Download - Trouble Shooting Guidemills97
-
7/28/2019 Trouble Shooting Guidemills97
1/31
Possible reasons Indications Remedies
Worm shaft bearing
failure
a)Play in worm shaft
b) Shaft seating on
bearing housing.
c) High frequency noise
Replace the bearings.
Improper surface contact
on some teeth on worm
set
Knocking sound Reset the worm gear set
to get proper contact
Interference of pump hub
with bushing
Cyclic rubbing noise Provide proper clearance
Worn out and dry
coupling
Noise from coupling Lubricate /replace
1
-
7/28/2019 Trouble Shooting Guidemills97
2/31
Possible reasons Indications Remedies
Scrapper or scrapper
guard touching
stationary components.
Periodic noise Ensure proper
clearance.
(6-15 mm)
Skirt touching mill bottom Rubbing noise Ensure proper
clearance.
(5-8 mm)
2
-
7/28/2019 Trouble Shooting Guidemills97
3/31
Possible reasons Indications Remedies
Foreign material in mill Noise on no load running
also
Remove foreign material
Roll touching bowl or gap
less
Reset the gap as per
procedure
Bowl assembly touching
stationary part
Periodic noise Minimum gap 3 mm radial
and 8-10 mm vertical
High load vibration Excessive movement of
spring adjusting stud
Proper spring compression
And sufficient ring roll gap
Journal spring assembly
bearing failure
Knocking sound Replace bearings
Loosening of separator
body flange bolts
Dust leakage from flange Tighten the flange bolts
Bull ring segments loose
due to improper assembly
or segment breakage
Visual and physical
inspection
Assemble properly
Cont
3
-
7/28/2019 Trouble Shooting Guidemills97
4/31
Possible reasons Indications Remedies
Excessive wear of bowl
extension ring or bowl.
Proper coal bed
formation not there.
No noise at no load
More noise at low load
Replace extension ring
Spring compression too
high
No noise at no load
More noise at low load
Reduce spring
compression
Roller assembly slipping
in to Bowl due toa)Keeper plate screw
failures.
b)Journal shaft pin or
locknut failure
Visual Correct
4
-
7/28/2019 Trouble Shooting Guidemills97
5/31
Possible reasons Indications Remedies
Air entering mill base Oil level goes down if oil
fill pipe cover is opened
Check Mechanical face
seal
Oil cooler puncture.
Cooling water entering
mill base
Over flow stops if cooling
water stopped.
Replace and repair
cooler.
Excess oil in mill base Correct oil level
5
-
7/28/2019 Trouble Shooting Guidemills97
6/31
Possible reasons Indications Remedies
Plugged of vertical shaft
hole
clean
Plugged or broken return
oil line
repair
Improper oil Change oil
Excess clearance
between pump and hub
Replace pump/ hub as
required
Plugged holes in lowerbearing housing clean
Accumulation of debris in
oil collector
clean
6
-
7/28/2019 Trouble Shooting Guidemills97
7/31
Possible reasons Indications Remedies
Improper/damaged
packing gland
Oil over flow from mill
base
Ref 4
Air vent pipe
closed/plugged
Allow venting
7
-
7/28/2019 Trouble Shooting Guidemills97
8/31
Possible reasons Indications Remedies
Breakage/leakage from
return oil line
Repair /replace
Puncture of oil cooler
tubes
Over flow stops if cooling
water stopped
Replace and repair
cooler.
Failure of vertical shaft
oil seal
Replace oil seal
8
-
7/28/2019 Trouble Shooting Guidemills97
9/31
Possible reasons Indications Remedies
Mating surface not
cleaned properly
Seal compound not
applied
Improper gasket used
Bolts not tightened
properly
Venting not adequate
9
-
7/28/2019 Trouble Shooting Guidemills97
10/31
Possible reasons Indications Remedies
Oil cooler pipes choked Clean cooler tubes
Inadequate supply of
cooling water
Maintain proper supply
Oil level high/ low Maintain proper level
Break down of lubricant Lab analysis replace
Air entering mill base Oil level goes down if oil
fill pipe cover is opened
Check Mechanical face
seal
Failure of bearings change
10
-
7/28/2019 Trouble Shooting Guidemills97
11/31
Possible reasons Indications Remedies
Over feeding
( mill capacity depends
on HGI, moisture,fineness etc.)
