Permanent way--Rails--Sleepers--Fastenings--and Permanent way laying.
Rails.--Accustomed as we now are to the substantial character of the
permanent way of our railways, we can scarcely realize that in the
earlier examples the rails or tram-plates were made of wood. The first
lines of which we find any record were those constructed to facilitate
the conveyance of coal, iron ore, stone, slate, or other heavy
materials to shipping ports or points of distribution. Speed was a
matter of little importance, the principal object being to introduce a
distinct surface or roadway which would allow a heavier load to be
hauled without increasing the hauling power. As a heavily loaded
wheelbarrow, difficult to move on an ordinary road, can be readily
wheeled along a wooden plank, so it may have been inferred that strong
timber, laid in parallel lines and level and even on the upper
surface, would form a track, or roadway, presenting far less
resistance than the ordinary gravelled or paved roads.
The wooden tramway was the first improvement over the ordinary road.
The idea once originated, various types were soon introduced, and the
sketch shown in Fig. 227 illustrates one which appears to have been
early suggested and largely adopted. Wooden cross-sleepers, A, A,
were placed at convenient spaces, and on the top of these strong
timber planks or beams, B, B, were spiked at proper distances to
suit the wheels of the waggons or four-wheel trucks, which had flat
tyres like ordinary carts. The spaces between the sleepers were filled
in with gravel or broken stone to form a roadway or hauling path for
the horses. A little later _double rails_ were introduced, by placing
a second or upper timber on the top of the lower one, as in Fig. 228.
[Illustration: Fig. 227, 228, 229, 230, 231, 232, 233, 234, 235]
This double rail arrangement not only strengthened the framework, but
by increasing the height allowed a greater quantity of suitable 184
material to be placed over the sleepers to protect them from wear by
the horses’ feet. It can be easily understood that a wooden tramway
could not be very durable. It would be affected by the sun, rain, and
snow, and particles of sand and gravel thrown on to the tram beams
from the hauling path would hasten the abrading or wearing away of the
soft portions of the timber into hollows, leaving the hard knots
standing out as projections. The uneven surface would produce a series
of blows every time a loaded truck passed along, loosening the pieces
and rendering the repairs constant and expensive. To obviate the rapid
wear of the tram-timbers continuous narrow bars of wrought-iron were
fastened on to the running-surfaces; these in a measure prolonged the
life of the timbers, but at the same time added to the number of the
pieces and fastenings to be maintained.
Primitive as this description of road appears to be, it was in use for
many years in some parts of the United States of America, and even
after the introduction of the early locomotives; timber was abundant
and cheap, and iron in any form was costly. These long thin strips of
iron, placed as in Fig. 232, had a tendency to become unfastened at
the ends, and to curl up in a very alarming manner, which earned for
them the soubriquet of _snake heads_. Although iron was only used to a
limited extent in the first instance, it was soon found to be a much
more suitable material for a tram-path than the best timber. As a next
progressive step we find that the tram-plates were made entirely of
iron, of full width for the wheel-tyres, and with a guiding flange to
keep the wheels on the proper track. In some cases the guiding flanges
were placed inside the wheels, as in Figs. 229 and 230, and in others
outside, as in Fig. 231. With the former plan a thicker covering of
gravel or broken stones could be laid down to protect the sleepers
under the horse-path.
These solid tram-plates were made of cast-iron, that metal being
considered the most convenient for manufacture and the least liable to
suffer loss from rust and oxidization. Another advantage of the
cast-iron was that broken tram-plates could be melted down and recast
at a moderate cost.
Long lengths of these cast-iron plate tramways were laid down in this
country and abroad, and short portions of some of them remain in
existence even to the present day. They were of immense service for 185
the transportation of heavy materials, and without their adventitious
aid many valuable collieries and quarries must long have remained idle
and undeveloped. In thus providing a level, smooth, and comparatively
durable wheel-track for the waggons, these tramways became the fitting
pioneers of the great railway system which was to follow.
Notwithstanding the great superiority of the cast-iron plates as
compared with the former timber beams, much inconvenience was still
caused by gravel and dirt falling on to the wheel-track and seriously
impeding the haulage of the waggons. To overcome this difficulty the
next step taken was to remove the guiding flange from the tram-plate
and transfer it to the wheel, thus developing and introducing the
original flanged wheel. This was a most important step, and paved the
way for other improvements. The rails, or _edge rails_, as they were
at first called, were made sufficiently high to allow ample space for
the wheel-flanges to clear the ground, and were secured to cast-iron
chairs placed on wooden cross-sleepers, or in some cases to stone
blocks, as shown in Figs. 233, 234, and 235. The narrow top of rail,
and its height above the horse-path, effectually prevented the
lodgment of gravel or dirt, and the flanges on the wheels ensured a
more even course. From the irregular and easily choked-up tram-plate,
the system changed to the clean rail and properly defined track.
Waggons could be hauled with greater freedom, and with less wear and
tear to themselves and to the roadway.
At this time the use of the steam-engine was becoming more general,
and a fine field was opened out for its application as a motive-power
on the tramways. Stationary engines, or _winding engines_, as they
were called, were first employed to haul the trucks by means of long
ropes passed round revolving drums, and supported at intervals by
grooved pulleys placed between the rails at suitable distances. In
this way fair loads could be conveyed, and at moderate cost; but the
system was found to be only suitable for short distances, and it had
the great drawback that horses or other motive-power were still
necessary for sorting or distributing the trucks before and after
their transit by rope haulage.
The next great advance was to place the steam-engine on wheels, to
enable it to haul and accompany the trucks. Crude and imperfect as the
primitive locomotives must have been, a very short trial of them 186
served to show that the rails of cast-iron then in use were totally
unfitted to form a trackway for the newly invented machines. The short
fish-bellied cast-iron rails were made in lengths merely to extend
from chair to chair; they possessed little or no continuity, and from
the inherent brittleness of the material they were constantly breaking
and giving way under the increased weights imposed upon them. It
became necessary to adopt a more reliable material, and attention was
naturally turned to forged or wrought iron. The suggestion once made
was promptly responded to by the iron makers. Special machinery was
designed and constructed, and very soon wrought-iron rails were
manufactured in large quantities. At first they were made very similar
in section to the fish-belly cast-iron rails, but in lengths to extend
over three or four sleepers. The increased length gave greater
stability to the road, and permitted an increase of speed. The
manifest superiority of the wrought-iron rails led to their universal
adoption, and a great impetus was thus given to their manufacture.
Improvements were made in the machinery for rolling, and more care was
bestowed in the working of the iron. Changes were made in the section
of the rails; the fish-belly form was discarded, and a double-head
type was introduced to give more lateral stiffness. At this period in
its history the capabilities of the _iron road_ began to be more fully
recognized, and the supporters of the system foresaw a great future
success, both for the conveyance of passengers as well as goods.
