Delay composition for detonators

This invention relates to a novel pyrotechnic delay composition characterized by low toxicity, moisture resistance and uniform burn rate. In particular, the invention relates to a delay composition of intermediate to slow-burning time range for use in both non-electric and electric blasting caps.
Delay detonators, both non-electric and electric, are widely employed in mining, quarrying and other blasting operations in order to permit sequential initiation of the explosive charges in a pattern of boreholes. Delay or sequential initiation of shotholes is effective in controlling the fragmentation and throw of the rock being blasted and, in addition, provides a reduction in ground vibration and in air blast noise.
Modern commercial delay detonators, whether non-electric or electric, comprise a metallic shell closed at one end which shell contains in sequence from the closed end a base charge of a detonating high explosive, such as for example, PETN and an above adjacent, primer charge of a heat-sensitive detonable material, such as for example, lead azide. Adjacent the heat-sensitive material is an amount of a deflagrating or burning composition of sufficient quantity to provide a desired delay time in the manner of a fuse. Above the delay composition is an ignition charge adapted to be ignited by an electrically heated bridge wire or, alternatively, by the heat and flame of a low energy detonating cord or shock wave conductor retained in the open end of the metallic shell.
A large number of burning delay compositions comprising mixtures of fuels and oxidizers are known in the art. Many are substantially gasless compositions; that is, they burn without evolving large amounts of gaseous by-products which would interfere with the functioning of the delay detonator. In addition to an essential gasless requirement, delay compositions are also required to be safe to handle, from both an explosive and health viewpoint, they must be resistant to moisture and not deteriorate over periods of storage and hence change in burning characteristics, they must be simply compounded and economical to manufacture and they must be adaptable for use in a wide range of delay units within the limitations of space available inside a standard detonator shell. The numerous delay compositions of the prior art have met with varying degrees of success in use and application. Some of the prior art compositions contain ingredients which are recognized as carcinogenic. Other compositions contain ingredients which are soluble in water which may lead to deterioration of the composition in a moist environment. For example, one widely known delay composition comprising a mixture of powdered tungsten metal, particulate potassium perchlorate and barium chromate and diatomaceous earth, contains both water soluble material (potassium perchlorate) and a carcinogen (barium chromate). Another known type of delay composition consists of a mixture of antimony and potassium permanaganate or a mixture of zinc, antimony and potassium permanganate. These compositions, because they contain a water-soluble salt oxidizer, tend to deteriorate in hot, moist storage or use environments. As a result, detonators containing such water-soluble materials must be constructed to positively exclude any moist atmosphere thus imposing problems in manufacture.
The present invention provides a pyrotechnic delay composition of intermediate to slow burning time which composition contains no recognized carcinogen or any water-soluble material. By "intermediate to slow burning time" is meant a burning time of from about 400 to about 3200 milliseconds per centimeter of length.
In accordance with the invention, an improved pyrotechnic delay composition is provided for use in a delay blasting cap assembly which comprises from 45 to 70% by weight of barium sulphate and from 30 to 55% by weight of silicon.

The inventio may be more clearly understood by reference to the accompanying drawing which illustrates in
FIG. 1 a non-electric delay detonator and in
FIG. 2, an electric delay detonator, showing the position therein of the delay composition of the invention.

With reference to FIG. 1, 1 designates a metal tubular shell closed at its bottom end and having a base charge of explosive 2 pressed or cast therein. 3 represents a primer charge of heat-sensitive explosive. The delay charge or composition of the invention is shown at 4 contained in drawn lead tube or carrier 5. Surmounting delay charge 4 is ignition charge 6 contained in carrier 7. Above ignition charge 6 is the end of a length of inserted low energy detonating cord 8 containing explosive core 9. Detonating cord 8 is held centrally and securely in tube 1 by means of closure plug 10 and crimp 11. When detonating cord 8 is set off at its remote end (not shown) heat and flame ignites ignition charge 6, in turn, igniting delay composition 4. Composition 4 burns down to detonate primer 3 and base charge 2.
With reference to FIG. 2, a tubular metal shell 20 closed at its bottom end is shown containing a base charge of explosive 21. A primer charge 22 is indented into the upper surface of charge 21. Above charger 21 and primer 22 and in contact therewith is delay composition 23 contained within a swaged and drawn lead tube or carrier 24. Spaced above delay charge 23 is a plastic cup 25 containing an ignition material charge 26, for example, a red lead/boron mixture. The upper end of shell 20 is closed by means of plug 27 through which pass lead wires 28 joined at their lower ends by resistance wire 29 which is embedded in ignition charge 26. When current is applied to wire 29 through leads 28, charge 26 is ignited. Flame from ignited charge 26 ignites delay composition 23 which in turn sets off primer 22 and explosive 21.
