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Coil Spring Design Basics

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Coil Spring Design Basics

Coil Spring Design Basics

smjmitchell

(Aeronautics)

(OP)

23 Feb 05 05:46

Hi All,

I need to do some work designing steel coil springs (approx 2" dia x 12" long - loads approx - lb). I am familar with the basic theory of coil springs for calculating stresses etc however I have a couple of questions of a more practical nature:

1. What are the most common steel alloys used in the manufacture of coil springs.

2. What maximum working stress levels, considering fatigue etc, are used for the common alloys or is there a general rule of thumb that is applicable to all steels (i.e. some percentage of max shear stress).

3. What is the normal level of heat treatment for the common steels (i.e. Rockwell C etc). What heat treatment specs (MIL-SPEC, SAE etc) are usually used by the industry.

4. What is a typical deflection to length ratio at rated load ... I am assuming that you would want some margin against the spring bottoming out at maximum load.

5. Are all springs shot peened or are there some situations where you peen and others where you do not ?

6. Are there any good references (spring design bibles) that spring designers use that provide guidance on practical issues such as those above.

I am just trying to educate myself so I am not a total vacuum of knowledge when I go to talk to the spring manufacturer.

Thanks, for any help. It will be appreciated.

Stephen

Replies continue below

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RE: Coil Spring Design Basics

desertfox

(Mechanical)

23 Feb 05 14:07

Hi smjmitchell

Material selection will depend on your operating enviroment,
theres's a complete list of spring materials and other information in the Design Handbook by Associated Springs
(Barnes Group).Materials such as grades of Stainless Steel,Phosphor Bronze, Carbon steel, alloy Steels etc are used to make springs.
Fatigue will depend on the frequency of spring operation and
in a situation of high cycle fatigue then shot peening would improve fatigue strength but is usually not worth doing for low cycle applications.
Heat treatment again would depend on service conditions and material but heat treatment is not always required.
Finally keep your spring operating between 15% and 85% of the full deflection range as outside these limits the spring rate is none linear.

regards desertfox

RE: Coil Spring Design Basics

jackpot

(Materials)

23 Feb 05 16:07

I might recommend three books to consider:

"Handbook of Spring Design" put out by SMI

"Mechanical Springs" by A. M. Wahl

or the

"Spring Design Manual AE-11" by SAE

Most springs that operate at temperatures below 250°F are made from a high carbon steel with a good surface finish called Music Wire (ASTM A228). Springs that operate above this temperature are typically Chrome Silicon (ASTM A401). There are many other materials as pointed out by dfox.

Generally speaking, Fatigue life is proportional to tensile strength. Anything that can be done to reduce surface defects helps like electropolishing, peeling or surface inspection will also improve performance.

Jack

RE: Coil Spring Design Basics

israelkk

(Aerospace)

23 Feb 05 17:22

I took the liberty to make a preliminary check if a 2" dia x 12" long helical compression spring can be designed for approx lb and it seems quite impossible even when I am using 17-7PH CH900. More then that, the highet to diameter ratio is quite high so the spring will buckle unless it is guided but, then you will face a friction between the spring and its guide which may render its ability to resist fatigue.

http://www.webspawner.com/users/israelkk/

smjmitchellI took the liberty to make a preliminary check if a 2" dia x 12" long helical compression spring can be designed for approx lb and it seems quite impossible even when I am using 17-7PH CH900. More then that, the highet to diameter ratio is quite high so the spring will buckle unless it is guided but, then you will face a friction between the spring and its guide which may render its ability to resist fatigue.

RE: Coil Spring Design Basics

smjmitchell

(Aeronautics)

(OP)

24 Feb 05 05:37

Thanks you all for your advice.

The spring I am looking at replacing is of Danly manufacture. A look in their catalog shows that the existing 2" dia x 12" (50mm x 300mm) long heavy duty spring could carry a peak load of approx 750 kg ( lb) at 72mm deflection. The extra heavy duty spring would carry kg at 60mm deflection (k = 16.66 kgf/mm). kg is approx lb. These are from the columns in their tables designated 0.3 million .. which I can only assume means a life at this load of 0.3 million cycles (I need to clarify this). These springs are made from rectangular section wire.

