CHAPTER ONE 1.0 INTRODUCTION 1.1 BACKGROUND OF STUDY Most food substances have its origin in plants, although Some foods are obtained directly from plants, and others from animal. But even animals that are used as food sources are raised by feeding them food which are derived from plants. Grains have been cultivated for thousands of years and they’ve been a major component of the human diet. Additionally, any food made from wheat, rice, oats, cornmeal, barley or another cereal is a grain product. These refined grain products are used in the making of bread, pasta, oatmeal, breakfast cereals, tortillas, and grits. Cereal grain is a staple food that provides more food energy worldwide than any other type of crop. Corn (maize), wheat, and rice – in all of their varieties – account for 87% of all grain production worldwide "Production STAT". 2008. The various types of grains include the following including wheat, oats, rice, corn (maize), barley, sorghum, rye, and millet. Grains are defined as a small, hard, dry seeds, with or without its fruit layers, harvested for human or animal consumption. Babcock, P. G., ed. 1976. The two main types of commercial grain crops are cereals such as wheat and rice, and legumes such as beans and soybeans. After being harvested, dry grains are more durable than other staple foods such as starchy fruits (plantains, breadfruit, etc.) and tubers (sweet potatoes, cassava, and more). Hence this durability has made grains well suited to industrial agriculture, since they can be mechanically harvested, transported by rail or ship, stored for long periods in silos, and milled for flour. Why process grains? In layman’s language, processing refers to the act of converting any material from one form to another. In agriculture, crop processing machinery is used to transform grains and other produce from their raw form to the refined and edible form. Crop processing also aims at preparing crops for convenient transportation, storage, and also for market and feeding to livestock. Based on latest technologies, these machines not only reduce time of operation but also saves the labor cost. It has been observed that grains tend to last from season to season, hence we can’t digest them raw. Grains must be flaked, cracked, puffed, popped or grounded before being consumed. And with the usage of mechanical devices in crop processing it reduces the quantity of the wastage to a greater degree. There are various reasons why grains need to be processed. One of which is that it adds value to the grain which results in the development of new products or the improvement of existing ones. Processing allows grain to be mixed with supplements, thereby increasing its digestibility, and affects its palatability, digestion and passage rates. Hence there is a high demand for grains to processed. Also in a developing country like Nigeria where most raw materials and finished flour product is being imported due to the unavailability of refined grained products, this lead to inflation of the price of similar food product that depends strictly on refined grain produce. hence the need for such grains to be cultivated and processed locally so as to reduce the cost food products. One of the major type of processed grain that is widely used in our present society is flour. Flour is a powder made by grinding uncooked cereal grains or other seeds or roots (like cassava). It is the main ingredient of bread, which is a staple food for many cultures, making the availability of adequate supplies of flour a major economic and political issue at various times throughout history. Wheat flour is one of the most important ingredients in Nigeria and other various North African cultures, it is the defining ingredient in their styles of breads and pastries. Nigeria is an important market for grains with a big population. Its government is moving to achieve greater levels of self-sufficiency. Nigeria is a huge export market for wheat with a very high demand for wheat flour for the production of bread, noodles, pasta, crackers and biscuits (cookies) etc. Hence, the processing of grains is one of the most important processing activity that needs to be carried out in the agricultural sector of Nigeria. This will in turn help to boost the nation economy and serves as an avenue for job creation. This will in turn influence the prices of some processed food which requires grains as one of its major constituent. 1.2 STATEMENT OF PROBLEM In Nigeria today despite the giant strides in modernization other areas still remain quite backwards in its production and food processing industries. There’s a high demand for the supply of wheat-based food, the cassava flour import has increased over the years and with present state of the economy there is a steady rise in cost of such refined grain products. Hence this has resulted to the emerging need for these refined grain product such as flour to be produced locally. There are various traditional or indigenous way of processing grains in our rural areas, one of which is, by pounding the dried grains in a mortar with a pestle and sieving it with a screen, but this can no longer meet the demand for the refined grain flour. Although there have been some mechanized methods adopted by small scale farmer and food processing unit, but this method has proven to be time and energy consuming and does not result in high quality grade produce and are bulky and therefore avoided by the indigenous manufacturers. Some