AUTOGENOUS WELDING AND CUTTING
"Now," said the scientist, after he and his young friend had finished some experiments, and were ready to talk about autogenous welding, "imagine a little white flame no bigger than a pencil point at the end of a brass pipe about the size, and not entirely unlike in appearance the old-fashioned taper holder with which you used to light the gas, and you have before you in the rough, a picture of one of the oxy-acetylene torches that will in a few minutes weld two pieces of almost any metal, or in a few seconds cut a solid plate of the hardest steel of several inches thickness almost as fast and easy as a carpenter could saw a board, and yet without taking the temper out of the metal."
Picking up what seemed to be a little brass rod bent at the end, the man turned a valve, applied a match, and as the gas burned up with a beautiful little flame of dazzling whiteness, he continued:
"This tiny flame, so easily controlled, is hotter than any produced by man except that generated by the electrical furnace, for it reaches a temperature of about 6,300 degrees Fahrenheit. Previous to the invention of these wonderful torches the oxy-hydrogen was the hottest gas flame, but it only reached a temperature of 4,000 degrees Fahrenheit."
"How do you use it?" asked the boy.
"Well, for instance, Uncle Sam is enabled to weldand cut steel plate in building his battleships, steelworkers to carry on their gigantic tasks, and wreckers to clear away tangled masses of steel beams far more quickly and easily than with the older methods.
"If you had visited one of the navy yards, a shipyard or any place where big work in iron and steel was being carried on as short a time as three years ago, you would have seen a man sitting for hours sawing away on the end of a steel beam, for instance, trying to cut it down to the required length. He would dull many saws, use a great deal of energy, and an appalling amount of the most valuable thing in the world—time. Again, you would have seen them welding pieces of iron and steel by the old blacksmith method, or riveting other pieces that could not be joined by heating them and pressing them together.
"To-day you would see fewer of these processes because autogenous welding and cutting by the powerful little oxy-acetylene torches is revolutionizing certain methods of working with metals. Instead of squatting at the end of the beam and sawing away like an old-fashioned carpenter, the modern iron worker takes up his little torch, turns a valve in the handle and concentrates the flame on the steel beam that he wishes cut. Almost instantly a shower of sparks on the under side of the beam shows him that the flame has burned its way through. Thenhe slowly moves the flame along the line where he desires to cut and the trick is done."
Illustrating with his own little laboratory torch, the scientist continued his explanation, saying that cutting is only one of the many uses to which this modern invention in steel working is put. Not quite so spectacular but every bit as useful is the autogenous welding by means of these magic wands. Welding metals has ever been more or less unsatisfactory. The old process of heating the two ends and then beating them together is cumbersome and practically impossible in many cases. Consequently inventors have sought other welding processes with wider application and greater facility ever since the first metal workers of earliest times forged crude chains and weapons. With this modern device two pieces of steel or other metal are brought to within a small fraction of an inch of each other and by the use of the oxy-acetylene torch and a thin strip or rod of metal are melted and fused together.
Although the acetylene flame gives off a far greater proportion of light than heat, it is a very powerful gas and Le Chetalier, a French inventor, was sure that he could put it to other uses than furnishing lights for automobiles, etc. To this end he tried mixing acetylene gas with oxygen, for there can be no fire or combustion without oxygen. He very properly figured that by introducing pure oxygen into the acetylene, the burning, or combustion, would begreater, and the heat of the flame greatly intensified. His experiments were ultimately successful, and it was then only a short step to the time when three different oxy-acetylene torches were in use. In France there were developed low pressure, medium pressure, and high pressure torches; but the last named has not been found commercially practicable in the United States, where the "medium pressure" torch is sometimes called the high pressure. As we are dealing entirely with the American use of the invention we also will call the two kinds of torches used here the low pressure and the high pressure.
The general principle of the torch is, as we see, the mixture of oxygen with acetylene in order to obtain a hotter flame, but right here we come to the difference between the low-pressure and the high-pressure tools. Both are made of brass pipes, terminating in the burning tip and connected at the rear of the handle with rubber tubes which run to the separate tanks holding the acetylene gas and the oxygen, but the method by which these gases are combined in the torch constitutes the principle differences in the two systems, with the consequent greater or less efficiency claimed by the manufacturers. Without going into the technical details, which are a matter of controversy between scientists as well as the various commercial concerns interested in the torches, it will be sufficient to say that in the low-pressure torch the acetylene gas is only usedunder a pressure of a few ounces, with the oxygen under a much heavier pressure, while in the high-pressure torches, the acetylene and oxygen both are under an appreciable pressure of several pounds.
