Silver plating aluminum

[Charles L. Cotton]

Does anyone have experience silver plating aluminum? I need to silver plate the inside of 4" diameter aluminum pipe to use in a homebrew duplexer for a 70cm repeater. It can be built without the plating, but it is much more efficient with the silver plating. I've done a little research and I've seen brush-on electroplating, spray silver plating (not paint), traditional electroplating, etc., but I have no idea which is recommended. I'm not going to use immersion electroplating because I only need the inside plated.

Also, does aluminum have to be copper plated first?

Chas.

[uthornsfan]

Could you not coat the outside with something that wont attract the silver during electro plating? Seems the easiest to me.

[jimlongley]

Dredging way back in my memory, I think you do have to copper plate first and that "traditional electroplating" is going to do the best job.

I will email my friend that I used to help with such things and see what he says.

[WildBill]

Charles -

You are always coming up with some out-of-the-ordinary-strange DIY project.

A flash of copper is typically used for nickel or gold plating, but I believe that, on aluminum, you plate with zinc prior to the final layer of silver.

I have seen a couple of references on Google that use a mixture of chemicals called zincate solution.

Kapton tape can be used to mask portions that don't need to be plated. This is standard operating procedure for many plating operations.

I would suggest contacting a local shop that does silverware restoration. They would already be set up for silver plating and maybe not too expensive.

[RoyGBiv]

Is it safe to assume that your required level of precision is low? You're not worried too much about uniform plating thicknesses, or aesthetics? it's just a question of "some half-way decent silver plating is better than a plain pipe"?

If yes....

How long is the pipe? 70cm (about 28 inches)?
Can you insert an applicator into the pipe and reach the entire surface (no extreme bends or impossible to reach areas)?

If yes.... then... it's possible to mechanically (by hand) plate the inside of the pipe.
Please use proper protective gear, good ventilation and use an applicator of some sort, do not try to stick your arm into the pipe, the etching solution will burn your skin and get into your lungs.

1. Surface prep.. Cleaning and pretreatment. Degrease, etch.
2. Remove the aluminum oxide layer using an anionic (negative ion) zinc solution (typically zinc hydroxide). (Google "zincate")
3. Replace the zinc layer in step 2 with Silver plate

Here's a guy that made a decent YT video of the mechanical application steps....

[youtube]http://youtube.com/watch?v=rBccQYs9uRU[/youtube]

You should purchase the zincate and silver solutions. It's not worth the trouble to try and make them, and results are not consistent.
Zincate: http://www.caswellplating.com/electropl ... fl-oz.html" onclick="window.open(this.href);return false;

I THINK(??) this is the right stuff to use for silver plating, but you should call Caswell to confirm.
http://www.caswellplating.com/electropl ... ution.html" onclick="window.open(this.href);return false;

Actually, you may just want to call Caswell and ask them what they recommend for your application, from start to finish.
I'm familiar with plating in large batches, so, please do recheck my suggestions with Caswell. They will help you.
They have online chat and their phone number is on the web site.

[Jumping Frog]

Plating onto aluminum is hard to do. Aluminum is very active and will oxidize quite rapidly. That makes transitioning from the activation baths to the plating baths tough because you have to keep the surface constantly wetted. It makes brush plating even tougher.

Still, there are plating shops that can do it. I know some places chrome plate (staring with copper, then nickel flash) onto aluminum. Not easy, but possible.

In the case of silver plating, presuming it is being done from a cyanide solution, there is likely no benefit from a copper flash. One of the traditional reasons to use a copper flash is that it is easy to get good adhesion from the cyanide copper process (and then just about anything can stick to copper), but if you're using cyanide silver baths you get that benefit already.

Yes, you can mask the pipe OD. There's a huge assortment of plating maskants that can easily accomplish that. For something as simple as a pipe OD I would use a simple (nonadhesive) plater's tape.

One last thought - does the pipe have to be aluminum? Using an iron pipe would obviously increase weight (might matter for your mast) but would make the plating job SO VERY MUCH EASIER.

Also, 4" Copper pipe is available and while it may cost more than aluminum, there would not be that much pipe for a 70cm duplexer and it would not be hard to plate.

[WildBill]

Plating onto aluminum is hard to do. Aluminum is very active and will oxidize quite rapidly. That makes transitioning from the activation baths to the plating baths tough because you have to keep the surface constantly wetted. It makes brush plating even tougher.

