NEW IDEAS IN ROAD ROLLER DESIGN.
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First Published Details of the Advance Steam Roller Built by Wallis and Steevens, Ltd.
TllE GREAT progress which has been made in road construction during recent _years has necessitated the employment of machinery vastly different in many instances from that which was previously in use. At one time, the old-fashioned steam-roller was looked upon as the last word, but with the coming of tarred macadam and asphalt road surfacings the imperfections of the ordinary roller rapidly became apparent,
Mach effort has of late been devoted to the production of rollers more suited to modern requirements, and of those perhaps the most satisfactory has been the tandem type, either motor or steam driven. Certain of these, however, show a tendency to rock and even overturn, and it is very difficult to get them to work right up to the edges of the road surface. .
With the masihines at present in use, the
situation ea n be summed up in this manner. With the ordinary roller a very good job can be made of the bottom, whilst the top finish is not entirely satisfactory ; with the tandem type, the bottom is not so good, but the finish is fairly satisfactory.
Much of the difficulty is caused by the fact that all roads have to be cambered, whilst at the crossings the road goes from camber to fiat. In the ordinary B28 roller all the wear and pressure are on. the inside of the rolls, and, therefore, there cannot be true consolidation. The tandem roller takes the main load in the centre of its rollers, and, when in use, tends to set up a series of potential or undeveloped ridges by reason of the surface being subjected to unequal pressure, and there is, of necessity, a considerable amount. of slip, which is shown in practice by the bright scarified appearance of the roller faces.
For work with asphalts quick reversing is an absolute necessity, for any dwell tends to cause the roller to sink.
Wallis and SteeVens, Ltd., built their first steam-roller about 45 years ago, and their latest. effort in this direction represents the experience accumulated over this period. The new roller, which is known as the Advance, has, in tho words of its builders, been designed with the idea of producing the best roller irrespective of cost, and it certainly embodies features which are quite unusual, and this in spite of, the fact that tge loco-type boiler and overtype engine have been retained.
In the normal roller the weight is very unevenly distributed between the rolls at the front and rear,but the weights are now practically even over the full roller width, thus giving even consolidation and a fine surface finish. This balancing is entirely irrespective of the fuel and water supplies, the two water tanks (together holding 100 gallons) being arranged at the &ides midway between the centres of the rolls.
Reference to our illustrations will show that this balancing is carried out across the machine as well as longitudinally. The footplate is exactly central, as is the double high-pressure engine, with its piston-valve gear. A fuel bunker is situated at each side of the tender, and even the toolboxes underneath these bunkers are balanced. Incidentally, the centre of gravity of the whole maohine is far lower than is the case with the ordinary type.
The front rolls are comparatively narrow, whilst the rear rolls are rime]] wider than is usually the case, and there is a very satisfactory overlap of the tracks.
Apart from these 'differences, it is difficult to see from the photographs where the really novel features exist. They lie mainly in the rolls themselves. For instance, the fore-carriage is of special design and is provided with a patented locking device, which enables the front rolls to be held either rigidly horizontally for straight rolling, or to be left free to adjust themselves to the surface of the road. To enable this to be done, the upright stud is formed in one with an inverted T, and at the ends of the horizontal arms of the T are holes corresponding with other holes in the fore-oarriage. Stout pins can be inserted into these holes when required, thus locking the fore-carriage to the upright stud, but permitting steering. The importance of this feature may not, at first sight, be realized. A. reference to the two illustrations at the head of this article will, however, show the effect. In one case, an obstruction in the road merely causes the rolls to lift at one side; but if the rolls be locked, a much greater pressure is exerted on the obstruction, so that, when in service, instead of merely bumping over elevations and forming potential potholes at each side, the roller flattens out the humps. It would not do to make the front rolls permanently inflexible, as the machine would then not be suitable for work on cross-roads, or when at an angle to the camber of the :end. .
