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Living Hinge

 
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Living hinge
 
 
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A living hinge is a thin flexible hinge
Hinge

A hinge is a type of Bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation ....
 (flexure bearing
Flexure bearing

A flexure bearing is a bearing which allows motion by bending a load element.A typical flexure bearing is just one part, joining two other parts....
) made from plastic
Plastic

Plastic is the general common term for a wide range of synthetic or semisynthetic organic chemistry solid materials suitable for the manufacture of industrial products....
 (rather than cloth, leather
Leather

Leather is a material created through the tanning of rawhides and skins of animals, primarily cattlehide. The tanning process converts the putrescible skin into a durable, long-lasting and versatile natural material for various uses....
, or some other substance) that joins two rigid plastic parts together, allowing them to bend along the line of the hinge. It is typically manufactured in an injection molding operation that creates all three parts at one time as a single part, and if correctly designed and constructed, it can remain functional over the life of the part.






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Mint Box Polypropylene Lid
A living hinge is a thin flexible hinge
Hinge

A hinge is a type of Bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation ....
 (flexure bearing
Flexure bearing

A flexure bearing is a bearing which allows motion by bending a load element.A typical flexure bearing is just one part, joining two other parts....
) made from plastic
Plastic

Plastic is the general common term for a wide range of synthetic or semisynthetic organic chemistry solid materials suitable for the manufacture of industrial products....
 (rather than cloth, leather
Leather

Leather is a material created through the tanning of rawhides and skins of animals, primarily cattlehide. The tanning process converts the putrescible skin into a durable, long-lasting and versatile natural material for various uses....
, or some other substance) that joins two rigid plastic parts together, allowing them to bend along the line of the hinge. It is typically manufactured in an injection molding operation that creates all three parts at one time as a single part, and if correctly designed and constructed, it can remain functional over the life of the part. Polyethylene
Polyethylene

Polyethylene or polythene is a thermoplastic commodity heavily used in consumer products . Over 60 million tons of the material are produced worldwide every year....
 and polypropylene
Polypropylene

Polypropylene or polypropene is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes....
 are considered to be the best resin
Resin

Resin is a hydrocarbon secretion of many plants, particularly Pinophyta. It is valued for its chemical constituents and uses, such as varnishes and adhesives, as an important source of raw materials for organic synthesis, or for incense and perfume....
s for living hinges, due to their excellent fatigue
Fatigue (material)

In materials science, 'fatigue' is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading....
 resistance.

A thinned section of the plastic bends to allow movement. The minimal friction
Friction

File:Friction alt.svgFriction is the force resisting the relative lateral motion of solid surfaces, fluid layers, or material elements in contact....
 and very little wear
Wear

In materials science, wear is the erosion of material from a solid surface by the action of another substance. The study of the processes of wear is part of the discipline of tribology....
 in such a hinge makes it useful in the design of microelectromechanical systems
Microelectromechanical systems

Microelectromechanical systems is the technology of the very small, and merges at the nano-scale into nanoelectromechanical systems and nanotechnology....
, and the low cost and ease of manufacturing makes them quite common in disposable
Disposable

A disposable product is a product designed for cheapness and short-term convenience rather than medium to long-term durability, with most products only intended for single use....
 packaging. These can flex more than a million cycles without failure.

History

A few years after the introduction of polypropylene
Polypropylene

Polypropylene or polypropene is a thermoplastic polymer, made by the chemical industry and used in a wide variety of applications, including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes....
 (PP) in 1957, "engineers at Enjay (now ExxonMobil) noticed an unusual phenomenon while studying pigment dispersion in very thin-walled color chips. Below a certain thickness, the PP molecules oriented in the direction of flow. Bending perpendicular to this orientation resulted in a stronger part that did not break with repeated flexing. Bob Munns, who worked at Enjay at the time, coined the term living hinge and the name stuck. The living hinge was introduced to the industry as a hinged recipe box at the 1963 NPE. Over the next 40 years, creative design engineers used living hinges in thousands of applications ranging from dispensing closures with hinged caps to automobile gas pedals and carrying cases. The current trend for parts consolidation and assembly minimization has created a renewed interest in integrally molded hinges."

Sources and notes


Further reading