Adhesion Matters - Adhesives for Trains

Episode Date: August 4, 2025

All aboard!  During this episode, we explain how adhesives and sealants have undergone a dramatic transformation from minor components to indispensable, strategic elements in modern rail car construction. This shift has been driven by the need for lighter, stronger, quieter, and more efficient vehicles, moving away from traditional mechanical fastening methods like rivets, bolts, and welds. The amount of adhesive used in an average rail car has skyrocketed 50-fold, from ~10 kg in the 1980s to up to 500 kg today, demonstrating their profound integration. These advanced bonding solutions offer significant advantages, including improved structural integrity, enhanced safety, weight reduction, noise and vibration damping, corrosion prevention, and greater design flexibility.  Future trends indicate a move towards more sustainable, eco-friendly, and "smart" adhesive technologies, although challenges remain in multi-material bonding and the recyclability of bonded components at their end-of-life.

You're stepping on to a sleek modern train, maybe a high-speed bullet train zipping through the countryside, or perhaps a massive freight car hauling tons of goods. What do you imagine is holding it all together? You know, heavy-duty rivets, strong welds. Well, today, we're taking a deep dive into the truly unsung hero of modern rail, adhesives and sealants. And believe me, it's not just about a bit of sticky stuff. It's about a revolutionary shift in how trains are designed and actually built.

That's absolutely right. Our sources today are quite a fascinating mix. We've got historical accounts, in-depth industry analyses, and technical reports of some of the leading chemical companies. So quite a range, then. Definitely. And we're going to uncover what we used to just call glue as utterly transformed rail car construction. We're talking about making trains lighter, stronger, quieter, and incredibly safe. Okay.

Our mission here really is to show you just how indispensable these advanced bonds. solutions have become and what a critical role they play okay let's unpack this then prepare to be surprised I think by the sheer ingenuity behind something is seemingly simple as a bond so when we think of early trains our minds probably go straight to massive steel structures right joined by countless rivets yeah and for the most part that image is pretty accurate but you're saying even way back 19th early 20th centuries adhesems had a role a small one one maybe. Exactly. A small but a significant role. Primarily, they relied on traditional animal

glues. Animal glues. Yeah, but these had severe limitations. They were really only suitable for interior applications, you know, bonding things like wood or canvas components. Because they couldn't chindle the elements. Precisely. They would simply soften or dissolve, exposed to heat or moisture. But what's fascinating here is that window glazing was an early exception. Windows. How so? Well, old steam-era rail cars actually use these putty-like sealants. to bed the glass into frames. So window ceiling was genuinely one of the very first adhesive applications

in rail cars. Huh. So these early glues were pretty fragile then. What was the turning point? What allowed adhesives to move beyond just like interior decoration? Well, a major breakthrough arrived in 1911. There was a report of a waterproof glue.

Okay, waterproof. That sounds promising. A synthetic marvel. Not quite, actually. It was still an animal glue, but mixed with formaldehy. Formaldehyde. Interesting. Yeah. And crucially, it could be applied cold and, most importantly, it could withstand wet conditions. Ah, that's the key. That innovation meant adhesives could finally be considered for exterior parts or parts exposed to the weather.

It really paved the way for much broader adoption in train manufacturing later on. A subtle shift, but it opened up enormous possibilities. Right. So fast forward to today, and we're obviously not talking about a few pounds of animal glue anymore. Not even close. And this is where the story gets, well, really compelling. The amount of adhesive in modern rail cars has absolutely skyrocketed. Just how dramatic is this increase we're talking about. It's quite remarkable, really.

An average rail car built back in the 1980s contained only about 22 pounds, maybe 10 kilograms, of adhesive. Okay, 22 pounds. In stark contrast, some state-of-the-art rail cars today use up to 1,100 pounds. That's 500 kilograms of adhesives in the... their construction. 500 kilos? That's a 50-fold increase. A 50-fold increase in just a few decades. And this isn't just, you know, a simple material substitution. This represents adhesives replacing hundreds, maybe even thousands of rivets, bolts, and welds. That's an astonishing leap. So why? What makes adhesive so much more appealing than those

traditional mechanical fasteners? What's justifying this massive shift? Well, it comes down to a really compelling array of benefits. They fundamentally reshape how trains are designed. and how they perform. Okay, like what? First off, light weighting and energy efficiency. Adhesives let manufacturers use lighter materials like composites. Ah, composites instead of just steel? Exactly.

And that directly translates to significant weight reduction. For instance, there are European regional trains, the AD trans ones, that use large fiberglass sandwich panels. These are bonded with polyurethane adhesive instead of being welded. And the result? A lighter, stiffer car body. For you, the passenger, this means better fuel efficiency. for diesel trains, better energy efficiency for electric ones, which, you know, reduces operational costs, and importantly, CO2 emissions. Makes sense. Less weight, less energy needed. What else?

