CRK Sebenza 25 pivot & and orange juice

Wavicle said:
Question to the kwackster: Was there any damage or impact to the titanium? I suspect the stainless pivot hardware was affected similarly to the blade.
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There wasn't any damage to the titanium handles or the steel pivot.
 
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kidcongo said:
A couple questions I have:

What lube were you using?
Were you running the pivot very loose....IE with a bit of a gap between the blade and washers?

This is really the first I've ever seen of any serious corrosion issues after a few years on this forum.
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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.
 
kwackster said:
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.
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Thank you for the reply! Not to re-kindle the nano-oil vs grease debate, but I wonder if the CRK grease would have prevented this? It makes sense that dissimilar metals will have galvanic corrosion when soaked in acid. You are essentially making some kind of battery. Maybe one of the properties of the Christolube grease is to prevent this corrosion. It is mentioned in their literature geared towards the diving community that the grease was developed for. Maybe the nano-oil in some way facilitated the reaction?

Having seen this, right or wrong, I am definitely sticking with the CRK grease to play it safe as I also cut a lot of fruit. Chris Reeve is a smart guy, and maybe his search for the right product to lube his knives he included corrosion tests.

How does the knife feel once you put it back together?
 
I also have a drawer full of decent kitchen knives, but I do enjoy using my CRK's so much , that I reach for them whenever I can. Let the chips fall where they may!
 
A good word to look up and research is passivation. Citric acid is sometimes used for this process.

Many years ago, I machined a grill that resembled a shroud on a fan. Solid 420 stainless steel. Took about 2 days to machine and was quite intricate.
Machine shops will generally send parts out for secondary or even tertiary processes..Coatings such as anodize, nickel plate etc. One of the processes is passivation. This part was sent out to be passivated over a long weekend. Apparently, they forgot about this part in the tank..What should have taken about 2-4hrs, went days. What we got back was a part that looked like it had sit at the bottom of an ocean for many years. Pitting was horrible.
I got the opportunity to make an extra part for this.
 
@Kidcongo:

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 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.
 
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Fruit knives by Sheffield makers had silver blades to avoid the corrosion of the citric acid. I never use my carry knives for food prep.
 
Per CRK customer service, the Sebenza needs grease for lubrication and PROTECTION! Thats why they say you must use grease and occasionally must take it apart and regrease. Frequency of take down depends upon use, they say once a year to be on the safe side.

CRK also says that rinsing your knife or washing it with soap and water is recommended when cutting nasty things. You don't need a full take down after each nasty job.

The Sebenza is functionally an engineered system, not using the correct materials or doing required maintenance will damage a Sebenza just like your car.

I cut everything with my sebenza, including fruit, follow the CRK instructions and have no oxidation, pittnig, etc. with my knife.
 
I cut fruit with my large Insingo all the time. When using it on oranges, I pinch the blade about 1.5" to 2" from the tip and cut the skin in sections so I can easily peel it off. Then I like separating the orange pieces by hand in sections naturally (naval oranges). That choked-up position gives me better control, and protects the pivot area from any squirting juice, too. I've never gotten juice into the pivot. When I slice apples, tomatoes avocados and other fruits, I use the entire cutting length, but have also never gotten juice or gunk into the pivot area. I always rinse the blade off after use on foods, especially acidic foods.

Jim
 
I did look up "passivation". Very interesting stuff.
After doing casual research, I began to think that grease or lubricant may not be good for stainless steel, if you don’t disassemble a knife often.

Stainless steels possess a layer of "passive" chromium oxide, which makes them stainless (by protecting iron from oxidation). This thin layer (said to be 3 nm thick) can be stripped off mechanically (scratches) but can be regenerated as free chromium on the metal surface reacting with oxygen molecules in the air. Citric acid seems to be used to remove free iron on the surface in the passivation process, thereby facilitating the formation of a clean chromium oxide layer, while this requires extensive rinsing to remove the acid and to prevent redepositing of iron.