Hitherto the tramroads or railroads had been used for minerals and
merchandize only, but it was now claimed that on a carefully
constructed line, and with improved locomotives and rolling-stock, it
would be possible to convey passengers more conveniently and rapidly
than by any other method.
[Illustration: Fig. 236, 237, 238, 239, 240, 241, 242, 243, 244, 245,
246, 247, 248, 249, 250, 251, 252, 253, 254, 255, 256, 257, 258]
Inventive minds were at work to accomplish so desirable an object, and
public enterprise was forthcoming to provide funds for the purpose.
The successful working of the first passenger line formed the dawn of
a new era in travelling, and similar lines were soon projected for
other places. The wrought-iron rails in use at this time were
generally of a double head form, and rarely exceeded 12 or 15 feet in
length. They were held by wooden pegs in cast-iron chairs, which were
secured to timber cross-sleepers or stone blocks, as shown in Figs. 188
234 and 235.
They were light in section, and it is stated that the first rails on
the Liverpool and Manchester Railway weighed only 33 lbs. per yard.
The railway system spread rapidly, and the constantly increasing
traffic of all kinds soon necessitated heavier rails. Various sections
were devised and tried on different lines, one of the main objects in
view being to obtain a steady road for the increasing speeds, as well
as one of durability. Some of these sections are shown in Figs. 236 to
258.
Sections 236 to 248 all required chairs to attach them to the
sleepers. The flange rails, 249 to 253, and bridge rails, 254 to 256,
also rail 257, were designed to rest direct upon the sleepers without
the necessity of chairs; and the Barlow rail, 258, with its great
width of 11 or 12 inches, was intended to be used without sleepers of
any kind, the gauge being secured by means of angle iron tie-bars.
Rails were rolled heavier and longer, and more care was bestowed on
the fastenings; but, notwithstanding these improvements, the
rail-joints still continued to be the weak point in the road. Even
with an extra large joint-chair and stout wooden key, there was much
vertical play at the ends of the rails, producing objectionable noise
and vibration in the running, and acting detrimentally on all the
fastenings. The introduction of fish-plates at the rail-joints, as
shown in Fig. 259, effected an improvement which cannot be overrated,
as by their adoption such security, speed, and smoothness became
attainable as were not before possible. With a pair of simple rolled
wrought-iron fish-plates, or splices, and four bolts--two through the
end of each rail--a better, smoother, and more effectual joint was
obtained than had ever been produced by the heavy cast-iron
joint-chairs. The system of fishing, or splicing, was at once admitted
to be the simplest and most direct method of joining the rails; and,
although minor detailed improvements have since been made, the
arrangement, as a principle, has never been superseded. Many miles of
fished rails were laid down with a chair, or support, placed
immediately under the joint, forming the method termed the supported
fish-joint; but experience proved that this mode of application did
not give such a good result as the suspended fish-joint, and the
latter plan has now been adopted on almost all railways.
[Illustration: Fig. 259, 260, 261, 262, 263, 264, 265, 266, 267, 268,
269, 270, 271, 272]
The experience obtained year after year in the wear of rails under 190
heavy traffic, led to continued improvements both in the method of
rolling and in the selection of the iron to form the rail-pile; one
description of iron was found more suitable for the head, or running
surface, and another for the vertical web; but, even with the best
machinery and most carefully assorted materials, high-class
wrought-iron rails were liable to lamination, and long thin strips of
iron became detached from the upper, or wearing, surface. The rail was
composed of many layers of iron, and it was not always possible to
ensure that they were all thoroughly welded, or incorporated together.
As early as 1854 a few experimental solid steel rails were laid down
on some of the principal railways, and gave excellent results as to
evenness of wear and durability, but their cost of manufacture
rendered their extended use almost prohibitory.
Compound rails of steel and wrought-iron, as in Fig. 260, were also
tried on several railways, but the practical results were not such as
to lead to a very extended adoption. In preparing the _pile_ for a
compound rail, suitable wrought-iron bars were placed to form the
lower member or flange, the web, and part of the head, and a slab of
steel was placed on the top to form the upper portion of head, or
wearing surface of the rail. It was intended that in the process of
rolling these distinct layers were to be incorporated together, to
form the section shown in Fig. 260. Doubtless many good wearing rails
were manufactured on this system, but the inherent difference of the
two materials, steel and iron, rendered it very difficult to ensure
such uniform incorporation as would withstand the constant pounding
under heavy, fast traffic. It was not until some years later that the
process of the Bessemer Converter was discovered and perfected, by
means of which steel can be produced in large quantities far more
rapidly and at much less cost than by any other method hitherto
adopted. The introduction of this process for making steel caused a
complete revolution in the material for rails. Steel which had
previously been excluded on account of its cost, could now be supplied
at a moderate price, and, from its compact and homogeneous character,
promised a very much longer wearing life than the best wrought-iron
rails that had ever been rolled. Experience has shown that these
promises have been fully verified; wrought-iron rails are things of
the past, steel rails have taken their place, and can now be purchased 191
at a less price per ton than the iron rails of twenty years ago.
It is interesting to note that out of the many varied sections that
have been designed, some of which are shown in the sketches described,
only two have practically survived--the bullhead rail and the flange
rail. The bull-head rail, Fig. 261, has grown out of the original
double-head rail, which had both the top and bottom members made to
the same section and weight, with the object that, when the upper
table had become so much worn as to be unfit for further use, then the
rail could be turned, and the other table, or head, brought into
service. Experience, however, proved that turned rails formed a most
uneven and unsatisfactory road, the long contact with the cast-iron
chairs resulted in serious indentations at the rail-seats, rendering
the rails totally unfitted for smooth running. In practice, therefore,
it has been found better to restrict the running wear to one head
only, and to give increased sectional area to that head, and, at the
same time to diminish the sectional area of the lower member to a
corresponding extent, but to retain the same width, so as to obtain a
full bearing surface on the cast-iron chair. Steel bull-head rails are
now adopted on nearly all the principal lines at home, and on several
of the leading lines abroad.
The flange rail, Fig. 265, was designed to give a broad, direct
bearing on the sleepers, and thus avoid the necessity of using chairs.
Rails of this section have been laid down on many of our lines at
home, and are very largely used on the Continent, in the United States
of America, and in our colonies generally. This section is, also,
nearly always adopted for narrow-gauge railways. Having fewer parts,
it makes a cheaper road than the bull-head rail, but is not considered
so strong or suitable for heavy and fast traffic. Comparing the two
rails shown in Figs. 261 and 265, each having exactly the same size
and sectional area in the head, it will be seen that there is more
material in the lower member, or flange, of the one rail than there is
in the lower member of the other; the weight per lineal yard being 79
lbs. for the former and 75 lbs. for the latter. But this small excess
in the weight and cost of the flange rail falls very short of the cost
of the cast-iron chairs and wooden keys necessary for the bull-head
rail.
