surface topography

tribology presentation

1. SURFACE TOPOGRAPHY Presented by A . Sabiha Khathun M.TECH (Machine Design) 16481D1501 Subject: Tribology GUDLAVALLERU ENGINEERING COLLEGE Sheshadri Rao Knowledge Village, Gudlavalleru,PIN:521356

2. Why surface finish is important in engineering application? Surface texture has marked influence on Function Lubrication pressure holding capacity resistant to wear and corrosion noise reduction bearing area friction etc.

3. Surface topography It comprises the small local deviations of a surface from the perfectly flat ideal (a true plane). Engineering surfaces never have an ideal geometrical shape, but instead include different deviations. With regards to the level of approximation they can be considered: smooth and even, smooth and wavy, rough and even, rough and wavy

4. So let’s begin by looking closely at a surface…

5. Micro-geometrical deviations – roughness (important for interaction of surfaces) Macro-geometrical deviations – waviness

6. Continued… Surface texture is one of the important factors that control  friction  and transfer layer formation during sliding. It is the nature of a surface as defined by the three characteristics of 1. Lay 2. Surface roughness and 3. waviness

7. Lay - The direction of the predominant surface pattern. Surface roughness - Closely spaced irregularities. Waviness - More widely spaced irregularities.

8. Importance of surface topography For many engineering applications the surfaces are manufactured in order to get some special functioning properties as bearing, sealing and lubricant retaining capabilities. These surfaces may be designed to have specific topographical features that are beneficial for specific functioning applications.

9. Surface roughness measurement methods and parameters 1. Profilometer 2. Optical interferometer 3. Atomic Force Microscope (AFM) Parameters: arithmetic mean value (R a ) and root mean square average (R q )

10. 1. Profilometer (stylus measurement)

11. 1. Profilometer

12. 2. Optical interferometer

13. 3. Atomic Force Microscope (AFM)

14. Analysis of the measured surface roughness parameter

15. Traversing length (LT)-represents the distance that is traversed across the surface by the stylus when characterizing the surface, i.e. measurement length. Assessment length (LM) is the length over which surface data is acquired and assessed. Sampling length ( LV reference length) -It is a length of a section inside the assessment length and it is equivalent to wavelength of the filter

16. Parameters of roughness : 1. Arithmetic mean value (R a ) 2. Root mean square average (R q )

17. 1. Arithmetic Mean Value (R a ) The most widely recognized and used parameter for surface roughness characterization. R a is arithmetical mean deviation of all the measured values in the assessed profile (LM) from the mean line of that profile.

18. 1.Arithmetic Mean Value (R a ) Averaging of data: ⇒ R a does not differentiate between profile peaks and valleys!! ⇒ R a or any other parameter by itself: not sufficient. ⇒ Additional parameters necessary: more sensitive & able to distinguish between surfaces with different shapes and/or ratios of peaks and Valleys.

19. 2 . Root mean square (R q ) : (RMS) deviation of the assessed roughness profile

20. Surface Roughness in Practice Surface roughness design requirements for typical engineering applications can vary by as much as two orders of magnitude for different parts. The reasons and considerations for this wide range include: Precision required on mating surfaces, Frictional considerations Fatigue and notch sensitivity, Electrical and thermal contact resistance, Corrosion resistance,. Subsequent processing,. Appearance Cost considerations,

21. CONCLUSION These factors should be carefully considered before a decision is made as to the recommendation about surface roughness for a certain product. As in all manufacturing processes, the cost involved in the selection should also be a major considerati on.

22. THANK YOU