R . L . G R A N T E xplosives T e s tin g S e c tio n , U. S . B u r e a u o f M in e s , B r u c e t o n , Pa.
J . E . T I F F A N Y C e n tr a l E x p e r i m e n t S t a t i o n , U. S . B u r e a u o f M in e s , P it t s b u r g h , Pa.
T h e in flu en ce o f th e fo llo w in g fa cto rs u p o n th e in itia tin g efficien cy o f d e to n a to r s w as s tu d ie d : b a se ch a rg e, p rim in g charge, rein forcin g ca p su le , an d o u ts id e d ia m eter o f sh ell.
T h e in itia tin g efficien cies o f laboratory-p rep ared d e to n a tors w e r t d eterm in ed by th e m in ia tu r e-c a rtr id g e te s t (7).
R esu lts in d ica ted t h a t th e in itia tin g efficien cy increased in th is order for th e fo llo w in g b a se ch arges: 80 m ercury fu lm in a te -2 0 p o ta s siu m ch lo ra te m ix tu re, te tr y l, PETN , h exogen . T h e efficien cy o f p r im in g c o m p o sitio n s, as d e
term in ed by m in im u m in itia tin g ch arges, w as as follow s:
(1) 80 lead azid e-20 lea d sty p h n a te ; (2) 80 lea d azid e-18 lead sty p h n a te -0 .5 a lu m in u m -1 .5 p o ta s siu m ch lo ra te and 60 lead azid e-40 lea d s ty p h n a te ; (3) 100% lea d a zid e, 80 lead azid e-17 lea d sty p h n a te —3 a lu m in u m , 40 lea d a z id e- 60 lead sty p h n a te , a n d 75 DD NP—25 p o ta s siu m ch lorate;
(4) 20 lead azid e-8 0 lea d s ty p h n a te a n d 80 m ercu ry fu l
m in a te -2 0 p o ta ssiu m c h lo ra te ; (5) 100% lead sty p h n a te . T h e u s e o f a copper rein fo rcin g ca p su le to en c lo se th e
T
H E question of w hat constitutes an efficient detonator is of critical im portance to designers and m anufacturers of detonators and to all who te s t and use explosives. T he behavior of detonators is no t clear because knowledge of th e initiatin g characteristics of detonators is incom plete. T his rep o rt studies the following four factors and th eir effects on th e initiatin g efficiency of detonators: base charge, prim ing charge, reinforcing capsule, and diam eter of detonator shell. T he influence of each factor was ascertained by m easuring th e initiatin g efficiency of labora
tory-prepared detonators by th e routine procedure of the m inia- ture-cartridge te s t (7). T he testing of detonators has been re
ported in previous publications (5, 6, 11, 26, 27). A nother pur
pose of this article is to present th e initiatin g characteristics of a series of hexogen-base detonators which, although p aten ted by Herz in 1920 (12), have n ot been described in th e literatu re or used in practice. B y th e m iniature-cartridge te s t these detona
tors are consistently superior to detonators containing other base charges.
The term s adopted by Chemical Abstracts are, for th e m ost p art, employed here for th e various explosives tested. However, the common nam e or designation, when this is widely accepted, is also used.
T he term “te try l” is employed for th e explosive chemically known as trim trophenylm ethylnitram ine.
P en taery th rito l te tra n itra te is commonly known in th is coun
try ¿s P E T N . T his compound is variously listed in th e literatu re as tetran itro p en taeiy th rito l, tetran itro p en taery th rite, pentrite, p enthrit, and niperyth.
“Hexogen” is th e term used by Chemical Abstracts for cyclo- trim ethylenetrinitram ine. In common usage in th is country it is frequently called “cyclonite” .
L ead sty p h n ate is known chem ically as norm al lead trin itro - resorcinate or th e lead salt of styphnic acid.
D D N P refers to diazodinitrophenol. I t is occasionally called dinol; Chemical Abstracts lists it under b o th “D D N P ” and
“benzoxdiazole, 4,6-dinitro-” .
