Many products involve the use of spring hinges. Makeup compacts and other personal skin and beauty care products are packaged in containers fitted with spring hinges. Many other varieties of small plastic containers are also fitted with spring hinges to make their use more convenient for consumers. Varied other consumer products also make use of spring hinges.
These products range from compasses, hand-held video game systems and pencil boxes to sunglasses and glasses cases. In the context of door hardware, spring hinges are often installed as cabinet hinges to help keep cabinet doors closed tightly when not in use. Some gate hinges can also be fitted with springs to keep them closed tightly or to make their use easier.
Full-sized doors in homes, offices and in other contexts generally are not fitted with springs to the extent that they used to be. Springs have widely been replaced by hydraulic door positioning equipment, though old storm doors in residences may still be equipped with springs.
The principle of operation for all spring hinges is the same, though spring hinge configurations can vary. A spring is a mechanical energy storage medium; when a spring is compressed, that energy is stored until the compressive forced exerted on the spring dissipates, at which point the spring expels the stored energy and returns to its pre-compression form.
Spring hinges take advantage of this in a number of ways. The simplest way is through the coiling of a rigid metal around the pin of a butt hinge. Once tightly coiled, the energy stored in the coil tries to release itself; in other words, the coil tries to uncoil itself. As it does this, the metal forces itself against the metal plates of the hinge, pushing it open.
This is what happens in small container lids when they are open. The hinge can be pushed closed if the compressive force is greater than the force exerted by the coil. In order to remain closed, the compressive force must not relent, or the hinge will reopen. Other spring hinge varieties can be more complicated, but the simple principle of stored energy applies to all configurations.