Determining the Initiating Efficiency of Detonators T h e Minia ture-Cartr idge Test R. L. GRANT, Bureau of Miner, Bruceton, Pa., AND J. E. TIFFANY, Central Experiment Strtion, Bureau of Mines, Pittsburgh, Pa. A new test, called the miniature-cartridge test, for evaluating the relative initiating efRciency of detonators i s applicable to both commercial and military detonators and is believed to provide a more accurate quantitative measurement of the initiating characteristicr of detonators than any previously used test. A brief review of other detonator tests employed for this purpose i s presented. The miniature-cartridge tett is based on the principle that the ability of a detonator to initiate an insensitive explosive constitutes the best means of measuring its initiating efficiency. The experimental technique combines the advantageous features of the sand test and the TNT-iron oxide insensitive powder test. A unique operation i s the subtraction of a detonator blank. This achieves a measurement of actual resultant effect of detonator in producing a greater or lesser degree of detonation in an insensitive explosive.
Mixturer of TNT-iron oxide were selected as representative of a wide range of insensitive explosiver. Results of tests with these mixtures are presented as curves for two series of detonators: mercury fulminate-pobuium chlorate (80-20) detonators, and tetrylbase detonators. From these, a procedure for a routine test is developed and outlined. Two reference initiating-efficiency curves, based on this routine test, for fulminate-chlorate (80-20) and tetryl-base detonators are presented, as are results of the routine miniature-cabbridgetest for determinations of the initiating efficiency of 7 selected commercial N o . 6 and No. 8 detonators. By comparing results of the miniaturecartridge test with those of the sand test, it i s shown that the latter i s questionable as a general method for measuring relative initiating efficiencier of detonators and i s of value only for special cases.
E
In the sand test, first proposed by Snelling (IO), a detonator is 6red in the center of a mass of Ottawa standard sand contained in an appropriate bomb. The quantity of sand crushed is taken as a criterion of the initiating efficiency of the detonator. The preaent a p r , which compares the results of the sand test with those of t f e miniature-cartridge test, indicates that, except for special cases, the sand test is generally misleading as a measurement of initiating efficiency. The lead-plate test ( 4 ) is widely used for control work in detonator factories. The detonator to be tested is placed vertically in the center of a lead plate 3.75 X 3.75 X 0.3 cm. (1.5 X 1.5 X 0.125 inch) and fired. The size of hole and the number and nature of striations produced provide a measure of the initiatin efficiency of the detonator. There is no evidence that t h e l e d plate measures ability of a detonator to initiate detonation in high explosives. I n the small Trauzl lead block ( 7 ) the detonator is inserted into a tightly fitting cavity in the block and fired. The increase in volume is taken as an index of the initiating efficiency of the detonator. As with the lead-plate test, no one has demonstrated that the small Trauzl lead-block test measures initiating efficiency. Esop’s original test (1,8, p. 163), reported in 1899,consisted of mixing cottonseed oil with a suitable explosive, such as picric acid or TNT, and determining the percents e of oil which could be added without preventing detonation %y the detonator being tested. The original method in several modified forms has been revived in Europe within recent years and studied further by Wohler, Roth, and Ewald (16, 16) and Haid and Koenen (6). The later tests consist of TNT-talc (hydrated magnesium silicate) pellets formed under pressures of 1250 kg. per sq. cm., having a diameter of 25 mm. a hei ht of 41 to 42 mm., and a hole for the detonator 25 mm. deep. %he diameter of the cavity made in a lead plate 3 cm. thick is used as a criterion of the extent of detonation. The percentage of talc is increased until this diameter ie 25 mm., the same &s that of the pellet, when it is assumed that detonation of the pellet is incomplete. Theoorrespondin percentage of talc is taken as a measure of the strength of the jetonator. It is reported that the results can be closely re roduced. In other modifications of the test the detonator and TKT-talc pellets were fired in (a) a lar e Trauzl lead block and the volume increase of the cavity forme3 waa measured, and ( b ) in the brisance meter and the compression of a copper cylinder was measured according to the method of Kast (6). I n the TNT-iron oxide insensitive powder test (14) the detonator is fired in a 3.1 X 10 cm. (1.25 X 4 inch) cartridge of TNTiron oxide weighing 70 rams. Various blends of TNT-iron oxide, each varying by 14 of iron oxide, are used. The blende which produce 20 consecutive detonations and 20 consecutive failures are determined. I n addition, 20 trials are made for each intermediate blend. A failure is indicated by the recove@ of a stub or butt crimp of the cartridge after the shot. The procedure is generally repeated with a standard detonator for cornpariaon purpcees. Deapite the considerable labor involved, some teating engrneers believe that the insensitive powder test reflects initiat-
