This article will take an in-depth look at compression springs.
The article will look at topics such as:
This chapter will discuss what compression springs are and the considerations when choosing compression springs.
Coil springs called compression springs can store mechanical energy when they are compressed. These open-coiled, helical springs provide resistance to compressive loading. When these springs are subjected to a compression load, they compress, grow shorter, and absorb a large amount of potential force.
The springs are forced back to their original lengths and forms after the load is reduced or eliminated by the stored energy. When weighted, compression springs become more compact. In contrast to extension springs, compression springs' spiral wires do not contact when they are relaxed; instead, when stressed, they are tightly compressed.
All springs store and release energy, which requires engineers and designers to have intimate knowledge of the physics of springs. One of the basic principles of springs is that they are simple mechanisms that behave in a very predictable fashion. An important aspect of the design of springs is Hooke’s Law, which states that the more a spring is deformed, the more force is necessary to deform it. As a compression spring is compressed, more force is required to compress it.
The spring constant determines the amount of force necessary to deform a spring, which is measured in standard international (SI) units, Newtons per meter, or in pounds per inch. A higher spring constant means that a spring is stiffer. The wire diameter, coil diameter, free length, and number of active coils are the determining factors for the spring constant.
Since different springs have a different spring constant, it is essential that manufacturers know what the spring constant is to ensure the spring performs properly. If the spring constant is too high, or the wire is too thin, a spring could fail. Large scale springs have to be precision manufactured to guarantee they will not destabilize and cause damage. Spring coiling machines are carefully calibrated using the most precise and accurate calculations such that the produced spring is the right one for the job.
The are various considerations when choosing compression springs which include:
Compression spring end types might be normal or customized. Standard ends can be open or closed, or they can be ground or not. Given the same number of coils, wire size, and outside diameter (OD), open or closed ends will alter the spring rate.
Closed ends stand vertically when placed on a flat surface since the last coil is closed. They are the most popular and economical ends since they do not require any form of extra processing. With applications that have a slenderness ratio, closed end compression springs will require a shaft or rod for extra support.
Ground end compression springs are closed end compression springs that have their ends ground to the size of the spring. The grinding process increases manufacturing time and the cost of each spring. Grinding of ground end compression springs gives them a slenderness ratio to be able to function without the need of a rod or shaft.
Double closed ends are similar to closed and squared ends. Instead of having one closed end, double closed end compression springs have two.. They are manufactured like extension and torsion springs with all coils touching. Double closed end compression springs have extra stability with a high slenderness ratio that requires a reinforced end in order to prevent buckling. They can be more economical than closed or ground end compression springs.
Open end compression springs are the least common type of compression springs because the open end does not allow the spring to stand or be stable without the assistance of a rod or shaft to keep the spring in place. AIl the coils are open and have pitch between them. Open end compression springs are used in applications where it is necessary to avoid increasing the solid height of the spring.
However, when combined with closed ends, this characteristic will enhance the squareness of the loading force and lessen spring buckling tendencies. Ground ends demand additional manufacturing work.
Certain manufacturers, while not all, offer closed and ground ends in their regular catalog stock designs; this is an important distinction to understand. Examples of special ends include expanded coils to snap into ring grooves, offset legs to serve as alignment pins, and decreased coils for screw attachment.
Carbon steel and exotic alloys are only a few possible spring materials. The most popular material is music wire, a high carbon spring steel. Stainless steel 302 improves overall corrosion resistance but is less strong than music wire.
Nickel alloys are chosen for their extreme high or low operating temperatures, specialized corrosive conditions, and non-magnetic properties. They are labeled under a variety of trademarks. In addition, copper alloys with superior electrical conductivity and corrosion resistance include phosphor bronze and beryllium copper.
Outer Diameter (OD): If the compression spring is going into a hole, its outside diameter should be considered. In any case, if any internal components of the device will surround the spring, those must also be measured. A spring's outer diameter (OD) will enlarge when it is compressed, which is also important to consider if the spring will be used in a tube or a bore. Outer Diameter is measured from the outside of the coil on one side to the outside coil on the opposite side.
The outside diameter of springs is also subject to manufacturing limitations, which can increase the assembly's needed envelope size. Most spring manufacturers will specify a work-in-hole diameter for a spring based on projected OD expansion and manufacturing tolerance. Use this information to more effectively express the product needs when obtaining custom-made springs or to easily choose from stock spring catalogs.
