EXAIR Super Air Knife: Overview

 

Loud and inefficient homemade blowoff

Drilled pipes, like the one shown above, are all too common in industrial settings for processes where a wide surface area needs to be treated. Their popularity can be attributed to how cheap and easy they are to make but in actuality they are very expensive to operate, as they waste large amounts of compressed air, and are very dangerous to operate.

We frequently take calls from customers looking for a more energy efficient, safer solution to replace these types of blowoffs. EXAIR manufactures 3 different styles of Air Knife – the Super, Standard and Full-Flow – that are the ideal solution for wide coverage applications. Today, I would like to provide an overview of our award wining Super Air Knife.

The Super Air Knife

The Super Air Knife is our most efficient air knife in regards to compressed air usage, using only 2.9 SCFM per inch of knife length @ 80 PSIG. It is also the quietest on the market today at only 69 decibels. The Super Air Knife provides the highest air velocity of the 3 styles offered by EXAIR and produces 2.5 ounces of force per inch at 80 PSIG operating pressure. We offer stock lengths from 3” up to 108” in single piece construction with available materials of aluminum, 303ss and 316ss. We also offer PVDF (Polyvinylidene Fluoride) up to 54” for harsh environments.

The Super Air Knife provides a laminar airflow across the entire length with hard-hitting force. They also give a 40:1 amplification rate meaning they entrain 40 parts of the surrounding room air for every 1 part of compressed air used, producing a large volume outlet flow.

Coupling Kit for the Super Air Knives

For applications requiring an air knife length longer than 108″, we offer a coupling bracket kit that allows you to connect two Super Air Knives together for a seamless, uninterrupted flow. Kits are available in aluminum, 303ss or 316ss to match the construction of the knife.

In addition, we also offer plumbing kits as an accessory item. For aluminum Super Air Knives, we offer cut to length nitrile/PVC hose and brass fittings and for stainless steel and PVDF knives we offer 316ss cut-t0-length pipe and fittings.

If you have any questions on how the Super Air Knife might fit into your process, please contact an Application Engineer.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

Proper Plumbing Means Proper Performance

36″ Aluminum Super Air Knife being used in a monofilament extrusion line

An EXAIR customer recently contacted me about the application shown above, using an aluminum Super Air Knife model 110036 as a component to a blow off application in a monofilament extrusion line.  The extrusions from this line are used in one of the end user’s main product lines, a personal health device used by over a billion people around the world.

The original problem of drying the extrusions can certainly be solved with the setup shown, but the output force from the knife was less than what the customer expected, and below the EXAIR published data.  We take great care in the collection and verification of our performance data, so this prompted a deeper dive into the application to determine what could be the cause.

Immediately upon seeing the application photos, there were two things which stood out.  The first was the angle of attack of the knife, and the second was the compressed air plumbing.  The angle of attack in the original setup was ~90°, nearly perpendicular to the extrusions passing through the airstream from the knife.  EXAIR always recommends an angle of attack of ~45° to increase time in contact between the airstream from the knife and the materials passing through the airstream.  Although a small adjustment, this angle significantly contributes to overall blow off performance.

5mm ID x 8mm OD tubing used to supply compressed air to the knife

But, the real issue with this application was in the compressed air supply.  The tubing for this knife was shown as having a 5mm ID and an 8mm OD, which will allow a compressed air flow of ~40 SCFM at 80 PSIG, maximum, without consideration to pipe length from the compressor.  The 36” aluminum Super Air Knife will require 104.4 SCFM at 80 PSIG operating pressure.  So, it was clear that there was a significant plumbing problem, leading to the reduced performance from the knife.

In order to prove this out, we first had to take a pressure reading directly at the knife.  When this was done, the operating pressure dropped from ~85 PSIG at the main header to less than 20 PSIG at the knife.  By taking this pressure reading directly at the knife we were able to gain valuable information as to the true operating pressure of the knife, which was far below what the customer expected, but which made perfect sense given the performance output.

The remedy in this case was to increase the size of the supply line to at least 15mm ID (approximately equivalent to a ½” schedule 40 line), and preferably to something in the range of 19-20mm (~a ¾” schedule 40 line).  Once this was done the knife operated flawlessly, and after adjusting the angle of attack this application was optimized for the best possible results.

Being able to find the source of the problem for this application was a great service to the customer.  Our engineers are well-versed in compressed air system requirements, and we’re available for help in your application if needed.  If you’d like to contact an EXAIR Application Engineer we can be reached by email, phone (1-800-903-9247), or Twitter.

Lee Evans
Application Engineer
LeeEvans@EXAIR.com
@EXAIR_LE