G'day all. Does anybody use air blast with oil mist to cool and lube their milling cutters?
Comments have been made elsewhere that flood coolant clears away the chips. I have also noticed that cutting oils tend to cause the chips top cling to the tool. I think the chips not clearing the cut can cause tool wear so cutting oils make the situation worse not better. I have stopped using cutting oils altogether.
I guess an air blast system could include a source of air (no trouble I have a compressor), a nozzle to direct the blast at the tool and a drip system to inject the oil into the air stream. The air will cool the tool, clear away the chips and deliver the oil.
I've no experience of an air blast system, but I'd be worried about swarf blowing across the workshop. Liquids are also much better that gasses for carrying away heat, so it might prove difficult to keep the temperature of the cutter down.
Post by Shawki Shlemon on Oct 25, 2007 9:56:15 GMT
I take small cuts and it takes me longer but I am not in a hurry . For yellow metals and cast iron I don't use anything but for steel I use cutting oil in small quantity and clean it away after every cut . It works for me .
I have been thinking about this over night......Industry usually uses best practice and if air or gas blasting could work then i think it might have been used, but to my knowledge it hasnt. That doesnt mean it wouldnt work though in our environment, but I think very high pressures would be needed, and would need to be contained around the cutter - we dont want swarf around the workshop.
However, as has been said, liquids are better at carrying away heat ( due to density and thermal characteristics ). Also, liquids are easier to recycle. They also capture rogue bits of swarf, and if the flow velocity is right it clears the cutter too.........why re-invent the wheel ?
in an industry setting "full flood coolant" is like turning a couple of hose pipes on the workpiece on full flow, it difficult to see the workpiece somethings the is so much, plus there is some times coolant through the tool (like drills) to make all the more effective. Even scaling this down to our size full flood should clear the chips out of a slot without trouble, the problem is then the coolant getting everywhere.
just remember that carbide tools in particular should either have full flood coolant or none at all.
In my experience, the best way to cut the most metal with milling cutters is a slow speed (I run carbide cutters slower that the recommended speed for HSS) and high feed rate, if you your cutter lasts (say) 4000 individual cuts, then doubling the amount of metal removed per cut will (almost) double the amount of metal removed in the life of the cutter, if you keep the heat down.
Sometimes I think I'm cynical, then I look at the world and see that I'm not as cynical as real life is.
Lets clear a fact up compressed air is used in industries for cooling process ; special nozzles are normally used to air reduce consumption. The process is nearly always regulated down normally to a couple of bar.
Volume will be the home engineers problem, as 230v 2.kw compressors give 12 cfm fad @ approximately 10Bar (forget the cylinder displacement claims from the cheaper end of the market).
For example a 2mm nozzle will consume 16.59 cfm at 10 bar way too much demand for a 2kw compressor where as a 1.5mm nozzle would consume 7.8 cfm @ 10 bar which would suit the demand of a industrial grade compressor 2kw compressor. However if we regulate down to 2 bar using a regulator after the receiver we could increase the nozzle to 3mm as this would consume 8.4cfm @ 2bar
In industry the size of the nozzle would be governed by the temperature generated and required cooling affect vs volume and pressure. Lower pressures are always preferred where possible.
From a compressed air point of view, one of the main reason every Bridgeport or Harrison has a coolant pump is the small size in Kw of the pump motor, compared to the correct size compressors motor which would be required. Also compresses air is heavily legislated within industry which also includes the same regulations as commercial boilers (PSSR 2002). However with the introduction of variable speed compressor compressed air for cooling is becoming more commonplace.
Notes CFM FAD or SCFM FAD = cubic feet per minute delivered at the stated pressure, (the S stands for standard), CFM on its own stands for the cylinder displacement of the compressor only and is marketing ploy to make the compressor look bigger than it really is, (screw and vane compressors are always CFM FAD)
If you try this method make sure your compressor is up to the job, ie make sure It knocks off and stays of for at least 5 minutes while blowing the cooling air.
Drain the receiver on completion and leave the tap open, ( next time you use the compressor start it first until it hisses out of the drain valve then shut the valve) this helps reduce down stream condensate, in this application blowing on to the machine and in to the sideways.
I'm not going to try to recall any gas equations, but the cooling effect of the compressed air expanding should have some effect, if only it can be directed to where it is needed.
I do a lot of work with drilling rigs on rock, and compressed air or air with mist is frequently used for flushing and cooling on shallow holes, typically with a 100kw plus compressor revving its guts out.
the equivalent for water or mud (bentonite, polymer or guar gum in water) flush is a 5 to 8 hp single cylinder engine going pop pop pop...
obviously, compressed air has the advantage that you're not getting rancid suds or oil all over yourself or the machine, but you will have the noise of the compressor running, and you will be paying through your electricity bill for any refrigerating effect that you get, wheras a five gallon drum of cutting oil or suds lifted onto a shelf and feeding by gravity is silent, cooled by mother nature and easily replenished (and your chiropractor needs the money ).