Page 18 - Demo

18continued on page 20We were making dinner the other night, our home version of Kung Pao Shrimp. I had a couple bottles of Kung Pao sauce sitting on the counter that I had removed the paper covering from the top of the bottles. For some reason, I decided to give one of the bottles a shake, and as soon as I shook it, the lid from the bottle flew off, and the sauce spewed out, splattering all over the counter, the side of the fridge, the coffee pot, the floor, and me. Yuk, what a sticky mess. I thought, what we have here %u201cis a failure to seal,%u201d after a few loudly stated expletives. Sure wish I%u2019d have checked the cap, or at least put my thumb on it before I shook. Oh well, too late now.That got me thinking, and yeah, I think about weird stuff all the time. Look around, and wherever you are, you see seals everywhere. There are seals on all the doors and windows in every building and car. Every food product you buy, usually anything containing liquids and gasses, has some type of seal. Without them, life could not exist as we know it. Think about our glovebox industry. That%u2019s the basis of what we do. We seal stuff. In simple terms, it is what we, the glovebox industry, are all about. Without a good seal, containment would not be possible. What is a seal, and how is it accomplished? Not as simple as you may think, but let%u2019s start with the simple. For my bottle of sauce to get to me from the manufacturer, it has to be sealed in a bottle. Without that, besides spilling all over, the sauce would be exposed to bacteria and dirt from the surrounding world, and would be pretty disgusting by the time I got it. And, as we know, for the basics of containment, you need a container, in this case, a bottle, a rubber seal, and a threaded lid to compress the seal. Atmospheric pressure is also in the mix here, but we%u2019ll get to that shortly.The lid for the bottle is metal, and the bottle is glass, and when you tighten the lid, it sits tight on the edge of the bottle opening. The problem is that the lid is not perfectly flat, and neither is the bottle edge, and when they come together, gaps between them leak. By adding the soft elastomer seal between the two surfaces, it conforms to the irregular surfaces of the bottle and the lid, filling up the inconsistencies or gaps as the lid compresses the rubber. That, my friends, is the basic principle of how almost every seal out in the world works. Atmospheric pressure can be utilized to enhance the sealing mechanism by helping the lid compress the seal. In the application of the bottle of sauce, during the bottling process, the sauce in the bottle is at an elevated temperature when the lid is placed on. Then, as it cools, the pressure in the bottle lowers to less than the outer atmospheric pressure, creating a vacuum in the bottle and causing increased push on the compressed seal on the bottle. Remember the crushed can experiment in high school? That%u2019s why you get the pop when you open it. If that is missing, it means that the seal has been lost and the sauce may be contaminated. But everybody knows this, right? I can hear my wife in the background, %u201cThank You, Captain Obvious! Shut up with your mansplaining%u201d%u2026Ha Ha!In the glovebox world, we use the same technique to seal our boxes. Every glovebox has windows, removable panels, and doors that require a seal to complete the containment. An elastomer (rubber) %u201cgasket%u201d is compressed between two hard surfaces, usually a panel and glovebox shell, filling up the gaps and inconsistencies in each mating surface. It%u2019s not quite as simple as the bottle of sauce, but it%u2019s the exact same concept. Although, don%u2019t be fooled by the simplicity of the bottle seal. Every seal application, especially when dealing with hazardous materials that have the capacity to kill someone, requires detailed analysis and consideration of the design details. You know, I thought this would be an easy subject to cover. After listening to me whine about the saucespewing event, and thankfully there were no actual witnesses%u2019, my son Thoughts from NewmanThe Art of the SealBy: John T. Newman, P.E.Atmospheric pressure can be utilized to enhance the sealing mechanism by helping the lid compress the seal.