Association for the Advancement of Science
Engineering and Architecture.
The Direction of Progress in Engineering.
When I accepted the office of president of this section, I did so believing that I should have the honour of personally opening its proceedings. Being, to my great regret, prevented from visiting Adelaide, I must be content to express the hope that the Session of this, the section of applied science, may be productive of pleasure to members attending, and of benefit to the several branches of our profession. The importance of these gatherings can hardly be overestimated, for at them the engineer is brought into close contact with every branch of Science; and to-day, to be successful, he must be, in the true sense of the term, a scientific man, quick to grasp the practical importance and to devise means for the application of those great discoveries, to the close sequence of which we have grown so much accustomed.
The march of progress in engineering is now so rapid that, on an opportunity such as the present, it may be as well to pause in the hurry of practical work and review the ground which has been covered in the last few years, with the object of so directing our course in the immediate future that we may occupy a position in the front ranks of future advance, I propose, therefore, to-day to consider the most recent developments in those branches of engineering with which I am most familiar; and, bearing in mind that it is the commercial and not the purely scientific or interesting aspect of an invention that deter- page 2 mines its adoption, to venture to point out the direction in which it appears to me that the light of past experience suggests future improvement.
Turning first to the cradle of all mechanical processes and engineering operations—the workshop—we find that the introduction of electrical welding has greatly facilitated the manufacture of wrought iron piping and the various small forgings used in the gun, tool, and agricultural implement trades, whilst the fact that there is no wasting of the material by this method is in itself a sufficient cause for its universal adoption for all descriptions of plate work. The simple fusing together now so often practised cannot, however, be regarded as satisfactory. At such a juncture the physical nature of the material must differ considerably from that of the remainder of the plate or bar, this nature having been to a great extent derived from the treatment received during manufacture. Electric welding to be efficient should, therefore, be accompanied by hammering, or by severe pressure from all directions.
A series of tests on the relative strength under alternation of stress of electrically-welded as against fused joints would probably result in much valuable information on the subject being obtained. The extent to which it is desirable to apply the process will greatly depend on the relative local cost of current and fuel, which will also be the chief factor in determining the use of electricity for heating purposes in connection with industrial operations. There is no comparison between the efficiency of direct and current heating; yet in Norway, where water power is abundant and fuel scarce, it is found profitable to utilise electricity to a considerable extent for the heating of nail rods. There a hollow carbon is brought to a high temperature by the passage of a low tension current, and the nail rod fed through it at a speed dependent on the degree of heat required. Rivets are also heated in a similar manner.
In the process of finishing surfaces there has been a marked advance. Milling is rapidly displacing planing and shaping. By milling is to be understood the shaping of metal by rotary cutters. The milling machine is capable, not only of doing with far greater expedition all the work usually executed by the planer and kindred tools, but also of preparing curved profiles hitherto finished by filing to template. It is essentially a sizing-machine, and the work turned out from it cannot be improved by any subsequent treatment. It owes its efficiency to the use of a series of cutting edges, and a continuous feed, as opposed to a single tool-point and intermittent action. This page 3 principle is capable of very extended application, and the metal-working machine of the future will probably resemble in general character the appliances used for the preparation of timber to-day.
Few who have had charge of workshops can have failed to have noticed the inefficiency of the means usually adopted for the conveyance of power from the prime mover to the various machine tools. The wear and tear, interference with space and light, and liability to accident accompanying belt transmission are familiar to most. So keenly was this brought home to me some five years ago that I elaborated a scheme for driving each individual machine by a small "Brotherhood" engine, actuated by compressed air. The problem is now, however, solved in a more simple manner by the use of electricity; and a few years hence we shall look with curiosity on photographs of the assemblage of shafts and strings now considered a necessary part of the equipment of a machine shop.
