510

THE COLLIERY GUARDIAN.

March 17, 1916.

AND TECHNOLOGY.

The writer left the district before the matter was
cleared up, but he was informed that the mica was still
in the switch three months afterwards. There was no
question of the motor or switch being overloaded.

• (2) Another fault was on a 45 horse-power, 3,000 volt
squirrel-cage induction motor, driving at one end,
through a flexible coupling, a centrifugal condenser
pump, and at the other encl an air pump by rawhide
pinion. The switching arrangements consisted of an
auio-transformcr starter with fuses on the running side
only, and a main switch which controlled three other
motors.

The motor was found to bo running excessively hot
early one morning, and the writer was informed that
the main switch had tripped the previous night. The
ammeter on the main panel showed the current taken
by the motor to be less than normal. An examination
of the fuses showed that one was blown. The main
switch and the auto-switch were also examined and
found in good order. When a new fuse was put in, the
motor worked quite satisfactorily.

(3)	The next case was a fault which occurred in a
500 volt horizontal three-phase oil-immersed controller
for a 50 horse-power open-type slip-ring motor. On the
barrel of the controller there were three short pieces of
| in. copper rod, completely covered' with mica, except
for him at each end, and used for making connection
between the incoming cables and the first step on the
controller. One of the copper rods passed under the
barrel contact of a different phase, but did not lie in
direct contact with it. When in service, the whole
barrel of ihe controller was completely immersed in
oil. The rod which passed under the contact of an
opposite phase was found to have •the. insulating cover of
mica burned away to a length of 1 in., and the copper
was also burned; so that there, was a short circuit
between these two phases. This fault worked through
all die high and low-tension switches in the sub-station
in the pit, and tripped the main switch in the power
house with -unusual violence. It blew off a part of the
cover of the trip coils of this switch, besides causing the
noodle of the ammeter of the switch in the power house
to go right over and stick there. The cover had to be
taken off to put the needle back.

(4)	Some time after that a fault took place on a
37/14 three-core armoured bitumen cable used as rotor
leads for a 300 horse-power, 3,000 volt motor. This was
caused by the heat of the place softening the bitumen
round the cores of the cable and causing a short circuit.
Immediately the switch was put on, and before the rotor-
switch handle‘was touched, the local switch and the-main
switch tripped, but the incoming, feeder switch did not
trip. As there was no resistance in the rotor circuit,
the rush of current through* the stator must have been
enormous.

(5)	At the colliery where the winter is at present
engaged there is a shaft exciter on the turbo-alternator,
and on the exciting switchboard there are earth lamps
to indicate a fault. Sometimes one of the lamps has
burned more brightly than the other, this showing an
earth on one side of the machine. This occurred two
or three times a day, and went away again without
anything being touched. To prove that .here was a fault
on the machine, the writer felt the brush gear and got a
distinct shock.

When the machine was shut down the excited arma-
ture, field coils, brush gear, and leads to alternator slip
rings were thoroughly tested with a megger, and a good
test was obtained. All the cables wore tested from the
terminals of the machine back to the exciting switch-
board, and were found correct. The writer then
examined the leads from slip .rings of the alternator
which pass under the soleplate. The rotor of the
alternator was also tested and found clear. The tost
lamps were still showing an intermittent earth, and one
of the fuses of the exciter was heating up rapidly. When
the auxiliary steam exciter was tried, the fault still
showed.

It was then decided to replace the leads from the slip
rings, and on doing so the leads were found to' bo
saturated with oil. . When .replaced, the fault was
cleared. As oil is supposed to be an insulator, it should
not have caused an earth, but the fact remains that it
did so. Since these loads were replaced, there has never
been an earth indicated.

__________________________________________________	___________________________________________________________________________________________________________

CURRENT SCIENCE

Use of Liquid Air for Blasting by a New Process.*

The first experiment with liquid air as an explosive
dates back nearly to the beginning of its industrial pro-
duction. Prof, von Linde made an explosive called

__________________________

“ Oxyliquit ” by mixing liquid air with charcoal. This
explosive broth, or pa^te, was put directly into the drill
hole and fired by means of cartridges and fuses.

