Kiln Mechanical behavior for Patrollers
Content
1
Thermal Expansion
2
Thermal Expansion effects on the shell
3
Thermal Expansion effects
4
Mechanical crankshaft
Kiln temperature profile > 110°C > 145°C > 180°C > 215°C > 250°C > 285°C > 320°C > 355°C > 390°C > 425 °C
500
Temp: °C
Max Avg Min
450
400
350
300
Average 250C
250
200
m
150
100
0
10
20
30
40
50
60
70
80
How to evaluate Expansion?
Expansionmm
1.2 (
C C T Final T Initial
100
) Lengthinitial ( m )
At 250°C, a 70 m kiln is 190 mm longer than at 25°C
Temperature must always be taken into account on kilns
On repair/replacement operations
On adjustments when done in cold conditions
1
Thermal Expansion
2
Thermal Expansion effects on the shell Shrinkage of the tyre on shell Thermal bending
3 4
Thermal Expansion effects Mechanical crankshaft
Shrinkage of the shell into the tyre
Under tyre shell temperature is greater than tyre average temp.
In normal operation
.. and more in start-up phase
High risk to shrink the shell at start-up
too quick preheating
too small cold clearance value
Consequences
Shell will be deformed permanently
Will possibly lose some bricks
Will probably have some problems of fixation
Will lead to potential shell cracks in the future
Thermal bending Variation of Temperature along kiln Max Average Min
400 350 300 250
door
200 150 100 GG
50
Pier
Pier
Pier
0 0
8
Why this variation (max/min) of temperature in a section?
16
24
31
39 is the 47 effect 55 of What this profile of temperature?
63
71
Thermal bending Variation of Temperature along kiln 400 350 300 250 200 150 100 50 0 0
8
16
24
Avg. 300 ° C
Length = 12 m
31
39
47
55
63
71
Expansion at 300 ° C = 1.2 x (300-20)/ 100 x 12 = 40 mm Differential = 11 mm
Expansion at 220 ° C = 1.2 x (220-20)/ 100 x 12 = 29 mm Avg. 220 ° C
Thermal bending Variation of Temperature along kiln 400 350 300 250 200 150 100 50 0 0
8
16
24
31
39
47
55
63
71
12m + 40mm
12m + 29mm
Due to the mass of the kiln, there is still a contact on each pier
.. but load is lighter at central pier and higher at the other one .. and opposite after half a rotation !
If the thermal bending is very high some tyres could even not touch the rollers!
Thermal bending causes
A defect in coating can lead
To different temperatures on the same section
Then to differential expansion
Then to kiln thermal bending
When the kiln is not properly rotated
During start-up
During kiln stoppage
When the kiln is not rotated after one incident
Importance of barring drive!
Thermal bending corrective actions
Modify process parameters
to get proper equal coating
Barring drive always to be ready to operate
If too late, shell replacement: Figuil (Cameroon) Example
Production incident, no barring during 10 min.
Tropical rain (which cools only top of shell)
Kiln bent forever (tyre/roller clearance 25mm)
Need for cut or shell replacement • Cost > 100.000 USD • Stoppage time needed > 10 days
1
Thermal Expansion
2
Thermal Expansion effects on the shell
3
Thermal Expansion effects Girth gear Kiln bearing liner
4
Mechanical crankshaft
Girth-gear root clearance increase
Girth-gear fixed on the shell Example of a 3-pier 4.6 m diameter kiln with pre-heater: Root clearance increases about 6 mm
Clearance
Kiln roller bearing
Kilns are generally rotating on roller shaft with liners
Few roller bearings because
very high loads and low rotating speed
expensive to design and use
Are there any limits?
