US2680068A - Ammonium nitrate blasting explosives - Google Patents

Description

Patented June 1, 1954 AMMONIUM NITRATE BLASTING EXPLOSPV ES Samuel H. Davidson, Largs, and Charles H. Rigby,

Saitcoats, Scotland,

assignors to Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Application April 12, 1949, Serial No. 87,108

Claims priority, application Great Britain May 3, 1948 5 Claims.

soaked through so that the ammonium nitrate tends to be dissolved out of the explosive before the shot can be fired and the cartridges become incapable of initiation or detonation.

Moreover trouble has also been experienced in the manufacture of ammonium nitrate gelatine explosives due to a tendency of these compositions to stiffen on storage for short periods in ordinary atmospheres, frequently making it difficult to extrude into cartridge form a composition that has been allowed to stand for more than a very short period, so that the explosive composition must be extruded into cartridge form without delay. This is not always convenient, especially when the explosive has to be transported to a separate building for extrusion.

This stiifening of ammonium nitrate gelatine explosive compositions is a result of the absorp tion of moisture from the atmosphere by the highly hygroscopic ammonium nitrate crystals, especially during the mixing operation. some time has passed this moisture absorption results in neighbouring crystals of the ammonium nitrate becoming cemented together to a certain extent. It is a matter of common experience that in unusually damp weather the consistency of the freshly mixed gelatine explosives tends to be unusually soft. In this case the unusually high absorption of moisture tends to delay the onset of stiffening and the composition may be softer than is, desirable when it is to be extruded into a cartridge form, but the subsequent stiffening of the resulting cartridges may be so pronounced that they lose their deformability and cannot be pierced for the insertion of a detonator.

We have now found that these defects occasioned by the effect of water on the ammonium nitrate in armnonium nitrate explosives can be 7 minimised by the inclusion in the composition of the explosive of a small percentage of a After Water swellable and soluble ether of a macromolecular polysaccharide. A proportion of the aforesaid ether ranging from about to 5% of the weight of the explosive composition may conveniently be included. The macro-molecular polysaccharide may be, for instance, a water swellable and soluble ether of cellulose or starch. It will be understood that as the aforesaid polysaccharide ethers are oxidisable ingredients it may be advisable to omit from the carbonaceous oxidisable composition at least a portion of the usual content of carbonaceous ingredients or to include an increased amount of an oxidising salt in order to preserve a satisfactory oxygen balance.

The inclusion of the water swellable and soluble salts of the macro-molecular polysaccharide enables ammonium nitrate semi-gelatine and powder explosives to 'be used in wet situations where it has hitherto been customary to use the somewhat more expensive ammonium nitrate gelatine explosives.

It would appear that when the explosive cartridge is submerged under water that the water swellable and soluble macro-molecular polysaccharide ether swells up in contact with the water and forms a surface protection for the interior of the explosive cartridge because of the low mobility of the swollen mass and the slow rate at which it interdiffuses with the surrounding water. The interior of the cartridge thus remains satisfactorily sensitive to detonation from the time the shot has been laid until the operator is ready to fire the shot. In the case of the ammonium nitrate gelatine explosives, the tendency of the composition to stiffen on storage for short periods in ordinary atmospheres is reduced, and the tendency of the explosive to have an unduly soft consistency when freshly mixed in moist atmospheres is likewise reduced so that extrusion is facilitated.

As examples of suitable water swellable and soluble cellulose ethers there may be used for instance a water soluble sodium salt of carboxymethyl cellulose, methyl cellulose, methyl ethyl cellulose or hydroxyethyl cellulose, and these may be employed in disintegrated fibrous or in powder condition. As an example of a suitable water swellable and soluble starch ether a water soluble sodium salt of carboxymethyl starch may be used.

We prefer to mix the above water swellable and soluble macro-molecular polysaccharide ether with the inorganic salts or with the other combustibles before incorporating these with the other ingredients of the explosive, although We 3 may also incorporate the water swellable and soluble ether into the finished explosive with equally efficacious results.

By way of illustrating our invention we give the following examples in which the parts and proportions of ingredients are 'by weight.

Emamp le 1 70.7 parts of ammonium nitrate containing 1% of china clay, and 9.0 parts of sodium chloride are thoroughly mixed with 4 parts of a water soluble methyl cellulose of 26.4% methoxyl group content soluble and swellable in water below 50 C. The resulting mixture is then incorporated with 10.5 parts of a nitrated 80:20 glycerine-ethylene glycol mixture absorbed on 5.8 parts of woodmeal. The powder explosive so obtained is tamped into waxed paper wrappers and is suitable for coal blasting.

