Buying a new can opener every time the blade gets dull can be expensive and wasteful. Perhaps the blade can be sharpened extending the life of the tool. This is a guide about sharpening the blade of a handheld can opener.
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I read somewhere that you can use foils to sharpen your can opener blade. Just fold it twice then run your can opener through them. I've done it several times before and it works. Just don't overdo it. :)
By Dudez 
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Here are questions related to Sharpening a Handheld Can Opener Blade.
Does anyone know of a place that sharpens hand held can openers?
By Pat M.
By Cricket 12/07/2011
pamphyila is right. You can sharpen can openers very easily by running sand paper through them. Get a good coarse grade and run it through the can opener several times and it will come out like new. I do this with my can openers (hand held and electric), scissors and even my hole punches!
Also Deeli is definitely right. Getting them sharpened would cost much more than buying a new one. Whereas you can buy a package of sandpaper for a couple of dollars and they will last you for years, and have many many uses.
I have a hand held can opener which has gotten very dull. Does anyone have tips for sharpening the blade?
We've had this U.S.A. made Swing-A-Way for fifteen years and it shows no signs of wearing out: around $9 online. I think the solution to your problem is just getting a quality can opener and you won't have to sharpen it! Here's a link to a picture I found that most closely resembles ours.
All I do is rinse it off under hot water, dab the excess water off with a towel, put it in the dish drainer to air dry before putting it back into an enclosed drawer. Hope that makes your life easier!