SIC-Stuck on LEGO

Science In The City

Stuck on LEGO

DEAR SCIENCE WORLD,

I’m in my thirties but I still asked for LEGO this Christmas. Besides the fact that I find its tinkling sound soothing, it gives me a creative outlet from my paper-pushing work week. I’ve always been curious—what makes LEGO bricks easy to both stick together and pull apart? Most things that stick together that well don’t come apart without something breaking. LEGO’s reusability ranks right up there with the magic of post-it notes. Please explain.

Adult LEGO Fan

Dear ALF,

We’re big fans of LEGO too. Did you know LEGO has been named “Toy of the Century” twice? Here are some scientific secrets that make the building bricks so successful.

Material Matters
All basic LEGO elements start as tiny granules made mostly of acrylonitrile butadiene styrene (ABS). ABS plastic is also used to make children’s music recorders and protective helmets—your first clue it’s a robust material. The ABS blend combines the strength and rigidity of acrylonitrile with the rubber properties of butadiene. The styrene (same as in Styrofoam) creates a shiny, resistant surface. ABS retains its integrity in temperatures from -25 to + 60°C. The “seeds” of ABS at the LEGO factory are heated much hotter, to 232°C (450°F), then injected into moulds where 25 to150 tons of pressure is applied. After a few seconds of cooling, new bricks are born. ABS absorbs moisture, so the entire moulding hall is kept at 50 per cent humidity.

Clever Design
Almost all LEGO pieces have two basic components—knobs on top and a network of tubes and walls underneath. The knobs are slightly larger than the tubular framework so when attached, the tubes push the walls out. The plastic wants to maintain its original shape so the walls push back. Friction is essential to keeping the pieces together. This type of connection system, which doesn’t require additional fasteners, is called an interference fit. To maintain the perfect level of ‘clutch power,’ the moulds and bricks must meet precise specifications, with an acceptable variance of only 0.005 millimetres—less than the thickness of a human hair. The quality control folks at LEGO report that for every million elements manufactured, only about eighteen are rejected.

The stud-and-tube coupling system offers another advantage of creative versatility. Two standard bricks can be joined twenty-four different ways. With six, you can try out all 915,103,765 assembly options! It definitely lives up to its advertising claim that “LEGO is a new toy every day.” Happy building!

Curator and LEGO-Buff, Rhoda Klein