6. Rolls
Rollers. Rollers serve mainly for recompacting, leveling and crumbling. At the same time, their task is to create a better contact between seeds and soil. Furthermore, they can be used as a means of spreading the tractor weight evenly across the whole width of the vehicle.
Figure 25. Various types of rollers: (1) plain roller, (2) grooved roller, (3) Cambridge roller,
(4) cross kill roller, (5) cage roller, (6) spiral roller, (7) toothed packer, (8) disk roller,
(9) tyre furrow press, (10) conventional furrow press with cross kill roller.
Usually, rollers should be used under dry conditions since wet soil will clog them easily unless scrapers are used to clean them permanently. According to their form, rollers can only compact the surface or act at a certain depth if they are shaped to penetrate through the topsoil. Many different forms are available (Fig. 25). Among them, the furrow press should be noted, which is used directly after plowing in order to give back to over-loosened soils optimum porosity and to make them traffickable again.
The two main types of roll are the flat roll and the Cambridge or rib roll. A furrow press is similar to a Cambridge roll, but the rings are spaced further apart. Cambridge rolls have a number of cast iron rings of 500-600 mm diameter on a heavy axle which leave a corrugated surface. Flat rolls are less common and have a number of cast iron rings with a flat outer rim on an axle. Others have one or more lightweight steel cylinders on an axle or a much heavier cylinder which can be filled with water to make a very heavy roll for grassland.
Rolls are normally trailed and were traditionally used in gangs of three - one wide and two narrow with a working width of up to 8 m. They are hitched one behind the other for transport. They can only be pulled at low speeds on public roads and have been replaced on most arable farms by hydraulic folding models up to 12 m or more wide with pneumatic tyred transport wheels. The outer sections are swung inwards on some models (Fig. 26), while others are folded in a gull wing formation.
Plate 26. Hydraulic rams fold this roll for transport.
Plate 27. A roll hydraulically folded for transport.
Plate 28. This flat roll has a heavy steel cylinder which can be filled with water to add weight when rolling grassland.
Plate 29. Furrow press with rear crumbier roll. One of the walking stick shaped drawbars is left in the correct position by a linkage on the plough so that the press is automatically re-connected to the plough when it starts the next furrow.
Uses
Cambridge rolls:
Breaking clods.
Firming the soil.
Pushing stones into the soil to reduce the risk of them damaging harvest machinery.
Leaving a finely ridged surface for broadcasting grass seed.
Flat rolls:
Breaking clods.
Providing a smooth, firm surface for drilling.
Pushing in stones on pastures (especially with the very heavy or water-filled type).
Maintenance. The axle bearings need regular lubrication when in use. The roll sections should be kept tight on the axle to make the rings turn in a straight line.