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View Full Version : sheet silver cracked apart - any idea why?



abyjem
31-10-2010, 06:25 PM
Hi folks,

I've a piece of silver sheet 0.8mm thickness. I've annealed it a couple of times before with no problems but when I annealed it today - it cracked.

I did everything as normal, moved the flame slowly across the surface, didnt even get it to glowing red and then waited a couple of seconds before putting into the quench. The quench was room temperature water. Everything just as I've done it before.

Photo below shows what has happened - its fractured in several places but one is huge and completely ruined the sheet.

any ideas? Its never happened to me before
anybody have this happen to them?
Did I do something wrong?
Was the silver faulty?

http://i7.photobucket.com/albums/y268/welliebird/DSCF0711.jpg

FVT
31-10-2010, 07:02 PM
Oh dear...that looks nasty:( I can't offer much advice but very interested to see what other people say. When exactly did the crack appear...before or after you quenched it?

abyjem
31-10-2010, 07:07 PM
after quenching but it didnt happen the second it went into the quench - it was n thewater a couple of seconds and then went!

Dennis
31-10-2010, 09:53 PM
Dear Faith,
I am not a metallurgist, but this is how I understand it. I have tried to use non-technical language so as hopefully not to get it wrong. But there are members more expert than I am in this subject.
Silver should only be annealed if it has been thoroughly hardened by hammering, rolling or drawing. The reason for annealing is to allow the crystalline structure to return to the state where the metal is soft enough to work with again. By repeatedly annealing the sheet when it did not need it , the structure of the alloy has been disrupted, so finally it just cracked.
Kind regards, Dennis.

stu_clouds
01-11-2010, 06:40 AM
Dennis is correct as far as i can see, im unsure why you have annealed a sheet that hasn't been worked. it only needs it once worked like dennis states.

Stu

jille
01-11-2010, 06:47 AM
I'm just a beginner so would you explain to me why this doesn't happen when you reticulate silver, I'm curious to know
thanks
Jill

abyjem
01-11-2010, 09:33 AM
Thanks for your replies.

Dennis and Stu,

I have actually worked the silver - as can be seen from the photo, it has had a number of discs punched from it and each time it came out of the disc cutter it was buckled slightly so I hammered it to straighten it again, thus hardening it up. If it had been soft enough to use in the disc cutter, I wouldnt have annealed it again but I am not an expert so please correct me if I am wrong in that. In total I dont think it has been annealed more than 4 times, including this last time and each time it has been because it was too hard and unyielding to be put into the disc cutter.

WhenI use my disc cutter it normally takes a couple of blows with a hefty hammer to cut through the sheet and as I understood it, this process alone has a ripple effect on the rest of the sheet, thus tightening the structure of the metal. Is this not right?

ps_bond
01-11-2010, 09:36 AM
I've done that before when reticulating - it usually means I've either overheated the metal while annealing or (more often!) quenched it too quickly.

abyjem
01-11-2010, 09:46 AM
Thanks for all your replies - its all a learning process for me - albeit a rather expensive one in this case!

I will phone Cooksons and ask them about it, thats where I got the sheet silver from. No doubt they will tell me I've done something wrong !

ps_bond
01-11-2010, 10:21 AM
I'll dig out Brepohl this evening and put together a slightly more technical post - short form is down to crystal growth and grain boundaries forming.

abyjem
01-11-2010, 10:52 AM
Now you're gonna blind me with science Peter - lol

I've just spoken to Cookson and they asked me to send back the sheet to be tested. The guy I spoke to did say he thought it was unlikely that I had over annealed it but will wait and see what the tests reveal.

Just thinking aloud - surely when doing several solder joints on one piece, its like annealing several times without actually working in between? so in theory, this could happen to something like say a ring that has had several joints soldered, and maybe a bezel cup soldered onto it. During each soldering process the metal is getting as hot as when I am annealing?

Dennis
01-11-2010, 07:04 PM
Faith,
There is a lot of logic in what you say, but you can't reason with a piece of metal, so I am waiting with baited breath for the final answer. Kind regards, Dennis.

Joe
01-11-2010, 07:51 PM
Nooo, don't listen to Faith Peter, I want the techy stuff!!

