3.

4 Hammer Mill Design

A delivery device is used to introduce the material to be ground into the path of the
hammers. A rotor comprised of a series of machined disks mounted on the horizontal shaft
performs this task. - Free-swinging hammer that is suspended from rods running parallel to
the
shaft and through the rotor disks. The hammer carries out the function of smashing the
ingredients in order to reduce their particle size. - a perforated screen and either gravity- or
air-
assisted removal of ground product. Acts to screen the particle size of the hammer mill to
ensure
particles meet a specified maximum mesh size.
27
Fig 3.1 Hammer mill
3.4.1 Feeder Design
Materials are introduced into the paths of the hammers by a variable speed vein feeder.
This type of feeder can have its motor slaved by a programmable controller to the main drive
motor of the hammer mill. The operational speed of the feeder is controlled to maintain
optimum
amperage loading of the main motor.
3.4.2 Screen Design
The amount of open area in hammer mills screen determines the particle size and
grinding efficiency. The screen must be designed to maintain its integrity and provide the
greatest amount of open area. Screen openings (holes) that are aligned in a 60-degree
staggered
pattern optimize open area while maintaining screen strength. This method will result in a 40
percent open area using 3.2 mm (1/8 inch) holes aligned on 4.8 mm (3/16 inch) centres.
28
Fig 3.2 Screen degin
Feed producers need to pay particular attention to the ratio of open screen area to
horsepower. Recommended ratio for grains would be 55 cm2 (~ 8-9 inches square) per
horsepower (Bliss, 1990). Not enough open area per horsepower results in the generation of
heat.
When the heat generated exceeds 44C to 46C (120-125F), capacity may be decreased as
much as
50 percent.
The removal of sized material from hammer mill is a critical design feature. Proper output of
material affects not only the efficiency of operation, but also particle size. When the correct
ratio
of screen area to horsepower is used and proper distance between hammers and screen face is
maintained, most of the correctly sized particles will exit the screen in a timely manner.
Anderson (1994) stated the particles that do not pass through the screen holes become part of
a
fluidized bed of material swept along the face of the screen by the high-speed rotation of the
hammers. As these particles rub against the screen and each other their size is continually
reduced by attrition. This excessive size reduction is counterproductive. Energy is wasted in
the
production of heat, throughput is restricted, and particles become too small.
3.5 Hammer Design
Hammer is used inside the hammer mill to impact smash ingredients up into smaller
particles, making it more suitable for uniform mixing and usage in feed. Hammer is available
in
a huge range of configurations, shapes, facings and materials. Hammer is available as single
holed or with two holes, with two holes allowing the hammer to be used twice as the wear is
29
done to one end of the hammer; the hammers can be rotated and used a second time. The hole
fits onto a rod inside the hammer mill and swings to hit the material.
The hammer design of hammer mill is determined by operating parameters such as rotor
speed, motor horsepower, and open area in the screen. Optimal hammer design and
placement
will provide maximum contact with the feed ingredient. Hammer mill in which the rotor
speed is
approximately 1,800 rpm, should be using hammers which are around 25cm (~ 10 inches)
long,
6.35cm (~2.5 inches) wide, and 6.4mm (0.25 inches) thick. For a rotor speed of about 3,600
rpm,
hammers should be 15 to 20 cm (~ 6-8 inches long, 5 cm (~ 2 inches) wide, and 6.4 mm (0.25
inches) thick.
The number of hammers used for hammer mill of 1,800 rpm, should be 1 for every 2.5 to
3.5 horsepower, and for 3,600 rpm, one for every 1 to 2 horsepower. Hammers should be
balanced and arranged on the rods so that they do not trail one another. The distance between
hammer and screen should be 12 to 14 mm (~ 1/2 inch) for size reduction of cereal grains.
The velocity or tip speed of the hammers is critical for proper size reduction. Tip speed is
the speed of the hammer at its tip or edge furthest away from the rotor, and is calculated by
multiplying the rotational speed of the drive source (shaft rpm) by the circumference of the
hammer tip arc. See the following formula:
3.5.1 Calculations
Feed per minute= (π D×RPM) ÷12 in ft.
