Triboelectric Effect: Big Name For a Simple Concept

February 5, 2009 — ndraker

Triboelectric effect is simply a large word that means when two materials of a certain nature come into direct contact with one another, they will become electrically charged. The “certain nature” that I mentioned above usually means materials that are electrically non-conductive. Wool, glass and PVC plastic would be three very good examples.

This is where things begin to not make much sense. Think about it, materials that are electrically non-conductive generate an electric charge when they are brought into close contact with one another. Notice I didn’t say anything about friction or rubbing action to cause the electric charge generation. The materials simply have to come together for this to happen. Friction or rubbing can be a component, but is not necessary.

It isn’t until you go to separate these materials in an application where you really begin to see the problem. This was the case for a customer who printed onto PVC boards. The board faces were covered with a protective film to protect against damage. Everything was going OK in the application until the film was peeled off the PVC board. The simple action of peeling off that protective film generated huge static charges due to the imbalance of positive and negative charges on each material surface. Again, note that there was no vibration, rubbing or friction of any kind.

Another good example of this kind of effect is when a material such as mylar is fed into a machine from a master roll. The action of the top layer of mylar separating from the roll will, again, produce a rather large static electricity imbalance.

EXAIR makes static eliminators and we can certainly help you with these static issues. I wanted to write an article to help clue people in on where to look within their application and why they would want to look in such places as it may not always be obvious what exactly is causing the static electricity to generate. If you know where the problem resides, you can then apply our static eliminating solutions more effectively.

Neal Raker
Application Engineer
nealraker@exair.com

Posted in Static Elimination, Uncategorized. Leave a Comment »

Cooling Without Cold Air?

February 4, 2009 — esmortimer

Contrary to what you may think, it is possible to cool something without using cold air.  Think about it.  You cool your coffee by blowing on it, and your breath is 98.6 degrees.  98.6 degree air may not feel cool to us.  But, it does feel cool to a cup of coffee at a steaming 150 degrees. 

This cooling process is called convection.  Convection is heat transfer that occurs due to movement of a heated gas or liquid away from the source of heat, carrying energy with it.  This principle is related to the 2nd Law of Thermodynamics, heat travels from hot to cold. 

As you blow across the surface of your coffee, the heat in the coffee is picked up by the cooler air that is being blown across it, and the breath then carries the heat away from the coffee, leaving it cooler, and much more tolerable to drink. 

Many of EXAIR’s cooling products are designed around this very principle.  Our Air Knives, Air Amplifiers, Air Wipes, and Air Nozzles have air amplification ratios of up to 40:1.  This means that they will entrain up to 40 parts of ambient air for every 1 part of compressed air consumed.  None of these products produce cold air.  Thus, this combined airflow is typically at room temperature.  But, if it is being directed at a surface that is well above room temperature, then the air will feel cool to that surface, and it will carry heat away from that surface, much in the same way as breathing on your hot coffee cools it. 

I spoke to a customer last week who had an application that very nicely demonstrated this effect.  They produce aluminum coated steel tubing for automotive exhaust systems.  The pipes range in diameter from 1.5″ to 3″.  The pipes are bent into various shapes, and the sections are then welded together to create particular exhaust system configurations. 

Often, the heat generated from the welding process causes the pipes to warp in the area near the weld.  This is not acceptable, and creates many rejected parts.  They needed a product that would cool the weld both quickly and evenly, so that they could keep the production line moving. 

I suggested a model 2404 4″ Super Air Wipe.  This product has a 4″ ID, so it will accommodate all the pipe sizes they deal with.  It also has a 40:1 air amplification ratio, so they can maximize the air flow onto the pipe, while minimizing the demand on their compressed air system.  The Super Air Wipe provides a uniform 360 degree airflow, so it will cool the entire weld at once, while maintaining a proper round tube.  The large volume of ambient airflow it creates will quickly carry away much of the heat from the welded area.

The Super Air Wipe will provide significant improvement in their current system, and will nearly eliminate any rejected parts due to weld-related heat warpage. 

If you want to learn how another one of our cooling products may work in your application, please give us a call or send us an email.  We would be glad to work with you.

Emily Mortimer
Application Engineer
emilymortimer@exair.com

Posted in Air Amplifier, Air Knife, Air Wipe, Super Air Nozzle. Leave a Comment »

Clear Instructions, Stay Focused or Split Your Chin Wide Open

February 3, 2009 — Kirk Edwards

You may have seen a couple posts about the dash of harsh winter weather we have experienced. It has left us with ice coated surroundings. My young son does not see treacherous walkways or slippery stairs; his vision of a non-stop playground remains.

