Cleaning/Drying of Optical Components

Question:

I am interested in learning how to clean and dry polished optical lenses/parts in one step without streaks or marks on the finished parts. Currently, we use an ultrasonic cleaner with Ensolve solvent in it. The parts must then be soaked in toluene and then hand dried to prevent streaking from the Ensolve solvent. With thousands of parts to clean, this has become very labor intensive. The primary materials used for the parts are barium fluoride, calcium fluoride, gallium arsenate, germanium, silicone, and zinc sellenide. Can you suggest a one step method for cleaning/drying the parts? The fluorides don’t handle sudden temperature changes and with optics, acids and/or bases are out of the question. I would appreciate any assistance you can give me. K.R.

Answer:

The one thing that stands out as being a potential problem is the use of the toluene as a final rinsing step. Generally speaking, toluene is a cut or fraction of a solvent blend that has a boiling range. Are you sure the streaking you experience is not from the toluene instead of the Ensolve? The higher boiling fraction may be responsible for some of the residues you are experiencing. Toluene also represents a flammability risk due to its low boiling point.

I would suggest focusing again on the cleaning process to make sure that you are not redepositing soils back onto the parts and that the toluene is simply rinsing them off. It is possible that you need a separate tank of the n-propyl bromide after the primary cleaning step. The cleaning solvent should dry fairly easily so you will not have to wipe them. Additionally, something like an air knife should help strip and dry the fluid.