Quality
Why clad pans warp on the hob
Three metals expand at different rates. A clad base is therefore a stack of materials pulling against each other every time it heats, and warping is what happens when that pull is not balanced.
At a glance
Specification at a glance
| Factor | Effect on warping | What to do |
|---|---|---|
| Diameter versus burner | A base wider than the burner bows at the rim | Match base to burner, state max ring size |
| Total thickness | Thicker resists bowing | Thicker base for wide pans |
| Fast heating empty | Steep gradient, high stress | Care instruction, and a diffuser plate |
| Quenching a hot pan | Rapid contraction on one face | Never quench; cool before washing |
| Induction hotspot | Heat concentrated in the coupled ring | Even ring contact, avoid small coils |
| Residual stress from cutting | A disc that dishes before use | Annealing and flatness control |
The physics in one paragraph
Aluminium expands roughly twice as much as stainless for the same temperature rise. The three layers are bonded, so they cannot slide; the stack bends instead. Heat the centre of a base and the aluminium wants to grow more than the steel that holds it, and the pan bows. Cool it unevenly and it bows the other way.
Why an empty pan is the worst case
Food and liquid carry heat away and keep the base closer to one temperature. An empty pan on a high flame builds a steep gradient from the centre to the rim, which is exactly the condition that produces permanent deformation. Half the warranty claims in this category are an empty pan on high heat.
Design choices that resist it
A base that is not much wider than the burner bows less. A thicker core resists more. A base with a slight designed concavity can sit flat when hot, which is a deliberate choice rather than a defect, and it has to be stated on the drawing so inspection does not reject it.
Process choices that prevent it
Annealing relieves the stress that cutting would otherwise release as a dished disc. Controlled cooling after bonding avoids locking in a gradient. Flatness measured a day after cutting catches what a same-hour check misses.
How to check flatness honestly
On a surface plate, with a feeler gauge, on pieces taken from the middle of the stack, at least a day after cutting, at room temperature. A check taken immediately after blanking measures the wrong thing.
Questions
Common questions
Is a slightly concave base a defect?
Not if it was specified. A designed concavity sits flat when the pan is hot. It must be on the drawing so inspection agrees.
Can a warped pan be flattened?
Rarely without damage. Once the stack has yielded, pressing it back disturbs the bond.
Does induction warp pans more?
It concentrates heat in the coupled ring, so a pan used on a coil smaller than its base sees a steeper gradient than on gas.
How thick should a 28 cm pan base be?
It is quoted against the structure, but wide pans generally need a thicker core than small ones to stay flat.
What flatness figure is normal?
It is agreed per order. The number is meaningless without the measurement conditions: place, timing and temperature.