Springs are elastic devices used in measuring, support and shock absorbing applications across various industries. These devices are typically made of plastic or metal to store mechanical energy from an opposing force and release it when the force is eliminated.
Common types of springs include extension springs, compression springs and torsion springs as well as some non-helical constructions. You may find them in mattresses, furniture, garage door systems, pressure sensors, medical devices, sports equipment, aircraft control systems, landing gear and just to mention a few.
However, not all springs are created equal. Some are meant for use in high-stress applications such as gym equipment, vehicle suspension systems, garage doors, or airplane landing gears, while others are means for low-stress applications such as window blinds and toys. Still others are general purpose and can be used in a wide variety of applications.
All in all, spring design and manufacturing is a delicate process that requires great care and adherence to specific standards. Here’s a look at some of the key points in spring design and manufacturing engineers use to ensure the final products meet performance and safety requirements.
Springs can be made of metals such as nickel alloys, steel alloys, and stainless steel or non-metals such as rubber, ceramics and urethane. The choice of material is important. Naturally, manufacturers will want to know the intended use of the springs so they can create them to clients’ exact specifications.
For example, if a spring is needed to perform optimally at super high temperatures, then materials that can withstand extreme temperatures will be used. It could also be that you work in corrosive environments, meaning you want springs made of materials that won’t weaken or rust upon exposure to moisture, acids or alkaline solutions. The choice of material also impacts the springs strength, cost and lifespan.
Stainless steel is the most common spring-making material. Typically, stainless steel has up to 1.5% carbon and 10.5% chromium to make it tougher, harder and resistant to corrosion, especially at extreme temperatures. Types of stainless steel include precipitation hardening. austenitic, and martensitic.
These also come in various grades. Precipitation hardening stainless steel is used to make springs with high tensile strengths and stress-resistance. Martensitic stainless steel springs are poor electrical conductors yet strongly magnetic and extremely resistant to corrosion. Meanwhile, austenitic stainless steel is used to make corrosion-resistant springs for medium to high stress applications.
High carbon is also a popular alloy for making springs. It contains up to 2.1% carbon and is not expensive to acquire but offers great versatility, including music wires for low-stress applications, hard drawn wires for average-stress applications, and high-tensile wires for high-stress applications.
Some manufacturers also use oil-tempered wires for general purpose applications and carbon valves for cyclic applications. But all high carbon springs don’t fare well in high-temperature settings or corrosive environments.
Nickel is another popular material among spring manufacturers. It can alloy with a variety of materials to offer extreme resistance to corrosion and high strength even at temperatures above 1400 Degrees Fahrenheit. Nickel alloy springs are the best for use in oil and gas rigs because they can withstand extreme alkaline and acidic conditions. They are also non-magnetic, meaning they have extensive applications in gyroscopes and other indicating instruments.
Apart from metals, you can also get springs made of non-metallic substances including ceramics, rubber and urethane. Ceramic materials have superb heat and abrasion resistance and can also be used to substitute steel products in highly corrosive environments or fields with strong magnetic and electric properties.
Designers and manufacturers have to consider load requirements and tolerance limits, too. Springs can only withstand a certain amount of load before failing. It depends on the spring type, material, dimensions, applications and environmental factors. Metallic springs are more resilient than plastic constructions. Load capacity can also be increased by widening the outside diameter, adding more coils and using thicker wires.
Generally, springs intended for high stress environments, such as vehicle suspension systems need to be able to withstand higher loads. The same goes for springs designed for high heat settings. They must be of materials that can tolerate extreme amounts of positive temperatures.
Additionally, springs must be manufactured within specified tolerance limits. Basically, once a spring’s intended or nominal size has been established, manufacturers are allowed to deviate from the specifications only up to certain limits beyond which their products become too tight or too loose resulting in accuracy problems, poor load bearing or even critical failure.
If you are wondering why tolerance limits are allowed, you should know that it’s because manufacturing processes aren’t always replicable. Tolerance limits allow manufacturers to deviate a little from standard or intended sizes but produce springs that will still satisfy required specs. For example, if the tolerance limit is +/- 0.025 inches, a spring with a 0.5-inch nominal diameter can actually be 0.475 -0.525 inches wide and still meet pre-established requirements.
Different types of spring tolerances include wire diameter tolerance which affects how stiff a spring can be or how much load it can bear, solid height tolerance which affects the amount of compression a spring can bear before twisting and free height tolerance which impacts deflection rate.
Additionally, spring experts must also design for squareness tolerance so their springs operate as desired when deployed and parallelism tolerance to ensure springs align well within their assemblies.
Environmental factors like humidity, temperature, chemical presence, vibrations and radiation have big effects on the spring properties. Temperature, radiation and presence of vibrations affect load capacity as they cause the spring material to expand or contract undesirably, making springs weaker.
Some metals also corrode easily at high or low temperatures. The same goes for springs in high humid environments or those with significant chemical presence.
