We’ve had this metal sphere knocking around in the basement and the shed for decades and I am curious what it was originally intended for or used for.
It’s 2.375 inches in diameter give or take maybe a couple mils, as best I could measure with my cheap home calipers. It’s dense, like steel, and holds a magnet. It’s mostly shiny, and the reflections are unchanging as I rotate it – there’s no wavering of the image, as in the reflections from a shiny spherical Christmas tree ornament – so it is as spherical as I can judge by eye. It has patches of very faint corrosion, like fine rust but dark brownish gray rather than vivid flaking brick-orange as in pure iron rust. It has no features anyplace on it; no seam or mold flashing, no holes or flats. Considering that it was often kept in boxes of junk or loose on workbenches and shelves, it surprisingly has no visible scratches or dents that I can find.
I suspect that it is a ball from a huge industrial ball bearing. Such a ball would be harder than typical steel, perhaps containing lots of chromium or other alloying agents. Or it might be a 400 series stainless steel, which would be hard, and rust slightly, and hold a magnet. One of the people in the household used to work for a photographer and helped with an advertising project for a maker of such bearings, some of them big enough to walk through, and would clean off the parts with solvent and rags. However this person has no memory of this ball, so that might be a red herring.
I am sure this is not from a ball mill. I have worked around ball mills, and those balls are coarse and typically depart visibly from spheres.
Any ideas? Any suggestions on how I could confirm it is a bearing ball, or disprove that it is?
Just tried looking for something identical at McMaster-Carr and found this, which I don’t think I could tell apart from it by any test I can do at home:
Bearing-Quality E52100 Alloy Steel, Hardened Ball, 2-3/8" Diameter. Bearing-Quality E52100 Alloy Steel, also known as chrome steel, is an extremely hard and wear-resistant material. It’s used for parts such as bearings, bushings, and punches.
A smarter Doper might have looked there first, but, well…
I’m always very careful when working with heavy, round objects, and X-Acto knives.
Both seem to roll off the workbench and land where they can do the most harm…
Quality steel doesn’t rust away like 20 cent screw driver, or the scratch on your car fender, does.
For the purpose of a ball in a bearing, you wouldn’t use stainless steel, more expensive but less life. It could crack due to fatigue, it is not as hard and wears faster, etc
if it was for decoration, it would be stainless steel. Don’t they use this size steel ball in some lawn games ?
In a hitherto unrelated story, my quest for intriguing bits of metal also happens to have landed me a a small bar of tungsten alloyed with thorium oxide, making it radioactive. And, it has the capability of rolling off the workbench. No reason I mention that detail.
So you heard the one about the monkey and the billiard ball…
I’m thinking the photographer’s assistant guy just forgot about the ball bearing, or just ended up with it by accident.
It’s either the boccino in a modern bocce set, or an alien artifact that will test human civilization on a series of similar puzzles only increasing in complexity, layered within; either acceptance in their hegemony or oblivion awaits.
I saw a bocce or petanque set recently at the local Goodwill that sounds much like the OP’s sphere. Those spheres though had different lines inscribed on each pair, probably so the players could tell their balls from one another. The tiny target sphere was featureless, but smaller than 2-ish inches in diameter.
I checked your profile and it says you live in the mid-atlantic area, an area known for iron ore and coal.
They are most likely balls taken from a ball mill used as grinding media. They could be high chrome ball mill valves - used in hematite grinding or coal pulverizing. Check this.
Depending on the feed size and the desired product size distribution many sizes of balls are used sometimes in the same mill. 60mm (the size you describe) is a common size for hematite plants that I know of. Most often, the balls are cast with two pieces - hemispherical joint - but sometimes the application requires good control on the size distribution and hence smooth balls.
And you need good hardness for grinding media (hence the hardness you describe). Look around yourself - or look into the previous occupants - there maybe iron ore or coal processing plants around you or the previous occupants may have worked there.
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