of these machines only provide on function, either grinding or sieving, therefore are not feasible, since some part of the process still needs to be carried out manually. Also, the existing mills such as the attrition mill, the hammer mill used by some industries show some inefficiency. Such inefficiencies are: Inability to produce uniform grind of the refined grain flour. Time taken to crush material to the size of the screen as in the hammer mill. Contamination of refined grain flour due to multi-purpose nature of the mill, particularly in non-specialized production processes To solve this problem a machine is needed that can process the major function of grinding, sieving and storage. It has to be affordable and reasonably small in size, to allow use by average indigenous farmers in grain processing. Without these, unrefined grains will have little value in the commodity market. 1.3 OBJECTIVE OF STUDY The main objective of this project is to design and fabricate a modified milling machine which combines both impact and shearing milling action coupled with a pneumatic conveying and clarifying action. The combined action is intended to lead to efficient milling of grains into fine powder. Unlike the normal hammer mill, it does not use a screen classifier; rather it employs air classifier in which the fine product is carried in the air-stream through the blower’s chamber. Also, less time is required for pulverization and due to the air-tight nature, dust spillage is minimized. The air circulating in the machine helps to cool the processed flour which improves the Quality of the flour produced. This project has the following specific objectives To develop a compact and portable in size allowing for easy transportation and less installation space. To design a mill pulveriser, which will be cost effective, and reasonably affordably. To fabricate a mill which will be easy to operate and maintain incorporated to vibration and noise. To design a pulveriser which will reduce the time of production and easy to operate and maintain. To develop a fully integrated machine which will be able to pulverize various grains and transport them to a storing unit for further processing and packaging. 1.4 JUSTIFICATION OF STUDY Engineering and technological advancement in our society has helped improve the standard of living in our present day world. Grain processing plays a key role in the socio-economic development of most west African countries. In Nigeria refined grains flour are used for the production of bread, noodles, pasta, crackers and biscuits (cookies). This has contributed to Nigeria’s wheat market which was estimated at just under $1 billion in U.S. exports as of 2010. Also the Demand for other grains such as corn, sorghum, millet is also very high but, there is a Production deficit of processed grains locally which results to the importation of various refined grains. However, Nigeria has a potential to increase its production through the application of improved processing methods and better marketing (Gourichon H, 2013). In most food processing industries, Conventional hammer mills that are extensively employed in the processing of solid minerals and grains suffers from a number of weaknesses that greatly hamper their productivity, efficiency and effectiveness. These weaknesses include the following The conventional hammer mill cannot produce materials whose particle size is less than 400µm. For the most commonly processed food minerals like grains, tubers, cassava, etc. The particle sizes produced are relatively large and they cannot be directly used for processing grains as flour to make bread, biscuit and foo-foo for local consumption [Beintema and Stads, 2004], [Eyo, 2008]. The fineness of the particles produced depend on the hole size of the screen sieve employed. Large particles can block the holes of the sieve screen thereby, reducing the output of the hammer mill. To maintain the output, the screen sieves are continuously changed. Hence, it requires the acquisition of a lot of expensive accessories which cannot be produced locally. Excessive dust particles are usually released into the atmosphere where hammer mills are operating. This constitutes a health hazard for the human operators and environmental pollution for the surrounding plants, animals and human communities. The defects and shortcoming of currently used hammer mills have meant that most hammer mill operators and owners in Nigeria are running their business at marginal profit levels. This is because virtually all the hammer mills being utilized are of old designs and pulverization is not achieved in these systems. 1.5 SCOPE OF STUDY This project will detail the process of manufacturing an integrated mill pulveriser for grain processing as carried out by the students involved in the project work. It will consider the steps of manufacturing and possible limitations and draw backs that may arise as a result of the production and manufacturing processes. It will also consider the design that should be incorporated into the design of the blower so as to obtain maximum efficiency during pulverization. The mill pulveriser is basically used for agricultural application and other various area of manufacturing where the need is of high importance. 