The invention is illustrated with reference to several series of tests summarized in the following Examples and Tables.
EXAMPLES 1-8
A number of delay compositions were made by intimately mixing together different proportions of barium sulphate and powdered silicon. The specific surface area of barium sulphate was 0.81 m.sup.2 /g while the specific surface area of silicon was 8.40 m.sup.2 /g. The mixtures were prepared by vigorous mechanical stirring of the ingredients in slurry form utilizing water as the liquid vehicle. After mixing, the slurry was filtered under vacuum and the resulting filter cake was dried and sieved to yield a reasonably free-flowing powder. Delay elements were made by loading lead tubes with these compositions, drawing these tubes through a series of dies to a final diameter of about 6.5 mm and cutting the resultant rod into elements of length 25.4 mm. The delay times of these elements, when assembled into non-electric detonators initiated by NONEL (Reg. .TM.) shock wave conductor, were measured. Delay time data are given in Table I below while the sensitivities of some of these compositions to friction, impact and electrostatic discharge are shown in Table II below.
TABLE I______________________________________ Length of Delay Number of Composition Element DetonatorsExample BaSO.sub.4 :Si.sup.1 (mm) Tested______________________________________1 70:30 25.4 20.sup.22 64:36 25.4 20.sup.23 62:38 25.4 20.sup.24 60:40 25.4 20.sup.25 58:42 25.4 20.sup.26 56:44 25.4 20.sup.27 50:50 25.4 20.sup.38 45:55 25.4 20.sup.2______________________________________Delay Time (milliseconds) Coefficient of Variation.sup.4Example Mean Min. Max. Scatter (%)______________________________________1 3385 3224 3541 317 2.402 5062 4834 5184 350 1.773 5325 5172 5476 304 1.714 5681 5527 5786 259 1.365 5936 5839 6003 164 0.666 5642 5529 5765 236 0.987 5089 4966 5360 394 1.958 4466 4256 4856 600 2.99______________________________________ Notes: .sup.1 BaSO.sub.4 specific surface area 0.81 m.sup.2 /g; Si specific surface area 8.40 m.sup.2 /g. .sup.2 Denotes detonators which incorporated a 12.7 mm long red leadsilicon igniter element and a 6.35 long red leadsilicon igniter element. Delay times quoted include delay time contribution of these two igniter elements, nominally 95 milliseconds. .sup.3 Denotes detonators which incorporated a 12.7 mm long red leadsilicon igniter element and a 6.35 mm long red leadsilicon-Ottawa san (SiO.sub.2) igniter element. Delay times quoted above include delay time contribution of these two igniter elements, nominally 160 milliseconds. .sup.4 Delay time coefficient of variation is delay time standard deviation expressed as a percentage of mean delay time.
TABLE II______________________________________ Electrostatic Impact.sup.2 Friction.sup.3 Discharge.sup.4 Min. Ignition Min. Igni- Min. IgnitionComposition Height tion Height EnergyBaSO.sub.4 :Si.sup.1 (cm) (cm) (mJ)______________________________________70:30 >139.7 >83.8 >256.565:35 >139.7 >83.8 >256.560:40 >139.7 >83.8 >256.555:45 >139.7 >83.8 >256.550:50 >139.7 >83.8 >256.545:55 >139.7 >83.8 >256.5______________________________________ Notes: .sup.1 BaSO.sub.4 specific surface area 0.81 m.sup.2 /g; Si specific surface area 8.40 m.sup.2 /g. .sup.2 In impact test, mass of fallhammer (steel) 5.0 kg. Samples tested in copper/zinc (90/10) cup. .sup.3 In friction test, mass of torpedo (with aluminum head) 2.898 kg. Samples tested on aluminum blocks. .sup.4 Discharge from 570 pF capacitor.
EXAMPLE 9
The relationship between means delay time and length of delay element was established for a barium sulphate-silicon 58:42 composition. Again, the tests were performed using non-electric detonators initiated by NONEL (Reg. .TM.). Results are shown in Table III below.
