Hi Folks,

Some years ago i worked as a greensand moulder, making iron
castings in naturally bonded sand (a british sand called
Red Mansfield).  To this sand was added about one quarter by
weight some crushed rock sand, which good old mother nature
had also incorporated a percentage of natural clay.  During the
preparation of this sand, which was crushed in a big pan mill,
To which was added about 5 to 8 per cent of coal dust, This
material, was obtained from our foundry suppliers and was finely
milled to the consistency of talcum powder, This particular
coal, was Anthracite and had a fixed carbon content of 90%,
and of low ash content.Now basically, the purpose of your coal
dust is to give a protective gas atmosphere, to protect the face
of the mould and prevent burning on & scabbing of the casting
surface, although a mould dressing of graphite was shaken onto
the mould surface and sleeked and trowelled as well, to give a
super casting finish, In spite of the use of graphite, the coal
dust is still a most important element in green sand moulding in
iron founding practice Should you use this material at home you
should find it beneficial, although dont go berserk adding to
much coal dust to your sand mix,or you will find your castings
turning out with the surfaces crazed or a "rat tailing" effect,
And also in the production of light section castings, miss runs.
Whilst i am typing i remember also coal dust makes your sand
more refractory, & improves the bonding of your sand grains,
gives better venting also. When our facing sand was prepared
it was as smooth & fine as silk (aim for your sand to be like
that) If you are making baked cores you might also wish to
paint the surfaces exposed to molten metal with a core wash
made up of graphite, coal dust, a little bentonite, and a trace
of mollasses added to water during mixing up your core paint,
Apply when the core is still warm,(not too hot)Remember to
check your cores are thoroughly dry before placing in your
mould    For a facing mixture for Aluminium, i find talcum
powder gives a lovely finish Give it a try Remember safety
is your consideration, You are responsible for the outcome of
your actions i dont accept any liability for your experiments,
or my info given in good faith. Take care and have fun.

braekirk67_sweeper@yahoo.co.uk