Why Do Razor Blades Dull So Quickly?

Why Do Razor Blades Dull So Quickly?

Although some work-from-homers may have abandoned daily shaving in recent months, who wouldn’t want a longer-lasting razor? Multi-blade cartridges usually only last a week or two before they begin to grab at the skin, then get tossed in the garbage. But what if someone could invent a razor that stays sharp for six months, or even a year?

That’s the thinking behind a recent experiment by researchers at the Massachusetts Institute of Technology, who tried to find out why steel razor blades go dull so quickly, especially when they are just cutting soft human hair. By observing and recording the cutting process under a scanning electron microscope, the team noticed that the hairs created small chips in the blade surface. These microscopic chips wreck the blade’s ability to cut hair, according to Cem Tasan, professor of materials science at MIT and an author on the study published today in the journal Science, a finding that nobody expected.

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

Tasan says razor blades are made of martensitic steels, some of the toughest materials known to mankind. Martenistic steel (named for a 19th century German metallurgist) is a super-hard alloy that is honed through heat and tempering, and is used in commercial razors, surgical instruments, ball bearings and bicycle disc brakes. What Tasan and his colleagues found is that, despite this strength, the blades fatigued rather quickly after multiple shaves.

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

Roscioli shaved every three days for a month with the same razor, and then brought it into the Cambridge lab. The researchers set up a device to take images of the blades under the microscope, which bounces a beam of electrons off the surface to gain information about the blades’ molecular structure.

“Our initial thought was that this was a wear problem, that material was being removed from the razor,” Tasan says. “We were expecting to see that over time the blade gets rounder and rounder. We didn’t see it.”

Instead, he continues, “we saw fracturing and chipping of the blade that is forming this C-shaped crack.”

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

Tasan says commercial disposable razors—those marketed to both men and women—typically use the same type of steel, but have different coatings and numbers of blades in the cartridge. (Razors marketed to men and women are similar except for handle design and the number of blades. Single-blade razors, often sold to women, don’t stay as sharp as long as multi-blade shavers, says Tasan.)

He says three factors make razors dull faster more quickly: The angle that the blade cuts against the hair, the microstructural uniformity of the steel-carbide alloy, and the presence of microcracks in the steel surface that occur in manufacturing during the honing process, in which the blade is sharpened by rubbing it against a coarse surface. “You try to get as hard a material as possible,” Tasan says, “but if hardness comes at expense of heterogeneity, the cracks can grow further.”

Photograph: Gianluca Roscioli

One shaving industry professional says that consumers are not worried as much about how long the metal blade lasts, but rather about its performance during each shave. “There’s a tricky tradeoff between closeness and comfort,” says Brittania Boey, chief commercial officer at Harry’s, a New York-based shaving supply manufacturer. “You can have blades that cut very short into the skin, but the tradeoff is with comfort. The trick with designing a cartridge is finding that balance.”

Boey says that customers surveyed by Harry’s who use the firm’s products have an emotional connection to changing their shaving cartridge. “When they throw away an older cartridge and click on something new, it signifies something fresh,” Boey says. At the same time, Boey says, Harry’s is potentially interested in new blade designs or manufacturing techniques, and often works with university labs to improve its grooming products.

“If there was a need that a customer wanted a much longer lasting blade, we would always consider the customer’s needs first,” Boey says.

Bryan Webler, an associate professor of materials science at Carnegie Mellon University, says the MIT study is a good example of identifying why a material performs the way it does. “The identification of a failure mechanism opens up new opportunities to engineer blade material composition or processing to create microstructures that will resist this type of failure,” he wrote in an email. This could be done by reducing microscopic rough edges on the blade edge, or thinking about ways to form a more uniform microstructure, he adds.

For his part, Roscioli says he is interested in further pursuing this line of research, perhaps by launching a startup that can fund additional experiments. His idea is to make a harder blade that will last longer by compressing the metal, instead of heating and sharpening it through tempering. That process would lead to a more uniform microscopic structure, with less cracking and chipping, Roscioli says.

The MIT team has already filed for a patent for this new razor manufacturing process, he says. “I really believe we can build a better blade,” Roscioli says. A better blade would be more expensive, he points out, but because longer-lasting blades would mean fewer get tossed in the trash, “it would reduce the impact on the environment.”

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