“ i r a h S ¿ " « i t D e v o te d t0 th e O p eratin g, T ech n ical and B u sin e ss
E . J . Me h r e n, Vice-President P ro b lem s o f th e C oal-M ining In d u stry Engineering EditorR . Da w s o n Ha l l
Volume 28 NEW YORK, JULY 9, 1925 Number 2
C orrecting a M isunderstanding
I
N OUR IS S U E of Oct. 23, 1924, we published an e d ito ria l w hich by general u n d e rsta n d in g re fe rre d to M r. G eorge H. C ushing, of W ashington, D. C. The e d ito ria l in question w as an a tte m p t, w ith o u t malice, to ta k e a hum orous view of a situ a tio n w hich h ad developed some in te n sity of feeling. M r. C ushing construed our h u m o r as a n a ssa u lt on h is m otives an d even on h is p rofessional sta n d a rd s. T he la tte r question w as to him th e p a ra m o u n t issue.W hile we did d isag ree w ith M r. C ush in g on th e m a tte r th e n u n d e r discussion, th e re w as no th o u g h t of im p u tin g w ro n g m otives to M r. C ushing in th e position he had tak en , n o r o f questioning h is p rofessional sta n d a rd s.
In ju stic e to M r. C ushing we re g re t th a t th e ed ito rial w as open to any m isco n stru ctio n and w ith d ra w any seem ing im p u ta tio n of m otive i t contained.
S till U n rep en tant
A
F E W W E E K S ago th e F e d e ra l T ra d e Com m ission donned §ackcloth and did penance in th e open m a rk et, b u t its la te s t re p o rt on a n th ra c ite show s th a t i t has n o t re fo rm ed a n iota. I ts sta te m e n ts being m ade a t th e eve o f a co n test f o r a new a n th ra c ite w age scale seem calculated to encourage th e m in e rs in th e ir d esire to compel th e public to pay a h ig h e r w age th a n th a t to w hich th e m en a re en titled . T he fa c ts have been published a lre a d y ; w hy re p e a t th em now ?“ In S eptem ber,” says th e Com m ission, “ th e g ro ss p ro fits realized by w holesalers re p o rtin g to th e Com
m ission ra n g e d as h ig h as $1.75 a ton and am ounted to
$1 o r m ore a to n on a b o u t 4 to 11 p e r cen t o f th e ir re p o rte d w eekly sales.” I t w ill be n o ted th a t th e Commission does n o t say how m any w holesalers got
$1.75 a ton. I t is as if a fo re ig n e r com m enting on o u r A m erican conditions s a id : “ In th e m ad race fo r w ealth, in th e U n ited S ta tes, derelictions ra n g in g even to m u rd e r a re com m itted.” A tr u e sta te m e n t b u t an u n fa ir one. No g ro u p is to be ju d g ed by a single m an.
“ F a ilu re o f th e in d u s try to in crease its m in in g capac
ity to m eet inci-easin g dem and h as re su lte d in th e esta b lish m e n t of an unduly h ig h p rice level,” say s th e Com m ission. T h is is n o t a fa ct. J u s t a t p re se n t th e p roduction is ahead of th e dem and. In 1922 th e re w as an actu al sh o rta g e of coal b u t, as th e Commission says tru ly , th e s h o rta g e in 1923 w as only a n ticip ated and n o t actual. A t o th e r tim es th e re h a s been a g lut of a n th ra c ite . T he condition f o r w hich th e Com m is
sion p ra y s w h e re in th e m ine capacity is equal to m eeting p erio d s of e x tra o rd in a ry dem and h as been w ith us to a la rg e e x te n t and will be f o r some tim e, unless th e re is a strik e . T he b itu m in o u s region h a s alw ays been re a d y to m eet such e x tra o rd in a ry dem ands and s tra n g e to sa y i t h as been u n iv ersally condem ned fo r hav in g been th u s equipped. Do we u n d e rsta n d th a t the Com m ission would have th e a n th ra c ite m ines also over
m anned an d overdeveloped?
The Com m ission says m ore m ines could be operated.
T h a t is tru e . A 'fe w m in es could be opened b u t th e y are in reg io n s w h ere th e coal p itch es heavily, is badly crushed, is expensive to m ine and w h ere th e m ines will provide m ostly sm all unsaleable coal. A s th e p ro duction is now ahead of dem and, w hy ppen such m ines?
F u rth e rm o re , th e re is a g lu t of sm all sizes, w hich are sold a t less th a n p roduction cost a t a loss o f $75,000,000 yearly. P rovided th e larg e sizes could be sold, would it pay to m ine th e m in eral in o rd e r to g e t them i f th e small sizes in consequence became a d ru g on th e m a rk et?
The lack of com petition is suggested as a cause of peak prices. S tra n g e to say, in th e b itu m in o u s m a rk e t when a sh o rtag e comes, th e in crease of p rice is g re a te r th a n in th e a n th ra c ite tra d e , th e reason being th a t th e old-line a n th ra c ite m ines a re reasonably su re of a f a ir profit and th e o p e rato rs do n o t feel ju stified in ask in g fo r as larg e a p rice as th e y can g et as is th e custom of m any independent o p erato rs in th a t region and a s is th e general p ractice of th e b itu m in o u s o p erato rs.
D on ’t Q ueer tlie L oading Scale
Y
E A R S AGO w hen th e m a c h in e -cu ttin g scale w as being fra m e d some m en who d id n ’t w a n t to buy m achines fo r c u ttin g coal advocated a w age scale th a t took aw ay m ost o f th e profit of m achines in Illinois.The sta te and even th o se m en them selves have suffered long from th is ill advised policy. W hen th e y b o u g h t m achines, th e y fo u n d them selves c o n fro n ted b y an in equitable w age scale th a t robbed th em o f th e p ro fits of th e ir en terp rise.
The sam e p o in t o f view m ay p re se n t its e lf to o th ers w ith re g a rd to th e loading-m achine scale. Those who do n o t desire to m odernize m ay tr y to p re v e n t o th ers from doing so and will lay th e ir s ta te o r d is tric t open to com petition fro m o th e r sta te s and w ith oil. I f a m an does n o t propose to use loading m achines h is sole r ig h t to action should be to p rev e n t a d ay scale b ein g p ro posed th a t will be low er th a n o th e r day scales and th a t, of course, is n o t likely to be attem p ted .
F avorable m achine scales a re needed in union d is
tric ts if th e y a re to b a ttle w ith com petition. T he h and- loading o p e ra to rs should n o t be selfish enough to prev en t th is, f o r if th e d is tr ic t does n o t m echanize on a reasonable b asis th e re will be p ro fit f o r no one.
C ertainly th e unm echanized will n o t be able to survive w h eth er th e scale f o r loading-m achine m en be h ig h or low.
