• 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
- 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