The detonation of the cartridge can still be satisfactorily initiated by means of a No. 6 commercial detonator after storing it for 4 hours under 6 inches of cold water even though the wrapper has been artificially perforated at several points.

Similarly perforated cartridges containing a composition similar to the above except that the water soluble methyl cellulose is replaced by 2 parts of woodfiour and 1 part each of additional sodium chloride and woodmeal and thus not in accordance with the invention cannot be caused to detonate by means of a similar detonator after standing under 6 inches of cold water for 15 minutes.

Example 2 70.7 parts of ammonium nitrate containing 1% of china clay and 9.0 parts of sodium chloride are thoroughly mixed with 4 parts of the water soluble sodium salt of a water soluble carboxymethyl starch. The resulting mixture is then incorporated with a 10.5 parts of a nitrated 80:20 glycerine ethylene glycol mixture absorbed on 5.8 parts of woodmeal. Ihe explosive powder so obtained is tamped into waxed paper wrappers, and is suitable for blasting in coal mines. The detonation of the cartridge can still be satisfactorily initiated, by means of a No. 6 commercial detonator, after storage for 8 hours under six inches of water, even though the wrapper has been artificially perforated at several points.

Example 3 17 parts of a nitrated 80-20 glycerine-ethylene glycol mixture and 1.8 parts of a mixture of polynitro aromatic hydrocarbons, consisting of 25% of trinitrotoluene and 75% of a mixture of isomeric dinitrotoluenes that is wholly liquid at 15 C. are mixed with 0.4 part of nitrocellulose, and into the resulting jelly are incorporated 0.5 part of woodmeal, 2.2 parts of comminuted oat husks, 2 parts of finely powdered anthracite, 1 part of sulphur and 0.3 part of chalk.

The mixture so obtained is then thoroughly incorporated with a mixture of 66 parts of ammonium nitrate containing 1% china clay, 7.8 parts of sodium nitrate and 1 part of a finely powdered water soluble sodium salt of oarboxymethyl cellulose containing 0.7 sodium carboxymethoxy groups per anhydroglucose unit of cellulose. The resulting moist powder is tamped into waxed paper wrappers and the resulting semigelatine explosive cartridges are suitable for quarry blasting.

Detonation of these cartridges can be satisfactorily initiated by means of a No. 6 commercial detonator after storage under six inches of water for 96 hours even though the wrapper is artificially perforated at several points.

Similarly perforated cartridges containing a composition similar to the above except that the water soluble sodium salt of carboxymethyl cellulose is replaced by an equal weight of ammonium nitrate and thus not in accordance with the invention cannot be caused to detonate by means of a similar detonator after storage for 2 hours under six inches of water.

Example 4 26 parts of nitroglycerine and 4 parts of orthonitrotoluene are stirred with 1 part of nitrocellulose and into the resulting jelly are mixed 1 part of woodmeal, 2.5 parts of finely powderd sulphur and 0.3 part of chalk.

This mixture is then incorporated for 30 minutes in a McRoberts mixer with an intimate mixture of 47 .7 parts of ammonium nitrate, 14 parts of sodium nitrate and 4 parts of finely powdered Water soluble sodium salt of carboxymethyl cellulose, containing 0.5 sodium carboxymethyl groups per anhydroglucose unit. The resulting gelatine explosive is then extruded into cartridges and wrapped with waxed paper. The explosive cartridges so obtained are suitable for blasting in quarries and mines.

The detonation of the cartridge can still be satisfactorily initiated with a No. 2 commercial detonator after 3 weeks storage under 10 feet of water, even though the cartridge has been artificially perforated at several points.

Similarly perforated explosive cartridges containing a composition similar to the above except that the water soluble sodium salt of carboxymethyl cellulose is replaced by 2 parts of sodium nitrate 1 part of woodmeal and 0.5 part of starch and thus not in accordance with the invention cannot be initiated with a No. 6 commercial detonator when stored for three weeks under similar conditions.

Example 5 15 parts of trinitrotoluene, 71.25 parts of ammonium nitrate, and 12.75 parts of sodium chloride are initimately mixed in an Atlas mixer with 1 part of finely powdered water soluble sodium salt of carboxymethyl cellulose, as used in Example 3.

The powder explosive so obtained is tamped into waxed paper wrappers and the explosive cartridges are suitable for use in fiery and dusty mines.

Artificially perforated cartridges containing this composition can still be fired with a No. 6 commercial detonator after storing for 8 hours under 6 inches of water.

Similarly perforated cartridges containing a composition similar to the above except that the water soluble sodium salt of carboxymethyl cellulose is replaced with 0.75 part of ammonium nitrate and 0.25 part of sodium chloride and thus not in accordance with the invention cannot be initiated to detonation after storage under 6 inches of water for hour.