Up to the years 1870-1875, it was the common practice to make the top,
or wearing surface of the rail, comparatively round, as shown on the 192
typical sections, Figs. 263 and 267. The effect of this sharp-curved
outline was to limit the first wearing, or contact surface to a narrow
strip along the head of rail, causing a tendency to groove or form
hollows in the treads of the wheel-tyres. As the rail wore down, the
upper surface assumed a much flatter curve, more closely assimilated
to the section of the wheel-tyre, and giving better results for
regular wear under heavy traffic. Profiting by this experience, the
rails of the present day are made much flatter on the head than they
were formerly, as will be noted from the sections shown on Figs. 261,
266, and 269, which represent types of rails now actually in use on
some of the principal railways.
In designing a rail for any given line, the section and weight of the
rail must necessarily be influenced by the weight of the rolling-stock
passing over it, and the amount of the traffic it has to sustain.
The engine, being the heaviest vehicle in the train, will give the
measure of the greatest weight on one pair of wheels. Engines vary
considerably on different lines, ranging from ten tons to eighteen
tons or more on one pair of driving-wheels, according to the
description of work to be performed.
Very often secondary or branch lines, with comparatively light
traffic, have steep gradients, necessitating engines as heavy as on a
main trunk line; but the number of trains on the former may not exceed
twenty per day, while on the latter they may amount to one hundred and
fifty or two hundred. It is evident that the rail which would last for
very many years under the small traffic, would have a very short life
under the frequent traffic. Hence the reason why it is found expedient
to give a large increase of material in the heads of rails carrying
the heavy, constant train service of many of our main lines.
Figs. 261, 262, and 263 are sections of rails in use on lines having
heavy engines and fast trains, but with a comparatively small daily
train service, and Figs. 264, 266, 267, and 268 are sections of rails
carrying the heavy, fast, and incessant traffic of some of our leading
lines.
On lines having small traffic, slow speeds, easy gradients, and
comparatively light engines, a reduced section of rail may be adopted;
but in doing so it is well to allow for any probable future
development of traffic which might cause the introduction of heavier
engines.
Figs. 269 to 272 show sections of rails varying from 72 to 60 lbs. per 193
yard, also a section of a 45-lb. steel flange-rail, much used on
3-foot narrow-gauge railways.
Valuable and interesting statistics have from time to time been
recorded, with a view to ascertain the average life of a steel rail,
by obtaining the number of million tons of train load which it would
sustain before it became worn down to such an extent as to be no
longer of service on the line. It will be readily understood that the
rate of wear of a steel rail will depend not only on the weight and
section of the rail itself, but on the class of rolling-stock, and the
description of traffic it has to carry. It will also be largely
affected by the circumstances of whether the line is on a level or on
an incline.
The writer has had careful measurement taken of the wear of the steel
flange-rail (Fig. 265), 79 lbs. per yard, and the result shows that
with a traffic not exceeding twenty-four goods and passenger trains
per day, one-tenth of an inch was worn off the top of the rail in ten
years on the comparatively level portions of the line; but that the
same amount of one-tenth of an inch was worn off in six years by the
same traffic, on the same district of the line, in places where the
gradients varied from 1 in 100 to 1 in 70. The heavy pounding of the
engines, and the working of the brakes tend very materially to shorten
the life of the rails on the inclines.
As now made, the steel rails manufactured under the converter process
exhibit great similarity in the analysis of their component parts; at
the same time it is well known that a slight preponderance or
reduction of one or more of the constituents will result in making the
steel hard or soft. The following statement gives the analysis of
twelve steel rails, six of which were classed as _hard_ steel, and six
as _soft_ steel:--
HARD STEEL.--ANALYSIS OF SIX STEEL RAILS WHICH BROKE EITHER IN
TESTING OR IN LINE.
-----------+--------+--------+--------+--------+---------+---------
| 1. | 2. | 3. | 4. | 5. | 6.
-----------+--------+--------+--------+--------+---------+---------
Carbon | 0·47 | 0·51 | 0·56 | 0·43 | 0·47 | 0·54
Silicon | 0·09 | 0·08 | 0·08 | 0·09 | 0·095 | 0·121
Sulphur | 0·06 | 0·06 | 0·06 | 0·06 | 0·054 | 0·056
Phosphorus | 0·07 | 0·06 | 0·06 | 0·08 | 0·08 | 0·057
Manganese | 1·23 | 1·10 | 0·90 | 1·23 | 1·15 | 1·26
Iron | 98·08 | 98·19 | 98·34 | 98·11 | 98·151 | 97·966
+--------+--------+--------+--------+---------+---------
| 100·00 | 100·00 | 100·00 | 100·00 | 100·000 | 100·000
-----------+--------+--------+--------+--------+---------+---------
SOFT STEEL.--ANALYSIS OF SIX STEEL RAILS WHICH STOOD THE TEST WELL, 194
AND BENT FREELY WITHOUT SHOWING ANY SIGN OF FRACTURE.
-----------+---------+---------+---------+---------+---------+---------
| 1. | 2. | 3. | 4. | 5. | 6.
-----------+---------+---------+---------+---------+---------+---------
Carbon | 0·35 | 0·39 | 0·37 | 0·34 | 0·35 | 0·250
Silicon | 0·06 | 0·07 | 0·07 | 0·08 | 0·07 | 0·069
Sulphur | 0·062 | 0·061 | 0·062 | 0·061 | 0·061 | 0·046
Phosphorus | 0·061 | 0·061 | 0·061 | 0·063 | 0·062 | 0·058
Manganese | 0·870 | 0·875 | 0·866 | 0·864 | 0·800 | 0·636
Iron | 98·597 | 98·543 | 98·571 | 98·592 | 98·657 | 98·941
-----------+---------+---------+---------+---------+---------+---------
| 100·000 | 100·000 | 100·009 | 100·000 | 100·000 | 100·000
-----------+---------+---------+---------+---------+---------+---------
Many rails which have been broken in the line under traffic have been
analyzed, and proved to be hard steel; while others, which have been
bent into all sorts of shapes, but not broken during accidents or
derailments, have also been tested, and proved to be of soft steel.