XPLOSIVES engineers have long needed and sought a satisfactory test for measuring the initiating efficiency of d e b nators. The numerous developments and improvements in detonators during the past decade (a), such as new and better initiating explosives, advances in features of construction, and more powerful booster-detonators, have accentuated this need. Most of the testa heretofore proposed for this purpose have possessed some serious deficiency. Generally, their value in measuring either absolute or relative initiating efficiency has been doubtful, while those few tests that were believed actually to evaluate relative initiating efficiency have been difficult and cumbersome to perform. From a viewpoint of safety it is of firshrder importance that a detonator have at least the minimum initiating efficiency required for performing the task assigned to it; otherwise the consequence may be a dangerous and costly misfire. Therefore, a satisfactory measurement of initiating efficiency would aid considerably in the study of the safety characteristics of detonators. The present paper presents a new test, which the writers call the “miniature-cartridge test”, for quantitatively evaluating the relative initiating efficiency of detonators. The test is based on the fundamental and generally accepted concept that the ability of a detonator to initiate an insensitive explosive constitutes the best means of measuring its initiating efficiency. It is believed that the miniature-cartridge test, which is applicable to both commercial and military detonators, gives a more accurate measure of the initiating characteristics of detonators than any of the previously proposed tests. OTHER DETONATOR TEsrs
Previous testa for determining the initiating efficiency of detonators have included the following: (a) sand test (8-I3), (b) lead-plate test ( 4 ) , (c) small Tram1 lead-block test (7), ( d ) nail test (7), (e) ESOP’stest ( I , 61,(fl desensitized dynamite tests (7), and ( 8 ) TNT-iron oxide insensitive powder test (6,I4). Hall and Howell (7) classified detonator tests into direct and indirect methods. I n the former the mechanical effect of the detonator is measured directly by firing tbe detonator independently of an explosive (tats a, b, c, and d ) . I n the indirect method the force or ene developed by an ex losive when initiated b study is determinei (testa e, f , and 0 ) . Ha: the detonator un% and Howell pointed out that d m c t methods should be used only subetantmte. in&$ methods, which were more like1 to measure initiatmg e5aency. Those who test detonators l a v e almost lost eight of this important consideration.
13
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Vol. 17, No. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
ing efficiency better than any of the urevious tests emploved. Its disad-’ Gantage is the difiEulty of differentiating between detonations. and failurea and the small ran e (approximatelv 2 to 12%) of adde8 iron oxide within which thLtest is workable (5). To some extent it is currently being used hy the industry.
Table I. k e e n Anelyms of TNT end Iron Oxide Used for
TNT-Im Oxide Mixtures ODdI,$. Iaoh
TNT
20 40 80 80 100
0.0531 0.0105 0.0088 0.0070
0.8 23.0
200
MINI ANRE-CARlRIDQE TEST
Essentially, the miniaturecartridge test consists of firing the detonator under test in an insensitive explosive and measuring the degree of detonation produced. For the test work various mixtures of TNT-iron oxide were selected to represent a wide range of insensitive explosives. The physical and chemical properties, especially the packing density, of the TNT-iron oxide mixtures are carefuUy controlled. The technique consists, briefly, of loading a 5-gram charge of a homoFigure 1. Miniatwe xeneous TNT-iron oxide mixture. Csrtridge Showing Which ia definitely controlled, into S. PartlylnsertedWood carefully made paper cartridge 1.25 Detonator Holder om. (0.5 inch) in inside diameter and and Fure Detonator 6.88c.m. f2.75inches) lone (Fieure 1). The packing densky %’ eonstant and the detonator is inserted to such a depth as to r d u c e maximum initiation. The extent of detonation of the Besensitized T N T is measured by firing the miniature cartridge and its detonator in the center of 1WO grams of the Ottawa sand in a steel homh of 7.5-cm. (Xineb) inside diameter (Fi re 2). The crushed sand which passes through a No. 30 U. S. %andard series screen represents the sand pulverized by the TNT-iron oxide and the detonator. From this value i s s u b t r a c e the detonator blank, which i s obtained by, similafly firing a miniature cartridge containing 5 grams of pure iron oxide and the detonator. The value of sand crushed, thus derived, represents the initiating efficiencyof the detonator. The miniature-cartridge test is therefore based on the reasonably sound concept that the desired measurement is not the force of a detonatnr itself, but the resultant effect of the detonator in producing a grester or lesser degree of detonation in an insensitive explosive. Furthermore, the experimental technique of the miniature-cartridge test combines the known advantages of the aend test and the TNT-iron oxide insensitive powder test. The conclusions and experience derived from independent experiments by the writers, not reported here, were utilized in developing the test
