Thank you Miguel for sharing the photo.
I hadn't expected that my poor drawing would be kept on webs when I drew it , though
I do wash ( the tip area only) and dry the HSA as my usual work. sometimes it helps , sometimes, it doesn't.
Even if it seems it doesn't help, particles on the disks may be collected by the washed clean sliders. so we can expect that the disk surface may be cleaner. And this is one of the idea for cleaning the surface .
1. Wash and Dry HSA and install into the HDD
2. Power on and wait for a short time like for 1 to 5 head seeks. because this is for the cleaning.
3. Take out the HSA , and the repeat the same steps from 1st through 3rd
After a while, disk surface may be cleaner. Then you install a good working HSA from a donor HDD.
Moreover, when slider crashes against disk badly , that produces particles ( dust) at outer area of the scratched line.
to avoid the dust area, I prefer to read from inner area of the disk towards outer area.
when the HDD is formatted as NTFS, then first target data for reading maybe $MFT and then analyse it and select target files and start reading form the sector which is the closest to the center of the disk and then to the outer area. We want to read necessary sectors but don't want no-data area that could cause another damage.
Well,this is my basic way for HDD which may have damage on the surface of the disks.
When the damage ( scratch ) is heavy, then the method above wouldn't help and it may damage more.
To prevent more damage to the disk, removing the contamination on the disks by burnishing would be preferable. To do so, we developed a machine that burnishes disk surface without requiring to remove the disk from the spindle motor so that the alignment issue can be avoided.
Please do not expect too much that this machine works perfectly for any damaged HDD. Sometimes, HDD becomes good enough to read SA only but UA....
And this method costs much higher than the above one. However I've had successful cases with ST****DM***
Btw, the burnishing process is the final step of disk production ( after lubrication at factory ) and the idea above is from the process at factories.
Even though my main corporate site is in Japanese, there are some photos. http://www.daillo.com/
The orange photo on the top area of the page was taken by OSA (Optical Surface Analyzer) and shows the depth of the lub layer ( ST3000DM001 )
At the middle of the page, there are vacuum oven and ultrasonic cleaner .