Some engineers are advocates for a hard steel rail, and claim for it
greater durability and longer wear; but even supposing such hard rail
should possess a slight superiority over the soft rail, it is well to
consider whether such assumed advantage is not obtained at the risk of
incurring greater liability to fracture. It must be borne in mind that
a rail, once placed in the road, is exposed to all the changes of
temperature from heat to frost, and has frequently to sustain
increased strains arising from loose sleepers, where the gravel or
ballast has been disturbed during heavy rains.
When writing a specification for steel rails, it is usual to state the
number of tons per square inch in tensile strain which the steel must
be able to sustain without fracture, and also to stipulate that some
of the rails will be tested by the falling-weight test. In the latter
test a rail is placed, say at 3 feet bearings, and in a similar
position to what it would occupy in the road, and a weight of eighteen
hundredweight, or one ton or more, according to section of rail, is
allowed to fall from a height of 9 or 10 feet, on to the rail, at the
centre between the bearings. With three blows from the given height,
the rail must not bend or deflect more than a specified amount. The
falling-weight test is, perhaps, rather a rough and ready one; but it
is always reassuring to prove that the rails will withstand such a
severe ordeal, as it must be a very exceptional circumstance in the
routine of railway working which will produce a blow or shock equal 195
in effect to the falling-weight test. The rails form such an important
part of the trackway, almost the very basis on which the traffic has
to depend for its safety, that, apart from the question of wear, no
effort should be spared to ensure their thorough soundness and
efficiency.
In modern practice rails are generally used in lengths varying from 25
feet to 30 feet. There is no difficulty in making them longer; but any
excess over the above lengths is found to be inconvenient for
transport, for handling in the line, and for making the necessary
allowance for contraction and expansion at the joints. Steel rails are
generally marked on the vertical web with the initials of the railway
company, the name of the manufacturer, and the year in which they are
rolled. This is done by cutting out the letters in the last pair of
rolls through which the rails have to pass before they are completed,
so that on the rails themselves the letters stand out in raised
characters, thus: G.N.R.I.......C. CAMMELL & C^o 1896. In this
manner the rails always carry for reference the name of maker and
date.
When comparing the relative merits of the flange-rail and
bull-head-rail permanent way, the question of strength and durability
must be considered, as well as that of economy. The flange-rail road
has undoubtedly fewer parts and fastenings, and when the flange is
wide, the sleepers sound, and the rail securely held down to the
sleepers, the result is a smooth running road. So long as the rail can
be maintained in a constant close contact with the wooden sleeper, the
running is almost noiseless, the jarring on the rails being absorbed
or taken off by the timber; but so soon as a little space or play
takes place between the spikes or other fastenings and the upper
surface of the flange, the rail obtains a certain amount of rise, or
lift, which comes into action upon the passing of every rolling load,
producing unsteadiness in the rail and a clattering noise in the
running. A flange of 5 inches, on a sleeper 10 inches wide, has a
bearing surface of 50 square inches (assuming the sleeper to be square
cut, without any wane on the edges), and this area of 50 inches is
only about half of the bearing surface on the sleeper of an ordinary
modern cast-iron chair.
Main-line locomotives have weights on the driving-wheels varying from
16 to 18 and 20 tons. Taking 18 tons as representing a common practice
for a large express engine, would give 9 tons as the weight imposed on 196
each rail by each driving-wheel Assuming this weight to be distributed
over three sleepers would give a dead weight of 3 tons per sleeper, or
134 lbs. on every square inch of the 50 square inches of surface, or
rail-bearing area, on each sleeper, without taking into account the
effect of the blow or percussion from the rolling load. The presence
of a loose sleeper throws additional weight on the adjoining sleepers,
and increases the destructive influence on the timber. The constant
application of heavy rolling loads on a small bearing area of timber
crushes and wears away the timber very rapidly. The small bearing
surface of the flange rail expedites the cutting down into the
sleeper, and as the rail beds itself further and further into the
wood, the fastenings must be driven or screwed down to follow the
flange. Spikes may be driven down, but the further they go they have a
less thickness of timber for a bed, and therefore a diminished hold.
Crab bolts are apt to become rusted or ironbound, so that they cannot
be screwed further, and must then be taken out and replaced with new
ones. The narrower the flange, the more rapidly does the rail-seat cut
down to a thickness inconsistent with safety. The sharp edge of the
flange-rail has a tendency to cut a channel in the spike, and it is
not at all an unusual occurrence to find strong square shanked
dog-spikes, which have been thus cut into to the extent of a third or
even half their thickness. The comparative narrow flange places the
spikes at great disadvantage in point of leverage for holding down,
and this weakness is soon made manifest, particularly on curves, where
additional crab bolts or other devices are rendered necessary to
counteract the tendency of the rail to rock and tilt over sideways.
When the head of the rail cannot be kept in its proper position, the
gauge becomes widened, and an irregular sinuous motion takes place in
the running of the train. This drawback has been found to be a serious
matter where light narrow flange rails have been adopted to carry
comparatively heavy, short wheel-base engines. In some cases
wrought-iron sole-plates, or even cast-iron bracket-chairs, have been
introduced to give more bearing surface on the sleeper and increased
support to the rail, but neither of the two methods give the same
simple complete hold to the rail that is obtained by the cast-iron
chair for the bull-head rail.
On the other hand, the modern cast-iron chair for the bull-head rail 197
has at least double the bearing surface on the sleeper to that of the
flange-rail seat, so that under the same circumstances of rolling load
as above described, the weight of 134 lbs. per square inch would be
reduced to half, or 67 lbs. The greater length given to the chair
effectually prevents any rocking action on the part of the rail, and
reduces to a minimum any lifting action on the spike. A good fitting
chair--especially when keyed on the inside--provides a most effectual
support to the rail both vertically and laterally, and maintains the
rail to accurate gauge. By giving proper clearance space at the tops
of the chair-jaws, a bull-head rail can be taken out by simply driving
out the wooden keys, and a new rail inserted without in any way
disturbing the chairs or spikes. To change a flange rail necessitates
the slackening and removal of a large number of the spikes and crab
bolts.
As the sleepers under the chair road suffer less from the crushing of
the timber, they have a much longer life in the line, and remain
serviceable until they are incapacitated from decay. This is a very
important item in places where timber sleepers are expensive. The
steadiness of the chair prolongs the efficiency of the spikes.
As the actual wearing portion of the rail is the head, or wheel
contact surface, a liberal area--consistent with the expected
traffic--must be given to that part, whether for a bull-head rail or a
flange rail. By comparing the two sections, Figs. 273 and 274, the one
for an 85-lb. bull-head rail, and the other for a 100-lb. flange rail,
it will be seen from the dotted lines that the heads of each rail are
almost identical, the difference of 15 lbs. being disposed of in the
flange of the heavier rail. Practically, therefore, we have 15 lbs.
per yard extra weight of steel in the rail, on the one hand, as
against the cast-iron chairs and steadier permanent way on the other.
