176

THE COLLIERY GUARDIAN.

January 25, 1918.

the reason, nor could the hardness, in the sense of
resistance to pressure. An inch cube of coke would
stand, he believed, anything between 60 and 80 kilogs.
of direct pressure, which was much greater than that
exercised by the burden of the furnace, which would
be about 4 kilogs. He thought it was more a question
of what had been termed 11 friability.” He had always
understood that the requirement in coke was that it
should not, in passing down the blast furnace, and
rubbing about the walls, etc., produce fine coke, but
that it should content itself with simply breaking up
into smaller pieces—that, in fact, the ultimate portions
of the coke should be hard, and, not quite so important,
that the block as a whole should be hard.

Mr. Ridsdale interposed that it was not the static
pressure that the coke would not resist. It was gener-
ally loaded off the berich into the trucks, in which
process it got a fall of 6 or 8 ft. Then it went to a
bunker, and, if the bunker were low or empty, it
might get a drop of anything from 20 to 30 ft. Then
it was taken to the furnace and put down, when it
might get a further drop of anything from 16 to 30 ft.
What was wanted was resistance to breaking up and
crushing when coke was dropped all these different
heights, and then had several tons of heavy ore dropped
on top of it.

Replying on the discussion, Mr. Hewson said he was
surprised that Dr. Stead did not know of Forsythe’s
book on the blast furnace, which was accepted by blast
furnace managers as a standard work, although he
believed that it was largely a compilation from other
works. He had consulted Bell’s book, but did not find
the principles laid down as clearly as by Forsythe. As
to phosphorus in coke, it was wanted specially low,
because many steel makers had had to comply with
very stringent regulations regarding the content of
phosphorus in steel. He hoped the time would soon
come when no one would need to complain if there was'
a fair amount of phosphorus in the coke. He pro-
posed to make further experiments on the hardness
question, from which he would expect to get a sharper
dividing line between good and bad coke. Gas coke
was certainly not desirable for modern blast furnaces.
If they had an old-fashioned blast furnace, perhaps
40 to 50 ft. high, gas coke might be used, but for a
furnace from 70 to 80 ft. high it could not be used
satisfactorily. Gas coke would give a hardness number
of from 90 to 92. As to sulphur in coke, Wuest and
Wolff said that about 85 per cent, of it was organic
sulphur, some of it sulphate, and some of it sulphide.

The Chairman remarked that the quality of coal was
certainly one of the very most important points, but
they found that, even in the same seam, there might be
some coal that would not coke at all, whilst other coal
made excellent coke. As to washing coal, there was
no doubt that it very much improved the chemical
analysis of the coke, but he would rather like to hear
what Mr. Hewson had to say on the point as to
whether it interfered at all with the physical qualities.
His impression was that washing coal might not always
improve the coke from that point of view, although it
might improve the analysis. One might have a coke
with a very good analysis, but it might be useless in
a blast furnace. As to hardness, he thought coke
makers were at a loss for a good method of hardness
testing. The usual method was to take a hammer and
break the coke on a bench, or to throw it down on the
bench and see into how many pieces it broke. Some of
these practical tests used by coke burners gave a very
good indication of the quality of the coke, but it
seemed to him that there should be some more scien-
tific method of dealing with it. He was not alto-
gether satisfied with the method described in the
paper. As to the size of coke, it was very difficult to
know what was really required. It went through a
good many processes of handling in getting down to
the furnaces, as Mr. Ridsdale had said, but, at the
same time, it might, if a good coke, still give good
results. As to surface, the old beehive coke used to
have a most magnificent glossy surface, almost like
silver, and, at one time, that used to be considered one
of the chief tests of a good coke. When he was in Ger-
many, enquiring into patent ovens, he found that the
laboratories there were very much better equipped than
those in this country. The Germans spent a great deal
more time on scientific points of coke making than was
given in this country; where we had one chemist, they
might have 20 or 30.

