Ask the Expert Question-and-Answer Archive
(Hard Chrome Plating)
by Randy Taylor, Advanced Tooling Corporation
Chrome Stripping and Masking
Q. I'm trying to find a straight answer to the question - does chrome strip affect the basis metal? I strip chrome off aircraft components of various types of steel, and the manufaacturers information says "mask areas not to be striped" but does not elaborate as to the need or reason for masking. We use sodium hydroxide and strip parts anodicly at 4-6V. Components can be complex in shape and masking/unmasking can be very time consuming. Is masking nessesary?
A. I'm going to go out on a limb here and say with a high degree of confidence that stripping chrome from common "ferrous, CRES steels, even titanium alloys" in an ambient to 110°F solution of sodium hydroxide and water is quite safe. An alternative solution is sodium carbonate & water.
That said, I would issue the following cautions.
1.) Bussing should be clean and in good condition, check and verify all DC connections to prevent arc burning.
2.) Rectifier should be routinely checked for meter accuracy and have a valid calibration tag.
3.) Alkaline chrome strip solutions are safe and reliable when new, but can degrade as impurities build and PH and chemistry become altered by dissolved metals and dilution.
Strip solutions are often sacrificial and have a relatively short life. So operators often take solution make up, additions and analytical responsibilities lightly. A good rule of thumb, no stripping solution is ever entirely safe. Always check parts frequently, never leave parts in a strip tank for more than a few hours and never take anything for granted.
Using a simple titration, check and record NaOH content and PH of the new strip bath, then periodically retest the bath weekly as it ages. In the same log book, jot down each job stripped by date, and total mil-square feet of chrome removed. By analyzing these data, you can quickly determine a safe bath life estimate based on through put.
My guess is that the instructions to “mask the areas not to be stripped” are referring to other chrome plated surfaces if any, which may be damaged if left unprotected.