D=Diameter in inches
RPM=Revolutions per minute
π =3.14
30
Fig 3.3 Arrangement of hammers
A common range of tip spee ds seen in hammer mill is commonly in the range between
5,000 and 7,000 m/min (~ 16,000 and 23,000 feet per minute). When the tip speeds exceed
23,000 feet per minute, careful consideration must be given to the design of the hammer
mills,
the materials used in its construction, and the fabrication of all the components. Simply
changing
the rotational speed of the drive source is not a recommended method of increasing hammer
speed in excess of 23,000 feet per minute. Impact is the primary force used in hammer mills.
Anything which increases the chance of a collision between a hammer and a target;
increases the magnitude of the collision; or improves material take-away provides an
advantage
in particle size reduction. The magnitude of the collisions can be escalated by increasing the
speed of the hammers.
3.6 Replacing wearing items
• Upper housing
• Takeout the bolts of joining the feed chute and upper housing
• Takeout Bolts of two halves of upper housing and joining of upper and lower housing.
Also detach the felt sealing ring from upper housing.
• Now these two halves of upper housing can be tilted by means of hinge bracket. During
replacing the parts these halves are to be supported by probes. In this position the
grinding glib plates and liners can be replaced.
31
Chapter - 4
4. Lubrication & Maintenance of Bearings
Refer drawing for bearing assembly and strictly follows the instruction as per lubrication
schedule. This is to be strictly followed. Bearing blocks are filled with grease at our works to
last
for nearly 4 weeks. However, check grease before commissioning the hammer mill. In case
the
machine was idle for a long time back the bearing for any rust formation and take necessary
action to remove it. Labyrinth alloys are to be full of grease all the time. While greasing, it is
necessary to rotate the shaft so that grease gets filled up all over the periphery.
Very six months labyrinth alloys are to be washed from old grease and filled with fresh
grease. To do thus, open the covers and clean with petrol or kerosene.
Every two years of operation the bearings blocks are to be dismantled. All parts and
bearings thoroughly cleaned and checked. Reassemble with fresh grease. Too much grease
heats
up the bearing while running. During initial period check the quantity by opening the covers.
Do
not wipe-off grease from nipple after greasing cycle is over. Wipe grease nipple clean before
greasing. Depending upon local condition the greasing schedule may have to be revised in
consultation with service engineer's from bearing manufacturer.
The upper hinge point of grinding wall brackets is to be cleaned and greased every 12
months.
32
 Frequency Lubrication
Types of
Indian
points
lubrication
of
oil
lubrication
Bearing
blocks on
rotor shaft
with
labyrinth
points
violet
1450
Grms
Servo-
gem-3
Bearing
blocks on
counter shaft
with
labyrinth
points
Manual
200 hrs. Lithium
250 Grms Liti
grease gun
based
on-
bearing
3
grease
3 kk

-Do-
Upper sliding
block of
grinding gib
-Do- -Do- -Do- -Do- 800 Grms 200 Grms -
Do-
Manual
Every 4
-D0- -Do- As
As
-
-Do-
brush
weeks
required
required
Do-
Table 4.1 Lubrication chart for Hammer mill
Lubricant
properties
33

Lubricant
making
First
filling
Qty.
during
running
HP
s.no Description quantity
1 Hammer 60
2 Hammer arm 60
3 Grinding Gib (straight) 4
4 Grinding Gib (curve) 12
5 Rotor pin 1 set
6 Spring dowel sleeve 60
7 Spring dowel sleeve 60
8 Spring dowel bush 60
9 Rotor shaft 1
10 End disc no.1 (Free brg.side) 1
11 Middle disc 14
12 Spring clip 24
13 End disc no .2 (fixed brg side) 1
14 Lock nut 4
15 Lock washer 4
16 Felt seal 4
17 Brg block assembly.(Fix + Free) Without bing 1+1
18 Brg block assembly .(fix + free) Witho earing 1+1
19 Spherical roller bearing with adopter 2
Sleeve
20 Spherical roller bearing with adopter Sleeve 2
21 Liners for housing 1 seet
22 Vee belt (matched set ) 8
23 Nib bolt M 16 * 60 Lg. with nylock 240
Nut and plain washer
24 Nib bolt M 30 * 100 Lg. with plain washer, 64
Hex lock nut & hex nut
25 Motor pulley 375 PCD, 8-SPC with taper 1
Lock bush
Table 4.2 Lists Of Essentials Spare Parts
34
4.1 Hammers description
Conventional bar hammers also become less efficient and effective as they wear, since
the initially-square edges become rounded. This reduced effectiveness also increases the
tendency of the hammers to lay back, thus further reducing efficiency. The hammers must
therefore be replaced more frequently than is desirable, in order to maintain optimum
efficiency
and effectiveness.
