A Departure in Steam Tractor Design.
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Green' s Model with Tandem-Compound Engine.
Many well-known engineering companies now build steam :Actors which come within the heavy motorcar regulations the Local Government Board, and one of the smartest of ese is built by Thomas Green and Son, Ltd., of Smithfield on Works, Leeds, which Impany is so widely known for ; lawn-mowers and rollers. he tractor which the above Impany has recently put upon .e market is a really good achine, and it has been built lecially for hauling purposes : nail size and low weight are prnbined with large engine )wer.
The general proportions are )od, as may he judged from Le line drawing of the general -rangement which we reproIce, whilst the three-quarter de view shows that it is of easing appearance. The )iler is constructed of best, lid-steel boiler-plates, each of hich is flanged in one heat r a hydraulic flanging press. II the seams are hydraulic
ly riveted, and the plates are strongly stayed throughout. he working pressure of the steam is 'Gelb. per square inch, it a certificate, which shows that the boiler has been tested a much higher figure, is given to the purchaser. We are de to give a reproduction of a drawing which shows the )iler in section, and this, together with the following
T,ures, will convey a clear idea of the soundness of its sign. The diameter of the shell is 24 inches, and the
ickness of the plates of which it is made is three-eights of inch ; the fire-box plates are of the same thickness, and
the flanged plates used for the " throat " and other parts are all thirteen-thirty-seconds of an inch thick. The tubeplates are seventeen-thirty-seconds of an inch thick, and there are thirty-one lap-welded tubes, the diameter of which is one and three-ctuarters of an inch. Yorkshire iron, screwed stays, seven-eights of an inch in diameter, are spaced four inches apart, round the sides of the fire-box. There is an extralarge mud-hole in the upper part of the shell, on the off-side, through which all the tubes are easy of access for scaling, whilst there are other and smaller mud-holes in the lower part of the shell, and at the base of the fire-box. All the usual and necessary fittings are conveniently mounted, and the boiler is neatly lagged with asbestos and sheet iron. The boiler has 67 square feet of heating surface, and a grate-area of 3.35 square feet.
The smoke-box is of an unusual form of construction. It is attached to the shell of the boiler by means of bolts which pass through flanged rings on the bailer shell and the smoke. box. The object of this arrangement is to provide that the smoke-box, leading-axle, and wheels may be taken bodily away and replaced by another form of smoke-box arranged to take a road-roller. Thus, with interchangeable smokebox and a pair of smooth-tired driving wheels, the machine may be used either as a tractor or as a road roller. _ In addition to an injector, there is an eccentric-driven, plunger feed-pump, mounted in the tender. This pump has
a double set of clack-, or non-return, valves, which may be examined and cleaned whilst the boiler is under steam. The water tank has a capacity of 75 gallons, and is built into the tender ; it may be rapidly filled by means of a water-lifter and zo feet of suction hose, which are provided for that purpose. The tender is constructed of stout, mild-steel plate ; it has all its corners flanged, and is so arranged that it is relieved of all pulling strains, these being transmitted directly to the driving axle.
The engine is of the compound type, with the cylinders arranged tandem fashion. The diameters of the cylinders are : high pressure, 4A•• inches ; low pressure, 8 inches ; and the piston-stroke is to inches. The cylinders are steam-jacketed, as may be seen in our illustration of them : they are mounted on the shell of the boiler, and over them is fixed a steam dome in such a manner that the cylinders are always surrounded with steam at the full boiler pressure. The crankshaft is of hammered, mild steel, and is carried in steel brackets which are fitted with gun-metal bushes. The
brackets register in holes which are bored in the lire-boxshell side-plates, in the manner shown in the arrangement of the transmission gear, the drawing of which we reproduce. The near-side end of the crankshaft carries a flywheel, which is 38 inches in diameter by 3,1 inches wide on the face : both edges, and the face are machined so that the flywheel may be used for power transmission by means of a leather belt. Arrangement ismade for two running speeds : the sliding pinions are so arranged, and interlocked, on the end of the crankshaft that it is not possible to get both sets of gears in mesh at the same dine. All the gears are of cast steel, with shrouded teeth. The changes of gear give running speeds of three and six miles an hour, with the engine running at its normal r.p.m. Intermediate speeds can, of course, be obtained by linking up the engine. All the parts composing the reversing gear are of Low Moor iron, and are case hardened.
The machine is supported over the solid-looking back-axle by means of two, conical,involute, spiral springs, and over the leading-axle by means of ordinary, laminated, plate springs. The slip winding-drum is provided with 30 yards of wire cable, and is easily locked, or unlocked, in relation to the driving-axle, by means of a single pin. The usual traction-engine type of steering, with diagonal shaft, worm and worm-wheel, and chains to the leading axle, is employed. A screw brake is provided, and this operates on the inner face of the driving-wheel rims.
A few of the principal dimensions are as follow : driving wheels, 4 feet 6 inches in diameter; leading wheels, 3 feet 4 inches in diameter ; overall length, 13 feet ; overall width, 5 feet 3 inches ; and capacity of the fuel bunkers, about 3 cwt.
It is just over twelve months ago that this company entered the field of steam-tractor construction. An example of the first type which it introduced was shown at the Royal Agricultural Society of England's show at Derby in June, 1906, and this was illustrated i.n "THE COMMERCIAL MOTOR in its issue of the 2Sth of June of that year. The machine then shown had a single-cylinder engine of 64 inches ir diameter, and the stroke of the. piston was to inches—the same length as that on the engine illustrated on these pages. The fact that the general design has not since then beer materially altered, (except the conversion of the engine to tandem-compound type, in order to meet the demand for more powerful machine) is of itself evidence that the origina designs had been well thought out and that their embodi. ment in the finished tractor has been fully justified. A moscomplete set of tools is sent out by the makers with eact machine, together with frost pegs and clips.