Thus in the low-pressure torch invented by Fouché, the oxygen is forced out of the nozzle by the pressure and the outrush sucks out the acetylene in the proper quantities. The two gases mix in a chamber at the end of the torch just above the tip and flow out into the air in this mixed form. The proportions of the gases in the low-pressure tool are about 1.7 of oxygen to 1.0 of acetylene.
The high-pressure torch, which has largely taken the place of the low-pressure one in France, and which we also see most frequently in this country, has a different method of mixing the gases, due to the fact that they both are under pressure. According to many authorities the tip where the gases are mixed is by far the most important factor in the success or failure of the tool. In the high-pressure torch the oxygen enters the tip from a hole in the centre, while the acetylene enters it from two holes, one on each side. They meet under high pressure at the upper end of the tip, and have the length of the hollow tip in which to mix, before they strike the air. The long, narrow hole in the tip is called the mixing chamber. Those who are interested in the high-pressure torch declare that it is the fact that the gases are positively mixed in proper proportion in the detachabletip, that so greatly adds to the efficiency of the tool. They declare that by allowing the acetylene to enter the tip laterally, at right angles with the oxygen, the blast of the oxygen is broken as it mixes with the acetylene, and the tendency of an oxygen flame to oxidize any metal with which it comes in contact by reason of an excess of oxygen in the flame is largely done away with. This, with the small diameter of the mixing chamber and the friction with the walls, gives a perfect mixture, according to the claims of the high-pressure torch enthusiasts. Moreover, the small hole which is the mixing chamber, effectually prevents serious accidents by flash-backs of the highly explosive acetylene, and also provides a much easier method of control. Each outfit has several different sizes of tips for various kinds of work.
The pressure under which the two gases are used is the other big difference between the high-pressure and the low-pressure torches, as said before. In the the high-pressure tool the oxygen is compressed about the same as in the low-pressure torch, while the acetylene is under several pounds pressure, just in accordance with the size of the tip used. In the low-pressure torch the pressure on the acetylene is only about ten ounces to the square inch, or only enough to keep it flowing. On account of this difference in the pressure making the big difference in the mixture of the gases, scientists have chosen to call the low-pressure torches injector mixturetypes, from the fact that the acetylene is sucked into the tip by an injector system, while the high-pressure torches are called positive mixture types, because the gases are mixed directly by pressure. In the latest high-pressure tool the mixture of gases is 1.14 parts of oxygen to 1 part of acetylene, while the low-pressure torch takes a proportion of 1.7 parts of oxygen to 1 part of acetylene.
The torches also vary in size from the little 8-ounce "jeweller's" torch, that the scientist used, to nineteen to twenty inches long and a weight of two and a quarter pounds. The average size, however, is twelve inches long with a weight of one pound. The welding torch is made up of two brass tubes, one for the acetylene and the other for the oxygen, connected at the two ends. At the nozzle end there is a sharp turn in the piping so that the tip is very nearly at right angles to the main pipes. At the handle end, are the connections for the rubber tubes that lead to the gas tanks, and the little valves by which the operator can control the flow of gas. The pipes carrying the gases to the tip are the same size the whole length, but at one end are enclosed in a larger tube, which serves as a handle.
Now that we have seen the general construction of the oxy-acetylene torches, we will assume that the tanks, which look like large soda-water reservoirs, are filled with pure oxygen and acetylene gas, and transported to some convenient point in a railroadrepair shop where great forges are spurting flames, and one can hardly hear the talk of a man beside him for the roar of the hammers and the compressed air riveters. Assume that some large expensive steel part of a locomotive has been broken and must be repaired quickly so that the engine can go out on the road to help haul an accumulation of freight.
In the old days an engine would have to be taken apart, a new part turned out at the steel mill, shipped to the shops, and the locomotive put together again. Nowadays it is only necessary to take enough of the machinery apart for the workmen to get at the broken parts. After cutting off the edges to be welded so that they make a small V, and supporting them within the fraction of an inch apart in the exact position and shape that they are to be repaired, the workman selects a rod of steel or iron, to use in somewhat the same way the tinker uses a strip of solder when he wants to repair a break in a kettle with solder and soldering iron.