Inner Diameter (ID): If the compression spring passes over a shaft or mandrel, the spring's inner diameter needs to be considered. To prevent friction, there must be a ten-thousandth of an inch between the shaft and the spring. Inner Diameter is calculated by subtracting two wire diameters from the outer diameter.
Free Length: To ensure that the compression spring is in a preloaded state and stays in position, it is advised that its free length be a little bit longer than the available space. Free Length is the length of a compression spring before it is compressed, loaded or experiences any force. It is the length of the spring from end to end or tip to tip.
Solid Height: The wire diameter and the total number of coils impact the solid height of the spring. Make sure the loaded height is not shorter or taller than the solid height.
The setting in which the spring will be used includes the temperature and additional components such as moisture. The more expensive the spring’s material, the higher the temperature a spring can withstand, but this will increase its cost.
Spring Pitch: Spring pitch is the distance between adjacent coils from the center of one wire to the center of another wire. The simplest method for measuring pitch is to measure the gap between the coils and add the thickness of a wire.
Active Coils: With compression springs, active coils are the coils that have pitch that deflect when the load is placed on the spring.
Total Coils: Total coils of a compression spring are all of the coils including the closed coils without pitch.
The use of compression springs requires an understanding of the number of total and active coils. Ones with closed and square ends or ground ends have one closed coil at each end, which are inactive. With open end compression springs, all of the coils in the spring are active and carry the load.
The compression spring's loading or travel needs to be considered as well. The relationship between the force needed to compress a spring by a unit of length—typically pounds per inch (lbs/in)—is known as the spring rate or spring constant. The product designer can therefore determine projected spring travel with a particular load. The spring is put under increasing strain as it is driven further. The substance of the wire may eventually give way under stress, leading to a phenomenon known as spring set. The spring won't re-expand to its initial unloaded length once it has been set. Nevertheless, depending on the assembly, this spring may be useful.
The selection of the wire diameter for a compression spring, as well as the material, is a critical part of the design process. The wire has to meet the load and travel requirements and the environmental conditions. The Rockwell hardness scale indicates how hard the material is and how flexible or brittle the wire may be. Certain wire diameters are measured using a Rockwell tester indentation hardness process where a load is applied to the wire, and the depth of its penetration is recorded.
| Compression Spring Wire Diameters | ||||
|---|---|---|---|---|
| Music Wire and Stainless Steel Wire Diameters | Chrome Silicone Wire Diameters | |||
| English Units | Metric Units | English Units | Metric Units | |
| 0.008 in | 0.203 mm | 0.08 in | 2.032 mm | |
| 0.009 in | 0.229 mm | 0.091 in | 2.311 mm | |
| 0.010 in | 0.254 mm | 0.098 in | 2.489 mm | |
| 0.011 in | 0.279 mm | 0.105 in | 2.667 mm | |
| 0.012 in | 0.305 mm | 0.118 in | 2.997 mm | |
| 0.013 in | 0.330 mm | 0.125 in | 3.175 mm | |
| 0.014 in | 0.356 mm | 0.135 in | 3.429 mm | |
| 0.015 in | 0.381 mm | 0.148 in | 3.759 mm | |
| 0.016 in | 0.406 mm | Up To | ||
| 0.017 in | 0.432 mm | 0.162 in | 4.115 mm | |
| 0.018 in | 0.457 mm | 0.172 in | 4.369 mm | |
| 0.019 in | 0.483 mm | 0.187 in | 4.750 mm | |
| 0.02 in | 0.508 mm | 0.312 in | 7.925 mm | |
| 0.021 in | 0.533 mm | 0.343 in | 8.712 mm | |
| Up To | 0.375 in | 9.525 mm | ||
| 0.362 in | 9.195 mm | 0.394 in | 10.008 mm | |
| 0.375 in | 9.525 mm | 0.406 in | 10.312 mm | |
| 0.394 in | 10.008 mm | 0.437 in | 11.100 mm | |
| 0.437 in | 11.100 mm | 0.453 in | 11.506 mm | |
| 0.453 in | 11.506 mm | 0.468 in | 11.887 mm | |
| 0.468 in | 11.887 mm | 0.5 in | 12.700 mm | |
| 0.5 in | 12.700 mm | 0.532 in | 13.513 mm | |
| 0.562 in | 14.275 mm | 0.562 in | 14.275 mm | |
| 0.625 in | 15.875 mm | 0.625 in | 15.875 mm | |
This chapter will discuss the manufacturing processes used in making compression springs and the materials used.
