C o a l A g e
A M c G r a w - H i l l P u b l i c a t i o n — E s t a b l i s h e d 1911
DEV OTED TO THE OPERATING, TECHNICAL, AND B D SIN ESS PROBLEMS OF THE COAL MINING INDUSTRY
N e w Y o r k , May, 1 9 3 1
Vo l u m e 3 6 Nu m b e r 5
♦ >
1
Mechanization and Profits
T h e EIGHTH ANNUAL
N ational Ex
position o f Coal M ining Equipment, to be held at Cincinnati, Ohio, M ay 11-15, focuses attention on the place of the machine in the industry at a time when surface values are shifting so rapidly that reappraisal o f funda
m entals as a basis for future action is most essential.
In PERIODS
o f easy prosperity, Topsy-like progress meets with little chal
lenge and still less criticism. Depression, however, inspires sharp introspective examin
ation of individuals, industries, and social and economic philosophies.
M e c h a n i z a t i o n
in the coal industry has been passing through a process of evolu
tion. Passion for volume, m otivated, in part at least, by the gospel o f mass produc
tion which swept over American industry a few years ago, has been one factor in the introduction o f the machine. Necessity for cost reductions, ever present and ever press
ing, has been another. Social impulses, for the m ost part, have been more obscure.
W i t h m a r k e t d e m a n d
at the cur
rent low-water stage, however, increased production is no longer a sound considera
tion. But the very conditions which have depressed the total volume make increased
productivity more desirable and imperative than ever before in the history o f the in
dustry.
T o
s u r v i v e p r o f i t a b l y,unit pro
duction costs must go down and unit produc
tivity must go up— with few er active units.
W age reductions, o f course, will cut unit production costs, but wage reductions are not the answer to the problem because they will not increase unit productivity. Only the ma
chine, properly employed, can do this.
Un t i l
a comparatively recent date,
it was popular to emphasize the fact that coal’s competition was primarily internal.
T h at situation no longer prevails. Indi
vidual coal operators may think they are still competing with fellow coal producers, but actually they are competing with gas, fuel oil, hydro-electric power and with combus
tion efficiency.
Ot h e r i n d u s t r i e s,
faced earlier with the problem o f inter-industry com peti
tion, have learned that increased unit pro
ductivity with its corresponding decreased unit costs is the answer to business at a profit when volume o f output is stationary or shrinking. Coal, too, must learn this les
son, and, in learning it, will see a new sig
nificance in mechanization and a fresh
urgency for its adoption.
W h ere Minu tes C o u n t— an d A re C o u n te d
M E C H A N I Z A T I O N
* Promises Stabilization O f Coal Industry
X P E R I E N C E changes m ethods and tim e alters view s concern
ing th e m echanization of mines.
T h e change has not been rapid, but nevertheless it is m easurable. In o rd e r th a t no o p p o rtu n ities be lost to speed u p the p ro g ress o f m achine installation, it is well to pause pe
riodically and gage th e ex ten t of alteration. T o this en d Coal Age has m ade a cross-sectional survey of m echanization as it stan d s today, in the com pletion o f w hich executives and o p eratin g officials in th re e im p o rta n t coal-m ining states w ere in terview ed. W h a t follow s is not editorial opinion o r in terp retatio n but th e experiences, view points, be
liefs, and suggestions o f operators who produce th e bulk of th e ir to n nage m echanically.
I t is held th a t no one fa cto r offers a m ore p ro m isin g influence tow ard stabilization of th e in d u stry than m echanization. A lread y th a t influ
ence is being definitely felt both by operators w ho have m echanized th eir properties and by those w ho have not. F ir s t installed fo r th e purpose of cost reduction as an end unto itself, th e m achines have since de
m onstrated th e ir utility as w eapons at high-w age m ines to com bat the destructive com petition o f m ines which have been d riv in g dow n wages and prices in th e ir w a r f o r business.
J he productive econom y o f m achines in ^ the hands o f w o rk ers w ho are paid th e highest w age rates is deal
ing on close to even te rm s w ith the w orst of th is com petition. U n d er m arket conditions less acute, this economy is y ielding a m arg in of true profit. W ith w ages a t some mines driven to an alm ost irreducible m inim um , it is felt th a t fu rth e r in tra
industry ad ju stm en ts are likely to do anything but drive m ark et prices lower.
G iving evidence to profit pos
sibilities, the presid en t o f a coal com pany operating tw o large m ines said :
“ M echanization gave us a profit of
$100,000 in 1930 fo r the first tim e in eight years. B ut one of o u r tw o m ines w as m echanized and o u r m ar-
P relim inary P rep aratio n s
O ver half o f the m echanization problem can be solved before the first loading u n it is in stalled. Readiness to serve is vital in such m atters as electri
cal pow er supply, ventilation, and haulage. U nless these p re lim inary preparations are first made, the o p erato r m ight- better save the purchase price o f loading equipm ent.
ket realization w as low er th a n fo r the previous y ear.” O n the stren g th of this experience his com pany is now m echanizing the second p ro p erty .
T he increase in the annual p ro d u c
tion of m achine-handled coal is not in general p roportion to the num ber of m ines being added to the list of mechanized plants. Som e o f th e in crease is com ing from the gradually increasing o u tp u t of those m ines at which m echanization is fully estab
lished. G row th in the num ber of days w orked is m ore the contributing
cause of this increase than a g ro w th in the daily plant tonnage.
W h e re is th is p a rtic u lar increm ent o f increasing m echanized tonnage g o in g ? Is it sw elling the c o u n try ’s annual production th a t m uch m ore beyond dem and and th u s m aking the m ark et still m ore th e b u y e r’s? N o.
By and large, every to n o f p ro d u c
tion gained by the m echanized m ines is being tra n s fe rre d fro m the p ro duction of m ines in the sam e m ark et w hich adhere to hand loading. T h e blow is falling first on th e h and- loading m ines w hich p ay w ages com parable w ith, and w hich operate under n atu ra l conditions sim ilar to, those found in th e m echanized m ines.
T h is is because the lim it o f p ro d u c tion-cost cutting, w ith o u t installing m achines or low ering w ages, has about been reached.
B a rrin g contingencies, o p erato rs of m echanized plants hold fo rth g re a t hope fo r the security of th eir future.
