19
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

Master Thesis Presentaion

Embed Size (px)

Citation preview

Page 1: Master Thesis Presentaion

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

Page 2: Master Thesis Presentaion

2Summary

Introduction

Background

Current Solution

Our Idea

Assessment scheme

Anodizing Process

Results and Discussion

Further developments

Page 3: Master Thesis Presentaion

3Introduction

This thesis is about a cost effective oxide coating technique to protect the bearing against Electrically Induced Bearing Damage (EIBD).

Page 4: Master Thesis Presentaion

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

Page 5: Master Thesis Presentaion

5Current Solution

Bearing Insulation Working Principal

Page 6: Master Thesis Presentaion

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 .

Page 7: Master Thesis Presentaion

7Our Idea

Replicate the Aluminium oxides coated bearing with a Hard anodized Aluminium sheet metal sleeve/Bearing cap

Page 8: Master Thesis Presentaion

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

Page 9: Master Thesis Presentaion

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

Page 10: Master Thesis Presentaion

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.

Page 11: Master Thesis Presentaion

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

Page 12: Master Thesis Presentaion

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

Page 13: Master Thesis Presentaion

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.

Page 14: Master Thesis Presentaion

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.

Page 15: Master Thesis Presentaion

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.

Page 16: Master Thesis Presentaion

16Case 5

Page 17: Master Thesis Presentaion

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.

Page 18: Master Thesis Presentaion

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.

Page 19: Master Thesis Presentaion

19