Cumulative Per Cent en screen Iron oxide
U. S.Standard Screen No.
75.6
0.4 0.9 8.7 56.2
0.0039
90.9
03.2
0.0029
80.1 99.3
90.2 91.0
...
Pa”
0.1
sand, whether initiated hy a No. 6 or a No. 8 stsndard electric detonator, after subtraction of the detonator blank. APPARAlUS
SANDBOXH. The steel sand homh Used in these tests has an inside diameter of 7.5 cm. (3 inebes) and sn inside height of 17.5 em. (7 inches) and is known as Bureau of Mines Sand Bomb No. 3. The bomb i s made of either goodquality machine steel or Shelby tubing and is shown, with its neoessary accessories, in Figure 2. SANDAND SCREENG. Quartz sand known as “Ottawastandard 20-30 sand” furnished by the Ottawa Silics Company, Ottawa, Ill., was used. The sand was rescreened and all which passed through a No. 20 Tyler Standard series screen (opening 0.082 em.. 0.0328 inch) and was caught on a No. 28 Tyler Standard series screen (openine 0.058 cm., 0.0232 inch) was retained for the tests. The No. 28 l r l e r and No. 30 U. S. Standard screens are considered equivslentl TEBTING-SIEVE SEAKER.This was one of the common sieve shakers, pmvided with a timer. BALANCES AND W E X Q ~ BThe . charges of TNT-iron oxide were weighed t o three deoimal places on a chemical balance. The sand w&;veighed to one decinlal place ou a pnu or,trip balance. TST. Grade I TKT having. B melting pumt ( I f at least 80.4” C. w s used. l i e screen nnillvsis is e i w n i n Table 1.
_theironaxide(Venetian1ed) ~ ~ _ ~ usedinthesetestsisgiveninT~bIe1. ~~~~~
.~~. ~~
~~
~
~~
~
~~
MATCHHEAPTYPE Ssrnss. I n these tests all fuse detonators were h r d tlwtrieally by iiuerting. into tiic detonator B uiatch head-type squib, ubraind [rum the Atlas Pouder, Company, \Yhninmon. Del. ’These ~ a i i i htierrnitr~da more ranid nerform-
I’APKR i’ms. The paper cup3 (Figure i) were prepsmd in the Iabormry as follows: Common 15-pound-base ahite tyrwwritrr paper is u s d . Itectanwlnr picrrs 7.5 X 12.18 cn). {ti X 4.675 inches) are rut havinrxmarmnal line drawn 0.94 CUI.(0375 inchi from the edge of the ionger ;de. Emh piece of paper is wrapped tightly around a IO-em. (4-inch) length of 1.2&cm. (0.5-inch)
Witbin certain limits, as the pacldng density of a TNT-iron oxide mixture increasw its explosive ower as measured by ita sand-crushing capacity decieases rapidyy. From experience with th-e experiments the decision was made to control the packing density within valuv of 0.94 * 0.02 gram per 00. If a detonator is inserted in an ex losive up to a point representing the length of the explosive ciarge in the detonator, the maximum initiating efficiencyof that detonator will 6e obtained within a s m d error. I n this reuort this is referred t o as the “depth of maximum initiation”. A 5-gram charge of TNT-iron oxide mixture produced results which were in practically the same relat{ve order as those for Iar r chmgea namely, 10 and 25 gram [In 1 %om. (0.75.inch) anr2.5-cm. (Zneh) inside diameter castridpes. respectively]. It w w dediieed~thatthese larg+r ebargea tended to mtrodure a ewhioning rKect eaiLwrl by the undetonawd portion of TNT-iron oxide. This c f k t nwvmted the iull iand-crushine rauaritv from bei&attsined and introduced an ezror. seriob f& t h i
Figure 9. Sand Bomb 3, Unasxmbld
January, 1945
ANALYTICAL EDITION
15