T hey see stabilizing forces arisin g from assurance o f increasing w age incom es to individual w o rk ers in th e face o f decreasing payroll. M achines g u aran tee a constantly increasing p ro ductivity and inverse reductions in u n it production costs to levels f a r beyond those th u s fa r attain ed . O nce the p ro p erties a re fully equipped and p ro p er consideration is given to am ortization, depletion, an d o th er reserves, th e u ltim ate in cap
italization has about been reached, so th a t financial independence will be m ore nearly attained. F u rth e r satis
faction is felt in th e economic possibilities o f regularized ru n n in g time, train ed w o rk ers, and m ore stable m arkets.
N o t all o f the o p erato rs see the strateg y o f m echanization in the sam e light. O ne view sees m ech a
nization as m ass production in th e literal sense and suggests th a t th e m achine be m ade to set th e pace of productivity in an aim to w a rd h ig h er
May, 1931 — C O A L A G E 223
and higher tonnages per machine shift. A second view bases mecha
nized operation on a balance between the daily productive rate of the ma
chine, the number of men on the ere«’, and care in face preparation.
The first view is focused on the pro
duction of coal for industrial uses, while the second embraces the general
market, including domestic.
Emphasis is laid on the necessity of deciding the proper set-up in rela
tion to the available markets. In
creasing machine productivity prob
ably will l>e accompanied by lowering unit production cost ; yet the margin between cost and realization may not be widened, because size quality has been sacrificed. A difference of 25 to 50 tons in the daily production per machine unit may give a difference of 3 to 7 per cent in minus l£-in.
screenings.
Practically all those interviewed make the admonition that prepara
tions .for mechanization be entered into cautiously. V isits to already mechanized operations which appear to offer tangible help should, of course, be made. But the results of these visits should be taken only for what they are worth ; usually they come from the best side of the picture. Vital information—mainte
nance costs, for example—may not be made available.
One executive remarked that the attitude of the coal industry on the exchange of technical information is not healthy, and is detrimental to mechanization. There are operators who give generously of their experi
ence, but they are the exception rather than the rule. While it is true that few coal companies keep plants closed to visiting mining men, the welcome is not always what it should be. Somewhere, somebody will hold back. There are operators who, when they come upon a “good thing,”
are inclined to guard their advantage
closely-—some one key, if not the entire plan.
More, there has been little district- or region-wide funding of experience on those factors in mechanization which cannot be seen merely by ob
serving operation. In consequence, each new entrant into mechanization is compelled to start nearer to scratch than would otherwise be necessary.
More than half of the mechaniza
tion problem can and should be solved before the first loading unit is installed. Unless management is prepared to provide unfailing elec
trical power, it might better save the expenditure for additional min
ing equipment. Readiness to serve is equally as important in the ventila
tion and haulage phases of operation.
Why better ventilation, which means also attention to complemen
tary problems of safety? In the
F inancing
Investment houses are full of idle money. Sums of that idle wealth are going out every day to ends which offer less physi
cal security than many coal mines can offer. The burden of proof rests with the oper
ator in orienting the credit server to a more favorable view toward coal.
speeding up of working advance, in
creased liberation of gas is the usual result. The more the machines, the greater the volume of dust, which certainly creates a distinct hazard in a seam of highly combustible coal.
Unvitiated air in sufficient quantity will add 15 to 30, or even more min
utes, to the period of productive effort of every man-sliift. In this connection it cannot be too strongly emphasized that time lost involves an expense which can never be recovered.
The ventilation improvement pro
gram should be no casual undertaking.
It may not involve new equipment but it does require that many tons of fallen rock in the clean-up of air- courses must be taken out of the mine. Merely to flatten falls to re
move humps from rubbing surfaces, and generally to ease the course of air flow, is no sure cure of ventila
tion ills.
Concurrently with the making of preliminary improvements, over-all
problems ot mechanization should be receiving attention. Working plans must be set up and estimates made of the capital needed and the profits expected. The study will involve the scrutiny and final rejection of a great many proposals. No estimate should be made without allowing a generous factor of safety in the margin of cost reduction. It is im
portant that enthusiasm not be per
mitted to err in the wrong direction.
Boards of directors are reported uniformly hard to sell on the idea of mechanization initially. No magical arguments or plans have been devised to win the board over to ready ac
quiescence. Faith in the judgment of the management personnel, aided by the clearness and conservativeness of proposals, bears most weight. The success of the first installation auto
matically takes care of future proj
ects. Particular attention is called to the importance of spending money wisely. As finances are a determin
ing factor, the question is not so much what management would like to do but what it can afford to do.
Is the time propitious for mecha
nization of the property? Aggrava
tions, whatever their nature, are better removed before operating conditions are changed. Those op
erators who have been most success
ful give much weight to the policy of confiding in the workers. They propose their plans to labor and make no attempt to carry them out until they have gained the favor of the majority. In this approach the disadvantages, as well as the advan
tages, of the new plan are revealed.
No promises are made that cannot with reasonable certainty be fulfilled.
A minor mistake in policy may delay the success of a plan to an extent that is far out of proportion to the initial objection.
Patience is a virtue which must be practiced in mechanization. The new methods are revolutionary to the job habits to which the miner has been long accustomed. On a contract basis, the miner was his own boss.
For some time he is lost under the new conditions and, unless properly handled, may expect the company to take every bit of the responsibility for his job and his safety. It is futile to expect or to attempt a quick change-over. That results will be forthcoming eventually is borne out by the experience of several com
panies that have been at mechaniza
tion from three to five years. They notice a gradual reduction in the unit cost, counter to a gradual increase in maintenance, which can be credited
224 C O A L A G E — V ol.36, N o.5
only to increased experience acquired by the w orkers.
L a b o r in m any fields is well in fo rm ed as to w h a t th e com petitive conditions are w hich the com pany m ust m eet. I t is gaining a g reater appreciation o f m ark et situations and w h at m ust be done to continue m ine operation. T h is know ledge is a sp u r to individual efficiency and should be im p arted to those w ho do n o t possess it. W h e re m echanization is properly established, the w o rk er body will elim inate the d r o n e ; at least it will not fight fo r him . ' S h iftin g o f the tro u b le-m ak er fro m one job to a n o th e r is a practice well w o rth rem em bering. I t will eith e r cure him or cause him to q uit of his ow n accord.
T h a t labor will respond to intelligent h andling is b orne o u t by th e record o f one larg e m echanized m ine which has had no strik e o r discharge of an em ployee in tw o years.
M echanization at th is early stage o f developm ent has cut dow n labor req u irem en ts as m uch as 50 per cent.