The selection of this filling rod, or wire, is all-important, for the skilful and successful iron worker uses a piece of metal that will fuse well with the parts to be repaired, at about the same temperature at which they themselves will fuse. Mild steel or Norway iron which is 90 per cent. pure is frequently used, but there are no hard and fast rules because every master mechanic has his own ideas about suchthings, and would not take the word of any manufacturing company.
Then the operator turns on his torch, lights it with a match, takes it in one hand, and the rod of welding steel in the other. Holding the end of the steel rod at the thin crack or bevelled edges between the pieces to be welded the operator directs the small flame on the point, holding the tip of the torch about a quarter to a half inch from the metal. It only takes a few seconds for the terrific heat of the flame to melt the strip of steel and the edges of the parts to be welded so that they all are fused together in one perfect mass.
Strange as it may seem, the brass tip of the torch does not melt in this heat because the pressure behind the gases forces them out with such velocity that the flame is far enough removed from the tip to do it no injury, just so long as the operator does not put the tip square against the metal and drive the flame back against it. This not only would melt the tip but probably would cause a flash-back in the torch.
As the end of the strip melts into the crack the operator moves up the steel, and moves his torch along the crack until the whole operation is complete. At the end the weld is very rough but when it is machined down it may be so perfect that it is difficult to tell where it was made, and the strength is equal to that of any other part of the piece.
In other words, the weld becomes homogenouswith the parts repaired. From this fact autogenous welding takes its name. Autogenous is defined as "self produced," or independent of outside materials.
Thus, we see that the autogenous process is a system of putting on new material, without either heating, compression, or adding flux (molten material) to the broken parts. In the foregoing paragraphs we have taken up the welding of steel parts, but the process can be as well applied to steel pipe, steel plate, iron, cast-iron, aluminum, copper, and other materials with only slight variations in the manner of using the torch.
The cutting process is even more spectacular because while the welding proceeds quietly, the cutting is accompanied by just enough fireworks to show us the progress of the tiny flame through the hardest and thickest of metals.
The cutting torch is the same as the welding torch with the exception of an additional pipe from which flows a jet of pure oxygen to give the flame the necessary cutting property. The greater the supply of oxygen the greater the combustion, and the more penetrating the flame. The acetylene gas flame heats up the steel—"fills the office of a preheater," said the scientist—while the oxygen jet follows close behind and makes a thin cut through the hot metal.
The extra pipe is the same size as the others and extends down to the end of the torch at an angle where its tip is clamped alongside the main tip. The rearend of the third tube is connected with a rubber hose like the others, which extends to the oxygen tank. The flow of oxygen is under higher, and individual working pressure, controlled by a valve. In a new style torch the extra hose is done away with and the separation of the oxygen is done in the torch.
When the modern steel carpenter wants to cut a hole, or saw off a strip from a piece of steel, no matter whether it be a steel beam, steel plate, or almost any other form of iron (except cast-iron), he attaches the cutting pipe, lights his torch and sets to work. Holding the tool about half an inch from the surface he directs the little blue flame, which is no more than three quarters of an inch long, and a quarter of an inch thick, against the spot where he desires to start cutting. He holds it there a few seconds, then there is a shower of sparks on the under side of the steel plate, indicating that the flame has eaten its way all the way through. The operator next moves the torch along the line where he wants to cut. The speed with which he can move is governed by the thickness of the steel to be cut. Half-inch ship steel, for instance, could be cut at a rate of more than a foot a minute. The heat of the flame melts a little of the steel, which drops down in molten particles, but the edge that is cut is sharp and clean, and its temper is as perfect as if the cutting were done with one of the laborious old-fashioned steel saws.
AN OXY-ACETYLENE GAS TORCH WELDNote the little torch in the man's left hand, the filling metal in his right, and the inserted picture of the apparatus.
AN OXY-ACETYLENE GAS TORCH WELDNote the little torch in the man's left hand, the filling metal in his right, and the inserted picture of the apparatus.
AN OXY-ACETYLENE GAS TORCH WELD
Note the little torch in the man's left hand, the filling metal in his right, and the inserted picture of the apparatus.
TINY 200-HORSEPOWER TURBINEThis engine could almost be covered by a derby hat. A part of the casing is removed to show the smooth disks.
TINY 200-HORSEPOWER TURBINEThis engine could almost be covered by a derby hat. A part of the casing is removed to show the smooth disks.
TINY 200-HORSEPOWER TURBINE
This engine could almost be covered by a derby hat. A part of the casing is removed to show the smooth disks.
