M c G r a w - H i l l C o m p a n y ,I n c . J a m e s H . M c G r a w , President E . J . M e h k e n , Vice-President
Devoted to th e Operating, Technical and Business Problem s of th e Coal-Mining In d u stry
R . D a w s o n H a l l Engineering Editor
Volume 28 N EW YORK, D ECEM BER 24, 1925 Num ber 26
W hat tlie P u b lic Wants
B
E C A U S E th e a n th r a c ite p ro d u c e rs have declined to h av e a n y th in g to do w ith th e P in c h o t eleven-point■“p eace” p ro g ra m , th e G overnor o f P en n sy lv a n ia c h a rg e s th e m - w ith w a r r in g a g a in s t th e public. T h a t t h e pu b lic is a re a l p a r ty to th e co n tro v e rsy betw een th e o p e ra to rs a n d th e m in e rs is well recognized. B u t b e fo re w e can acknow ledge a n y t r u t h in th e P in c h o tia n in d ic tm e n t, we m u s t u n d e rs ta n d cle arly w h a t th e objec
tiv e s o f th e pu b lic a r e a n d how th e y coincide o r conflict w ith th e o b jectiv es f o r w hich p ro d u cers a n d m in e rs h a v e been fig h tin g since July.
W h a t does th e public w a n t? F i r s t an d fo rem o st, th e p u b lic w a n ts a n u n in te r r u p te d supply of coal. I t w a n ts th e o ld-tim e a s s u ra n c e t h a t coal can be h a d w h en ev er th e co n su m e r is disposed to o rd e r fuel. Second, th e p u b lic w a n ts to p u rc h a se t h a t coal a t th e low est possible p ric e . I f th e issu e is ra ise d , th e public is w illin g t h a t t h a t p ric e sh a ll be h ig h enough to f a ir ly co m pensate b o th th e c a p ita l a n d th e la b o r em ployed in th e p ro d u c tio n a n d d is trib u tio n o f coal. T h ese a re th e sum to ta l o f its w a n ts.
T h e p u b lic h a s com plained in re c e n t y e a rs t h a t th e se sim p le w a n ts h av e n o t been m et. T h e a n th r a c ite p ro d u c e rs h av e conceded th a t th e r e is m e r it in t h a t com- p la in t. To m e e t th e fir s t dem and o f th e pu b lic th e y h a v e a sk e d re p e a te d ly t h a t th e m in e rs jo in w ith th em in a n a g re e m e n t w h ich w ould m ake f u tu r e s trik e s im possible. T h e b a s is o f th a t proposed a g re e m e n t is t h a t d is p u te s b etw een em ployers a n d em ployees w hich c a n n o t be s e ttle d by d ire c t n e g o tia tio n s sh all be su b m itte d to a n im p a r tia l b o a rd o f a r b itr a tio n .
T o m e e t th e second d em and o f th e public, th e op er
a to r s h a v e d eclared t h e i r o p position to f u r t h e r in c rease s in th e c o st o f p ro d u c tio n . T h e u n ion, in te r m in a tin g th e w a g e n e g o tia tio n s w ith th e p ro d u c e rs a t A tla n tic C ity la s t su m m e r, re fu se d to g iv e th e em ployers th e o p p o rtu n ity to p re s e n t th e g ro u n d s f o r t h e ir o pposition to f u r t h e r in c re a se s in la b o r costs. T h e u n io n scale co m m itte e d isp u te d th e claim t h a t th e in d u s try could n o t p a y h ig h e r w a g e s w ith o u t p a ssin g on th e co st to th e co n su m e r a n d th e n denied th e o p e ra to rs a h e a rin g on t h a t claim .
U n io n le a d e rs an d G o v ern o r P in c h o t have accused th e o p e ra to rs o f d e clin in g “ to yield one jo t o r t ittle of th e ir o rig in a l p o sitio n .” T h a t a c c u satio n , how ever, co n v en ien tly ig n o re s th e f a c t t h a t th e o p e ra to rs hav e o ffered to s u b m it th e ir ju s tific a tio n to th e ju d g m e n t o f a n im p a r tia l b o a rd o f a r b itr a tio n w ith u n re s tric te d p o w e r to d e te rm in e th e issu es. T h e g r e a te s t conces
sio n t h a t th e u n io n le a d e rs h a v e been w illin g to m ake in th e pu b lic in te r e s t is a n a g re e m e n t to s u b m it to a r b itr a tio n how m u ch h ig h e r, i f an y , w a g es m ig h t be adv an ced . A r b itr a tio n to p re v e n t f u tu r e su sp e n sio n s h a s been re p e a te d ly re je c te d b y M r. L ew is a n d h is a sso c ia te s.
T h e p u b lic w a n ts a n a ssu re d su p p ly o f fu e l a t a f a i r p rice . T h e public w a n ts a r e th e o p e ra to rs n ecessi
tie s. F o r in s is tin g upon m e e tin g th o se w a n ts, M r.
L ew is an d G overnor P in c h o t c h a rg e th e o p e ra to rs w ith w a r r in g a g a in s t th e public.
On Solid Ground
R
UM OR H A S IT t h a t th e B r itis h v is ito rs w ho have . j u s t d e p a rte d w e re p rin c ip a lly im p re sse d in th e ir tr ip s th ro u g h th e m in es o f th is co u n try , n o t so m uch w ith o u r m ech an ical developm ents a s w ith o u r p ra c tic e of k eeping o u r h au la g e ro a d s in solid coal in s te a d of in th e “g o a f or b ro k e n ” as th e y w ould te r m it. T h e B r itis h use m uch longw all a d v a n c in g a n d so h av e ro a d s th a t lack perm an en cy , w ith cru m b lin g ro o fs a n d m oving sides. T he in v e s tig a tio n s o f th e v is itin g p a r ty seem ed to convince th e m t h a t longw all r e tr e a tin g w as b e tte r because i t afforded good ro o fs an d a re d u c tio n of tim b e rin g .I n some cases w h e re p erm an en ce is d esired , as in th e a n th r a c ite re g io n w h e re th ic k beds a r e m in ed u n d e r heav y cover, g an g w a y s in th e rock o r in u n d e rly in g coal beds too th in to m in e an d w h ere rock h a s to be lifte d o r b ru sh e d hav e been u sed w ith success. T h ey fre q u e n tly h av e in a h ig h d eg ree th e p e rm an en ce th a t is so d esirab le. T im b e r is n o t needed, o r m ay be used sp a rin g ly .
T he g an g w a y s a re tr u ly “ in th e solid,” a n d n ow adays w ith m ach in es so re a d ily av ailab le f o r lo ad in g ro ck it is to be expected t h a t th e m ileag e o f such g a n g w a y s w ill be g r e a tly in creased , especially f o r d ra in a g e p u r poses. M an y a m in e m a n a g e r i f he could hav e fo reseen th e tim b e r costs, delays, d a n g e r a n d m a in te n a n c e ex
pense t h a t h is g a n g w a y s in th e coal e n ta ile d w ould have ch e e rfu lly faced th e expense o f p lacin g th e m in solid s t r a t a w h e re th e y w ould hav e been su b je c t to less s tr a in fro m m in in g o p e ra tio n s. I n fa c t, th e e la b o ra te tim b e r
in g in som e o f th e w o rk in g s su g g e s ts fo rc ib ly th a t tu n n e ls in th e ro ck m ig h t fre q u e n tly be m ad e to replace p re s e n t g a n g w a y s w ith im p ro v em en t in som e cases in th e g ra d ie n ts o f th e ro ad w ay .