p rim in g ch arge in creased th e in itia tin g efficien cy o f a d e to n a to r fro m o n e to th ree grades. As th e o u ts id e d ia m eter o f a d e to n a to r w as in crea sed , th e in itia tin g efficien cy o f th e d e to n a to r d ecreased as a n ap p roxim ate inverse str a ig h t-lin e fu n c tio n . T e sts w ith th e lea d -p la te te s t produ ced r esu lts in s u b s ta n tia lly o p p o site order to th o se o f th e m in ia tu r e-c a rtr id g e te s t w h en th e d ia m e ter o f th e d e to n a to r w as varied. T h e in itia tin g efficien cy o f th e variou s k in d s o f d eto n a to rs w as c a lcu la ted in te rm s o f u n it w e ig h t o f explosive ch arge in th e d e to n a to r and th e n sy s tem a tica lly ta b u la ted ; d eto n a to rs w ere th u s classified accord in g to in itia tin g ch a ra cteristics. T h is c la ssifica tio n , a lo n g w ith selected curves, revealed th a t h ex o g en -b a se d eto n a to rs are u n ifo rm ly m ore efficien t th a n d eto n a to rs w ith o th er b ase ch arges. T h ese curves also d isclo sed th a t b o th q u a n tity a n d q u a lity o f th e explosive ch arge¿n a d e t
o n a to r m u s t be con sid ered in rela tio n to th e in itia tin g e f
ficien cy o f th a t d eto n a to r.
T he weights of the explosive charges in th e detonators de
scribed are designated by centigram s (0.01 gram ). Convenient whole num bers, rath er th a n decimal fractions, result; and weigh
ings of th e charges in the laboratory-prepared detonators are accurate to a centigram . A tendency has been noted in this country, especially in specifications, to use grains; although they provide whole num bers, “grains” are cumbersome and confusing.
T he initiating efficiencies of th e detonators studied were de
term ined by th e routine m iniature-cartridge te s t (7). T he screens used in th e previous work were retained for th e tests described here in order to ensure intercom parison of results.
E F F E C T O F B A S E C H A R G E
M odem detonators are compound detonators loaded with a base charge, a prim ing charge, and sometimes an ignition charge (5,16). T he relative efficiencies of th e following four base charges were studied: 80 m ercury fulm inate-20 potassium chlorate mix
ture, tetry l, P E T N , and hexogen. T he first was selected because it constitutes th e charge of stan d ard detonators in this country and m ercury fulm inate is th e oldest of detonator charges. The common base charges in use to d ay are te try l (17, 32) and P E T N (3); th e la tte r has been introduced w ithin th e p a st decade.
Hexogen was chosen because its high ra te of detonation (approxi
m ately 8400 m eters per second) indicated th a t it m ight be an ef
fective base charge. Herz p aten ted this compound in 1920 (12) and suggested it as a d etonator charge (13). I t has no t been used in practical detonators, however. Its p reparation and properties have been studied and described by Desvergnes (4), Somlo (23), T onegutti (31), G uastalla and Raccin (10), Sollazo (22), and Stettb ach er (24).
Ex p e r i m e n t a l. Gilding-m etal shells, of outside diam eter 0.69 cm. and w ith the usual depressed bottom s, were used. The shells were identical to those on th e m arket, and th is p articular diam eter represents th e m ost common detonator.
661
I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
F ig u re I. E ffect o f B a se C harge o n I n itia tin g E fficien cy o f D e to n a to rs
F or th e first series of detonators containing 80-20 fulm inate- chlorate, th e base charge was loaded in increm ents of 50 eg. (0.5 gram) a t a pressure of 63 kg. per sq. cm. (900 pounds per square inch). T he prim ing charge was also 80-20 fulm inate-chlorate, weighed 50 eg. for each detonator, and was pressed a t 49 kg. per sq. cm. (700 pounds per square inch).
F o r th e next three series of detonators containing tetry l, P E T N , and hexogen as base charges, detonators were prepared having 25, 50, 75, 100, and 125 eg. of each base charge pressed a t 98 kg. per sq. cm. (1400 pounds per square inch). T he prim ing charge for all of these detonators was 75 eg. of 80-20 fulm inate- chlorate, loaded singly and pressed a t 49 kg. per sq. cm.
Figure 1 shows th e results of th e initiatin g efficiencies of the four series of detonators as determ ined by th e routine m iniature- cartridge test. Since each
point represents six trials (two each for th e 80-20 and 70-30 T N T -iro n oxide m ixtures and two for the d etonator blank), th e set of four curves includes a to ta l of one hundred tw enty trials.
Co n c l u s i o n s a n d Di s c u s s i o n. Figure 1 indi
cates th a t th e order of in
creasing initiating efficiency f o r t h e b a s e c h a r g e s studied is: 80 m ercury ful
m in ate-2 0 potassium chlo
ra te m ixture, tetry l, P E T N , h ex o g en . F u rth e rm o re , reference to tables of detona
tion rates reveals th a t th e results are in th e same ap proxim ate relative order as th e respective rates of deto
n atio n of th e base charges.
