DESIGN, CONSTRUCTION AND PERFORMANCE EVALUATION OF AN AXIAL-FLOW MILLET THRESHER

Abstract

This study focused on the design, construction, and performanceevaluation of an axial-flow millet thresher. The specific objectives were to design the components of the thresher based on the engineering properties of millet; construct the thresher using locally available materials; evaluate the performance of the machine in terms of threshing efficiency, cleaning efficiency, and grain damage; determine the optimal operating parameters (cylinder speed, feed rate, and moisture content); and conduct an economic analysis of the thresher. The design calculations were based on standard mechanical engineering principles. The machine consisted of a threshing cylinder, a concave, a cleaning unit (fan and sieves), a feeding chute, and a power transmission system. Performance tests were conducted using pearl millet at different moisture contents, cylinder speeds, and feed rates. Data were collected on threshing efficiency, cleaning efficiency, percentage of unthreshed grains, and percentage of broken grains. The data were analyzed using Analysis of Variance (ANOVA). The findings revealed that the machine performed optimally at a cylinder speed of 700 rpm, a feed rate of 100 kg/h, and a moisture content of 10% (wet basis). At these settings, the threshing efficiency was 98.5%, the cleaning efficiency was 96.2%, and the percentage of broken grains was 2.1%. The economic analysis showed that the thresher is a viable investment with a short payback period. The study concluded that the designed and constructed axial-flow millet thresher is efficient, affordable, and suitable for smallholder farmers. It was recommended that the design be promoted and made available to local fabricators for mass production.

Chapter One – Introduction

1.1 Background of the Study

Millet is a group of small-seeded cereal crops that are of immense importance to food security in the semi-arid tropics of Africa and Asia. In Nigeria, pearl millet (Pennisetum glaucum) is a staple food crop, particularly in the northern regions, where it is a primary source of energy, protein, and essential minerals. It is a resilient crop, capable of growing in harsh environments with low rainfall and poor soils, where other cereals like maize and rice may fail. The crop is deeply embedded in the cultural and dietary traditions of many communities. (Food and AgricultureOrganization [FAO], 2021).

The processing of millet, from harvesting to the final edible product, involves several steps, including threshing, winnowing, and milling. Threshing, the process of separating the grain from the panicle (the seed head), is a particularly critical and often labor-intensive operation. The efficiency and timeliness of threshing have a direct impact on the quantity and quality of the grain that is available for consumption and sale. Post-harvest losses during threshing can be significant if the operation is not carried out properly. (Adebayo, Oladele, and Sanusi, 2021).

The traditional method of threshing millet in Nigeria is manual, typically involving the beating of harvested panicles with sticks or trampling underfoot. This method is extremely labor-intensive, time-consuming, and inefficient. It is also associated with high levels of grain loss and contamination with sand and other foreign materials. The drudgery of manual threshing is often borne by women and children. The need for a more efficient and less laborious method of threshing is therefore paramount. (Adebayo et al., 2021).

The mechanization of agricultural processing is a key strategy for improving efficiency, reducing post-harvest losses, and enhancing the livelihoods of smallholder farmers. A mechanical thresher can process large quantities of millet in a fraction of the time required for manual threshing. This not only saves labor but also allows farmers to process their harvest in a timely manner, reducing the risk of losses due to weather or pest attack. The development of appropriate, affordable technologies is essential for promoting agricultural development. (Srivastava, Goering, and Rohrbach, 2019).

Various types of mechanical threshers have been developed for different crops. The axial-flow thresher is a design that has gained popularity due to its versatility and effectiveness. In an axial-flow thresher, the crop material is fed into the machine and moves in a spiral path along a rotating cylinder, parallel to the cylinder’s axis. The threshing action is achieved through a combination of impact and rubbing between the cylinder, the concave, and the crop material itself. This design is known for its ability to handle a wide range of crops and its relatively gentle threshing action, which can reduce grain damage. (Kepner, Bainer, and Barger, 2018).

