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topic 21872

Chromium plating - heating coil material

adv.    industrial heating systems

2003

Q. We are plating hard chrome, but are having difficulty with heating coil failures. We are currently using stainless steel coils with thermal fluid at the moment. Can anyone suggest an alternative material?. Are there any materials more corrosion resistant or suitable than stainless steel?

Thanks,

Chris Perrett
- Cardiff, South Wales, UK


2003

A. If there is no fluoride catalyst in your hard chromium plating bath, then titanium would be a better choice. Otherwise, lead heating coils may be a better choice.

Lyle Kirman
consultant - Cleveland, Ohio


2003

A. Hi Chris,

Initially I, too, thought of titanium ... but did have a lot of success using PVDF heating (sic. cooling!) coils.

The heat transfer isn't as good as metal but the corrosion resistance scintillates.

Go and ask any reputable (thermo)plastics fabricator or try G.F. Fischer.

freeman newton portrait
Freeman Newton
White Rock, British Columbia, Canada

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



2003

Q. Thanks for the response people. I've found a little more about our problem. We are plating sulphate type chromium, running at 50-55 °C. The concentration of the solution is 250 g/l chromic acid, and 2.5 g/l sulphuric acid. The heating coils are manufactured from 316 stainless steel. The tank is lined with plastic (PVC or similar). We use lead alloy anodes. The thermal fluid is circulated through the heating coils at 150-160 °C.

I am a little concerned that this temperature (combined with high concentrations of chromic acid) is high enough to disturb the passive chromium oxide coating of the stainless steel, rendering it less corrosion resistant, leading to the premature failure of the heating coil. Has anyone any thoughts or previous experience of this?

Many thanks,

Chris Perrett [returning]
- Cardiff, South Wales, UK


2003

A. Typical for 316 SS is 1-2 years. Double the wall thickness and you will slightly more than double that time. A thick walled titanium will last 2 - 10 years. If the coil becomes anodic for any reason, even at low millivoltages, the life of any metal coil will be significantly reduced. I am not in love with plates. Tubing needs to be seamless. If you use threaded pipe, the fittings need to be very heavy. If you use welded, it should be Tig welded with lots of backup gas or preferably in a bubble chamber if not electron beam welded. Not a job for a novice or a sloppy welder.

Teflon supercoils are a bit fragile, but if protected are excellent because of the huge surface area. (watch the pressure!) You can use less area if you are willing to start your heat cycle a couple of hours earlier. Hard chrome generates a huge amount of heat, so I would assume that you are running the coil on a cooling cycle more than you are on a heat cycle. Heat is for startup only.

James Watts
- Navarre, Florida


2003

A. Chris,

I'm somewhat confused. You say you're running the fluid through your heating coils up to 160 °C ... I would have thought that you wanted COOLING, just like James Watts infers!

Also, PVDF is good up to 140 °C and I would have thought it to be definitely structurally stronger... & less expensive .. than teflon coils.

Back in '79 I came across a weird set-up. Rather narrow chrome tanks in which very large diameter paper making rolls were plated. The heat build-up was enormous ... I suggested that they PUMP some of the hot liquid into a horizontal PVC mist eliminator (12 micron, a so-called Chromic Dry Scrubber in those days) where, due to the cooling effect of the ambient air being sucked up by the fumehoods, it could be easily caught and returned, nicely cooled, thank you, back to the chrome tank.

This worked apparently very well. They replaced one of the two PVC blade banks in around 2000... a Vancouver Company called EBCO ... and the system is apparently still going on and ON!

Freeman Newton
Freeman Newton
White Rock, British Columbia, Canada


October 7, 2015

Q. What is "PVDF"? Is it a material for cooling coil for chrome tank?

Brijesh koradia
SHREEJI PLATERS - Vapi, Gujarat, India


wikipedia
Polyvinylidene fluoride

October 2015

A. Hi Brijesh. PVDF is Polyvinylidene Fluoride. It's a fluorinated plastic with exceptional chemical resistance similar to Teflon, available in sheets, pipe, and some molded or cast parts like pump parts. It's resistant to chromic acid / chrome plating solution, but I'm not really sure that it is a better choice than Teflon for cooling coils because soft flexible Teflon coils are available as commercial products, whereas to my knowledge you would have to have the PVDF custom fabricated into a semi rigid piping grid at pretty fabulous cost.