dowel rod, which serves as a mandrel, one end of the rod being rolled along the line. This provides exactly three wraps. A moistened Dennison’s label No. 201 is then wrapped around the cartridge. The cartridge is crimped neatly at the proper end and the crimp flattened by striking the dowel rod with a hammer while the cartridge is placed against a hard surface. Two strips of label approximately 0.94 cm. (0.375 inch) wide and 3.75 cm. (1.5 inches) long are pasted across the bottom, which is again flattened as above. The resulting paper cup has an inside diameter of 1.25 cm. (0.5 inch) and a height of 6.56 em. (2.625 inches), and weighs approximately 1 * 0.05 gram. WOODDETONATOR HOLDERS.These holders are made in a lathe from common 1.25-cm. (0.5-inch) diameter dowel rod. A hole is drilled Ion itudinally through a length of the rod, of a size so that a particjar detonator will have a snug but sliding fit within the hole. The holders are cut into 0.94-cm. (0.375 inch) lengths. TNT-IRONOXIDEMIXTURES.The TNT-iron oxide mixtures should be made up in at least 500-or 10Wgram batches. The calculated amounts of T N T and iron oxide are separately weighed to 0.1 gram, mixed on a heavy piece of paper, then screened through a No. 30 U. S. Standard screen. The luinps that do not pass are separately crushed and remixed. This operation is repeated at least 6 times. The mixture is placed in 240-ml. (8-ounce) bottles and occasionally remixed by rolling contents in the bottle. BASIC PROCEDURE F O R MINIATURE-CARTRIDGE TEST
STEP 1. WEIGHING CHARGEAND PREPARING MINIATURE One of the paper cups is filled with 5 grams of the CARTRIDGE. desired TNT-iron oxide mixture. The weighings are made to three places primarily to control the packing density.
Figure 4. Cross-Sectional Diagram Showin Method of Embedding Miniature Cartridge in Sand in {and Bomb
-
V = I/.l(rrD*L * d Y ) = 12.87(D2L - d‘i)
WOOD DETONATOR
NT-IRON OXIDE
Figure 3.
Cross-Sectional Diagram of Miniature Cartridge
The detonator and wood detonator holder are then inserted into the mixture in the cup (Figure 3). The desired depth, I , to which the detonator is t o be inserted is controlled by dimension a, which has been previously ascertained. The correct dimension, L, which will give a packing density of 0.94 =t0.02 is obtained from the calculation described in step 2. Dimension L is measured with a ruler and a small mark is made on the outside of the chrtridge at point b with a sharp pencil. While the detonator is beifig inserted, the cartridge is rolled gently between the fingers to prevent localized packing of the mixture and to obtain a uniformly distributed charge. The wood detonator holder is pushed in until the roper dimension L is obtained, while the detonator is manipulatex until dimension a is obtained. The miniature cartridge should be made carefully. STEP 2. CALCULATION OF PACKING DENSITY. From Figure 3, the volume of the charge of TNT-iron oxide mixture is
where Vis the volrirne in cc., D is inside din:nctc.r of the papcr cup, L i s length of T S 2-iron oxide charge, rl is thc: outsidc diameter of the detonator, and 1 is the depth of ixi..c.i,tion of the detonator. The density is calculnted by dividing tttc wight (5 grams) by the volume. If D is 0.50 inch, L is 1.825 inches, d is 0.272 inch, and 1 is 0.75 inch, V is calculated to be 5.32 cc., from which the packing density is found to be 5.00/5.32 or 0.94 gram per cc. Ordinarily, since the density is specified, the usual calculation will be for L, which may be computed from the above by substituting 5.32 for V . STEP3. LOADING A N D FIRIKG IX SAND BOMB. In tlic bottom of the sand bomb are placed 300 grams of rescreened Ottawa sand (Figure 4). The miniature cartridge, Kith inserted detonator, is placed vertically and centrally in the bomb, so that its bottom just rests on top of the sand; then a 700-gram portion of sand is poured in around the cartridge. The bomb is tapped about 10 times with a hammer to settle the sand and is then closed securely. The leg wires should extend out of the sides of the bomb through small slits provided for them. The bomb is then placed on a solid surface, preferably concrete, and within some kind of bombproof because of the possibility of the bomb’s rupturing should it be weak or the charge heavy. The chargc is then fired. STEP4. SCREENING PULVERIZED SAND. After the shot, the bomb is opened and the contents are placed on a piece of heavy manila paper. The metal particles are picked out and discarded. I t will be found that the portion of TKT-iron oxide which did not delonate has been compressed by the force of the shot into a hard kernel. This is broken up by rolling under a flat piece of wood along with any other lumps or cinders of sand. The sand is then screened for 3 minutes on a KO.28 Tyler Standard or a No. 30 U.S. Standard screen in a testing-sisve shaker. The screen is removed from the shaker, arid any lumps of sand found in the unscreened sand are crushed between the fingers. The sand is given an additional 100 shakes by hand on the table tdp. The crushed sand which has passed through the No. 28 Tyler screen is then weighed to the nearest 0.1 gram. STEP5. DETONATOR UANK. The dctonator blank is determined h repeating steps 1 to 4,inclusive, except that 5 grams of iron oxi& are substituted for t,he TNT-iron oxide. TESTS O F F U L M I N A T E - C H L O R A T E D E T O N A T O R S W I T H TNT-IRON O X I D E MIXTURES
A series of three 80-20 mercury fulminate-potassium chlorate detonators, containing a total charge of 1.00, 2.00, and 3.00 grams, was prepared in the laboratory. These correspond, re-
Vol. 17, No. 1
INDUSTRIAL A N D ENGINEERING CHEMISTRY
16
PRIt!%h]
yM“,}
OF TETRYL-BASE D E T O N A T O R S W I T H TNT-IRON O X I D E MIXTURES
10
NO. 6
100
1 50
2 00
2 50
50
50
50
50
50
loo
1 50
2 00
2 50
300
To cover a wider range of initiating efficiency, a seriea of three detonators containing tetryl as the base charge was prepared with 0.25, 0.75, and 1.25 grams of tetryl, respectively, and having a constant priming char e of 0.75 gram of 80-20 fulminate-chlorate (see schematic sketcfes of Figure 6) A determination of the minimum charge of 80-20 fulminate-chiorate required to initiate 1.25 grams of tetryl gave a value of 0.40 gram, using the method of Taylor and Cope (IS). The same shells as in the previo? series were used. The base charge was loaded and pressed in increments of 0.25 gram at 98 kg. per sq.‘ cm. (1400 pounds per square inch). The top surface of the tetryl w w made concave by the use of a convex press pin. The priming charge was pressed at 700 pounds per square inch. The results with these detonators of a procedure similar, to that for the fulminate-chlorate detonaton are shown BS curves in Figure 7. DISCUSSION OF CURVES OF flGURES 7 AND 8
Figure 5. Schematic Sketches of Mercur Fulminate-Potassium Chlorate (80-20) Reference betonrtorr
BEE,%]
0.50
0.75
1.00
1.25
0’75
.75
.75
.75
0.75
“;My*} 1 . 0 0
1.25
1.50
1.75
2 00
PRI$G%.]
Figure 6.
