C o a l ge
A M c G ra w -H ill Publication— Established 1911
D E V O T E D T O T H E O P E R A T I N G , T E C H N IC A L A N D B U S IN E S S P R O B L E M S O F T H E C O A L - M I N I N G IN D U S T R Y
New York, July, 1931
Volum e 3 6. . . . Number 7
V
On Trial
W h e n d i s t r i c t a f t e r d i s t r i c t
in the bituminous coal fields p a rte d company w ith o rg a n iz e d lab o r a few years ago, they em b a rk ed upon an experiment in internal regu latio n w ith o u t precedent for success in the h isto ry o f the industry. T o d a y the re
sults o f th a t experiment are finding expres
sion in w id e sp re a d labor disturbances.
N o
o p e r a t o rneeds to be told the causes which underlie the reappearance o f industrial s trife in Kentucky, Pennsylvania, Ohio, a n d W e s t Virginia. T h e i r inevitability was fo re to ld when a m a jo r p a r t of an over
d eveloped and d isorganized industry ex
c hanged the restrictions of contractual labor relations fo r unlicensed indulgence in ruinous wage and price competition.
T h a t t h e m a j o r u p h e a v a l s
have
been engineered by an organization alien to o ur na tio n a l philosophy is m ore significant than palliative. Communism feeds upon d e s p e ra tio n ; the fact th a t the N a tio n a l M i n e r s ’ U n io n has been able to m ake such h e adw ay should be provocative o f deep thinking by those who really believe in A m erican concepts o f a p artn ersh ip between capital a n d labor.
I f
l e a d e r s h i pin bituminous coal—
both m a n a g e m e n t and labor— is to make such an a p p ro a c h to this m a jo r problem of industrial relations, passion and prejudice must be b a r r e d fro m the deliberations.
I olitics, too, has no place. T r a d it io n a l a tt i tudes m ust give way to f ra n k acceptance o f realities and un rese rv ed consideration o f h ow these realities best m ay be met.
Al l i a n c e
with the N a tio n a l M in e r s ’ U nion is unthinkable because the ultim ate aim o f t h a t o rg an iz atio n is the destruction of our p re s e n t capitalistic civilization. D is
trict unions w ith o u t national affiliations are h a n dicapp ed by the same limitations as com
pany unions; th e difference in lim itations is only one o f degree.
E l i m i n a t i o n
o f these org an izatio ns fro m consideration natu rally raises the ques
tion w h e th e r reestablishm ent o f the U n ite d M in e W o r k e r s , o r some o th e r national union, to the position of dominance held by the In dianapolis gro u p p rio r to 1920 is the only way out. Such a suggestion is ana th e m a to m any o p e ra to rs who have never recog
nized the union and to many o thers who suf
fered u n d e r its control.
T h e q u e s t i o n,
nevertheless, is there.
I t must be answ ered either by a d e m o n s tra tion o f a yet unrevealed ability on the p a r t o f the employers to p reserv e decent indus
trial relations w ith o ut union help or by a d em on stratio n on the p a r t o f o rg an iz ed labor th a t it is now rea d y to play the eco
nomic rôle it once sacrificed to internal
politics. Any o th e r answer is illusory— or
worse.
f o u r t h o f a s e r i e s o f a r t i c l e s o n t h e f u n d a m e n t a l s o f m o d e r n c o a l p r e p a r a t i o n
E L E C T R IF IC A T IO N P R O B L E M S + In Modern Preparation Plants I
By E. J.'GEALY
E le ctric a l E n g in e e r P itts b u r g h Coal Co.
P itts b u r g h , Pa.
B
E F O R E d is c u s s in g th e e le c tr ifica tio n o f m o d e r n co a l p rep a ra tio n p la n ts su ch as u s e w a sh in g p r o c e ss e s, o n e sh o u ld n o t fa il to c o n sid e r th e fa c t th a t p r o g r e ss , b e fo r e m an v y e a r s e la p se , m a y m a k e n o t a f e w " o f ou r p r e se n t id ea s o b so lete.
C erta in fu n d a m e n ta l p r in c ip le s, h o w e v e r , sh o u ld b e a d o p ted in o u tlin in g th e e le c tr ific a tio n p ro g ra m , a n d w h e n th e y a re fo llo w e d th e fin al r e su lt is n ot lik e ly to b e e m b a r r a ssin g , at le a s t n o t u n til so m e y e a r s a ft e r c o n str u c tio n is co m p leted .
P a s t m eth o d s o f e le c tr ific a tio n and p a st ty p e s o f e q u ip m e n t sh o u ld first be stu d ied , n o t w ith th e id e a o f s la v is h ly fo llo w in g o ld p r a c tic e s b u t ra th er w ith th e v ie w to a d o p tin g all th a t is g o o d in th em , an d to a v o id in th e n e w p la n t c h a r a c te r istic s and u n its w h ic h in fo r m e r p la n ts h a v e b een p ro v ed u n s a tis fa c to r y . W h o le s a le d isreg a rd o f p r e se n t p r a c tic e h a s in m a n y in s ta n c e s p r o v e d d is a str o u s an d e x tr a v a g a n t. S till m o r e im p o r tan t, p erh a p s, it is to rem em b er th a t w h e n e ffo r ts a r e m a d e to r e v o lu tio n iz e e v e r y th in g a t a s in g le str o k e th e c h a n g e s m a y b e so ill- ju d g e d th a t th e y w ill a c tu a lly retard r a th er th a n aid p r o g r e ss.
U s u a lly th e co m p a n y w h ic h u n d er
ta k es th e d e sig n an d c o n str u c tio n o f a m o d ern p rep a ra tio n p la n t is o n e w h ich is a lrea d y o p e r a tin g m in e s and tip p le s, b u t e v e n i f it b e a n e w c o m p an y its m e th o d s o f a p p ly in g e le c tr ic ity w ill p e r fo r c e b e d icta ted in part b y p a st m e th o d s o f th e in d u s tr y . It is im p o r ta n t to rem em b er th a t th e e m p lo y m e n t o f u n u su a l ty p e s o f e q u ip m en t in p la c e s w h e r e su c h eq u ip m en t
is n o t n e c e s s a r y p la c e s a n e e d le s s b u id e n o f c o s t on th e p la n t, n o t o n ly d u r in g in s ta lla tio n b u t th e r e a fte r , b e
c a u se th e c o m p a n y , d u e to th e u n u su al ch a ra cter o f th e p a rts in v o lv e d , w ill
346
h a v e a lw a y s to k eep a d d itio n a l rep air p a rts in sto c k .
S im p lic ity a n d e c o n o m y , th e r e f o r e , sh o u ld g u id e th e d e s ig n e r in h is s e le c tio n o f e le c tr ic a l e q u ip m e n t, i n e v e n th e m o s t m o d e r n p la n t, u n its w h ic h n o w r e p r e se n t th e b e s t p ra ctice w ill, o f n e c e s s ity , h a v e to b e rep la ce d b y o th e r s la te r , an d sp e c ia l ele c tr ic a l e q u ip m e n t o r ig in a lly a d a p ted to th e s e u n its, if n o t o f s o m e w h a t g e n e r a l a p p lica b ility , p ro b a b ly w ill b e c o m e at le a s t a p a rtia l lo s s a s s o o n a s th e c h a n g e is m a d e and, i f it b e n o t c h a n g e d , its r e te n tio n in a n y e v e n t w ill b e lik e ly to r e su lt in lo s s e s .