W h a t to do w ith th e su rp lu s w orkers has been no easy problem . Division o f labor, of course, is economically unsound. B ut to re fu se w o rk to men who know no o th er job th a n m ining, in slack tim es, w ould b rin g d ire r con
sequences. D espite its a tten d in g evils, division of w ork in g tim e betw een all m en on th e payroll is the p ra c tice generally recom m ended. B etter tim es, retirem e n t, and sh ifts to other in d u stries will eventually correct this trouble.
In th e earlie r days, m anagem ent of m echanized m ines w as perplexed
by the old-m an problem . T h e m en up in years w ere n atu rally even m ore concerned and a situation of u n rest ensued. M any com panies decided to take care of the old m en and, on looking back, state th a t this move has been of inestim able value in self- satisfaction and in m orale upbuilding.
T hey declare th a t less resistance is attached to the rem oval o f ten young men th an to one old m an. A m ong other things, reten tio n of th e m an' p ast fifty has given the y o u n g er ele
m ent some assurance o f job security in th e ir declining years.
A s already m entioned, visits to other plants do not give all the in form ation necessary fo r final selec
tion and adoption of m achines.
U n d er these circum stances, m achine tests are suggested. C om panies that have followed th at policy have had their m ines labeled by some as labora
tories of m echanization. B ut the o u t
come of those tests has show n th a t they w ere on the rig h t track, fo r by th at procedure they avoided those
S tabilization
Already the stabilizing influence of machines is be
in g felt by operators on both sides of the mechaniza
tion fence. Machines are putting mines paying high w age scales on an equal footing with operations where w ages are lower and working hours longer.
It is felt that wages cannot be driven beyond the low est lim it now prevailing; that for this reason the plants now mechanized w ill enjoy a consider
able measure o f profit in the future over and above their present return. Tonnage gains to mechanized mines are being transferred from hand-loading mines.
m istakes w hich so frequently are m utely evidenced on the scrap heap o r in som e rem ote crosscut.
I t is said th a t com panies w ith reputable credit standing should have no tro u b le in obtaining the coopera
tion of m a n u fa c tu rers in testing m a
chines w ith o u t m aking o u trig h t p u r
chases. N atu rally , the m an u fa c tu rer should not be expected to foot any p a rt o f the bill. I f in doubt as to the type o f m achine best suited to conditions, com petitive tests are nec
essary. A n equitable a rran g em en t m ight be entered into by agreeing to pay the m a n u fa c tu rer 6 per cent in
terest on the selling price of the m a
chines d u rin g th e period o f te s t; by agreeing also to cover depreciation a t a rate of so m uch a day fo r the days the m achines actually operate and on the basis of the expected w ork in g life of the m achines ; by agreeing finally to pay a blanket sum sufficient to d e
fra y the e x tra o rd in a ry expense as
sum ed by the m a n u fa c tu rer in install
ing, tak in g out. and reconditioning the m achines fo r resale in case they cannot be adopted.
H a n d in hand w ith the new m an agem ent set-up th ere m u st be a m ore com prehensive and responsive ac
counting system fo r m echanized op
eration. U n d e r hand loading, the y ard stick m ost generally used w as the num ber o f to n s produced. E x act know ledge o f costs was im p o rtan t, but not nearly as vital as to the m echa
nized operation. Efficiencies dropped slowly and the declines w ere n o t a b urden on the plant ow ner alone. T h e w o rk er felt the pinch as directly as did the ow ner. U n d e r m echanization, rising costs m ay figure as a loss to the m iner ultim ately, but not c u r
rently. E x perience has show n th a t hig h costs in m echanization cannot be reduced to a norm al level in as little tim e as was required fo r th e ascent.
F o r these reasons, it is said costs in m echanization m ust be know n in de
tail daily.
O p erato rs w ho have been using
M ay, 1931 — G O A L A G E 225
m echanized equipm ent fo r as m am as five years agree th a t th ey are now less w orried about obsolescence than they w ere at the b eginning o f th eir experience. I im e has show n th at loading equipm ent is no exception to the requirem ent o f thorough devel
opm ent and testing b e fo re it is ready fo r general use. H ow ever, an e)c m ust be kept on all new m achines and inventions for guidance and a d ju st
m ent of the depreciation and for ob
solescence rate. Incidentally, the m achines in service longest, w hen of a p roved type, a re frequently the bes.
producers.
M en in the industry know th at bor
row ed m oney, w hen properly spent in coal-m ine im provem ents, can be m ade into an attractiv e investm ent. T h e ir jo b is to establish that fact in finan
cial circles. As the industry has had a succession o f sm all-profit years, financial houses are inclined to scan the o p erato r's record w ith m ore th an custom ary thoroughness w hen asked fo r a loan. Y et th e ban k er holds no brief fo r coal o r any o th er bran ch of industry, but considers each case in dividually.
In a conversation not long ago the president o f a sizable coal company broached the topic o f m echanization.
L oading m achines, he said, w ere a w o n d erfu l help. Installed a t one of his m ines, they each saved th e labor o f fo rty m en. N o t fo rty , w as the quiet reply of his listener. T h irty , then anyw ay, h e added. N o r th irty , o r even tw enty. A t this he became perplexed and. to use his w ords, asked. "H o w m any, th e n ? " H e was u n in fo rm ed o f the fact th a t w hile m a
chines elim inated certain jobs they created others. N o doubt it is fo r reasons such as th is th a t m uch o f the difficulty has arisen.
W ith the situ atio n as it is.
w hat can be done? I n th e first place the o p era to r m u st be fran k . C a rd s f o r th e h and being played should be laid o n th e table an d rules fo r the new deal d ra w n up.
M en
Properly handled, labor will show a natural im provem ent in efficiency w ith o u t p ro p o rtio n ate additions to supervi;ory forces.
If labor is apprised o f the com pany’s problem s, it w ill show greater desire to co operate.
D ivision o f w orking tim e is economically unsound, but hum anism and expediency rec
om m end ad o p tio n o f this p lan in slack time.
R etention of the old m an is a m orale upbuilder.
T h e b an k er is th e only frie n d w ho can help the coal o perator. F o r the operato r not to tell the tru th is to cru cify him self and his fellow operators.
Investm ent houses are full o f idle m oney. B ut the tru stees are unw ill
ing to invest w illy-nilly, w ith o u t sub- .'•tantial evidence of the bona fide c h a r
acter o f the enterprise. Sum s of that idle w ealth are going out every dav to ends w hich offer less physical security than m any coal m ines in need of help can offer.
