Why Do Freezer Doors Use Magnets to Close?

11 October 2018

Door magnets are added to freezers because cooling equipment has a flaw. Correction, it’s not a system flaw, just a simple law of physics, one that’s not always easy to remedy. A sealed enclosure by design, freezers trap air. Consequently, a positive system pressure develops because of the refrigeration unit. Left unattended, positive pressure causes the dreaded “door pop-open effect.” Door magnets prevent such seal breaking incidents from occurring.

Freezer Door Magnets

Sturdy but simple discrete magnets line a freezer door. There’s a blocky magnetic core, which mates with a flat plate on the swinging door. On another unit, the discrete fittings are replaced by an extruded gasket, a flexible seal that exhibits magnetic properties. Compounded with the flexible plastic during the formulation stage or added as a sintered core, the magnetic gasket holds the swinging panel secure, even when the positive pressure rises.

Why Do Freezer Doors Pop Open?

Well, there are complex air currents flowing in some of these units. Sealed so that the chill air temperature is maintained, it’s not easy to balance the interior pressure against the outer atmospheric pressure. If the refrigeration unit spikes its power output, or if an external door opens elsewhere inside the building, or even if another door on the freezer opens suddenly, a non-magnetized appliance door will open all by itself. In terms of physical laws, which tend to be inviolable, the system will attempt to equalize the pressure, and that attempt will cause the pop-open effect.

Determining the Pop-open Culprits

The refrigeration unit is guilty, but it’s not the sole villain in this tale. There are chemical processes occurring in the perishable items stored inside a freezer. They can alter the pressure differential. Defrosting cycles raise enclosure temperatures. As temperatures rise, molecules become excited. In other words, when the temperature climbs, so does the internal pressure. As mentioned earlier, even if the equipment consistently delivers a balanced volume of air, the opening of an outside entrance could just trigger a pressure equalization incident, so the freezer door comes ajar, just slightly.

Finally, multi-door freezers use door magnet, too. To close the frosty chamber and keep everything safely chilled, the magnets anchor the door. Then, as a door further down opens and closes, the magnetically latched panel stays securely locked. Otherwise, the closing of that second door would be enough to pneumatically drive air forward and into the sealed cooling area, at which point any unsecured doors would open a crack, just enough to cause a serious energy compromising event. Essentially, at the end of the day, unsecured freezer doors can be opened by sudden pressure changes, unless door magnets are fitted.

Mark Connelly
C&M Coolroom Services
E-mail: markconnelly@cmcoolrooms.com.au
Mobile: 0412 536 315

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