1.6 LIMITATION OF STUDY The main constraint in this project can be said to be the availability of necessary funding. Due to the fact, that this is a manufacturing project, the procurement of raw materials, metal sheets, motor, suction blades and other components necessary for the completion of the machine requires considerable funds. CHAPTER TWO 2.0 LITERATURE REVIEW 2.1. A REVIEW ON GRAIN PROCESSING The use of grinding machine is one of the oldest and simplest methods of processing agricultural raw material alternative to the traditional methods of grain processing using stone, mortar and pestle. However, in considering the food processing industry, it has been characterised by a labour and production output shortage due to the lack of support by the government and the ideology on the pursuit of white collar jobs by most Nigerian graduates. Nigeria now due to the failing of its agricultural sector now depends on mostly imported refined grains to meet up with the high demand and shortage of processed food. Although there have been recent developments which has led to the Mechanization of most field activities in agriculture, and to a certain extent it has overcome some basic challenges faced by small scale farmers and local food processing industries. The advancement of science and technology reduces complexities from many agricultural processes. Modern technologies in area of irrigation, plantation, harvesting, has made the entire agricultural cycle more economical and easier than ever. This led to the fabrication of various machineries such as feed mill, grain dryers, rice huller, winnowing machine, threshing machine etc. These machines are co Mechanization was not only used to replace human labour but also increased productivity and the areas covered. Over the years there have been various modification made on theses equipment so as to increase its output efficiency and specialization. Thus the development of a mill pulveriser. This system consists of a conventional hammer mill integrated with a blower and a sieve. Which aids the pulverization by making only fine grounded grain particles is being covey through its passage unit and stored. A mill pulveriser is a modification of a hammer mill that utilizes air flow to separate various particles. The development of a mill pulveriser incorporates the design of a hammer mill and a blower. A hammer mill is a type of crusher, which can be used for grinding rock, forage, grains or other large size particles into smaller pieces by the repeated blows of little hammers. It is designed to convert larger pieces of material into smaller particle sizes. 2.2 HISTORY OF HAMMER MILL The invention of hammer mill dates back to the 4th century around Zhao dynasty period in china (1050 BC -221 BC). The invention, involved conversion of rotary water wheel energy to linear trip hammer energy. The trip hammer evolved out of the use of mortar and pestle which in turn gave rise to the tilt-hammer and then trip hammer device. This device was used in the pounding and polishing of grains, which help reduce the labour of pounding manually with hands and arms. In Chinese mythology Fu Hsi was said to have invented the pestle and mortar, which is so useful, and later on it was cleverly improved in such a way that the whole weight of the body could be used for treading on the tilt-hammer, thus increasing the efficiency ten times. Afterwards the power of animals donkeys, mules, oxen, and horses was applied by means of machinery, and water-power too used for pounding, so that the benefit was increased a hundredfold. (Caves Books Ltd 1986). Although Chinese trip hammers in China were sometimes powered by the more efficient vertical-set waterwheel, the Chinese often employed the horizontal-set waterwheel in operating trip hammers, along with recumbent hammers. The recumbent hammer was found in Chinese illustrations by 1313 AD, with the publishing of Wang Zhen's Nong Shu book on ancient and contemporary (medieval) metallurgy in China. There were also illustrations of trip hammers in an encyclopedia of 1637, written by Song Yingxing (1587–1666). This gave rise to future designs which has evolved over the years. A patent was first issued in 1830 for a machine with a wooden box containing a cylindrical drum, revolving at 350 revolutions per minute, on which hammers were attached. The machine was designed to shatter any rock fed into the box. This machine never went into commercial production, but is considered as the forerunner to the hammer mill. The hammer mill has gone on to become the most widely used crusher utilizing high-velocity impacts to break rocks. However, while initially designed to crush rocks, the hammer mill was adapted for grinding grain for livestock feed. It was discovered that many types of forage benefit in nutritive value after being broken down. The Gehl company produced the first grain grinding hammer mill in the 1920s. It dominated the market for 30 years, during which time it also developed a portable truck mounted mill. Developing a Screenless Hammer Mill In 1990, Carl Bielenberg of Appropriate Technology International (ATI) began developing a screenless hammer mill. His prototype separated flour from larger particles through an opening in the circumference of the grinding chamber. Flour passed through the opposite side of the rotating blades while the larger pieces continued inside the chamber. Initial tests produced a larger, courser material than conventional hammer mills. He developed a series of improvements, but was incapable of designing a machine that could perform to the standards of conventional mills. He presented his machine to a series of MIT students in hopes