E c o n o m y m u s t a lw a y s b e in th e m in d o f th e elec trica l e n g in e e r ; h e m u s t d o h is u tm o st to g e t th e m o s t o u t o f e v e r y d o lla r h e sp e n d s. T h is d o e s n o t n e c e s s a r ily m e a n th a t th e eq u ip m en t sh o u ld b e ch ea p or th e m eth o d s o f in s ta llin g e le c tr ic a l u n its b e n ig g a r d ly . I n m o r e p la c e s th a n o n e can b e se e n in s ta n c e s w h e r e s e c tio n s o f p la n ts m u s t e v e n tu a lly b e r e co n str u c te d a t g rea t c o s t b e c a u se e x c e s s iv e e c o n o m y w a s u se d in th e p rim a ry in s ta lla tio n . M u c h w o u ld h a v e b een sa v e d i f th e p la n t a n d its e q u ip m en t h a d b e e n b e tte r d e s ig n e d a n d er e c te d in th e first in sta n c e .
B u t, th o u g h it b e tr u e th a t p a r
sim o n y is a fa u lt ra th er th a n a v ir tu e , s o a lso is it tru e th a t, in th e s e le c tio n o f a c c e ss o r ie s, ca re m u s t b e ta k e n to a v o id so ela b o ra te and c o s t ly a d e sig n a s w ill d e te r th e c o m p a n y fr o m a tte m p tin g to b u ild a p la n t o f m o d e r n ty p e. T h a t w o u ld b e u n fo r tu n a te in d eed , fo r m a n y o f th e u p -to -d a te ty p e s
o f m a c h in e s h a v e b een g iv e n a d eq u a te trial an d h a v e a b u n d a n tly p r o v e d th eir v alu e.
A n e w e le m e n t in d e sig n , h o w e v e r , is b e g in n in g to m a k e it s e lf f e lt . In
f u t u r e la r g e in v e s tm e n ts in p r ep a ra tio n p la n ts m a y b e m a d e w ith o u t fea r o f lo s s , b e c a u se th e y w ill b e op eratec m o re h o u r s th a n 8 o u t o f 2 4 . C o n v e r s e ly , b e c a u se th e c o s t s o f p r e p a ia - tio n b y a ll m o d e r n m e th o d s a r e n e c e s
sa r ily la r g e it m a y b e fo u n d th a t o h o u r s is fa r to o s h o r t a tim e m a d a y to e ffe c t a n e a r n in g su fficien t to p ay in te r e s t a n d a m o r tiz a tio n c h a r g e s.
In a fe w y e a r s p r ep a ra tio n p la n ts m a y b e w o r k in g o n a s c h e d u le o f tw o n ig h t s h if t s o n ly , or m a y b e o p e r a te d c o n tin u o u sly .
B e c a u s e o f th e ra p id fo r w a r d ste p s b e in g m a d e in th e details^ o f co a l p r e p a r a tio n th e u tm o s t fle x ib ility m u st be p r o v id e d in th e e le c tr ic a l sy s te m . N e w m a c h in e r y b o u g h t f o r trial s h o u ld b e e q u ip p ed w ith ty p e s o f e le c - tr ic a l d r iv e s a n d c o n tr o ls th a t ca n b e sa lv a g e d at fu ll v a lu e i f th e n e w m a c h in e d o e s n o t p r o v e to b e a b e n e fic ia l a d ju n c t o f th e p r o c e ss.
T h r o u g h o u t th e d e s ig n in g o f th e p la n t, th e la y o u t, s e le c tio n , a n d in sta lla tio n o f th e e le c tr ic a l e q u ip m e n t m u s t b e b o r n e in m in d . I n th e p a st th e e le c tr ic a l d e ta ils h a v e b een fitted in to th e p la n t in th e b e s t m a n n e r p o s sib le a ft e r all th e o th e r d e ta ils h a v e b een fix e d . T h is s o m e tim e s n e c e s s i
ta t e s im p r o p e r a n d u n s u ita b le s e le c tio n a n d in s ta lla tio n o f th e elec tric eq u ip m e n t. B e c a u s e o f th e fle x ib ility o f e le c tr ic w ir e a n d c o n d u its , th is d is a d v a n ta g e m a y n o t b e o b v io u s , but n e v e r th e le s s it is a lw a y s p resen t w h e n e v e r th e s o lu tio n o f elec trica l p r o b le m s h a s b een tr e a te d a s a n a ft e r th o u g h t.
N o r is th e e le c tr ic a l p a r t o f th e in s ta lla tio n to b e r e g a r d e d a s o f se c o n d a r y im p o r ta n c e . S o m e o f the C O A L A G E — V o l.3 6 ,N o.7
m o s t far-reach in g- c h a n g e s in p lan t o p e r a tio n h a v e r e su lte d fr o m b r o a d e n in g th e a p p lic a tio n o f elec trica l e q u ip m en t. E le c tr ific a tio n h a s n o w g r o w n to th e p o in t w h e r e th e p o w e r bill o f a co a l c o m p a n y is o n e o f its la r g e ca sh e x p e n d itu r e s . I n c o n s e q u en ce, a sm a ll p e r c e n ta g e o f r e d u c tio n in th e p o w e r c o s ts r e p r e se n ts a la r g e s a v in g in d o lla rs.
S u r p r is in g a s it m a y so u n d , w h e r e p o w e r is p u rch a sed th e s c h e d u le u n d er w h ic h p a y m e n ts f o r e n e r g y are m ad e m a y d e te r m in e h o w th e p la n t sh o u ld be b u ilt. F o r e x a m p le , s o m e tim e s by o p e r a tin g a p la n t a t n ig h t, p o w e r can be p u r c h a se d a t a c o n sid e r a b le re d u c tio n , an d i f th e n , a lso , it can b e o p er a te d a t h a lf lo a d in th e d a y tim e w ith o u t d is tu r b in g th e s a v in g s d u e to n ig h t o p e r a tio n , it w o u ld be h ig h ly e c o n o m ic a l to b u ild th e p la n t in tw in p a rts, r u n n in g b o th p a rts at n ig h t and o n ly o n e p a rt d u r in g th e d ay. In so m e in s ta n c e s su c h a n a r r a n g e m e n t w o u ld s a v e a m a x im u m o f p o w e r c o st an d a t th e sa m e tim e g iv e th e p la n t e q u ip m e n t a h ig h o p e r a tin g load fa c tor, all o f w h ic h is o n e o f th e fe w w a y s r e m a in in g w h e r e b y th e coal in d u str y can e ffe c t a la r g e s a v in g .
E le c tr ic a l la y o u ts a n d p la n s fo r n ew p la n ts m u s t, th e r e f o r e , b e m a d e w ith a c le a r v is u a liz a tio n o f th e fu tu r e d e m a n d s o f th e in d u s tr y . O n ly r e c e n tly h a v e c a p ita l in v e s tm e n ts fo r elec trica l e q u ip m e n t, p o w e r b ills, a n d elec trica l d e la y s b e c o m e m a tte r s o f p rim a ry in te r e s t. T o d a y , in s o m e in s ta n c e s th e y d e c id e h o w m a n y h o u r s th e p lan t sh o u ld o p e r a te a n d , fu r th e r m o r e , w h ic h h o u r s o f e a c h d a y sh o u ld be c h o se n f o r th e r u n n in g p erio d .
T o fa c ilita te o p e r a tio n , m a in te n a n ce, n e w c o n str u c tio n , e tc., ev e r y e ffo r t s h o u ld b e m a d e to k eep th e y a rd o f th e p r e p a r a tio n p la n t fr e e fr o m o v e r h e a d w ir e s , p o le s , and b ra ck ets. T o th is en d th e c o n d u cto rs
F ig. 2— E xam ple o f the U se o f Standard Equipm ent le a d in g to an d a r o u n d th e p lan t
sh o u ld b e p laced u n d e r g r o u n d or run a lo n g g a lle r ie s , w a lk w a y s , etc.
