June 13, 1913.

THE COLLIERY GUARDIAN.

1291

950-yard run of two 0*40 square inch (19/0'164 in.)
double-braided aluminium conductors to carry 150 kw.;
(b) a 2,100-yard run of two 140 square inch (37/0'222 in.)
bare aluminium conductors to carry 500 kw. Forty-yard
spans were allowed for aluminium and 50-yard spans for
the equivalent copper cable. Line (a) erected complete,
including all poles, was 25 percent, cheaper in aluminium
than in copper. Line (b) erected complete, including all
poles, was 27J per cent, cheaper in aluminium than in
copper. If insulated aluminium underground cable had
been used for line (6), the capital cost involved would
have been nearly double what it was.

In 1912 a 6.600-volt three-phase line was built for the
Ebbw Vale Steel, Iron and Coal Company Limited, for
whom Messrs. Walter Dixon and Co., of Glasgow, act
as consulting engineers. The 5,850-yard run of line
using 7/0T96 in. bare aluminium wires, and capable of
carrying 1,100 kw. without any overloading, showed a
saving in favour of aluminium of 20 per cent.

Jointing of Conductors.

On Insulated Cables.—The author would offer this
warning on the jointing of insulated aluminium cables.
So far as his experience goes, there is not a single solder
which is permanently satisfactory, and he cannot recom-
mend either cast aluminium joints or autogenous
welding, owing to the effect of the heat on the insulation.
But he can confidently recommend mechanical joints of
the types illustrated in figs. 1 and 2. These joints have
been in use for some years on the Manchester Corpora-
tion cables, which are 1'66 square inches in section.

OUTERCORE

INNER CORE

Fig. 5.—Special Joint for 1'4 square inch
Aluminium Conductor for Use under Stress.

The author is now able to give additional information
concerning them. Figs. 1 and 2 show the “ straight-
through ” joint used on the above cable, and figs. 3 and 4
show how the cable was connected to a copper cable.

On Overhead Lines.—Usually, in this country joints
on copper and aluminium conductors on overhead lines
are made at an insulator, so as not to be under stress.
Copper joints can be easily made in various ways.
Probably the best method on overhead lines, or on
insulated cables carrying any considerable current, is
by means of flexible copper braid bound and soldered
to the joint. This system has been patented by Mr.
Chas. Vernier, for use on both overhead and under-
ground conductors. There are various ways of jointing
aluminium conductors on overhead lines.

A specially-designed joint for use under stress was
employed on Messrs. Newton, Chambers and Co.’s
1'4 square inch line. It is clearly shown in fig. 5, and
has been quite successful. To prevent electrolytic
action, the steel holding - bolts were stoved and
enamelled.

Suspension of Lead-covered Cable on Overhead Lines.

Frequently on overhead lines it is necessary to employ
lead-sheathed paper-insulated pilot and telephone cables.
Sometimes also in colliery and other yards it is necessary
to carry insulated cables overhead, and to support them
by hangers attached to a steel suspending cable. With
these, in the past, there has been much trouble, owing to
cracking of the lead sheath. The causes of this have
been the subject of much investigation, and even now
are not entirely understood. It is, however, satisfactory
to know that the troubles have been eliminated by the
use of the method of suspension covered by Mr. C. E.
Elder’s patent,* and by the addition of 3 per cent, of
tin to the lead sheath. Briefly, the system consists of
very short chrome-leather supporting hangers, placed
12 in. apart, and fastened to a stranded steel suspending
cable in such a way that they have no longitudinal
movement. At every tenth hanger a sherardised flat-
steel spring is sprung on the hanger for clamping it to
the cable and so preventing any longitudinal movement
of the cable relative to the hanger. In special cases—
for example, on a steel gradient—every hanger may be
clamped to the cable.

Examination of Arguments against Aluminium
Conductors.

Two frequent arguments against the use of aluminium
are (a) that aluminium has an uncertain scrap value;
and (6) that there are considerable difficulties in jointing
the metal satisfactorily. This latter point has already
been fully dealt with. In regard to (a), at one time
there was a difficulty in selling scrap aluminium, but
now there is none. Clean, commercially pure aluminium
scrap, as obtained from cables or from overhead lines,
can readily be sold at about £22 per ton below the
market price of aluminium-wire bars, whereas the price
of clean electrolytic copper scrap is about £6 per ton
below the price of wire bars.

