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Sandblasting of aluminum diecastings

Q. Hi,
I would like to ask what is the recommended Sandblasting for Aluminium diecast parts or Aluminium parts in general which will not affect the outlook much since we need to do some painting/powder coating finish.

Thanks and more power!

Regards,

Reymund Joseph Costa
QA Engineer - Singapore
March 30, 2023

A. Hi Reymund. There may be exceptions or special cases but I don't think sandblasting is the correct pretreatment for aluminum, especially diecastings. I believe that vibratory finishing or equivalent, followed by chromate conversion coating (or trivalent conversion coating) is more appropriate.

If you do not agree please share your thoughts.
Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Q. Hi Mr. Mooney,
The intention to use sandblasting was to improve the adherence of the paint on the die casting surface as we see the casting finish is smooth.

As we have tried to sandblast it with 100 grit and it looks good enough for the paint to stick.

We will be trying to paint and to compare the surface with sandblasting and without sandblasting.

I will update here later on when we have done our trial.

Thanks again!

Reymund Joseph Costa
QA Engineer - Singapore
April 1, 2023

A. Hi again.
Yes the paint should stick better after you break through the smooth skin and expose the porosity of the interior of the casting, but you may find it to not be a good tradeoff -- but good luck.
Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Alternatives as a pretreatment for painting on a die cast part is blasting using glass beads or grit. Korund, or aluminium oxide, is also quite good, giving different surface textures. The Korund is more like little jagged stars than spheres and creates a rough and broken surface, but is quite suitable for paint, in particular with a Conversion Coating like a hexavalent or trivalent chrome.

Keep in mind that hexavalent chrome conversion coating is cancerous and thus, everyone should wear the appropriate PPE. And I recommend that anyone handling the parts after treatment wear white cotton gloves at the very least.

Both pretreatments are prone towards fingerprints which will not help your painter.

M Stammerjohann
- Horsens, Denmark
April 27, 2023

A. Hi Reymund,

Use aluminum oxide blast media. It will not cause issues in further process steps. A lOx 140 grit is a good place to start your trials.

Avoid any silicated media including glass bead at all costs.

Cheers

Rachel Mackintosh
- Greenfield, Vermont
June 9, 2023

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