that they could produce a more successful machine. An MIT student named Amy Smith headed the project. Her redesigned mill was capable of running continuously without clogging. It was also capable of being manufactured in a small village workshop. This second aspect was extremely important to Smith. After discovering the failings of conventional hammer mills, she was determined to develop a machine that would be useful for third world countries. Many African women used the hammer mill to grind grain, but its screen was prone to breaking. Screens cannot be produced locally and are expensive to replace. So Smith dedicated her research to “the African women who cannot afford the 5 cents it takes to mill a kilogram of flour and thus spend hours performing the back-breaking labour necessary to prepare food for their families. Hence the development of screenless hammer mill also known as a mill pulveriser 2.3 What is a Mill? A mill is a device that breaks solid materials into smaller pieces by grinding, crushing, or cutting. Such comminution is an important unit operation in many processes. There are many different types of mills and many types of materials processed in them. Historically mills were powered by hand (e.g., via a hand crank), working animal (e.g., horse mill), wind (windmill) or water (watermill). Today they are usually powered by electricity. The grinding of solid matters occurs under exposure of mechanical forces that trench the structure by overcoming of the interior bonding forces. After the grinding the state of the solid is changed: the grain size, the grain size disposition and the grain shape. Milling could also be referred to the process of breaking down, separating, sizing, or classifying aggregate material. For instance, rock crushing or grinding to produce uniform aggregate size for construction purposes, or separation of rock, soil or aggregate material for the purposes of structural fill or land reclamation activities. Grinding may serve the following purposes in engineering: increase of the surface area of a solid manufacturing of a solid with a desired grain size pulping of resources. For the purpose of our study we will be considering majorly mill pulveriser. Which is the most effect type of mill for achieving high quality refined grains. A conventional mill pulveriser is a device consisting of a rotating head with free- swinging hammers, which reduce rock, grains or similarly hard objects to a predetermined size through a perforated screen [Sci-Tech Dictionary, 2003]. A mill pulveriser commonly known as a screenless hammer mill is like a regular hammer mills, is used to pound grain. However, rather than a screen, it uses air flow to separate small particles from larger ones. Conventional hammer mills in poor and remote areas, such as many parts of Africa, suffer from the problem that screens break easily, and cannot be easily bought, made or repaired. Thus regular hammer mills break down and fall into disuse. The screenless hammer mill uses air flow to separate small particles from larger ones, rather than a screen, and is thus more reliable. The screenless hammer mill is claimed to be 25% cheaper and much more energy efficient than regular hammer mills, as well as more reliable. Hammer mills pulveriser are widely utilized in the agricultural, wood, mining and chemical industries. The vast majority of Nigerians live in the rural areas [Okpala,1990] and are predominantly engaged in agriculture[Anifowoshe,1990]. Nigeria is blessed with equatorial [Morgan and Moss, 1965], tropical [Clayton, 1958], guinea [Jones, 1963], sudan [Olajire, 1991] and sahel [Pande, et al, 1993] climatic zones; thus making her suitable for the profitable cultivation and production of a wide variety of grains [FAOSTAT,2004]. The farmers rely on ancient and antiquated methods that are inefficient for storing the grains and processing [Biewar, 1990], [Igbeka and Olumeko, 1996], [Adejumo and Raji, 2007], and thus lead to large storage losses due to rodents, damp, fungi and natural decay [Agboola, 1992], [Agridem, 1995]. Furthermore, the grains and other similar farm products in their unprocessed states are bulky, difficult to transport and fetch very low prices in the market [Dixon, et al, 2001], [Taylor, et al, 2006]. This is a major cause of poverty amongst rural farmers [Killick, 1990], [Umoh, 2003] that encourages rural-urban migration [UNEP, 2006]. Thus, to guarantee access to food [Simon, et al, 2003], [Sanchez, et al, 2005], reduce rural-urban migration and encourage sustainable development [Barber, 2003], [Altieri, 2004], the processing of agricultural products like grains or solid minerals like clays and feldspars into more valuable products by the use of hammer mills must be encouraged and fostered. GRAIN PROCESSING EQUIPMENTS In many countries worldwide, grain processing is of economic importance, producing flour and cereal from the refined grain. In addition, with success small farming and micro food processing unit has evolved over the years in developing countries and utilises the use of some basic equipment’s. Grain processing equipment’s used in refining grains may be classified by speed, as follows Low Speed Medium Speed High Speed Low Speed mill A low speed mill utilizes the principle of impact and attraction. An example of a low speed mill is the Ball and tube mills. A ball mill is a pulveriser that consists of a horizontal rotating cylinder, up to three diameters in length, containing a charge of