Just so no one misunderstands my last post, the cleaning process I was referring to is not like sand blasting, or any other type of blasting. It is more like gentle tumbling, but with iron or steel shot. It is less severe than shotblasting or peening, and will not affect your metal's qualities. The cleaning removes no metal, and will not require you to go to an undersized bearing, unless the journals are severely pitted. A light polishing is all that they will need. The rest of the crank will come out as new.
On embrittlement, cast iron is simply much more resistant to such chemical intrusions. Diesel blocks suffer from cavitation damage on the interior sides of the water passages, due to high energy impacts of steam bubbles in the coolant. This process, which can pinhole and ruin a block, is NOT related to embrittlement. It is strictly a mechanical problem, not a chemical one. It happens because the rapid oscillation of a running diesel actually pulls the iron away from the coolant faster than the coolant can move, so a bubble of vacuum or rarified steam will form. When this implodes, it actually removes a divot of iron from the block. Continuous pitting will pinhole the walls of the water passages. It is not unlike cavitation damage to pump impellers and boat propellors.
Under the right conditions, such as high pressure steam boilers, cast iron will suffer from embrittlement in time, but not as badly as steel. Put simply, it has to do with enegry levels, and relative structure of the metal. Cast iron is less "organized" and less homogenized than steel, so it is less affected by all corrosion processes. Raw pig iron is even less so, and it is common to find pig iron sprues in the ground near the sites of old blast furnaces, centuries after the furnaces are gone. After all that time in the ground, they are little affected, and sometimes not even rusted. Silica makes the iron more resistant, and a lot of pig iron is very high in combined silica. The old dodge engine blocks were made from a very high silica cast iron, and are almost indestructible. I always felt the the best of these were the ones made at the Windsor plant.
Comments anyone?
CJ
In a message dated Fri, 12 Oct 2001 4:33:08 PM Eastern Daylight Time, King <landy@pacificcoast.net> writes:
>
> >It's true that a crankshaft will suffer from this problem, if acid dipped
> or tank treated in strong caustic. The degree of damage depends on the
> temperature, the pressure, and the structure of the steel itself.
> >CJ
> >
> Thanks for the enlightenment.Interesting bit.I use to have a friend who
> worked for the airlines in the mechanics section and he did this sort of
> thing for me once in awhile but he doesn't work there anymore.He said they
> used some sort of wet blasting.
> A though on the above-caustic doesn't remove rust and most shops use it for
> cleaning.Why is it you never hear of any block failure due the caustic soaking?
> Andre
This archive was generated by hypermail 2b29 : Fri Dec 07 2001 - 00:36:25 PST