The Manufacture of Modern Railway Lines
OF all the purchases made annually by railway companies, probably the largest individual item, both in value and weight, is that of steel rails. Every year enormous quantities of steel rails must be bought, in order to replace those which have worn out in service and require replacement. British railways themselves “consume” over 200,000 tons of rails annually for replacement purposes alone.
A MODERN BLAST FURNACE. Up the inclined skip-
Although these rails are, for the most part, made to standard specifications, special attention is constantly being directed, by variations in the analysis of the steel, by the use of alloys, and by heat treatment, to the production of a rail which will afford a better resistance to abrasion, so that its life in the track may be prolonged. The object of the research is not so much a harder steel, as might be generally supposed, but the combination of hardness with toughness; that is to say, the resilient properties of india-
In the operation of steelmaking there are three independent stages. The first is the reduction of the ore to metallic iron; the second is the refinement of the iron and its conversion into steel; and the third is the rolling of the steel from the ingot to the finished rail. The first stage is carried out in the blast-
The reason why it is customary to group blast-
Towering above the plant, and easily its most commanding feature, are the blast-
There are three constituents in the blast-
Charging is constantly in progress, for the blast-
POWER IS SUGGESTED by this photograph of a row of blast-
Most important of all is the “blast”, from which the furnace derives its name. This is introduced at the base of the furnace, just above the hearth level, through a series of water-
In the earliest blast-
Part of the hot blast-
Then the gas is turned into another stove, and the cold air from the blowers is carried through the heated stove, extracting its heat before passing into the furnace. Some of the stoves are thus always acquiring heat, while others are giving it out, and the blast-
On entering the furnace the oxygen in the blast is quickly consumed, producing carbon monoxide, which is the principal agent in the reduction of the charge. For those interested in chemical formulae, it may be stated that the reaction which takes place in reducing the iron oxide or ore (Fe2O3) is this: Fe2O3 + 3CO = 3CO2 + 2Fe.
As the earthy constituents mixed with the ore would otherwise be infusible, the limestone is added to the charge to provide a “flux” which will combine with them, at the temperature of the furnace, to produce a fusible slag. This slag, being lighter, floats on the top of the metallic iron, which collects in liquid form in the hearth at the bottom of the furnace.
From an upper vent the slag is being tapped almost continuously. It is run into great ladles which are usually taken outside the works area to be tipped on to the vast slag-
In these progressive days, however, many uses are found for what was at one time no more than a waste product; among them are railway ballast, “tarmac” or tarred broken slag for road making, and the manufacture of slag concrete and slag bricks. A very large proportion of the blast-
Many years ago, it was customary to allow the gaseous product of the smelting to burn to waste in enormous flares at the top of the furnaces; but no such wasteful procedure is followed to-
The charge of the blast-
But if the iron is to be converted into steel, it is not cooled, for that would involve wasteful loss of heat. It is therefore run in its molten condition into a ladle, and the ladle is rapidly passed -
In its present condition the iron is “cast iron”, a brittle and more or less impure product. Steel, on the other hand, is a very pure form of iron with which certain constituents -
The Bessemer Process
In the original process of steel production devised by Henry Bessemer in 1855, refinement of the iron was carried out in a bottle-
This was placed in a horizontal position to receive the charge and, after a powerful air-
Then came the invention of the Siemens-
ALMOST HUMAN in its ingenuity is the charger used for inserting the various ingredients of the charge in the open-
Refinement of the iron in this way is a much slower process than in the Bessemer converter, as the time occupied in making a “heat” of steel is eight to ten hours, as compared with twenty minutes or so in the Bessemer process. But it is a “slow but sure” procedure; for open-
One important matter must be mentioned at this stage. The bugbear of the steelmaker is phosphorus, for its tendency is to make the steel brittle. Only the class of ore known as “haematite”, which is the purest, is reasonably free from phosphorus. When haematite iron is being converted to steel, an acid reaction takes place in the converter or furnace, and such phosphorus as there was in the original iron remains in the steel, but it is so small a percentage as to be negligible.
Steel made from such ores is known as acid steel, and may be either Bessemer acid or open-
A FIERY TORRENT. Ninety tons of molten steel are seen in this remarkable illustration. They are being teemed into the immense ladle in the foreground after the steel has been converted from iron in the open-
But the major proportion of the world’s iron ores are less pure than haematite, and have a fairly high phosphorus content. It was in 1878 that two chemists named Thomas and Gilchrist discovered that this excess phosphorus could be removed by lining the converter with dolomite, or magnesian limestone, which would furnish a “base” for the removal of the phosphorus in the slag.
This was the genesis of the “basic” steel working. In this country the majority of steel production is by the basic open-
On the Continent rails are made chiefly from basic Bessemer steel, but for certain technical reasons this is not regarded in Great Britain as the equal of basic open-
The present standard analysis to which the bulk of British rails are made, if of basic open-
Carbon from 0.50 to 0.60 per cent.
