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Hi, Bob...


Yes, I've been silent for a while now. My move back home to Melbourne form Singapore went well... my attention has been on home renovation and building the workshop and not much progress on the locos. The workshop is taking longer than I expected to set up but I'm getting there. My model engineering tools have had to make way for carpentry and brick laying stuff!


 



My wife keeps saying if I didn't build the workshop to microscopic engineering tolerances... it would have been finished way sooner ! All good fun though. Just as soon as work on the locos start again I'll post.


How about yourself? What are you working on? 
 

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Sulphuric acid makes the best pickle and also the best means of cleaning parts prior to silver soldering. Citric acid and clear vinegar work too but a 10% solution of Sulphuric Acid is fast and more effective at removing the remains of the flux too. (I find citric and vinegar pretty useless).

However, I make no excuse for saying that when diluting any inorganic acid like Sulphuric Acid, always add acid to water[/b] [/b]never the other way about. The act of dilution is a very exothermic reaction. That means a lot of heat is generated. If you add water to concentrated acid then the reaction is extremely unpleasant - hot acid is likely to spit everywhere.

Please always store concentrated acid and diluted pickle in a safe place away from children and pets. Its not nice stuff to have around but its darned effective as a cleaner and pickle for silver soldering so dilute, store and use with care.
As an afterthought. I am pretty useless at soft soldering but i find silver soldering to be a most satisfying job. With a little care with cleaning component parts first and then the careful application of flux and finally heating up to a dull red and watching the silver solder 'flash' round the joint is a pleasure. But the best bit comes when you take the item out of the pickle and see the copper and brass parts shining brightly and a neat meniscus of silver keeping all the parts together. Almost as a good as a steam-up and a cold day!
Andrew
 

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As I built the boiler for my gauge 1 Climax, I posted many photos on flickr. There are 115 photos in the set -


http://www.flickr.com/photos/edhume3/sets/72157604664938888/





In this photo I am using copper tongs with a 10% sulphuric bath. I do have eye protection on but I am somewhat casual about gloves. I am right next to a sink and fully prepared to rinse off quickly if I splash my hand. A covered plastic container like this one is big enough for gauge 1 boiler work.

By the way the copper sulphate will plate out rapidly on tool steel or mild steel but not stainless steel. This provides a quick test for stainless - dip it in and see if copper plates to it.
 

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We switched to citric acid a couple of years ago and have no problems. Copper/brass gets shiny and the residues of flux (we use the commercial stuff from McMaster) dissolves fairly easily. Though diluted sulphuric acid worked faster, we find it very annoying, as even tiny splashes develop holes in clothing, usually days/weeks after the soldering session.
Regards
 

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Ed Hume said - ”By the way the copper sulphate will plate out rapidly on tool steel or mild steel but not stainless steel. This provides a quick test for stainless - dip it in and see if copper plates to it.”

That’s a very useful tip Ed, thanks. Basically that is why is worth being a member of MLS for those simple tips which come in handy.

Henner mentions the problems with handling dilute Sulphuric Acid as a pickle. I have found that using tongs at arms length is the best way to go. When the boiler or work piece comes out of the pickle then put it into a bucket of water straight away to rinse. Having water available in case of a splash is good practice. I wear old clothes and work in the garden when I am doing a bit of Silver Soldering. I wear eye protection and generally get everything organized before starting the work in hand. I mix up fresh flux each time and work with the lower temperature solders like ‘Easy-Flo”. Now that Cadmium is banned from Silver Solder in Europe, it doesn’t ‘flash’ round a joint as easily but it still works well enough for me.
Andrew
 

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Yep, old lab rats could quickly identify which sweatshirt was worn on the sulphuric acid day in the lab. After a few days on cotton and many other textiles, everything looks normal until wash day. Then major moth attack - holes everywhere a tiny drop made contact. Diluted and cool, sulphuric is slow acting on organic matter - including human beings. Heated, or concentrated above about 70%, it shows a powerful affinity to water and will dehydrate anything it contacts. I still remember the high school demonstration of pouring some concentrated sulphuric into a beaker filled with table sugar - in seconds it turned to solid black carbon - stripped the water right out of the sugar, that is why it is called a carbo-hydrate, a hydrated carbon atom skeleton. Below about 70%, sulphuric has enough water of hydration to stop the dehydrating action, but the strong acid attack remains.

And yes, sulphuric acid is the most dangerous one when adding to water due to the hydration action. SLOW addition of acid to water, preferably in an ice bath, is called for. The other common mineral acids do not generate the tremendous heat of hydration, but the same rule applies. Adding a small amount of water to concentrated sulphuric generates enough heat to flash the water to steam, splashing acid everywhere.

So, goggles and protective clothing are strongly advised. Fumes include assorted sulfur oxides - all toxic and corrosive. Without a fume hood, maintain plenty of fresh air unless you happen to have a respirator fitted with acid fume cartridges. And do not forget that any acid reacting with metals generates hydrogen gas - iron filings and mineral acid are still used as hydrogen generators.
 

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A pair of inox BBQ tongs is nice to have next to the pickle bath. But don't use them for anything else afterwards.

Regarding HCl, this might be usable for this, but I won't allow it inside the workshop. It rusts everything even if kept in a closed container.
 

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Ed - Thanks for the boiler fabrication photos. Nice to see how it's really supposed to be done!

For pickling I use sulfuric acid from the hardware store plumbing section, but the dilution I mix is probably between 1:20 and 1:30 with water. It's not overly aggressive but it works. I wear eye protection and old clothes. I really need to find some more rigid tongs than the plastic BBQ tongs I currently have. They don't grip well - not rigid enough - and large parts can slip when fishing them out of the pickle causing the acid solution to splash. I need to do better as it's not something to be casual about.

The pickle is stored outdoors in a covered rectangular plastic container that fits inside a black plastic battery box. I used to keep the pickle in a container with a plastic gasketed cover, but the gasket disintegrated over time. Thanks to George's post I now know why.

Steve
 

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I realize that this comment is "off thread", but I've also found that pickling brass or copper parts is a good prep for painting. Brass, especially, takes paint more readily when cleaned this way beforehand. I've got some sodium bisulfate (purchased from Sulphur Springs many years ago) that works great.
 
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