For lines where the traffic is small, weights light, speeds low, and
economy of construction imperative, the flange-rail permanent way will
be very suitable.
The writer has had long mileages of each description of permanent way
under his charge, both at home and abroad, for many years, and the
result of his experience has shown that, although a fairly good road
may be made with flange rails, still, for constant, heavy, fast
traffic, the bull-head rail with cast-iron chairs makes a much
stronger, more durable, and better permanent way than any flange
railroad.
[Illustration: Fig. 273, 274]
Briefly summarized, the principal advantages and disadvantages of the 199
two kinds of rails stand as follows:--
ADVANTAGES.
Bull-head Rail. Flange Rail.
Large bearing surface of chair Fewness of parts, and less
upon the sleeper, and greater cost.
stability of the rail.
Smaller quantity of ballast
Longer life of wooden sleeper. required to cover up the foot
of rail.
Impossibility of rail tilting
over outwards. More lateral stiffness than
the bull-head rail.
Facility for changing a rail
without disturbing the
fastenings in the sleepers.
Easier to maintain, owing to
less disturbing strains on the
fastenings.
A bull-head rail is more
readily set or laid to follow
line of curve.
In most cases the one set of
chairs will serve for a second
set of rails.
Perfect straightness of rail:
it is very rare to find a
crooked bull-head rail.
Easier to roll, and more
likely to obtain uniformity of
steel.
DISADVANTAGES.
Bull-head Rail. Flange Rail.
Bull-head Rail. The small rail-seat area on
sleeper throws great crushing
Greater cost. weight on the timber.
More ballast required to cover Shorter life of wooden
up the rail. sleepers from the cutting down
of rail-seats.
Less lateral stiffness than
the flange rail. The edge of flange cuts the
spikes after a few years.
The undulation of the rail
under trains tends to raise
the spikes, and causes lateral
movement in the rails.
More difficult to maintain, in
consequence of greater
tendency of the fastenings to
work loose.
Difficulty in getting flange
rails straightened laterally.
More difficult to set to
follow regular line of curves.
More difficult to roll, and
less likely to obtain
uniformity of steel.
Tramway Rails.--Tramways on streets or public roads are now
universally recognized as important branches of the railway principle.
Their smoothness of movement, increased accommodation, and many other
advantages as compared with the old road omnibus, render it no longer
necessary to call for special advocacy when there is a possibility of
their introduction. They occupy a position so thoroughly appreciated 200
by the public that any check on their reasonable use or extension
would be considered as detrimental to the interests of the travelling
community.
As a rule, these tramways are laid down on streets or roads previously
constructed for the ordinary road traffic, where all the preliminary
work of earth filling, bridges, drainage, etc., has already been
accomplished, and there only remains the selection and laying down of
the rails or permanent way over which the tram-cars will have to run.
The description and weight of permanent way to be adopted will depend
largely upon the weight of the cars to be used and the system of
motive-power decided upon for the haulage--whether horses, steam,
cable, or electricity.
As the portion of the streets or public roads along which the tramway
has to be laid will, in all probability, have to be occupied and
traversed by all kinds of vehicles besides the tram-cars, it is
absolutely necessary that the permanent way for the tramway should be
of such description as to require the least possible amount of
adjustment of fastenings or opening out of the roadway for repairs.
Where the entire width of the street, including the space between the
tram-rails, is paved with stone setts, the opening out of even a short
length for repairs is tedious and costly, and causes considerable
obstruction to the street traffic. It is most important, therefore,
that the rail and its fastenings should not only be strong enough for
its own tram service and the carts and drays which will pass over and
across the track in all directions, but it must possess the minimum
necessity for disturbance.
Figs. 275 to 279 are sketches of a few of the many types which have
been brought into use in various places.
Where the public roads are wide, and a space can be set apart at the
side for the special use of the tramway, the arrangement shown in Fig.
275 will be simple and efficient. It is very similar to an ordinary
railway permanent way with the ballast filled in flush with the top of
the rails. The rails are shown as flange or flat-bottom rails, fished
together at the joints, and properly secured to transverse sleepers of
wood, iron, or steel. The space between and outside the rails is
filled in with small-sized broken stone ballast or good clean gravel,
and forms an even surface, over which animals or cattle may pass
without risk of being thrown down.
[Illustration: Fig. 275, 276, 277, 278, 279]
Fig. 276 represents a system which was laid down extensively, especially 202
for horse tramways, but not proving efficient, has been superseded by
other types of a stronger and more durable description. The rail was
rolled with a continuous groove to provide clearance for the flanges
of the car-wheels, and the sides of the rail were turned down so as to
fit over the longitudinal timber sleeper, to which the rail was
secured by staple-dogs, as shown. Cast-iron chairs, spiked on to
wooden cross-sleepers, held the longitudinal sleepers in position. The
wooden sleepers were favourable for smooth running, but the section of
the rail, practically a light channel-iron laid on the flat, was most
unsuitable for carrying weight or for making a proper joint.
Experience proved this road to be very difficult to maintain in good
order for easy traction. The staple-dogs worked loose after a little
time, and the rail, having scarcely any vertical stiffness, rose and
fell during the passage of every car-wheel, resulting in most uneven
joints and a clattering roadway.
With the view to obtain a stronger and more permanent support for the
rail than the longitudinal timber sleeper last described, various
forms of cast-iron chairs were devised. Fig. 277 represents one of
these patterns. The rail, which is of T-section with a
continuous wheel-flange groove, is secured to the cast-iron chair by
the cross-pin, as shown. Although this cross-pin may in time work a
little loose, it cannot work out, being kept in position by the
paving-setts on each side. The cast-iron chairs are placed at
convenient distances, and being set in a bed of concrete, do not
require cross-sleepers or tie-bars. This type makes a strong road, but
the rail-joints cannot be made so even or efficient as with the more
modern form of rail.
Rail manufacturers are now able to roll a section of rail combining
the vertical stiffness of the ordinary flange, or flat-bottom, rail
with the running-head and continuous wheel-flange groove, considered
the most suitable for heavy tramway traffic. The introduction of this
section of rail has contributed greatly to the increased efficiency
and durability of the permanent way for street traffic; and as the
ends of the rails can be secured by ordinary fish-plates, there is the
great acquisition of even joints and increased smoothness in the
running of the tramcars. This rail can be rolled of various weights to
suit the rolling loads. On some tram-lines a moderately heavy section
has been adopted, and secured to transverse sleepers of rolled iron or
steel laid on a bed of concrete. On others similar rolled metal
sleepers have been used, but laid longitudinally. For some descriptions 203
of traffic a much heavier section of rail has been used, having a base
sufficiently wide to provide ample bearing on a bed of concrete
without the intervention of either transverse or longitudinal
sleepers.
