master thesis presentaion
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LABORATORY OF BIOLOGICAL STRUCTURE MECHANICS
www.labsmech.polimi.it
Master’s Thesis presentation
Assessment of anodic aluminium oxide coatings towards an alternative solution to spark erosion damage of bearings
Thesis Presented by: Ranganath Nagaraju
Supervisor : Prof. Antonello Vicenzo
2Summary
Introduction
Background
Current Solution
Our Idea
Assessment scheme
Anodizing Process
Results and Discussion
Further developments
3Introduction
This thesis is about a cost effective oxide coating technique to protect the bearing against Electrically Induced Bearing Damage (EIBD).
4Background
Electrically Induced Bearing Damage (EIBD)
Capacitive coupling between the rotor shaft and the stator windings Magnetic field dissymmetric around the rotor Electrostatic coupling from internal source
Three possible sources of stray current
5Current Solution
Bearing Insulation Working Principal
6Issues with Current Day Solution
1) Insulated bearing: Constrain with the size and the cost of the bearing.
2) Ceramic bearings: Is quite effective but a more expensive solution .
7Our Idea
Replicate the Aluminium oxides coated bearing with a Hard anodized Aluminium sheet metal sleeve/Bearing cap
8Assessment scheme
Morphological Assessment of oxides at Anodizing temperature
Selection of Electrolyte Solution
Selection of Aluminium Alloy
Selection of Current density
Analysing the oxide hardness
Analysing the oxide toughness
9Anodizing Process
Set the Electrolyte temperature
Note the Anodizing area
Determine and set the input current
Weigh the Initial Sample W1
Alkali Cleaning with NaOH
Acid Cleaning with Nitric acid
Weigh the sample after cleaning W2
Seal the oxide in hot water
Place the sample in the cell and ON the
power supply
Weigh the sample after anodizing W3
Determine the oxide thickness
10Results and Discussion
Case 1. SEM Analysis of the Sealed and Unsealed oxides of varied anodizing temperature and oxide thickness
Density of pores higher in 0C.
Pore size higher at higher temperature.
11Case 1
The size of the pores in 10 C is higher than in 5 C, in order to reduce this kind of defects, we have make sure that the anodizing temperature is low, we adequately seal it by selecting a suitable sealing time and optimise the oxide thickness.
Sealed oxides 10 C with 10 microns
Unsealed oxides 10 C with 25 microns
Sealed oxides 5 C with 10 microns
12Case 2
Case 2. Scrutinize for the appropriate anodizing temperature
8
10
12
14
16
18
20
20 15 10 5 0
Temperature in Degree celcius
We
igh
t d
iffe
ren
ce in
mill
i gra
ms
Weight differenceSample 1
Weight Difference forsample 2
0
5
10
15
20
25
20 15 10 5 0
Temperature in Degree Celcius
Fin
al
Po
ten
tial
in V
olt
s
Final Potential Sample1
Final Potential forsample 2
0
2
4
6
8
10
12
20 15 10 5 0
Temperature in Degree Celcius
Ox
ide T
hic
kn
ess
in
mic
ron
s
Average oxidethickness Sample 1
Average oxidethickness sample 2
The samples at 5 C and 10 C have less variations, hence concluding the apparatus is more efficient at these temperatures
13
Case 3. Study the hardness of the formed oxides on the aluminium substrate with reference to the indenter distance from the oxide / aluminium interface
Case 3
The hardness of the oxide not only reduces by the anodizing temperature but also across the oxide thickness with reference to the distance away from the substrate.
The reduction of the oxide hardness across the oxide thickness is much higher at higher temperature.
14Case 4
Case 4. Analyse the anodizes samples of different temperature to estimate the load at first crack (Micro Indentation)
The oxide toughness will increase with decrease in anodizing temperature and almost remain constant . It’s the results of high density of oxides at the low anodizing temperature.
15Case 5
Case 5. Micro Scratch testing to estimate the load at first crack during scratching
Oxide thickness itself gives an mechanical advantage towards toughness and its been evident that higher the thickness higher is the load required to break the oxides.
16Case 5
17Case 6
Case 6. Impedence mesaurement
The impedance measurement on the worst sample (20 C with 10µm oxide thickness) reveals that it maintains an impedance 4x107 Ω at 100 Hz and at 50 Hz the value is predicted to rise, hence predicted it satisfies the resistance requirement.
18Further Developments
Improve the toughness
Since we suspect the possibility of the oxide damage due to fretting between the contact surfaces at the fitment. One of the predicted solution could be polymer sealing the oxides.
Determine the electrical properties of the oxides
Both Break down voltage and the electrical resistivity has to me estimated as per the ASTM guidelines D159, D150 and D257.
Preparation on the product
All these analysis should be executed and confirmed at the prototype level and these require a special bearing setup. And this should be performed under professional guidance.
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