1. Introduction
Cotton is the most important cash crop in Pakistan. In 2017–2018, an area of about 2699 million hectares was cultivated with total production of 11,935 thousand bales [
1]. In the past, the area dedicated to the cultivated of cotton crop decreased due to increased pest and insect attacks, higher input costs, and the nonprofitability of the crop. The pink bollworm is major threat to sustainable cotton production. Every year, its effects grow in severity because it easily completes its life cycle in the currently used cotton sowing and harvesting practices in Pakistan. Therefore, it is necessary to dismantle the housing facilities for pink bollworm in the off-season period.
At the time of final picking of cotton crops, the cotton stalks are manually removed from the field and then transported to a storage point. During storage, the hidden pink bollworm in the bolls completes its life cycle and propagates, leading to its transfer to next coming crop. The pink bollworm life cycle comprised of four stages: egg, larva, pupa, and adult. The time required from egg to egg varies according to temperature and other conditions, but generally, is is about one month during the summer months. Larvae immediately begin to bore into squares or bolls after hatching. The burrow into cotton bolls to feed on the cotton seeds, and in the process, destroy the cotton lint. The adult pink bollworm is a mottled brown to grey moth which is about 38 mm in length. Pink bollworms emerge from pupae in an approximately 1:1 male to female ratio. Around 2–3 days after emergence, the female mates and prepares to lay eggs. In this way, the life cycle continues. The development of the pink bollworm from egg to adult takes 25–35 days; as such, there are typically five to six generations during a cotton-growing season.
Due to the inadequate availability of energy resources for the rural population, a significant portion of cotton stalks are used as fuel for household daily activities such as cooking and heating. This activity not only allows the pink bollworm to complete its life cycle, but also gives rise to environmental issues such as emissions of carbon dioxide (CO
2) and nitrogen oxides (NO
x) [
2].
The manual removal of cotton stalks is a laborious and time-consuming activity; therefore, researchers have attempted to develop methods and machines for pulling and combining cotton stalks in the field. Bansal et al. [
3] designed a stubble collector-cum-planker. It consists of a wooden plank fitted with steel spikes on iron frame, and has a fitting mechanism. Yumak et al. [
4] conducted a study to develop a two-row cotton stalk pulling machine after harvesting cotton. The machine had a field capacity of 9.2 ha/h with a 95% pulling efficiency, leaving 2% and 6% rates of stalk breakage and unpulled stalks, respectively. Gangade et al. [
5] conducted a comparative study on various methods of cotton stalk removal and concluded that the removing/uprooting efficiencies for a tractor operated uprooter, a tractor operated slasher, and a tractor drawn v-blade were 80%, 100%, and 99%, respectively. Sheikh et al. [
6] developed a two-unit digger for cotton stalk uprooting. The unit consisted of a horizontal cutting edge of 0.4 m length. Ramadan and Y.Y.R [
7] developed and evaluated a cotton stalk puller prototype, the appropriate of which were a tilt angle of 45° with a rotating speed of 18.9 m/s under a moisture content of 19%. Murugesen et al. [
8] designed and developed a tractor-drawn cotton stalk puller-cum-chipper. Test rigs were used to determine the uprooting and cutting forces for cotton stalk. Sridhar N. et al. [
9] investigated the influence of the selected level of variability of three operational speeds (i.e., 2, 3, and 5 km/hr), three levels of peripheral velocity (i.e., 18.75, 24.27, and 27.80 m/s), and three numbers of blades (i.e., 2, 4, and 6) on the shredding efficiency (determined in terms of the length of cut of the stalk) of an experimental shredder.
Recently, some progressive farmers have been using either rotavator or disc plows to eradicate cotton stalks after harvesting. It was reported that rotavator destroys only 50 percent of cotton stalks in the field, which negatively affects the seed bed preparation for the next crop [
10]. The major issue in the use of the rotavator for cotton stalk removal is that the cotton bolls remain unchopped. The per-acre cost of operation of the rotavator is also high because of its high fuel consumption.
