“Melting” ceramic hob

[LindaMac]

My mother has been using ceramic hobs for the past 10 year with no problems. However, today she put a roasting tin on her hob to keep the oil hot while she put potatoes in it to roast (as she has done numerous times in the past). After a few minutes she found the enamelled tin had stuck to the hob. It was impossible to get off without forcing it with a knife between the two. It resulted in a small portion of the heating “ring” on the hob being pitted and a piece missing from the hob (like a chip from it thesize of a pound coin, but with no sharp edges) and the enamel gone from the bottom of the roasting tin. That part of the hob is of course ruined. The hob is about a year old and this particular heating “ring” has been used very little. Any ideas what could have caused this as she is now terrified that she will ruin the rest. Thanks in advance for any advice.

[iadom]

Re: “Melting” ceramic hob

She should have a look at the instruction manual that came with the hob. You will almost certainly find that it advises using only certain types of pans on a ceramic hob. I don’t think that enamelled based pans etc are suitable.

[LindaMac]

Re: “Melting” ceramic hob

Thanks for your reply, but I have been through instruction book (took time as my mother lives in Spain and I had to translate it!) and it makes no reference to the use of enamel on the hob. It only says that anything plastic should never be put on it. The only thing it mentions about causing possible damage to the hob is burnt on sugar.

[NigelS]

Re: “Melting” ceramic hob

Just a thought….
Simply defined, enamel is glass, transparent ground glass mixed with oxides to provide the colouration, which is applied on to metal with a higher melting point. Enamel is a form of glass. The players are:

SiO2 = Silica, also called quartz.
K2O = Potassium Oxide.
Na2O = Sodium Oxide. (Makes glass softer.)
CaO = Calcium Oxide. (Makes glass harder.)
PbO = Lead

Glass = SiO2 + Na2O, K2O, CaO
When you replace K2O (potassium oxide) with PbO (lead), you get enamel: SiO2 + Na2O, PbO, CaO. Lead lowers the melting point and raises the refractive index.
Finally, metal oxides are added to give the enamel color. For example, cobalt oxide creates blue enamel.It’s fused to the metal at a high temperature in a kiln.
What you seem to have done is melted the enamel from the pan that has fused with the glass on the hob. Although the melting point of the glass on the hob should be relatively high ( 2,500C for a Norex type glass), the enamel may have softened at a much lower temperature (from 300C or so). Both the glass and enamel are similar substances and so the ability of the enamel to make a bond with the glass surface is is significantly increased. The enamel effectively became glue that bonded the gravy pan to the hob. If your mother had used an aluminium, iron or steel pan this problem shouldn’t have happened.
The use of pyrex saucepans is also ok because the pyrex has a much higher melting point than enamel. Most thermally non-expanding glass have melting points around 2500C.
Sorry, all this doesn’t help you to repair the hob surface!
Check your household insurance for “accidental cover”. I’m not sure whether the hob counts as “contents” or “buildings”
Nigel

[iadom]

Re: “Melting” ceramic hob

Thanks for that very informative post Nigel. I do recall that when Hotpoint introduced their very first ceramic hob cooker 25 years ago or more, they actually included a full set of special ultra strong, flat based pans with the cooker.

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