Porosity in SG Iron

Hello Ajay Yadav

You have not stated the size/weight of the casting, or wall thickness, before machining.

If you could advise back here, with a few digital photo pictures in your reply, it would be helpful.

It may be that the mould pattern needs alteration, to avoid sharp corners, which initiate cracking in the casting.

Do you "heat treat" the castings, to relieve casting stresses, before machining the parts - This is essential in the case of larger castings.

If porosity, check your mould sand for absolute dryness, as a small amount of dampness creates steam when the molten iron is poured, with probable cracking in some areas.

If it is a problem with porosity, you could avoid that by making your mould pour in a different orientation, (place it at a different angle), or add an extra vent, see if that allows steam/air to vent/escape properly.

The alternative would be to coat the porous area from the inside, with a filler type of setting liquid. (2 pot Epoxy Resin does the job well, dependent on pore sizes), or over-machine the bearing housing, and fit an oversized steel insert ring to retain the bearing - I have seen this done in earlier years.

Reply back here with thank you.

Kind Regards....

Its a 65mm length /86mm in diameter casting ,with a integrated flange to have bolting holes and cylindercal portion with stated length of 65mm /86Dia.. Approximate weight of the casting is 2KG.As far as heat treat is concern we are not doing.

Hi, all.

Even the information given doesn´t allow to assess the problem completely, it seems the problem arises when machining cast parts (I suppose SG stands for Spheroidal Graphite). The post text talks about "problem" but title is: Porosity in SG Iron.

So, it seems there are no cracking problem which could be produced by a poor model design. Cracks use to appear in the surface and it is not necessary to machine the part to detect it.

The problem then must be as the title says "porosity" but could be small shrinkage too

In this case is a question of risers, vents and chills design (sizing, positioning) without forget the reaction between the molten metal and the mold. Humidity can be present (There are casting process with "green sand") and decomposition of binders added to the sand/clay could rise the amount of gases present.

Before looking for alternate material, look for the properness of the casting process.

Best regards and good luck.

If you made the castings, you should know your defect, and potential causes - hence your own solution. If you didn't make the castings, contact the foundry - tell them precisely the nature of the "contineous problem" - they will need a lot more info than is contained in your initial coment.

Thanks for your suggestion. We are not making castings but procuring it from a foundry. Foundry persons could not resolve the problem ,thats why i am putting here.

please give more info as asked in other posting.

one option is to impregnate your casting with a porosity sealant.

low viscosity resin that is vacuumed into the pores then heat cured.

If you are procuring casting from outside source then may be your supplier is not experienced in making S.G.Iron casting which needs special process. Better try to located other more reliable supplier. You can not control process at your supplier's end.

Investigate the mould. Please excuse the assumption about your location, but local practice may be relevent.

http://www.indianfoundry.com/faq/index.html#2