Industrial Web Search Buyer's Guide Sector
Elastomer parts and the seals built from them: O-rings, gaskets, lip seals, molded and extruded rubber components, rubber-to-metal bonded parts, and the non-elastomer sealing components that extend the family. This sector covers the molders, extruders, converters, and seal manufacturers who make them, the compound and specification system the industry runs on, and the compliance regimes that attach to rubber in food, water, and medical service.
Overview
A working orientation to the sector before you request quotes: how the products divide, what actually governs performance, and the kinds of companies you will end up talking to.
The first fork is the duty, because sealing divides before products do. Static sealing, surfaces that do not move against each other, is the world of O-rings in glands, die-cut and molded gaskets, and extruded profiles. Dynamic sealing, surfaces that rotate or reciprocate, is the world of lip seals on shafts, O-rings under different rules, and, past rubber's limits, spring-energized seals in tougher materials. Around the seals sits the broader rubber component family: molded parts from bumpers to diaphragms, extruded profiles, rubber-to-metal-bonded mounts and rollers, and liquid silicone rubber parts at the boundary with custom molding. Mechanical seals for pumps are engineered devices covered by the pump sector, and hose and fittings under fluid handling; this page covers the elastomer components and the seals built from them.
What governs performance is the compound, and the compound is chosen by chemistry first. The media and temperature eliminate elastomer families before anything else selects among them, which is why the fluid list, including the cleaning chemicals nobody writes down, is the most consequential line of an RFQ. Within the surviving families, parts perform as their specific compound, not their polymer name, and the sector's specification system exists for exactly this: a line callout under the standard classification specifies performance that any molder can quote and any lab can verify, whereas a polymer name and a color specify nothing. The rest of the outcome is geometry and time: glands designed to the size standards' tables rather than measured from worn seals, tolerances cited from the rubber industry's own classes rather than imported from machined parts, and shelf life managed from the cure date, because vulcanization starts a clock that storage conditions speed or slow.
Five kinds of companies supply this sector. Custom rubber molders compress, transfer, and injection mold parts to your drawing and are the center of the custom market, with in-house or through compounders compound development. Seal manufacturers and their distributors supply the standard product world with O-rings, lip seals, and engineered sealing lines, with deep stock in standard sizes. Gasket fabricators and converters die-cut sheet goods into flat parts quickly and without tooling, and they overlap the converting trade that serves the adhesives sector. Extruders run profiles continuously and handle the splicing and joining that turn them into finished loops. Compounders formulate and supply the materials themselves, and their datasheets and compliance documentation stand behind everyone else's parts. It also tells you what to search for: a custom-molded part means molders; a standard seal by size means manufacturers and distributors; a flat gasket tomorrow means converters; a long profile means extruders; and a material question means the compounder's technical service. The distinction determines who owns the compound, who holds the compliance paperwork, and how quickly your part can be made.
Sourcing Considerations
The decisions below are the ones that most often cause regret later. The first two, defining the duty and specifying the compound, determine everything after them, including the answers to the other four. The detail sits in the guides at the bottom of this page.
State whether the seal lives between stationary surfaces or rides on moving ones, list every fluid it touches, including cleaning and sanitizing chemicals, and provide the actual temperature range and pressure. Chemistry eliminates elastomer families before anything else is selected among them, and the media list is the most consequential line in the RFQ. A perfect part in the wrong family fails on schedule.
Write the material as a line callout under the standard classification, with the suffixes your duty needs, compression set at temperature above all, or name an approved compound and record the callout it meets. A callout specifies performance any molder can quote, and a lab can verify; a polymer name and a hardness describe thousands of materials and enforce none. Require approval for compound substitutions, because sister compounds differ invisibly.
Dimension O-ring glands from the size standards and the published squeeze guidance for the duty, decide clearance, surface finish, and backup rings from the operating pressure, and cite dimensional tolerances from the rubber industry's own published classes rather than importing machined-part tolerances, because cured rubber moves and flexes. Seal failures blamed on the rubber are usually gland problems, and unquotable rubber drawings are usually tolerance problems.