Example 6 15 parts of trinitrotoluene, 78.5 parts of am monium nitrate containing 02% of parafiin wax and 2.5 parts of finely powdered aluminium are intimately mixed in an edge runner mill with 4 parts of the water soluble sodium salt of carboxymethyl cellulose as used in the preceding Example 3.

The powder explosive so obtained is tamped into waxed paper Wrappers and the explosive cartridge so obtained can still be initiated with a No. 6 commercial detonator after storage under water at 25C. for 96 hours even though the wrapper has been artificially perforated at several points.

Similarly perforated cartridges containing a composition similar to the above except that the water soluble sodium salt of carboxymethyl cellulose is replaced by an equal weight of ammonium nitrate and thus not in accordance with the invention cannot be initiated with a No. 6 commercial detonator after storage for 3 hours under similar conditions.

Example 7 A gelatinous type of explosive composition containing ammonium nitrate and according to the invention is produced as follows: 32.5 parts of nitroglycerine, 1.8 parts of the liquid mixture of polynitro aromatic hydrocarbons as used in Example 2, 2.5 parts of Woodmeal and 0.3 part of chalk are stirred with 1 part of nitrocellulose until a stiff jelly is formed. This jelly is then intimately mixed with 51.5 parts of ammonium nitrate, 7.4 parts of sodium nitrate and 4.0 parts of finely powdered water soluble sodium salt of carboxymethyl cellulose as used in Example 3. This composition can be compared for plasticity or softness using a modified type Vicat penetrometer with an otherwise similar mixture in which the 4.0% sodium salt of carboxyrnethyl cellulose is omitted. A cord of each composition of 30 mm. length and /8" diameter is placed on end under the pin of the penetrometer which has been modified by fixing a fiat disc on the pin. The disc is lowered to touch the top surface of the sample under test and a reading taken. A weight equivalent to 800 gms. is then allowed to rest on it for 60 secs. when a further scale reading is taken. The decrement in length of the column of material, which has taken place under this load, calculated to a percentage of the original length is regarded as a measure of the plasticity or softness of the mixture. The temperature of the mixture during the tests is kept between 18 and 22 C. The results are shown below.

Percentage yield or degree of plasticity or softness of mixture at various times after mixing It will be apparent from the results of this test that the introductiof of a proportion of water soluble sodium salt of carboxymethyl cellulose into a gelatinous type of explosive containing ammonium nitrate substantially retards the hardening up of the said explosive over short periods of storage thereby enabling the latter to be extruded into cartridges with greater convenience.

We claim:

1. A blasting explosive composition comprising ammonium nitrate with at least one other self-explosive sensitizing agent therefor and a small proportion of water-swellable and soluble ether of a material selected from the group consisting of cellulose and starch, said ether being uniformly distributed throughout the composition.

2. A blasting composition as claimed in claim 1 wherein the proportion of said ether is from about 0.5 to 5% by Weight thereof.

3. A blasting explosive composition comprising ammonium nitrate with at least one other self-explosive sensitizing agent therefor and a small proportion of a water-sweilable and soluble ether of cellulose, said ether being uniformly distributed throughout the composition.

4. A blasting composition as claimed in claim 3 wherein the proportion of said ether is from about 0.5 to 5% by Weight thereof.

5. A blasting composition as claimed in claim 3 wherein the said ether is a water-soluble sodium salt of carboxymethyl cellulose.

References Cited in the iiie of this patent UNITED STATES PATENTS Number Name Date 1,992,217 Kirst et a1 Feb. 26, 1935 2,231,043 Winning Feb. 11, 1941 2,314,809 Winning Mar. 23, 1943 2,314,832 Kirst et a1. Mar. 23, 1943 2,333,367 Carey Nov. 9, 1943 2,345,582 Carey Apr. 4, 1944 2,358,384 Davis Sept. 19, 1944 2,358,385 Davis et a1 Sept. 19. 1944 2,389,771 Gaver Nov. 27, 1945 2,570,827 Madison et al. Oct. 9, 1951 FOREIGN PATENTS Number Country Date 359,163 Great Britain Oct. 22, 1931 OTHER REFERENCES Industrial and Engineering Chemistry, volume 37, pages 943-947, October 1945.

Claims (1)

1. A BLASTING EXPLOSIVE COMPOSITION COMPRISING AMMONIUM NITRATE WITH AT LEAST ONE OTHER SELF-EXPLOSIVE SENSITIZING AGENT THEREFOR AND A SMALL PROPORTION OF WATER-SWELLABLE AND SOLUBLE ETHER OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF CELLULOSE AND STARCH, SAID ETHER BEING UNIFORMLY DISTRIBUTED THROUGHOUT THE COMPOSITION.