Hard chrome plating I.D. of small tubes

A. To do this will require an electrode inserted down through the bore. With the length you have and the very small size of the bore it will be almost impossible to do.

The electrode will be so small to clear the walls that it will have no rigidity.

Why do you need chrome?

It might be better to consider electroless nickel. Not as hard as chrome unless you can harden by heat treatment but the process does not require any electrode or auxiliary fixturing.

Regards

A. Hi Nitin.

If you like to plate a so small inside diameter. Is better to use a Platinum (Pt anode or silver thread anode. plant the anode in the middle of the diameter and tighten with CPVC and pull firm the anode with plastic screw. You can't use lead anode because the current can't go through a lead anode in this small diameter, and you may also get a roughness in chromium deposit if you uses lead anode. Use a current about 20 ampere per /dm2. I'd also recommend a little agitation in the chromium solution. But it's easier to plate electroless nickel in your case.

Good Luck.

Regards,

A. I am a skeptic! For most parts, it would be commercially unfeasible to try to put a thousands of chrome inside a 3 foot tube that is only 0.080" in dia. The definition of "uniform" adds a lot to whether it is practical.

Unless there is some drastic reason, I would look at using pumped EN for this job.

Boroscope

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A. I am a hard chrome plater and I plate the id of tubes about 3 feet long. I put about a 1/2 thousandth per side. I use steel rod as an anode and I pump chrome through the tube. It's not a stagnant bath. Short reverse etch then 1 1/2 amps per square inch for 1/2 hour. If you don't use a pump you'll burn the tube with a stagnant bath. I check to see if I have chrome throughout the whole tube using copper sulphate ⇦this on eBay or Amazon [affil links] then a boroscope. I then check the thickness with an I.D. mic. Hope this helps

? Hi Ashok. Almost nothing is impossible, but many things are impractical, and this sounds like it might be one of them :-)

Can you tell us what this project is about so people can perhaps suggest what they think might be other practical approaches, like maybe copper plating a stainless steel tube?

Regards,

A. Hi Ashok

It is possible but not easy. This is very similar to the problem of chrome plating inside rifle barrels.

Firstly, it is not possible to use a conventional lead anode. It will not carry the current without overheating and the resistance means that the voltage, and therefore the current, drops along the length.

The solution is to use a copper wire anode to carry the current which must be plated with a reasonably thick layer of lead. Anode current is fed from both ends and a spring tensioner is needed to keep it straight as well as a jig to keep it central.

In addition, it is necessary to pump the solution through the tube to avoid chemical depletion.

At least the copper tube should be relatively simple to pre-clean

Good luck.

A. How about electroless nickel guys! Sounds more practical.
All the best.

A. Your part is almost identical in dimension to an M-16 rifle barrel, which have been plated by the thousands and millions.

I don't know how many different shops plated those barrels, but the one shop I visited used lead coated steel wire as the internal anode. The barrel was held in a fixture, and the wire pulled taut and centered in the bore. Barrel and fixture were completely immersed, and the steel wire was thereby kept cool enough to do the job.

A. Well what is the quantity to be Chrome Plated?
I have Internally Zn Plated up to 50 microns on internal diameter of 12 mm Tube of Length 2000 mm. I would suggest if you can find a source for spiral wound lead wire on an 2.5 mm diameter steel rod this would increase the Surface area of the said Anode mounted on an insulated fixture with screw type adjustment so as to tighten the Anode. Use perforated fixtures and air agitation for this process.
Dest regards,

A. Hi,

Use a pump from a chrome bath which has the right temperature and let it flow back again into the bottom of the pipe to the chrome bath. The anode should be close enough to the area which shall be plated. If you not have a lead anode, nickel plated iron can be used as an anode.

A. Hi George

The process is well known for plating inside rifle barrels

Pumping the solution through the tube is easy but be prepared for leaks etc.

The anode is the main challenge. Lead has a relatively high electrical resistance and there can be a significant voltage drop along the anode. Two possibilities. Feed current from both ends and use a copper or brass rod coated with lead.

The anode can get hot and expand causing it to bow and short circuit to the tube walls so your centering arrangement should include some sort of spring tensioner.

A. Plating hard chrome in gun barrels, shotguns and rifles, is done every day.

The installations I have seen did not need pumps as the gas flow brings fresh solution into the barrels.

The anode is high strength steel wire, lead coated.