Spring Hinges and More Spring Hinges
While they seem to be getting harder to find, the house I grew up in had all screen doors with spring hinges. They would allow them to be easily opened, but also to swing shut once they were let go. At our new house, all screen doors are sliding doors, or else there is no screen door at all. They were often used because of their ability to make doors close tightly when not in use. While house and office doors of this type have been mostly replaced with hydraulic door positioning equipment, old storm doors might still be constructed in this way. Today, they are more often found in makeup compacts, compasses, hand held video game systems, pencil boxes and glasses cases.
Spring hinges differ from other hinges due to how they are equipped with springs that are designed to either assist or impede door movement. The main purpose of the spring hinge is the same; however, because there is such a wide use of applications for these products, the configurations can vary. These products are often also thought of as self closing. A popular use is in kitchens where the doors can close on their own, or like the old doors that were able to close on their own. Another situation in which these are popular is hospitals where doors in this fashion can be used for privacy and to prevent diseases from easily transferring.
The way these products work is the spring acts as an energy storage medium. In other words, when it is compressed the energy is stored until the compressive force dissipates. Once this happens the spring is able to release the stored energy and return to its original form. In general, the coil wants to uncoil itself. When it is compressed, the energy is stored up, but the coil is trying to release it. The energy to compress the coil must be greater than the force exerted by the coil, and the object keeping it in the coiled position must also remain stronger and more secure than the coils pressure.