674

THE COLLIERY GUARDIAN

October 1, 1915.

At every colliery where compressed air is used, an
official should be appointed -to be directly responsible
for the maintenance in good condition of the under-
ground compressed air plant, and his duties should
include periodic tests of the air consumption of coal
cutters and other air motors.

Operating the Machine.

The cost of operating a compressed air coal cutter
comprises the following items :—

(a) Interest on the cost of the coal cutter and its
accessories, and its proportion of the piping; (b) depre-
ciation; (c) labour; (d) power; (e) cutter picks, oil, etc.;

Tasiz of Costs of Machine, Cmty.ng Per Shift ano Per Ton

W

IB'

(C)

Intercut JJLS./Lqji £<£0

”	'Q|' pF-R Annum

Fieprecia-iqn ,.2> _I2*Z 7” On V.4.~0
k SB Per Annum

Labour

0-52

A-00

Per Ton
0 I

0 21



2 76

(E-) Cutter Picks . Oil, Etc
(f) Repairs

13 o

a 4

tl 10

I no

1 so

Io*

Table VIII.—Costs of Undercutting.

and (/) repairs. These items may be divided into two
groups :—a, b, and c, which are not affected by the
amount of work done during a shift; and c, d, and e,
which have relation to the work done. In Table VIII.
assumed values based on 260 shifts per annum are given
to the first group, and the second group is based upon
100 sq. yds. undercut, yielding 600 tons of coal. The
items of the first group represent a charge per
shift, incurred by the establishment of the coal cutter,
and it is clearly desirable that the amount should be
divisible by the largest possible number of tons of coal
output per shift.

The effects of restriction of cutting speed, due to
derangement of the machine or to fall of air pressure
below that required to drive the machine at its normal
speed, are—

(a)	The air consumption, already an expensive item,
is increased.

(b)	The cost per ton for the items 1, 2 and 3, are
increased in inverse proportion to the reduction in
tons output.

The effect of a fall of pressure from, say, 30 to 201b.
per sq. in. at the machine may halve the cutting
speed, and double the volume of air per square yard cut.
The area undercut in a shift will be halved, the output
will be about 50 tons instead of 100, and the cost per
ton will be doubled.

Cutter Picks.—Among the lessons to be learned from
tests of air consumption, one of the most valuable is the
importance of giving due attention to the proper form
and adjustment of the cutter picks. In the operation
of the machines no fault is more common than the use
of cutter picks the points of which do not cut sufficient
clearance for their bodies, nor for the cutting member
of the machine to which they are attached. The result is
not only overloading of the motor, and undue strain and
wear of all the working parts of the machine, but also
reduced cutting speed, with the consequent increase of
air consumption per square yard cut, and the usual
penalties of reduced output.

The chief elements of satisfactory operation of a coal
cutter may be summarised as (a) uniformity of pressure
of air supply; (b) maintenance of the machine in good
condition, especially in regard to the air motor and to
the cutter picks; (c) preparation of the face in advance
of the cutting shift; and (d) instruction of the drivers
in the structure of the machine and in the functions of
its component parts. It follows that the driving of a
coal cutter, with due regard to economy of air and to its
vital function of undercutting, requires a greater degree
of care and more instructed intelligence than are applied
by the average driver. Many costly machines are being
driven to-day by men who are utterly ignorant of their
construction, and to whom the casings that enclose them
are boxes of mystery. This is not fair either to the
machine or to the men. No better investment could be
made than the systematic instruction of machine
operators in the details of the construction of their
machines, in the nature of the adjustments upon which
satisfactory and economical working depends, and
especially in the elementary principles upon which the
form of cutting tools are based.

Comparison with Electric Coal Cutter.

The purpose of the curves in fig. 14 is to illustrate
how sensitive to change of load is the efficiency of a
compressed air coal cutter, and how much more its
power efficiency in operation is dependent upon the skill
of the driver than is the case with an electric machine.
The curves are drawn from results of actual tests, and
the compressed air and electric machines are represented
on the same scale of energy, the compressed air and the
electricity supplied to the machines being reduced to the
equivalent brake horse-power hours. The form of the
curve of the electrically-driven machine may be taken as
closely approximate for all electrically-driven coal
cutters. The curve of the compressed air machine will
not bear application so wide, it refers to a particular
machine, and although fairly characteristic, its form is
only to be taken as roughly representing compressed air
machines in general.

The positions of the curves on the scale depend—other

things being equal—upon the hardness of the materials
cut by the machines. The two machines tested worked
under similar conditions, cutting in easily-holed coal,
and the two curves given are therefore comparable both
as to their forms and their positions on the scale. The
favourable position of the electric machine on the scale
is due to its working in a closed circuit, and having no
exhaust pipe from which to vomit unused a large pro-
portion of the energy supplied to it.