Fewer T ypes o f E quipm ent and Fewer T roubles
“ T ’D C E R T A IN L Y like, som etim e, to w o rk w h e re all J_ th e eq u ip m e n t is th e sam e,” sa id th e c h ie f e le c tric ian of a la rg e m in e. A f te r a p a u se he ad ded, “ B u t th e n , you don’t g e t p a id f o r d o ing n o th in g . T h e c h ie f a t a sta n d a rd iz e d m in e w ould h a v e a sn ap , an d m o re th a n likely w ould be p a id a c co rd in g ly .” H e w as n o t, neces
sa rily , c o rre c t in h is conclusion t h a t s ta n d a r d iz a tio n of eq u ip m en t w ould m ean t h a t th e com pany w ould m ak e a sa v in g b y p a y in g a low er s a la ry to its c h ie f e le c tric ian . S uch m en a r e p a id f o r t h e ir know ledge a n d f o r b ein g on th e jo b re a d y f o r em erg en cies, in s te a d of f o r th e a c tu a l p h y sical a n d m e n ta l w o rk p e rfo rm e d . N e v e rth e less, th is c h ie f e le c tric ia n c o rre c tly ju d g e d th e im p o r
ta n c e o f s ta n d a rd iz a tio n .
One ev id en t a n d d ire c t a d v a n ta g e o f s ta n d a r d s is 879
880 C O A L A G E Vol. 28, No. 26 th e red u ced sto ck o f r e p a ir a n d s p a re p a r ts n e c e ssa ry
to in s u re c o n tin u o u s o p e ra tio n . L ess space a n d less la b o r a r e re q u ire d to s to re a n d m a in ta in th e stock, an d i t is m o re c e r ta in t h a t n e c e ssa ry p a r ts a r e on h a n d w hen th e call com es. F e w e r r e p a ir m en a re needed, an d b e tte r w o rk is done b ecause th e m en a r e m o re f a m ilia r w ith th e d e ta ils o f th e eq u ip m en t. C ases of ab u se by m a c h in e o p e ra to rs to one ty p e of m ach in e, in o rd e r to g e t th e chance to use a p r e f e r r e d ty p e , a re e lim in a te d ; a less p e rc e n ta g e of delay m ak es i t possible to o p e ra te w ith fe w e r m a c h in e s; m ech an ical tro u b le s a r e m o re re a d ily detected, a n d p e rm a n e n t im p ro v em en ts th e re b y effected. In v e s tig a tio n u su a lly w ill rev eal th a t, a t low -cost m ines, h ig h ly s ta n d a rd iz e d e q u ip m en t an d m eth o d s a re in use.
An After-tlie-W ar R eadjustm ent
B
E C A U S E of th e c h e a p e n in g o f m oney a n d th e a p p re c ia tio n o f goods, s a la rie s h av e in g e n e ra l been ra is e d th ro u g h o u t th e U n ite d S ta te s , b u t n o t a d e q u ately in th e g o v e rn m e n t service, th o u g h in c re a se s hav e been g ra n te d to th o se w hose em olum ents a r e com m only know n r a t h e r a s w ag es th a n as sa la rie s .J u s tic e dem an d s t h a t th e co m p en satio n s o f th o se in th e g o v e rn m e n t se rv ice sh all ris e a n d fa ll re a so n a b ly in accord w ith th e s a la rie s a n d w ag es of th e p u b lic in g e n e ra l. I t m u s t be rem em b e red t h a t none o f th e m h a s a w ay o f su p p le m e n tin g h is e a rn in g s lik e C on g ressm en b y p e rfo rm in g unofficial service.
J u s t a t p re s e n t p re s s u r e is b e in g b ro u g h t to ra is e th e s a la rie s o f d is tr ic t ju d g e s 33 p e r c e n t fro m $7,500 a y e a r to a m in im u m o f $10,000 w ith a m a x im u m se t
$1,000 below th e s a la ry of c irc u it ju d g e s w h e re v e r th e d is tr ic t p o p u la tio n exceeds 2,000,000. T h e c ir c u it ju d g e s, w ho hav e been rec e iv in g $8,500, w ould have, t h e ir s a la rie s in c re a se d so a s to ra n g e fro m $3,000 to $15,000. T h e S u p rem e C o u rt ju d g e s w ill be ra is e d fro m $14,500 to $20,000 a n d th e C h ief J u s tic e fro m
$15,000 to $20,500.
S ince 1891 th e sa la rie s of d is tr ic t ju d g e s h av e been ra is e d 50 p e r cent, of c irc u it ju d g e s 381 p e r c e n t an d ju d g e s o f th e S u p rem e C o u rt 16 p e r cent. T h e s a la ry o f th e c h ie f ju s tic e is less th a n a t h i r d t h a t o f G re a t B r ita in ’s le a d in g ju d ic ia l a u th o r ity a n d h a lf t h a t of Ire la n d ’s p rin c ip a l ju d g e . T h e L o rd C h ief J u s tic e of S cotland g e ts tw o -th ird s m ore th a n o u r C h ie f J u s tic e a n d th e r a te in In d ia is b u t $1,000 less.
T h a t is n o t all. T h e s a la rie s f o r s ta te ju d g e s a re low er th a n th e s a la rie s f o r fe d e ra l ju d g e s in a la rg e n u m b e r o f cases. A ju d g e o f th e S u p re m e C o u rt of P e n n sy lv a n ia o r N e w Y o rk g e ts $3,000 a y e a r m ore th a n a ju d g e in th e S u p rem e C o u rt of th e U n ite d S ta te s, y e t i t is now pro p o sed to ra is e th e s e sa la rie s in th e first-n a m e d s ta te . T h e pro p o sed bill w ill add only $743,000 to th e n a tio n a l b u d g e t, a n d th e to ta l cost f o r all th e s a la rie s o f all th e fe d e ra l ju d g e s in th e U n ite d S ta te s w ill be less th a n tw o ce n ts p e r y e a r f o r e v ery p e rso n in th e U n ite d S ta te s .
N o less th a n six ju d g e s in th e N ew Y o rk d is tr ic t h av e re c e n tly re sig n e d to e n te r legal p ra c tic e w hich n e ts th e m m uch la r g e r r e tu r n s . T h e p re s id e n t h a s fo u n d o th e rs to rep lace th e m , doubtless, b u t th e c h a r
a c te r o f th e ju d g e s m u s t decline if th e ir p r e s e n t sa la rie s a re to c o n tin u e ; first, b ecau se th e b e st m en w ill n o t e n te r th e serv ic e of th e g o v e rn m en t, a n d second, b ecause th e y w ill leave b efo re th e y becom e definitely p o sted on all th e m a tte r s w h ich a ju d g e m u st decide.
P rogress o f the Strike
E
V ID E N T L Y th e boys a r e n o t to be o u t o f th e tre n c h e s by C h ristm a s, a lth o u g h i t is ru m o re d h e re a n d th e re th a t peace in th e m a tte r o f th e coal s tr ik e m a y n o t be f a r off. T h e m a in s tr a te g y o f th e M ine W o rk ers, upon w h ich t h e i r officials depended, h a s so f a r failed , in th e lack o f e n th u s ia s tic re sp o n se o f pu b lic s e n tim e n t in t h e i r fa v o r and th e expected a m o u n t of clam or an d p re s s u re upon th e g o v e rn m e n t to in te rv e n e .A nd th e g o v e rn m e n t a t W a sh in g to n p e rs is te n tly re f u s e s to ju m p w h e n th e s tr in g s a r e pu lled b y th e officials o f th e s tr ik in g coal u nion. W ag es in th e a n th r a c ite in d u s try , th e y recognize, a n d th e public recognizes, a r e a lre a d y h ig h e r in p ro p o rtio n t h a n in m o st s im ila r in d u s trie s — th e y a re f a r h ig h e r, fo r exam ple, th a n th o se w ith w h ich th e m e ta l m in e rs a re c o n te n tin g them selv es w ith o u t co m p lain t. T h e a n t h r a c ite m in e rs (o p e ra to rs a n d w o rk m e n ) should clearly pex-ceive t h a t f u r t h e r r a is in g of co sts is n o t only in a d visab le b u t im possible, b ecause i t w ould m ean a f u r t h e r loss o f th e a lre a d y in se c u re a n th r a c ite m a rk e ts and a c o rre sp o n d in g blow to a n th r a c ite la b o r an d c a p ita l.
A n y f u r t h e r in c re a se in m in in g costs, i t is realized , m u s t be p assed on to th e p u b lic ; a n d th e p ublic h a s clearly in d ic a te d t h a t in t h a t case i t w ill ta k e its b u s i
n ess elsew here.
