Tag: tool cooling

Compressed Air Is Cool

Published on by Russ Bowman

Recently, I had the pleasure of assisting an engineer whose company makes honing tools.  One particular item is a large, heat treated, alloy steel part.  When it comes out of the furnace, it’s over 1,700°F.  Needless to say, it has to cool off quite a bit before they can do anything with it.  He was doing the best he could with some large shop fans when he called me to pursue the possibility of doing it quicker with engineered compressed air products.  His goal was to cool the part to 600°F in fifteen minutes.

For those of you without an engineering background (or for you engineers who “phoned it in” during Heat Transfer and Fluid Flow), there are 2 components to convective heat transfer: temperature differential, and flow of the cooling medium.  Increase either or both of these, and you get better results.

In this particular case, the temperature differential between the part (1,700°F) and ambient (80°F) is already huge.  Now, a Vortex Tube device could cool the air an additional 50° or so, but that wouldn’t really have much overall effect.  That left us looking at increasing the air flow.

We considered several options, but the Super Air Knife’s 40:1 amplification ratio made it the obvious choice for maximizing flow, while minimizing consumption.   I didn’t do the CAD drawings (although CAD is my favorite video game), but I supplied my customer with the 3D models he needed to design his system.  He incorporated three 12” Super Air Knives, supplied with plumbing kits.  He mounted them with our Universal Air Knife Mounting Systems.  It made for a very nice looking little rig.

Based on the initial data, my heat transfer calculations were in the “close but no cigar” range – making some conservative assumptions, I figured it could take as long as half an hour to reach 600°F.  When all was said & done, though, the cooling performance was a great improvement over the fans, and even better than my calculations indicated it would be – the system actually cooled the part to 200°F in twenty minutes.  Which was curious, because I actually paid attention in, did well in, and, dare I add, even enjoyed HT/FF.

As I come to grips with my failure to know everything, I’m encouraged that the as-yet unknown variables were skewed in our favor.  Yeah; compressed air is cool.  Even cooler than I thought.

Russ Bowman
Application Engineer
EXAIR Corporation
(513)671-3322 local
(800)923-9247 toll free
(513)671-3363 fax
Web: www.exair.com
Blog: http://blog.exair.com/
Twitter: twitter.com/exair_rb
Facebook: http://www.facebook.com/exair

All You Wanted to Know About Coolants

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Coolants are used in the metalworking industry whether it be cutting, grinding, bending, stretching or stamping to perform two functions:

  • Provide lubricity to reduce friction and the heat generated by it.
  • Dissipate and carry away the heat  from the tooling and the part.

To say that this is all it does, would be a gross over simplification. Material, tooling, and tolerances all pose their own unique requirements. The type of coolant and the additives in them address these specific and complex machining issues.

Types of machining coolants

Straight Oil (100% petroleum or mineral oil)

These may have additives designed to improve specific properties. For severe applications, straight oils may contain wetting agents (typically up to 20% fatty oils) and extreme pressure (EP) additives such as sulfur, chlorine, or phosphorous compounds.  These additives improve the oil’s wettability; that is, the ability of the oil to coat the cutting tool, work piece and metal fines. These additives also enhance the anti-welding properties to control BUE (build up edge on the tool).

Advantages – Excellent lubricity, good rust protection, good sump life, rancid resistant

Disadvantages – Poor heat dissipation, increased risk of smoking, misting, and fire, oil film on work piece requires subsequent wash operation, limited to low-speed, severe cutting operations

Soluble Oil

Petroleum oil (60%-90%) and water are mixed together with emulsifiers and other chemicals to form oil-in-water emulsion making a milky solution. Normal milky emulsions have particle size ~ 2 to 50 microns in diameter.

Advantages – Good lubrication, Improved cooling capabilities, General-purpose product for light to heavy-duty operations

Disadvantages – More susceptible to rust problems, Susceptible to tramp oil contamination and bacterial growth, Susceptible to evaporation losses and may form precipitates on machine

 

Synthetic

Synthetic Fluids contain no petroleum or mineral oil base and instead are formulated from alkaline inorganic and organic compounds along with additives for corrosion inhibition. They are generally used in a diluted form (3 to 10%). Synthetic fluids often provide the best cooling performance among all cutting fluids.

Advantages of synthetic fluids: very good cooling ability, good lubrication properties, good stability in hard water, good corrosion protection, low mist, easy handling, cleaning and maintenance.

 Disadvantages of synthetic fluids: some toxicity, easily contaminated by foreign oils, relatively high cost.

Semi Synthetic Fluids

These are similar to soluble oils since they are water-based emulsions. However, there is usually 5 to 20% mineral oil emulsified into the water to form a micro emulsion. The emulsion particle size is 0.1 to 0.01 microns in diameter.

Semi-synthetic fluids combine advantages (and disadvantages at some extent) of mineral emulsions and synthetic fluids: They have better corrosion protection than synthetic fluids and better cooling and wetting capabilities, easier handling and maintenance than mineral emulsions.

Disadvantages of semi-synthetic fluids: misting, relatively poor stability in hard water, contaminated by foreign oils, some toxicity.

Maintaining the cleanliness of your coolant will extend its life and prevent health hazards. Using the EXAIR Chip Trapper to pump out your machine sump on a scheduled basis will filter out problem causing debris. Watch a video of the chip trapper in use.

