A spring is a device that changes its shape in response to an external force, returning to its original shape when the force is removed. The energy expended in deforming the spring is stored in it and can be recovered when the spring returns to its original shape. Generally, the amount of the shape change is directly related to the amount of force exerted. If too large a force is applied, however, the spring will permanently deform and never return to its original shape.
There are several types of springs. One of the most common consists of wire wound into a cylindrical or conical shape. An extension spring is a coiled spring whose coils normally touch each other; as a force is applied to stretch the spring, the coils separate. In contrast, a compression spring is a coiled spring with space between successive coils; when a force is applied to shorten the spring, the coils are pushed closer together. A third type of coiled spring, called a torsion spring, is designed so the applied force twists the coil into a tighter spiral. Common examples of torsion springs are found in clipboards and butterfly hair clips.
Still another variation of coiled springs is the watch spring, which is coiled into a flat spiral rather than a cylinder or cone. One end of the spring is at the center of the spiral, and the other is at its outer edge.
Some springs are fashioned without coils. The most common example is the leaf spring, which is shaped like a shallow arch; it is commonly used for automobile suspension systems. Another type is a disc spring, a washer-like device that is shaped like a truncated cone. Open-core cylinders of solid, elastic material can also act as springs. Non-coil springs generally function as compression springs.
Very simple, non-coil springs have been used throughout history. Even a resilient tree branch can be used as a spring. More sophisticated spring devices date to the Bronze Age, when eyebrow tweezers were common in several cultures. During the third century B.C., Greek engineer Ctesibius of Alexandria developed a process for making "springy bronze" by increasing the proportion of tin in the copper alloy, casting the part, and hardening it with hammer blows. He attempted to use a combination of leaf springs to operate a military catapult, but they were not powerful enough. During the second century B.C., Philo of Byzantium, another catapult engineer, built a similar device, apparently with some success. Padlocks were widely used in the ancient Roman empire, and at least one type used bowed metal leaves to keep the devices closed until the leaves were compressed with keys.
The next significant development in the history of springs came in the Middle Ages. A power saw devised by Villard de Honnecourt about 1250 used a water wheel to push the saw blade in one direction, simultaneously bending a pole; as the pole returned to its unbent state, it pulled the saw blade in the opposite direction.
Coiled springs were developed in the early fifteenth century. By replacing the system of weights that commonly powered clocks with a wound spring mechanism, clockmakers were able to fashion reliable, portable timekeeping devices. This advance made precise celestial navigation possible for ocean-going ships.
In the eighteenth century, the Industrial Revolution spurred the development of mass-production techniques for making springs. During the 1780s, British locksmith Joseph Bramah used a spring winding machine in his factory. Apparently an adaptation of a lathe, the machine carried a reel of wire in place of a cutting head. Wire from the reel was wrapped around a rod secured in the lathe. The speed of the lead screw, which carried the reel parallel to the spinning rod, could be adjusted to vary the spacing of the spring's coils.
Common examples of current spring usage range from tiny coils that support keys on cellular phone touchpads to enormous coils that support entire buildings and protect them from earthquake vibration.
Steel alloys are the most commonly used spring materials. The most popular alloys include high-carbon (such as the music wire used for guitar strings), oil-tempered low-carbon, chrome silicon, chrome vanadium, and stainless steel.
Other metals that are sometimes used to make springs are beryllium copper alloy, phosphor bronze, and titanium. Rubber or urethane may be used for cylindrical, non-coil springs. Ceramic material has been developed for coiled springs in very high-temperature environments. One-directional glass fiber composite materials are being tested for possible use in springs.
Various mathematical equations have been developed to describe the properties of springs, based on such factors as wire composition and size, spring coil diameter, the number of coils, and the amount of expected external force. These equations have been incorporated into computer software to simplify the design process.
The Manufacturing Process
The following description focuses on the manufacture of steel-alloy, coiled springs.
