Impeller Shafts - Why Ceramic?

[Dodders]

Just an idle thought - I was looking at buying a spare impeller shaft for my Eheim external filter yesterday, just in case I manage to snap it whilst cleaning. I found myself wondering "why are these ceramic (and snappable), and not stainless steel (unsnappable). Anyone got any ideas?

 

[Tizer]

because, believe it ot not ceramic impeller shafts will not wear as quickly as stainless steel and has a very high temperature resistance. A metal shaft will get very very hot. I've used a small round lolly stick in the past, it lasted about a week but bought me time until i could get to a shop

 

[Dodders]

Thanks, that makes perfect sense although I had imagined that heat wouldn't be an issue given the pretty enormous built-in water cooling system!

 

[nurglespuss]

Yep its all heat tolerance.

Have you ever got a bit of flexible/stiff metal wire and bent it back and for a few times? it gets ver hot very quickly!

Its also why they use ceramics in expensive brake systems, and in the re-entry tiles on the space shuttle ;P

 

[raptorrex]

interesting question this!

i cant see heat being a problem, its water cooled. lol.as SS use used in many filters (successfully) that one has no legs.

but ceramic is low friction and does not corrode. both mean, with care, the shaft will last far longer than an SS item. its also, probably, far straighter than SS, and less effected by heat expansion adding further to its reliability.

 

[nurglespuss]

Ceramic is low friction but running at high speed, in a very small shaft cross-section, hence the neccesity for being very heat tolerant, even though water cooled (water cooling isn't that efficient anyway).

 

[moochy13]

these are extremely easy to snap.

dont ask me how i know.

 

[Tizer]

If water cools the hot metal, whats going to cool the hot water...

 

[StandbySetting]

Ceramic generally has a higher Young's modulus than Stainless steel so will cope better with stresses and strains before actually fracturing, and is fairly cheap and easy to replace, the only friction that will occur is between the impeller, shaft and the magnet at the end with water, so I doubt heat is one of the reasons, as the shaft is held in place using a magnetic field.

Not all impellers have ceramic shafts anyway, some of the older Koralia models have Stainless Steel shafts.

 

[raptorrex]

Ceramic is low friction but running at high speed, in a very small shaft cross-section, hence the neccesity for being very heat tolerant, even though water cooled (water cooling isn't that efficient anyway).

the cross section of a ceramic saft is the same as that of an SS shaft. indeed, an SS shaft can be used as a backup.( some even fit Eheim shafts in filters made by others) as has been said, SS is used by many makers. heat is not even relevant to SS or ceramic.