F r e q u e n tly c o n v e y o r p a s s a g e w a y s can b e u se d fo r th e c o n d u c to r s , bu t w h e r e th is is n o t p o ss ib le , tr e n c h e s m a y be d u g an d th e ca b les su p p o rted o n b ra ck ets or in s u la to r s in sp ecia l in c lo su r e s. W h e r e v e r h e a v y traffic, su ch a s railroad cars, m in e ca rs, or w a g o n s, m u s t p a ss o v e r e le c tr ic c ir c u its, th e ca b les sh o u ld b e c a r r ie d in a s tr o n g ly r e in fo r c e d p a s s a g e w a y , or, p ro b a b ly b etter y e t, in an ir o n c o n d u it laid in a tr e n c h an d a d e q u a te ly p ro tected b y co n c r e te .
T h e elec tric load c u r v e an d o th e r p o w er c h a r a c te r istic s in R h e o la v e u r p la n ts, o f v a r io u s s iz e s , c o m p le te w ith C a rp en ter d r y e r s, k iln -ty p e h ea t d r y ers, slu d g e r e c o v e r in g u n its, e x p e r i
m en ta l eq u ip m en t, e tc., a s o p era ted b y th e P ittsb u r g h C oal C o. r e v e a l th e fo llo w in g d a ta :
T h e load c u r v e d u r in g o p e r a tin g h o u r s is q u ite f l a t ; it is e v e n su c h th a t in a lm o st an y m o n th th e th ree h ig h e s t fifte e n -m in u te m a x im u m d e m a n d s, ob tain ed fr o m a g r a p h ic w a ttm e te r , Fig. 1— Control and Pushbuttons Are Located N ear the Equipm ent
W hich They R egulate
ra rely v a r y m o r e th a n 3 p er cen t. T h e load fa c to r o f th e p la n ts, b ased on th e m o n th ly fifte e n -m in u te d e m a n d s and k ilo w a tt-h o u r e n e r g y c o n su m p tio n , is b e tw e e n 4 0 an d 5 0 p er c e n t d u r in g th e w h o le y e a r . T h e m a x im u m d e m a n d o f th e s e p la n ts is a p p r o x im a te ly 200 k w . p er lOO to n s o f p la n t c a p a c ity . T h e k ilo w a tt-h o u r s p er to n o f co a l p a sse d th r o u g h th e p la n t is b e
tw e e n 1.5 an d 1.9 th r o u g h o u t th e y e a r . A ll o f th e s e fig u r e s a re in flu e n ced , o f co u r se , b y th e n u m b er o f o p e r a tin g h o u r s, o r, in o th e r w o r d s, by
th e m a rk et fo r coal.
F o r m e te r in g a n d co n tr o l p u r p o se s th e c o m p o n e n t p a rts o f th e p lan t sh o u ld be o p e r a te d fr o m d iffe r e n t c ir c u its. T h e p la n t n a tu r a lly d iv id e s it s e lf in to th e fo llo w in g d i v i s i o n s : (1) p u m p in g , (2) m ech a n ica l d r y in g a n d slu d g e r e c o v e r y , ( 3 ) w a sh in g ,
( 4 ) lo a d in g an d m ix in g clea n coal, ( 5 ) d u m p in g o f raw co a l, (6) tip p le o p era tio n , ( 7 ) h e a t d r y in g , (8) s c r e e n in g and siz in g , an d ( 9 ) m is c e lla n e o u s.
E c o n o m y w o u ld se e m at first to d ic ta te th a t th e m eters, s w itc h e s , and c o n tr o ls fo r th e s e se v e r a l s u b d iv isio n s s h o u ld b e se t up in s id e th e p la n t or c lo s e ly attach ed to it, bu t th is lo c a tio n in se v e r a l in s ta n c e s h a s p ro v ed d isa d v a n ta g e o u s, b e c a u se o f v ib r a tio n , m o istu r e , d u st, fire risk , a c c id e n t h azard , in crea sed in s u r a n c e r a tin g s, an d th e n e c e s s ity f o r p la n t c h a n g e s.
In fu tu r e , th e d a n g e r s o f ' o il c ir c u it b rea k ers m a y n o t h a v e to be fa c e d , fo r th e r e is a d e fin ite tren d to w a rd a ir-b rea k o v e r lo a d circ u it break ers. W it h th e s e , so m e o f th e d is a d v a n ta g e s o f a s u b s ta tio n w ith in th e str u c tu r e a r e o v e r c o m e ; n e v e r th e le s s , b e st p r a ctice d ic ta te s th a t th e su b sta tio n b e lo c a te d a t a p o in t r e m o te fr o m th e m a in p la n t, b e c a u se o f th e c o n sid e r a tio n s a lr e a d y m e n tio n e d .
July, 1931 — C O A L A G E 347
I f a ir-b rea k fe e d e r sw itc h e s a re u sed , tr a n s fo r m e r s w ill b e t h e o n ly o il-c o n ta in in g e le c tr ic a l d e v ic e s n e e d e d ab ou t th e p la n t, an d a s th e n u m b er o f th e s e is lim ite d , an d a s th e y m a y b e read i y in sta lle d o u t o f d o o r s, th e y c e a se to be a n y real h a z a r d ; th u s th e d a n g er o f a fire fr o m th e ig n itio n o f o il u sed w ith ele c tr ic a l e q u ip m e n t is a lm o st e n tir e ly e lim in a te d .
S e p a r a te m e te r in g o f th e m a in b ra n ch c ir c u its h a s p r o v e d a v a lu a b le aid to e c o n o m y . T h is m e te r in g sh o u c c o n s is t o f a p e r m a n e n t w a tt-h o u r m eter w ith a m a x im u m -d e m a n d in d ica to r to g e th e r w ith p ro p er m eter p lu g s or s w itc h e s fo r g r a p h ic a lly d e
te r m in in g th e p h a se c u r r e n ts and k ilo w a tt lo a d b y m e a n s o f p ortab le in str u m e n ts. T h e p u r p o se is to e lim i
n a te th e c o st o f se p a ra te in d ica tin g m e te r s fo r each o f th e fe e d e r s and to p r o v id e su fficien t g r a p h ic in s tr u m e n ts to b e u sed o n th e c ir c u its w h en p erio d ica l te s ts a re m a d e. _
H o w e v e r , th e m a in in c o m in g panel sh o u ld b e e q u ip p ed w ith a n in d ic a tin g a m m e te r a n d th e f o llo w in g g ra p h ic in s tr u m e n ts : w a ttm e te r , v o ltm e te r , r e a c tiv e k v a . m e te r , a n d a w a tt-h o u r m e te r w ith a m a x im u m d em a n d a t
ta ch m en t. A r e a c tiv e k va. m eter is m u ch m o re d e sir a b le th a n a p o w e r - fa c to r m e te r , b e c a u se it n o t o n ly p r o v id e s p o w e r -fa c to r in f o r m a tio n but g iv e s a d ir e c t in d ic a tio n o f th e reac
tiv e c o m p o n e n t o f th e lo a d .