Yes, there is a limit of pressure on a liner
Special mode of friction, low speed, negative influence
Kiln roller bearing liner Temperature
Depends on friction -> related to rotation
Torque liner about Torque motor x (0.03 to 0.05)
Depends on the load -> related to
Design. (FLS, POLYSIUS, CLE, FCB using approx. same design limit)
Quality of geometry and lubrication
Most of the torque used to lift the material inside the kiln / Very little converted to heat through the shaft/liner contact
Alignment of kiln tires Shell axis deformation (permanent or thermal)
In case of severe liner overheating, this torque can suddenly increase
Expansion effect on Kiln bearing liner
When the kiln starts, tyre will heat the roller, then the shaft After 48 hrs, the shaft diameter will be bigger but the liner support will remain cool (water cooling) The expansion of the shaft will reduce the oil film thickness… and the contact will increase SHAFT (HOT)
SHAFT (COLD)
Contact Surface
Kiln bearing liner overheating cycle Viscosity decreases
Overheating
Shaft diam. increases
More wear
Less clearance
Less oil
Kiln bearing liner -> Emergency procedures
Best method = Oil re-circulation with cooling and cleaning
Small units available on the market with installation on request
In case of small problem, putting the kiln on barring can save you!
Time to decrease shaft temperature, get proper viscosity back, come out of the vicious cycle
Cool by air roller flank to limit kiln heat transmission to shaft
Oil usage
The best oil cannot solve contact pattern problems Very thick oil or synthetic oil cannot solve too low clearance between shaft and liner
Check if this synthetic oil can be mixed with mineral Check if this synthetic oil does not chemically attack any bearing part
put the highest viscosity you can, assuming the real viscosi ty will drop very quickly because of temperature (oil viscosity diagram versus temperature must be known)
Kiln bearing liner -> Musn’t
Fan cooling: dangerous on bearing
Housing open = Dust contamination = Be careful! Are you sure you are cooling the shaft or the housing? (think of expansion)
Cool the roller flank with water
Water on roller is dangerous
Permanent application or heat shock leads to spalling
Use grease or molycot is forbidden
very dangerous can block the oil pocket, preventing any oil from entering to lubricate liner and shaft
Expansion Conclusion
Heat is a very important parameter for kiln shell Attention should be always given to temperatures
Maximum temperature
But also differential
Mechanical staff must take extreme care in case of kiln thermal bending
Content
1
Thermal Expansion
2
Thermal Expansion effects on the shell
3
Thermal Expansion effects
4
Mechanical crankshaft Misalignment Brick Failure
Kiln Misalignment
As an example on 3 piers, a mechanical bend is one tube which is deformed so the 2nd section is rotating when sections 1 and 3 are perfectly set-up in line
Wrong Kiln Alignment
Wrong alignment of shell at erection due to
Subcontractor’s lack of know-how
Deformed new or old shells
Not properly chosen shells to be replaced
SHELL ECCENTRICITY OR "CRANKSHAFT" KILN SHELL AXIS UNDER TYRE
POOR ALIGNMENT OF SHELLS
Wrong Kiln Alignment effects
On a poorly aligned 3-station kiln, tire 2 too high by about 10 mm
Overload = 8 t/mm x 10 mm = 80 t (TC calculation)
Permanent load supported by this tire = 80 t higher than normal
Possible problems (depending on design safety coefficient) on
Bearing liners overheating
Tyre (wear, holes, crack, …)
Rollers (wear, holes, crack, …)
Shaft crack
Brick failures • Too high load => too high ovality => problem of bricks
Frame cracks
Shell cracks
Brick Failure
If not followed by stoppage (major cause) Too long run with missing bricks / Too high temperature on the shell with bricks Some indicators
If the circumference of hot-spot is > 90° of the total, it becomes dangerous for the kiln shape, otherwise it will create only l ocal deformations (but still bad) Axial hot-spots are less dangerous than radial
Brick Failure effect
Brick Failure effect
Brick Failure effect
Mechanical crankshaft without visual indications
Possible Since kilns are generally very flexible, you may have a crankshaft but as the kiln deforms during rotation, the deformation is not visible Sometimes kilns are affected by several crankshafts in opposite phases