Then there's noise, vibration, and harshness reduction in NVH. Right, making the ride smoother. Much smoother. NVH isn't just some technical term. It's really what differentiates a relaxing journey from a jarring, tiring one. Traditional fasteners, like rivets and bolts, they transmit every bump. Turning the train into a big drum, basically. Pretty much, yeah. But flexible industrial adhesives, like those from the leading brands, they act like tiny shock absorbers. They absorb vibrations, minimize acoustic intrusion.

It just creates a much quieter, more comfortable environment inside. I can appreciate that. What about strength? Are they really as strong as welds or rivets? That's a great question. It's about enhanced structural integrity and durability. See, instead of concentrating stress at individual points like a rivet does, Adhesives provide a continuous bond line.

Spreading the load out. Exactly. Distributing stress evenly across the entire joint area. This leads to significantly enhanced overall structural strength and longevity. Think of it this way. An adhesive sealant might replace dozens of rivets when securing a floor panel to the chassis. Okay. It spreads the load uniformly across the whole surface, not just at those specific points.

It makes the entire structure much more robust. Interesting. What else is driving this? Well, there's aesthetics and design flexibility. Adhesives create clean, weld-free joints. That dramatically improves the visual appearance, both outside and inside the train. Sleaker look. Yeah.

And beyond just looks, they make it easier to bond to similar materials like metal to composite or metal to plastic, things that are difficult or impossible to weld. Opening up design possibilities. Totally. It gives engineers entirely new options. And then there's cost-effectiveness. Really? I'd assume high-tech glues are expensive.

The materials themselves are specialized, yes, but adhesives can lead to substantial savings in labor and overall materials. You reduce the need for specialized welders or riveters, and assembly processes often get simpler, which speeds up production. Okay, that makes sense from a manufacturing perspective. And there's corrosion, prevention, and sealing. Adhesives and sealants provide excellent protection against moisture getting in and against corrosion. That's crucial for parts constantly exposed to harsh weather. They create a continuous impenetrable seal. Preventing water getting under the floor, for example.

Exactly. Stopping that kind of hidden corrosion you might find in older designs. And finally, these materials are engineered for harsh conditions. Right. They're not just craft glue. Definitely not. They're specially formulated to endure constant vibration, shock, extreme weather-think freezing minus 40 Celsius up to scorching plus 80 Celsius. Plus, they often provide critical electrical insulation in sensitive areas

adding another layer of safety. Wow, okay. So it's a whole package of benefits driving this. Oh, yes. So it's clear these adhesives are everywhere now, but some of their applications are genuinely unexpected. You might not even realize where this glue is doing the heavy lifting. What are some of the most surprising places we find them?

Oh, absolutely. And thinking about the bigger picture, adhesives contribute in ways that fundamentally change how the train performs, often invisibly. Like where? Well, take glued train windows. In modern high-speed trains, the windshields and the side windows are often glued directly to the body structure. It's a technique called direct glazing.

Just glued in, no frame? Essentially, yes. And it's not just for looks, though it does look cleaner. It actually means the window itself becomes a structural part of the train body. Wow. Strong enough to withstand incredible pressure pulses, like when entering tunnels at 300 kilometers per hour. Plus, it drastically improves aerodynamics and cuts down wind noise inside. Okay, that's impressive. What about inside the train?

Yeah, seats and interiors. It's not just the exterior. Lots of interior elements are held by adhesives. Flooring and passenger coaches, for instance, is frequently glued down. Why glue the floor? For a seamless finish, mainly. And to eliminate any loose screwheads that could become trip hazards over time, even seat components. The seats themselves. Yep. From the foam cushions bonded to the frames to the fabric or leather covers, often attached with high-strength glue, instead of visible bolts or staples. advantages cleaner look definitely a quieter ride because there are fewer things to rattle

and importantly enhance safety by removing hard metal fasteners from passenger areas where you might bump into them huh i never thought about glued seats what else is quirky well here's a slightly quirky one attaching auxiliary equipment on the roof like antennas and stuff exactly antennas GPS units cable housings using adhesive avoids drilling holes through the roof Ah, preventing leaks. Precisely. No holes means no potential water ingress. It simplifies installation and maintenance, too, and keeps the train absolutely watertight, even at high speeds and in rough weather.

Clever. Anything safety critical. Definitely. Think about brake pads bonded. Not riveted. This is a critical safety application. Breaks. They glue brake pads on.