tumbling or cascading steel balls, pebbles, or rods. A tube mill is a revolving cylinder of up to five diameters in length used for fine pulverization of ore, rock, and other such materials; the material, mixed with water, is fed into the chamber from one end, and passes out the other end as a slurry. Both types of mill include liners that protect the cylindrical structure of the mill from wear. Thus the main wear parts in these mills are the balls themselves, and the liners. The balls are simply "consumed" by the wear process and must be re-stocked, whereas the liners must be periodically replaced. The ball and tube mills are low-speed machines that grind the grain with steel balls in a rotating horizontal cylinder. Due to its shape, it is called a tube mill and due to use of grinding balls for crushing, it is called a ball mill, or both terms as a ball tube mill. The grinding in the ball and tube mill is produced by the rotating quantity of steel balls by their fall and lift due to tube rotation. The ball charge may occupy one third to half of the total internal volume of the shell. The significant feature incorporated in the mills design is its double end operation, each end catering to one elevation of a boiler. The system facilitated entry of raw grains and exit of pulverized fuel from same end simultaneously. This helps in reducing the number of installations per unit. Medium Speed mill This type of mill consists of two types of rings separated by a series of large balls, like a thrust bearing. The lower ring rotates, while the upper ring presses down on the balls via a set of spring and adjuster assemblies, or pressurised rams. The material to be pulverized is introduced into the centre or side of the pulveriser (depending on the design). As the lower ring rotates, the balls to orbit between the upper and lower rings, and balls roll over the bed of grain on the lower ring. The pulverized material is carried out of the mill by the flow of air moving through it. The size of the pulverized particles released from the grinding section of the mill is determined by a classifier separator. If the refined grain is fine enough to be picked up by the air, it is carried through the classifier. Coarser particles return to be further pulverized. Vertical spindle roller mill Similar to the ring and ball mill, the vertical spindle roller mill uses large "tires" to crush the grain seeds. These mills are usually found mostly in large food processing plants. Raw grains and minerals are fed through a central feed pipe to the grinding table where it flows outwardly by centrifugal action and is ground between the rollers and table. Hot primary air for drying and grain transport enters the wind box plenum underneath the grinding table and flows upward through a swirl ring having multiple sloped nozzles surrounding the grinding table. The air mixes with and dries grains in the grinding zone and carries pulverized grain particles upward into a classifier. Fine pulverized grains exit the outlet section through multiple discharge pipes leading to the storage unit, while oversized grain particles are rejected and returned to the grinding zone for further grinding. Pyrites and extraneous dense impurity material fall through the nozzle ring and are ploughed, by scraper blades attached to the grinding table, into the pyrites chamber to be removed. Mechanically, the vertical roller mill is categorized as an applied force mill. There are three grinding roller wheel assemblies in the mill grinding section, which are mounted on a loading frame via pivot point. The fixed-axis roller in each roller wheel assembly rotates on a segmentally-lined grinding table that is supported and driven by a planetary gear reducer direct-coupled to a motor. The grinding force for grain pulverization is applied by a loading frame. This frame is connected by vertical tension rods to three hydraulic cylinders secured to the mill foundation. All forces used in the pulverizing process are transmitted to the foundation via the gear reducer and loading elements. The pendulum movement of the roller wheels provides a freedom for wheels to move in a radial direction, which results in no radial loading against the mill housing during the pulverizing process. Depending on the required grain fineness, there are two types of classifier that may be selected for a vertical roller mill. The dynamic classifier, which consists of a stationary angled inlet vane assembly surrounding a rotating vane assembly or cage, is capable of producing micrometre-fine pulverized grain particles with a narrow particle size distribution. In addition, adjusting the speed of the rotating cage can easily change the intensity of the centrifugal force field in the classification zone to achieve grain fineness control real-time to make immediate accommodation for a change in fuel or boiler load conditions. For the applications where a micrometre-fine pulverized grain is not necessary, the static classifier, which consists of a cone equipped with adjustable vanes, is an option at a lower cost since it contains no moving parts. With adequate mill grinding capacity, a vertical mill equipped with a static classifier is capable of producing grain fineness up to 99.5% or higher <50 mesh and 80% or higher <200 mesh, while one equipped with a dynamic classifier produces refined grain fineness levels of 100% <100 mesh and 95% <200 mesh, or better. 