[Milsurplus] "Foam In Place" Packing

[Jim Whartenby]

Interesting topic!I found this link after a few minutes of using our friend Mr. Google.http://www.sealedairprotects.com/NA/EN/products/foam_packaging/instapak-quick_calc.aspx

Seems that 50 pounds is the upper limit of the graph found in the above link.  For rack mounted radios of the R-390A size, the bottom seems to be around 250 square inches which is also off of the chart in the above graph.  So this chart isn't all that helpful in answering Dave's question.
The link below is a guide to picking the foam bags for various size cardboard boxes.http://www.sealedairprotects.com/NA/EN/Pdf/quick_vol_guide.pdf
The #100 bag will fill a volume of 23 X 21 X 2 inches which seems to meet the requirements Dave made.
So a 50 pound radio with about 250 square inch base will stress the foam at approximately 0.2 pounds per square inch.  Even the 75 pound R-390A stresses the foam at only 0.3 pounds per square inch.  Neither seems all that bad to me so I found some "foam in a bag" from something I bought recently which is about 15 X 7 X 2 inches and did a simple experiment.  
I guess my thumb has about a square inch of surface area.  Putting this block of "foam in a bag" on a bath room scale and pressing down with my thumb showed that the foam did not dent until about 20 pounds registered on the scale.  Even a dent caused by 30 pounds per square inch seems to recover after a few minutes.  So this concern about "foam in the bag" does not seem to be a show stopper.
If you don't have a solid bottom on your radio, perhaps making a cardboard cutout about the size of the box will allow the foam to expand evenly under the radio as the foam sets up.  Other size bags can be used to protect the radio's sides and front and another #100 size bag will protect the top.
As usual, my concern would be which method is cheaper!  Unused "foam in the bag" is easier to store until needed but foam board insulation from Lowe's is just so convenient!Jim

      From: David Stinson <arc5 at ix.netcom.com>
 To: milsurplus at mailman.qth.net 
 Sent: Thursday, December 28, 2017 5:34 AM
 Subject: [Milsurplus] "Foam In Place" Packing
   
This "Foam In Place" packing:
So let's say I have a 50 lb radio and a box big
enough for it.  How does this work?  If I put one
of those packs in the box under the radio, will it
really lift that 50-lb radio up and leave an
acceptable layer of material under it? Exactly how
does this work?

73 OM DE Dave AB5S
   

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