Various relations are derivable from Figure 1 for exam ple, th e relativ e in itiatin g efficiencies of detonators having equal w eights of to ta l charges.
By entering th e graph along th e 100-cg. vertical ordinate, it is found t h a t a d eto n ato r containing, for exam ple, 25 eg. of te try l an d 75 eg. of 80-20 fulm inate-chlorate prim ing charge is equivalent to a No. 7 fulm inate-chlorate reference detonator.
H aid and K oenen (11) rep o rted results for ful
m inate-chlorate, tetryl-base, and P E T N -b ase detona
to rs th a t are in close agreem ent w ith those of Figure 1. T hey suggested th a t th e in itiatin g efficiency of an explosive m ay be expressed in term s of its brisance value, B , w hich th ey calculated from the following form ula:
B = A X D X T / 273 X V 0 where A = density
D — ra te of d eto n atio n
T = absolute explosion tem p eratu re Fo = gas volum e produced by explosive
E F F E C T O F P R I M I N G C H A R G E
T he chief function of a prim ing charge in a d eto n ato r is to tran sm it full d eto n atio n to the less sensitive b u t usually m ore pow erful base charge. B ecause th e prim ing charge is generally a sensitive and expensive explosive, a relativ ely small q u a n tity is desirable.
T he common prim ing charges stu d ied in th is section have been selected from those used in detonators- in th e U nited S ta t s and in Europe, especially G reat B ritain and G erm any. T hey include 80 m ercury fu lm in ate-2 0 potassium chlorate m ixture, lead azide (15, 32), lead sty p h n a te (15, 28), lead azide-lead sty p h n a te m ixtures (15, 18), and 75 D D N P -2 5 potassium chlorate m ixture ( 1 , 3 ) . In addition, th e effect of alum inum , alone an d w ith potassium chlorate, w hen m ixed with lead azide and lead sty p h n ate, was tested.
De t e r m i n a t i o no p Mi n i m u m In i t i a t i n g Ch a r g e. Among the im p o rtan t properties of a prim ing com position is th e minimum charge required to deto n ate th e base explosive in th e detonator.
F or determ ining th is characteristic th e well-know n procedure of T aylor and Cope (29) was followed. Some details differ, how
ever, and are n oted in th e following outline of th e procedure used in this study.
F ig u re 2. D e te r m in a tio n o f M in im u m I n it ia t in g C h arges o f L ead A zid e, L ead St v n lm p i«
a n d T h eir M ix tu res for 125 C g. o f T e try l ’
July, 1945 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 663
A charge of 125 eg. was loaded in five 25-cg. increm ents in to a gilding-m etal shell having an outside diam eter of 0.69 cm. E ach increm ent was pressed a t 98 kg. per sq. cm. T he 125-cg. charge represents th e m axim um w eight of base charge studied in these experim ents. Varying w eights of prim ing charge, in 5-cg. incre
m ents, were th en inserted as a single charge on to p of th e base charge and pressed a t 49 kg. per sq. cm. F o r these experim ents no reinforcing capsule was employed. An electric m atch head of th e copper acetyhde type, obtained from A tlas Pow der Com pany, was inserted into the d eto n ato r an d th e shell carefully crim ped a t th e top. T he detonator was placed in th e center of 350 gram s of O ttaw a stan d ard sand, introduced ia portions of 100 plus 250 gram s into Bureau of M ines bom b N o. 2 having an inside diam e
te r of 2 inches (19). T he bom b was closed and fastened securely, and the detonator fired. T he w eight of sand crushed served as a criterion of w hether th e base charge d eto n ated ; it was deter
m ined by screening through a No. 30 U. S. S tan d ard series screen (opening, 0.059 cm. or 0.0232 inch). T he w eight of priming charge, to th e nearest 5 eg., which produced three complete d e t
onations, w ithout p artial or incom plete detonations, was taken as th e minim um initiatin g charge.
Table I gives th e m inim um in itiatin g charges of th e various priming compositions for base charges of tetry l, P E T N , and hexogen. The general conclusion from these results is th a t hexo- gen is more sensitive to detonation th a n P E T N which, in tu rn , is more sensitive th an tetry l. If other factors are equal, a greater sensitivity to detonation is a desirable p ro p erty in a base charge.