0’25
The interpretation of the curves of Figure 7 must be considered in terms of explosives which are relatively “sensitive” or “insensitive” to detonation. The developed explosive power of a sensitive explosive is independent of the magnitude of the initiating impulse, providing that impulse is above a certain minimum. On the other hand, the developed explosive power of an insensitive explosive is dependent upon the initiating impulse. The TNT-iron oxide mixtures of Figure 7 represent a wide range of insensitivity to detonation. It will be noted that the three curves for the fulminate-chlorate detonators intersect slightly to the left of the y axis (l00y0 TNT). This point may be considered as representing a transition from insensitive to sensitive explosives under the particular conditions of test. The same interpretation applies to the tetryl-base detonrrtors. It is to be noted further that the curve for the detonator containing 0.25 gram of tetryl crosses the two curves for the detonators containing 2.00 and 3.00 grams of fulminate-chlorate. However, when the sand crushed is plotted against the weight of explosive charge in the detonator (Figure 8), for each TNT-iron oxide mixture the curve for the tetryl-base detonators is above that for the fulrhinate-chlorate detonators for the same TNT-iron oxide mixture. In other words, any given TNT-iron oxide mixture will differentiate between the initiating efficiencies of detonators to a more or less satisfactory degree. For a routine
Schematic Sketches of Tetryl-Base Reference Detonaton
spectively, to No. 6, No. 8, and No. 10 Bureau of Mines standard detonators (see schematic sketches of Figure 5). The base charge of 80-20 fulminate-chlorate in 0.50-gram incrementa was charged at a pressure of 63 k per sq. cm. (900 pounds per square inch) in gilding-metal shellstaving an outside diameter of 0.69 cm. (0.27 inch) and a depression in the bottom. For all detonators of this series the 454 priming charge was 0.50 gram of 80-20 fulminate-chlorate, which WBS pressed at 49 kg. per sq. cm. (700 pounds per square inch). The press pins had a “flat” bottom (actually 400 slightly convex). Tests were made with each detonator (steps 1 to 5, inclusive) in a 5-gram charge of T N T and in various mixtures in which the T N T was replaced with 10,20,30, and 40%, respectively, of iron oxide. Figure 7 depicts the curves obtained by plotting the sand crushed against the per cent of iron oxide in the TNT-iron oxide mixture. The depth to which each detonator was inserted in the TNT-iron oxide mixture (depth of maximum initiation) was 1.25, 2.5, and 4.06 cm. (0.5, 1, and 1.625 inches) for the Nos. 6, 8, and 10 detonators, respectively. At least two trials were made for each determination and two additional trials for the detonator blank (step 5). The blank was subtracted before the points in Figure 7 were plotted.
i
1
1
I
I
i
I
I
I
L\ I
Each point of Figure 7 representa a t least two shots. The grand average of the “maximum deviation from the average” was 1.4% baaed on the total weight of sand crushed.* Thia constitutes a meaeUre of the reproducibility of the minieture-cartridge tat,
Fiymre 7.
Sand Cruahed by 5 Grams of TNT-lron Oxide Mixture Only Cent of Iron Oxide In Mixture
R Per
ANALYTICAL EDITION
January, 1945
17
teat the problem then resolves itself into the selection of a mixture or combination of mixtures which will be most suitable for the purpose. Accordingly, 80-20 and 70-30 TNT-iron oxide mixtures were selected and used and the results averaged. Briefly, the important reasons for this selection were: The average height of each curve given in Figure 7 was computed. The corresponding percentage of iron oxide in the TNTiron oxide mixture pvinf a sand-crushing value equal to the average height was oun for each curve and averaged. This grand average was 26, which meant that if a sin le mixture of 74-26 TNT-iron oxide were used the resultg wouldte in the same general order as though the whole series of TNT-iron oxide mixtures were used. Since a single mixture was considered a too severe limitation, two mixtures were decided upon for use. The vertical spread between the curves of Figure 7 is a proximately greatest in the region represented by the 80-20 an870-30 mixtures. It was found that for the mixtures having a high T N T content (from about 85-15 to 100-0) the results were not as reproducible as for mixtures of lower TN+ content. PROCEDURE F O R R O U T I N E MINIATURE-SARTRIDGE TEST
The outline of the procedure for the routine method of making the miniature-cartridge test is as follows: DETERMINATION OF DEPTHOF MAXIMVMINITIATION. The length of charge in the detonator is equal to the depth of m m mum initiation. The best means for determining the length of charge has been found to be the opening of the detonator by some safe method (3). In this work this measurement was rounded to the length nearest the next 0.25-inch increment (0.5, 0.75, 1 inch, etc.). DETERMINATION OF DETONATOR BLANX. Following the procedure of step 5, the detonator is inserted to a depth equal to the depth of maximum initiation in 5 grams of iron oxide. Two trials, each within 5y0 deviation from the aver e, are made. DETERMINATION OF THE AVERAGE OF %AND%RUSHED BY THE 80-20 AND 70-30 TNT-IRON OXIDE MIXT~JRES.At least two trials are made with each of the 80-20 and 70-30 TNT-iron oxide mixtures following the procedures of steps 1 to 4, inclusive, and the results are averaged. Each trial should not deviate by more than 5% from the average. The detonator blank is subtracted from this average. The routine method involves a minimum of 6 trials requiring about 30 minutes each.
