Figure 11-44.-Steel-wheeled roller.Figure 11-45.—Drive wheel rolling action.Pneumatic-tired rollers may be equipped with 15-,17-, 20-, or 24-inch tires. Air pressure in the tires mayvary for different types of material, such as 50 to 60 psito finish asphalt and 100 psi to compact a granularsubbase. The tires must be inflated to nearly equalpressure with variation not exceeding 5 psi to applyuniform pressure during rolling.coarse materials and asphalt. This roller produces asmooth, solid surface under favorable conditions, butmay fail to compact areas narrower than the roll, and donot compact deeply in proportion to their weight. Thesteel- wheeled roller does not change shape to bringsuitable support for itself. Rather it sinks until enoughbearing area has come in contact with the roll to supportFigure 11-43 shows the action of a pneumatic-tiredthe roller weight.roller. Pneumatic-tired rollers are used because theThe drive wheel is ahead of the tiller wheel in theindividual wheels can exert a kneading action in smalldirection of travel. The tiller wheel functions as theareas that wide, rigid steel drums tend to bridge.steering axle. As shown in figure 11-45, there is aSTEEL-WHEELED ROLLERSA steel-wheeled roller, as shown in figure 11-44, isused for compaction and finish operations on basedownward vertical force caused by the weight or thewheel. The arrows, concentric with the steel wheel,represent the rotational force on the wheel. This force istransmitted to the base of the wheel, as the roller is11-23
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