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Understanding Compression Springs: A Guide for Innovators and Manufacturers

Understanding Compression Springs: A Guide for Innovators and Manufacturers

What is a Compression Spring?

A compression spring is made of round spring wire and has the shape of a helical coil. There are adjacent coils with pitch that make up its length.   A compression spring is designed to store or release elastic energy when compressed. It can also absorb shock or maintain a force between two surfaces. Compression Springs are designed to operate with a compressive load. As the name suggests, compression springs are compressed under a load or force thus storing elastic energy and then releasing it to return to their original uncompressed length. Their helical coil design allows them to resist compressive forces, making them indispensable in mechanisms that depend on this resistance to function. Their applications are vast, ranging from automotive suspensions,  medical devices, robotics to every stroke of the  keyboard. 

Compression springs are  helical wound components in a wide range of applications, from AI robots to high tech medical devices . At Compression Spring, our goal is to empower makers, inventors, and industry professionals with a deeper understanding of every element within a compression spring to how a compression  spring works and all its physical and mathematical properties. We will delve into calculating compression spring rate, load, loaded height, physical dimensions, spring material options, and all the mathematical formulas to help you understand compression springs at a very deep level.

Core Attributes of Compression Springs:

  • Wire Diameter: The diameter of the spring wire from one side of the wire to the adjacent side of the wire. 
  • Outer Diameter: The outside diameter of a compression spring from one side of the outer diameter to the adjacent side of the outer diameter.
  • Mean Coil Diameter: The average of measurements from outer diameter to inner diameter. The best method to calculate for mean diameter is either subtract one wire diameter from the outer diameter or add one wire diameter to the inner diameter. This will give you the “Mean Coil Diameter” of the spring. Mean coil diameter is used to calculate the spring rate and the stress of a compression spring. 
  • Inner Diameter: The Inside diameter of a compression spring from inside one side of the inner diameter to the adjacent side of the inner diameter.
  • Free Length: The length of a compression spring in a free uncompressed state also known as spring length or overall spring length. 
  • Total coils: The total amount of helical wound coils that contain pitch and have no pitch in a compression spring, meaning all coils in a spring. 
  • Active Coils: The amount of helically wound coils that contain pitch to exert energy when a spring is compressed. 
  • Solid Height: Solid height for compression springs is defined as the point at which all wires in your spring are touching and no more force can be exerted by the spring. Also known as coil bind height where all spring coils are in contact with each other and the spring cannot compress further.
  • Compression Spring Rate Definition: Spring rate k or spring constant is the proportion of a spring’s force in (pounds or newtons) to one unit of travel (inch or millimeter). It is a constant force value which helps you calculate how much load you will need with a specific distance of compression travel and it will also help you calculate how much compression travel you will achieve with a certain load force.

Compression Spring End Types: 

Understanding the significance of the compression spring end types is crucial for ensuring proper spring fit and function within an assembly. The following are the most common compression spring end types.

 

