Hammer mills, description, mechanism, application and efficiency

1. HAMMER MILLS
A SIZE REDUCTION MILL
A short description
UNIT OPERATION
Prosanta Dev Nath,
Chemical engineering,
KUET

2. HAMMER MILLS
The type of mills which uses
a series of hammers mounted
on the machine shaft for
size reduction by the method
of rapid impact , is called the
Hammer Mill
Introduction

3. SIZE REDUCTION
It is a mechanical process by which too coarse bulk particles are converted into small fine
powers
It can be done by completely two stage processes
1. Crushing
2. Grinding
Reducing coarse lumps or aggregates of several feet to a size
no smaller than ½ or ¾ inch (13-19 mm). It is usually done dry.
Reducing small particles of size range ½ or ¾ inch to sizes
as small as several microns. It can be done both wet & dry.

4. MECHANICAL SEPARATION
 It is the fractionation of feed crushed material
from bulk particles.
 It is mainly assisted by size reduction

5. HAMMER MILLS
(DESCRIPTION)
Hammer mills are whole purpose machines that are designed to crush, grind, and
mill material
They are also called the cereal processor as they were widely used for food grinding at
ancient time
The method that hammer mills uses for grinding is Impact Method
Impact method
Particles collide by a single rigid force

6. EFFECTING FACTORS &
EFFICIENCY
For determining the efficiency, we find three most contributing factor-
Under all conditions high reduction ratios are obtained
But a high rotor speed with a low to moderate feed rate is found to give better performance of
the mill.
How much is the size reduction, lose of material and power consumption, illustrates the
efficiency of the mill.
1.The feed rate
2. Rotary speed(rpm) of the mill.
3. Size of screen

7. EFFECTING FACTORS &
EFFICIENCY
Regarding size distribution, an study shows us that the hammer mill products are
observed to exhibit Rosin–Rammler type size distribution.
1
This indicates narrow distribution, product max. fine particles.
≅
Last for power consumption, power capacity of hammer mills vary according to the
application. The industrial hammer mills use the electric motor of power over 2000 to
5000 horsepower.
D10=10% particles are smaller
D90=90% particles are larger
𝐷90
𝐷10

8. Advantages Limitations
1. Rapid in action & capable of grinding
many types of materials
2. Easy to install& operate and operation
is continuous
3. Little contamination of product
4. Particle reduction size can be easily
controlled by speed of rotor, hammer
type, size & shape of the screen
1.Heat build up is more,
product degradation is
possible
2.Can not be employed to mill
sticky, fibrous and hard
materials
3. Screen gets clogged

9. DIFFERENT PARTS OF HAMMER MILLS

10. MECHANICAL CONSTRUCTION
HAMMER MILL

11. Material Inlet : Through the inlet, materials are passed to the milling chamber.
Short Description Of The Parts
Hammer & Chain Shaft Assembly : There are three parts in this assembly –
3. Link Shaft : It rotates along with the hammers connected with chains.
2. Heavy-duty Chain : It connects the hammers with the link shaft.
1. Hardened Hammers : Hammers are the main component for size reduction of
materials which breaks, grinds or blends the materials. For double rotor chain hammer,
hammer mill features two rotors with 84 hammer.
For single rotor chain hammers, it features 36 or 72 hammers

12. Heavy-duty Casing : It is the casing of hammer and chain shaft assembly. It is typically
made of heavy-duty steel or stainless steel. Some are also made with steel with other
double material like tungsten carbide for increasing durability, strength and resistance to
corrosion.
Short Description Of The Parts
Removable Screen :Typically located at the bottom of the mill. The
screen covers the full width of the mill and is held in place by a
retaining plate at the base of the grinding chamber. The size of the
screen openings can be adjusted to control the size of the final product.
Fig: Removable screens

13. Roller Bearing : It reduces the friction during the rolling motion of the shaft.
Mounting Base : It provide supports for the other parts of hammer mill.
Drive Motor : An electric motor drives the hammer mill which rotates the link shaft
and the hammers.
Drive Guard : It guards the rotor and the drive belt.
Short Description Of The Parts