Flat parts at speed favor die-cutting with no tooling; shaped parts require molds, with compression, transfer, and injection molding trading tooling cost against cycle speed as volumes rise; long perimeters favor extrusion, with the joint method specified; silicone at high volume favors the dedicated process for liquid silicone rubber. Show suppliers the assembly, not just the part, and let the geometry and the program quantity choose the route.
Food, hygiene, potable water, and medical requirements each attach to the complete compound, including the cure system, and each is a separate hurdle a compound must clear individually. Name every applicable regime in the RFQ, obtain the documentation for the exact compound quoted, including its post-cure status where the regime requires one, and reconfirm on any compound change. Certified and uncertified compounds sit side by side in every supplier's line, and the part cannot tell you which it is.
Specify the remaining shelf life at delivery under the elastomer storage standard, record cure dates, store seals in cool, dark, and unstressed conditions, rotate stock, and maintain lot traceability in the compliance file. Shelf life varies enormously by family, and the critical spare aging in a hot drawer is the classic failure. An undated elastomer part in stores is a question, not an asset, and the paperwork is part of the product.
Glossary
The terms you will meet on a compound datasheet, a seal drawing, or a molder's quote, in plain English.
A hard ring, usually PTFE, installed beside an O-ring on the low-pressure side to prevent the seal extruding into the clearance gap at high pressure. Backup rings extend an O-ring's pressure range without changing the seal itself, and whether a gland needs one is a function of pressure, clearance, and hardness that gland design guidance answers.
The complete formulated material a part is made from consists of the base elastomer plus fillers, plasticizers, cure system, and additives, all developed and owned by a compounder or molder. Parts perform as their compound, not their polymer family, so the compound identity, or the line callout it must meet, is what a specification controls and a substitution changes.
An elastomer's failure to spring back after prolonged compression, measured by the standard test as the percentage of deflection that is not recovered. It is the property that most often ends a seal's life, because a seal that has taken a set no longer pushes against its surfaces. Low compression set at your temperature is worth specifying explicitly for any long-term static seal.
The three ways rubber parts are molded: compression molding presses a preform into a heated mold, the cheapest in tooling and the slowest in cycle time; transfer molding pushes material from a pot into closed cavities, improving consistency; injection molding shoots heated compound into the mold, the fastest at volume with the costliest tooling. Geometry, volume, and tolerance move parts between them.
Rubber goods carry the quarter and year of their vulcanization, and their storage life runs from that date under the aerospace shelf-life standard's recommendations, which vary widely by elastomer family. The clock starts at cure, not receipt, so purchasing controls specify remaining life at delivery, storage conditions, and rotation, especially for seals kept as spares.
The chemistry that crosslinks the elastomer, most commonly sulfur or peroxide systems, each producing different heat resistance, compression set, and compliance status from the same base polymer. Buyers meet it because food, potable, and medical work often requires specific cure systems, and because two compounds of the same polymer and hardness can age very differently.
Removing the thin flash left at mold parting lines from cured rubber parts, by hand, tumbling, or cryogenic processes that freeze the rubber brittle. The specification should state where flash is unacceptable and what the maximum remains elsewhere, because deflashing is a real cost. A mold in good condition is the cheaper way to reduce flash.
The standardized tolerance tables for molded and extruded rubber, published in the rubber industry association's engineering handbooks, grade achievable tolerances by dimension size and by class, from high-precision to commercial. Rubber moves with cure shrinkage and flex, so citing a class from the tables, rather than importing machined-part tolerances, makes a drawing moldable and quotable.
The hardness of an elastomer, measured by the standard indentation test and reported most often on the Shore A scale, with a customary tolerance of several points. Hardness stands in for stiffness in seal and part design, but it says nothing about chemical resistance or aging, so it is one line of a specification, never the whole of one.
The standardized letter codes for elastomer families under the rubber nomenclature standard include NBR for nitrile, EPDM for ethylene-propylene, FKM for fluorocarbon, and VMQ for silicone. The codes are the sector's shorthand for chemistry, and knowing that each names a family, within which compounds vary widely, keeps the shorthand from being mistaken for a specification.