The advantages which the electric system possesses over its rival are numerous; not the least being the fact that an idle machine absorbs no power, there being no lengths of shafting and accompanying belting to be kept in motion, whether the whole or a single machine of the group is employed. That electric-driving has passed the stage of experiment is evident when we find that Messrs. Siemens are in their own work steadily doing away with the many independent engines they once possessed, concentrating the production of motive power, and distributing it electrically to the various shops, the machines therein being driven either individually or in groups, according to the nature of the work on which they are employed.
Messrs. Sienens inform me that a considerable economy in fuel, wages, and upkeep has already been effected, and that they propose to complete the application of this system. Messrs. Easton and Anderson have for the past live years been driving electrically two overhead travelling cranes, one a 20-ton crane of 40ft. span, in which a single five-unit motor running continually effects the necessary movements through the medium of spur gearing. The current is conveyed to this crane by an angle iron supported on wood blocks, and running along the shop wall. One face is ground up bright and contact made by a sliding spring. The return is through the rails. The second crane is of 15 tons capacity and has a separate motor for each motion, which is stopped, started, or reversed, as required, the current being collected and returned by means of overhead wires. So satisfactory has been the performance of these cranes and of other page 4 electrically-driven machines that Messrs. Easton and Anderson contemplate a complete re-arrangement of their driving plant, substituting for independent prime movers a central generating station with triple-expansion engines, from which power will be electrically distributed throughout their workshops. The Northern Railway of France find that, at a small repairing shop, substituting electric power at 6d. per B.T.U., with a separate motor to each machine, has effected an economy of 50 per cent, (all charges and depreciation included) as compared with the cost of the previous arrangement of gas-engine and belting. In mining operations hand labour is being rapidly replaced by power. Coal-cutting machines have effected a saving of about 15 per cent, of the coal vein otherwise wasted in the form of fine coal and dust. The coal is obtained in more solid and larger blocks, whilst the cost of production has been reduced by from 20 per cent, to 30 per cent, as compared with hand labour.
The transmission of power underground has been accomplished by the use of compressed air, hydraulic pressure, and wire ropes—the efficiency of such methods being from 30 per cent, to 40 per cent. By the adoption of electricity, however, the efficiency of transmission can be raised to over 50 per cent., and as this can be accomplished with a reduced capital expenditure, accompanied by a more portable and easily erected plant capable of supplying the power necessary for getting, hauling, pumping, and lighting, it would appear that electricity is in the future destined to become the principal transmitter for mining purposes. It is true that its use in fiery pits cannot at present be regarded as absolutely safe; but enclosed motors, non-sparking switches, and Mr. Atkinson's safety cable have greatly diminished risks which will, no doubt, eventually be completely removed.
The safety cable mentioned consists of a main and a subsidiary conductor, in circuit with each being a fuse. These conductors are connected with the same terminals at dynamo and motor, the current dividing between them in proportion to their carrying capacity. If now the main conductor be broken, the subsidiary conductor remaining intact, no spark results at the breaking, the circuit still being closed but the whole current is thrown on the subsidiary conductor, and its fuse is melted, which occurrence, by means of a suitable mechanical arrangement, causes the whole circuit to be switched off. To carry this principle into effect the cable is composed of a closely wound spiral of tinned copper wire (several wires being arranged in parallel), which is braided over, but not heavily insulated. Over this is laid a stranded conductor of the required area, and the whole is then fully insulated. If the cable be torn down by a fall, or broken in any way page 5 by tension, the inner conductor extends to an unlimited extent and maintains the circuit until, by the action of the fuse, the whole cable is disconnected.
Closely connected with mining are the tunnelling machines, which have so lightened what was perhaps the most tedious work the civil engineer could he called on to execute. The driving of the Mersey and the trial borings for the proposed channel tunnel marked a new era in such operations. An average forward progress of ten yards in twenty-four hours, with a maximum of fourteen, was obtained in the new red sandstone of the Mersey tunnel, whilst the grey chalk of the channel was pierced at a maximum rate of over a yard per hour, the heading in each case being 7ft. in diameter. In extensions of the London Underground Railway the needle system has proved expeditious and remarkably efficient in preventing subsidence, there having been absolutely no disturbance of the heavy buildings under the foundations of which the works have been carried.