Looking at the OP's images, the rust developed only where potential scratches occur, i.e. the contact sites with washers. They made me think that lubricants may prevent scratched metal surfaces from regrowing the passive layer by blocking oxygen from the air. As pointed in the above post, citric acid may dissolve iron from the unprotected surface (etching). The surface lacking the chromium oxide layer is prone to rusting as well. Of course, rusting also needs oxygen, but this reaction seems to be facilitated at low pH. So if you have citric acid dissolved in the lubricant in the pivot (it is soluble in oil to some extent), the scratched surface might be more vulnerable to both etching and rusting with lubricant than without.

Just an opinion of a non-chemist. Any inputs from real experts would be great.



Miso
 
Miso,

I'm no expert, but that's an accurate description of the process. Smith and Wesson for many years "passivated" their stainless handguns. The surface had a milky finish and was more resistant to corrosion. They used nitric or citric acid.

While it's certainly possible the citric acid removed some of the chromium, the stainless stock beneath is fairly resistant to rust or corrosion. S35VN is about three times as resistant to corrosion as 440C.

I don't think CRK would recommend the grease without sound reasoning.
 
A huge number of CRK owners are also users, and many of those are cutting fruit with their knives. If this was a common problem we would have seen it here before, considering the thousands and thousands of CRKs carried every day, worldwide. I can't recall any issues like this in the few years I've been lurking and contributing here. Myself, I cut fruit, including oranges, all of the time with my CRKs, and hardly obsess over washing them. I even use my CRKs at the beach, and don't take them down afterwards. I've not experienced anything like this, so some othe factor is aggravating this particular issue.

My guess: Either nano-oil is bunk in the knife and evaporates out of the pivot leaving no protection, or Nano oil reacts with the orange juice to allow galvanic corrosion to take place between the metals, becoming some sort of electrolyte. I work in shipyards, and the localized deep pitting looks exactly like the galvanic corrosion you get on bronze and stainless parts (dissimilar metals) in presence of seawater on a ship. Maybe since the CRK grease is a dry film, it doesn't allow the electrolysis to take place as it does with a fluid like nano-oil. Unlike some knives that use bearings or teflon, CRKs have two different metals in contact with each other, which will create a weak battery if you add acid.

I dunno.......but my advice is steer clear of any "nano" products and stick with a proven system if your cut any fruit with your crk.
 
JB in SC said:
Miso,

I'm no expert, but that's an accurate description of the process. Smith and Wesson for many years "passivated" their stainless handguns. The surface had a milky finish and was more resistant to corrosion. They used nitric or citric acid.

While it's certainly possible the citric acid removed some of the chromium, the stainless stock beneath is fairly resistant to rust or corrosion. S35VN is about three times as resistant to corrosion as 440C.

I don't think CRK would recommend the grease without sound reasoning.
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Stainless typically means resistance to oxidation, but doesn't necessarily mean it can't oxidize. Many stainless steels have varying degrees of resistance to oxidation with the highest resistance to oxidation going to 17-4 IIRC.. Nasty stuff..I hate machining it, but then again..it's not the worst material to machine.
I know that you are aware of this, otherwise, we wouldn't be discussing corrosion resistance. The reason I brought up passivation is because that is essentially what is happening with fruits like Oranges, lemons and limes as well as a host of others.

Here is a snippet of an article- Ironically, it's from a machining publication that I subscribe to.

"Laboratory tests have indicated that citric acid passivation procedures were more prone to “flash attack” than nitric acid procedures. Factors causing this attack included excessive bath temperature, excessive immersion time and bath contamination. Citric acid products containing corrosion inhibitors and other additives (such as wetting agents) are commercially available products that reportedly reduce sensitivity to “flash attack”."

Source;
http://www.mmsonline.com/articles/how-to-passivate-stainless-steel-parts

Now, passivation is a solute of lower concentration of citric acid..Likely, the fruits concentrate in Lemons and Limes, higher than Oranges..is added over time and repeated without proper maintenance doesn't help.
I do remember that Chris specifically named acidic fruits needing more vigilance..but I will have to contact Tim and Anne for this information.
 
bhyde said:
Stainless typically means resistance to oxidation, but doesn't necessarily mean it can't oxidize. Many stainless steels have varying degrees of resistance to oxidation with the highest resistance to oxidation going to 17-4 IIRC.. Nasty stuff..I hate machining it, but then again..it's not the worst material to machine.
I know that you are aware of this, otherwise, we wouldn't be discussing corrosion resistance. The reason I brought up passivation is because that is essentially what is happening with fruits like Oranges, lemons and limes as well as a host of others.

