1. TYPES OF LINERS, DIAPHRAGMS USED IN
BALL MILL, MAINTENANCE OF BALL MILL
INTERNALS
By-
Kapil Kukreja (Group Manager-CME-PSD-NCB)
2. BALL MILL MAINTENANCE
CONTENTS
• Introduction
• Mill General Overview
Mill Inlet
Mill Discharge
Mill Liners
Ball Charge
Intermediate Diaphragm
Discharge Diaphragm
Mill Bearings
Mill Drive System
• Inspections and Maintenance
• Case Study
3. Why grinding is required?
• The level of unreacted free lime (CaOfree) is an indication of
incomplete reaction. Under similar conditions of temperature and
residence time the level of free lime will depend only on the physical
and chemical characteristics.
• The higher the free lime in the samples the more difficult it is to burn
and the higher the burnability index.
• To increase the surface area for easy burning of raw material and
fuel.
• To achieve the desired particle size (Blain size) in cement
BALL MILL MAINTENANCE-INTRODUCTION
4. Operation % Power Consumption % Cost of total equipment
Crushing & Stacking ~5% ~7 %
Grinding ~70% ~55%
Pyro processing ~20% ~35%
Packing ~5% ~3 %
Role of grinding process in cement industry?
• Out of 70% of power ~30% power is required for RM and Coal Mill.
• Raw Material and coal/ pet coke/ lignite grinding involves drying and
grinding of materials
• Clinker is dry and significantly more difficult to grind than raw materials
and coal
• Cement is ground much finer than raw meal and coal
• Requirements to particle size distribution of the finished product are
much more strict when grinding cement rather than grinding raw
materials and coal
BALL MILL MAINTENANCE-INTRODUCTION
5. Grinding Systems
How much to grind ?
Raw Materials (~12 to15 % retained on 90 micron sieve, ~1.0 % retained
on 212 micron sieve) Why?
Coal/ Lignite (~12-15 % retained on 90 micron sieve) Why?
Pet Coke (~2-4% retained on 90 micron sieve) Why?
Cement (Depends on type and grade of cement) Why?
BALL MILL MAINTENANCE-INTRODUCTION
10. 11
Ball mill-Advantage
• Combined drying and grinding
• Reliable - long service life
• High fineness
• Good for abrasive material
Ball Mill- Limitation
• High specific power consumption
• Maximum moisture ~8%
Ball Mill- Process Control
• Product fineness
• Mill draft control
• Mill velocity control
• Mill temperature control
BALL MILL MAINTENANCE-GENERAL OVERVIEW
17. PURPOSE OF MILL LINERS
• To protect the mill body
• To participate in Crushing and Grinding Process
The mill liners can generally be classified into
(a) smooth
(b) Lifter and
(c) segregation or classifying types
based on the requirements of the grinding process of the mill.
18. Bolt Saving Mill Lining Bolt Less Mill Lining
FASTENING OF MILL LINERS
Installation of Bolt Saving Mill Lining
• Generally shell liner hardness
should be equal to media hardness
• Manganese steel liners are used 200-
260 BHN Hardness is obtained.
However, Chromium and Ni –hard
steel achieve hardness value of 400-
450 BHN which substantially reduces
the wear.
Bolt Lining
19. -- STEPPED LINERS (Lifters)
-- SMOOTH LINERS (Obsolete)
-- CLASSIFYING LINERS
-- ANGULAR SPIRAL LINERS
-- GROOVED PLATE LINERS
-- RUBBER LINERS (Rubber liners are best suited for the wet
grinding with relatively small sieved feed and media sizes. They are
not generally suitable for hot conditions during dry grinding or
when stresses are caused by high speed or large size media or when
there is excessive sharpness of the material)
-- CERAMIC LINERS (Various ceramic lining materials available
are silex, steatite and alumina oxide. These liners are used for
grinding non-metallic materials where iron contamination would
harm the products
TYPES OF MILL LINERS
21. TYPES OF LIFTER LINERS
Used for coarse grinding in first chamber of tube mills. These
liners impart lifting action to the balls, which in turn grind the
material by impact forces.
Selection of wave liners depends on the Grinding Media Size
22. TYPICAL DESIGNS OF CLASSIFYING LINERS
The principal
factors for
designing a
classifying liners
are
1-Mill diameter
and
2-Ball size.
As the diameter of
the mill increases
so the classifying
angle within the
range of
approximately 15-
25 degrees.
23. COMPARED RESULTS OF TWO
COMPARTMENT MILLS WITH AND WITHOUT
CLASSIFYING MILL LINERS DIAMETER: 4.3M
AFTER
MODIFICATION
BEFORE
MODIFICATION
OUTPUT, tph
SPECIFIC SURFACE
AREA, cm2/g
RESIDUE ON 90 µ
SIEVE
SPECIFIC ENERGY
CONSUMPTION,
kWh/t
90
3350
3250
100
1.8 0.8
36.6 32.5
24. GROOVED TYPE MILL LINERS
• The slipping motion (friction) between the
surfaces of the grinding media and the mill
liners leads to high wear which seems
Washed Out groove.
• The use of grooved shell liners not only
result in reduction in wear but also a
decrease in specific power consumption
• Grooved liners for the coarse grinding
compartment weigh approx. 15% less, and
for the fine grinding compartment,
designed as classifying liners, the weight
of the plates is even 30% less
• According to the manufacturer, the
consumption of grinding media is reduced
by about 40%
26. MILL PARTITION SINGLE WALL
• Single wall partitions allow pre-ground
material to pass without special
classification
• The material being ground is pushed
towards the partition by new feed entering
the mill; after passing through the slots, the
material enters the next mill compartment.