Fig. 278 is a sketch of the modern rail as laid down on a rolled steel
transverse sleeper, the rail being held in position either by
turned-up clips, wedges, bolts, or any of the devices in use for
similar duty in the rolled-steel sleepers for ordinary railway
permanent way.
Fig. 279 shows a modern rail of a heavier section, with a wide flange
resting direct on a continuous bed of concrete. The gauge is
maintained by bar-iron tie-bars placed vertically so as to fit in
between the courses of the paving-setts, the ends being forged and
screwed to pass through holes in the vertical web of rail, and secured
in position by nuts. Both in this, and in type Fig. 278, ordinary
fish-plates are adopted at the rail-joints, as indicated by dotted
lines.
In the last two examples above described all the materials are of the
most durable description, and the least liable to wear or decay, but
it will be necessary to guard against making the fastenings and the
bars too light for the duty they have to perform. There should be
ample material in the head of the rail to allow of a fair wearing
down, and the continuous flange groove should be sufficiently deep to
meet this wearing away without causing the wheel-flanges to strike the
bottom of the groove.
[Illustration: Fig. 280, 281, 282, 283, 284, 285, 286, 287, 288, 289,
290, 291]
Fish-plates.--In the first examples of the newly invented
wrought-iron fish-plates they were made to the depth to fit in between
the upper and lower tables of the rail, as shown in Fig. 280, a small
space or clearance being left between the inner sides and the vertical
web of the rail. Ordinary nuts and bolts were used in most cases, but
in some instances one of the fish-plates was tapped, as in Fig. 281,
forming one long continuous nut, and in others both fish-plates were
tapped, as in Fig. 282, and right and left handed bolts were used.
Neither of the two arrangements of tapped fish-plates proved
sufficiently successful as to lead to their general adoption. When the
bolts became rusted in, or iron-bound, it was found to be almost
impossible to remove them without permanently damaging the
fish-plates. With the four right and left handed bolts the operation
of tightening, or removing, the fish-plates was very tedious, as each
bolt had to be turned a very little at a time, one after the other. 205
Independent bolts and nuts, either of iron or steel, are now
universally used; plain holes, with sufficient allowance for work and
expansion, being punched or drilled in the rails and fish-plates.
For many years the depth of the fish-plates continued to be made the
same as the space between the upper and lower members of the rail, as
shown in Fig. 280; but with the heavier loads and higher speeds of our
modern railway working it has been found necessary to strengthen the
joints by providing deeper or stiffer fish-plates, as shown in Figs.
283, 284, and 285. For bull-head rails the fish-plates have been
brought down underneath the lower table, and in some cases extended
down sufficiently far to admit of a second set of fish-bolts under the
rail. For flange rails some fish-plates are used simply of the form of
angle irons, and others have the angle portion carried out beyond the
end of the flange, or foot of rail, and then turned down vertically to
a depth of an inch or more below the rail. The latter makes a very
strong fish-plate.
Fish-plates, like rails, are now almost universally made of steel.
The efficiency and durability of a fish-plate depends materially upon
its angle of contact with the under side of the head of the rail, and
the extent of its contact surface. It would be an error to suppose
there is little or no wearing away in fish-plates, as in reality there
is very considerable wear, and especially in rails of lighter section.
If the under side of the head of rail has a curved outline, as in the
rail in Fig. 287, there will be some difficulty in ensuring a perfect
fit in the fish-plates; the curve of the one may not quite correspond
to the curve of the other, and the contact surface will be very small.
It is better to make these contact surfaces in straight lines, and to
a wide angle rather than to an acute angle. In Fig. 288 the under side
of head and corresponding top of fish-plates are set at an acute
angle, and fish-plates to this pattern will soon wear up to the
vertical web of rail, and cause a loose noisy joint.
In Fig. 284, showing a different type of rail, the contact surfaces
are set at a very much wider angle, and will allow much more wear
before the fish-plates can work close up to the web of the rail.
When once the fish-plates are close up to the web, the best and 206
tightest bolts cannot prevent the vertical play in the ends of the
rails.
A hammering sound will announce each successive drop of the wheels
from one rail to the other, more distinctly, perhaps, at slow speeds
than when travelling quickly, but existing equally under both
conditions. The unpleasant jarring sensation is annoying to the
passengers, and has a straining, loosening effect on all the bolts and
fastenings. Unless the fish-plates have a thorough continuous bearing
against the upper and lower shoulders of both the rails, it will be
impossible to obtain a smooth even joint. A road may have good rails,
good chairs, and good sleepers, but if the fish-plates are worn and
loose the entire permanent way may be pronounced faulty, and all on
account of a minor defect which can be easily remedied. With strong,
properly fitting fish-plates, the position of the joints should be
imperceptible when passing over them in a train.
The writer has had many miles of line where the fish-plates have worn
hard up to the rail web. In cases where the rails were good, with the
prospect of a long life, new fish-plates of suitable section have been
provided. In others, thin wrought-iron plate liners, 1/16 or 1/12 of
an inch thick, have been inserted, as in Fig. 291, so as to bring the
plates well out from the web, and allow the fish-bolts and fish-plates
to exercise the free gripping action which is absolutely necessary to
prevent the vertical rising and falling of the rail-ends during the
passage of a rolling load. Fish-plate liners of the above description
have given excellent results, and have restored the efficiency of the
fish-plates for several years.
Chairs.--All rails which partake of the double head section, or have
a base not wider than the head, require supports or carriers to attach
them to the sleepers, and to secure them in their proper upright
position. In the days of the original _edge rails_, at the
commencement of the railway era, these supports were very
appropriately termed _chairs_, and this name has now been adopted in
all parts of the world. Cast-iron is the most suitable material for
railways chairs, being much cheaper in cost and less liable to loss or
deterioration from rust than wrought-iron. Cast-iron chairs can be
formed to suit any section of rail, and from the nature of the
material they cannot be bent or twisted out of shape so as to
interfere with the gauge or cant. They may break during an accident or
derailment, but the fracture can be detected at once, and the broken 207
chair quickly replaced.
The chair performs the very important duty of distributing the weight
of the rolling load on the upper surface of the sleeper. If the under
side or base of the chair is small, and the rolling load large, the
chair will very rapidly wear or imbed itself into the wood of the
sleeper, shortening the life of the latter in a very palpable manner.