The writer is aware of three cases in which
aluminium conductors were erected in the United
Kingdom during the past 10 years, with unsatisfactory
results, and has been at some pains to investigate them.
He is of opinion that these failures were solely due to
(a) inferior metal and insufficient knowledge of working
it at the time. These causes no longer exist,
(ft) Inexperience in erection. There is now, however,
sufficient experience to draw upon, so that there need be
no fear of difficulties from this cause.

* British patent, 1912, No. 4975.

Summary.

(1)	Up to the present, aluminium has not made any
serious impression on the use of copper for electrical
work in the United Kingdom, but it is coming
increasingly into favour.

(2)	The initial difficulties in regard to the purity of
aluminium, methods of working it, &c., have been over-
come, and it can be safely used as a conductor on an
equal footing with copper.

(3)	For mining work in the United Kingdom, at the
present prices of copper and aluminium, insulated cables
with copper conductors, and for all pressures, are the
cheaper, while, for overhead lines, aluminium conductors
are the cheaper.

(4)	Paper-insulated lead-sheathed cables are cheaper
than bitumen-insulated cables, whether the conductors
be of copper or of aluminium.

(5)	Both copper and aluminium conductors can be
efficiently jointed by well-proved methc ds.

Shipments of Bunker Coals.—During May, the quantity
of coal, &c., shipped for the use of steamers engaged in
the foreign trade was 1,618,844 tons, as compared with
1,671,312 tons in May 1912 and 1,715,181 tons in May
1911. The aggregate quantity soshipped in the first five
•complete months of the present year was 8,366,021 tons, as
against 6,564,682 tons and 7,884,191 tons in the corresponding
periods of 1912 and 1911 respectively.

North of England Institute of Mining and Mechanical
Engineers.—A general meeting of the members of the
Institute of Mining and Mechanical Engineers will be held
in the Wood Memorial Hall, Newcastle-upon-Tyne, at two
o’clock to-morrow (Saturday). The following paper will be
open for discussion: “ The Lighting Efficiency of Safety
Lamps/’ by Mr. T. A. Saint. The following apparatus will
be exhibited and described : Nos. 3 and 4 Gray-Sussmann
electric safety lamps ; the Wolf alkaline electric safety
lamp ; the Ochwadt self-registering water gauge.

Royal School of Mines.—About 100 gathered together

at the Monico Restaurant on Monday evening on the
occasion of the fortieth annual dinner of the old students of
the Royal School of Mines. Mr. Frank Merrioks, A.R S.M.
was in the chair.—“ The Royal School of Mines ” toast was
proposed by Mr. W. H. Trewartha James. Royal School of
Mines men, Mr. James remarked, were to be found who had
reached the top of their profession and were of world-wide
reputation; some of the standard text books used in the
mining profession were written by associates of this school,
and it was interesting to note that during the past few
years no less than 27 important papers had been accepted
and discussed by the Institution of Mining and Metallurgy,
all of them contributed by associates of the Royal School of
Mines. In concluding, Mr. James remarked that the
Government should not grudge the expenditure it was
making on technical education. He asserted that no expen-
diture was repaid so liberally as that the Government had
made in connection with the mining and metallurgical
industry, having regard to the large amount the country
was making out of that industry.—Mr. Frank Merricks, in
responding to the toast, said he often thought they were
apt to forget what they owed to La Beche, Smyth and
Percy, who were responsible for the foundation of the
Royal School of Mines. If they could see the enormous
increase in the mineral production of England and the
Empire that has taken place since their time they would be

astounded. Last year the value of the metals and minerals,
including coal and precious stones, produced in the British
Empire amounted to roughly <£250,000,000. Was not an
Empire with a yearly mineral production of that value
worthy of a Royal School of Mines in the metropolis of its
Mother Country apart from, and independent of, any
university ? For some reason or other, Mr. Merricks went
on to observe, the advisers to the Government—mostly the
members of the various Royal Commissions—had appa-
rently tried to belittle and smother the Royal School of
Mines. He contended, however, that an efficient School of

Mines was as important to England and the Empire, with
its enormous mining industries, as a University devoted to

Fig. 13.

some seams sufficient packing material may, without
blasting, be obtained from falls in the goaf. An
example of successful application is D (fig. 1). In this
case “ blind drifts ” are ripped for packing materials at
intervals of about 30 yards, and the method is effective
in controlling the roof. The cost of ripping and of
building the packs is approximately the same as the
former cost of wood pillaring. The example H (fig. 2)
(also see fig. 13) is another illustration of successful
application of the method.

