The Making of Hinges
Thousands of years ago, hinges were fabricated by blacksmiths who labored over firey crucibles, painstakingly forging them, one at a time. Fortunately, the days of creating one hinge at a time have been replaced by machinery and technology that allow for hinges to be produced en masse to accommodate the needs and demands of a very fast-paced world.
Here are a few highlights regarding what goes into the fabrication of hinges:
To begin with, steel – the main product of iron and carbon – is a common base metal for hinges, but can also be modified. For example, when chromium is added, the result is stainless steel. Stainless steel hinges are excellent choices for locations where corrosion is an issue, such as marine environments.
Transforming a lump of ore into a work-of-art decorative hinge is almost always produced in a large smelter as opposed to the use of an open-fire. When heated to just the right temperature, metals respond and will take on whatever shape they are destined to be. One type of hinge– cast-bronze hinges – begin with bronze being melted and poured into a mold and finished by hand to ensure a perfectly-smooth finish.
Stamping and Extrusion
Countless hinges are stamped out of metal that has been flattened into sheet or coil form– typically steel, aluminum, stainless steel, or brass. Stamped hinges offer high quality, and precision, and at lower cost than machined or extruded hinges, due to the efficiencies of progressive die metal stamping. Metal-stamped hinges are often efficiently produced in presses utilizing metal forming processes such as punching, forming, bending, piercing, and others, depending on both the design of the component, and the design of the die.
Some high precision hinges are the result of what is called ‘extrusion’, or forcing metal into a die, under extreme pressure. Hot and cold metals can go through the process of extrusion where the final hinge product is generally thicker than stamped varieties. Extruded hinges can be of commercial quality but are also used for very demanding architectural and aerospace purposes. The process of extrusion begins by heating the stock material (for hot or cold extrusion), and then loading the material into a container in a press. A dummy block is placed behind the press; and a ram presses on the material to push it out of the die. After the extrusion is stretched and straightened, it can be heat-treated or cold-worked.
Heat Treating and Cold Working
In most cases, metal for hinges is cast or forged into a desired shape after it is made malleable through the application of heat. Heat-treating is used to alter the physical (and sometimes chemical) properties of the material, via heating or chilling. Extreme temperatures allow for a hardening or softening of the material.
Cold working, on the other hand, is a metal-working technique that strengthens the metal by changing the shape without the use of heat, Here, the metal is subjected to mechanical stress to cause a permanent change to the metal’s crystalline structure! The process gets its name since it is performed at temperatures below the metal’s recrystallization point. Cold working is commonly applied to steel, aluminum and copper which, as a result of the process, have improved tensile strength and hardness.
Quality is the Bottom Line
In the end, it is important hinges meet the requirements of their application, such as; 1) having holes that are drilled or punched with precision so every screw fits exactly as it should 2) possessing edges and features that are smooth, to avoid abrasion and/or 3) ensuring every component of each hinge properly aligns when it is subjected to the weight load it must accommodate. Whether a hinge is part of a laptop computer, part of an elevated freeway viaduct, or part of a solar-array panel in outer space, the quality behind the manufacturing process is the bottom line– the hinge must performs its job as seamlessly as possible for as long as possible.