{"id":3497,"date":"2026-10-10T14:30:19","date_gmt":"2026-10-10T06:30:19","guid":{"rendered":"http:\/\/www.205northnine.com\/blog\/?p=3497"},"modified":"2026-10-10T14:30:19","modified_gmt":"2026-10-10T06:30:19","slug":"what-is-the-hardness-of-bonded-seals-417b-b2bff1","status":"publish","type":"post","link":"http:\/\/www.205northnine.com\/blog\/2026\/10\/10\/what-is-the-hardness-of-bonded-seals-417b-b2bff1\/","title":{"rendered":"What is the hardness of bonded seals?"},"content":{"rendered":"

Hey there, let\u2019s cut to the chase: if you\u2019ve ever worked with hydraulic or pneumatic systems, you\u2019ve probably heard of bonded seals. And if you\u2019re here, you\u2019re probably stuck on one question\u2014what even is \u201chardness\u201d when people talk about these little game-changing parts? As a bonded seal supplier who\u2019s been in this game for over a decade, I\u2019ve fielded this question more times than I can count, and the short answer is it\u2019s not just a random number on a spec sheet\u2014it\u2019s what makes or breaks whether that seal stops leaking mid-shift (or lasts 10 years without a hitch). Let\u2019s break this down like we\u2019re chatting over coffee, no stuffy engineering jargon that makes your eyes glaze over. Bonded Seal<\/a><\/p>\n

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First off, let\u2019s get one thing straight: bonded seals are different from regular O-rings. They\u2019re that hybrid part\u2014usually a metal core (think steel, sometimes stainless or brass) with a soft elastomer (rubber-like) layer molded or bonded right on top. That metal core is the skeleton, and the elastomer is the seal that squishes into place to block fluid or gas. So when people ask about hardness, they\u2019re almost always talking about that elastomer layer, not the metal core (unless we\u2019re being super specific, and we\u2019ll get to that later).<\/p>\n

Now, how do we measure this hardness? You\u2019ve probably heard of the Shore scale\u2014Shore A and Shore D, mostly. Let\u2019s keep it simple: Shore A is for soft, squishy stuff like rubber bands or pencil erasers, and Shore D is for harder materials, like hard plastic or skateboard wheels. Most bonded seals use Shore A, because they need that flexibility to conform to uneven surfaces (think rough machined flanges or bolt holes) and create a tight seal. For context, a Shore A hardness of 50 is like a new basketball, 70 is a good solid eraser, and 90 is pretty darn rigid\u2014like a thick hard hat shell.<\/p>\n

Wait, but why does this even matter for a bonded seal? Let\u2019s take a real-world example: if you\u2019ve got a hydraulic system on a construction site, or a machine at a factory that\u2019s running 24\/7. If your seal is too soft (say Shore A 40), it\u2019ll squish too much when you torque the bolts down. Sure, it seals at first, but over time, all that pressure will push it out of the groove, or it\u2019ll get damaged when you\u2019re tightening the bolts\u2014boom, leak before you even fire up the machine. On the flip side, if it\u2019s too hard (Shore A 90), it can\u2019t flex enough to fit into small gaps or conform to slightly uneven surfaces. You\u2019ll end up with gaps between the seal and the surface, which means fluid seeps out. No good.<\/p>\n

So what\u2019s the sweet spot for bonded seals? From my experience as a supplier, most of our standard bonded seals run between Shore A 60 and 80. Why that range? It\u2019s the balance zone. 60 is soft enough to conform to minor surface imperfections\u2014like a tiny scratch in a flange that\u2019s too small to fix with machining. 80 is hard enough to hold its shape during installation, so you don\u2019t have to baby it when tightening bolts, and it can handle higher pressure systems without deforming. We tweak it based on the application too, of course. If someone needs a seal for a high-pressure hydraulic press? We lean more towards 75-80 Shore A. If they need a seal for a low-pressure pneumatic line with tight, small parts? Maybe 65-70. It\u2019s all about matching the hardness to what the seal is actually going through.<\/p>\n

Wait a second, I mentioned the metal core earlier\u2014why does that factor into hardness? The metal itself isn\u2019t measured in Shore, but it does play a huge role in how the seal performs overall. For example, if you\u2019re working in a super corrosive environment (like food processing equipment or chemical plants), we use stainless steel cores, which are a bit harder than regular carbon steel, so they resist rust and hold their shape even when the elastomer is flexing. Carbon steel cores are cheaper, so we use those for general-purpose applications, and they\u2019re hard enough for most standard setups. The metal\u2019s hardness complements the elastomer\u2019s\u2014you don\u2019t want a floppy metal core holding up a soft elastomer, same as you don\u2019t want a rock-hard elastomer paired with a weak metal core that bends when you torque bolts.<\/p>\n

Let\u2019s talk about common myths I hear all the time. Myth #1: \u201cHarder is always better.\u201d Nope, I\u2019ve seen seals with Shore A 90 crack when the machine vibrates\u2014they\u2019re so rigid they can\u2019t absorb movement, so they split. Myth #2: \u201cAll hardness scales work the same.\u201d No way\u2014Shore A and Shore D aren\u2019t interchangeable. If a part is Shore D 50, that\u2019s way harder than Shore A 50, like 10x harder, basically. We have to double-check specs all the time, because customers mix those up more than you\u2019d think. Myth #3: \u201cHardness is the only thing that matters.\u201d Yeah, no\u2014material type (nitrile, EPDM, Viton) plays a role too. A Viton seal at Shore A 70 is way more heat-resistant than a nitrile one at the same hardness, so hardness isn\u2019t the end-all-be-all, but it\u2019s the foundation.<\/p>\n