THE TESLA TURBINE PUMPDriven by a 1/12-horsepower motor. The little pump here shown is delivering 40 gallons of water per minute against a 9-foot head.
THE TESLA TURBINE PUMPDriven by a 1/12-horsepower motor. The little pump here shown is delivering 40 gallons of water per minute against a 9-foot head.
THE TESLA TURBINE PUMP
Driven by a 1/12-horsepower motor. The little pump here shown is delivering 40 gallons of water per minute against a 9-foot head.
This cutting process is of especial value to navy yards, shipyards, and wreckers, where there is a great deal of steel to be cut. Uncle Sam uses it at most of his navy yards, for in building his battleships there are thousands and thousands of holes to be cut in steel plates, plates to be shaped, and beams to be cut off to required lengths.
When the scientist and his young friend visited the Brooklyn Navy Yard to see this process in operation the naval constructors had made considerable headway on the framework of the great DreadnaughtNew York, in course of building there. The huge steel ribs of the ship towered upward amid the scaffolding nearly as high as a five-story building. In laying this steel framework, and shaping the plates that will make the hull, bulkheads, and decks, there will be millions of holes to be cut, and virtually miles and miles of plates to be shaped. Instead of sawing these the workmen were cutting them with the oxy-acetylene torches.
Half a dozen men were at work, all cutting as fast as possible, and the great steel plates, and beams were coming and going as quickly as ever boards were passed along by a carpenter. The lines that were to be cut were all marked out in advance so the men never put out their torches. The only cessation in the work was when one of them stopped for a minute or so, to wipe his eyes, for in spite of the dark goggles worn by all operators of the oxy-acetyleneprocess the intense flame is very hard on the eyes.
One reason why the cutting process is so popular in shipyards is because in making steel ships, holes are cut in the plates, ribs, and beams, wherever possible without lessening the strength, to lighten the frame.
Probably the most picturesque use of the cutting device is by wreckers of steel structures. Nowadays whenever there is a bad fire the building is left a tangled mass of steel pipes and girders that can only be cleared away with the greatest risk of life, and the greatest difficulty. The process always was a long, tedious one until the oxy-acetylene cutting came into use.
Thousands of New York boys saw the device in use during the winter of 1911-1912 when they visited the ruins of the Equitable Life Assurance Society fire. The sight is unmistakable. Far up in the ruins you see a man bending over a great twisted steel beam that it might take weeks to pull out of the débris. Soon there is a shower of sparks, and the part that is sticking out is cut off and ready to be sent to the street and hauled away. The device has been used in the ruins of a large number of disastrous fires, lately, particularly where men have been entombed in the collapse of ceilings, and haste means everything in getting out their bodies. Also, it was very successfully used in cutting up the old battleshipMainebefore the hull was removed from Havana harbour.
CHAPTER VIIITHE TESLA TURBINE
DR. NIKOLA TESLA TELLS OF HIS NEW STEAM TURBINE ENGINE A MODEL OF WHICH, THE SIZE OF A DERBY HAT, DEVELOPS MORE THAN 110 HORSEPOWER
"HOW would you like to have an engine for your motor boat that you could almost cover with a man's derby hat and yet which would give 110 horsepower?" asked the scientist of his young friend one day when they had been talking about boats and engines.
"I never heard of any real engine as small as that," said the boy. "I used to play with toy engines, but they wouldn't give anywhere near one horsepower, much less 110."
"Well, I think I can show you a little engine that, for mechanical simplicity and power is about the most wonderful thing you ever have seen, if you would like to make another visit to Dr. Nikola Tesla, who told us all about his invention for the wireless transmission of power the other day. Doctor Tesla invented this little engine and he is going to do great things with it."
Of course the boy jumped at the opportunity, for what real boy would miss a chance to find out all about a new and powerful engine?
"Is it a gasoline engine?" he asked.
"No, it is a steam turbine, but if you know anything at all about turbines you will see that it is entirely different from any you ever have seen, for Doctor Tesla has used a principle as old as the hills and one which has been known to men for centuries, but which never before has been applied in mechanics."
After a little more talk the scientist promised to arrange with Tesla to take the young man over to the great Waterside power-house, New York, where the inventor is testing out his latest invention. We will follow them there and see what this wonderful little turbine looks like.
Picking his way amid the powerful machinery and the maze of switchboards, the scientist finally stopped in front of a little device that seemed like a toy amid the gigantic machines of the power-house.