The City and South London Railway, which, starting from the Monument, traverses the bed of the Thames, and has its other terminus at North Brixton, is carried for the whole of its length in a pair of tunnels 10 feet 6 inches in diameter, lined with cast-iron segments. The heading was driven the full diameter of the tunnel by means of a cutting shield forced forward by hydraulic jacks abutting on the completed portion of the work. As soon as the advance of the shield permitted it a new ring of segments was put in place, the cutting and lining thus proceeding almost simultaneously. The space between segments and bore was filled with grout forced in by air pressure. Where much water was met with, a stream of grout played on the working face, greatly assisted the air pressure in retarding the flow. The work proceeded at an average rate of 13ft. Gin. per day.
The tendency of modern practice is thus (when the nature of the material to be pierced admits) to conduct boring operations on a large scale in a very similar manner to that in which they are effected on a small one, namely, by the removal at one operation of a core the full diameter of the finished cross section, and, where lining is necessary, to supply it in the form of large segmental pieces or even to mould it in place. In the other operations connected with railway formation, the use of machinery has greatly increased the rapidity of execution. The excavation of cuttings and foundations, formation of embankments, ditching, and even track-laying and ballasting, can be much facilitated, if not entirely performed, by mechanical appliances, the adoption of which is rapidly becoming general.page 6
The production of reliable steel of great strength and moderate price gave a great impetus to the construction of long-span bridges. That over the Firth of Forth, with its spans of 1,061 feet, height above bed of Forth of 570 feet, and in which 50,000 tons of steel and iron were used, will probably remain unsurpassed in dimensions until a material of still higher grade is introduced.
Turning now to inland locomotion, we find that extremely high speeds have been lately attained in England and America, and we are promised still greater velocities on specially constructed electrical railways. Such speeds as 120 miles per hour are of course possible, but would necessitate a considerable distance between the tracks, and an expenditure of energy at the rate of about 250 horsepower, in overcoming air resistance alone. It must also be remembered that it would now be difficult to locate a railway of this kind in a district so populated as to afford reasonable prospect of paying traffic without its being brought into direct competition with some existing steam line having greater facilities for the exchange of vehicles, and which has probably been constructed at a far lower capital expenditure. Though the immediate future of high speed electrical railways is not promising, electricity is fast displacing other methods of traction on tramways and light railways.
In America, horse traction is being superseded by the overhead conductor, or, as it is there termed, the trolly system, on which-150 tramways, with a total of 4000 miles of track, are now being worked. An electromotive force of 500 volts is used, and geared motors are universally adopted.
In England there are two remarkable examples of electric light-railways—the City and South London Railway, and the Liverpool Overhead Railway. The City and South London Railway is about three miles long, and is carried for the whole of its length in the cast-iron tunnels previously described. The average speed of the trains, including stoppages, is eleven and a-half miles per hour, and their gross weight about 40 tons each. The locomotives are of 100 horsepower, and are carried on two axles, on each of which a motor acts directly. The current is collected from an insulated channeliron conductor laid between the rails, fed at intervals by a 61-14 B.W.G. Fowler-Waring cable. The generating station is at the Stockwell terminus of the line, where there are four dynamos, each capable of supplying 150 amperes at 500 volts.page 7
The Liverpool overhead railway may be classed as one of the most interesting of modern engineering achievements. It consists of six miles of double track of standard gauge running on a plate-iron viaduct alongside the Liverpool Docks, and, for the greater part of its length, over the existing dock railway. There are in all fourteen stations, and the steepest gradient is 1 in 40. The main generating station (placed near the centre of the line) contains four 400 horsepower engines, each driving a dynamo capable of an output of 175 amperes at 500 volts. The conductors are inverted channel irons of steel, laid between the ordinary rails and carried on pot insulators. They are jointed by copper fishplates. The current is conveyed to the cars by means of hinged cast-iron shoes, the return being through the ordinary rails, which are electrically jointed at the fishplates. A train consists of two bogie cars, and is capable of seating 114 passengers; each car is furnished with a single motor, the armature of which is mounted directly on one of the bogie axles. The line was first opened for traffic on March 5th last, and during the first three months 71,122 train miles were completed. Trains are now run every five minutes, which necessitates twelve trains in traffic. The average total output at the Central Station is G50 ampéres, at 430 volts; the consumption of small coal is at the rate of 241bs., costing ¾d. per train mile. The trains stop at all thirteen stations, and complete the six miles in twenty-five minutes, the average speed, including stoppages, being 14.4 miles per hour. Not the least interesting feature of this line are the signalling arrangements, winch are effected electrically, and are perfectly automatic.
