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Pressure Casting Clear

This How To will help you understand the process of Pressure Casting. We have chosen to work with the Alumilite Clear to demonstrate the difference between a casting that has been pressure cast and one that hasn't.


These are the items we used to mix and pressure the Clear: Pressure Pot, shop air, Alumilite Clear, Alumilite's Gram Scale, a 6 oz mixing cup, two 1 oz cups, and a stir stick.


Measure Alumilite Clear using a mix ratio of 1:1 by weight. It will not cure properly if you mix it by volume.


Once measured properly, mix thoroughly. The open time is approximately 5-6 minutes. Be sure to scrape the sides and the bottom of the container. It is very important to make sure you get the mixed resin into the pressure pot and to apply the air pressure prior to the resin starting to gel.


For our demonstration we will pour the mixed Clear into two 1 oz cups. The bubbles are many but very small. They are hard to see in this picture. They do show up better once the material has cured.


Here we are placing one of the cups in the Pressure Pot to be pressure cast.


It is very important to fasten all of the knobs down tightly to the lid. The red knob you see is a shut off valve which allows us to hold the pressure within the tank while disconnecting the air source after it has reached the proper air pressure in the tank. That valve does not come with the Pressure Pot. The regulator, safety release valve, and guage do come standard.


Before putting air pressure on the tank make sure to back the regulator all the way off. Then connect the air and adjust the regulator to allow the tank to fill up with 35-40 psi. The tank is rated to 50 psi and should never run over that air pressure. Alumilite's Pressure Pots have an automatic safety release valve on the top of the tank in case the regulator was accidently set allowing the pressure to release before the pressure builds too high in the tank to potentially cause damage.


We let the material set for 45 minutes before releasing the air pressure and removing it from the Pressure Pot. The size and mass of a one ounce cup will cure faster than a thin walled piece allowing us to demold it faster. We first disconnect the air source, release the air pressure from the pot, and then remove the knobs around the lid. You only need to make sure to pressurize the casting until you know it has hardened up. The concept behind pressure casting is to crush the bubbles to a point that we would not see them and then hold the bubbles in that state until the resin sets up. Once the resin sets up and hardens the bubbles will not be able to expand back to their original shape and size and will never be noticed in your finished casting.


We remove our Alumilite Clear cup from the Pressure Pot and see no air bubbles in the poured cup at all.


Here you can see the difference between the castings on the left that has been pressure cast compared to the cup that was just mixed and poured without the use of pressure. The cup that was pressure cast does not have any air bubbles. The cup that was not pressure cast has hundreds of small champagne sized bubbles throughout the entire casting.

 

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