[taneq]

Somehow you never quite get the real raw material when you ask for samples, no matter how careful you are.

I worked on a system once upon a time that fed steel balls into a ball mill. We tested it thoroughly in the workshop with the same steel balls used on the customer's site, but when we went to commission it, it jammed non-stop.

Turns out a hundred randomly selected balls won't contain most of the outliers that you'd get in even one tonne of balls, and when you're feeding 5 tonnes per hour, that's a lot of jams. We had balls with big craters in them, half-balls, balls with two halves offset by 50%, and everything in between. Not the kind of thing you could rely on rolling nicely.

Also, of course, when you ask a mill ball manufacturer for a sample, they might be inclined to send you the very nicest examples they can find, because they think you might buy their product...

Anyway, unless you're super careful about sourcing legitimate feed samples it's easy to think you're testing against the real product when you really aren't.

[orthecreedence]

I found your comment fascinating (and frustrating). Dealing with bad inputs on a web form can be tricky. Dealing with bad inputs made of steel seems like a lot more work =].

What comes out of a steel ball mill? And why is steel made into (misshapen) balls before this process?

[taneq]

Oops, I meant to come back to this but stuff happened. It certainly was a lot of work to get it halfway reliable. I think they were working on adding a vibrating motor to keep things moving even if they weren't rolling - while I was there they just had a guy poke it with a bit of rebar every time things hitched up.

A ball mill is used to grind things into paste, usually for further processing. In this specific case it was a SAG mill (https://www.mogroup.com/portfolio/sag-mills/) and it was frikkin' huge, powered by a 10MW electric motor. It ground up ore-containing rocks from a mine which were then processed to produce lead and zinc. The balls roll around in the mill and help to grind up the ore, which I guess works better if they're round, which they will be before long due to wear and tear no matter what shape they go in. They come out as tiny ball bearings. It was quite an interesting project!