I should clarify a couple of issues.

lb is the peak or limit load that may only be seen a few times in the life of the spring. Normal operating loads are likely to be half this.

Yes the spring will be contrained inside a tube to prevent buckling.

I have some flexibility to change the spring length, diamter etc to get the required characteristics. The peak loads will ultimately be determined by the deflections of the spring and so I need to use an interative design process to refine the geometry.

Steve

RE: Coil Spring Design Basics

TVP

(Materials)

24 Feb 05 15:42

smjmitchell,

In addition to the info already provided, here is some more food for thought:

1. Most common alloys are Cr-Si alloys like SAE or (ASTM A 401) or plain-carbon grades like - for music wire (ASTM A 228).  Alloy grades are quenched and tempered to a martensitic microstructure.  Carbon steels are patented to pearlitic microstructures (extremely fine pearlite).

2. Stress levels should be maintained below ~ MPa for fatigue applications using commercial quality wire (ASTM A 401) that is shot peened.  This works out to ~ 60% of the UTS.  Higher stresses can be tolerated with improved spring steels like ASTM A 877 (valve quality), which has reduced limits for decarburization, non-metallic inclusions, and surface defects.  Other improvements in fatigue strength are produced by variations to the shot peening process like double shot peening (high intensity followed by low intensity).

3. Hardness depends a great deal on the grades used and how they are fabricated (hot winding vs. cold winding).  A general range is ~ 47-53 HRC for hot winding, which means the springs are wound hot, then quenched and tempered to the desired hardness of 47-53 HRC.  Cold winding uses wire that has already been quenched & tempered (or patented in the case of music wire) to very high strengths.  This wire is purchased to tensile strength ranges, not hardness.  The tensile strength for ASTM A 401 ranges from - MPa depending on wire size.  This translates into ~ 47-58 HRC, with the highest levels only attainable in very small diameters.  A good source of heat treating info is MIL-H-.

4. If at possible, try to limit the travel so that spring is not completely closed (compressed from some nominal length to the solid length).  Stresses increase greatly as you approach the solid length.  However, properly processed springs can be taken to solid with fatigue lives in excess of 100,000 cycles.

5. Any spring that requires good fatigue life should be shot peened.  Usually only small diameter springs or springs that are very lightly stressed are not shot peened (think springs in ink pens).

6. Jackpot and the fox provided information on good resources for spring design, calculations, etc.  Another excellent resource is the Euronorm standard EN -1 Cylindrical helical springs made from round wire and bars &#; Calculation and design - Part 1: Compression springs.  It is available in English (BS or DIN) or German (DIN) versions.  

RE: Coil Spring Design Basics

Wobulator

(Electrical)

3 May 05 05:59

I need to design a compression spring to diplace 50 mm for each kilo of load and an overall displacement of 300 mm. Any help would be well apreciated.

Wobulator

RE: Coil Spring Design Basics

NickE

(Materials)

3 May 05 08:19

wobulator- start a new thread.

RE: Coil Spring Design Basics

israelkk

(Aerospace)

3 May 05 10:06

First I agree with NickE.

However, your info is not enough.
How much space you have for the spring?
What is the maximum outside diameter?
What is the maximum free and compressed length?
How much the maximum force the spring will see?
How many times the spring will see the force, is it for static or cyclic application?
Is the wire material need to be corrosion resistant?
If it need not to be from stainless steel is it to plated and if so what type of plating?
Is the spring guided on a rod or inside a hole?
How about bucking of the spring and friction with the rod or hole?
etc.

A spring design is a job for an experienced mechanical engineer. Spring design is not just plugging the numbers into the formulas, and as you see from my previous questions there are many issues that the spring designer has to take into consideration.

http://www.webspawner.com/users/israelkk/

WobulatorFirst I agree with NickE.However, your info is not enough.How much space you have for the spring?What is the maximum outside diameter?What is the maximum free and compressed length?How much the maximum force the spring will see?How many times the spring will see the force, is it for static or cyclic application?Is the wire material need to be corrosion resistant?If it need not to be from stainless steel is it to plated and if so what type of plating?Is the spring guided on a rod or inside a hole?How about bucking of the spring and friction with the rod or hole?etc.A spring design is a job for an experienced mechanical engineer. Spring design is not just plugging the numbers into the formulas, and as you see from my previous questions there are many issues that the spring designer has to take into consideration.