Regards,

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


2003

Q. Hi everyone.

The tanks (approx. 1600 liter capacity) are run with relatively small components to plated, and hence require slight heating even at high loads. Our plating shop has given up on the 316 SS heating coils (at last), following another failure. Titanium coils are soon to be installed. My question is this: Should the titanium coils be anodically protected (i.e. physically wired to the anode bus-bar)? Some people we have spoken to advise it, while others say the titanium should not under any circumstances contact any part of the anode. Any advice would be much appreciated. Ideally we would like to use electrical heaters with a fluorocarbon coating, but due to various constraints this will not be possible.

Regards...and...Confused,

Chris Perrett [returning]
- Cardiff, South Wales, UK


2003

A. I am going to disagree with Jim, which is a rare thing, but I have seen many titanium coils with warning labels and even grounding clamps that tell you that you must connect the coil to the anode rod (perhaps due to belief that titanium oxide rather than titanium metal is resistant to acid) and you must maintain anodic polarity to preserve it and/or on the principle that by connecting to the anode rods the anodes will galvanically protect the coils. But on the other hand, I have heard that, depending on the exact alloy, the oxide has a breakdown voltage which may be less than what you might use in chrome plating. Also in chrome plating there are no soluble anodes to galvanically protect the coil anyway.

thumbs up signWhile I don't like to parrot the old line "talk to the manufacturer", here's the thing. I was an engineer with three suppliers of plating equipment for many years, so we specified titanium coils and electric heaters hundreds of times, and there were a handful of dramatic failures. In one case we ended up with several pallets full of perforated titanium heaters. So, it's simply the case that if you don't do exactly what the manufacturer says, you end up with the responsibility regardless of what really caused the problem. If they say don't connect to the anodes, and you do, a failure will be your responsibility even if the problem was really a bad run of alloy; if they say do, and you don't, it's your responsibility too. Demand that the manufacturer tell you clearly whether to connect the coil to the anode, earth ground, or nothing--not necessarily because it will make any difference, but because you can't let them shift the responsibility for a failure to you :-)

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


2003

A. Ted, we do not really disagree. Somewhere between zero volts and the voltage to anodize Ti, there is a voltage that will break down the Ti. I do not have a clue as to what that voltage is. I do agree with the statement of do what the manufacturer says. Further, I have no experience with Ti heat exchangers, only electric heaters.

James Watts
- Navarre, Florida


2003

A. Chris
I've used titanium coils for cooling different types of chrome solutions for 20 years and are still using the original coils. They are not electrically connected to either the anode or cathode, but I'm sure the cooling system will be grounded somewhere. My rectifiers are Floating(neither the anode or cathode is earthed) and the way some of the anodes bend I'm sure they touch the coils, but this doesn't cause any problems,until one of the operators shorts out a job on the coil and blows a hole in it, and our Mr fixit welds it up. For heating the solution I use 3Kw PTFE "bat" heaters controlled by a thermostat in a glass tube filled with water. On a 1600L vat I would use 2 heaters(or one if using about 400A continuously)

Regards Steve.

Steve Kelson
- Sandbach UK


sidebar August 13, 2012

Q. Sir
We are working in MEMS, i.e., micro electro mechanical systems. Sir we are doing an ice detector using a heater.
Sir can you please tell me any material for a heater so that we can work out fast with our project?

pooja joshi
student - pune, India


August 13, 2012

Hi Pooja. Sorry but I am lost. You can't be talking about chrome plating, or even chromic acid. Are you talking about a heater for water? Is this to be an electric heater, or is it a pipe coil with some heating medium running through it? What does the heater have to do with the ice detector?

Apologies, but we're not there with you reviewing your project notes, and you haven't yet given us even a clue what you are talking about :-)

Regards,

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

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