2.4 Mill pulveriser utilization in Nigeria These machines were originally designed and manufactured in Britain and the United States of America in the early 1930’s (Lynch and Rowland, 2005). They were brought into Nigeria by the tin mining companies in Jos and were copied by local artisans. Since then, there have been no significant improvements in their design or method of operation. The lack of innovation in the areas of design and operating principles of hammer mills has constituted the greatest hindrance facing the growth of solid minerals and grains processing industries in Nigeria. Although it is known that highly efficient, economical and fast speed models of hammer mills and pulveriser are being utilized in the chemical, powder, nuclear and food or grain processing industries, a recent search on the internet revealed that there is no single drawing of any type, model or prototype available on the web. This implies that manufacturers of this equipment regard their designs as proprietary. Moreover, there are no published articles describing the working principles of these new designs. Thus, a successful growth and development of the solid minerals and grains processing sector of the Nigerian economy would depend largely on the design and fabrication of indigenous machines and equipment [Spangenberg, 2002]. These would be machines and equipment whose technology, maintenance, replacement, upgrading, efficiency and reliability are well understood and undertaken locally without the need for minimal contribution from any foreign expert or technology. This paper reports on the design and construction of a hammer mill with end suction lift capability and hopes that the commercialization and widespread application of the device will contribute significantly to the growth of the grains processing industries in Nigeria. The problems experienced by the refined grain production include the following: (a) Design faults (b) Construction faults (c) Difficulty of financing (d) Operational problems due to incorrect screen size or poor maintenance and (e) Organizational problems arising from the differences of approaches and lack of coordination. All these aspects need to be taken into account. Therefore, the general design was based on the process of allowing a strong and durable metallic object inform of hammers to beat any material that obstruct its way during operation, thereby resulting into breakage of the material which can also be referred to as size reduction in comminution operation. This usually occurs in an enclosed chamber called the crushing chamber. From which it falls through a sieve located directly under the crushing chamber which is then transported with the aid of a suction compressor fan which will help to transport the crushed grains into a storage unit. The physical and mechanical properties of the mineral to be crushed were studied as this would help immensely in the design of various components of the rotor. The engineering properties and some other parameters are the main factors considered before design of the machine. CHAPTER THREE 3.0 RESEARCH METHODOLOGY 3.1 INTRODUCTION Design is the transformation of concepts and ideas into useful machinery (Bernard et al., 1999). The procedures in the design and construction of the modified cassava milling machine are explained. Theoretical design and material selection: The materials for the construction of the modified cassava milling machine are: the shaft, pulley, belt, electric motor, the bearing, the mild steel plates, mild steel angle bars and mild steel cylindrical tube. These materials were selected based on the power requirement in the milling of dried cassava chips to flour. By mere feeling, it was found that cassava chips when dried to moisture content of 5% (wb) can be crushed into powder with the human fingers. Thus, the power required for its milling is low. Hammer mills for fine pulverizing and disintegration are operated at high speeds. The rotor shaft may be vertical or horizontal, generally horizontal (Perry and Don, 1998). The shaft carries hammers, sometimes called beaters. The hammers may be T-shaped element, bars, or rings fixed or pivoted to the shaft or to disks fixed to the shaft. The grinding action results from impact and attrition between lumps or particles of the material being ground, the housing and the grinding elements. It also consists of a heavy perforated screen (Henderson and Perry, 1982) which can be changed. Though it is a versatile machine and its hammer wear does not reduce its efficiency, yet the power requirement is high and it does not produce uniform grind. Common types available in the industry include the Imp Pulveriser, the Mikro Pulveriser, the Fitz Mill, etc. Another class of size reduction machines is the Ring roller mills. They are equipped with rollers that operate against grinding rings (Perry and Don, 1998). Pressure is applied with heavy springs or by centrifugal force of the rollers against the ring. Either the ring or the rollers may be stationary. The grinding ring may be in a vertical or a horizontal position. Ring-roller mills also are referred to as ring roll mills or roller mills or medium-speed mills. Ring-Roller mills are more energy efficient than hammer mills. The energy to grind grain to 80% passing 200 mesh was determined as: hammer mill-22hp/ton; roller mill- 9hp/ton (Luckie and Austin, 1989). Common types available include the B/W Pulveriser and the Roller Mill. The third class available is the Attrition Mills. The disc attrition which