Ballasting optimizes traction and reduces operating costs

The modern agricultural tractor is a self-propelled machine whose main functions are to increase agricultural productivity per rural worker, make work in the field less arduous and more attractive, reduce production costs and improve environmental conditions, such as soil, to facilitate seed germination and plant growth (Goering et al, 2003).

To perform such functions properly, with greater traction efficiency and reduced fuel consumption, it is necessary to perform periodic maintenance, choose the tractor power that best suits the work to be performed and provide the tractor with a slip of the drive wheels (also called reduction of the route) of between 10% and 15% on agricultural soils during operation (Monteiro and Silva, 2009).

The slippage of the drive wheels depends on the type of tire and its condition, the resistance conditions of the ground, the contact of the wheel with the ground and the torque on the wheels. The greater the adhesion of the ground with the drive wheel, the less the slippage, and one way to increase the adhesion is through tractor ballasting.

For efficient use of the tractor, adjustments are necessary to the machine according to its intended use. Adjusting the ballast of a tractor, in addition to providing greater grip between the ground and the wheels, and thus contributing to increased traction in most cases, can also help reduce fuel consumption, which contributes to reducing agricultural production costs.

Despite its importance, many Brazilian farmers rarely or never change the ballast on their tractors. This compromises the tractor's performance, and as a consequence of lower performance, there is greater fuel consumption, greater wear and tear on the machine and higher agricultural production costs.

Given these premises, the objective of this study was to group together some references on the subject, for informative material for farmers.

Ballast

Ballasting is the procedure of increasing the mass of tractors with the aim of increasing the adhesion of the ground with the driving wheels, and thus providing an increase in the traction capacity and stability of the tractor-implement assembly, the latter making the tractor safer with regard to the risk of tipping over.

With the proper use of ballast, it is possible to increase the useful life of the tire and improve its performance, in addition to reducing problems of loss of traction, excessive slippage and fuel consumption. Therefore, ballast leads to improvements in terms of operational performance (Monteiro, Lanças and Guerra, 2011; Spagnolo et al, 2012).

Excess ballast in agricultural tractors leads to reduced tractor performance, increased fuel consumption and increased wear on parts, since the tractor will be using part of its power to move the excess mass. In addition, greater tractor weight leads to greater soil compaction. Insufficient ballast leads to excessive slippage, high fuel consumption and premature tire wear.

The total gross mass of the tractor with the correct amount of ballast is a function of the tractor's drivetrain: two-wheel drive; front-wheel power assist; or four-wheel drive, and the speed of travel in the field. Table 1 shows the tractor mass/power ratio as a function of travel speed.

Since only the drive wheels provide traction, it is also important to distribute ballast properly between the front and rear axles. The ideal mass between the axles is affected by the type of drive and whether the attached implement is pulled or mounted. Table 2 provides a rule of thumb for distributing tractor mass to the front and rear wheels depending on whether the implement is pulled, semi-mounted, or mounted.

The data in Tables 1 and 2 determine the necessary mass of ballast that will have to be added to the front and rear of the tractor, so that slippage is between 10% and 15%, and thus provide fuel savings and better traction efficiency.

Procedure for ballasting

There are two types of ballast: liquid and solid. Liquid ballast consists of adding water to the tractor tires according to the manufacturer's recommendations. Solid ballast can be done using metal discs attached to the rear wheels or metal plates mounted on the front of the tractor.

For water ballast, simply position the tire nozzle at the top to fill it with 75% water; position the nozzle at the top and forming a 45º angle with the ground surface to fill with 60%; with the nozzle in the middle position of the tire to fill 50%; with the nozzle in the bottom position forming a 45º angle with the ground to fill 40%; and with the nozzle at the bottom to fill 25% (Monteiro and Silva, 2009).

Ballasting is closely linked to tractor slippage, so a practical procedure to determine whether or not the agricultural tractor has the ideal amount of ballast and whether the slippage rate is between 10% and 15%, ideal for movement on agricultural soils, is to simply observe the marks left by the tractor's driving wheels on the soil (Monteiro and Silva, 2009), as can be seen in the box.

Studies on ballast in agricultural tractors

A study conducted by Lopes et al (2005) compared the performance of a 4hp 2x121 TDA agricultural tractor according to tire type, water ballast condition and speed. Their results showed that for tractors operating at higher speeds, water ballast was important to increase effective field capacity and reduce specific fuel consumption of agricultural tractors.

Monteiro, Lanças and Guerra (2011) compared the performance of an agricultural tractor equipped with radial and bias tires with different liquid ballast in three surface conditions of a Red Nitosol. The results of the study show that the best tractor performance occurred in the condition of 75% water in the tires, for the tractor equipped with bias tires, and 40% water in the tires, for tractors with radial tires. For both ballasts, the tractor presented higher travel speed, lower slippage, lower specific fuel consumption and greater power and efficiency in the drawbar.

Performance studies of agricultural tractors carried out in works by Gee-Clough, Pearson and McAllister (1982), Jadhav et al (2013) and Sharma, Gaba and Singh (2016), concluded that ballasting provides increased traction efficiency, greater power available at the drawbar and lower specific fuel consumption of the agricultural tractor.

Side rollovers are fatal accidents that frequently involve agricultural tractors. Studies related to the stability of agricultural tractors, such as those developed by Li et al (2016), Ahmadi (2013), Baker and Guzzomi (2013), Gravalos et al (2011), show that adjusting the ballast weights in agricultural tractors is extremely important, since this procedure modifies the tractor's center of gravity, providing greater stability, reducing the possibility of rollover, and therefore providing greater safety to the operator.

Ballast must be distributed correctly, following the instructions in the tractor manual. Poor ballast distribution leads to increased fuel consumption, greater soil compaction and can even destabilize the tractor (Pranav and Pandey, 2008).

In light of these studies, it is clear that failing to ballast an agricultural tractor or doing so incorrectly leads to a reduction in overall operating efficiency and an increase in operating costs, given that fuel consumption is increased and the tractor's power is poorly utilized, which consequently increases the final cost of agricultural production.

Conclusions

Ballasting an agricultural tractor must be a procedure carried out before any activity carried out by the tractor in the field. Ballasting must be done in accordance with the manufacturer's manual and provide the tractor with a drive wheel slip of between 10% and 15% during operation on agricultural soils.

Correct ballast plays an important role in tractors. In addition to improving traction efficiency and reducing the specific fuel consumption of agricultural tractors, it also regulates slippage and increases stability, providing greater safety for the operator. This results in a reduction in agricultural production costs.

Different tracks, depending on the type of ballast

Characteristic types of marks left by tractor drive wheels on agricultural soil:

(a) excessive slippage, poorly defined marks and the need to increase the amount of ballast;

(B) insufficient slippage, clearly visible marks on the ground, need to reduce the amount of ballast on the tractor;

(C) amount of ballast and correct skating, well-defined marks on the end and sliding in the center.

*Per Lucas, Federal University of Viçosa