  • Closed and Squared Ends: This configuration provides a flat surface without grinding and is best suited for springs with a slenderness ratio of less than 3.5. Closed and squared ends offer stability and reduce the likelihood of falling over under load. Suitable for applications where the compression spring's slenderness ratio is less than 3.5 and is required to stand up vertically straight without support.
  • Closed and Ground Ends: By grinding the ends of the spring, a more precise and flat surface is achieved, allowing for better contact with the load. This end type is preferred for high-precision applications requiring uniform load compression and is often used in manufacturing and automotive industries. Closed and ground ends are recommended for springs with a slenderness ratio greater than 4.
  • Open Ends: Springs with open ends are not modified after coiling, resulting in a natural, slightly uneven end. The advantage of open ends is that one can obtain more travel since open ends have no dead coils on each end thus freeing up solid height space to provide more travel. This option is suitable for applications where end precision is not critical, offering a cost-effective solution without sacrificing performance.
  • Double Closed Ends: A specialized option where both ends of the spring are closed but not ground, offering enhanced vertical stability and resistance to lateral forces. This end type is particularly useful in applications requiring the spring to align with minimal guidance. Double ends take up more solid height but the payoff is stability.
  • Triple or more closed ends: A custom hybrid option that has many advantages: An option for fine wire diameter springs of .005 to .025 thousand of an inch. Where  compression springs that have a fine wire diameter and large spring index need extra stability when compressing the spring.
  • An option for having multiple closed ends on one side of the spring for threading the springs inner diameter over a threaded bolt or threaded shaft. Multiple closed ends offer a way to secure and assemble a spring over a thread. The springs wire diameter must synchronize with the thread size as well as the compression springs inner diameter must coincide with the bolts outer diameter for proper fit.
  • One Closed End and Multiple Closed Ends:  An option for having one closed end and multiple closed ends on the other side of the compression spring. This end type offers stability on the base of the spring as well as a closed end on the top of the spring.  This end type can be ground for a more precise flat surface offering superior stability.
  1. Compression Spring Wire Material: Spring tempered wire is used in all coil compression springs. This wire is spring tempered and has a rockwell hardness factor of between C41-60. There is an ample gamut of spring material varieties listed below.

Compression Spring Wire Material Types:

Acxess Spring provides a diverse array of material options for compression springs, ensuring optimal performance across various applications and environments.

  • Music Wire (ASTM A228): Renowned for its high tensile strength and robustness, music wire is the go-to choice for springs requiring high load capacities and fatigue resistance. Ideal for applications demanding acute precision and strength.
  • Stainless Steel 302: Offers excellent corrosion resistance and is used in applications where the spring is exposed to corrosive environments. Its durability and longevity make it suitable for food industry machinery, medical devices, and marine applications.
  • Hard Drawn (ASTM A227): A cost-effective option, hard drawn wire is used in applications where material strength is crucial, but exposure to corrosive elements is minimal. Commonly found in commercial products and industrial machinery.
  • Other Materials: For specialized applications, Acxess Spring also offers springs in exotic materials such as Beryllium Copper, Phosphor Bronze, Chrome Silicon and more, here is a listing of all the unique properties of popular spring materials to meet specific environmental and operational demands.

Compression Spring Plating Options

Plating and finishes for compression springs not only enhance the aesthetic appeal of a spring but also significantly improve its corrosion resistance, other plating options give you electrical conductivity, and overall durability. Acxess Spring's plating options include:

  • Zinc Plating: Matt chrome in color, offers excellent corrosion resistance, making it a popular choice for springs used in outdoor or humid environments. Zinc plating also provides a clean, bright appearance and additional protection against rust. 
  • Black Zinc: Black in color offers good corrosion resistance, making it a good choice for springs used in outdoor environments. Black zinc plating also provides a clean appearance and additional  rust protection. (Lalo Show Icon)
  • Black Oxide: Black matt in color, primarily used for aesthetic purposes or to minimize light reflection, black oxide also offers mild corrosion resistance and reduces friction between coils, making it ideal for applications requiring a sleek appearance without extensive exposure to corrosive elements. 
  • Gold Iridite: Provides superior corrosion resistance and electrical conductivity, making it an excellent choice for electronic components. The gold iridite finish is often used in electrical connectors and high-reliability applications where performance cannot be compromised.
  • Nickel Plating: Offers a lustrous shiny silver chrome appearance and is electrically conductive. This bright glossy chrome finish is aesthetically appealing. 
  • Copper Plating: Copper in color is primarily used for springs that need to be conductive, great for springs that go into battery or electrical contacts. 
  • Gold Plating: 14K Gold Electroplating is used for high electrical conductivity compression springs. This plating requires placing the compression springs on a copper wire necklace or placing the springs individually on a rack to perform the gold electroplating more costly but greater conductivity.

How to Measure a Compression Spring?