A vote of thanks to Mr. Hewson ended the meeting.

Industrial Crisis in Denmark.—Owing to the failure of
supplies from the western countries, the industrial crisis in
Denmark has become acute. The imports of coal during
the past year were insufficient. The normal consumption in
this country may be estimated at 300,000 tons monthly. In

1916	the imports amounted to 200,000 tons monthly, but in

1917	they dropped to less than 100,000. Prospects seem
more uncertain than ever.

Compensation Act and Irish Colliery Workers. — In a
colliery case last week in the Wigan County Court, it was
urged that Irish colliery workers’ cases of injury were
peculiarly difficult to deal with under the Workmen’s Com-
pensation Act on account of the injured workers, who were
in receipt of weekly compensation payments, getting out
of touch with the colliery authorities after returning to
Ireland. It was stated that the applicant, Thomas Kilroy,
of Carn, Swinford, co. Mayo, usually came to this country
every summer, sometimes working on the land and some-
times in a mine. In 1913 he was employed as a dataller at
the Hindley Hall Collieries of Messrs. Crompton and Shaw-
cross. By a fall of roof he was injured in the hip and leg.
Before that his earnings averaged 29s. a week. Respon-
dants stopped the compensation of 14s. 6d. per week in
May 1917, on the ground that Kilroy was not incapacitated,
or that, if he was, he could still earn 29s. The matter was
referred to a medical referee, who considered that there was
partial incapacity as the result of the accident. The
respondents offered light work, bringing in 25s. weekly,
plus 9s. war bonus. His Honour said that if the parties
could not agree he would order the payment of 2s. weekly,
being half the difference between past earnings and the
wage of the employment now offered. It was agreed that
the respondents should pay a lump sum of £110.

WIRE ROPES AND FACTORS OF
SAFETY.*

By M. H. Sigafoos.

The application of wires in the form of ropes for
engineering purposes was first introduced in 1813 for
use as supporting ropes on the Geneva suspension
bridge. They were, however, not constructed in what
to-day would be strictly classed as wire rope, but were
formed of a series of wires laid parallel with one
another and bound together by means of smaller wires
which in turn were covered with tarred yarn. There
seems to be no authoritative data available as to the
number and sizes of the individual wires used in
making up the supporting ropes for this bridge, but it
is taken for granted that the material from which the
wires were produced was undoubtedly charcoal or BB
iron which at that period, and for some time later, was
almost exclusively used in the production of wire
ropes.

At a later date, 1835, some ropes of this type were
produced for the Freiburg suspension bridge, which
has a span of over 800 ft. in the clear. The support-
ing ropes for this bridge were composed of about 20
bundles of iron wires laid parallel, each wire being
0-125 in. in diameter and the combined total making
a rope about 5| in. in diameter. There is no doubt
that this type of rope, when properly constructed,
would present a breaking efficiency nearly equal to
the tensile strength of its individual component wires,
and perhaps it is the only wire-rope construction in
which each wire bears as nearly as possible its due
and proportionate share of the load stress. Ropes of
this class, while not extensively manufactured, have
been applied on the Niagara suspension bridge and
the Ohio River bridge and have been used for the large
main supporting cables on the Brooklyn suspension
bridge; also more recently on the new East itiver or
Williamsburg bridge. This type of wire rope is known
as the “ selvagee ” construction. Unfortunately it
cannot be utilised for hoisting purposes.

