What materials are used to make Bellow Type Load Cells? Bellow Type Load Cell
If you’ve ever had to spec or source load cells for packing lines, tank weighing, or even industrial process automation, you’ve probably run into bellow type ones. They’re kind of the unsung heroes of heavy-duty measurement—flexible, durable, and built to handle messy, high-wear environments that would eat through other load cell types fast. But here’s the thing: most people don’t stop to ask what exactly goes into building these workhorses. As someone who’s been supplying bellow type load cells for over a decade now, I’ve gotten this question from new engineers just starting out, and seasoned maintenance techs who’ve seen cheap knockouts fail way too many times. Let’s break it down straight, no stuffy jargon, and talk about why every material choice matters.
First off, let’s get on the same page about what a bellow type load cell is, quick. Unlike flat beam or s-beam cells that have simpler outer casings, the “bellow” is the star here—it’s that flexible, accordion-shaped cover that wraps around the core strain gauge assembly. That bellow does more than just look cool, right? It keeps out dust, moisture, food debris, chemical splashes, whatever your industrial space throws at it. So every part of the cell, from that outer bellow to the innermost strain gauges, is picked to hold up to that protection.
Let’s start with the big one that everyone asks about: the bellow itself. This is the first line of defense, so you can’t cheap out here. We use two main materials for bellows, and it all depends on the application. For standard industrial stuff—like packaging lines, general tank weighing, indoor or mild outdoor use—go-to is 300-series stainless steel, specifically 304 or 316. Wait, people mix these up all the time, so let’s set that straight. 304 is the workhorse, cheap enough, resists rust from most common moisture, and holds its shape really well. It’s perfect for places where the only “contamination” is a little water from a floor wash or dust floating around. But if you’re dealing with harsher stuff—food and beverage plants, chemical processing, marine environments—you step up to 316 stainless. That one has extra molybdenum in it, so it fights off acid splashes, saltwater, even harsh cleaning chemicals way better. I once had a customer who bought a cheaper load cell with a 304 bellow for their brewery’s keg filler; it rusted through in 6 months from beer and sanitizer fumes. Switched to 316, and they haven’t had an issue in 4 years. Trust me, that’s not something you want to cut corners on.
Wait, sometimes you’ll see bellow type load cells with other materials, like nylon or plastic? Those are super niche, only for low-load, indoor, totally clean applications, right? We hardly ever stock those because even a little moisture or a dropped tool can crack them. So if a supplier tries to sell you a bellow cell with a plastic bellow for heavy industrial use, run. That’s not built to last.
Next, the core structure inside the bellow—this is where the actual weight measurement happens, so material here is critical for accuracy, not just durability. The main body that holds the strain gauges? Again, stainless steel, but not the same as the bellow. We use 17-4 precipitation hardening stainless steel here, or sometimes called PH stainless. Why that? It’s crazy strong, but also super stable dimensionally. That means when you put weight on it, it bends just the right amount, and springs back exactly to its original shape—no permanent stretching, no drift over time. Think about it: a load cell’s accuracy only works if the core doesn’t change shape after 10,000 weigh cycles. 17-4 holds that. We also machine it to really tight tolerances—like a few thousandths of an inch—so that the strain gauges get consistent, repeatable signals every time. No wonky readings that make you throw out a whole batch of goods because the scale was off.
Now, the strain gauges themselves—those are the tiny, sensitive things that turn force into an electrical signal, right? You can’t see them, they’re glued to the core structure, but their material choice is make-or-break. Most strain gauges in industrial load cells are made from thin metal foil, usually constantan alloy. Constantan is perfect here because it has a stable electrical resistance that changes predictably when it’s stretched or compressed by weight. Some high-precision ones use even better alloys, like karma or platinum-tungsten, for super accurate measurements, but constantan is the standard for 90% of industrial bellow cells because it’s reliable and doesn’t break the bank. We only go for the higher-end gauges if a customer needs lab-level accuracy, like for pharmaceutical weighing.
Then there’s the adhesive that glues those strain gauges to the core. Another thing people sleep on! You can have the best gauge and best core, but if the glue fails, you get bad readings or a broken cell. We use cyanoacrylate (super glue, basically) for standard applications, but for harsher, high-temperature environments, we switch to epoxy or even polyimide adhesives. That glue has to be strong enough to hold the gauge tight through thousands of expansions and contractions, resistant to chemicals, and not change its properties with temperature shifts. If the glue gets soft from heat or contaminated with oil, the gauge will slip, and your readings start going haywire. I’ve seen a whole line stop production because a load cell’s gauge glue dissolved in hydraulic fluid—cost that customer way more than spending an extra $20 on the right adhesive up front.
