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

Best choice for Manganese Phosphate bath?

I'm an I&C engineer working on a new project concerning a chrome plating facility. I have to put some RTD's into a manganese phosphate bath to monitor the temp. I am having a hard time finding the chemical resistance chart entry for this so I cannot yet choose a material to have the RTD encased in to avoid corrosion. Would anyone know the best choice? The bath runs about 210 deg F.

Kim McClafferty
MSE-TA, Inc. - Butte, Montana, USA
2000

---

2000

Kim,

Being (nearly) clueless about plating, I haven't the slightest clue what RTD's are supposed to mean. Results of a Terrible Disaster, perhaps? Please elucidate in future so that the hoi-polloi will (perhaps) understand better.

Seeing the temperature is quite high (for many plastics) my first thought would be why not use ordinary mild steel as I presume, probably incorrectly, that the phosphate side might not attack m.s.

If you consider plastics, think of fibreglass (not the boat resins but the corrosion resistant types) unless you can get the tank 'scratched' in which case think about a homogenous thermoplastic. CPVC or PVDF (but you give no inkling at all of the tank size, do you?)and if the tank is largish, then fibreglass reinforce the thermoplastic ... but this has to be done by a competent dual laminate fabricator as a highly trained fibreglass fabricator per se would NOT do a good job!

Have fun! Cheers !

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

---

'RTD' is this context means 'resistance temperature detector' -- along the lines of a thermocouple in application. I have seen plain steel tanks and tumbling barrels used for manganese phosphating, but type 316SST is a better approach. Considering the probable small size of the case, and the ready availability of 316SST, it sounds more practical than trying to rustproof a plain steel case.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2000

RTD's do not have an infinite life so it is not all that critical. Obviously, steel is out as it will phosphate rapidly and it will become a sensing insulator. 316 is fine, Inconel is better and consider teflon. I have used all three and they all work.

James Watts
- Navarre, Florida
2001