Limit coal flow to mill
capacity
Insufficient air flow Maintain proper air flow
Separator body cover
plate wear
Air should only flow in
areas identified
Improper internalclearance
Set as per guidelines
Jamming of rolls See
Wear of mill parts like
roll, bullring, liners, bowl
extension ring etc.
Rebuild/ replace wear
parts as required
Cont11
-
7/28/2019 Trouble Shooting Guidemills97
12/31
Possible reasons Indications Remedies
Improper setting of ring
and roll gap and journal
head and spring seat
gap
Set as per manual
Low spring pressure Excessive jumping Set as per manual
High coal fineness Lab analysis See
Blocking of air inlet vane
/ classifier vane
visual clear
Coal pipe choking Cold pipe see
Sand accumulation in
mill
Purge the mill
12
-
7/28/2019 Trouble Shooting Guidemills97
13/31
Possible reasons Indications Remedies
Improper setting of ring
and roll gap and journal
head and spring seat
gap
Set as per manual
Unequal spring pressure Set as per manual
Unequal roll wear
between journals
Set as per manual
13
-
7/28/2019 Trouble Shooting Guidemills97
14/31
Possible reasons Indications Remedies
Mechanical face seal
failure
Air leakage through
cored holes
Set as per manual
Mill base not properly
cleaned
clean
Running mill with high
rejects
See 10
14
-
7/28/2019 Trouble Shooting Guidemills97
15/31
Possible reasons Indications Remedies
Improper setting of
classifier
visual Reduce number
Excess spring
compression
reduce
15
-
7/28/2019 Trouble Shooting Guidemills97
16/31
Possible reasons Indications Remedies
Improper setting of classifier visual increase number
Low spring compression increase
Improper alignment of
classifier vane
visual correct
Puncture in classifier cone repair
Plugging in classifier cone clear
High mill air flow Maintain proper air flow
Excess wear of mill parts Repair/ replace
Improper setting of ring and
roll gap and journal head
and spring seat gap
Set as per manual
Low mill outlet temperature see
Improper sampling Follow procedure
More gap between cone
and feed pipe
correct
16
-
7/28/2019 Trouble Shooting Guidemills97
17/31
Possible reasons Indications Remedies
High mill outlet
temperature
Keep MOT within limit
High sulfur in coal Keep MOT within limit
High volatile matter incoal
Keep MOT within limit
Mill idle with partially
pulverized coal/ coal
Ensure proper purging/ emptying of
mill during normal shutdown.
Use inert medium if provided.
Putting burning coal inmill avoid
Rapid change in fuel
moisture
Mill outlet temperature should be
kept in auto
Accumulation of rejects
in mill
See 16
17
-
7/28/2019 Trouble Shooting Guidemills97
18/31
Possible reasons Indications Remedies
Mill running with
excessive rejects
See 10
Pyrite hopper choked/
overfilled
clean
Tramp iron spout choked clear
Tramp iron gate closed open
Scrapper failure Repair /replace
18
-
7/28/2019 Trouble Shooting Guidemills97
19/31
Failure of vertical shaft is generally due to
fatigue. The shaft is subjected to stress cycles
which may lead to fatigue failure. The shaft has
been designed adequately for keeping the stresslevel beyond endurance limit but due to wrong
operation and maintenance the shaft can be
stresses beyond endurance limit. Under normal
circumstances the bending load of each roll isbalanced on vertical shaft. Cont..
