Full Version: metal finishing for star
From: ram (MCTAWARDS) [#1]
27 Oct 2006
To: ALL
Hi all,
I want to make star as shown in the pic.
need more details of metal finishing, tooling. kindly help.
with regards,
ram
From: Stunt Engraver (DGL) [#2]
28 Oct 2006
To: ram (MCTAWARDS) [#1] 28 Oct 2006
The zinc stars have been hollow. In both cases, I assume they're cast from molds.
If the starts themselves don't need to be engravable, they could probably be injection molded plastic and vacuum plated.
From: Harvey only (HARVEY-ONLY) [#3]
28 Oct 2006
To: ram (MCTAWARDS) [#1] 28 Oct 2006
While they look like the paperweights I get, I am fairly sure they are not.
They may be metal plated plastic. It is quite an involved process to do that. The right plastic, cleaning, activation, silver plating for conductivity, then nickle plating. To make it appear gold in color a yellowish lacquer is then applied. It is not dissimilar to making LP pressing stampers.
From: ram (MCTAWARDS) [#4]
28 Oct 2006
To: Harvey only (HARVEY-ONLY) [#3] 28 Oct 2006
Dear Harvey,
Do we silver plate the plastics? how..
for activation... need more details ..plz.
with regards,
ram
From: Dave Jones (DAVERJ) [#5]
28 Oct 2006
To: ram (MCTAWARDS) [#4] 28 Oct 2006
There are plating solutions known as "electroless" plating solutions. (do a google search on electroless)
These bond a very thin layer of metal onto virtually any material without needing electricity like an electroplating system. Once you have that layer you can then use standard electroplating systems to build up a much thicker layer of metal.
There are electroless solutions involving many different types of metals (copper, nickel, silver, tin, etc...). Which one to use depends a lot on what metal is going to then be electroplated on top of it.
From: Harvey only (HARVEY-ONLY) [#6]
28 Oct 2006
To: ram (MCTAWARDS) [#4] 28 Oct 2006
I will see what I can remember, scant as it is.
First we used, I believe sodium phosphate solution to remove any oils.
Blasted that off with pure water, 12 Megohm.
Activated with stanus chloride, not stanic chloride. It needed to be relatively fresh or it changed to stanic. (Hydrochloric acid and tin, leave an extra tin strip in the mix to help keep it active longer. Blast off with pure water.
I do not remember the full formula and procedure to make the silver nitrate solution, but it was many steps with a day in between, then adding another chemical till it turned faintly brown, then a day and adding another till it turned clear, another day and something else till it turned faintly brown again, then leave in a dark room for three weeks. It would have probably been cheaper to buy it but we made it.
Make a developer solution of rock candy and water. Sugar is a great developer.
Pour the nitrate solution and sugar water together over the item, swish it around for about two minutes under bright lights and it will form a 10 micron coating of silver on the plastic.
Then nickle plate it in a solution of nickle sulfamate, sulfuric acid and boric acid. I do not remember the amounts but it was about 400 gallons of sulfamate, a cup of 12 molar sulfuric acid then a pouch of boric acid which was left in the tank to achieve saturation. We used either 100 or 200 amps for 3.25 square feet of plated of record. The current per square foot is critical, each element plates out best at a certain current. (We got rid of tramp calcium at about 600 amps, and tramp copper at about 40 amps. Those two can cause cracking of the silver plate when starting.)
A chemical supply house can help you with specifics. So can the book 'Chemistry Cookbook'.
It has been over 20 years since I had to control this process, so a lot is gone from memory. You may find a nickle plating company who can do it for you at not too high a price.
From: Mike (MIKEN) [#7]
2 Nov 2006
To: ALL