IDFuel, the Industrial Design Weblog - Post details: Hinges, both living and dead

Hinges, both living and dead

08/15/05

Here's a chance to check out two materials that seem pretty unrelated at first glance: Leather and polypropylene. While they are engineered from very different processes, some of the applications are pretty similar.
wallet

Leather is a material that has a grain running every direction. Unlike wood, fabric, or duct tape, it won't prefer to split along a certain direction, which makes it pretty tough for certain applications. The strength derives from a crack or tiny cut not being able to propagate and fail catastrophically, giving the engineer a little breathing room.

swift

It's also a material whose flexibility can be altered according to the steps in a production process. Leather bike seats (some with titanium parts, amazingly) are designed to be "broken in" by the rider, to fit their particular pelvic structure. The leather is made flexible by soaking in water before riding the first time, and beign ridden until the shape of one's hind end is permanently dried into the shape of the saddle. Thereafter, the saddle retains the shape in a durable surface, without using a high-temperature process.

leatherhinge

Flexibility is also a neat property of leather. Without the need for a machined assembly, a designer can make a door hinge, a snowshoe that flexes with the user's stride, or a briefcase hinge. Notice that vinyl was used in most of the briefcase, but the designer used leather selectively to achieve the flexibility and duty cycles demanded by luggage.

The plastic version of this built-in flexibility is called a living hinge . Assuming that a designer doesn't want to put a leather hinge on the top of a Tic-tacs box, a living hinge offers an insanely cheap way to implement movement in plastic. No hinge axles or bearing surfaces are required, and it comes out of the mold ready to move. The hinge structure is built into an injection-molding tool, and the guidelines (here and here)for engineering it are pretty straightforward. There are some issues of durability when the hinge is subjected to a twisting load, as even the strongest material can tear when you load it at the egde (leather does this too). Interestingly, a well-designed plastic hinge has the "grain" of the polymers running lengthwise through the hinge, making it resistant to exactly the direction of tearing that would make it fail.

2hinges

What can a designer do with this? There's an opportunity to think laterally, and find new uses for materials both natural and artificial. Find the strenghts of applications that have worked in the past, and ask if you can improve it by using a new process on an old material, or vice-versa.

Permalink

Previous post: Viral...Viruses

Next post: More Team, More Fuel

Hinges, both living and dead

08/15/05

Search

Categories

Archives