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

Faraday's Law

 

I have the common problem of electroforming into sharp corners, has any one worked out a way to overcome this. Even if it is long winded way I would be interested. My main concern is making two halfs of a mould for roto molding.

Kenneth Foyn
Cold Castings - Durban, South Africa

---

I don't think Faraday's Law of Electrolysis has much to do with it, nor does the Faraday Cage effect. But electricity will take the path of least resistance, and ions will be reduced where the electricity goes. So what you need to do is use shields or auxiliary anodes designed such that the inside corner is the path of least resistance.

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

How about masking off one surface into the corner and electroforming the part that is not exposed. Next repeat the process but this time tape off the already electroformed part and expose the part that was formerly taped off. In this way Mr. Faradays Law becomes just a guideline that can be safely ignored and you will be able to lay down metal right into a right angled corner.

If I sound authoritative do not let this fool you. I have never done it, however I have electropolished into corners and Mr. Faraday is alive and well in this specialty as well. It worked great for me and I hope it works for you too.

Good Luck,

John Holroyd
- Elkhorn, Wisconsin

---

 

Ted,

Your comments set me thinking about my own response to this question. You are right. Faradays Law relates to electro-magnetic induction which has absolutely nothing to do do with this problem. An example of my own sloppy thinking. I knew what I meant and what the question meant. Faraday is intimately connected with this issue in my mind and I have often used the Faraday cage in explaining this and similar phenomena, but, his law is about something else entirely. This is where I must take issue with you. In my opinion it is the Faraday cage effect that is responsible for the lack of plating in the corners. True it is a limiting case of the cage effect but it is the same effect. In addition I think that we are indebted to Micheal Faraday for giving us one of the most powerful methods of visualizing this effect, namely lines of force.

Just for giggles I have done a finite element analysis of the current density in a sharp, right angled corner and it is zero. It does not matter how I configure the anodes it is still zero in the very corner. Add an insulating shield and the problem is solved.

Stay well and keep on keeping us intellectually honest.

John Holroyd
- Elkhorn, WI

---

Okay, I think you could be right that this is the limiting case of the Faraday Cage effect, John. But no corner is infinitely sharp, i.e., no corner continues to look exactly the same to the incredible shrinking man standing in it as he shrinks. So, realistically, while the current can be very low in a sharp corner, I don't think it's actually remains at zero with well placed auxiliary anodes.

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