Plating both outside AND inside of a tube

Q. how to enhance my salts Paray in crimping hose alkaline zinc plating

SALT SPRAY
TEST CHAMBERS

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A. Thicker plating or switching to an alloy zinc process are the general solution to increasing salt spray hours.

Luck & Regards,


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

A. Yes, thickness variations of two or three times, or even more, is not a lot. However, you should determine if your plater is using an acid or an alkaline process as the alkaline processes offer significantly more uniform thickness, and it may be possible to reduce the thickness variation without redesigning the part. You should also tell us if the parts are racked or barrel plated.

A. Kevin,

Because you are plating an I.D. you actually reduce the I.D. by 2x the plating thickness. We plate eye unions and we will spec the pre-plate I.D. oversize by 2x the upper specification of the plating thickness so as to be in specification after plate. However since yours is a close fit, (with I assume a shaft) you may want to plug the I.D. to prevent plating build up from changing the I.D. For your future reference, if you plate a thread your thread pitch will increase 4x the plating thickness. I hope this helps.

A. Mr Ziegman:

I have been plating hubs similar to the ones you speak of for quite some time. I can relate to your problem because I have had parts over plate in this area. You are correct in your posting of concentrated electricity, or High Current density. Typically Chloride Zinc baths (acid zinc), because of their very high efficiency, can fluctuate in distribution well beyond the 2x you are referring to. First thing I would do is to inquire about your suppliers chemistry. If its alkaline and you can pinpoint some kind of frequency, I might have some other suggestions.

• Topic 12211 "Zinc Plating Internal Threads: dimensional changes & coverage issues"

A. It is not uncommon when nickel plating tubing work to finish the cycle with a dip in a phosphatizing process so the inside of the pipe gets rustproofed whereas the phosphating does nothing to the plated surface. I am not sure exactly how this would work in the case of zinc plating if the zinc surfaces need a subsequent chromate conversion coating, but hopefully it's food for thought.

A. Gary,

I have one crazy idea and that's to employ what a professional pipe bender uses for tight radius bends in metals, particularly copper.

They use a material called 'ROSIN' ... it is poured into the pipe and sets rock hard. It is removed, after the pipe has been heat formed, going by memory, by just using hot water, ie. it's a water miscible material.

I'm not sure of the affect the plating acids might have but at least it's worth a try as it is as cheap as wurst, can be easily applied & removed. In other words it could act as a plug at each end.

May I suggest you approach a local specialist in pipe bending. And if this works, let us know, OK?

A. Some other fabricators of tubing that you describe have found that alkaline zinc gives them better results than parts plated in Acid Chloride Zinc. The main reason given, is that the Acid Zinc baths form an active surface on the inside of the tubes, which flash rust rapidly. The Alkaline Baths keep a passive surface which has less tendency to flash rust.

Make sure, that the tubing is free of rust prior to going into the plating tank. Many times the tubing arrives at the plater with considerable internal corrosion. Preplate pickling does wonders for such tubing. Post Plate corrosion on the insides usually necessitates stripping of the zinc, pickling to remove the oxide and replating. A costly and inefficient method.

Some firms specify proprietary silicated compounds after the plated part is chromated, to give longer storage times after plating. A good chemical manufacturer can assist you with that selection or option.

A. Hello Gary,

After chromate passivation, a good rinse followed by a water soluble lacquer dip may give temporary protection from flash rusting inside the tubular surface.Once dried, rust preventive oil may be applied.

A. There are 2 issues at play here.

1. The main issue is stop putting the finish, acid and sand blasting on the inside. This is a big no-no in our world of fluid power. You are removing the tubing dia. The ID is just as important as the OD of the tubing. And if I call out for a .032 wall thickness it is not for the dia. it is for the working pressure. And so on; I can go on with the hydraulic issues but it will go on and on.

