You didn't give a lot of detail about processing conditions, etc, but
here is my $0.02:
The blistering sounds like it is related to heating rate. In binder-
treated parts, if the temperature rise in the debinder furnace is too
fast, i.e. the parts are heated too rapidly, it can cause the binder to
outgas at a high rate, creating the blisters. I suggest decreasing the
heating rate and seeing if that works.
For the second problem, it may be atmosphere related, specifically, too
dry an atmosphere. In my experience, you want a wet atmosphere for
successful debinding. The wet atmosphere breaks apart the long-chain
binder molecules and flushes them out of the furnace. It sounds like
what you are seeing is the binder thermally decomposing in/on the porous
part surface, rather than being flushed away from the part surfaces.
What is the atmosphere source? I have seen equipment where the
atmosphere is bubbled through water to add water vapor to it before it
is introduced to the furnace.
Also, make sure you have good atmosphere flow into the furnace. As the
binder molecule chains break apart, they need to be continually flushed
out and replaced with fresh atmosphere.
Hope that helps some.
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