How is a Razor Blade Made?
The best scissors, penknives, razors and lancets are made of cast steel. Table knives, plane irons and chisels of a very superior kind are made of shear steel, while common steel is wrought up into ordinary cutlery.
In making razors, the workman, being furnished with a bar of cast steel, forges his blade from it. After being brought into true shape by filing, the blade is exposed to a cherry-red heat and instantly quenched in cold water. The blade is then tempered by first brightening one side and then heating it over a fire free from flame and smoke, until the bright surface acquires a straw color (or it may be tempered differently). It is again quenched, and is then ready for being ground and polished.
The Story of the Tunnels Under the Hudson River[58]
The building of the Hudson River tunnels was probably one of the most daring engineering feats ever accomplished. As is well known, the Hudson River, for the length of Manhattan Island, is approximately a mile wide, reducing in width at the Palisades north of Hoboken. In consequence of the unusual geographical situation, all trunk lines and other transit facilities in New Jersey terminate on the westerly shore of the Hudson, and passengers were of necessity compelled to use ferries to reach New York. A conservative estimate, which was confirmed by various counts, indicates that, prior to the construction of the tubes, the annual passenger traffic between New Jersey and New York was 125,000,000, and to handle this great volume of traffic the transportation companies assembled in the Hudson River a fleet of rapid ferry boats and maintained them up to the highest and most modern standards. But this very expeditious ferry service was not enough, and for many years there was a demand for facilities for more rapid transportation of the tremendous population residing in the suburban district of New Jersey tributary to New York City. As far back as 1873, a company had been organized to construct a tunnel under the river, but had met with numerous and most discouraging difficulties and obstacles, so that it was finally compelled to abandon the work, although it succeeded in building a considerable length of structure. Efforts were made at various times after that date to revive the work, with little or no results. In 1902 it was resumed, however, and a few years later was pushed to a successful end.
During the undertaking, more than 40,000 men were engaged in air-pressure work and there were many thousand more who did not work under air pressure. This vast army of men consisted of all nationalities and all grades and conditions of labor. The skilled tunnel workmen are men of character and ability, usually young, of good intelligence and sound of body, without a streak of fear or cowardice in their makeup. All of those characteristics are essential to under-water air-pressure work.
As is quite generally known, air pressure and tunnel shields were used in all of the under-water work. It might be well to here correct the misconception which exists in the minds of many, that the use of air pressure for such purposes is something comparatively new. This is not the case. The use of air pressure was a very early invention, and it is a matter of record that in 1830, Admiral Cochrane, afterwards Lord Dundonald, was granted letters patent for the use of air pressure in tunnel construction. The modern engineer has merely developed the art to a high degree.
The method of construction used in the Hudson River tunnels has been designated the “shield method.” In this type of construction, the primary part of the tunnel structure consists of an iron shell, formed of segmental rings, bolted together through inside flanges, and forming a large articulated pipe or tube, circular in section. This iron shell is put in place segmentally by means of a shield, an ingenious mechanism which both protects the work under construction and assists in the building of the iron shell.
The New Short Cut to New York
Hudson River Tubes of the Hudson & Manhattan R. R. Co.
A tunneling shield consists essentially of a tube or cylinder slightly larger in diameter than the tunnel it is intended to build, which slides over the exterior of the finished lining like the tubes of a telescope. The front end of this cylindrical shield is provided with a diaphragm or bulkhead in which are apertures which may be opened or closed at will. Behind this diaphragm are placed a number of hydraulic jacks, so arranged that by thrusting against the last erected iron ring the entire shield is pushed forward. The hind end of the shield is simply a continuation of the cylinder which forms the front end, and this hind end, or tail, always overlaps the last few feet of the built-up iron-shell tunnel.