Before school yesterday, his instructions were clear: gather his school work, walk out to the van, and get in the van for a ride to school. As young minds may do, his apparently wandered into an opportunity to grab a shovel and start chipping away at the ice on the driveway. Only moments later he found himself a victim of decreased friction, poor balance and poor judgement, which resulted in 6 stitches on the chin.

Even with clear instructions is it sometimes hard to stay focused and get the job done.

EXAIR knows it is difficult to remain focused in many situations and under different circumstances. We understand this difficult economy can take its toll on our abilities to prioritize or find motivation to work on previously unimportant or unseen problems. But we do have the instructions and tools to make your compressed air system more efficient:

1. Measure your air consumption
2. Locate and fix any compressed air leaks in the system
3. Upgrade your end use blow off applications with engineered products
4. Turn off the compressed air when not needed for production
5. Use intermediate storage of compressed air near the point of use
6. Control the pressure at the point of use to minimize consumption

These six steps to optimize your compressed air consumption do work. EXAIR has the products to make each step possible and to help prevent you from taking one to the chin.

Kirk Edwards
Application Engineer
kirkedwards@exair.com

Posted in Compressed Air Optimization. Leave a Comment »

Compressed Air 101

February 2, 2009 — japanfalone

I saw an infomercial for a palm sized air compressor that ran off of C size batteries. The host claimed extraordinary power of this unit to produce 100 PSI. Being in the fluid power industry I could only laugh at the uselessness of this product. It may be able to achieve those pressures, but the volume of air would be miniscule. I guess if you were blowing up party balloons or topping off air in your basketball it would have some use.

While the limitations of this compressor are obvious to pneumatic professionals, it does exemplify a lack of understanding in the industrial world as to the relationship of compressed air pressure and volume as they apply to the ability to do work. All too many process engineers focus on pressure and overlook volume when considering their compressed air capacity and delivery requirements. I see this verified by undersized air lines, valves, restrictive quick connections, and undersized air compressors.

Let’s start at the source of a compressed air system, the compressor, which in simple terms is a mechanical device that converts energy from a motor (electric or gas) into stored energy in the form of a compressed gas. So it stands to reason that the more volume of compressed air generated, the more energy, and hence the greater ability to do work. Work is measured in horsepower so the more energy you need the more compressor horsepower you will need. 

Whenever you install a pneumatic component, check out its air consumption to see if you have the compressed air capacity needed. An industry rule of thumb is that you get 4 standard cubic feet of air per horsepower. So if you are trying to drive an impact wrench that uses 16 SCFM, doing the math, you will need at least a 4 horsepower air compressor. On a 115V circuit, a 4 horsepower compressor would require 30 amps. Obviously then this is not a home/contractor style air compressor. It would need to be run off of a 220V circuit.

From the air compressor you will need to pipe the air to the point of use. Here is where a lot of folks get into trouble with undersized plumbing. Even though the impact wrench may have a 1/4″ pipe port, depending on the distance, you may or may not be able to use 1/4″ pipe. As the air passes through the pipe, there are frictional losses. The longer the pipe, the more resistance there is to flow. To counteract the resistance, the size of the pipe needs to be enlarged.

Here is a table that you can use as a reference guide. Using the impact wrench example you see that you can use 1/4″ pipe for 25’ of length. Over that you must use 3/8″ pipe.

  100 feet 50 feet 25 feet
1/8 NPT 4 SCFM 6 SCFM 8 SCFM
1/4 NPT 10 SCFM 15 SCFM 20 SCFM
3/8 NPT 20 SCFM 30 SCFM 40 SCFM
1/2 NPT 40 SCFM 55 SCFM 80 SCFM
3/4 NPT 80 SCFM 120 SCFM 160 SCFM
1” NPT 150 SCFM 225 SCFM 300 SCFM

Quick disconnects and push to connect fittings are another source of flow restriction. Pictured here is an example where a client was not able to get the performance from his air product. The unit required a fair amount of compressed air thus had a 1/2 NPT air inlet. 

work-003

The client installed a reducer from 1/2 NPT to 1/4 NPT. That in itself should have been a clue as to why he was not getting enough air to the unit but he went on to add a quick disconnect. This next picture shows the extreme reduction in trough hole diameters. It is apparent as to why this client could not get the performance from his air product.

 work-0071

Compressed air is an area of study all its own. The few paragraphs here are only intended to get you thinking of some of the associated variables. If you have questions I would invite you to call EXAIR’s application engineering department 1-800-903-9247.

Joe Panfalone
Application Engineer
joepanfalone@exair.com

Posted in Compressed Air Optimization. Leave a Comment »
Newer posts »