The order of efficacy of th e prim ing compositions, w ith the best listed first, follows:
1. 80 lead azide-20 lead sty p h n ate
2. 80 lead azide-18 lead sty p h n ate-0 .5 alum inum -1.5 potas
sium chlorate and 60 lead azide-40 lead sty p h n ate
3. 100% lead azide, 80 lead azide-17 lead sty p h n a te -3 alum i
num, 40 lead azide-60 lead sty p h n ate, an d 75 D D N P -2 5 potas
sium chlorate
4. 20 lead azide-80 lead sty p h n ate and 80 m ercury fu lm in ate- 20 potassium chlorate
5. 100% lead sty p h n ate
Ta b l e I. Mi n i m u m Ch a r g e s o f Pr i m i n g Co m p o s i t i o n s (t o Ne a b e s t 5 C g.) Re q u i r e d t o De t o n a t e 125 C g . o f Ba s e
Ch a r g e
P rim in g C om position T e tr y l P E T N Hexogen W ith o u t R einforcing C ap su le
80 m ercury f u lm in a te -2 0 p o ta ss iu m ch lo rate 40
L ead azide 25
80 lead azid e- 20 lead s ty p h n a t e 15 60 lead azid e-4 0 lead s ty p h n a te 20 40 lead az id e-6 0 lead s ty p h n a te 25 20 lead azid e-8 0 lead s ty p h n a te 40
Lead styphnate® 150
75 D D N P - 2 5 po tassiu m ch lo rate 25 18 lead azid e-1 7 lead s ty p h n a t e - 3 alu m in u m 25 80 lead az id e-1 8 lead s ty p h n a te - 0 .5 alu m i
n u m -1 .5 p o ta ssiu m chlorate 20
W ith Reinforcing C ap su le 80 m ercury fu lm in ate- 2 0 po tassiu m ch lo rate 20 80 le ad azid e-2 0 lead s ty p h n a te & 5
° R esult is approxim ate.
& Small hole (d iam eter 0.15 cm.) in in n er copper capsule; p rim in g ch arg e pressed u n d er capsule a t 98 kg. p er sq. cm.
Le a d Az i d e- Le a d St y p h n a t e Mi x t u r e s. M ixtures of lead azide and lead styphnate have long been used as prim ing charges for detonators (9, H , 18) and have been employed in foreign det
onators, especially those of G reat B ritain and G erm any (25, 30). These mixtures, however, are n o t found in detonators m arketed in the U nited States. P roperties of th e tw o constitu
ents evidently complement each other; th e low ignition tem perature of lead styphnate compensates for th e higher ignition tem perature of lead azide, while the high initiating power of lead azide amends the low power of lead sty p h n ate (18, 27).
Of th e various lead azide-lead sty p h n ate m ixtures, th e 80-20 is th e best according to th e results of T able I. I t is superior to either lead aaide or lead sty p h n ate alone. As little as 5 cg. of
35 35
10 6
5 5
20 iè
15 15
5 5
F igu re 3. E ffect o f P rim in g C harge o n I n itia tin g E fficien cy o f D eto n a to rs
this m ixture completely detonates 125 cg. of either P E T N or hexogen, whereas 35 cg. of th e fulm inate-chlorate m ixture are re
quired. T he priming composition used by Rheinish-W estfaelische Sprengstoffe was reported to be th e 40-60 lead azide-lead styph
n ate m ixture (21). Figure 2 presents th e relative initiatin g values of th e lead azide-lead sty p h n ate m ixtures.
In i t i a t i n g Ef f i c i e n c y Te s t s. T he relative in itiating ef
ficiencies of various detonators prepared w ith th e three base charges (tetryl, P E T N , and hexogen) and th e several priming compositions were determ ined by th e routine procedure of th e m iniature-cartridge test. A t this point th e following arb itrary rule, which provided a safety factor of 2 to 3, was established and used for all subsequent detonators tested: T he w eight of priming charge for use in a detonator is taken as betw een two and three tim es th e minim um in itiating charge. These detonators were prepared like those described in the section on "E ffect of Base Charge” , in which th e base charges were pressed a t 98 kg. per sq. cm. and th e prim ing charges a t 49 kg.
Figure 3 shows tw o curves for hexogen-base detonators th a t compare th e m ost effective prim ing charge w ith one th a t is rela
tively ineffective. T he prim ing charges selected are the 80-20 lead azide-lead sty p h n ate and th e 80-20 m ercury fulm inate- potassium chlorate m ixtures, respectively. Curves for the other priming charges (except for lead styphnate) will, in general, fall betw een these tw o curves, provided the same weight of th e same base charge is used. T able I I gives th e m ake-up of th e various detonators tested and th eir relative in itiating efficiencies.
