polished rods; maybe not.

[Lazy JW]

Smitty,
I didn't mean to imply that there is no benefit to cryo trearment, only that the benefit appears to be quite small. The boys who are really into precision benchrest rifle shooting are willing to go to great lengths to gain any advantage, however small it may be. Also Nascar engine builders will do a lot to gain a little. As a saw filer trying to manage my department to make a profit for the company, the cost/benefit ratio just wasn't enough to get me to spend the owners money in this fashion.
Joe

 

[Anonymous]

Sitting here the morning of The Glorious Fourth, before I walk out for some coffee. So far, it's delightfully quiet. There's a wooden boat festival on Lake Union I might take in . . . .

"Knife-edge" cranks? The only crank I've seen was streamlined, with a semi-airfoil shape. Contrary to popular belief among racers and others, you don't need or necessarily even want a sharp leading edge for good airflow. If you wanted to reduce the drag of a one-inch wide crank counterweight, all you need to do to the leading edge is put a 1/4" radius on each corner. The trailing edge takes a lot more grinding and fairing-in, but you still don't have to taper it to a point or even close to it. Oh, you guys surely know all this, but you sure see a lot of misdirected attempts at streamlining when you go to the races, don't you?

I'm just a dumb welder, so I don't read engineering studies (can anyone read the writing of engineers??). But in the dumbed-down articles I read about cold-stabilization, no explanation was given on how/why it works. Indeed, it seemed that nobody knew, which would explain why such varied results were seen and why there was such controversy. I supposed it might have to do with a residual transformation of martensite. But some parties were reporting mechanical improvments even in non-metals! Maybe the simple act of getting a material cold, without any intension of getting phase transformations,etc., will generally have a beneficial stress-relief effect when the material is brought back up to room or working temperature. We've all heard about how Packard and others would put their green block castings outside for a year of aging in heat and cold of the northern Midwest before machining. But stress-relieving doesn't account for Northrop reporting 20-30% less wear on cryo-treated drillbits.

 

[StrangeRanger]

I think it works like this: the cryo treatment causes the part to shrink, breaking apart the gain structure into smaller and more random grains. As the part returns to room temperature it expands to it's "normal" size but the now randomized grains are compressed slightly giving a more homogeneous part, with fewer internal stress risers and a slight increase in strength from the preload. In parts like connecting rods, this slight compressive load will reduce the magnitude of the reversed stress cycle which greatly increases fatigue life.

At least that's the theory. As to whether it actually works???