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Tips & Tricks: Living Hinges


Living hinge fiture 1 A living hinge (or plastic hinge) is a cleverly designed thin section of material that joins two bodies together, such as the hinge on pill-boxes or lunch boxes. A properly designed hinge made from the correct materials (usually polypropylene or polyethylene) should provide a very long life, but other materials such as nylon or acetal can be used if only a limited life is required.

The secret to living hinges is getting the shape and thickness right. Below a certain thickness (about 0.4 mm) the plastic molecules will orient themselves along the direction of flow, resulting in high strength in bending perpendicular to this direction. Also, a thinner section will have lower strain on the outer surfaces compared to a thicker section. Living hinge fiture 2

The diagram to the right shows some recommended dimensions for living hinges. The thickness of the hinge can be modified with the given range to change the stiffness and feel of the hinge. The recess on the inner surface of the hinge is also very important to avoid a sharp notch as the hinge is closed.

Living hinges can be very useful, but they do need to be carefully designed for each application. For more information on living hinges, get in touch with us.


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