Is Micro-chipping the cause of dull razors?

[Larrin]

Recently there was a journal article in Science demonstrating that razor blades could micro-chip just from cutting hair. Professor John Verhoeven contacted me to say that he had done a followup study to see what the primary dulling mechanisms are for razor blades. Professor Verhoeven is well known for his work on Wootz Damascus and writings on knife steel metallurgy so I of course offered to publish his findings. https://knifesteelnerds.com/2021/01/11/what-causes-razor-blades-to-dull/

 

[BitingSarcasm]

Though I feel more nerdy than usual for reading that, it was an interesting read and answered some questions I had mused on about razor dulling. I just shave around the edges of my beard, so I was curious what the mechanism for dulling was with such minimal use. I guess I can abandon my plan to braid high-tensile strength rope from beard hair, sigh. My inner geek really wants to get my razor blades under an electron microscope, too. I wonder if Keratin molecular strands have areas of greater density that break the chips off the razor, or is it that they increase the drag in relation to the rest of the blade and the movement of the user levers out chips? Fun stuff, thanks for bringing it in Larrin!

edited because spellcheck thinks Larrin should be Larkin and I didn’t notice before posting

 

[Twindog]

I was surprised that these blades chipped at all, because they're gently cutting something 50 times softer.

Any idea on what caused the chipping?

Thanks for the basic information on the blades: stainless steel, run harder than I expected at 62-63 Rc. The apex was 0.2 microns. Do you know what the angle of the edge was?

Thanks again for cool information.

 

[OrangeBlueOrangeBlue]

I was surprised that these blades chipped at all, because they're gently cutting something 50 times softer.

Any idea on what caused the chipping?

Thanks for the basic information on the blades: stainless steel, run harder than I expected at 62-63 Rc. The apex was 0.2 microns. Do you know what the angle of the edge was?

Thanks again for cool information.

Larrin : Does the fact that the blades are mounted so that they flex, in combination with the thinness of the edge (0.2 microns) promote fracturing along the grain of the metal?

Also, I'd always understood the "replacement time" to be based on the lifespan of the lubricating strips, rather than the blades.

 

[Larrin]

I was surprised that these blades chipped at all, because they're gently cutting something 50 times softer.

Any idea on what caused the chipping?

Thanks for the basic information on the blades: stainless steel, run harder than I expected at 62-63 Rc. The apex was 0.2 microns. Do you know what the angle of the edge was?

Thanks again for cool information.

I would look at the original Science article if you want to see more about the chipping mechanisms.

 

[Larrin]

Larrin : Does the fact that the blades are mounted so that they flex, in combination with the thinness of the edge (0.2 microns) promote fracturing along the grain of the metal?

Also, I'd always understood the "replacement time" to be based on the lifespan of the lubricating strips, rather than the blades.

You stop using your razor when the lubricating strip is gone?

 

[goldie]

So is it necesarry to have up to 5 blades for shaving? Does 5 blades last longer than 3? Ive used 3 bladed razors and they seem to be fine anything less it seems they get clogged up more w hair.Would 3-5 blades microchip less because theres more blades than 1 or 2?

 

[Twindog]

So from the Science journal article, the chipping is caused by the sharpening grind marks on the edge, which are little stress risers. If a stress riser on the edge hits the whisker just right, it can cause a crack that leads to a chip.

I don't know what angle the razors are set at, but I presume it's acute, which combined with a thin apex and a thin BTE width, would make the edge especially prone to cracking, especially at 63 Rc.

I know a lot of people like toothy edges, but those edges are prone to microchipping, as well as tooth deflections and breaks.

In the book Knife Deburring by Dr. Vadim Kraichuk, the author says it is a myth that coarse, toothy edges cut better: "A knife edge sharpened to rougher finishes will have larger scratches than a finely honed edge, and those scratches can be thought of as pre-existing flaws; the sub-surface damage is also more pronounced and extended. A coarser edge does bite initially, however, the knife dulls faster as the teeth get broken off and as the edge chipping develops along those flaws."

Perhaps, we should be using much finer grits when sharpening. This variable could result in some of the differences that we see from testers of edge wear: those using more coarse edges will see difference edge wear than those using more refined edges.

 

[Larrin]

So is it necesarry to have up to 5 blades for shaving? Does 5 blades last longer than 3? Ive used 3 bladed razors and they seem to be fine anything less it seems they get clogged up more w hair.Would 3-5 blades microchip less because theres more blades than 1 or 2?

In Dr. Verhoeven's study the leading blade micro-chipped less than blades 2 or 3, and little wear was seen in any of the blades. So I'm not sure that there is anything to indicate in the study that more blades would last longer. But number of blades was not a variable in the study.

 

[Larrin]

So from the Science journal article, the chipping is caused by the sharpening grind marks on the edge, which are little stress risers. If a stress riser on the edge hits the whisker just right, it can cause a crack that leads to a chip.

I don't know what angle the razors are set at, but I presume it's acute, which combined with a thin apex and a thin BTE width, would make the edge especially prone to cracking, especially at 63 Rc.

I know a lot of people like toothy edges, but those edges are prone to microchipping, as well as tooth deflections and breaks.

In the book Knife Deburring by Dr. Vadim Kraichuk, the author says it is a myth that coarse, toothy edges cut better: "A knife edge sharpened to rougher finishes will have larger scratches than a finely honed edge, and those scratches can be thought of as pre-existing flaws; the sub-surface damage is also more pronounced and extended. A coarser edge does bite initially, however, the knife dulls faster as the teeth get broken off and as the edge chipping develops along those flaws."

Perhaps, we should be using much finer grits when sharpening. This variable could result in some of the differences that we see from testers of edge wear: those using more coarse edges will see difference edge wear than those using more refined edges.

I'm not sure teeth breaking off is a mechanism supported by experimental evidence. But regardless, polished edges would always be better for razors. The article primarily talks about the microstructure of the steel such as the carbides, and they suggest eliminating the carbides would lead to better behavior. Razors are sharpened to relatively high levels of polish so it's not as if they are leaving a "coarse" finish on purpose. There will always be flaws of some size, it just depends on how large.

 

[Bigfattyt]

If I remember correctly, another important variable was shaving with the grain, vs against. The hairs shaved against the grain were more prone to causing the stress and micro-fracture/chipping.

 

[OrangeBlueOrangeBlue]

You stop using your razor when the lubricating strip is gone?

I was talking about "wide perception" of a one-to-two-week replacement period discussed in the article. My understanding is that razor companies use short-lived lubricating strips to encourage people to replace their razors more frequently, or at least before the blades themselves are dull.

I actually use a DE razor, so no lubricating strips to speak of. When I used cartridge razors, I'd keep the same one for months.

 

[soc_monki]

I shave about once every 2 weeks. My razors last for months, I don't even worry about the lubricating strip, I have shaving cream for that...

Yes, I'm a cheap bastard.

 

[unwisefool]

I have found that the hair on my feet is much more abrasive than the say the hair on my upper back. A foot razor only lasts about 5 uses while a back one I can see up to 12 uses.

 

[Alberta Ed]

I shave about once every 2 weeks. My razors last for months, I don't even worry about the lubricating strip, I have shaving cream for that...

Yes, I'm a cheap bastard.

I don't even use shaving cream, just hot water with my single blade BiCs. Even cheaper. Could use my Ivan Campos Scandi instead of the BiC, but I like my ears and nose as they are. Not to mention my throat.

 

[soc_monki]

I don't even use shaving cream, just hot water with my single blade BiCs. Even cheaper. Could use my Ivan Campos Scandi instead of the BiC, but I like my ears and nose as they are. Not to mention my throat.

I have sensitive skin... No cream, no shave! I'm a pansy!

 

[RoyalHolic]

I use a double edge safety razor because it's cheap and effective and will last a lifetime! I know the throw away razors are handy and can do the job a little bit faster especially if you have the 3/4/5 versions but seems like a waste to me.

My razors seem to go rather dull on the 3rd or 4th go around and I only shave probably once a month so that's not too bad in my eyes.

I use Shark Platinum blades they seem better than others that I have used.

 

[jbmonkey]

good article on an interesting subject. the drying razor and not letting mineral deposits develop and extending the life of them...... makes a whole lot of sense. no reason to buy more than ya need to. stop throwing money away I hear they arent cheap anymore either. dont know as I have had a beard for decades now.

 

[Bigfattyt]

Interesting read. I have seen the evaporated deposits discussed as a mode of loss of smooth shave before. I need to start a program of drying my razors.

I also have seen a discussion of placing the razor in a preservative fluid between shaves fo avoid the evaporation deposits of minerals on the blade. Though I can't remember for the life of me what not corrosive fluid that was being used to avoid the deposits??


I keep my razors for a goodly amount of time....

And my razor also gets used by the wife....something I have in the past not done but for years now, my razor is in the shower where I shave wet, with a hand held mirror.. and the wife comandeers it, because it is there........

Maybe I need to reestablish the "my razor, her razor parameters". I shave only a line on my cheeks above the beard and a line on the neck below the beard.

I think I have only had a clean shaven face twice in the past 15 years or so?

 

[BluntCut MetalWorks]

I think, a reasonable answer to - statement from this article

"Interestingly, the number of chips on the leading blade was found to be significantly less than the middle and trailing blades in each study."​

may identified a key mechanism lead to micro chipping.

Further more, quote from other study

A hair-splitting way to get dull
Razors eventually become dull after shaving even though the blade is about 50 times harder than the hair. Whereas edge rounding and brittle cracking of a blade's hard coating were thought to be responsible, a detailed microstructural investigation by Roscioli et al. shows a different mechanism. A combination of out-of-plane bending, microstructural heterogeneity, and asperities—microscopic chips along the smooth edge—sometimes caused fracture to occur if the conditions lined up. This fracture originated at the hair-edge asperity interface and created chipping that dulled a blade faster than other processes.

Science, this issue p. 689​

Authors tossed a bunch of factors on the wall - umm until "conditions lined up". OK then, so conditions lined up, however it wouldn't solve the "Interestingly..." observation.

So from the Science journal article, the chipping is caused by the sharpening grind marks on the edge, which are little stress risers. If a stress riser on the edge hits the whisker just right, it can cause a crack that leads to a chip.

I don't know what angle the razors are set at, but I presume it's acute, which combined with a thin apex and a thin BTE width, would make the edge especially prone to cracking, especially at 63 Rc.

I know a lot of people like toothy edges, but those edges are prone to microchipping, as well as tooth deflections and breaks.

In the book Knife Deburring by Dr. Vadim Kraichuk, the author says it is a myth that coarse, toothy edges cut better: "A knife edge sharpened to rougher finishes will have larger scratches than a finely honed edge, and those scratches can be thought of as pre-existing flaws; the sub-surface damage is also more pronounced and extended. A coarser edge does bite initially, however, the knife dulls faster as the teeth get broken off and as the edge chipping develops along those flaws."

Perhaps, we should be using much finer grits when sharpening. This variable could result in some of the differences that we see from testers of edge wear: those using more coarse edges will see difference edge wear than those using more refined edges.