S/S Thickness on Copper vs Aluminum

Something I’ve been wondering about lately. On most bi-metal copper cookware, the stainless steel layer is 0.2 mm. Yet on most clad (aluminum tri-ply) cookware, the stainless steel layer is 0.4 mm - 0.5 mm.

Why the difference? Is there a metalurgical / engineering reason for s/s to be thicker on aluminum?

I think it’s just a practical matter. Copper is stronger and has a higher melting temperature than Aluminum used as a core metal, or aluminum bi-metal. The thicker stainless used with aluminum may cut down on pans warping or denting. It may have an effect on delamination, although that’s just me guessing.

Copper bimetal pans have been produced and sold with thicker than .2 stainless lining, I own several examples. But .2 stainless linings seems to provide the best conductivity while still providing good wear.

Yes. The reasons are technical and have to do with creation of the two different kinds of sheetstock, and specifically bonding.

It is very difficult to bond SS directly to copper, just as it is to bond SS to pure aluminum. Falk’s 1983 process patents solved the former problem (and was licensed to all the other makers of the copper bimetal), but there are limits on forming copper bimetal pans with lining layers thicker than those used. For example, Falk used to disclose that its stockpots cost so much because fully 40% were defective out of the 80-ton press–something in the bimetal sheet breaks in the stretching.

If you research clad, what you find is that the “sandwich” is a very carefully-chosen mix of material layers which will bond well, be formable, and stable. This is the #1 explanation (dirty secret, really) of the reason for multi-layer clad. You can have your high-purity aluminum or copper core, but it needs something between it and the SS–usually a lower-purity aluminum. Demeyere and others used to brag about silver in their sandwiches, but it has zero to do with performance, and everything to do with bonding and forming. Adding an induction layer complicates matters even further.

Falk’s sheetstock is formed under great heat and 850T of pressure, and would be impossible without proprietary heat resistors. It results in an intercrystalline structure that is not present in clad. While All-Clad’s triply is made at about 1000F for reasons of ductility and bond strength, the process of roll-bonding can be done at room temperature. But the SS needs to be thicker.

Aloha,
Kaleo

I own a copper sauce pan that has about a .8 mm stainless lining-very thick. So I think the limit in thickness goes the other way. That is, it’s my guess that it’s difficult to stretch a very thin lining. And Falk was trying to make just such a performance pan to compare to tin.

I have seen a thin stainless lining on a new Mauviel copper pan tear at the top of the pouring edge. And I remember Falk had problems drawing their deeper pots, even somewhat recently, although I’ve not seen or heard of the same problem with Mauviel for some reason. And with Falk, I think it was the stainless lining that gave them the problems- Although they also mentioned in one of their patents, the copper getting an orange peel effect… Falk USA has stated that their patent expired in 1994, along with any fees associated with it.
http://www.google.com.mx/patents/US4591394
Quote:
FalkUSA
Hi, The patent expired in 1994. I don’t think the rumor of them manufacturing and distributing bimetal has served them well over the years. Falk is a small, family-owned company that takes pride in their cookware designs and hand-finishing, as well as the contributions they’ve made to the industry regarding the patented technology. I think a lot of that has been lost through misinformation. Its much more in line with the size of a Brooklyn Copper than a Mauviel. Take a look at their manufacturing video sometime if you want to get a better sense of their operation.
Quote:
FalkUSA
Hi, just to clear up the stainless steel speculation, Falk uses 200 micron austenitic 18/8 stainless steel. This is a non-reactive stainless steel that is widely used in the cooking industry. As you probably know, the 18 refers to the percentage of chromium in the alloy, which gives SS its non-reactive nature. The 8 refers to the nickel content. There is no noticeable difference in reactivity between the two grades, however the presence of some nickel in SS is important. 18/0 would be a problem. Both 18/8 and 18/10 are considered Type 304 stainless steels and are both considered non-reactive grade. The reason that Falk doesn’t use 18/10 is because of the additional rigidity of that product. At only 200 microns thickness, with 18/10 there’s a slight risk of micro-tears, cracking or other damage to the SS during the production process…"

Who made your 0.8mm SS-lined saucepan, and when was it made? Are you confident that what you’re seeing at the edge is the actual thickness of the SS foil?

Falk also says their process patent originated in 1983. So I don’t know how/if 11 years figures

I have hired a metal bonding expert to consult on our pan project. I will ask him these questions.

Aloha,
Kaleo

PS: Mauviel also has extraneous steel staples pressed into its bimetal occasionally. The thin SS holds up well; the staple gets pressed into and displaces the copper.

I’m very confident abou the thick stainless linings- sometimes the lining stops slightly above the copper at the edge. The first time I had a pan with that thick of a lining, it was labeled “Villedieu Modele Depose Gaor 50 France Atelier du Cuivre”. Although it was 3.5 mm total thickness- in that size, I sent it back because the lining was so thick. But it had another unique feature- no inside rivets.

