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Sweat, shit and switches

3 years ago

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David Twohig | Engineer


27 April 2021

Next time you reach for a switch in your car, spare a thought for the engineers who designed and tested it. Of course, they have done the obvious – produced an attractive, comfortable shape, and designed the electro-mechanical gubbins behind the façade to make sure they last for anything from 10,000 to 100,000 operations.

They’ve made sure it passes all applicable regulations – and yes, there are stacks of them – dictating the shape, colour and brightness of the symbol, the precise radii of the button, and, crucially, the damage it might inflict on your body during a frontal crash. But did you know they’ve also had to test to see how well it resists our sweaty paws?

Human sweat is nasty, corrosive stuff, a cocktail of various salts, oils and acids. Enough to attack certain plastics and the inks and pigments used in switch markings. To ensure the switch lasts a decade or, hopefully, more, car makers use automated test rigs that subject the switch to pressure by sweat-soaked pads made from foam or rubber to represent our fingers. These ‘fingers’ press the switch thousands of times, which is then put through various temperature and humidity cycles, designed to provoke all and any chemical reactions with our perspiration. And this needs to be done to all interior parts we might touch by the way – not just switches.

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