Introduction: Two-wheeled tractors are used to disturb the topsoil in greenhouses and small gardens. These machines consist of a rotating shaft connected to a gearbox, on which a set of flanges is mounted. Blades are attached to each flange in a specific arrangement. When the flanges rotate, they come into contact with the soil, lifting and throwing it backward, thus breaking up the soil and creating a suitable seedbed for planting agricultural products. A transmission system transfers the necessary and generated force from an engine to the blades for soil cutting. Notable features of these machines include reasonable prices, high operational speed, easy mobility due to lightness, and simple maintenance and repair. Rotary cultivators or rotary soil mixers are also used to prepare the soil bed and control weeds in fruit orchards. In this research, the most suitable blade for producing a double-purpose rotary-trencher machine equipped with a V-shaped gearbox was designed and produced.

Materials and Methods: Catia software (V5-6R2018) was used for the design and Abaqus software (6.14-4) was used for mechanical analysis of the designed blades. First, the blades were designed with three different surfaces 42.75, 38.53, and 35.39 cm2. The goal was to achieve a blade design that not only creates a suitable tilled soil surface but also maximizes soil displacement to ensure the device performs acceptably during furrow creation. The blade stress analysis was performed based on the Von Mises criterion and finite element analysis (FEA). After the design of the blades, to ensure their strength against the forces exerted from the soil surface, FEA and examination of the mechanical strength of the selected alloy (ST52) were performed in Abaqus software. Then, the blade spread design was cut using a CNC machine, forged using a blacksmithing mold, and bent with a 38-millimeter radius. After this stage, the surface of the blades was hardened. The evaluation of the device in the disturbing of the topsoil with three blade models at three blade shaft speeds (200, 300, and 400 rpm) was performed in three repetitions in the form of a factorial experiment in a completely randomized design using SPSS software. The disturbing of the topsoil and the depth of the created trench were considered as criteria for evaluating the rotation speed and dimensions of the blades.

Results and Discussion: The maximum force applied to blades showed that the maximum stress obtained with surfaces of 42.75 cm2, 38.53 cm2, and 35.39 cm2, based on the Von Mises criterion, was 0.74, 0.7, and 0.188 MPa, respectively. Also, the maximum principal stress in these three blade models was 0.27, 0.24, and 0.122 MPa, respectively. The results illustrated that the maximum stresses obtained are much lower than the yield stress or ultimate strength of the alloy used in the blade. To do the topsoil tillage operation 6 flanges of blades (18 blades) and to do trenching two flanges of blades (6 blades) were installed on the axis of the gearbox. The results from comparing Mean Weight Diameter (MWD) values of the disturbed topsoil showed that by increasing rotation of the blade shaft, the soil disturbing significantly increases. On the other hand, results showed that the increase in the surface of the blade was not significant in disturbing the topsoil particles. Also, the blades were evaluated by creating a trench. Two flanges of the blades (6 blades, Fig 1. b) are performed when the machine moves backward (Fig 9-a and Fig 11). The machine's reverse speed was kept constant at 2 km/h. The results clearly showed that the surface of the blades has had a significant effect on the performance of creating a trench, and with the increase of the blade's surface, the amount of soil transferred out of the trench has increased. However, increasing the blade surface increased the trench depth, but increasing the blade's axis rotation was not as significant as the blade surface because the backward speed of the machine is constant and slow.

Conclusion: In this research, a new type of blade for a dual-purpose rotary-trencher machine was designed, analyzed, produced, and evaluated. The results of the statistical analysis showed that the blade's surface has no effect on the tillage quality, but the rotation speed of the blades was significantly effective. On the other hand, in the operation of creating a trench, the surface of the blade was significantly effective, and with the increase of the surface, the depth of the created trench increased due to the movement of more soil particles. Finally, a blade with a surface of 42.75 cm2, made of ST52 alloy steel, with a forged and hardened edge, and a bending radius of 38 mm was proposed for this type of dual-purpose soil rotary-trencher machine. Therefore, this machine equipped with the designed blade model is suitable for both topsoil disturbing and trencher.