Why do razor blades get dull so quickly?

Some work-from-homers may have given up on daily shaving in recent months, but who wouldn’t want a more durable razor? Multiblade cartridges typically only last a week or two before they start to grab the skin and then be thrown in the trash. But what if someone could invent a razor that stays sharp for six months or even a year?

This is the thinking behind a recent experiment conducted by researchers at the Massachusetts Institute of Technology, who attempted to find out why steel razor blades get dull so quickly, especially when they are just cutting hair. soft humans. By observing and recording the cutting process under a scanning electron microscope, the team noticed that the hairs created small chips on the surface of the blade. These microscopic chips destroy the blade’s ability to cut hair, according to Cem Tasan, professor of materials science at MIT and author on the study published today in the newspaper Science, a discovery that no one expected.

“We want to design new materials that are better and that last longer,” says Tasan. “This blade problem is a great example. We’re so used to it that you don’t think about it. You use the razor for a few weeks, then move on. “

Tasan says razor blades are made of martensitic steels, some of the strongest materials known to mankind. Martensitic steel (named after a 19th-century German metallurgist) is an ultra-hard, heat and tempered alloy that is used in commercial razors, surgical instruments, ball bearings, and brakes bicycle disc. What Tasan and his colleagues found was that despite this strength, the blades got tired quite quickly after multiple shaves.

Tasan and graduate student Gianluca Roscioli designed an experiment to examine the progression of blade wear after each shave. After examining several different commercial razors, the team found that they were all made from a similar hardened steel-carbide alloy. Because the materials were similar, the experiment only used one brand of razor.

Roscioli shaved every three days for a month with the same razor, then brought it to the Cambridge lab. The researchers set up a device to take images of the slides under a microscope, which bounces an electron beam off the surface to obtain information about the molecular structure of the slides.

“Our first thought was that this was a wear issue, that the material was being pulled from the razor,” says Tasan. “We expected that over time the blade would become more and more round. We haven’t seen it. “

Instead, he continues, “we saw the blade that forms this C-shaped crack fracture and flake off.”

This video shows how the tiny shavings form in the blade after slicing through human hair.

Tasan says commercial disposable razors – those sold to men and women – generally use the same type of steel but have different coatings and number of blades in the cartridge. (Razors marketed for men and women are similar except for the handle design and number of blades. Single-blade razors, often sold to women, do not stay sharp as long as multi-blade razors, Tasan said.)

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