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Need polypro tank advice

I currently have a powder coating job shop. We are getting into electroless nickel plating as an allied service. All the literature and advice steers me toward 1" thick polypro tanks for the nickel vats. Since I have the ability to spray fusion bonded polypropylene powder, why can't I build my own vats of mild steel and line them myself? We can apply a 20-30 mil lining that will be permanent. The lining can be holiday tested for pinholes and can be patched. If necessary, we can even insulate the outside of the vats. I can do this for a fraction of the costs of pure polypro tanks. Anyone have any experience along these lines? The only answers I seem to get are......"well, no one has done it that I know of?"

Paul Norman
- Odessa, Texas
1998

Actually some of the literature and advise may be steering you toward cathodically protected stainless steel tanks these days, but certainly polypropylene has been the standard for many years now. I would agree that I know of nobody who has done what you describe on electroless nickel tanks, but they have used heavy organic coatings on steel tanks for other plating and processing solutions.

Electroless nickel, however, is a really tough application for two reasons. First, the temperatures are very high (nearly boiling) which means that you'll have severe thermal stress due to differing coefficients of expansion between the poly and the steel, and if there are any plasticizers or other ingredients rather than 100 percent pure polypropylene, there will be strong impetus for them to leach out. Secondly, electroless nickel can spontaneously plate out and have to be removed with strong nitric acid and possibly mechanical scraping.

In my opinion, the days of steel tanks being used in plating shops are numbered anyway. To try to go back to them for this most difficult application is a mistake.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
1998

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1998

What you propose has been done, but in very limited cases. I think that this is largely due to inertia and to the cost of transporting the equipment to a site, not to mention the oven requirement. Thermally sprayed polypropylene literature shows up every now and then.

Comments:

I do not think that 0.025 average is thick enough to provide long term chemical resistance.

I would think that testing would be reasonable to find out what the tendency of micro pinholes would be.

A sprayed finish is not going to work well because the surface roughness is going to provide sites for plating to start on your tank. Rotationally molded tanks do not do well in electroless for that very reason, and they are relatively smooth. A fabricated PP tank will look like it has been polished.

Your process seems to be reasonable for the tanks on the rest of your line.

Wall thickness of a PP fabricated tank is totally dependent on the size of the tank. 1/4" is more than adequate for a 5 gal tank. 1/2" is regularly used on 300 gal tanks, with a significant amount of external reinforcing. 1" is frequently used on the bottom of this size to allow rabbiting a grove for the wall which provides superior strength.1" is probably the standard on larger tanks.

If you would like, email me and I will offer a couple of suggestions for reasonable quality suppliers.

Another thought, where are your platers going to get their training. This is not a "you just dip it" process if you want optimum economy and quality.

James Watts
- Navarre, Florida

I agree with Mr. Watts, the use of polypro tanks and their thickness is dependent on the size. I have several PP tanks in my facility that were custom made.

Steve Sarten
- Oak Ridge, TN
1998

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1998

Hi,

James Watts' comments are very applicable. A lousy 0.025" liner via spray techniques is far too thin and will quickly fail ... may even be somewhat porous to the chemistry(certainly sprayed on PTFE is!).

The other thing is that the other above comments are talking just about PP by itself as a tank ... with the drawback of its poor design modulus & high co-efficient of thermal expansion and necessary heavy wall thickness.

Why isn't anyone even thinking about 'bonding Fiberglass to the Polypropylene'? A perfect synergistic marriage. Heck, the last symposium by N.A.C.E. in San Diego had all the top U.S. and Canadian dual laminate Companies there. For the record, the first ever paper on this subject was held at a N.A.C.E. conference back in l972 in Toronto. Mine!

The advantage of an 'armoured' thermoplastic is that a) the operating temperatures and pressures can be HIGHER than the pure thermoplastic, the wall thicknesses can be less and the strength much greater.

Back in l970 Alcore Fabricating near Toronto was making dual laminate l5 foot dia chlorate tanks for Hooker Chemical in Columbus, Mississippi. No one in the USA had this technology at that particular time.

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

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1998

Many suppliers have long offered tanks constructed of a polypropylene liner (say 1/4" thick) inside a fiberglass shell. Sometimes aluminum foil is inserted between the two layers so that the liner can be spark tested. While laminating two materials is the most practical way to fabricate some tanks built of some materials (Kynar with a fiberglass backing comes to mind), I'm not sure that I see the advantage to bonding the polypropylene to the fiberglass in typical plating room applications.

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

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1999

Ted,

Re your comments about inserting aluminum foil between the two very different materials of FRP and PP. firstly, it is absolutely MANDATORY that this work is carried out by only experienced dual laminate fabricators in order to achieve a first-class bond. Secondly, any foil or 'conductive' resin is only applied around the weld areas. Spark testing intensity depends on the thickness of the thermoplastic liner (otherwise you can burn holes!)You spark test twice. First the liner and then after fibreglassing.

The advantages of dual laminates is that the fibreglass vastly enhances the structural strength and rigidity and allows higher temperatures and reduces the high expansion rate to that of FRP by itself, IF PROPERLY MADE.

This is not a cheap method ... nothing that is good is cheap. Do not expect Joe Blow, if he is just a fibreglasser, to make a successful dual laminate job!

The world's first dual laminate tanks were PVC;FRP for Robert Shaw Fulton Controls. Toronto, l96l? 2'x 2' x 4-l2' high. They ceased their plating operations 13-1/2 years later. I saw those tanks. They had NOT CHANGED, they were STILL THE SAME as virtually new. They had distorted at the top due to unknown (to us) higher temperatures and to our total ignorance of proper fibreglassing thickness/reinforcing in those days. Alcore Fabricating in Richmond Hill near Toronto. Managed now by Manfred Junkert who was the assistant plant foreman in those days.

Heck, if those tanks lasted well over a decade, I guess that they sure paid for themselves, wouldn't you think?

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

The original author was looking for a cheaper way out.
Fiberglass laminated tanks are nice, but as you say, expensive. I have seen well made PP tanks that were over 10 years old, used daily and were still in good shape, so the laminate is an option, not mandatory, and quite possibly not cost effective on smaller tanks.

I personally doubt if the original person was going to go the high dollar initial cost route, regardless of long term effectiveness.

James Watts
- Florida
1999

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1999

I am the author of the original letter and I agree...I was looking for a cheaper route. After spraying some poly powder and after seeing a tank made by a manufacturer, I must concede...the manufactured tank is much smoother. I have been pushed many directions by tank vendors, but I will go with poly tanks. The poly powder is not useless, however. I can use it to coat hooks, racks, and accessories.

I thank you all for the input. You will see my name here again. Thanks

Paul Norman
- Odessa, Texas