Reverse-rotational rotary tiller for reduced power requirement in deep tillage

In this paper details of rotary tillage regarding the movement of tilled soil are presented. A noticeable reduction of tillage power requirement was achieved during rotary tillage. The soil movement depended upon the direction of rotation and the ratio of tilling depth (H) to blade radius (R). With the differences in the soil movement, four kinds of rotary tilling patterns were determined. Increase in operating power generally resulted when a large amount of tilled soil was re-tilled in the zone of blade rotation. Improvement of backward throwing of the soil was required for power reduction, especially in deep tillage. A backward throwing model of soil by the blade was developed on the basis of trochoidal motion of the blade and sliding motion of the soil over a scoop-surface on the horizontal portion of the blade. The throwing model estimated the conditions for avoiding re-tillage, such as direction of rotation and shape of scoop-surface. The throwing model was applied to the design of the shape of the scoop-surface which enabled maximum backward throwing of the soil sufficient to avoid re-tilling. At tilling depths greater than 300 mm, reverse rotation with the new shaped blades brought about a tillage power reduction by about a half compared to forward or reverse rotation with conventional blades.     

The present state of force prediction models for rotary powered tillage tools

In the past, investigators of rotary tillage tools have concentrated their efforts in developing relationships between the power requirement and operational parameters of tillers. Many researchers have developed empirical force and torque prediction models without giving due consideration to the strength properties of soil. In the absence of proper soil-tool behaviour equations, the designers of rotary tools have relied on these empirical approaches. In recent years, the authors have proposed the first theoretical model for two-dimensional soil failure by a rotary powered blade. The presently available state-of-the-art ideas on rotary tilling force prediction models has been presented in this paper.     

The mechanics of soil cutting by a rotating wire

The cutting of soil by a rotating wire analogous to the tip of a rotary tiller blade while cutting a two-dimensional soil slice over a range of ‘fetch-ratios’ (bite length/depth-ratios) in a quasi-static condition is presented. A theoretical models based on Mohr-Coloumb soil mechanics has been proposed to predict forces on the wire (tip). The model is dependent upon observed passive general shear failure of the soil slice towards the curved free surface of a previous cut and the lateral local shear failure towards the undeformed soil. The predicted forces in a frictional soil and in a pure cohesive medium (artificial clay) agreed well with experimental results.     

Developing an excavation torque model for dense cohesionless soils

Torque encountered during the rotary excavation of soils (e.g., when using the DJM method for deep soft ground improvement) poses a serious detrimental effect not only to the excavating machines but also to the viability of a project as a whole. Consequently, this research investigates ways and means of realizing the reduction of torque encountered during the excavation of cohesionless soils. In this paper, the development of a torque model for a rotary excavation of cohesionless soils is proposed. Whereas in most of the soil tillage theories (i) the cutting tool is usually partially exposed at the surface, and (ii) excavation is generally longitudinal, this model is significant because; (i) the excavation process is radial, and (ii) the blade is completely immersed in the excavated medium. Various theories for the prediction of forces acting during the interaction of cutting tools and soils in conjunction with localized modeling of all the other forces, applied and adopted to suit this excavation geometry, have been applied in the development of the torque model. Experimental data was obtained from excavation experiments performed on compacted completely saturated sand samples. Within the experimental and theoretical limitations, the results showed that this model represented the excavation process.     

Effect of rotation direction of a rotary tiller on draft and power requirements in a Bangkok clay soil

Experiments were conducted in a Bangkok clay soil to evaluate the performance of a rotary tiller equipped with reverse or conventional blades. The conventional rotary tiller was equipped with C-type blades whereas the reverse-rotary tiller had new types of blades. Tests were conducted on wet land as well as in dry land. Tests were conducted at tractor forward speeds of 1.0, 1.5 and 2.0 km/h. A power-take-off (PTO) power consumed was calculated from the PTO torque and speed. The results indicated that the PTO power consumption was less for the reverse-rotary tiller compared to the conventional tiller for all passes and forward speeds. For both rotary tillers, power consumption decreased as the number of passes increased, whereas power consumption increased when the forward speed was increased. At all forward speeds, the power consumption was the highest during the first pass and lowest during the third pass. The maximum difference of PTO power requirement was after the first pass at 1.0 km/h forward speed. The reverse-rotary tiller consumed about 34% less PTO power under this condition.     

