My worst casting ever!

[ironman]

Here are some photos of a casting I thought I had thrown out.

It brought back memories when I knocked it out of the mold. How could it be so bad?

A lack of knowledge made this casting so bad! That was 15 years ago since then I have learnt a few more things.

[awemawson]

So what were the issues causing the problem, that 15 years of experience has cured?

[Meldonmech]

Hi,
      I think the sand mould was too damp causing steam to be trapped in the casting. Or may be bits of sand swept into the casting during the pour, caused by the sand being too dry?

                                                                                              Cheers David

[MetalCaster]

Analyzing defective pours is an art.

I have been studying it, and have gotten better at identifying the problem, but it is a bit of an art.

I have found that it is critical to eliminate as many variables as possible, ie: use clean metal of a known composition, measure and record you pour temperature if possible, and try the same piece with a different mould material such as sodium silicate bound sand.

Moisture content of the sand is suppose to be extremely critical with resin binder systems (according to the binder rep).  Basically sand used with resin binder has to be about as dry as you can get it.

I used petrobond with iron and had some washing and sand inclusions where the mould began to fail.
Too much oil in the petrobond creates a whole different defect, which generally is external to the part, unlike the photos here which are internal to the part.

I am going to guess gassing from steam from water-based sand since the holes are so uniformly spaced around the part.

[ironman]

Green sand porosity decreases over time with grains shattering, parting dust, adding bentonite to restore weak sand and coal dust turning to coke. There is a shelf life for molding sand and I went way past it.