Anealing Castings

[durhambuilder]

I'll start by saying not sure if this is the correct term or not!

Three of my four cast iron horns machined beautifully the fourth had a several hard spots which destroyed a couple of my best milling cutters . Anyway a long afternoon and night in the woodburner had it glowing bright red for 8hrs and then it cooled down in the ashes overnight, machined good as gold after that.

The question is should I give all the the iron castings the same treatment 'just in case' or would it be best to go ahead and machine them and only anneal if necessary?

Cheers

Julian

[Deleted]

Julian
If you have any doubt my advice is to anneal them.
JB

[GWRdriver]

Julian,
Although cooking in the fire has worked for a simple casting it affords no way of controlling temperature. My fear would be that more detailed and critical castings, spoked wheels for instance, would potentially run the risk of being cracked due to uneven heating and cooling. This may be overly cautious but I wouldn't want to have to replace castings with prices what they are now. In answer to your question, if I discovered the first few to have hard spots I would probably then anneal the rest of my castings, but to avoid fatal damage I would have the critical or detailed ones done in a proper oven.

[Deleted]

Nov 15, 2011 13:31:16 GMT GWRdriver said:

Julian, to avoid fatal damage I would have the critical or detailed ones done in a proper oven.

Julian
Harry is quite right about temperature gradient and control. I do all mine in our electric pottery kiln, and it works well. Perhaps if you looked up a local pottery club they could do them for you?
JB

[Deleted]

I learned my lesson a few years ago. As soon as you get your castings, take a trial cut across each of them. (Don't put them away under the bench until needed, which may be several years later!). Don't risk a milling cutter, but use a fly cutter with a carbide tip. If any castings show up as having hard spots, don't mess about, just send them straight back to the supplier and ask for replacements.

[Myford Matt]

I bought a nice second-hand controllable oven at my club recently. What temperature and for how long should I heat CI to anneal it?

The castings are typical 5-inch size castings – wheels, cylinders...

Cheers

Matt

[GWRdriver]

Matt,
It seems that every source quotes a slightly different range for basic annealing of grey iron, but heating to around 825°C (1500°F), held for 1 hour per inch of maximum section, and then cooled very slowly, is typical and produces the desired results.

[durhambuilder]

Thanks for the help guys much appreciated, I've had the castings for a fair while so will have to work with them whatever. I'll do as superseven suggested and give them all an initial skim, if any need annealing I'll worry about the pros and cons of woodburner vs proper kiln / oven at the time.

Cheers

[Myford Matt]

Thanks GWR

'Cooling very slowly'... does that mean turn off the oven and let it cool naturally, or should I reduce the temperature in the oven by, say 100ºC every 10 minutes.

Or do either, just don't drop it in a bucket of iced water?!

[GWRdriver]

Matt,
Cooling too fast, and unevenly, is what got them to their poor state to begin with so cooling as slowly as practicable is needed. I think turning off the oven and allowing them to cool naturally, say overnight, is the usual practice.

[Myford Matt]

Thanks Harry

Sounds like very useful advice

Cheers

Matt