US 3304211 A
Description (OCR text may contain errors)
United States Patent 3,304,211 PELLETIZED EXPLOSIVE 0F TRINITROTOLUENE PRILLS COATED WITH SODIUM AND AMMO- NIUM NITRATE IN AN ORGANIC BINDER Robert J. Anderson, Toronto, Ontario, and John F. Short, Willowdale, Ontario, Canada, assignors to Union Carbide Canada Limited, Toronto, Ontario, Canada, a corporation of Canada No Drawing. Filed Mar. 30, 1965, Ser. No. 444,047 5 Claims. (Cl. 149-11) This invention relates to novel explosive compositions and in particular to improved ammonium nitrate blasting compositions-resistantto the action of Water and capable of use in boreholes containing standing Water.
In large scale blasting operations, it has been found most effective to use loose free running granular or pelletized explosives rather than stick explosives or explosives in rigid containers, since the use of such free running blasting agents enables complete filling of the borehole, regardless how irregular, resulting in the maximum concentration of the explosive in the borehole. However, ammonium nitrate possesses essentially no water resistance, and therefore when such compositions are to be employed in Wet boreholes, particularly those containing standing water, the ammonium nitrate must be packed in a flexible plastic bag to protect it from contacting moisture. The disadvantages accruing from this technique are obvious since, in the field, such flexible plastic containers easily become ruptured or torn in handling or in insertion in the borehole. Moreover, even when waterproofed by one of other various methods, ammonium nitrate, being less dense than water, segregates in a wet borehole and results in a low efficiency explosion.
Accordingly, despite the additional expense, the more dense and water-soluble explosives, such as trinitrotoluene, are finding greater acceptance particularly in wet borehole applications.
It is accordingly an object of this invention to provide a pelletized free running explosive composition.
It is a further object of this invention to provide such a free running blasting composition which contains ammonium nitrate and sodium nitrate. It is a further object of this invention to provide such a blasting composition which may be readily employed in wet boreholes, even those containing standing water.
The novel explosive compositions of this invention comprise pellets which contain a trinitrotoluene portion consisting of trinitrotoluene prills and an oxidant portion consisting essentially of ammonium nitrate and sodium nitrate which oxidant portion is admixed with a binder system comprised of calcium ligna sulfate and polyethylene oxide, The trinitrotoluene prills serve as seeds for the pelletization operation in the manufacture of the explosive, and hence the novel pelleted explosive compositions of this invention essentially comprise a layer of binder and oxidant, i.e., ammonium nitrate and sodium nitrate, adhered to and around a trinitrotoluene prill.
This pelletization procedure enables production of an explosive composition having a density up to about 90 pounds per cubic foot, which composition is also substantially water resistant. By the term water resistant in this application is meant that the pelletized explosives can resist both segregation of the oxidant portion from the trinitrotoluene, and leaching of the oxidant from the pellet for as long as six days in a moisture containing environment.
To facilitate the attainment of high density in the ultimate compositions of this invention, the trinitrotoluene prills employed to seed the pellets are preferably of high density themselves, e.g., having an absolute density of from about 1.50 to 1.60 grams per cubic centimeter. It
is also preferred that the trinitrotoluene prills be essentially spherical in shape and uniform in size since such characteristics facilitate the pelletizing procedure.
To assure proper density as well as desirable explosive characteristics the novel pelletized explosive of this invention comprises from about 25 to about 40% by weight trinitrotoluene in the form of prills as hereinbefore set forth, from about 2 to about 10% by Weight of the binder system comprising calcium ligna sulfate and polyethylene oxide, with the remainder being comprised of the oxidant portion of the explosive composition which oxidant por tion contains at least 50% by weight based on the oxidant portion itself of sodium nitrate, the remainder "being ammonium nitrate. The use of greater amounts of ammonium nitrate in the oxidant portion will usually result in an explosive having an absolute density too low to serve the purposes of the instant invention. Furthermore, although employing more than 40% by weight trinitrotoluene in these explosives is wholly operative, since the cost of the finished explosive is dependent almost directly upon the amount of trinitrotoluene employed, the use of greater amounts of trinitrotoluene is not preferred because of economic factors.
The binder system employed in the novel explosive compositions of this invention is present in sufficient amounts to adhere the oxidant to the trinitrotoluene prill during the pelletization procedure and to provide water resistance, as defined above, to the composition. The binder is composed of from about 40 to about 70% by weight polyethylene oxide and from about 60 to about 30% by weight calcium ligna sulfate. In these proportions, these binder ingredients provide an excellent pelletizing cement for producing the explosive according to this invention and also provide a fuel for the overall explosive composition.
