High speed grinding of carbon steel

[ivan]

Usually avoided, but maybe coming into fashion because of particularly cool cutting Norton blue wheels recently discussed.

Proir to reading this post, a purchase waiting for the next trip to the US, was a misting device. This sprays a continual fine mist at the grinding point, which is supposed to be much more effective than dipping, and also less messy. (I guess the mist evaporates instead of dripping on the floor)

Then I read of a similar device for cooling when grinding, that uses just air - no, really - it uses the drop in temperature you get as compressed air expands. If you have compressed air, looks a winner. Anyone know more about this?

 

[9fingers]

I would think the water vapourisation scheme will be much more effective.

The cooling effect of the latent heat of vapourisation occurs on the surface of the workpiece whereas the cooling due to expansion of the compressed air occurs at the jet where is expands.

Not tried either but just mental application of the physics behind each method.

Bob

 

[Digit]

The answer is it works very well, under the right conditions!
But if you're thinking of simply connection you compressor to a pipe on the grinder I would advise you to forget it!
You need a good flow of low pressure air, not high pressure, blasting grinding dust around the shop is not a good idea.

Roy.

 

[ivan]

Yes, I was surprised by what I read; in this commercial machine shop device the high pressure air appeared to enter a small expansion chamber (cylinder about 40x150) mounted at the back of the grinder, and the air was delivered by the usual coolant snap (together) lock system to the grinding point, presumably at somewhat lower velocity. The expanded air was claimed to be close to 0 deg C. Unfortunately A level physics and adiabatic expansion is a very distant memory, so I hesitate to calculate the flow rate needed to get this temp drop.

 

[Inspector]

http://www.exair.com/Cultures/en-US/Pri ... t+Systems/

The "cold gun" needs 15 cfm of flow as a minimum. My 5 hp (29 Amp/220Volt) compressor would just keep up.

Poke around the Exair site and you'll find lots of applications for compressed air.

 

[ivan]

Thanks Inspector, just knew there'd be a snag (15 cu ft min). Looks like a misting device is back in the running for my 3Hp compressor.

 

[Inspector]

You could just try a small garden sprayer (new so you don't die). The kind you pressurize by pumping up. Some have a very fine tip and will spray a mist. You aim it at the side of the wheel and the moisture travels outward to the periphery of the wheel. The vapour cools the tool but it also comes out from all points of the wheel cooling and "moisturizing" the area. Nice in a hot shop but not so much in the cold when you want to keep the shop tools rust free.

In the end though it might be simpler to buy a wheel with a soft bond that cuts cooler without the water.