1240

THE COLLIERY GUARDIAN

December 17, 1915.

CURRENT SCIENCE

Radiation and Convection from a Heated Wire in an
Enclosure of Air.

Dr. T. Barratt, in his paper read before the Physical
Society of London on October 22, recorded experiments
made to determine the numerical relation between the
radiation and the convection losses from a heated metallic
wire or rod placed in a gas at constant temperature. The
method consisted in (1) measuring the amount of heat
required to maintain the temperature of the wire a given
amount (about 10 degs. Cent.) above that of the sur-
rounding gas, the surface of the wire being (a) coated
with a dead black varnish, (6) uncoated; (2) comparing
the radiations from two surfaces exactly similar to (a)
and (b) by means of a thermopile. He found that if the
total heat lost from unit surface of the wire is a
times greater from a “ black ’’ wire than from a “ bare ”
one, while the radiation from the black surface is b
times more than that from the unblacked surface, then

r2 = a~\ and Ll = b (a~b\
c a — 1’ c a — 1

where r2, rr are the radiations from “ black ” and
“ bare ” surfaces respectively, and c is the convection.
The experiments indicate that of 100 parts of “ total
heat ” lost from & wire at air temperatures, 2-5 consist
of radiation for a “ bare ” wire, and 12-6 for a “ black ”
wire. At 100 degs. Cent, these percentages become 4-4
and 20-7 respectively. With wires of different
diameters the total heat loss per square centimetre
decreases as the diameter of the wire increases.

Economy of Mechanical Stoking.

In the Engineering Magazine, Mr. Clarence Coapes
Brinley shows how the automatic stoker is effective in
reducing cost’s in labour and fuel, and how easily it can
be operated to handle fluctuating loads. For hand-
firing a man cannot be expected to handle more than a
ton of coal per hour with any degree of efficiency. For
this reason hand-firing requires one fireman for about
every 600 or 700 horse-power. When mechanical
stokers are used in conjunction with mechanical hand-
ling equipment, one operator can handle from 5,000 to
6,000 horse-power. The burning of low-grade coals with
efficiency is made possible by the regular and continuous
feeding of the coal into the furnace, and the constant and
even air supply which is the result of minimising the
necessity of opening the furnace door. But the best
results from burning low-grade coals are obtained with
those stokers which employ forced draught. Since the
capacity of any boiler is limited by the amount of coal
that may be burned in its furnace and by the efficiency
with which this coal is consumed, it is obvious that a
greater amount of coal can be burned over the same
grate area, in a mechanical stoker, and at a higher
efficiency, than is possible in a hand-fired furnace. But
an increase in boiler capacity is economical only within
certain limits. Increased capacity means increased
maintenance costs, and where firebrick arches are used,
it is not considered good practice to operate above 150
per cent, of rating, but where under-feed stokers are
used the boilers may be run economically at 200 per
cent, of rating. If boilers can be operated at such
rating by mechanical stokers, then it requires, for a
given capacity, only half as many boilers as would be
needed with hand-fired furnaces. The saving in space
and boiler equipment will therefore compensate the
cost of stoker installations.

There are two so-called scientific methods of burning
coal in furnaces, and these are responsible for the
development of three distinct types of mechanical
stokers—the chain grate, the over-feed, and the under-
feed.

The first method, progressive combustion, requires
that the green coal be fed gradually and regularly into
the edge of the fuel bed at the front of the furnace.
Here the coal is coked, and the volatile gases are dis-
tilled. These gases, mixed with the proper amount of
air, move across the incandescent fuel bed, and are
consumed before leaving the combustion chamber. The
coked coal is then advanced to finish its combustion, and
forms an incandescent bed to consume the gases from
the fresh coal which has taken its place. This pro-
gressive movement is continued while the fixed carbon
is being consumed and the ashes are being deposited at
the rear of the grate. This method is employed in both
the chain-grate and over-feed types of stokers.

The second method, under-feed combustion, requires
that the green coal be forced on to the grates under-
neath the incandescent fuel. Here the coking process
takes place, and the volatile gases pass up through the
incandescent fuel, and are consumed before leaving the
fire. The coked coal is then forced up by fresh coal
entering from below, completes its combustion, and
forms an incandescent fire to consume the gases from
the coal. This method is employed by the various
types of under-feed stokers.

The author proceeds to describe the leading types of
mechanical stokers now in the market, showing the
differences of each type, the different makes of the lead-
ing manufacturers being taken as examples.