I n m o d e r n p la n ts th e tr e n d is to p u t o n th e sw itc h b o a r d fe w e r o f th e u n n eed ed in d ic a tin g ty p e m e te r s and
o f th e le s s fr e q u e n tly u sed d e v ic e s , and in ste a d p r o v id e m e a n s fo r p o s i
tiv e ly p r o te c tin g th e c ir c u its and e a sily ch e c k in g th e lo a d an d tr ip p in g m e c h a n ism , so a s to be su r e a t all tim e s th at th e p o w e r r e q u ir e m e n ts a ie k n o w n an d th a t th e d e v ic e s fo r p r o tectio n w ill n o t fa il o f th eir p u rp o se.
S ta n d a r d s fo r th e v o lt a g e o f p rep a - r a tio n -p la n t e q u ip m e n t h a v e b e co m e m o re or le s s fix e d . B e c a u s e th e m o to rs o f th e la r g e s t p r ep a ra tio n p la n ts u su a lly h a v e n o t e x c e e d e d 100 h p ., it h as b een fo u n d th a t 4 4 0 - v o lt , th r e e - p hase, 6 0 -c y c le c u r r e n t, w h ic h iff h ig h ly d e sira b le fo r m o to r s o f 1 hp . u p w ard , fills all r e q u ir e m e n ts.
B e c a u se o f th e fa v o r a b le sta r tin g c o n d itio n s o b ta in ed fr o m th r e e -p h a se 4 4 0 -v o lt m o to r s, th e y a r e to b e p r e fe r r e d to s in g le -p h a s e m o to r s e v en w h e r e th e s e are o f sm a ll s iz e . H o w
ever, w h e r e th e m o to r s a re o f le s s ca p a city th an 1 h p ., s lig h t m o istu r e so m etim es p resen t m a k e s 220- or 110- v o lt m o to r s p r e fe r a b le , e sp e c ia lly th e la tter. T h e 4 4 0 -v o lt, th r e e -p h a se m o to r in siz e s sm a lle r th a n 1 hp . is difficult to in s u la te a d e q u a te ly and m ay b e g r o u n d e d or s h o r t-c ir c u ite d .
F o r certain c o n d itio n s o f se r v ic e th e g rea ter fle x ib ility a tta in e d b y th e u se o f m etal w ir in g tr o u g h is o f g r e a t v a lu e. T h is is p a rticu la rly tru e w h e r ev er rig id iro n c o n d u it w o u ld ren d er d ifficult th e a d d itio n o f w ir e s in a g iv e n sectio n , or th e ta p p in g o f th e cir c u its a t a later date.
J u n ctio n b o x e s sh o u ld b e p r o v id e d in v a r io u s lo c a tio n s o n c o n d u it r u n s,
a s it is m u ch e a sie r to e x te n d and ru n o u t b r a n ch es fr o m su c h b o x e s th a n to break in to th e r ig id c o n d u it fo r th is p u rp o se. S u c h b o x e s a lso o b v ia te th e n eed fo r p u llin g lo n g s e c tio n s o f w ir e a ro u n d b e n d s an d fit
tin g s and en a b le th e w o r k m a n to m a k e m o r e s a t is f a c to r y c o n n e c tio n s to th e w ir in g .
F o r lo c a tio n s w h e r e c h a n g e s, a d d i
tio n s , an d im p r o v e m e n ts a re to b e m a d e in th e e le c tr ic e q u ip m e n t, m etal w ir in g tr o u g h s and fittin g s are r a p id ly b e c o m in g a v a ila b le . W it h th e m m a n y c ir c u its can b e in sta lle d in a s in g le tr o u g h s y s te m , w h e r e a s w ith r ig id c o n d u it se v e r a l ru n s w o u ld be n e c e ss a r y . A n o th e r a d v a n ta g e o f m e ta l w ir in g tr o u g h s is th a t m o istu r e in th e s y s te m ca n b e r e a d ily d ra in ed .
W h e r e ir o n c o n d u its p a ss th r o u g h c o n c r e te flo o rs or b in s an d w h e r e , t h e r e f o r e , w a t e r . m a y c o m e in c o n ta c t w ith th e p ip e s, th e y sh o u ld be g iv e n a c o a tin g o f tar or a sp h a ltu m . F o r th e sm a lle r s iz e s in g le -c ir c u it lin e s c lo s e to m o to r s or c o n tr o ls th e u s e o f th r e a d le ss c o n d u it fittin g is g o o d p ra ctice.
A t r ig h t-a n g le d tu r n s in th e co n d u it s y s te m s w h e r e fittin g s a re u se d , it is fr e q u e n tly a d v is a b le to u s e a T ra th er th a n an L . T h is a r r a n g e m e n t p r o v id e s fo r an e x te n s io n o f th e c o n d u it sy s te m fr o m th e o p e n e n d o f th e T fittin g w ith o u t d is tu r b in g th e o r ig in a l c o n d u it run. T o fa c ilita te th e p u llin g o f w ir e s , lo n g - s w e e p e lb o w s sh o u ld b e u se d , so as to a v o id sh a rp tu r n s in th e c o n d u it sy s te m .
Fig. 3— D rives for H eat D ryer
348
C O A L A G E — V ol.36. No.7
A T T A C K S A N D R O C K
+ V^ith Duckbills and Rockcutters
T
W O rock tunnels have been driven recently, one by the Colony Coal Co., at Dines, W yo., an d one by the U nion Pacific Coal Co. a t W in to n , in the sam e state, in w hich duckbills w ere used to push th eir w ay into th e rock and fo rw ard it to shaking conveyor pans fo r loading. A t the first operation, it was decided th a t a cross-m easure tunnel should be d riv en to connect the s u r
face tra m w a y w hich serves m ines 8, 9, and 10 w ith a point on Seam No. 15.
D ecision w as m ade to excavate the tunnel to th e co rre ct g ra d ie n t by c u t
tin g the rock on the floor level w ith a coal-cutting m achine. F o r th is p u r
pose a 16-in. feed w as placed on a G oodm an 12A A m in in g m achine, the feed being cut in h alf by th e use of a sheave on th e jack pipe and the end of the feed rope being b ro u g h t back to a hook on the side o f th e machine.
T h e c u tte r b a r w as cut off to a 5-ft.
length.
By the use of a special steel bit fu rn ish ed by the G oodm an M an u fac
tu rin g Co., beds o f shales and sand
stone w ere cu t w ith o u t difficulty.
1 wo lim estone beds w ere encountered each ab o u t 2 ft. thick. T hese could not be cut by the m achine. T he total length o f th e tu n n el w hen completed proved to be 570 ft., and because it was know n th a t it w ould be o f about that length, it w as decided to drive it w ithout laying trac k , though 570 ft.
is too g re a t a distance over w hich to operate a com bination o f one shaker j-onveyor and a duckbill. E xperience as show n th a t th e distance should
T u n n l ^ aCta f O fr ^ r ti0 le e n tttlecJ “ N ew R o ck D riv en k?. D in e s a n d W in to n , W yo., E quinnprt .o f S h a k e r C o n v e y o rs befo re th o tp D u c k b ill L o a d e r s " a n d re a d I n s t i t u t e % R o c ,k y M o u n ta in C o a l M in in g
• P h £ ? ’ J u i i e 4- 5’ D e n v e r, Colo.
R o c k S p ri
^ n^ . ’0
U n io n P a c if ic C o a l Co., W y o U P erintei’d e n t ’ C o lo n y C o a l Co., D ines,Wnton?rW yodent’ Uni0n Pacifl0 CoaI Co"
By C. E. SWANN*
W. D. BRYSONt and T. FOSTERt
not exceed 300 ft. C onsequently, a shaker conveyor, w hich did not, of course, carry a duckbill, w as installed behind the other shaker to receive the rock as delivered and fo rw ard it to destination.
