How things work: Electric Iron and its thermostat

Hello, friends. The idea to write this piece struck me just this morning – when I was helping my home minister/manager/ringmaster/better-half (read: wife) with ironing her clothes. Don’t tell her about these adjectives I just used to denominate her (she would not appreciate this verbal imagery, you see). The striking point was when she asked to switch off the iron immediately, lest it should get overheated. I assured her – that would not happen. We use a 2017 model iron and since the past several decades (at least I have lived 3 of them myself) they’ve been making irons with a thermostat control. It’s a simple mechanism that prevents overheating.

I’m sure most of you have noticed the red indicator lamp on the iron go off every few minutes – that’s right – it’s because of the thermostat mechanism. Before thermostat happened, we had the plain old (kinda heavy) irons that got hotter and hotter with each passing minute. In case you ran to get the door/phone and conveniently forgot about the iron – you had to be prepared for trouble. While you ran the risk of getting the iron overheated, you also wasted precious electricity. And if you were bird-brained enough to USE that overheated iron – even for a second – you burnt a gaping hole in your shirt/pants/any other garment that you intended to press/iron.

Still sounds Greek? I’ll break it down… A household/electric iron uses a simple combination of heat and pressure (manual) to remove creases from clothes. When an electric current is passed through a coil /heating element present in the iron, it heats up. This heat is then transferred to the base plate (the smooth, flat surface that you place against clothes while ironing) through conduction, which is how your clothes get pressed/ironed.

Now the concern… If the iron is continuously drawing electricity from the power supply (left plugged unattended), the heating element continues getting hotter. This causes energy wastage (as an iron consumes a great deal of electricity even in a few minutes), ruins your clothes, and in the worst cases, causes nasty accidents. I had a contact burn that got my entire palm (right hand) in blisters. Too bad, I’m right-handed!!!

Then came the thermostat era. Although globally, it was ushered in 1926 by The Liberty Gauge & Instrument Co. of Cleveland, Ohio (thanks to Joseph W. Myers of Jackson, Michigan), India had to wait till the early ‘70s and even then, it was meant only for the affluent class. I got to lay my hands upon one (with thermostat control) only towards the early ‘80s.

A word or two about how a thermostat works…

The thermostat in an iron uses a bimetallic strip. As the name suggests, a bimetallic strip is made up of two different types of metal (with different coefficients of expansion) that are bonded together. When the strip gets heated, the metals expand differently. This bimetallic strip is connected to a contact spring through small pins.

At moderate temperatures, the contact point remains in contact with the bimetallic strip. However, when the temperature of the iron exceeds a certain degree, the strip begins to bend towards the metal with a lower coefficient of expansion. As a result, the strip is no longer physically connected to the contact point, the circuit breaks and current stops flowing.

a/above: normal temperature

b/below: iron becomes too hot

Given that the circuit remains open for some time, the temperature of the iron drops, the strip acquires its original shape, the circuit is completed and the current flows again. This cycle is repeated until you switch off its power supply from the mains. This is why your iron switches on and off of its own accord.

In case you were curious about the innards of an electric iron, here you are:

Thermostat-based irons are now commonplace – however, only a few of us know how this gadget works. I don’t blame anyone for the lack of knowledge. We live in an era when every bit of knowledge that we are given, is so heavily job/work oriented – we tend to ignore other pieces of knowledge that could be equally interesting. A non-conformist that I am – I was blessed with an inquisitive mind. Hence the interest and hence the article.

Want to know (in layman/simple terms) how some of the other mundane gadgets work, ask me. If I know it already – the response will be immediate. All I intend to do is to BE SIMPLE while explaining. I hope I have achieved in this article. Any kind of feedback would be most appreciated.

Bye for now.