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Your instructions recommend placing flasks into a preheated oven to begin
burnout. Can the ovens be cold?
Do you have any recommendations for steam dewaxing?
How can I be certain that all of the wax has burned out of my flask before
I pour metal into it?
Sometimes I cannot cast a flask as quickly as I had planned. Is it acceptable to
burnout a flask, let it cool to room temperature and then reheat it for casting several days later?
Our facility casts five days a week but we do not invest on weekends. What should we
do to store the flasks we invest on Friday so they can be cast on Monday without problems?
Our burnout ovens are set on the same cycles. However, sometimes it
appears that the wax doesn’t burn out as thoroughly as at other times. Can you offer any help?
Do you recommend gas or electric burnout furnaces?
What happens to all the control chemicals in the investment during the burnout cycle?
Is there any harm in holding the flasks at the highest level in my burnout cycles for
extended periods of time?
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Jewelry Questions
Your instructions recommend placing flasks into a preheated oven to begin burnout. Can the ovens be
cold?
Do you have any recommendations for steam dewaxing?
We
cannot offer any recommendations on the dewax operation, per se. But it is critical that you place the steamed molds in an oven preheated to 350oF (150oC). Hold the molds at this temperature for 2 to 4
hours to dry the molds uniformly. Although you no longer will utilize this phase of the process to melt out the wax, it is critical to mold drying. Failure to do so can result in internal mold cracking
and finning defects.
How can I be certain that all of the wax has burned out of my flask before I pour metal into it?
The best method of determining whether the wax has burned out completely is a visual check of
the flask interior. Pull the hot flask from the oven, turn it over and look at the sprue. The interior of the flask should be pure white, a good indication that the wax is completely gone. If the
sprue interior has a gray or other color to it, place the flask back into the oven and continue the burnout cycle.
Sometimes I cannot cast a flask as quickly as I had planned. Is it acceptable to burnout a flask, let
it cool to room temperature and then reheat it for casting several days later?
No. When a flask is heated to temperatures that allow wax melting, the ingredients of the
investment actually undergo a thermal change that is not reversible when the temperature is lowered. If heat is then reapplied, the behavior of the investment does not replicate the initial heating cycle.
The flask stands a high risk of cracking when reheated, especially if this reheat cycle takes
place quickly. A caster may also see defects such as porosity and shrink or poor fill due to the interiro cavities being below desired casting temperatures. While the outside of the flask may become
red hot quickly on a reheating cycle, the refractory loading of the investment will delay the heat transfer to the inner portions of the mold.
Our facility casts five days a week but we do not invest on weekends. What should we do to store the
flasks we invest on Friday so they can be cast on Monday without problems?
On
occasion, casters experience a defect that we call “Monday morning cracking”. This defect is caused by flasks drying before they are burned out. If dry before they are placed in the oven,
the flasks will dry unevenly and start cracking. Stresses inside the flasks can create the cracking defect. If you invest flasks on Friday, two options are available to reduce cracking during a burnout
that may take place several days later.
First, you can seal the set flasks in a plastic bag with a wet towel inside the same
bag. This will keep the investment from drying out completely over the weekend. Or, you may choose to let the flasks sit and dry out, but you should immerse the flasks into water for a few minutes
before you place them in the burnout oven. This action will rewet the flask completely and allow the flask to dry at a controlled rate.
Our burnout ovens are set on the same cycles. However, sometimes it appears that the wax
doesn’t burn out as thoroughly as at other times. Can you offer any help?
Even though a group of ovens are set for the same burnout cycles, it is unlikely that the oven
loading is consistent for all burnout loads. Different size flasks and varying amounts of flasks in an oven will vary the work the oven is required to handle. You can increase the burnout efficiency by
placing the flasks on a rack in the oven, rather than setting them directly on the oven floor. Airspace between the opening of the sprue and the surface below will increase the air exchange and assist the
carbon from the wax to burn out faster.
It is important to maintain an oxidizing, or oxygen rich, environment in the oven. This
can often be accomplished by opening the oven door slightly.
Do you recommend gas or electric burnout furnaces?
Either system will work well, provded the ovens are not overloaded with flasks and are kept in good working order.
What happens to all the control chemicals in the investment during the burnout cycle?
Is there any harm in holding the flasks at the highest level in my burnout cycles for extended periods of
time?
You should not experience any problem, provided the molds are not cooled and then reheated.
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