By W . SA U ER
Consulting E ngin eer L u dw ig sd o rf, K re is N eu rode, Germ any
Fig. 1—S iem en s-S ch u ckert L am p
T
H E thought that the hard working miner laboring under hazardous conditions should be provided with light facilities equal to those almost universally provided in industry is not new. England made a trial of electric incandescent lighting in the nineties, but the m anufac
turers of flame safety lamps fru s
trated the displeasing competition, alleging that the new method of lighting was not safe. Germany then conceived the same idea, and tests were made first in U pper Silesia and then in Lower Silesia at the Wenceslaus mine. T here may have been other installations also.
I t seemed easy to connect the lighting socket to an electric cable already installed in the mine and to insert a 25-watt incandescent lamp into the socket. This size of lamp seemed ample compared with that of the ordinary 2-volt portable lamp of 2 to 4-watt capacity.
But the test was a failure. Though the lamp burned clearly and steadily, one saw hardly anything, because the lamp made so much glare. Owing to the black, light-absorbing, surround
ings the illumination it gave was in
sufficient for vision.
A larger bulb increased the glare, and it became necessary to decrease the intensity of the light from the filament by using a suitable outer globe. Frosted-glass globes did not, however, hide the glowing filament;
consequently the light was not dis
tributed uniformly.
A rtic le e n title d "D ie B n tw lc k lu n g u n d P r a c tis c h e D u rc h b ild u n g d e r A b b a u b e le u c h - t u n g ,” p u b lis h e d In T e c h n is c h e B la e tte r , W o c h e n s c h r ift z u r D e u ts c h e n B e r g w e r k s - z e itu n g , 1929.
Enameled globes gave a smooth distribution at first, but not for long, for the rough surface of the enamel collected coal dust, rapidly rendering the globe generally non-transparent.
Only by the use of opalescent glass globes could 150-watt bulbs be intro
duced. Bulbs of this power gave the desired light at the face.
Fig. 1 shows the lamp and Fig.
2 a lamp with a globe not mad?
entirely of opal glass, that glass form ing merely a 2-in. ring around the lamp, and the rest of the glass being clear. This type of lamp elim
inates glare and yet has a high stand
ard of efficiency. T he lamp proved a success.
A system of flood-lighting provided for a longwall face, 525 ft. long in a 6-ft. seam on a 25 deg. incline may be presented (see Fig. 3 ). Setting
Fig. 2—Schanzenbach Lamp
the lamps 13.12 ft. (4 m .) apart, the number of lamps will be 40 and the power consumption 6 lew. In order that the installation may be made by unskilled labor, all connec
tions should be made detachable.
The transform er is connected with the main circuit and may be consid
ered stationary, as it will not have to be moved more frequently than once every one or two months, pro
vided the light cable is sufficiently long. The light-connecting cable be
tween the transform er and lighting feeder is detachable. T he cable is removed whenever the coal is drawn from the longwall face, which is at intervals of about two days.
To facilitate the work, the lighting cable is divided into detachable lengths 39 ft. (12 m .) long, it being easier to drag out these shorter lengths than to handle a single string of 525 ft. From each cable-section three detachable branch cables lead to the lamps. Fig. 7 shows one such lamp disassembled.
As the price and weights of the connecting plugs for the cable sec
tions were prohibitive, ordinary con
necting boxes without switches were adopted. By means of hoop-iron locks (F ig. 7) provision was -iade for locking the plugs so that they could not be unlocked except with the aid of a separate key kept by the chief electrician, who, was instructed not to unlock the plugs when the line was charged. Special plugs are now being designed with simplified lock
February, 1930 — C O A L A G E 97
ing devices by which the electrician can be relieved of this work. A second difficulty was found in p ro viding suitable fuses for the lamp cable because of its reduced gage.
L abyrinth branch plugs eventually were adopted, complying with the national electric code.
A t first, cable fuses were not pro
vided, as fuses were embodied in the lamp itself. T he fuse in the lamp case did not prove a success in actual operation, so a suitable cable fuse was soon developed. T he design en- ables the user to extend the length of the lamp cord, which is usually 3 ft., a convenient feature in mining service.
A t first, the lamp was protected merely by a cast-iron outer case (F ig . 1), but to protect the glass globe a strong wire guard was p ro vided. By using a sheet-iron body
(F ig. 8) the weight of the lamp was reduced from 13.8 lb. to 5.3 lb. The form er threaded glass globes were found to be unsuitable and were re
placed by globes with flanges. Guided by a desire to provide means whereby the lamp, in case of emergency, could be opened easily and quickly without the possible loss of small parts, the number of bolts and screws has been reduced to a minimum. A knee- lever lock sim ilar to that used for bottles (F ig. 6 ) has been found satis
factory.
A third requirem ent is strength.
T he lamp m ust w ithstand the rough usage so typical of m ining service.
It has to endure blows, the fall of pieces of roof, the corroding effect of m oisture and the strains of the cable. T he connecting plugs are in
closed in heavy cast-iron casings.
T he lamp and the cable m ust there
fore be of careful design.
Rubber-coated cable has been sub
m itted to many tests to ascertain its mechanical strength and resistance to moisture. T he lamps also have proved satisfactory. L ast year the system stood an acid test. T he roof in the workings fell fo r a length of 82 ft. T hree lamps were completely
buried. One of these went on burn
ing. T he rest of the installation con
tinued in operation entirely u n affected.
Safety regulations require that
ade-T o ta l C o s ts Per Y e a r 6,000 Mark*
F ig. 4— C ost D istrib u tio n fo r F loodligh tin g
quate protection be afforded against casual contacts with live parts and against fire or explosion hazards.