A suggestion offered to w ard the initiation o f m echanization financing follow s: A sk fo r a m odestly small loan— say $20,000— fo r th e pu rch ase of one o r tw o m achines. G ive a c h at
tel m ortgage, partly secured by col
lateral, and agree to pay 5c. to 10c.
of the saving from each to n produced.
S et up a sinking fu n d to take care of these paym ents and live up to the agreem en t religiously. Show th a t business is m eant by sending a check m onthly tow ard reduction of the notes. N ot until the p a rticu lar equip
m ent is b etter th an half paid fo r should additional m achine financing be sought.
P ro p e rly applied, loading equip
m ent will cut the cost of production 40c. o r m ore a to n in thick coal.
W h a t is to be done w ith the balance o f the saving a f te r the equipm ent debt is satisfied? T h e an sw er su g gests a new leaf in th e o p eratio n of coal m ines. I t involves the accounta
bility of the operato r to his investors, fo r w hose p ro p e rty he is tru ste e . In th at capacitv he is d u ty bound to set aside increm ents o f net receipts fo r in te rest paym ents on bonds, fo r di
vidends on p re fe rre d stock, fo r d ivi
dends on com m on stock if a balance rem ains a fte r depreciation and de
pletion. H e is certainly bound to tak e care of the last tw o charges, so th a t w hen the coal is all gone the original investm ent rem ains. H e m ust, in o th er w ords, respect the tru e m eaning o f am ortization. A n d in the division o f savings, the w o rk ers m u st not be forgotten.
U n d e r highly favorable conditions and in thick-seam m ines a m achine- sh ift production of 200 tons is not considered inviting. A t a 250-ton stage, sa tisfacto ry p e rfo rm an ce has been attain ed only as applied to de
velopm ent w ork. B eyond th a t m ark th e loading m achine begins to yield a re tu rn . A t 300 to n s th e operation is g ettin g "somewhere, a n d a t 350-400 tons real profit can be expected.
T h e re is fascination, it is said, in n o t
ing th e slow b u t accelerating g ro w th o f th e p ro fit m arg in d u rin g th e re tire m e n t o f the first h alf o f th e investm ent in m echanized equipm ent, and the m ore a b ru p t rise o f profit th e re a fte r.
C O A L A G E — V o! J o . No-5
T IM E S T U D IE S
« Increase Efficiency A t Strip M i nes
T IM E is a vital elem ent in the operation of any m ining p ro p erty, the im portance of which increases alm ost directly as m echa
nization approaches 100 p er cent. A t a m odern strip mine, all the principal operations are carried on by m a
chinery, m ost o f w hich operates in cycles.
T h e P itts b u rg & M idw ay Coal M ining Co., w hich operates strip m ines in K ansas, O klahom a, M is
souri, and A rk an sas, finds th a t com
plete tim e studies of the various oper
ations in a strip p it are indispensable to good m anagem ent. In this brief resume of the studies w hich this com pany has m ade, em phasis will be placed fo r com parison on tw o o p era
tions w here conditions are quite d if
fe re n t n am ely : M ine N o. 10 located at M idw ay, K an., 7 m iles northeast of P ittsb u rg , K an., and M ine No. 15, located n ear M ineral, K an., 22 miles southeast of P ittsb u rg .
In general, the su rface in the area being m ined is flat and the coal dips about 22 ft. in a m ile in a n o rth w est
erly direction and aw ay from the O zark up lift. All the coal m easures m ined in this a rea are in the Cherokee shales, the basal m em ber of the P e n n sylvanian fo rm atio n , w hich rests un-
conform ably upon the M ississippi limestone.
A t M ine N o. 10 the low er of the two coal seam s is being extracted.
T h is seam is ap p ro x im ately 3 ft. thick and overlaid w ith blue slate, occa
sional sandstone, d rab shale, and soil.
T h e M ineral m ine is w orking the upper seam of coal, w hich is ap p ro x i
m ately 90 ft. above th a t w orked at M ine N o. 10 and is approxim ately 22 in. thick. T h is is a clean seam, overlaid w ith fro m 1 to 3 ft. of hard black carbonaceous shale, above which is blue slate, d ra b shale, and soil. A t both m ines the relatively gentle regional dip and flat to p o g rap h y have m ade it practicable to lay out the
pits* approxim ately parallel to the property lines, w hich obviously is an advantage in m eeting d rain ag e and haulage problem s.
T h e principal difference in the m ethods pursued at the tw o m ines lies in the m an n er of hau lin g and tran sp o rtin g coal. A t M ine N o. 10 (see Fig. 1), the older of the tw o mines, the car track s a re o f n arro w gage and located in the pit, th e first pit being opened near the tipple, w ith the operation prog ressin g th e re fro m , m aking it necessary to m aintain center openings o r haulagew ays be
tween the c u rre n t pits and the tipple.
It has been found expedient a t this mine to relay the m ine tra c k piece
meal as the shovel advances, tea rin g up the track ahead of th e shovel which was used in the previous pit, in place of sw inging the strip p in g shovel over a w ide berm , w hich is the practice in Illinois and Indiana. T h is is done to reduce the w idth o f the berm and to decrease th e angle through which the strip p in g u nit m ust be swung. W e believe th a t th is in creases the efficiency of this u nit to a point that offsets the cost of con
tinually building and re-laying the track. In th is case, the coal is loaded directly w ith a horizontal-type loader into drop-bottom cars in the pit.
A t the M ineral m ine (see F ig . 2 ) the tracks are m aintained on the s u r
face at the top of th e high wall of the pit instead of at its foot. T h e property w as opened u p on th e crop line and the tipple constructed back of the line of m axim um digging depth, so that developm ent w o rk a t this m ine is advancing to w ard the tipple, and the coal on the su rfa c e is transported over the area th a t is later to be stripped. T h is system of h a u l
age necessitates the use of a “d e r
rick,” or “bank m achine,” which
•T h e w h ole operation is described a s a m ine and each len g th o f ex c a v a tio n or w ork in g fa ce is know n a s a pit, th e p its in this ca se b ein g p arallel to ea ch other.
By H. C. WIDMER
M in in g E n g in e er P itts b u r g & M id w a y Coal M in in g Co.
P itts b u r g , K a n .
hoists a “sk ip ” from the p it to th e 35- ton drop-bottom cars on the su rface.
T h e follow ing tim e studies give some indication of the relative m erits of these tw o system s.