When the openings in the bulkhead are closed, the tunnel is protected from the inrush of water or soft ground, and the openings may be so regulated that control is maintained over the material passed through. After a ring of iron lining has been erected within the tail of the shield, excavation is carried out ahead. When sufficient excavation has been taken out, the jacks are again extended, thus pushing the shield ahead, and another ring of iron is erected as before.
One of the Sixty-seven-Ton Tunnel Shields
For the erection of these heavy plates, a hydraulic swinging arm, called the “Erector,” is mounted, either on the shield itself or on an independent erector platform, according to conditions. This erector approaches closely the faculties of the human arm. It is hydraulically operated and can be moved in any desired direction. This method of construction can be followed in almost every kind of ground that can be met with, and it is especially valuable in dealing with soft, wet grounds. In passing through materials saturated with water, the shield is assisted by using compressed air in the working chamber.
Cutting Shield Head
The employment of compressed air under such conditions is really a rather simple thing in itself, and means merely that the pressure of air in the chamber where men are working is maintained at a point sufficient to offset the pressure of the hydrostatic head of water and thereby prevent its inflow. A crude comparison may be made by saying that if the ceiling of a room was weak and threatening to fall—if we filled the room with sufficient pressure of air, it would support the ceiling and prevent it falling in. In tunnel work, air is supplied under compression from the mechanical construction plant located on the surface, and the pressure of air maintained in the working chamber is determined by the depth of the work below tide level, as the hydrostatic head increases with the depth.
Control of air pressure is never entrusted to any but the most reliable, competent and experienced man, as it is of the utmost importance that air pressure be maintained properly. The first impulse of an inexperienced man, should he notice an inrush of water, would be to increase the air pressure, which might be a very dangerous thing to do. An experienced man, however, would very likely first lower his pressure in such an emergency, and then put up with the nuisance and difficulty of having a good deal of water in his working chamber. By doing this, he would permit the greater external pressure to squeeze the soil into the leaking pockets and thereby choke the leak.
Apron in Front of Shield, Five Minutes Before Shoving
To improperly or inopportunely raise the air pressure would be quite likely to result in the air blowing a hole through the roof of the tunnel heading, allowing all air pressure to escape, and permitting an uncontrollable volume of water to rush in and flood the work.
The outer shell of the tunnel shield is composed of two- or three-ply boiler plates, and the interior is braced with a system of steel girders. The shields used weighed approximately sixty-seven tons each. Sixteen or eighteen were used. To move the shield forward, each shield was equipped with sixteen hydraulic jacks, arranged around the shield circumferentially. These jacks were controlled by a series of valves, which were so designed that any one jack or any set of jacks desired could be operated. This was necessary as the direction of the shield was, as it were, guided by the pressure of the jacks. When it was desired to alter the direction of the shield, either upwards or downwards, or to the right or left, the jacks on the opposite side to which the shield was to point, were operated. The hydraulic pressure operating these jacks was 5,000 pounds per square inch, and the total energy, when all jacks were employed at the same time, was equivalent to 2,500 tons, which was equal to eleven tons per square foot of heading.
Cutting Edge of Shield in North Tunnel
Air pressure used to prevent the inflow of water and soft dirt varied from nothing up to forty-two pounds, although a fair average throughout was thirty-two pounds. It varied, of course, according to the condition encountered.
The working chamber is the space between the tunnel heading where work is in progress and the air-lock. The air-lock is a device used for the purpose of enabling workmen and materials to pass from the portion of the tunnel where the atmospheric pressure is normal into the portion where the air pressure is greater than normal; that is, the working chamber. The air-lock is a cylinder, usually about six feet in diameter and twenty feet in length, with a heavily constructed iron door at each end. This lock is placed horizontally in the tunnel at such a level as the conditions of the work necessitate, but usually near the bottom, and around this cylinder, and completely filling the cross-section of the tunnel, a concrete bulkhead is built and is known as the lock bulkhead. The two doors open in the same direction; the one at the normal pressure end opening into the cylinder, and the one at the heading end opening away from the cylinder. One door is always closed, and both doors are closed during the operation of entering or leaving the air-pressure section.