In th e fo rm u latio n of a f a i r scale th e union should join w ith th e o p erato r. T he lab o rin g m an should do all he can to advocate an d a s s is t th e in tro d u ctio n of m achinery th a t reduces toil. I t should be recognized union effort— one of th e axiom s of unionism needing n e ith e r a rg u m e n t n o r proof. F u rth e rm o re , th e w age should be on a day b asis so as to m ake i t im possible fo r any o p e ra to r to ru n h is m ine w ith o u t due co-ordina-
37
S3 C O A L A G E VOL. 28, N o . 2 tio n of effort. The h a n d loader o f th e p a s t h a s h a d to
w a it too long fo r cars. How long would he hav e h ad to w a it h ad th e o p e ra to r been p ay in g d ay w ages? T he in tro d u c tio n o f th e day-w age b asis will be th e end of th e o p e ra to r who p e rsists in ru n n in g h is m in e w ith o u t re g a rd f o r th e efficiency of all p a r ts o f th e o p eratio n . The loader should be as assiduously ten d ed as th e m o to r m an o r tip p le h a n d an d such a tte n tio n w ill n e v er be p aid to h is needs till he becomes a day m an w ith h is idleness a m a tte r of apprehension to h is em ployer.
We have said t h i s 'f o r f a r m ore th a n te n y e a rs and th e im portance o f th is idea is ju s t b eg in n in g to be ap p reciated . We advocated a com bination w age— p a r t day ’s p ay and p a r t a tonnage ra te — b u t, now th e a r g u m e n t is being acknowledged, it a p p ears th e re w ill be no h a lf w ay m easures b u t th a t m in e rs and o p e ra to rs will combine to estab lish a d ay w age th a t p u ts th e whole b u rd en of d isco n tin u ity on th e o p e ra to r and gives him all th e profit th a t c o n tin u ity affords. P e rh a p s th a t is n o t th e u ltim ate solution b u t it seem s a t th e p re se n t th e one likely to rule, especially in conveyor-belt, h and- loading m ines w here th e pro d u ct of each m an cannot be read ily segregated.
We A lso B eliev e in H igh W ages
J
OHN L. L E W IS says in h is book th a t th e h ig h w ages of A m erican w orkm en a re a m a tte r of p rid e to all A m ericans. Those m en a re dead o r converted to a b e tte r mode of th o u g h t, he declares, who a t one tim e advocated low w ages. We can rejoice th a t P h ilad elp h ia pays m ore th a n tw ice th e w ages paid in London, th re e tim es th e w ages paid in P a ris an d nearly five tim es th e w ages paid in Eom e, M adrid and V ienna. W e hope these la rg e w ages will continue. We a re su re th e y will.T hey re p re se n t a h ig h p ro d u ctiv ity of labor and capital, g re a te r th a n is a tta in e d in E urope.
M r. Lewis m ay not have sta te d a fa c t w hen h e said th a t h ig h w ages in them selves c o n stitu te A m ericanism , b u t i t is tr u e th a t th e y reflect a n e n te rp rise th a t is ty pically A m erican. We hope th e s p irit of u ntram m eled achievem ent will be continued, th a t th e sto re of n a tu ra l w ealth th a t aids such achievem ent will n o t be too rap id ly depleted and th a t as th e re su lt of th e en erg y of u n fe tte re d in d u stry re m a in in g relativ ely unchecked and th e rich es of th e e a rth n o t being unduly exhausted, we m ay continue to see h ig h w ages in A m erica f o r m any y ears.
H e rb e rt H oover is re p o rted to have said a t th e con
ference in the H otel A m bassador, N ew Y o rk C ity : “ I t h as alw ays been m y belief th a t th e te s t of civilization is th e scale o f living of its whole people.” In th is all will a g re e b u t—
I t d o e s'n o t follow th a t we rejoice w hen, by a com bine and strik e s th a t paralyze th e country, any body o f m en ob tain a w age th a t they could not g e t by supply and dem and and m ake th e public pay fo r th e p ro d u ct m ore th a n is p roperly due. We do n o t rejoice in a n y such achievem ent. I f it is A m ericanism , as M r. Lew is volubly contends, i t is n o t th e kind of A m ericanism of w hich we a re proud.
I t does n o t follow th a t we rejoice w hen hig h w ages m ake coal suffer in com petition w ith th e oil f o r dom estic purposes.
I t does n o t follow th a t we rejoice w hen an undue w age ra te m akes it possible fo r w orkm en to live on two d ay s’
w ork a w eek w hile o th e rs who have to buy th e ir p ro d u ct m u st w ork six or ru n in debt.
I t does n o t follow th a t w e rejoice w hen w e find one section o f th e coal field able to ta k e th e business e n tire ly aw ay fro m a n o th e r by p a y in g m erely a norm al w age w hile th e o th e r section p ay s a su p ern o rm al one.
I t is n o t a co n trib u tio n to A m ericanism w hen one in d u stry , th e a n th ra c ite , w ith an h o u rly w age t h a t w as a lread y h ig h e r in 1914 th a n w as p aid in o th e r in d u s
trie s , g ets an in crease in w ag e of 192 p e r cen t in ten y e a rs w hile th e m a n u fa c tu rin g in d u s trie s g et an increase of 129 p e r cent, th e ra ilro a d s one o f 141 p e r cent, th e illu m in a tin g g as in d u s try one of 111 p e r cen t and th e electric lig h t and pow er one of 121 p e r cent, as is shown in th e N a tio n a l In d u s tria l C onference B o a rd ’s re p o rt w hich we published la st week.
Now, we h ear, th a t th ese h ig h ly p aid m en w a n t y et m ore pay. T he m in ers a re a sk in g a 10 ,p e r cent increase, and th e day lab o rers a w age advance th a t in some cases ru n s up to 21.75 p e r cent. I n a d d itio n th e re a re o th e r provisions th a t a re som ew hat difficult to evaluate, such as w e ig h t allow ances and p ay m en t fo r th e placing o f sheet-iron, props, tim b er, forepoling, abnorm al shoveling and rock, fre e lig h ts, jack h am m ers and a ir to o p erate them , so th a t th e in crease dem anded m a y av erag e 30 p e r cent o r m ore w hich on th e b asis of th e pre-w ar, 1914, ra te s is 88 p e r cent, b rin g in g th e increase if g ra n te d , w hich i t will n o t be, up to 282 p e r cen t above th e p re -w a r figure, tw ice th e increase obtained by ra ilro a d m en, th e g ro u p th a t n e x t to th e coal m in ers g o t th e la rg e s t r a te of increase.
T h is is -n o t A m erican ism ; i t is the new feu d alism — th e outcom e of a privileged e ra fo r th a t k in d o f u n io n ized labor th a t believes th a t all is rig h t, if you can
“p u t i t over.”
T h e Man w ith Tw o P rices
H
A R D LY A N Y R E P U T A T IO N is w orse f o r an o p e ra to r o r a w holesaler th a n to be a m an who sends o u t h is salesm en to g e t a s la rg e a sum f o r h is p ro d u ct as he can above a c e rta in base price. B u t th a t is how coal is o ften sold. In f a c t th e salesm an is comm ended who “ s tin g s ” an u n su sp ectin g , u n in fo rm ed buyer. A t such tim es a s th e p re s e n t th e salesm an usually is in th e hom e office a t le a st once every day try in g to g e t a p rice to quote th a t en tire ly w ipes out profit.
