{"id":551,"date":"2026-10-09T15:31:15","date_gmt":"2026-10-09T07:31:15","guid":{"rendered":"http:\/\/www.kenzomexicocity.com\/blog\/?p=551"},"modified":"2026-10-09T15:31:15","modified_gmt":"2026-10-09T07:31:15","slug":"what-is-the-tear-strength-of-vacuum-cast-parts-4d8e-3ddc9c","status":"publish","type":"post","link":"http:\/\/www.kenzomexicocity.com\/blog\/2026\/10\/09\/what-is-the-tear-strength-of-vacuum-cast-parts-4d8e-3ddc9c\/","title":{"rendered":"What is the tear strength of vacuum – cast parts?"},"content":{"rendered":"

Hey everyone, if you\u2019ve ever worked with rapid prototyping or small-batch manufacturing, you\u2019ve probably heard of vacuum casting\u2014right? As a vacuum casting supplier, I get asked this question all the time: \u201cWhat\u2019s the tear strength of vacuum-cast parts?\u201d It\u2019s not a one-word answer, I\u2019ll tell you that, and the confusion makes sense because tear strength is one of those specs that doesn\u2019t translate across every material or part design. Let\u2019s break this down like we\u2019re chatting in the shop, no boring jargon dumps (promise). Vacuum Casting<\/a><\/p>\n

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First, let\u2019s keep it real: vacuum casting isn\u2019t injection molding\u2014they\u2019re two totally different processes, so the tear strength numbers won\u2019t match up. Wait, what\u2019s tear strength, anyway? Simply put, it\u2019s how much force a material can take before it rips, right? Think of it like trying to pull a piece of tape apart\u2014thicker tape takes more force, same idea with parts, but way more precise. Tear strength is measured in units like kN\/m (kilonewtons per meter) or pli (pounds per linear inch), and it\u2019s super dependent on what material we cast, the part\u2019s wall thickness, and even how we process the silicone mold or pull the vacuum.<\/p>\n

Let\u2019s start with the materials, because that\u2019s the big variable here. Most vacuum-cast parts are made from polyurethane (PU) resins, and we stock everything from rigid, acrylic-like PUs to flexible, rubbery ones. For the rigid stuff\u2014like if you\u2019re making a prototype phone case or a plastic gear\u2014tear strength usually lands around 2 to 5 kN\/m. Wait, that\u2019s for rigid? Yeah, they\u2019re stiffer, so they don\u2019t tear as easily in a side-to-side rip, but they\u2019re more prone to snapping if you bend \u2019em too much. Then the flexible PUs, like the ones used for phone grips, seals, or gaskets\u2014those have way higher tear strength, typically 10 to 20 kN\/m. I\u2019ve seen some soft, medical-grade PUs hit 25 kN\/m too, but those are specialized.<\/p>\n

But here\u2019s the thing: numbers don\u2019t mean jack if you don\u2019t know the part\u2019s design. A thin, 1mm wall will have lower tear strength than a 5mm wall of the same resin\u2014simple physics, more material to pull apart. Also, if a part has sharp corners or undercuts with tight radii, that\u2019s a weak spot. Vacuum casting has a trickier time with tight radii than injection molding, right? Because the silicone mold can only stretch so far, so we have to adjust our mold making to smooth those edges a little. If we skip that, sharp corners act like a starting point for a tear, so even a high-strength resin will fail at a lower force.<\/p>\n

Now, let\u2019s talk about how we process the resin, since that\u2019s where my job as a supplier matters. When we do vacuum casting, we pull a hard vacuum to eliminate bubbles, but if we pull it too hard or for too long, the resin can get denser or start to degrade? Wait, no\u2014actually, bubbles are the bigger enemy here. A tiny air pocket in a cast part is a tear waiting to happen. I\u2019ve had a customer come back with a part that ripped way too easy, and it turned out we had a micro-bubble in a critical load point. We adjusted our vacuum time and resin mixing speed, and fixed that problem no sweat. Also, the temperature of the mold when we cast\u2014too cold, and the resin cures unevenly, leading to weak spots; too hot, and it might cross-link wrong, killing tear strength.<\/p>\n

Wait, let\u2019s compare this to what people might be used to. If you need a part with the tear strength of an injection-molded ABS, which is around 3 kN\/m, we can get super close with a rigid PU. If you need something like a flexible EPDM seal (which is 15-20 kN\/m), we can match that too with our flexible PUs. The biggest difference is that vacuum casting is for low volumes\u2014usually 1 to 100 parts\u2014so we can use custom blends that injection molding can\u2019t be bothered with, tailored to exactly what the customer needs.<\/p>\n