I t is to be hoped t h a t th e outcom e w ill be a m ore h e lp fu l a n d co -o p erativ e fo rm o f u n io n ism . T h e coal in d u s tr y is a n a tio n a l problem , n o t so m uch b ecause o f a n y close o rg a n iz a tio n am o n g coal o p e ra to rs (in d eed th e F e d e ra l G o v ern m en t a n d coal com m issions hav e com plained of th e lack o f a n y c e n tra liz e d co m p eten t o rg a n iz a tio n o f c a p ita l w ith w hom p a rle y could be h eld ) ; i t is a n a tio n a l problem , an d in tim e o f s trik e s a p p e a rs to be a n a tio n a l m onopoly, th ro u g h th e re c e n t m onopoly o f m in e lab o r. W h a t th e coal in d u s tr y needs is f r e e r co m p etitio n , w h ich in d eed h a s been p a r tly o b ta in e d in th e p r e s e n t em erg en cy by th e in c re a se d a c tiv ity o f th e b itu m in o u s in d u s try .
C l o s e A n a l y s i s o p A c c i d e n t s w ill p re v e n t t h e ir re c u rre n c e . A n y ac c id e n t t h a t m ig h t hav e cau sed a n in ju r y b u t d id n o t should be in v e s tig a te d a n d th e re s u lt reco rd ed . N o a c c id e n t should be g ro u p e d u n d e r a sin g le cause, b u t cro ss-in d ex ed a n d c ro ss-reco rd ed u n d e r all th e v a rio u s elem en ts s u rro u n d in g o r c a u sin g i t — n eg ligence, lack o f in s tru c tio n , sickness, feebleness, age, ig n o ran ce , o r lack of s ig h t o f v ic tim w h e re th e re is one, lack o f lig h t, tim e o f day, d a y of w eek, f a u lty tra c k , w e a th e r co n d itio n s, seam o f coal an d p a i't of m ine.
T h e P u b l i c D o e s n ’t D e s i r e know ledge f o r its g u id ance. I f i t th in k s so m e th in g is b e in g h id d e n fro m it, i t n a tu r a lly becom es an x io u s to find o u t w h a t i t is. W ith a s c e rta in m e n t com pleted th e in te r e s t dies. T h e fa c ts a re no lo n g e r new s. T he p a p e rs w a n t “exclusive stu ff.”
I f th e y all g e t a sto ry , especially w ith o u t a sk in g f o r it, th e y w on’t ta k e th e tro u b le to p r i n t it. B u t if i t ’s a se c re t, t h a t ’s a n o th e r m a tte r . P e rh a p s a little g r e a te r coal p u b lic ity w ould do no h a rm .
S e e i n g T h a t A n t h r a c i t e is fa ced b y co m p etitio n fro m s u b s titu te s a n d t h a t co m p etitio n can be p ro v ed by m a n y public u tte ra n c e s a n d o th e r u n q u e stio n a b le evi
dence, i t is tim e t h a t le g isla tio n im p o sin g d iffe re n tia l ta x a tio n on a n th r a c ite be rep ealed , th u s lo w erin g th e cost on t h a t com m odity to th e co n su m er.
De c e m b e r 24, 1925 C O A L A G E « 8 1
Improved Blasting Methods Increase Proportion Of Lump Coal in Output"
Standard S h o o tin g P ra ctice S h o u ld B e A d o p ted — S h o th o le P la ce m e n t, S ize o f C artridge, K ind of S tem m in g , A ll E x e r t N o n -C u m u la tiv e In flu en ces
B y J. E. T iffa n y t
P i t t s b u r g h , P a .
Fig. 2—Results of a Snubbing Shot
S n u b b i n g m a y b e a c c o m p lis h e d b y h a n d p ic k i n g , b y w e d g in g , b y m e c h a n ic a l m e a n s o r b y t h e u s e o f e x p l o s i v e s . T h is i l l u s t r a t io n s h o w s t h e e f f e c t o f fir in g a l i g h t s h o t in a s h a l l o w hcrfe d r ille d n e a r th e c e n t e r o f t h e f a c e a s h o r t d is t a n c e a b o v e t h e u n d e r c u t.
of T echnology; one in th e N aom i m in e of th e H illm an Coal & Coke Co. a t F a y e tte C ity, P a ., a n d th e o th e r in th e B a n n in g N o. 2 m in e o f th e P itts b u r g h Coal Co.
a t W h its e tt, P a .
A ssu m in g t h a t i t is d e sire d to im prove th e p ro d u c t of a given m ine, how sh all th e n e c e ssa ry in v e s tig a tio n proceed?
A th o ro u g h in sp ectio n of all w o rk in g places is th e firs t step . In th is w o rk th e p h y sical c h a ra c te ris tic s o f th e coal bed, p a r tic u la rly a s to f r ia b ility , m u st be co n sid ered . O b se rv a tio n s should also be m ade o f th e th ic k n e s s a n d h a rd n e s s o f each bench, an d th e p o sitio n , n a tu r e a n d th ic k n e ss o f th e b a n d s o f s la te a n d bone, also th e c h a r a c te r of th e ro o f an d b o tto m . W h ere sh o ts a re fired in w o rk in g places t h e i r effect on th e coal, ro o f a n d rib s should all be c a re fu lly observed. In sp ec
tio n s m ade in o th e r m in es w o rk in g u n d e r s im ila r co n d itio n s o fte n p ro v e o f value a n d m a y f u r n is h w o r th w hile su g g e stio n s f o r th e so lu tio n of th e pro b lem in h an d .
In m in es w h e re im p ro v em e n t in th e q u a lity o f o u t
p u t is d esired , a s ta n d a rd m ethod o f d rillin g a n d sh o o t
in g is seldom in vogue. T h e p lacem en t an d d ire c tio n of sh o th o les w ith re sp e c t to th e rib s, th e roof, a n d to each o th e r, v a ry w idely. A s a ru le b la s tin g c h a rg e s a r e fo u n d to be excessive an d n o t p ro p e rly confined by a sufficient q u a n tity o f in co m b u stib le ste m m in g . A s a re s u lt evidence ca n fre q u e n tly be discovered o f blow n- o u t sh o ts. E n tir e ly asid e fro m th e h a z a rd s a tte n d in g su ch p ra c tic e s, th e explosive h a s no chance to p ro d u c e effective re s u lts . T h e coal will be fo u n d to be m uch b ro k en an d in m a n y cases is n o t loosened in a m a n n e r su ita b le f o r lo ad in g onto m in e c a rs.
This p o rtio n o f charge is ineffective
. Under-
\ c u t
Fig. 1—A Gripping Undercut
S u m p in g t h e m a c h in e a t a n a n g l e t o th e r ib a n d w i t h d r a w i n g it in a s i m i l a r p o s it io n r e s u l t s in t h e b a c k o f t h e c u t b e in g w id e r th a n t h e f r o n t . R ib h o le s a r e li a b l e t o b e d r ille d in t o s o lid c o a l t h u s s e r i o u s l y d e c r e a s i n g t h e e f f e c t i v e n e s s o f t h e ir e x p l o s i v e c h a r g e s .
S
U C C E S S F U L coal m a rk e tin g u su a lly h in g e s upon th e th o ro u g h n e ss of p re p a ra tio n a n d th e p e rc e n tag e of lum p co n tain ed in th e m in e p ro d u ct.
M ethods em ployed in b la s tin g th e coal fro m th e w o rk in g fa c e an d all 'o p e ra tio n s in c id e n t th e re to a r e of p r im a r y im p o rta n c e because su b se q u e n t c a re in p re p a r a tio n c a n n o t a to n e fo r lack of skill in b rin g in g th e coal dow n. In o rd e r to o b ta in a m ore m a rk e ta b le p ro d u c t a n d sim u lta n e o u sly in c re a se s a fe ty a n d effi
ciency in coal sh o o tin g i t is n e c e ssa ry to s ta n d a rd iz e all o p e ra tio n s in c id e n t to m in in g .