Now, as regards the rear rolls, these are mounted on a patent flexible rear axle, So arranged that the rolls can be set at any definite camber required, or can be left to adjust themselves to any camber within the limits for which the machine is designed, as, normally, a three-roll machine cannot avoid marking. We are not yet at liberty to disclose exactly how this flexible axle operates. Thatit is effective has been shown in the rollers -which are already in service, and the fact that the design embodies a means for flexibly supporting the rear end of the roller greatly assists in permitting this to operate at higher speeds than is usual, and to travel with greater ease and comfort by road to the scene of operations.
We will now deal with the other features of interest. Of these, one of the most important, and one whichadds greatly to the strength and rigidity of the whole construption, is the tender which, in the new roller, is formed by extending the boiler horn-plates backwards, whereas in the ordinary roller the tender is baited to the back of the boiler. It will readily be understood that this provides a much stouter job.
The boiler itself is of ample capacity and has short tubes which can easily be swept by a straight brush from the front end. To enable this to be done the smokebex door is pivoted at the bottom, and can either be dropped down or lifted away altogether. The space between the front rolls and the smokebox is sofficient to allow the brush to be used.
We have already referred to the engine, but have not mentioned that the valve gearing is of a modified Stephenson type. The cylinders, which have a bare and stroke of 41 ins. and 9 ins, respectively, are completely steamjacketed, the jacket being in direct communication with the boiler. Renewable cast-iron liners are provided for the piston valves. These valves have no lead, and this fact, combined with the absence of a flywheel, assists in obtaining the instarbtaneous reverse which is so necessary with rollers of this type. This reversing can be effected without touching the stop valve, and at any speed within the capabilities of the machine.
Great care has been taken in the balancing of the crankshaft. It is carried in bearings of ample size, the brasses, being made in three parts, and so-fitted that, by slackening off the caps and tightening up the wedges, they can be adjusted without removal.
tiThe two sliding pinions of the twospeed gear are carried inside the hearings. They mesh with spur wheels on the countershaft, and thence the drive is carried to the differential gearing on the third-motion shaft. The differential gearing is enclosed and runs in oil, and the whole of the gears are machine out.
An important detail of the differential gear is that this can be locked when required. To effect this, the pins on which run the planet pinions are each tightened by a nut. Each pin carries a cone at its inner end This presses into the pinion, which is forced against a second cone at the outer end, the two cones acting as an effective brake by which each pinion is firmly locked to the case.
The final drive to the rear rolls is by a spur pinion at the end of each of the differential shafts. These mesh with large externally toothed rings bolted to the rolls. This gearing is set under the rim of each roll, so that dirt does not drop on to the teeth_ The rolls themselves are gunmetal bushed and constructed of forged steel plates. The inner faces of the final-drive gear rings act as •drums for the Fern-do-faced brake blocks, which are brought, into action by means of a hand screw.
The steering is very positive, being by means of a machine-cut worm and quadrant fitted to the top of the farecarriage stud. The steering is rendered easier by carrying the fork bead in a ball bearing. The equipment includes two injectors, a water lifter, a steam cock` for heating tar, etc., automatic sprayers for the hind wheels, and an automatic cylindee lubricator.
Two lengths of armoured suction hose and a rose -piece are provided, the main piece is 15 ft. long and the auxiliary piece has a length of 13 ft,
There are only two live steam cocks, the other functions being controlled by two three-way cocks.
Safety is ensured by the provision of double Ramsbottom-type safety valves and a fusible plug.
Reference to the illustrations will show that the piping has been cut down to the minimum. This certainly constitutes a very great improvement.
Attention has been paid to the ques. tion of preventing obstruction of the driver's view. For instance, there are
no hood standards at the front, the hood being ‘there supported by a bracket belted to the chimney. A small hut noteworthy point is that the hoed is so arranged that the water runs off at the four corners.
In its-present form, this roller weighs 6 tons, but it can be provided in weights up to 8 tons, according to requirements. It will be exhibited at the Roads and Transport Congress and Exhibition at the Agricultural Hall, where it will be accompanied by a standard 10-ton railer of the normal typo.