300
-
250
-
,0’
,TETRYL-SASE DETONATORS
,’
-x..
,d‘
FULMINATE-CHLORATE DETONATORS,
,oo.o
,+/’
-x7/ v)
4
5200
-
’
9 I : VI 3
u P o 150 z
-
100
-
50
-
5
0
I
I
1.o 1.5 2.0 2.5 3.0 TOTAL EXPLOSIVE CHARGE IN DETONATOR, GRAMS
Figure 8. Sand Crushed by 5 Grams of TNT-Iron Oxide M i x t u r a Only VI. Total Weight of Explosive Charge in Detonator
0
1
2 3 4 5 WEIGHT OF TOTAL CHARGE IN DETONATOR, GRAMS
6
Figure 9. Initiating Efficiency Curves for Two Series of Reference Detonators M I N I A W R E - C A R T R I D G E TEST ON TWO SERIES O F REFERENCE DETONATORS
The miniature-cartridge test evaluates the initiating e5ciency of a given detonator relative to that of some other detonator. Hence i t becomes desirable to establish reference detonators for comparison purposes. The generally accepted definition for a No. 6 detonator is that promulgated by the Bureau of Minee for a standard No. 6 d e b nator-namely, that i t shall contain 1 gram of 80-20 mercury fulminabpotassium chlorate. The corresponding No. 8 and No. 10 detonators contain 2 and 3 grams, respectively, of the same mixture. For commercial detonators, a No. 6 (or No. 8) detonator is one that contains the same charge as the standard No. 6 (or No. 8) or a charge equivalent in initiating efficiency. This equivalency has never been rigidly specified because there haa been no widely accepted test for measuring initiating efficiency. The first series of reference detonators was made as similar as possible to the above-mentioned standard fulminate-chlorate detonators. They included the Nos. 6 , 7 , 8 , 9 , and 10 grades and contained 1.0, 1.5, 2.0, 2.5, and 3.0 grams, respectively, of this mixture (see Figure 5 for general make-up). They are called “reference” detonators and not “standard” detonators because they were merely selected by the writers for test purposes and are not to be construed as Bureau of Mines specifications. It is believed that the definitions of standard detonators have been heretofore treated rather loosely (7, 8, Ig). The initiating efficiency curve for the fulminate-chlorate reference detonators is plotted in Figure 9. This curve was determined by the procedure of the routine miniature-cartridge test, using the following depths of maximum initiation: 0.5, 0.75, 1, 1.25, and 1.625 inches for the Nos. 6, 7, 8, 9, and 10 detonators, respectively. The detonator blank was subtracted before the points for this curve were plotted. The second series of reference detonators contained tetryl as the base charge and 80-20 fulminate-chlorate aa the priming charge (Figure 6). This series was chosen because: (1) the initiating efficiency curve of the fulminate-chlorate series of detonators (Figure 9) did not cover a sufficiently wide range to
I
175
COYYERWL H COUUERWL Mol
F
0
L
COHULRCIAL
C O ~ ~ L Kw~ NO 6 cLlclI(E
coUy~~cuL N fUSE O8
LLLClRE DflONATOR DiTDWllOR OF YAKfb
p e m t presentation of the d e t d e d structural features of these detonators, but diagrams of some similar typical detonators have been pre-
January, 1945
A N A L Y T I C A L EDITION
(9) Mr~nroe,C. E., and Ti5my. 3. E., U. 5. Bur. Mines, Bull. 346 (1931). (10) Snttlling, W.O., Prac. Ew.Soe. West. Pmm.. 28,673 (1912). (11) starm. C. G.,and Cope. W.C., U. 9. Bur. Mines. Tech. Papm 1 2 5 (1916). (12) Taylor. C. A., and Munroe, C. E., U. S. Bur. Mines, Rcpt. I n o c A W h 2558 (1923). (13) Taylor. G.B., and Cope, W.C., U. 8.Bur. Mines, 2 ' 4 . Pnpsr 162 (1917). (14) U. S. Treasury Dept.. Procurement Div.. Erplosives and Blast-
Measurina the
If
19
ins Aooesaories. General Schedule of Supplies,Class 4, Suppl. 1 (Jan.1 to Deo. 31,1944). (15) Wehler, L.. 2. ges. Schim-Spwstoffw.. u), 145-50. 165-9 (1925): 21,1-5.35-8,55-7.97-9, 121-3 (1926). (16) Wahler. L.,Roth, J. F.. snd Ewald. K., I t i d , , 22, 95-9, 135-9 (1927). A s s r a a n i o from Bnmm of Minm Technical Paper 677 (in prcss): puh. M~W. fished by per-aian of the Director. u. s. ~~e~~
xistent Corrosivity" of IJsed
ine
Oils
R. G. LARSEN, F. A. ARMFIELD,
AND L. D. GRENlD T Shrll Development Company, Emeryville, ~
A test for determining the "existent conorivity" of used engine oils independently of previous history provides a means ior evaluating in simple lashion, by the use of test *ips coated with lead or other mebl in gredueted thicknesses, a property of used oils not heretofore setisfadorily rnearured by routine engine oil tnh. It also has pncticel application in determining the caun of bearing failures and indiceting necossety oil drain periods.
