The authoritative public forum
  for Metal Finishing since 1989
-----

Polishing inside of copper moulds

2004

We are making copper moulds in house by electroforming (spray silver on plastic mother moulds), then we strip the silver inside by sand-blasting and finally do electroless nickel plating inside the copper moulds.

My question is: after sand blasting, the inside is semi-lusting. We hope there is a method, like polishing or chemical treatment, could get mirror shine. Our moulds dimension is cylinder shape, diameter 1"-2", length:6"-8". Hope you can help me, I appreciate your suggestions.

Roots

Roots Gu
plastics - Toronto, Ontario, Canada

---

I think I understand the process you are describing but not the need for sandblasting. If you chemically strip the silvering, or just leave it there, you won't have the problem. If you do sandblast it then you would need to either buff the copper or try a leveling electrolytic nickel before the electroless nickel.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004

---

2005

Thank you for your response, Ted.

We care very mucn about the inside texture because we will cast plastisol into moulds later and make profiles. We hope the inside is very smooth and glossy just like mirror after EN plating.

Our competitor are using a kind of enbrightening liquid to level inside after sand blasting, and they can get inside glossy. Do you know what kind of brighten liquid can get this result?

thanks.

Roots Gu
plastics - Toronto, ON, Canada

Most effective and obvious way to produce an ultramirror finish inside an electroformed mold is to provide that same finish on a metallic mandrel and give it a thin chrome flash afterwards to facilitate subsecuent separation. I'd bet your competitor is doing just that.

Guillermo Marrufo
Monterrey, NL, Mexico
2005