A t M ine N o. 10 a 750 B ucyrus- E rie shovel, having a 16-ctt,yd. dipper w ith an 8 5 -ft. boom and 54-ft. d ip p er sticks, is used ; and a t M ine N o. 15, a t M ineral, a 385 B u c y ru s-E rie shovel having a 12-cu.yd. d ip p er w ith an 80 -ft. boom and 54-ft. dipper sticks, is in operation. T h e two shovel crew s are sim ilar, consisting in each case of a “ ru n n e r,” a shovel engineer, one oiler, and one o r tw o groundm en, as conditions w a rra n t.
A t both operations, in an effo rt to reduce th e angle of sw ing o f th e s trip pin g unit, it has been th e practice to stack the first d irt fro m the cut in a pilot wall n ear the toe of th e spoil p ile; behind th is pilot wall th e ov er
b u rd en takes the angle o f n atu ra l repose of earth . B efo re th e shovel moves up, tw o o r th re e buckets are taken on the inside o f the pilot w all, giving it an angle o f slope o f a p p ro x i
m ately 3 to 1. T h e d irt placed be-, hind th e pilot wall assum es the n atu ral angle of repose. B y this m ethod o f stacking, m ore overburden is dropped n ear the shovel, w hich con
sequently can do its w o rk w ith a m inim um angle o f sw ing, thereb y in creasing the percentage o f tim e of the total cycle d u rin g w hich it is actually digging d irt from th e hig h wall.
E ach shovel is equipped w ith a c h art (see F ig. 3 ) th a t records th e sw ings o f the shovel an d clocks any loss in tim e th a t the shovel m ay e x perience th ro u g h o u t th e strip p in g day. In addition to this, each shovel
“ ru n n e r” o f th e various sh ifts m akes out a shovel report, listin g th e delays he has experienced th a t d ay and e sti
m atin g the tim e lost by each delay.
T h ese reports, as well as th e s h o v d -
M a y, 1931 - C O A L A G E 227
sw ing charts, are sent into the engi
neering office a t P ittsb u rg , and a strip p in g rep o rt, the item s of which follow, is com puted.
T h e ch a rt is headed “ D ata of S trip p in g Shovel,” M ine N o. ---, T ype Shovel ---. O n horizontal lines a re m arked the days of the m onth w ith a line f o r totaling the colum ns. T hese fo rm th e first column, and th e n u m b er o f sh ifts the second. T h e n follow th ree colum ns on coaling, broken into tim e lost, num ber of stops, average tim e ; th ree on m oving up, broken into tim e lost, num ber of m oves, averag e tim e ; tw o on oiling, including total and average tim e ; tw o on changing tim e, also in cluding total and average tim e.
O th e r delays recorded in still other colum ns a re : T u rn in g shovel around, w ater trouble, boiler trouble, w aiting fo r loader to pass, cleaning dipper, cleaning up slide, p u ttin g on new hoist cable, pow er line, electric trouble, hoist m achinery, sw ing m a
chinery, boom, boom m achinery, ropes,' cats, dipper, d ipper sticks, base, propelling m achinery, com pressor, lubrication, gen erato r, lights, changing shifts, m oving dinky track, and trouble w ith shovel track. F o u r
T a b le I— C o m p a ris o n o f P e rfo rm a n c e o f 7 5 0 - B - W it h 385-B E le c t r ic S h o v e l in 1930 750-B 16-Cu.Yd. 385-B 12-Cu.Yd. Differences Electric Shovel Electric Shovel in
Mine No. 10 Mine No. 15 Performance (a) A verage num ber of possible 8-hr sh ifts P = r m on th 67.1 5 4 .4 — 8 .7
(b) A verage tim e lo s t ou t of p ossible sh u ts par m o n th , o-nr. . «
shifts ... ,:>’ b
(c) Percentage efficiency of shovels (figuring possible shifts) g
1 0 0(1—6+0) ... ... W g * 247,300 - 8 2 , 0 0 0 (ri) A verage m o n th ly y a r d a g e . ... . . . . — 420 ( i) T o ta l yard age m o v ed per possib le 8-hr. sh ift; d —a 4,900
m A v e r a g e m o n t h l y s h o v e l a d v a n c e , f t ... 4 485 , + 15 3 (u) P ercen ta g e of sh o v e l sw in g s of 90 d eg. or l«£S... » 9 .9 _____
(h) A verage tim e of cycle, s e c . . . --- , 5 ¿ 2 — 16
(i) A verage to ta l tim e loat per 8-hr. strip p in g sh ift, m m . . . . 78 « _ . .
(i) A verage m o n th ly 8-I1 r. sh ift of a ctu a l d ig g in g (no d ela y s) 4 9 . 3
( i ) A verage m o n th ly yard age per a ctu a l hour of d iggin g ^ ^ — 115
( i ) A v e r a g e m o n t h l y y a r d a g e p e r a c t u a l h o u r d u g ( n o d c - ^ 3
(m ) P crraitago'cfficiericy of strip p in g sh o v e ls on sh ifts a c tu - , 4 9
ally worked...
In this and succeed ing tab les n o n e of th e figures are carried to th e n um b er of decim al places cu sto m a ry in m ak in g th e calcu lation s, so th a t p erfect ag reem en t on ch ecking th e ca lcu la tio n s ca n n o t b e a n ticip a te d .
colum ns are allow ed fo r troubles otherw ise unspecified, one fo r to talin g tim e lost out of sh ifts d u g fo r the one day, one fo r the theoretical w o rk ing tim e and one fo r the percentage of w orking tim e lost.
A sum m ary at the foot of the table gives the total num ber of possible 8-hour shifts, the total tim e lost out of 8-hour sh ifts dug in h o u rs and m inutes, and the percentage of effi
ciency o f the shovel fo r th e operations of the m onth u n d e r record.
T hese rep o rts in general list every possible delay that the shovel encoun-
p ig . 1— M e t h o d o f S tr ip p in g W i t h M i n e C a rs E n te r in g P it
Coat ¡oodecf out Previous
tered d u rin g the m onth, and they give th e num ber of possible 8 -h o u r sh ifts w orked. By “ possible s h ifts ” is m eant all sh ifts w h ere th e crew is o rd ered out, including Sundays, on the assum ption th at the S unday rep air w ork w as necessary o r the m en w ould not have been in stru cted to report.