is sometimes called the Burr mill consists of a set of two hard surfaced circular plates pressed together and rotating with relative motion (Onwualu et al., 2006). Stones are replaced by steel disks mounting interchange metal or abrasive grinding plates rotating at higher speeds, thus permitting a much broader range of application. They are used in the grinding of tough organic materials, such as wood pulp and corn grits (Perry and Don, 1998). Grinding takes place between the plates, which may operate in the vertical or horizontal plane. The material is fed between the plates and is reduced by crushing and shear. Though the power requirement is low, operating empty may cause excessive burr wear and a lot of heat is generated during shearing action. The objective of this study is the development of a modified milling machine which combines both an impact and shearing milling action with a pneumatic conveying and clarifying action. The combined action is intended to lead to lead to efficient milling of cassava into fine powder. Unlike the normal hammer mill, it does not use a screen classifier; rather it employs air classifier in which the conceptual design was based on the principle of design by analysis (Nortion, 2006). The methodology was to introduce special features into the hammer mill pulveriser so that certain lapses noticed in the convectional hammer mill is reduced to a bearable level. 3.2 LIST OF PARTS The major components of the new hammer mill are Inlet tray, Throat, Magnetic chamber, Rotor, Crushing chamber, Hammer mill body, Hammers/Beaters, Screen, Bearings, Blower/ fan compresor Discharge tank, Table or stand, Mechanical drive, Pulleys. Inlet tray/Hopper: This is the pathway through which the material to grinded will be pour into the hammer mill. The inlet tray was fabricated with a 3mm thickness metal plate (Mild steel). The tray was braced on the sides by 1inch by inch angle iron of the same dimension. Inside the tray we have a gate which is used in regulating the flow of feed into the crushing chamber of the hammer mill. Throat: This provides the passage for the material to be grind into the crushing chamber. This was also fabricated with 3mm thickness metal plate. Rotor: This is shaft of 30mm diameter that is holding 3 circular discs of diameter 90mm and is these circular discs that are carrying the hammers/beaters. Crushing chamber: This is unit houses the rotor that holds the beaters and the screen for sieving. Hammer mill body: This was made of 3mm thickness plate with dimension 400mm length & 215mm width & height 420mm. The hammer mill body is made in such a way that it can easily be assembled & disassembled. Hammers/Beaters: The hammers/beaters are a rectangular 3mm thickness metal that does the grinding of material. It is 85 x 30mm in dimension with a drill hole of 12mm at 30mm interval from both ends. Screen: The screen act as a sieve for grinded materials before it will be finally discharged. It was fabricated with 6mm thickness metal plate with many drilled hole which will act as the sieve for the grinded material. Bearings: The bearings provide sliding motion between the main shaft and the shaft holding the hammers. Discharge: This is the section through which the grinded material will be passed out it will also be made with a 3mm thickness metal sheet. Table or stand: This is the platform on which the whole machine is mounted. It was made with mild steel I-beam. It was made of 2 inches by 2 inches’ angle iron. It is the base to which the hammer mill body and the prime mover is bolted Mechanical drive: A 5.5Hp, 3600rpm petrol engine was used as the prime mover of the machine through belt transmission. Pulleys: Two pulleys were used for this machine which was the driver and the driven pulleys respectively. The driver pulley is mounted on the mechanical drive engine while the driven pulley is mounted on the rotor of the hammer mill machine. 3.3 DESIGN CONSIDERATIONS. Determination of the Shaft Speed The transmission system used is belt transmission via a pulley (specifically v-belt selection) using a mechanical drive petrol engine of 3600rpm with pulley of diameter 130mm (D1) and the diameter on that of the rotor is 198mm (D2). Thus to calculate the shaft speed, the following parameters are used: ………………………(1) Where N1 = revolution of the smaller pulley, rpm. N = revolution of the larger pulley, rpm. This shaft speed is only obtained when there is no slip condition of the belt over the pulley. When slip and creep condition is present, the value (3600 rpm) is reduced by 4% Determination of the Belt Contact Angle The belt contact angle is given by ……………………… (2) [Hollowenko et al, 2004] Where R = radius of the large pulley, mm r = radius of the smaller pulley, mm The angles of wrap for the pulleys are given by ……… (3) [ Hollowenko et al, 2004] ……… (4) [Hollowenko et al, 2004] Where α1 = angle of wrap for the smaller pulley, deg α 2= angle of wrap for the larger pulley, deg μ a/sin ½ Comparing the capacities, e θ of the pulley, Where μ = coefficient of friction between the belt and the pulley = 0.25 (assumption); = angle of groove ranges from 300to 400. Assume = 400 (Joseph E. Shigley, Choles R.Mischke: Mechanical Engineering Design, 2001) and o Using μ = 0.25; Θ = 40 0.25 x 3.04/sin20 For the smaller pulley e = 9.22 0.25 x 3.04/sin20 For the larger pulley e = 10.68 Since that of smaller pulley is smaller, the smaller pulley governs the design. 