Lesson 2: Basic Lids
Taught by Professor Timothy Cann
Okay, people, settle down. We only have a five minute class today, and we have a lot of ground to cover. If you look in your syllabus, you'll find that today we're going to cover basic lids. First off, what's a lid? Well, quite simply, it's the piece at the top of the can that you remove to open the can. Simple enough? Good, we'll move on then. While there are quite literally hundreds upon hundreds of different lids that we could make, today we're going to cover five of the most basic designs, but first, a little lid anatomy.
Okay, now have a look at figure 2.1, on the right. This is the cross section of a basic slip cover. The red portion is the body of the tin, and the green portion is the lid. If you roll your cursor over the diagram, you'll notice that a number of terms pop up. First, we'll look at the curl. There are, in fact, two of them, the circles at the edges of both the lid and the body. Roll your cursor over the diagam and have a look.
2.1 - Slip Cover Cross Section
The edges of tin plate are very sharp, so to eliminate the risk of injury, and also to make it easier to secure or remove the lid, the edges of both the body and the lid are curled up very tightly, making them smooth and rounded. Also, take note of the bead. This is a small ridge that runs all the way around the body, and it helps both to secure the lid and create a tighter fit. The straight portion of the lid that comes into contact with the body is called the skirt, and the part immediately above that connects to the top is called the side radius.
But don't be fooled! If you look at figure 2.2, the top view of a rectangular tin, you'll notice that the bend in the lid that translates from one side to another is called a corner radius. The two are easy to confuse, and you don't want to lose points on the final exam. Slip covers are the most common lids for decorative tins, and you've seen them on all sorts of cookie and candy tins.
2.2 - Rectangular Tin, Top View
A common variation on the basic slip cover is the slip cover with a stacking feature. A stacking feature is a small groove that runs around the side radius of a tin, so that when another tin is stacked on top, the bottom of the top tin fits snugly on the stacking feature of the lid of the bottom tin. Figure 2.3 illustrates the stacking feature, and shows the bottom of another tin (also in red) fitting into the stacking feature.
2.4 - Full Friction Plug
Our next lid is the full friction plug, which is illustrated above and to the right in figure 2.4. On a full friction plug, rather than slip over the outside of the body, the lid fits inside the body, with the curl securing it. One of the most common uses of a full friction plug is for car wax tins, as well as many other tins that contain waxes or pomades. Our next type of lid, the single friction plug, introduces a couple of new terms. You'll notice that an item in blue has been added to figure 2.5. This blue piece is the ring. The ring is permanently connected to the body of the tin by means of a seam. If you roll your cursor over figure 2.5, these new terms will be illustrated. The lid nests inside the tin, as with a full friction plug, but unlike the full friction plug, the tin secures inside the ring, rather than inside the body of the tin itself. If this seems like an odd design, think again... you probably have one of these tins in your house. Single friction plugs are commonly found on tins that contain cocoa or dry mustard. Lastly, we have the multiple friction lid. This lid is similar to the single friction plug in that it has a ring, but the ring has an extra groove, creating multiple points of contact (hence multiple friction!), and creating a more secure fit. Multiple friction lids are most commonly used on paint cans, and other such cans that contain dangerous substances or chemicals. Well, that's it for today, class... no homework, but be prepared for a pop quiz next week.
2.3 - Slip Cover with Stacking Feature
2.5 - Single Friction Plug
2.6 Multiple Friction Lid