using plastic bolts in a walk-in cooler?

At the grocery store where I work, the walk-in freezer doors/doorframes
got banged up over time, so they fixed them.... The way they did this
was by taking the old door & latch off, and by putting a whole new door
frame+door inside the old opening.
Recently I noticed that the new frames are all held on by plastic
allthread rods. Why is this?
See pics here-
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tiny-fied-
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The first/top photo is an overall view of the door.
The replacement frame is highlighted in red, and the five rods holding
it in are shown by faint green arrows.
The second pic is a close-up of one of the plastic allthread rods, and
the (metal) nut and washer attaching it. You can see that the plastic
charred a bit from being cut with a power saw. The inside of the rod
(visible inside the freezer) is done exactly the same as the outside.
All the doors they fixed were done this way--with plastic bolts
(w/normal zinc-steel nuts & washers) holding the door frames in, but
metal bolts everywhere else.
???????
I thought maybe it was a safety-breakaway sort of thing, but these
coolers are constructed VERY flimsy. I'd give it about a 50/50 chance of
the nuts just pulling through. Is there some other reason, or is that all?
Reply to
DougC
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DougC fired this volley in news:6e1Pq.72609$ snipped-for-privacy@newsfe05.iad:
It's because the plastic rods don't conduct heat. Therefore, they won't get cold on the outside, and "sweat" (condense moisture).
Had it been done in a robust way, they'd have used phenolic or fiberglas spacer rods, either self-threaded, or with pressed-in threaded inserts. Then they'd have bolted them from both sides with metal hardware.
But it's not a shortcut or designed to be weak. It's to prevent thermal conduction through the fastening system. They were just too cheap to do it stronger than that.
Besides... I'll defend them some; if the rods are of the correct type of plastic (say, annealed (or tempered) nylon, or acetal) and correctly sized, they will be strong enough, even if not as strong as metal fasteners.
LLoyd
Reply to
Lloyd E. Sponenburgh
Less heat loss? Insignificant, yes, but..
Reply to
Kristian Ukkonen
Not insignificant! The greatest cost in grocery stores after the employees is the refrigeration. Maybe I misunderstood, it may even be GREATER than the employees.
Jon
Reply to
Jon Elson
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So you can bust out if accidentally locked in?
Reply to
Steve Walker
YOu may have answered it yourself. They're built so flimsily that metal bolts would have pulled the nuts through without the worker thinking about it. Plastic probably reduces that tendency. There is also the possible safety feature of plastic. OSHA, in its many splendored workings...
-- We are always the same age inside. -- Gertrude Stein
Reply to
Larry Jaques
Remember the latches on refrigerators - back before magnetic seals?
No way one could get out if the door closed.
Reply to
Richard
Every walk-in cooler/freezer that I've ever seen had a handle on the inside and a mechanism so simple as to be jam-proof. I.e., you couldn't get locked in.
The cross-sectional area of 6 1/2" bolts is so much less than the surface area of the cooler/freezer that it's hard to imagine that the heat transfer would be significant. Not significant relative to the loss from people going in and out all day long, either.
But then I can't think of any other reason. Corrosion-free comes to mind, but that's what anti-seize is for.
Bob
Reply to
Bob Engelhardt
Just calculate the heat flux through a long piece of steel allthread.. I can promise it will not be that much..
The refrigeration heat loss from other sources certainly can cost a lot of money.. Like the unshielded shelves for groceries/cheese etc.. Or the customers opening the doors to get the milk cartons/soda/beer.. Or the employees going in/out from the storage getting stuff..
Reply to
Kristian Ukkonen
The thermal conductivity of steel is about 1100x that of fiberglass insulation. So ten 1/2" steel rods would conduct as much heat as 15 square feet of insulation.
Reply to
Ned Simmons
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Well, by the time you multiply it by some number of separate pieces, maybe it isn't so small after all.
Might as well save what can in the design process would be my thought even though the folks designing the walkin coolers/lockers aren't tasked w/ the overall store refrigeration loss calculation, they may as well do their part in new gear. Plus, plastic is now probably cheaper than the metal rod, anyway. :)
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Reply to
dpb
Ok, a few dollars a year based on a quick calculation of heat flux trough a 10cm thick wall.. Perhaps still within reason to use plastic if it is easy.
Reply to
Kristian Ukkonen
No harm in using the plastic. I have to admit, the loss was rather bigger than I expected, when I actually calculated it..
Reply to
Kristian Ukkonen
Ok, I am a commercial refrigeration servicman so I will try to weigh in on this one. It would not be the end of the world if steel were used and the condensing unit was sized properly, other than the fact there would always be ice on the bolts and a little puddle of water under the hinges. Most commercial walk in boxes have foamed in place construction I.E. two skins of sheet metal with urethane spray foam between. There is nothing there for a screw or bolt to secure itself to. There is supposed to be a 1/4" plate steel behind the area where the hinges are placed and threaded screws are supposed to hold the hardware in place, with out penetrating the inside of the walk in. Things happen to the plate etc. and drastic measures have to be used to correct the problem. I like well nuts (expandable rubber covered nuts) for situations like this. In your case they put a whole door/frame skin assembly over the existing door and most likely caulked/silconed the heck out of it. The plastic allthread is there for looks. You would have to take a forklift and several prybars to get it to budge now. Where I work we make our own walk in coolers with a two x four wood frames (not legal in all areas per building codes). When a lag screw strips out we drill the hinge hole a little bigger a go to the next larger screw or lag bolt or use well nuts...........or put a new skin on with plastic allthread. :-) Lyndell
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or tiny-fied-
Reply to
Lyndell Thompson
My grand mother in Ohio had one of those. With grand kids around, lucky no one got hurt.
Christopher A. Young Learn more about Jesus
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Remember the latches on refrigerators - back before magnetic seals?
No way one could get out if the door closed.
Reply to
Stormin Mormon

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