Locate the problem and then select the possible cause to find a probably solution.
Investment Cracks or Explodes During Heating
Phosphate based investments such as Aurivest require a clean mixing environment and complete homogeneity. All mixers should be thoroughly cleaned and follow the mixing instructions that come with the investment. Hand mix the liquid and powders at room temperature until the powder is fully blended with the liquids. Machine mix for 60 seconds under vacuum which allows the chemical reactions required for proper set-up to complete.
Different rings types and sizes can affect the setup and evolution of vapors. Rings that do not allow the easy escape of moisture, such as plastic rings, may require longer time for the investment to fully setup. Larger diameter rings also affect the setup time. The instructions recommend at least 15 minutes of bench set before placing in the burnout oven; however if larger sized rings or plastics are used, an additional 5 to 10 minutes should be given to allow full setup of the investment.
Do not use investment if it is too thick, warm, and hard to pour because it will not set evenly. Aurivest has approximately a 4 minute working time after mixing.
Too Loose or Too Tight a Fit
Changing the ratios of special liquid to water will change the fit of the coping. Regardless of the changes in liquid, the total volume must remain constant as described in the instructions.
- Tighter Fits: Less Water and more Special Liquid
- Looser Fits: Less Special Liquid and more water
Aurivest must be completely mixed under vacuum for 60 seconds. Too short a mixing time can result in tight fits.
Porosity in Coping
All mixers should be thoroughly cleaned and follow the mixing instructions that come with the investment. Because Aurivest is so fluid, do not put on a vibrating table before mixing – this will introduce air and bubbles into the investment. It is sufficient to slightly vibrate the mixing bowl during pouring but do not introduce air into the mixture.
Cracking of Rings with Pressables
When processing pressable ceramics, follow instructions regarding the heating and processing of the pellets. This includes:
- Burn out of the mold and plunger in a calibrated oven using the recommended temperatures.
- Quickly transfer the heated ring and plunger to the pressing furnace. Place the room temperature pellet(s) in the
ring and place warm plunger on top.
- Follow the pressing conditions in the manual. When at pressing temperature use 16 minute hold with a 7 minute
press unless using an Ivoclar oven.
Also note, if using a reusable plunger, do not grind surfaces which might cause improper pressure during the pressing