What's new

No can opener? No problem!

By David Shaw, 4 April 2019

When opening a tin can, chances are you’ll turn to a can opener or use a ring pull. But these are not the only ways to crack open a tin. In this activity, try using sandpaper to remove the top of a can!

Safety: Open tins can be sharp, ask an adult to supervise this activity. Do not use dented cans.

You will need

• Steel can of food
• Wet and dry sandpaper – we found 180 grit worked well
• Paper towel
• Water

What to do

1. Put your sandpaper down on a flat surface, such as a table.
2. Put the can on the sandpaper, upside down. The end you want to open should be touching the sandpaper.
3. Hold the sandpaper with one hand and the can with the other. Rub the can against the paper firmly but gently. Be careful not to rub your hand on the sandpaper, or you’ll scrape your skin!
4. Every minute or so, stop and look at the top rim of the can. You want to see three distinct layers of metal.
5. While you’re grinding, you might hear the noise drop in pitch. That’s a sign you’re getting close!
6. When you can see three layers of metal all the way around the rim, stop grinding – you’re almost ready to open the can.
7. Wet some paper towels with water and gently wipe the top of the can. Get rid of all the metal dust so it doesn’t fall in the food, then wash your hands.
8. Make sure the can is the right way up and then squeeze it. The lid should pop right off the top! Be careful handling the can and lid – the edges can be sharp.
9. Before you eat the contents, check to see if there’s any black powder on top of the food. That’s probably metal powder. In small quantities it’s not dangerous, but it will make your food taste funny, so scoop it off.
10. When you’re finished, remember to recycle the can and lid!

What’s happening?

Canning has been around for more than 200 years. It’s been a great way to preserve food ever since, often keeping it safe for years without refrigeration.

There have been some truly remarkable examples of long-life cans. When the steamboat Bertrand sank in 1865, it was carrying several cans including brandied peaches, oysters, plum tomatoes, honey, and mixed vegetables. Over 100 years later in 1974, chemists tested the food inside and declared it safe to eat!

A can is usually made of three pieces of metal. There are circles for the top and bottom, and a pipe or cylinder to make the sides. To attach the ends to the sides, the two pieces are folded around each other and then welded. When you sand away the top layer, you break the lid away from the folds and weld, allowing it to pop off.

Not so tinny

Although they are called tin cans, they are usually made of steel. You can check that yourself with a magnet – magnets don’t stick to tin. They will stick to steel that contains iron!

Steel is a good material for cans because it is cheap, strong and easy to recycle. Over long periods of time it can rust, so many cans are coated in a thin layer of tin. On the inside, cans are often coated in plastic to prevent food acids from dissolving the metal.

Try a different kind of preserving – drying potpourri

If you’re after more science activities for kids, subscribe to Double Helix magazine!