MODERN ROAD ROLLERS.
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A Brief Description of the Types which are noW in Vogue.
THE DESIGN of the heavier types of steam road roller of 10 tons to 12 tons weight does not appear to have undergone any radical changes in recent years, but, nevertheless, many detail improvements have been made which have peatly enhanced the efficiency of these 'well-tried types. For example, piston valves have now displaced slide valves in
nearly all cases, and this change haii rendered improved and lighter valve gears possible, and, at the same time, has reduced the fuel consumption.
The Stephenson link-gear still largely, used, although there are a few exceptions. Marshall, Sons, and Co., for example, use a radial valve gear in which only one eccentric is required. per cylinder. It is new the accepted practice to mount the cylinders on a machined bed, which is, in turn, riveted to •the boiler, so that therels no direct bolt or
rivet connection between cylinders and boiler.
Much attention is now devoted to the 'disposition of the controls and the driver's; view of the work, so that it is now a simple matter for one man to take complete control. Good brakes are the rule, the shoes being lined with asbestos fabric in many cases.
Boilers have been jinproved both in design and manufacture. Siemens-Martin mild-steel plates are now generally used, hydraulically riveted. Methods of construction have been adopted which 'obviate the use of stays, and so improve the circulation and simplify cleaning operations. Pressures of 180 lb. per sq. in. to 200 lb. per sq. in are usually used, the boilers undergoing a test at double
• the working pressure liefore leaving the works.
Interchangeability is a feature of the modern road roller; improved manufacturing methods, the rise of jigs, and standardization ensure that spare parts can be placed in position witliOut the laborious chipping, filing, and hand-fit ting which .were once the rule. This means a great saving in time and expense.
Interchangeability of various components is also Studied. Thu's, in the Arehog and Porter roller, both the rear roller wheels are provided with a boss
for the scarifier attachment, so that the rollers are perfectly interchangeable. It is an advantage to change them after -considerable running with the scarifier, as one will wear more rapidly, than the other.
Another development which has.faken place consists in the provision of a simple means for detaching the rollers and replacing them with wheels which enable the road roller to be used as a traction engine. In the Fowler, Aveling and Porter, abd.Robey road rollers this replacement; can be effected without any elaborate lifting tackle, the time taken being only a few hours. Renewable railer rams' form another feature which is now quite common.
Another interesting adaptationof the road roller is the multi-purpose vehicle evolved by Fowler and Cu., Ltd. This is -a combined rolling, tar-spraying, grunting and gritting apparatus, and was fully described in The Commercial Motor dated August 23rd, 1921. A-considerable saving is rendered possible by using_ this machine, and it has been -successfully. used by many road contractors.
While there will always be a demand for the heavy steam-roller, developments and improvements in methods of road .making and, repairing have created •a de inatirl•for lighter machines with a quick reversing action. Such machines arc required for rolling bituminous carpets, surfacing tar-macadam, patching, etc. Tandern steam-rollers are now made by several firms to meet this .demand, machine& of 5 tons to 7 tons weiert being manufactured by Ayeling and Porter, Robey, Armstrong-Whitworth, 'etc._
Anindependent frame is used which cm-ries the boiler and relieves thisim. -Portant'unit of all driving strains. The rolling width of these machines is about 4 ft., and the short wheelbase conduces to easy mantruvring„ The minimum.. turning radius is ci small as 12 ft in some designs_ In the Aveling and Porter tandem roller, • steam•Iclerated 'steer ing is incorporated. A feature of the Rohey is a very quick reverse and smooth drive, which obviate the formation Of .ridges and road waves.
With the advent of lighter ma...chilli:4 it is not surprising to find that several well-known firms have realized the possibilities of the internal-combustion engine. Barford and Perkins, Ltd:, market two machines of 7 ton-sand 9-tons weight with water ballast) which are driven by 20 h.p. paraffin engines. This company have also introduced a ileSir 14-ton roller driven by a four-cylinder 35 h p. paraffin engine, and at the other end of the sea.te they have a 36-cwt. footpath roller, also paraffin driven. Arrostren -Whitworth; Ltd., also Market an oil-driven roller, in addition to the heavy steam-driven variety. The new Fowler oil-driven roller was described in last week's issue of Th.e. Commercial Motor ; another interesting design is the Ruston-Hornsby Mon motor roller., Thenew Armst-rong-Whitworth light roller is of the •steam-driven tandem type, a chassis taking the driving strains and carrying a locomotive-type kroner.' -The two-cylinder engine is mounted on the boiler and is fitted with Stephenson link motion for reversing. Both front and rear rollers are. in halves, the rear (driving) roller being provided with differential gear. An exceptionally short wheelbase, equable distribution, of weight, and convenient grouping of the controls all tend to makefor case 'in handling and steering. . This roller is primarily intended for surfacing work where rapid.r,olling and a smooth-finish are. required.
These paraffin-engined rollers are provided with several interesting forms of change-speed gear, which make the changes available both when running forwai'd and When reversing. .Thegearhoses are of very sound constroction, with machine-cut gears and roller bearings. An epicyclie reversing gear mounted in the flywheel transmits the drive -to the three-speed gearbox of the Fowler machine, and so all three speeds are available for forward and reverse motions.
There is little doubt that the paraffin• engined motor road roller will prove of great utility in.. localities where the . Water supply is neither clean nor copious, and where coal fuel is comparatively. expensive. It will be interesting to see whether the internal-combustion engine -will make much headway against its steam-driven rival for -heavy road roller work, but', for the lighter types, it may be said to have already established