1 Cold winding. Wire up to 0.75 in (18 mm) in diameter can be coiled at room temperature using one of two basic techniques. One consists of winding the wire around a shaft called an arbor or mandrel. This may be done on a dedicated spring-winding machine, a lathe, an electric hand drill with the mandrel secured in the chuck, or a winding machine operated by hand cranking. A guiding mechanism, such as the lead screw on a lathe, must be used to align the wire into the desired pitch (distance between successive coils) as it wraps around the mandrel.
Alternatively, the wire may be coiled without a mandrel. This is generally done with a central navigation computer (CNC) machine. The wire is pushed forward over a support block toward a grooved head that deflects the wire, forcing it to bend. The head and support block can be moved relative to each other in as many as five directions to control the diameter and pitch of the spring that is being formed.
For extension or torsion springs, the ends are bent into the desired loops, hooks, or straight sections after the coiling operation is completed.
- 2 Hot winding. Thicker wire or bar stock can be coiled into springs if the metal is heated to make it flexible. Standard industrial coiling machines can handle steel bar up to 3 in (75 mm) in diameter, and custom springs have reportedly been made from bars as much as 6 in (150 mm) thick. The steel is coiled around a mandrel while red hot. Then it is immediately removed from the coiling machine and plunged into oil to cool it quickly and harden it. At this stage, the steel is too brittle to function as a spring, and it must subsequently be tempered.
- 3 Heat treating. Whether the steel has been coiled hot or cold, the process has created stress within the material. To relieve this stress and allow the steel to maintain its characteristic resilience, the spring must be tempered by heat treating it. The spring is heated in an oven, held at the appropriate temperature for a predetermined time, and then allowed to cool slowly. For example, a spring made of music wire is heated to 500°F (260°C) for one hour.
- 4 Grinding. If the design calls for flat ends on the spring, the ends are ground at this stage of the manufacturing process. The spring is mounted in a jig to ensure the correct orientation during grinding, and it is held against a rotating abrasive wheel until the desired degree of flatness is obtained. When highly automated equipment is used, the spring is held in a sleeve while both ends are ground simultaneously, first by coarse wheels and then by finer wheels. An appropriate fluid (water or an oil-based substance) may be used to cool the spring, lubricate the grinding wheel, and carry away particles during the grinding.
- 5 Shot peening. This process strengthens the steel to resist metal fatigue and cracking during its lifetime of repeated flexings. The entire surface of the spring is exposed to a barrage of tiny steel balls that hammer it smooth and compress the steel that lies just below the surface.
- 6 Setting. To permanently fix the desired length and pitch of the spring, it is fully compressed so that all the coils touch each other. Some manufacturers repeat this process several times.
7 Coating. To prevent corrosion, the entire surface of the spring is protected by painting it, dipping it in liquid rubber, or plating it with another metal such as zinc or chromium. One process, called mechanical plating, involves tumbling the spring in a container with metallic powder, water, accelerant chemicals, and tiny glass beads that pound the metallic powder onto the spring surface.
Alternatively, in electroplating, the spring is immersed in an electrically conductive liquid that will corrode the plating metal but not the spring. A negative electrical charge is applied to the spring. Also immersed in the liquid is a supply of the plating metal, and it is given a positive electrical charge. As the plating metal dissolves in the liquid, it releases positively charged molecules that are attracted to the negatively charged spring, where they bond chemically. Electroplating makes carbon steel springs brittle, so shortly after plating (less than four hours) they must be baked at 325-375°F (160-190°C) for four hours to counteract the embrittlement.
- 8 Packaging. Desired quantities of springs may simply be bulk packaged in boxes or plastic bags. However, other forms of packaging have been developed to minimize damage or tangling of springs. For example, they may be individually bagged, strung onto wires or rods, enclosed in tubes, or affixed to sticky paper.
Various testing devices are used to check completed springs for compliance with specifications. The testing devices measure such properties as the hardness of the metal and the amount of the spring's deformation under a known force. Springs that do not meet the specifications are discarded. Statistical analysis of the test results can help manufacturers identify production problems and improve processes so fewer defective springs are produced.
Approximately one-third of defective springs result from production problems. The other two-thirds are caused by deficiencies in the wire used to form the springs. In 1998, researchers reported the development of a wire coilability test (called FRACMAT) that could screen out inadequate wire prior to manufacturing springs.