N o s ta n d a r d ro u n d of sh o ts applicable to all m in es is possible b ecause w o rk in g places d iffer g r e a tly in w id th a n d h e ig h t, f u r th e r m o r e , coal beds v a ry a p p re c ia b ly in te x tu r e a n d in th e n u m b e r an d p o sitio n of th e b a n d s o f im p u rity co n tain ed . B y p ro p e r in v e s tig a tio n , how ever, i t u su ally is possible to devise a s ta n d a r d m eth o d ap p licable to a n y p a r tic u la r m ine. H ow th is m a y be accom plished an d th e r e s u lt o f te s ts m ade by th e U; S. B u re a u o f M ines will be h e re s e t fo r th . T h ese te s ts show th e re la tio n s e x is tin g b etw een th e m e th o d s o f p la c in g a n d c h a rg in g th e holes, th e a c tu a l q u a n tity o f lum p produced and th e p o ssib ilitie s of im p ro v in g b la s tin g p ra c tic e . T h e tr ia ls h e re d epicted w ere c a rrie d o u t in tw o la rg e m in es w o rk in g th e P itts b u r g h bed, an d in one s o u th e rn Illin o is m ine, o f 4,000 to n s cap acity , w o rk in g th e No. 6 m e a su re o f t h a t s ta te .
T h e firs t tw o in v e s tig a tio n s w e re p ro secu ted u n d e r a fello w sh ip a g re e m e n t w ith th e C a rn e g ie I n s titu te
• A b s t r a c t o f p a p e r e n t it le d “ R e c e n t D e v e lo p m e n t s In S h o o t in g C o a l” p r e s e n t e d w i t h t h e a p p r o v a l o f t h e a c t i n g d ir e c to r o f t h e U . S. B u r e a u o f M in e s , b e f o r e t h e W e s t V i r g i n i a C o a l M in i n g I n s t i t u t e , N o v . 24, 1 9 2 5 . M r. T if f a n y c o v e r e d th e s a m e -sub
j e c t a t t h e C o a l M in in g I n s t i t u t e o f A m e r ic a , P i t t s b u r g h , P a ..
D e c . 10, 19 2 5 .
f E x p l o s i v e s t e s t i n g e n g in e e r , P i t t s b u r g h E x p e r i m e n t S t a t io n , U . S . B u r e a u o f M in e s.
882 C O A L A G E Vol. 28, No. 26
Fig. 4—T ight or B uster Shot in a S lant Hole
M u c h o f t h e c o a l lo o s e n e d b y t h i s k in d o f a s h o t m e r e l y s e t t l e s d o w n in p la c e w i t h o u t b e in g t h r o w n o r r o lle d o u t u p o n t h e m in e flo o r . I t r e q u ir e s c o n s id e r a b le p ic k w o r k t o d is lo d g e It r e a d y fo r lo a d i n g .
a s show n in F ig . 1. W hen fired, th e explosive ly in g in th e solid c a n n o t p e rfo rm a m a x im u m of u se fu l w ork, c o n seq u en tly i t s h a tte r s th e coal im m e d ia te ly a b o u t i t a n d m a y e x e rt u n d e sira b le fo rc e upon th e ro o f. T h is is p a rtic u la rly th e case i f coal is le f t up as a ro o f p ro te c tio n . T h is c o n s titu te s a n a d d itio n a l h a z a rd in m in in g , f o r w hen th e ro o f is in ju r e d in b la s tin g g r e a te r diffi
cu lty a n d co st is e n ta ile d in p re v e n tin g i t fro m fa llin g . T en d en cy to m ak e c u ts g rip p e d a t th e r ib s is com m on to all ty p e s o f m in in g m ach in es, th e b r e a s t m a ch in e included. H ow ever, w ith th is l a t t e r ty p e a n o th e r diffi
c u lty is en co u n tered , nam ely, t h a t sm all p illa rs o r noses o f coal, com m only called “ s p ra g s ,” a r e liab le to re m a in a t th e back o f th e u n d e rc u t. W ith som e ty p e s of t u r r e t m ach in es, also, a place c a n n o t be c u t to u n ifo rm d ep th . I t is possible, how ever, b y th e e x e rc ise of p ro p e r ca re , to c u t th e rib s in a d ire c tio n p a ra lle l to th e lin e of s ig h ts . W hen u n d e rc u ttin g h a s been com pleted a s till f u r t h e r im p ro v e m e n t m a y in m a n y cases be m a d e b y s n u b b in g ; t h a t is, b y in c re a s in g th e h e ig h t o f th e u n d e rc u t alo n g i ts o u te r edge b y p ic k in g o r b la stin g .
W h ere s n u b b in g is p ra c tic e d th e coal u su a lly rolls f o rw a rd in to th e room w hen i t is loosened by th e b la st.
T h is b re a k s th e m a te ria l less th a n w h en th e explosive is called upon to p e rfo rm th e double d u ty o f b o th b re a k in g th e coal dow n a n d tu r n in g i t over. In sn u b b in g te s ts m ad e a t th e N ao m i m in e a n in c re a se o f 5 p e r cen t
— fro m 64.2 to 69.2 p e r c e n t— in th e p ro p o rtio n o f coal Fig. 3—Placem ent of the Snubbing Shot
I n t h i s c a s e th e s n u b b in g s h o t h o l e w a s d r ille d 2 ft . 4 in . d e e p a n d p la c e d 2 ft. a b o v e t h e k e r f a n d 7 f t . f r o m t h e r i g h t h a n d rib .
W hen th e se o b se rv a tio n s h a v e b een com pleted, fo r m u la tio n o f a new sy ste m w h ich m a y lead to a s ta n d a r d p ra c tic e in d rillin g a n d b la s tin g m a y b e com m enced.
T h e m eth o d o f sh o o tin g should no lo n g e r be le f t to th e ju d g m e n t o f each in d iv id u a l m in e r. T h e q u a n tity of explosive loaded in to each hole w ill also h av e to be s ta n d a rd iz e d . D iffe re n t m e th o d s m u s t b e tr ie d o u t u n d e r s tr ic t su p e rv isio n and, i f possible, th e coal p ro duced should be sc reen ed s e p a ra te ly so as to a s c e r ta in w hich p ra c tic e y ield s th e m a x im u m p e rc e n ta g e o f lum p.
In v e s tig a tio n s in th e s o u th e rn Illin o is m in e r e f e r r e d to co n tin u ed f o r m o re th a n tw o m o n th s b e fo re a s u it
able b la s tin g m eth o d w as evolved. D u rin g th is tim e no a tte m p t w as m ade to ch an g e th e p ra c tic e s follow ed by th e m in e rs. D u rin g th e firs t m o n th a f t e r th e s ta n d a r d m eth o d w as a d o p ted no im p ro v e m e n t w as n o ticeab le in th e q u a n tity o f 6-in. coal. D u rin g th e second m o n th , how ever, b e tte r re s u lts becam e a p p a r e n t a n d an in c re a se o f 1.53 p e r c e n t above th e a v e ra g e o f th e te n m o n th s p r io r to th e com m encem ent of th e in v e s ti
g a tio n w as n o ted . Som e of th is im p ro v e m en t m ay hav e r e s u lte d fro m th e use o f l i - i n . d ia m e te r c a r tr id g e s in place o f 13 in., w h ich th e y su p p la n te d . D u rin g th e second m o n th th e lum p coal w as in c re a se d b y 2 p e r c e n t; th is im p ro v e m e n t u n q u e stio n a b ly b e in g d ue to th e s ta n d a r d m eth o d s ad o p ted to g e th e r w ith th e re d u c tio n in c a r tr id g e d ia m e te r. T h ro u g h all s u b se q u e n t m o n th s th is im p ro v em en t w as s u s ta in e d a n d th e good r e s u lts o b ta in e d w ere f u r t h e r im p ro v ed b y in s tr u c tio n s g iv en th e m in e rs, b y closer s u p e rv isio n a n d b y th e co -o p eratio n o f all in te re s te d p a rtie s , b o th m in e offi
c ia ls a n d m in e rs.
