Flask Liner 2.5 inch for 3 inch tall flasks
This is a non-asbestos ceramic fiber flask liner material. It has 3 purposes for platinum or stainless steel casting in phosphate bonded invested flasks. The first purpose is to move water from the investment towards the top and bottom of the flasks. The second purpose is to create a cushion to handle the thermal expansion of the silica investment material as it goes through it's beta phase expansion during the burnout cycle. This cushion prevents your mold from cracking during the extreme temperatures of the burnout cycle. The third purpose is make cleaning the phosphate investment out of the mold after the casting, quenching, and devesting process is complete by reducing the amount of investment from sticking to the inside walls of the flasks. The paper is about 1 inch shorter than the flask so that you can have 1/2 inch top and bottom of the flask where the investment material does make contact to secure the invested mold in the flask during operations.
Using the wrong material, especially one that burns, will cause the investment cylinder to slip out of the flask after burnout or it will cause cracking inside the flask which will result in fins on your castings. Not all casters use flask liner but they would be much happier if they did.