Core Making

Baked Cores

In my earlier videos you will see I was using a baked core.
Here is the recipe:
525g       Wickes sharp sand, sieved with kitchen sieve to remove larger stones
             ( Wickes is a builder’s supplier in the UK)
18g         Flour ( plain)
10g         Solvite wallpaper paste, dry weight, mixed with minimum amount of water.
12.5 ml.  Boiled Linseed Oil

Put sand in a plastic bag and add flour. Shake till mixed. Add paste and work the bag between your hands until mixed then add the linseed oil. Make the mix as dry as you can so it will harden quicker.

Ram into core mould . Leave in a warm place until you feel its safe to beak the mould , It will still be quite soft and needs cooking slowly, in the kitchen oven, building up to full oven temperature of  250C when it will be a dark colour and begins to smoke. Best done when Mrs Myfordboy is out !

Coat with talc to give better surface finish.

A baked core gives a very strong core which will withstand a lot of handling. 

For cores I now use Sodium Silicate which is quicker and cleaner to make.

Core making with Sodium Silicate
I am now using some core sand and sodium silicate from Artisan Foundry and they have given much better results than the pottery suppliers product previously used. The sodium silicate is thicker and has a light brown colour, the pottery suppliers was clear. The finished core is very smooth and no loose sand falls off. The finish is so good it could be used a mould instead of greensand.

Following the recommended ratio given on the bottle, I weigh out  500g of  60 grit silica sand, add 10ml of sodium silicate and mix using a paint stirrer in an electric drill.  
This is then rammed into the core box with a removable wire in the centre to vent, and C02 gas passed through for up to 20 seconds.
The core hardens by chemical reaction and can be removed from the core box and used immediately.
I am using a bottle of gas sold as carbon dioxide welding gas .
Removing the Core
After casting the core sand can be removed by soaking in  water once cooled off.