Conclusion.

Test Records.—This paper is not an indictment of the
compressed air system, but in effect it is an indictment
of the prevailing improper conditions of its below ground
employment.

The test records have been collected during several
years, and filed for reference. The cumulative strength
of the evidence as to the thoroughly unsatisfactory posi-
tion in regard to efficiency of the compressed air system
in underground use is irresistible, and it leaves no refuge
for the doubter. Until the writer examined the mass
of correlated test records and reviewed them, he did not
fully realise how deeply in the slough of inefficiency the
system was submerged, and he feels that this paper in
the course of preparation has acquired the unpremedi-
tated character of a disclosure, but the facts having been
elicited, they ought to be communicated.

As explained, the tests were made under ordinary
working conditions, with simple meters and pressure
gauges. The officials at any colliery can make similar
tests, to confirm or refute the application to their own
case of the general statement as to inefficiency; after
taking actual measurements, they will at least know
where they stand : at present they do not know.

Remedial Measures.—Reform of the existing condi-
tions does not involve scrapping and replacing valuable
plant. On the contrary, mitigation of the most extra-
vagant of the losses is neither expensive nor very diffi-
cult, and would not only immediately raise the operative
efficiency, but would increase the productive capacity
of existing plant. Many compressing plants are now

ZSO.

24C

3co

700

?2O

22C-

200.

34o.

loo

120

60

ISO

ISO

SO

140-

0

A - Compressed air
B * Electric

Fig. 14.—Energy used at Various Rates of
Cutting by Compessed-air and Electric
Coal-cutters.

IO	20	50	40

Ratk of CuTTiNa Inches Pew Minute

overtaxed, and enlargements are in contemplation; but
why purchase additional plant without definite knovr-
ledge of the relation between the volume of air being
compressed, and the volume that ought to be sufficient
if properly utilised? When 30 per cent, of the total
volume compressed is being lost by leakage, the pur-
chase of new plant, instead of stopping the leaks from
the old one, is to pile extravagance on extravagance.

Need for Competent Supervision.—We have seen that
the efficiency of the compressed air system is peculiarly
sensitive to the condition of the plant, and that there
are, therefore, special reasons why its underground
system of piping and accessories should be kept under
close observation and control.

Colliery managers of to-day have to deal with very
complex organisations; to them an air compressing plant
is merely a means to an end, and, if the end is reason-
ably well served, their other preoccupations usually
prevent too close enquiry as to the efficiency of the
means. In the case of electricity, colliery managers
have readily availed themselves of expert advice as to
the selection and general arrangement of plant both
above and below ground, and there is now installed at
every colliery an official electrician—in many cases with
his own staff of operatives—who is directly responsible
for the condition of the plant under his charge. Where
are the mining compressed air engineers?

The Compressed Air Engineer.—The terms “ electrical
engineer,” “ hydraulic engineer,” “ gas engineer,”
“ locomotive engineer,” and half-a-dozen other kinds of
engineer are familiar to us; but compressed air appears
to be the ugly duckling : nobody owns it.

There is not, in the whole range of engineering, another
important branch in which there remain so great possi-
bilities of improvement in efficiency as in compressed
air practice, and the prospects should therefore provide
an alluring field of endeavour for engineers.

Compressed air engineers do not exist, in a general
sense, because there is no demand for them. Users of
compressed air in collieries have not yet realised that
they require expert guidance in planning and operating
their equipments, not only on the surface, but also in
regard to every underground detail. The existing con-
dition of inefficiency, when it is recognised, ought to
create a demand for compressed air specialists; men with
comprehensive knowledge of the scientific principles
which govern all the problems from the alpha to the
omega of the system, and familiar with the practical
application of these principles, not only in regard to

compressing air, but in the various phases of its trans-
mission and application. If it were known that men
with the necessary training were in demand, technical
colleges in the mining districts wrould specialise in
instruction in compressed air engineering. If a small
fraction of the engineering capacity that is being con-
centrated upon electrical work were diverted to com-
pressed air, there would soon be a different history to
write.

COAL MINING ORGANISATION
COMMITTEE.

DIGEST OF THE EVIDENCE.

(Continued from page (22.)

Mr. F. Parker Rhodes.

Mr. Fredk. Parker Rhodes, secretary of the South
Yorkshire Coal Trade Association, gave evidence on April 15.
Witness said the loss of output throughout the country
appeared to be about 28 millions, or something like that.
In their own case the reduction in output, as far as he
could tell, would be something like 13 per cent. That loss
in output curiously enough did not correspond exactly
apparently with the percentage of men lost, and to some
extent labour must have come in in the place of those who
had gone.

