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Blakeo

Cyro treating RB Block?

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Has anyone here attempted to cyro treat a Rb block? I've seen a few build threads where guys suggest it, but never any results. 

MotiveDVD proved the Rb blocks are soft, cyro treating would help harden the blocks and make them less likely to crack between the bores. 

I've got my Rb25 series 2 block at the cyro treaters atm and will compare it when it gets back (hopefully this Friday)   

Rb25 series 2 block (untreated) : 238

 

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How are you going to compare it - do you have some kind of test available?

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Not sure being harder is the answer to stop cracking, be interesting to see your results

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Hardness != crack resistance.

It does correlate with wear resistance. Generally harder materials are less tough and more brittle. It's a cake and eat it too situation.

The reason RB blocks like to split is about how material is where, and the weak design features (where a little more bracing here and there would have made the block stiffer, even if they had cast it with cheese).

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Is that 238 number a test of hardness ?

If so which one ? Is it Brinell, Rockwell, Knoop or Vickers ?

My understanding of Cryo treatments is that it is a stress reliving process - cooling the metal down to a very low temp and bringing up to a very high temp over a long period of time, usually around 48 hours.

I believe this realigns the dendritic crystalline structure of the metals for greater rigidity and thus greater strength. 

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I think it is fair to say that cryo treatement is not about hardness. It is, at the minimum, about toughness, which is an engineering term.

I don't know if it is as useful on cast iron as it is on steels though. And there is much more anecdotal evidence that it toughens things like transmission input shafts and the like (ie, I cryo treated it and I haven't broken it yet) than there is really good materials lab measurements of what the mechanical improvements to parts actually are. It's getting better than it used to be, but I think it's still a little vague as to exactly what happens to the materials.

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I know that RIPS has built a number of tough RB30s which rev to 10,000 and more and make 1000 Kw without blowing up with a number of measures including bracing and grout filling - but I don't know if RB25/26 blocks differ radically from RB30 blocks.  The ideal solution seems to be Bullet billet blocks but at $14.000 they are probably not for everyone!

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RB30 blocks are weaker up the top because they are taller up there without any real additional bracing. The cylinder walls on RBs are not all that thick, the block deck is not all that thick. It's really just a fairly light casting in that area and its surprising that they do as well as they do. It's not surprising that they split when you push them too far.

RB26 blocks are broadly the same as 25 blocks in that area. Not as good as JZ blocks though.

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5 hours ago, KiwiRS4T said:

How are you going to compare it - do you have some kind of test available?

Yes I'm using a hardness tester using the Leeb rebound hardness test. 

 

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24 minutes ago, Blakeo said:

Yes I'm using a hardness tester using the Leeb rebound hardness test.

But note what I've said above. It's a bit like measuring the colour change and trying to infer a strength change. Not necessarily related, not necessarily related with a positive or negative coefficient. Just not the right measure of the change that you're looking for.

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Very interesting approach Cryo treatment of a block. I think every one will be interested to see the results - good on you for having a go. That said I'm really not sure how you can really measure / quantify the improvement. This is a pretty interesting read:

https://www.enginebuildermag.com/2017/03/big-chill-cryogenic-metal-treatment-benefits-may-not-visible-real/

One thing as previously mentioned is that the material definitely becomes more brittle. Another thing I picked up which I thought was interesting was the mention of completing any machining before the Cryo process, indicating a substantial increase in hardness. Whether this translates to a cast iron block not cracking as easily is yet to be seen I guess.

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Got the block back from the cyro treaters today. I tested the block, using the same tool as before. It tested as 242. I don't believe this is a big enough increase for it to be due to the cyro treating, could be more due to different testing temperature differences or slight tool inaccuracy. 

Time for full build to begin now :) 

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When you originally tested the hardness, did you run multiple tests and take an average? Or did you test multiple areas of the block and take an average? 

What I'm wondering is, is the 242 within the range of your original hardness testing? 

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4 out of 240 is well within the range of 6 tests in the same spot. These ball drop hardness testers are only so precise.

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