TABLE III______________________________________ Length (L) of Number of Composition Delay Element DetonatorsExample BaSO.sub.4 :Si.sup.1 (mm) Tested______________________________________9 58:42 6.35 20.sup.2 12.7 20.sup.2 25.4 20.sup.2______________________________________ Relation between Mean Delay TimeDelay Time (milliseconds) (T) and Delay Coefficient of Element LengthMean Min. Max. Scatter Variation (%) (L)______________________________________1449 1381 1515 134 2.26 T = 234.7 L -3022 2934 3104 170 1.24 8.0 ms5936 5839 6003 164 0.66 (Correlation coefficient 0.9998)______________________________________ Notes: .sup.1 BaSO.sub.4 specific surface area 0.81 m.sup.2 /g; Si specific surface area 8.40 m.sup.2 /g. .sup.2 Each detonator incorporated a 12.7 mm long red leadsilicon igniter element and a 6.35 mm long red leadsilicon igniter element. Delay times quoted include delay time contribution of these two igniter elements, nominally 95 milliseconds.
From the results shown in Table III, it can be seen that a strong linear relationship exists between mean delay time and length of barium sulphate-silicon delay element. This characteristic is important in manufacturing processes that utilize drawn lead delay elements, as it affords control of nominal delay times by simple manipulation of element cutting lengths.
EXAMPLE 10
A evaluation of the low-temperature timing performance of barium sulphate-silicon compositions was made by subjecting non-electric detonators containing a BaSO.sub.4 -Si 58:42 pyrotechnic mixture to a temperature of -45.degree. C. for a period of 24 hours. The detonators were subsequently fired at that temperature by means of NONEL (Reg. .TM.) shock wave conductor and their delay times were noted. Timing results are given in Table IV below.
TABLE IV______________________________________ Test Composition Temperature Number of DetonatorsExample BaSO.sub.4 :Si.sup.1 (.degree.C.) Tested/Number Fired______________________________________10 58:42 20 20/20.sup.2 58:42 -45 15/15.sup.2______________________________________Delay Time (milliseconds) Coeffi- cient of % Change in Varia- Delay Time % Change tion (20.degree. C. to in DelayMean Min. Max. Scatter (%) -45.degree. C.) Time/.degree.C.______________________________________3022 2934 3104 170 1.24 3.84 0.0593138 3068 3218 150 1.48______________________________________ Notes: .sup.1 BaSO.sub.4 specific surface area 0.81 m.sup.2 /g; Si specific surface area 8.40 m.sup.2 /g. .sup.2 Each detonator had a 12.7 mm long red leadsilicon igniter element, a 6.35 mm long red leadsilicon igniter element and a 6.35 mm long barium sulphatesilicon delay element. Delay times quoted include delay time contributions of igniter elements, nominally 95 milliseconds.
As seen from the results in Table IV, the temperature coefficient of the BaSO.sub.4 :Si 58:42 composition over the temperature range -45.degree. C. to +20.degree. C. is 0.059 percent per degree C. Also, it can be noted that no failure occurred in these low-temperature firing tests.
EXAMPLE 11
In order to assess the effect of the specific surface area of silicon on the delay time characteristics of barium sulphate-silicon composition, three mixtures, each consisting of BaSO.sub.4 -Si in the mass ratio 58:42, were prepared. Silicon samples of specific surface area 8.40, 7.20 and 6.05 m.sup.2 /g were used in the preparation of the compositions under test. The delay times of these compositions were measured in assembled NONEL (Reg. .TM.) initiated non-electric detonators. The results which were obtained are summarized in Table V, below, where it can be seen that as the fuel specific surface area is decreased the greater is the delay time of the composition.
TABLE V______________________________________ Specific Sur- face Area of Length of Number of Composition Silicon Delay Ele- DetonatorsExample BaSO.sub.4 :Si.sup.1 (m.sup.2 /g) ment (mm) Tested______________________________________11 58:42 8.40 25.4 20.sup.2 58:42 7.20 25.4 20.sup.2 58:42 6.05 25.4 20.sup.2______________________________________Delay Time (milliseconds) Coefficient of VariationMean Min. Max. SCatter (%)______________________________________5936 5839 6003 164 0.666603 6453 6749 296 1.268065 7495 8351 856 2.61______________________________________ Notes: .sup.1 BaSO.sub.4 specific surface area 0.81 m.sup.2 /g. .sup.2 Each detonator incorporated a 12.7 mm red leadsilicon igniter element and a 6.35 mm red leadsilicon igniter element. Delay times quoted include delay time contribution of these two igniter elements, nominally 95 milliseconds.