E F F E C T O F R E I N F O R C I N G C A P S U L E
I t is generally conceded th a t th e use of a reinforcing or inner capsule to enclose th e prim ing charge has th e effect of producing a lower minim um charge necessaiy to detonate th e base composi
tion (26, 27). This is a ttrib u te d to the additional confinement and to a focusing of th e shock wave from the prim ing charge in th e direction of th e base charge. A nother advantage of a reinforcing capsule is th a t it provides additional m echanical protection around th e usually sensitive prim ing composition and thus im
proves th e safety features of th e detonator.
T he experim ents of this section consisted of obtaining the ini
tiatin g efficiencies of tw o series of detonators m ade sim ilarly,
664 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y preceding sections. T he reinforcing copper capsules were 0.64 cm. (0.25 inch) in length and 0.64 cm. in outside diam eter. For T able I I and plo tted as curves representing four series of detona
tors in Figure 4. T he conclusion indicated by these results is th a t, in general, th e use of a reinforcing capsule increases th e initiating effi
ciency of a d etonator one .to three grades. The extent of th e increase depends upon th e degree to which th e reinforcing capsule decreases th e m ini
m um initiating charge of th e prim ing composi
tion. From th e curves of Figure 4 it is possible to determ ine detonators equivalent in initiating efficiency.
E F F E C T O F S H E L L D I A M E T E R
Mi n i a t u r e- Ca b t r i d g e Te s t. D etonators with gilding-m etal shells having th e following differ
en t outside diam eters were studied: 0.59 cm. usual shell-draw ing m achines. T he wall thickness of all shells was th e same, approxim ately 0.022 cm.
(0.009 inch), as was th e thickness of their efficiency is approxim ately an inverse straight-line function _l_---WEIGHT OF TOTAL EXPLOSIVE CHARGE IN DETONATOR, CENTIGRAMS
F ig u re 4 . E ffect o f R e in fo r cin g C a p su le o n I n itia tin g E fficien cy o f D e to n a to r s
July, 1945 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 665 also determ ined. T able I I I gives th e results obtained.
If th e values in T able I I I for detonators of de th e m iniature-cartridge te s t is substantially satis
factory, th e above experim ents perm it th e conclusion th a t th e lead-plate te s t produces erroneous results when detonators of different diam eters are compared.
EFFICIENCY EXPRESSED AS UNIT WEIGHT OF CHARGE
Figure 7 gives plots of eleven series of detonators selected from Figures 1, 3, 4, and 5, and recalculated to express th e efficiency per u n it weight of explosive charge. E ach curve represents a series of detonators w ith a range of base charge from 25 to either 100 or 125 eg., w ith th e exception of curve 1 which depicts a series
I
f
OF TOTAL EXPLOSIVE CHARGE IN DETONATOR, CENTIGRAMS
F igu re 5. Effect o f D ia m eter o f S h ell o n I n itia tin g
666 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
75 125 175 225 275
TOTAL WEIGHT OF EXPLOSIVE CHARGE IN DETONATOR, CENTIGRAMS
F ig u re 7. I n itia tin g E fficien cies o f E leven S eries o f D e to n a to r s Expressed a s U n it W e ig h t o f E xp losive C h arge in D e to n a to r
of sta n d ard fulm inate-chlorate detonators. T he curves were selected for Figure 7 to illu strate th e influence of th e factors studied in th is report. T he relations of th e various factors affect
ing initiatin g efficiency are sharply depicted by these curves:
base charge, curves 1, 2, 3, and 4; reinforcing capsule, curves 2 and 5; prim ing charge, curves 6 and 7; and diam eter, curves 8, 9, and 10.
C urve 11 represents a high-efficiency d etonator combining all th e advantageous features of th e previous detonators. I t pos
sesses th e following characteristics : T he base charge is hexogen, an d th e prim ing charge is 80-20 lead azide-lead sty p h n ate pressed under a copper reinforcing capsule. T he shell is gilding m etal having an outside diam eter of 0.59 cm. Its initiatin g efficiency, as indicated b y th e m axim a of th e curves of Figure 7, is of the order of five and a half tim es th a t of a fulm inate-chlorate detona
to r on an equal-weight-of-explosive-charge basis. F u rth e r in
vestigation of o th er factors would probably reveal detonators of
vestigation of o th er factors would probably reveal detonators of