As a material vital to numerous industries, spring steels hold certain characteristics that set them apart from other types of steel. But what is spring steel and what makes it so useful? In this article, we&#;ll discuss exactly what spring steel is, its properties, various grades and common applications.
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The selection of materials used in spring fabrication and design in general is determined by knowing the tensile and yield strengths of the various alloyed metals. In making spring steel, in addition to its carbon content, which is generally in the range of 0.5% to 1.0%, spring steels may also be alloyed with combinations of nickel, manganese, chrome, vanadium, molybdenum or other elements.
However, the one common element that is a must in the composition and manufacture of spring steels is silicon. This material is highly regarded for its durability as well as its ability to retain its shape and flexibility. Its alloying properties are not only particularly well-suited for use in alloy spring steel applications, but its characteristics help give the material its defining high-yield strength.
Steel is an alloy of iron and carbon, with other elements added to enhance its properties. There are different types of steel, each with unique properties, depending on their specific composition and processing techniques.
Spring steel is a specific type of steel, engineered for its high yield strength, elasticity, hardness and resilience, which makes it suitable for use in springs and other applications such as retaining clips and tabs.
In terms of which is better, it really depends on the application. For components like springs, automotive suspension components, and other mechanical parts that must withstand cyclical stresses, spring steel is superior to alloy steels.
However, for applications that don&#;t require high elasticity, resilience, and tensile strength, regular or other forms of steel will be suitable and more cost-effective. There are downsides to using spring steel such as the extra considerations needed for machining and welding it.
Spring steel has many unique properties that make it ideal for producing springs and other similar components, including:
The process of hardening spring steel is another important step in giving the material its high yield strength. Hardening can occur through heat treatment or a process referred to as work hardening; this is the hammering, rolling, drawing or other physical means that can be applied to increase its hardness.
Hardening via heat treatment, as the name suggests, is achieved by heating up the steel, and then quenching the material to bring it down to ambient room temperature. After heat treatment, the steel is tempered to ensure that it does not become brittle as well as to prevent or relieve it of internal stresses.
Heat-treated spring steel is used for such products as saw blades, knives, and flat springs. Work hardening methods are achieved by rolling the material to reduce its thickness. The process increases the material&#;s tensile strength and produces spring steel sheets, strips, rods and bars.
Popular spring steel grades include the following SAE grades (ASTM grades):
As a general-use steel, spring steel has a wide range of commercial applications. You can find it in just about any piece of manufacturing equipment, including:
Spring steel is a unique and versatile material with exceptional properties such as high yield strength, elasticity and resilience. Its composition and heat treatment processes set it apart from regular steel, making it ideal for various applications, including springs, clips, fasteners, and machinery. Contact us at Metal Supermarkets to learn more about spring steel grades and how they can fit your specific needs.
We hear from a lot of engineers that they learned a good deal about round wire design theory in school but not much about flat springs. Why is that? Who determined that flat springs aren&#;t interesting or cool enough?
Considering the multitude of industries and products that utilize these types of springs, we think they are not just &#;cool&#;, but that understanding them is a critical step in good machine design. In fact, Leonardo Di Vinci (he was kind of smart!) utilized flat steel springs in many of his inventions that were centuries ahead of their time &#; the self-propelled cart and car as well as the first iteration of a helicopter just to name a few.
For sure, if they were good enough for my buddy Leo (who&#;s home town and grave site I have actually visited), then they are good enough for the rest of us and it&#;s time to change this prejudice against flat springs!
During the next several blogs, we&#;ll present a summary of the various types of flat springs, their common applications and limitations, as well as design considerations. In this first article, we&#;ll focus on constant force (aka Conforce®) springs.
Constant force springs provide a nearly flat gradient as opposed to round wire extension and compression springs.
Common Applications
Counterbalancing: ie. Windows and shades, hospital tables, X-ray machines, industrial equipment, military tank seats, etc
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Push or Pull: ie. Staple and nail guns, surgical staplers, drug delivery device, motor brushes, toasters, cup holders, fire dampers, retail displays, etc
Constant Force Design and Ordering Considerations
First, select the material considering the environment the spring will live in then determine life (cycle) and force required (consider hysteresis). You&#;ll then need to determine the space available, mounting method (spool, no spool), and end detail and attachment, including straight section on the end of the spring (&#;pick-up&#;). How many will you need and how quickly?? What are the critical characteristics and tolerances as well as packaging requirements? Will you issue a blanket order with releases or ship all at once?
Mounting Methods
Understanding Constant Force vs Constant Torque
Constant force springs provide a linear extending/retracting force whereas constant torque springs provide a rotational force (torque)
Limitations of Constant Force Springs
Cycle Life &#; the maximum number of cycles in our world is 100,000 measured as an extension and retraction of either the whole spring or a portion of it. Keep in mind that low design estimates will lead to early failure while high estimates make the spring larger and more expensive than necessary
Sample Design Chart (all Force values are estimates only):
Material Selection &#; the most common material is type 301 stainless steel. Texture-rolled high carbon steel can be used when a lower cost is required for high volumes; Inconel 625, and Elgiloy are utilized for the most demanding applications. Material thickness generally runs from .002&#; &#; .031&#; and tensile strength range from 270,000 &#; 310,000 psi. Finally, our standard finish is a deburred edge but you can request a &#;round&#; finish for a smoother edge.
Cost &#; 301 Stainless is the most&#;commonly specified material. As stated above, texture-rolled high carbon costs less in high volumes but Inconel and Elgiloy are significantly more expensive. Over-designing a spring will also require more material and, thus, a greater cost.
Force & Diameter Relationship
Spring force is generally constant as long as the diameter is constant. Longer springs increase in force slightly as they are extended (unless measures are taken to flatten the gradient). The normal tolerance for a constant force spring is +/- 10%
As the spring diameter is increased the spring force decreases and cycle life increases (lower stress). There is a direct relationship between the ID and the tolerance &#; if the ID must be held to a tighter tolerance then the load, tolerance must increase.
Testing and Inspection
Considering customer requirements, the following design aspects are typically tested and inspected: coil diameter, end detail (hole diameter; and location, pick up, etc); length; load or force; drum size and mounting; and &#;workmanship&#;.
Conclusion
Flat steel springs can be the forgotten &#;critical component&#; in engineering schools but they are not that difficult to understand if you work with the right supply partner. Don&#;t underestimate the importance of a good design and quality workmanship since a poor design and poor quality can have disastrous effects.
We hope you found this first article, focusing on constant force springs, valuable. Feel free to contact the leader in flat steel spring design and manufacturing &#; Vulcan Spring & Manufacturing &#; and look for future announcements detailing new, helpful blogs.
At Vulcan, we go &#;Beyond the Spring&#; and we&#;re here to help!
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