Compression Springs

Introduction

This article will take an in-depth look at compression springs.

The article will look at topics such as:

• Principle of Compression Springs
• Manufacturing Processes and Materials Used to Make Compression Springs
• Types of Compression Springs
• Applications and Advantages of Compression Springs
• Common Problems in Compression Springs
• And much more…

Chapter 1: Principle of Compression Springs

This chapter will discuss what compression springs are and the considerations when choosing compression springs.

What are 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.

How Compression Springs are Designed

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.

Considerations When Choosing Compression Springs

The are various considerations when choosing compression springs which include:

Compression Spring End Types

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

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 Ends

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

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

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.

Compression Spring Material Considerations

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.

Compression Spring Physical Considerations

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.

Compression Spring Load Considerations

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.

Compression Spring Wire Diameters

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.

Types of Compression Spring Wire

• High Carbon Spring Wire - High carbon spring wire includes music wire and hard drawn wire, which are made from different percentages of carbon and manganese. Depending on the carbon content, they have a Rockwell hardness of C31 or C60 with a working temperature of 250°F (121°C).
• Alloy Steel Wire - Alloy steel wire is made of carbon, chromium, and silicon with a Rockwell hardness of C48 to C55 and a working temperature of 475°F (246°C).
• Stainless Steel Wire - The grades of stainless steel used to produce compression wire are Series 302, 304, 316, A313, and 17-7 PH. Most stainless steel is made of chromium and nickel with series 316 having molybdenum as an extra ingredient. Stainless steel wire has a Rockwell hardness of C35 up to C57 with working temperatures that vary between 550°F (288°C) and 650°F (343°C).
• Non-Ferrous Alloy Wire - Non-ferrous alloy wire includes phosphor bronze and beryllium copper. Their Rockwell hardness varies between C35 up to C104 with working temperatures between 200º F (93.8°C) and 400°F(204°C).

Chapter 2: Manufacturing Processes and Materials Used to Make Compression Springs

This chapter will discuss the manufacturing processes used in making compression springs and the materials used.

Compression Springs Manufacturing Processes

The manufacturing processes used in making compression springs include:

Coiling

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.

Stress Relieving

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.

Finishing

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:

• Grinding: Designers must grind the spring's ends flat, enabling them to adhere to other surfaces more readily.
• Strength Peening: Strength peening prevents metal fatigue and fractures in steel despite heavy use and frequent flexing.
• Setting: Designers thoroughly compress the spring so that all of its coils touch in order to establish its intended length and pitch permanently.
• Coating: Designers can coat the spring with non-corrosive paint, submerge it in liquid rubber, or plate it with another metal, such as zinc or chromium, to avoid corrosion.
• Packaging: Designers develop specialized spring packagings, such as bulk packaging in boxes or plastic bags.

Materials Used to Make Compression Springs

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 cone shaped springs 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.

Characteristics of Compression Spring Material

• Cold-drawn, hard-drawn wire is the least expensive spring steel, typically employed for static loads and low stresses. The material is not suited for temperatures below zero or more than 2192°F (1200°C).
• Cold-drawn, quenched, tempered, and all-purpose spring steel is known as oil-tempered wire. However, it is not appropriate for unexpected loads, exhaustion, or temperatures below zero or above 3272°F (1800°C). Alloy steels are useful when we opt for severely stressed circumstances.
• Chrome Vanadium: is an alloy spring steel that can withstand high temperatures and stresses of up to 3992°F (2200°C). It has strong fatigue resistance and long shock and impact load endurance.
• Chrome Silicon can be used to make springs under a lot of stress. It provides outstanding performance for long life, shock loading, and temperatures up to 4532°F (2500°C).
• Music wire is most frequently employed in small springs. It can endure repeated loading at high pressures and is the toughest material with the highest tensile strength. It cannot be utilized at temperatures below zero or above 2192°F (1200°C). Music wire is typically a popular choice for springs.
• Widely utilized alloy spring materials include stainless steel.
• Brass and phosphor bronze springs both have good electrical conductivity and corrosion resistance. They are utilized frequently for contacts in electrical switches. Brass springs can be used in extremely cold temperatures.

Chapter 3: Types of Compression Springs

Different types of compression springs include:

Convex Compression Springs

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.