I was advised to leave new castings outside for 2-3 months. The repeated heating and cooling by the sun would releive the stresses. Others suggested to put them at the base of a large fire pit and allow them to cool slowly in the ashes.

I had plenty of other parts to make and left them to weather outside for about 3 months. Did not have any problems with distortion after machining but don't know if there would have been any if I had machined them sooner.

Paul.

The first job I had in 'straya was at a company that made mining machinery. The car park was used to season castings, and there were a lot of them. Apparently the "seasoning time" was related to the length of the grass. It was advisable to be really careful when parking the car to avoid hitting a casting.

cheers

Bill

When I started work in 1963 castings where left out to weather for months and years depending on how many the foundry produced. This kept the foundry busy as they never had to let the furnace die but just kept pouring metal. I was told at the time it was to allow the casting to stress relieve. Fast forward over 50 years and I was asked to machine a batch of castings in my home workshop, I asked the question re how long the castings would be kept for before I received them and the answer was that castings where no longer weathered due to better heat control with the electric furnaces and better quality iron. I did around 90 castings, no chilled skin or blow holes in any of them.

Many years ago I worked on an "SIP" jig borer that was made in the 1930's. The guy who did the maintenance reckoned the the iron castings were left for 7 years to season before being machined. I initially thought this was a sign of quality. I've no idea how true this is, I'm now sceptical. The castings were, no doubt, of the highest quality, perhaps not needing much seasoning? Surely in the 7 years wait improvements and upgrades to the machine would happen rendering the castings unsuitable? Even back then heat treatments to stress relieve the casting were available.

I would guess a good way to season an iron casting would be to rough machine, take the "skin" off, then heat treat to stress relieve.

John

Even in the late 90's crankcase and bed plate castings at Ruston were 'seasoned' in the manner previously mentioned, left to stand outside initially then part machined and returned outside and then finally brought back in for finishing. Not sure if this appllied to smaller castings like cylinder heads etc.

As regards the aggressive shot blasting would help relive stress, crankshafts are shot peered in the fillet radius of journals to deliberately induce a stress in the surface to better resist fatigue failures initiating at the surface.

Paul.

If you do use the oven make sure you have due authority from the domestic authorities.

Edited By Brian Oldford on 27/04/2020 10:12:19

Can't understand the reluctance of some to use a domestic oven for tempering PROVIDING you've thoroughly cleaned the item before sticking it in the oven. Used to save any bits I needed to blue till after the Sunday roast was cooked, frugality, oven up to temp, so dangling bits of metal on wires in there no problem.

Regards Ian.

[This posting has been removed]

Part of the problem comes from foundries that kick open the cast just as soon as they can, best left to cool in the sand until easy to handle, earlier ensures you get stresses and chilled areas. Perhaps a good rusting allow the chilled areas to rust away!

In 2008 I bought a XJ9511 milling machine, which is a clone of the Sieg X2. I think the XJ9511 was made by Real Bull. I bought this machine in the full knowledge that there were likely to be 2 possible problems, one of which happened within a few weeks. (If you remember, in those days there was/are a lot of problems with the plastic gears and the electronics boards on these machines.) What I didn't bargain for was that the table bowed like a banana. At the time I was quite literally a newbie when it came to milling machines – I had never used one, and indeed never seen one on the flesh so to speak, so it was 2011 before I got round to having it reground by Slideway Services, (Brian Caddy?)

On speaking to the proprietor afterwards, he exclaimed that this was one of the worst he had ever come across! So was it lack of ageing? Or something else, although it is difficult to see what else it could be. And before anyone asks, I haven't checked it since.

In fact, as I got to know the machine, I discovered all or most of the problems that afflicted Chinese machinery of that age – casting sand where there should have been none, angle grinder marks on those parts of the slides etc that were normally hidden from sight, etc.

Now, before anyone accuses me of having a rant about Chinese machinery, when I bought I was well aware that there were likely to be problems, but having said that, I learned a lot by rectifying some of them so in that respect I am reasonably happy about having bought the machine in the first place.

Peter G. Shaw

A complicated subject Chas!

