The parts of a plough which work in the soil -the disc or knife coulter, the skimmer and the body - are attached to legs or stalks which are in turn bolted to the plough beam or frame.
The base of a plough body is called the frog and the soil wearing parts are bolted to it.
The share and the moldboard are the main engaging parts of the moldboard plow (Fig. 12.).
Figure 12. Moldboard plow bottom with main parameters and share forms (a) regular, (b) winged plane, (c) bar point, (d) mounted or welded point.
The share makesthe horizontal cuts the bottom of the furrow slice from the soil below and when it is worn it is important to fit a new one. The share is shaped so that it pulls itself into the ground. As the share wears away, it becomes blunt and the plough will require more power to pull it through the soil. A plough body with a worn share will not have enough 'suck' (see Figure 2.) to ensure that it penetrates the ground to its full working depth.
Figure 13. Suck is necessary for a plough body to maintain its working depth and lead helps to maintain the correct furrow width. Both can be checked with a straight edge. A plough body without suck needs a new share and the landside should be replaced if there is no lead.
The share is a plane part with trapezoidal shape. It cuts the soil horizontally and lifts it. Common types are regular, winged plane, bar-point and share with mounted or welded point. The regular share conserves a good cut but is recommended on stone-free soils. The winged plane, share is used on heavy soil with a moderate amount of stones. The bar-point share can be used in extreme conditions (hard and stony soils). The use of the share with mounted point is somewhere between the last two types.
Manufacturers have designed shares of various (trapezium, diamond, etc.) with bolted point and wings, often separately renewable. Sometimes the share cutting edge is placed well in advance of the moldboard to reduce the pulverizing action of the soil.
The mouldboard (see Figure 14.) lifts and turns the furrow slice. They are made in various shapes, each producing its own furrow profile and surface finish.
Figure 14. A sword share.
The function of the moldboard is to lift the soil cut by the share and to let it undergo an action of torsion and inversion. The intensity of this action depends on the type of the moldboard. At present three types are mostly used: helicocylindrical (universal), digger (cylindrical), and helical (semidigger) (Fig. 15.).
The standard (universal) type is by far the most widely used one because of its adaptation to almost all situations and soil types, except in the most extreme conditions.
The cylindrical moldboard is very intense in its action (bulldozer action). On the other hand, the semidigger type is well suitable for rapid and returning action but limited on the depth.
The mouldboard extension or tailpiece helps to press down the furrow slice, which is particularly important when ploughing grassland.
The landside absorbs the side thrust of the plough against the furrow wall.
A heel iron is bolted to the end of the rear landside and helps to carry the back of the plough. The landside and share are arranges give ‘'lead” towards the unploughed land, thus helping to maintain the correct furrow width.
The coulter makes the vertical cut, separating the furrow slice from the unplowed land. It can be shaped in several ways.
A knife coulter serves a similar purpose. The knife coulter, fastened to the beam by a clamp, as now less used. This is really knife which takes up less space on the plough than a disc coulter but it leaves a less defined furrow wall. Disc coulters and knife coulters are not a standard fitting on most modern ploughs.
The disc coulter cuts the side of the furrow about to be turned.
Multi-furrow ploughs, particularly those used for on-land ploughing, usually have disc coulters on the rear bodies to overcome the tendency for this type of plough to crab when in work.
The skim coulter or skimmer turns a small slice the corner of the furrow slice into the furrow bottom before it is turned by the board. This reduces the likelihood of trash exposed between the furrows. Most skimmers have a small mouldboard and a share. There are various sizes of skimmer and a large one may be needed when there is a lot of surface vegetation and for ploughing in heavy dressings of farmyard manure.
Sword shares with a short vertical knife which cuts the lower part of the wall of the furrow about to be turned are fitted to some ploughs. These shares give increased clearance between adjacent bodies compared with a coulter.
Plate 16. This plough has an auto-reset mechanism on each leg with a leaf spring which allows the body to swing backwards when it hits an obstruction. The body is automatically returned to the working position after the obstruction is passed.
Figure 17. Operation of auto-reset mechanism a reversible plough.
Safety Devices.Most plough makers offer an automatic reset system (see Figure 17) for tough conditions or rocky soils. The re-set mechanism allows each body to move rearward and upward to pass over obstacle (e.g. rocks hidden below soil surface) without damage. A heavy leaf or coil spring mechanism, which holds the body in its working position under normal conditions, resets the plough after the obstruction is passed.
Another type of auto-reset mechanism uses an oil (hydraulic) and gas accumulator. Shock loads cause the oil to compress the gas, when the gas expands again the leg returns to its working plowing position after passing over the obstacle. The most simple mechanism is a breaking (shear) bolt that needs replacement. Shear bolts which break when a plough body hits an obstruction are a cheaper overload protection device. It is important to use the correct replacement bolt.