(hand raised) stupid question time!

[jonwelder]

Dear Ed, in a question about quench oil temperature, you said you heated Parks oil to 130. and cracked the next 3 blades..... I gotta know,,,, what was happening and what went wrong? I smell a lesson I'd rather learn the easy way than the hard way!! Thanks! ... Jon

[Ed Caffrey]

The lesson is that Parks 50 is a MUCH faster quench than what I had thought. It should be used at room temp.
Prior to the Parks, I had (and still do) used Vet grade mineral oil, so when I first started with the Parks, I went with what I knew (the pre-heat to 130F).....which obviously wasn't the right thing to do.

[jonwelder]

OH!! Now I understand!

Just for the record, and others info, here in the mid-west at grain elevators, mineral oil is sprayed on the grain when it's first brought into the pits and conveyors, to keep dust from flying around. It's poured out like water, so they really don't keep track of how much is used ect. SOOOOOO... I get my mineral oil for free, from friends who still work in the grain elevators!!!

[ron58]

OK,i'll ask this one.how did heating the parks crack the blades?it would seem that the cooler oil would crack them!?????????????????????

[Ed Caffrey]

Quenching in oil is counter intuitive..... You would normally think that cool/cold oil would cool the steel faster, when in reality it's just the opposite.

Whenever oil is cool/cold, and you place (as an example) a 1500+ degree piece of steel into it, the oil immediately surrounding the steel flash boils, forming a vapor pocket around the steel, which holds the heat in. When most oils are heated, it keeps the vapor pocket from forming, and allows the heat to dissipate more rapidly....and sometimes (as is the case with Parks 50) it allows the heat to dissipate too quickly. This causes the surface of the steel to shrink too fast, and the resulting stresses cause the cracking.

There's a lot of other things happening at the same time, but without getting too long winded, that's the simple way to explain it.

[ron58]

thanks ED,now with this parks oil you don't get the vapor pocket as with the other oils,and would you know why?

[Ed Caffrey]

Ron,

I can't give a specific additive or the exact reason that the vapor pocket doesn't form with the Parks, but my suspicion is that Parks 50 either has such a low viscosity that the vapor pocket cannot form (or minimally form), or one of it's ingredients is some kind of a "wetting agent" that inhibits/reduces the forming of the vapor pocket. Either way, in my experience, the Parks 50 works best at room temp. To qualify that statement, I will add that my shop interior temp never gets below 55F (where the thermostat stays set in the winter), but I've often wondered if the Parks were say 35-40F, if a person would have to pre-heat it.....just never have had the chance to test that thought.

[WBE]

You get a vapor jacket even with brine. It just doesn't last very long, and the salt almost instantly forms a protective barrier. In the case of room temp Parks #50 not cracking the steel, is because of the vapor jacket. The vapor jacket happens with any quench. It is the time it remains that determines the outcome, whether good or bad.

[ron58]

a vapor pocket or vapor jacket,are they the same thing?and if so i thought that's what you don't want to happen!

[WBE]

It's going to happen. What you want in most cases is control of it to keep it at a minimum, but in the case of Ed's experience, the oil was designed to be at it's best at room temp. If you read Ed's last post carefully, he said the Parks #50 has an agent that "inhibits" the vapor formation. it doesn't stop it though. Just inhibits. When he quenched in room temp #50 he got more vapor formation, slowing the cooling effect and reduceing thermal shock to the steel, than he got when he quenched in warmed oil. Heated oil cools faster because of less of a vapor jacket due to being thinner. There is a point where this becomes counterproductive however, when the oil gets hotter than around 150? it begins to retard the cooling speed due to the temp. When red hot steel goes into the oil, or water/brine, it does not make contact with the quenchant, until the vapor jacket disperses. If it were me, using Parks #50, and the room temp was much lower than 70?, I would warm to maybe 75?/80?.

[ron58]

thanks guys!

[jonwelder]

I guess I did not mean to start a long thread,, but for several years I've had this nagging question about quench oil: Does quenching oil, like mineral oil "wear out"??? In time or with use, does it stop working as a quench, and how would it effect hardening of the blades?