Bentonite Clay

I've just been give 3 25Kg bags of Geotechnical grade bentonite clay. It's in 8mm soft pellets.

I want to use this as a binder for green sand casting.

Any suggestions as to how to crush it, or can I use as it is and mix to a paste before combining with the sand.

Here is the ideal machine for the job

... but I believe some "pug mills" are similar; so it might be worth talking to a local Potter.

MichaelG.

If your moulding sand is in a plastic condition and you are not talking about tons of the stuff you could just wedge it.

Rough mix the correct quantities in layers for preference pressed together. Bang it all up into a block and cut in half with a cheese wire. Pick up the top half, turn it over and bang it down again on the first piece. Turn it on its end and repeat.15 mins or so of this will have mixed the two components thoroughly. This does the same as the pug mill. never done it with moulding sand but this is the standard potters method for mixing clays.

regards Martin

Seems to be handy stuff, rarely mentioned in the ME

from 2768, casting things from scrap aluminium

"There have been several articles
on the subject in THE Model ENGINEER,
for example, within the last
few years.
The main casting, in particular,
provided " problems, mainly with
regard to coring. The cores were
prepared in a core-box made of
plaster, and this was quite satisfactory
for producing them.
In the early attempts, however,
much trouble was experienced with
the cores breaking up or causing
blow-holes—this in spite of the fact
that they were baked in the oven
and apparently free from moisture.
This trouble persisted until some
“ Bentonite ” was obtained and used
in preparing the cores. For fine
castings of this nature, proper
moulding sand, etc., is a necessity,
and the mould must be well vented
at places where air bubbles are
likely to form. A riser is used to
give a head of metal above the
highest point of the pattern."

Edited By Ady1 on 25/04/2014 11:49:40

If the pellets are soft as in not dry they may not crush well. Possibly they are meant to be just added to water to make pure clay for potters. Since you want a powder to mix with sand better I suggest drying them well ie right through first, then for grinding perhaps a cement mixer with bricks if you don't have any neighbours.

Possibly some adaptation of a garden shredder would do. The fast whizzy kind with the exit blocked would work like a big kitchen blender, or the slow grindy kind might work with adapted grinder wheels.

BTW do the bags have a manufacturer or source indicated that might be useful to others looking for some.

It seems to be quite expensive, if this is anything to go by, so nice gift:

http://mistralni.co.uk/products/sodium-bentonite-grg

Edited By Bazyle on 25/04/2014 13:14:38

It might be worth looking here, before proceeding. ...

If my reading is correct, those pellets are designed to swell with the addition of water.

MichaelG.

Edited By Michael Gilligan on 25/04/2014 13:18:42

This is a bit better price

**LINK**

BTW I don't think it will work well as is. The idea of bentonite is that it is an extremely fine clay and sticky so every grain of sand can get coated and bind the lot together. If you add the pellets they will just get covered in a layer of sand and sit there and be very difficult to disperse mechanically. The only other way of dispersing it is to mix to a very liquid slurry and add the sand. Then you would need all summer to dry it out again.

Having looked at the pellets, they are quite damp so I'll try drying some off before crushing, the name on the bag is Mikolit, they are intended for sealing bore holes and Geotechnical equipment

I have used pellets before to make greensand like this:

> they are intended for sealing bore holes and Geotechnical equipment

The powder is very useful for repairing leaky clay lined ponds.

Neil

Fullers earth cat litter is bentonite, and quite useable as a refractory for some purposes. Granular though

Cheap, and sold by most pet supplies stores.

http://www.pet-supermarket.co.uk/Products/CMP193/pettex-premium-grey-fullers-earth-cat-litter?utm_source=google&utm_source=cpc&utm_campaign=ps_productTargets&CAWELAID=720017470000025836&gclid=CLX-qLr9-70CFerpwgodRFEA3w