Computer-operated coiling machines improve quality in two ways. First, they control the diameter and pitch of the spring more precisely than manual operations can. Second, through the use of piezoelectric materials, whose size varies with electrical input, CNC coiling heads can precisely adjust in real time to measurements of spring characteristics. As a result, these intelligent machines produce fewer springs that must be rejected for not meeting specifications.
Demands of the rapidly growing computer and cellular phone industries are pushing spring manufacturers to develop reliable, cost-effective techniques for making very small springs. Springs that support keys on touchpads and keyboards are important, but there are less apparent applications as well. For instance, a manufacturer of test equipment used in semiconductor production has developed a microspring contact technology. Thousands of tiny springs, only 40 mils (0.040 in or 1 mm) high, are bonded to individual contact points of a semiconductor wafer. When this wafer is pressed against a test instrument, the springs compress, establishing highly reliable electrical connections.
Medical devices also use very small springs. A coiled spring has been developed for use in the insertion end of a catheter or an endoscope. Made of wire 0.0012 in (30 micrometers or 0.030 mm) in diameter, the spring is 0.0036 in (0.092 mm) thick—about the same as a human hair. The Japanese company that developed this spring is attempting to make it even smaller.
The ultimate miniaturization accomplished so far was accomplished in 1997 by an Austrian chemist named Bernard Krautler. He built a molecular spring by stringing 12 carbon atoms together and attaching a vitamin B12 molecule to each end of the chain by means of a cobalt atom. In the relaxed state the chain has a zigzag shape; when it is wetted with water, however, it kinks tightly together. Adding cyclodextrin causes the chain to return to its relaxed state. No practical application of this spring has yet been found, but research continues.
Where to Learn More
"Coil Spring Making Process—Automotive." Industrial Engineers and Spring Makers. http://www.ozemail.com (November 2000).
"H & R Spring Overview." http://www.hrsprings.com/abouthr.html (November 2000).
Silberstein, Dave. "How to Make Springs." http://home.earthlink.net/-bazillion/intro.html (November 2000).
A spring is a location where groundwater naturally emerges from the Earth's subsurface in a defined flow and in an amount large enough to form a pool or stream-like flow. Springs can discharge fresh groundwater either onto the ground surface, directly into the beds of rivers or streams, or directly into the ocean below sea level.* Springs form the headwaters of some streams.
Flow from a spring can range from barely detectable (in which case the spring is usually called a seep) to more than 30 cubic meters per second, which is about 30,000 liters (7,900 gallons) each second. Temperatures of spring water range from near water's freezing point to its boiling point.
Human Interest in Springs
Springs have captured the imagination of scientists and philosophers for thousands of years. In fact, many of the earliest ideas about the hydrologic cycle were inspired as people tried to understand the source of spring water. For many people, springs are the most obvious and interesting evidence of groundwater. Spring water also has practical uses. For example, in arid regions, springs have played a role in determining where humans have chosen to settle.
Spring water also is associated in the public's mind with exceptional quality, and bottled spring water is a booming business. Spring waters, particularly those from mineral and hot springs, have long been believed to possess therapeutic and medicinal value. However, no scientific evidence exists regarding their medicinal value. To the contrary, water from hot springs often contains large amounts of toxic dissolved materials, such as arsenic, that have leached from underground layers of rocks.
How Springs Form
Most of the water that emerges at springs is meteoric in nature: that is, it originally fell as rain or snow on the surface of the Earth. At hot springs near active volcanoes, some of the water may have originated from magma, molten rock that also contains dissolved substances such as water. As magma cools and crystallizes in the Earth's crust, it releases much of this water. Spring water also can be ancient sea water, although it usually is diluted with meteoric water.
Conceptually, the groundwater system associated with springs is simple. It consists of:
- A recharge area where water enters the subsurface;
- An aquifer or set of aquifers through which the water flows; and
- A discharge point where water emerges as a spring.
