DESIGN & CONSTRUCTION OF HAMMER MILL MACHINE

Processing involves conversion of raw materials into varied forms of finished products. It is carried out in different fields of science and engineering. Agro and Agro allied industry, food manufacturing, pharmaceutical, ceramic, civil engineering industries etc are involved in processing.

The breakdown of large stones to an acceptable size for road construction is the business of the quarry industry (civil engineering). The grinding (milling) of clay materials for the purpose of production of glazes, angobes and ceramic wares eg cups, plates, wall and floor tiles is the business of the ceramic industry.

In pharmaceutical industry, a collection of different drug materials are crushed and homogenously mixed to form drugs for human consumption. In the chemical industry, certain chemicals are extracted by first crushing the raw materials to an acceptable particle size before extraction can be effectively achieved.

The process of breaking down large particles to medium size particles and in turn milling them, to micron sizes is achieved. These machines are designed on different principles eg compression, impacts, attraction etc.

In compression, the materials to be reduced in size are compressed between two metallic surfaces eg roller-shafts, thereby causing them to break to pieces. This is then carried on continuous bases to achieve high productivity in impact operations, the materials to be reduced in size are given a high radial force and are compelled to hit a metallic anvil as in cracker machines thereby achieving the breaking of the raw materials to several smaller particles. Also, the raw materials could be compelled to hit a stationary metallic surface (anvil) or could be directed to hit a dynamic (rotational) metallic hard surface eg rotational hammers thereby achieving the breakage of the raw materials.

The broken smaller materials are then run into a receiver from where they are collected and used for the desired purpose. 

In attrition principle, the materials to be broken down to smaller particles are given a rotational motion, causing them to rub against one another or against, harder materials on continuous basis. This brings about continuous wear of the materials. The worn off materials are collected later and are used for the desired purpose.

Machines used for particle size reduction include the following:

Jaw crusher

Roller crusher 

Gyrator crusher

Dry pan crusher

Back and Wilcox pulverizer

Ringroll crusher

Hammer-mill

Ball-mill

Nut crackers

Attrition mills

Micro-mills etc

The use of any of these equipments depends on productivity, particle size requirement and nature of materials to be handled. These machines could as well be employed in particle size reduction in the food processing industry. Hammer mills, micro-mills especially serve this purpose.

It is with the view to reduce the particle sizes of dry and hard materials used in products processing that necessitated the idea of designing, constructing and testing of a hammer-mill machine.

This machine has high acceptability in agro and agro-allied processing, pharmaceutical and food processing industries.

The hammer mill and micro mill machines are very much alike. The difference lies on the particle size achieved with the two machines. While the particle size achieved with the micro-mill lies in the neighbourhood of (1-30) micron, that of the hammer mill lies between (30-100) micron. The micro-mill has extra gadgets connected to it for the collection of the dust particles. Both the hammer mill and micro-mill operate at high angular velocities (speed) depending on the requirement of the materials being handled. These machines can be used to crush different kinds of dry and hard materials ranging from palm kernel shells, bones, dry seeds, coal, plastics, rubber materials and even stones.

Description and principle of operation of the Hammer mill machine:-

The assembly and hammer arrangement of the hammer-mill machine is shown in appendix.

The hammer-mill machines consist of the following components namely.

Structural base

Bottom casing

Top casing (Hammer casing)

Rotary discs

Transmission shaft

Hammers

Disc separators

Hammer hangers

Particle sieve

Transmission bearings

Drive pulley

Driver pulley

V-belts

Electric motor

Electric motor mounting

Tensioning device

Robust hinges

Inlet hopper

Inlet regulatory device

Out-let regulatory device

Bearing seats

Split pins

Locking device

Lock nuts

Lock washers

Sprang washers

Transmission key

Key seat

Bolts and nuts

Hammer mill by nature is a robust machine in order to withstand the vibration, which may arise as a result of high speed requirement of the machine. The speed range is in the neighbourhood of (2,500  10,000) rpm depending on the material being crushed.

All the components enumerated above are systematically assembled and are all carried by the structural base of the machine. The pulley on the electric motor is connected to the pulley on the shaft via the double v-belt. The shaft is suspended on bearings mounted on their sitting on the two sides of the bottom casing. The bottom casing is bolted strongly on the structural base. The hammers, discs and their hangers and separators are carried at the middle of the shaft inside the bottom casing. The bottom casing is connected to the top casing using robust hinges, so that the top casing can open in one direction only. When closed they are held together by a locking device. The parabolic top casing is open to some extent at the top. On this opening the inclined hopper with its regulatory device is connected. The hopper and the top casing form one component.

The semi-circular particle sieve is mounted inside the bottom casing. The inclined outlet channel is connected on one side of the bottom casing immediately below the sieve. Because of the incline, particles that drop from the sieve of the incline, rush down straight to the outlet channel where they are collected into a receiver. The bolts and nuts, locking devices, split pins, lock nuts are used for securing components on their correct positions.

Principle of Operation

The high speed of the electric motor is transmitted to the shaft via the pulleys, belts and bearings. The hammers at their different positions then stand upright during the high-speed operation in between the spacing discs. The walls of the casings housing the hammers and the hammers themselves are made so close that no incoming materials will escape being hammered before dropping on the sieve. The angular speed of the hammers are so high that, this is imparted on the incoming materials from the hopper, thereby splitting the materials into several small particles continuously which will then pass through the tiny holes on the sieve on to the outlet channel.

The little vibration undamped helps to push the materials from the hopper to the hammers and then the particles from the sieve to the outlet channels, thereby making the machine self-acting. The crushed materials are collected in a receiver.

Advantages:

High productivity in crushing is achieved with this machine

All the materials of construction of this machine are locally available.

The cost of construction of this machine locally is by far lower than the cost of importation.

The machine is self aching, thereby reducing operational labor.

The machine is easy to operate and requires only one operator.

Time saving is highly achieved by the use of this machine when compared with manual crushing.

The overall production cost is within the reach of an average Nigerian.

The machine can be adapted for small, medium and large scale processing enterprises.

The local design, construction and testing of this machine will encourage our scientists, engineers, technologists to aspire for higher goals in design and construction of more complicated and precision industrial machineries.

Objective

 The objective of this project is to design, construct and test a hammer mill for particle size reduction of dry and hard materials used for industrial product processing so as to enhance productivity and reduce human labor to the bearest minimum.

Scope

This machine is applied only to crushing to micron size dry hard materials. The machine when completely built and tested is expected to crush about (100-250)kg dry materials in an hour.

Methodology

  In the course of carrying out this project, the following steps of work will be followed.

1).Intensive literature survey will be carried out so as to broaden our knowledge in particle size reduction and related areas. 

2).Based on the literature review the concepts of hammer mill design will be developed. The concepts will be reviewed severally and sketches of various concepts made. Finally the required design will be developed.

3).Selection of parameters based on the adopted concept and design will be made.

4).Scientific principles, standard engineering theories, equations and data will be adopted during the design analysis.

5).Design calculations and specifications of every component of the machine will be carried out after which the assembly of the components will be done.

6).A standard blue print ie assembly and component drawings will be produced. Based on these drawings, the construction of the machine will be carried out.

7).The components will be produced one after the other in accordance with the stipulations of the blue print, after which the practical assembly of the component to form the machine will be done.

8).Test runs of the machine will be carried out. First the machine will be tested for dynamic synchronization of running parts without load. Secondly the machine will be tested again severally on load.

9).Corrections on test, non performance will be carried and characterization of the machine will be carried out based on data generated during test runs on load.