Chilled cast iron

Got a bar of grey cast iron, absolute pig to machine.

HSS tool got simply deformed upon attempt to turn it and now need general regrind and carbide tool barely cope with it leaving surface which looks somehow "tortured".

How deep such a layer might be?

Should I consider this bar faulty and throw it away or after chewing through first 2-3 mm there will be some "normal" iron?

Martin

I was given some old cast iron sash weights that had a hard surface like yours.

I cut anend off with an angle grinder and then tested the core with a centre punch to determine the

depth of hard ness, some went to the scrap man!

I then used a carbide tool to get through the surfaces of the ones I felt usable.

Hope this helps

Steve

Slow speed high torque on the backgear with a 5% (or 10%) cobalt tool for 95% of the job

Finish off with carblde at high speed (or cobalt if you resharpen it)

(If your lathe is stiff enough the backgear part of the job will look not bad)

Use a live centre with fixed steady support to increase stiffmess if possible

GL

Edited By Ady1 on 07/12/2017 00:27:39

Try annealing it. Find a friend with a coke boil er or stove. Put the cast iron into the centre of the fire. Bring to red heat, then cover with fuel and let it "cook" for a few hours, then let the fire go out. Leave the casting in there till it has all cooled down. It worked for me on a set of Clarkson casting that I had, which were un-machineable.

Maurice

Very unusual for cast iron bar as that is a joy to machine, sounds like you have a bit of old round sash weight or similar which can vary a lot in how easy they machine..

As Maurice says if you can get the whole bar to bright red and hold it there for half an hour and then allow to cool as slowly as possible you may find it easier to machine but for the effort and cost of the gas you may be better off paying for a decent bit of continuous cast iron bar.

When faced with chilled castings I put em in the woodstove for an evening and fish them out next morning.

The last chilled window weight I had made it's self known to me before it went in the lathe, I dropped it, and it fell in half, the fracture was shiny, silvery, crystaline. I did try it in the lathe, and with a Carbide tool managed to turn off the rough outer skin, and face the end. Its in the scrap bin, I may try to anneal it one day if I get desperate.

Ian S C

I have some cut offs from sash window weights as well, was going to light up the BBQ & soak them until the BBQ went cold so far the BBQ has remained stored away since we've only had 3 days of summer this year hence I miss the opportunity... ah well there's always next summer...

​I did have a chilled casting on my S10V standard flange, managed to get it to size with brazed carbide tip tool but supported with live centre for safety & low revs... the top face was machined using 2" 4 tip carbide face mill as this was the only way I could get a decent finish on it...you can see the uniform chilled area on the OD.



​Using carbide tip tool to get OD to size... bloody hard!



George.

To echo Maurice, I too had some Clarkson castings that were severely chilled in areas. I put then in my kiln at 1400 deg F for about 2 hours and left them in the kiln overnight to cool. They then machined beautifully. If you can find a friend with a small pottery kiln that is the way to go

John

Many years ago the corners on the valve face of my 10V were chilled, first time I encountered this.

If you have a chilled sash weight, the best thing to do is drop it on your foot as this will hurt less than trying to machine it.

Neil

Many thanks for your comments.

All of them helped to understand the problem. My material is a bar.

Smelter peoples have said that they are making such bars from excess of smelt as occassionally they sell and if not, they can always be remelted. It is not a sash piece. Had few and they were actually OK.

I have managed to turn it after all. Once diameter have gone from 42 to 38 mm no more troubles was encountered. Ordinary carbide insert was good enough to chew by hard part. HSS stood no chance. I have few CBN inserts for hard materials but in this case it would be wasteful to deploy them.

Regarding heat treatment - I have large fireplace so with enough of wood it might do the trick. Good to know for the future. What are you using to prevent scaling while heating metal to red heat?

Martin

I can confirm that the woodstove treatment works. I often pick up lumps of metal that have been left lying around at work: when we replace, for instance, small track components on the railway, the old ones usually just get thrown down the bank as nobody can be bothered to take them to a scrap bin. I have quite a few large (30mm-ish) nuts and bolts that are still usable but, more importantly, after 'normalising' in the woodstove, will machine beautifully. I assume they are high-tensile, as before normalising, they can't be sawn or filed easily.

One caveat, however, is that if you are normalising something like a flywheel, make sure you support it adequately, or you may end up with something Salvador Dali would have been proud of!

Regards,

John.

Usually find the edges of castings are pot hard after doing a lot of work on them, not wanting to heat up thin flywheels as John says, I find that mounting the Dremel in the vertical slide usually gets a good finish on them.

Slow but faster than returning the casting and finding the same problem with the new one.

Not usually enough metal to get under the skin of the castings I seem to buy.

Skin around the edge was pot hard, dremel fixed it. Pic won’t seem to respond to repositioning though, right way when taken.

Chilled cast iron can be glass hard.

Cash Iron camshafts, in engines, are often poured with chills in the mould, to chill deliberately for hardening. The cams are then ground, rather than turned or milled.

A batch of cylinder block castings, that had been inadvertently chilled, ruined every carbide inserted tooth cutter in a multi station transfer line.

Annealing, if possible, before hand, or as soon as discovered, should solve make life easier.

Howard