They do now. In the past, brake shoes were riveted. Today, the friction material for train brakes is usually bonded with high temperature adhesives, like phenolic or epoxy types, to the steel backing plate. Is that better than riveting? It provides more uniform stress distribution across the pad. And you can utilize the entire pad surface for braking, not just the area around the rivets. So yes, it contributes significantly to railway safety and reliability.

Okay, that's a big one. Are freight cars using this tech too, or is it mostly passenger trains? Oh, no. Freight cars use adhesive too. Even those heavy freight rail cars, which you might think of as purely mechanical beasts, They benefit as well. Newer refrigerated cargo box cars, for instance. They use bonded composite insulation panels. For better insulation.

Exactly. Saves weight and improves thermal efficiency. It creates a continuous insulated shell without any bolt penetrations that could cause cold leaks. And specialized sealants are used to weatherproof seams and joints on things like hopper cars, protecting cargo like grain from rain and contamination. So it really is across the board from high-speed passenger trains to heavy freight. It is indeed. So these clearly aren't just variations of super glue we're talking about. It really sounds like there's a highly specific adhesive chemistry for every single

job, a real marvel of material science. You're absolutely right. The choice of adhesive is finely tuned to each specific application. It's like picking exactly the right specialized tool for a particular task. So what kind of chemistries are we talking about? When we talk about advanced chemistries, the rail industry relies on some pretty powerful compounds like metacrylate structural adhesives or MMAs. Think of MMA as the sort of speedy, versatile glue. Good for quick, strong bonds on large surfaces. They offer high strength, flexibility, and they cure rapidly at room temperature, which helps

manufacturing speed. Okay. What else? Then you have epoxy. They're kind of the heavy-duty, rock-solid choice. You use those for critical structural points that demand very high strength and extreme resistance to, you know, weather and chemicals. Right.

And then things like polyurethane-based adhesives or MS polymer sealants, they're valued more for their elasticity, their flexibility. So they're perfect for areas like sealing window glass or expansion joints where you need some movement, but also a continuous seal. A whole toolbox of glues. And who makes this stuff? Well, behind these innovations are several leading manufacturers. These are the real pioneers in the field. The companies like Dow, DuPont, Hankle, Huntsman, they're at the forefront. Big chemical names.

Exactly. They develop these specialized adhesive chemistries for pretty much every rail application imaginable. You'll find the products used for everything from sound damping and anti-slip flooring. We talked about noise reduction. Right. To crucial protection for electronics on board. And many of their formulations are specifically engineered to meet those really strict fire safety standards we'll probably talk about. Okay. They develop high performance, structural adhesives that actually replace mechanical fasteners, specialized solutions to reduce that noise and vibration, the NVH.

Henkels-Tarrison, you mentioned. Exactly. And advanced fiber-resistant composite resin systems, which are vital for lightweighing things like battery housings on electric trains. Their collective innovation is really what drives the capabilities of modern rail. So it's clearly not just about the chemical companies inventing these amazing glues, is it? There must be a whole support system. And you mentioned strict rules, ensuring these trains are fundamentally safe. How does that whole ecosystem work?

Yeah, it's a highly specialized market. You're right. And the pivotal role of technical distributors, it's absolutely critical here. Distributors, like wholesalers. They are far more than just logistics providers, actually. Think of companies like Bodo Miller-Chimi. They are specialist solution providers. They act as trusted partners for those major manufacturers we just mentioned, Dow, DuPont, Huntsman, Henkel.

They basically bridge the gap between. in the cutting-edge chemical development and the practical needs of the train manufacturers on the ground. So there are the experts making sure the right adhesive is used correctly for the right job. Precisely. They provide crucial technical advice, training for the assembly workers. They even conduct customer-specific application tests in their own labs. They have labs for this. Oh, yes. Like the one Bodo-Miller-Chimi has in Poland, which is certified to a key standard, D-I-N-6701-2. They ensure global reach, but with local presence and expertise.

Their commitment to quality and safety is underlined by certifications like ISO-9,00 and that industry-specific D-I-N-67012 for adhesive bonding in rail vehicle manufacturing. Okay, DIN 67012. That sounds important. It is. And that brings us to another paramount aspect, the criticality of fire safety standards, specifically EN-455-452. Ah, the fire standard. You mentioned it earlier. Yes. This European standard is mandatory. Absolutely mandatory for all materials and components. used in rail vehicles across Europe and widely influential elsewhere. It was introduced to unify standards and really raise the level of protection against on-board fire incidents. Okay. And how do these standards directly impact our safety as passengers?