Rock was not only tra n sp o rte d to the m outh of m ine but delivered over the side o f the hill, th u s entirely elim i
nating the need for m ine cars. T he total length o f the rear conveyor w hen fully extended w as 400 ft." m aking the total tran sp o rtatio n distance 700 ft. T he pan lines w ere suspended from the ro o f by the use o f £-in.
chains. T h e g rad ie n t o f the p an line ranged from 1 to 2 p er cent against the travel of the rock, but the tunnel itself was driven level, the dim ensions Being 8x12 ft. I t was tim bered fo r about half its length w ith 10-in.
wood crossbars on 5-ft. centerg and top lagging.
A ir was furnished by a Jeffrey blow er fan equipped w ith 12-in. V en- tube discharge line suspended on the roadw ay tim bers. T he day sh ift and night sh ift each consisted of tw o men who cut, drilled, and blasted the rock and loaded it w ith the aid of the equipm ent stated, tim bered the tu n nel. and extended the shaker tro u g h s
and a ir tubing. A s no rock cars w ere used to haul the rock, tw o m en con
stitu ted each sh ift and they averaged l-h ft. o f tunnel apiece. T h e cost w as as follow s:
Per
Total Foot
Rockwork, labor o n ly... $2,433.96 $4 27 Timbering (230 ft.) labor o n ly 362.88 \ . 28 Total labor cost per foot tim bered... $5.55
T h e o th e r tunnel, located a t W in ton, w as d riv en as p a rt o f the connec
tio n betw een the tipple an d a new m ine opening. T h is tu n n el w as to cut th ro u g h tw o ro u n d in g projections on the outcrop and to come to light fo r a sh o rt distance betw een these tw o salients. T h e g rad ien t of the tunnel, w hen com pleted, was to be ^ p e r cent in fav o r of the loads.
T he n o rth half of the tunnel, which will be term ed Section A , w as driven first and kept in the coal seam , w hich was 6^ in. thick, but u n fo rtu n ately , the g rad ien t proved not to be regular, though the level o f th e coal seam in the cen ter o f this section w here it had been intersected by an old air- course was, stran g e to relate, alm ost exactly on the tru e g rad ien t. Betw een
July’ 1931 — C O A L A G E
349fr o m a p o in t a b o u t 10 in . b ack o f th e e d g e to a p o in t fa r e n o u g h a h ead o f th e s h o v e l to a llo w it to b e tu r n e d up . T h u s th e ste e l rib a cted a s a g u id in g sh o e to ra ise th e s h o v e l o v e r an y o b str u c tio n . T h e r a tc h e t d o g s a lso w e r e se t ju s t s n u g e n o u g h th a t th e y h eld u n til s o m e th in g u n u su a lly h a rd w a s e n c o u n te r e d , an d th e n th e y w o u ld slip an d sa v e th e e q u ip m e n t fr o m d a m a g e.
A s far as co u ld b e a r r a n g e d , th e c y c le o f o p e r a tio n s w a s a s fo llo w s : T h e n ig h t c r e w , c o n s is tin g o f a ra tch et m an , lo a d in g -e n d m a n , an d d r iv e r , w o u ld d rill, sh o o t, a n d c lea n u p th e co a l a n d a ls o th e ro ck th r o w n o u t b y th e to p r o w o f ro ck h o le s . I f p o s s ib le , th e y sta r te d to d rill th e b o tto m h o le s a lso .
T h e d a y c r e w c o n s is te d o f ra tch et m a n , fa c e m a n , lo a d in g -e n d m a n , an d d r iv e r . T h e y fin ish e d th e d r illin g o f C
A
I kv n .ifk b ill in Sidetrack a t W in ton ; N o te th e b o tto m rock , sh o t th e h o le s , Fig. 2- H a n d h n g Sandrock b>. Duckb^
^ c ic a n e d u p th e d is lo d g e d m a teria l, an d se t th e tim b e r . T w o m e n in an i „ f c ,,rr:nn A a n d th e en d s, w e r e p laced on 5 - f t . c e n te r s a n d w e ll a v e r a g e 0 f 4 h r. w o u ld p la c e o n e lagge<l on to p . B e c a u se o i th e m - ) 2- f ,.“ w o o d c ro ssb a r o r a 1 7 -f t. s te e Ï ' »1 S f ^ a s b ad a m i req u ired ab ility to secu re th e r o o f a n d m a k e sM I n th e w id e p „ t „ ( , h e tu n n e l A s th e roo < sectio n of the the place safe enough fo r a m echani- th e e n tjre j ob 0 f loading 68 cars of close im 1 hand. W h en cal loading crew , the first 60 ft w as m uck an d in sta lling one steel tim b er tu n n e ' ' Pnd o f Section A had driven by hand. A s soon as m echam - t g pe r f0rm ed in tw o 8 -hr. sh ifts, th e n o r t h e d of b ^ o n ^ v cal loading w ith duckbills w as sta rte d , T h e ^ m oved readily along the>een c i\ - duckbill loader w as an attem pt w as m ade to cut the sane - convevor, b u t th e coal a t tim es w as equipped ‘ extension. rock w ith a m ining m achine, b u t th e ft d fine th a t it trav eled w ith
" " A m Î f i t m a ch in e w a s ^ r o v id e d to rock w a s to o h a rd so a r o w o f d n - in su ffic ie n t s p e e d.
a t thp rnal and th e n o r th e r n h o le s on th e g r a d e lin e w a s s u b s ti j n ¿[riving th e tu n n e l th e sh a k er e n i o f S e c tio n \ w a s e x te n d e d so u th tu ted . T h e s e h o le s w e r e h e a v ily sh o t. c o n v e y o r w a s s e t u p tw ic e , th e first u n til it m e t th e so u th e r n e n d o f th e T h e d u ck b ill w a s fo u n d to w o r k su e - s e t . u p d r iv in g 3 l5 f t . an d th e se c o n d sa m e se c tio n T h e n th is se c tio n w a s c e s s fu lly , m a k in g U s o w n floor a s
^
f t _ T h e c o s t o f se c tio n B w h .c h t r a d e d b-v b r u sh in g th e to p an d sh o o t- it a d v a n ced . w a s la r g e ly 111 rock a n d 6 9 0 ft lo n g , in * u p th e b o tto m till a tru e g r a d ie n t T h e sh ak er c o n v e y o r s w e r e s u s - w a s as in th e a c c 0 m p a n y in g tab le.s ? p en d ed fr o m th e r o o f w ith f - m .
w a s e s ta b b sh cd . d r iv . c h a in s ; th e d u ck b ill, a ft e r b e in g cu t C ost of Section B, T ram w ay Tunne , h J s f c S A " L o S r S t i o n . B . down' to a l » g th o f 3 0 in ., w a s w |8e d A , D , « , . w , o . ^ ^ w a s d r iv e n on a tr u e g r a d ie n t fr o m to th e ratch et pan an d th e ra tch et p an Dri]lingandbl ü ... $2.65 on e end to th e o th er, a n d h e r e th e bars w e r e e x te n d e d d o w n to th e e n d 6; „
c o a l r o l l e d e v e n m o r e th a n in S e c tio n o f th e d u ckbi l w h ic h j>vas f u t oiso
\ causin«- th is se c tio n t o b e p r a c ti- str e n g th e n e d by w e ld in g a — c a lly a rock tu n n e l fr o m e n d to en d . a lo n g its cen ter, th is rib e x t e n d in g Total cost...