A common mistake I see customers make is picking a resin based on ultimate tensile strength alone. Tensile is how much it pulls before stretching and breaking, but tear strength is about how it responds to a focused rip force\u2014totally different. For example, a soft, stretchy PU might have a high tensile strength, but a low tear strength because it\u2019s so squishy that a small nick will tear right through it. So we always ask customers two things: what\u2019s the part\u2019s function, and what\u2019s the worst case it will encounter? If it\u2019s a bracket that gets pulled sideways, we focus on tear strength; if it\u2019s a clip that snaps open and shut, maybe tensile is more important.<\/p>\n

Let\u2019s throw in a quick example from last month. A customer making a prototype for a vacuum cleaner hose needed a part that could bend repeatedly without tearing. They first picked a rigid PU, but when we tested it, it ripped at 3 kN\/m\u2014way too low. We swapped to our medium-flex PU, which hit 14 kN\/m, and adjusted the part\u2019s wall thickness from 2mm to 3mm to add more material at the bend points. End result? They tested 1,000 bends, no tears at all. That\u2019s the value of working with a supplier who knows how to tweak both material and design for tear strength, not just pull off a cast.<\/p>\n

Now, what about edge cases? If you\u2019re making a part for medical devices, we have medical-grade PUs with tear strength up to 22 kN\/m that meet ISO standards. For automotive prototypes, we can get heat-resistant PUs that hold 8 kN\/m at 80\u00b0C, which is perfect for under-hood parts that don\u2019t see full production yet. And if you need something super flexible\u2014like a silicone-like part? Wait, some people use silicone resins in vacuum casting too, right? Those have even higher tear strength, around 15 to 30 kN\/m, but they\u2019re more expensive and less rigid, so we only go that route if the customer needs that rubbery, stretchy feel.<\/p>\n

Wait, let\u2019s address the elephant in the room: why is there no universal number? Because every job is different. A vacuum-cast part for a toy won\u2019t need the same tear strength as a part for a aerospace prototype, and that\u2019s where my job comes in. I don\u2019t just say \u201ctear strength is X\u201d and send the parts\u2014I work with customers to match the right resin, adjust the design to reduce stress points, and test samples before we do a full run. No point in delivering parts that fail when they get to testing, right?<\/p>\n

A quick note on testing, too. We don\u2019t guess at tear strength\u2014we use the standard ASTM D624 test, same as most manufacturing. That means we cut a standard shape from the cast part, pull it at a constant speed, and measure the force needed to tear it. So when a customer asks for \u201ctear strength of at least 10 kN\/m,\u201d we can test a sample and show them the number, no guesswork. That\u2019s way better than old-school methods of \u201chow hard did I pull it with pliers.\u201d<\/p>\n

Let\u2019s wrap this up so it\u2019s not a novel. The short answer to \u201cwhat\u2019s the tear strength of vacuum-cast parts?\u201d is: it depends on the PU resin, wall thickness, part design, and our processing. For rigid parts, 2-5 kN\/m; flexible parts, 10-20 kN\/m (sometimes higher for specialized resins). But the real takeaway is that as a vacuum casting supplier, we don\u2019t just cast parts\u2014we help you get the tear strength you need for your specific use case. Whether you\u2019re prototyping a new consumer good, a medical device, or an automotive part, we can tweak every variable to make sure your parts don\u2019t tear when you need them to hold.<\/p>\n

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If you\u2019re working on a project and aren\u2019t sure which resin or design will give you the right tear strength, hit us up to chat through it. No pushy sales talk, just real talk about what works for your prototype or low-volume run. We can send sample tear test data, adjust mold designs, and even do small test casts to make sure everything lines up before you commit to a full order. That\u2019s what we do, y\u2019know? Make vacuum casting work for your exact needs, not just a generic spec sheet.<\/p>\n

Molding Services<\/a> References
\nASTM D624, Standard Test Method for Tear Strength of Rubber and Thermoplastic Elastomers
\nPolurethane Materials for Rapid Prototyping, Society of Manufacturing Engineers, 2021
\nVacuum Casting Process Fundamentals, Rapid Prototyping Association, 2022<\/p>\n

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Dongguan Xinchuan Precision Manufacturing Co., Ltd.<\/a>
As one of the most professional vacuum casting manufacturers and suppliers in China, we offer a quick lead time for customized orders. Please feel free to buy precision vacuum casting made in China here from our factory. Contact us for quotation.
Address: #16 Gangjian Road, Changping Town, Dongguan City, Guangdong, China. 523000
E-mail: FreeQuote@xcprecision.com
WebSite: https:\/\/www.xcprecisions.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

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