tives produce t tect against oorroslon. I t was the purpose Of the present wort to develop a simple teat which would give a reliable indication of the corrosivity of used oils, and thus t o guide the engineer in determining the cause of bearing failures; and to help the operator decide when an oil change is necessary. Most of the testa reported in the literature (4, 8, If, 1s) are used to predict what is termed by Waters and Burnham (M)as "potential corrosivity"-i.e.. the extent of corrosion wbich occum during the service life of the oil. Such methods are useful in the research necessary to provide oils qf improved performance, but they do not answer the needs outlined above. Engine testa give only the combined results of corrosivity of the oil modified by the action of any protecting surface films formed on the bearing. Since these two phenomena often represent a delicate balance. lack of corrosion-in one particular e-ngine may not ensure rhc 9ame fortunate condiriom in a similar engine under slightly different condirions. Furthermore, the engine must be torn doun and bearings removed before any observation of corrosion can be made. What these teats do not measwe is the unmodified corrosivity of the oil at any given time, or what has been called "existent corrosivity" (18)). As already mentioned, many operators use the acidity of an oil as a criterion of existent corrosivity. Waters and Burnham (f3)
ECAUSE of efficient and compact design, internal combustion engines can today be COnStNCted which produce considershly more power for a given weight than was possible before. As part of this development, the bearings now employed are smaller and are required to carry considerably greater loads and owrate at hieher temperatures. These advances, however, have oitcu been arcomplished with little regard to chemical relationships. Thw metals now used in bearingj can withstand higher loads and temperatures but are more susceptible to chemical attack tlran those greviowly used. This led to bearing failures at first, but the situation has subsequently been largely corrected through the efforts of oil manufacturers to understand the nature of the failures involved. Lubricants now produced give improved performance in many ways and ~ v the e engine designer greater latitude. Unfortunately, occasional bearing failures still occur. TLese may be traceable to mechanical Step Type Wedse Type factors such a 8 poor alignment and fit, poor cooling due to insufficient oil flow, poor bonding of the hearing alloy t o the hacking, or imperfect structure of the allay, or ta weakened structure as a result of chemical attack. Normally, the only certain method of deciding which of these factors caused failure is microscopic examination of the cross-sectioned bearing. Improvement in oil performance has generally been accomplished by the use of additives. Often these additives are detergent in nature and prevent the formationof films which normally U K D M lA8ORAT6SY protect the bearing, thus leaving it susceptible USmLEm to corrosive attack. A second additive may then he used to prevent corrosion by reducing oxidation or by passivating the surface. When these additives are depleted, normal or even increased corrosion may ocsur; it is, therefore, , . . . ..UF..-. - . . . .. desirable to change oil before the critical stage bas been reached. I n practice, the oil is usually changed when acidity develops, since it is assumea that acids cause corrosion. Yet it is well 1F5T STRlP ATTAWEE TO MP mcX knowd that acid number alone is not a reliable indication of corrosivity. I n fact, certain addiFigure 1. h e n - S t e p and Wedge-Type Corrosion Tolt Strips ~~
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