Joe Panfalone
Application Engineer

Phone (513) 671-3322
Fax   (513) 671-3363
Web: www.exair.com 
Twitter: www.twitter.com/exair_jp
Facebook: http://www.facebook.com/exair

The Cold Gun Really Does Work!

Published on by Brian FarnoLeave a comment

“The High Power Cold Gun really does work!”  That’s a statement a customer I spoke with recently told me during a phone conversation.   Our catalog and flyer had come across his desk many years ago and he had just passed it by like it was another piece of junk mail.   Well when his application suddenly went from being able to use liquid coolant to having to cut dry, his cycle times and process times greatly increased.  He searched for a solution to the problem he was seeing and the tooling manufacturers were trying different coatings and his operators were trying to get him to reprogram the part.  He knew there was a way to avoid all of these recommendations but could not find it.  Until, he was sitting at his desk and remembered seeing EXAIR on a piece of paper with an Aircoolant system.  He did a quick search on the internet and found our homepage. 

Once he was on our site he immediately found the Cold Gun Aircoolant System.  He ordered a 5330, a High Power Cold Gun System w/ two cold outlets.  When he got the unit in, he immediately hooked it to the machine and fixed the nozzle to dispense the cold air directly at his cutter contact area.   The part ran and for the first time since they had started running the process dry, the machine was cutting a good part at his old cycle time. 

The operators couldn’t understand it and the owner even had a hard time himself.   That was until the machine stopped and they felt how cold the air was coming out of the Cold Gun and they saw the finish on the part.  They put it on several different applications that were running into similar problems with surface finish and tool life and it proved to be a worthy tool for their production line.  

Recently, he had a business acquaintance contact him with a similar problem on a stainless steel milling application.   Our customer immediately recommended the Cold Gun to him and even gave him one from his own machine to try out. 

It is interactions like this that help us to succeed and we thank all of our customers for these interactions.  This is also how we are able to have a case study for every product we offer. 

This is just one of many customer applications that we have helped with over the years.  Our application index and case study files are yet another way that we are able to help our future and existing customers with their compressed air needs.   If you have an application you aren’t sure we have done before, please contact us and let us know.  If it hasn’t been tried before, we’ll do our best to help you find an EXAIR product to make it work.

About Vortex Tubes

Published on by Kirk EdwardsLeave a comment

Vortex Tubes are a phenomenon of physics generally used for spot cooling and we get many questions about them. Typically we have customers ask “how do they work?” or “when did you come up with them?”. The latter question is the easy answer…

We did not come up with Vortex Tubes, George Ranque did in 1928. George was developing and testing a vortex pump he designed and observed a warm air exhaust and cold air exhaust from opposite ends of his pump. He got so excited about this development, he shut down the research and development of the pump he was working on and jumped headlong into the commercial potential of this hot and cold air product. He started a small firm which soon failed and the visibility of the Vortex Tube along with it.

Recognition of a Vortex Tube increased again in 1945 with a scientific paper published by  Rudolph Hilsch. The paper became popular enough to raise awareness and continued interest in the potential of Vortex Tubes.

The first question, “how do they work?”, is the tough one. First, here is what they do – A Vortex Tube uses compressed air as a power source, has no moving parts, and produces hot air from one end and cold air from the other. The volume and temperature of these two airstreams are adjustable with a built-in valve on the hot air exhaust. Temperatures as low as -50F (-46C) and as high as +260F (+127C) are possible.

Again, how do they work? Nobody knows for certain. If I could choose who to try to explain it I would choose Julius Sumner Miller to explain it, there is nothing this guy couldn’t explain, but alas, he is no longer with us. We can still enjoy his passion for physics (and his unique delivery) through YouTube. Here he discusses Bernoulli, the video is a bit long but take the opportunity to learn about Professor Miller if you have the time.

Nobody has been able to “do the math” to prove exactly how it functions but there is a widely accepted theory. Compressed air is supplied to the Vortex Tube and passes through nozzles tangent to an internal counterbore. These nozzles set the air in a vortex motion. This spinning stream of air turns 90 degrees and passes down the hot tube (thin tube part of a Vortex Tube) in the form of a spinning shell, like a tornado. A valve at one end of the tube allows some of the warmed air to escape. What does not escape heads back down the tube as a second vortex inside the low pressure area of the larger vortex. This inner vortex loses heat and exhausts through the other end as cold air.

While one airstream moves up the tube and the other down it, both rotate in the same direction at the same angular velocity. That is, a particle in the inner stream completes one rotation in the same amount of time as a particle in the outer stream. However, because of the principle of conservation of angular momentum, the rotational speed of the smaller vortex might be expected to increase. (The conservation principle is demonstrated by spinning skaters who can slow or speed up their spin by extending or drawing in their arms.) But in the Vortex Tube, the speed of the inner vortex remains the same. Angular momentum has been lost from the inner vortex. The energy that is lost shows up as heat in the outer vortex. Thus the outer vortex is warm and the inner vortex is cooled.

Yes, I know – you too are longing for Professor Julius Sumner Miller to explain. Thanks for reading.

Kirk Edwards
Application Engineer
kirkedwards@exair.com