2. The answer is when you form the tubing and install the flare, nuts, etc. If present just install end caps so the inside is not effected. Or should I say contaminated. If no ends on the tubing then install plugs. Bottom line do not get any contamination inside of the tubing.

If you need help call a local hydraulic shop and get some advice. Remember you must not contaminate the inside of the tubing. It is important nothing is inside or whatever equipment your tubing is going onto will be effected. And always clean the tubing with the asap hydraulics hose/tubing cleaning system. This will remove any contamination left inside from forming. This is a bullet projectile that cleans the tubing inside.

A. Yes, simply running the parts through the necessary pretreatment steps will probably strip any previous cad or zinc plating from them. Electroplating is driven by current, and I'm sure that you can picture that virtually no current will flow from the anodes all the way to a spot on the inside of a tube because it will take the path of least resistance instead.

It is certainly possible to plate the insides but it may be prohibitively difficult depending on the particular parts and their value. Plating the inside requires "stringing" an auxiliary anode through the center of each tube and probably also involves some kind of pumped solution transfer because stagnant solution within the tube may not contain enough zinc or maintain the right balance.

A. It certainly is not world class for aero parts but you can zinc plate in and out by hot dip galvanizing. Most commercial pipes and fittings are processed this way and have all their surface protected.

A. Hi there,

Electrolytic zinc plating will be really hard to accomplish inside the tube.
You can use hot dip zinc plating, or other process where you do not apply current, maybe Electroless Nickel.

Saludos.

A. Another method to plate zinc or cad for that matter, is using a brush plating process. We have experience in running electrodes down the ID's of pipes or tubes in order to get deposits of a variety of metals onto the surface.

There are several factors that must be determined at the onset of work; these include length of the tube and deposit thickness, but the process has been successful on previous applications

A. Yes, it is possible to plate inside tubes today. You will need in principle 2 main conditions: a, the suitable electrolyte; b, the matching internal anodes. As electrolyte I recommend alkaline zinc electrolyte and an internal auxiliary anode. With both of this you may come close to your target.

A. Hi Bojan. The devil is in the details. In conventional plating with no special internal anodes and without solution pumped through the tube, a tube of 2 cm diameter or more may nickel plate 1-2 cm deep, which could total over 2 cm if you count from both ends. But a 1/2 cm dia "straw" will not plate on the inside.

How critical is the chrome? Because I think you have a good shot at getting full coverage of nickel, but only enough chrome coverage to just make it around the bend, not inside the tube. For non-critical components, I think a lot of people would be satisfied with that. Good luck.

Regards,

A. If you are after corrosion protection and a good wear surface, consider electroless nickel.
If you want it to look more like chrome, look into electroless cobalt. It is a bit more expensive but will make your life a lot easier.

?. Hi Dawn. The thread has wandered a bit, so we don't know if you are talking about zinc plating, nickel-chrome plating, or electroless nickel. What is the length and inside diameter of the tube? Is it made of steel? Thanks!

Regards,

A. Hi Dawn. I haven't personally been involved in ID plating of long tubes like this, and hopefully someone else will tell us both about it. But we both know that as you plate the metal out of the small volume of plating solution inside a tube, its concentration will decrease to unworkable, and that's why you need flow. So you could calculate how much copper you are trying to plate and how much flow you would need for the copper concentration to not drop more than say 5 pr 10 percent, and assure that the flow rate is adequate to keep the concentration within the target range.

You might also calculate and/or measure whether there will be a temperature rise within the tube that may be problematic. I think the short answer is that there is probably not a flow rate that is too high for successful operation, but there is surely a flow rate that is too low, and you will be able to at least approximately calculate that. Good luck.

Regards,

A. Hi Kirk. I assume there is a typo in your posting, and you mean "full length of the ID". An internal anode is a good idea considering the touch-and-go dimensions and the type of part, whereby if done right it seems to just barely work most of the time. I think it will be simpler, faster and cheaper than struggling to try to get by without it. But yes this will require special jigging that someone has to pay for.