'Cast-iron', isn't one material. Broadly, it's Iron with a lot of Carbon, but in the past it also contained Silicon, Phosphorous, Sulphur, Manganese and other muck. Impurities change the properties of cast-iron significantly, and – before chemistry fixed it – where ore came from mattered.

Before the industrial revolution top-quality iron came from Sweden because they have large deposits of pure Iron ore plus wood for charcoal, pure Carbon. British ironmasters struggled at first because our ores are mixed and they tried to swap Coal for expensive Charcoal. Unfortunately coal also contains many local impurities. Any success seemed like magic!

However, with a simple furnace impure cast-irons can be melted and easily moulded. Bit hit & miss, but some areas were able to make useful iron with local characteristics. Scottish iron was better than Lancashire iron for some purposes and vice-versa. Making metal was more art than science.

During the 19th century improved chemistry found the impurities. Sulphur and Phosphorous are both very damaging and chemists showed how to remove them from ore and coal. Knowledge replacing skill and folklore.

So, rather than relying on the furnace master, he got a better furnace, materials, and operating guidelines. A large enterprise would have a chemist testing iron during the melt to guarantee consistency. The quality of cast-iron improved enormously. Science displaced guessing.

Nothing is ever simple! Many jobbing foundries bought in metal, including scrap, and did practical casting work of the cheapest possible kind. Sash-weights can made with almost zero skill using left-overs, perhaps poured cool without bothering to remove slag, and then hosed down to get them out quickly. Today old sash-weights are notoriously poor quality with an exceptionally hard skin.

Structural and ornamental iron-work and machine parts got more care. However, it's fairly easy to get manual casting wrong. Experts taking care and getting the timing spot on do well, less reliable from the 'B' Team zonked out at shift-end, or when management rush stuff out the door. Blow-holes, slag inclusions, shrinkage, cavities, chilling, heat stresses, etc.

Stress inside large mouldings due to uneven cooling was a major problem in the 19th century and still can be. Machining stressed castings can cause the whole thing to warp, very bad on a lathe or milling machine! Large complex castings seem more likely to warp than small.

One solution is to rest precision castings outdoors for a year or three. Fairly obviously, this is another hit and miss method, but – because it's expensive – it became associated with quality. Slow cooling in an oven works too. Peeing on the casting is lore, not science.

Science hadn't done with cast-iron. Iron was studied to get a solid understanding of how to get specificied results. Repeatable hardness, machinability, toughness, brittleness, stainless, etc. Now thousands of different alloys are available.

Cast-iron's main advantages are cheapness, moulding, machinability, compression strength, and absorbing vibration: excellent for making machine tools and engine blocks. Having to wait months for castings didn't appeal to early car-makers or US machine tool firms. The US developed cast-irons that didn't need to be seasoned. This is Meehanite, about 30 variants, used in a defined way in an upgraded foundry rather than poured by eye.

After 1935, seasoning cast-iron hinted the manufacturer was old-fashioned! Unfortunately too often true: in the 1920's buying a British lathe meant waiting a year or more for delivery, while American machines could be had in weeks. Some kind of strange conservatism caused British firms and workers to favour waiting for machines built to last 60 years or more, missing the point that 1995 would be a different world. Move with the times or else!

Today, cast-iron is all over the place. At one end it's a state-of-the-art engineering material. At the other, crude foundries casting cheapo street furniture, weights, and novelties. In between, almost anything else depending on need. The decision to season or go clever mostly depends on cost. It depends on some mix of foundry capability, run size, and when the customer needs the castings. Seasoning doesn't necessarily indicate quality, rather it's just a tool.

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?

Dave

Edited By SillyOldDuffer on 27/04/2020 12:38:14

In the 80s, CI stage castings for projectors were left to weather for 6 weeks prior to machining – that was the theory but sometimes it was a lot longer. We were late nearly all the time.

Part of the reason was crazy-tight operation times used to calculate capacity requirements. The smallest projector had IIRC a 14" x 8" stage and was ground on top to a 16 microinch finish and flat within 0.0002" TIR.

Time Allowed: 3 minutes.