O th e r possible sh ifts are those lost due to w aiting on dum p room , floods, and o th er delays due to clim atic con
ditions. T h e efficiency of the shovels on these rep o rts is calculated by a consideration of th e n u m b er of p o s
sible sh ifts d u rin g the m o n th an d also of the actual w o rk in g sh ifts. T h ese rep o rts list all th e delays encountered d u rin g the m onth, the m axim um tim e lost being found in m oving the shovel fo rw ard , in repairs, an d in m o to r and o th er electric trouble. A recap itu la
tion of general strip p in g d ata on th e shovels at Alines N os. 10 an d 15 fo r the y ear 1930 is given in T able I.
In T able I it is in te re stin g to observe th a t the average m onthly vardage p er actual h o u r d u g , assu m ing no delays, fo r th e 16-cu.vd.
bucket is S38 cu.vd., w hereas fo r the 12-yd. bucket on the 385-B shovel it is 635 cu.yd. T h e s e are figures based on a v e a r’s operation and are in direct p ro p o rtio n to the capacity o f the dippers, o r in the ratio o f 16 to 12.
T a b le II — A n g le o f S w in g , 16- Y d .
S t r ip p in g S h o v el
D e g . P er C ent
45 and l e s s ... 20.6 45 to 6 0 ... 2.X
60 to 75 ... 12.1
75 to 9 0 ... *0.1 90 to 1 0 5 ... 15.9 105 to 1 2 0 ... 10.4 120 to 1 3 5 ... 3-S 95.0
O bviously, there are m any o ther conditions th a t would have d istu rb ed th is ratio. H ow ever, the fact rem ains th a t even though the angle of sw ing has been reduced a t M ine N o. 15 as com pared w ith Aline N o. 10, this reco rd o f p erfo rm an ce is identical.
228 C O A L A G E — V oL36. -Vo-5
T a b le I I I — C o m p a ris o n o f P e rfo rm a n c e o f 75-B W i t h 50-B S h o v e l in 1930 75-B 4-C u.Y d . 50-R 2-C u.Y d . D iflcrcn ces E lectric L oader E lectric L oader in
M in e N o . 10 M in e N o . 15 Perform ance T o ta l av era g e m o n th ly lo a d in g tim e per d a y , m in ... 441 463 + 2 2 T o ta l av era g e m o n th ly tim e lo s t per d a y , m in ... 39 17 — 22 C o a l lo a d ed per a ctu a l m in u te o f lo a d in g tim e , t o n s ... 4 .1 2 .7 — 1. 4 A v era g e num ber of load er sw ings per c a r ... 3* 2 2 | + 19 A v era g e tim e of sw in g o f load er, s e c ... ... ^2 32 . . . .
A v era g e num b er of cars load ed per hour w orking t im e 2 1 .8 * 5 . 1 f — 16. 7
A v era g e tim e lo s t per m o v e up, s e c ... - 35 34 — 1
T o ta l av era g e coal a ctu a lly loaded per d a ily sta rt, to n s. . . . 1,843 1,248 — 595 T h eo retica l coal per d a ily sta rt, t o n s ... 1,978 1,298 — 680 L o a d in g tim e lo st, per c e n t ... 6 . 6 3 . 9 — 2 . 7 E fficien cy of lo a d in g sh o v e ls, per c e n t ... 9 3 . 4 96. 1 + 2 . 7
* 1 1 . 5- t on cars, f 3 5-ton cars.
T h e n a tu re of the h a rd cap rock d irectly above the coal at M ine No, 15 undoubtedly explains w hy the cycle of this u n it is slow er th a n th a t at M ine No. 10, w h ere th e digging is easier.
T h e average tim e p er cycle on the 16-yd. m achine fo r the y ear 1930 was 48 seconds. I t w as observed th a t the angle of sw ing d u rin g this period was as in T able I I .
T h is sam e in fo rm atio n on the 12-yd. m achine show s a slightly re
duced angle of sw ing and an av er
age cycle of ap p ro x im ately 48 sec
onds. O bviously, the m a tte r of com pletely filling th e bucket, due to the difference in the n a tu re of the over
b urden, is the rem ain in g fa c to r th at has influenced these proportions, for the y ardage m oved by the tw o shovels is in d irect p ro p o rtio n to the dipper capacity, and as th e length of cycle in m inutes is the sam e, and as the angle of sw ing is g re a te r w ith the shovel a t N o. 10 m ine, the digging tim e of th a t shovel m ust be proportionately less.
T h e strip p in g u n it at mine N o. 10 is foltowecl up by a 75-B horizontal- th ru s t loader w ith a dipper capacity of 4 cu.yd. T h is loader is one of the largest h o riz o n ta l-th ru st loaders in use anyw here. A t M ine No. 15, a 50-B 2 f-y d . horizontal, th ru s t loader is used to load the coal into the “skip”
of the b an k m achine. T h ese loaders are of the sam e type, although d if
fe re n t in size and. th ere fo re, of d if
fe re n t d ip p er capacity.
A ccom panying d a ta on the 50-B loader w ere taken w hen the loader had a 2-yd. dipper, this dipper having been recently replaced w ith a 2-}-yd.
dipper w hich, th o u g h m ade longer, is of the sam e w idth and has been made of the sam e depth, because the thin seam of coal being loaded w ould not p erm it of a n y increase. E ach loader is equipped w ith a recording time- clock w hich records delays in th s same m a n n er as th e c h a rts on the stripping shovels. T h ese loaders are operated by one m an, th e coal at M ine N o. 10 being loaded directly into 15- to n S a n fo rd -D a y cars, on 42-in. gage track, hauled by 20 -to n V ulcan steam
locomotives, w hereas at M ine N o. 15 the coal is loaded into the b ank-m a
chine skip of 7-ton capacity.
T h e bank m achine used a t M ine N o. 15 is a 50-B B u c y ru s-E rie unit, operated by one m an. Coal from the bank-m achine skip is elevated and dum ped into 35-ton S a n fo rd -D a y autom atic dum p coal cars of stan d ard track gage.
T h e coal a t M ine N o. 10 is hauled out of the p it and dum ped into a 100- ton capacity hopper and elevated over the screens of a tipple of a capacity of 2,750 tons p e r 8 -hour w orking day, and the coal fro m M ine N o. 15 is hauled on the high wall, or n atu ral ground, approxim ately tw o -fifth s as far as a t M ine N o. 10, th e coal being dum ped into a 180-ton hopper and p ut th rough a tipple of a capacity o f 3,500 tons per 8-hour sh ift.
