E-Vacs: Shrinking Foam Packages

In-Line E-Vac Family

A foam manufacturer was looking for a way to reduce the size of their shipping packages.  The type of product was a polyurethane open-cell foam that they would place inside plastic bags to ship.  With shipping charges, the dimensional weight, not actual weight, is used, and it can be very costly.  Since it was open-cell foam, they wanted to evacuate the air from the plastic bags.  This would decrease the package volume and reduce shipping costs dramatically.

The company gave me some details on the product and their process.  The polyurethane foam had a density of 1.1 lb./ft3 (18 Kg/M3), and they were bagging pieces of the foam in plastic bags with the dimensions of 30” long by 10” diameter (0.75m long by 0.25m diameter).  They attempted to use a shop vac to reduce the volume; but, it was too loud and too cumbersome for their process.  They also noticed that the vacuum level was not enough to maximize the shrinkage.  They searched the internet for a better way, and they found the E-Vac™ Vacuum Generators.  They contacted EXAIR to get more information.

The EXAIR E-Vacs use compressed air to create a vacuum by a venturi method.  It can reach vacuum levels up to 27” Hg (91 kPa).  They are very compact and lightweight, and they do not have any moving parts to wear.  So, they are very durable and long lasting in systems with cycling or continuous operations.  In comparison, a typical electric vacuum has a vacuum pressure near 6” Hg (20 kPa).  With the EXAIR E-Vac having a vacuum level 27” Hg (91 kPa), we can draw out much more air to reduce the volume.

At EXAIR, we pride ourselves on customer service.  With this application, I was able to setup a representative sample for testing.  I shot a short video to show the power of our smallest E-Vac.  The video shows a representative sample with a smaller bag.  You can see the volume change with polyurethane foam.

In addition to the video, I was able to calculate the time to evacuate the package to 27” Hg (91 kPa).  EXAIR manufactures seven different sizes of High Vacuum E-Vac Generators with different flow ranges.  The above customer requested an evacuation time in about 30 second.  With Equation 1, I can determine the correct E-Vac size to meet the requirement.

Equation 1:  q = V * ln(p0 / p1)  / t
q = Vacuum flow rate (SCFM)

V = enclosed volume (ft^3)

p0 = atmospheric pressure (“Hg)

p1 = end vacuum pressure (“Hg)

t = evacuation time (min)

Details:
Volume of cylindrical plastic bag: V = 1.36 ft3

Atmospheric air pressure: p0 = 29.92” Hg

Final absolute air pressure: p1 = (29.92” Hg – 27” Hg) = 2.92” Hg

Time to evacuation: t = 0.5 min.

Thus,

q = V * ln(p0 / p1) / t

q = 1.36 ft3 * ln(29.92” Hg / 2.92” Hg) / 0.5 min

q = 6.3 ft3/min or 6.3 SCFM

From the specification on our E-Vac, I was able to recommend the model 810013M.  At 80 PSIG, this model has a vacuum flow rate of 6.85 SCFM; plenty enough to hit the target time.  After installing the E-Vac in their packaging process, they were able to reduce the size by almost 70%.  This was very helpful in reducing the dimensional weight for each shipment; saving the company and their customers much money.

If you would like to send samples in for vacuum test or need calculations for performance improvements, EXAIR Application Engineers will be happy to assist you.  EXAIR always likes to go that extra mile for our customers.

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

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