The author says that among the points to be con-
sidered in choosing a stoker are :—The initial expendi-
ture involved, the cost of operation, and the mainten-
ance charges. The over-feed stokers average roughly
about five, chain-grates about six, and under-feed
stokers about seven dollars per rated boiler horse-power.
For the under-feed type this includes the forced draught
system. The operation of the fan and the rams for an
under-feed stoker consumes about 2| per cent, of the
steam produced by the boiler. For the over-feed type
and the chain-grates less than 1 per cent, of the steam
produced is consumed in operating the stoker. The
maintenance charges will be affected largely by the
number of moving parts that come in contact with the

AND TECHNOLOGY.

incandescent fuel. In the chain-grate we have the
maximum number of such parts, and in the under-feed
stokers the minimum. In the under-feed stokers there
is always a layer of green coal between the grates and
the incandescent fuel, which protects them from the
heat of the furnace. Replacing or repairing burned out
firebrick arches is the most costly item in furance main-
tenance, and these arches are not required’with under-
feed stokers, the fuel bed being directly ber vath the heat-
absorbing surfaces of the boiler.

Efficiency of Goke for Boiler Firing.

According to the Gas World, the Wandsworth,
Wimbledon, and Epsom District Gas Company have
been conveying all their coal requirements at their
Epsom works from their riverside station at Wands-
worth by means of steam-driven motor lorries, fired by
coke. Advantage was recently taken of this fact by
the London Coke Committee to give a demonstration
for the benefit of a few interested guests. For the
purposes of the demonstration, two Foden steam
wagons, picked at random from the cars owned by the
company, were used, each wagon, with its trailer, carry-
ing between nine and 10 tons of coal, and each having
a gross weight of approximately 20 tons. The road
between Wandsworth and Epsom has gradients as steep
as 1 in 16, and the surfaces (for the most part tarred
macadam) were in good condition, offering what may be
called a give-and-take country road. One wagon and
trailer took one hour and 50 minutes to cover the 11
miles; the other took one hour and 45 minutes. Each
unit was “up to the legal limit,’’ and blowing off at a
safety valve all the time. The net consumption of coke
for one wagon and trailer was 15'2 lb. per mile (1681b.
for the journey); the corresponding consumption for the
other wagon and trailer was 17'2 lb. per mile (1901b.
for the journey)—this wagon had the heavier load (by
about 7 cwt.), and travelled the quicker. No alteration
had been made to the wagons other than the use of fire-
bars spaced to give 50 per cent, of area between the bars,
to afford the necessary freer supply of air, as compared
with what is required when coal is used as fuel. Mr.
Charles Davies, representing Foden’s Limited, speaking
at the end of the journey, said his company appreciated
the importance of an alternative fuel, and he should try
to arrange for the Foden works at Sandbach to supply
alternative firebars to suit the consumption of coke. At
the same time, it was an easy matter for any user to get
a set of the right sort of firebars cast.

New Safety Governor.

An improved type of overwinding and overspeeding
apparatus for use in connection with hoisting engines
serving either shafts or slopes is the Roybel emergency
governor.

The construction and operation of this machine are
extremely simple (says Coal Age). Referring to the
accompanying drawing, the flyballs A are driven by the
sprocket B, which in turn is driven direct by chain from
the drum of the engine. The stem of the governor,
which carries two separate springs, terminates at its
lower end in a disc carrying the pin C. As the speed of
the engine increases and the balls fly out, the stem
descends, and at a pre-determined maximum allowable
speed the pin C clears the lever D by a small amount.
The flyballs are now opposing only one of the stem

Roybel Safety Governor.

k a)
K B

springs. If the speed is increased, exceeding the pre-
determined amount, the flyballs compress both springs,
and the pin C strikes and throws the lever D. This
immediately applies steam to the brakes through the
three-way valve E.

Motion from the sprocket wheel B is transmitted
through the intermediate shaft and gears F and the long
pinion G to the worm H, which drives the worm wheel
I. Near the rim of this wheel, at a point adjustable to
suit the conditions, is placed a double or graduated
incline J. The arrangement is such that, when the land-
ing is approached, this incline lifts the lever B into close
proximity to the pin C, and unless the speed is properly
reduced, and the pin C allowed to rise with the disc and
governor stem, the lever B will be thrown and the
engine brought to a standstill.

When the hoist is complete, and the cage stands in
the dumping position, the steep portion of the incline J
is touching the lever D, and any further movement of
the cage in an upward direction will apply the brakes.

Overwinding, overspeeding, and moving the cage in the
wrong direction are thus impossible.