The methods and machines which are currently utilized to remove cotton stalks from the field do not fulfill requirements, nor do they contribute to controling pink bollworm. Thus, no machine is available which can perform the operations of pulling, chopping, and shredding cotton stalk. To meet the requirement of cotton stalk removal for the preparation of the field for the next crop, the Agricultural Mechanization Research Institute Multan and Agri. Tech. (PVT) Industries, Multan designed and developed a cotton stalk puller/shredder. The main aim of this machine was to pull the cotton stalk and subsequently chop and shred it, along with the remaining cotton bolls, at the time of harvesting the cotton crop. Recently, computer models and software have been used to design and develop the machine elements. Finite element simulation is a numerical technique which is widely applied to study stress strains, deformation, and heat transfer. In the past, various researchers have conducted finite element simulations of agricultural machines [
11,
12,
13,
14]. Makange et al. [
15] analyzed the failure in the shovel due to different loading conditions at different speeds in medium black soil using the ANSYS software. Jafari et al. [
16] developed a bentleg plow and evaluated its attachments by comparing them to conventional ones using the finite element method. Tarighi et al. [
17] developed and analyzed the lower link of a three-point hitch of a ITM-1500 tractor model, with concerns to both static and dynamic environments by using FEA method. Kumar and Mohanraj [
18] used ANSYS software for designing and optimization of rotary tillage tool based on simulation and finite element analysis.
The objective of this study was to evaluate the field performance of the cotton stalk puller shredder for best utilization and improvement in the machine. Further, finite element analysis of various machine parts was also performed for the improvement in the machine.
2. Materials and Methods
2.1. Experimental Site
The experimental tests of the cotton stalk puller shredder machine were carried out at agricultural experimental farm MNS University of Agriculture, Multan. Pakistan (30°07′31.1″ N, 71°26′16.2″ E). The lyrelatively homogeneous soil texture was clay loam. The bulk density was 1.52 g/cm3 and the percentages of sand, silt, and clay were 40.7, 29.8 and 29.5, respectively.
2.2. Machine Specifications
A tractor operated cotton stalk puller shredder Model AGRITECH-CS-PULLER/Shredder-1 was designed and developed by Agricultural Mechanization Research Institute and a well known agricultural machinery manufacturing company named Agritech. Pvt. Ltd. Multan, Pakistan. The overall dimensions of the machine were 2133.6 × 3048 mm. The height of the mainframe of the machine was 686 mm from the ground. The tractor power required for operation of the machine was in the range of 65–85 hp. The specifications of each assembly are described in
Table 1.
2.3. Description of Machine Components
The machine was attached with the tractor using the three-point hitch and driven with the help of PTO shaft. The machine consists of three sub-assemblies, i.e., cutting assembly, pulling assembly and shredding assembly (
Figure 1). The function of cutting assembly is to cut the soil bed and cotton stalk from the roots of the plants. The pulling assembly of cotton stalk puller shredder consists of sets of chains and sprockets mounted on the shaft. The shredding assembly consists of three cylinders of different diameters. The clearance between these cylinders was adjusted so that the optimum size of shredded material can be obtained without any hurdle.
2.3.1. Soil Cutting Blade Assembly
The cotton stalk puller equipped with two blades was attached at an angle to cut the soil as well as cotton stalk from the root system (
Figure 2). The depth of cutting the soil was adjusted according to the root depth of the cotton plant. Cutting roots helps in loosening the anchorage of roots in the soil and aids in less uprooting force. This was the first version of the machine. There were no stones found in the cotton field.
2.3.2. Stalk Pulling and Shredding Assembly
This is the assembly used for pulling stalks to feed to shredding assembly. The height of spikes attached with sprockets was adjusted according to the plant. Clearance between the chains was adjusted according to the diameter of the cotton stalk (
Figure 3).
The shredding assembly was provided to chop the cotton stalk into small pieces which can be easy to incorporate into the soil. Three cylinders of different diameter were used, which were provided with cutting knives mounted on the surface of the cylinder. These knives are equally spaced and their gap was adjusted according to the required size of the chopped stalk (
Figure 3).
2.4. Soil Measurements
Soil physical properties (moisture content, bulk density) were determined by collecting 10 undisturbed soil samples (15 cm long and 5 cm diameter) at random from the experimental field before the commencement of the experiment. The soil was weighed before and after oven-drying, at 105 °C for 24 h to quantify the bulk density and dry basis soil moisture content. (
Table 2).