Here is a snippet of an article- Ironically, it's from a machining publication that I subscribe to.

"Laboratory tests have indicated that citric acid passivation procedures were more prone to “flash attack” than nitric acid procedures. Factors causing this attack included excessive bath temperature, excessive immersion time and bath contamination. Citric acid products containing corrosion inhibitors and other additives (such as wetting agents) are commercially available products that reportedly reduce sensitivity to “flash attack”."

Source;
http://www.mmsonline.com/articles/how-to-passivate-stainless-steel-parts

Now, passivation is a solute of lower concentration of citric acid..Likely, the fruits concentrate in Lemons and Limes, higher than Oranges..is added over time and repeated without proper maintenance doesn't help.
I do remember that Chris specifically named acidic fruits needing more vigilance..but I will have to contact Tim and Anne for this information.
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Interesting article, thanks!

All stainless materials will corrode at some point, about all they do is slow down the process :) The CRK FAQ's (as linked in an earlier post) recommend more frequent cleaning when used for acidic fruits, et al.

17-4 PH can be gummy, according to my machinists friends. I imagine it becomes easier if it's hardened. Machining is still an art, CNC or not.
 
this isn't rocket science.... this is common sense.... if you subject your knife to an acidic or otherwise corrosive substance you should take a minute or so and wash it clean .... the fluorinated PFPE grease will help prevent corrosion as well

the below statement taken from CRK FAQs

"It's good to clean your knife from time to time and make sure there is no built up of dirt around the pivot and lock area. If you use the knife around a particularly corrosive substance - acid food (oranges, tomatoes, etc), blood, salt water, be sure to wash it off in fresh water and lubricate the pivot.

We recommend using our specially formulated Fluorinated Grease or a high quality gun oil to lubricate the pivot - you should only need a drop or two."
 
JB in SC said:
Interesting article, thanks!

All stainless materials will corrode at some point, about all they do is slow down the process :) The CRK FAQ's (as linked in an earlier post) recommend more frequent cleaning when used for acidic fruits, et al.

17-4 PH can be gummy, according to my machinists friends. I imagine it becomes easier if it's hardened. Machining is still an art, CNC or not.
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Thanks for pointing out that the information was provided earlier. I will skim posts and not really get all the information provided. Need to pay more attention.

Yes, 17-4PH is gummy. Gummy to a machinist, for those that are not aware, is that it doesn't like to "break a chip". Imagine a tangle of razor wire that you have to continually remove. Kovar, Invar..a few other materials that are on my um....list.

Anyway, all this is speculation based on some of my past experiences.. Educated guesses if you will.
 
ti lock said:
this isn't rocket science.... this is common sense.... if you subject your knife to an acidic or otherwise corrosive substance you should take a minute or so and wash it clean .... the fluorinated PFPE grease will help prevent corrosion as well

the below statement taken from CRK FAQs

"It's good to clean your knife from time to time and make sure there is no built up of dirt around the pivot and lock area. If you use the knife around a particularly corrosive substance - acid food (oranges, tomatoes, etc), blood, salt water, be sure to wash it off in fresh water and lubricate the pivot.

We recommend using our specially formulated Fluorinated Grease or a high quality gun oil to lubricate the pivot - you should only need a drop or two."
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My question is whether grease or oil really prevent corrosion on stainless steels, especially when they are contaminated like in the OP’s case.

If a knife can operate without any lubricant, you can easily wash off contaminants and do not prevent air to get in to the pivot area for the steel to form a new chromium oxide layer if necessary. In this sense, traditional knives without washers or knives with polymer washers (in stainless steels) may be more suitable for acid food, as they can run without lubricant and without getting scratched in the pivot area.

Just my 2 cents.



Miso
 
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