The design of a thresher requires a careful consideration of the engineering properties of the specific crop to be threshed. These properties include the size, shape, and density of the grain; the force required to detach the grain from the panicle; the terminal velocity of the grain and chaff (which is important for cleaning); and the moisture content of the crop. These properties determine the design parameters of the machine, such as cylinder speed, concave clearance, and the size of the sieves. (Kepner et al., 2018).

The performance of a thresher is evaluated using several key indicators. Threshing efficiency is the percentage of grains that are successfully separated from the panicle by the machine. Cleaning efficiency is the percentage of grains that are cleanly separated from the chaff and other foreign material. The percentage of broken grains is a measure of the mechanical damage inflicted on the grain during threshing, which is a critical quality parameter. An ideal thresher maximizes the first two and minimizes the last. (Srivastava et al., 2019).

The optimization of thresher performance involves determining the best combination of operating parameters. The key parameters include the speed of the threshing cylinder, the feed rate (the rate at which material is fed into the machine), and the moisture content of the crop at the time of threshing. These parameters are interdependent, and their optimal settings must be determined through systematic experimentation. A factorial experimental design is typically used for this purpose. (Montgomery, 2017).

The economic viability of a thresher is a critical consideration for its adoption by farmers. The cost of the machine must be weighed against the benefits it provides, including labor savings, reduced losses, and increased output. An economic analysis, including a calculation of the payback period and the return on investment, is essential for demonstrating the value proposition of the technology. The affordability of the machine is a key factor, particularly for smallholder farmers. (Heady and Dillon, 2018).

The use of locally available materials in the construction of agricultural machinery is a key principle of appropriate technology. It reduces the cost of the machine, makes it easier to repair and maintain, and supports the local economy. The design of a thresher that can be fabricated by local artisans using common materials (e.g., sheet metal, angle iron, bearings) is therefore highly desirable. This approach promotes the sustainability and widespread adoption of the technology. (Srivastava et al., 2019).

This study is therefore designed to design, construct, and evaluate the performance of an axial-flow millet thresher. The machine will be built using locally available materials, and its performance will be tested under different operating conditions. The study will determine the optimal settings for the machine and assess its economic viability. This will provide valuable evidence for promoting the mechanization of millet threshing in Nigeria. (Emmanuel and Okafor, 2022).

The findings of this study are expected to be of significant value to a wide range of stakeholders. For smallholder farmers, the study will provide a design for an affordable and efficient threshing machine. For local fabricators, the study will provide a blueprint for manufacturing the thresher. For researchers, the study will contribute to the literature on agricultural machinery development. Ultimately, the study aims to contribute to the reduction of post-harvest losses and the improvement of livelihoods in the millet value chain. (World Bank, 2022).

1.2 Statement of the Problem

The traditional method of threshing millet in Nigeria is a major constraint on the productivity and profitability of millet farming. The core problem is that manual threshing is labor-intensive, time-consuming, inefficient, and associated with high levels of grain loss and contamination. This bottleneck in the processing chain limits the ability of farmers to bring their produce to market quickly and in good condition, thereby reducing their potential income. The need for a practical, affordable mechanical solution is acute. (Adebayo et al., 2021).

A fundamental problem is the high level of drudgery and the time burden associated with manual threshing. The operation is physically exhausting and is often carried out by women and children, who are already burdened with other household and farm tasks. The problem is that this time-consuming activity prevents them from engaging in other productiveactivities, such as education or income generation. The mechanization of threshing would free up their time and reduce their physical burden. (Doss, 2018).

The problem of significant post-harvest losses during manual threshing is a major economic concern. During the beating and trampling process, a significant amount of grain is lost as it shatters and scatters on the ground. The problem is that these losses, which can be as high as 10-15% of the total harvest, represent a direct economic loss for the farmer. The use of a mechanical thresher, which is designed to contain the crop material, can drastically reduce these losses. (FAO, 2021).

There is a significant problem with the contamination of grain during manual threshing. Because the operation is often carried out on bare ground, the threshed grain frequently becomes contaminated with sand, stones, and other foreign materials. The problem is that this contamination reduces the quality and market value of the grain. It also makes the grain less safe for consumption. A mechanical thresher with a built-in cleaning system can produce cleaner, higher-quality grain. (Adebayo et al., 2021).