A dynamic model for soil cutting by blade and tine

A dynamic model for soil cutting resistance prediction by blade and tine was developed, taking account of shear rate effects both on soil shear strength and soil-metal friction, besides the conventional soil slice inertia, for both brittle and flow failure of soil. The model was verified with a series of tests in a soil bin with a blade and a tine, and the results were acceptable.     

Influence of the axle load, tyre size and configuration on the compaction of a freshly tilled clayey soil

Enhancement of the potential root growth volume is the main objective of farmers when they establish a conventional tillage system. Therefore, the main function of primary tillage is to increase soil’s structural macroporosity. In spite of this, during secondary tillage operations on these freshly tilled soils, the traffic on seedbeds causes significant increases in soil compaction. The aim of this paper was to quantify soil compaction induced by tractor traffic on a recently tilled non consolidated soil, to match ballast and tyre size on the tractors used during secondary tillage. The work was performed in the South of the Rolling Pampa region, Argentina. Secondary tillage traffic was simulated by one pass of a conventional 2WD tractor, using four configurations of bias-ply rear tyres: 18.4×34, 23.1×30, 18.4×38 and 18.4×38 duals, two ballast conditions were used in each configuration. Soil bulk density and cone index in a 0 to 600 mm profile were measured before and after traffic. Topsoil compaction increased as did ground pressure. Subsoil compaction increased as total axle load increased and was independent from ground pressure. At heavy conditions, topsoil levels always showed higher cone index values. From 150 to 450 mm depth, the same tendency was found, but with smaller increases in the cone index parameter, 22 to 48%, averaging 35%. Finally, at the deepest layer considered, 600 mm, differential increases due to the axle load are great enough as to be considered similar to those found in the upper horizon, 36 to 64%, averaging 55%. On the other hand, bulk density tended to be less responsive than cone index to the traffic treatments. Topsoil compaction can be reduced by matching conventional bias-ply tyres with an optimized axle weight.     

Force and pressure distribution under vibratory tillage tool

Experiments were conducted to study the force requirement and pressure distribution under vibratory tillage tools in a soil bin with a sandy loam soil. The tool was oscillated sinusoidally in the direction of soil bin travel. An octagonal ring transducer and pressure sensors were used to measure the forces and soil pressure on the blade. The tool was operated at oscillating frequency of 4.5–15.6 Hz and amplitude of 11–26 mm. The soil bin travel speed was varied from 0.05 to 0.224 m/s. The test results obtained showed both the horizontal force and the vertical force decreased with increase in oscillating frequency. The normal pressure on the blade surface varied considerably. The peak normal pressure was found to increase with increase in oscillating frequency, oscillating amplitude and soil bin travel speed. The change in average normal pressure with change in oscillating frequency and amplitude was also investigated.     

Prediction of soil structures produced by tillage

A statistical method for describing the distribution of aggregates and voids within tilled soil is used as the basis for a prediction technique. Transforms of aggregate-void and void-void transition probabilities are used in such a way that factors can be defined which describe how the soil structure differs under a range of circumstances. A standard structure is defined for a given soil as that which is produced at the 5 cm depth by one pass of a set of tines working at 10 cm depth when tillage is done at a speed of 1.4 m/s in soil at a water content equal to the plastic limit and which has previously grown a cereal crop. Factors are defined which describe deviations from this standard structure as a function of depth in the tilled layer, implement type, previous use of the soil, number of implement passes, water content at time of tillage, and subsequent compaction of thettilled layer. Application of the inverse transform then enables estimates of the distributions of aggregates and voids in the tilled layer to be predicted for required, specified conditions.     

Prediction of soil structures produced by tillagePrédiction des structures du sol produites par labourageVoraussage der durch bodenbearbeitung erzeugten bodenstrukturen

A statistical method for describing the distribution of aggregates and voids within tilled soil is used as the basis for a prediction technique. Transforms of aggregate-void and void-void transition probabilities are used in such a way that factors can be defined which describe how the soil structure differs under a range of circumstances. A standard structure is defined for a given soil as that which is produced at the 5 cm depth by one pass of a set of tines working at 10 cm depth when tillage is done at a speed of 1.4 m/s in soil at a water content equal to the plastic limit and which has previously grown a cereal crop. Factors are defined which describe deviations from this standard structure as a function of depth in the tilled layer, implement type, previous use of the soil, number of implement passes, water content at time of tillage, and subsequent compaction of thettilled layer. Application of the inverse transform then enables estimates of the distributions of aggregates and voids in the tilled layer to be predicted for required, specified conditions.     