In the invention, fewer hammers are employed these hammers are uniquely configured in
order to provide optimum performance both initially and throughout their useful life.
Two primary embodiments are described herein, although many other variations are
possible within the scope of the invention. In each embodiment, multiple impact points are
provided by tips at different radii from the axis of rotation of the hammer mill, and the tips
preferably are at substantially the same radius from the axis of rotation of the hammer about
the
hammer support shaft, so that efficiency is maintained even as the hammers lay back, as will
be
explained later herein. The multiple impact points produce a more effective result, by
partially
sizing the debris on initial impact, before more precise final sizing in the grinding chamber.
Angled surfaces on the hammer tips provide more effective shearing and tearing action than
with
conventional bar hammers. Wear patterns are such that grinding efficiency as the hammers
wears
down is maintained throughout the life of the replaceable tips.
Preferably, but not essentially, the hammers weigh substantially more than conventional
hammers, to provide a higher energy impact, and to reduce the tendency of the hammers to
lay
back.
Additional features of the invention will be described or will become apparent in the
course of the following detailed description.
Hammer mill generally has three more or less circular steel disks 32. A shaft mounted
on bearings of the frame of a grinder (not shown), extends through the center of disks. During
the operation of the grinder, shaft is rotated at approximately 1100R.pm more or less, by a
35
motor (not shown). A positive engagement between shaft and disks results in those disks
rotating
together at that same angular speed.
The hammer mill may be built to carry any desired number of hammers. Several examples
are
illustrated, namely the versions in fig-6. Hammers are generally arranged in pairs. Each pair
of
hammers is mounted in tandem on the hammer mill, although it should be clear that a mill
could
be constructed with only a single hammer at each location, or with three or more hammers at
each location, depending on the desired width of the mill.
Fig-4.1 Hammer heads type-1
Hammer mill shown in fig-6 has four 60 hammers arranged around the shaft. Each
periphery contains 12 hammers in 5 series depending on the number of hammer support
shafts or
hammers in the assembly.
36
Fig 4.2Hammer heads type-2
Two types of hammers are described as examples of the invention. The first type is shown
in fig 4.1and fig 4.2. Both types preferably but not necessarily use the same shank member.
Shank member has a central bore through which passes one of the hammer support shafts.
Although it is convenient from a manufacturing cost viewpoint to use the same shank for
each type of hammer, it is not essential that the shanks be identical nor that there is a separate
shank member at all. The hammers could be constructed with different shanks, or in one
piece if
desired, and with or without replaceable wear components. The invention is not intended to
be
limited to embodiments having a common shank, even though that may be preferable.
The shank, as seen best in fig 4.1and fig 4.2.has a tongue for engaging the remaining
portion of each hammer, as will be subsequently described. The side opposite the one side
has a
well with corrugated walls for accepting molten lead. This permits the weight of shank
members
to be maintained to within 1 gram of each other by using molten lead, that tolerance being
important for maintaining optimum hammer mill balance.
Hammers in the present invention preferably weigh in the range 8to 9 kilograms in
comparison with a prior art bar hammer weighing typically
about7kgs. Lighter hammers embodying the features of the invention could be used, and are
contemplated as being within the scope of the invention, although the results may not be as
37
impressive. Approximately 80 percent of the mass of the hammer is outside the radius of the
hammer support shaft, and the center of gravity of the overall hammer is on the center lines
shown in fig 4.2
The second type of hammer preferably uses the same shank member as the first type of
hammer, although as mentioned above, it could instead be produced as one piece. However,
the
tip portion does not have replaceable tips as in the first type of hammer, but instead has three
integral "claws", split in the middle to provide six integral tips.. The shape of the claws and
tips
is designed to rip into tree stumps and the like, the rake angle of approximately 15 degrees at
the
tips produced combined shearing and tearing action for greater efficiency. The tips of this
type of
hammer are configured to withstand heavier use than the tips of the first type, are capable of
tearing through a broader range of materials, and are not as subject to breakage when
encountering contamination such as rocks, steel, etc.