"This is the small turbine," says Tesla. "It will do pretty well for its size."
The little engine looked like a small steel drum about ten inches in diameter and a couple of inches wide, with a shaft running through the centre. Various kinds of gauges were attached at different points. Outside of the gauges and the base upon which it was mounted, the engine almost could havebeen covered by a derby hat. The whole thing, gauges and all, practically could have been covered by an ordinary hat box.
Yet when Tesla gave the word, and his assistant turned on the steam, the small dynamo to which the turbine shaft was geared, instantly began to run at terrific speed. Apparently the machine began to run at full speed instantly instead of gradually working up to it. There was no sound except the whir of well-fitted machinery. "Under tests," said Tesla, "this little turbine has developed 110 horsepower."
Just think of it, a little engine that you could lift with one hand, giving 110 horsepower!
"But we can do better than that," added the inventor, "for with a steam pressure of 125 pounds at the inlet, running 9,000 revolutions per minute, the engine will develop 200 brake-horsepower."
Nearby was another machine a little larger than the first, which seemed to be two identical Tesla turbines with the central shafts connected by a strong spring. Gauges of different kinds, to show how the engine stood the tests, were attached at various places. When Tesla gave the word to open the throttle on the twin machines the spring connecting the shafts, without a second's pause, began to revolve, so that it looked like a solid bar of polished steel. Outside of a low, steady hum and a slight vibration in the floor, that steadied down after the enginehad been running a little while, there was no indication that enough horsepower to run machinery a hundred times the weight and size of the turbine was being generated.
"You see, for testing purposes," said Doctor Tesla, "I have these two turbines connected by this torsion spring. The steam is acting in opposite directions in the two machines. In one, the heat energy is converted into mechanical power. In the other, mechanical power is turned back into heat. One is working against the other, and by means of this gauge we can tell how much the spring is twisted and consequently how much power we are developing. Every degree marked off on this scale indicates twenty-two horsepower." The beam of light on the gauge stood at the division marked "10."
"Two hundred and twenty horsepower," said Doctor Tesla. "We can do better than that." He opened the steam valves a trifle more, giving more power to the motive end of the combination and more resistance to the "brake" end. The scale indicated 330 horsepower. "These casings are not constructed for much higher steam pressure, or I could show you something more wonderful than that. These engines could readily develop 1,000 horsepower.
"These little turbines represent what mechanical engineers have been dreaming of since steam power was invented—the perfect rotary engine," continuedDoctor Tesla, as he led the way back to his office. "My turbine will give at least twenty-five times as much power to the pound of weight as the lightest weight engines made to date. You know that the lightest and most powerful gasoline engines used on aeroplanes nowadays generally develop only one horsepower to two and one half pounds of weight. With that much weight my turbine will develop twenty-five horsepower.
"That is not all, for the turbine is probably the cheapest engine to build ever invented. Its mechanical simplicity is such that any good mechanic could build it, and any good mechanic could repair such parts as get out of order. When I can show you the inside of one of the turbines, in a few moments, however, you will see that there is nothing to get out of order such as most turbines have, and that it is not subjected to the heavy strains and jerks that all reciprocating engines and other turbines must stand. Also you will see that my turbine will run forward or backward, just as we desire, will run with steam, water, gas, or air, and can be used as a pump or an air compressor, just as well as an engine."
"But most of your research has been in electricity," Tesla was reminded, for no one can forget that Tesla's inventions largely have made possible most of the world's greatest electrical power developments.
"Yes," he answered, "but I was a mechanicalengineer before I was an electrical engineer, and besides, this principle was worked out in the course of my search for the ideal motor for airships, to be used in conjunction with my invention for the wireless transmission of electrical power. For twenty years I worked on the problem, but I have not given up. When my plan is perfected the present-day aeroplanes and dirigible balloons will disappear, and the dangerous sport of aviation, as we know it now with its hundreds of accidents, and its picturesque birdmen, will give way to safe, seaworthy airships, without wings or gas bags, but supported and driven by mechanical means.
"As I told you before when we were talking of the wireless transmission of power, the mechanism will be a development of the principle on which my turbine is constructed. It will be so tremendously powerful that it will make a veritable rope of air above the great machine to hold it at any altitude the navigators may choose, and also a rope of air in front or in the rear to send it forward or backward at almost any speed desired. When that day comes, airship travel will be as safe and prosaic as travel by railroad train to-day, and not very much different, except that there will be no dirt, and it will be much faster. One will be able to dine in New York, retire in an aero Pullman berth in a closed and perfectly furnished car, and arise to breakfast in London."
