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Model Railroading > BNSF 72’ Frostline Reefer (Part 11) – Welded Plug Doors

Date: 11/18/22 02:07
BNSF 72’ Frostline Reefer (Part 11) – Welded Plug Doors
Author: tmotor

This is Part 11 of a series on the BNSF 72’ Frostline Reefer project.  (Parts 1 thru 10 were posted earlier.)
While we are on the subject of Plug Doors, let’s cover the Econo Frost’s welded version.  Initially I thought they had just replaced the rivets with stitch-welds.  However, there was also a design change in the sheet metal surrounding the gearbox (beneath the Handle).
The previous Plug Door versions have a depression stamped into the sheet metal for the gearbox, and to clear the Crank Arms.  To eliminate the need for this depression, the design was changed to have the sheet metal flush with the bottom of the gearbox.  This means the sheet metal is now an inch deeper (towards the center of the car).   This requires an additional stairstep on the sides to accommodate the flange of the vertical ribs.  The horizontal ribs that are above and below have their legs on the gearbox-side made longer to have the flange match the new depth of the sheet metal.
Increasing the depth of the sheet metal meant making the door “thinner”.  This means less room for insulation on the inner wall.  On a reefer, less insulation is going in the wrong direction.  But, presumably the door was less expensive, so they went with it.  At the time fuel costs weren’t what they are today, so it made sense to just increase the size of the fuel tank to compensate for inefficient insulation. 
Of course, today they are singing a very different tune.  New reefers are routinely fitted with Plug Doors having exterior insulation, and the formed depressions in the sheet metal have returned.  The Plug Doors seen on recent reefers use the same design as found on the Frostline Reefers (with exterior insulation), but are held together with stitch-welds instead of rivets.  This allows for faster fabrication (short-term savings) and gives maximum insulation (long-term savings), keeping the accountants happy.  :-D
I don’t think I will be modeling the Econo Frost Reefer (not right now anyway).  It is not just a modification of the Frostline Reefers (with the plastic roofs) that preceded it.  Thought they share many of the same dimensions, they are totally different designs.  However, I am documenting the Econo Frost Reefers now, so I will have dimensions for the CAD geometry if it becomes a future project. 

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