Vendor's Degreasing Liquid?

Question:

We have a vendor that uses a proprietary aqueous mixture of 5-10% phosphoric acid and 1-5% alcohol (2-butoxyethanol, or butylcellosolve) to degrease aluminum parts prior to cleaning/etching/deoxidizing the aluminum for chromating. Our in-house use of a non-etch alkaline soap cleaner has been an old and reliable standby and now our vendor has decided to use an acidic cleaner and has raised some questions. While I know the butylcellosolve is popular in some household cleaners (i.e.. liquid "Fantastic"), I am not sure if most of our aluminum alloys (series 6000, 7000, 2000 and 5000) would sufficiently degrease water soluble and possibly light machine oils?

Maybe you have some pros and cons for this type of phosphoric acid and alcohol degreasing solution? T.A.

Answer:

I will give you my opinion, but you also need to be asking these questions to your cleaner supplier. It sounds like you were using an alkaline cleaner that you were satisfied with and then changed to the phosphoric acid-based cleaner at the recommendation of the same supplier. What was the rationale behind the change? Cost savings? Increased performance? How was the new process going to be validated (salt spray after chromating)? Whenever making a process change, it is important to clearly define why you are changing, what the expectation is and how are you going to measure its effectiveness.

The phosphoric acid/butyl cellosolve mixture you described could be effective by itself as a cleaner but that may not be all that is in there. If you mix it vigorously, does it foam at all? If it does, that would indicate there are also surfactants in the cleaner. If it does not foam, that doesn't automatically indicate there are no surfactants, since some are low foaming.

It is likely there are one or two surfactants in the acid mixture. Some of the nonionic types of surfactants would be able to withstand the low pH from the acid. However, some of them do not go into an aqueous solution very well. The butyl cellosolve is often referred to as a coupling agent. So while it is reasonably good at cleaning, it is even more effective at keeping surfactants in solution that would otherwise separate. The surfactants will boost the cleaning efficiency significantly and allow you to remove the types of oils you described above.

The other benefit of this type of cleaner for your operation would be less effect from dragover. The cleaner will obviously be rinsed between cleaning and chromating, however, since the chromating tank is acidic, it would be advisable to have an acidic cleaning process upstream that would minimize the neutralizing effect that an alkaline cleaning process could produce with even a minimal amount of carryover.