A spring is a device that changes its shape under the action of an external force. When the force is removed, it returns to its original shape. The energy consumed by the spring is stored in the spring and can be restored when the spring returns to its original shape.
Generally, the amount of shape change is directly related to the magnitude of the applied force. However, if too much force is applied, the spring will permanently deform and never return to its original shape.
Springs are mainly of the following types. Among them, the most common one is composed of a wire wound into a cylindrical shape or a conical shape. A tension spring is a coil spring whose coils are usually in contact with each other.
When a force is applied to stretch the spring, the coils are separated. In contrast, the compression spring is a coil spring having a space between the continuous coils; when a force is applied to shorten the spring, the coils are squeezed together.
The third type of coil spring, called a torsion spring, causes the external force to twist the coil into a tighter spiral. Common examples of torsion springs appear in the clipboard and butterfly hairpins.
Another variation of the coil spring is the watch spring, which is coiled into a flat spiral disk instead of a cylinder or cone. One end of the spring is at the center of the spiral and the other end is at its outer edge.
Some springs are not made with coils. The most common example is a leaf spring, which is shaped like a shallow arch and is commonly used in automotive suspension systems. The other type is a disc spring, a washer-like device similar to a truncated cone. The open solid core cylinder and elastic material can also act as a spring. Non-helical springs generally function as compression springs.
Very simple, non-helical springs have been used throughout history. Even elastic branches can be used as springs. More complex spring devices can be traced back to the Bronze Age, and eyebrow tweezers are more common in several cultures. In the third century BC, Ctsii Bius, an engineer in Alexandria, Greece, developed a process for making "elastic bronze" by casting the proportion of tin in the copper alloy, casting the part, and hardening it with a hammer. He tried to use the leaf springs to operate military catapults, but they lacked strength. In the second century BC, another catapult engineer, Byilo's Philo, built a similar device and apparently achieved some success. Padlocks are widely used in the Roman Empire. At least one type of padlock uses curved metal leaves to keep the device closed until the metal leaf is locked by a key compression lock.
The next major development in the history of spring was in the Middle Ages. A power saw designed by Valadde Hunnururt uses a water wheel to push the blade in one direction while bending a rod; when the rod returns to its unflexed state, it pulls the blade in the opposite direction.
The coil spring was developed in the early fifteenth century. By replacing the gravity system and using a spring mechanism to power the timepiece, watchmakers can create reliable portable timing devices. This advancement has made it possible for precise astronomical navigation of ocean-going vessels.
In the eighteenth century, the industrial revolution promoted the development of large-scale production of spring technology. In the 1780s, British locksmith Joseph Bramah used a spring winding machine in his factory. Obviously it was modified from a lathe, and the machine replaced a cutting head with a row of wires. The wire on the reel is wrapped around a fixed rod on the lathe. The speed of the lead screw is such that the reel is parallel to the auger and can be adjusted to change the spacing of the spring coils.
The current common examples of using springs are small coils that support the keys on the phone's touchpad, to the huge coils that support the entire building and protect them from seismic vibration.
| Raw materials
Ferroalloys are the most commonly used spring materials. The most popular alloys are high carbon materials (such as steel wire for guitar strings), oil-quenched tempered low carbon, chrome silicon, chrome vanadium and stainless steel. Other metals sometimes used to make springs are beryllium copper, phosphor bronze and titanium. Rubber or urethane can be used for cylindrical, non-helical springs. Ceramic materials for coil springs have been developed in very high temperature environments. One-dimensional fiberglass composites are being tested for springs.
Various mathematical equations have been developed to characterize the spring based on factors such as wire composition and size, coil diameter, number of coils, and amount of expected external force. These equations have been incorporated into computer software to simplify the design process.
The following is a brief introduction to the manufacturing process of steel coil springs.