EXAMPLE 12
The suitability for use in electric detonators of one of the compositions of the invention was determined. The oxidant-fuel combination which was evaluated was 60:40 BaSO.sub.4 -Si by mass. Barium sulphate of specific surface area 0.81 m.sup.2 /g and silicon of specific surface area 8.40 m.sup.2 /g were employed. Electric detonators, each having a delay train consisting of a 6.35 mm long red lead-silicon-Ottawa sand (SiO.sub.2) igniter element superimposed on a 25.4 mm long barium sulphate-silicon delay element, were assembled and fired. Statistical data on the timing performance of these detonators is condensed in Table VI. Included in Table VI, for comparison, are the corresponding timing results obtained for the same mixture in non-electric, NONEL (Reg. .TM.) inidiated detonators.
TABLE VI__________________________________________________________________________ Delay Time (milliseconds) Composition Detonator Length of Delay Number of Coefficient of VariationExample BaSO.sub.4 :Si.sup.1 Type Element (mm) Detonators Tested Mean Min. Max. Scatter (%)__________________________________________________________________________12 60:40 Non-electric 25.4 20.sup.2 5681 5527 5786 259 1.36 60:40 Electric 25.4 20.sup.3 5075 4905 5173 268 1.33__________________________________________________________________________ Notes: .sup.1 BaSo.sub.4 specific surface area 0.81 m.sup.2 /g; Si specific surface area 8.40 m.sup.2 /g. .sup.2 Denotes detonators which incorporated a 12.7 mm long red leadsilicon igniter element and a 6.35 mm long red leadsilicon igniter element. Delay times quoted include delay time contribution of these two igniter elements, nominally 95 milliseconds. .sup.3 Denotes detonators which incorporated a 6.35 mm long red leadsilicon-Ottawa sand (siO.sub.2) igniter element. Delay times quoted include delay time contribution of this igniter element, nominally 85 milliseconds.
The barium sulphate/silicon delay composition of the invention may in some cases, advantageously contain a proportion of red lead oxide. The inclusion of red lead oxide has the effect of somewhat speeding up the burning time of the composition without any adverse effect on either toxicity or water solubility. Typically, such a three-component composition comprises from 15 to 60% by weight of barium sulphate, from 25 to 75% by weight of red lead oxide and from 5 to 40% by weight of silicon. While the two-component delay composition of the invention comprising barium sulphate/silicon mixture provides a burning time of from about 1300 to 3200 milliseconds per centimeter of length, the three-component barium sulphate/silicon/red lead oxide mixture provides a somewhat higher burn rate of from about 400 to 2750 milliseconds per centimeter of length.
The further aspect of the invention comprising the addition of red lead oxide to the barium sulphate/silicon delay composition is illustrated with reference to several series of tests which are summarized in the following Examples and Tables.
EXAMPLES 13-19
A series of seven delay compositions comprising barium sulphate/red lead oxide/silicon mixtures were compounded in which the silicon proportion was varied from 5.7 percent to 35.0 percent by weight of the total composition while the ratio of oxidants barium sulphate/red lead oxide was held constant at 0.80. The effect of these formulation changes on composition delay time was measured. In the formulations the specific surface area of silicon was 1.79 m.sup.2 /g; barium sulphate and red lead oxide had specific surface areas of 0.81 m.sup.2 /g and 0.73 m.sup.2 /g respectively. The mixtures were prepared by vigorous mechanical stirring of the ingredients in slurry form utilizing water as the liquid vehicle. After mixing, the slurry was filtered under vacuum and the resulting filter cake was dried and sieved to yield a reasonably free-flowing powder. Delay elements were made by loading lead tubes with the compositions, drawing the lead tubes through a series of dies of decreasing diameter to a final diameter of about 6.5 mm, and cutting the resultant rod into elements. Non-electric detonators initiated by means of NONEL (Reg. .TM.) shock wave conductor were loaded with the delay elements, fired and the delay times noted. A summary of the delay times is given in Table VII, below.