T h é coal w a s s o s o f t th a t it co u ld n o t b e su p p o rted w ith o u t fa lls , e v e n a ft e r
th e tu n n e l se c tio n w a s r e m o v e d , a n d
. .‘ Ti mber cabbing
e v en th e rock o v e r th e c o a l p ro v ed ]Z"~: ' ...
s o w ea k a n d b ro k en th a t it w a s c o n -
.
tro lled w ith d ifficu lty . _ C o n se q u e n tly ™ *» « «» «t--- ^ th e tu n n el v a ried in h e ig h t fr o m 8 to
14 ft.
T h is se c tio n w a s d r iv e n 12 ft. w id e fo r 3 5 0 ft . a n d w a s th e n w id e n e d to 18 ft. fo r th e r e m a in in g 2 9 0 ft., w h ic h le n g th w a s to se r v e a s a la n d in g at th e to p o f th e m a in slo p e o f X o . 1 m in e , w h ic h , lik e th e co a l sea m , d ip p ed at a ste e p a n g le . F o r th e 3 5 0 ft ., 1 2 -ft.
w o o d cr o ssb a r s w e r e u se d fo r s u p - s i
1 excrete block,
life.Rock
p o r t, b u t, a ft e r th e w id e n in g to 18 f t ., 1 7 -ft. steel I -b e a m s 10 in . d eep w e r e in sta lle d . 5 -in . ste e l H -b e a m s a c tin g
a s le g s . A ll tim b er an d ste e l s e t s F ig. 3—Cross-Section of Sidetrack
-Omm
350 C o A L A G E - Vol.36. N o J
H Y D R A U L IC B A C K F IL L IN G + A s Europe Practices It
H
y d r a u l i c backfilling, which in the a n th racite region of P ennsylvania is generally designated “ flushing,” has been known to m ining engineers fo r about 60 years. D u rin g at least fo u r decades it has been the su b ject of m uch con
tro v e rsy and speculation, here and abroad. Som e engineers regard h ydraulic packing m erely as a sec
o ndary item in th e com plete problem of ro o f control and su b sid en ce;
others give it an im p o rta n t place in a g ro u p o f innovations w hich may ultim ately lead to sa fe r and m ore economical m ining m ethods.
G enerally speaking, th e first view
point is held th ro u g h o u t the a n th ra cite region o f P en n sy lv an ia, while the la tter opinion is typical of cu rren t th o u g h t in coal-m ining circles on the continent o f E u ro p e.
A lthough hy d rau lic backfilling was originated and first b ro u g h t to prac
tical use in the a n th ra cite field, it m ust be ad m itted th a t it has gained the increased a tte n tio n of coal-m in
ing engineers th ro u g h o u t the world m ainly fro m its large-scale adoption in E u ro p e an m ines.
O ne of the earliest installations for backfilling w as th a t o f the Dodson Colliery, P lym outh, P a., w here S u p erin ten d en t D avis introduced the practice in 1891. H is purpose, how ever^ seems to have been prim arily to dispose of th e silt a n d even the sm aller grad es o f coal, w hich at that time could n o t be m arketed. T he rapid accum ulation o f such m aterial, together w ith slate and o th er refuse, made necessary th e p u rch ase of large surface areas on w hich expensive refuse h andling equipm ent had to be built. I t w as in the search fo r a rem edy fo r th is situ atio n th a t the novel idea of flushing em pty u n d e r
ground cham bers w as conceived. T he
By HENRY A. DIERKS
M
ining Engineer
S tu a r t,
James & Cooke, Inc.
New York City
use of flushing in connection w ith ro o f su p p o rt came only as a result and not as a fo re ru n n e r of the actual application. A fte r a large q u an tity of silt had been flushed into the em pty cham bers, it w as observed th at the subsidence w hich the cru sh in g of room pillars had h ith erto caused w as conspicuously absent in the backfilled area.*
Because of its ability to m inim ize or even prevent subsidence, hydraulic backfilling arrested the atten tio n of E uropean m ining engineers when they were searching fo r a m ethod which would perm it the m ining of coal seams u n d er a densely popu
lated area, w here subsidence and dam age done to surface buildings w as n ot only costly but practically p ro hibited by law.
T he first application o f hydraulic backfilling in E u ro p e w as at a coal mine in U p p er Silesia and occurred in about the y ear 1900. Since then it has found steady and increasing favor throughout the continent o f E u ro p e, not only in m ines op eratin g u n d er built-up areas but also in m ines w ith thick seam s, w here a large p a rt of the pillar coal is likely to be lost if the seam is mined w ithout backfilling.
In the 30 years of its application to E u ro p ean coal m ining, the h y d ra u lic packing m ethod has b ro u g h t about distinct changes in m ining system s, due to realization of the fact that complete extraction o f the coal can be attained only w hen the operations o f m ining the coal and backfilling th e
• I t a p p ears from p. 99, B u lletin N o . 245, o f th e U. S. B u reau o f M ines, “M in in g o f T hin C oal B e d s in th e A n th r a c ite R egion o f P e n n sy lv a n ia ," b y D. C. A sh m ead , th a t s iltin g w a s first p racticed in th e la te r s i x tie s and in th is in sta n ce fo r th e e x p r e ss purpose o f su r fa c e su p p ort. F o r m a n y y e a r s no fu rth er u se o f th is m ethod o f su p port w a s attem p ted.
spaces are kept in p ro p er relation, the one to the other. H erein lies the d is
tinction betw een the developm ent and application of hydraulic packing in A m erica and in E urope.
T h ro u g h o u t the P ennsylvania a n thracite field, flushing is generally con
sidered only as a secondary, o r a u x iliary, m ining operation, and em pty cham bers are backfilled only to p re vent, o r reduce, ro o f caving and sub
sidence, to stop dangerous squeezes, o r a t the m ost to recover a p ortion o f the pillars. U sually, no attem p t is m ade to combine coal ex tractio n and flushing into a synchronized operation.
H y d rau lic backfilling, h ere as well as abroad, consists essentially in the m ixing of the solid packing m aterial w ith w ater and conducting the m ix tu re th ro u g h the pipe line fro m the su rface to the cham ber to be back
filled. T h e re the solid m aterial is deposited, w hile the w ater d rain s off and is pum ped back to th e su rface.
W e can th erefo re classify th ree m a jo r phases of the process, each w ith its p articu lar requirem ent of m achinery and e q u ip m e n t: ( 1 ) M ix in g w a te r in su rface plant w ith m aterial to be packed; ( 2 ) conducting m ix tu re th ro u g h pipe lin e; ( 3 ) deposition of backfill underg ro u n d .
A n attem pt will be m ade to give in b rief form some o f the m ore im por
ta n t im provem ents w hich have been sought or accom plished in th e appli
cation of h ydraulic packing in E urope, and in pointing out the various developm ents o f th is process on th at continent. D ifference in m ethods is due to the v aria n t condi
tions of different m ines and to the
July, 1931 — C O A L A G E 351
m any and vigorous req u irem en ts of th e several m ining law s, also partly to diverging view s of m ining men.
( 1 ) M ix in g o f P acking M aterial and D esign o f S u rfa c e P lant— T h e m echanical co nstruction and a rra n g e m ent of the v ario u s devices fo r the p rep a ratio n o f th e solid packing m a
terial and its p ro p e r m ix in g w ith w a te r show m uch v a riatio n fro m mine to mine, due to local conditions and m aterial available.