E ach loader “ ru n n e r” sends in his tim e-clock show ing w h ere the delays occurred and w hat delays happened, these tim e charts also being sen t to the office at P ittsb u rg , w here a m onthly loading data ch art is com puted and the efficiency o f the tw o loaders found. A ll delays in loading d u rin g the day are tabulated on this loader sheet, w hich is entitled “ D ata on L o a d e r.”
U n d e r the usual in fo rm atio n as to m ine num ber, type of loader, and m onth of record are horizontal lines rep resen tin g the various days in the m onth. T h e first colum n is fo r the d ate of the m onth, the n e x t 23 are fo r delays, those actually listed fo r record being w recks, sw itching, w aiting on cars, m echanical trouble, electrical trouble, changing hoist ropes, dipper latch, w aitin g on horseback excavator, breakdow n of tipple, coaling, boiler trouble, w aitin g on coal shooters.
O th e r colum ns give to tal tim e lost, total tons of coal lost, actual loading time, actual coal tonnage loaded, actual coal tonnage loaded p er m inute, theoretical loading tim e, theoretical coal tonnage, percentage of loading tim e lost, and date. T h e figures fo r the m onth are footed a t the bottom
of the line o f colum ns.
T he principal delays in loading are
F ig . 2— System o f S t r ip p in g W h e r e C a rs T r a v e l o n T o p o f H i g h W a l l
M a y, 1931 - C O A L A G E 229
due to loss of tim e in sw itching, to w aiting on cars, and various m echan
ical troubles. T h e general average loading data on the tw o loaders are as in T able II I .
T hese records show the quantity of coal actually loaded p er m inute by the tw o loading shovels, an d also that the 50-B 2-yd. shovel is actually load
ing 32 per cent m ore coal th a n the 4-vd. shovel, w hen th e ir respective sizes are taken into consideration.
T h e interposition of the loading and elevating o f th e 7-ton skip be
tween th e 50-B shovel and the rail
road cars w ould seem likely to cause th e loss of m uch tim e and slow up operations considerably, b u t the diffi
culty is less th an m ight be anticipated because the loading of the skip takes only 1.7 m inutes and the average to n nage loaded p er skip is approxim ately 6 tons, so th a t 3.1 tons is loaded p er m inute of actual operation.
T h is speed is attained, in p a rt, b e
cause th e capable bank-m achine op
e ra to r can reduce th e loss of tim e by low ering his skip, a f te r dum ping, to a point convenient to the bucket of the loading shovel, so th at the ru n n e r of th at m achine can reload his skip by sw inging the bucket th ro u g h only a few degrees.
I t is on th e track th a t the principal loading tim e losses are sustained.
T he trip s a t M ine N o. 15, w here the 2-yd. 50-B shovel is w orking, are composed o f th ree 35-ton coal cars draw n by a 25-ton V ulcan gasoline locomotive, w hereas at M ine No. 10 each trip is com posed o f eight coal cars o f an average capacity of 114 tons. T h e filling o f these small cars by the 75-B shovel causes a loss o f m uch time. T h u s it happens th a t the shovel th a t seem s to be w ork in g at a disadvantage loads a tonnage alto
gether out of p ro p o rtio n to its size.
O p e ratin g data on the b ank m achine a re as in T able IV .
A dvantages in loading w ith a bank m achine in strip m ining are th a t in many cases the average dead haul from the pit to the tipple can be ma-
Fig. 3— R ecorder fo r R eg isterin g O p e ra tin g D elays U sed on B oth S trip p in g and L o ad
ing Shovels; T ak en F rom 16-Y d. S hovel
terially decreased. A lso th e tra c k on the high wall need n o t be to rn up in m oving, these haulage track s being slid over w ith a caterp illar tra c to r for a distance equal to the w id th of the n e x t pit, w hereas tim e is lost a t M ine N o. 10 because only a 15-ft. berm is carried on th e coal and th e tra c k m u st necessarily be com pletely to rn up ahead o f the shovel and then rebuilt.
T a b le IV — T im e S tudy o f W o rk O f B ank M ach in e T o ta l average num ber of skip s per 8-hour
w orking d a y ... 259
A verage lo ad per skip , t o n s ... 5 .3 A v era g e num ber of skip s per 35-ton ca p a city
coal ca r ... • 6 .9 T o n s of coal load ed per skip per a c tu a l w ork
in g m in u te ... ...
A verage tim e load in g skip b y load er, m in u tes 1.7 A verage tim e lo st d a ily in m o v in g b a n k m a
chine, m in u tes... »8*
A t M ine No. 10, w here the haulage is on the coal, th re e train s a re used to haul the coal from the coal face to th e tipple, this coal being hauled thro u g h th ree openings, the opening used depending upon the position of the stripping shovel and th e q u an tity of coal th at has been loaded out of the pit. Some tim e is lost in w aitin g on trains, sw itching, cars off track, and mechanical defects in the cars.
T he average tim e lost in w aitin g on tra in s per day is 11 m inutes. Som e
Fig. 4— C h art M e asu rin g S w ing o f S hovel and N o tin g D elays in O p e ra tio n ; T aken F rom 12-Cu.Yd. Shovel
O O ^ C O O 0.0 o o ~ O O O o o o o c
of this loss o f tim e m ay be caused by m echanical defects in th e trip or by doors being dow n in th e coal cars.
T h e average tim e lost in sw itching is 1^ m inutes. A s previously stated, th e re is a sm aller loss o f tim e in load
ing at M ine N o. 15 because cars of la rg e r capacity are used and because th ere are few er cars p er trip , thereby causing less delay in dum ping. T h e m anner o f dum ping the cars into the hoppers is identical, both o f the m ines using the sam e m ake o f car, although it requires approxim ately 3 m inutes m ore to dum p the eight 114-ton coal cars th a n it does to dum p the th re e 35-ton cars.
I t has been m y desire to give a b rie f resume of the strip p in g and m ining operations, and d ata obtained fro m records kept on th e ir p e rfo rm ance a t th e m ines m entioned in this article. N o attem p t has been m ade to give th e com plete records k ep t on the strip p in g shovels and loaders, o r on the tim e ch a rt k ep t a t th e tipple o f every m ine, as this w ould entail too long an article. T im e c h a rts in each tipple show th e daily tim e actually spent in loading coal, also each delay is recorded, this m ak in g a re p o rt sim ilar to th a t kept 01a the shovels.
