This article will take an in-depth look at compression springs.
The article will look at topics such as:
This chapter will cover what compression springs are and the key factors to consider when selecting 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.
Compression springs return to their original length and shape once the load is reduced or removed, due to the stored energy. When under load, these springs become more compact. Unlike extension springs, the coils of compression springs do not touch when relaxed; they are tightly compressed when stressed.
All springs store and release energy, making it crucial for engineers and designers to understand spring physics thoroughly. Springs are simple mechanisms that behave in a predictable manner. An essential principle in spring design is Hooke’s Law, which states that the force required to deform a spring is proportional to the amount of deformation. As a compression spring is compressed, the force needed to compress it increases.
The spring constant, measured in Newtons per meter (SI units) or pounds per inch, determines the force required to deform a spring. A higher spring constant indicates a stiffer spring. Factors affecting the spring constant include wire diameter, coil diameter, free length, and the number of active coils.
Understanding the spring constant is crucial for manufacturers to ensure proper spring performance. If the spring constant is too high or the wire is too thin, the spring might fail. Large-scale springs must be precisely manufactured to avoid destabilization and potential damage. Spring coiling machines are meticulously calibrated using accurate calculations to ensure the produced spring meets the required specifications.
There are various considerations when choosing compression springs, including:
Compression springs can have various types of ends, which might be standard or specially designed. Common end types include open, closed, ground, and ungrouded. The configuration of these ends—whether open or closed—can influence the spring rate, even if the wire size, number of coils, and outside diameter (OD) remain constant.
When placed on a flat surface, closed-end compression springs stand upright due to their last coil being closed. These ends are favored for their simplicity and cost-effectiveness as they do not need additional processing. For applications with a high slenderness ratio, closed-end springs might need additional support from a shaft or rod.
Ground end compression springs are a type of closed-end spring where the ends are precisely ground to match the spring's dimensions. This grinding process, while enhancing the spring’s precision, adds to both the manufacturing time and cost. The ground ends provide the spring with a suitable slenderness ratio, allowing it to operate effectively without requiring additional support from a rod or shaft.
Double closed end compression springs feature two closed ends rather than just one, akin to closed and squared ends. They are produced similarly to extension and torsion springs, with all coils in contact. The double closed ends enhance the spring's stability and provide a higher slenderness ratio, necessitating a reinforced end to avoid buckling. These springs can often be more cost-effective compared to closed or ground end compression springs.
Open end compression springs are less frequently used because their open ends prevent the spring from standing or remaining stable without additional support from a rod or shaft. With all coils being open and spaced apart, these springs are employed in situations where minimizing the spring's solid height is crucial.
When paired with closed ends, open ends improve the evenness of the applied load and reduce the likelihood of spring buckling. However, ground ends require extra processing, which adds to the production cost.
Not all manufacturers include closed and ground ends in their standard inventory; this distinction is important to note. Custom end types might feature expanded coils designed to fit into ring grooves, offset legs for alignment, or reduced coils intended for screw attachments.
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 selected for their ability to withstand extreme temperatures, harsh corrosive environments, and non-magnetic properties. They come under various brand names. Additionally, copper alloys such as phosphor bronze and beryllium copper are valued for their excellent electrical conductivity and resistance to corrosion.
Outer Diameter (OD): When a compression spring is to be inserted into a hole, its outer diameter must be taken into account. If the spring will be surrounded by any internal components of the device, their dimensions should also be measured. The outer diameter (OD) of a spring will expand when compressed, which is crucial to consider if the spring is used within a tube or bore. The OD is measured from the outer edge of the coil on one side to the outer edge of the coil on the other side.
The manufacturing process imposes limitations on the outer diameter of springs, potentially affecting the required envelope size for assembly. Spring manufacturers often provide a work-in-hole diameter based on expected OD expansion and manufacturing tolerances. This information is essential for specifying your needs when ordering custom springs or selecting from stock catalogs.
Inner Diameter (ID): When a compression spring is intended to fit over a shaft or mandrel, its inner diameter must be considered. To avoid friction, a small clearance of at least ten-thousandths of an inch should be maintained between the shaft and the spring. The inner diameter is determined by subtracting twice the wire diameter from the outer diameter.
Free Length: To ensure that the compression spring remains in a preloaded state and maintains its position, it is advisable for the free length to be slightly greater than the available space. Free Length refers to the length of the compression spring when it is not compressed, loaded, or subjected to any force. It is measured from one end of the spring to the other end or tip to tip.