Going into the air pressure, the door at the heading end is held closed by the pressure of air against it while one is entering the lock, after which the outer door is also closed. A valve is then opened which permits the air to flow from the working chamber into the lock, until the lock becomes filled with air of the same pressure as exists in the heading. As soon as the pressure is thus equalized, the door at the heading end can be opened and the workmen pass into the heading. Going out, the operations are simply reversed. After the heading door is closed, with the workmen in the air-lock, a valve is opened which permits the air in the lock to exhaust into the normal air, until the pressure within the lock reduces to the same as that outside, when the outer door can be opened and persons inside the lock pass out. Both operations must be gradual, as a sudden change from normal to high pressure, or vice versa, would be very dangerous to anyone.
Shield Cutting Edge Breaking Through Wall at Sixth Avenue and Twelfth Street, Looking South, October 23, 1907
In tunneling under the river, nearly every conceivable combination of rocks and soils were met, but for the most part the material was silt. In such material, with a pressure of 5,000 pounds per square inch on the shield jacks, the shield was pushed through the ground as though one pushed a stick into a heap of snow, pushing aside the silt, and thus obviating the necessity of removing any excavated material. Sand or gravel, or any material which would not flow or become displaced by the shield, of course, had to be excavated ahead of the shield, and removed from the heading prior to pushing it forward. In the silt the most satisfactory and economic progress was attained, and a record was made of seventy-two feet of finished tunnel, completely lined with iron, in one day of twenty-four hours.
The most difficult combination that had to be dealt with under the river was when the bottom consisted of rock and the top of silt and wet sand. In such cases, and there were many of them, the upper section of soft ground was first excavated and the exposed face securely supported with timbers ahead of the shield, and the rock underlying then drilled and blasted. This was very tedious and expensive work. Exceedingly small charges of dynamite had to be used and the procedure conducted with the utmost caution.
In the course of their progress, the shields were subjected to the most intense strains and hard usage, as may well be imagined. One of the shields is [illustrated]. It was used to construct the south tunnel of the up-town pair of tubes, and passed from under the Hudson River, through Morton, Greenwich and Christopher Streets, into Sixth Avenue, and north to Twelfth Street, a total distance of 4,525 feet, of which 2,075 feet was through rock overlaid with wet sand. During the progress of this shield, 26,000 sticks of dynamite were exploded in front of the cutting edge, causing great damage to the structure of the shield, so that when it arrived at its destination at Sixth Avenue and Twelfth Street, it was in such a condition of distortion that it was with difficulty that the tunnel lining could be erected behind it.
North Tunnel, Showing Commencement of New Work
In pushing a shield forward with the battery of powerful hydraulic jacks, each advance is of two feet, and must be followed immediately by installation of the permanent lining in the rear. In the early days, brick work was used for lining, and in recent years it has also been used to some extent, but even with the use of quick-setting Portland cement, neither brick work nor concrete has proved successful for subaqueous work, as the cement cannot reach the required strength within the time it is feasible to leave the shield standing before advancing it again.
Hole Broken Through the South Tube of the New York and Jersey Tunnel Looking West
During the early work on the north tube of the uptown tunnels, a point was reached where the rock was sixteen feet above the bottom of the tunnel, and the overlying silt was in a semi-fluid state. Five barges of clay had been dumped in the river over this point to make a roof for the tunnel, but the fluid clay could not be controlled, and crept through the doors of the shield. After trying all known methods to get through, it was decided to bake this wet clay by means of intense heat. Two large barges of kerosene were sent into the tunnel, and an air pipe connected to them. Fine blow-pipes were also attached, and the fire from the blow-pipes was impinged on the exposed clay until it became caked sufficiently dry and hard to overcome slipping. It required eight hours of this baking to dry the clay hard, and, during this period, water had to be played continuously on the shield to avoid damage due to the high temperature. It is believed that this was the first time that soft material met with in tunneling under a river has been solidified by means of fire. Seven days after passing this troublesome point, the rock suddenly disappeared and the work proceeded without further trouble.
