I want you to advise me regarding a rolling mill issue. Noticed that my rolling mill leaves small pits when rolling metal. Initially I thought my poured metal is porous but it turned out not be this, since newly bought metal sheet does the same thing. It is like many small marks (mostly roundly shaped).
I think my rollers are contaminated with something. Could it be not fully dissolved flux?
As to how to fix this. I tried a polishing paste which seemed to only fix it slightly. Is it a good idea to use sandpaper to briefly clean the surface? Anyone who experienced something similar?
Any suggestion is appreciated,
Do you oil your rollers only to have them pick up some kind of dirt that you don’t remove before you roll? I have done that…Rob
No, not the case. It did the same thing right after polishing the rollers with paste.
These are the marks I’m talking about, those small pinholes
All I can suggest is a good cleaning then a very close look with a magnifier to see what you can see. There have been discussions about how to polish your rollers in place. Try doing a search on this topic. I do wonder if you were to run a piece of carbon paper over a plain piece of paper lightly through your mill if this would help you locate the problem. Good luck and let us know what you find…Rob
Thank you for your suggestions.
The problem with this is not that it has lots of pinholes and is visually unappealing, it is more because after a number of passes through the mill the exterior will begin to flake off due to the grouped marks, I believe.
I guess back to basics. Have you cleaned the rollers? I use simichrome to clean and polish then oil with 3 in 1 oil. Is your ingot sanded smooth to start with and no little burrs sticking up? Is your ingot well annealed? Standard wisdom is to anneal after you have reduced by 1/2. I anneal more often. After you pickle, do you make sure that the ingot is rinsed well and dry? I usually leave the ingot on the solder pad to make sure that it is dry. Have you rolled any copper? Copper can leave all kinds of nasty stuff on your rolls. That’s all I got. Good luck…Rob
Yes. I polished with a metal polishing paste (similar to Simichrome).
To avoid debating the ingot state, I gave it a try with freshly bought sheet (silver and gold) and they all come shiny when bought. After a single pass, they look like in the picture.
And no, no copper. But it looks like there is some kind of dirt that gets into those pinholes, a white substance (looks like borax after it dries). Which in theory has no reason to be there since the rollers are newly polished and cleaned.
Curiosity Are your rolled ingots perfectly smooth and shiny at the end?
perhaps post some pictures of your rolling mill, and close up photos of your rollers…
it makes sense that if pits/ depressions result after rolling then there is something on/ protruding from the rollers…or something like grit is introduced from the ingot when rolling
(since you did not have this result after rolling clean sheet)
after annealing, i rinse in water, pickle in food grade citric acid pickle, dry it off on a towel, then final dry off using a blow dryer to thoroughly dry ingot, before introducing to rollers.
do you have oiled sponges on your rollers?
is there any grit/ dust/ lint on your rollers?
My rolled ingots are eye-clean, no pits, smooth and a matte sheen…not super shiny…
…drier white residue…?…perhaps residue from polish…?
…borax/ flux doesnt make sense if ingot is clean and dry before rolling
I had same results after rolling clean new sheet. Two different suppliers, fine silver, argentium silver and gold. In the past I thought it might be porous ingots but it turns out it’s not that.
I had a look at the rollers with a loupe, can’t see anything.
Could not dissolved flux from past mark the rollers? Could hardened steel get marked by borax?
Here is a picture of the rolls:
How did you rule out porosity in the ingots? That seems like the logical explanation to me.
Tried with multiple pieces of sheet from two different suppliers, also different materials: gold, fine silver and argentium. They came as sheet, I put them straight into the rolling mill. Some I annealed, some not, same result after the first pass.
Would you say that it could still be porosity? Is there any chance for that?
There is probably dust or left over polishing residue from polishing your rollers. We wedge foam rubber that is soaked in oil at both the top and the bottom of the rollers. So that with every rotation the rolls are cleaned and oiled. We also always keep our rolling mill covered with an old pillow case when not in use.
look at your rollers and compare their smoothness to the flat part in the V grooves…
when i look at your photos, the rollers look textured…?…
I see that. Well, I have no explanation. This is what it looks like after some polishing. It might just be how the steel looks, because it feels smooth to the touch, no texture felt by the fingernail. Also had a look with a loupe in other areas and it looks the same, even the smooth part of the V groove.
Another day, better lightning, another picture
I just fitted mine with two sponges and I have to say that the marks reduced by 90%. So it looks like my rollers had some dust stuck to them which was impressed upon the metal.
Do you remove the foam rubbers at the end of the day or leave them there?