Witness continued : As to the increase of that output, it
appears to me really that, for practical purposes, only one
or two methods can be used by which improvement can
be arrived at. We have undoubtedly at the present moment
a considerable number of absentees. The absentees at the
present time, taking the face workers, amount to about
15 per cent. From that must be deducted about 6 per cent,
for unavoidable absenteeism. I had the figures taken out
at one particular place, and found that on the day before
the last day of the pay, the last working day of the week
before making up, the percentage of absentees fell, and on
several occasions that it was as nearly as possible 6 per
cent. I find, looking at the present time and looking at
the period ten years back, comparing our last year, 1914,
with the year 1904, the increase in absentees is very marked.
I find that in 1904 it was slightly under 10 per cent.,
whereas to-day it is about 15 per cent. But it is only fair
to say that to-day it is not quite as bad as it was last year.
Last year it was over 16 per cent., and I think the reason
for that is that the war has acted as a stimulus to some
people, and they attend better than they did. My experi-
ence is that the men who have joined the Forces are a gocd
class of men. Now as to the causes for absenteeism, there
can be only two. One is something that makes a man
desirous of stopping away, and the other is something from
outside that induces him to stop away. I think it is
impossible to avoid coming to the conclusion on the figures
that increased earning power has something to do with
it; when you have earned so much over a given amount of
money you are inclined to say—“ Rest and be thankful,”
or one might put it : ‘‘Rest, if not thankful.” Then there is
another thing it is impossible to shut one’s eyes to. I cannot
help coming to the conclusion that what happens on Satur-
day and Sunday has a good deal to do with the large absence
from work on Monday. The two worst days invariably are
the Monday and the day following the making-up day. In
one pit, where the percentage is 15 per cent., as near as
possible, Monday shows about 30 per cent, and Thursday
about the same percentage. The pay is made up the day
before, and the first day they are idle is Thursday, and they
say : “ We will make it up somehow.” Drink does not
affect the Thursday at all, but drink affects the Monday.
Absenteeism is prevalent more in part of a class than in
the whole of a class. There are a number of men who are
good, steady, thrifty men, who scarcely miss a day at the
pit and who, if they are away, have some very good reason
indeed for being away. I think as far as the drink question
is concerned that really the great evil is in the growth of
clubs, and I am not sure that has not something to do
with the increase of absenteeism in the last ten years, as
well as the increased wage-earning powers. I do not know
that there is any necessity to close public houses and clubs
altogether. You cannot attempt to regulate men by Acts
of Parliament. They are grown men, and are entitled to
their own views. All I suggest you can do is to prevent
excess where it affects the neighbourhood industrially, and
I do not think there ought to be any distinction made
between clubs and public houses. You are doing no good
by closing a public house, where it is necessary to close it, if
you leave the clubs open. I certainly would not advocate
the closing of clubs and public houses in a mining district
and allowing them to be open elsewhere. I do not think
that drinking is greater in the neighbourhood of large towns
than in country places. It really is connected with the
facilities for getting intoxicants. Of course, large towns
affect the problem in one way; that is to say, in the neigh-
boorhood of a large town you have more amusements.

Continuing, witness said : There is another method of
increasing the output that has been alluded to, and that is
the possibility of extending the use of machinery. Person-
ally I do not see the slightest advantage to be gained in
that direction. In the first place, speaking of my own
district, I think that coal-cutting machinery is already in
use where it would pay to put it in use. It is not every
pit that is suitable for the use of machinery, and the
description of seam must lend itself to it. If you are going
to alter any haulage system or anything of that kind in
order to increase your output, all I can say is, if a colliery
manager came to me and told me that a change of machinery
in this emergency would increase his output, I should say at
once, ‘‘ Why on earth have not you done it before? ” Again,
assuming it were possible to do it by a change in that
direction, the time that would be occupied would be pro-
hibitive really. You cannot alter the system of haulage in
a large colliery, and substitute another in place of it, without
interfering very considerably with the productive capacity
of the place while you are doing it, and it is a long job
to get it done.

Another method of increasing the output that has been
suggested is the suspension of the Eight Hours Act. With
regard to that I do not myself think that “ suspension ”
is the right term to use. I do not think it is of any use
suspending the Eight Hours Act if you mean by that the
sweeping away of the Act altogether for the moment. It
has caused a great revolution in mining. We have all of
us had to adapt our circumstances to it, and they have been
adapted. If you attempted to make a revolutionary change
back again you would incur risks that are far beyond any
advantage you would gain. On the other hand, I do