38
39
Material to be crushed : Coal Bulk density : 1.1 T/Cu.m . Moisture content of feed material :
10 – 12% (upto 20% during rainy season ) Feed size : 0 – 100 mm (0 to 50 mm with
occasionally
Coming upto 100 mm max.) Product size : - 3
mm (81 -84% ) Capacity (throughput) : 75 TPH
TECHNICAL DATA
TYPE : Reversible swing hammer with open
Bottom Size : 1212/12 Rotor diameter : 1200
mm Rotor width : 1200 mm No. of Hammers : 60 Speed : 40 M/Sec.(645 RPM) Approx. @
960 RPM
60 M/sec (965 RPM) Approx. @ 1440 RPM
Drive : Through 'V' belt & Gear coupling Motor recommended : 160 KW (215 HP)/ 1485
RPM with AC
Variable frequency drive for soft start and Variable speed. V- belt : 106 SC06300 (spec)
matched set for 8 nos. Motor pulley : 375 mm PCD -8 groove SPC with taper lock
Bush no. 5050
Machine pulley : 560 mm PCD- 8 groove SPC with taper lock
Bush no.5050
Fly wheel : 570 dia with taper lock bush no.5050
Gear coupling : 105-HI-Cliff
Gross weight : 12.0 tones (approx.)
Table 4.3 Application data of old hammer
40
Material to be crushed : Coal Bulk density : 1.1 T/Cu.m . Moisture content of feed material :
10 – 12% (up to 20% during rainy season )
Feed size : 0 – 100 mm (0 to 50 mm with occasionally
Coming up to 100 mm max.)
Product size : - 3 mm (88 -92% ) Capacity (throughput) : 75 TPH
TECHNICAL DATA
TYPE : Reversible swing hammer with open
Bottom Size : 1212/12 Rotor diameter : 1200 mm
Rotor width : 1200 mm No. of Hammers : 60 Speed : 40 M/Sec.(645 RPM) Approx. @ 960
RPM
60 M/sec (965 RPM) Approx. @ 1440 RPM
Drive : Through 'V' belt & Gear coupling Motor recommended : 160 KW (215 HP)/ 1485
RPM with AC
Variable frequency drive for soft start and Variable speed. Vee belt : 106 SC06300 (spec)
matched set for 8 nos. Motor pulley : 375 mm PCD -8 groove SPC with taper lock
Bush no. 5050
Machine pulley : 560 mm PCD- 8 groove SPC with taper lock
Bush no.5050
Fly wheel : 570 dia with taper lock bush no.5050
Gear coupling : 105-HI-Cliff
Gross weight : 12.0 tones (approx.)
Table 4.4 Application data of new hammer
41
4.2 ISO9001-2000
4.2.1 ISO Certificated for Crusher Hammer:
Crusher hammers are highly wear-resistant parts. DSMAC manufactures this type of
crusher hammers with external refining and pressure casting technologies. Manganese steel is
purer and the matrix is more compact. This crusher hammers have a service life longer than
those made of common steel and is safer to use.
4.2.2 ISO Certificated Crusher Parts Foundry Crusher Hammer Feature
• Crusher hammers casted the Tungsten Titanium alloy in the high-manganese steel
substrate, It may resist the severe grinding abrasion.
• Crusher hammers service life has been enhanced by 50% compared to the ordinary steel!
• Compared to the similar products, crusher hammers have the advantage strong wear
resistance and low price.
4.2.3 ISO Certificated Crusher Parts Foundry Crusher Hammer Application
➢ 1. DSMAC manufactures this type of Crusher Hammers with external refining and
pressure casting technologies. ➢ Crusher hammers aim at the crushing of limestone with
abnormal content of SiO2. ➢ Crusher Hammers can be used in hard condition of serious
abrasion.
Standard: ISO9001: 2008 Machine Type Crusher Deformation Temperature Casting Molding
Techniques Pressure Casting Model Number Crusher Spare Parts Material High Nickel Cast
Iron Model NO Wear Resistant Parts high nickel hammers Molding Style Stepped tapered
bar Life time 10 Months Trademark DSMAC Crushing capacity More Technology
Advantage Tungsten Titanium Alloy Application Hammer Crusher, Limestone Crusher etc.