Blistering and fracture of an elastomer seal when high-pressure gas that has dissolved into the rubber expands during rapid depressurization. It is a known hazard in gas service; resistant compounds exist and are qualified by test, and a buyer sealing high-pressure gas should say so, because the failure destroys seals that were perfect for the liquid version of the duty.
Rubber shapes produced continuously through a die, from cord and tubing to complex door and enclosure seals, cured in line and cut or joined to length. Corners and closed loops are made by splicing or molding joints, whose strength and appearance differ, so how a profile becomes a finished loop belongs in the specification alongside the cross section.
How an elastomer behaves in the media it contacts, as judged by swelling, shrinkage, hardening, and property loss in standard immersion tests. Compatibility concerns the compound and the specific fluid at the operating temperature, including cleaning chemicals the drawing forgets, and it is the first question in elastomer selection because the wrong chemistry fails regardless of the part's quality.
A static seal cut, molded, or dispensed to sit between two flanged surfaces, sealed by bolt load compressing it. Gasket behavior depends on flange flatness, bolt load, and material, and the choice among die-cut sheet, molded rubber, and other gasket types follows the geometry, the media, and the available compression, not habit.
The gland is the groove an O-ring or seal lives in; squeeze is the percentage the seal is compressed when installed. Standard design guidance defines gland dimensions and squeeze ranges for static and dynamic service, and O-ring failures blamed on the rubber are usually gland problems: improper squeeze, excessive clearance, or a finish that abrades the seal.
The compact material specification is built on the standard rubber classification system, encoding elastomer type and class, hardness, tensile strength, and suffix requirements in a single line. A line callout specifies performance rather than a supplier's compound, allowing multiple molders to quote the same material honestly, and it is the professional alternative to specifying a color and a polymer name.
A rotary shaft seal in which a flexible elastomer lip, usually spring-loaded, rides on a rotating shaft to keep lubricant in and contamination out. It is specified by shaft and bore size, lip material and design, and the shaft's surface finish and hardness, which the seal depends on. It is a catalog product family with custom versions at the edges.
A two-part silicone injection molded on dedicated equipment, curing rapidly with heat, suited to high-volume, high-precision silicone parts and to the food, medical, and infant applications where silicone's compliance record leads. It sits at the boundary of this sector and custom molding: the part is a seal or elastomer component, and the process is injection molding with its own tooling economics.
The circular-cross-section elastomer ring that is the default seal of general industry, sized in the inch-based standard's dash numbers and the international standard's metric series. The size standards cover dimensions and tolerances only, so a dash number plus a material specification, never the dash number alone, is what defines an O-ring purchase.
An oven treatment after molding that completes cure and drives off residuals, standard for some elastomer families and required by several food and medical compliance regimes. Whether parts are post-cured affects properties, extractables, and compliance status, so where it matters it is specified, not assumed to have happened.
Molding rubber directly onto prepared metal inserts so the cured part and the metal are joined, the construction behind mounts, bushings, rollers, and bonded seals. The bond depends on the metal's preparation and adhesive system as much as the rubber, and bond requirements and their test method belong on the drawing because a bond failure looks like a rubber failure and is not one.
A U-shaped jacket, usually PTFE, energized by a metal spring that maintains lip contact where an elastomer would take a set or be attacked: extreme temperatures, aggressive chemicals, and dry running. It extends sealing beyond rubber's limits at a higher cost and serves as a reminder to the sector that not every sealing component is an elastomer.
The primary division of sealing duty: static seals separate surfaces that do not move against each other, while dynamic seals ride on reciprocating, rotating, or oscillating surfaces. The same O-ring size applies to different squeeze, finish, and material rules in the two duties, and determining which one the application is comes before any product selection.
The percentage increase in an elastomer's volume after immersion in a fluid, the headline number from the standard immersion tests. A modest swell can be tolerable or even helpful in a seal; a large swell softens and destroys one. Swell data is compound- and fluid-specific, and asking for immersion results in your actual media is better than relying on a generic compatibility chart.