Measuring a compression spring accurately is crucial for its performance and compatibility with your application. Key dimensions and how to measure a compression spring include:

 

  • Wire Diameter: To measure the wire diameter (WD): Place the lower jaws around the springs wire diameter as shown in the picture then slowly push the jaws of the caliper so that the two parts of the lower jaws touch the wire diameter.

Hint:  You can also lay the spring down and place the lower jaws of the caliper around the wire diameter to get an accurate measurement.

  • Outer Diameter (OD) To measure the outer diameter of a compression spring use a digital caliper (as shown). Measure at one side of its widest outside point then measure the other side from its widest outside opposite point to get the correct outside diameter of the compression spring.
  • Inner Diameter (ID): Insert the upper jaws of the digital caliper into the inside diameter of the spring making sure to measure the largest part of the ID. Make sure to rotate your spring slowly with one hand and with the other pull the thumb screw outward so that the upper jaws get an accurate measurement. (Lalo Show picture)
     

Hint: Hold the spring vertically straight so that the upper jaws go into the inside diameter, and make sure the tip of the spring coil is at high noon or 12 O`clock.  then rotate the spring a bit to the left then to the right as you pull the thumb screw. You will feel the larger part of the spring’s inner diameter that's the  measurement you want. 

  • Free Length: How to measure the free length of compression springs (FL) :
    Hold your compression spring horizontally straight as shown then insert the lower jaws around the length of the spring making sure to measure the entire vertical  length of the spring.   
  • Total Coils (TC): How to count total coils in a compression spring:
    Hold your spring as shown in the picture to the left. Start counting on the second wire which is the first complete coil then count all the coils until the last coil. This spring has 8 total coils. 
  • Active Coils (AC): How to count active coils in a compression spring. 
    Active coils are the coils that have pitch in between the coils (also known as open wound coils). This spring has 8 total coils but since the first and last coils are closed we cannot consider them active coils  therefore we subtract the 2 closed coils and we get 6 Active coils with pitch. 
  • Solid Height: Calculating Solid Height - Closed And Square Ends:
    The formula for calculating solid height on closed and square ends is:
    Total Wires = Total Coils + 1 
    Solid Height = Total Wire * Wire Diameter 

Take the total number of coils and add 1 then multiply by wire diameter to get solid height. 

  • Calculating Solid Height - Closed And Ground Ends:
    The formula for calculating solid height on closed and ground ends is:
    Total Wires = Total Coils 
    Solid Height = Total Wire * Wire Diameter 
  • Calculating Solid Height - Double Closed Ends:
    The formula for calculating solid height on double closed ends is:
    Total Wires = Total Coils + 1 
    Solid Height = Total Wire * Wire Diameter 
  • Calculating Solid Height - Open Ends:
    The formula for calculating solid height on open ends is:
    Total Coils + 1 = Total Wires 
    Solid Height = Total Wire * Wire Diameter 

Measurement Tips for Precision

  • Consistency Is Key: Always measure using a digital or dial caliper and use methods for consistency across different compression springs.
  • Multiple Measurements: To mitigate variances, take several measurements at different points and calculate the average.
  • Understand Tolerances: Familiarize yourself with the manufacturer’s tolerances to recognize acceptable measurement variations that won't impact performance.
  • All our springs come with detailed blueprints /spec sheets that have all compression spring tolerances on every compression spring dimension. 

By adhering to these measurement principles, you ensure the compression spring not only fits within its designated space but also meets its performance requirements precisely. Accurate measurements form the cornerstone of effective spring application, directly influencing the reliability and functionality of your project.

How to Calculate a Spring Compression:

Calculating spring compression involves understanding how much a spring compresses under a given load. This can be calculated by dividing the load by the spring constant (the change in load per unit of deflection). The formula is Compression= Load/Spring Constant (K ). The spring constant is usually provided by the manufacturer or can be calculated based on the spring material type, wire diameter, outer diameter, and the number of active coils.