Analysis of the PTO load of a 75 kW agricultural tractor during rotary tillage and baler operation in Korean upland fields

In this paper, the PTO severeness of an agricultural tractor during rotary tillage and baler operation was analyzed. The S–N curves of the PTO driving gears were obtained through fatigue life test. To obtain the S–N curves of the PTO driving gears, the breakage time and rotational speed of the gears were measured through observation of the bending stress with changing torque. The torque acting on the PTO was measured and analyzed during rotary tillage and baler operation. Rotary tillage and baler operation were conducted at two ground speeds and two PTO rotational speeds at upland field sites with similar soil conditions, respectively. The load data were inverted to a load spectrum using rain-flow counting and SWT equations. Modified Miner’s rule was used to calculate the partial damage sum. The severeness was defined as the relative ratio of the damage sum. The results showed that the damage of the PTO increased when the ground speed or the PTO rotational speed increased. The effect of the PTO rotational speed on the severeness of the PTO was more significant than that of the ground speed. The severeness of the PTO of rotary tillage was greater than that of baler operation.     

A non-linear 3-D finite element analysis of soil failure with tillage tools

A non-linear 3-D finite element model was developed to study the soil failure under a narrow tillage blade. The weighted residual method was applied to formulate the finite element model. The Duncan and Chang hyperbolic stress-strain model was used in the analysis. This finite element model also takes into account friction at the soil-tool interface, and progressive and continuous cutting. A FORTRAN program was written to carry out the finite element analysis. The results provided soil forces, a progressive developed failure zone, displacement field and stress distribution along the tool surface. Tillage were conducted in the laboratory soil bin to verify soil forces from the finite element analysis. The comparison between the results from the finite element model and those from the soil bin tests was reasonably good.     

Vibration characteristics of a power tiller

The vibration characteristics of a power tiller (two-wheel tractor) were studied. Tests were conducted at 1000, 1200, 1400, 1600, 1800, 2000, and 2200 rpm engine speeds in a stationary condition, and at 1000, 1200, 1400, 1600, and 1800 rpm engine speeds during transportation and tillage. Tests during tillage operation were conducted in the Bangkok clay soil. For the measurement of vibration, three semiconductor strain-gauge-type accelerometers, capable of sensing vibration signals in three mutually perpendicular directions, i.e. horizontal, lateral and vertical modes at the same time, were used. Vibration characteristics of the power tiller were found to be quite complex. In general, it was observed that, in any working condition, due to an increase in engine speed of the power tiller, the acceleration and frequency of vibration increased. At the same operating speed and test condition, the intensity of the vibration was the highest in the vertical mode and the lowest in the lateral mode. The maximum vibration intensities were observed during second plowing and the lowest vibration intensities were when stationary on an off-road surface. The vibration intensities, when compared to the ISO standard 2631, were found to exceed the standard during field operations.     

Investigation of elemental shape for 3D DEM modeling of interaction between soil and a narrow cutting tool

Discrete Element Method (DEM) has been applied in recent studies of soil cutting tool interactions in terramechanics. Actual soil behavior is well known to be inexpressible by simple elemental shapes in DEM, such as circles for 2D or spheres for 3D because of the excessive rotation of elements. To develop a more effective model for approximating real soil behavior by DEM, either the introduction of a rolling resistance moment for simple elemental shape or the combination of simple elements to form a complex model soil particle shape cannot be avoided. This study was conducted to investigate the effects of elemental shape on the cutting resistance of soil by a narrow blade using 3D DEM. Six elemental shapes were prepared by combining unit spheres of equal elemental radius. Moreover, cutting resistance was measured in a soil bin filled with air-dried sand to collect comparative data. The elemental shape, with an axial configuration of three equal spheres overlapped with each radius, showed similar results of soil cutting resistance to those obtained experimentally for the six elemental shapes investigated.     