The manufacturing processes used in making compression springs include:
Coiling first feeds the wire through a process of straightening. The coiler will generate better parts if the wire is straighter when it enters the coiler. During this step, CNC machinery with preprogrammed settings modifies the arms and arbores to produce the spring, adjusting factors including the spring's free length, pitch, and coils. A high-speed camera records images as the machines create the spring, allowing us to measure each component and make adjustments as necessary to keep it within tolerance. The product then moves on to the process of alleviating stress after the machine cuts the spring from its wire.
The substance of the wire is stressed during the coiling process, which makes it brittle. We fix this by heating the spring in an oven, which causes the coil to solidify in its new shape and generate metallic links. For a predetermined period, the oven maintains the temperature of the coil of wire at the proper level before slowly allowing the coil to cool.
Depending on its intended application, the wire is treated to a number of finishing operations once it has gone through the stress-relieving process. Completing a spring converts it from its initial form into a specific tool that will enhance its potential applications. The following are a few of the procedures involved in spring finishing:
Steel materials that can be used to make compression springs include stainless steel, hard-drawn steel, steel music wire, and spring steel. Compression springs with wider wire diameters may sustain more forceful use than springs with smaller wire diameters. In general, the larger the wire, the stronger the spring. Decreases in the coil diameter of the spring can also increase its strength.
Due to its resistance to corrosion even when frequently exposed to moisture and chemicals, stainless steel is a strong choice for these applications. Steel is resilient and sturdy; it can endure continuous use without breaking.
In addition to spring steel, other types of steel and even plastic can be used to make springs. However, incorrectly matching a spring with its application can result in early failure, which can cause damage to nearby items and, in certain situations, injury to humans.
It is crucial to choose the right material for spring composition. Choosing a spring properly will maximize its efficacy and lifespan. For spring materials, steel alloys are typically employed. Low carbon, high carbon, stainless steel, chrome silicon, and chrome vanadium alloys are common alloys. Some metals, such as titanium, phosphor bronze, and beryllium copper alloy, are employed occasionally as springs. Ceramic materials are used for coiled springs used in high-temperature environments.
Due to its high carbon steel composition, music wire can be utilized for high-intensity applications, including gym equipment, lawn and garden tools, and home improvement items. Strings made of music wire have elasticity moduli of 30,000 psi and minimum tensile strengths of 230-399 psi.
The springs typically found in commercial products like pens, office supplies, toys, and other indoor-use items are made of hard-drawn wire, a medium carbon steel. These springs can be specifically adapted to various applications because of their wide range of hardness, with Rockwell hardnesses ranging from C31 to C52.
Different types of compression springs include:
Convex springs, also known as barrel-shaped springs, feature coils with larger diameters in the center and coils with smaller diameters at either end. When the springs are squeezed, their designs enable the coils to fit inside one another. A compression spring with the top and bottom outer diameters smaller than the center outer diameter is known as a convex spring. Convex springs are used to generate linear force.
Barrel springs can be produced in a wide range of diameters, allowing for an infinite number of designs. Because it may save space, eliminate buckling, and come in various shapes to better fit any designs, a barrel spring is preferred by end users over a generic compression spring. Telescoping or non-telescoping barrel springs are both possible. Manufacturers use convex springs in applications where more stability and movement resistance are needed when the springs deflate. They are mostly used in the toy, furniture, and automobile industries.
Conical springs are cone-shaped tapering springs. One end of the spring has a diameter greater than the other, and the coils all around the spring give a progressive taper or form shift. Some conical springs have diameter variations between coils that allow each coil to fit the one before it. These springs tend to increase stability while lowering the solid height. Some cone springs have their diameters adjusted to the point where, because of their tapered cone shape, they will exhibit a telescope effect when compressed. This allows the user to fully compress the spring, causing all of the coils to collapse inside of one wire diameter, giving more travel or deflection. This is the best option if the product's creator requires a greater deflection or travel distance.
Conical springs are superior to standard compression springs in terms of stability. Since the larger outer diameter of tapered springs is typically on the bottom, they provide better stability, are less likely to buckle, and do not lose their balance when compressed.
The following image depicts the coned disk that makes up a Belleville spring. Julian Belleville created it and registered its design in France in 1867. The image below depicts the typical load-deflection characteristics of a Belleville spring. There are many different load-deflection curves available due to the difference in the (h/t) ratio. Plate clutches, brakes, relief valves, and a wide range of fastened connections require Belleville springs.