14. 𝐖𝐨𝐫𝐤𝐢𝐧𝐠 𝐏𝐫𝐢𝐧𝐜𝐢𝐩𝐥𝐞 𝐨𝐟 𝐇𝐚𝐦𝐦𝐞𝐫 𝐌𝐢𝐥𝐥

15. 𝐖𝐨𝐫𝐤𝐢𝐧𝐠 𝐏𝐫𝐢𝐧𝐜𝐢𝐩𝐥𝐞 𝐨𝐟 𝐇𝐚𝐦𝐦𝐞𝐫 𝐌𝐢𝐥𝐥
Hammer mills work on the straight forward principle that most materials will crush,
shatter and pulverise upon impact. We can describe the whole process of a hammer mill
in 3 steps -
Feeding mechanism:
Crushing
Pulveriser screen

16. 2. Crushing: When the material are fed into the crushing chamber,
they are struck by ganged hammers (typically rectangular pieces of
hardened steel) which is attached to a shaft that rotates at a high
speed, generally around 2000-6000 rpm. The material is crushed
or shattered by a combination of repeated hammer impact,
collision with the wall of the crushing chamber and particle on
particle impact.
1. Feeding mechanism: Materials that need to be crushed fed into the crushing chamber
through the feed chute typically by gravity or metered feeding system
𝐖𝐨𝐫𝐤𝐢𝐧𝐠 𝐏𝐫𝐢𝐧𝐜𝐢𝐩𝐥𝐞 𝐨𝐟 𝐇𝐚𝐦𝐦𝐞𝐫 𝐌𝐢𝐥𝐥

17. 𝐖𝐨𝐫𝐤𝐢𝐧𝐠 𝐏𝐫𝐢𝐧𝐜𝐢𝐩𝐥𝐞 𝐨𝐟 𝐇𝐚𝐦𝐦𝐞𝐫 𝐌𝐢𝐥𝐥
3.Pulveriser screen: After the process of crushing, the crushed material now is collected
and passed through a screen that filters fine and properly sized material from the coarse
material, while retaining them for a further grinding.
• The quality of the product depends on the screen size, shaft speed and the configuration
of hammer. Generally speaking, a large number of hammer, fast shaft speed and a small
screen will help make a perfect product. On the other hand, a lesser number of hammer,
slow shaft speed and a big screen will result in a coarse product.
 How do we get good products
from the hammer mill?

18. APPLICATION
HAMMER MILLS
Powder Production: In the pharmaceutical and chemical
industries, various types of hammer mills are used for
powder making. All required ingredients are crushed in
hammer mills, and an intermediate grade of powder is
obtained. Nearly precise grain size can be obtained in using
the hammer mills
Legume, grains, and food product grinding: In the food
processing industries, the hammer mills are used to grind
various types of legumes. They are mainly used to grind
soya, nutshells, groundnuts, and different types of beans.
The hammer mills with low hammer blows are used to
remove hard nutshells.
Fig: Sample of ground
particles
Fig: A section of hammer mill for
grinding
Roll 1929010

19. Speeding up the dissolution process: In chemical, food and pharmaceutical
industries, the hammer mills are used for formulation and quick dissolution. During
the dissolution, the small-sized particles dissolve faster. Therefore, hammer mills are
used for fast formulation.
Mixing solid dry and fibrous material: As this equipment mills
or reduces the average size of materials, it does the mixing at the
same time. This results in a final product with smaller particles
whole ingredients are evenly distributed within the content.
Fig: Mixing different
powders
APPLICATION
HAMMER MILLS

20. Enhances Activeness of an ingredient: Many ingredients
bring active reactions when added to certain formulations
they are slightly crushed using hammer mills to enhance
their activeness.
Fig: A curcumin powder
Easy scrapping and recycling processes: In industries like automobile and mechanical,
the hammer mills are used for scrapping purposes. The irreparable overused automobile
parts are scrapped by hammering and the crushed metal is sent for melting. The molten
material is used for new production and recycling.
APPLICATION
HAMMER MILLS