Effect of rainfall on the surface micro-relief of tilled soil

Surface micro-reliefs after four different tillage treatments were measured with a relief meter. Measurements were taken at the time of tillage and on four successive dates. The relief measurements were used to calculate the autocorrelation functions, the power spectra, and the distributions of surface slopes. Changes in parameters of these functions are related to estimates of the cumulative rainfall kinetic energy between the readings and the tensile yield stress of aggregates from the tilled soil. The effect of rainfall was to reduce the roughness to a given proportion in a time which was independent of the initial roughness of the surface, and hence independent of the type of implement used.     

Pulverization characteristics of clay soil

Soil pulverization and failures during chip formation using rotating simple wedge-shaped blades for microsite preparation were analyzed to determine soil cutting characteristics. Equations were developed for soil bite size and blade projected area, and a new term was proposed relating the power requirement for rotating the pulverizer blade to the power required for penetrating the soil profile. The results of this study indicated that the rotational power requirements, in general, increased with increases in rotational and downward speeds, and the penetration power was slightly affected by the rotational speeds and was very small in comparison with the rotational power. The soil bite size appeared to play a great role in identifying the power requirements of a pulverizer blade. A substantial increase in rotational power requirement at the same rotational speeds was required due to increases in bite sizes; this increase might be due to the increases in soil-blade friction forces. During soil pulverization, chip dimensions were affected by the operational speeds, soil strength, blade geometry, and number of pulverizer blades. The pulverizer shaft diameter has little influence on the total power requirements but definitely affects the soil packing sequence of the planting cycle when the soil pulverizer for microsite preparation is incorporated into the planting head. An example illustrating the use of the data presented in this study is included to assist in the selection and sizing of a soil pulverizer's power unit.     

Mechanics and mechanism of cut resistance of protective materials

A sliding sharp edge penetrating material is one of the most dangerous cases of cutting because it requires the smallest applied load. A better understanding of the cutting mechanism is a fundamental step to develop new and more performing protective materials. This study aims at analyzing cutting mechanics and mechanism in the presence of friction. The International Standard ISO 13997 cut test method consists in measuring the distance that a straight blade slides horizontally to cut through a material under a constant applied normal force and was used to investigate cutting phenomena.In practice, cut resistance of a material is contributed by the intrinsic strength of material and the frictional distribution. Two types of friction distributions are involved in cutting: a macroscopic friction induced by the gripping of the material and by the applied normal load on the two sides of the blade; and the other the sliding friction associated with cut through of the material that occurs along the face of the blade tip. For most materials, frictional forces due to lateral gripping could be several times greater than the friction due to the applied normal force. Thus, the cutting energy required for breaking molecular chains is much smaller than the energy dissipated for friction. The elastic modulus, the structure of the material as well as the sliding velocity have significant influence on the friction. Therefore all these properties can affect the cutting resistance results.     

An investigation of the bevameter soil physical measurements in the prediction of soil tool draft

The relationship between the parameters measured during soil testing using the bevameter system and the horizontal forces acting on a simple soil-cutting blade were investigated. Field experiments were conducted on untilled, compacted soil and on recently-tilled soil. On both soils, five sites were randomly chosen and bevameter and draft measurements were performed The parameters measured were modulus of soil deformation, wet and dry bulk density, soil moisture content, tool operating depth, tool operating velocity and horizontal draft. A statistical analysis of the data indicated that a mathematical model for predicting draft should contain the following variables: operating depth, dry bulk density and modulus of deformation. A linear regression analysis of draft versus modulus of deformation showed significance at the 95% confidence level on the untilled sites at all measured depths. A similar analysis of the tilled site indicated significance at the 70 mm depth only. The usefulness of the bevameter deformation modulus as an indicator of draft was found to be limited to shallow depths.     

Performance evaluation of an animal drawn puddling implements under controlled soil-bin conditions

Trials were conducted to evaluate the performance of three commonly used puddling implements, i.e. animal drawn rotary puddler (I₁), 3-tine tiller (I₂) and local plough (I₃) under controlled soil bin conditions for different numbers of passes of each implement. The performance of the rotary puddler was found to be better when operated more than twice under the controlled conditions in terms of quality and quantity of puddling. It was found that the rotary puddler gave a higher puddling index and required less energy to puddle the soil. The rotary puddler provided good “puddle” with a puddling index of 50% after two passes whereas, the other two implements required more than five passes for the same quality of puddling or puddling index in sandy clay loam soil