The machine is equipped with a dial provided with
double pointers — one connected with and controlled
from the tight drum, and one from the loose drum. The
relative position of the pointers then indicates the level
being served. As the cage leaves the dumping point,
the red semaphore at the top of the dial swings down,
while when the other cage approaches the dump, a sema-
phore in the other side appears. This gives a visual
indication to the engineer of which cage is to be lowered.
This dial indicates at all times the exact position of each
cage, and which landing it is serving.

When the signal to hoist men is given, the engineer
gives a return signal by throwing a lever. This not
only gives the bottom eager a visual signal (usually an
electric light), but by revolving the crank disc K, moves
endwise the worm shaft carrying the worm H and pinion
G, thus revolving the worm wheel I until the incline J
takes a position corresponding to the ground landing.
It now becomes impossible for the cage to approach the
ground landing at too great a speed, or to pass it. A
second worm on the same shaft as the worm H operates
the worm wheel L, which, through a sprocket chain,
actuates the pointers on the dial. The machine is
extremely simple in design, while its operation is posi-
tive. Machines of this type have been in use for some
time at various mines in the anthracite region, and thus
far have given satisfaction.

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.

Deliveries from the collieries during November showed
a further decline, owing to the continued shortage of
railway wagons, and therefore stocks had to be increased
at the pits, even those having their own wharves on the
Rhine-Herne Canal, craft suitable for plying on the canal
being also scarce. In these circumstances, the colliery
industry is not in a very favourable condition; "wages
having increased, large sums to be disbursed for the
maintenance of officials and men in the field, whilst
local rates have gone up considerably. A large number
of collieries are making no profit at all; and deriving
benefit from the war is out of the question, the only
favourable factor being that coke stocks, valued at the
old rates, have now found a market. The situation is
reflected by the reduced dividends of the large companies
which operate under the most favourable conditions,
those of the Gelsenkirchen, Harpen, Hibernia, and Konig
Ludwig, for example, having fallen from 11, 8, 15,
18 per cent, to 6, 6, 8, and 7 per cent, respectively. The
Coal Syndicate has decided to leave the price of coal,
coke and briquettes unchanged for the month of January
and February, against the wishes of an important
minority who considered an advance necessary in the
circumstances. The supply of coke to large consumers
suffered greatly from shortage of wagons, the distribu-
tion being less than a million tons in November, and
hardly likely to improve during the present month.
One cause of the shortage of railway wagons was the
circumstance that those arriving at the Rhine harbours
laden with coal were reloaded with waterborne Belgian
coal and despatched to the northern ports, instead of
returning empty to the collieries.

Coal and Iron Market in Upper Silesia.

During November the coal market was in a satis-
factory condition, the enquiries for all grades being
larger than could be met. Wagons, too, were more
plentiful than in the previous month, though still
inadequate to cope with the traffic. Whilst supplies of
open burning coal were fairly satisfactory, much diffi-
culty was experienced in getting enough gas and coking
coal. This is no new feature, these coals being usually
scarce in the district; and at present there is an extra
demand for them from centres normally supplied from
England. The loss of men called up to the army
cannot be fully made good by employing men hitherto
unskilled in the industry; and the resulting increase in
the cost of production has not been counter-balanced by
the advanced prices fixed by the Convention. The
cokeries are asking for increased supplies, so that they
may maintain and even increase their output; and the
demand for coke is so active as to absorb, not only the
present restricted output, but also the old stocks, which
have consequently shrunk to very small dimensions. In
the iron industry, supplies of foreign ore suffered no
interruption in November, so that the blastfurnaces have
ample material in hand to keep them busy for some time
ahead. The great advance in the price of ore, etc., has
naturally made pig iron dearer to produce, and present
prices of the product must therefore be regarded as
nominal, and profits small. Stocks of pig iron are
practically non-existent.

Siegerland Iron Market.

In the ore market the situation remains unaltered,
the Convention having left prices of spathic ore for the
first quarter of 1916 at the old level, viz. : 16'50 mk. per
ton for raw and 24'50 mk. for roasted, though rates for
brown ironstone have been advanced to 16'80 mk. Owing
to the Westphalian Pig Iron Association having largely
restricted its specifications to grades made from
manganiferous Siegerland ore, the demand for phos-
phoritic ores from the Lahn, Dill, and Hessian mines
has diminished. In pig iron the demand for high grade
pig, especially that suitable for war material, continues
active, enquiries for export being also good. Orders at
local iron works are chiefly for steel iron, and
spiegeleisen, but makers have to contend with serious