Silicon from 0.10 to 0.30 per cent.
Sulphur not to exceed 0.05 per cent.
Phosphorus not to exceed 0.05 per cent.
Manganese from 0.90 to 1.20 per cent.
Reliance is placed on the carbon for hardness, and on the manganese for toughness, a good internal structure, and a smooth outer skin; silicon helps to purify the metal; but sulphur and phosphorus, which would make for brittleness, must be reduced to a minimum. The remainder of the steel content, of course, is almost entirely iron obtained from the ore.
The solid part of the charge is inserted by an ingenious electrically-
From time to time the charge is sampled, and the samples are quickly analysed, chiefly by automatic means, at a small laboratory on the melting-
CASTING THE INGOTS. The ladle has now been carried by the two strong arms of the overhead crane to the casting-
By an overhead crane, probably of at least one hundred tons capacity, a gigantic ladle has been brought to the tapping side of the furnace. The plug in the tapping hole is withdrawn, and out pours the stream of molten steel, of almost incredible brilliance into the ladle. During this pouring, there are added to the ladle carefully calculated quantities of ferro-
When the ladle has been filled with anything from 50 to 90 tons of molten steel, it is taken away to a platform under which runs a train of empty ingot-
In preparation for rolling, the ingot is first “stripped” -
The string of ingots from the “heat” or “cast” of steel that has just been teemed is now brought to the rail-
At the correct moment a huge pair of electrically-
Because of its heat, the metal is in a plastic condition. As it moves to and fro between the rolls -
Hydraulic shears now neatly cut off both ends of the ingot, with just as much ease as one might slice through a cheese. The amount of “crop” so taken off is very important; it must not be too little, especially from the top of the ingot, which usually contains certain defects; and it must not be too much, or waste would result.
Next the lengthy bar of glowing metal -
What was the ingot now resembles a red-
Nowadays care is taken of the cooling out by passing the rails through a “Sandberg oven”, which evens out the cooling in much the same way as the soaking-
ROLLING THE INGOT begins in the cogging mill, controlled from the overhead platform in the foreground. The dial on the left-
When cool each rail is passed to the straighteners, who, by the use of machines which can exert a heavy local pressure, take the kinks and bends out of the rail and leave it perfectly straight. Next it is transferred to the ending machines, which grind both ends to a smooth surface, and to an exact length; the latter is not allowed to vary by more than three-
Now comes the important stage of inspection. For this purpose the rails are passed out on to the inspection banks. Here they are laid out in neat rows, from 100 to 300 at a time, head upwards and touching, looking like a solid floor of steel of the beautiful blue-
A Vital Inspection
But first the inspector will have witnessed the prescribed tests. From every heat or cast of steel, whether made in a Bessemer converter or open-
Once in every 100 tons a tensile test is also taken. For this purpose a piece of steel is cut from the railhead and very carefully shaped in a lathe to a diameter of 0.564 in, which gives a cross-
It may be added that every rail has impressed on the end a number showing from which particular cast it has been cut. On the “web”, or middle portion of the rail, also, there is rolled, in raised lettering, the “brand” which shows the name of the manufacturers, the steel process, the section, and the month and year of manufacture.
THE FINAL STAGE of rolling takes place in the finishing mill through which the rail, still at a temperature of nearly 1,000 degrees centigrade, is here seen passing. In the background are the roughing rolls, where a rough impression of the section is being rolled into the bar.
When the railway company’s inspector has satisfied himself that the tests are in order, there follows the detailed inspection of the rails. Every rail is measured for length, and turned over in such a way as successively to expose to view both sides and the foot, so that any rails with surface defects may be marked out. During this procedure the inspector and the works representatives walk up and down examining the length of the rails. The heads of the rails are then similarly “walked”.
Templates are applied to the section of the rail and the drilling; the rail-
At most rail rolling-
Such is the size of a modern ironworks and steelworks plant that it has to maintain a railway system of considerable size on its own premises, sometimes equipped with signal-
THE COOLING BANK. To the right is the oven, in which the cooling of the rails is retarded so that the rail may cool evenly through a certain critical range of temperature. If the rails were allowed to cool too quickly undesirable stresses might develop in the metal, and impair its efficiency.
It is largely due to the many precautions and the continued research which is carried on in steelworks that all possibility of accidents caused by flaws in rails has been practically eliminated. And nobody who has inspected the process of modern rail manufacture can have failed to have been impressed by the thoroughness of the modern methods, employed in this vital side of railway industry.
Steel rails can be classed into two types -
Rails when laid on the track almost invariably have an inward cant of something like 1 in 20, and the wheel treads of the trains are coned accordingly when new. Nowadays, railway companies prefer to use longer rails than previously, but the average rail length is about 60 ft. Germany, however, differs; in that country the standard rail length is 30 metres, that is 98 ft 5 in.
[From part 18, published 31 May 1935]