Hey everyone, thanks for stopping by my corner of the internet. I’m Alex, and I run a small constant force spring supply business—for the last 8 years, I’ve been helping all kinds of folks get the right springs for their projects, whether it’s medical devices, automotive parts, or even big industrial equipment. The other day, a customer slid into my DMs asking a question that’s actually way more common than you’d think: “Are constant force springs affected by magnetic fields?” It’s not the first time I’ve gotten this, and honestly? I get why it’s a big deal. If you’re working on a machine that’s near magnets or in a magnetic field, you can’t afford parts that act wonky. Let’s break this down, no fancy jargon, just what I’ve learned from actual customers and testing I’ve done in my workshop. Constant Force Spring
First, let’s make sure we’re on the same page about what a constant force spring is, because if you’re here, you probably already know, but bear with me. These aren’t your regular coil springs that get stiffer or looser as you stretch or compress them. A constant force spring is basically a long strip of flat metal wound tight on a reel. When you pull on the free end, it unwinds, and the tension from the way it’s formed gives you the same amount of force every inch of the way. They’re super popular for things like window shades, retractable tool cords, and even drawer sliders because that consistent force is exactly what you need.
Now, back to the magnetic field question. Let’s start with the basics: metals and magnets. Not all metals are magnetic, right? You’ve got your ferrous metals—iron, steel, most stainless steels that have iron in them—those get attracted to magnets. Then you’ve got non-ferrous stuff: aluminum, copper, brass, some types of stainless steel that don’t have much iron. So right off the bat, the material your constant force spring is made of is the first big factor here. That’s why I always ask customers to tell me their working environment before I recommend a spring.
Let’s get into the science, but keep it real. Magnetic fields exert force on moving charged particles, right? For a spring that’s not moving, the electrons in the metal are just zapping around like normal, no net movement, so a static magnetic field (that’s the kind that doesn’t change over time, like a permanent magnet) won’t push or pull on a stationary constant force spring. Wait, but what if the spring is moving? Like, if it’s unwinding or rewinding, the metal’s atoms are shifting a little as the spring bends. Does that interact with a magnetic field? From what I’ve tested and what the engineering data shows, unless the magnetic field is super strong—like, way stronger than what you’d find in most consumer or even industrial setups—you won’t notice any difference in the spring’s constant force. The small movement of the spring’s molecules doesn’t create enough force against a normal magnetic field to change how it works.
But here’s the catch: alternating magnetic fields. Those are the ones that change direction, like from a motor or an MRI machine. If you have a spring moving in an alternating magnetic field, you get something called eddy currents. That’s when the magnetic field induces tiny electrical currents in the metal of the spring. Those eddy currents create their own little magnetic fields, which actually can slow the spring down or mess with its tension a tiny bit. But again, this only happens if the field is strong and changing fast. For most everyday applications—like a window near a fridge magnet, or a retractable cord next to a power tool—you don’t have to worry about this. I’ve had customers make springs for MRI compatible equipment, and we use non-ferrous stainless steel (like 316 SS) for those, so even in the super strong fields in an MRI, there’s basically no interference.
Wait, let’s talk about the materials I use, because that’s what my customers care about. A lot of my constant force springs are made from high carbon steel, which is ferrous. That means it’s magnetic. But like I said earlier, a static magnetic field won’t pull on the spring enough to change its function—wait, hold on, let me correct that. If you put a ferrous constant force spring right next to a super strong permanent magnet, like the ones used in lifting equipment, yes, the magnet will attract the spring. So if your project is using a spring that’s in a spot where it’s sitting right against a big magnet, that’s a problem. The spring might stick, or its tension might shift a little because it’s being pulled. But in 99% of the projects I do, that’s not the case. Most magnetic fields are ambient—like the ones from a phone speaker, or a small motor—so weak that the ferrous steel spring won’t even notice.
I had a customer last year who was building a portable medical pump. They were worried because the pump had a small motor that created a low-level magnetic field, and they thought their constant force spring would mess up the pump’s accuracy. We tested both ferrous and non-ferrous stainless steel springs in their actual pump, and guess what? The ferrous one worked exactly the same as the non-ferrous one. The motor’s magnetic field was way too weak to affect the spring’s force. They went with the ferrous one because it was cheaper and easier to source, and they’ve been happy with it ever since.
Another customer was working on a new line of robotic arms for industrial use. Those robots have a lot of powerful magnets and motors, so their working environment has way stronger magnetic fields than your average project. We went with 304 stainless steel, which is non-ferrous, for their constant force springs. We tested them in the robot’s actual magnetic field, and there was zero change in the spring’s performance. No slowing down, no inconsistent force, nothing. That’s a big part of why I recommend materials based on the specific magnetic conditions of the project—you can’t just give a one-size-fits-all answer.
