention. Example 1 I Short ?bered asbestos _______ ___-_...._. _____ __ Water _-__.' ___________ __~_; _____________ __ ",Dried sheaths . prepared Taccording to formulation weighed 89 to 95 grams. 10 ' 5 5 10 this , . While all of the above examples relate to the use of sodium bicarbonate as a ?ame suppressing Example 2 chemical, and it is usually preferred that this A sheath was prepared in accordance with the procedure of Examplel except that it was com cient and economically used'?ame suppressing chemicals, other ?ame suppressing chemicals, posed of 25% ?ne perlite and 75% sodium bicar bonate. Loading was again easy and wet employed in the present invention. chemical be used, it being one 0! the most e?i such as those listed hereinbefore, may also be 2,418,518 sheaths of these examples were prepared in the same manner as that described‘ for Examples 5. expanded perlite and yet the-advantages of the present sheathing compositions will be retained. The Epsom ‘salts binding agent appears to crystallize in an interlacing needle formation which assists in making the sheaths cohesive. and 6 above. Other similar materials such as plaster of Paris The following three examples show formula tions using 70 mesh sodium chloride or powdered borax as ' ?ame suppressing chemicals. The In each case the ?ne expanded may also ‘be used as binding agents. These ma 'perlite was used. terials being hydrated salts have the additional value of being ?ame suppressing chemicals them Example 7 _ - ‘ Per cent 10 selves. . Sodium chloride- _________________ __._ ____ .._ 75 Sheaths of the present invention may be packed Expanded perlite ________ s. ______________ __ 20 Short ?bered asbestos"... ________________ __ 5 in any convenient manner. In addition to the - tamping and vibration packing examples given Water‘ _____________________ -i __________ __ 15 above, extrusion and pelleting procedures may, for example, be employed. v Sheaths prepared from this formulation loaded well, exhibited satisfactory wet strength and dried Other ?brous materials than short ?bered as to form good ?rm sheaths having a weight range bestos may be used to provide increased ?exibility in the sheaths of the present invention. For ex» ample, wood pulp may beused for this purpose. 20 Also sheaths of the present invention may include any of the numerous binder and ?ller ingredients of from 71 to 72 grams. Example 8 ' ' Per cent Sodium chloride ________________________ __ 70 Epsom salts _________________________ __-___. Short ?bered asbestos ____________ _._Y_.____-__ Expanded perlite_-__'.. ____________________ __ 10 5 15 in the art. - What is claimed is: p , _ 1. A sheathing composition for explosive car 25 Water _____________________________ __'____ . l0 tridges comprising a ?ame suppressing chemical and expanded perlite.‘ ‘ Y sheaths prepared according to this formula 2. A sheathing compositiongfor explosive car tion loaded easily, showed excellent wet strength tridges comprising a ?ame suppressing chemical, and dried to form entirely satisfactory sheaths expanded perlite. and a binding material. which were somewhat stronger than the sheaths 30 3. A sheathing composition for explosive car of Example 7. . These sheaths weighed 82 to 85 tridges comprising sodium bicarbonate and ex grains.v I ‘ panded perlite. Example 9 ' _ 80 Short fibered asbestos__'_ ________________ _‘ - 45 as to loading and as to wet and'dry character istics. They weighed from 62 to 64 grams. 60 ‘ It will be readily seen that the present inven tion provides a sheathing material which affords great?exibility in sheath density since sheath density may be varied with the amount of ex panded perlite included, this amount being sub ject to wide variation for use in di?erent situ It is round that as little as 2% and as much as 65% by weight of the dry ingredients I 5. A sheathing composition for explosive car tridges comprising sodium bicarbonate, expand ed perlite, magnesium sulphate and asbestos 5 These sheaths were also entirely satisfactory ' ations. . 35 ed perlite, and magnesium sulphate. Expanded perlite____e ___________________ __ , 15 .. ‘ tridges comprising sodium bicarbonate, expand ‘Per cent Borax Water ' 4. A sheathing composition for explosive car of sheaths of this invention may be made up of 50 ?ber. 6. An explosive cartridge sheathed with,a com position according to claim .1. - 7. An explosive cartridge sheathed with a com ’ position according to claim 2. 8. An explosive cartridge sheathed with a com- ' position according to claim 3. , 9. An explosive cartridge sheathed with a com position according to claim 4. 10. An explosive cartridge sheathed with a composition according to claim 5. ' ' CARL D. PRATT. ‘JAMES A. FARR.