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+--- Thread: How Razor Blades Dull (/showthread.php?tid=551)
How Razor Blades Dull - Rick Kr - 08-17-2020
An interesting line of discussion came up recently in a maillist on the making of bamboo fly rods, in regard to dulling of edges. This may be old news to knife sharpeners, but as it pertains to razors, something we use as references or standards, I found it interesting and confirming.
Relevant discussion from the original thread is further below, immediately below are links to the source information referenced in the discussion.
Rick
Article URL
https://www.sciencemag.org/news/2020/08/your-hair-can-crack-steel-when-it-hits-right-spot?utm_campaign=news_daily_2020-08-13&et_rid=17102816&et_cid=3445815
Video URL
https://www.youtube.com/watch?v=6kgw6j9n_2o#action=share
On 8/17/2020 5:32 AM, H...V... via Rodmakers wrote:
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> On 17 Aug 2020, at 14:27, T...S... via Rodmakers <rodmakers@lists.canerodmakers.com> wrote:
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>> What they don’t talk about, and the razor companies don’t tell you is that what causes most early failure in a blade is actually corrosion. Stainless is not naturally corrosion resistant, what makes it so is a microscopically thin layer of oxide that forms on it’s surface. When you shave, that oxide wears away allowing corrosion to start. As long as the metal is exposed to oxygen in the air, the oxide layer will restore itself fairly quickly, and the steel is again protected.
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> I assume that is a chromium oxide? As far as I know it is primarily the chromium content that makes stainless steel ’stainless’ - and iron oxides are, for the most part, and that includes all non-esoteric oxides, non-passivating, i.e. an iron oxide layer (aka rust) does not prevent further oxidation underneath - unlike e.g. an aluminium oxide skin on aluminium.
On 8/17/2020 5:07 AM, H...V... via Rodmakers wrote:
> Note that there is nothing special about the ‘process’ they describe - see also their introduction:
>
>> Steels for sharp edges or tools typically have martensitic microstructures, high carbide contents, and various coatings to exhibit high hardness and wear resistance. Yet they become practically unusable upon cutting much softer materials such as human hair, cheese, or potatoes. Despite this being an everyday observation, the underlying physical micromechanisms are poorly understood because of the structural complexity of the interacting materials and the complex boundary conditions of their co-deformation. To unravel this complexity, we carried out interrupted tests and in situ electron microscopy cutting experiments with two micromechanical testing setups. We investigated the findings analytically and numerically, revealing that the spatial variation of lath martensite structure plays the key role leading to a mixed-mode II-III cracking phenomenon before appreciable wear.
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> It’s only their detailed look at what’s happening at the ‘between nano and micro’ scale, after each individual use that is (somewhat) new.
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> So yes, this is definitely also what’s happening to our plane blades on bamboo, and to plane blades on ’normal’ wood, and to kitchen knives while cutting onions on a chopping board.
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> Way I understand it is the extent of this process is primarily dependent on the alloy type and heat treatment of the steel. My guess is that razor blade steel is harder, more crystalline, than our plane blade iron.
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>>> On 17 Aug 2020, at 13:56, T...S... via Rodmakers <rodmakers@lists.canerodmakers.com> wrote:
>>>
>>> Dear All,
>>> here is an interesting study and especially a nice video how razer blades become dull.
>>> Perhaps same is happening to our plane blades due to the hard cane fibres.
>>> https://www.sciencemag.org/news/2020/08/your-hair-can-crack-steel-when-it-hits-right-spot?utm_campaign=news_daily_2020-08-13&et_rid=17102816&et_cid=3445815
>>>
>>> br
>>> Tapani
>>>
>>> Rodmakers List - https://rodmakers.canerodmakers.com
RE: How Razor Blades Dull - grepper - 08-17-2020
Interesting stuff Mr. Rick! Thanks for the post.
I'm claiming absolutely no knowledge of exactly how razors dull, but rather just blurting out what came to mind when I saw your post.
I know razor blades dull from corrosion and it's easy to prove with your edge tester. There was some discussion on that here but more related to knives:
http://bessex.com/forum/showthread.php?tid=356&pid=3684#pid3684
Because the razor is so sharp and therefore thin I'm not surprised the edge gets crushed in. I had not known of the fracturing, but, OK. There are the images of it. Maybe that varies between brands, but whatever, there it is in the presented evidence.
We know that the majority of blades, or at least the majority of dullness is the result of rolling. That said, I've always guessed that razors might be a special case because the blades never suffer surface contact like a knife impacting a cutting board. It's more like a chef who only thinly slices shashimi whilst never contacting the cutting board. There is just never much force applied to the edge.
