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What's the true surface roughness with iron-casting?

I noticed that in every design work or the supplier website say that the iron-casting surface with sand-casting can have a surface roughness of 6.3 micron. However, when I see the true castings, they are very rough and more close to a classic value of 0.2 mm. How there have a such big gap there?

Thanks for all the answers in advance!

Jerry Pan
fluid engineer - Urbana, Illinois, USA
2005

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2005

Yes, you CAN have an as-cast surface roughness of 6.3 microns on cast iron.

It is easily achieved by a knowledgable foundry, and incurs extra manufacturing cost because of the particular moulding materials that need to be used.

The cheapest moulding materials will give the rougher surface that you refer to. So if the purchaser has not specified any particular surface roughness, the foundry may well choose to use the cheapest manufacturing route - a route which hap[pens to give the roughest surface.

If you want a smoother cast surface, specify it in your enquiry, be prepared for the casting price to be marginally higher than it otherwise would be, and double check that the foundry has agreed to the requirement.

As I say above, a knowledgeable foundry can produce it with no difficulty. If castings are in fact supplied with a non-complying surface roughness, you simply reject them because they don't comply with the agreed specification.

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.