Close su p e rv isio n o f b la s tin g an d all th e o p e ra tio n s in c id e n t th e r e to is a m a jo r f a c to r in a n y cam p a ig n to in c re a se th e p e rc e n ta g e of lum p coal. T h is should s t a r t b e fo re th e fa ces a re cu t. A place t h a t is p ro p e rly cleaned b e fo re u n d e rc u ttin g w ill give b e tte r re s u lts
Usual E n try Drilling
T h is m e th o d o f h o le p la c e m e n t w a s e x t e n s i v e l y u s e d in e n t r y f a c e s p r io r to t h e i n v e s t i g a t i o n d e s c r ib e d in t h i s a r t ic le .
th a n one in w hich th e face o v e rh a n g s a n d th e c o rn e rs a r e n o t sq u a re .
F u n d a m e n ta lly a n explosive m u s t h av e a t le a s t tw o f r e e fa c e s o f coal to w o rk upon in o rd e r to b r in g dow n th e m a te ria l p ro p e rly . F o r th is re a so n i t is n e c e ssa ry to p ro d u ce one o f th e s e fa c e s a rtific ia lly by e ith e r h a n d o r m ech a n ical u n d e rc u ttin g o r b y a n o ver-cut, m iddle- c u t o r s h e a r. A s h e a rin g c u t m a y also be used in com b in a tio n w ith e ith e r one o r b o th o f th e o th e r o p e ra tio n s.
T h e se c u ts should be m ad e a s c a re fu lly a s possible in o rd e r to o b ta in r e c ta n g u la r faces. E a c h c u t m u s t be u n ifo rm in d e p th a n d m u s t n o t g rip a t th e rib s. I f th e c u t g rip s a t th e rib s th e te n d e n c y is to g r ip th e d rillh o les also. W h en su ch holes a r e c h a rg e d an d fired th e y do n o t b r in g th e coal dow n in a s a tis f a c to r y m a n n e r a n d since i t is w edged a t th e r ib s i t does n o t roll f o r w a r d in to th e w o rk in g place. T h is fo s te r s th e n a tu r a l te n d e n c y on th e p a r t o f th e m in e r to u se excessive c h a rg e s o f explosive.
S uch c h a rg e s do n o t im p ro v e co n d itio n s, w h ile th e y s h a tte r th e coal serio u sly .
G rip p ed holes a re fre q u e n tly d rilled beyond th e c u t
F I G . 6
Decem ber 24, 1925 C O A L A G E 883 p a s s in g over a l i - i n . b a r sc reen w as o b tain ed . H ow
ever, w hen th e se sam e te s ts w e re re p e a te d in th e B a n n in g N o. 2 m ine, w h e re th e coal h a s d iffe re n t p h y s
ical c h a ra c te ris tic s , sn u b b in g d id n o t alw ay s re s u lt in ro llin g i t fo rw a rd . I n th is m in e th e coal clu n g to th e r ib s an d sn u b b in g p roved of no p a r tic u la r a d v a n ta g e . W hile h a n d sn u b b in g p roduced m o re lum p coal in th e B a n n in g No. 2 m in e th a n w a s o b ta in e d fro m u n sn u b b ed sh o ts, th e im p ro v e m e n t w a s n o t sufficient to offset th e q u a n tity o f slack p roduced in th e c u ttin g a n d s n u b b in g o p e ra tio n s.
F ig . 2 show s th e re s u lt o f a sn u b b in g sh o t placed as show n in F ig . 3. T h e p ro p o rtio n o f lum p o b ta in e d w ith th is s n u b b in g sh o t w as m o re th a n 1 p e r c e n t h ig h e r th a n t h a t p ro d u ced by h a n d sn u b b in g . In a room 20 ft. w id e se v e ra l to n s o f coal is picked dow n in sn u b b in g , only 40 p e r c e n t o f w hich is l j - i n . lum p. A lm o st 10 p e r c e n t o f slack is p roduced in su ch a room a s th e r e s u lt o f b o th c u ttin g a n d sn u b b in g o p e ratio n s.
T e s ts should, th e re fo re , be m ade b e fo re decid in g
F I G . 6
Drilling Adopted
T h i s p la c e m e n t a n d d rillin g - grave b e t t e r r e s u l t s th a n t h a t s h o w n in F i g . 5 a n d w a s a c c o r d i n g l y a d o p te d a s s t a n d a r d .
il a
No. 3 J j cartridges, t j " x 6 i " o r 4 cartridges,
U xB'
No. 2 n J cartridges, IJ x b t“ or 4 car friges, ij" x 6 "
No. I
j '
/ / cartridges /J'x éi or 2 cartridges ¡ i’x 6"
-r iZ-...
upon th e a d o p tio n o f sn u b b in g in an y p a r tic u la r m ine.
I t will be fo u n d t h a t w h e re th e coal does n o t cling to th e rib s a f t e r b e in g sh o t, sn u b b in g w ill p e rm it i t to t u r n over in s te a d of re m a in in g in a n u p r ig h t p o sition.
T he s n u b b in g o p e ra tio n can be p e rfo rm e d by explosives, by h a n d , e ith e r u s in g w edge a n d sledge o r pick, o r by m ech an ical m eth o d s, such a s a ir-d riv e n p u n c h e rs, d rills o r h am m e rs, o r by e le c tric c h a in m ach in es.
U n d e rc u ttin g does n o t y ield its fu ll a d v a n ta g e s un less th e c u t is cleaned o u t b e fo re sh o o tin g . T h is d e ta il should be g iv en close a tte n tio n . T h e m in e r o r th e m a ch in e r u n n e r ’s h e lp e r should be p ro v id ed w ith a s c ra p e r o r lo n g -h an d led shovel f o r th is p u rp o se. B u g d u st cleaned o u t fro m such a c u t should be loaded b efo re sh o o tin g .
A cco rd in g to L. E . Y oung, in a p a p e r p re se n te d b e fo re th e A m e ric a n M in in g C ongress, M ay 29, 1925,
“ D a ta a r e n o t av ailab le to w a r r a n t d efin ite conclusions b u t th e outlook is t h a t a c o m b in a tio n of s h e a rin g an d s n u b b in g w ill p rove to be th e m o st d e sira b le p ra c tic e fo r m echanical lo a d in g ; f o r th e success o f m echanical lo ad in g d epends v e ry la rg e ly on how th e coal is sh o t do w n .” To th is m ig h t be ad d ed th e f u r t h e r fa c t th a t im p ro v e m en t will acc ru e to p ro p e r p lacin g o f th e sh o t- holes, since th is fo rm s one o f th e m o st im p o rta n t te ch n ic al d e ta ils o f b la s tin g o p e ra tio n s. In o rd e r to shoot a place s a tis fa c to rily , e ith e r fo r h a n d o r fo r m ach in e loading, th e r ib s m u s t be cleaned p ro p e rly
\ ' ■■/>
V ‘ I
Vi-fc 4 v « \ w V
: I' S 'il
: Il i II/ H
P IG . 7
Usual Room Drilling
/o'-—
No. 4 No. Z No. /
4 cart ridges 3car fridges 2 cartridges J
T -
, f '
-6 —w-?*
No. 3 4 cartridges
■ 26 —
<---6'---M an d th e m a ss sh o t be so sh a k e n up t h a t i t can be shoveled w ith a s little pick w o rk a s possible. Im p ro p e rly placed holes, w h ich hav e to be h eav ily loaded in o rd e r to b rin g dow n th e coal, w ill s h a tte r th e m a te ria l a d ja c e n t to th e explosive c h a rg e , w h ile a t g r e a te r d ista n c e s fro m i t fissu res w ill be p ro d u ced even in th e m a te ria l le f t in place. T h is ad d s to th e difficulty o f firin g su b se q u e n t sh o ts. T h e q u a n tity of coal th u s s h a t
te re d d ecreases a s th e p lacem en t of th e holes is im proved, w hile sim u lta n e o u sly th e q u a n tity o f explosive n e c e ssa ry w ill be decreased.
P ro p e r p lacem en t o f sh o th o les w ill depend upon th e te x tu re of th e coal a n d th e d ire c tio n a n d n a tu r e o f th e face an d b u tt cleats. In th e B a n n in g No. 2 m ine, te s ts w e re co n ducted w ith w o rk in g places 10 a n d 18 f t. w ide on b o th th e b u tts an d faces. S h o t holes w e re placed in th e sam e m a n n e r f o r each te s t an d th e sam e b ra n d o f explosive w as used. A s m ig h t hav e been expected, th e n a rro w b u tt w o rk in g s gav e th e p o o re st re s u lts , 54 p e r cen t o f lum p, w hile th e w ide fa c e s afforded th e b est.