Later, I found a similar pan marked Ruffoni Italy and bought it because it was less $$. It has the exact same handle with no rivets on the inside and the same 2 brass tacks on the outside that look like rivets. (this one on Ebay has the thick lining) http://www.ebay.com/itm/RUFFONI-COPPERWARE-COPPER-SAUCE-POT-5-x-2-75-/252302734236?hash=item3abe6a339c:g:EF0AAOSwx-9Wziwk

I believe it was out-sourced by the same people who made the Atelier du Cuivre. Atelier du Cuivre are still producing these handles with no inside rivets for their pans. Some with silver- http://ruthreichl.com/2013/12/2013-gift-guide-day-ten.html/
More here for sale http://www.epicuriensdefrance.com/Casseroles-en-cuivre-Art-de-la-table/p/3/2192/0/

Scroll down to see a modern copper pan of theirs with thin stainless but no rivets http://www.huffingtonpost.com/karen-williams/the-secret-to-a-stressfre_b_4315727.html They also make a rivet less version with a removable handle.

While I believe the staple story relating to bimetal, I also think at least in some cases it’s a tin lined pan with a dribble of tin on the copper.

Alexander: Is the Atelier du Cuivre the same workshop that is still in Villedieu? Link: Site du web

I was wondering if they used they same construction today or if they only make the thinner (2mm) pans with a thin SS (or tin or silver) lining. I missed going into their shop and factory tour, as we ran late when we stopped in Villedieu.

I’m reasonably sure it’s the same, and they also have a Paris address as well. Like a lot of copper manufacturers, I would assume most of their wares are thin and expensive, will some sold for the ‘tourist trade’ bought as an impulse item while on vacation. The sort of thing where you almost feel obliged to pick something up at their gift shop as a remembrance of your visit.

That being said, the stainless lined pans are obviously ‘pressed’ and made with heavier manufacturing equipment, that would be off limits as part of a tour for vacationers. The rest, who knows? They could likely make anything. The problem is getting orders and costs. The Ruffoni pan with the unusual handle was identical to the Atelier du Cuivre- that tells me that occasionally there is mutual cooperation between families. And that they have tried to innovate to stay in business.

Kaleo, I’ve occasionally come across your mentioning of a pan project, here, and on Chowhound.

What exactly is your project? It sounds intriguing. Are you able to talk about it?

I can give you a little background if you email me. kaleokahu@mail.com

@alexander – they do have a boutique (shared with other brands) in Paris. But the workshop is in Villedieu. The tourist experience still looks pretty neat

In the videos in the link above you can see how they deliver to a 2* chef and other customized orders. The price list for the standard stuff is on the website. They speak a little about their silver additions as well. Not clear if the press you mention is another building. If I’m back again visiting our friends I’ll be sure to allocate time for a visit – I also want to go to the Mauviel factory just outside of town.

1 Like

Sorry, I’m not seeing any pans at any of these links that look like they have 0.8mm SS linings. The Ruffoni pictured is only a 5" pan. It’s lining is not 1/4 of its overall thickness.

Can you post a close-up edge photo of your 0.8mm saucepan?

Aloha,
Kaleo

I am such a luddite but maybe I can get help posting a photo later. I searched Gaor 50 copper and came up with this old listing-scroll down for images- that mentions in the description the thickness and shows it in the 6th- 11th photo fairly well. You may have to expand the image’ http://www.ebay.com/itm/Gaor-50-Atelier-Villedieu-3mm-French-5-75-Copper-Sauce-Pan-SS-Made-In-France-/291450451239?nma=true&si=%2BfjMrhJDkF5SwGve9PPzRqjYO9U%3D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

I see what you mean now, thanks.

Next question: Do you know if these are actually deep drawn from bimetal? I suspect they may be made differently, perhaps by fusing two nested pots, one SS one copper. They must be welding the handle studs to the liners, however they’re made. Those stepped edges are strange.

Ha, this is why I like French copper pots, no moving parts and yet just enough intrigue, integrity and history to acknowledge a certain admiration for them. Why re-read the love letters of Abelard and Heloise? Simple things are sometimes the most profound.

Anyway, Sic et Non, yes and no. I was curious about the handle attachment, but since they use the same system on their silver lined pans, it cannot be welded to a lining. It is brazed. (I believe). Even the lug (brass or bronze)- for the removable handle version is done similarly. There must be a brass or bronze fitting that is brazed to the copper side of the pan.

As far as the stepped edges- yes, on some of the pans the stainless lining peaks above the copper sides - it is almost like a pan within a pan, or when I first saw it, I thought of a stainless pan ‘jacketed’ in copper. I don’t know. But I’m inclined to think it was still pressed together and the inner circumference of the stainless allows it to rise a bit taller in the pressing process.

Imagine having 2 identical oranges and taking the peal of one and placing it over the other unpeeled orange … Yet I saw some where the edges were almost even? And the thickness of the copper seemed to varied with the larger Gaor, but not the Ruffoni. It is what it is.

I love my ancient Revereware cookware. Especially the hard to find anymore 4 qt single handle pot. I have even been collecting pieces in thrift stores for my adult children. What can you tell me about it.

Kaleo, sent you an email last week.

Sorry, didn’t get it. kaleokahu@gmail.com

“Food is a pretty good prism through which to view humanity.”

― Jonathan Gold