Anaerobic sealants create reliable, leak-proof seals in metal-to-metal assemblies because they cure only in the absence of air and the presence of metal ions. A recurring question on the production floor is whether an activator is always required. The answer depends on the metal, the gap, the temperature, and the cycle time you need. The Anaerobic Cure, Briefly Anaerobic sealants contain initiators that react with metal surfaces once oxygen is excluded. That reaction generates free radicals, which polymerize the liquid resin into a solid. Cure speed and completeness depend on: Metal type: some metals catalyze the cure far more actively than others. Bondline gap: tighter gaps exclude oxygen more effectively and cure faster. Temperature: warmer parts and surroundings accelerate the reaction. When an Activator Becomes Necessary Many anaerobic sealants cure adequately on their own. An activator becomes important in specific situations: Passive metals: stainless steel, anodized aluminum, zinc-plated surfaces, cadmium, chrome, and titanium carry few active surface ions and slow or inhibit the cure. An activator deposits the catalytic species the reaction needs. Larger gaps: anaerobic sealants target close-fitting parts, typically up to 0.5 mm. Wider gaps trap oxygen and interfere with cure; an activator helps overcome that inhibition. Low temperatures: in a cool workshop or on cold parts, cure slows markedly. An activator restores a workable cure time. Faster cycle times: even on active metals, an activator can sharply reduce fixture time in high-volume assembly. Marginal surface condition: an activator can help overcome minor residual contamination, though it never replaces proper cleaning. The Cost of Skipping an Activator When One Is Needed When a passive substrate or cold part slows the cure, the visible symptom is a joint that has not fixtured by the time it reaches the next station. Less visible is partial cure: the sealant near the metal reacts while material in the center of a wider gap stays soft. That joint may pass a quick handling check and still leak under pressure or vibration weeks later. On plated fasteners and stainless flanges, an untreated surface can extend fixture time from minutes to hours, which is rarely compatible with a moving line. An activator removes that variability, giving a predictable fixture time regardless of incoming part passivation. What an Activator Does Anaerobic activators are usually solvent-based solutions carrying a catalyst, often a copper compound or similar accelerator. Sprayed or wiped onto the metal, they leave a microscopic film of active material that promotes polymerization, allowing the sealant to cure on otherwise slow surfaces or in less favorable conditions. The solvent must flash off fully before the sealant is applied. Applying an Activator Correctly Apply a thin, even coat to one mating surface only. Allow the solvent to evaporate completely, following the data sheet dwell time. Assemble within the activator's open time; effectiveness declines after prolonged exposure. Avoid heavy application, which can leave residue that weakens the bond. Getting activator use right is often the difference between a consistent line rate and unpredictable fixture times. Email Us to…

Two sealing chemistries handle most industrial leak-prevention work: room temperature vulcanizing (RTV) silicones and anaerobic sealants. They cure by different mechanisms and suit different joints, and choosing the wrong one is a common cause of persistent leaks. How Each Sealant Cures Anaerobic Sealants Anaerobic sealants are single-component liquids that stay fluid while exposed to air. They cure only when confined between close-fitting metal surfaces, starved of oxygen, and in contact with active metal ions such as iron or copper. The result is a rigid thermoset plastic that fills microscopic surface imperfections and creates full surface-to-surface contact. Key characteristics: Cures in the absence of air, in contact with metal. Designed for small, close-fitting gaps, typically up to 0.5 mm. Primarily a metal-to-metal technology. Cures rigid and adds shear strength to the joint. Strong resistance to oils, fuels, and coolants. Heat resistance generally 150 to 200 degrees C for standard grades. Disassembly can require localized heat. RTV Silicone Sealants RTV silicones cure by reacting with atmospheric moisture at room temperature, releasing a byproduct such as acetic acid or alcohol, and forming a flexible elastomer. Key characteristics: Cures on exposure to humidity. Fills larger, uneven gaps, often 6 mm or more. Adheres to metals, many plastics, glass, ceramics, and