The application of electric traction to existing roads will be attended with considerable difficulty. To fully equip one of the great lines on the conductor system would mean enormous expenditure, and, in the goods yards, prohibitive complication; but when it is apparent that prospective economy warrants such expenditure being incurred, there should be no insurmountable obstacle to main line and branches being so fitted.
The marshalling at goods yards could be carried on by steam or storage locomotives, and the other motors supplied with sufficient storage capacity to enable them to effect shunting operations at way stations. It is to be remembered, however, that an improved storage system might remove the existing necessity for the conductor. In the meantime we have a proposal to apply electric traction to existing railways in such a manner that no special plant beyond the actual locomotive is required. The engine (at present being constructed on page 8 the plan of M. Heilmann) differs from the ordinary locomotive in the fact that instead of the engine proper being coupled directly to the driving axle, it actuates a dynamo, the current from which is utilised to turn the engine wheels through the medium of motors placed directly on the axles.
At first sight it would appear that such an arrangement could only result in loss; but a little consideration will show us that vexatious limits as to diameter of wheels, size of boiler, and length of wheel base disappear, whilst the total weight of the engine can be utilised for adhesion. Coupling rods are not required, and all reciprocating parts can be balanced without the introduction of disturbing forces in themselves fatal to the attainment of high speeds; and as the efficiency of transmission is high, and the engine can be run continually at the most economical expansion ratio, the fuel economy of the machine will probably be greater than that of any existing locomotive. It has also the advantages of being capable of attaining a higher velocity, and of dealing indiscriminately with express and goods traffic.
Only practical experience can determine whether these results can be obtained without a disproportionate expenditure in first cost and upkeep. At present it would appear that this locomotive is destined to form a link in the chain of transition from direct steam to electrical traction on our railways, but that it will in turn be displaced by a conductor or storage system.
The excessive waste of material which occurs in the stoppage and control of the movement of railway trains is well-known, and attempts have from time to time been made to reduce this loss and to obtain some return for the energy given up during retardation. It is a matter for surprise, therefore, that no efficient electrical brake has yet been introduced; by electrical brake being understood, not an arrangement where electricity simply replaces fluid pressure as means for actuating the brake blocks, but one in which there is no frictional contact, the kinetic energy of the train being absorbed in the production of electrical currents. On electrical railways it would probably be found economical to conserve this energy, but for present application such complication would be better avoided.
With respect to steam navigation, the high rate of speed now maintained over long voyages and the regularity with which such are accomplished are remarkable. These results are, doubtless, in some measure due to an increased size of vessel, but chiefly to the page 9 great advance which has boon made in marine engine construction. The adoption of high boiler pressures, triple expansion engines, and the free use of steel has enabled the marine engineer to so increase the efficiency of his machinery that we now find 2.4 indicated horsepower per gross ton of vessel attained, as against the one horsepower per ton often years since. An indicated horsepower is produced for a consumption af a little over l¼lbs. of fuel, and the careful proportioning of details has rendered stoppages from breakdowns of rare occurrence.
