Rheocasting is no Golden Paint - Part 2

Implementing new technologies is always complex, as the surroundings must be adapted. In last week’s article, I described the issues with the standard HPDC ingate in Rheocasting. In the picture, you can see exactly the negative effects.

HPDC Ingates in Rheocasting

The part shown below has the normal HPDC ingate that spreads out in individual fingers. Then, it thins down even more before connecting to the part. The intention is to figuratively spray the melt into the part. That works excellently for liquid HPDC, and you can also cut it with the trim press.

But Rheocasting is a different animal. Rheocasting uses a slurry with thixotropic properties. These thixotropic properties allow for slow, laminar filling of the part with outstanding properties.

However, the liquid and solid particles are segregated when you force this thixotropic slurry through a thin HPDC ingate. You also create surfaces that cannot recombine due to oxidation, and they also entrap air.

The picture below shows how the HPDC ingate limits the effectiveness of the Rheocasting process. The large feeding pore on the surface is visible. An X-ray image of the part would show even worse properties.

Just so you know, this part is not a series production part. It is the training part of the Bühler Application Center in Uzwil, explicitly designed to show feeding issues. And, of course, they know exactly how to design a Rheocasting ingate, which has already been built. It was just a trial to show the detrimental effect on the casting quality.

What does an Ingate for Rheocasting look like?

When working with thixotropic fluids, the worst thing to do is break the surface of the slurry. So, your ingate has to keep the slurry-front as uniform as possible. So, instead of splitting the gate into individual fins, it has to be a more uniform gating, looking like a whale tail.

This way, the slurry stays compact and fully utilises the shear forces, the pocket warmer effect, and the laminar fill. This gives you the perfect properties for your casting!

You would also turn the shown casting 90 degrees to fill the thickest areas first and have the best solidification path possible. But that would make a terrible training tool, as the filling works perfectly. 🙂

Level up your castings!

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