Solid Height: The solid height of a spring is determined by the wire diameter and the total number of coils. Ensure that the loaded height of the spring does not exceed or fall short of its solid height.
The operating environment of the spring, including factors like temperature and exposure to moisture, affects its performance. While more costly materials can endure higher temperatures, they also increase the overall expense of the spring.
Spring Pitch: Spring pitch refers to the space between adjacent coils, measured from the center of one wire to the center of the next. To determine the pitch, measure the gap between coils and then add the thickness of the wire.
Active Coils: In compression springs, active coils are those that compress and deflect when a load is applied to the spring. These coils are responsible for the spring's movement and functionality.
Total Coils: The total number of coils in a compression spring includes both the active coils and any closed coils without pitch, which are not involved in deflection.
When selecting compression springs, it's important to understand both the total number of coils and the number of active coils. Springs with closed or ground ends have inactive coils at the ends, whereas open-end compression springs have all coils active and engaged in carrying the load.
Consideration of the compression spring's loading or travel is crucial. The spring rate, also known as the spring constant, measures the force required to compress the spring by a unit length, typically expressed in pounds per inch (lbs/in). This value helps designers estimate the expected travel of the spring under a given load. As the spring is compressed further, it experiences increasing stress. Over time, this stress can lead to a condition called spring set, where the spring fails to return to its original length once the load is removed. Despite this, such springs may still be functional depending on the specific application.
Choosing the appropriate wire diameter and material for a compression spring is essential to ensure it meets load, travel, and environmental requirements. The wire's hardness, as measured by the Rockwell scale, provides insight into its rigidity and flexibility. This scale assesses material hardness by applying a specific load to the wire and measuring the depth of the resulting indentation. This process helps determine how well the wire will perform under stress and its overall durability.
| 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 explore the various manufacturing techniques employed in the production of compression springs, as well as the materials utilized in their creation.
The production of compression springs involves several manufacturing methods, which include:
In the coiling process, wire is first straightened before being fed into the coiler. The accuracy of the final product improves when the wire is properly straightened before entering the coiler. During coiling, CNC machinery with preset configurations adjusts various parameters, such as the spring's free length, pitch, and number of coils. High-speed cameras capture images of the coiling process, enabling precise measurement and adjustment to ensure that the spring meets tolerance specifications. After coiling, the spring is cut from the wire and then undergoes a stress-relief process.
During the coiling process, the wire's material undergoes stress, making it prone to brittleness. To address this, the spring is heated in an oven, allowing it to stabilize in its new shape and form metallic bonds. The oven maintains a consistent temperature for the coil for a specific duration, ensuring proper hardening before gradually cooling the coil.
After undergoing the stress-relieving process, the wire may undergo various finishing operations based on its intended use. These finishing steps transform the spring from its initial state into a refined component optimized for specific applications. The following are some of the finishing procedures involved:
Various steel materials are suitable for manufacturing compression springs, including stainless steel, hard-drawn steel, steel music wire, and spring steel. Generally, springs with larger wire diameters can endure more significant forces compared to those with smaller diameters. In essence, thicker wire typically results in a stronger spring, and reducing the coil diameter can also enhance its strength.
Stainless steel is particularly advantageous due to its corrosion resistance, even in environments frequently exposed to moisture and chemicals. Its durability ensures that it can withstand prolonged use without failing.
While spring steel is commonly used, other steel types and even plastic materials can also be utilized for making springs. However, improper selection of a spring for a specific application can lead to premature failure, potentially causing damage to surrounding components or posing safety risks.
Selecting the appropriate material for springs is essential for optimizing their performance and durability. Steel alloys are commonly used for spring manufacturing, including low carbon, high carbon, stainless steel, chrome silicon, and chrome vanadium alloys. Occasionally, metals such as titanium, phosphor bronze, and beryllium copper are used, while ceramic materials are employed for springs in high-temperature settings.
Music wire, known for its high carbon steel content, is suitable for demanding applications such as gym equipment, lawn and garden tools, and home improvement products. It exhibits an elasticity modulus of 30,000 psi and minimum tensile strengths ranging from 230 to 399 psi.
Hard-drawn wire, a medium carbon steel, is commonly used in springs found in everyday items like pens, office supplies, toys, and other products designed for indoor use. These springs can be customized to various needs due to their diverse hardness levels, with Rockwell hardness ranging from C31 to C52.
Various kinds of compression springs are available, including:
Convex springs, often referred to as barrel-shaped springs, have a unique design where the coils are wider in the middle and taper towards the ends. This design allows the coils to nestle into each other when compressed. Specifically, in a convex spring, the outer diameters at the top and bottom are smaller compared to the diameter at the center. These springs are commonly used to produce linear force.