T h e m aterials used fo r hydraulic backfilling can be arra n g e d in a scale o f preference, at the top of which
unquestionably sta n d s q u artz sand in lines. F o r long lines w ith m any bends its p u re st form . Sand has the g re at and rises, the biggest pieces of pack- advantage th a t it can be used w ithout ing m aterial should n o t exceed 11 previous crushing. W hen rock, slate,
or refu se are to be used as a packing m aterial, a cru sh in g and conveying plant becom es necessary, and this greatly increases the cost, l h e sizes to w hich rock, refu se, o r ash clinkers are to be b roken depends on the diam eter and the length of the pipe line, as well as on the w ater pressure available. T h e la tte r, o f course, is fixed by the vertical distance betw een the su rface and the seam w hich is to be backfilled.
E x p erien ce covering a period of m any years has show n th a t m axim um sizes from 2 to 2,\ in. can be flushed th ro u g h short and n early stra ig h t pipe
Fig. 2— Plant for Flushing Sand, Ashes and R efuse A.. Open B in
B . M onitor C. R o ta r y Screen
D . R o ller M ill on P e r fo r a te d M at E . C hannel L e a d in g to F lu s h in g P ip e
in.
In E urope, w herever crushed m aterial is used, the m aterial flushed rarely exceeds in diam eter the sizes stated.
W h ere it is available in large q u an tities near the mine, sand is used e x clusively as packing m aterial. I t is brought to the m ine fro m the sand pit in special dum p cars. S an d can be flushed w ith less w ater th a n any o th e r backfilling m aterial. It gives a rela
tively incom pressible su p p o rt, and perm its the w ater to d rain off rapidly.
O nly few m ines, how ever, are in the enviable position of having a suffi
ciently large sand deposit in close proxim ity. M ost m ines are com pelled
Buche+
elevator
F ig . I— Com plete Flushing Plant
A . Open Sand B i n ; C a p a city C u.Ft.
B . M onitor, W a te r P r e ssu r e 22o Lb.
C. R o ta r y Screen D . F u n n e l W ith G ra tin g E . W ro u g h t-Iro n F lu s h in g P ip e s F . D istrib u to r a t L a n d in g G. R o ek -a n d -R e£ u se B u n k er H . M a g n et fo r T ram p Iron K . H am m er M ills
L. B u n k er fo r C rushed M a teria l
Valves
Pipe dtam. 6*
to use a m ix tu re o f various packing m aterials. T h e kind of m ix tu re used depends on w h at m aterials can be m ost econom ically obtained, on the experience gained in the use of certain m aterials, o r on the ju d g m en t of the engineers as to the resu lts likely to be derived from the use of desig
nated m ix tu re s u n d e r certain con
ditions.
In a certain m ine, a m ix tu re com
posed of equal volum es of sand, ashes and w ashery re fu se gave a sa tisfa c to ry backfill. E v en u n d er the heaviest
p ressu re th e m aterial yielded only 12 p e r cent o f its original volum e.
T h is could have been su rp assed only by a backfill m ade solely o f sand, w hich generally w ill lose no m ore un d er com pression than 5 p er cent of its fo rm e r bulk, but w hich in this case w as not available in sufficient quantities o r a t low enough cost. If only re fu se and ashes had been used, the backfill w ould have sh ru n k at least 25 to 30 p er cent. T h e sand fills th e m inute spaces betw een the irre g u la r pieces o f slate an d clinkers and gives the backfill consistency and stren g th .
W h e re different m aterials are used fo r flushing, the in g red ien ts are rarely m ixed b efo re being b ro u g h t into contact w ith w ater, b u t are fed into the pipe line at differen t points, the sand being first m ixed w ith the w ater and the o ther constituents added later.
In som e E u ro p ean coal-m ining areas, such as the R u h r d istric t in G erm any, no sand is available as packing m aterial. C ru sh ed rock, silt, slate, ashes, and re fu se fro m the w ashery are used instead. T h ey re quire an elaborate p rep aratio n plant and because they are flushed in m ax
im um sizes th eir d istrib u tio n con
sum es a large q u a n tity of water.
Som e of these m aterials ren d er the w ater acid, th u s co rro d in g th e pipe lines and pum ps. T w o typical instal
lations fo r flushing a m ix tu re o f sand
and crushed m aterials a re show n in accom panying F igs. 1 an d 2.
R e fe rrin g to F ig . 1, it will be noticed th a t the sand is dum ped into an open bin, the floor o f w hich has a pitch of 10 deg. T h is bin generally is built o f concrete o r brick. T h e floor is covered w ith h ard glazed tile o r sheet steel. F a cin g the open side of the bin are m ounted one o r two m o n ito rs w hich supply a stream of w ater fro m c en trifu g al pum ps at a p ressu re of 150 to 225 lb. per sq.in.
Thus the sand is th o ro u g h ly m ixed w ith the w ater, as in hydraulic m in
ing. T h e sem i-liquid m ix tu re flows to w a rd an open channel leading to the vertical pipe line in the sh a ft. T o p rev en t pieces of wood, large stones, o r o th er u n desirable m aterial, which m ay clog the pipes, fro m en terin g the pipe line, the m ix tu re is conducted
Fig. 3— Elbow and U nderground Flush ing Pipe
E lb o w o f E c c e n tr ic C ross Section W ith G u id in g R ib a n d S ig n a l H o le s. R ig h t : R e v e r sib le O val P ip e o f T w o R ein forced
¿segments "Welded T o g e th er
th ro u g h a slow ly revolving ro tary screen. H e re all such m aterial is retained and occasionally picked out by hand.
C rushed rock and w ashery waste are introduced into the sand stream b efore it en ters the ro ta ry screen.
T he crushed m aterial comes from the cru sh in g plant, w hich usually consists o f a com bination of g yratory crushers and h am m er mills. A ro ta t
ing d istrib u to r u n d er the b u n k er gate insures a constantly u n ifo rm feeding of crushed m aterial into the flushing cu rren t. This feed in g device is ad
justable so th a t autom atically any percentage m ix tu re can be obtained.
A dditional w a te r is allow ed to flow into the channel w h ere necessary to assure sm ooth ru nning. A few m in
utes before and a fte r each flushing operation w a te r is sent th ro u g h the pipe line to w ash aw ay any solid m aterial w hich m ay have settled in
e elbows and valves o r a t other points.
T he funnel connecting the open channel w ith the vertical pipe line is considered an im p o rtan t p a rt o f the plant. It is shaped and placed in such a fashion th a t the flushing c u r
re n t will en ter th e pipe line w ithout d raw ing in any air, th u s elim inating a ir knocks, w hich m ay prove in ju rio u s in long pipe lines w here the p ressu re is enorm ous.
Fig. 2 depicts a flushing p lan t of sm aller capacity than th a t in F ig . 1 and one designed fo r handling a m ix tu re composed o f clayey sand, ashes, and w ashery refu se. T h is kind of plant generally is favored w here the flushing m aterial is n o t taken th ro u g h a pipe line in the sh aft, but is con
ducted to some d istan t p oint w here it is fed th ro u g h a borehole.
( 2 ) C onducting M ix tu r e T h ro u g h P ipe L in e— In itial and m aintenance cost of the pipe line are the biggest single cost factors in the econom y of hydraulic packing. I t is fo r th is "rea
son th a t no o ther u n it o f the p lan t has received m ore attention o r has been subjected to m ore changes and im provem ents. E x p erim en ts and trials covering m any years have been m ade w ith pipes of all shapes and m a te ria ls ; y et the problem is still fa r from being solved satisfactorily.
F rom o rd in ary w ro u g h t-iro n or cast-iron pipes, the search fo r better conduits progressed to pipes m ade of wood, bronze, and m anganese steel.
A s none of these m aterials reduced abrasion sufficiently to w a rra n t the higher initial cost, steel pipes lined w ith glass, rubber, porcelain, or te rra cotta w ere tried, but soon discarded.