S hotholes t h a t slope up a t an a p p re ciab le angle, such a s a re com m only em ployed in th e P itts b u r g h bed, h av e m an y d isa d v a n ta g e s, w h ich w ill be d iscu ssed la te r.
F ig . 4 show s th e re s u lt o f firin g a t ig h t sh o t in a w ide b u tt w o rk in g .
In th e te s ts in th e P itts b u r g h bed, w h e re th e coal m in ed ra n g e s fro m 6 to 7 f t. h ig h a n d th e w o rk in g places w ere 10 f t. w ide in e n trie s a n d 20 f t. w ide in room s, i t w as fo u n d t h a t only tw o holes w ere n ec essary . In m o st places w h e re lum p coal is a n im p o rta n t c o n sid e ra tio n , b e tte r re s u lts a re p ro c u ra b le by u sin g only tw o holes.
W h ere th e coal is o f a to u g h e r n a tu re , how ever, esp e
cially if i t becom es n e c e ssa ry to use h eav y c h a rg e s o f explosive, i t is fo u n d b e tte r to em ploy m o re holes ch a rg e d lig h te r. A com m on p ra c tic e follow ed in th e P itts b u r g h bed is to place th e holes fro m 12 to 15 in.
fro m e ith e r rib an d 2 f t. below th e d ra w -sla te . Such holes a r e d rilled p a ra lle l to th e rib b u t slo p in g u p w a rd to w a rd th e ro o f a t such a n an g le t h a t th e f a r t h e r end is a b o u t 4 in. below th e d ra w -sla te a n d 6 in. in f r o n t of
s ' //
/ X---
s II
F I G . 8
Adopted S tand
ard Drilling
■2<^*— 4'- 4c ... - a '- ---
Ü No. 4 2 to 3 car tr. ¡J'x 61" or 3 to 4 cartr. U x S "
No.3—2{ cartr.
¡J'xéi’orJ
cartr. i J ' x S "
■ 21
8 No.2 , 3cartr.lJ"x6i or 4 cartr. U "x S '
o N o ./, licartr. I j ' x b i or 2cartr. U “x S '
884 C 0 A L A G E VOL. 28, No. 26
Fig. 9—Result of a T ight Shot in a S lant Hole
T h i s c o a l m e r e l y i s c r a c k e d a n d ■will r e q u ir e q u it e a b it o f p ic k i n g to b r in g i t d o w n r e a d y f o r lo a d i n g o u t. T h is i m p o s e s m u c h m o r e w o r k o n t h e m in e r t h a n a s h o t t h a t r o lls t h e c o a l w e l l o u t o n th e flo o r .
th e r e a r of th e u n d e r-c u t. I n o th e r w o rd s, a v e rtic a l lin e d ropped fro m th e r e a r end o f th e hole w ould re a c h th e k e r f 6 in. a h e a d ( t h a t is, n e a r e r th e fa c e ) o f th e back o f th e u n d e r-c u t. A s a ru le a b o u t 2-in. holes a re d rilled . T h ese a r e com m only em ployed in th e coke re g io n s o f P e n n sy lv a n ia w h e re lum p is no p a r tic u la r o b je ct. One hole, know n a s a “ b u s te r ” o r b re a k e r shot, is placed a t th e c e n te r o f th e face, o r a t som e p o in t b etw een th e r ib holes.
As a ru le , in n a r ro w w o rk th e n e c e ssity f o r a th ir d hole w ill depend la rg e ly upon th e te x tu r e o f th e coal.
I n s o u th e rn Illin o is w h e re th e c le a ts a re less p ro n o u n ced a n d th e te x tu r e is o f a to u g h e r n a tu re , a t h ir d hole w a s d rilled , a s show n in F ig . 5. A f te r m a k in g a n u m b e r of te s ts i t w as fo u n d a d v a n ta g e o u s to place No. 1 hole 3 f t. above th e b o tto m a n d th e sam e d ista n c e fro m th e rib . T h is w a s d rilled re la tiv e ly flat, a s show n in F ig . 6.
In th e No. 6 bed o f s o u th e rn Illin o is th e “blue b a n d ,”
a s tre a k of h a r d g r a y shale, a b o u t 14 in. th ic k , o ccu rred in th e m jn e in v e s tig a te d a t a u n ifo rm h e ig h t o f a p p ro x i
m a te ly 18 in. above th e floor. T h is h a d to be c o n sid ered w h en p lacin g th e shotholes. P re se n c e o f th is b lu e b an d led to th e ad o p tio n o f sn u b b in g , u su a lly accom plished by firin g a sn u b b in g shot. T h e hole f o r th is sh o t should be d rille d in a n a lm o st h o riz o n ta l p o sitio n , a s show n in F ig . 7. F ig . 8, how ever, show s th e m eth o d o f d rillin g finally ad o p ted as s ta n d a rd . F o u r holes a r e used, t h e i r
Fig. 10— Result of a T ight Shot in a F la t Hole
In t h is c a s e t h e c o a l i s m u c h m o r e b r o k e n t h a n in F i g . 9.
H o w e v e r , s n u b b in g b e f o r e s h o o t i n g p r o b a b ly w o u ld h a v e im p r o v e d t h e r e s u l t s a t t a in e d .
n u m b e rs on th is d ra w in g in d ic a tin g th e o rd e r in w h ich th e y a re fired.
S id e holes sh o u ld alw a y s be d rille d p a ra lle l to th e lin e o f s ig h t an d should b e fro m 1 to 3 f t. fro m th e rib , d e p e n d in g on th e k in d of s h e a r w h ich th e y w ill p roduce.
T e s ts m ad e in th e P itts b u r g h bed show ed t h a t f o r a t i g h t sh o t a d ista n c e o f 12 in. w as m o s t ad v a n ta g e o u s, b o th fro m th e s ta n d p o in t o f lum p p ro d u c tio n a n d t h a t o f o b ta in in g a good sh e a r. B e tte r re s u lts , how ever, w e re o b ta in e d in th e to u g h e r Illin o is bed w ith holes placed 3 f t. fro m th e rib .
R e lativ ely fla t holes d rilled 10 in. below th e to p o f th e coal p ro d u ced 5.1 p e r c e n t m o re lum p th a n d id th o se s ta r te d 24 in. below th e to p a n d sla n te d u p w a rd . F ig . 9 show s th e r e s u lt o f firin g a t i g h t s h o t w ith a s la tin g hole, w h ile F ig . 10 d isp lay s th e r e s u lt o f th e sam e k in d o f a s h o t w ith a flat hole placed a s show n in F ig . 11.
T h e re s u lts o£ a b u t t sh o t a r e show n in F ig . 12.
N o ho^e should ever be c h a rg e d w ith a g r e a te r am o u n t o f p e rm issib le explosive th a n th e lim it p re sc rib e d b y th e B u re a u o f M ines, o r 14 lb. p e r shot. T h e p re s e n t p u b lish ed lis t o f p e rm issib le s c o n ta in s b ra n d n am es o f a b o u t 150 explosives. T h o se com m only used in coal m in in g a r e to be fo u n d in C lass la , th e p rin c ip a l in g re d ie n t o f w h ich is a m m o n iu m n itr a te . B o th th e
Fig. 11—Placem ent of F la t Holes in Room Face
N o s n u b b in g w a s h e r o a t t e m p t e d . P i t c h i n g th e h o le s fla t o r n e a r ly s o a l l o w s t h e e x p l o s i v e to e x e r t i t s f o r c e in a d ir e c t io n a t r i g h t a n g l e s to th e b e d d in g p la n e s o f t h e c o a l.
s a fe ty an d p h y sical c h a ra c te r is tic s o f th e se explosives h av e been te s te d b y th e B u re a u .