The polyethylene oxide preferably employed in this invention possesses a high moleucular weight having a reduced viscosity of at least 1, preferably from about 1 to as high as about 20. Reduced viscosity is determined from a sample containing 0.2 gram of polyethylene oxide in millimeters of acetonitrile. These values correspond roughly to polyethylene oxide polymers having a molecular weight in the range of at least 100,000, preferably in the range of about 100,000 to about 4 or 5 million.
The pelletization operation may be effected in a standard conventional rotating mill. The trinitrotoluene prills, the oxidant portion of the explosive, and the binder system consisting of polyethylene oxide and calcium ligna sulfate are premixed with a small amount of water sufficient to create a thick paste of the nitrate and the binder. Preferably, from about 10 to about 15% by weight of Water based upon the weight of the entire composition is employed. It is preferred to utilize the nitrate portion of the composition and the binder in finely divided form to improve the mixing of these ingredients. The pellet once formed is then dried at elevated temperatures preferably by a steam drying operation. In one preferred mode of operation, excess binder within the pellets is gently squeezed out to the drying operating by submitting the pellets to the motion of a non-sparking ballbearing grinder operating at relatively low speed. This tends to improve the density of the pellet and to speed the drying operation. Excess binder removed by this procedure can be recovered and reutilized in subsequent batches of explosives. In the drying operation, essentially all the water added prior to the pelletization is preferably removed from the prills.
By the above procedure, pellets of varying sizes may be obtained. Of course, the ultimate size of the explosive pellets will be dependent upon the size of the trinitrotoluene prills used as a seed therein. Pellets ranging in size from about A to about in diameter are preferred since their size results in a minimum of space between the pellets, and hence enables efiicient charging of boreholes. The trinitrotoluene prills should therefore be chosen accordingly.
The novel pelletized explosive of this invention may also optionally contain a metallic fuel in an amount of up to about 20% by weight. The inclusion of such a fuel naturally increases density, oxygen balance, and velocity of detonation, and consequently such factors must be considered in the selection of the fuel and the amount thereof. Such metallic fuel is, of course, employed in a finely divided state to provide uniform comingling of the ingredients and is added to the other ingredients in the pelletization. Metallic fuels which are useful in the explosives of this invention include ferrosilicon, aluminum, iron, manganese, ferromanganese, magnesium, and various magnesium alloys such as magnesiumsilicon alloys. Inasmuch as the use of metallic fuel contributes towards the density of the overall explosive, the addition of this ingredient concurrently implies that the minimum prescribed amount of trinitrotoluene can be employed. Hence, when such a metallic fuel is employed, it supplants in part the oxidant portion of the explosive composition as hereinbefore prescribed.
Although the explosive of this invention, due to its free running nature, is primarily useful in applications where it is poured directly into a borehole, the compositions of this invention may also be employed in conventional containers such as paper and the like.
The invention has been described in detail in the foregoing specification, nonetheless, it will be apparent to those skilled in the art of explosive manufacture that many variations are possible without departure from the scope of the invention.
What is claimed is:
1. A pelletized explosive composition having a density greater than water which comprises a trinitrotoluene prill, abinder, and an oxidant portion consisting essentially of at least 50% by weight based upon the oxidant portion of sodium nitrate and ammonium nitrate, said oxidant portion and said binder being a'hered around said prills to form the pellets.
2. The pelletized explosive composition of claim 1 wherein said binder consists essentially of calcium ligna sulfate and polyethylene oxide.
3. A pelletized explosive composition having a density greater than that of water comprising from about 25 to about 40% by weight trinitrotoluene, from about 2 to about 10% by weight of a binder consisting essentially of calcium ligna sulfate and polyethylene oxide and from about to about 75% by weight of an oxidant portion consisting essentially of at least 50% by weight based upon the oxidant portion of sodium nitrate, and ammonium nitrate, said explosive constituting a pellet wherein said binder and oxidant portion are adhered around said trinitrotoluene prill to form a pellet.
4. The pelletized explosive composition of claim 3 which contains up to about 20% by weight of a finely divided metallic fuel. 7
5. The pelletized explosive composition of claim 3 wherein said binder portion consists of from about 40 to about 70% of calcium ligna sulfate and from about to about 30% polyethylene oxide.
References Cited by the Examiner UNITED STATES PATENTS 3,053,707 9/1962 Davis et al 149-8 3,112,233 11/1963 Friedman et a1 14911 X 3,160,535 12/1964 Wells 149105 X CARL D. QUARFORTH, Primary Examiner.
B. R. PADGETT, Assistant Examiner.