These are the benefits of Belleville springs:
Concave springs, also known as hourglass springs, have a coil that is narrower in the center than it is at either end. The springs' symmetrical shape contributes to keeping them centered at a specific location. A concave spring saves space, eliminates buckling, and benefits numerous specialized places with its design distribution. The end coils of a concave spring are wider than the center coils; therefore, the pressure is distributed unevenly, improving stability. There are more alternatives because there are numerous different configurations to select from that may be included in any design.
Straight coil compression springs have the same OD and ID throughout the length of the spring.
Each coil of a straight spring has the same diameter. The ends of a straight coil compression spring can be ground or closed and have a bearing surface of 270o. The cylindrical shape of straight coil compression springs differentiates them from the cone shape of tapered compression springs.
A volute spring has cone-shaped coils rather than wire with a round, oval, or square cross-section. Similar to a conical compression spring, they operate similarly. The cone shapes slide over one another rather than being forced together by compressive force. Compared to a non-conical compression spring of the same length, a volute spring will compress down to a lower solid height.
The coils in variable pitch springs are spaced more widely in some places and closer together in others. Pitch is the term for the distance between adjacent coils of wire. Variable pitch springs have different intervals between each coil along the length of the spring.
To drive cartridges or bullets into the chamber of a handgun, magazines use compression springs with oval or rectangular coils. These springs need to be manufactured with extreme accuracy and strict quality control. There are many different spring design options available, with variations in length, coil count, and required force. Since most magazine springs operate close to their solid height, rate becomes a crucial design consideration.
A torsion spring is a mechanical tool that stores and releases rotational energy. The torsion spring is attached to a mechanical part at each end. The winding of the spring is tightened and stores potential energy when it is turned around its axis at one end. As the other end is kept fixed, it is deflected about the body's centerline axis. The spring stores more potential energy as the winding becomes tighter and resists more rotating force. The spring will unwind as it performs an elastic rebound after being released, releasing the tensioned energy.
The opposing end of the spring experiences an equal rotating force, which might impart torque on the attached mechanical component. Mechanical parts can be statically held in place by torsion springs. As the spring is twisted to create a tighter winding, it is more susceptible to bending stress than rotational stress.
Unlike compression and tension springs, which are affected by linear and rotational forces, these springs are different because only rotating force is involved. To return to their original winding after being twisted, they also rely on the material's elasticity.
Depending on the direction of rotation, tension springs can exert force either clockwise or counterclockwise. To provide the most force, a torsion spring must be turned in the direction of the winding.
There are several uses for torsion springs in practically every industry and numerous variations of these springs.
Tapered compression springs are cone shaped with a tapered body that has a larger outside diameter at the base and smaller outside diameter at the top. They offer stability in conditions where ordinary compression springs will buckle. Tapered compression springs have a solid low height for greater stability and resistance to surging. The solid height of tapered compression springs can be as low as the diameter of one wire. Tapered compression springs resist compression forces or store energy in the push mode.
This chapter will discuss the applications and benefits of compression springs.
The applications of compression springs include:
The advantages of compression springs include:
The disadvantages of compression springs include:
Common problems associated with compression springs include:
When one end of a helical spring is resting on a rigid support and the other end is suddenly loaded, the coils will not deflect uniformly because it takes time for the tension to propagate along the spring wire. The spring's end coils in touch with the applied load first absorb all of the deflection before transferring a significant portion of that deflection to the adjacent coils. A compression wave travels through the coils to the supported end before reflecting to the deflected end. This phenomenon can also be seen in a closed water body when a disturbance flows in one direction before returning to where it first appeared. This compression wave moves endlessly down the spring. Resonance will happen if the applied load is variable and the space between load applications is the same as the time needed for the wave to move from one end to the other. The coils experience extremely high strain and massive deflections as a result. The spring could just barely fail in these circumstances. This occurrence is called surge.
The following techniques can be used to stop the springtime spring surge:
The spring behaves like a column and may fail by buckling at a relatively modest load when the free length of the spring (LF) is greater than four times the mean or pitch diameter (D), according to experimental findings. The following relation can be used to compute the critical axial load (Wcr) that results in buckling.
Buckling can be avoided by:
Compression springs can store mechanical energy when they are compressed. These open-coiled, helical springs provide resistance to compressive loading. When these springs are subjected to a compression load, they compress, grow shorter, and absorb a large amount of potential force. The springs are forced back to their original lengths and forms after the load is reduced or eliminated by the stored energy.
Thus, the selection of compression springs has to be made in consideration of the intended application, characteristics, benefits, and disadvantages of compression springs.
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