Platinum sticks to crucible during casting

[Cabllan]

Hi, I'm just getting into platinum investment casting. I've done several trials with a few different alloys in a vacuum induction furnace and for reasons I don't understand the melt sometimes sticks to the crucible walls when poured, leaving a trail behind. I'd like to avoid this because it means not enough metal ends up in the mould riser which could compromise the casting and because I want to avoid revert as much as possible to minimise impurity pickup and the evaporation of alloying elements from the melt. I paint the crucible (made of silica) with yttria stabilised zirconia paint beforehand which is presumably suitable for Pt alloys. I use a superheat of about 150-200 C. Has anyone had this issue before? I suspect it might be avoided by using a different paint or a higher superheat, but experimenting is expensive so I thought someone could help.

 

[Lou]

Recommend you switch from silica, which may interact with platinum, to yttria stabilized zirconia crucibles.

Pt/Pd interact with silicon, particularly in nonoxidizing and reducing conditions. Obviously you won't have any good casting if the Pd is melted in air. Platinum is fine (PtIr anyway).

 

[Cabllan]

Thanks, will look into different crucible material. The YSZ paint is supposed to prevent contact with the silica mould but maybe the layer is too thin and gets stripped off during melting. Do you know if any particular Pt/Pd alloys have a reputation for sticking? There are a good number of formulations out there (PtCu, PtPd, PtCo, PtRu, PtInGa).

 

[Lou]

PtCu and PtCo and PtGa...all need inert melted as they make sticky oxides which may reduce silica.

 

[Lou]

Check your melt hygiene. Can you melt Ti and get a clean casting??

 

[zachy]

Cabllan, hello, I think you have a problem with your temperature sensor, you should not trust the reading offered by the infrared sensor, you must train your eye, and determine the casting point of the molten metal, generally platinum turns white intense and begins to jump a little, remember that you must put 10% more metal for the piece according to the weight of your lost wax, the feeders must be a little thicker and shorter, so that the piece fills completely, the casting Platinum should be short and fast.

Your investment is very important that the desenseration curve is adequate, use deionized water, and be very careful if you are using a 3D printer, as a final piece, as some leave traces of carbon and damage the platinum alloy that is very sensitive to contamination with carbon.

If you put pictures of your casting attempts, I think I can help you ... I think yours is a lack of temperature.

Are you doing the casting in a vertical vacuum induction furnace? or horizontal?

Regards