Re-use of oil-bond sand?

[MRA]

Hi Folks

I've got my waste-oil furnace running well, and after 3 or 4 goes at turning al scrap into ingots, I'm going to have a go with a pattern and some sand.

I acquired a bucket of 'new' oil-bond sand, and a bucket of 'used'. The 'used' is rather black, contains a lot of lumps which break up fairly easily if one laboriously goes through it by hand, and lacks some of the 'stick' of the fresh stuff.

Anyone add oil to 'used', to re-constitute it? Anyone have any ideas for a simple mill to break up the lumps? And is there any merit to my hunch that 'new' might be used around the pattern, backed up with 'used' for the remainder of the flask?

Yes, I'm cheap. Currently only paying for electric to run my air blower!

cheers

Mark, Manchester UK

 

[HowSisler]

I have always used the new ones and Lumps has always been the reason why I always avoid using the old ones :hDe:.You have struggle with the lumps.:fan:

 

[Jasonb]

Bit about revitalising it in this thread

http://www.homemodelenginemachinist.com/f36/how-do-i-fix-petrobond-20436/

You can force it through a wire sieve to get the lumps out, use new fresh stuff up against the pattern and the older stuff to fill in the spaces.

J

 

[MRA]

Thanks Jason.

I am rather limited for space; I have a cement mixer (coincidentally) at the moment, recommended in that thread, but I suspect the wife is not going to put up with it in the front garden for long!

So - today I tried another approach, which worked well. I remembered I had cycled past an old plaster mixer (the ones with a spiral impeller welded to a bit of hex bar, which fit in a drill) in a tip by the road. I went back today, and it was still there. I cut it in half, and put it in my big old pillar drill.

I used a steel wastepaper bin as a mixing bowl, and 1/3 filled it with horrible lumpy dry burnt sand. Switched on slowest speed (340 rpm) and lowered impeller.

The nice bit happened unexpectedly - because the bin was not clamped to the base, it wanted to jiggle slowly round clockwise when the impeller was placed close to the bin edge. So I screwed some blocks to the drill base T-slots to guide it, and voila - self-acting mixer.

It broke the lumps up lovely after a few minutes, and the bond improved a lot.

Now a UK/US English question - what's 'rubbing alcohol' (ref in above thread)? Methylated spirits, or something more exotic?

cheers
Mark

 

[sssfox]

The English equivalent of rubbing alcohol would be surgical spirit. This is a mixture of ethanol, methanol (to make it undrinkable) and sometimes oil of wintergreen or methyl salicylate.

There is another cheap form of alcohol available in the UK called methylated spirit. This is similar to surgical spirit but contains pyridine as well as methanol and a purple dye to make it undrinkable. It is used as a cleaner and a fuel.

 

[MRA]

Coming back on this one, much later.

In the end I used a little caster oil (because I had some and I didn't know what else to do with it) in the reconstituted, used oil-bond sand, and the bond seemed good. First impression (a plaque with quite a lot of lettering detail) went very well once I remembered to dust it with talc - without that, it tore up the impression of the lettering as I removed the pattern from the sand. The casting in Al came out very well. Next stop, bronze!