In 1834 a mining engineer named Albert, of
Clausthal, Germany, finally succeeded in fabricating,
with considerable difficulty, a “ stranded ” wire rope
composed of iron wires. He put this rope in operation
for hoisting ore in the shafts of the Harz mines, where
its superiority was immediately recognised over its
hempen predecessor. In 1837 Albert, before an
engineering society in Berlin, read a paper on the
construction and manufacture of stranded-wire ropes.
This paper advocated the production of wire ropes
along the same lines of construction as were previously
applied to the manufacture of hemp and fibre ropes,
then employed exclusively in the mining industry.
The size of the wire entering into the manufacture of
the first stranded-wire rope produced by Albert is said
to have been 0-144 in. in diameter, with a tensile
strength of about a thousand pounds each, or
approximately 27-5 tons per square inch of actual
cross section. The exact number of wires in the
strands and the number of strands employed are
uncertain, but ropes manufactured between 1835 and
1838 were made up of four wires to the strand, each
wire being about 3/32in. in diameter and the ropes
composed of four, six and eight strands.

Commercial Manufacture of Wire Ropes.

Immediately after the first successful experiments
carried out by Albert, Messrs. Felten and Guilleaume,
of Cologne, began to manufacture wire ropes upon a
commercial scale, for mining purposes in Germany
and France.

In England, before a meeting of the British Associa-
tion, held at Newcastle in 1838, Mr. Taylor, F.R.S.,
read a paper on wire ropes, by Count Brenner, and
in the same year Mr. R. S. Newall, of Dundee, acting
upon information and advice from a friend who was
studying mining conditions in Saxony, designed some
rather crude machinery for the purpose of manu-
facturing wire ropes with four strands, each strand
containing four wires. Mr. Newall carried on some
experiments with his early inventions, on which he
gradually improved, until in August 1840, he was
granted his first letters patent in England for
improvements in the manufacture of wire ropes and
the machinery designed for the process. With these
improvements there apparently came the introduction
of cores or “ hearts,” as Mr. Newall’s patent related
to the construction of rope with wires laid around
a core or heart to form the strand, and several strands
laid around a central core or heart to form the finished
rope. A company was formed, and, under Mr.
Newall’s personal supervision, wire ropes were manu-
factured in England on a commercial scale.

In the United States wire rope was first manu-
factured in the early ’forties and has been improved
upon year by year until the present time, when it
represents the very highest development of this means
of- hoisting and haulage. In the last fifty years there
has been a gradual change from the use of one kind
of rope material to another, and this was brought
about by the demand for an increased production
by speed and efficiency. At first iron was practically
the only material used, and this continued to be the
case until the introduction of crucible cast steel,
which opened the second period in the manufacture of
wire rope. The third period came with the introduction
of higher-carbon steel, known by the trade as plough
and special high-strength steel. In none of these
periods has the material in the production of wire
rope of the preceding period been forgotten, for
certain operations still demand iron cables, and there
are other operations in which it is out of the question
to substitute plough steel or the special high-strength
steel for cast steel.

Materials Used in Ropes.

The material entering into the manufacture of wire
ropes is perhaps of greatest importance in the wire-

* Paper read before the Mining Section of the National
Safety Council, New York.

rope industry, for upon its quality depends largely
the final result of the finished product. Through
careful selection, constant experimentation and
analysis, with minute researches into the physical and
chemical properties of the raw materials, the industry
is guided toward the production of a dependable wire
rope with durability and ductility as two of its fund-
amental qualities.

Until recent yars it was generally conceded that
the foreign steels were by far the best, due principally
to the use of Swedish ores. Foreign steel material
as imported by the American manufacturer for wire
rope purposes is made to meet rigid specifications.
This ensures as nearly as possible a uniform quality
Such steel is carefully tested and analysed to verify
the percentages of manganese, silicon and carbon as
well as of sulphur and phosphorus, which must be
extremely low. Acid open-hearth steels are generally
admitted to be of better quality than basic open-
hearth, and it has been suggested that this is due to
the higher oxygen content in the basic steel.

Much has been claimed for the qualities of chemi-
cally treated steels, such as vanadium, chromium,
etc., and in many instances the manufacturers of
steel products have proved the claims made for them.
So far as their use in the manufacture of wire rope
is concerned, however, they are still in the experi-
mental stages, and no data are yet available. With-
out doubt such elements may eventually be used in
connection with domestic ores and a finished article
be produced for the wire-rope industry similar to the
articles that have been produced in other industries.