• The openings in the center of the partitions
are made for mill ventilation.
• They are subjected to high wear, from media
from both sides of diaphragm plate. With the
increasing wear slots become wider and this
allow coarser particle to pass through
diaphragm to the next compartment.
27. MILL PARTITION – DOUBLE WALL
1, 2 Walls
3 - Curved Cascader
4- Central Pipe
• These diaphragms contain one slotted plate at feed end and one blind plate on the other end,
with the space between them of approximately 25-30 cms.
• The partition consists of two front walls and the deflector plates, which are attached to the
outer ring. The transportation of the ground material from the cascader is throtled in such a
way that the entrance of the ground material into the partition wall is controllably delayed.
In this way the level of the ground material dams up within the level of the grinding media
in front of the partition wall and undergoes, in this way, an intensive size reduction.
32. BALL MILL MAINTENANCE-GENERAL OVERVIEW
Discharge Diaphragm
6.1 Discharge diaphragm
framework
6.2 Lifter
6.3 Support
6.5 Slotted plate
6.10 segments of filler ring
6.11 Insulation
33. 6.1 Discharge diaphragm framework
6.3 Support
6.4 Support
6.6 End disc
6.7 Cone
6.8 Clamping ring
6.9 Grid
6.10 Segments of filler ring
6.11 Insulation
DISCHARGE DIAPHRAGM
40. BALL MILL MAINTENANCE
1. Breakdown maintenance :It means that people waits until equipment fails
and repair it. Not desirable
2. Preventive maintenance
It is a daily maintenance ( cleaning, inspection, oiling and re-tightening ), design
to retain the healthy condition of equipment and prevent failure through the
prevention of deterioration.
It is further divided into periodic maintenance and predictive maintenance:
Periodic maintenance-Time based maintenance
Predictive maintenance-This is a method in which the service life of important
part is predicted based on inspection or diagnosis, in order to use the parts to
the limit of their service life
3. Corrective maintenance
It improves equipment and its components so that preventive maintenance can
be carried out reliably. Equipment with design weakness must be redesigned to
improve reliability or improving maintainability
49. BALL MILL MAINTENANCE-Preventive Maintenance Check List
Daily
1. Check for abnormal sound in the main gear box and temperature
2. Check oil leakage from the gear boxes
3. Check material leakage from liner bolt holes
4. Check oil temperature & pressure and check pump for inlet
trunnion bearing/outlet trunnion bearing for abnormal noise,
temperature and vibration
5. Clean all equipment thoroughly
6. Check oil level of trunnion bearings, countershaft bearings and main
gear box, make up the level, if necessary
7. Check proper lubrication of girth gear and pinion
8. Check the water spray compressor for oil leakage, abnormal sound
and temperature
50. 1. Check bearings of main gear box by shock pulse meter
2. Check correct liner bolts for tightness/damage
3. Check correct meshing of girth gear with pinion
4. Check bolts assembling both halves of girth gear
5. Check all units (including mill pilot drives)
6. Check all coupling bolts/bushes for wear/damage
7. Check oil cooling pump for smooth operation
8. Check mill fan hole seal
9. Check the packing of trunnion bearings and gear guard,
tighten the packing or replace if necessary
BALL MILL MAINTENANCE-Preventive Maintenance Check List
Monthly
51. Quarterly
1. Carry out oil analysis of trunnion bearing, replace, if
necessary
Half Yearly
1. Check trunnion surface and counter shaft bearing surface for
scoring
2. Fasten lining plates and separating grates to the shell, ensure
perfect seating
3. Carry out servicing of heat exchanger
4. Check lining bolts for wear/breakage, if necessary replace
5. Clean slots provided in the grate
6. Check for correct lubrication of trunnion, counter shaft bearings,
girth gear and pinion
7. Inspect the condition of lining plate provided in the feed spout and
drying chamber for wear, replace if necessary
8. Check the condition of inlet chute and discharge chute for wear
BALL MILL MAINTENANCE-Preventive Maintenance Check List
Quarterly and Half Yearly
52. Yearly
1. Check girth gear and pinion teeth for wear
2. Check gear box internals for foreign material and loose fixture,
check the bearing clearance
3. Overhaul all L P and H P lubricating pumps for turnions (inlet
and outlet ) and gear boxes
4. Analysis the oil for gear boxes top up/replace oil as required,
inlet and outlet trunnion bearings must be filled with
recommended oil up to the maximum level
BALL MILL MAINTENANCE-Preventive Maintenance Check List
Yearly
55. BALL MILL MAINTENANCE
Problem Analysis at initial; Stage
A Crack was observed by maintenance engineer and ultrasonic
testing was performed to know the depth of crack and found that
about 60mm deep and 1300 mm long
Root cause-Fatigue due to prolonged services
56. BALL MILL MAINTENANCE
POSSIBLE SOLUTIONS
Case-1 : Replacement by new one
Case-2 : Repair of existing one
Selected Option-Repair of existing one
59. BALL MILL MAINTENANCE
XUPER 660NH
• It provides excessive moisture guard protection.
• High ductility (Ability to elongate under load without cracking)
• High Strength (559MPA)
• High Impact Resistant
Nucleotec 2222
• Ni and Cr based alloy which hold H2 to prevent migration and
cracking.
• Good under massive stress
• Good where post weld heat treatment is not possible.