It’s crucial to consider these factors when selecting spring materials. For instance, a car suspension will have to deal with cold winters and hot summers and therefore the spring material must be able to withstand both temperature extremes. It must also be able to resist salt and other chemicals on roads.
Popular materials for making springs for vehicle suspension systems include high-carbon steel, chrome silicon steel and fiberglass-carbon composite. The latter is typically lightweight yet strong. However, it also costs more than high carbon and chrome silicon steel.
When designing springs for medical devices you have to keep in mind the ability of the material to withstand sterilization and also resist damage from bodily fluids. Popular materials for springs intended for medical devices include titanium, stainless steel and Hastelloy.
On the other hand, when designing springs for use in spacecraft, it’s important to pick materials such as Inconel, niobium, Hastelloy and titanium that can withstand extremely high temperatures and the vacuum of space. These materials are also the best for springs intended for use in other high heat applications such as ovens, industrial furnaces, and gas and oil production.
Springs can be of the compression kind, designed to withstand great forces by shrinking in size and storing mechanical energy which they then release outwards and expand when the force is released. They are used in various applications including vehicle suspension systems, engine mounts, conveyors, wheelchairs, surgical instruments, and other appliances.
Compression springs feature coils that remain apart when at rest and only come together when squeezed. The springs are manufactured using spring coiling machines or a former and the distance between the coils i.e., the pitch is an important factor. When the springs compress, the pitch reduces in size, allowing the springs to store mechanical energy until they can expand to release it.
Another common type of spring is extension springs, designed to resist stretching. These springs are typically tightly wound eliminating any pitch between the coils. That way, the coils come apart with great resistance when pulled on both ends.
The resistance allows the coils to store mechanical energy which is released when the forces are removed, allowing the spring to snap back into its normal state. They are usually formed using wire forming or coiling machines and typically feature hooked ends.
Applications that use extension springs include garage doors, trampoline mat suspenders, window blinds rolling systems, washing machines, dryers, tape measures, squirt guns and pop-up toys.
The third type of springs is torsion springs. They are mainly used to oppose rotation. To make them, a wire is wrapped around a mandrel and then heated up. After that it’s good to go for use. They are used in garage doors counterbalance systems to provide the resistance needed to keep the door open or closed as desired.
You can also find them in window blinds, keeping blinds rolled up when not in use. They are also used in retractable pen clips, pop up toys, clip boards etc.
Besides the above main three, springs can also be leaf springs which are flat single or multi-layered steel structures used in vehicle suspensions. There are also constant force springs designed to provide a specified force per extension or compression distance. These are typically used in medical devices.
Spring rate is the amount of force needed to generate an inch or millimeter of compression. Some manufacturers call it the deflection rate and it’s a good indicator of the strength of a spring. To achieve the desired spring rate, manufacturers can experiment with different materials and alloys, change wire diameter, increase or decrease the number of coils, etc.
The allowable standard deviation for spring rates is +/– 10 percent. That means, if the nominal spring rate is 15 pounds of force per millimeter, the actual spring rate shouldn’t be below 14 pounds of force per mm or above 14 pounds of force per mm.
The thickness, length and diameter of the spring wire matters, too. It may be hard to believe but these properties affect the spring’s load capacity which is the amount of load it can support before failing. They also affect the spring’s fatigue resistance and overall performance.
Of course, the diameter measurement of a spring is simply the horizontal distance between its widest points. Springs with wider diameters can carry heavier loads and are thus suitable for use in high load applications such as vehicle suspension systems. That’s because a bigger diameter results in a bigger cross-sectional area.
That said, you will need more wire to achieve the number of coils you want otherwise you will end up with a spring with very few coils leading to reduced deflection. Deflection simply refers to the distance a spring can travel when loaded.
Spring length is a measure of the vertical distance on an upright spring. It has an impact on the deflection rate as well as the overall fatigue life. Naturally, a shorter spring doesn’t have a long travel distance which means it stores mechanical energy within a small area increasing the chances of breaking or permanent deformation. It’s all about energy distribution when under pressure.
For springs that go through frequent compression and expansion such as in garage door systems, better work with those boasting longer lengths to benefit from increased fatigue life.
The diameter of the spring wire is another key design and manufacturing factor. Generally, springs made of thicker wires have higher load capacity and resistance to fatigue. They are the best for use in high stress applications such as aircraft landing gear, vehicle compression systems, conveyors, garage door systems, etc.
To summarize, there are key points in spring design and manufacturing that help ensure the products meet performance and safety requirements and also guarantee reliability. The last thing you want is a spring that fails miserably after just a few uses because the manufacturer didn’t consider the application and environmental factors when deciding on the spring material and dimensions.
Always work with the manufacturer to ensure you get springs that actually meet the requirements of the project you want to undertake. While at it, check to ensure the manufacturer stays faithful to recommended tolerance limits and tests their products to ensure they meet certification standards.
If you need help learning more about different standards for spring manufacturing, don’t hesitate to ask. We are a team of experts with broad experience in the field and will be happy to help you learn more about our springs and find the ones that suit the applications you have in mind.