"Pitted" chrome rollers

[Anthony Hyatali]

HI,
I have a customer with a Web Leader. Currently they are experiencing issues with 2 chrome rollers on 1 of thier their 4-high tower's. The chrome rollers are pitted, looks like something attacking or eating away at them. what do you think may be causing this issue?

p.s. they only showed me the rollers on the 4-high, they said it is happening on some other units, but not all of them.

Thanks in advance for your help!

 

[cheetoh]

If it is only happening to some of the rollers and not all of them, I would say that it is possible the problem has something to do with the way the rollers were chromed, In other words a bad roller? Just my guess.

 

[Anthony Hyatali]

Yeah, that's what i though, however the maintenance supervisor thinks it's caused by the fount. I was in there today testing the pH but it's @ 5.6 in tank 1 6.1 in tack 2 and 5.3 in tank 3...how long does it take for chrome rollers to "wear out"?

Oh, Thanks for your response!!

 

[Cornishpastythighs]

I guess the first question I have is how old are the chromes now? I have had chrome rollers in presses that lasted for many many years and worked fine even with wear lines in them. Chromes showing 'pitting' I would have thought would be caused by chemicals but as you point out the Acid is higher than I usually run 4.0-4.5pH. Have they been cleaned with some form of abrasive pads/substance. Chromes like all press parts have a life expectency but I guess it can vary depending on the care and maintenance they receive.

 

[Dan Roll]

Chrome plated rollers are subject to a certain amount of galvanic corrosion if they are exposed to an electrolyte. In this case, it does not matter what the pH of your fountain solution is, but what the conductivity is. The higher the conductivity, the stronger an electrolyte solution you have. When an electrolyte is exposed to dissimilar metals, a galvanic battery is formed and the least noble metal involved will corrode, often quite quickly. Usually, chrome rollers have a steel surface that has been copper plated, then nickel plated, and then chrome plated. When plated this way, the electrolyte is only exposed to the chrome and nickel layers (the chrome layer is always a bit porose) and nothing usually happens. If chrome has been plated directly on the steel, it is a different situation entirely. The electrolyte will corrode away the steel from under the chrome and if the steel does not rust, pits will form where the chrome has become unsupported and broke off, or if the steel rusts, bubbles will form in the chrome where it is being forced away from the steel surface by the rust. All of this can be accelerated rapidly if there is any stray electrical current available. Owners of printing presses would find a visit to an electro-plating facility very educational, it is amazing how much metal can be applied or removed from a surface with so little chemistry, electricity, and time.

 

[Al Ferrari]

Best damed explanation I've ever read about this.

Thanks Dan,

Al Ferrari

 

[Cornishpastythighs]

Hear, Hear. Its good to learn different stuff. Thanks

 

[Alois Senefelder]

Chromed Rollers

Chromed Rollers

Gentlemen,

Hard Chrome.

It is a common misconception that chrome plating provides corrosion protection. This is not the the case, only slight protection is given. Hard Chrome is porous at the microscopic level, which can let moisture and chemicals through to attack the base material. If the roller is to be used in a damp enviroment, or the dampening systerm of Lithographic Presses, a layer of Nickel Plating is required, prior to Hard Chrome Plating.


Regards, Alois

 

[Al Ferrari]

Hello Alois,

This is well supported by what Dan Roll already posted earlier. It would be well worth reading that post.

Al

 

[Anthony Hyatali]

wow, thanks for the information Dan! I greatly appreciate it!
their conductivity is around 1800..having that said, I have no idea how old the chromes are or how they were plated.
Either way your response was very informative!!