The existence of a spring requires that below the surface (the area commonly called the subsurface), the infiltrating water encounters a low permeability zone and is unable to continue to move downward as fast as it is supplied at the surface; as a result, the water spreads laterally until it intersects the land surface where erosion has lowered the topography to the water's level (e.g., on the side of a canyon).*
A range of geological structures and topographic features can direct water to the surface and form a spring. Many seeps and small springs are associated with topographic depressions where the water table intersects the Earth's surface. Larger springs usually are formed where geological structures, such as a faults and fractures, or layers of low-permeability material, force large amounts of water to the surface.
Characteristics of Springs
Springs may be considered curious features because water appears to flow directly out of rocks. Yet springs are less mysterious when one understands where the water came from and how long it has been in the subsurface.
Origin of the Water.
The question of where the water came from is specifically asking from what region the water originates—commonly termed the recharge area. The recharge area is usually, but not always, surrounded or outlined by topographic highs such as ridges and mountaintops. It is within the recharge area where the water, generally from precipitation, sinks below the surface and travels to the spring.*
Age of the Water.
The question of how old the water is (i.e., the water's age) refers to the amount of time that the water was located in the subsurface before emerging at the spring. Water enters the ground at different locations and moves at different speeds. The age of the spring water is thus defined as the average time the water spent in the subsurface before emerging as a spring.
Water ages can be estimated with chemical tracers , provided the chemical behavior of tracers in the subsurface is known. One example of a useful tracer is tritium, a radioactive form of hydrogen. Tritium decays radioactively to helium at a known rate. By measuring the relative abundance of tritium and helium produced by the decay of tritium, it is possible to determine the age of the water.
If recharge rates to the groundwater system are low (as they are in arid regions), and the distances traveled by the water are great, then the age of spring water can be large. Some of the springs in arid Nevada may be discharging water with average ages of hundreds to thousands of years.
In general, when water age is old, variations in the flow of water from the spring will be small. In contrast, springs with large variations in flow (and seasonal springs that are sometimes dry) usually discharge so-called "young" water that was in the subsurface only weeks to months.
The temperature of spring water is related to the amount and rate of groundwater flow. As depth below the Earth's surface increases, temperature increases. As a result, deep circulating groundwater can be warmed. If groundwater velocities are low and the springs are small, most of the heat will be conducted though the rocks and the water will remain cold. If the springs are large, the spring water also will be cold because the volume of water is too great to be adequately warmed. The warmest springs occur when discharges are moderately large, and often are found in regions where the subsurface is unusually warm, such as volcanically active areas.*
As groundwater flows to a spring, its composition and temperature may change depending on the materials through which the water flows, the length of time the water is below the surface, and the geological setting. Springs provide access to water that has reacted with rocks in the subsurface at distant regions, and in some cases, in distant periods of time. Spring water can thus provide an opportunity to obtain information about subsurface geological and hydrological processes. In regions with no wells or boreholes, spring water may be one of the only sources of information about the subsurface.
The geologic setting of a region determines whether a spring will occur, whether it will be small or large, and what the characteristics of its water will be. The discharge of large volumes of groundwater at a spring requires two factors:
- Recharge area must be large and/or recharge rate must be high so that large volumes of water can enter the groundwater system; and
- Aquifer permeability must be large so that water flow can be concentrated in a relatively small area.
These conditions are most often satisfied either in volcanically active regions with young volcanic rocks (such as the Oregon and California Cascades), or in karst terrain where subterranean passages are dissolved in carbonate rocks, often limestone.
An example of a large spring is the one from which the Metolius River in the Cascade Mountains of central Oregon abruptly appears. The Metolius Spring discharges more than 3 cubic meters (100 cubic feet) per second, which is equivalent to 792 gallons every second, and at a temperature that is at a nearly constant 9°C (48°F). This rate of discharge is also equivalent to nearly all the precipitation that falls in the spring's 400-square kilometer (154-square mile) recharge area. The groundwater flows through young lava flows and is brought back to the surface along a large fault.
see also Bottled Water; Cavern Development; Earth's Interior, Water in the; Fresh Water, Natural Composition of; Geothermal Energy; Groundwater; Hot Springs and Geysers; Isotopes: Applications in Natural Waters; Karst Hydrology; Life in Extreme Water Environments; Mineral Waters and Spas; Tracers in Fresh Water.
