384

THE COLLIERY GUARDIAN.

February 19, 1915.

the men have become used to the new conditions,
giving with six tubs 165 tons of coal per hour when
using the decking plant, as against 108 tons of coal per
hour when decking by hand, or an increase of output
over the old method of over 50 per cent., with a decrease
of labour of 33', per- cent. It should be understood,
however, that the actual times of winding will remain
the same, the saving of time being solely accounted for
by the better decking facilities.

Another important feature is the elimination of all
laborious work for the “ onsetters,” as by this new
arrangement the tubs gravitate on to the decks of the
secondary cages, the operating rams push off and
change the tubs simultaneously, and the secondary
cages are again emptied by means of tilting decks, so
that the tubs run off and away on their inclined roads
without assistance.

The erection, of the plant was carried out without
interfering in any way with the normal winding

82*.

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Fig. 6.—Ingoing Side of the Plant.



Fig. 7.—Stairway to Upper Deck of Plant.

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operations of the pit, and the changing-over arrange-
ments were completed in a few days, while the colliery
was standing for the Christmas holidays.

The photographs illustrate the surface arrangement
at the Jubilee pit, and show the headgear and decking
plant structure as described above. Referring to them in
detail, fig. 4 (seepage 381) shows the general arrangement
of the headgear, decking plant, and winding-engine house;
photograph (fig. 5) is taken on the “ full ” side of the
plant and shows the right-hand auxiliary cage being
discharged of its full tubs, the bottom tubs have been
run out, and the man is just operating the handle to
lower the auxiliary cage to discharge the two upper
decks; photograph (fig. 6) shows the “ empties ” or
ingoing side of the plant, and empty tubs will be seen
over the barrels on the right-hand side of the picture.
Above the timber stack will be seen the three sets of
pushing-out gear for simultaneously changing the tubs;
photograph (fig. 7) is a similar view to photograph
fig. 6 but taken on the opposite side of the plant,
showing the approach stairway to the upper deck of the
cage, viz., on which the men ride up and down the pit.

The Lateral Friction

By H. W. G.

There has lately been some enquiry from practical
men for a simple formula connecting the various
factors which determine the amount of lateral friction
encountered by a winding rope as it travels from one
side of the drum to the other. The object of this paper
is to submit such a formula, and to initiate a discussion
which shall, if possible, serve to solve the entire
problem. The problem, of course, is already solved by
the Koepe system, but a satisfactory solution for the
case of the ordinary wide dram has yet to be found.

Let A = the angle of maximum friction. When the
rope between the pulley and the drum lies in the same
vertical plane as that of the pulley there is no lateral
friction. This line of no friction will hereafter be called







the “ centre line.” When the rope has diverged to its
utmost limit from the centre line it makes an angle A
with that line, and A is therefore called the angle of
maximum friction. In no circumstances, however, need
the angle A exceed 3 degs., and in many cases it need
not exceed 1 deg. Hence, since the range of A does not
exceed 3 degs., it may, in this particular case, be taken
as practically true that the tangent of the angle varies
as the angle itself, and the use of those trigonometrical
symbols which so many practical men abhor may thus
be avoided.

It has been proposed to reduce the angle A by so
reducing the width of the drum that the rope is obliged
to “ mount ” and coil upon itself during the latter half
of the wind. Personally, it appears to the writer that
the proposed remedy cannot be applied without at the
same time introducing additional friction, which may
possibly be of a more destructive character than that
already due to the existing values of the angle A.