So how do we pick the right hardness for a custom order? When a customer reaches out to me, the first questions I ask are: What\u2019s the system pressure? What\u2019s the temperature range it\u2019ll be exposed to? What\u2019s the surface finish of the flanges or grooves it\u2019s going into? And is there any vibration or movement involved? If they don\u2019t know the answers, I\u2019ll ask them to send over their spec sheet or even a sample of the part it\u2019s going into. For example, last month a customer called panicking because their bonded seals were leaking on a farm tractor hydraulic lift. They\u2019d been using Shore A 50 seals because they thought softer was better for fitting, but the high pressure (over 2000 PSI) was squishing them out. We swapped them for Shore A 75, and boom, no more leaks. Another customer doing food processing needed EPDM bonded seals for a conveyor system, and the FDA required a Shore A 65 to be flexible enough for food-grade cleaning solutions and tight gaps. That\u2019s the kind of back-and-forth we do every day as a supplier\u2014we don\u2019t just send a part, we make sure it works for their specific job.<\/p>\n

Wait, what about testing hardness? We do that in our shop with a Shore durometer\u2014super simple tool, like a little metal pin you press into the elastomer, and it gives you a number. We test every batch to make sure it\u2019s within \u00b12 Shore points of what we quote\u2014consistency is key, right? If one batch is 68 and another is 72, that\u2019s a 50% difference in softness, which would cause some of them to leak. We also test for how the hardness holds up over time\u2014like, will the elastomer harden from heat exposure? That\u2019s called \u201caging,\u201d and we account for that when we recommend hardness. If a seal is going to be exposed to 200\u00b0C (392\u00b0F) for years, we\u2019ll pick a slightly softer Shore A so it doesn\u2019t get too hard as it ages, because aged seals are more likely to crack.<\/p>\n

Let\u2019s wrap this up with why this matters for you, the person buying these seals. If you\u2019re a maintenance tech on a factory floor, or a engineer designing a new machine, or even a hobbyist fixing your old tractor\u2014getting the hardness right means less downtime, less money wasted on replacement seals, and less headaches. As a bonded seal supplier, our job isn\u2019t just to sell you a part that has a Shore number on it. It\u2019s to make sure that number is the right one for your application, so your machine runs smooth, no leaks, no stress.<\/p>\n

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If you\u2019re dealing with a project right now and you\u2019re not sure what hardness you need, hit us up. We\u2019ll walk you through the questions, get you the right part, no confusing sales jargon, no hidden fees. We\u2019ve got standard seals in stock for most common uses, and we can do custom ones if you have a weird, specific application. Don\u2019t waste time guessing\u2014reach out, let\u2019s make sure your bonded seals are hard in all the right ways.<\/p>\n

Rubber X Ring<\/a> References:<\/p>\n

    \n
  1. Shaw, M. C., & Rips, I. F. (1995). Seal Design Handbook. Marcel Dekker.<\/li>\n
  2. ASME B1.20.1-2013, Pipe Threads, General Purpose (Inch). American Society of Mechanical Engineers.<\/li>\n
  3. Rubber & Plastics News. (2021). Understanding Durometer Hardness Testing for Elastomers. KWI Media.<\/li>\n
  4. Hydraulic Seal Technology Association. (2020). Bonded Seals: Selection, Installation, and Maintenance Guidelines. HSTA Publications.<\/li>\n<\/ol>\n
    \n

    DEDE SEAL Co., Ltd.<\/a>
    DEDE Seal Co., Ltd. is one of the most experienced bonded seal manufacturers and suppliers in China for over 35 years, featured by quality products and good price. Please feel free to buy bulk customized bonded seal made in China here from our factory. Welcome to contact us for pricelist.
    Address: Hunan Road, Pudong New Area, Shanghai, China
    E-mail: info@dedeseal.com
    WebSite:     https:\/\/www.dedesealing.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

    Hey there, let\u2019s cut to the chase: if you\u2019ve ever worked with hydraulic or pneumatic systems, … What is the hardness of bonded seals?<\/span>Read more<\/a><\/p>\n","protected":false},"author":5,"featured_media":3497,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3460],"class_list":["post-3497","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-bonded-seal-4c5c-b2fe6c"],"_links":{"self":[{"href":"http:\/\/www.205northnine.com\/blog\/wp-json\/wp\/v2\/posts\/3497","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.205northnine.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.205northnine.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.205northnine.com\/blog\/wp-json\/wp\/v2\/users\/5"}],"replies":[{"embeddable":true,"href":"http:\/\/www.205northnine.com\/blog\/wp-json\/wp\/v2\/comments?post=3497"}],"version-history":[{"count":0,"href":"http:\/\/www.205northnine.com\/blog\/wp-json\/wp\/v2\/posts\/3497\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.205northnine.com\/blog\/wp-json\/wp\/v2\/posts\/3497"}],"wp:attachment":[{"href":"http:\/\/www.205northnine.com\/blog\/wp-json\/wp\/v2\/media?parent=3497"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.205northnine.com\/blog\/wp-json\/wp\/v2\/categories?post=3497"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.205northnine.com\/blog\/wp-json\/wp\/v2\/tags?post=3497"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}