Two things need to happen during sintering:
The part shape is supported, and
Oxygen is prevented from reaching the part
We solve part shape support with Sintering Refractory Ballast – Al2O3 and Talc (for copper and bronze) or Steel Blend (for the steels).
We solve for oxygen with Sintering Carbon
Lots of you have asked if these powders can be reused and the answer is absolutely Yes!
With Copper and Bronze, you’re using the Al2O3 and Talc and those will have a nice long life for you. Use fresh ballast when you’re doing something new and don’t want there to be any unknown variables. Otherwise, use it over and over.
By the way, the difference between these two is that the talc moves more easily so it’s great for that sintering process when your part needs to be able to move as it shrinks in.
Your print needs more firm support during debind and the Al2O3 is better at that.
Could you get away with just using one or the other? Yes, but best practice is to use each where indicated.
When working with steel, you’ll use Steel Blend for that Refractory Ballast and again, you’ll use that for many sintering cycles. You will eventually notice the color begin to change. That’s because one of its ingredients is being used up over time. Eventually, you will need to replace that material. You’ll know it’s time when it no longer has a black or dark gray hue but rather looks more yellow-ish.
Sintering Carbon – the one used for oxygen management – is meant to be consumed as it grabs all the oxygen present and keeps it from reaching your metal part.
But, at the end of your sintering cycle, any part of the Sintering Carbon that looks nice and black – just like it did when it went in the kiln – can be filtered out and used again.
Don’t worry if some of it gets into your Ballast material. That’s ok.
You can slow the rate that Sintering Carbon gets used up by simply adding a cover to your crucible. This can be kiln paper (in our store), a ceramic plate, tool steel wrap or anything like that that can take the heat. Make sure you’re not sealing the crucible though. There does still need to be some air movement – we’re just doing what we can to minimize that without eliminating it.
So, bottom line, Yes! Reuse your Refractory Ballast materials and your Sintering Carbon.
If you have more questions, reach out to us at [email protected]