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topic 4428

What lining is better for a decorative chromium plating tank?


(2000)

Q. We have a decorative chromium plating line in our shop and our chrome tank is made of carbon steel lined with a flexible PVC liner of 100 mils, over time the liner has "cracks" on the solution level. Almost on top of the tank walls. We attribute this to the interaction of the plating solution, temperature (55 °C) and the oxygen on the border line of the solution.

As plant manager I have to decide what liner or protective finish is best for this kind of application. We have used in the past also Koroseal lining, vulcanized to the tank walls.

Can PPL thanks be used for chrome plating ? Or a lining made of high density polyethylene is better?

Please help me on this. Thank you in advance Enrique.

Enrique Segovia
plating shop - Monterrey, Mexico


(2000)

A. The most common approach for such tanks is Koroseal lining glued in place (Koroseal is a brand name for flexible PVC and there are other brands).

Typically and historically here in the U.S., the lining thickness is 3/32", with a 6" wide second layer extending above and below the solution level.

No, polypropylene tanks should probably not be used; polypropylene is susceptible to oxidizing agents and chromic acid is a mighty powerful one.

There are alternatives, including titanium tanks, PVDF linings, etc., but the above-described Koroseal lining is hard to beat without spending a fortune.

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2000)

A. I have used Koroseal and vinyl liners. Thick vinyl liners with a shock absorber bottom for dropped parts and a second layer of vinyl welded on from the top of the tank to 6" below the liquid level is the long term cheapest and most functional. A liner comes out easily. Koroseal is hard to patch on a chrome tank, and is terrible to remove.

We used 140 °F for hard chrome and it is very hard on tanks/liners, especially Koroseal which works quite well at 120 °F.

I would look at 0.125 as a minimum thickness of vinyl and would prefer closer to 0.185. There are different qualities of vinyl.

James Watts
- Navarre, Florida


(2000)

A. One manufacturer of drop in liners fabricates the PVC liner with a Teflon skirt or upper layer. Misting formed above the solution deposits chrome solution on the liner above the solution level. Even a secondary layer (skirt) of PVC will deteriorate rapidly in some applications.

The Teflon, at least, will protect the PVC below it from oxidation. Water evaporates off the exposed material allowing nearly pure chromic acid to contact the resin. Since the flexible PVC contains in excess of 20% plasticizer, a phthalate ester, oxidation takes it's toll first on the plasticizer, causing shrinkage, cracking and eventual failure of the liner.

Bonded Koroseal gives better lifetime than a drop-in in this application since it is glued to the tank wall and cannot flex.

Charles R. Reichert CEF-SE
plating shop - Seattle, Washington


(2000)

Q. Thanks to Ted, James and Charles for your help on letter 4428.

James, isn't PVC a Vinyl? If not, what is the difference between Koroseal and a Vinyl? What about Hypalon ? I read that it has better resistance to higher Temperatures, but with a note that the oxidation of sulphur from rubber linings on the Hypalon could in some cases alter the Sulphate-chromate balance for bright chrome plating. I was ready to install Hypalon until I found this, should I avoid Hypalon even as it has a better temperature resistance? Thanks again for your help. Enrique

Enrique Segovia [returning]
plating shop - Monterrey, Mexico


(2000)

A. Koroseal is a BF Goodrich trade name for a flexible PVC (Vinyl) lining.

To my knowledge, rubber linings (including hypalon) are completely incompatible with chromic acid.

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


(2000)

A. I am not into the chemistry of plastics enough to tell you the differences.

I think that the main difference is that "vinyl" has a lot more plasticizers in it than "PVC".

James Watts
- Navarre, Florida


(2002)

A. I believe before any determination can be made, you would have to know if this is a fluoride bath. A non-fluoride bath is far less aggressive than a fluoride bath.

Shane Lobdell
- Lexington, Nebraska, USA


(2007)

wikipedia
PVC

A. Vinyl is PVC. From Wikipedia:
Polyvinyl chloride, (IUPAC Polychloroethene) commonly abbreviated PVC, is a widely used thermoplastic polymer. In terms of revenue generated, it is one of the most valuable products of the chemical industry. Globally, over 50% of PVC manufactured is used in construction. As a building material, PVC is cheap and easy to assemble.

Joe Haughawout
- Dallas, Texas


January 7, 2009

RFQ: We are running a chrome plating solution. Recently, there are cracks on our chrome tank. We have coated the tank with epoxy resin but the solution does not last very long. I understand that most people use Koroseal coating on the chrome plating tank. Can anyone recommend the supplier for the Koroseal coating. Thank you.

Tom
printing plant - Thailand
outdated

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Ed. note: Current RFQs are listed on our "Looking for Product & Services for Our Finishing Shop" page.



April 21, 2014

A. I know this a few years late to the thread, but Koroseal is simply a registered trademark name for a particular formulation of PVC.

Flexible PVC is made up of PVC resins, plasticizers and stabilizers. Like most any product, there are different quality levels of these components. Cheap and inexpensive resins and plasticizers are used for things like children's toys or garden hoses. More robust formulations are needed for industrial applications. The Koroseal PVC has a long earned reputation for having the most robust formulation in the marketplace, and is why it is the long standing material of choice for chrome plating solutions, let alone most any other metal finishing solution.

Andrew Hotchkies
tank linings - Claremore, Oklahoma



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