RE: Coil Spring Design Basics

suneelnewaskar

(Mechanical)

16 Jul 05 04:41

Dear Sir,
I am looking for springs that each spring shall support
200 kg load , deflection is 30 mm , but these shall operate
at 400 cycles per minute . Thsese springs shall be used in power press operation . Me i do not have any dimensional constraint . Because i am going to use them as ha hangers.
I shall be thankfull if you can upgrade me on this
With best regards
suneel

RE: Coil Spring Design Basics

israelkk

(Aerospace)

16 Jul 05 12:11

Firstly you should start a new posting instead of entering a new design problem in an existing post.

To your specific design problem:

1. Are you looking for a catalog spring or a custom designed spring?
2. Is the spring load changing from zero load to 200kg or from another load to 200kg?
3. To correctly design and avoid resonance phenomena, what is the mass that the springs "see" when they are working?

http://www.webspawner.com/users/israelkk/

suneelnewaskarFirstly you should start a new posting instead of entering a new design problem in an existing post.To your specific design problem:1. Are you looking for a catalog spring or a custom designed spring?2. Is the spring load changing from zero load to 200kg or from another load to 200kg?3. To correctly design and avoid resonance phenomena, what is the mass that the springs "see" when they are working?

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News

What is the Strongest Spring Material?

The Importance of Spring Material Strength

Springs are an essential component in various industrial and consumer applications. Their primary function is to store mechanical energy and release it when needed.

Springs can be found in everyday items such as pens, watches, and cars. The strength of a spring material plays a crucial role in determining its performance, durability, and lifespan.

Weak springs can deform or break under stress, leading to malfunctions or accidents. Therefore, identifying the strongest spring material is critical for ensuring safety, reliability, and optimal functionality.

Highlighting The Significance of Identifying The Strongest Spring Material

Identifying the strongest spring material provides numerous benefits to manufacturers and end-users alike. For manufacturers, using the strongest spring material means producing high-quality products that meet or exceed industry standards while reducing costs associated with frequent replacements or repairs due to weak springs. For end-users, stronger springs mean more reliable products, safer to use and perform better over time.

Furthermore, identifying the strongest spring material allows for innovation in product design by enabling engineers to create new applications that require higher-strength springs than previously possible. Understanding the importance of identifying the strongest spring material is crucial for manufacturers and end-users.

It ensures safety, durability, and optimal functionality while promoting innovation in product design. In the following sections of this article, we will discuss various factors that affect spring material strength and compare different materials to identify the strongest option on the market today.

Overview of Spring Materials

Springs are mechanical devices designed to store and release energy by exerting force when compressed, stretched, or twisted. They are essential components in many products, from toys and appliances to vehicles and machinery. For a comprehensive check, this overview of spring materials and their properties.

Springs can be classified based on their application, shape, function, and material. The most common types of springs include compression, extension, torsion, leaf, and flat springs.

Definition and Types of Springs

Compression springs are helical coils that resist compression forces applied axially along their axis. Extension springs are similar to compression springs but extend instead of compressing when loaded. Torsion springs have a body of wire twisted into a helix that exerts torque around an axis when deflected from its free position.

A leaf spring is formed by stacking several thin strips of metal on each other in increasing length, with the shortest strip at the center forming an eye through which the bolt passes for attachment purposes. Flat spring exhibits characteristics similar to tension and compression spring; it exerts force in either direction perpendicular to their plane.

Common Materials Used for Springs

Springs can be made from various materials depending on their specific applications, such as music wire (high-carbon steel), chrome silicon steel alloy (Cr-Si), stainless steel alloys (17-7PH), titanium alloys(Ti-6Al-4V), nickel-based alloys(Inconel 600), etc&#; Steel is the most common material for making industrial-grade springs because it has a high strength-to-weight ratio, good elasticity, corrosion resistance properties, etc.. It also has better fatigue resistance properties than materials like copper or brass, making them suitable for long-term usage without any failure under cyclic loads.

