Ball mill internals презентация

Content
Partitions
Single wall diaphragm
Full liftered double wall diaphragm
Adjustable double wall diaphragm
Outlet partitions
Slots design
Ventilation screens

Content
Partitions
Single wall diaphragm
Full liftered double wall diaphragm
Adjustable double wall diaphragm
Outlet partitions
Slots design
Ventilation screens

Different types of partitions
Partition between chambers
Single wall diaphragm
Double wall diaphragm full lifting
Double wall diaphragm with adjustable blade
Outlet partition

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

Content
Partitions
Single wall diaphragm
Full liftered double wall diaphragm
Adjustable double wall diaphragm
Outlet partitions
Slots design
Ventilation screens

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

Content
Partitions
Single wall diaphragm
Full liftered double wall diaphragm
Adjustable double wall diaphragm
Outlet partitions
Slots design
Ventilation screens

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

Full liftered double wall partition
3. Material is gravity dropped through
the center hub and into the next
compartment
1. Material fills the chamber ,
in between the slotted plates
and blind plates
.
2. Material is lifted by
mill rotation
Lifters can be curved, straight or adjustable. Assembly is sometimes called a partition's spider.
1
3

Full liftered double wall partition
Advantage
Accelerate material flow in the mill
Disadvantage
Tendency to empty the first chamber

Content
Partitions
Single wall diaphragm
Full liftered double wall diaphragm
Adjustable double wall diaphragm
Outlet partitions
Slots design
Ventilation screens

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

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

3rd generation diaphragms
4th generation diaphragms
Flow control
Pfeiffer Adjustable Partition

Content
Partitions
Single wall diaphragm
Full liftered double wall diaphragm
Adjustable double wall diaphragm
Outlet partitions
Slots design
Ventilation screens

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

Bi-rotator mill outlet partition
Characteristics
Good permeability for pore pressure drop
Poor flow control
To manage the material filling rate, the only way is to plug the slots
Material discharge
Air flow + fines particles
1st chamber side
2nd chamber side

Content
Partitions
Single wall diaphragm
Full liftered double wall diaphragm
Adjustable double wall diaphragm
Outlet partitions
Slots design
Ventilation screens

Slots design
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.

Slots design
Angles of the slots
Inlet angle 70° to 90°
Outlet angle 12° to 14°
moulded
Pfeiffer
Bazzi

Slots design
Size of the slots
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

Slots design
Best design
(concentrically)
Beyond here, the slot begins to widen
With the slot flared out, material can pass freely without jamming
Some metal will peen over the slot, but it will break off here in time

Peening of slots
Consequence: slots
have to be opened by
manual grinding
Slots design

Outer Grate Casting
Cast grooves to protect slots

Lifter bar on partition
Role: avoid wear of the partition by ball rotation on the surface

Content
Partitions
Single wall diaphragm
Full liftered double wall diaphragm
Adjustable double wall diaphragm
Outlet partitions
Slots design
Ventilation screens

Ventilation Screens
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
Good permeability
Total lack of permeability