If the quantity of parts is small, the special jigging can be accomplished in a short lead time but labor intensively with fairly standardized racks, plus copper wires, platinum clad titanium auxiliary anode material, and platers tape or masking materials. If it's a production job, custom designed racks, made of properly plastisol covered copper and stainless are no problem except for cost and lead time.

Regards,

Dear Ted,

Thank you for your reply and yes, that was a typo, should be ID of course. I'll work with a couple facilities to get some jigs set up. The quantity is roughly 1,200 pcs and we're well late.

Thanks again.

A. Hi.
Yes, an auxiliary anode inside the ID would do the trick. I'm not sure, but for an ID of 7", I would think an alkaline zinc bath should be able to plate inside the tube.
The beauty of alkaline zinc is its ability to plate inside low current density areas.

A. Hi Ramesh. You didn't include the units in your dimensions, nor the type of plating, but since you are a silencer manufacturer, you probably mean that the tubing is 101.6 mm in diameter (4") and 1.6 mm thick (1/16"). I doubt that you will get consistent full coverage in a 300 mm bent length (11.8") without auxiliary anodes, but are you sure it is required? Zinc plating is sacrificial, and "good" rather than perfect interior plating might be satisfactory for this application. Are you sure zinc plating will hold up to the temperatures of your application?

Then again you may be contemplating nickel plating?

On the third hand, I thought most silencers these days were made of stainless steel :-)

Regards,

A. The Manhattan Project needed to chrome plate the inside of pipes for gaseous diffusion plant. They found an old guy and his son working in their garage; they used the pipe as the tank, put chemicals and electrodes in side pipe, capped it, rotated it and viola. I just recall recall reading about in the book Manhattan Project

A. Hi Ravi. You haven't told us what the tube is made of, or how long it is, but the general principle presented on this page and on thread 4153 is that you need to run an anode through the center of the tube, and probably flow solution through it as well. Good luck.

Regards,

A. Hi Thanura. I don't understand what you mean by "there is a issue regarding zinc plating on the inside".

An approach I have seen is to do the chrome plating of the outside first, then go into a phosphatizing solution which leaves the chrome plating okay, but reacts with the bare steel inside diameter to create an iron phosphate coating. If you can afford to plug and unplug the tubes, you might have additional processing options.

I think the readers and myself have only a very vague idea of your situation so far.

Regards,

A. Hi Nikhil. Certainly electroless nickel plating would be easier than any electroplating process, and is well suited towards this. However, please tell us why you want to plate them so we know what platings sound useful and non-useful. What flows through them, hydraulic oils?

Luck & Regards,

A. You have not said whether chloride, cyanide, or alkaline. In either case "throwing power" is maxed out, at the expense of efficiency, with higher Cl or CN or Caustic, and lower metal. If such an adjustment does not get the inside, then you must use an inside anode. An inside anode in this case may be a flexible steel wire with beads, the beads prevent shorting and the wire anodes the current on the inside.

A. Hi Ebanezer. In addition to Robert's questions, we don't know if you are attempting to barrel plate this component, which will prove impossible.

The plating goes where the current goes, and pretty much in proportion to it; and the current certainly will not flow to the middle of the inside of this long narrow tube without the auxiliary anodes which Robert mentions.

The problem is not that this component is unplateable, it's that plating the inside of the thread will cost perhaps 20X or 50X what it would cost to barrel plate just the outside :-(

Luck & Regards,

A. Hi again. Sorry to hear of your troubles with rack plating but I think you will never get electroplating coverage in the middle of a 45 mm (1-3/4") long M10, 8.38 mm (about 5/16") minor diameter female thread without auxiliary anodes -- but send a drawing to mooney@finishing.com for posting here if you think I'm misunderstanding.

Electroless nickel plating might work but is much more expensive than nickel plating.

Luck & Regards,