The issue of the lack of access to affordable and appropriate threshing machines is a key barrier to mechanization. While some imported machines are available, they are often expensive, complicated to operate, and difficult to repair with locally available parts. The problem is that these machines are not well-suited to the needs and resources of smallholder farmers. A locally designed and fabricated thresher, built from readily available materials, would be a more appropriate and sustainable solution. (Srivastava et al., 2019).

The problem of the lack of local technical capacity for the design and manufacture of agricultural machinery is a systemic challenge. While engineers are trained in Nigeria, their expertise is not always effectively channeled towards solving the practical problems of smallholder farmers. The problem is that this leads to a dependence on imported technologies. The development of local design and fabrication capabilities is essential for achieving sustainable agricultural development. (Emmanuel and Okafor, 2022).

There is a significant problem with the lack of empirical performance data for locally designed threshers. Many promising designs are developed but never rigorously tested and evaluated. The problem is that this lack of data makes it difficult for farmers and other stakeholders to assess the performance of these machines and to have confidence in their reliability. The systematic evaluation of the thresher, as proposed in this study, is essential for building trust and promoting adoption. (Kepner et al., 2018).

The problem of optimizing the thresher for the specific properties of pearl millet is a key technical challenge. The physical and mechanical properties of millet grains and panicles vary depending on the variety and the moisture content. The problem is that a thresher that is not properly adjusted for these properties will have poor performance, resulting in low threshing efficiency or high grain damage. The determination of the optimal operating parameters is therefore critical. (Srivastava et al., 2019).

The issue of the high moisture content at harvest is a common constraint. Farmers often harvest their millet before it is fully dry, particularly if the threat of pests or bad weather is imminent. The problem is that threshing grain at high moisture content is more difficult and results in higher levels of grain damage. The performance of the thresher at different moisture contents is therefore an important factor to evaluate. The need for farmers to dry their harvest adequately is also important. (FAO, 2021).

The problem of the scarcity of data on the specific engineering properties of Nigerian millet varieties is a constraint on the design process. The design of a thresher requires accurate data on the size, shape, and strength of the grain. The problem is that this data is often not readily available for local varieties. This study will therefore need to measure some of these properties as part of the design process. The generation of this local data is a valuable contribution in itself. (Emmanuel and Okafor, 2022).

This study is designed to address these problems by designing, constructing, and rigorously evaluating an axial-flow millet thresher built from locally available materials. The study will systematically optimize the machine’s operating parameters and assess its economic viability. The core problem this research aims to solve is the lack of an affordable, efficient, and locally appropriate solution for mechanizing millet threshing, which is a major bottleneck in the value chain. (World Bank, 2022).

1.3 Aim of the Study

The aim of this study is to design, construct, and evaluate the performance of an axial-flow millet thresher.

1.4 Objectives of the Study

The specific objectives of this study are to:

1. Design the components of the axial-flow millet thresher based on engineering principles.
2. Construct the thresher using locally available materials.
3. Evaluate the performance of the thresher in terms of threshing efficiency, cleaning efficiency, and grain damage.
4. Determine the optimal operating parameters (cylinder speed, feed rate, moisture content) for the thresher.
5. Conduct an economic analysis of the thresher.

1.5 Research Questions

The following research questions were formulated to guide this study:

1. What are the key design parameters for an effective axial-flow millet thresher?
2. Can the thresher be constructed using readily available local materials?
3. What are the threshing efficiency, cleaning efficiency, and grain damage levels of the constructed thresher?
4. What is the optimal combination of cylinder speed, feed rate, and moisture content?
5. Is the designed thresher economically viable for smallholder farmers?

1.6 Research Hypotheses

The following null (H₀) and alternative (H₁) hypotheses were tested in this study:

1. H₀: The cylinder speed does not have a significant effect on the threshing efficiency of the machine.
   H₁: The cylinder speed has a significant effect on the threshing efficiency of the machine.
2. H₀: The feed rate does not have a significant effect on the threshing efficiency of the machine.
   H₁: The feed rate has a significant effect on the threshing efficiency of the machine.
3. H₀: The moisture content of the millet does not have a significant effect on the percentage of broken grains.
   H₁: The moisture content of the millet has a significant effect on the percentage of broken grains.
4. H₀: The interaction between cylinder speed and feed rate does not have a significant effect on the cleaning efficiency.
   H₁: The interaction between cylinder speed and feed rate has a significant effect on the cleaning efficiency.
5. H₀: The use of the thresher does not lead to a significant reduction in threshing time compared to manual methods.
   H₁: The use of the thresher leads to a significant reduction in threshing time compared to manual methods.

