1. SURFACES

 

• No surface is perfectly smooth, but the better the surface quality, the longer a product generally lasts, and the better is performs.

 

• Surface texture can be difficult to analyze quantitatively. Two surfaces may be entirely different, yet still provide the same CLA (Ra) value.

 

• Recent developments in production technique, and metrology equipment have made it possible to specify and measure surface quality.

 

• There are standards, such as the CSA B95 1962.

 

• Surface Quality can be important when dealing with,

- lubrication - small indentations can hold lubricant

- resistant to wear - smoother surfaces wear less

- tool life - rough surfaces will correlate to shorter tool life

- fatigue/stress raisers -

- corrosion - smoother surfaces easier to clean, less surface area to erode

- noise reduction - smooth surfaces make less noise when rubbing, for example meshing gears.

- fit - pressure seals could leak through pits

 

• Surface geometry can be quantified a few different ways.

 

 

• Real surfaces are rarely so flat, or smooth, but most commonly a combination of the two.

 

 

 

• Some other terms of interest in surface measurement,

- Surface texture - all of the details that make up a surface, including roughness, waviness, scratches, etc.

- Lay - the direction of the roughness on a newly manufactured surface. The roughest profile will be perpendicular to the lay.

- Flaws - small scratches, cracks, inclusions, etc.

- Cutoff - a value selected to be less than the waviness, but greater than the roughness length. This is controlled using electrical or digital filters. Typical values might be; 0.010”, 0.030”, 0.100”

 

 

1.1 MEASURES OF ROUGHNESS

1.2 METHODS OF MEASURING SURFACE ROUGHNESS

1.3 OTHER SYSTEMS

1.4 PRACTICE PROBLEMS

1.5 PRACTICE PROBLEMS

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