W here a com pany is n o t a one-price firm , every b u y e r is tr y in g to b e a t down its price. Q u ality is n o t con
sidered. P ric e is th e sole th o u g h t. In f a c t th e b u y e r does n o t believe th a t a p ro d u ct sold by h a g g lin g is a h ig h -g ra d e pro d u ct. H e usually does th in k th a t— and ju s t th a t— of a com m odity sold a t a fixed price. Coal is enough d ifferen t so th a t th e b u y er w ho finds a set p rice im m ediately concludes he h a s lig h te d on a su p e rio r a r tic le ; w hereas, if 'th e re is a v a ria b le p rice th e p u r ch a ser assum es th a t th e p ro d u cer o r w holesaler h as an a rtic le th a t he h as difficulty in selling. A nd th e a s
sum ption is correct.
Two prices do n o t pay. I t m ay be w ell to low er prices o r ra ise th em b u t n o t to v a ry th em f o r an y p a rtic u la r custom er. T he sam e p rice for. all closes co n tra c ts quickly, saves selling costs an d enhances th e s ta n d in g o f th e seller an d th e re p u ta tio n of th e goods. The w ord of pow er is, “You can ’t g e t m y coal fo r a n y such gyp figure.” T he com panies selling coal th ro u g h o u t th is co u n try should have th e m oral s tr e n g th an d b u si
ness acum en to in s tru c t salesm en to have no o th e r sell
in g policy, despite fierce com petition.
Ju l y 9, 19 2 5 C O A L A G E 3 9
Rock-Dust Barriers Have Im portant Part to Play In P rotection o f Soft Coal Mines
B u reau o f M in e s E n g in e e r D e c la r e s for D r o p -B o tto m T y p e w ith D is ta n t T r ip p in g V a n e s— C overs K e ep D u s t D r y an d R e a d y — V -T r o u g h s H a v e M a n y D is a d v a n ta g e s
B y G eo rg e S. R ice
C h ief M in in g E n g in eer, U . S. B u reau o f M ines, W a sh in g to n , D. C.
T
H E R A P ID A D O PT IO N of rock d u stin g as a m eans of fo re sta llin g m ine explosions has recen tly b ro u g h t co n sid eratio n of d u st b a rrie r s aa a su p p lem en tary preventive agency stro n g ly to th e fro n t.T h is a rtic le tra c e s th e h isto ry of th e d u st b a rrie r, its v ario u s ap plications and will describe th e ty p e of b a r r ie r w hich is now considered to be th e m ost effective.
I t is o f th e drop-bottom type, ac tu a te d by vanes located a t a d istan ce and is covered w ith sh eet iro n to keep th e d u st dry.
A sh ale-d u st, flam e-arrestin g b a r r ie r (“a rrêt-b a r
rage” ) w as th e first su g g e stio n fo r th e p rev en tio n of coal-dust explosion p ro p ag atio n , g ro w in g o u t of th e in v e stig a tio n s conducted a t L iévin, F ran ce, by Taffanel.
The prin cip le involved w as th e co n cen tratio n of m asses of incom bustible d u st a t in te rv a ls th ro u g h o u t th e m ine passages, designed to ex tin g u ish th e flame by coking and in te rp o sitio n , th u s a rre s tin g p ropagation, r a th e r th a n g en eralized rock d u stin g as first proposed by S ir W illiam G a rfo rth and inten d ed to p re v en t first ign itio n . T affanel’s in itia l recom m endations w ere f o r th e em ploym ent of te n shelves, each 20 in. wide, ex ten d in g across th e passagew ay, n e a r th e roof, on w hich the in e rt d u st w as to be piled.
W hen large-scale coal-dust explosion te s tin g w as be
g u n by th e B u re a u of M ines u n d er m y direction, a t th e E x p e rim e n ta l M ine in 1911, T affanel b a r r ie r s w ere used to lessen th e fo rc e of explosions o r to stop th em a t th e end o f a p red eterm in ed te s t zone.
I t w as fo u n d in h u n d red s of tr ia ls in w hich th ese b a r r ie r s w ere used, th a t w hile in a g r e a t m a jo rity of cases th e y w ere successful, especially a f te r m ore shelves
w ere used th a n h ad been o rig in ally prescribed, never
theless th ey som etim es failed w hen th e explosion wave had so little force as n o t to displace th e d ust, o r w hen th e explosion m ovem ent w as extrem ely ra p id b u t lacked violence. T h is la tte r condition m ay be encountered w ith a road d u st of h ig h ash content, w ith a sm all p ercen tag e of fire dam p p resen t.
The loaded T affanel b a r r ie r p re se n ts a V -shape to the approaching p re ssu re wave. T h is is n o t conducive to displacem ent of th e loading. F u rth e rm o re , as th e shelves a re fixed, considerable violence is n ecessary to ru p tu re and discharge th e load. In th e explosion d is a s te r w hich occurred in th e L a Clarence M ine, Pas-de-C alais, F ran ce, in 1912, some of th e o rig in al T affanel b a rrie rs failed. T h is caused M r. T affanel to in crease th e nu m b e r of shelves in each b a r r ie r to fifteen, and in subse
quent p ra ctice th ro u g h o u t F ra n c e , still m ore shelves have been added. They, how ever, w ere m ade n a rro w e r and balanced on a n a rro w su p p o rt so th a t th e y would tip over and launch th e ir con ten ts u n d e r th e action of a relatively w eak a ir wave.
The La Clarence fa ilu re and c e rta in o th e r shortcom in g s d em o n strated by te sts conducted a t th e E x p e ri
m ental M ine a t B ruceton, P a., led m e to develop in 1912 to 1915 wrh a t I term ed “closed” b a r r ie r s w hich would op erate u n d er th e action of a sm alle r force th a n w as necessary w ith th e T affanel design. T he la tte r types of th ese closed b a rrie rs , te ste d a t B ruceton, w ere alm ost universally successful. T hey a re described in Technical P a p e r 84 (U. S. B u reau of M ines) published in 1915, and subsequently in B ulletin 167, in w hich a re given th e full re su lts of th e various te sts.
F IG . 1
Tripped in the Open
T h is sh o w s the effect o f sp rin g in g th e m ech an ism o f a trough barrier carried on a fram e b u ilt up above ground. In a ctu a l operation it is e s
se n tia l th a t th e rock d u st con tained in a barrier sh a ll fa ll in su ch a w a y a s to form a co n tin u o u s cu rta in e x ten d in g e n t i r e l y a cro ss th e h e a d in g an d p e r sistin g for an a p p r e c i a b l e len g th o f tim e so a s t o effe ctiv ely sm oth er a n y e x p losive flam e.
40 C O A L A G E Vol. 28, N o . 2
FIG . 2
A fter a Light B last
H ere is a ty p e B co n cen tra ted b a r rier a s it appeared a fte r a lig h t e x p lo sio n . T h is k in d o f b arrier is tripped by a d v a n c e v a n e s an d sp ills its d u st in a w h o le se ries o f sh e e ts th a t p e r s is t u n til th e e x p lo siv e w a v e a r rives. T h e flam e th u s is e ffe c tiv e ly b l a n k e t e d and sm oth ered . I f the ex p lo sio n is n ot v io le n t no p a rticu la r d a m a g e is done to the barrier.
