Cleaning brass in Ultrasonic cleaner

[ColinR]

I clean my brass in a heated ultrasonic cleaner with 3 tablespoons of citric acid crystals in about 2 litres of water. The brass goes bright almost immediately, but it takes a little longer to get the powder residue from the inside and primer pocket. I understand from what I read that citric acid passivates the brass and causes no harm. However, sometimes the brass will come out with a copper coating, or at least a copper coloured coating that is not easily removed although tumbling does take it off. I assume this is copper being liberated from the brass. Does anyone know of any damage this might cause, or is it just surface reaction?

Also I dry the brass after washing and neutralising the acid in the oven at about 50 - 75C. Will this cause any annealing effect on the brass?

[saddler]

Also I dry the brass after washing and neutralising the acid in the oven at about 50 - 75C. Will this cause any annealing effect on the brass?

I do know that following the above example WOULD make my tinitus a lot worse - as swmbo would whack me on the head with a heavy blunt object if I deemed to use the crematorium for drying off my brass cases!!

Annealing needs the brass to be cherry red - NOT a worry at the temps you are drying the cases at...

[Doz]

I clean my brass in a heated ultrasonic cleaner with 3 tablespoons of citric acid crystals in about 2 litres of water. The brass goes bright almost immediately, but it takes a little longer to get the powder residue from the inside and primer pocket. I understand from what I read that citric acid passivates the brass and causes no harm. However, sometimes the brass will come out with a copper coating, or at least a copper coloured coating that is not easily removed although tumbling does take it off. I assume this is copper being liberated from the brass. Does anyone know of any damage this might cause, or is it just surface reaction?

Also I dry the brass after washing and neutralising the acid in the oven at about 50 - 75C. Will this cause any annealing effect on the brass?

I'm no chemist but I believe your copper coloured coating is where the zinc has been dissolved out of the surface leaving pure'ish copper behind. I can't tell you whether this is a bad thing or not although it doesn't sound too great! As to the temperature issue, I'm almost certain that sort of temperature will have no effect on the properties of the metal whatsoever.

EDIT: I took so long writing this Saddler beat me to it re. temperature... smile2

[rox]

I clean my brass in a heated ultrasonic cleaner with 3 tablespoons of citric acid crystals in about 2 litres of water. ...

My research and experimentation lead me to similar conclusions and results to yours. I never solved the surface copper problem, although reports indicated that the passivation process was 'self-limiting' for citric cleaning of brass. Whatever the cause, I was never satisfied with the results, the throughput or the amount of interaction required. Even a more substantial commercial machine required multiple cycles to process just 20 or 30 cases, so cleaning the results of a day's shooting (100 cases or so) could take a lot of work. On top of the work, the results certainly didn't look good, left a question-mark over possible effects on the brass, and I still ended-up manually cleaning the pockets first. I never subscribed to the 'neutralising' idea though; how can you exactly match the pH and quantity of the neutralizing agent to achieve this? It just replaces one chemical which attacks the surface with another, which still needs to be removed by rinsing. It might even negate or remove the passivated surface protection.

Eventually I switched to Stainless Steel tumbling. The overall time, and perhaps even overall work, probably isn't that much different, but the results are almost perfect and I can toss-in 100 .308 cases, leave them for 3 hours, after which 10 or 15 mins to separate, rinse and remove excess water then they can be left to dry naturally or with a little assistance from a radiator, sun or fan. Large ultrasonic cleaner for sale anyone?

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[ColinR]

Doz, I think you are right. I thought it was copper coming out of the brass but a search on the internet talks of dezincification where it is the zinc being dissolved into the solution leaving just copper. It does not happen with all cases but I noticed it recently when cleaning Ruag .338LM cases. I think I will experiment with the amount of citric acid, temperature and time. Thanks for the lead which I will research further.

[ColinR]

Rox, I am surprised that you did not get better results. I clean all my brass in the ultrasonic cleaner with great results - the coppering problem with some cases is only a minor nag. My cleaner comes from a company called James, has two transducers, 2.3 litre capacity, timer, variable heater, model # Sonic3000M. Apart from washing and drying I do nothing more to the cases with regard to cleaning. The insides and primer pockets look like unfired brass. I was always concerned that primer pocket cleaners/brushes contributed to wearing the pockets, but no such concerns now. I reckon I clean upto 100 .308 cases and 50 .338LM cases at a time and it takes about 20 minutes. For smaller amount the time is much less. The water turns black from all the residue released from the cases.

If I were you I would certainly reinvestigate this method of cleaning - sounds like your unit was not up to the job.

[rox]

Strange. Mine was also dual transducer, roughly double the size and power of yours. I only had the copper problem after lengthy immersions though. Do you use any particular method to suspend the cases, or are they just in a basket?

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[ColinR]

Rox I use the stainless steel basket that came with the unit which sits on the bottom of the bath, so not really suspended.
I tend not to use the basket with pistol cases as they fall through and can be a pain when you lift the basket to occaisionally agitate the solution. Then I just give it a stir. I use food grade anhydrous citric acid powder - about 3 tablespoons to 2 litres of water and the results are nothing short of fantastic and quick too! My unit also has a heater which I set to the highest setting. My only concern has been that of the copper, but does not seem to happen to any marked degree with Lapua cases.

[rox]

about 3 tablespoons to 2 litres of water and the results are nothing short of fantastic and quick too!

Interesting. I may have another go with that concentration when time permits - do you replace the solution each cycle? Thanks!

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[phaedra1106]

I used to use an ultrasonic cleaner, used warm water as I was told hot discolours the brass. Only thing I did that's not mentioned is rinsing the cases in a solution of water with bicarbonate of soda added to passivate the cases stopping any chemical reaction continuing. After that a good dry in a towel (swung round as a DIY cetrafuge!) and popped in a warm oven until fully dry.