TABLE VII__________________________________________________________________________ Length of Number of Delay time (milliseconds)Composition delay element detonators Coefficient ofExample BaSO.sub.4 :Pb.sub.3 O.sub.4 :Si.sup. 1 (mm) fired Mean Min. Max. Scatter variation (%)__________________________________________________________________________13 41.9: 52.4: 5.7 25.4 20.sup.2 7034 6867 7318 451 1.5614 41.5: 51.8: 6.7 25.4 20.sup.2 5324 5186 5423 237 1.1915 40.0: 50.0: 10.0 25.4 20.sup.3 1779 1739 1815 76 1.1816 37.8: 47.2: 15.0 25.4 20.sup.3 1106 1078 1148 70 1.6317 35.6: 44.4: 20.0 25.4 20.sup.3 1365 1324 1418 94 1.8318 31.1: 38.9: 30.0 25.4 20.sup.3 2541 2492 2593 101 1.1319 28.9: 36.1: 35.0 25.4 20.sup.3 4155 4010 4348 338 1.75__________________________________________________________________________ Notes: .sup.1 Silicon of specific surface area 1.79 m.sup.2 /g .sup.2 Denotes detonators which incorporated a 12.7 mm long red leadsilicon igniter element and a 6.35 mm long red leadsilicon igniter element. Delay times quoted include delay time contribution of these two igniter elements, nominally 95 milliseconds. .sup.3 Denotes detonators which incorporated a 12.7 mm long red leadsilicon igniter element and a 6.35 mm long red leadsilicon-Ottawa san (SiO.sub.2) igniter element. Delay times quoted above include delay time contribution of these two igniter elements, nominally 160 milliseconds.
EXAMPLES 20-27
In a series of eight tests, formulations comprising barium sulphate/red lead oxide/silicon mixtures were compounded in the same manner as described in Examples 13-19 in which the silicon proportion was held constant at 6.7 percent by weight while the ratio of oxidants barium sulphate/red lead oxide was varied from 0.26 to 0.90. Again, the specific surface areas of barium sulphate, red lead oxide and silicon were 0.81, 0.73 and 1.79 m.sup.2 /g respectively. The delay time characteristics of the compositions, tested in non-electric NONEL initiated detonators, are shown in Table VIII. It should be noted that a control sample of composition containing no barium sulphate was included in these tests. The performance of this control sample, containing of Pb.sub.3 O.sub.4 /Si in the ratio 93.3:6.7, is also shown in Table VIII.
The data shown in Table VIII demonstrates that in the case of BaSO.sub.4 /Pb.sub.3 O.sub.4 /Si compositions in which the proportion of silicon is fixed, any increase in the proportion of barium sulphate (at the expense of red lead oxide) has the effect of retarding the delay time of the composition.
TABLE VIII______________________________________ Length of Number of Composition delay element detonatorsExample BaSO.sub.4 :Pb.sub.3 O.sub.4 :Si.sup.(1) (mm) fired______________________________________20 44.2:49.1:6.7 25.4 10.sup.(2)21 42.2:51.1:6.7 25.4 10.sup.(2)22 40.7:52.6:6.7 25.4 20.sup.(3)23 37.2:56.1:6.7 25.4 20.sup.(3)24 34.2:59.1:6.7 25.4 20.sup.(3)25 29.2:64.1:6.7 25.4 20.sup.(3)26 24.2:69.1:6.7 25.4 20.sup.(3)27 19.2:74.1:6.7 25.4 20.sup.(3)-- nil:93.3:6.7 25.4 20.sup.(3)______________________________________Delay time (milliseconds) Coefficients ofExample Mean Min. Max. Scatter variation (%)______________________________________20 7454 7329 7565 236 0.9921 6114 6019 6290 271 1.1922 4941 4894 4988 94 0.5023 2844 2773 2916 143 1.5924 2132 2096 2169 73 0.8225 1642 1621 1658 37 0.5626 1393 1380 1416 36 0.6227 1202 1190 1211 21 0.45-- 449 406 473 67 4.60______________________________________ Notes: .sup.(1) Specific surface area of silicon 1.79 m.sup.2 /g .sup.(2) Denotes detonators which incorporated a 12.7 mm long red leadsilicon igniter element and a 6.35 mm long red leadsilicon-Ottawa san (SiO.sub.2) igniter element. Delay times quoted include delay time contribution of these two igniter elements, nominally 160 milliseconds. .sup.(3) Denotes detonators which incorporated a 12.7 mm long red leadsilicon igniter element and a 6.35 mm long red leadsilicon igniter element. Delay times quoted include delay time contribution of these two igniter elements, nominally 95 milliseconds.