Since this primitive method gave unsatisfactory
results, it was modified by filling a suitably prepared
cardboard cylinder with an explosive substance, prefer-
ably by dipping the whole in liquid air. This method
gave results, but was lacking in safety, and depended on
the skill of the workmen and quickness of manipulation.
The trouble was due largely to the enormous difference
in temperature between the liquid air and the surround-
ing rock, so that the air rapidly evaporated in the -hole.
The maximum theoretical life of a blasting cartridge was
thus only .10 minutes, while in practice it was still
shorter.

Interesting experiments have been made in France by
Georges Claude, and odier experiments which improve
upon the von Lindo method have been conducted in
Charlottenburg, Germany, by Kowatsch, with the
co-operation of von Baldus.

In order to prevent a rapid evaporation of the liquid
air, Kowatsch puts the cartridge with the dry carbon
container in ihe drill hole before introducing the liquid
air, and avoids the dangerous loss of time by necessary
preparations, such as tamping the hole after the mixture
has been made. The liquid air is not introduced until
time for shotfiring. This reduces the evaporation period
to a minimum.

The cardboard cylinder contains a perforated partition
tube, in which is placed a perfectly innocuous mixture
of infusorial earth and oil on asphalt, or of soot and
paraffin.. The central partition tube encloses a card-
board tube, over which is thrust another cardboard tube
to serve for carrying off the evaporation product of the
liquid air. If several holes are to be fired at once, the
clecrric wires are connected.

The liquid air intended for each hole is provided in
a suitable quantity in a small flask, to the opening of
which is attached a metal tube with a conical point, into
which tube is introduced the centra] tube of the
cartridge. To charge rhe cartridge, it suffices to raise
the back end of the flask. The liquid air is then lifted
by pressure of its evaporation products (just as water
containing gas is lifted by pressure of carbonic acid) in
the metal tube, and is forced into, the cartridge. At the
moment, when the shot is fired by an electric fuse, the
liquid air combines with the components of the charge
and causes an explosion of extraordinary energy.'

Winding Engines at Coal Mines in New South Wales.

In a paper read before the Electrical Association of
Australia, Mr. J. F. Dent describes the only two electric
winders in 'use in the coal mines of New South Wales :
one at the Abcrmain Colliery, and the other at the Rich-
mond Main Colliery. The first-mentioned is connected
through gearing to a 105 horse-power direct-current
250-volt motor, and is used to draw coal from tire bottom
to the top seam. Only single-deck cages holding one
skip are used. The system of control is by means of a
reversible controller, and powerful foot brakes are pro-
vided. The winder at Richmond Main is direct-couplcd
to a very large 800-volt direct-current motor, 800 to
1,850 brake horse-power, and is fitted with overspeed
and overwinding gear, also compressed 'air brakes. The
system of control is Siemens-Ilgner system, a flywheel
converter set being installed. The converter set con-
sists of an alternate-current 3,300-volt motor, driving a
direct-current 800-volt 720 kw. generator, to supply cur-
rent to the winding motor. The exciter for the
generator, and also for the winding motor, is mounted
on the end of the converter shaft, with the flywheel at
the other. A clutch is provided, so that the flywheel
can be put out of gear, and. the winder worked on .the
Ward-Leonard system when the leads are light. Double-
decked cages, each holding four skips, are used; but
as this mine is only in the development stages, no figures
as regards the capacity of winder are available.

Breakdowns in Colliery Electrical Plant.

■ . At a recent meeting of ihe East of Scotland branch
of the Association of Mining Electrical Engineers, Mr.
Roger Devine submitted some interesting notes on
unusual breakdowns in colliery electrical plant that had
come under his personal notice :—

(1) While at a colliery in Ayrshire, ho was,’ho said,
called out one night to see :o a breakdown of a large
pumping sot, consisting of a 200 horse-power, 3,000 volt
three-phase slip-ring induction motor driving a ram
pump. The motor was controlled by an oil-immersed
swiich and a rotor switch of the liquid type. The pump
and motor had been running well for about three months.