P e rm is s ib le explosives p o ssess th r e e c h a ra c te ris tic s w h ich influence t h e ir p ro d u c tio n o f lum p coal, nam ely, d e n sity , u n it deflective c h a rg e , a n d r a te o f d e to n a tio n . T h e B u re a u p u b lish e s th e w e ig h t in g ra m s o f th e l i x 8-in. c a r tr id g e s o f each explosive. T h e se w e ig h ts v a ry fro m 137 to 181 gm . o r m ore, c o rre sp o n d in g to a s tic k c o u n t o f 165 to 125 p e r 50-lb. case. In th e lig h te r b ra n d s 3? s tic k s o f H x 8 -in . size w eig h a b o u t a p o u n d ; in th e h e a v ie r v a rie tie s a b o u t 24 stic k s. T h e lig h te r a c a r tr id g e th e g r e a te r w ill be th e d ista n c e alo n g th e borehole th r o u g h o u t w h ic h th e explosive fo rc e g e n
e ra te d by i t w ill be- d is trib u te d , p ro v id ed a u n it deflec
tiv e c h a rg e is co n sid ered . T h e u n it deflective c h a rg e is t h a t w e ig h t o f a n explosive in g ra m s w h ich w ill give th e sam e sw in g on th e b a llis tic p en d u lu m a s 227 gm . (4 lb.) o f th e 40 p e r cent, s t r a i g h t n itro g ly c e rin d y n a m ite ad o p ted as a s ta n d a r d by th e P itts b u r g h t e s t in g s ta tio n o f th e B u re a u o f M ines.
I t h a s been fo u n d by te s ts co n ducted on five d iffe re n t b ra n d s o f explosive, used u n d e r id e n tic a l c o n d itio n s b u t in q u a n titie s p ro p o rtio n e d ac c o rd in g to t h e i r re sp ectiv e deflective c h a rg e s, t h a t each explosive b ro u g h t dow n th e sam e q u a n tity of coal, w ith , how ever, d iffe re n t p ro p o rtio n s o f lum p. T h e r a te s of d e to n a tio n of th e se explosives v a ry an d to th is w as a ttr ib u te d th e difference in th e p e rc e n ta g e o f la rg e size produced.
T he r a te a t w h ich a file of explosive d e to n a te s in fe e t o r m e te rs p e r second is know n as its r a te o f d eto n a tio n . F ig . 13 show s th e re la tio n betw een th e r a te o f d eto n a-
tio n a n d th e p e rc e n ta g e of lum p coal p ro d u ced in th e live te s ts m ade. T h e h ig h e s t p o in t of th e se g ra p h s in d ic a te s th e p e rm issib le explosive h a v in g th e d e to n a tio n r a t e m o st s u ita b le f o r th e phy sical te x tu r e o f th e coal m in ed . A ny explosive h a v in g a d e to n a tio n r a te e ith e r g r e a te r o r less p ro d u ces a d ecreased p e rc e n ta g e o f lum p, th is d ecrease b ein g p ro p o rtio n a l to th e v a r ia tio n in th e d e to n a tio n ra te .
In lo ad in g a borehole in coal all th e c a rtrid g e s r e q u ire d should be placed to g e th e r a t th e r e a r of th e hole w ith th e p r im e r (th e c a r tr id g e c o n ta in in g th e d e to n a to r) placed la s t o r n e a re s t th e collar. T he fu lm in a te end o f th e d e to n a to r should p o in t to w a rd th e m a in body o f th e ch arg e . A w ooden ta m p in g stic k should be used to p u sh th e c a r tr id g e s hom e. Incom b u s tib le ste m m in g only should be em ployed, as coal d u s t o r slack in v ite s d is a s te r by explosion. M o ist clay fo rm s a n excellent ste m m in g m a te ria l a n d can be m ade u p in to dum m ies. W h ere a p la stic m a te ria l is n o t a v a il
able, how ever, th e ste m m in g m a y be placed in ta m p in g b ag s. T h e firs t tw o du m m ies should be p re sse d lig h tly a g a in s t th e explosive c h arg e, w h ile th e re m a in d e r of th e s te m m in g should be ta m p e d fo rc ib ly in to th e d rill hole, w h ich should be filled to its m o u th . In firin g such a c h a rg e a lead w ire n o t less th a n 100
f t . in le n g th should be em ployed.
T h e s h o tfire r should n e v e r d e to n a te a sh o t except fro m som e p o in t w h ere h e c a n n o t be in ju re d . W h e re v e r p o s
sib le i t is good p ra c tic e to fire one hole a t a tim e an d load o u t th e coal b ro u g h t dow n by i t b e fo re firin g th e n e x t sh o t. T e s ts in a P e n n sy lv a n ia m in e h a v e show n t h a t w hen all th e coal loosened by th e t i g h t o r b u s te r s h o t w as loaded b e fo re th e b u tt, o r
Fig. 14—T ight Shot W ith A ir Spacing
I n lo a d in g - t h i s s h o t a w ir e s p a c e r w a s in t e r p o s e d b e t w e e n th e e x p l o s i v e c h a r g e a n d th e s t e m m in g . T h is a ff o r d e d a c u s h io n a g a i n s t w h ic h t h e e x p lo s iv e m i g h t a c t . T h e e x p l o s i v e f o r c e t h u s w a s s p r e a d o v e r a l a r g e r in t e r n a l a r e a o f th e b o r e h o le th a n w o u ld h a v e b e n t h e c a s e h a d t h e s p a c e r b e e n o m it t e d .
Decem ber 24, 1925 C O A L A G E
is
Fig. 12—Result of a B utt Shot
A t m a n y , i f n o t m o s t, c o a l o p e r a tio n s th e p e r c e n t a g e o f lu m p c o a l In t h e m in e p r o d u c t d e t e r m in e s th e m a r g in o f p r o fit t h a t c a n b e m a d e , b e c a u s e th e lu m p is th e o n ly g r a d e t h a t c a n b e s o ld a t a p r ic e a p p r e c ia b ly e x c e e d in g th e c o s t o f p r o d u c tio n . A p p a r e n t l y t h i s s h o t p r o d u c e d a s a t i s f a c t o r y p r o p o r tio n o f t h i s s iz e .
Fig. 13—Influence of Detonation Rate on Proportion of Lump Produced
N a t u r a l l y , t i g h t s h o t s p r o d u c e l e s s lu m p t h a n b u t t s h o t s . A c e r t a i n r a t e o f d e t o n a t io n a l s o t e n d s to m a k e t h e p e r c e n t a g e o f lu m p a m a x im u m . A n y r a t e g r e a t e r o r l e s s th a n t h i s c r i t i c a l s p e e d ■will h a v e a n a d v e r s e e f f e c t o n t h e s i z e o f t h e c o a l p r o d u c e d .
second shot, w as d e to n ated , 2.6 p e r c e n t m o re lum p coal w as p ro d u ced th a n w h e n only a b o u t h a lf th e coal loosened by th e t i g h t s h o t w as loaded o u t b e fo re th e second sh o t w as d eto n ated .
A s a ru le, b e s t r e s u lts a r e a tta in e d w hen c a r tr id g e s of a p p reciab ly less d ia m e te r th a n th e hole in to w hich th e y a re loaded a r e em ployed. In th e Illin o is te s ts w h e re 2-in. holes w ere loaded w ith l i x 8 - i n . c a rtrid g e s , in place of 13 x 6-in., b ecau se o f th e excessive q u a n titie s o f explosive used p r io r to th e te s ts , th e s u b s titu tio n could be m ad e on a s tic k -fo r-stic k b a sis. W h ere only a p ro p e r c h a rg e o f 13 x 6-in. c a r tr id g e s hav e been em ployed, a b o u t one m o re c a r tr id g e of th e l i x 8 - i n . size w as n ecessary . B y th is m e a n s th e a ir-sp a c e a s w ell a s th e le n g th o f th e c h a rg e w as in c reased . T h eo retically , th e use of a c a r tr id g e o f sm all d ia m e te r should re s u lt in th e p ro d u c tio n o f a g r e a te r p e rc e n ta g e of lum p coal, because w hen th e sam e w e ig h t of c h a rg e is used th e sm aller d ia m e te r g re a tly in c re a se s th e le n g th o f c h arg e.