2.1.3. Determination of the Belt Tension The belt tension is given below [Khurrmi and Gupta, 2007] Maximum Tension in belt ……………………………(5) Centrifugal Tension in belt …………………………… (6) ……………………………(7) To get tension in slack side using the relationship below ………………………………(8) Where T1 = the tension in the tight side of belt, N T2 = the tension in the slack side of belt, N S1 = the maximum permissible belt stress, MN/m The allowable tensile stress for leather belting is usually 2-3.45MPa [3] Let 2.4MPa = 2.4 M = mass per unit length of belt Let = belt density = 1000kg for leather belt A = area of belt, B=Belt breadth= 12.5mm T=belt thickness= 8mm v = linear velocity of belt V = N = speed of motor = 36006rpm, d= diameter of motor pulley=130mm = centrifugal force acting on the belt 2.1.4. Determination of the Torque and Power Transmitted to the Shaft Power required by the shaft is given by …………………………(9) 1hp = 0.75kw Maximum power of petrol engine is 5.5hp and power required by engine is 3.23hp so 2 hp was an appropriate selection. Torque at the main shaft is given by ……………………(10) Determination of the Hammer Weight ……………………………(11) It can be seen that the action of the weight of hammer shaft on the main shaft is negligible. Determination of the Centrifugal Force Exerted by the Hammer Centrifugal force exerted by the hammer can be calculated as given by: ……………………… (12) Hammer Tip speed ……………………… (13) The angular velocity of the hammer is given by ……………………… (14) The centrifugal force on the hammers, Fh, is given by ………………… (15) Where, = centrifugal force = number of hammers = mass of each hammer = radius of hammer = angular velocity of hammer Assuming inelastic impact between the hammers and material, the velocity of material, Vm, given by ........................................(16) . Where = velocity of material being milled = mass of material being milled = number of material impacted The minimum width of hammer, wh, to withstand the centrifugal force at impact is given by ............................. (17) Where = width of hammer = diameter of hammer = thickness of hammer = working stress on hammer Determination of the Hammer Shaft Diameter The bending moment on the shaft is given by …………………… (18) References Rei Reinhardt H. Howeler, Christopher G. Oates and Antonio Costa Allem, Strategic environmental assessment: an assessment of the impact of cassava production and processing on the environment and biodiversity. Food and Agricultural Organisation of the United Nations /International Fund for Agricultural Development, Rome, vol. 5: 7, 2001. Kolawole,P.O., Agbetoye, L.A.S. and Ogunlowo, S.A., Sustaining world food security with improved cassava processing technology: The Nigeria Experience, 2010. Stephen, K.A. and Eric, K.G. Modification of the designs of cassava grating and cassava dough pressing machines into a single automated unit. European Journal of Scientific Research 38(2):306-316, 2009. Nyerhovwo, J.T. Cassava and the future of starch. Electronic Journal of Biotechnology 7(1), 2004. Stephen. A. and Eric, K.G., Modification of the design of cassava grating and cassava Dough pressing machine into a single Automated Unit. European Journal of Scientific Research. 38 (2): 306-314, 2009. Anderson, S. 1994. Large Rotor High Speed Hammermills: Beyond Screen Size. Feed Management, Vol. 45, No. 9, 20-22. Bliss, B. 1990. Hammermilling Technology. Bliss Industries, Inc., Ponca City, OK. Goodband, Robert, Mike Tokach, and Jim Nelssen. 1995. The effects of diet particle size on animal performance. Cooperative Extension Service, MF-2050. Kansas State University, Manhattan. Igbeka, J. C., Jory, N. and Griffon, D., Selective mechanization for food processing. Journal of Agriculture Mechanization in Asia and Latin America 23(1):45-50, 1992. Odighoh, E. U., grain production, processing and utilization. In Chan Jr., H.T. (Ed.), Handbook of Tropical Foods. Marcel Dekker, Inc., 145-200, 1983. Olayeni O.O., Gender analysis of training needs on the prevention of hazards associated with processing in Osun State, Nigeria. Unpublished M.Sc. thesis Obafemi Awolowo University Ile-Ife, 75. 2012. Omolehin, R.A.;Ogunfiditimi, T.O. Adeniji, O.B., Factors influencing adoption of chemical pest control in cowpea production among rural farmers in makarfi local government area of Kaduna state, Nigeria. 54-56, 2007. Ogunjimi, S. I., K.S. Obaniyi and Adedeji I. A, Peri-urban and urban farmers’ perceptions of mini-livestock farming in southwestern Nigeria. The international journal’s Research Journal of Social Science and Management. 02(02):81-83 June-2012, Jibowo A.A., Essentials of Rural sociology. Gbemi Sodipo press, Abeokuta, Nigeria. ‘Second Impression, pp 229-236, 2000. Rogers E. M, Shoemaker P.C., Diffusion of innovations. The Free Press of Glancoe, N.Y., pp 367. Adesoji S. A., Assessment of Fish farming management practices in Osun state Nigeria PhD Thesis Obafemi Awolowo University. 4-10, 2009. Ajala, A.O., Ogunjimi, S.I and Farinde, A.J., Assessing the effectiveness of improved cassava production technologies among cassava farmers in Osun state, Nigeria Wudpecker Journal of Agricultural Research 1(7):281-288, August 2012. Kehinde, A. T. Adefemi, J.O. Tayo, O.S. Michael and O.A. Obafemi Technology Choice and Technical capacity in grain Production. Food Reviews international, 7 (1): 89, 2007. Davies, R.M., M.O. Olatunji and W. Burubai, Mechanization of maize Processing in Iwo Local Government Area of Osun State, Nigeria. World Journal of Agricultural Sciences 4 (3): 341-345, 2008. 33