What is the difference between cast casing and fabricated casing ?

[rQuestionEngineering]

Referring to centrifugal compressor casings.
What is the difference between cast casing and fabricated casing ?
What are the advantage of each and what is considered to select one of these manufacturing processes ?

 

[TugboatEng]

A cast casing is exactly how it sounds, it's cast. A fabricated casing we welded together from smaller pieces.

Why chose one or the other?

A fabricated casing saves the cost of building a mould and developing a casting procedure

A fabricated casing is inherently weldable which can simplify repair.

Cast casings are less laborious to produce.

Cast casings use less material.

Cast casings don't need to be weldable and can take advantage of improved metallurgical properties.

Cast casings allow for greater geometric freedom.

One must also consider the capabilities available. Large castings require even larger facilities to produce. Fabricated casings can be produced in any shop.

 

[JohnRBaker]

If you look up the terms 'casting' as compared to 'fabricated' it should be pretty clear. And I suspect that whether it's a compressor or some other bulky machine, it doesn't really make a difference. Where I used to work we produced gearboxes for large continuous chemical mixers. Some of these were cast and some were fabricated, but over time, most of the cast gearboxes were replaced with fabricated versions. The primary reason why was that it was getting harder and harder to get good large castings, particularly when you only produced one or two gearboxes a year of any one model. I know that for awhile we had raw castings in our inventory left over from when we had our own foundry, but we were forced to close the foundry due to the cost of complying with the ever changing clean air regulations. And once the last costing had been used, we started to fabricate them as we had a heavy plate shop and the skilled labor and tools to weld them. Granted, if we still had our foundry or access to a supplier with a foundry, the casting would probably have cost less, but when you're only producing any one gearbox once or twice a year, fabricating the gearbox case was reasonable and acceptable.

John R. Baker, P.E. (ret)
EX-'Product Evangelist'
Irvine, CA
Siemens PLM:
UG/NX Museum:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[drawoh]

bayan1999,

Are you designing a compressor or buying one? If you are buying one, you don't care how they fabricated it. Look at the cost, the size and weight, and the performance curves.

If you are designing one, the comments above, apply.

--
JHG