Cold roll. A wire having a diameter of 0.75 (18 mm) can be coiled at room temperature using one of two basic techniques. Wrap around a shaft called a shaft or mandrel. This can be done on a dedicated spring winding machine, a lathe, an electric hand drill with a mandrel clamped to the collet or a winder operated by hand shaking. A guiding mechanism, such as a lead screw on a lathe, must align the line with the desired pitch (distance between successive coils) as it wraps around the mandrel. Alternatively, the wire can be coiled without a mandrel. This is usually done with a central navigation computer (CNC) machine. Push the wire onto the support block so that it faces a grooved head, deflecting the wire and forcing it to bend. The head and the support block can be moved relative to one another in five directions to control the diameter and pitch of the spring being formed. For tension or torsion springs, after the winding operation is completed, the ends are bent into the desired loop, hook or straight section.
Hot roll. If the metal is heated to soften it, the thicker wire or bar can be coiled into a spring. Standard industrial coilers can handle steel wires up to 75 mm in diameter. According to reports, some custom springs are made of 150 mm bars. The steel is heated and wound around the mandrel. It is then immediately removed from the coiler, placed in oil, rapidly cooled and hardened. At this stage the steel is too brittle to function as a spring and must be subsequently tempered.
Heat treatment. Whether the steel is hot rolled or cold rolled, this process creates stress in the material. In order to release this stress and maintain the steel's unique elasticity, the spring must be heat treated by tempering. The spring is heated in the furnace, held at the appropriate temperature for a predetermined time, and then allowed to cool slowly. For example, a spring made of wire is heated to 500 ° F (260 ° C) for one hour.
Grinding. If the design requires that the ends of the springs are flat, the ends are ground at this stage of the manufacturing process. The spring is mounted in the fixture to ensure that the orientation is correct during the grinding process and is controlled on the rotating grinding wheel until the desired flatness is achieved. When highly automated equipment is used, the spring is held in the sleeve and both ends are grounded at the same time, first by the coarse grinding wheel and then by the thinner grinding wheel. A suitable fluid (water or oil-based material) can be used to cool the spring, lubricate the grinding wheel, and carry away the particles during the grinding process.
Shot peening. In this process, the fatigue life of the steel during repeated bending is strengthened, and the metal fatigue and cracking are resisted. The entire surface of the spring is exposed to a series of small steel balls that are hammered to smooth and compress the steel below the surface to obtain residual compressive stress.
Tuning. In order to permanently fix the length and pitch of the spring, it will be fully compressed so that all the coils are in contact with each other. Some manufacturers repeat this process many times.
coating. To prevent corrosion, the entire surface of the spring is painted, impregnated in liquid rubber, or coated with another metal such as zinc or chromium. One such process is a mechanical coating process that involves rolling a spring in a container with metal powder, water, a promoter, and glass beads to press the metal powder against the surface of the spring. Alternatively, in electroplating, the spring is immersed in a conductive liquid, which corrodes the plated metal rather than the spring. A negative charge is applied to the spring. The plating metal is dissolved in the liquid and it is given a positive charge. When the plating metal dissolves in the liquid, it releases positively charged molecules that are attracted to the negatively charged spring where they form a chemical bond. Electroplating can embrittle carbon steel springs, so shortly after plating (less than four hours), they must be baked at 325-375 °F (160-190 °C) for four hours to counteract embrittlement. The root cause is that electroplating can cause hydrogen embrittlement.
package. A specific number of springs can simply be bulk packed in a box or plastic bag. However, other forms of packaging have been developed to reduce spring damage or tangles. For example, they can be individually bagged, bundled on wires or rods, enclosed in tubes, or affixed to sticky paper.
| Quality Control
Various test devices are used to verify that the completed springs meet the specifications. The test device measures the hardness and spring force of the metal and the amount of deformation under known loads. Springs that do not meet specifications will be discarded. Statistical analysis of test results can help manufacturers identify production problems and improve processes, resulting in fewer defective springs.
About one-third of defective springs are caused by production problems. The other two thirds are caused by defects in the spring wire. In 1998, the researchers reported a spring linear test that could be used to screen out unacceptable wires.
Computer operated winders can improve quality in two ways. First, they control the diameter and pitch of the spring more precisely than manual operation. Secondly, by using a piezoelectric material whose size varies with current input, the winding head can accurately adjust the measured value of the spring characteristic in real time. As a result, these smart machines reduce the number of springs that must be discarded if they do not meet specifications.