Q u a n tita tiv e te s ts hav e show n t h a t w h en 1-in.
c a r tr id g e s w e re s u b s titu te d f o r th o se H in. in d ia m e te r, 4.9 p e r cen t m o re lum p p a ssin g ov er a l i - i n . sc re e n w as produced. In a c tu a l p ra c tic e , how ever, a c a r tr id g e a s sm all a s 1 in. should h a rd ly be em ployed, because, a s
2,400 Rate o f
886 C O A L A G E VOL. 28, NO. 2 6
Fig. 15—Effect of Both Snubbing and A ir-Spacing
T h is w a s a t i g h t s h o t , y e t a s m a y b e s e e n a f a i r p r o p o r tio n o f lu m p w a s r e a liz e d . A n y o n e I m p r o v e m e n t in s h o o t i n g m a y a p p r e c ia b ly i n c r e a s e t h e p r o p o r tio n o f lu m p y ie ld e d , b u t t h e s e b e t t e r m e n t s a r e n o t a d d a b le , t h a t is, t o t a l im p r o v e m e n t s e c u r e d f r o m tw o im p r o v e d p r a c t ic e s w i l l n o t a m o u n t to th e s u m o f t h e b e t t e r m e n t s a t t r i b u t a b l e to t h e s e m e t h o d s u s e d s i n g l y .
th e d ia m e te r is d ecreased, d e te rio ra tio n of th e explosive in s to ra g e is in c reased . A l j - i n . c a rtrid g e , how ever, m ay be used to a d v a n ta g e u n d e r o rd in a ry c irc u m sta n c es.
M eth o d s o th e r th a n d e c re a sin g th e d ia m e te r o f th e c a r tr id g e m a y be em ployed f o r a irc u s h io n in g . F o r exam ple, a w ire sp a c e r o r a paraffined p a s te b o a rd tu b e m ay be used, o r ro ck d u s t m a y be em ployed f o r all o r a p a r t o f th e ste m m in g . U n d e r c e rta in co n d itio n s m o re lum p coal m a y be p ro d u ced by a c o m b in atio n o f tw o o r m o re o f th e se m eth o d s. T h e use of sp acers, how ever, o f w h a te v e r k in d , does n o t m e e t th e re q u ire m e n ts of som e s ta te law s an d up to th e p re s e n t tim e th e B u re a u of M ines h a s n e ith e r ap p ro v ed n o r condem ned t h e ir use.
In u sin g a w ire sp a c e r th e explosive is placed in th e b o tto m of th e d rill hole, th e sp a c e r p u sh e d in n e x t an d th e re m a in d e r o f th e hole tig h tly ta m p e d to th e collar w ith clay stem m in g . B y th is m e th o d a n in c re a se of 5.4 p e r cen t in lum p coal h a s been o b tain ed . F ig . 14 show s th e re s u lt of a t i g h t sh o t loaded in th is m a n n e r.
A n in c re a se o f 7.4 p e r c e n t in lum p w as o b ta in e d by co m b in in g th is m e th o d w ith sn u b b in g . F ig . 15 show s th e re s u lt o f a ti g h t s h o t a n d F ig . 16 t h a t of a b u tt sh o t w ith th is ty p e of lo ading.
In v e s tig a tio n s hav e also been m ad e w ith ro ck d u s t ste m m in g a n d m e th o d s of lo ad in g t h a t com ply fu lly w ith th e s ta tu te s of P e n n sy lv a n ia , w h ich re q u ire t h a t a hole m u s t be ta m p e d solidly w ith in co m b u stib le ste m m in g th r o u g h o u t its e n tir e le n g th . F o r th is reaso n , in th e te s t all dum m y c a rtrid g e s w ere m ade o f th e sam e d ia m e te r a s th e hole, w h ich in t u r n w as e n tire ly filled. Tw o d iffe re n t rock d u s ts w e re em ployed, nam ely, a lim esto n e an d a sh ale d u st. A b o u t 85 p e r c e n t o f each v a rie ty w ould p a ss th ro u g h a 200-m esh screen.
B oth d u sts w ere te s te d w ith a 6-in. clay p lu g ta m p e d in th e co llar of th e hole. T h e lim esto n e d u s t w as also tr ie d w ith o u t clay p lu g a n d w ith one 24 in. long.
U n d e r s im ila r co n d itio n s o f ta m p in g , th e lim esto n e gave a h ig h e r p e rc e n ta g e of lum p coal th a n d id th e sh ale d u st. T h is v a ria tio n m a y be ex p lain ed by th e d iffe re n t a c tio n s of th e tw o m a te ria ls . T h e lim esto n e a p p e a re d to a c t a s a m ed iu m f o r tr a n s m ittin g th e fo rc e o f th e explosion u n ifo rm ly th ro u g h o u t th e e n tir e le n g th of th e drillhole, w hile w ith th e sh ale th e ac tio n m ore n e a rly a p p ro x im a te d a c u sh io n in g effect due to th e p a ck in g of th e d u s t in to a sm a lle r volum e.
Fig. 16— A B utt Shot Snubbed and Air-Spaced
N o t e t h e la r g e p e r c e n t a g e o f lu m p c o a l p r o d u c e d . S u c h r e s u l t s a s t h e s e i n d ic a t e e m p h a t i c a l l y t h a t t h e r e a l i z a t i o n f o r t h e t o t a l o u t p u t m a y b e a p p r e c ia b ly e n h a n c e d b y d e p a r t in g f r o m t h e “ b y - g u e s s - a n d - b y - g o s h ” m e t h o d s f o l l o w e d b y m o s t m in e r s in t h e m a t t e r o f s h o o tin g , a n d s u b s t i t u t i n g t h e r e f o r c a r e f u l l y s y s te m a t i z e d p r a c t ic e s t h a t h a v e b e e n p a i n s t a k i n g l y e s t a b l i s h e d a s t h e r e s u l t o f a c t u a l e x p e r i m e n t .
W hen rock d u s t ste m m in g w as em ployed in a s la tin g hole, 4.3 p e r c e n t m o re lum p coal w a s p ro d u ced th a n w ith m o ist clay, w h ile 5.1 p e r c e n t m o re la rg e m a te ria l re su lte d fro m a fla t hole th a n w a s o b ta in e d w ith m o ist clay in a s la n t hole. H ow ever, w h en th e se re s u lts w e re c o m p ared w ith th o se o b ta in e d w ith a fla t hole an d m o is t clay stem m in g , th e in c re a se w as only 0.8 p e r cent.
A f te r a s ta n d a r d m eth o d o f sh o o tin g h a s been w o rk ed o u t c a re fu lly an d fo u n d ap p licab le to th e m a jo rity o f places w ith in a m ine, i t should be p u t in to effect a n d rig id ly a d h e re d to. A s ta n d a r d m eth o d p ro p e rly e n forced, even th o u g h i t m a y n o t be th e b e s t a v a ila b le , is f a r b e tte r th a n a s m a n y d iffe re n t w ay s o f s h o o tin g a s th e r e a r e m in e rs em ployed.
Coal m in e ex ecu tiv es d e s irin g to in c re a se th e p ro p o r
tio n of t h e ir lum p p ro d u c t should c a re fu lly c o n s id e r th e fo llo w in g d e ta ils : D rillin g a n d s h o o tin g p ra c tic e s should be sta n d a rd iz e d an d closely su p erv ised . T he ribs- should n o t be p e rm itte d to g r ip th e u n d e r-c u t, w h ic h should be o f u n ifo rm d ep th . All b u g d u s t should b e cleaned o u t o f th e u n d e r-c u t w ith a s c ra p e r o r lo n g han d led shovel b e fo re th e fa c e is sh o t. A f te r each sh o t th e coal b r o u g h t dow n by it should be loaded o u t.
S id e holes should n o t g r ip th e r ib s . All sh o t holes should be d rille d p a ra lle l to th e b e d d in g p lan es. O v er
lo ad in g sh o th o les sh o u ld be a v o id e d ; th is w ill d ecrea se th e p ro p o rtio n o f lum p coal. E a c h hole sh o u ld b e ta m p e d fu ll w ith in co m b u stib le s te m m in g m a te ria l. I f p ro p e r a tte n tio n
is p a id to th e s e d e ta ils, a n in c re a s e in th e p ro p o rtio n o f lum p coal p ro duced m a y be confidently expected.