By reducing the operating voltage against ground to 43, apprehension is entirely removed on this score.
F ire- and explosion-proofness in
any electrical equipment, of course, must be only relative-; 100 per cent of safety is not feasible. Assuming that compliance is made with all safety regulations, two sources of danger remain : T he cable and the incandescent lamp.
T he cable is always exposed to danger of rupture should the roof fall. F irst, the copper conductor will rupture owing to its lower elas
ticity; a fte r that the elastic rubber coating of the cable may break; if, however, it does not do so, there will be a vacuum around the break in the cable and the spark created by the rupture will do no harm. M ore
over, by letting the cable sag loosely the roof in falling will not subject the cable to any excessive tensile stress.
I t has been proved that such falls do not injure the insulation between the copper wires or the outside pro
tective coating, except possibly when the cable is forced upon sharp edges such as those of conveyor pans or when shots drive objects against the cable. It is assumed, of course, that only the best quality of rubber-hose cable is used.
T he incandescent light with its glowing filament and its brittle glass
F ig. 5— Increased P rodu ction F ro m F loodligh ts
bulb is a source of danger. F o r this, unfortunately, there does not seem to be any substitute. However, the bulb can be protected by a heavy glass globe, and the latter in tu rn by a strong wire guard, afid then the protection is substantially equal to that afforded by the flame safety lamp.
Fig. 3— F loor P lan o f F ace Illum ination
98 C O A L A G E — V ol.35,N o.2
Fig. 7— P a r ts o f S iem en s-S ch u ckert L am p;
a, L a m p ; b, Connection B o x ; c, Section B o x w ith H o o p -Iro n L ock
P e r M in e C a r C e n ts
W a g e s w ith o u t f lo o d lig h tin g ... 57 W a g e s w ith f lo o d lig h tin g ... 61 W a g e s a v in g s d u e to f l o o d lig h tin g .. . 6 C o st o f flo o d lig h tin g ... 2.3S S a v in g s fro m f lo o d lig h tin g ... 3.62
A nother suggestion was that an inert gas cushion of, say, carbon dioxide should be placed between the bulb and the globe, and that the globe should be of glass reinforced by wire. In case the globe breaks, the wire net in the glass prevents large pieces from dropping out. The carbon dioxide, accordingly, can escape only slowly into the methane- air m ixture surrounding the globe.
If the bulb is broken at the same time, the inrushing air and carbon dioxide will burn out and cool the glowing filament before an explosive m ixture of gas can form within the bulb walls. There is a danger that the attendant will let the lamp con
tinue to burn if the bulb is not broken by the violence that crushes the globe.
Such a lamp would be inadequately p ro tected ; therefore a radial arm a
ture of metal bars has been put be
tween the bulb and the globe so that when the globe is broken, the bulb also will be shattered and conse
quently the attendant will have to re
place both or go without light. This second suggestion has been prelimi
narily covered by a patent appli
cation.
A fte r two years’ operation, an in
vestigation of the cost of upkeep showed that the installation with 40
T o keep on the safe side, let the savings be assumed as 2.38c. only.
If 73,286 cars are mined per year, as in the mine considered, the net saving will be S I,785. But the profits really are higher, for they are in di
rect proportion to the wages paid.
In the calculation these have been set quite low in comparison with those in other coal-mining districts. M ore
over, the greater cleanliness of the coal produced may be of more eco
nomic importance than any pro
ductive efficiency.
There are other advantages in good light. A miner due to the noise of modern machinery, cutters, con
veyors, loaders, hoists and locomo
tives, is deprived of his sense of hearing. Danger sounds for him no audible warning. A good illuminating system is, indeed, a welcome substi
tute. W ith it he can see danger:
the early formation of crevices in the roof, the approach of a piece of timber in a conveyor or chute and so forth,
H e may also spare his eyesight.
It is conceivable that the system will eliminate the eye disease known as nystagmus. The increased volume of illumination reveals his fellow workers as human beings, not merely shadows; without effort he discrimi
nates between coal and slate; both hands are free for work.
Voluntarily he works h ard er;
without realizing it, the quality of his work improves. M anagement is simplified, inspection duties are made less arduous. Is not floodlighting worthy of adoption by reason of its contribution to safety, even suppos
ing, contrary to the facts stated, that the system does not furnish any savings in operation whatsoever?
Fig. 6— F riedm an & W o tf L am ps W ith K n e e-L evcr L ock S im ila r to T h at U sed on B o ttles
lamps described in the early part of the article was operated for an an nual cost of $1,429 and this charge was distributed as shown in Fig. 4.
The cost of floodlighting when compared with wage costs was 3.5 per cent, which is a charge not out of line with that now incurred in other industries. The cost per ton mined was 2.38c. T he increase in coal production, if only that from April to May is considered, equals 0.276 car per miner per shift (see Fig. 5 ). _
Assuming a wage of $1.43 per shift the results can be sum m arized:
F ig. S—N e w S iem en s-S ch u ckert Lam p W ith S pecial K e y
It has been suggested that gas un
der pressure be provided in the space between the bulb and the glass globe, the object being to disconnect the circuit of the bulb automatically by means of a diaphragm switch if, owing to the glass globe breaking, the gas pressure falls. This plan has been adopted for electro-pneumatic lamps. But the method is not with
out fault. T he action of the dia
phragm is slow and consequently an explosion was not averted in cases where the bulb and the globe broke simultaneously.
February, 1930 — C O A L A G E 99