Fatal Attraction - Using Magnets in Your Projects

Fatal Attraction – Using Magnets in your Projects

Since their discovery in 1984, small, powerful neodymium magnets have become ubiquitous, finding their way into disc drives, power tool motors and even toys.  Nothing else comes close when spooky action at a distance is required (at least until quantum computers are on the shelf at the $2 shop). So, faced with the challenge of devising a new Christmas workshop, adding a bit of magnetic levitation seemed to tick the box for Awe and Whimsy.

Next came the risk assessment process, which is a part of all SLQ program development, and soon there were more red flags than at a May Day parade because in 2012, small powerful magnets were banned from use in Australia 

     in any toy, game or puzzle (including but not limited to an adult desk toy, an educational toy or game, a toy, game or puzzle for mental stimulation or stress relief).

This followed the hospitalization of almost 40 children between 2004 and 2008 due to the ingestion of magnets, which sometimes fatally punctured intestines as they collected inside the little magnetovours.

So what is small? How strong is powerful? International standards use a device called a small parts cylinder to define smallness – basically a cylinder about the size of an old film canister (31.5mm diameter and 51mm high for those born digital). If the object fits in without squashing, it will fit into the throat of a small child, too.  Which sort of covers all the cheap, shiny neodymium magnets you can buy, unless they are bigger than a ping-pong ball. But what about strength?

Magnets have complicated physics, and measurements of ‘strength’ can include flux density and field strength (which can be related by a value for the magnetic permeability of free space), torque, and lifting power among others.  International standards use a unit which does not appear in any physics text: kG2 mm2 . The kG refers to kiloGauss, not kilograms, but the squaring is a mystery until diligent Googling revealed how this is measured for regulatory purposes - if your calculation gives a value greater than 50 kG2 mm2, the magnet is outlawed. Using data from reputable suppliers of magnets, and a bit of basic maths, it turns out that all available neodymium magnets on the Australian market exceed this limit. 

So, how can you invoke the magic of magnets without risking hefty fines and scourging on social media? 

You could use weaker, ferrite magnets instead (even if they fit into the category of a small part), provided the maths holds up. But they might not be strong enough to achieve your mysterious aspirations, and the device still needs a warning label or you could use a design with a single magnet – since the ban only refers to two or more being present. 

Embedding the magnets into a larger part is problematic (some Australian guidelines explicitly include magnets fitted into toys), and ISO level testing to prove they would not be dislodged in the hands of destructive infants is required.

Or you could make something that is not a toy, since the legislation excludes many uses such as in computer equipment, bicycles, trampolines and model steam engines which are exempted under the definition of toy for some reason and really, thank goodness because who doesn’t love a good model train set?
Just as well that creativity is energized by constraints.


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