 

Spring compression, or how much a spring compresses under a given load, can be derived from the spring constant and the applied load using Hooke’s Law:

F=kx

Rearranging for compression (x) gives:

x=F/k

Using the maximum load of 25 lbs and the spring rate of 20.022 lbs/in:

X = 25/20.022 ≈ 1.249 inches of spring compression or deflection

This simple equation shows the compression spring’s capacity to compress 1.249 inches under a load of 25 lbs without exceeding its elastic limit of 1.561 inches.

Example is based on Part Number PC072-600-15100-MW-2750-CG-N-IN

How to Calculate a Compression Spring Constant k:

The spring constant, or spring rate k, is a critical parameter in the design and application of compression springs, directly influencing how strong  a spring will perform under load. Calculating the spring constant allows engineers and designers to precisely predict how much force is required to compress the spring by a certain amount of distance traveled, ensuring that the spring meets the specific needs of the application. The formula to calculate the spring constant is k = Gd^4 ÷ (8D^3 * n), where:

  • k is the spring constant (spring rate),
  • G is the modulus of rigidity of the spring material,
  • d is the wire diameter,
  • D is the mean coil diameter, and
  • N is the number of active coils.

This calculation provides a foundation for understanding the spring's behavior, enabling the selection or design of springs that align perfectly with the operational demands of the application. Acxess Spring’s Spring Creator 5.0 simplifies this process by automating calculations, ensuring precision and efficiency in spring selection and design.

The spring constant (k), also known as the spring rate, indicates the spring's stiffness or spring rate of force. While Acxess Springs Spring Creator 5.0 provides the spring rate directly, let’s illustrate an example of how it could be theoretically calculated if we had started with basic dimensions and properties:

Given:

  • Wire Diameter (d) = 0.043 inches
  • Mean Coil Diameter (D) = Outer Diameter 0.390 - Wire Diameter 0.043 inches = 0.347 inches mean diameter
  • Total Coils (N) = 8.250

The spring constant formula for a compression spring is:

k = Gd^4 ÷ (8D^3 * n)

Assuming a modulus of rigidity (G) for Stainless Steel 302 (which typically ranges around 11.2 x 10^6 psi), the calculation would detail the theoretical underpinnings of determining k, leading to the provided 16.282 lbs/in as a practical outcome.

Example based on Part Number: PC043-390-8250-SST-1000-CG-N-IN

How to Calculate Compression Spring Load:

Calculating the load on a spring is pivotal in the design process, involving the determination of the force required to compress the spring to a desired extent. This calculation is foundational, as the load directly influences the spring's dimensions and material selection to withstand operational forces. In technical terms, the load is often derived from the application's functional requirements—whether supporting the weight in a valve or absorbing shock in a suspension system. The calculation involves understanding the maximum forces the spring will encounter and ensuring the spring's design can accommodate this with an adequate safety margin.

Calculating the spring's maximum load capacity involves understanding the spring's design limitations and material properties. For a spring with a spring rate of 16.282 lbs/in and a maximum deflection of 0.604 inches, the maximum load capacity can be determined using the formula:

Maximum Spring Load = Spring Rate × Maximum Spring Deflection (Travel)

Plugging in the values:

9.837 lbs = 16.2820 lbs/in × 0.604 inches

This calculation indicates the highest force that can be safely applied to the spring without risking permanent deformation, based on its material (Stainless Steel 302 ASTM A 313) and design parameters.

Example based on Part Number: PC043-390-8250-SST-1000-CG-N-IN

How to Calculate Compression Spring Loaded Height:

Calculating a compression spring's loaded height or (compressed height) is opposite of calculating distance traveled. This involves determining the compressed height of a spring when subjected to a specific load of force. This is crucial for ensuring the compression spring fits within its operational environment when compressed. The calculation requires knowledge of the spring's uncompressed free length and its compression spring rate under load, often utilizing the formula:

Loaded Height = Free Length - (distance traveled or compression distance).

Accuracy in this calculation ensures that the spring will not only fit within the assembly at its working state, but also function as intended without undue stress or risk of bottoming out.