You mentioned hazard levels. What do those actually mean for us sitting on the train? It's designed specifically for your safety. Railway vehicles get classified into three hazard levels, H.O.1, HL2, HL1, HL2, and three based on. based on their design and how they operate. For example, a key factor is how frequently and for how long they spend running through tunnels. Ah, because escape is harder in a tunnel fire. Exactly. So if you're on a long-distance high-speed train that frequently goes through lengthy tunnels, that vehicle in every single material in it from the seat fabric to the window adhesive,

the flooring everything must meet the highest standard, hazard level three. Got it. Highest risk, highest standard. Right. And materials are also categorized into 26 distinct product requirements, R1 to R26, depending on where they are used. R1 might be for interior wall surfaces, R26, for small electronic components. So adhesives have to meet specific R numbers, too.

Absolutely. Adhesives must undergo rigorous testing. They look at things like flame spread, smoke opacity, how much smoke it produces, and the toxicity of that smoke. They have to meet these very precise fire, smoke, and toxicity criteria for their specific application and hazard level. And this isn't optional. Not at all. Compliance isn't merely a suggestion. It's a strict prerequisite for selling trains or components in Europe.

And this pressure drives continuous innovation towards inherently safer materials. Okay, that's reassuring. So looking ahead then, what does all this mean for the future of rail transport? What are the next big leaps we might see in adhesive technology? And what challenges still need to be tackled? Yeah, the rail industry is definitely transforming rapidly. It's driven by innovation, the push for sustainability, and constant demands for enhanced performance. So what's next for the adhesives themselves?

In terms of technological advancements, we're seeing ongoing innovation in high-performance adhesives, things with even better durability, better multi-substrate adhesion, sticking different things together even more reliably. Especially with materials like those MMAs we talked about, for joining mixed materials like composites and metals. Any really futuristic stuff? While there's cutting-edge research into nanomaterials being incorporated into adhesives, bio-based polymers, trying to move away from purely petrochemical sources, and things like dual cure systems. Dual cure. Yeah, systems that might use UV light for a quick initial hold rapid fixturing, and then a secondary chemical cure for full strength.

That could enable even faster assembly lines. Interesting. What about sustainability? That seems key now. Absolutely. A significant trend is the push for sustainable and eco-friendly adhesives. We're seeing more bio-based formulations using natural materials, and an increased focus on using recycled content. content in the adhesives themselves. Like the trains themselves using recycled material. Exactly. Olsman's Metropolis Metro Trains, for example, already incorporate about 28% recycled materials

overall. The adhesives need to follow suit. There's also the rise of what you might call smart adhesives. Smart glue. Well, maybe not thinking glue, but multifunctional sealants. And also, specialized adhesive tapes are becoming huge, used for everything from masking during painting to managing cables, damping noise, even light. labeling, all contributing to more efficient, sometimes automated manufacturing.

Tate's are adhesives, too, of course. That's incredible progress. But, you know, every innovation often comes with its own set of challenges. What are the major hurdles engineers are grappling with now? You're right. There are significant hurdles. We mentioned multi-material bonding. It's still complex. Different materials expand and contract differently with temperature, have different surface properties. Getting a durable long-term bond is always an engineering challenge. Makes sense. But a major challenge, and this really touches on the larger implications of this technology, is the recyclability of bonded components.

Ah, the end-of-life problem. Exactly. While metals from trains are highly recyclable, it heases, especially when they're bonding different materials together in these complex assemblies, create a paradox. A paradox. How so? They enable incredibly sustainable design during the train's operational life through lightweeting better fuel efficiency. But they can really complicate recycling,

recycling at the end of life. Because you can't easily separate the materials. Precisely. Composites and varied plastics once they're bonded together are particularly difficult to separate and recycle efficiently. Often, this bonded material ends up as just shredder residue, which goes to landfill. So the very thing that makes them sustainable in use also makes them harder to recycle. That's a fascinating and really important paradox for the industry to solve. It is. It highlights the urgent need for what they call debondable adhesives or easily separable adhesive systems to support a true circular economy for trains.

Right, glues, you can unglue somehow when needed. That's the goal. And beyond that, we also continue to see challenges like fluctuations in raw material prices, which impacts production costs for these specialized chemicals. And there's always a continuous need for customized solutions because the requirements across different rail applications, high speed, metro, freight are just so specific. So constant innovation is still needed on multiple fronts. Absolutely. Well, as you can see, adhesives are clearly not just glue anymore, not by a long shot.

They are fundamental, high-tech components that are quietly enabling the rail systems of tomorrow, making them faster, safer, more efficient, in ways we rarely even consider when we step on board. Indeed. And as we continue to push for faster, lighter, greener trains, the question becomes, What unseen innovations in bonding technology will define the future of transport? And critically, how will we balance the incredible advantages these materials offer with that crucial challenge of managing their end of life responsibly? Definitely something to mull over next time you're on a train, isn't it?

Thanks so much for joining us for this deep dive.