T he B ritis h have adopted generalized rock d u stin g on th e th eo ry th a t i t is m uch b e tte r to p re v e n t “ig n i
tio n ” th a n to t r y to stop “p ro p a g atio n .” T he B u re a u of M ines’ in v e stig a to rs conceded th a t th is w as a fa ct, b u t th ey believed it h ig h ly desirable to have secondary defenses. I t is m uch e asier to employ rock d u stin g successfully in m ines u sin g th e longw all system , w hich p rev ails in G reat B rita in , th a n in th e room -and-pillar m ethod alm ost u n iv ersal in th is country.
In longwall w o rk in g s old roads a re c u t off an d th e re a re no extensive open gobs, w h ere as in room -and-pillar woi-k, generalized rock d u stin g is n o t so easily accom
plished u n d er m any m in in g conditions. M oreover, in th e longw all system th e ro ad rib s a re rock, w hich e n tails some n a tu ra l rock d u stin g . In room -and-pillar w ork, on th e o th er hand, th e sides of th e p assagew ays have rib s o f coal, and som etim es th e ro o f is of th e sam e m a terial. T h is increases th e fo rm a tio n o f coal d u st th ro u g h ab rasio n o r spalling. C a rry in g rock d u st
in g to th e faces of room s in old w orkings, or even into airw a y s in w hich th e re a re no tra c k s, is a difficult problem in such m ines.
T h e re is also th e com plication th a t w h ere w a te rin g is employed in connection w ith u n d e rc u ttin g and espe
cially w here its use is com pulsory a t all th e faces, as is th e case in U tah , th e a ir in th e room s and r e tu rn a irw a y s is extrem ely hum id. T h is is n o t conducive-to th e m aintenance of d ry rock dust, a lth o u g h i t h as been fo u n d experim entally th a t any in e r t d u st th a t is d is
trib u te d helps in th e w e ttin g of th e coal d u st th ro u g h contact. T h a t is, i t h as been d em o n strated by ex p eri
m e n t th a t a m ixed coal and rock d u st becomes w etted rapidly, w h ere as coal d u st alone re s is ts w e ttin g .
A s long as rock d u stin g in th is c o u n try w as con
sidered as being academ ic— since w ith few exceptions it w as n o t p racticed u n til about tw o y e a rs ago— th e te c h n iq u e to m eet th e special conditions encountered in A m erican m ines w as n o t developed. R ecently, how ever, g r e a t advances in th is d irectio n have been m ade.
W ith th e w ide adoption of rock d u stin g d u rin g th e p a s t y e a r— i ts use as an a lte rn a tiv e fo r w a te rin g being m ade m a n d ato ry in U tah , w hile sim ila r legal m easu res a re b ein g seriously discussed in o th e r s ta te s — th e ques
tio n of b a rrie rs h as become in creasin g ly im p o rta n t.
F ield in v estig atio n s and d ire c t in q u irie s fro m o p e ra to rs have developed th e follow ing im p o rta n t a p p licatio n s of b a r r i e r s :
(1 ) To isolate old w o rk in g s, especially th o se on th e v en tilatio n re tu r n , so a s to p re v e n t th e p ro p a g a tio n of an explosion o rig in a tin g in a d ja c e n t activ e w o rk in g s o r one s ta r tin g in w orkings t h a t have been abandoned e ith e r te m p o ra rily or p erm an en tly .
(2) P ro te c tio n of a irw a y s an d m anw ays on w hich no tra c k s have been laid, especially th o se v e n tila te d w ith re tu r n a ir w hich c a rrie s and deposits fine float d u st from th e active w orkings. T h is applies p a rtic u la rly w here th e ro ad s a re n o t sufficiently close to haulagew ays o r th e re a re no connecting cross-cuts w hich w ill p e rm it rock d u stin g th ro u g h th e stoppings.
(3 ) F o r th e p ro te c tio n o f panels. F o r th is p u rp o se b a rrie rs a re placed a t e n tra n c e s an d ex its so th a t if a n explosion of g as or coal d u st occurs w ith in th e panel, i t m ay be stopped a t th e p o in ts o f eg ress an d n o t re a c h o th e r p a rts o f th e m ine, o r vice versa.
(4) A s an a u x ilia ry to g en eral d u stin g , b a r r ie r s m ay be placed a t in te rv a ls in m a in ro ad w ay s w hich m ake coal d u st ra p id ly th ro u g h to p p in g fa llin g fro m trip s , and being pulverized u n d e r th e action of traffic. W hen so placed as to p ro te c t h aulagew ay zones, b a r r ie r s fo rm an especially valuable secondary d efen se; f o r exam ple, in case th e d u st in any zone increases in com bustible co n ten t to th e d a n g e r p o in t b efo re th e n e x t cleaning up and re ro c k d u stin g in th a t zone ta k es place.
(5 ) T em p o rary b a r r ie r s m ay be placed in th e v ic in ity of w ork in g faces w h ere i t is n o t deem ed feasib le to rock d u st o r w here w a te rin g is em ployed to supplem ent d u stin g . Such b a rrie r s a re m oved ah e ad as th e face advances.
The B u reau o f M ines h a s recom m ended d esig n s f o r closed b a rrie rs covering th e firs t fo u r o f th e above applications, alth o u g h doubtless new p lan s m ay be de
vised th a t m ay prove cheaper to c o n stru c t a n d still be effective. P ra c tic a l ap p licatio n to th e fifth case h a s no t y e t been s a tis fa c to rily w orked out.
G eneralized rock d u s tin g depends upon th e follow ing p rin c ip le s: A coal d u st explosion can p ro p a g a te itse lf only by th e c o n sta n t ra is in g of a dense cloud of inflam m able d u st ahead of th e flame. Some have th o u g h t
Ju l y 9, 1925 C O A L A G E 41 th a t th e com bustible d u st norm ally p re se n t in th e a ir
of a coal m ine m ig h t p ro p ag ate an explosion. T his, however, is not the case. In o rd e r to p ro p a g a te ex
plosive inflam m ation a cloud of coal d u st m u st be so dense as to be im p en etrab le to vision. The a ir waves ahead of th e explosion, term ed advance or “p io n eerin g w aves,” co n stan tly s tir up th e d u st in f r o n t of th e flame and p e rm it its continuous explosive com bustion.
A n explosion m ay die aw ay or be ex tin g u ish ed by any one of thi-ee m e a n s :
(1 ) No com bustible d u st m ay be p re se n t over a considerable d istan ce of p assag ew ay ; i t has n o t been found feasible to m a in ta in th is dustless condition in m ines.
(2 ) The d u st m ay be so th o ro u g h ly w etted th a t it will stick to g e th e r o r to th e w alls and will n o t be ra ised by a b last. T his req u ire s fro m 20 to 30 p er cent of w a te r— 30 p e r cent fo r th e finest d u st not including th e w a te r of com position, th u s s ig n ify in g a condition of mud.
(3) E xplosive com bustion m ay be p rev en ted from proceeding, by th e in tro d u ctio n of in e r t rock-dust p a r ticles w hich ab so rb h e a t and also act as a c u rta in be
tw een th e p artic le s of coal dust.
