Cracks in sheet metal

[purplepepper8]

Hi,

I have been struggling with my sheet metal cracking while rolling for a long time now, and I can’t seem to find a solution that works for me. I have tried different annealing temperatures, rolling while reducing the pressure only slightly, quenching in water and alcohol.

Once I melt it, I roll it down without any issues until I anneal it for the first time. The cracks form in the sheet after this (when I pass it through the roller). This seems to happen almost every time with 18 karat gold, with not much luck. Sometimes randomly it works without any issues but I don’t know what I am doing differently. And quite often if I get through the first anneal and subsequent rolling without it cracking, it doesn’t seem to crack later on. The cracks form perpendicular to the direction of rolling in between the sheet, and they don’t really go deep, but they always remain all the way through. Would love any advice on this matter.

Thank you,
Aman

 

[Sinterklaas]

Try not annealing at all. You need to keep the same side up. And always put the same side first in the rolling mill. Dont rotate the sheet. Us a marker and put some arrows on it pointing to the end you will stick in first.

Try it.

If it doesn't work you can try annealing. But I find that cracks will occur because of quenching to early. Dont quench when the metal is red. Quench (I just use water) when the glow is gone and it goes from dull red to grey.
If you quench to fast after heating it will induce a thermal shock in the metal. Which will turn in to visible cracks when rolling.

Also dont take to big of a step when turning the rolls. Small steps. And if you keep consistent rotation of the rolls you can get nice flat sheets. That dont have a banana shape

Maybe you can post a picture of your cracked sheet.

 

[pblack]

Are you working the ingot before going straight to the rolling mill? Forging the ingot to compress the metal and reduce it (gently) will help prevent cracks. The rolling mill is harsh on the metal so jumping straight to it can cause issues.

Check out John Sartin's video about turning an ingot into sheet.

 

[purplepepper8]

Try not annealing at all. You need to keep the same side up. And always put the same side first in the rolling mill. Dont rotate the sheet. Us a marker and put some arrows on it pointing to the end you will stick in first.

Try it.

If it doesn't work you can try annealing. But I find that cracks will occur because of quenching to early. Dont quench when the metal is red. Quench (I just use water) when the glow is gone and it goes from dull red to grey.
If you quench to fast after heating it will induce a thermal shock in the metal. Which will turn in to visible cracks when rolling.

Also dont take to big of a step when turning the rolls. Small steps. And if you keep consistent rotation of the rolls you can get nice flat sheets. That dont have a banana shape

Maybe you can post a picture of your cracked sheet.

Not annealing at all? But what about when it work hardens?
I do keep the same side first in the rolling mill.

Thanks for the tips about the quenching and the small rolls. Will try it.

I dont have a photo at the moment but if/ when it cracks again i will take one and share

 

[purplepepper8]

Are you working the ingot before going straight to the rolling mill? Forging the ingot to compress the metal and reduce it (gently) will help prevent cracks. The rolling mill is harsh on the metal so jumping straight to it can cause issues.

Check out John Sartin's video about turning an ingot into sheet.

Thank you for the tips. will try it out and check out the video

 

[monk]

my uneducated guess would be to first analyze the technique/s you're using to produce the ingot. are you using the same procedure from pour to pour? using the same procedure eliminates variables that can occur in the ingot. iv'e never done gold, but have experimented with silver, copper, and and other metals. i found that straying from a workable technique could cause problems. jm2cw

 

[Sinterklaas]

Not annealing at all? But what about when it work hardens?
I do keep the same side first in the rolling mill.

Thanks for the tips about the quenching and the small rolls. Will try it.

I dont have a photo at the moment but if/ when it cracks again i will take one and share

If the metal is good then you can just keep rolling. From 3mm thick to 1mm thick without annealing. But only if you keep the same side up AND the same side first. Dont rotate the sheet dont flip the sheet. It should work.

If it doesn't work then try the other tips.

If there are contaminants in the metal that can also cause problems.

 

[DaveAtWeirs]

If you spot a tiny crack at the side, file it out so that its entirely gone before going any further. Any crack will get bigger/longer, like a perforation in paper.
I tend not to quench, get it glowing dark cherry red (like right before it starts to melt) and then let it cool down slowly. Then I give it a light buff with 800-1000 grit emery to check the surface and keep it clean and make sure there's nothing that got stuck to it in the heat. Sometimes little flakes of fire scale from the tweezers or tiny bits from the solder pad can get stuck on there and can act like a perforation which will lead to cracks.
Sinterklaas is right though, I've rolled down 18ct a few mill without annealing (mostly cuz I was in a hurry, lol).

