Improvement On A Design, Construction And Testing Of Rice Paddy Pre-Cleaning Machine

ABSTRACT

A portable cereal cleaning machine was developed to use forced air from a rotary fan and reciprocating sieve driven by an eccentric shaft for separation of grain from grain-impurity mixture. The machine was constructed from locally sourced materials and capable of being operated with an electric motor or internal combustion engine. Two sieves of 8 mm diameter and 3 x 2 mm² oblong apertures were used for the upper and lower sieve respectively. The sieve assembly suspended by hangers experienced horizontal oscillation and small vertical motion thus displacing the grain from its stationary position to effect sorting and cleaning. During the test, the angle of tilt of the sieve was varied between 3 and 8° while the hanger angle and fan speed was maintained at 5° and 240 rpm respectively. The machine optimum performance was 98% product purity at a total separation efficiency of 71 % for Paddy rice at 3° tilt angle. Results indicated that paddy rice could be effectively separated from light materials of much lower terminal velocity and also from heavy materials like stones and leave stalks due to difference in geometrical and aerodynamic characteristics. Whole grains and glumes were successfully separated into different receptacles.

Introduction

Agriculture is the largest single industry in the world, and seed production is an important segment of this industry. Seed, as it comes from the field, contains various contaminants like weed seeds, other crop seeds, and such inert material as stems, leaves, broken seed, and dirt. These contaminants must be removed, and the clean seed properly handled and stored to provide a high quality planting seed that will increase farm production and supply uniform raw material for industry. The procedures used to meet present quality standards result in a loss of up to 50 percent of the good seed even though many special machines and techniques are used for seed cleaning and handling [1].

Portable Paddy Cleaning Machine is designed to remove foreign materials and impurities such as sand particles, stones, paddy straws and foreign seeds from paddy. This machine provides farmers an alternative replacement of current conventional method should the farmers want to extract the paddy seed in small scale amount [3]. Currently, they only use a traditional winnow technique as to obtain the seeds to be used next season or before processing paddies to become rice.The performance of this machine is very efficient where the percentage of clean paddy is observed to be at 95%. It helps farmers improvise their traditional method, reduces purchasing cost of paddy seed and utilizes the cleaning process at low cost and less maintenance [2].

 

Foreign materials get into cereals during harvesting, handling and transportation. These unwanted materials must be significantly reduced or completely removed for good market value for grains and their products. Also the quality of flour, bread and macaroni is affected by the degree of cleanliness of seeds that go into this product [3].

In Nigeria until of recent, the demand for consumption of locally produced rice is low. This has been attributed to poor harvesting and post harvest handling method which encouraged the presence of contaminants such as stones, stick, chaff and leave stalk as well as low operational quality of the processing equipment [4, 5].

Many types of processing equipment have been developed and are used in many parts of the world to clean seeds, grains and beans. Most of these machines are expensive and require electricity to operate. These are therefore beyond the reach of majority of our farmers (peasant) who produce more than fifty percent of food crops in Nigeria [6]. The traditional method of winnowing employed by the peasant farmers cannot effectively handle the increased grain production of the country. Hence, there is need to develop cereal cleaner which is portable, low cost and can operate with petrol / diesel engine in rural areas and electric motor in urban areas.

S.M.  Henderson,  R.L.  anrdd  Perry (1976) stated that mechanical methods of separating rice from foreign materials depend on the difference in such characteristics as size, shape and specific weight. It has also been observed that chaff – like materials were removed from cereals like wheat, rye and soybeans at air velocity of 3.05 m/s which is less than their terminal velocities [8]. Terminal velocities of some rice varieties grown in the South West of Nigeria were found to exist in the range of their mean values between 5.06 to 5.19 m/s and there were no significant differences among the different varieties [9]. At low feed rate of 22 – 34 kg/min, chaff materials were dispersed by air blast before reaching the upper sieve of a combine [10]. B. Hollatz, and G. R. Quick (2003) established that at high feed rate in a combination of aerodynamic and mechanical process, grain –  impurity mixture form a mat on the sieve rather than been separated.

Orientation of particles as well as combined effect of frequency, amplitude of oscillation, the screenslope, hanger angle as well as the friction between particles and screen is parameters that should be considered for effective screen sizing. Grain size determination is important in the design of screen opening [12]. Grains are best assumed spherical and their spherical mean can be obtained by taking geometric mean of their mutually perpendicular axes and sphericity is the percentage of ratio of the spherical mean and the major diameter [13]. When the value of sphericity is greater than 85 %, circular shaped sieves is sufficient for final separation while those that within 32 to 50 % require an oblong shaped sieve [14]. Optimum tilt angle of sieves for a cereal cleaner occurred between 4 and 5° when operating between 300 and 350 rpm with a cleaning efficiency of 61 % [6].

This machine was designed as a pre – cleaner for paddy rice cleaning and can be operated by electric motor or diesel engine. It cleans and sort grains by the use of reciprocating sieve arrangement in a sieve assembly and air blast from a rotary blower.

1.2                                   PROBLEM STATEMENT

Generally, the hand threshing and the traditional handling used in most developing countries case a larger percentage of foreign matter with the paddy, and it time consuming which involves much labour. Thus, more cleaning is required. It was for this purpose that rice paddy pre-cleaning machine was fabricated. Rice paddy pre-Cleaning Machine is designed to remove foreign materials and impurities such as sand particles, stones, paddy straws and foreign seeds from paddy. This machine provides farmers an alternative replacement of current conventional method should the farmers want to extract the paddy seed in small scale amount.

1.3                                    AIM OF THE PROJECT

The main aim of this work is to fabricate a paddy cleaning machine to perform simple pre-cleaning operation.

1.4                               PURPOSE OF THE PROJECT

The purpose of rice paddy pre-cleaning machine is cleaned to:

1. Reduce requirements for drying
2. Remove materials that could cause paddy deterioration during
3. Remove materials that could damage the conveying and milling
4. Remove materials that cause a reduction in the
5. Reduce storage

1.5                                  SCOPE OF THE PROJECT

Pre-Paddy cleaner is designed to separate impurities like straw, dust, lighter particles, stones from paddy, so the next machines will work more efficiently when paddy is cleaned in paddy cleaners. Different sieves can separate large, small and light impurities from wheat, paddy, corn and oil bearing materials. The cleaners are manufactured with single blower or double blower with double deck, having capacity to clean 1t to 12t of paddy per hour. This machine is used in rice mills as cleaning machine for processing rice in bulk quantities, they are necessary units for a complete rice milling plant. These paddy pre-cleaners are manufactured using high grade components and raw material, which are sourced from our local environment.

1.6                           APPLICATION OF THE PROJECT

Apart from using this device for rice paddy pre-cleaning, this machine can also be used to separate large, small and light impurities from wheat, corn and oil bearing materials.

1.7                            LIMITATION OF THE PROJECT

This machine is heavy and takes up a lot of space. In addition, the current paddy cleaning machines are not portable. The proposed paddy pre-cleaning machine is capable of removing dust, sticks, stones, and other impurities.

1.8                                         METHODOLOGY

In the course of carrying this study, numerous sources were used which most of them are by visiting libraries, consulting journal and news papers and online research which Google was the major source that was used.

1.9                                                         PROJECT ORGANIZATION

The work is organized as follows: chapter one discuses the introductory part of the work,   chapter two presents the literature review of the study,  chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.