1.7 Significance of the Study

This study holds significant value for a wide range of stakeholders. For smallholder millet farmers , the study will provide a design for an affordable, efficient, and easy-to-operate threshing machine. The adoption of this technology will drastically reduce the labor and time required for threshing, reduce post-harvest losses, and improve the quality of their grain. This will lead to higher incomes and improved livelihoods. The machine’s use of local materials makes it a sustainable and appropriate technology.

For local fabricators and artisans , the study will provide a detailed blueprint and specifications for manufacturing the thresher. This will create new business opportunities and contribute to the growth of the local agricultural machinery industry. The use of common materials and straightforward construction techniques will make it easy for them to replicate the design. This will also make the technology more accessible to farmers.

For researchers and academics in agricultural engineering, this study will contribute to the body of knowledge on machinery design and performance evaluation. The methodology, from the initial design calculations to the factorial performance testing, will serve as a valuable reference. The study will also generate local data on the engineering properties of millet, which is a useful contribution to the literature. It will inform the development of more efficient and appropriate processing technologies.

For policymakers and development organizations , the study will demonstrate the potential of local innovation to address post-harvest challenges. The findings can inform programs aimed at promoting agricultural mechanization and reducing food losses. The study highlights the importance of supporting local design, fabrication, and dissemination of appropriate technologies. It contributes to the broader goal of achieving food security and sustainable agricultural development.

1.8 Scope of the Study

This study is focused on the design, construction, and performance evaluation of an axial-flow millet thresher. The study involves the mechanical design of the thresher components, the construction of the machine using locally available materials (sheet metal, angle iron, etc.), and the testing of the machine’s performance. The performance evaluation is conducted using pearl millet at three different moisture contents, three cylinder speeds, and three feed rates. The key performance indicators are threshing efficiency, cleaning efficiency, and the percentage of broken grains. The study is limited to the axial-flow design and to pearl millet. The study does not cover the evaluation of the thresher for other cereal crops or the design of other types of threshers.

1.9 Limitation of the Study

This study is subject to certain limitations. The primary limitation is that the performance tests were conducted under controlled laboratory conditions, which may not perfectly replicate the variability of field conditions. The study focused on a single variety of pearl millet, and the performance may differ for other varieties with different physical properties. The moisture content was measured on a wet basis, and the specific moisture levels used in the experiment may not cover the full range experienced by farmers. The economic analysis is based on a specific set of cost and price assumptions, which may vary over time and by location. The long-term durability and wear characteristics of the machine were not assessed in this short-term study.

1.10 Definition of Terms

For the purpose of clarity, the following terms are defined as they are used in this study:

1. Axial-Flow Thresher: A type of threshing machine where the crop material moves in a spiral path along a rotating cylinder, parallel to the cylinder’s axis.
2. Threshing: The process of separating grains from the seed heads (panicles) of a crop.
3. Threshing Efficiency: The percentage of grains that are successfully separated from the panicle by the thresher.
4. Cleaning Efficiency: The percentage of grains that are cleanly separated from the chaff and other foreign material.
5. Grain Damage: The percentage of grains that are split, broken, or bruised during the threshing process.
6. Cylinder Speed: The rotational speed of the threshing cylinder, measured in revolutions per minute (rpm).
7. Feed Rate: The rate at which crop material is fed into the thresher, measured in kilograms per hour (kg/h).
8. Moisture Content: The amount of water present in the crop material, expressed as a percentage of the total weight (wet basis).
9. Concave: The stationary, curved component of the thresher that surrounds part of the threshing cylinder.
10. Engineering Properties: The physical and mechanical properties of a material (like millet) that are relevant to its interaction with machinery.