Sample Polishing and Preparation

1. Mount specimen using standard procedure for the chosen mounting material, such as acrylic and Bakelite resins. Each material type requires separate steps for proper mounting, ask instructor or other MTU faculty for specifics.
2. Apply low grit pad (usually 80-120 grit) to working wheel of a metallographic auto polishing machine
   • Make sure bad is correct type for sample, i.e. Ferrous vs. Non-Ferrous, and hard vs. soft
   • Most grit papers are Silicon Carbide. If the paper being used is not, be sure to make not of this for when the samples undergo whatever type of analysis they are needed for, as the polishing element may affect the analysis results.
3. Load samples into auto polisher.
4. Turn dial for sample pits until headless screw inside force column, visible through vertical slit on side of the column, reaches the second etched line from bottom of column rotator. Each line represents 10 newtons of applied force to the samples as they are grinded.
5. Turn on water for the polisher to allow some lubrication while machine is running
6. Turn on auto polisher and run until sample is sufficiently flat. (First run only)
   • For subsequent runs, run for specified amounts of time. Record time for each grit level.
   • Turn off water after each run finishes.
7. Remove samples and clean.
   • Run under cold water and clean with small amount of soap.
   • Use cotton pads to wipe with. Do NOT use paper towels, as this may introduce micro scratches to sample when moving to lower grit pads.
   • After washing off soap, rinse with ethanol. Use hair dryer to evaporate ethanol and leave sample clear.
8. Remove lower grit pad from work wheel and replace with higher grit.
   • Do not increase grit over double the first grit, i.e. Moving from 240 grit to 480 is okay, but jumping to 600 is not.
   • This rule of thumb can be bent if it is the first grit increase, but do not jump over 320 grit. This is the intermediate grit size that must be done before moving to the greater grit sizes.
9. Repeat steps 3 through 8 until sample finishes with 1200 grit.
   • Pressures and run times may vary, depending on preference of user and/or quality of polishing after each run
10. Take clean intermediate diamond polishing and apply 6 micron diamond polishing paste to pad. Use glove to spread paste across pad.
11. Apply to work wheel and load samples
12. Apply load of 20N and run machine for approximately 10 minutes.
    • If not polished enough, rerun for another 10 minutes, as needed
    • There should be no water used at this grit level. Water would wash away diamond paste.
13. Repeat step 7.
14. Remove pad from work wheel and save in personal storage for any later use.
15. Repeat steps 10 through 14 for 3 and 1 micron diamond pastes, and 0.5 micron Colloidal Silica.
    • For Colloidal Silica, run time should only be about 90 seconds.
16. Look at sample under optical microscope. If polished properly, few micro scratches should be visible. If not, re-run samples with 0.5 micron Colloidal Silica until satisfied with results.