Pneumatic Tire Roller

Overview

A pneumatic tire roller compacts and seals asphalt with rows of smooth rubber tires rather than steel drums. As the tires roll, their footprints flex and move the asphalt slightly under the surface, a kneading action that closes voids and presses the mat into a tight, sealed surface that a steel drum cannot match. This makes the machine the tool of choice for the intermediate rolling pass on a hot asphalt mat and for sealing the surface of chip seals and thin overlays. The tires also leave no flat-spot marks if the machine stops, and their contact pressure can be tuned by changing tire inflation and machine ballast, so one roller covers a wide range of mixes and lifts.

The machine is built on a Roller Frame carrying a Front Wheel Set and a Rear Drive Wheel Set of tires, a Ballast System system to set its weight, a Engine and Drive for smooth low-speed drive, a Tire Conditioning system that keeps the tires working, and a Operator Station for the operator.

The tire sets

The rolling is done by two rows of Smooth Pneumatic Tire units. The Front Wheel Set carries four smooth tires, each on a Front Wheel Hub, mounted on an Oscillating Mount so the row can rock and keep every tire in contact on an uneven mat, and steered by a Steering Cylinder. The Rear Drive Wheel Set carries five driven tires set so they fall in the gaps between the front tires. This offset is deliberate: between the two rows the tires cover the full width with no untouched strips, so a single pass kneads the whole mat. The smooth tread is what does the sealing, because a flexing rubber footprint works the asphalt surface rather than just bearing down on it.

Contact pressure and ballast

The key adjustment on this kind of roller is contact pressure, the force each tire presses into the mat. Two things set it: tire inflation and machine weight. The Ballast System system varies the weight through a Ballast Box that can be filled with Ballast Weight blocks, sand, or water through the Ballast Door. A light machine on soft tires gives gentle pressure for a thin or tender mix, while a heavily ballasted machine on firm tires gives the high pressure a thick lift needs. Matching pressure to the mix and lift is how the operator avoids both under-compaction and shoving the mat around.

Drive and engine

Asphalt rolling needs a smooth, steady, low speed and frequent direction changes without jolts that could mark the mat. The Engine and Drive meets this with a hydrostatic drive. A Diesel Engine diesel turns a Hydrostatic Pump whose output runs a Drive Motor into the rear axle, so speed is set infinitely from a lever with no gear changes and the machine reverses smoothly. The rear axle drives through a Drive Axle and a Final Drive reduction at each hub. A Cooling Package package handles the heat and the Fuel Tank carries a shift of fuel.

Keeping the tires clean and warm

Hot asphalt sticks to cold or dry rubber and tears the surface up, so the Tire Conditioning system keeps the tires fit to seal. A Water Tank feeds a Spray Pump and Spray Bar nozzles that wet each tire, sometimes with a release agent, so asphalt releases instead of building up. A Tire Scraper on each tire lifts off any asphalt that does pick up. Just as important, the tires must stay warm: a cold tire chills the mat and smears it, so a Heat-Retention Skirt heat-retention apron keeps the tires hot enough to stay tacky and seal rather than mark. Getting the tires to the right temperature is part of warming the machine up before the day starts.

Operator station and use

The operator works from the Operator Station, a ROPS Canopy ROPS structure with a swivelling Operator Seat for forward and reverse views and a Control Console holding the Drive Lever, the spray controls, and a tire-pressure readout. In service the roller follows the paver in the intermediate position, making overlapping passes at a steady speed while the mat is still hot, kneading it to density and sealing the surface. Because it leaves no drum marks and its pressure is tunable, it is also used for the finish pass on surface courses and for rolling sprayed seals, where the smooth tires press the chips into the binder without crushing them.