Tesla's plans for the airship are far in the future, but his turbine is a thing of the present, and it has been declared by some of the most eminent authorities in the world in mechanical engineering to be the greatest invention of a century. The reason for this is not altogether on account of the wonderful feats of Tesla's model turbines, but because in them he has shown the world an entirely unused mechanical principle which can be applied in a thousand useful ways.
James Watt discovered and put to work the expansive power of steam, by which the piston of an engine is pushed back and forth in the cylinder of an engine, but it has remained for Nikola Tesla to prove that it is not necessary for the steam to have something to push upon—that the most powerful engine yet shown to the world works through a far simpler mechanism than any yet used for turning a gas or a fluid into the driving force of machinery.
"How did you come to invent your turbine while you were busy with your wonderful electrical inventions?" Tesla was asked.
"You see," he answered, "while I was trying to solve the problem of aerial navigation by electrical means, the gasoline motor was perfected; and aviation as we know it to-day became a fact. I consider the aeroplane as it has been developed little more than a passing phase of air navigation. Aeroplaningmakes delightful sport, no doubt, but as it is now it can never be practical in commerce. Consequently I abandoned for the time being my attempts to find the ideal airship motor in electricity, and for several years studied hard on the problem as one of mechanics. Finally I hit upon the central idea of the new turbine I have just been showing you."
"What is this principle?"
"The idea of my turbine is based simply on two properties known to science for hundreds of years, but never in all the world's history used in this way before. These properties are adhesion and viscosity. Any boy can test them. For instance, put a little water on a sheet of metal. Most of it will roll off, but a few drops will remain until they evaporate. The metal does not absorb the water so the only thing that makes the water remain on the metal is adhesion—in other words, it adheres, or sticks to the metal.
"Then, too, you will notice that the drop of water will assume a certain shape and that it will remain in that form until you make it change by some outside force—by disturbing it by touch or holding it so that the attraction of gravitation will make it change.
"The simple little experiment reveals the viscosity of water, or, in other words, reveals the property of the molecules which go to make up the water, of sticking to each other. It is these propertiesof adhesion and viscosity that cause the 'skin friction' that impedes a ship in its progress through the water, or an aeroplane in going through the air. All fluids have these qualities—and you must keep in mind that air is a fluid, all gases are fluid, steam is fluid. Every known means of transmitting or developing mechanical power is through a fluid medium.
"It is a surprising fact that gases and vapours are possessed of this property of viscosity to a greater degree than are liquids such as water. Owing to these properties, if a solid body is moved through a fluid, more or less of the fluid is dragged along, or if a solid is put in a fluid that is moving it is carried along with the current. Also you are familiar with the great rush of air that follows a swiftly moving train. That simply means that the train tends to carry the air along with it, as the air tries to adhere to the surface of the cars, and the particles of air try to stick together. You would be surprised if you could have a picture of the great train of moving air that follows you about merely as you walk through this room.
"Now, in all the history of mechanical engineering, these properties have not been turned to the full use of man, although, as I said before, they have been known to exist for centuries. When I hit upon the idea that a rotary engine would run through their application, I began a series of very successful experiments."
Tesla went on to explain that all turbines, and in fact all engines, are based on the idea that the steammust have something to push against. We shall see a little later how these engines were developed, but it will suffice for the moment to listen to Doctor Tesla's explanation.
"All of the successful turbines up to the time of my invention," he says, "give the steam something to push upon. For instance"—taking a pencil and a piece of paper—"we will consider this circle, the disk, or rotor of an ordinary turbine. You understand it is the wheel to which the shaft is attached, and which turns the shaft, transmitting power to the machinery. Now it is a large wheel and along the outer edge is a row of little blades, or vanes, or buckets. The steam is turned against these blades, or buckets, in jets from pipes set around the wheel at close intervals, and the force of the steam on the blades turns the wheel at very high speed and gives us the power of what we call a 'prime mover'—that is, power which we can convert into electricity, or which we can use to drive all kinds of machinery. Now see what a big wheel it is and what a very small part of the wheel is used in giving us power—only the outer edge where the steam can push against the blades.
"In my new turbine the steam pushes against the whole wheel all at once, utilizing all the space wasted in other turbines. There are no blades or vanes or sockets or anything for the steam to push against, for I have proved that they hinder the efficiency of the turbine rather than increase it."
