CRK Sebenza 25 pivot & and orange juice

[kwakster]

The owner of this Sebenza 25 religiously eats an orange every day at breakfast; the fruit is cut with the knife into several parts, and afterwards the knife is rinsed under a hot tap.
Over time the orange juice slowly found it's way into the pivot, making the action sticky and the knife slow to open.
Last time the knife was opened was in the first week of March 2016, and today i opened it again.

This is how the S35VN blade surface looks after i cleaned off all the sticky gunk, first with a soft tootbrush and some dishwashing liquid, then with some nail polish remover, and finally in an ultrasonic cleaner (to get the last debri out of the pits)
Given enough time the citric acid in the orange juice clearly seems to damage the S35VN steel, and in some spots the pitting is deep enough to trap the point of a needle.
Pics can be clicked 2 x for a bit more detail.

[Aloha]

Interesting.

[ducttapetech]

Very interesting.

[Aloha]

I would have though S35VN would be way more resistant to an oranges PH level.  I would have also thought that rinsing the knife would at the very least dilute the oranges PH limiting or eliminating the damage. 

I typically use a fixed blade to cut such items, acidic.  I am able to wash thoroughly afterwards.  Could it be he wasn't as fastidious?  I wonder if the lubricant somehow trapped some of the oranges liquid? 

     

 

[SteveC]

Defective steel perhaps, I find it hard to believe that OJ would do that   

[Aloha]

Certainly not scientific however the salt water concentration I'd think was higher than orange juice.  Considering they left on the salt water while he rinsed off the orange juice in hot water. 

[AimlessWanderer]

This is why I don't use folders with food stuffs. They are so much harder to clean and maintain

[pfrsantos]

Defective steel perhaps, I find it hard to believe that OJ would do that   

Of course not!

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[kwakster]

The lube i used on this Sebenza was 85 weight Nano-Oil on the washers and a few tiny drops of 10 weight Nano-Oil between pivot & blade.
This provides the user with a little easier "hydraulic" opening & closing action compared to CRK grease and also lasts a long time.
I always set the pivot tight enough so there isn't even a hint of blade play, yet the blade falls closed on it's own once the lockbar is held aside with my thumb.

What may have happened is that the citric acid in the oranges over time first slowly dissolved all or most of the oils and then proceeded to act as an electrolyte between the washers and the blade, thus slowly etching those black pits into the steel.
This was suggested by a member on the German forum, and i think he could be on to something.
Maybe the holes in the washers played a role too by holding the citric acid longer than closed washers would have done, but that is just me speculating.
BTW: just before disassembling & cleaning the knife still opened & closed comparable to one that has dried CRK grease in it's pivot.

[Sparky415]

   

  

[captain spaulding]

I may be in the minority but this does not really surprise me especially given the time frame between disassembling and thoroughly cleaning the knife. Given how corrosive acidic things such as fruits can be I would basically expect this to happen even with S35VN. The severity of the pitting is the only thing that slightly throws me off but again given the time and acidity combined with the theory of the electrolyte effect between the blade and washer and it makes perfect sense.

[Syph007]

Oh thats not a bearing knife, it has washers adjacent to the blade?  What is the washer material?

Looks electrolytic to me.  If there was debris in there it would have made curved gouges not pits. 

Interesting for sure. 

[powernoodle]

Patient: Doc, it hurts when I do this.

Doctor: Well don't do it then!

Maybe its time to keep that pivot dry.  Who knows - rinsing it with water every could factor into it as well.  But you're right, most likely its the OJ.  I'm strange, but I've never used a folder on food, and never let anything get into the pivot.  It would creep me out knowing that there was mung in there.

[kwakster]

I don't know if CRK grease would have done a better job protecting the blade from the orange juice, but my guess is that most lubricants would have been dissolved by the citric acid, especially given the repeated & prolonged exposure to it.
From testing a few years ago i've learned that the citric acid in just one lemon was enough to corrode the sharp apex away from the edge on a ZDP-189 kitchen knife in about 15 minutes after cutting the lemon into slices and not washing or rinsing the blade afterwards.

In a corrosion test done on a few forums a while ago by member Loonybin a product called Eezox proved to be the clear winner, while Nano-Oil finished somewhere in the middle of the pack, and CRK grease wasn't tested.
On the subject of lubricating properties however (which weren't part of that specific test) Loonybin stated that 5 weight Nano-Oil was the best lubricant he had ever come across.
Personally i like & use all of the Nano-Oil products, from the 5 weight to the Nano-grease, and so far i've found nothing better.
I even use Nano-Oil products as additives in the both the engine & transmission of our 11 year old Toyota, and fuel consumption changed from +/- 1 in 12,5 km to +/- 1 in 15 km.
I don't think that the Nano-Oil itself played a part in the corrosive reaction on this Sebenza, nor have i ever found this to be the case when using it for any other applications.

The Sebenza is now put together again using only the 5 weight Nano-Oil, as besides very good lubricating properties this almost watery thin version also has very good penetrating properties, something i think could be of benefit with this degree of pitting in the blade steel.
The knife action feels like new again, and the pivot pitting doesn't translate into any tactile feedback.

Something to consider when using Nano-Oil is that although the various oils themselves do take part in the initial lubrication process, their main function is to act as a transport mechanism for the nano particles, which are responsible for the more long term lubrication once they are embedded in the phosphor bronze and the blade steel.
To get maximum embedding i re-assemble the knife with a few drops of oil on washers & pivot area, then proceed to overtighten the pivot, open & close the blade several times (so while the blade feels a bit stuck), and then open the pivot screw just enough so the blade falls closed when the lockbar is held to the side.

[kwakster]

From the same owner, a small Sebenza made in 2014.
Disassembled & cleaned for the last time in January 2016, and put together using 85 as well as 10 weight Nano-Oil.
Has been used to cut a lot of cardboard boxes as well as 5 oranges a day since then, and was rinsed afterwards under a hot tap, never disassembled.

Just took it apart for the first time again.
Corrosion on the pivot area of the blade is less than on the Sebenza 25, but the bushing has suffered quite a lot.
(pics can be clicked 2 x for a bit more detail)