2.5. Crop Measurements
The parameters of cotton filed was determined for analyses the forces required for uprooting and cutting the stalk. The most important parameters for crop include depth and thickness of taproot, spreading of lateral roots, the diameter of the stalk, moisture content of stalk, average height of the cotton plant, variety of crop and type of sowing bed. The length of tap root was measured using a measuring tape. The diameter of the cotton stalk was measured using a Vernier caliper. The moisture content of cotton stalk was determined using the oven dry method. Furrow beds were constructed by bed shapers. The seed of cotton crop was planted manually, which resulted in variation in the plant-to-plant and row-to-row spacing (
Table 3).
2.6. Experimental Setup
Cotton stalk puller shredder was tested in two different fields, i.e., the first field (in which cotton stalks have leaves and bolls) and the second field (cotton stalks having few bolls). Three machine forward speeds (1.8, 2, 2.2 km/h) and three levels of engine speed (1500, 1800, 2000 rpm) were used to study their effect on the percentage of pulled cotton stalk, blockage and percentage of bolls crushed.
2.7. Shredding Efficiency
The size distribution of chopped stalk is used as a measure of the shredding efficiency of the machine. Randomly selected the area (3 in each row) of the size 1 × 1 m
2 to collect the chopped stalk after operation of puller shredder. The collected chopped was stalk further separated based on size and then determined percentage weightage (
Figure 4). The size of these chopped stalks was measured with the help of measuring tape.
2.8. Statistical Analysis
To verify the influence of examined factors (explanatory variables) on the observed (dependent) variables, a two-way analysis of variance (ANOVA) was used. An analysis of variance was conducted for each of the following dependent variables: Blockage (%), Bolls crushed (%), Pulled stalk (%). Independent variables were tractor engine speed (rpm) and forward ground speed (km/h). The tractor engine speed had 3 levels (1500, 1800 and 2000 rpm), whereas the forward ground speed also had 3 levels (1.8, 2 and 2.2 km/h).
A least significant difference (LSD) test was used to indicate homogeneous groups. The obtained data were statistically analyzed using the STATISTIX (version 8.1 Analytical Software, Tallahessee, USA). All analyses were conducted at the significance level
p = 0.05 [
19,
20].
2.9. Design Analysis and Optimization Using Computer Software
The mechanical analysis of different machine parts was performed on ANSYS 17.2 academic version to analyze the effect of different stresses acting on cutting blad and main frame. The analysis data provide a basis in design work to utilize suitable material. A static structural analysis was used to study the effect of stresses on total deformation and hence, the forces in structures or components due to loads were determined 3D models of blades attached at different angles and designed using Solidworks software and static structural analyses of these blades were carried out using ANSYS software.
There was a blade attached at four different angles selected for structural analysis using the finite element method. The following four different angles arrangement with the blade were selected:
Blade attached at 30°.
Blade attached at 45°.
Blade attached at 60°.
Blade attached at 75°.
The dimensions of these blades were measured using a measuring tape. Three-dimensional drawings of these blades were prepared in Solidworks according to dimensions taken.
2.9.1. Building the Model
A solid model of soil cutting blade of cotton stalk puller shredder was created using Solidworks software. The study was focused on the deformation of the blade during cutting operations in soil. Therefore, not all the components of the cotton stalk puller shredder were used in the FEM analysis. The academic version of ANSYS was used for the FEM stress analysis process. The FEM analysis was set up in 3D, linear, static and isotropic material model assumptions. The material used for cutting blade is high carbon steel. The material properties of soil cutting blades are shown in
Table 4 below.
2.9.2. Mesh Generation
To build the finite element model, the blade meshed. The meshing size used was fine to obtain a highly accurate quantitative analysis.
Table 5 shows the total number of elements and nodes obtained during meshing operation in three types of blades.
2.9.3. Boundary Conditions
The boundary conditions are considered the critical factor for the correctness of a calculation. The mechanics of boundary conditions involved in this study was the force and forward speed. For the 85 hp tractor, the maximum force of 3000 N and forward speed 2 km/h were calculated and applied as boundary conditions of the blades.