ROAD ROLLER, a self-propelled machine primarily de signed for compacting loose or granular material composing the surface or sub-base of a road. In conjunction with scarifying and scraping attachments it is used for breaking up or loosening the road surface or sub-base, preliminary to further treatment.
The Macadam Road Roller has three wheels or rolls, two being mounted on a common shaft for driving the machine and the third for steering purposes. The steam engine-driven macadam roller is customarily fitted with a boiler of the locomotive type the supporting structure of which forms the main frame, where the wheels, engine and other necessary parts are mounted. Some machines have been built fitted with boilers of the vertical fire tube type. The steam engine has two high pressure cylinders and cranks at 9o°. Engines of one cylinder are occasionally used. Two speeds are usually provided, the speed change being accom plished by means of sliding gears. Macadam rollers are also fitted with gasolene or kerosene internal combustion engines. The en gine is usually mounted on a structure which constitutes the main frame of the roller. The engines in common use have one horizontal cylinder, two horizontal opposed cylinders or four vertical cylinders in line. A power-driven air compressor is com monly used for operating an attached scarifier.
The Tandem Road Roller has two wheels or rolls mounted one behind the other on a frame which carries the driving mechanism and accessory parts. One of the rolls is driven and is commonly called the driving roll. The steering roll is separated into three or four parts to facilitate steering and to prevent marking the road surface. The rolls are approximately the same length, but if there is any difference in length the steering roll is shorter. The steering roll is of smaller diameter than the driving roll.
The tandem roller is designed primarily to compact and smooth bituminous road surfaces, the work being done while the surface is readily compressible. It is used only to a limited extent to compact non-bituminous surfaces or sub-bases. It is not usually provided with attached road scarifiers or scrapers. Means are provided for wetting the face of the driving roll to prevent the bituminous matter adhering to it. For the same reason the work done by the roller is usually confined to that which will not indent the working surfaces of the rolls. In order to prevent the rolls from marking a soft bituminous surface it is necessary that the engine be provided with a quick acting reverse mechanism so that the stop will be momentary. Manual and mechanical steering devices are provided. The steam engine-driven tandem roller is fitted with a boiler of the vertical fire-tube type. The steam engine has two high pressure cylinders with cranks at 9o° and may be either vertical or horizontal. No change speed gears are provided. The internal combustion engine-driven tandem roller is provided with a two-cylinder opposed or four-cylinder vertical engine using gasolene as fuel. Sliding gears are provided for speed changes and reversing. On account of the time element involved in changing gears the operation of the roller is not as uniform or flexible as with the steam engine, except with expert operation. Steam engine-driven road rollers are usually designed to use coal as fuel. Wood may be used without boiler change it the work to be done is not too exacting. Petroleum fuel oil may be used by providing a special fuel tank and oil burner and spe cial brick work in the fire-box of the boiler. At the present time (1929) the Diesel or semi-Diesel type of internal combustion en gine is not used for power be cause a suitable design of engine has not been commercially de veloped. (F. A. BR.)