In every case the increased life of the pipe line could not be justified by the increased cost, and finally w ro u g h t- iron and cast-iron pipes regained a predom inant position.
T h ro u g h o u t all these costly ex p eri
m ents it was found th a t the hardness of the m etal was not the sole d e te r
m ining factor in abrasion, but that the m icroscopic stru ctu re of the pipe
w as an im portant elem ent in its e x pectancy of life. F o r th is reason w ro u g h t-iro n pipes o f a hom ogeneous s tru c tu re w ere found to be m ost eco
nom ical o f any in w ith stan d in g a b ra sion. T oday, the vertical p o rtio n of the pipe line in nearly every well- designed flushing p lan t is equipped w ith w ro u g h t-iro n pipes of the seam less type, and cast-iron pipes are used u n d erg ro u n d , because o f th e ir low er cost.
I t is obvious th a t elbows and bends a re su b ject to m ore p ressu re and a b ra sion th an the stra ig h t p o rtio n o f the pipe line. F u rth e rm o re , unlike the stra ig h t portions o f the pipe, they-, cannot be tu rn ed to p rev en t the exces
sive w ear th a t m ay occur a t any one spot. E lbow s m ust, th e re fo re , be considered as the w eakest points in a pipe lin e ; they m ake the carriage o f silt in pipes u n d er heavy p ressu re dangerous. O nce they are w o rn to such an ex ten t th a t the w ater p re s
su re exceeds the u ltim ate stre n g th of the m etal in the th in n est portion, they not only crack but b u rst w ith hazard to hum an life. T h e sudden b reaking of an elbow m ay cause m uch dam age to the mine, as the flushing m aterial will flood o r even choke the gangw ays b efore the accident is noticed.
T o overcom e the in h eren t w eakness o f the o rd in ary elbow, the thickness o f the m etal has recently been in creased in th a t p a rt of the filling w hich is p articu larly subjected to abrasion. F u rth e rm o re , a lo n g itu dinal rib is provided inside the elbow to prevent the c u rre n t fro m acq u ir
ing a spiral m otion and to lead the g re a te r p art o f the solid m aterial along th a t portion of the wall w here the thickness is greatest.
In o rd er to have an indication w hen abrasion has actually reached the dan g er limit, a nu m b er o f small holes are drilled fro m the outside into the body o f the elbow to a given depth. A s soon as the m etal is w orn off to the deepest point o f any one of these holes, w a te r will seep th ro u g h , Fig. 4— Longw all M in in g W ith H ydraulic Backfilling
S/Flushing pipe line
J>- in nil i t i i i B f t M t t i i i w
[
-Mauic*ge rooo/ [
July, 1931 — C O A L A G E 353
pipe fine
F ig . 5 Sh ortw alï M ining W ith H ydraulic Backfilling
indicating' th a t the elbow should be replaced.
T hese sam e fe atu res, w hich were fo u n d to give excellent results in elbows, are now incorporated also in stra ig h t pipes. L o ngitudinal ribs are draw n into the pipes of the vertical pipe line in o rd e r to p rev en t the c u r
ren t from trav elin g in spirals. T h is provision reduces abrasion and causes the c u rre n t to travel w ith less resist- ance.
F o r the horizo n tal p o rtio n of the line u n d erg ro u n d , oval pipes w ith an increased wall thickness are claimed to give excellent service. T hey have gained m uch favor, because they are supposed to cause the flushing m ate
rial to travel u n ifo rm ly and w ithout turbulence. Such pipes have also an appreciably increased life, yet the a d ditional cost is small. T h e y are m ade by w elding to g e th er tw o tro u g h s w ith a w all thickness o f about § in. at either end of the vertical diam eter.
T o w ard the sides the thickness of the walls is g rad u ally reduced to £ in.
T h e m aterial used is a special hard S iem ens-M artin steel w ith an u lti
m ate stren g th o f 100.000 lb. p e r sq.in.
In service these pipes can be tu rn ed once, th u s doubling th e ir life.
A ctual figures as to the life o f a pipe line a re available but they van- over such a w ide ran g e th a t no g en
eralization can be safely attem pted.
C a refu l installation, stric t su p e r
vision and, still m ore, th e kind of m aterial flushed d eterm ine largely the life o f a pipe line.
A s to the pipe diam eter, it seems
alm ost universal practice to use a 6-in. pipe fo r the vertical p o rtio n of the pipe line and an 8-in. pipe fo r the horizontal o r inclined portions. In a certain mine, w here the en tire pipe line, vertical and horizontal, con
sisted of 6-in. pipes, th e ratio of solid m aterial to w ater w as 1 to 5.
A fte r the horizontal line w as built of 8-in. pipes, this ratio could be m ade 1 to 3, effecting an appreciable saving in pum ping costs.
M ost m ines, especially those which adopt a strict correlation of m ining and flushing, have tw o pipe lines in
stalled in the sh aft, one of w hich is considered a reserve. T h e d istrib u to r at the end of this dual pipe-line in
stallation is of special im portance and should be designed fo r long service.
Its lower part, w hich the flushing cu r
re n t strikes, is subjected to heavy abrasion. T h e re fo re it is made w ith a bulge w hich can be filled w ith an abrasion-resisting m aterial. A spe
cial cement producing an extrem ely hard filler generally is used fo r this purpose and is economical, as it can be easily repaired or replaced.
Fig. 6— M odified Room -and-Pillar System W ith H ydraulic Backfill
(3 )
Deposition o f Hydraulic Back
fill Underground in Connection W ith Various Mining Systems—
F ro m a purely theoretical standpoint h y d ra u lic packing can be applied to any m ining system . T h e full advantages of th e process, how ever, are obtained only in operations w here backfilling and ex tractio n of coal a re m ade into synchronized phases of one single system .
I n E u ro p ean coal m ines, hydraulic backfilling has been com bined w ith long-face and shortw all m ining w ith a m arked degree of technical success and economy. A t the p resent tim e, how ever, it is considered m ost a d a p t
able to a m odified room -and-pillar system , of which it is m ade an in te gral p a rt and w ith w hich it is w elded into a system o f its own.
F ig s. 4 and 5 show diag ram s of the application o f hydraulic packing w ith long-face and shortw all m ining, re spectively. F ig. 6 depicts the m ore ideal practice of a m odified room - an d -p illar system com bined w ith h ydraulic backfilling.
’ T h e b a rrie rs to hold back the pack
ing are built of props to w hich chicken w ire and b u rla p are nailed.
W o o d planks generally a re too e x p en sive fo r b a rriers. W h e re slate o r rock from ro o f falls o r p a rtin g s are available, they are o ften used to build th e b a rrie rs w holly or in p a rt. S p e
cial care is taken to secure a tig h t backfill ag ain st th e ro o f, so th a t no treach ero u s crevices a re le ft there.
T h is is accom plished by poin tin g the end of the pipe line u p w ard an d let
tin g th e backfill a t all tim es slope to w ard the end o f th e pipe instead of aw ay fro m it.
In deep m ines and in those w here h y d rau lic backfilling is practiced on a large scale, the collection and p u m p
ing back of the w a te r becom es quite a problem and an item o f heavy e x pense. In facing this problem an e n tirely new packing process has been evolved in w hich instead of a c u rre n t of w ater, one of a ir is used to carry th e solid packing m aterial th ro u g h th e pipe line. P n eu m atic packing, its p resent developm ent and its fu tu re will be considered in a later article.
354 c: O A L A G E — V o l.36.. N o.7