I've only ever had this happen with sheet that was contaminated in my own melt-pot. Very unlikely with Cookies sheet, but if it's going to happen with a supplier, it's better with a big company like Cookies who'll review and replace rather than fob you off.

I can't think of any reason why it might have happened with sterling in this shape. Please press Cookies to tell us what testing they did when they reply, we're really interested, not in a critical way.

Tabby66
01-11-2010, 08:16 PM
I agree with Joe, press Cookies for an answer Faith. It would be really good from a learning perspective to understand why this has happened.

ps_bond
02-11-2010, 08:53 AM
OK, the brief version from Brepohl is that excessive grain growth causes mechanically weak metal which can crack (either working or quenching too fast).

Excessive grain growth through annealing is usually caused by 1 or more of the following 4 factors:

Insufficient working of the metal prior to annealing.
Heating to annealing temperature too slowly.
Holding at annealing heat too long.
Heating too high.

Fundamentally, as you work the metal - as Dennis has said - you are distorting the grains, or crystals. They can take a certain amount of distortion, causing the grain boundaries to become progressively more stressed, until any attempt at further deformation will result in the metal cracking (where the stress in the grain boundaries has become too much for the grains to hold together). So, we anneal - this involves taking the metal up to a point where the grains can recrystallise, relaxing the strain on the grain boundaries, coupled with a small amount of grain growth; time & temperature have to be more-or-less right to get the metal to the state we want it to, but if it wasn't worked enough beforehand, you don't have the stressed structure to work with so you are only really going to encourage excessive grain growth.

Brepohl's much more thorough than that - hope it wasn't too over-tech!

That said, as you've got the offer to have the metal tested I'd go for it - but that looks like you've got firestain in the picture?

daisychain
02-11-2010, 09:46 AM
A student of mine had something similar happen when he was soldering a big piece of silver. Essentially the soldering didn't work as he wasn't using a large enough flame. He tried again and again (at home btw not in class where I could have seen what was going on and helped!), each time heating the silver up too slowly, only up to about annealing temperature rather than the temperature needed for soldering, and after about the fifth attempt it cracked - a very expensive lesson for him! The reasons for the cracking were two of the factors that Peter listed -
Heating to annealing temperature too slowly.
Holding at annealing heat too long.

abyjem
02-11-2010, 08:03 PM
Crikey, with all the things that need to be just about right - its a wonder I havent buggered it up before now then!

The sheet went back to Cookson today so hopefully I will find out the bad news soon.

Dennis
02-11-2010, 08:39 PM
Crikey, with all the things that need to be just about right - its a wonder I havent buggered it up before now then!


And so say all of us, us ,us. Dennis.

Ruby123
02-11-2010, 11:49 PM
Take a piece of thin plastic and bend it back and forth and you will see that it starts to go white then eventually breaks. This is what has happened in essence to your sheet silver, the "grain" structure has been adversely affected by repeated "working" , both physical and through energy changes (heat / cold) during the annealing process. Eventually it will happen, everything has a life span :) Also remember that the Silver sheet will be alloyed with some other element that will have contributed.

cheers,
Ruby

abyjem
03-11-2010, 04:57 PM
Thanks Peter - I rather take exception to my post being hijacked, especially by spam for a naff website!

ps_bond
03-11-2010, 05:17 PM
I'm still mulling which way this one goes.

mizgeorge
03-11-2010, 06:34 PM
Oh I don't know Peter, I'm still amused at a student of metallurgy selling fake pandora beads and 'tibetan silver' ;)

Joe
03-11-2010, 09:33 PM
Do you think we could get a moderator to trim Ruby's posts out? I do mean all of them! Will try to get the other forum's he's posted on to do likewise.

Such a pity because this is exactly the sort of thread that makes forums really worth-while! Thank you so much for posting Faith!

ps_bond
04-11-2010, 08:35 AM
Oh I don't know Peter, I'm still amused at a student of metallurgy selling fake pandora beads and 'tibetan silver' ;)

Oh? I'd only had the briefest of skims of the front page. Might go back and have another look later on. This is, of course, more work than the big red "ban" button. :)

abyjem
29-11-2010, 08:21 PM
Just to let you all know - I've still not had the piece of silver back from Cooksons yet? been 4-5 weeks now at least - several phone calls - wish I hadnt bothered to send it back.....