Comparing his turbine to other engines Tesla says, "In reciprocating engines of the older type the power-giving portion—the cylinder, piston, etc.—is no more than a fraction of 1 per cent. of the total weight of material used in construction. The present form of turbine, with an efficiency of about 62 per cent., was a great advance, but even in this form of machine scarcely more than 1 per cent. or 2 per cent. is used in actually generating power at a given moment. The only part of the great wheel that is used in actually making power is the outside edge where the steam pushes on the buckets.
"The new turbine offers a striking contrast using as it does practically the entire material of the power-giving portion of the engine. The result is an economy that gives an efficiency of 80 per cent. to 90 per cent. With sufficient boiler capacity on a vessel such as theMauretania, it would be perfectly easy to develop, instead of some 70,000 horsepower, 4,000,000 horsepower in the same space—and this is a conservative estimate.
"You see this is obtained by the new application of this principle in physics which never has been used before, by which we can economize on space and weight so that the most of the engine is given over to power producing parts in which there is little waste material."
Tesla then went on to explain the details of his new turbine. Leading the way to a small model inhis office he unscrewed a few bolts and lifted off the top half of the round steel drum or casing. Inside were a number of perfectly smooth, circular disks mounted upon one central shaft—the shaft that extends through the machine, and corresponds to the crankshaft of an ordinary engine. The disks all were securely fastened to the rod so that they could not revolve without making it also turn in its carefully adjusted bearings. The disks, which were only about one sixteenth of an inch in thickness, and which he said were constructed of the finest quality of steel, were placed close together at regular intervals, so that a space of only about an eighth of an inch intervened between them. They were solid with the exception of a hole close to the centre. The set of disks is called the rotor or runner.
When the casing is clamped down tight, the steam is sent through an inlet or nozzle at the side, so that it enters at the periphery or outside edge of the set of disks, at a tangent to the circle of the rotor. Of course the steam is shot into the turbine under high pressure so that all its force is turned into speed, or what the scientists call velocity-energy. The steel casing of the rotor naturally gives the steam the circular course of the disks, and as it travels around the disks the vapour adheres to them, and the particles of steam adhere to each other. By the law that Tesla has invoked, the steam drags the disks around with it. As the speed of the disks increasesthe path of the steam lengthens, and at an average speed the steam actually travels a distance of twelve to fifteen feet. Starting at the outside edge of the disks it travels around and around in constantly narrowing circles as the steam pressure decreases until it finally reaches the holes in the disks at their centre, and there passes out. These holes, then, we see act as the exhaust for the used-up steam, for by the time the steam, which was shot into the turbine by the nozzle under high pressure, reaches the exhaust, it registers no more than about two pounds gauge pressure.
DIAGRAM OF THE TESLA TURBINEA—Steam Inlet. B—Disks. C—Path of the Steam. D,D´D´´—Exhaust. E—Reverse Inlet. F—Shaft.
DIAGRAM OF THE TESLA TURBINEA—Steam Inlet. B—Disks. C—Path of the Steam. D,D´D´´—Exhaust. E—Reverse Inlet. F—Shaft.
DIAGRAM OF THE TESLA TURBINE
A—Steam Inlet. B—Disks. C—Path of the Steam. D,D´D´´—Exhaust. E—Reverse Inlet. F—Shaft.
For reasons which will be explained later, ordinary turbines cannot be reversed, but Tesla's inventioncan run backward just as easily as forward. The reverse action is accomplished simply by placing another nozzle inlet on the other side of the rotor so that the steam can be turned off from the right side of the engine, for instance, and turned into the left side, immediately reversing its direction, with the change in the direction of the steam. The action is instantaneous, too, for as we saw in the experiments Tesla showed us, the turbine began to run at practically top speed as soon as the steam was turned on.
The disks in the little 110-horsepower engine which we saw, were only a little larger than a derby hat were only nine and three quarter inches in diameter, while in his larger turbines he simply increases the diameter of the disks.
Tesla further explained that the 110-horsepower turbine represented a single stage engine, or one composed simply of one rotor. Where greater power is required he explained that it would be easy to compound a number of rotors to a double, or triple or even what he calls a multi, or many stage, turbine. In engineering the single stage is called one complete power unit, and a large engine could be made up of as many units as needed, or practicable.