EXAMPLE 28
The effect of the specific surface area of silicon on the mean delay time of barium sulphate-red lead oxide-silicon composition was assessed. The formulation selected was BaSO.sub.4 /Pb.sub.3 O.sub.4 /Si in the ratio 44.2:49.1:6.7 respectively by weight. Silicon samples of specific surface areas 1.79, 3.71 and 8.40 m.sup.2 /g were used to make the compositions under test. The results which were obtained are condensed in Table IX, where it can be seen that the mean delay time decreases as silicon specific surface area is increased.
TABLE IX______________________________________ Specific Sur- Length of Composition face Area of Delay ElementExample BaSO.sub.4 :Pb.sub.3 O.sub.4 :Si Silicon (mm)______________________________________ 44.2:49.1:6.7 1.79 25.428 44.2:49.1:6.7 3.71 25.4 44.2:49.1:6.7 8.40 25.4______________________________________ Delay Time (milliseconds) Coefficient Number of of Detonators VariationExample Fired Mean Min. Max. Scatter %______________________________________ 10.sup.(1) 7454 7329 7565 236 0.9928 20.sup.(2) 1535 1492 1568 76 1.24 20.sup.(2) 753 746 761 15 0.55______________________________________ Notes: .sup.(1) Denotes detonators which incorporated 12.7 mm long red leadsilicon igniter element and a 6.35 mm long red leadsilicon-Ottawa san (SiO.sub.2) igniter element. Delay times quoted include delay time contribution of these igniter elements, nominally 160 milliseconds. .sup.(2) Denotes detonators which incorporated a 12.7 mm long red leadsilicon igniter element and a 6.35 mm long red leadsilicon igniter element. Delay times quoted include delay time contribution of these igniter elements, nominally 95 milliseconds.
EXAMPLES 29 and 30
The relationships between mean delay time and delay element length were determined for two of the compositions of the invention namely BaSO.sub.4 /Pb.sub.3 O.sub.4 /Si in the ratio 29.2:64.1:6.7 and also in the ratio 41.5:51.8:6.7 by weight. Lead-drawn delay elements of lengths 6.35, 12.7, 25.4 and 50.8 mm made with these compositions were assembled into non-electric, NONEL (Reg. .TM.) initiated detonators, subsequently fired and the delay times noted. Results are shown in Table X. From these results it can be seen that, for the two formulations tested, strong linear relationships exist between mean delay time and delay element length. This characteristic is important in manufacturing processes which utilize lead-drawn delay elements, as it affords control of nominal delay times by simple manipulation of element cutting lengths.
TABLE X__________________________________________________________________________ Relation Delay time (milliseconds) Between Mean Length of (L) Number of Coefficient Delay Time (T)Composition Delay Element Detonators of Variation & Length (L) ofExample BaSO.sub.4 :Pb.sub. 3 O.sub.4 :Si.sup. 1 (mm) Fired Mean Min. Max. Scatter % Delay__________________________________________________________________________ Element29 29.2:64.1:6.7 6.35 20.sup.2 478 452 502 50 2.64 T(ms) = 62.17 12.7 20.sup.2 859 844 870 26 0.72 (L) + 74.4 ms 25.4 20.sup.2 1646 1629 1660 31 0.57 (Correlation co- 50.8 20.sup.2 3237 3204 3267 63 0.58 efficient 0.9999)30 41.5:51.8:6.7 6.35 20.sup.3 1134 1074 1243 169 3.51 T(ms) = 205.5 12.7 20.sup.3 2602 2402 2690 288 2.75 (L) - 33.1 ms 25.4 3 5392 5178 5506 328 1.57 (Correlation co- 50.8 20.sup.3 10317 9896 10490 594 1.49 efficient__________________________________________________________________________ 0.9993) Notes: .sup.1 Specific surface area of silicon 1.79 m.sup.2 /g .sup.2 Denotes detonators which incorporated a 12.7 mm long red leadsilicon igniter element. Delay times quoted include delay time contribution of this igniter element, nominally 70 milliseconds. .sup.3 Denotes detonators which incorporated a 12.7 mm long red leadsilicon igniter element and a 6.35 mm long red leadsilicon-Ottawa san (SiO.sub.2) igniter element. Delay times quoted include delay time contribution of these two igniter elements, nominally 160 milliseconds.
