Green Sand For The Hobby Foundry. Mixing & reconditioning green sand.

November 29, 2004   Business News
(PRLEAP.COM) Green sand, can also create a lot of frustration for the hobby foundry worker when it is not correctly prepared.
Ramming & moulding difficulties can be experienced.

There are other alternative foundry moulding techniques or methods which can be used, but none come close to green sand for the simplicity and ease of use…. Once you understand how to get the best from it.

The quickest & easiest way to obtain a good supply of ready to use green sand, is to locate a small commercial foundry (search around foundries specialising in
art castings, sculptures etc) willing to sell, or supply you with a couple of bags of well prepared, ready to use green sand.

By acquiring correctly prepared green sand will certainly help you to understand & familiarise you with exactly how a well prepared green sand medium should feel like when you need to recondition it.

If you happen to be supplied with green sand that's down in condition, i.e. unsuitable to use for moulding, the sand can be reconditioned with a small addition of new olivine sand, and an addition of a small amount of bentonite. (Binder).

The green sand will need to be thoroughly reworked to regain the correct properties for moulding.

The BIG draw back for the hobby worker attempting to make a batch of new green sand from scratch is the process of "mulling".

A mulling machine is like a ball mill which rolls/compresses/mixes the moist sand particles until every tiny grain of sand has a small amount of bentonite
binder attached to it.

If the particles of sand are not sufficiently coated with bentonite binder, you may experience sand pulls,
or drops in the mould, or the mould may fall apart when you lift the cope to remove patterns.
The sand may also be difficult to ram to the correct mould hardness.
The binder is the secret ingredient that holds the sand mould together.

Few hobby foundry workers can afford the luxury of a green sand muller, however some have managed to build a suitable mulling machine for hobby use.

The Motorised Gyratory Riddle is also a very efficient machine for preparing and reconditioning green sand.
Used casting sand can be processed through the power driven riddle to eradicate hard sand lumps & foreign
matter.
The motorised riddle will fluff and aerate your sand, and with the correct amount of water added to the green
sand, the riddle will provide sand that is as cool and smooth as silk, and excellent to work with.

The Gyratory riddle can also be used to mix additional binder and new olivine sand into old green sand stock.
(Though it is nowhere near as efficient as the Muller.)

Once the reconditioned sand has been cycled a few times through the moulding/casting operation, it
seems to resume it's proper moulding characteristics.

But if the green sand is full of burnt clay fines, then it is probably time to dispose of it, and start preparing new sand stock base.

A reasonable green sand mix can be made up from the following:

Start with a hundred pound weight of washed silica sand with a fineness grade of 130 to 160 AFS.

Add Southern Bentonite at 4% by weight.
A small amount of wood flour; 1 to 1.5%.
And an addition of sea coal if you can find some, say 2% by weight.
Moisture content required is from 4 to 6%. by weight.

Now you need to use a Muller, as explained above, to process and prepare your new green sand.

Mulling green sand is a processing problem that will create difficulty for the hobby foundry worker.
Incorrectly prepared green sand will drive you nuts while you're trying to mould with it.


AlTERNATIVE METHODS OF SAND MOULDING.

Method 01:
Co2 Gas & Sodium Silicate Sand Moulding.

An alternative moulding method to green sand is of course the Co2 method of making sand moulds & cores.

While a small number of home foundry workers may have already advanced to Co2, most novice hobby workers may be quite happy to try their hand with green sand at first.

The Co2 process consists of mixing a clean, dry silica sand with a silicate-based binder (sodium
silicate).
Then scooping & compacting the sand into the mould box, the sand/silicate mould is then injected with carbon dioxide (Co2).

The carbon dioxide gas instantly reacts with the sodium silicate, which immediately sets the sand mould.
The moulds are then parted to remove the patterns, then closed, ready to pour the molten metal.

The Co2 system is very easy to utilise once you are familiar with the chemistry involved. The hobby Metalworker could even start using this moulding system from the outset, instead of using green sand.

The only problem the hobby foundry worker may find is that the chemicals required are generally only available in 200 litre containers, the smallest
sized container you'll find is 20 litre drums, and even this quantity may be too much to use before the shelf life is reached.

Once the correct percentage of chemical mix is arrived at for the given sand being used, you'll be amazed at the ease of moulding with this method.

To carry out this type of sand moulding also requires the necessary gassing equipment, while not being of a complex nature, the equipment consists of a small tank of Co2 gas, a regulator to control the gas flow & line pressure, a suitable length of gas line hose, and a hand held trigger type of injecting gun (A cheap hand held workshop air blower gun will do).


Method 02: COLD SET RESINS.

Another easy to use sand moulding system is the silicate/catalyst cold set moulding system. This involves carefully measuring the resin & catalyst to
be mixed with the sand before lightly ramming the mould.

Once thorough silicate mixing is achieved, the mould is left to "air" harden, or what's known as "cold set"
for about 15 minutes, before the mould boxes are pulled apart to remove patterns, etc.

Simple tools can made in the home workshop to enable this modern technology to be used effectively.

You do not need any expensive equipment to use this moulding system. The only drawback is that the sand cannot be reused, so you'll need to think about your sand disposal methods.

Both of the above alternative sand moulding systems are worth exploring, even for the novice or hobby foundry worker.
Foundry supply houses will be able to provide you with complete product user guide reference sheets on request.


Article written and supplied by:
Col Croucher.
Author and Publisher of respected Hobby Foundry ebooks for the novice metal caster.
http://www.myhomefoundry.com
ebook Publishers. Australia.
FAX: + 61 3 57 22 4654
email: mailto:colin@myhomefoundry.com

Contact Information
Colin Croucher
The Home Foundry Publications
FAX: + 61 3 57 22 4654.
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