"Then do you mean to say," Tesla was asked, "that the only thing that makes the engine revolve at this tremendous speed is the passage of steam through the spaces between those smooth disks?"
"Yes, that is all," he answered, "but as I explainedbefore, the steam travels all the way from the outer edge to the centre of the disks, working on them all the time; whereas in the ordinary turbines the steam only works on the outside edge, and all the rest of the wheel is useless. By the time it leaves the exhaust of my engine practically all the energy of the steam has been put into the machine."
This is only one of the many advantages that Tesla points out in his invention, for the turbine is the exemplification of a principle, and hence more than a mechanical achievement. "With a 1,000-horsepower engine weighing only 100 pounds, imagine the possibility in automobiles, locomotives, and steamships," he says.
Explaining the large engines that he is testing, one against the other, at the power plant, the inventor said:
"Inside of the casings of the two larger turbines the disks are eighteen inches in diameter and one thirty-second of an inch thick. There are twenty-three of them, spaced a little distance apart, the whole making up a total thickness of three and one half inches. The steam, entering at the periphery, follows a spiral path toward the centre, where openings are provided through which it exhausts. As the disks rotate and the speed increases the path of the steam lengthens until it completes a number of turns before reaching the outlet—and it is working all the time.
"Moreover, every engineer knows that, when a fluid is used as a vehicle of energy, the highest possible economy can be obtained only when the changes in the direction and velocity of movement of the fluid are made as gradual and easy as possible. In previous forms of turbines more or less sudden changes of speed and direction are involved.
"By that I mean to say," explained Doctor Tesla, "that in reciprocating engines with pistons, the power comes from the backward and forward jerks of the piston rod, and in other turbines the steam must travel a zigzag path from one vane or blade to another all the whole length of the turbine. This causes both changes in velocity and direction and impairs the efficiency of the machine. In my turbine, as you saw, the steam enters at the nozzle and travels a natural spiral path without any abrupt changes in direction, or anything to hinder its velocity."
But the Tesla turbine engine, claims the inventor, will work just as well by gas as by steam, for as he points out gases have the properties of adhesion and viscosity just as much as water or steam.
Further, he says that if the gas were introduced intermittently in explosions like those of the gasoline engine, the machine would work as efficiently as it does with a steady pressure of steam. Consequently Tesla declares that his turbine can be developed for general use as a gasoline engine.
The engine is only one application of the principle of Tesla's turbine, because he has used the same idea on a pump and an air compressor as successfully as on his experimental engines. In his office in the Metropolitan Tower he has a number of models. Pointing to a little machine on a table, which consisted of half a dozen small disks three inches in diameter, he said: "This is only a toy, but it shows the principle of the invention just as well as the larger models at the power plant." Tesla turned on a small electric motor which was connected with a shaft on which the disks were mounted, and it began to hum at a high number of revolutions per second.
"This is the principle of the pump," said Tesla. "Here the electric motor furnishes the power and we have these disks revolving in the air. You need no proof to tell you that the air is being agitated and propelled violently. If you will hold your hand down near the centre of these disks—you see the centres have been cut away—you will feel the suction as air is drawn in to be expelled from the outer edges.
"Now, suppose these revolving disks were enclosed in an air-tight case, so constructed that the air could enter only at one point and be expelled only at another—what would we have?"
"You'd have an air pump," was suggested.
"Exactly—an air pump or a blower," said DoctorTesla. "There is one now in operation delivering ten thousand cubic feet of air a minute."
But this was not all, for Tesla showed his visitors a wonderful exhibition of the little device at work. "To make a pump out of this turbine," he explained; "we simply turn the disks by artificial means and introduce the fluid, air or water at the centre of the disks, and their rotation, with the properties of adhesion and viscosity immediately suck up the fluid and throw it off at the edges of the disks."
The inventor led the way to another room, where he showed his visitors two small tanks, one above the other. The lower one was full of water but the upper one was empty. They were connected by a pipe which terminated over the empty tank. At the side of the lower tank was a very small aluminum drum in which, Tesla told his visitors, were disks of the kind that are used in his turbine. The shaft of a little one twelfth horsepower motor adjoining was connected with the rotor through the centre of the casing. "Inside of this aluminum case are several disks mounted on a shaft and immersed in water," said Doctor Tesla. "From this lower tank the water has free access to the case enclosing the disks. This pipe leads from the periphery of the case. I turn the current on, the motor turns the disks, and as I open this valve in the pipe the water flows."