EXAMPLES 31 and 32
An assessment of the low temperature timing performance and reliability of the BaSO.sub.4 /Pb.sub.3 O.sub.4 /Si compositions of the invention was made by subjecting non-electric detonators containing two of the above mentioned pyrotechnic mixtures to a temperature of -45.degree. C. for a period of 24hours. The detonators were subsequently fired at that temperature by means of NONEL (Reg. .TM.) shock wave conductor and their delay times were noted. Results are given in Table XI. It can be noted that no failure occurred in these low temperature firing tests.
TABLE XI______________________________________ Length of Delay Test Number of Composition Element temp. DetonatorsExample BaSO.sub.4 :Pb.sub.3 O.sub.4 :Si.sup.(1) (mm) (.degree.C.) Fired & Tested______________________________________ 25.4 20 20.sup.(2) /20.sup.(2)31 29.2:64.1:6.7 25.4 -45 20.sup.(2) /20.sup.(2) 25.4 20 20.sup.(3) /20.sup.(3)32 41.5:51.8:6.7 25.4 -45 20.sup.(3) /20.sup.(3)______________________________________Delay time (milliseconds) Coefficient ofExample Mean Min. Max. Scatter Variation (%)______________________________________ 1646 1629 1660 31 0.5731 1836 1800 1875 75 1.10 5392 5178 5506 328 1.5732 7123 6752 7319 567 2.11______________________________________ % Change in Delay time % Change in DelayExample (20.degree. C. to -45.degree. C.) time/.degree.C.______________________________________31 11.54 0.17832 32.10 0.494______________________________________ Notes: .sup.(1) Specific surface area of silicon 1.79 m.sup.2 /g .sup.(2) Denotes detonators which incorporated a 12.7 mm long red leadsilicon igniter element. Delay times quoted include delay time contribution of this igniter element, nominally 70 milliseconds. .sup.(3) Denotes detonators which incorporated a 12.7 mm long red leadsilicon igniter element and a 6.35 mm long red leadsilicon-Ottawa san (SiO.sub.2) igniter element. Delay times quoted include delay time contribution of these two igniter elements, nominally 160 milliseconds.
EXAMPLE 33
In order to demonstrate the suitability of the composition of the present invention for use in electric detonators, the timing performance in electric detonators of a mixture of BaSO.sub.4 /Pb.sub.3 O.sub.4 /Si in the weight ratio 29.2:64.1:6.7 was determined. Results are shown in Table XII. Included in Table XI for comparison, are the corresponding timing results obtained for the same mixture in non-electric, NONEL (Reg. .TM.) initiated detonators.
TABLE XII______________________________________ Length Deto- of Number ofEx- Composition nator Element Detonatorsample BaSO.sub.4 : Pb.sub.3 O.sub.4 : Si.sup.(1) Type (mm) Tested______________________________________ 29.2: 64.1: 6.7 Non- 25.4 20.sup.(2)33 electric 29.2: 64.1: 6.7 Electric 25.4 10.sup.(3)______________________________________Delay time (milliseconds) CoefficientExample Mean Min. Max. Scatter Variation (%)______________________________________ 1642 1621 1658 37 0.5633 1559 1528 1584 56 1.07______________________________________ Notes: .sup.(1) Specific surface area of silicon 1.79 m.sup.2 /g .sup.(2) Denotes detonators which incorporated a 12.7 mm long red leadsilicon igniter element. Delay times quoted include delay time contribution of this igniter element, nominally 70 milliseconds. .sup.(3) No igniter element was used in electric detonators.
The components of the novel delay composition of the invention must be in a finely divided state to insure intimate contact between the oxidants and fuel. Measured in terms of specific surface area, the barium sulphate ranges from 0.5 to 3.0 m.sup.2 /g, preferably 0.8 to 2.7 m.sup.2 /g, the red lead oxide ranges from 0.3 to 1.0 m.sup.2 /g, preferably from 0.5 to 0.8 m.sup.2 /g, and the silicon ranges from 1.4 to 10.1 m.sup.2 /g, preferably from 1.8 to 8.5 m.sup.2 /g. The oxidizers and fuel may advantageously be slurried with vigorous stirring in water as a carrier, the water removed by vacuum filtration and the filter cake dried and sieved to yield a free-flowing, finepowder ready for use.

Number	Name	Date	Kind
2586959	Kerr et al.	Feb 1952
4008109	Norton	Feb 1977

Delay composition for detonators

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