EXAIR Super Air Knife vs. Blower-type Air Knife

Super Air Knife Blower Air Knife

Super Air Knife                           Blower Air Knife

A plastic company was developing thin layered films in their laboratory on a miniature prototype machine. It was designed for trial runs to make 24” wide material from various plastics, blends, and thicknesses.  They would place the plastic pellets into a hopper, and the material would be melted and extruded into a flat sheet.  To harden the material, it would land onto a cold drum, a large cylinder that had chilled water running through it.  To keep the sheet on the surface of the cold drum, they had a blower air knife.  In addition to the blower air knife, they had to use two ¼” copper air lines blowing on the outside section of the film.  Whenever they decided to make a change to their process, change material runs, or even for clean up; they had to move the blower air knife from the cold drum.  This was a hassle as it had a 3” hose attached to a blower.  It was very cumbersome and awkward to handle.  They heard about the EXAIR Super Air Knives, and they wanted me to do a comparison to their current system.  I was glad to compare the EXAIR 110224 Super Air Knife to their blower-type air knife system.

 

  1. They were getting “stretch” marks on the plastic film.
    • Blower-type air knife – Hot air is generated by the blower system. When the hot air hits the cool surface, it will cause an uneven hardening of the material, causing stretch marks.
    • Super Air Knife – It has a 40:1 amplification ratio. That means that 40 parts of the ambient air is entrained with 1 part of compressed air. Being that the ambient air is much cooler than the hot air from the blower system, it actually aides in cooling. There is no thermal shock to the material, and hardening is better and faster.
  2. They required an even force across the surface of the plastic film to keep against the cold drum.
    • Blower-type air knife – Their design had one 4” line feeding into the side of the blower air knife. This would cause 2 issues for an even force. As the velocity of the air hits the opposite side of the knife, the closed end, a turbulent air flow is developed. Also, there would be a slight negative pressures at the entrance caused by the velocity of the air entering. This turbulent mayhem and slight negative pressure are very inconsistent in force and velocity. The reason that they had to add the additional two ¼” copper lines to blow compressed air on the outside edges.
    • Super Air Knife – The flow that is delivered from the Super Air Knife is laminar. This means that the force and velocity is consistent across the entire length, even on the outside. With this even force, the film is held evenly and securely onto the cold drum.
  3. They needed maneuverability for change overs and clean up.
    • Blower-type air knife – To keep the needed pressure on the film, they had to have the blower air knife ¼” from the surface of the cold drum. So, before a change over or clean up procedure is started, they had to remove the knife and attachments. This was time consuming, cumbersome, and a headache to move.
    • Super Air Knife – With the compact design, the Super Air Knife has a large force in a small package. It has a footprint of 1 ¾” X 1 ½” X 24” long with only two ¼” NPT compressed air lines feeding it. The force measurement is equivalent from 3” to 12” away from the surface. Now, they could mount the Super Air Knife far enough to not disrupt their cleaning or change-over procedures. This saved them much time in changing to different materials and clean up.
  4. They wondered about the compressed air usage.
    • Blower-type air knife – This device does not require any compressed air to operate, but because it could not keep the film against the cold drum on the outer edges, they did have to use compressed air. With the two ¼” copper tubing at 80 psig, they were using a total of 79 SCFM of compressed air.
    • Super Air Knife – As a direct comparison to their air usage, the Super Air Knife would use 70 SCFM of compressed air at 80 psig across the entire width of the film. But with the unique design to entrain 40 parts of ambient air, it gives the Super Air Knife a powerful force. They were able to reduce the air pressure to 40 PSIG to keep the film on the cold roll, which also cut the air consumption to 41 SCFM. This efficient design helped them to save on compressed air without the added cost of the electricity to run the blower motor.
  5. Any other comparisons between the two products
    • Blower-type air knife – With the sound of the blower and the turbulent air flow, the unit was very loud. It had a sound level over 90 dBA, and with the operators working around this system, they required PPE for hearing.
    • Super Air Knife – These units are very quiet. At 40 PSIG, the sound level is only 61 dBA. (Just as a reference, the sound level is 72 dBA at 100 PSIG). This was very nice for the operators as they did not need to wear the ear plugs to work around their machine all day.

When it comes to using the EXAIR Super Air Knife, it has many benefits over the blower-type air knife. We can even include the initial cost in which we would be about 1/10 the cost of a blower-type air knife system.  For this customer above, they were delighted to replace that system with the Super Air Knife, and start running plastic film effectively, efficiently, and quietly on their miniature prototype machine.

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

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