As I mentioned, razors are a special case not only because of what they cut but also because they are so sharp and sharp, by definition equals thin. Really thin, (35 - 50 BESS), in the case of a razor. It only makes sense that anything that thin is delicate and won't hold up to much impact or abuse. That's why I'm of the opinion that getting a general purpose blade razor sharp makes little sense. That super sharpness quickly rolls and is ephemeral at best.
I question one the the quotes somebody made in your post, but it is out of context and not exactly clear what they are referring to:
"So yes, this is definitely also what’s happening to our plane blades on bamboo, and to plane blades on ’normal’ wood, and to kitchen knives while cutting onions on a chopping board."
IMHO, the majority of dulling with blades contacting wood is the result of rolling. Maybe there is caving in and microscopic fracturing too, but the majority of dullness is due to rolling. I believe this because I have taken microscope images of rolled edges created by slicking tomatoes on a cutting board.
I checked out a disposable razor I had that had become too dull to shave with. It was still very sharp, 65, 75, 75 along the edge, but shaved for crap. I examined it under the scope and could not find any rolling. At the time I chalked the inability to see roll up to the limitations of my USB microscope and guessed it might be corrosion too.
Maybe there was some tiny amount of rolling, but the evidence you preseont suggest it was a fractured, corroded, bashed in mess at the edge.
Good stuff Rick. Thanks for taking the time to post it. Good food for thought.
RE: How Razor Blades Dull - Mike Brubacher - 08-19-2020
Great posts Rick and Grepper so thank you very much. Oxidation certainly affects the edge sharpness of razor blades but there is little reason to believe other than that all known dulling factors likely enter the picture at some time or another (and perhaps some unknown ones as well). A local guy here began selling a product nationally that was designed to increase the usable life of disposable razors. It amounted to nothing more than a small container filled with green liquid. Rather than tossing your razor down on the sink counter after shaving, you tossed it in the liquid and left it there. I suspect that he was disposed to the oxidation theory as well. A local TV station tested the system/product and the TV testers seemed to agree that the liquid had significantly extended the usable life of their razors. Don't know if the guy enjoyed much financial success or even if he and his product are still around. Maybe Gillette paid him a million bucks just to go away.
Personally, I've got bigger shaving fish to fry. Our new Labrador pup, Nelson, has developed an affinity for most things plastic. He snatches my disposable razors off the counter and my wife's out of the shower - then destroys them. His timing is impeccable and he can strike before you're done drying your hair. He's managed to pop the blades out on two occasions but hasn't consumed them. We don't worry too much about the sudden increase in the cost of grooming but are concerned about the price of a trip to the emergency vet. Besides - the little guy has really grown on us. We don't want him to commit hari-kari before he's even a year old.
RE: How Razor Blades Dull - blgentry - 08-20-2020
In no particular order:
Mineral oil, in a little container, is something some people keep their shaving razors in, specifically to combat corrosion. I'm told it works well, but I've never bothered.
My DE razor blade of choice, Gillette Silver Blue, loses it's crisp, yet smooth, feel after 6, 7, 8 days of use. Testing with the BESS tester, they actually seem to get SHARPER after this time period, yet they do not shave as well. GSBs are platinum coated (I think). I theorize that the coating is what is wearing away, revealing a "not as smooth" steel edge, which is marginally sharper than the coated edge. It's no problem either way: GSBs cost $0.18 in quantity, so I just throw them away (in a blade safe) after they don't cut as well any more. My razor blade cost per year is $10 or less.
DE shaving isn't for everyone, but I like it a lot. Mike, you might consider it. DE razors (the part that you hold in your hand) are typically metal and not something that your new dog would probably go after. Buy once, cry once.
Brian.
RE: How Razor Blades Dull - Mike Brubacher - 08-20-2020
That's not a bad idea Brian and particularly in view of the fact that we have enough safety razor ammunition on hand here to last several lifetimes. When I was first considering venturing into this business I was perusing the straight razor forums and saw the term "harsh" used to describe a bad shave. The term interested me because I had no concept of what a "harsh" shave was. Since then, my understanding is that a harsh shave is delivered when the edge either loses (or never had) a polished finish. It's sort of like polished vs. toothy in knife edges. Both may be sharp but they perform differently in different tasks. I wonder if you are describing a "harsh" shave as well in your experiences. Could be due to coating loss or perhaps some chipping of the edge, through use, has occurred and maybe both.