A band of stone in a seam worked with gate-roads
may be, for lack of stowage space, an expensive

; ton. Where ripping of the roof is not feasible and
packing material from other sources is not available,
the lack of a band of stone in the seam, or immediately
’ above or below it, may be a positive bar to the use of a
conveyor. The existence in a seam of a strong stone
i band from which the coal parts well may only slightly
affect the fillers. With traveller conveyors the fillers
begin at the inner end of the face, working towards the
loading road, and the stone packers may commence
work an hour or two after the fillers, and proceed
simultaneously but in arrear of them.

Soft and brittle roofs, which bend down from the
coal-head, or are so brittle that they break up at the
face, give much trouble with conveyors, especially in
thin seams where the sagging roof may not leave
sufficient working height or the debris from falls may
not find stowage room in the goaf. Many conveyors are,

pure science. Referring to the recent publication of the nuisance, and may detract from the value of the seam,
Final Report of the Royal Commissioners appointed four * but with conveyors it becomes an asset worth pence per

years ago to enquire into the University education of
London, Mr. Merricks said that there could be no doubt as
to what the future fate of the Royal School of Mines would
be if this report should receive his Majesty’s gracious con-
sideration. Personally, he could not believe there was much
chance of the report being adopted, but should such a mis-
fortune occur, it would be the duty of all old students who
have any love for their school and for the noble profession
to which they belong to combine and agitate against such a
calamity. For England to be deprived of a Royal School of
Mines would be an everlasting disgrace and a national
disaster.—Mr. T. A. Rickard, the honorary secretary, said he
felt it an honour to take the position which had been filled
by the late Mr. Arthur Claudet, who was a man who had at
heart the welfare of the Royal School of Mines. Mr. Rickard
contended that it was time the old students of the Royal
School of Mines did something more than dine. They had
dined for 40 years, and it was up to them to do something

serious. As a beginning, he suggested they might carry on # Krom a paper read before the South Wales Institute
the work Mr. Claudet had commenced.	| of Engineers and published in the Proceedings.

UNDERGROUND CONVEYING.*

By Sam Mayor, M.I.E.E.

(Continued from page 1222).

Roof.

Conveyors have, in respect of roof control, introduced
new problems which require careful study. These
problems arise from the necessity for maintaining a
perfectly straight line of face with uninterrupted
commuication through its length, coupled with the
necessity, where coal-cutters are used, for supporting a
greater width of exposed roof between the face and the
waste. The character of the roof may preclude the
joint use of coal-cutters and conveyors, and the alterna-
tive may be presented of selecting one or other; the
choice will, of course, be determined by the cost of
getting the coal by hand. Punctual and periodic
forward movement is desirable not only in respect of
the output of coal produced, but is vital to the securing
of good roof conditions.

The expectations in respect of saving ripping costs by
the use of conveyors have been over-sanguine. In the
absence of packing material ripped from gate-roads
and of dirt from the seam, it is clear that the support,
where support other than timbering is necessary, of
about 100 yards even of a good roof, between the pack-
walls which line the loading road and the return airway
at the extremities of the face, requires special treatment.
That the treatment has not always been adequate to
the occasion, has often been due to anxiety to realise in
full measure the estimated saving in ripping. Further,
the provision and maintenance of intermediate escape
roads for the men is a contingency to be reckoned with
in some seams.

In order to avoid expensive timbering, it may be
sound economy to incur expense in ripping the roof, to
provide material for pack-walls or square stone pillars
in the waste at suitable intervals. Difficulties and

dangers have been overcome and salvation of conveyor
faces has been effected by this method.

Estimates of saving in ripping should therefore be
conservative, and where packing material is not available
the introduction of conveyors, especially under strong
roofs, should be based chiefly upon economies in filling,
in tramming, and in getting a larger and cleaner output
rapidly cleared. It is to be noted, however, that in