Investment apart from playing the stock market, is a exceedingly fine powder that when mixed with water in carefully regulated amounts, is poured into the flasks around and over the wax completely covering it. The water and the powder are first mixed in a ordinary mixing bowl using a electric beater for about four minutes. The powder is 'always' tipped at a regular pace into the water to prevent a lumpy mixture. There is a strict time limit on working the investment as it begins to cure inside nine minutes depending on the temperature of the water and of the room. The mixture is blended into a smooth creamy consistency.
I then place the bowl into a vacuum pump which sucks all the air from the mixture. This ensures that no or very few air bubbles are left inside which may adhere to the wax which when cast have to be scraped and cut off.
I then pour the investment into the flasks and evacuate the pots with the mixture. This removes any remaining air bubbles from the wax itself and helps the investment to get into any cracks and crevices. I do four flasks at a time which is the most I can get under the vacuum hood and I can cast up to 19 at a time.
I leave the flasks to cure for about an hour. I then strip off the packing tape and remove the rubber base, leaving only the flask with the white investment surrounding the wax of which I can only see the round sprue inside the small dome shaped indentation. This indentation will hold the molten bronze while it is being fed into the interior of the investment. It acts as a reservoir, is called a button and has to be big enough to take the first 'hit' of bronze otherwise it may ( and does on occasion ) spray red hot drops of bronze at high speed in all directions. My caster has steel walls enclosing it for this very reason but the molten metal can spray onto the floor which happily burn holes in the moth [ bronze ] eaten carpet below. I place all the flasks into a ex-kitchen oven and gently heat them to 150degreesC causing the wax to slowly flow out of the moulds into a tray placed below.
This preliminary melt-out is essential to the well being of the main dewaxing kiln. The wax is very corrosive and the less wax that is removed in the kiln the better. I can, after straining the wax, re-use it. Placing the flasks into the kiln, I set it to turn itself on at 7pm that evening. It takes around one and a half hours to get to the optimum temperature, 600 degrees C where I hold it for two hours to thoroughly burnout all the wax.
The automatic controller then turns everything off and allows the kiln to very slowly cool down to 230 degreesC overnight. A slow cooling will prevent any cracking of the mould. If I have done everything right, I will have pure white investment in the flasks with no sign of any wax. I then begin casting and with 19 pots this can take up to three and a half hours depending upon what it is that I am casting. If there is wax present when I cast, it forms a skin on the bronze which has to be removed, a tiresome job in some cases. Now the flasks are ready to be centrifugally cast
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