Ploughs for all soils
Agricultural soil is extremely variable, and therefore advanced ploughs are needed for tillage, both in equipment and construction materials. Adjustments and careful set-up to the characteristics of the tractors are important parameters for the best quality of work
Traditionally, the plough has always been the symbol of farm mechanization. However, for some years now, the popularity of the plough seems to have waned to the benefit of other tillage solutions, which appear to be more beneficial in terms of agronomy and energy.
Actually, reference must be made to the specific pedo-climatic characteristics of agricultural soils: the classic combination of ploughing + harrowing in the Mediterranean area is still absolutely valid. The sharp inversion of horizons that is achieved is mainly helpful to speed up the humification of buried biomass to restore an appropriate organic matter content in the soil. This is too often overexploited by intensive monocultures, fertilized exclusively and for a long time with mineral fertilizers.
However, the "strength" of ploughing as a fundamental intervention in primary tillage is also effectively confirmed by the market (Italian). Many manufacturers of different sizes are actively present on the market, offering a vast range of technical solutions designed to obtain the best results in a plurality of operating conditions.
Adjustments
However, for quality ploughing, a careful tool adjustment is essential. In addition to the depth of course, and also in relation to its type, the plow must be oriented correctly in the three basic directions. Particular attention must be paid to the direction of advancement in order to counteract the damaging lateral thrusts that cause reductions in working capacity, increased fuel consumption and wear of the implement. For this reason, all plows are equipped with a series of devices for their positioning in relation to the tractor: from basic mechanical solutions, particularly on the most accessorized models, we have long since moved on to hydraulic management, which saves time and effort. A similar consideration can be made, for multi-share implements, of the special role played by the first body, whose working width conditions affect that of the others that follow.
All of this, of course, must also be proportional to the plough's angle of attack, which defines the overall working width, which in some cases can also be varied on the move during normal operations.
In or out of furrow?
Ploughing can be carried out with two tractor wheels in the furrow created in the adjacent pass or all wheels advancing on the field level. Both solutions offer different benefits and drawbacks: briefly, with the wheels in the furrow, the plough works more in line with the tractor, but the tires on one side of the machine have a quite different grip from those on the other side. This is due both to the difference in weight of the vehicle that rests on them (due to the inclination of the tractor) and to the fact that the grip is not the same since one pair of wheels exerts traction on the bottom of the furrow
(= bare ground), while the other works on a surface that is typically covered with grass and/or residues of the previous crop. These problems are solved by ploughing outside the furrow, but in this case, the tractor's pull is not in line with the direction of the plough, thus resulting in lateral forces. Until recently, specific ploughs had to be adopted for one or the other solutions. Now, however, thanks to their extensive adjustment possibilities, models are available that can operate in both modes.
Wide headstock
To maximize traction, modern tractors are equipped with increasingly wide tires, with cross-sections as large as 700 or 800 mm for higher horsepower models. In furrow ploughing, this leads to no minor compaction of the soil ploughed in the adjacent pass with subsequent transit. To overcome this problem, many manufacturers offer significantly wider than standard mouldboards, which can leave a broader bottom of the furrow and laterally move away a greater quantity of soil, thus creating a smaller overburden.
Safety
In addition to the three basic fractions (i.e., sand, silt, and clay), the skeleton, i.e., gravel, stones, and rocks, must always be considered in primary tillage. The latter, and in particular those that are completely buried, can cause significant problems when ploughing, causing even serious breakages.
For this reason, in such conditions, ploughs have long been equipped with safety devices: the simplest and most economical is the shear bolt, which, if stressed (by shear or sometimes by traction) beyond the breaking point, disconnects the body involved in the impact with the stone, avoiding damage. In more modern terms, reversible mechanical or hydraulic devices have been installed, capable of raising the body at an angle of up to 60-70° (and possibly moving sideways for 20-25°) after impact with the stone, and then lowering it promptly to continue working. These are calibrated springs or hydraulic cylinders integrated with nitrogen accumulators, whose intervention threshold can also be adjusted as needed.
