Aluminium cleaning advice please.

[Nick]

TFR, the non-alkaline ones, are good, however I've found that getting into the crevices of  some components, e.g. vane capacitors, can be tricky - this is where an ultrasonic cleaner (UC) really wins.

If you have access to an UC, use it - I use Tikopur R33 as I use it as the general cleaner in my UC, so it's around, but TFR would probably be fine too as it's basically similar stuff in a retail version...

Industrial cleaner like R33 are insanely concentrated - you normally use R33 in a 1:100 dilution.

Crud on the plates can also affect the value by acting as a dielectric. Might be interesting to measure max/min capacitance before and after cleaning.

I didn't measure the sections (C25 & C26)  before cleaning, but both sections now read 17pF - 550pF. The "550" value is really really close on both sections, like 549.4 & 548.7pF, so I suspect that is either a highly unusual coincidence, or deliberate!

The Trader Sheet states that they are nominally 528pF which is only 4% lower, but there are two 40pF LO trimmers  (C28:MW & C27:LW), so I suspect that they were probably always 550pF and the trimmers compensate as they are supposed to... I used an LCR40 that's still in calibration (so nominally +/- 1.5%) and did a "lead compensation" just before taking the photos below.

       

[Amie]

Thanks all...

I'm the dishwasher so initially I'll try manual cleaning in sodium carbonate, (we have some), in hot water. One of these components is a big ceramic insulated 500pF triple gang, its a pull from a scrap set that I want to use for experiments, but worth saving anyway... it's filthy with a bit of spotty corrosion on the plates. The other is a twin, and is very bad, that'll be the practice one! I do have a friend with an ultrasonic bath cleaner but they're not local, I'll wait rather than use anything too vicious. These capacitors are made in a way they can be disassembled easily if it's needed, though I'd rather not do that unless completely necessary.

I've measured them and will report what the difference is after cleaning, rinsing, drying, and greasing.

Thanks again.
Amie.

[Kalee20]

I've been giving this some thought. I've heard reports that putting in a dishwasher works well, but not tried it - like the OP, the dishwasher is me...

So failing that, I do like the suggestion of Alubrite. I'd also suggest alloy wheel cleaner, for cars - after all, the stuff is designed to be compatible with aluminium.

Alkali solutions are good for cleaning oil, grease, etc owing to their saponification effect - the oils are turned to soaps. Unfortunately, aluminium tends to react with alkalis, chemically, it likes behaving as a non-metal rather more readily than as a metal.

Sodium hydroxide is a no-no. Sodium carbonate is much weaker as an alkali, but just as it will attack the aluminium far more slowly than caustic soda, it may well have a similarly slow effect on the muck. What's wanted is something aggressive to muck, but not to aluminium. Hence the wheel cleaner suggestion. Another may be engine degreaser, eg Gunk.

Whatever, my attack would be to use those, and then be sure to remove all traces - finger over the end of a tap comes to mind to get a powerful squirt between tha vanes and in the crevices. Then oven-dry for several hours at 50 deg C.

Another option might be to soak in paraffin, which just dissolves grease and oil.

Finally, when dry, relubricate the bearings - I use clock oil for a sliding bearing, and molybdenum disulphide grease thinned down with paraffin for ball-bearings, applied with a small medical syringe to get it where it's needed. The paraffin evaporates of course, but by then the grease is where it's needed.

[Amie]

Thanks Peter

I think you're right about the rinse cycle being most important, also good idea thinning the grease for the bearing...



Amie

[Nick]

Finally, when dry, relubricate the bearings - I use clock oil for a sliding bearing, and molybdenum disulphide grease thinned down with paraffin for ball-bearings, applied with a small medical syringe to get it where it's needed. The paraffin evaporates of course, but by then the grease is where it's needed.

The points about rinsing and clock oil are important. Rinsing, obviously, to remove any non-PH 7 contaminants (should ideally use deionised water, but not that important) but, for those that don't know, modern watch/clock oil does not dry and become tacky with time - they are synthetic oils, typically silicone-based, and are very thin. The traditional watch oils were a combination of neatsfoot and mineral oils which become gummy over time and could be acidic thus damaging metal - watchmakers had a nice business in regularly cleaning mechanical watches because of this! Neatsfoot oil is made from the bones & feet of cattle, "neat" being an OE term for cattle, i.e. not one for vegetarians or vegans etc...

[Radio Fixer]

Used the dishwasher many times before I had an Ultrasonic Cleaner. Think it was a quick wash cycle with half a tablet. Works well but be sure to remove any mica plates from the trimmers. Rinse with tap water and then deionised. Be sure to lube after: grease for the ball race and thin oil for the plain bearings.

Dont ever do this on ones with painted end plates as the whole works will be jammed up with paint particles and the plates will now look very tatty.

Since having the USC I have used that with this general purpose cleaner:https://cpc.farnell.com/ambersil/6330001300/ultrasonic-cleaning-liquid-1ltr/dp/SA02601?st=ultrasonic%20cleaning%20solution

Ambersil from CPC

Then a part of an article I wrote (Zetavox) about how I dealt with corrosion:

"And then another funny; I found one of the fixed plates was loose at the top and another had a ‘chewed’ fixing screw. Why would anyone think they needed to mess with these? So the decision was made to remove the fixed plates noting where everything came from. It did allow a much better clean up and I could look at the aluminium corrosion of the plates under a magnifying light. It wasn’t bad and interestingly more on the fixed plates with virtually none on those of the rotor. Those are of course at earth potential so perhaps over decades the polarity on the fixed plates makes a difference.
I tried an Internet WikiHow method on the corrosion which was soaking in a white vinegar and water solution. As the very weak solution recommended by them had no effect I increased it to 1:1 although some suggestions used the vinegar neat and left items overnight. My mixture seemed effective and after a few hours’ soak the white had changed colour a little to a darker grey. Emboldened that a longer soak was not going to just leave sludge in the bottom of the container I tried overnight. Afterwards it was difficult to see any corrosion so perhaps it had been successfully neutralised. The items were all finished off by copious rinsing in tap water, followed by a soak in de-ionised water. Then after all this cosseting, the parts had a luxurious warm stay on top of the CH boiler. Before putting back together I re-sprayed the chassis end plates and the cover light grey which is the norm for this gang and was the colour inside."


Gary

[Amie]

...soaking in a white vinegar and water solution.

Having read Gary's post and because it was in a very dirty state I thought to try a soak in the washing soda followed by the vinegar treatment if necessary. I wasn't confident enough to go straight into doing the triple gang one, but picked on another grotty example from the junk box.

I did end up removing the rotor from the frame, the only thing I  needed to do that was loosening the pressure screw for the back of the rotor shaft as my victim had a very helpful rotor contact system that doesn't have to be removed first, that normally means removing a rivet.

We don't have a dish washer or USC so the cleaning was a manual enterprise. I used a piece of felt to clean the loose muck between the plates after the first soak. Second time I re heated the solution on a camping stove, stirring the brew as I did so. After this there still appeared to be some corrosion spots between the rotor plates, so the soda solution was changed for vinegar, and the capacitor given another slosh round while heating. If nothing else the old saucepan I used is now the cleanest one we have! After a good rinse in boiling water the visible corrosion has now gone, so I'm claiming it a success. The parts are now sitting on top of the hot water cylinder to dry before being reassembled.

Next I'll try the Alubrite on another victim, see how that goes before moving on to the main feature of the big triple...