MIT study reveals why razor blades go dull cutting humble old hair

MIT study reveals why razor blades go dull cutting humble old hair
Science has discovered why razor blades go dull even though the hairs they cut are much softer than steel
Science has discovered why razor blades go dull even though the hairs they cut are much softer than steel
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Science has discovered why razor blades go dull even though the hairs they cut are much softer than steel
Science has discovered why razor blades go dull even though the hairs they cut are much softer than steel

A team of engineers at MIT led by C. Cem Tasan has discovered why steel razor blades go dull even when cutting hair that's 50 times softer than them. Using an electron microscopic, they found that under the right conditions a single hair can chip a blade edge.

One of the more frustrating of everyday mysteries is why razor blades go dull as quickly as they do? Intuitively, stainless steel blades should last longer than about a week. Because they are made to cut through soft hairs, they should last for months and, if they're coated with even harder materials, they should last even longer.

However, razor blades don't last and other steel blades, like knives and scalpels, also go dull even when used exclusively on softer materials. According to MIT, this is because there's more going on than a simple wearing down of metal, such as happens when a blade is rubbed against something harder, like a whetstone. Instead, what happens is that if a razor blade strikes a hair under the wrong conditions, it becomes stressed, cracks, and then chips due to a mechanism called stress intensification. This chipping leads to more cracks, leading to more chipping in a cascading cycle, ultimately resulting in a very dull razor and an unpleasant shave.

"Our main goal was to understand a problem that more or less everyone is aware of: why blades become useless when they interact with much softer material," says Tasan, the Thomas B. King Associate Professor of Metallurgy. "We found the main ingredients of failure, which enabled us to determine a new processing path to make blades that can last longer.

"We are metallurgists and want to learn what governs the deformation of metals so that we can make better metals. In this case, it was intriguing that, if you cut something very soft, like human hair, with something very hard, like steel, the hard material would fail."

To learn more about what happens when a blade meets hair, MIT graduate student Gianluca Roscioli shaved with disposable razors and then examined the blades under a scanning electron microscope. When he did so, he found very little wear or rounding. He did find chipping, but this wasn't consistent along the edge.

In a more sophisticated test, Roscioli constructed a micro-mechanical apparatus made up of a movable stage and two clamps to hold a commercial razor blade and to anchor test hairs of various diameters donated by lab colleagues. In operation, the device would cut at various depths and angles, and it could fit inside the electron microscope.

An analysis of the magnified blades showed that they did not chip when they cut the hair perpendicularly but did so more often when the blade met the hairs at an angle. Computer simulations derived from the collected data showed that it wasn't just the angle was important, but also the consistency of the steel in the blade. If metal varied along the edge, this produced weak spots where chips could occur.

In hopes of improving blade quality, the team has filed for a provisional patent for a process to make razor steel more homogeneous.

"The basic idea is to reduce this heterogeneity, while we keep the high hardness," says Roscioli. "We’ve learned how to make better blades, and now we want to do it."

The research was published in Science.

Source: MIT

Interesting, bt my blades last me for two months before I even think about chaning them. I do have a soft beard.
I figured out an extremely simple method of making the blades last for months on end. Don't shave !!. No jokes apart I shave immediately after taking a shower. Don't even need any fancy shaving foam. Regular bath soap lightly applied does the trick. BTW soap is only for the razor to glide easily on the face and not cut your self. Does absolutely nothing to make the beard soft.
Been shaving for 60 years and found that currently BIC is by far THE BEST disposable razor around, bar none.
Yup, I shave my head and my face, go through razors way too quickly.
How exactly is one material 50 times softer than another material? wouldn't 1 times softer be zero softness? Nonsensical?
As a consumable product, no one making them has the slightest interest in making them last longer. Mine usually go two or three months before getting bad enough to swap them out. I use 5 blade cartridges from a major manufacturer, and shave in the shower 7 days a week. They last a decent time, but cost a small fortune. Whatever soap I happen to be using... no commercial foam or lotion. I've always suspected those have ingredients that speed up the blade wear process.
I've been using Atra and Atra Plus blades for as long as they have been available and they last on average about 1 month before needing replacement. Over the years blades/cartridges have become more and more expensive. I hope this will not become another excuse to increase prices.
Robert Hebert
When razor blade manufacturers began reducing volume of the lubricant strip(s) on each razor a few decades ago is when the longevity of the blades reduced proportionally because the lubricant also contained oils that reduced rusting... Even stainless steel rusts... The rust is just the same color as the original steel. Keeping your blades dry between shaves will increase their life... Even fresh new blades rust if not protected from moisture.
Have been using the same blade for 2 years since I bought a razorpit. Requires 20 seconds of sharpening at each use while the water is heating up.
John Strube
If you really want to up your shave game, and save money at the same time. Ditch the multi blade razors and go back to what our grandfathers used. The double edge safety razor. The best blade I have found is the Gillette Platinum. You get less ingrown hairs, a smoother face, and the things cost about a buck each. There are many razors to choose from, mild to aggressive. Give it a shot.
Ralf Biernacki
The manufacturers make money selling replacement blades. As a matter of fact, Gillette was the company that pioneered this approach to sales, which is now used for computer printers among other things; sell the main item at a loss, than more than make up for it by overpricing the refills. Thus the makers of these razors would be shooting themselves in the foot by introducing durable blades; their business model relies on making the least durable blades the market will bear. They will buy this discovery and all associated patents, then bury them.
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