Velcro fasteners, those little pads of fuzzy plastic hooks and eyes, have found low and high-tech uses in and out of this world.
In the clothing industry they are used instead of press-studs and zips. In medicine, they are used to attach the chambers in the Jarvik 7 artificial heart. In the space shuttle, astronauts use Velcro tape to stick trays, food packages, scientific equipment, and occasionally themselves, to some convenient surface to prevent them floating away in the weightless environment.
Swiss engineer Georges de Mestral conceived the idea that evolved into Velcro after a walk in the woods one day in 1948. He came back home with burrs stuck to his socks and to his dog, and decided to investigate why burrs stick so well to wool.
Under the microscope he saw how tiny hooks on the ends of the burrs caught in loops in the wool.
De Mestral soon devised a method of reproducing the hook and loop arrangement in woven nylon. He called the product Velcro, a contraction of velours and crochet, the French word for ‘hook’. The original patent on Velcro expired in 1978 and there are now many imitations, but Velcro remains a registered trade name.
Velcro is made by weaving nylon thread to produce a fabric containing densely packed little loops. This forms the looped part. To form the hooked part, loops in a separate piece of fabric are cut, so that half of each loop becomes a hook. The fabric is heated to set the loops and hooks permanently in shape. It is then dyed, bonded to a suitable backing and cut to size.
Velcro is particularly long-lasting. It can usually be fastened and unfastened many thousands of times and may well outlast the product to which it is attached.
Velcro is designed to be peelable – to be opened by hand with comparatively little effort. However, it has very high shear strength – resistance to sideways forces. Some Velcro is so strong in shear strength that a piece less than 5in (120mm) square can support a load of 1 ton. This property has prompted experiments in using Velcro to make aircraft bodies. The aim is to replace rivets with Velcro strips, saving weight and making assembly simpler.
How burrs grip
The tiny seed pods (or burrs) of goosegrass have barbs which get caught in woollen clothing and animal fur.
The tiny nylon hooks on one piece of Velcro catch the loops on the facing piece, exactly as grass burrs catch onto woollen socks when you walk through woods. A thumbnail-size piece of Velcro contains about 750 hooks, with 12,500 loops on the other side. They can be fastened and unfastened thousands of times without wearing out, and are used on clothing instead of press-studs or zips.