This is why you remove the oxide and plate with zinc using the zincate mixture. The zinc coating protects the aluminum from further oxidation.

[WildBill]

I am curious to get some more details, like the length of the pipe in question.

I am also wondering why it has to be aluminum - if it is long tube maybe the weight?

Also why silver? Since it is part of a radio antenna system, I am assuming it is for the conductivity.

That said, why aluminum and why silver?

[mcscanner]

...to use in a homebrew duplexer for a 70cm repeater...

Chas.

Question like that could only be asked by a ham. I took a minute to confirm... Extra Class!

Building a duplexer from scratch. That is a serious project.

73, Mike KE5MC

[Charles L. Cotton]

I am curious to get some more details, like the length of the pipe in question.

I am also wondering why it has to be aluminum - if it is long tube maybe the weight?

Also why silver? Since it is part of a radio antenna system, I am assuming it is for the conductivity.

That said, why aluminum and why silver?

A duplexer is actually a tuned resonate circuit that is used to isolate certain frequencies from the transmitter and receiver of a repeater, while also rejecting other radio frequencies (RF) from nearby transmitters. The one we plan to build will have six cavities each about 8 to 8.5 inches long, so plating them should be easy in terms of access to the inside diameter. Aluminum is a good RF conductor, but the silver plating increases the Q of the circuit reducing what is called insertion losses. Copper is also a good conductor, but as it tarnishes and any corrosion builds up, efficiency diminishes. Once a duplexer has been tuned, you really don't want to touch it, much less open it for cleaning! We can actually get by without the silver plating and we may do that, but only if plating is either impractical or cost-prohibitive. Steel is a poor RF conductor and isn't used in duplexers.

We are forming a youth amateur radio club with a goal of having chapters all over Texas. We are getting a Yaesu DR-1X repeater, but we are also working on making repeaters from Motorola and Kenwood commercial radios to help chapters that may not be able to afford a new commercial or ham repeater. Duplexers start around $950 and go up, sometimes way up, depending on the environment the repeater will in in terms of RF interference. Eric and I want to build a duplexer primarily to learn how to do it so we can teach chapter sponsors in other cities. We will probably cut some of the components and make others so that new chapters can just buy them at cost and we'll teach them how to assemble a duplexer. Building it is a job, but tuning them is the tough part! Neither Eirc or I have a spectrum analyzer, so we'll have to get someone to tune it.

Now that was far more than you wanted to know!

Chas.

[Charles L. Cotton]

...to use in a homebrew duplexer for a 70cm repeater...

Chas.

Question like that could only be asked by a ham. I took a minute to confirm... Extra Class!

Building a duplexer from scratch. That is a serious project.

73, Mike KE5MC

I see you're a fellow Extra Class. Since you have a 2X2 call, did you once hold an Advanced ticket? That's a nice station you have Mike.

Chas.
KD5GR

[cheezit]

Ive played with spray glue and metal tape before, if its mounted in say like an attic it may survive a while.
Kf5zys.

[WildBill]

Now that was far more than you wanted to know!

Chas.

Thanks Charles. Now it is very clear to me.

[Owens]

Charles,
I'd be interested in yhow this turns out. I'm in the process (slowly) of setting up a D-STAR system. duplexer prices is down right scary!

73,
N5QNS

[Charles L. Cotton]

Charles,
I'd be interested in yhow this turns out. I'm in the process (slowly) of setting up a D-STAR system. duplexer prices is down right scary!

73,
N5QNS

If we are successful, we'll build a second one to document the process with photos, videos and detailed construction steps. If we just wanted one duplexer, we'd bite the bullet and buy one, but the goal is to make it possible for new chapters to build what they cannot afford to buy. Based on my research, homebrew duplexes were once far more common (1960's and 1970's), but in recent years this seems to have developed a reputation of being a black art. The overall structure is relatively simple, especially if you use copper that can be soldered. (We're sticking with aluminum.)

In addition to the obvious, ham radio, the club is actually going to be used to promote a new youth shooting project I've started, as well as student ministry activities at our church. Yeah, I know. This has a lot of people scratching their head trying to see what ham radio, shooting and Christ have in common. Let's just say it's a new approach.

Chas.