The heat-driven crosslinking that turns raw compound into finished rubber, fixing the part's properties permanently at cure. It is why rubber parts cannot be remelted or rewelded like thermoplastics, why the mold and the cure schedule are where quality is made, and why the cure date on the package is the beginning of the part's life story.
Standards
What each standard governs and why a buyer should care. Which ones apply depends on the part, the duty, and the food, water, or medical service it comes into contact with.
Material classification and test methods
ASTM D2000 is published by ASTM International; SAE J200, essentially identical, by SAE International. The classification system for rubber materials includes building line callouts that encode the elastomer's type by heat-aging performance and class by oil-swell resistance, along with hardness, tensile strength, and suffix requirements for properties such as compression set and low-temperature performance. It applies to nearly every custom rubber purchase because a line callout specifies performance rather than a single supplier's compound, allowing multiple molders to quote the same material and letting you enforce it by test. Specifying rubber by polymer name and color instead is the habit this standard exists to replace.
Published by ASTM International. The nomenclature standard for rubber and rubber latices defines the letter designations the industry uses for elastomer families, including NBR for nitrile, EPDM for ethylene-propylene-diene, FKM for fluorocarbons, VMQ for silicones, and CR for chloroprene. It applies as the vocabulary of every datasheet, callout, and conversation in the sector. Its practical caution is built into its purpose. Each code names a chemistry family within which compounds vary widely in properties and compliance, so the code starts a specification, and the line callout or named compound finishes it.
Published by ASTM International, with counterpart methods published internationally. The test methods behind rubber datasheets and line callout suffixes: durometer hardness, tensile properties, compression set, fluid immersion and volume swell, tear strength, and heat aging. They apply whenever compounds are compared, specified, or accepted, because a property value is only meaningful with its method, conditions, and specimen attached, and callout suffixes cite these methods by construction. For properties your application lives on, compression set at your temperature, swell in your actual media, ask for test results under the named method rather than reading a compatibility chart's generalities.
Seal sizes, tolerances, and storage
SAE International publishes AS568; the International Organization for Standardization publishes ISO 3601. The O-ring size standards: the inch-based dash-number series and the international metric series, each defining dimensions and tolerances, with cross-references between them for common sizes. They apply to essentially every O-ring purchase and every gland designed to take one. Both are size standards only: a dash number says nothing about material, hardness, or compliance, so a complete O-ring specification is the size designation plus a material specification. A gland is designed to the standard's dimensions and the published squeeze guidance rather than measured from a worn seal.
Published by the Association for Rubber Products Manufacturers (ARPM), the United States trade association for molded, extruded, and lathe-cut rubber products, successor to the Rubber Manufacturers Association for these publications. The handbooks define the industry's standard dimensional tolerance classes for molded and extruded rubber, grading achievable tolerances by dimension and precision class, along with practice for gaskets and extrusions. They apply to any custom rubber drawing, where citing a tolerance class from the tables makes the part quotable and inspectable. Machined-part tolerances imported onto rubber drawings are this sector's characteristic specification error, and these tables are the correction.
Published by SAE International as an aerospace standard, formerly the recommended practice ARP5316 that much documentation still cites. The storage and shelf-life standard for elastomer seals, recommending storage conditions and shelf-life limits that vary widely by elastomer family, measured from the cure date marked on the goods. It applies to seal purchasing and stores practice in any industry that keeps critical spares, aerospace or not, because elastomers age on the shelf. Specify remaining shelf life at delivery, store as the standard recommends, rotate stock by cure date, and treat an undated bag of seals as a question, not an inventory.
Application compliance
Administered by the United States Food and Drug Administration under Title 21 of the Code of Federal Regulations, principally the section covering rubber articles intended for repeated food contact, which lists permitted ingredients and extraction limits. Compliance applies to the complete compound, including its cure system and additives, and suppliers state this in the compound's documentation. It applies if the seal, gasket, or part comes into contact with food or drink during production or service. Require the compliance statement for the exact compound quoted, state the food types and temperatures involved, and reconfirm on any compound change, because two compounds of the same polymer can sit on opposite sides of the rule.