* From a paper read before the North of England Institute
of Mining and Mechanical Engineers.

t Greenwell Medallist.

of Winding Ropes.*

HALBAUM.f

Moreover, there does not seem to be any real necessity
for introducing such an innovation. The maximum
angle A, however, may be kept at its lowest possible
value by so attaching the rope to the drum that it lies
truly in the centre line when the cage is at “ meetings,”
or half-depth. In that case the lateral travel on either
side of the centre line can never exceed half the width
of the working part of the drum. In some cases there
may be a little difficulty attaching to the centring of
the rope at the middle point of the wind, but it is
evident that this difficulty might easily be overcome by
fitting the winding drum—at any rate for- the lower-
portion of the wind—with a spiral screw-tread, which
would guide the rope in the path required to ensure its
centring itself at the middle point of the wind. It is,
of course, a point for debate whether such a spiral
screw-tread would afford a better, or a worse, solution
of the difficulty than that furnished by the proposal to
over-coil the rope on a drum of half the width. It
must, however, be noted the “ spiral screw-thread ” here
referred to is not a grooved tread. In the formula
about to be stated, however, it is assumed that the rope
does lie truly in the centre-line when the cages are at
meetings. It is assumed, therefore, that the angle A
occurs at each end of the wind, as this arrangement, in
the opinion of the writer, is probably the better solution
of the difficulty.

The formula; also assume that the normal diameter
of the rope being d inches, the width of drum occupied
by each coil of rope on the drum will be 1'1 d inches.
That is to say, 10 per cent, is allowed for spread and
clearance and for any slight flattening of the rope
which may occur as it coils on the drum under-
stress of the load.

1 he ropes being centred at “ meetings ” :—

.	10 H

A ~ R L ................

where H = height of the banking level above

onsetting level; L = length of the rope extending from
the pulley to the drum; and R = ratio of the drum
diameter to the normal diameter of the rope (= from
110 to 150 in practice). H and L may be taken in any
units, but both must be in similar units. If it be
ordered that A shall not exceed a given predetermined
numerical value, the winding engine must either be
placed at such a distance from the pit that:—

the

(1);

the

(3);

or, the drum must be of such a diameter that:—

R 10H

R ~ A L ................

that is to say, if D == dram diameter, and d — rope
diameter, both stated in similar units, the following
formula must be taken:—

,	10 H

D “ d x AL

(4).

The width of drum required for each i ope is W,and:—

\ ................(5);

7 A L
or	+

where x — the additional width required to accommodate
the two or three spare coils of rope that remain on the
drum when the cage is at the pit bottom. In (5), W, x,
and H (or L) must all be taken in the same units (fe t,
inches, etc.).

It will be seen by (1) that, since H cannot be altered
for a given mine. A can be reduced only by increasing
L or R, or both. There is a practical limit to the
permissible value of L, since most managers prefer the
engineman to have a clear view of the banking operations
and the cages. Probably L may legitim Gely be extended
to 50 yds., and, if so, any reasonable valu“ of R will
reduce the angle A of maximum friction to al out
1.J degs., even in the case of the deepest British
coal mines, always provided that the ropes are so
adjusted as to centre themselves at meetings. In the
case of the shallower mines, the lateral friction should
be quite a negligible quantity.

The value of R may be increased in either or both
of two ways, namely—the diameter of the drum may be
extended, or the diameter of the rope may be reduced,
say by substituting a locked-coil rope of equal strength
but smaller diameter in place of the ordinary type of
rope frequently employed. Unfortunately, however,
any increase of the drum diameter magnifies the
moment of the load, necessitating bigger engines, or
higher steam pressures, if the engines and drums are
coupled direct, as is both usual and advisable where the
load is large. The writer believes that, as the problem of
electric winding approaches more closely to its complete'
solution, the present necessary connection of the bigger
engine with the bigger drum will disappear, owing to the
already proved and increasingly manifest superiority
which electrical systems possess in the matter of elas-
ticity.

Several attempts have been made to minimise or
destroy the angle A by drastic rearrangements of the
winding plant. In one of these, the winding engine
itself has a lateral movement that keeps the rope
centred during the whole of the wind. Another
proposal is to place the winding engine close to the pit,
take the rope away from the pit to a distant pulley, pass
it round this distant pulley, and then back to the
winding pulley at the pit top. By this means a gi eat
amount of lateral friction is avoided, and a large amount