A spring with a free length of 1.000 inches and a maximum travel deflection of 0.604 inches under load is designed to compress within its maximum operational load limits of 9.834 lbs. With a spring rate of 16.282 lbs/in, calculating the loaded height involves subtracting the compression spring's travel from the free length: 1.000 inches − 0.300 inches (Travel) = 0.700 inches loaded height. This loaded height ensures that the spring, when compressed by the load of 4.885 lbs, will not exceed its max travel of 0.604 inches nor will it exceed its maximum spring load of 9.837 lbs, thus avoiding potential damage or failure.

Example based on Part Number: PC043-390-8250-SST-1000-CG-N-IN

What's the Difference Between Compression Spring Load and Compression Spring Constant?

Understanding the distinction between compression spring load and compression spring constant is essential for precision engineering. The spring load refers to the external force applied to compress the spring, which can vary depending on the application's requirements. It represents the operational demand of the spring. In contrast, the spring constant k is an intrinsic physical metallurgical property of the spring that indicates its stiffness or resistance to compression. Defined technically as the force required per unit of displacement (K = F/x), the spring constant is determined by the spring's material, outer diameter, wire diameter, and number of coils. Recognizing this difference allows engineers to design compression springs that are not only capable of handling the expected load but also exhibit the desired performance characteristics in terms of compression and energy absorption.

The difference between spring load and spring constant is exemplified by the specific dimensions of this spring. The spring load, capped at a maximum load of 9.834 lbs, is the force the spring is designed to withstand, influenced by its application requirements. In contrast, the spring constant k, or spring rate, of 16.282 lbs/in, signifies the spring's stiffness—how much force is needed to compress it by one inch of distance. This spring's design, with a wire diameter of 0.043 inches, total coils of 8.250, and closed and squared ground ends, directly influences its spring constant. The spring constant reflects the spring's inherent characteristics determined by its physical dimensions and material type and metallurgical makeup, distinct from the operational force or load it accommodates in use.

Example based on Part Number: PC043-390-8250-SST-1000-CG-N-IN

Maximize Your Design with Spring Creator 5.0

Spring Creator 5.0 revolutionizes custom compression spring design, providing a comprehensive yet user-friendly online tool that simplifies the engineering process. This platform offers:

  • Instant Calculations: Quickly obtain key spring metrics such as spring constant, maximum load or force capacities, ensuring your design meets specific requirements.
  • Visual Design Aid: Generate real-time 3D spring blueprints and 3D Spring CAD models, making it easier to visualize the spring within your assembly and facilitating seamless 3D CAD integration.
  • Online Spring Force Tester: See your compression spring perform in a real time animation showing your springs maximum force and maximum compression travel.
  • Cost Estimation: Early cost analysis feature helps align your design with budget constraints, promoting cost-effective engineering solutions.
  • Accessibility: Access the tool from anywhere, streamlining your spring design process and supporting collaboration across different locations.

Embrace efficiency and precision with Spring Creator 5.0, your partner in innovative spring design, backed by the expertise of Acxess Spring.

Navigate Our Extensive Catalog with Ease

Our Online Spring Finder 5.0 simplifies your compression spring search for the perfect compression spring, allowing filters by dimensions, rate, load, material, end type, and more. Over 70 trillion spring designs are ready for shipment. For compression spring projects requiring specific characteristics, our advanced compression spring search and compare features ensure you find exactly what you need. Enjoy weaker and stronger spring selection with thousands of extra spring designs that are generated when you do a spring search. 

Empower Your Projects Today

Acxess Spring’s commitment to providing high-quality, precisely engineered custom or stock compression springs is evident in their extensive compression spring selection, offering over 70 Trillion Custom and Stock springs. Coupled with the innovative Spring Creator 5.0, Acxess Spring empowers professionals across industries to bring their visionary compression spring projects to life, ensuring reliability, efficiency, and excellence in every spring.

Created by Alfonso Jaramillo Jr
President Acxess Spring
Over 40 Years of Experience in Spring Engineering and Manufacturing