Quite a few questions here while I was gone to the Blade show.
On how long the oil should last- as has been mentioned a good quench oil is designed for heavy use over time by industry and not change in its performance so a knifemakers level of production will not even register on the scale in comparison… however…. Industry also takes good care of that oil, and so can run thousands of parts daily over long periods and not see changes while a careless knifemaker can trash the oil in one use if he doesn’t take care of it. Keep the oil clean, do not flash it or introduce contaminants. Catching the oil on fire is about the worst and I can’t advise people enough that if they wish to edge quench a jug of canola or other alternative that you don’t mind replacing every time is probably the way to go. Keep the oil covered and clean when not in use as dust is bad but perhaps the worst contaminant is moisture. If you keep a good mineral based engineered quenchant clean and working in the temperature range it was designed for, it should last you many years.
The polymer has also already been well described here. It is a water soluble solution that allows you to use water without blowing your blades apart. It mostly acts to regulate the last part of the liquid cooling phase at and below Ms, but it also helps even the heat extraction in the higher parts of the cooling curve. The hassle, as has also been mentioned, is that it needs to be carefully and continually regulated to keep it in the correct concentrations for what you are doing. I can’t even keep the correct concentrations, due to evaporation, in my coolant/cutting fluid sumps of my machinery, my quench tank would drive me batty.
Please be careful not to fall into the trap of concluding that if a product looks like, or works similarly to one of these carefully engineered products that it is interchangeable. Believe me I have been there and done that over my years of making and rarely, if ever has that been the case. I have even found that products with the same chemistry (that which is listed at least) are not interchangeable, as they were designed for completely different tasks, and the small little chemical or property differences that are not mentioned make huge changes; very small unmentioned chemistry changes can be very powerful.
One other note, most of those quench oils that you get from tool and machinery suppliers is actually repackaged Houghton products. They are still very good, but that is often the true source and where you can get data on them. Houghton is the oldest and perhaps the largest distributor of these products and so we are often working with their stuff and don't know it.