On opening up the switch, it was found that a short
circuit was .taking place between two of the trip coils
which wore wound with enamel wire. The wires of the
coils, which were about tin. apart, were found to be
burned and pitted where the current had been arcing
across. As it was essential that the pump should be
started as soon as possible, and as it would take some
considerable time to get a now switch installed, the
writer tried putting a sheet of thick mica between the
coils. This was done, and then the motor was started
up and ran without a stop.

On taking the matter up with the makers, they stated
that as the switch was tested with 6,000 volts before
being immersed in oil, they could not see how it was
now defective. When their representative arrived, the
writer ran the motor without the mica, when the same
thing occurred again, and it also did not recur when
the mica was again inserted.

* From an article by M. Przyborski, mining inspector,
Budapest, Hungary, in the Montanistische Rundschau.

rather more tar, highly viscous and holding more water
in suspension; about the same quantity of liquor, and
262 cut. ft. less gas of higher calorific value. The
mixed coke is of excellent appearance and burns well
in an ordinary domestic hearth. It . was noticed that
the carbon deposited upon the retort differed from that
usually found.

Gas from Pitch.

Mr. Alex. Yuill, manager of the Dundee Gas Works,
has recently carried out some interesting experiments,
with regard to the use of pitch for gas making. The
coal used in combination with the pitch was a first-class
Lancashire double nut, freshly obtained and dry. The
pitch used was obtained from a mixture of 65 per cent,
vertical retort tar and 35 per cent, of horizontal retort
tar. It softened at 80 degs. Cent., “twisted” at
75 dogs. Cent., and fused at 95 degs. Cent. To obtain a
thorough admixture of pitch and coal it is' best to
break up the pitch into small pieces; even the pitch
dust can be employed with advantage.

The following are the results of the tests :—

Average results of tests per ton of Coal Coal 2,0151b.
material employ ed.	2,240 lb. Pitch 225 lb.

Gas made per ton (corrected) (cu. ft.) 12,103 ... 11,841
Illuminatingpower(No.2 Met. burner) 15'70	... 15’83

Calorific value.............. (gross) 574T	... 612’5

CO., _____.........................(percent.)	1’95	...	2’03

Coke ...............................(lb.) 1.400 ... 1,358

Tar...............................(gals.) 7’91	...	8 75

„ ___________________________(sp. gr.) 1’225 ...	1’220

Liquor _________________________(gals.) 15’4	... 16’0

,, strength (degs. Twad.) .......	2£	...	2£

THE GERMAN AND AUSTRIAN COAL
AND IRON TRADES.

We give below further extracts from German
periodicals that have reached us, showing the course of
the coal and iron trades in Germany and Austria :—

Ruhr Coal Market.

In February, the conditions as regard's distribution
were again generally satisfactory to the consumers,
though the shortage of railway wagons hindered delivery
of both coal and coke at the beginning and end of the
month. The enquiry for fuel, both in the home and
neutral markets, is so active that the surplus of lean
coal, anthracite briquettes and nuts left over from the
house coal trade, owing to the mild weather, find a ready
outlet; and a whole series of inland consumers are still
waiting offers of gas flaming and bituminous coals, being-
unable to obtain them in sufficient amount. Foreign
sales are now concluded on the currency of the pur-
chasing country, a measure which “ will, no doubt, not
fail to accomplish its purpose of checking the rise in
exchange in adjacent countries.” The desire of the
military authorities that the production of coke and its
by-products should be maintained has an important
influence on ihe situation, and a scarcity of small coal
and -small nuts will have to be reckoned with, as
hitherto. Whilst the domestic consumption of coke has
been unsatisfactory for some time, the blast furnaces are
•taking increasing quantities, the output of pig iron having
attained, in January, a higher figure than hitherto
during the war. The strong current in the only avail-
able channel in the Rhine in the vicinity of the
Bingerloch (which has been closed by a wreck) neces-
sitated the towing of all large barges singly, and thus
further delayed traffic, so that some of the tipples in
the Ruhr harbours have had to stop working for want
of craft. The rise in the river also flooded a number of
coal stock yards, and the lower crane wharves, causing
a stoppage of nearly a week, and great congestion at
the railway sidings. The Kohlenhandelsgesellschaft
has fixed the selling prices from March 1 to July 31, at
the old level, except that washed bituminous and
flaming smalls have been reduced 1 mk. per ton, whilst,
coke is advanced 1’50 mk. per ton.