The short narrow chair naturally gives less stability than the larger
and broader chair. The chair shown in Fig. 292, which was much used
for 75 lb. rails some twenty years ago, has much less base area and
stability than the chair shown in Fig. 293, adopted for rails of a
similar weight in the present day. The former had a bearing surface on
the sleeper of only 53 square inches, as compared with 89 square
inches in the latter. The base area of the chair must be in proportion
to the weight it has to carry and distribute, and it would be false
economy to stint the surface area of one of the details which
influences so materially the stability and durability of the permanent
way.
As will be seen in Figs. 294, 295, and 296, the chairs at present used
for 80, 85, and 90 lb. rails have a much larger bearing surface than
the chair shown in Fig. 292.
With the wider chair, a much longer and better seat can be given to
the under table of rail, and a greater length of jaw for holding the
wooden key. The longer the rail-seat the steadier the rail and the
smoother the running.
The keys are generally made of hard wood, sometimes compressed by a
special process, cut slightly taper, or wedge, shape, and driven in
between the jaw of the chair and the vertical web of the rail. On some
railways the key is placed outside the rail, as in Fig. 297, and on
others inside the rail, as in Fig. 298. The latter method possesses
many advantages over the former. The outer jaw of the chair can be
brought well up to the under side of head of rail, giving the rail
more lateral support and better means of preserving the correct cant;
and, as in this chair the outer jaw permanently fixes the gauge, the
working out of one or more of the keys does not leave the rail exposed
to be forced outwards and widen the gauge, as in the case with dropped
keys in outside keying. Another and very important advantage of inside
keying is that platelayers, when inspecting the road by walking
between the rails, can readily examine the keys on both sides.
[Illustration: Fig. 292, 293, 294, 295, 296, 297, 298, 299, 300, 301,
302, 303, 304, 305, 306]
Chairs have been made, as in Fig. 299, with a recess in the rail-seat, 209
to hold a piece of prepared wood, or other suitable semi-elastic
material, the object being to provide a rest, or cushion, softer and
more yielding than the cast-iron. The idea looks well in theory, but
in practice the pounding on the rail compresses or crushes the wood
lower and lower into the recess, slackened keys have to be tightened,
and when the wood has been worn or crushed away down to the level of
the stop ribs, A, A, the under side of rail has no longer any
seat, or rest, beyond the two narrow ribs of cast-iron. These afford
such a very limited support that the rail becomes notched, and
produces a very rough clattering road. It is a very simple matter to
take out an old key and put in a new one, but to replace a wooden
cushion in a chair recess involves the entire removal of either the
rail or the chair. Chairs with wooden cushions have not been adopted
to any great extent, the tendency of modern practice being to reduce
as far as possible the number of parts of the permanent way, and to
provide those parts with ample bearing or contact surfaces.
Although the general practice has been to cast the chairs in one
piece, chairs have been made in two pieces, as in Fig. 300, fastened
together and to the rail by a bolt passing through the latter, the
castings being secured to the sleeper with spikes. At first sight this
pattern of chair appeared to possess some features in its favour. The
castings were simple, keys were dispensed with altogether, and the
under side of rail was not in contact with the cast-iron. A short
experience, however, proved that the drawbacks far outweighed the
apparent advantages. Holes for the through-bolts had to be punched at
fixed distances in the rails, and although this could be readily done
at the works, for the general use on the line it was necessary to
resort to the tedious process of drilling by hand for a large number
of holes on curves, and for rails cut to form _closers_.
Sleepers.--Wood possesses so many suitable qualities that we can
readily understand why it was early selected as the proper material
for sleepers. It can be cut to any size and shape, holes can be bored,
spikes can be driven, and bolts can be screwed into it without any
difficulty and without causing injury to the timber, while the
semi-elastic nature of wood absorbs the vibration of the rails and
fastenings, and provides a sound-deadening seat so conducive to smooth
running. Its only drawback is that it is perishable from wear and 210
decay. Were it not for this defect, railway sleepers of wood might be
considered as simply perfect.
With a view to greater permanency and durability, stone sleepers were
tried. These consisted of square blocks of good hard stone, measuring
about 2 feet wide each way and 12 inches thick. Holes were cut in the
stone, and plugs of hard wood inserted. The cast-iron chairs were then
placed on the top of the blocks, and the iron spikes driven through
the chair-holes into the wooden plugs. The elements of permanency were
there certainly, but a rougher road it would be impossible to
conceive. The stone was solid and unyielding, there was a total
absence of softness and elasticity, and the harsh noisy effect
produced when running over the stone-block road very soon became
intolerable. Stone-block sleepers were found to be a failure, and were
all removed. On some of our old lines, numbers of them, with the chair
marks plainly visible, may be still seen in loading banks, buildings,
sea walls, and other works for which they were never originally
intended, but for which their size and weight render them very
appropriate.
Wooden sleepers are used in two forms, transverse and longitudinal. In
the former, as in Fig. 301, the sleepers not only carry the rails, but
also preserve the gauge; in the latter as in Fig. 302, the
longitudinal sleepers only support the rails, additional timbers and
strong fastenings being necessary to maintain the gauge.
Longitudinal sleepers have been used to a large extent for bridge
rails, it being supposed that with the broad continuous sleeper a
lighter and shallower rail could be adopted, which would be equally
efficient as a heavier rail on cross-sleepers. Excellent running roads
have been made with longitudinal sleepers, notwithstanding the
difficulty of making a good bridge-rail joint; but it is well to bear
in mind that almost all the lines which originally adopted this form
of permanent way have since reverted to the ordinary cross-sleeper
road. The longitudinal sleeper road is an expensive road to lay down
and maintain. The main pieces are of large scantling, must be of good
quality of timber, and are consequently costly. The cross-pieces, or
transomes, must be carefully fitted and secured with heavy ironwork.
Where there is much traffic, the removal and renewal of one of the
long timbers is much more difficult than the renewal of several ordinary 211
cross-sleepers. Again, decay may take place on only one portion of a
main timber, but there is no alternative but to remove the entire
piece.
For gauges varying from 4 feet 8½ inches to 5 feet 3 inches,
cross-sleepers are cut to the length of 8 feet 11 inches, and are
generally rectangular in section, as in Fig. 303, measuring 10 inches
in width by 5 inches in thickness. On some of the lighter railways
with small traffic, sleepers are often used only 9 inches wide by 4½
inches thick, while occasionally on some lines, and in places where
there is exceptionally heavy and constant traffic, sleepers 12 inches
wide by 6 inches thick are adopted.
Half-round sleepers, as in Fig. 304, are used on many lines because
they are cheaper. In some cases the flat side of the sleeper is placed
downwards, and the rail or chair is fastened into an adzed seat cut in
the round side; and in the others the round side is placed downwards,
and the flat side of the sleeper carries the rail or chair. Triangular
sleepers, as in Fig. 305, have also been used, made by cutting the
blocks diagonally, so as to obtain the greatest possible width. They
were laid with the flat side upwards, and the apex downwards. They
were difficult to keep packed, and have not been adopted to any great
extent.
