1.95M

Category:

mechanics

Ball mill internals

1. Ball Mill Internals

GRINDING I – Training Session

2. Content

Ball Mill Internals
Content
• Partitions
• Single wall diaphragm
• Full liftered double wall diaphragm
• Adjustable double wall diaphragm
• Outlet partitions
• Slots design
• Ventilation screens
KUJ – July 2012 – Grinding I - 2

3. Content

4. Different types of partitions

Ball Mill Internals
Different types of partitions
• Partition between chambers
• Single wall diaphragm
• Double wall diaphragm full lifting
• Double wall diaphragm with adjustable blade
• Outlet partition
KUJ – July 2012 – Grinding I - 4

5. Purposes of a partition

Ball Mill Internals
Purposes of a partition
• Main partition roles
• Keep grinding media in several compartments
• Material flow control (double wall)
• Help air flow (lowest pressure drop)
• Specific roles
• For intermediate partitions: control the compartment
output material size
KUJ – July 2012 – Grinding I - 5

6. Content

7. Single wall partition

Ball Mill Internals
Single wall partition
• It is only a ball screen between the chambers
Advantage
• Do not take much
space
Disadvantages
• No flow regulation
• Small difference of ball
filling rate between
chambers
KUJ – July 2012 – Grinding I - 7

8. Content

9. Double wall partition

Ball Mill Internals
Double wall partition
• It is the most common partition
Outer Grate Segment
Inner Grate Segment
Center Hub or Cone
Center Screen (Mill Sweep)
Typical Chamber Filling Level
KUJ – July 2012 – Grinding I - 9

10. Full liftered double wall partition

Ball Mill Internals
Full liftered double wall partition
3. Material is gravity dropped through
the center hub and into the next
compartment
Side View of a Partition
2. Material is lifted by
mill rotation
3
Gas Flow
BM Load Level
1
.
1. Material fills the chamber ,
in between the slotted plates
and blind plates
Lifters can be curved, straight or adjustable.
Assembly is sometimes called a partition's spider.
KUJ – July 2012 – Grinding I - 10

11. Full liftered double wall partition

Ball Mill Internals
Full liftered double wall partition
• Advantage
• Accelerate material flow in
the mill
• Disadvantage
• Tendency to empty the first
chamber
KUJ – July 2012 – Grinding I - 11

12. Content

13. Adjustable double wall partition

Ball Mill Internals
Adjustable double wall partition
• Purpose
• Control the empty zone before the partition by
regulating the material level in the partition
• Control different filling rates in both chambers
KUJ – July 2012 – Grinding I - 13

14. Slegten Adjustable Partition Wall

Ball Mill Internals
Slegten Adjustable Partition Wall
• Fitted with scoops inside the partition.
• Position of the scoops to adjust to control the flow (trial and
error)
Scoop in full closed
position
Scoop in full open
position
Material level
KUJ – July 2012 – Grinding I - 14

15. Pfeiffer Adjustable Partition

Ball Mill Internals
Pfeiffer Adjustable Partition
3rd generation diaphragms
4th generation diaphragms
Flow control
KUJ – July 2012 – Grinding I - 15

16. Content

17. Compound mill outlet partition

Ball Mill Internals
Compound mill outlet partition
• Purpose
• Evacuate the material flow
out of the mill
• Allow the nibs to go out of
the mill
• Two existing types
• Full lifting
• With flow control
KUJ – July 2012 – Grinding I - 17

18. Bi-rotator mill outlet partition

Ball Mill Internals
Air flow + fines particles
Bi-rotator mill outlet partition
• Characteristics
• Good
permeability for
pore pressure
drop
• Poor flow
control
1st chamber
side
2nd chamber
side
• To manage the
material filling
rate, the only
way is to plug
the slots
Material discharge
KUJ – July 2012 – Grinding I - 18

19. Content

20. Slots design

Ball Mill Internals
Slots design
s
The ground material is transferred
through the slots.
The design of the slots, slot width and
stability of the slot shape have an
important process function.
40-70
s+3
KUJ – July 2012 – Grinding I - 20

21. Slots design

Ball Mill Internals
Slots design
moulded
• Angles of the slots
• Inlet angle 70° to 90°
Bazzi
• Outlet angle 12° to 14°
Pfeiffer
KUJ – July 2012 – Grinding I - 21

22. Slots design

Ball Mill Internals
Slots design
General Rule
• Size of the slots
Discharge
Diaphragm
=
Intermediate
Diaphragm
+
2 mm
• Raw Mills
• Transfer diaphragm:16 to 20mm
• Intermediate diaphragm:10 mm
• Discharge diaphragm:12 mm
• Cement Mills
• Intermediate diaphragm:6 to 8 mm
• Discharge diaphragm:8 to 10 mm
KUJ – July 2012 – Grinding I - 22

23. Slots design

Ball Mill Internals
Slots design
Some metal will peen
over the slot, but it will
break off here in time
Best design
(concentrically)
With the slot flared
out, material can pass
freely without jamming
Beyond here, the slot begins to widen
KUJ – July 2012 – Grinding I - 23

24. Slots design

Ball Mill Internals
Slots design
• Peening of slots
• Consequence: slots
have to be opened by
manual grinding
KUJ – July 2012 – Grinding I - 24

25. Outer Grate Casting

Ball Mill Internals
Outer Grate Casting
• Cast grooves to protect slots
KUJ – July 2012 – Grinding I - 25

26. Lifter bar on partition

Ball Mill Internals
Lifter bar on partition
• Role: avoid wear of the partition by ball rotation on
the surface
KUJ – July 2012 – Grinding I - 26

27. Content

28. Ventilation Screens

Ball Mill Internals
Ventilation Screens
Good permeability
• Purpose
• Insure gas flow
• Preventing balls from passing
between compartments
• Specifications
• Maximum permeability (cleanliness)
• Mechanical behaviour with the
90 mm balls
• Screen# < 40 mm in C1
• Screen# < 15 mm in C2
to prevent 20 mm balls from escaping
• Corrective measures
• Cleaning or replacement
Total lack of permeability
KUJ – July 2012 – Grinding I - 28

29. Partition control - Reminders

Ball Mill Internals
Partition control - Reminders
• Wear control
• Slot size and dimensions
• Lifter of the step partition
Discharge
Diaphragm
=
Intermediate
Diaphragm
+
2 mm
• Cleaning actions
• Nibs in the slots
• Foreign materials on central screen (raw mill essentially)
• Maintenance action
• Remove slot peens with a disc grinder
KUJ – July 2012 – Grinding I - 29

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