Factors Affecting Spring Material Strength

Chemical Composition and Properties

The chemical composition of a spring material plays a significant role in determining its strength. High-carbon steel alloys are generally more suitable for creating strong springs due to their hardness and durability.

Steel alloys with added elements like chromium, vanadium, or silicon increase their strength and corrosion resistance. However, it&#;s important to note that choosing the right composition is just one factor in achieving high spring strength.

Manufacturing Process and Techniques

The manufacturing process of a spring has a significant impact on its final strength. Each type of spring requires unique techniques during production to ensure optimal strength.

The coiling process, for example, can affect the final product&#;s strength by manipulating the material&#;s molecular structure. Cold coiling results in higher tensile strength but lower ductility, whereas hot coiling provides better ductility but reduced tensile strength.

Heat Treatment and Surface Finishing

Heat treatment refers to the controlled heating or cooling of materials to modify their properties without altering their shape. This technique is essential for optimizing the strength of many types of springs by modifying their internal structures.

For instance, quenching steel springs after coiling can significantly increase hardness and tensile strength while tempering them reduces the brittleness induced by quenching. Surface finishing is an essential process that affects the look and properties of springs&#; surfaces while preventing corrosion over time.

Removing surface impurities through electroplating or coating with chemicals like zinc or chrome oxide layer on top of steel springs enhances durability. Selecting suitable chemical compositions and appropriate manufacturing techniques, including heat treatments and surface finishing processes, are crucial in producing strong, durable springs for various industrial purposes.

Comparison of Strongest Spring Materials

Steel Alloys

Steel alloys are the most commonly used materials for springs. The most popular steel alloys for springs are chrome-vanadium, music wire, and stainless steel. Chrome vanadium is the strongest and toughest of all spring steels and has excellent fatigue properties.

Music wire is a high-carbon steel alloy with good fatigue life and can handle high stresses but is brittle. Stainless steel is a corrosion-resistant material that can withstand harsh environments and temperatures.

Music Wire

Music wire is a type of spring steel that has been cold-drawn and quenched to achieve its high tensile strength. It has an excellent fatigue life but is susceptible to hydrogen embrittlement, which makes it brittle over time. Music wire can handle high stresses, but its brittleness makes it unsuitable for applications subjected to shock loads.

Chrome Silicon

Chrome silicon is a type of spring steel that contains chromium and silicon in its composition. It has excellent fatigue resistance, corrosion resistance, and good heat resistance properties. Chrome silicon can withstand higher stress levels than other spring materials like music wire or stainless steel; therefore, it finds applications in industries such as aerospace or automotive.

Stainless Steel

Stainless Steel springs have excellent resistance to corrosion due to their chromium content, which forms a passivation layer on the material&#;s surface corroded by acidic environments or salts. This makes them ideal for chemical processing plants where corrosive chemicals are used.

Non-Metallic Materials

The rise of advanced composites technology increased demand for non-metallic materials with superior mechanical properties to their metallic counterparts.

Carbon Fiber Reinforced Polymer (CFRP)

Carbon Fiber Reinforced Polymer (CFRP) is a composite material that consists of carbon fibers embedded in a polymer matrix. It has a high strength-to-weight ratio and excellent fatigue properties, making it suitable for use as spring material in aerospace or automotive applications.

Glass Fiber Reinforced Polymer (GFRP)

Glass Fiber Reinforced Polymer (GFRP) is another composite material containing glass fibers embedded in a polymer matrix. It has an excellent strength-to-weight ratio and is used mainly in construction for lightweight structures such as bridges or beams. The strongest spring material depends on the specific application requirements.

Steel alloys are widely used for their availability and affordability, but non-metallic materials like CFRP or GFRP can offer superior mechanical properties. Each type of material has pros and cons, so choosing the right one is essential based on factors such as stress levels, environment, and cost-effectiveness.

Advantages and Disadvantages of Strongest Spring Materials

Steel Alloys

Steel alloys are the most commonly used spring material due to their high strength, durability, and corrosion resistance. This material is readily available and relatively affordable compared to other spring materials.

However, one of the main disadvantages of steel alloys is their heavy weight, which may limit their use in applications requiring lightweight springs. Additionally, steel alloys have limited flexibility when compared to non-metallic materials.