Don't forget you're spreading the metal over it's full surface, kinda like squashing a ball of playdough, the edges are taking the brunt of the stretch and they'll want to crack cuz that's the quickest way to alleviate the stress in the metal. Make sure to go down in very small increments through the sizes when starting cuz that's when it'll most likely form the really small cracks that will get bigger and tear through it as it goes down. Once its fairly flat you can go down through the sizes in larger increments cuz it'll flow along the length instead of just stressing the edges with bulging.

 

[purplepepper8]

If the metal is good then you can just keep rolling. From 3mm thick to 1mm thick without annealing. But only if you keep the same side up AND the same side first. Dont rotate the sheet dont flip the sheet. It should work.

If it doesn't work then try the other tips.

If there are contaminants in the metal that can also cause problems.

Yes im trying this now - to keep going to atleast 60% reduction in thickness without annealing. Thank you

 

[purplepepper8]

If you spot a tiny crack at the side, file it out so that its entirely gone before going any further. Any crack will get bigger/longer, like a perforation in paper.
I tend not to quench, get it glowing dark cherry red (like right before it starts to melt) and then let it cool down slowly. Then I give it a light buff with 800-1000 grit emery to check the surface and keep it clean and make sure there's nothing that got stuck to it in the heat. Sometimes little flakes of fire scale from the tweezers or tiny bits from the solder pad can get stuck on there and can act like a perforation which will lead to cracks.
Sinterklaas is right though, I've rolled down 18ct a few mill without annealing (mostly cuz I was in a hurry, lol).

Don't forget you're spreading the metal over it's full surface, kinda like squashing a ball of playdough, the edges are taking the brunt of the stretch and they'll want to crack cuz that's the quickest way to alleviate the stress in the metal. Make sure to go down in very small increments through the sizes when starting cuz that's when it'll most likely form the really small cracks that will get bigger and tear through it as it goes down. Once its fairly flat you can go down through the sizes in larger increments cuz it'll flow along the length instead of just stressing the edges with bulging.

Thanks for your response.
The cracks dont form on the side but all over the surface of the sheet and they dont tend to get deeper but remain even as i keep rolling. Im going to try annealing less often, particularly in the beginning

 

[DaveAtWeirs]

Interesting, I've not come across problems like that. I have a deal with me metal supplier where I can give them the gold I was going to melt down and for a very minimum fee they will give me the equivalent weight in whatever thickness of gold sheet I need. It means less money changing hands so less taxes and saves a bunch of time in rolling stuff down. That might be something you could organize to save your sanity

 

[purplepepper8]

Interesting, I've not come across problems like that. I have a deal with me metal supplier where I can give them the gold I was going to melt down and for a very minimum fee they will give me the equivalent weight in whatever thickness of gold sheet I need. It means less money changing hands so less taxes and saves a bunch of time in rolling stuff down. That might be something you could organize to save your sanity

Yeah this is an option but i want to be able to learn this bec i think long term it will be more convenient. Thanks for the idea

 

[bud2]

I'm don't comment very often but I'll put my two cents in here. Background first - I make my living out of jewellery, for 40 years. I try to recycle as much as possible due to the dollar savings. Similar to you I've had problems but much more problems with silver than gold. But even though silver has pushed up in price now, my labour is pushing up to. I'm not going to waste too much time on casting silver ingots with scrap of questionable origin. It could have been recycled 1, 2 or half a dozen times already. The alloy may have been burnt out and would never roll without cracking. Just buy in a thick sheet and roll it out to what you want for multiple projects.

Gold is another animal altogether. Much more forgiving (and much more expensive). My advice is to check your scrap re quality then your melting and pouring procedure. Then follow the advice given by others above. Frankly, gold gives me very little problems. Good metal melted properly and poured properly is tough as.

Re the video clip. Everything he says is spot on! Am I gonna follow it? Not a chance. Way too much labour. I was just thinking about my mold for rods. It has three sides. How would he work with that? I'm not going to file any of my 18K off before I start working on it. So sorry, I'll just do it in my ol' 'rough as guts' way.

Bud