Chapelle, Frank, James E. Landmeyers, and Francis H. Chapelle. The Hidden Sea: Ground Water, Springs, and Wells. Tucson, AZ: Geoscience Press, 1997.
Lamoreaux, Philip E., and J. T. Tanner, eds. Springs and Bottled Waters of The World: Ancient History, Source, Occurrence, Quality, and Use. New York: Springer-Verlag, 2001.
Manga, Michael. "Using Springs to Study Groundwater Flow and Active GeologicProcesses." Annual Reviews of Earth and Planetary Sciences 29 (2001):203–230.
Meinzer, M. O. Large Springs in the United States. U.S. Geological Survey, WaterSupply Paper 557 (1927).
Waring, G. A., R. R. Blankenship, and R. Bentall. Thermal Springs in the United States and Other Countries of the World; A Summary. U.S. Geological Survey, Professional Paper 492 (1965).
* Photographs of hot springs occur in the following entries: "Fresh Water, Natural Composition of;" "Hot Springs and Geysers;" and "Life in Extreme Water Environments."
* See "Groundwater" for a generalized diagram showing a recharge area to aquifers.
* See "Groundwater" for a schematic of a gravity spring.
* See "Lakes: Chemical Processes" for a photograph of a saline lake with a lakebed spring.
A site where groundwater emerges from the subsurface is known as a spring. Springs present the most familiar manifestation of groundwater, and have been utilized as drinking water sources throughout history. These natural features have sometimes been viewed mysteriously and the waters regarded as having therapeutic, medicinal, or magical properties. These misconceptions continue today, including the belief that spring water is of superior quality or purity. Fallacies such as this are exploited in the sales of beverages and other products. Unfortunately, water that flows naturally from the ground is conveyed with no more special properties than the same groundwater that is drawn from a nearby well. In fact, because of the exposure at the surface, spring water is potentially more easily contaminated than water drawn from a properly constructed well.
Springs can be classified based on their groundwater source (e.g., water-table springs and perched springs). Water table springs discharge where the land surface intersects the water table. Perched springs, however, flow from the intersection of the land surface with a local groundwater body that is separated from the main saturated zone below by a zone of relatively lower permeability and an unsaturated zone . In addition to the location of the water table, groundwater discharge at springs is commonly controlled by other factors such as stratigraphic contacts, faults and fractures , and cavern openings. The relationship of local topography and geologic structure to the point of groundwater discharge is one of the most common classification systems for springs.
Springs are also classified based on magnitude of discharge, chemical characteristics, water temperature , type of the groundwater flow system, and others. Because springs allow them to easily and directly access the groundwater, hydrogeologists often use information of this nature to help interpret the groundwater flow system of an area .
The quantity of discharge from a particular spring is determined by three variables: aquifer permeability, groundwater basin size, and quantity of recharge. The largest springs can have a discharge of over 1,000 cubic feet per second. However, springs of this size are rare. A spring with a discharge
insufficient to support a small rivulet is referred to as a seep. The flow from a seep is commonly so low as to preclude measurement.
See also Karst topography; Porosity and permeability; Saturated zone
The constant temperature and rich oxygen content of spring water attracts fish in both cold and warm weather times. As a result areas around underwater springs provide prime fishing since they can draw exceptionally large numbers of fish. Springs in conjunction with submerged weed beds are especially productive.
Underwater springs in Henry’s Lake are well-known fish producers. They are concealed in areas of submerged weed beds. When the weather is hot, locate an underwater spring and the fish will consistently be there. The difficulty is locating an underwater spring hidden in the midst of such a large expanse of
water. Once found, map its location by triangulation or record it on a GPS. The ability to easily return to underwater springs simplifies fishing. A thermistor on a remote cord is a must in probing a spring’s exact location. Fish mill about in incredible numbers simplify fishing because their greed instincts strike up competition for your offering. A variety of flies such as leeches, dragonfly, damselfly, scuds, or a baitfish imitation can be fruitful. Even after spooking the school, resting the area is all that’s needed for them to return.