Non-Metallic Materials

Among the strongest non-metallic spring materials are carbon fiber-reinforced polymer (CFRP) and glass fiber-reinforced polymer (GFRP). CFRP has a high strength-to-weight ratio that makes it lightweight yet strong enough to handle high loads. It is also corrosion-resistant and can withstand harsh weather conditions.

However, CFRP is expensive and not widely available, which limits its use in certain applications. GFRP shares similar advantages with CFRP but has lower strength-to-weight ratio than CFRP.

Both steel alloys and non-metallic materials have their advantages and disadvantages when used as spring materials. Steel alloys are readily available, affordable, and durable but can be heavy-weighted. In contrast, non-metallic materials like CFRP offer higher strength-to-weight ratios suitable for some lighter applications but are typically more expensive.

Recap on the importance of identifying the strongest spring material:

In any industry, spring materials ensure that machines and devices perform effectively. The right material is critical to maximize productivity, efficiency, and durability. The article has provided an overview of different types of spring materials, focusing on identifying the strongest among them. Highlight the strengths and weaknesses of each material:

Steel alloys offer high strength, durability, and availability at an affordable price. They are commonly used for heavy-duty springs, but their weight limits flexibility in some applications. Music wire provides an excellent strength-to-weight ratio but lacks corrosion resistance unless coated or plated.

Chrome silicon offers similar properties as music wire with added corrosion resistance but is more expensive. Stainless steel provides excellent corrosion resistance but can be costly compared to other steel alloys.

Non-metallic materials such as Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP) offer lightweight alternatives with high strength-to-weight ratios and excellent corrosion resistance. However, they are limited in availability and relatively expensive compared to steel alloys. Summarize:

Identifying the strongest spring material depends on several factors, such as chemical composition, manufacturing techniques, heat treatment process, surface finishing methods, cost-effectiveness, and availability. Steel alloys such as music wire or chrome silicon provide excellent strength-to-weight ratios, while stainless steel has added corrosion resistance properties.

Non-metallic materials like CFRP or GFRP offer lightweight alternatives with high-strength characteristics but are limited in availability and relatively costly compared to common steel alloys. The importance of selecting a strong spring material cannot be understated.

A weak or inferior quality spring could lead to equipment failure, resulting in significant business losses or safety risks for individuals using devices installed poorly or incorrectly. Investing in high-quality spring materials is crucial in ensuring productivity and safety.

FAQ&#;s

1. How do high-carbon steel alloys like music wire compare to other spring materials regarding fatigue resistance and durability?
Music wire, a high-carbon steel alloy, offers superior fatigue resistance, especially when compared to materials like copper or brass. However, its susceptibility to hydrogen embrittlement can affect its long-term durability in specific applications.

2. How do added elements like chromium or vanadium influence the strength and corrosion resistance of steel alloys used in springs?
Adding elements like chromium, vanadium, or silicon to steel alloys enhances their inherent strength and corrosion resistance. For instance, chrome silicon steel alloy exhibits improved fatigue and corrosion resistance compared to traditional steel.

3. Can you detail the impact of cold and hot coiling on a spring&#;s tensile strength and ductility?
Certainly. Cold coiling generally results in springs with higher tensile strength but reduced ductility. In contrast, hot coiling tends to offer better ductility at the expense of some tensile strength.

4. How does the rise of advanced composites technology affect the demand for non-metallic spring materials?
Advanced composites have increased demand for non-metallic materials like Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP). These materials offer exceptional strength-to-weight ratios, making them suitable for specific applications that demand lightweight yet robust springs.

5. Regarding corrosion resistance and applicability in harsh environments, how does stainless steel compare to non-metallic materials like CFRP?
Stainless steel offers excellent corrosion resistance due to its chromium content, making it ideal for environments with corrosive chemicals or salts. However, while non-metallic materials like CFRP also exhibit corrosion resistance, their suitability varies based on the specific composite and its resistance to environmental factors.

These FAQs are designed to address more in-depth technical aspects that industry insiders would be familiar with. Adjustments can be made as needed to fit specific contexts or areas of focus.

Want more information on supplier of high-quality coil springs? Feel free to contact us.