Ad v a n c e Air Wa v e s Mi x In e r t Du s t
In th is th ir d p reventive m easure, th e well-known rock d u stin g m ethod, th e in e rt d u st is applied in such q u a n ti
tie s and in such position th a t th e a ir waves, which alw ays precede a coal d u st explosion and in fa c t make it possible, will b rin g up and m ix the in e rt d u st in th e a ir a t th e sam e tim e th ey th ro w th e coal d u st into suspension.
T he u n d erly in g principle upon w hich b a rrie rs operate is th a t th e y launch suddenly so m uch in e r t d u st into th e advance a ir waves th a t in stead of th e explosive flame b ein g ex tin g u ish ed g rad u ally over a long distance, it is alm ost im m ediately quenched by th e g re a t excess o f in e rt d u st co n cen trated a t th a t point.
Fig. 3—Effect of a Violent Explosion
H -'V y exp losion w a v es m a y c o m p letely dem olish a d u st barrier, i n i s is o f d ecid ed ly se co n d a r y im portance, h ow ever, a s the pri- n" KOnst erai i0n is th a t the prop agation o f th e d u st exp losion sh a ll be stopped. T h is is the en tire ob ject o f a n y barrier
W hen th e rock-dusting m ethod began to be used
‘'several y ears ago, some m in in g engineers and o p erato rs who had read of b a rrie r s or seen them successfully used in e x tin g u ish in g te s t explosions in th e E x p erim en tal Mine, accepted th e general idea b u t ap p a re n tly did not fully u n d e rsta n d some of th e v ital fa c to rs of design.
They, accordingly, e ith e r modified the B u re a u ’s designs o r made e n tirely new ones of th e ir own.
One of th e types favored because of its cheapness w as th e V -tro u g h b a rrie r w hich h ad been extensively used a t B ruceton, alth o u g h n o t considered by B ureau in v e stig ato rs as being th e b est design. C e rtain a lte ra tio n s w ere introduced. T h u s th e V -tro u g h s w ere m ade m uch sm aller and th e spaces betw een th em w ere n a r rowed. T h is a rra n g e m e n t is rep o rte d to have been successful in sto p p in g a n u m b er of explosions in the M iddle W est. I t h as n o t been followed by th e B u reau in th e designs w hich recently have been extensively introduced in th e Rocky M ountain field.
U ndoubtedly, m any m in in g en g in eers and o p erato rs will devote some a tte n tio n to d esig n in g b a rrie rs . I t is fo r th is reason th a t I h ere p re se n t w h a t I believe should be th e principles g o v ern in g such d e s ig n s :
(1) P re feren ce fo r th e so-called “closed” b a rrie r, over the T affanel shelves, re s ts upon th e fa c t th a t the fo im e r p rev en ts th e in e r t d u st loading fro m becom ing w et in the presence o f hum id a ir w hich would n ullify its usefulness. I t also obviates co n tam in atio n by float
in g coal dust. To accom plish th is end th e in e rt d u st should be com pletely inclosed and if th e b a rr ie r is not placed tig h tly a g a in st th e ro o f a t a p o in t w here it is dry, it should have a cover of galvanized iro n o r its equivalent. Oilcloth has been used a t the E x p erim en tal M ine and has served successfully over a long period.
In th e re tu rn s of c e rta in o th e r m ines it has shown a tendency to rot.
(2) A b a r r ie r should be so sen sitiv e th a t an a ir wave ex e rtin g a p ressu re of only 2 o r 3 lb. p e r sq u are inch (a s m easured a t r ig h t angles to th e d irectio n o f tra v e l) will cause it to operate. A V -tro u g h b a r r ie r as o rd in arily installed does not m eet th is condition.
T he small V -shaped co n tain ers do not p re se n t enough su rfa c e and th e sides o f th e individual tro u g h s are inclined and consequently do n o t sta n d a t r ig h t angles to th e advance of th e a ir wave. F u rth e rm o re , th e bot
tom edge is held by th e V -notch w hich sim ultaneously acts as a su p p o rt and a hinge. S up p lem en tary vanes, such as a vertical board on top of each tro u g h , would increase th e ir sen sitiv en ess to shock w aves and aid in th e ir capsizal.
(3 ) In some cases an explosion m ay s t a r t strongly, a s by a blow n-out shot or an ig n itio n of fire dam p.
S tro n g a ir waves a re th u s in itia te d , b u t th e coal d u st inflam m ation w hich m ay follow, a t firs t m ay proceed slowly so th a t th e com bustion zone lags f a r behind th e pio n eerin g a ir w aves th a t move a t th e r a te o f sound (1,100 f t. p e r second). To provide f o r such a case th e b a r r ie r should n o t dum p en m asse b u t should be so a rra n g e d th a t m uch of th e d u st will s if t down gradually o r cascade over b a rs o r g rid s so as to rem ain in su s
pension u n til th e com bustion wave arriv e s. T h is con
d itio n is n o t m et by th e o rig in a l T affanel b a r rie r nor by th e sim ple V -tro u g h , w hich d ischarges its load en m asse.
(4) To provide f o r extrem ely ra p id flame p ro p ag a
tion, as in a m ain h aulagew ay w here th e explosion m ay trav el a t th e r a te o f 3,000 o r 4,000 ft. p e r second, it is im p o rta n t th a t trip p in g vanes should be located about
42 C O A L A G E Vol. 28, N o. 2
Boy Gets Thrill
B o y s liv in g a t B lue D iam ond, K y., h ad no ch an ce to ride a irp la n es so th a t th e y took their a ir th r ills b y riding sh o r t d ista n c e s on the tra ctio n rope o f an a eria l tr a m w a y u sed by the B lu e D iam ond Coal Co. T h is sp ort w e n t on u n k now n to the coal co m p a n y u n til one day r e c e n tly w h e n a 10- y ea r-o ld b o y grabbed the rope ah ead o f the bucket, fa ile d to le t go soon en ou gh an d w a s ca rried o u t a c r o ss the 2 00-ft. deep v a lle y , over a b u rn ing r efu se dum p and in to th e top o f a 90-ft. d ead -end tow er sh o w n in the b a ck ground o f th e a cco m p a n y in g p icture. There the lad le t go ju s t in tim e to a v o id g e ttin g m a n g le d and sn a tc h e d a h old on th e to w er str u c ture. H e clim bed down to h om e an d m other T ram rid in g h a s ceased
Fig. 4—“They Shall Not Pass”
B arriers, in rea lity , are d ea d fa lls d elib era tely s e t in th e ru n w a y s o f m in e exp losion s. If properly con stru cted and m a in ta in ed no exp losion , reg a rd less of its direction or speed o f travel, can g et by. T h is illu stration sh o w s a trough barrier w ith its op eratin g v a n es ready to throttle and kill a n y m in e d isa ste r o f this kind th a t m ay tra v erse th is h eading.
100 ft. in advance of th e b a r rie r. T h is d istance th e B u re a u ’s experim ents have show n to be sufficient to s ta r t th e m echanism in m otion fo r dum ping th e b a r r ie r in am ple tim e. The b a rrie r, how ever, should n o t be en tirely dependent on such v an es; th e re should alw ays be supplem entary m eans fo r trip p in g it, in case any accident should befall th e advance vane o r th e w ires connecting it w ith the b a rrie r.