19
-
7/28/2019 Trouble Shooting Guidemills97
20/31
Possible reasons Possible reasons Possible reasons
Using rolls with unequal
wear
Using different spring
compressions
Spring breakage
Foreign material entry in
mill
Improper locking of
spring assembly
Improper setting of ring
roll
Jamming of rolls Roller in lifted position
due to jamming of
trunnion bushing
High spring compression
20
-
7/28/2019 Trouble Shooting Guidemills97
21/31
Possible reasons Indications Remedies
Coal HGI reduced Lab analysis
High moisture in coal Low MOT Prevent moisture
addition
High pulverized coal fineness Lab analysis correct
Low spring compression reset
Low air flow Maintain correct air flow
Higher gap between roll & ring
and journal head and spring
assy.
reset
Wear of roll & ring replace
Low mill outlet temperature See
Coal pipe choking see
Wear of bowl extension ring change
21
-
7/28/2019 Trouble Shooting Guidemills97
22/31
Possible reasons Indications Remedies
Instrument air leakage Attend leakage
Solenoid valve damaged replace
Victaulic coupling too
tight
Without coupling MDV
operates
Insert shim between
coupling flanges.
Air cylinder seals
damaged
Change seals
Valve fouling with body Grind and correct
Valve shaft not aligned
properly
Correct the bushes.
Fouling of clevis and
brackets with air cylinder
Grind adjust to suit
22
-
7/28/2019 Trouble Shooting Guidemills97
23/31
Possible reasons Indications Remedies
Classifier vane shaft
bent
Straighten or change
Classifier link lever
length not equal
Use turn back signal to
make free
Bearings / Grease seals
damaged
replace
Classifier vane fouling Remove the fouling
23
-
7/28/2019 Trouble Shooting Guidemills97
24/31
Possible reasons Indications Remedies
O ring oil seal between
upper and lower journal
housing damaged
Oil marks on the flange replace
Upper journal housingseal damaged
Oil leakage from top ofjournal housing
replace
Journal shaft ( seating
area) damaged
By measurement Repair and change shaft
24
-
7/28/2019 Trouble Shooting Guidemills97
25/31
Possible reasons Indications Remedies
Bearings damaged Change bearing
Oil contaminated Replace oil after
cleaning
Oil Inadequate Top up oil
No bearing clearance Follow procedure
Upper journal housing
rubbing with journal head
Ensure clearance
25
-
7/28/2019 Trouble Shooting Guidemills97
26/31
Possible reasons Indications Remedies
Inadequate seal air
supply
Check up air supply
Journal shaft plug open Replace plug after
cleaning journal
assembly.
26
-
7/28/2019 Trouble Shooting Guidemills97
27/31
Possible reasons Indications Remedies
Mill fire
Foreign material
Casting defectHammering
27
-
7/28/2019 Trouble Shooting Guidemills97
28/31
Possible reasons Indications Remedies
Mill fire
Foreign material
Casting defectHammering
Excess wear of bull ring
Improper surface contact
between bull ring and
bowl
28
-
7/28/2019 Trouble Shooting Guidemills97
29/31
Possible reasons Indications Remedies
Oil contamination
Worm shaft bearing.
Housing damagedBearing heated
excessively
Assembly without
clearance
Bearing hammered in toposition
Poor quality bearing
Thrust bearings not
properly assembled
29
-
7/28/2019 Trouble Shooting Guidemills97
30/31
Possible reasons Indications Remedies
Scraper rubbing Scoring marks Maintain proper clearance.
Scraper holding bolt failure Change bolt
Lower skirt boss breakage
Scraper blade breakage change
Lower skirt boss thread
damage
Use other boss if available
or use bigger bolt.
Scraper pin excess clearance Change holder
Foreign material
Scraper fouling with cover plate Change warped cover
plate
Excess rejects See 10
Pyrite hopper choked clear
30
-
7/28/2019 Trouble Shooting Guidemills97
31/31
Possible reasons Indications Remedies
Increase in raw coal moisture Do not add moisture
Insufficient primary air Maintain proper air flow
Primary air temperature low Try to increase
Excess cold primary air Close cold air damper/gate
Hp heaters not in service Take HP heater in service
Boiler load low Increase boiler load or take
more mills in service
Moisture retained in pulverized
coal low
Eco bypass not used use
SCAPH not charged
31