Tuesday, November 1, 2011

The Flat Tire: Off Topic

Well after much debate and secret vote, we've decided to start a new division here at the Flat Tire, called the Off Topic Department(OTD).
I mean some times things not bicycle related, or related to what ever the hell goes on around here comes up but never makes it to the Flat Tire pages but is sort of interesting anyways.
So every so often we'll have an Off Topic(OT) well topic(T), cause you know, it's difficult to come up with original material like every day.
If you know what I mean.
So anyways, today's Off Topic Topic(OTT) is a big bronze thingy:

I thought this was pretty cool cause it's not like every day you see a large propeller not attached to anything.
Most of the time these things are like underwater, something you never see but need if you want to make any progress travelling across a body of water.
These thingys are made of nickle bronze, which is different from the bronze I worked with which was silica bronze, what the difference is I guess is obvious.
I suppose the nickel is in there so the bronze doesn't corrode.
More on that later.
These humungasoid propellers were in the shop cause they ran over something:

As you can see the blade on top really took a karang somewhere, the bottom one got dinged too, but the blade on top is really messed up.
What happens is you get all sorts of vibrations and oscillations so you gotta straighten them back up.
Now this being bronze, it ain't so easy, it involves a lot of pounding and a lot of heat.
Anyways, the interesting thing I found was, and this is interesting, trust me, is that because of the damage, a strange thing happens.
Air collects around the shaft area, bubbles sort of hug the base of the blades causing oxidation:

Apparently some sort of hydrodynamic voodoo takes place that causes the air bubbles to stick to the blades thus causing that ugly stuff which must be welded up and finished off.
How do I know?
Well the other half of this twin screw(which turns in the opposite direction by the way) was there too, undamaged, and it showed little to no oxidation.
You'd think bubbles would have a hard time hanging around something spinning at like 2000 RPMs, but it does!
Or they do.
Or something.
You learn something new everyday!
Even if it is a bit off topic.
Nice propellers by the way, I wish I had one.
That's getting a bit off topic though.
Sort of.


Steve A said...

Cavitation is a different situation than corrosion. It is wear due to tiny bubbles, in this case in Hawaii; exploding on the part. It is a harmful relative of ultrasonic cleaning.

John Romeo Alpha said...

This cavitation phenomenon requires further field study. I am willing to spend significant time in various locations around Hawaii to collect data.

limom said...

Steve A, I'll take your word for it.

JRA, you can apply for a grant at the Flat Tire Science Division, Office of Esoteric Research(FTSD,OER).
I hear they're pretty loose with their cash.