German Coal Syndicate Report for January.

The total coal output for January was 7,547,000 tons
(5,934,000 tons in January 1915), or 311,266 tons (233,452
tons) per working day; total distribution, 7,817,000 tons
(6,079,000 tons), or 323,607 tons (251,999 tons) per
working day; total participation, 8,743,000 tons
(7,104,000 tons); calculated distribution, 6,005,000 tons
(4,670,000 tons), or 247,629 tons (193,569 tons) per
working day, being 68’68 per cent. (65’74 per cent.) of
the participation. Total deliveries of coke, 1,998,677
tons (1,195,155 tons), or 64,473 tons (38,553 tons);
briquettes, 353,366 tons (350,401 tons), or 14,512 tons
(14,524 tons) per working day.

German Production of Medium-Hard Steel in January.

According to the report of the German Iron and Steel
Makers’ Association, the output of medium-hard steel in
January amounted to 1,224,732 tons (1,165,465 tons in
December), or 48,989 tons (44,825 tons) per working
day. Of the above total, 583,744 tons (567,451 tons)
were basic Bessemer steel, 14,393 tons - (14,886 tons)
acid Bessemer steel, 506,217 tons (473,808 tons) basic
open hearth steel, 26,852 tons (19,330 tons) acid open
hearth steel, 46,056 tons (42,523 tons) basic cast steel,
24,946 tons (25,179 tons) acid cast steel, 8,230 tons
(7,736 tons) crucible steel, and 14,294 tons (14,579 tons)
electro-steel. The production in the various districts
was as follows :—Rhenish Westphalia, 696,141 tons
(667,334 tons); Silesia, 116,163 tons (103,467 tons);
Siegerland and Hesse-Nassau, 27,692 tons (25,445 tons);
North, East, and Mid Germany, 50,601 tons (44,710
tons); Saxony, 22,949 tons (21,258 tons); South Ger-
many, 11,686 tons (10,899 tons); Saar district and
Bavarian Rhinepfalz, 95,283 tons (92,489 tons); Elsass-
Lothringen, 101,555 tons (104,089 tons); and Luxem-
burg, 102,662 tons (95,774 tons).

Fuel Traffic in Ruhr Harbours During March.

Total shipments to Coblenz and places higher up
river, 561,010 tons (431,183 tons in January 1915); to
places below Coblenz, 20,076 tons (15,673 tons); to
Holland, 110,888 tons (171,502 tons); to Belgium, 24,058
tons (109,079 tons); to other destinations, 48,281 tons
(6,315 tons). Total shipments from Duisburg-Ruhrort,
597,294 tons (566,592 tons); Rheinproussen, 68,758 tons
(71,687 tons); Schwelgern, 20,838 tons (34,951 tons);
Walsum, 77,422 tons (60,522 tons); aggregate, 764,312
tons (733,752 tons).

New Saar Coal Prices.

The settling prices for Saar coals for the period between
April 1 and September 30 next have been fixed as follow :
Flaming coals: Large, 16-80 to 18 mk.; screened
through-and-through, 15-60 to 17 mk.; through-and-
through, 13-60 to 16 mk.; slack, 11-20 to 13-60 mk.
Washery products: Cubes, 50/80 mm., 18-20 to 18-60
mk.; nuts I., 35/50 mm., 18-20 to 19-40 mk.; nuts II.,
15/35 mm., 17-60 to 18-40 mk.; nuts III., 8/15 mm.,
16-60 mk.; nuts III., 4/15 mm., 15-80 to 16-80 mk.;
nuts IV., 4/8 mm., 15 mk.; nuts slack, 2/15 mm., 15-40
mk.; fine slack, 10-40. to 11-40 mk. Bituminous coals :
Large, 18-60 mk.; through-and-through, 15-40 to 15-80
mk.; slack, 13-20 mk. Washery products: Cubes,
50/80 mm., 18-60mk.; nuts I., 35/50 mm., 18-60 mk.;

It appears, therefore, that a ton of the pitch used in
these experiments yielded 9,488 cu. ft. of gas. Com-
pared with the all-coal results the admixture of coal
and pitch yielded rather less coke per ton of material;