Recommeded Investment Mould Set-up
•Ring of 100g = patterns under 0.75g.
•Ring of 200g = patterns under 2g.
•Patterns should be covered with 5-6mm investment material over the top.
•The distance between the wax-up and the ring wall is 7-9mm.
•The distance between the patterns is 5-9mm.
•All patterns should be placed outside the thermal zone in order to prevent porosity present on the patterns. (Refers to picture 1)
Picture 1 Correct pattern placement
•The investment material should be stored in refrigerator.
•The expansion liquid : Water: powder ratio is various for different investment material.
•It is recommended to follow the instruction of each material (For example Table 1).
Table 1 The recommend ratio instruction of a 3D printing investing material.
•It is highly recommended to use the investment material especially designed for the 3D printed wax-up.
•The following materials can be used as a reference.
•Link 1:VarseoVest C&B – Phosphate-bonded, shock-heat precision investment material, especially for casting 3D printed crown and bridge frameworks (bego.com)
•Link 2: KeyVest - KeyPrint (keystoneindustries.com)
•It is recommended to apply the wetting agents which allows the investment to cover the pattern completely therefore reduce the potential air bubble entrapment.
•The wetting agents should be dried completely before investing.
•Mix the investments under vacuum to remove air and Ammonia. This will ensure a dense and bubble-free investment that promotes uniform expansion.
•Insert the warm ring into the warm furnace, never cool the ring completely.
•It is suggested to apply a very thin layer of wax on the outer surface of printed pattern. The veneer of wax helps to distribute the force acts on the investment. It has been proven effective to prevent the ring crack issue.
•Put the smaller ring into the furnace holding at 950℃ for 30 mins, 40 mins for greater size ring.
•After put the ring into the furnace, leave the chamber door slightly open for around 10 mins before closing for smaller ring, 15 mins for larger ring. For exhaust gases leave furnace and maintain the ring soaks in heat.
•The plastic material should be heated slower and subsequently stay in the burnout furnace for longer to allow melt and flow out of the mould without pressure build-up.
•Put the ring inclined to allow more oxygen flows in, thus improve the efficiency of burning. (Refers to picture 2)
Picture 2 The suggested muffle placement in the furnace
Do not quench the casting ring immediately after casting.
•Alloy and investment should cool to room temperature.
•Uneven cooling shrinkage between the casting and the investment can apply tensile forces to the casting.