Such vanes should be scientifically p ro p o rtio n ed so th a t th ey will not tr ip u n d er th e action of an y sm all shock wave such as th a t se t up by th e slam m ing of a v e n tila tin g door, by a h ig h p re ssu re v e n tila tin g c u rre n t o r by d istu rb a n ces caused by d is ta n t b la sts of explo
sives. A vane should be op erated u n fa ilin g ly , however, by th e shock wave of even th e lig h te st, slow est-m oving explosion, such as m ay occur w hen th e com bustible con
te n t of the a ir is n e a r th e low est lim it p e rm ittin g flame p ro p ag atio n .
(5 ) The a rra n g e m en t of th e b a r r ie r should provide fo r a m inim um delay in lau n ch in g th e load of dust.
T h is can be accom plished m ost effectively by p ro v id in g f o r discharge of th e d u st a t th e bottom . T h is condition is n o t m et by e ith e r th e T affanel o r th e V -tro u g h b a r rie rs. The la tte r m u st sw ing th ro u g h an arc of about 90 deg. b efore th e rock d u st load even begins to discharge.
(6) T affanel te s ts in F rance, as well as those con
ducted by th e B u reau of M ines in th is co u n try , have indicated th a t th e loading of th e b a rrie r, or se t of individual u n its w hich m ake up a b a rr ie r, should be ab o u t 100 lb. p e r sq u are foot of e n try cross-section.
Such a loading should be som ew hat in creased if th e cross-sectional a re a is less th a n 50 sq .ft. and p erh ap s som ew hat decreased if it is g re a te r th a n 60 sq .ft. T h is loading is deemed necessary except w here th e re is su p plem ental rock d u stin g in th e im m ediate v icin ity , in w hich case th e am ount of d u st m ay be som ew hat les
sened.
(7) D u st fo r loading a closed b a r r ie r m ay be any kind of dry, in e rt m ate rial, 50 per cent o f w hich will pass th ro u g h a 200-mesh screen. Inasm uch as th is d u st will not norm ally e n te r into th e m ine a ir an d be b reath ed by th e w orkm en, it need not be non-siliceous as is th e case in generalized rook d u stin g . I t is d e sir
able, however, to use fo r closed b a rrie rs a d u st th a t has no hygroscopic qualities. T h a t is, one w hich will not ten d to absorb m oisture.
(8) The m ate ria l of w hich any b a r r ie r c o n ta in e r is
m ade usually will be wood. If, however, th e b a r r ie r is
• located in an extrem ely w et or h um id place, i t m ay be desirable to m ake th e sides and cover of galvanized iron o r some sim ila r m aterial.
(9) A ny closed b a rrie r , if used in a h aulagew ay or m anw ay, should be so a rra n g e d th a t if i t should be accidentally trip p e d m en u n d e rn e a th will n o t be stru c k by th e m oving p a rts . In some cases th is m ay necessi
ta te recessing th e b a r r ie r into th e roof, alth o u g h usually a place can be selected w h ere th e n a tu ra l ro o f is suffi
ciently high.
(10) In lo catin g a b a rr ie r, if th e re is any choice of position, i t is advisable to avoid places w h ere th e ro o f is unusually h ig h o r w here th e w id th is excessive, b u t to locate it a t some p o in t on th e roadw ay w here th e cross-sectional a re a is n o t over 60 to 70 sq .ft.
O rd in arily th e b a r r ie r u n its should n o t be m ore th a n 8 f t. w ide and it is d esirab le to have th e bottom of th e b a r r ie r n o t over 7 to 8 f t. above th e floor. A n explosion p assin g th ro u g h a place of th is k in d will have such velocity th a t th e p io n eerin g a ir w aves will th o ro u g h ly m ix th e in e r t d u st loading in th e a ir, w h ereas if located in an ex trem ely h ig h place th e m ix
in g m ay n o t be so th o ro u g h and th e explosion m ay p ass over or u n d er th e b a rrie r. In explosions of a feeble c h a ra c ter, as d em o n strated by th e te s ts in th e E x p e ri
m ental Mine, th e flame usually does n o t com pletely fill th e passage, y e t th e h e a t and gases would prove fa ta l.
Ba r r i e r s Me e t Sp e c i f i c a t i o n s
These su g g ested specifications fo r closed b a r r ie r s a re m et by th e B u reau o f M ines’ bo tto m -d u m p in g tro u g h b a rr ie rs (n o t V -tro u g h ) and by th e co n ce n trated b a r rie r s detailed in th e plans of Technical P a p e r 84 and B ulletin 167. B oth th ese desig n s employ advance vanes and also supplem ental trip p in g a rra n g e m e n ts a t th e b a r r ie r s them selves.
N o doubt o th er designs will be evolved fro m tim e to tim e. E v en tu ally it m ay be desirable, as know ledge of th is su b je c t grow s th ro u g h th e application of b a r rie r s in com m ercial m ines, th a t th e B u reau o f M ines estab lish p e rm issib ility specifications, like th o se f o r explosives and electrical m ach in ery in te n d ed fo r use in d u sty o r gaseous operations.
Ju l y 9, 1925 C O A L A G E 43
M ining M ethod Cuts Cost in Steep Anthracite
E a c h C hain P illa r in N e a r ly V e r tic a l K id n e y B ed S erv es as B a tte r y for B r e a st A b o v e — M a in ten a n ce o f G a n g w a y s I s L o w — C oal B o x e s S u p p o rt H a n g in g W a ll a t W a n a m ie
B y D ev er C. A sh m ead
A n th r a cite M ining E n g in eer, U . S. B ureau o f M ines, W ilk es-B a rr e, P a.
G
E N E R A L L Y S P E A K IN G , steep-pitch m in in g in th e P en n sy lv an ia a n th ra c ite reg io n is associated w ith th e S outhern, E a s te rn M iddle and W estern M iddle fields. In c e rta in p o rtio n s of th e N o rth e rn field, how ever, m ay be found com paratively sm all a re as w hich re q u ire th is ty p e of m ining. The m ethods here employed, th o u g h follow ing th e sam e g en eral lines as those of o th er fields, differ fro m them m ore or less in detail. T he en g in eer fa m ilia r w ith th e flat m in in g of th e N o rth e rn field w hen confronted w ith steep-pitch operatio n s is liable to in tro d u ce v a ria tio n s to th e m e th ods usually followed th a t m ay o r m ay n o t be of value to his b ro th e r en g in eer in o th er fields. T h is p ap er discusses conditions and th e m ethods adopted a t th e W anam ie Colliery of th e L ehigh & W ilkes-B arre Coal Co. a t W anam ie, P a., w here gangw ay m ain ten an ce is low and costly b a tte rie s a t m ain b re a st m ouths are unnecessary. The section o f th e w orkings p a rtic u la rly re fe rre d to is th a t w hich lies in th e No. 45 tu n n el a re a o f th e K idney bed. F ig . 1 is a m ap of th is locality.The coal h ere ra n g e s in th ick n ess fro m 5 to 7 ft. and th e pitch fro m about 17 to 90 deg., a s is shown in th e accom panying cross section, F ig . 2. T he p a rtic u la r p a r t of th e w orkings th a t will be described is th a t w here th e K idney bed is sta n d in g vertical.
