SEASONING OF CAST IRON

[Peter G. ShawParticipant @peterg-shaw75338]

Dave/SOD

Warping isn't a problem I've found on my Chinese tools and I doubt they had any special treatment. Although the castings are rough, they're OK where it matters. Anyone found a warped bed on any machine, new or old?

Please see my post at the bottom of the previous page. For more information about this problem see:

https://www.model-engineer.co.uk/forums/postings.asp?th=50641

FWIW, I know of another MiniMill which shows the same problem but nowhere near as bad as mine did.

Peter G. Shaw

[Roger WhiteleyParticipant @rogerwhiteley62172]

I haven't seen a eutectic diagram like that for over 40 years, but I did study metallurgy at university when metals were metals and carbon fibre nanotubes were a thing of science fiction. Stress relieving works a bit like a massage – cycles of heating and cooling that are nowhere near the melting points, whatever the reason, quality castings, machined properly, always seemed to come from engineering companies who aged them.

You can't hurry quality! Love the story about the BMW car engines, that sounds entirely likely.

A chilled skin is a nightmare, because the impurities, which generally lower the melting point of the iron in the first place, gravitate and solidify at the skin whilst the centre is still molten, the carbon levels are also much higher so the result is a skin with all the rubbish in, and as I write this, I seem to recall that there's a degree of 'atomic migration' which results from the seasoning process that improves machinability – SG iron is best, because the graphite doesn't form flakes at inter crystal boundaries, but spheres, in an 'ocean' of more pure iron. Flakes cause stress raisers, which make cast iron brittle, spheres don't .

[Former MemberParticipant @formermember32069]

[This posting has been removed]

[Roger WhiteleyParticipant @rogerwhiteley62172]

Barrie, the only bit of that segment that bothered me was the statement 'a turbocharger is like a supercharger' or word to that effect. Because that just ain't true, but it was dumbed down for television, so we'll have to let it go.

[Mick B1Participant @mickb1]

Posted by Roger Whiteley on 29/04/2020 14:03:03:

…

A chilled skin is a nightmare, because the impurities, which generally lower the melting point of the iron in the first place, gravitate and solidify at the skin whilst the centre is still molten, the carbon levels are also much higher so the result is a skin with all the rubbish in,

…

There's sometimes some use in an otherwise-undesirable characteristic.

At a time in the 1860s when the French appeared possibly to be ahead in the ironcladding of warships, the points of cast Palliser shells were deliberately chilled to improve their penetration.

[Martin KyteParticipant @martinkyte99762]

I don't know for sure but are we getting a bit of a case of half the story here. I understand that in some circumstances it's prudent to 'age' castings, or indeed any lump of metal between the rough machining stage and the final machining stage. Essentially churn most of the metal off that needs to be off and then let the thing settle down and assume its final shape or get all it's 'wriggling about ' out of it's system. Only then can final machining be carried out with the expectaion that it will not move any more. I certainly have heard of surface plates being treated in such a way and if you machine a crank shaft out of solid it's wise to leave it oversize and put it to one side for a few weeks to settle down.

regards Martin

[TrevorhParticipant @trevorh]

In the Industrial Printing industry the manufacturers always age the cast Central impression Cylinders for 12 months before machining the face

The castings can be anything from 20 Ton upto 40Ton typically 2 metres wide and a diamter of approx 2.5 metres

these are then machined to a TIR of 0.02mm across the face and ends

this happens with most German and Italian manufacturers

The Italians have a storage area at the back of the factories with lines of these castings – quite impressive

Trevor

Edited By Trevorh on 29/04/2020 15:22:31

[Howard LewisParticipant @howardlewis46836]

Various comments.

It was said that pre WW 2, Austin Motor Company left cylinder block and head castings out doors for at least two years to stress relieve.

As an Apprentice, during my 3 month stint n the Toolroom, on one Friday afternoon, I was given a machined Aluminium casting to scrape and blue. It was left flat. On Monday morning, the same could not be said of it!,

More recently, a cylinder block which had been finish honed before assembly, if measured after the engine had been tested and stripped could show up to 0.004" ovality on a 3.875"bore.

A block which had been relinered and reused always gave better results.

One day, a load of castings, which had stood outside for some months, were fed into the transfer line. Every cutter was promptly ruined, and nothing could be done until the wreckage emerged at the other end.

Investigation showed the castings to be extremely hard. From the cast date it was established when the metal had been poured. At the time the foundry was having the outside walls replaced. The very hot castings had been knocked out out of the boxes, and snow had blown onto them, chilling them!

Camshafts were locally hardened by placing chills in the mould so that the cams would be chilled and hardened while the shaft proper was left soft.

Howard

[Roger WhiteleyParticipant @rogerwhiteley62172]

Howard, I worked at Canley just after it had been closed – in the bits that remained open, I spent a fascinating three months with the freedom of the machine shops that had been making Triumph engines and gearboxes – one of the glories was a Herbert B vertical drill, with a size 0 Jacobs chuck used to drill oil holes in camshafts. It cost me £25 through the asset disposal scheme. A Clarkson tool and cutter grinder cost me a tenner. Sadly both are no longer in my workshop – the Clarkson was a heavy bit of kit, and took a lot of moving. Even dismantled". The only problem with the Clarkson was that it came without any tooling, otherwise it would have been really useful..

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