In addition to endeavoring to a r rive a t tim e studies o f th e ir m ining equipm ent, each y ear officials com p u te the ratio o f a m an-days to to n s of coal m ined p er day at each mine.
T h a t a t M ine N o. 10 fo r 1930 w as 1 :17.8, w hereas a t M ine N o. 15 it w as 1 :16.4.
A c h a rt also is kept on th e life of the differen t m akes of hoist ropes used on the strip p in g shovels, this ch art show ing th e m ake of th e hoist ropes, th e date the rope w as placed on the shovel and the date o f replace
m ent, the total n u m b er o f cubic y a rd s o f o v erburden m oved by each hoist rope, as well as the actual cost o f the ro p e per one th o u san d cubic y a rd s of o verburden stripped.
E v e ry effort is m ade to provide tim e studies o f the different m ining operations, in o rd e r to prom ote m ore efficient and m ore rapid loading, and to enable th e different u n its to fu n c
tion p ro p erly a n d keep in step one w ith an o th er. T h e tipples a re capable o f ta k in g m ore coal th an is b ein g run over them , an d if th e m ark et w a r
ra n ts it, production in th e p its th e m selves can easily be increased. I t is th e p u rp o se o f the P itts b u rg & M id w ay Coal M in in g Co. to have as its goal an increased m ining efficiency in every d epartm ent, thereb y placing on th e m ark et a coal th a t can com pete w ith anv other.
230 C O A L A G E — V o l.36, N o .5
M E C H A N I Z A T I O N A C T S
* W here Gravity Fails
A L T H O U G H n atu ral conditions n arro w the field of successful JL J L m echanization in the southern end o f the an th racite region, em ploy
m ent o f m echanical m eans frequently has been fo u n d to be highly profitable w here n atu ra l aids to easy operation fail. T h is, fo r exam ple, has been the experience of the B uck R u n Coal Co., w hich som e tim e ago introduced a longw all face in a coal seam ap p ro x i
m ately 4 ft. thick.
T h e face w as about 90 ft. long, but w as later lengthened to 150 ft.
Seventy-five L o rain jacks w ere used in th re e single row s, though som etim es in tw o row s connected by heavy block
ing. EickhotT and Cosco shaker chutes w ere laid in fro n t of the face;
they delivered the coal to o th er shaker chutes which c arrie d it along a head
ing to a crosscut, w here it could be loaded into cars on the gangw ay.
A s it form ed a basin w ith steep sides, the coal seam had a varying inclination. T h e u p p er p a rt of the longw all face w hen sta rte d was on a slope of 25 deg. T h e low er end w as inclined only 11 deg. W h e n the long
wall face w as abandoned its u pper end w as a t an inclination of 20 deg. and the low er end at 18 deg.— the slope had becom e alm ost u n ifo rm ; so uni
fo rm ly steep th a t th e shaking chutes had been rem oved, being replaced by galvanized sheet iron over which the coal ra n w ith o u t any assistance.
T h o u g h the floor rolled irregularly and so gave som e trouble, it was fo u n d possible to cut the coal w ith the face lying stra ig h t up th e dip. Jeffrey u n d ercu tters did the cu ttin g w ithout difficulty, b u t w ith o u t any apparent increase, it is said, in the size of the coal obtained. In all, the face w ent fo rw a rd 450 ft.
T h e operations o f the longwall face, the cu ttin g m achines, the shak
ing chutes, a n d th e jacks w ere satis
factory, and th e only reason fo r dis
continuing the w o rk w as th a t the coal becam e too th ick fo r th e jacks.
T ho u g h these w ere 5 ft. in length, they w ere too sh o rt fo r 8 ft. coal even w ith blocking. So a plan th a t had been successful fro m the first had to
be discontinued and o p p o rtu n ities fo r resum ption have not been found since.
Som e details o f conditions m ay be given. T h e floor wras quite solid and the ro o f consisted o f a falling stone o r draw ro ck 6 to 8 ft. thick over w hich w as a stro n g co n g lo m e ra te ; so stro n g th a t the face advanced 200 ft.
before the rock failed. I t should be noted th a t over p a rt of th a t 200 ft.
the opening w as only 90 ft. w ide and th e re a fter the w id th w as only 150 ft.
Consequently w ith a stro n g ro o f such as this the opening w as n o t w ide enough to fav o r collapse.
T h ough the longw all w as ab an doned, the use of shaking chutes w as not, but these latter are n o t extended up the dip fo r the full length of the room s in w hich they are used. T h ey go up only so f a r as th e inclination rem ains below 11 deg. T h e re a fte r galvanized sheet iron spiked to the posts is used up to a p oint w here th e inclination is, say, 22 to 24 deg., and then the coal will ru n quite readily on the bottom w ith o u t any sheet iron.
H ow ever, in general w here shaking chutes are being used (th e seam being on an inclination o f less th a n 24 deg.) the coal sta rts dow n a galvanized steel sheet till it comes to a 10-deg. slope, w here it enters a shaking chute and proceeds to the car a t the entry.
T he bed m ined is th e B uck M o u n tain and the w orkings at this m ine
By R. DAWSON HALL
E n g in e erin g E d ito r, Coal A g e
are n e a r the end o f the dip, w here it begins to shape itself like the point of a som ew hat b lunt spoon. T h e roads w hich attem p t to follow th e contours m ake sizable rep resen tatio n s o f sem i
circles.
S haking conveyors have been used on the su rface fo r the loading of stock coal, and here duckbills also w ere used. F o r norm al loading they w ould have given en tire satisfaction, though it is said a shaking chute will not c a rry as m uch sized coal as it will m ine-run. H ow ever, the req u ire
m ents usually w ere abnorm al. A n o rd e r w ould come in fo r 5.000 or 6,000 tons of n u t to be delivered in a
few days, so th a t an e n tire cargo could be loaded.
In o rd er to avoid dem u rrag e, e x trem e expedition w as desired and that seemed best served by tw o steam shovels th a t happened to be available.
O rd e rs of this kin d could n o t be loaded o u t o f the m ines. Indeed, a com pany w ould have to be o f unusual m agnitude to produce such a tonnage o f one single size in the space o f a few days. W h e n such o rd ers come they are filled by trip le -sh ift o p era
tion w ith steam shovels and from stock.
A t the m ines of the P in e H ill Coal Co., M inersville, the conditions do not
F ig. 1— D ia g ram m a tic S ketch o f L o n g w all a t B uck R un
M ay, 1931 — C O A L A G E 231