New York and New Jersey Tunnel Showing Signal and Car
Another unusual situation occurred in the south tunnel of the uptown tubes. When the shield had advanced 115 feet from the Jersey side, the night superintendent in charge of the tunnel work, in his anxiety to push the work, disobeyed instructions, and the tunnel got away from him and was flooded, and his men had a narrow escape with their lives. In order to regain the tunnel, several schemes were considered, including that of sending a dredge through to dredge out the bed of the river just in advance of the shield, a sufficient depth to enable a diver to go down and timber up the exterior opening of the doorway, where the silt and mud had come through and filled the tunnel. This plan had to be abandoned, as the river above was almost entirely occupied by shipping that could not be interrupted.
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An X-Ray View of a Busy Half-Mile Under the Ground on the Jersey Side of the Hudson River
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Cross-Section on Sixth Avenue at Thirty-third Street, New York
| 1. | Foot Passage | 4. | New Rapid Transit Subway |
| 2. | Manhattan Elevated Railroad | 5. | Hudson and Manhattan Railroad Station |
| 3. | Street Surface and Metropolitan Street Railway | 6. | Pennsylvania Railroad Tunnel |
Finally the difficult situation was met by obtaining two large and heavy mainsails, which made a double canvas cover measuring about sixty by forty feet. This canvas cover was then spread on a flat barge, small sections of pig iron being attached around the edges of it. Ropes were carried to fixed points to hold it in exact position. The barge was then withdrawn, and the canvas cover dropped to the bed of the river, and, most fortunately, it settled over the point where the leak had occurred, and a large number of bags of dirt were then deposited on it. An opening was then made in the bulkhead of the tunnel below, and for eight days material, under hydrostatic pressure, forced its way into the tunnel, where it was loaded on cars, and finally the canvas was drawn into the hole, stopping it up. Additional material was then deposited into the river to fill the cavity, and finally the tunnel was recovered, pumped out and work resumed. This event is of somewhat historical interest, in that the two mainsails which were used were procured from the owner of the famous American cup defender, the well-remembered “Reliance.”
Probably the most unique and interesting pieces of construction are the three junctions on the Jersey side of the river, where the uptown tunnels from New York diverge, north to Hoboken and south to Jersey City and New York downtown. For safe and expeditious operation of trains, where the schedule is only one and one-half minutes, it was imperative that grade crossings should be avoided. By grade crossings is meant the tracks of one service crossing the tracks of another service at the same grade. At the point in question, this was a knotty problem to solve, owing to the unusual operating conditions which had to be met, there being six separate and distinct operating classes of trains to be handled around this triangle.
To meet this situation, three massive reinforced concrete caissons were built on the surface. They are practically large two-story houses, each being over one hundred feet in length, about fifty feet in height, and about forty-five feet in width at their widest point. The bottom edges were sharp, and, with the use of air pressure and great weights, the three structures were sunk in the ground to the same grade as the intercepting tunnels, and the tunnels were then driven into them.
Particular attention should be given to the Jersey City to Hoboken tube, in the lower part of the caisson in the foreground, in the accompanying [illustration], which curls around the Hoboken to Jersey City tube, and rises to the elevation of, and connects into, the New York to Hoboken tube, at the caisson in the background, at the left of the illustration. Very few of the people who travel through the tube are probably aware of such manipulation. At the same time, the arrangement absolutely avoids any grade crossing whatever, and without such an arrangement of tracks the road could not be operated with trains run so closely together as under the prevailing system.
In constructing the river tunnels the work was carried on simultaneously from opposite sides of the river, the tunnels meeting under the river, and it is interesting, if not remarkable, when one considers the difficulties under which the engineering work had to be carried on, to note that the tunnels met with practically absolute accuracy.