3-A Sanitary Standards are published by 3-A Sanitary Standards, Inc. (3-A SSI), with European hygienic design guidance published by the European Hygienic Engineering and Design Group. The 3-A standards include criteria for multiple-use rubber materials in dairy and food equipment, as well as equipment standards governing gasket and seal design for cleanability. They apply when your components enter hygienic processing equipment, where your customer's quality system will specify the requirement. The material criteria and the food contact regulations are separate hurdles, and a compound can clear one. Still, not the other; specify where they apply, and ask suppliers which of their compounds have the documentation.
The Class VI plastics designation is published by the United States Pharmacopeia (USP); ISO 10993 by the International Organization for Standardization. The biological evaluation regimes cited for elastomers in medical and pharmaceutical service: the USP classification is a compendial test set widely referenced on silicone and elastomer datasheets, and the ISO series structures device biocompatibility by the nature and duration of contact. They apply if the component is part of a medical device or drug-contact system, where selection starts from compounds with existing data and medical change control, and the required evaluations follow from the device maker's regulatory pathway. Bring the requirement to the compound decision and include a value change notification as part of the purchase.
Published by NSF, an independent standards and certification body, as an American National Standard and National Standard of Canada. The drinking water system components standard evaluates whether materials in contact with potable water contribute contaminants above allowable levels, and elastomer seals, gaskets, and O-rings in water systems are within its scope. It applies to components for potable water treatment and distribution, where most United States jurisdictions and Canadian provinces require certification. Certification is attached to the specific compound and product, so confirm that the exact item quoted is certified, as a molder's product line routinely contains certified and uncertified compounds side by side.
Frequently Asked Questions
Direct answers to the questions buyers ask most often when sourcing in this sector.
The application first: static or dynamic duty, the media it touches including cleaning chemicals, the temperature range, and the pressure. Then the part: a drawing or model with dimensions toleranced to the rubber industry's classes, the material as a line callout or named compound requirement including hardness, and any compliance the service demands, food, potable, hygienic, or medical. Then the manufacturing context: quantities and program life; parts moving between compression, transfer, and injection molding; tooling setup; whether flash (the thin excess rubber at mold parting lines) and gate locations (where material enters the cavity and leaves its mark) matter; and any bonding to metal with its test requirements. The items most often missing are the media list and the operating temperature, and both select the chemistry, which is the decision everything else stands on.
Start with the media and temperature because chemistry is eliminated before anything else is selected. Nitrile handles petroleum oils and fuels at moderate temperatures and is the industrial default. EPDM excels in water, steam, weather, and many aqueous chemicals, but fails with petroleum. Fluorocarbons take high heat and aggressive chemicals at a higher price. Silicones cover the widest temperature range with strong food and medical applications, but are mechanically weak and perform poorly under dynamic conditions. Chloroprene balances weather and moderate oil resistance. These are family-level truths: within each family, compounds vary widely in properties and compliance, so the family answers the first question and a line callout or named compound answers the specification. When two families survive your conditions, compression set at temperature and price usually decides.
It is the compact material specification built under the standard rubber classification system: a coded line stating the type, from heat aging performance, and class, from oil swell resistance, plus hardness, tensile strength, and suffixes adding requirements such as compression set and low-temperature performance, each tied to a standard test method. Its value is that it specifies performance, not a supplier: any molder can propose a compound meeting the callout, quotes become comparable, incoming parts can be verified by test, and a supplier change does not orphan the drawing. The alternative, specifying a polymer name, a hardness, and a color, describes thousands of materials and enforces none of them. If a supplier's compound is genuinely required, name it and record the callout it meets, so the requirement survives the relationship.