Maschio Aratri in Concordia Sagittaria (VE) offers models equipped with both devices. The classic solution with the shear bolt is recommended for those terrains where stones and obstacles are only occasional: simple and reliable, it requires quick replacement, which can also be carried out in the field. The hydraulic system with adjustable preload from the driver's seat mounts cylinders with an increased bore to support a higher load on the first and last body. In the complete version, indicated for soils with a considerable presence of large stones, the hydraulic system intervenes primarily. Still, if the pressure applied to the headstock should exceed the maximum threshold, the shear bolt will be activated.
Heat treatments and special materials
All agricultural soil working equipment is built with steels suitable to substantially withstand two types of stress: friction due to the soil sliding on the tools and impacts with the important components of the skeleton. These imply respectively progressive wear and tear and the danger of breakage. In addition to the disconnection devices of the part affected by the impact with the foreign body, the best resistance of the material is obtained with an increase in the surface hardness of the item while maintaining the highest flexibility of the internal structure.
This result is obtained through various processes, the most common of which are hardening and case-hardening. However, different solutions are also adopted on this issue, such as the use of boron steels or components, such as the verse, made of three layers with other characteristics.
For parts subject to the highest stress, such as the coulter, plate inserts made of even harder materials, such as tungsten carbide, are used. Their manufacture requires exact control of each production step. After sintering, several compression forming steps are performed to obtain the inserts that will be placed by brazing in their final position. Sometimes a heat treatment of the entire working organ is carried out at 800°C, for better structural uniformity of the piece.
For some time now, the search for better wear resistance has also been directed towards non-metallic materials other than steel. In certain cases, plastics can be a valid alternative, such as constructing coulters and mouldboards. In this case, technological development has focused on reducing friction between the tool and the ground in order to decrease the traction force required to break up the soil.
Among the various solutions, those that have achieved considerable success concern the coating of the sliding surface of the headstock with polyethylene or Teflon. Alternatively, the entire headstock is made of polyethylene, often supported by a steel reinforcing skeleton.
More specifically, Robalon, developed fifty years ago by the Austrian company Röchling Leripa Papertech, is ultra-high molecular density polyethylene (UHMW-PE), combined with molybdenum disulfide, binders, and UV stabilizers.
Compared to traditional metal constructions, this plastic material features reduced friction and therefore less wear, low adhesion on the surface in contact with the ground and, obviously, a lower weight (up to 60% less), with the same dynamic resistance. This makes it particularly suitable for working in sticky soils, where soil sticks to the headstock. It is not surprising, therefore, that many manufacturers have in their catalog models with mouldboards made of (or covered with) plastic material. Such as the De Franceschi company of Villanova (PD), which manufactures ploughs with mouldboards made of ceramified polyethylene, which it claims saves diesel fuel and work speeds 12% higher than the traditional model.
Maneuverability and transport
The two side plough models with a high number of bodies involve a considerable encumbrance during maneuvering and transport, causing problems in operating in narrow headlands and on narrow streets.
Some manufacturers have solved the problem by equipping ploughs with mechanisms that can offset their longitudinal axis by up to 45° with respect to the tractor's.
This function can be activated directly from the driver's seat on the most advanced models. It is beneficial for fast transfers on public roads in the presence of traffic, especially when driving through narrow bends and traffic circles with a reduced radius.
The fenestrated mouldboards
In order to reduce the demand for traction force during ploughing, for several years now, fenestrated mouldboards (or strip mouldboards) have appeared on the market. In this version, the headstock is made of a series of solid bars placed side by side in parallel and suitably spaced to recreate the traditional monolithic shape and extension.
With the same quality and thickness of the steel, the fenestrated mouldboards are characterized by a lower structural stiffness. Still, they involve 20% less friction than the traditional ones, with a proportionally lower traction demand. Moreover, the discontinuity of the fenestrations also slightly increases the disintegration of the clods produced, saving a certain amount of energy in subsequent refining operations. The first types of fenestrated mouldboards did not work well in soils rich in the skeleton because stones and pebbles got stuck in the cracks, thus increasing the friction of the working body. The problem has been solved by making the fenestrations divergent towards the rear, thus facilitating the element's rolling, and unloading of stones. A further advantage of the fenestrated headstock over traditional ones is its lightness, which brings considerable benefits, particularly in road transport.