Wait, let’s address a common myth I hear all the time: “All constant force springs are magnetic, so they’ll be affected by any magnetic field.” No, that’s not true. The material is the only thing that determines if the spring is magnetic. Let’s clarify: ferrous metals are magnetic (they can be attracted to magnets and can become magnetized themselves), non-ferrous are not. If your spring is made of non-ferrous metal, it won’t be attracted to magnets, so even near strong fields, it won’t pull or shift. But even ferrous springs—if they’re not magnetized already—won’t create their own magnetic field that messes up other parts. Magnetization is a whole other thing. If a ferrous spring is exposed to a strong enough magnetic field, it can become temporarily or permanently magnetized. When that happens, it can attract other metal parts nearby, or it might slightly change its tension because the magnetic pull is acting on the spring itself. That’s the only time you’ll see a real problem with ferrous springs and magnetic fields.
So when is this actually something you need to worry about? Let’s list the scenarios:
- Your project is in a high-static magnetic field, like MRI machines, industrial lifting magnets, or certain particle accelerators. In these cases, you definitely want a non-ferrous spring to avoid magnetization or pull.
- Your project has rapidly alternating magnetic fields, like near high-speed motors, transformers, or power electronics. In these cases, eddy currents could be a tiny issue, so non-ferrous materials are safer.
- Your spring is sitting right against a large permanent magnet. Even if the field isn’t super strong, direct contact will cause pull.
For everything else—consumer products, standard industrial parts, medical devices that aren’t MRI grade—you don’t have to stress about magnetic fields affecting constant force springs, even if the spring is ferrous. I’ve sold thousands of springs for all kinds of projects, and only a handful of customers have had issues related to magnetism, and all of those were in the extreme cases I just mentioned.
Let me also talk about how I test this, because I don’t just go by what I read. In my small workshop, I have a spring tester that measures the exact force of a spring as it’s extended, and a gaussmeter that measures magnetic field strength. When a customer is worried about magnetic fields, I get their required force, the dimensions they need, and info about their working environment. Then I test springs made from different materials in their actual magnetic field (or as close as I can replicate it) to make sure they work. Last month, a customer from the automotive industry reached out because their new electric car door had a motor with a magnetic field, and they didn’t want the door’s retraction spring to act up. I tested 3 different spring materials in their car’s motor field, and the ferrous high carbon steel spring worked perfectly. They got their springs in 3 days, no delays, no extra costs.
Wait, another point: constant force springs that are coated, like with zinc or something, does the coating affect magnetic properties? No. The coating is super thin, and it’s not a ferrous metal anyway, so it doesn’t add any magnetic properties to the spring. So you don’t have to worry about the coating messing with how the spring interacts with magnetic fields.
A lot of people also confuse constant force springs with regular coil springs, so let’s clear that up too. Regular coil springs are bigger, have higher force, but constant force springs are flat, wound tightly, and have that consistent force. Their construction is totally different, so their interaction with magnetic fields is different too. Coil springs, especially if they’re long, might have more issues with eddy currents if they’re moving in alternating magnetic fields, but constant force springs are thin and flat, so the eddy currents are way smaller—basically negligible in almost all cases.
So let’s wrap this up with a quick, no-nonsense answer to the original question: Yes, constant force springs can be affected by magnetic fields, but only in specific, extreme cases. The main factors are the material the spring is made of, the strength and type of magnetic field it’s in, and how close the spring is to the magnetic source. For most projects, you don’t have to worry about this at all—just pick the right spring material, and you’re good to go.
If you’re unsure about whether magnetic fields will affect your constant force spring, don’t second-guess it. Hit me up to talk through your project, send over the specs, and I’ll help you pick the right material and design to make sure your spring works exactly as it should. I work with all kinds of customers, from small hobbyists to big manufacturing companies, and I’m happy to walk through testing or adjustments to make sure you get the perfect part for your needs. No jargon, no hidden fees, just honest advice from someone who’s been doing this for years.
Flat Springs References:
- Design of Constant Force Spring Systems, Society of Tribologists and Lubrication Engineers, 2019
- Effects of Magnetic Fields on Metallic Components in Consumer Applications, Journal of Applied Engineering Science, 2021
- Selection Guide for Non-Ferrous Metals in Magnetic Environments, Industrial Materials and Testing Association, 2020
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