Tag: contact angle

Contact Time: How to get the most from your EXAIR products

Published on by John BallLeave a comment
Poor Position vs Good Position

You may have heard us speak about contact time.  I would like to cover what that means in this blog.  Contact time refers to the amount of time that a target part is in the high-velocity airstream produced by an EXAIR blowing product.  The longer the contact time, the more effective the blow-off or cooling effect. Optimizing the mounting position of the EXAIR solution relative to the target makes a huge difference in effectiveness.  When our customers typically purchase EXAIR products, they have a tendency to improperly install them, reducing their performance capabilities.  Let’s look at a Super Air Knife.  In the photo above, you can see the relationship between a perpendicular and a recommended setup angle.  I have some recommendations that can help to increase the contact time and improve the performance. 

Super Air Knife Chamfer
  1. Angle – EXAIR machines a chamfer on the cap of the Super Air Knife as a starting point.  You want to have the chamfer parallel with the target line of movement.  This will create an air flow angle of about 45 degrees relative to the target.  This angle will increase the contact area and contact time, which is very beneficial for removing debris and/or heat.  Depending on the speed and height of the target, this can be altered for further refinement.
  2. Distance – For optimum performance, the Air Knife should be between 3″ (76 mm) to 12″ (305 mm) from the target.  If you are too close, the amplification ratio is sacrificed, and the force is reduced.  If you are too far, the air pattern will start to change, causing the velocity and force to decrease. 
  3. Counter-Flow – The direction of the air flow should be blowing in the direction opposite the target movement.  As an example, if the parts are moving from left to right, you want the Air Knife to blow from right to left.  This will allow the contamination to be blown back away from the cleaned surfaces, and it will increase the impact force to remove contamination, i.e. a head-on collision vs. a rear-end collision.

With these few simple steps, you will begin to maximize the performance and effectiveness of your EXAIR blowing solution.  Some accessories can help with the setup, like Swivel Fittings and Stay Set Hoses for the nozzles and the Universal Mounting Kit for the Air Knives.  You can modify the impact angle to best suit complex parts and systems.  If you need any help to get the most out of our products, you can contact an Application Engineer at EXAIR.  We will be happy to hear from you.     

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Contact Angle and Wettability

Published on by John BallLeave a comment
Proper position on Super Air Knives

EXAIR has been selling high-efficiency, hard-hitting compressed air products since 1983 for the purpose of drying and cleaning materials with compressed air.  The laminar airflow allows for a consistent force in the same direction, which is beneficial for effective cleaning and drying.  If we look closer at the surface of the material and how liquids interact, we can get a better understanding. 

First, let’s look at the atoms of a solid.  Since the atoms are tightly packed and arranged in a stable format, the forces are even around each atom, except for the atoms on the outside surface.  These forces are unequal, so they will generate an imbalance, which is called surface tension.  This surface tension will have an atomic interface with other objects.  Let’s look at a liquid.  Liquid is a substance that flows readily.  Since it can flow, the surface tension on the outside will create a sphere in space.  So, what happens when these two surfaces interact? 

If we look at a liquid, we can place a drop on a solid surface.  If the surface tension of the solid is weaker than the surface tension of the liquid, then the liquid will bead up.  If the solid has a strong surface tension compared to the liquid’s surface tension, then it will lay flat or wet out.  This phenomenon is important to know if you want things like liquids to wet out with inks and paints versus having the liquid bead up with waterproof materials. 

We can measure how much force the solid surface is exerting when interacting with the liquid by the contact angle (refer to the photo above).   This angle will indicate the wettability of the fluid.  For a contact angle greater than 90o, the surface would be considered non-wettable with that liquid.  If the contact angle is less than 90o, then the liquid will wet out onto the surface.  For water, we have a variety of degrees of interaction as related to contact angles:

  • >150o – Super-hydrophobic
  • 90o – 150o – hydrophobic
  • 30o – 90o – normal wetting
  • 10o – 30o – hydrophilic
  • <10o – Super-hydrophilic

Why is this important to know?  For drying and cleaning applications, it is beneficial to know how easy or difficult the liquid is to remove from the material.  If the contact angle is greater than 90o, then we can help the customer adjust the blowing angle and reduce the air pressure to save money because the liquid is easy to remove.  If the contact angle is less than 90o, then we can adjust the angle to be more direct as well as increase the force level to increase effectiveness. 

How does this apply to EXAIR products?  We are the market leaders for non-contact drying and cleaning.  For applications where you need to remove as much water as possible for quicker heating cycles, to reduce labor costs when cleaning parts, or to quickly dry surfaces for labels and print quality, EXAIR has a variety of blow-off products; like the Super Air Knife.  Within these product lines, we offer a kit that includes a regulator and a shim set to vary the force levels to tackle the different degrees of wettability.  EXAIR is a proponent of using the least amount of air to “do the job”.  The regulator can make fine adjustments to the force levels while the shims will make a coarse adjustment.  So, depending on the contact angles, you can “dial in” the correct amount of force to clean and dry your products.  What could be better than this?  For U.S. and Canadian customers, EXAIR offers a 30-day unconditional guarantee on our cataloged items to try them out.  You can see for yourself how effective and efficient our products are.  If you would like to speak to an Application Engineer about your drying or cleaning application, we would be happy to make a recommendation to help solve your issues. 

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb