For some historical reason I have a rectangular gully in my drive, which has (and probably always has had) a standard square cast iron grid over it, which overlaps the gully by about 2", so it looks crap, wobbles, and lets rubbish in.
I thought I'd try and cut off the offending overlap; however knowing the propensity of cast iron for shattering I thought I'd check here before diving in. Would an angle grinder do it OK? Ot would it need a hack saw (which might well mean 'sod it ;et's have a plastic grid instead!!)
We used to nick it with a saw or grinder, then break it with a hammerblow and there was a small risk of breakage. Nowadays I'd just grind all the way through and not worry.
BTW - grinding cheap cast iron is a filthy job, owing to the free carbon going everywhere.
Had a go last night; my (little 5") grinder protested muchly, taking about 10 mins to cut through just one of the 7 elements of the grid. So I'll reluctantly be including a nasty little plastic grid in my next Screwfix order!
The one cut it made was adnittedly nice and clean, and the grid got extremely hot. Out of interest, why wasn't there the usual shower of sparks while i was using the grinder (this being cast iron)?
This surprises me, I relined the firebox of my Jotul stove with cast iron cut from some manhole covers I'd broken by driving over them (client had lost site drainage plans). My 5" Makita with standard metal cutting disc took longer than with mild steel but didn't wear noticeably worse.
This will be to do with how the cast iron oxidation sites are occupied with carbides, so don't burn as readily. Mild steel gives yellow sparks of burning steel, cast iron just dull red hot dust.
Right, he's back, with fire extinguisher, silicone spray, a couple of other things and a £10 radio controlled amphibion - says it's for me beaue I've always wanted a boat but really it's to cheer him up after the session we had with the oncologist this morning :-) I shan't let him go shopping without me again.
He says that there are many different grades of cast iron, which we all knew really if we'd thought about - I'm not talking about wrought iron or steel, mild or any other kind.
He can't say for sure without knowing the quality of your item but most cast irons won't send out white sparks because of the lubrication effect of the free graphite (the carbon Andy Dingley mentioned). Spouse would expect dull red sparks if anything (as Guy suggested).
The heat generated by the grinding is also dependent on the quality of the iron - not your equipment or your skill so don't feel inadequate on either count.
It's not a simple matter - if it were you wouldn't need every batch of iron to be controlled by laboratory analysis according to the job for which it's intended. But as with most things we all tend to generalise ...
He's been thinking about it and said that it might be a ductile iron even though it's cast, that would make it more suitable for a gully grid where there would be traffic (even pedestrian traffic).
That adds another element to the matter. I wish I hadn't said anything :-)
Then, of course, there's the type of abrasive you were using ... PLEASE don't ask for an explanation of that!
I'm surprised - were you using a metal cutting disk, not a stone or a grinding disk ?
You can identify steel grades quite well by "spark testing" like this (web search for more)
Cast iron is a crude mixture of iron and carbion, not an alloy like steel. Look with a magnifying glass and you'll see the separate particles. When you grind it you get these dull red glowing particles of iron, and very few sparks (burning particles). It's mainly because the graphite lubricates the cut and keeps the heat down, so not lighting the sparks in the first place. Also the iron has a relatively low energy when burning, so tends to go out rather than burning up.
If you grind highly-alloyed high speed steel, then the sparks "burst" some distance from the wheel. They're hot sparks to begin with, but their burning causes them to get even hotter as they fly.
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