Table 4.5 Product details of stepped taper Crusher Hammer
42
Standard: ISO9001: 2008
Machine Type Crusher
Deformation Temperature Casting
Molding Techniques Pressure Casting
Model Number Crusher Spare Parts
Material High Manganese Steel
Model NO Wear Resistant Parts high manganese hammers
Molding Style Taper
Life time 12 Months
Trademark DSMAC
Crushing capacity More
Technology Advantage Tungsten Titanium Alloy
Application Hammer Crusher, Limestone Crusher etc.
Table 4.6 Product details of taper Crusher Hammers
4.3 Advantages
➢ High and constant capacity
➢ Low space requirem ent
➢ High machine availability
➢ Long lifetime
➢ Easy replacement of wear and spare parts through hydraulic opening device
➢ Broad range of applications
➢ High reduction ratio
In case one side of the beater heads is worn, the rotor direction can be reversed by
switching the motor accordingly. This will increase the service Life of the beater heads and
reduces downtimes during maintenance procedures.
43
4.3.1 Crushing Action – Adjusting the grinding wall to the crushing radius (gap width), the
rotor Diameter, the rotor speed (m/s), and the perfect combination of these Variables are
major factors in determining the reduction ratio and productize – The grinding wall is fitted
with grinding ledges and a replaceable grate in The lower section to reduce oversized grain
4.3.2 Specification – Feed size: up to 300 mm (12 in) – Product size: up to <1 mm depending
on type and size of feed material – Reduction ratio: 1: 30 – Installed power: up to 1800 kW
(2414 hp) 4.4 Material used for preparation of hammer head 4.4.1 Cast iron
Cast irons are basically the alloys of iron and carbon in which the carbon varies
between 2.0 to 6.67%.For commercial applications the cast iron contain carbon in the range
of 2.3 to 3.75% with other elements. Various types of cast irons are available in market, but
mostly we prefer white cast iron because of more hardness and wear resistance.
4.4.1.1 Composition
Carbon - 2.3 to 3.0% Silicon - 0.5 to 1.3% Sulpher – 0.06 to 0.1% Phosphorous -0.1 to 0.2%
Nickel - 3 to 5% Chromium – 1 to 3%
4.4.2 Hammer Head Material
Steel is an alloy of iron and carbon in which the carbon content is in between 0.008 -
2%. In order to increase the hardness manganese is added to steel alloy which is called as
manganese steel.
4.4.2.1 Composition
Carbon – 1.2 to 1.8% Manganese - 10 to14% Compare to manganese steel, cast iron is having
more carbon content. So brittleness is more in cast iron. Here we require low brittle and high
hardness material in order to sustain high rubbing action. Finally we prefer manganese steel
for the preparation of hammer head.
44
Chapter – 5
Theoretical Results and Conclusions
Theoretical Result 1. Contact area of the hammer head is increased. 2. Material of hammer
head is change(cast iron to manganese steel)
Therefore, the following result is obtained
Aspects Before design After Design Crushing efficiency(<3mm) 81-84% 88-91%
Life time of Hammer head 10 Months 12 Months
Conclusion
The main aim is to convert the coal into coke, because the ash content in the coal is
more compared to coke. To improve the quality of coke, the complete combustion of coal is
required.
In order to get complete combustion of coal, the size of coal is decreased by using
Hammers. The main conclusion of this project is increasing of crushing efficiency and also
got the good quality of coke. The life of hammer head is also increased due to the change of
material (Cast iron to Manganese steel).
45
References
[1]DDBarkan, Dynamics of base and foundation, McGraw-Hill. [2]V.Kolousek et al.,
building structure under dynamic effects (in Czech), SVTL, Bratislava.1967. [3]A. Major,
Dynamics in civil engineering. Academician kiado, Budapest, 1980. [4]D.Makovicka et al..,
calculation of building structures loaded by dynamic effects of machines (in Czech),
commentary to CSN 73 0032, Vydavatelstvi UNM, praha, 1980. [5] Power plant engineering
by PK NAG [6]Material science by Kodigiri [7] Power plant engineering by Aurora