Hi Henry,
It's strictly a mechanical thing. As I explained, the rapid vibration of a diesel can be so violent that millions of low pressure bubbles form at the boundary of the water jacket. These eventually implode like tiny shaped charges, taking small pits of iron out of the jackets. More correctly, it is actually the fluid coolant rushing back in with such violence to refill the void, that it takes a hunk of metal out. The anti-cavitation additives are intended to increase the coolant's resistance to this by lowering its vapor pressure. It's debateable how effective such additives are. It's always much better to cure the causes of the vibration.I also should mention stress related corrosion. Steel, as I explained, is made up of a crystal structure, and the strength of it is related to the strength of the bond between adjacent crystals. When you harden steel, you change the physical shape and form of the crystals, and the way that they are packed in together. The harder the steel, the harder the individual crystal
s are stressed to hold on to each other. Soft or mild steel is fairly "relaxed". Since hard steel is closer to the threshold of the crystals' ability to hold on without slipping, it tends to be more affected by corrosive processes. Very hard steels are more "glassy" and tend to develop intergranular cracks easier then the "gummier" soft steels. The tense state of the components in hard steels make it much more reactive, as it exists at a much higher energy level. That's why hard steels rust easier, and why ferrous metals rust worse where they are bent or formed. A bracket, for example, will always rust faster at any bend or drawn area. Cha
nces are great that it already has millions of microscopic networks of tiny cracks from the forming processes. Mild steels on the other hand, will not rust as fast in cold worked areas, but in a more uniform manner. The closer you get back to the mother iron, the less you have to worry about rust. The more noble and high tensile your steel is, the more it is affected. Again, this is oversimplified, but it does satisfy casual curiosity about why rust behaves as it does.
Cheers!
CJ
In a message dated Fri, 12 Oct 2001 7:36:15 PM Eastern Daylight Time, "ygmir" <ygmir@onemain.com> writes:
> Hi,
> I thought cavitation on diesels was from an electrolytic action. They sell
> an additive for the radiator that is supposed to help this. Or, is this
> something on the other side of the cylinder?
> Henry
This archive was generated by hypermail 2b29 : Fri Dec 07 2001 - 00:36:25 PST