A352 LCB Inperfections in a valve seat 1

[McRamis]

We are using ASTM A532 LCB for a valve body casting. When we machine the valve seat we are often left with a pit/inclusion/porosity. Has anyone else come across similar issues with this material? Is there something that can be done in the casting process or the design the part to keep the "pits" out of the seat area?

 

[pwtomlin]

It's not that surprising to find porosity in LCB. If it is a gas defect, it could be a melting process issue or an issue of venting (particularly if the defect is located off a core). If it's shrink, the foundry should be able to do something about it from a gating/risering design aspect. If you're consistently finding the defect in the same area you need to get in touch with the foundry that produces the casting, there's definately steps that can be taken to reduce the occurance of the defect.

 

[arunmrao]

An experienced foundryman recognises the problem in the seating area and ensures producing a sound casting. This cannot be attributed to the alloy LCB but can happen in any other alloy too.

Radiographic test of this area will reveal the nature of defect. It is commonly a shrinkage or a sand inclusion.

For a shrinkage defect place a proper size feeder on top in the belly region . Also in the core use Zircon sand in the seating area and place internal chills too. This will ensure faster cooling and a sound casting.

If it is sand inclusions,please take a look at the cores and the mold coats applied. If it is a No Bake core,using a water based coating instead of spirit base will help.

Hope this will help eliminate the defects in your castings. Please come back and let us know.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[CRMagruder]

If this is a chronic problem, you can change the purchasing agreement with the foundry to supply the casting to you in the rough-machined condition to solve the problem. The amount of machine stock to your final machined surface will depend on the size of the casting.

The key is to have the foundy machine the casting or have a sub-contractor in their area machine it, and return it to the foundry for surface inspection. This can be mag particle or liquid penetrant, which is much cheaper than x-ray. The inspection criteria can be from A352 or something like ASME Section VIII, Div 1, Appendix 7, or a tighter criteria that you specify.

If there is a defect on or just under the surface, the foundry will likely find it and have to weld repair it. If it is a large defect, then they will have to stress-relieve it after welding and re-inspect. This will greatly reduce the chance that you will find the defect on final machining.

You will have to pay more for the casting, but if this is a repeated problem, you could end up with a shorter lead time for your casting.


arunmrao is right, this is a problem that is inherrent in the casting process. The trick is to keep the monkeys where they belong.

 

[EdStainless]

The other trick is to ask for very specific results. You don't need the entire casting to be free of porosity, just some critical areas.
There should be very little cost associated with this.

If this hasn't been a chronic problem then it makes we wonder about changes in foundry practice. Is the tooling unique for your part? Has it been modified recently?

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[stanislasdz]

Hi all

It's too easy to say " see the foundry to enhance the foundry proccess " !!! less esay to say it than to solve problems

As you know all, inclusions is a big problem in sand casting !

Ps :There is no a exact science to predict

- The locations of inclusions
- The amount of inclusions
- The motion of the inclusions during pooring
- What kind of inclusions from sand or from melting

Actually there is no part withtout inclusions....as i said to say that foundry is gullty is more easy...given a solution is less easy ..

here an exemple of some Researchs on the effect of the Liquid flow on the inclusions.

Sorry my english is bad !