St r u c t u r e o p Ad j a c e n t St r a t a
The top rock or h a n g in g wall consists of a m ix tu re o f coal, bone and slate, w hich ra n g e s in th ick n ess fro m 3 to 5 ft. Im m ediately above th is, th e m ain roof is a sandy slate. The foot wall or floor of th e bed is so ft sandstone. A t th e p a rtic u la r p o in t shown, th e g an g w ay is approxim ately 300 ft. below th e su rface . The coal is of a shelly n a tu re , b u t does n o t ru n as it does in some places in th e low er coal fields. A sam ple, tak en n e a r chute No. 7 in th e m onkey heading, and analyzed a t
T h is a rticle is published w ith the perm ission o f th e D irecto r of the B u reau o f M ines, D ep artm en t o f the Interior.
th e P itts b u rg h S tatio n of th e B u reau o f .Mines, show ed th e follow ing re s u lts :
C o a l, A i r D r i e d C o a l, As R e c e i v e d M o i s t u r e ... 0 . 9 1 2 . 0 V o l a t i l e m a t t e r ... 5 . 4 4 . 8 F i x e d c a r b o n ... 8 2 . 1 72 9 A s h ... 1 1 . 6 1 0 .3
100.0 100.0
G angw ays a re driven in th e coal 12 ft. w ide and 6 ft.
h ig h clear of th e rail. C hutes a re tu rn e d off th e g a n g w ay every 50 ft. and a re driven 12 ft. wide. T h irty
Section Through No. 45 Tunnel
T h is is in th e K id n ey bed. H ere th e coiil m easu re sta n d s v e r tica l and a m ethod of m in in g differin g so m e w h a t from th a t f o l
low ed in ste e p ly p itc h in g b ed s elsew h ere in th e an th ra c ite fields .has been adopted.
A t this point the g a n g w a y is a p p ro x im a tely 300 ft. below the su r fa c e and the bed sta n d s p ra ctica lly v ertica l. All p a ssa g e s are driven w ithin the coal, le a v in g the rock o f both fo o t- and h a n g in g - w a lls intact.
feet in the clear above th e gangw ay a m onkey h eading is driven, th a t is, leaving a p illa r 30 ft. th ick betw een th e passages. B re a sts 24 ft. w ide a re tu rn e d off of th is monkey h ead in g on 50-ft. centers, leaving p illars betw een 26 ft. thick. T he cen ter lines o f th e pillars a re directly over th e c e n ters of th e chutes, as shown in F ig . 3, th u s b rin g in g th e b re a sts d irec tly over th e cen ters of th e chain p illa rs betw een th e g an g w ay and th e monkey heading. T his a rra n g e m e n t obviates th e building of a b a tte ry a t th e m outh of each b re a st, fo r th e coal in th e box th a t is co n stru cted in th is opening re s ts directly on th e chain pillar.
A fte r the gangw ay h as been driven, a concrete sto p p in g is b u ilt in each crosscut. T h is is poured from th e top, th e old wooden sto p p in g being used as th e bottom of th e form . Two holes a re le ft in th e stopping so th a t m a te ria l m ay be tak en th ro u g h fo r its co n stru c
tion. As soon as th e sto p p in g h a s been poured, however, these holes a re sealed. W hen it is desired to reopen them all th a t is necessary is to knock o u t th e wooden fram e. A cross section of a crosscut is show n in F ig . 4.
W hen th e tim e comes to commence d riv in g a b re a s t th e two holes in th e concrete a re opened. One o f th ese is about 8 ft. w ide an d serves as a coal chute. T he o th e r hole serves as a m anw ay, being j u s t w ide enough fo r a person to pass th ro u g h . A tr a p door is m ade
44 C O A L A G E Vol. 28, N o . 2
P illa r M onkey H e a d in g
C hain P illa r
M anways<%
C hufas
F IG . 3
Details of Mining
A bove th e g a n g - w a y a m o n k e y h e a d in g Is driven, the tw o p a ssa g e s b e in g co n n ected by ch u te s. A b ove each p illa r b etw een the m o n k ey an d m ain h e a d in g a b r e a st is d riven upw ard, a coal b o x b e in g c a r ried up its center.
T h is is k ep t f u ll and g iv e s fo o tin g fo r the m in ers a s the b r e a s t a d v a n ces.
S u rp lu s c o a l is sh o v ele d over to the ch u te s upon eith er sid e from w h ich it is d r a w i off in to m in e ca r s in the m a in h e a d ing.
th e b a tte ry fo r its b re a st. In s ta r tin g th e b re a s t a sh o t is fired in th e roof, im m ediately over th e m onkey h ead ing, so th a t v e n tila tio n w ill be m a in ta in e d . W hen th e n ex t round o f holes h a s been drilled, th e coal is shoveled into th e n e a re s t chute, a f te r w hich th e coal box is s ta rte d and by th e rem oval o f coal, space is provided fo r th e circu latio n of a ir th ro u g h th e m onkey head in g . A s d riv in g of th e b re a s t proceeds, th e box is b u ilt upw ard so th a t th e m en have th e coal in it upon w hich th ey can sta n d w hile w o rk in g a t th e face. T he box is kept co n stan tly n e a r th e face and alw ays full. S u r
plus coal m ined w hile th e b re a s t is b ein g d riv e n is ru n down th e m anw ay an d d raw n off in to th e coal chutes fro m w hich, in tu rn , it is periodically w ith d ra w n to m ine cars. N o coal is draw n fro m th e bottom of th e b a tte ry u n til th e b re a s t is finished.
In th e lif t n e a re s t th e su rfa c e no reserv e p illa rs a re left. In th e n e x t l if t below, how ever, tw o a d jo in in g b re a sts out of every ten a re le ft in place as a reserv e pillar, th u s fo re sta llin g th e developm ent of a squeeze and p re v e n tin g any m ovem ent of th e g ro u n d fro m tra v e lin g any appreciable distance.
H and m achines a re u tilized fo r d rillin g coal an d jack - h am m er drills a re em ployed in rock. M onobel is th e explosive used, w ith cap and fu se to d etonate it.
A f te r th e b re a s ts have been finished in a section of th e h eading, second m in in g will be commenced. Two tr ia n g u la r p illa rs of coal a re to be le ft im m ediately above th e chute opposite th e la s t pillar, one on each side w ith a b a tte ry placed betw een them . N ex t a box w ill be c a rrie d up as th e p illa r b re a s t advances, u n til i t reach es its lim it. T hen th e coal fro m th e b re a s t on th e outside of th e one ju s t d riv en will be draw n . W hile th is is b ein g done, a b re a s t w'ill be d riv en in th e n ex t p illa r and th e coal th e n d raw n fro m th e box in th e b re a s t j u s t com pleted in th e prev io u s p illa r an d so on u n til all o f th e p illa rs have been m in ed o u t an d th e boxes draw n.
T he chain p illa r w ill be d raw n back as ra p id ly as second m in in g is com pleted so th a t th e gan g w ay s will n o t have to be m ain ta in e d f o r an y u n reaso n ab le len g th of tim e. The m ain sav in g effected by th is m ethod of m in in g re su lts fro m th e f a c t th a t i t is n o t n ecessary to build expensive b a tte rie s a t th e m o u th s o f th e m ain b re a sts.