Barrel springs are versatile and can be manufactured in various diameters, offering numerous design possibilities. They are often favored over standard compression springs due to their ability to save space, reduce buckling, and adapt to different shapes to fit specific needs. These springs can be designed to either telescope or remain non-telescoping. In applications requiring enhanced stability and resistance to movement when compressed, manufacturers prefer convex springs. They are commonly utilized in industries such as toys, furniture, and automotive.
Conical springs, shaped like a cone, have a diameter that tapers from one end to the other, with coils gradually decreasing in size along the length of the spring. This design allows for a progressive change in the coil diameter, enabling the coils to nest within each other. Such springs enhance stability while reducing the solid height. Some conical springs are designed to achieve a telescoping effect when compressed, where the tapered shape allows the coils to collapse into a smaller diameter, increasing the available travel or deflection. This makes them an ideal choice for applications requiring significant compression travel.
Conical springs offer enhanced stability compared to conventional compression springs. Their tapered design, with a larger outer diameter at the bottom, ensures improved stability and reduces the likelihood of buckling. This design helps maintain balance and performance even under compression.
The image below illustrates a Belleville spring, which is characterized by its coned disk design. Invented by Julian Belleville and patented in France in 1867, this spring's load-deflection characteristics vary depending on the (h/t) ratio. Belleville springs are widely used in applications such as plate clutches, brakes, relief valves, and various types of fastened connections.
Here are some advantages of using Belleville springs:
Concave springs, also referred to as hourglass springs, feature a design where the coil diameter is reduced in the center compared to the ends. This symmetrical design helps to maintain the spring's position and minimizes space usage while reducing the risk of buckling. The broader end coils contribute to an uneven pressure distribution, enhancing overall stability. With a variety of configurations available, concave springs can be tailored to fit many specialized applications.
Straight coil compression springs feature a uniform outer and inner diameter along their entire length.
Each coil in a straight coil compression spring maintains a consistent diameter. The ends of these springs can be ground or closed, offering a 270° bearing surface. Their cylindrical form distinguishes them from tapered compression springs, which have a conical shape.
A volute spring features coils with a cone shape rather than a round, oval, or square cross-section. Much like a conical compression spring, it functions in a similar manner. Instead of being compressed into a smaller space, the cone shapes nestle over each other. As a result, a volute spring typically achieves a lower solid height compared to a non-conical compression spring of the same length.
Variable pitch springs feature coils with varying spacing along their length, with some sections having wider gaps and others being more tightly wound. The term "pitch" refers to the distance between adjacent coils. In variable pitch springs, these intervals differ along the spring’s length, allowing for a range of performance characteristics.
Magazines utilize compression springs with oval or rectangular coils to propel cartridges or bullets into a handgun's chamber. These springs must be produced with high precision and stringent quality standards. Various design options are available, including differences in length, coil count, and force requirements. Given that magazine springs often operate near their solid height, the spring rate is a critical factor in the design process.
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.
Torsion springs generate an equal and opposite rotational force at their ends, which can apply torque to the connected mechanical components. These springs are designed to hold mechanical parts statically in place. As the spring is twisted to tighten the winding, it faces more bending stress compared to rotational stress.
In contrast to compression and tension springs, which deal with linear and rotational forces, torsion springs are unique in that they operate solely under rotational forces. They rely on the material's elasticity to return to their original winding position after being twisted.
Torsion springs can exert force in either a clockwise or counterclockwise direction, depending on the direction of the twist. To achieve maximum force output, the spring should be twisted in the direction of its winding.
Torsion springs are utilized across various industries and come in numerous variations to suit different applications.
Tapered compression springs feature a cone-shaped design, with a larger outer diameter at the base and a smaller diameter at the top. This tapered form enhances stability, reducing the risk of buckling compared to standard compression springs. These springs are known for their low solid height, which improves stability and resistance to surging. The solid height of tapered compression springs can be as minimal as the diameter of a single wire. They are designed to resist compression forces and store energy when compressed.
This chapter will explore the various applications and advantages of compression springs.
Compression springs are utilized in a variety of applications, including:
Pens: A compression spring can be observed by examining a ballpoint pen. This spring enables the pen to write while exposing the tip and then shields the tip inside the housing to prevent the ink from drying out. This makes it possible to use pens without cumbersome and easily lost caps.
