Pot bases - Laminating aluminium/copper and stainless steel 2

[revdode]

This question is a little odd but perhaps one of you can help.

A friend recently asked how cooking pot bases were made, the type which are a sandwich of aluminium and copper sometimes with a ferritic stainless steel layers on the bottom of a 18/10 stainless pot the base is then encapsulated with another cover of stainless.
It's not my area I guess he just thought I'd know, which I don't and even my guesses (adhesives) seem moderately outlanding given the punishment these get from heat and cleaning.

Anyone have any experience of this as it's driving me nuts? Failing this I may have to "borrow" a pot from the kitchen and examine it with an angle grinder and chisel.

Cheers

 

[sreid]

I believe the word you are looking for is "Cladding."

 

[dutycycle]

It is possibly done by a process similar to vacuum rolling where high pressure and moderate heat(below the melt of the lowest material)is used to bond the materials together.

Smooth high polish surfaces can be 'bonded' even at room temperature.
Engineers slip gauges will do this.The bond is not permanent but requires a twisting action to release them.

Although slip gauges are of the same metal,this principle may apply to copper/aluminium/steel sandwitches that are vacuum roll formed too?
As far as I am aware there is no intermingling of materials at the boundary layer in vacuum rolling processes?

It could also be done using brazing?

 

[CoryPad]

As sreid stated, the process is cladding. Here is a description from the ASM Handbook:

The cladding process is generally differentiated from other bonding processes, such as brazing and welding, by the fact that none of the metals to be joined is molten when a metal-to-metal bond is achieved. Also, there are no intermediate layers, such as adhesives. The principle cladding techniques include cold roll bonding, hot roll bonding, hot pressing, explosion bonding, and extrusion bonding. Regardless of the technique used, the bond is achieved by forcing clean oxide-free metal surfaces into intimate contact; this causes a sharing of electrons between the metals. Gaseous impurities diffuse into the metals, and nondiffusible impurities consolidate by spheroidization. All the techniques involve some form of deformation to break up surface oxides, to create metal-to-metal contact, and to heat in order to accelerate diffusion. The techniques differ in the amount of deformation and heat used to form the bond and in the method of bringing the metals into intimate contact. Cold and hot roll bonding apply primarily to sheet (less than 5 mm, or 0.2 in., thick), but explosion bonding is usually restricted to thicker gages (up to several inches).

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[EdStainless]

Pot and pan stock is almost all roll clad. The various materials are cold rolled to achive the bonding.
In some combinations the plates are edge welded to seal them and then the space is evacuated.

The biggest issue is getting the surfaces clean. Really, really clean.

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