With the exception of a limited number of larch and fir sleepers grown
in the country, most of the sleepers for our home railways are
imported from the Baltic. They are brought over in logs, or blocks,
each 8 feet 11 inches long, some square and others circular in
section, and when sawn down the middle, each block forms two sleepers.
The preservation of timber from decay is a subject that very early
occupied the attention of engineers and all those interested in
railways. A railway sleeper is particularly exposed to deterioration
the lower portion being surrounded with moist ballast, whilst the top
portion is more or less uncovered--two different conditions in the
same piece of timber. Several processes have been tried, such as
Kyanizing, Burnetizing, Boucherizing, etc., but the system which has
given the best results, and is now almost universally adopted, is that
known as creosoting. This method consists of forcing liquid creosote,
under considerable pressure, into sleepers or railway timbers which
have been prepared or dried by ordinary natural seasoning or by
special artificial means. Creosote is a dark, oily liquid, distilled 212
from coal tar, varying in its composition according to the quality of
the coal from which it is obtained, and ranging in its specific
gravity from 11·08 to 10·28.
Creosote oils of light specific gravity were at one time in favour,
but experience proved that, to some extent, the light oils were
volatile and also soluble in water, and that heavy rains washed out
the constituents which were essential for the preservation of the
timber. On the other hand, by heating the heavy oils and using high
pressure the napthaline which is dissolved only by the heat, is forced
into the wood, fills the pores, and solidifies.
Creosote is obtainable in large quantities, at prices varying from
twopence to fourpence per gallon, according to the demand and cost of
production. Newly delivered sleepers or railway timber contain so much
sap or water that it is impossible to force a sufficient quantity of
creosote into them until they are properly seasoned or dried.
The seasoning is generally arranged by sawing each block into two
sleepers, and then stacking the sleepers on edge in tiers, leaving a
space of four or five inches between each of them for a proper
circulation of air. The sleepers should then be left for nine to
twelve months to season, although more may be necessary in some cases
if the blocks were particularly wet at the time they were sawn.
When ready for the process the sleepers are placed in the creosoting
cylinder, which is generally about 60 feet long by 6 feet in diameter
with semi-spherical ends. One of the ends is fitted with strong hinges
and fastenings, and forms the doorway. The sleepers are packed
carefully inside, and the doorway made tight. The machinery is then
set to work to exhaust the air from the cylinder and allow the
creosote to flow in amongst the sleepers. When the cylinder is full
the force-pumps are started to force in more creosote up to the
pressure prearranged and regulated by the safety-valve, in some cases
100, 110, or 120 lbs. per square inch. The creosote should be heated
to 112° or 120° Fah., to dissolve the napthaline and reduce all the
component parts to a thoroughly fluid condition.
The success of creosoting depends almost entirely upon the effectual
seasoning of the timber. Only a very small quantity of creosote can be
forced into wet or unseasoned sleepers, even with the best machinery
and exceptionally high pressures, while a thoroughly dry sleeper will 213
readily absorb from 2⅓ to 3 gallons. More could be forced into the dry
sleeper if necessary, but a little consideration will show there would
be no advantage in doing so. In railway sleepers there are two
elements of destruction at work--one the decay of the timber, and the
other abrasion or wearing away of the wood itself from the constant
pounding of the passing loads.
More particularly does this wearing-away take place with the flange,
or bridge, rails, their distributed bearing surface on the sleeper
being less than the cast-iron chairs.
A thoroughly well-creosoted 5-inch sleeper laid originally with a
thickness of 4-¾ inches in the centre of rail-seat, as in Fig. 306,
will wear down 1½ inches, the timber remaining quite sound.
The writer has had to take out thousands of sleepers where the seats
of the flange, or bridge, rails had been pounded or worn down so deep
into the wood as to leave too small a thickness of timber to carry the
rail with safety. These sleepers had to be taken out of the road, not
on account of decay, but because they were actually worn down too thin
to be of service. They had done their work well for a long series of
years, and were perfectly sound when taken out. No increased quantity
of creosote would have made them last longer, and any increased
quantity of creosote would have been waste.
Two and three quarter gallons of creosote is a very good and suitable
quantity for a 10 inch by 5 inch rectangular sleeper, but not more
than half this quantity can be forced in if the sleeper is wet or
unseasoned.
Sleeper-blocks are generally cut from the upper part of the tree, and
do not therefore consist of the best portion of the timber, yet
sleepers made from the soft, coarse-grained Baltic wood, properly
creosoted, will last from twelve to eighteen years in the line in this
country, while uncreosoted they would perish from decay in six or
seven. The benefit is great when, by adding from eightpence to a
shilling for the cost of creosoting, the life of the sleeper may be
doubled or trebled. Of course, there are countries, like the far west
of America, where the lines pass through vast forests, and where
sleepers may be had for the mere cost of cutting. Creosoting in those
places would be out of the question, and would cost four or five times
the value of the plain sleeper. It is found, also, that in tropical
countries and in dry climates at high altitudes creosote loses its 214
efficiency, and in those districts the best creosoted soft-wood
sleeper perishes from a species of dry rot in three or four years.
Where wood sleepers have to be used in tropical climates it is better
to obtain them from the timber of the district, although in many cases
suitable trees are difficult to procure and the cost of land transport
is very heavy.
The soft cushion-like effect of a sound, properly packed wooden
sleeper contributes so largely to form an easy, smooth-running road,
that so long as they can be obtained at a moderate cost, and are
fairly durable, wooden sleepers will always be preferred to those of
any other material. The great question will be the supply. Creosoting
and other wood-preserving processes have done much to prolong the life
of sleepers, but the rapidly increasing extent of mileage throughout
the world, together with the enormous number of sleepers required
annually for maintenance or renewals, must before very long severely
tax the powers of supply.
In the great timber-producing territories the axe is often heard, but
the planter is rarely seen. Vast forests are cleared away, and their
sites transformed into busy towns or cultivated lands; and unless some
great change takes place, and planting be carried out on a large
scale, some other material will have to be adopted for this important
item of our permanent way.
Appearances would indicate that at no very distant date iron or steel
will take a conspicuous part in the formation of future railway
sleepers.
More than thirty years ago several descriptions of cast-iron sleepers
were introduced into notice and tried on some of our leading home
railways. Cast-iron was at that time considered more suitable for the
purpose than wrought iron, as it was very much less costly in price,
and could be readily worked into any desired form or size, with the
advantage that the castings would all be duplicates of one another.
[Illustration: Fig. 307, 308, 309, 310, 311, 312, 313]