Influence of radial and diagonal tires on soil compaction

In recent years, loads on the wheelset have increased, especially on self-propelled machines. The agricultural machinery and tire industry responds to this fact with the development and optimization of new rolling stock concepts such as high-flotation radial tires and tandem axles, helping to minimize the impacts of high loads on the ground and reducing the risk of compaction.

The term "contact area" refers to the area of ​​the tire that is in contact with the ground support surface, and is an important indicator of the tire's load distribution capacity to the contact surface. Furthermore, it is in this area that the efforts made between the tire and the ground are transmitted. Determining the contact area between the tire and the ground plays an important role in the intensity of compaction. The estimation of the tire contact area contributes to the determination of contact pressures, stress-propagation and potential risk of compaction which, in turn, affects crop productivity. The tire's traction with the ground can be increased by increasing the contact area. Additionally, the fuel consumption of tractors is dependent on rolling resistance which, in turn, is a function of the contact area between the ground and the tire.

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The use of tires with a larger diameter and the same width causes a larger contact area, since the length of the contact area is directly proportional to its diameter. Tests of tires of different construction types: radial, diagonal and bias-belted BPAF (Low Pressure and High Flotation) help the industry to look for improvements in structure and compounds, seeking technologies that are more suited to the consumer's reality. In this sense, the agricultural sector demands current technical results to guide the best investment option in wheels that reduce the effects of soil compaction and contribute to greater productivity.

To analyze the factors that help reduce compaction, a group of researchers from Unesp developed work with the aim of evaluating soil compaction, tire/soil contact area, elastic deformation and settlement provided by diagonally belted tires ( BPAF) and radials.

The test was carried out at the Agroforestry Machines and Tires Test Center (Nempa), Unesp, Botucatu Campus (SP). To determine the studied tire variables, a hydraulic press and a soil box were used. The box was filled with a soil sample classified as Red Oxisol (LV), with 35% clay, 62% sand and 3% silt, with a water content of 0,10kg/kg, being divided into four layers of 0,10m high. After filling each layer of the box, a compactor roller was used to level and compact the soil with an average density of 1,4kg/dm³.

Four different types of tires were used, two with low pressure, high flotation (BPAF) diagonal belts: 600/55-26.5 and 600/50-22.5 and two with radial construction: 600/55R26.5 and 600/50R22.5 , both from the Trelleborg brand.

The load applied to the tires was defined based on the average load of 53kN (5.400kgf) per tire, based on data collected in ten weighings carried out in plants in the state of São Paulo, obtained in trucks for transshipment of two rear axles, loaded with net capacity of 117,70kN (12.000kgf) and 32m³ of volumetric capacity. Pressures were defined as indicated by the manufacturer's tables (Trelleborg, 2013).

Each tested tire was placed on the press shaft and loads were applied using the hydraulic system (Table 1), obtaining the impression of the tire's tread and the settlement on the deformable surface. After each pressing, images of each contact area were obtained using a digital camera supported on a fixed platform elevated on the structure of the hydraulic press.

The digital images were transferred to a microcomputer and graphic readings of these contact areas were obtained using the computer program. To evaluate the settlements in the soil sample from the box, a profilometer was used and to determine the total deformations, a graduated scale was attached to the structure of the hydraulic press.

After each pressing of the tire on the soil sample, the soil's resistance to penetration (cone index) was determined using an electronic penetrometer with data acquisition and storage. This operation evaluated the soil's resistance to penetration in the tire/soil sample contact area and externally the witness, with the purpose of obtaining an increase in the soil's resistance to penetration of each tire contact after suffering the loads imposed by the press. 12 points were measured, obtaining the cone index values ​​at six points longitudinally on the center line of the tire pressing, alternating claws and between tire claws, and six points transversely at a distance of 10cm between each perforation in the part with the greatest pressure of the tires. tires. To determine the increment values ​​for soil compaction, four random drillings were carried out outside the site of soil deformation (control).

The values ​​for tire-soil contact areas, elastic deformations, settlement and increase in soil resistance to tire penetration are presented in Table 2.

Treatments R2 and D2 presented a larger contact area compared to the others (Table 2) and did not differ from each other, with treatment R1 presenting a contact area 14% smaller and treatment D1 presenting a contact area 15% smaller compared to to treatment R2.

The smallest increases in soil resistance to penetration were obtained in treatment R2, while treatment D1 presented the greatest resistance to penetration of the soil sample from the box. Treatment R1 obtained greater deformation and a smaller increase in penetration resistance when compared to treatment D1, with the same rim diameter.

Despite all tires having the same unloaded tread width, the diameter of the tires in treatments R2 and D2 were larger than in the other treatments, having a higher load capacity than the others, which made it possible to work with lower inflation pressure. to the other treatments, contributing to an increase in the impression of the contact area in both width and length, for greater elastic deformation and consequently less settlement and increased soil resistance to penetration (Table 2).

As shown in Figure 1, treatment R2 presented a Cone Index below 2MPa, indicating that in superficial layers the tire with a larger diameter and radial construction obtained better results. Treatment D1 presented a Cone Index of 2,83MPa at a depth of 0,10m, being the highest value obtained among all treatments and treatment R1 did not reach values ​​greater than 2MPa. Cone Index values ​​greater than 2MPa have been associated with conditions that impede root growth, damaging the aerial part of plants, according to reports from several researchers in the area.

CONCLUSIONS

Rims with larger diameters showed the best results. The radial construction tire, with a 26,5” diameter rim, stood out with a larger contact area, greater elastic deformation and lower settlement, therefore contributing to minimizing the effects of compaction, assessed by the soil’s resistance to penetration. . The diagonal belted tire (BPAF) and 22,5” rim obtained the highest increase in resistance to penetration of the soil sample and the lowest elastic deformation. The results show and confirm that the correct use of construction types and tire models minimizes soil compaction.

Thiago Martins Machado - UFMT; Mauro Bueno Oliveira - Trelleborg; Kléber Pereira Peças - Unesp; José Augusto Artioli - Trelleborg; Indiamara Marasca - UniRV

Article published in issue 168 of Cultivar Máquinas