Efficient cutting with double discs in seeders

Analysis of the forces acting on a lagged double disc with different angles of attack, for a seeder-fertilizer, shows the efficiency of this system in opening furrows in direct planting.

It has long been known that the reactions resulting from the penetration of breaking elements into compacted soil reduce the useful life of components, generate greater effort in the planting line and unwanted maintenance costs, often in the middle of sowing.

In view of these considerations, it is noted that the forces that act on double disc elements can be better evaluated, since, according to the literature, it is known that the double disc acts on the surface layer of the soil, that is, the one with the greatest compression.

The objective of this article is to evaluate the efforts at different angles of attack of the double disc, identifying whether or not this variation has significant relevance for reducing the load on the planting line, in addition to contributing to the country's scientific production, with solid information that will serve for the technological advancement of companies in the agricultural machinery sector.

According to Portella (2001), special attention should be given to the soil-breaking elements of seeders, mainly due to the difficulties imposed by this cultivation technique. One of them is the disruption of the soil at the seeding line, which is aggravated by the increasing increase in crop residues on the surface. These crop residues were around three tons per hectare (dry matter), when direct planting began in Brazil, in the 1970s, and currently exceed ten tons per hectare, depending on the crop rotation system adopted.

The development of seeders for direct planting in Brazil was based on the improvement of soil breakers. Each machine model has its construction particularities, versions and options for ground breaking mechanisms. The most commonly used systems are: mismatched double disc system for sowing winter crops, with reduced spacing between sowing lines (less than 200mm) and multiple system (cutting disc, knife and double disc), for sowing crops summer season with larger spacings between rows (above 300mm).

The efficiency in soil breaking in a PD seeder is anchored in three pillars: straw cutting; straw flow; opening of sowing and fertilization furrows. Therefore, for good performance in terms of soil breaking, in addition to considering the geometry of the breaking elements, their arrangement and arrangement under the seeder must be considered.

DOUBLE DISKS OUT OF LATE AND/OR MISMATCHED

The double disc is composed of two flat discs of different diameters, with the centers of the discs coinciding or not. Due to its configuration, it cuts the straw and opens a groove in the soil for placing seeds and/or fertilizer.

According to Mion et al (2008), the double disc presents advantages in relation to transverse efforts compared to a cutting disc, as the arrangement of a disc on each side guarantees greater stability and support. Due to this constructive arrangement and greater area of ​​friction with the ground, the double disc requires greater vertical force to cut the straw and break the soil.

Acting forces

A factor of great influence in direct planting are the forces acting on the breaking elements, which play an important role in the performance of seeders-fertilizers. Most of the time, the forces that act on these elements are directly associated with soil cover, planting speed, soil type and soil moisture content.

Studies carried out by Machado et al (2007) indicate that the force required to pull a seeder for Direct Planting is lower than that recommended by agricultural machinery manufacturers in their prospectuses. The authors mention that this divergence is due to the increase in areas with different types of soil cultivated under direct seeding and, in order to avoid problems in the recommendation of traction force, they present values ​​well above what is necessary.

EFFECT OF WORKING DEPTH

Sowing operations for the main commercial crops (wheat, soybeans, corn and sorghum) are at a depth limit of between 2cm and 7cm. Therefore, the resistance that the soil offers to the penetration and movement of the breaking element at this depth limit is mainly influenced by the clay content, degree of compaction and moisture content (Portella, 1983).

EFFECT OF WORKING SPEED

Work speed also plays a very important role in the direct seeding operation, both for efficient crop deposition and in the distribution of resulting efforts in the tractor-seeder set.

siqueira et al (2001), evaluating four seeders-fertilizers in the soybean SD operation, detected a significant increase in the requirement for traction force and average and maximum power on the drawbar, when the travel speed varied from 4,7 km/h to 8,3 .XNUMXkm/h. 

Trintin et al (2005) prove in tests carried out that the increase in speed causes an increase in the operational capacity of the set and, consequently, an increase in fuel consumption and average power demand on the drawbar.

MATERIALS AND METHODS

The tests conducted in this work were carried out in the area of ​​the Stara experimental farm, belonging to Stara Indústria de Máquinas Agrícolas, in the municipality of Não-Me-Toque (RS), in August 2014.

Using a dynamometric car specially developed for this research, the vertical, horizontal forces and moment acting on three double disc supports with different angles of attack were measured. The travel speed was varied in three levels, as well as the working depth in two levels.

DYNAMOMETRIC CAR

To obtain data on the acting forces identified by this study, a dynamometric car manufactured by the Stara engineering sector was used. This carriage consists of a header attached to the tractor and a set of wheels driven by a pair of hydraulic actuators which, through the tractor's command, are positioned at the exact working height.

At the bottom of the car is the testing unit made up of the planting line assembly where the double disc supports with their respective angle variations were coupled.

TEST PERFORMANCE

The data collection and acquisition system used was HBM's MGC Plus, powered by a direct current unit. A piece of software reads and converts the collected signals for both pre- and post-processing, Catman Easy, also from HBM. Both were fixed to the dynamometer table.

The study consisted of double discs in the phased disc configuration, which is currently the most used soil breaking element in winter crops. Each support had a different angle of attack (34°, 36° and 38°).

The cutting pressure of each support varied between (210kgf and 294kgf) and was regulated in the helical spring pressure system of the planting line. In each cutting pressure variation two depths (3,5cm and 5cm) and three speeds (4km/h, 8km/h and 12km/h).

Depth adjustment was adjusted using the depth limiter set attached to the double disc support. Both the cutting depth and speed used in this study were due to the operational capacity of the seeder-fertilizer and tractor set currently sold.

The test took place in a field area with spontaneous ryegrass soil cover, with a total length of 150m, divided into three plots of 50m.

RESULTS

Data were collected on horizontal forces, responsible for the traction component of the planting line, and vertical forces, responsible for the pressure component on the planting line to obtain the working depth.

Analyzing the data from Table 1 it appears that only the angles tested and the depth of work (position) had significant statistical differences. Between the angles, the one with the lowest force required was 34 degrees and the depth of 35mm work required around 30% less horizontal force. Surprisingly, the speeds did not show significant differences, that is, driving the seeder between 4km/h and 12km/h does not change the demand for traction for these tested dual discs.

But, when analyzing the Vertical Force, it was observed that there were statistical differences between all components, with significant significance for the depth of work as expected. Greater depths required greater forces vertical. The lower working speed also required less vertical force, proving several studies, which conclude that increases in speed cause there is a lower planting depth. Therefore, to maintain depth it is necessary to increase the force on the double disc (pressure).

CONCLUSIONS

From this activity it was possible to conclude that the work on angles of attack of double discs lagged may reduce energy demand in planting lines, optimizing both the components (bearings, bearings, etc.) and the structure of seeders. It is concluded in the same way that the speed of work acts only on the vertical component of the force.

Fernando Capellari, José Antonio Portella, UPF

Article published in issue 149 of Cultivar Máquinas.