To the active competition between the great English torpedo boat builders much of this progression can be traced, and the new water tube boiler of Mr. Thornyeroft promises, from its comparative lightness, to enable a further stride to be taken in high speed navigation. But is advance in this direction to be completely dependent on the engine-builder? The naval architect has certainly somewhat reduced the weight of the hull, hut the form of vessel has remained for many years practically unchanged. The great improvement in the speed of our large racing yachts that (under similar conditions of stillness and displacement) has followed the adoption of great beam, shallow body, and round lines, points to the possibility of a beamy, pram-bowed vessel of moderate draught being propelled with a less expenditure of power than is required in the case of the pointed tanks now so common. Between the seaworthiness and comfort of the two types there could be little comparison.
In conclusion, I would refer to the long distance transmission of power. Passing over as experimental the now historical installation at Frankfort, where 300 horsepower was electrically transmitted 108 miles, with a stated efficiency of 78 per cent., we find that the adoption of the high tension alternating current system has rendered it possible to transmit power over long distances with commercial success. An electromotive force of 10,000 volts is now recognised as a safe pressure if proper precautions be used. With high pressures the cross section and cost of conductor is greatly reduced. The smallest sized wire having the necessary strength for line work (No. 6, B. and S.) will, at 4,000 volts, transmit 100 horsepower ten miles with 80 per cent, efficiency. When pressures exceeding 5,000 volts are employed it is advisable, on account of difficulties connected with the insulation of the machines, to make use of transformers, the current being raised for transmission at the generator and again reduced at the motor terminals. As transformers having an efficiency of 97 per cent, are now constructed the loss from this arrangement is insignificant compared with the saving in cost of the conductor.page 10
The want of a perfected alternating-current motor has alone delayed the rapid extension of this system; but this difficulty has apparently been completely overcome by the recent inventions of Nicholas Tesla, and has been reduced to a minimum in an installation which has for the last two years been in regular work in America.
At the Gold King Mine, Colorado, power was required for operating crushers and stamps: fuel could only be procured from long distances at enormous cost, but a few miles from the mine water power was available; the intervening country, however, was so rough and so often snowed up that no ordinary means of transmission could be made use of. Electricity was therefore adopted. The plant consists of a Pelton wheel driving an alternating-current generator. The current is carried by a bare wire up the mountain side to the mine at a height of 2,500ft.; here it drives a 100 horsepower synchronous motor, which is started by the assistance of a small motor of the Tesla type. The efficiency of the system was found on test to be 83½ per cent, at full, and 74 per cent, at half load, losses in generator and motor, but not those of conductor, included. So satisfactory has been the practical working of the plant that a 750 horsepower generator and a 300 horsepower and some smaller motors have lately been added.
Long distance transmission for lighting purposes has for the last three years been in satisfactory operation at Portland, Oregon. The falls of the Willamette River, thirteen miles from Portland, are estimated at 250,000 horsepower, 300 horsepower of which is utilised by means of turbines driving two alternating-current dynamos. The current, generated at 4,000 volts, is carried by a No. 4 B. & S. wire on ordinary glass insulators across country to the sub-station at Portland, where it is received at 3,300 volts, and reduced by transformers to 1,100 volts for distribution through the city to ordinary transformers, by which it is again reduced to 50 volts. Additions have lately been made to the plant, the total capacity of which is now 8,750 sixteen-candlepower lights. Works for the utilisation and electrical distribution of the great energy of Niagara are being actively prosecuted.
The immense waterpower of the world is now available, and can be conveyed to situations where the difficulty of procuring fuel has hitherto prohibited mining and other operations. It will be possible for manufacturing to exist far removed from coal measures, and even for industries, the profitable prosecution of which has been dependent page 11 on abundant fuel supply, to be carried on without such aid. To the small manufacturer the supply of cheap and readily applied motive power will be a great boon, and we may look for a revival in the prosperity of the small workshops now almost crushed out of existence by the competition of their more powerful rivals. The utilisation of power obtained at a distance may, in fact, be expected to effect a change in industrial operations hardly inferior in magnitude to that brought about by the introduction of the steam engine. I think, therefore, you will agree with me in considering the successful transmission of power over long distances as "the greatest mechanical achievement of the age."
Christchurch Press Company Limited, Printers, Christchurch.