Wait, what about the electrical connections? That’s another part inside the bellow. The wires that carry the signal from the strain gauges to the outside world—we use copper wires insulated with PVC or Teflon, depending on temperature. For cold environments, like freezers that go down to -40°F, PVC gets brittle, so we use Teflon insulation. For hot environments, like metal stamping plants where it’s up to 250°F, Teflon is also better because it doesn’t melt or break down. And to seal those connections tight, we use polyurethane or silicone sealants. Silicone is better for low temperatures, polyurethane for higher chemical resistance. The goal here is that no moisture or dust gets into the signal wires—if it does, you get static, dropouts, or total signal loss. We had one customer in a steel mill where the humidity was super high; they were using load cells with bad insulation, and the signal would cut out every time it rained. Switched to our Teflon-insulated wires and silicone seals, no more issues.
Let’s not forget about the optional add-ons that some bellow cells have, because those material choices matter too. Some have a hermetically sealed connector—those use glass-fiber seals instead of rubber, so they’re totally airtight for explosive environments or super harsh chemical plants. Others have a coating on the outside of the bellow, like epoxy or powder coat, for extra scratch resistance in places where forklifts or heavy equipment might bump them. That’s a good add for warehouse areas where damage is common, but again, only works if the base bellow is stainless steel.
Now, why does all this material stuff matter for you, the person buying or using these load cells? A lot of suppliers will cut corners here—they’ll use cheaper 200-series stainless steel for the bellow instead of 304, or regular steel for the core instead of 17-4, to save a few bucks. But what happens then? The bellow rusts through in a year, the core stretches and drifts, the strain gauges slip. You end up spending more on replacements, downtime, lost product, than if you’d just bought a good quality cell with the right materials in the first place. I see this all the time—customers come to us after buying 3 cheap load cells in 2 years, and one of our well-built cells lasts 5 years for the same price. That’s the ROI, right?
As a supplier, I get it—price is a big factor. But you can’t compromise on the materials that protect the core measurement parts. When we spec out a bellow type load cell for a customer, we first ask what environment it’s going in: is it food grade? Do they need it for high temperature? What’s the load range? Then we pick the exact stainless grade for the bellow, the core material, the strain gauge alloy, the adhesive, the wires, everything. No one-size-fits-all here. For example, a cell for a produce packing line in a mild climate gets 304 bellow, constantan gauges, PVC insulation. A cell for a marine cargo scale gets 316 bellow, karma gauges, Teflon insulation, glass seals. A cell for a paint mixing tank gets 316, epoxy adhesive, polyurethane seal. It all lines up.
I’ve had customers ask me if there’s a “better” material than stainless steel for bellow cells. Honestly? For 99% of industrial applications, no. Stainless is the sweet spot—strong, corrosion-resistant, workable, affordable. The only time you might use something else is super specific, like titanium for ultra-high-load cells in deep sea applications, but that’s super niche and way more expensive. For 90% of what people need, stainless is the way to go.
Another thing that’s not a material, but ties into material choice: how the parts are finished. For the bellow, it’s not just the grade of stainless, it’s how it’s welded and polished. A well-made bellow has TIG-welded seams, not spot-welded, so there’s no weak point where rust can start. The edges are rounded, not sharp, so they don’t catch on stuff or crack over time. For the core, it’s stress-relieved after machining, so it doesn’t warp as it’s used, which keeps the measurements accurate. That’s part of the material process too—working with the material properly so it performs as intended.
Let me wrap this up, because I know when you’re looking for load cells, you just want to know what to look for to make sure you’re getting something that works. The next time you’re shopping for bellow type load cells, don’t just ask the price. Ask: what stainless grade is the bellow made of? What’s the core material? What alloy are the strain gauges? What’s the insulation on the signal wires? If the supplier can’t answer that, or tries to give you vague answers like “stainless steel for all parts,” be wary. We always give that info upfront, because we stand by the materials we use—we don’t cut corners.
If you’re tired of load cells that fail too soon, give us a shout. We can help you spec the right bellow type load cell for your exact application, no guesswork, no cheap parts that will leave you high and dry. Just tell us what you’re weighing, the environment it’s in, and any accuracy or durability needs, and we’ll hook you up with something that lasts.
Sensor Accessories References:
- Load Cell Handbook: Design, Selection, and Application, 5th Edition, CRC Press
- Stainless Steel Materials Selection Guide for Industrial Components, American Iron and Steel Institute
- Strain Gauge Technology for Industrial Measurement Systems, Omega Engineering Technical Manual, 2021
- Bellow Type Load Cell Design and Corrosion Resistance Standards, International Organization for Standardization (ISO) 10360-6:2019
Huzhou Zhihe Technology Co., Ltd.
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