Firearms: Whenever considering tension, consider compression springs. Take into account the strain needed to fire a bow and arrow. The crossbow is a much simpler weapon if the human component is replaced with a compression spring. Technological advancements continue with the modern semi-automatic handgun, which uses a compression spring to absorb the energy produced by recoil and then redirect it to advance the slide or bolt and reload the weapon for the subsequent shot.
The benefits of compression springs are as follows:
Putting a component back in the right position: Door latches on both automobiles and building doors are an additional advantage that demonstrates how frequently utilized and essential compression springs are. Imagine raising a handle to open a door to get the greatest understanding of how a spring operates. The lock mechanism's compression spring would restore it to the locked position if the motion was used without pulling the door open. The spring can be compressed by tugging or turning the device; if it retains its position, the spring will stay compressed; otherwise, it will latch once more.
The drawbacks of compression springs are as follows:
Typical issues related to compression springs include:
When one end of a helical spring is placed on a rigid support and the other end is abruptly loaded, the coils do not deflect evenly. This is because it takes time for the tension to propagate along the spring wire. Initially, the coils at the end closest to the applied load absorb most of the deflection before passing some of it to the adjacent coils. A compression wave travels through the spring towards the supported end and then reflects back to the deflected end. This behavior is similar to a disturbance traveling through a closed water body before returning to its origin. This compression wave can continue traveling along the spring. If the applied load varies and the intervals between load applications match the time it takes for the wave to travel from one end of the spring to the other, resonance occurs. This causes the coils to experience high strain and significant deflections, potentially leading to the spring's failure. This phenomenon is known as surge.
The following methods can be employed to prevent spring surge:
Experimental data suggest that when the free length of a spring (LF) exceeds four times its mean or pitch diameter (D), the spring acts like a column and may buckle under relatively low loads. The following formula can be used to calculate the critical axial load (Wcr) that leads to buckling.
To prevent buckling, consider the following measures:
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.
A coil spring is an elastic element made of metal or heavy plastic in the form of curls or ringlets of round wire or cord that is wrapped around a cylinder. The winding of a coil spring can be loose or tight in a helical shape depending on the application for which it is made...
Extension springs are helical wound springs that are so closely coiled together to create initial tension in the coils. This initial tension creates resistance against the force applied to its ends for extension. The initial tension helps determine how closely and...
Springs are a flexible machine element that store mechanical energy when subjected to tensile, compressive, bending, or torsional forces. When the spring is deflected, it stores energy and at the same time exerts an opposing force...
A torsion spring is a mechanical device that stores and releases rotational energy. Each end of the torsion spring is connected to a mechanical component. As the spring is rotated around its axis on one end, the winding of the spring is tightened and stores potential energy...
Wire mesh is fabricated by the intertwining, weaving, or welding of wires of various thicknesses to create proportionally equal parallel rows and intersecting columns. Also known as wire fabric, wire cloth, or...
Contract manufacturing is a business model in which a company hires a contract manufacturer to produce its products or components of its products. It is a strategic action widely adopted by companies to save extensive resources and...
Hardware cloth is a woven mesh made by interlacing various sizes of wire to form a metal fabric that can be used for animal cages, fence material, strainers, and filtering screens. The differences between the various types of hardware cloth...
The phrase "wire mesh" describes two- or three-dimensional structures constructed of two or more metallic wires connected by various techniques. In a wide range of settings, wire mesh products are...
Welded wire mesh is a series of wires that are welded where the individual wires cross. The openings of the mesh varies depending on the type of wire used and the function of the mesh. Regardless of size and wire, welded wire mesh is permanent and...
Wire baskets are made from a series of wires that are woven together or welded to form a shape of a basket. They can also be defined as containers that are made by use of an openwork pattern of metal...
Wire cloth is a woven (or nonwoven) sheet or web material with a series of openings across the surface. Wire cloth is also known as: Metal Fabric or Metal Cloth; Wire Mesh, Metal Mesh, or Alloy Mesh...
Wire shaping is a complex method that encompasses a wide range of dimensions, forms, and textures. The technique of creating a usable product by wire bending and shaping is known as custom wire forms...
Wire forming is a method for applying force to change the contour of wire by bending, swaging, piercing, chamfering, shearing, or other techniques. The various techniques for wire forming can produce any type of shape, form, or configuration...
A wire handle is attached to a bucket, pail, or other type of container to make it easy to lift the container and transport it. They are made of durable and sturdy metals capable of lifting several pounds...
A wire rack is a level wire form utilized to stock and exhibit a number of products, usually retail. The bottom surface on which such goods are stored is made of several latticed or interlaced metal strands...