eli5 How does razor blade dull on hairs when razor blades are made of steel and they are much higher on mohs scale?
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They did some experiments with shaving hairs in an electron microscope. Turns out that hairs actually make tiny chips in the blade. Cool article linked below.
https://wonderfulengineering.com/scientists-figure-out-how-soft-hair-can-dull-super-hard-razor-blades/
It’s not just hair. You have to remember other ingredients are in the mix. Shaving cream, oils, skin cells, persperation, blood, water, debris, soap scum and other buildup, plus whatever the razor is factory coated with.
All that stuff is being scraped against micro blades that are by design meant to degrade quickly.
How else is Gillette going to get you to buy new razor blades?
Maybe they are engineered to bend to force customers to buy more ?
Think of it like aluminium foil. it’s metal but very easy to bend.
Stack hundreds of sheets of it and you’ll have a thick piece of aluminium which is very strong (because it’s basically solid aluminium)
Now offset the layers them slightly so you have a wedge shape and now you have something that looks like a blade i.e. a thick part on one side and a very thin part on the other.
The thin part is basically just a few sheets of aluminium, and you know how easy it is to bend a few sheets right? This is exactly what happens at the microscopic level
I do not know much of the science behind it, but I read somewhere once that evaporation of water on the razor blade and the corresponding corrosion is what causes most of the dulling.
I figured if I could preempt water evaporation with something that does not cause corrosion then I might be able to prolong the blade’s lifespan.
Nowadays I spray my razor blade royally with 70% isopropyl alcohol after usage and cleansing and it extended the lifespan of my blades by a factor of 4 or 5.
Can highly recommend this.
Here’s an ELI5. Steel is harder than wood, wouldn’t you agree? Like steel nail can scratch wooden plank, but a wooden shank won’t scratch a Steel sheet. That’s Mohs scale. But mohs scale does not account for geometry much. If you take a wooden block and hit it on a steel nail, the nail would bend as the resistance to bending depends upon the geometry of the nail itself in addition to its material properties. That’s why thinner nail is easier to bend than thicker nail.
When the razor blades are manufactured they are sharpened to a very thin edge. That makes them razor sharp, thus the phrase, but that sharp edge is inherently weak to bending because it’s so thin. When we use that blade, over time the edge starts to bend and the pointy sharp edge is rolled into a thick blunt edge. This blunt edge must be sharpened by some grinding tool like a grinding stone or sandpaper to scratch away the rolled metal on the edge to make it sharp again. At this stage Mohs scale comes into picture as you’re scratching the metal away.
To retain the sharpness for longer, knives and sword smiths do edge hardening to harden the metal at the edge and make it less susceptible to bending
How does water erode rocks?
While friction and collision with the hairs does microscopic damage to the blade, that is not generally what makes the blade dull quickly. When you rinse the blades after shaving, and leave them to air dry, the evaporating water leaves dissolved metal ions stuck to the blade’s point, rendering it “fuzzy” with microscopic crystalline spikes. The way to avoid this is to chase all the water off a wet blade with alcohol or oil before letting it dry. I’ve tried this myself and it can make a disposable blade last 6 months or more.
Most of the wear and tear is due to corrosion. If you dip the blade in alcohol, and wipe off, it well last much longer.
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