Wires made from materials intended for the manu-
facture of wire rope for ordinary purposes are divided
into three classes, as previously stated ; namely, iron
with a breaking strain of approximately 80,000 lb. per
square inch, cast-steel, often erroneously called
crucible-cast, which has a breaking strain of 170,000
to 180,000 lb. per square inch, and plough-steel with a
breaking strain of 200,000 to 250,000 lb. per square
inch. Wire of higher tensile strength is often drawn,
but this is rarely used for any other purpose than
for standing rigging on racing yachts, where maxi-
mum strength with the lightest possible weight i^s
essential. Such wires are sometimes drawn to
260,000 lb. per square inch. Small sizes of even
higher tensile strength are drawn for wire rope or
strands for aeroplane guys.

Life, Stresses, and Speeds.

There has been much discussion on the question,
When has a wire rope reached the end of its useful-
ness, and when should it be removed? Up to the
present, it seems, the question remains unanswered—
at least, satisfactorily. In an exhaustive investiga-
tion conducted by the Bureau of Standards (Bulletin
75) on this subject the recommendation was made
that a rope should be removed after a certain number
of broken wires appear in each of the strands. These
tables have undoubtedly been compiled from stated
loads, speeds, head-sheave and drum diameters; from
shafts of various depths, the torsional and load
stresses being taken into consideration. It is, no
doubt, a useful guide, provided it can be applied
where conditions are the same or as nearly alike as
those from which these tables and figures were com-
piled. However, as there is no standard of sheave
and drum diameters, except those recommended by
rope manufacturers, or any set rule for maxi mum
loads, it is evident that with each variation in the
diameter of sheaves or loads there will be a variation
in the bending and load stresses. Both stresses are of
great importance, and each has a direct bearing on the
factor of safety. The various conditions of operation
that exist in different mines make it almost impossible
to find any two that are alike. There can always be
found considerable differences in the diameter of
sheaves, loads, and speeds, therefore it is obvious that
no set rule can be laid down by which all mining
operations can be governed.

In the catalogue of the wire-rope manufacturers
are to be found the “ proper working loads ” of wire
ropes for the given sizes and grades. This proper
working load in almost all cases is approximately 20
per cent, of the breaking strength of the rope, and
would appear to be a factor of safety of five. > This
however, is not the case, and it is important, in
„ calculating the proper size of rope for a certain load
with a required factor of safety, that this proper
working load should not be confused with the actual
factor of safety.

While the proper working load does show approxi-
mately one-fifth of the breaking strength of the rope,
it does not by any means indicate that in operation a
rope, selected on account of its showing a proper
working load in the list corresponding to the load
which it is desired to lift, would have a factor of
safety of five. This is due to the fact that in addition
t) the working load there are other stresses to which
ample consideration must be given; the most impor-
tant of these is the stress due to bending over the
sheaves and drums. If the rope to be used is
operated over standard-sized sheaves and drums as
recommended by the rope manufacturers, the general
average of this bending stress equals about 10 per
cent, of the approximate breaking strength of the
rope.

For instance, in a cast-steel wire rope, 1 in.
diameter and composed of six strands having 19 wires
to the strand, the approximate breaking strength is
30 tons and shows a proper working load of one-fifth
or 6 tons. This, however, is only to be used on a
minimum-size sheave or drum of 4 ft., as recom-
mended by the manufacturer. The bending stress
would be 2-7 tons, or 9| per cent, of the approximate
breaking strength of the rope. It is thus evident
that by adding 9| per cent, to the 20 per cent, load
stress we have utilised 29| per cent, of the ultimate;
and, instead of an apparent factor of safety of five,
we actually have only 3-41.

This factor is still further reduced by the stress
due to starting the load, and also in some cases by