Ball Burnished Cases

enekoizagirre · Jan 15, 2012

Hi there,

here are some pictures of my newly ball burnished cases. Pretty good result (maybe a little too shiny but it's OK), no material is removed and it has a shot peening effect on the cases.

Hobot · Jan 15, 2012

Looks like about the best protective decorative treatment that could be done
to ole porous rough shod castings. Hurts a bit to look at, we all like that!

swooshdave · Jan 15, 2012

Did you mask off the sealing surfaces?

bwolfie · Jan 15, 2012

Where did you have this done and how much?

Hobot · Jan 15, 2012

Its a good process to know about for reloading brass too.

Detailed in depth here
http://www.journalamme.org/papers_vol22_2/1113.pdf

cmessenk · Jan 15, 2012

enekoizagirre said:
Pretty good result (maybe a little too shiny but it's OK...

Very Nice....now the fun part is keeping them that way

enekoizagirre · Jan 15, 2012

No masking needed, it was made here in Spain, www.baster.es (web is in spanish). Engine cases, gearbox cases, head and primary inner case for 100 euros.

Hegel · Jan 16, 2012

Shiny, shiny! 8)

I wonder if there's some where here in the U.K that does a similar process?

How come they missed between the fins?

Tintin · Jan 16, 2012

Hegel said:
I wonder if there's some where here in the U.K that does a similar process?

Probably hundreds, it's not really special and many machining companies offer this kind of finishing. The process is know as ball burnishing, trowalising (named after the company TROmmel-WALther), tribofinishing, vibratory finishing, tumble finishing, whatever ... and is an industry standard. As usual you can go over the top and apply a chemically enhanced version known as Isotropic SuperFinish (ISF). NASCAR does that on complete blocks, mainly to aid oil drainage in the V.

How come they missed between the fins?

It depends on the size of the grinding "stones".

However I consider this mod to cooling fins pretty useless, maybe even deadly for the engine due to the surface reduction and the aerodynamic influences (boundary layer etc.). It looks good but technically speaking it is a change for the worse in the case of the head. On the housings, hm, yes, okay ...

Tim

rvich · Jan 16, 2012

How is this different than shot peening or tumbling?

enekoizagirre · Jan 16, 2012

However I consider this mod to cooling fins pretty useless, maybe even deadly for the engine due to the surface reduction and the aerodynamic influences (boundary layer etc.). It looks good but technically speaking it is a change for the worse in the case of the head. On the housings, hm, yes, okay ...

surface reduction? I was told there was no dimension change, so why should any surface reduction happen?

Hegel · Jan 16, 2012

Thanks Tim

I have to have a look around for when I put the 850 cases together

It depends on the size of the grinding "stones"

Ah, gotcha. Another media type first to clean between the fins then.

<edit> I wouldn't have thought there'd be much difference in head cooling (Not that I'm an expert, or anything), with this finish? Considering some folk spray the head black, reducing the turbulence across the fins, etc. I'm not trying to start a bun fight...Just like to know is all :wink:

Skyguyz · Jan 16, 2012

, maybe even deadly for the engine due to the surface reduction and the aerodynamic influences (boundary layer etc.).

Tim

Aerodynamic influences/boundary layer? Do explain?

Tintin · Jan 16, 2012

enekoizagirre said:
surface reduction? I was told there was no dimension change, so why should any surface reduction happen?

Erm, that's a joke, right? Why do you think it is shiny by now? :shock:

What happens is that the peaks are either plastically deformed or removed - depending on the actual process in the tumbler - and of course this is a dimensional change, but we're talking about µm here. "No dimensional change" in this sense applies to engineering dimensions, tumbling doesn't remove enough material to alter usual tolerances so even after several hours of trowalising a part that fit the specs before will still fit them.

The thing is that heat transfer depends on the surface roughness and for the case of an air-cooled fin the bigger (aka more rough) the surface is this is usually better.

Tim

Tintin · Jan 16, 2012

Skyguyz said:
Aerodynamic influences/boundary layer? Do explain?

A rough surface will create a larger boundary layer than a smooth one - and heat transfer happens mainly in the boundary layer. In order to be able to work properly a cooling fin needs enough aera to transfer the heat and enough boundary layer volume to dump the heat into. Both is changed by polishing and IMHO the change is for the worse.

Tim

Skyguyz · Jan 16, 2012

Tintin said:
Skyguyz said:

Aerodynamic influences/boundary layer? Do explain?

Click to expand...

A rough surface will create a larger boundary layer than a smooth one - and heat transfer happens mainly in the boundary layer. In order to be able to work properly a cooling fin needs enough aera to transfer the heat and enough boundary layer volume to dump the heat into. Both is changed by polishing and IMHO the change is for the worse.

Tim

Click to expand...

The fins on a Norton are so rough to begin with. and ball polishing them slightly as to have an actual aerodynamic effect is remote. The boundary layer in aerodynamic terms is relative to the surface and increases rapidly with distance from the surface and the flow is laminar. I question the real possibility that polishing the fins on a Norton will change the the boundary layer smoothness as to have an actual aerodynamic effect that is worth mentioning.

Just saying.

enekoizagirre · Jan 16, 2012

I agree with Skyguyz...

Tintin · Jan 16, 2012

Skyguyz said:
I question the real possibility that polishing the fins on a Norton will change the the boundary layer smoothness as to have an actual aerodynamic effect that is worth mentioning.

Judging by the visual difference (and I've seen heads which have been polished far more than this one and an ISF treatment will end up in a far smoother surface again) I don't agree about it not being worth mentioning - but as far as polishing parts is concerned we obviously have different opinions anyway.

Tim

slimslowslider · Jan 16, 2012

As far as optimising heat transfer, I reckon you do not want any boundary layer at all, you want turbulent flow at the least.

http://en.wikipedia.org/wiki/Turbulence

Skyguyz · Jan 16, 2012

Tintin said:
Skyguyz said:

I question the real possibility that polishing the fins on a Norton will change the the boundary layer smoothness as to have an actual aerodynamic effect that is worth mentioning.

Click to expand...

Judging by the visual difference (and I've seen heads which have been polished far more than this one and an ISF treatment will end up in a far smoother surface again) I don't agree about it not being worth mentioning - but as far as polishing parts is concerned we obviously have different opinions anyway.

Tim

The resulting boundary layer separation in this case is nil. If the fins were a airfoil shape then the case would have merit. The fins here are parasitic drag producing and the laminar flow is turbulent at best. Just my opinion.

*The difference of opinion of polishing parts for aesthetics is another topic and doesn't apply, agreed

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Ball Burnished Cases

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