Fig. 4—Details of the Coal Chute
A h e a v y concrete sto p p in g is b u ilt a cro ss th is v e r tic a l p a s s a g e w ay. T h is co n ta in s tw o openings. T he la rg er o f th e s e p erm its the p a ss a g e o f c o a l b u t th is m a ter ia l se r v e s to p lu g th is op en in g so fa r a s th e circu lation o f a ir is concerned. T he sm a ller h o le is used a s a m a n w a y , the a ir b ein g controlled by m ean s o f a tra p door cover.
C on crete sto p p in g
to fit over th is la tte r opening so th a t th e a i r will n o t be sh o rt-circu ited by it. W hen th e chutes a r e filled w ith coal th e y a c t as stoppings.
L a g g in g on top o f th e tim b e rs in th e m ain gangw ay is m ade sufficiently s tro n g so th a t i t a c ts as a b a tte ry . W hen it is desired to load cars fro m th e chutes, some o f th is la g g in g is removed, allow ing th e coal to p ass from th e chute into th e m ine car.
As previously stated , th e cen ter lines of th e b re a s ts coincide w ith th e ce n ter lines of th e ch ain p illars betw een th e gangw ay and th e m onkey h eading. T h is m eans th a t directly opposite th e end of th e b re a s t is th e face of a p illar. Consequently, each p illa r becomes
Battery
P iU a r
Morn w ay Monkey heading
Ju l y 9, 1925 C O A L A G E 45
Synchronous Apparatus Can Im prove Pow er Factor
W h e th e r a C o al C o m p an y G e n e r a te s or B u y s E n e r g y M u ch L o s s and E x p e n s e in A lte r n a tin g -C u r r e n t C ircu its M a y B e A v o id e d b y th e
U s e o f P ro p er C orrectiv e D e v ic e s
B y R . C. M uir
A s s is ta n t E n g in eer, In d u str ia l D ept. G eneral E le c tr ic Co., S ch en ecta d y , N . Y.
T
H E IM P O R T A N C E of m a in ta in in g good pow er fa c to r conditions in th e a lte rn a tin g -c u rre n t pow er c irc u its a t coal m ines is as g r e a t as in any o th er in d u stry . W h e th e r a coal com pany g e n e ra te s its own e n erg y o r p u rch ases it, th e o p e ra tin g pow er fa c to r ofits lines affects pow er costs th u s re a c h in g in to the expense of p ro d u cin g coal. In v e stm e n t in p o w er-facto r im provem ent devices m ig h t m ake m uch h e a v ie r ex p en d i
tu re s f o r ad d itio n al equipm ent u n necessary, n o t to speak o f o th e r sav in g s to be m entioned in th is article.
B efo re defining pow er fa c to r, it m ig h t be s ta te d th a t, in m ost a lte rn a tin g -c u rre n t system s, th e c u r re n t lag s beh in d th e voltage, chiefly on account o f th e m a g n e tiz in g c u rre n t of tra n s fo rm e rs , in d u ctio n m otors, control equipm ent and o th e r devices. T h is m a g n e tiz in g cu r
re n t is a reac tiv e c u rre n t la g g in g 90 deg. behind th e voltage, w h ereas th e active c u rre n t is in phase w ith th e voltage. T he to ta l or actu a l c u r re n t in th e line is th e re s u lta n t g eom etric sum o f th e two, th e reac tiv e c u r
r e n t and th e active c u r re n t b ein g its tw o com ponents.
R e fe rrin g to F ig . 1, w hich is a sim ple vector d iag ram Fig. 1-— Illu stra
tion of Power Factor
T h e a c tu a l cur- ren t in th e line ( 0 1 ) is m ad e up of an e n e r g y com po
n en t (O X ) and a r e a c tiv e com p onent
( X I ) .
by w hich m o st pow er fa c to r problem s can be solved, 01 is th e actual c u r r e n t; it la g s behind th e voltage O E by th e angle 0. The activ e com ponent in phase w ith th e voltage is O X a n d th e re a ctiv e com ponent 90 deg. out o f phase is X I . T he pow er fa c to r of a c irc u it is th e r a tio of th e active com ponent of th e c u rre n t to th e actu al c u rre n t, o r th e r a tio O X h - 0 1 w hich is th e cosine of angle 0.
T he common definition of pow er fa c to r is th e ra tio of th e tr u e pow er to th e a p p a re n t pow er. T he a p p a re n t in a th re e phase c irc u it is V 3 E I, w hich is kilovolt
am peres ( k v a .) ; th e actu al pow er is V 3 E I cosine
A s the load in creases, th e lin e lo ss in crea ses re g a r d le ss o f the pow er factor, but n o te how ra p id ly th e lin e lo ss becom es g rea ter w h en th e pow er fa c to r is poor.
0, w hich is kva. tim es pow er fa c to r and gives k ilo w atts (k w .). I t is a p p a re n t th a t kilovolt-am peres and kilo
w a tts are one an d th e sam e th in g a t u n ity pow er fa c to r and th a t, f o r pow er fa c to rs o th e r th a n u n ity , th e c u rre n t f o r a given k ilo w att load in creases inversely w ith th e pow er facto r.
G enerators, tra n s fo rm e rs and pow er lin es a re lim ited by th e ir c u rre n t c a rry in g capacity. C onsequently, leav
in g aside c e rta in o th e r u n d esirab le effects o f lowr pow er fa c to r on g e n e ra to r design and voltage reg u latio n , the tr u e power load w hich a given g e n e ra to r, tra n s fo rm e r o r line m ay c a rry is p ro p o rtio n al to th e pow er facto r.
In o th er w-ords, th e k ilo w att load th a t can be carrie d a t 80 p e r cent pow er fa c to r is only 80 p e r cent of the k ilo w att load th a t could be c a rrie d a t u n ity pow er facto r.
The in v estm en t in g e n e ra to rs, tra n s fo rm e rs and lines, th erefo re, in creases as th e pow er fa c to r decreases and, w hen th is involves ad d itio n al equipm ent, p a rtic u la rly u n d erg ro u n d cables, th e increased in v estm en t m ounts rapidly.
The FR, or h e a t loss is p ro p o rtio n al to th e sq u are of th e c u rre n t and, consequently, in creases inversely as th e square of th e pow er fac to r. F ig . 2 show s th e re la tio n betw een pow er fa c to r and line loss fo r an y c irc u it w hen c a rry in g a co n sta n t k ilo w att load. F ig . 3 shows th e actual line loss fo r a 1,000-ft., th ree-p h ase, 60-cycle, 440-volt line of No. 0 w ire a t v a rio u s loads and pow er facto rs. T hese curves te rm in a te a t th e sa fe c u rre n t- c a rry in g cap acity of th is p a rtic u la r line and th e %rario u s curves show clearly th e increased line loss a t th e lower pow er fa c to rs as well as th e decrease in sa fe load- c a rry in g cap acity w ith decrease in pow er facto r.
T he voltage drop in creases ra p id ly w ith decreasin g pow er fa c to r, depending on th e re sista n c e and re a c ta n ce of th e line. F ig . 4 show s th e line drop in a th ree-p h ase, 60-cycle, 440-volt c irc u it, 1,000 f t . long w ith 9-in. spac-