Measuring a used O-ring is unreliable both ways. For reordering, a worn seal has swollen or shrunk in service and taken compression set, so its measured dimensions may match no standard size; identify the size from the equipment documentation or from the gland dimensions against the size standard's tables, then specify the dash number or metric designation plus the material, because the size standards define dimensions only. For design, glands are dimensioned from the standard's tables and the published squeeze guidance for static or dynamic duty, with clearance, finish, and backup rings decided by pressure. Most O-ring failures blamed on rubber are gland problems, and a gland designed from a caliper reading of an old seal inherits every error from the old installation.
Seal failures cluster into a few readable patterns. A seal that leaks without visible damage has usually taken compression set: it has stopped pushing back, which points to temperature or time beyond the compound's ability, and to explicitly specifying set performance next time. A swollen, soft, or gummy seal met chemistry it could not tolerate, often a cleaning fluid nobody listed. A nibbled or extruded edge means pressure pushed the seal into the clearance gap: a gland and backup ring problem. Blistered seals after gas service point to explosive decompression. Cut or twisted seals were damaged at installation. Cracked, hardened seals aged, in service or in storage past their shelf life. The failure mode names the fix, which is why sending the failed seal to the supplier beats describing it on the phone.
Die-cutting from cured sheet suits flat gaskets: it requires no mold, uses cheap tools, turns quickly, and draws on the full range of sheet materials, making it the default for flanges, enclosures, and low-to-mid volumes, and it is converter territory. Molding earns its tooling when the gasket is not flat, needs a profile or cross-section die-cutting cannot make, integrates features such as bolt holes with molded-in grommets or a retaining bead, or runs at volumes where molding's piece price wins. Between them sit extruded and spliced profiles for large perimeters, and dispensed form-in-place gaskets for assemblies that want the seal applied rather than placed. The geometry, the available compression, and the volume determine the choice, and a converter and a molder will each tell you honestly which side of the line your part sits on if you show them the assembly.
They age, at rates that differ enormously by elastomer family, and the aerospace shelf-life standard, widely applied outside aerospace, recommends storage limits by family measured from the cure date marked on the goods. Some families are effectively unlimited in proper storage; others are conservatively limited. Storage conditions matter as much as time: heat, light, ozone, and deformation age rubber early, which is why the standard specifies cool, dark, relaxed storage. The purchasing consequences: specify remaining shelf life at delivery, record cure dates, store correctly, rotate stock, and pay particular attention to critical spares, because the seal that waits ten years in a hot drawer for its emergency is the one that fails when installed. An undated elastomer part in stores is a question, not an asset.
Each regime attaches to the complete compound, cure system, and additives included, not to the polymer family; each is a separate hurdle a compound must clear individually. Food contact is governed by the federal rubber article provisions, which specify the exact compound, food types, and temperatures. Hygienic equipment adds the sanitary standards' material criteria, which your customer's quality system will name. Potable water runs through the drinking water components standard, with certification attached to the specific compound and product. Medical and pharmaceutical service cites the compendial plastics classification and the device biocompatibility series, scoped by the device maker's regulatory pathway. The buyer's discipline is identical in all four: name the requirement in the RFQ, obtain the documentation for the exact compound quoted, and reconfirm whenever the compound changes, because sister compounds differ invisibly.
When the part is silicone, the volumes are high, and the geometry is precise: liquid silicone rubber is injection molded on dedicated equipment with rapid heat cure, delivering high-volume silicone parts with excellent consistency, flashless tooling options, and the compliance pedigree that makes silicone the default in food, infant, and medical products. Its economics are molding economics: real tooling investment repaid by cycle speed at volume, so low-volume silicone parts usually stay with compression or transfer molding of conventional silicone compounds. Its supplier base overlaps custom injection molding as much as rubber molding, and multi-shot versions overmold silicone onto thermoplastics. If your part is silicone at tens of thousands of units per year or more, ask molders about it by name; below that, ask whether conventional silicone molding meets the same drawing for less tooling.
Buyer's Guides
In-depth guides covering the decisions above.
Buyer's Guide
Selecting seal and gasket materials for chemical, thermal and pressure service, how the three constraints interact, and what to confirm before ordering.
Read the guideMore coming
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