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A Study on Disc Inclination Versus Soil Forces on Discs Sharpened on the Concave Sides

M. Maqsudar Rahman
Senior Scientific Officer
WMM Division, Bangladesh Rice Research Institute, Cazipur 1701, Bangladesh'

J. Kilgour
Senior Lecturer
Silsoe College, Cranfield Institute of Technology, Bedford, U.K.

Abstract/ Executive Summary:

A study was undertaken to minimise the soil forces on disc tillage tools for land preparation by varying the orientation or geometry of disc. A three-disc-gang tillage tool of variable geometry named 'the variable geometry disc' was tested in a soil bin (sandy loam soil) for 20^oand 30^o disc angles at 0^o, 10^o and 20^o tilt angles. The variable geometry disc consisting three discs of 457 rnm diameter each with 610 mm radius of curvature was sharpened on the concave sides. The discs were fitted to a common axle in such a way that all the three discs together could be set at 20^o and 30^o angles to the horizontal plane, i.e. disc angles and 0^o, 10^o and 20^o angles to the vertical plane, i.e. tilt angles. Results showed that the draught, side and vertical forces decreased as,the disc angle increased from 20^o to 30^o. The optimum position was found at 30^o disc and 20^o tilt angles where the draught (1.51 kN), vertical (0.27 kN) and side forces (1.11 kN) and specific resistance per unit furrow area (31.2 kN/m') were minimum. At this point the maximum penetration was achieved with a good soil break at subsurface and a good levelness of the tilled soil at the surface.

Keywords: Power Tiller, Tractor, DiscTillage

Location:

Start Date:

End Date:

Program Area: Farm Mechanization

Commodity: Performance evaluation

Objectives:

To identify the soil forces on discs, sharpened on the concave side at different disc and tilt angles and
To find out the optimum disc and tilt angle combination in which the specific draught and side thrust will be minimum and penetration will be improved by minimising the vertical upward force of the soil.

Methodology:

A test was conducted with a disc tillage tool with discs sharpened on the concave sides at different disc and tilt angles. The axle of a disc harrow is usually set at variable angles to the line of travel. Disc angle is the angle in the horizontal plane between the path of the travel and a line passing through the face of the disc. Tilt angle is the angle viewed from the side of the disc between the plane of the disc and vertical line. A variable geometry disc was used in the experiment. It consisted of three discs of 457 mm dia. each with 610 mm radius of curvature. The discs were sharpened on the concave sides. Each disc, fitted with a nylon bush bearing, was fitted with the common axle in such a way that the axis of the bush bearing was at 20^o to the common axle. This arrangement facilitated the setting of the discs at various tilt angle by rotating the axle around its axis and setting of the discs at various disc angles by rotating the common ade in a horizontal plane through vertical axis. The test was conducted in a soil bin with sandy loam soil prepared in three 50 mm soil layers with the help of 'cariage', a soil bin preparation equipment. The variable geometry disc tillage tool was completely mounted to the trailing end of the carriage through an Extended Octagonal Ring Transducer (EORT) by means of four M 36f bolts. This EORT was used to measure the draught, vertical and side forces of soil on the disc during operation in the bin. The initial moisture content and the bulk density of the soil in the bin was 9.7 per cent and 1.57 gm/cc with the angle of internal shearing resistance, ?=27^o and cohesion, c=10 kN/m². These parameters of soil in the bin were kept uniform as much as possible throughout the experiment by careful and uniform preparation of the soil before each test runs. The angle of soil metal friction was λ=24^o. The experiment was conducted at 20^o and 30^o disc angles at 75 mm depth of cut and at each disc angle with three tilt angles 0^o, 10^o and 20^o. The disc tillage tool was pulled by the carriage during the test run. The carriage wheels ran on two parallel rails on both sides of the bin so that the test equipment, i.e. the disc tillage tool trailed behind the carriage at a uniform working depth of 75 mm and at a uniform travel speed of 0.5 m/sec for all test runs. In each test run, three measurements were taken at 3 spots in the run with the help of EORT. To record the soil force data, EORT was connected to Whitstone Bridge Circuit. In each test run, the profile of the disturbed soil and cleared furrow bottom was recorded by a profile meter. The test was not possible with disc angle beyond 30^o and tilt angle beyond 20^o because of the capacity of the variable geometry disc implement.

Source of Information: Joumal of the lnstitution of Engineers, Bangladesh, Agricultural Engineering Division, Vol. 25/AE, No. 1, Dec. 1998

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The optimum position of the disc was found a1 30^o disc angle and 20^o tilt angle combination for discs sharpened on the concave, side where the draught, side and vertical forces and the specific resistance were minimum. At this point the soil pulverization and soil breakout at the bottom of the disturbed soil were also good. Disc penetration was also good at this point because of minimum vertical upward thrust. This study provides an information on which the design/development of an attachment of disc tillage tool behind a tractor or a power tiller for land preparation may be undertaken.

Knowledge Management: Journal