painted surfaces. Cures to a flexible, rubber-like film. High flexibility suits thermal movement, vibration, and dynamic joints. Some formulations withstand over 300 degrees C. Generally easier to peel or scrape away during service. Cure Byproducts and Corrosion RTV silicone chemistry matters when electronics or sensitive metals are nearby. Acetoxy-cure grades release acetic acid, which can corrode copper, brass, and some coatings and irritate operators in enclosed areas. Neutral-cure grades, using oxime or alkoxy chemistry, release milder byproducts and are the safer choice around electrical contacts, bare copper, and enclosed housings. Anaerobic sealants release no atmospheric byproduct, since they cure only in the confined joint, but the rigid cured film means a joint sealed this way is harder to open later. Dispensing and Application Anaerobic sealants are applied as a continuous bead to one clean, dry flange face, encircling all bolt holes, then assembled promptly so the joint closes before the surface film can begin to set. RTV silicones are applied as a bead sized to the gap, with parts brought together within the skin-over time, typically a few minutes. Both benefit from automated dispensing on higher-volume lines for consistent bead placement and volume, which reduces both squeeze-out waste and thin spots that leak. A Direct Comparison Feature Anaerobic Sealants RTV Silicone Sealants Curing trigger Absence of air plus metal contact Atmospheric moisture Best gap range Small, precise, machined flanges Large or irregular, stamped sheet metal Material compatibility Primarily metal-to-metal Wide range of materials Cured state Rigid thermoset plastic Flexible elastomer Structural contribution Adds rigidity and shear strength Provides flexibility and vibration damping High-temperature limit Good, 150 to 200 degrees C typical Excellent, often over 250 degrees C Disassembly Can require heat Generally easier When to Choose Which Choose an anaerobic sealant when you have…

Two machined metal surfaces that look perfectly flat to the naked eye are, under magnification, a landscape of microscopic peaks and valleys — and that gap is exactly where anaerobic flange sealant does its work. The Basic Chemistry Behind the Name An anaerobic flange sealant is a single-component adhesive that cures in the absence of air and in the presence of metal ions — hence "anaerobic," meaning without air. Applied as a liquid or gel to a flange face, it stays liquid as long as it's exposed to atmospheric oxygen. Once the two mating surfaces are brought together and oxygen is excluded from the joint, the metal ions at the surface catalyze a rapid polymerization reaction that converts the liquid into a durable, solvent-resistant thermoset plastic filling every void in the joint. Why Traditional Gaskets Leave Gaps Anaerobics Don't Traditional pre-cut gaskets can bridge some surface irregularities under clamping pressure, but they can't conform to every microscopic imperfection on a machined flange — and those unfilled voids are where leaks eventually start. Because anaerobic sealant is applied as a liquid before it cures, it flows into gaps a solid gasket simply can't reach, producing full surface-to-surface contact rather than a series of point contacts under compression. Characteristics That Explain Why They're Widely Used No shrinkage or creep: curing happens without solvent loss, so the seal doesn't relax or loosen the way compressed gaskets can over time. High strength and durability: the cured bond resists vibration, thermal cycling, and shock without losing joint integrity. Chemical resistance: most formulations tolerate oils, fuels, coolants, and hydraulic fluids without degrading. Gap-filling range: typically effective up to roughly 0.5 mm, depending on the specific product, which covers the vast majority of machined-flange tolerances. Even stress distribution: full surface contact spreads load evenly across the joint rather than concentrating it at a few high points. Where Anaerobic Flange Sealants Are Used Engine and transmission housings, pump and compressor assemblies, hydraulic and pneumatic system connections, machined flanges, and bearing caps all rely on this class of sealant to hold pressure and exclude contaminants without the bulk or replacement cost of a traditional gasket. In each case, the deciding factor is the same: a rigid, close-fitting metal-to-metal joint that needs a seal capable of filling microscopic surface variation rather than bridging a larger, more flexible gap. How Cure Time Interacts With Assembly Scheduling Anaerobic sealants typically reach handling strength well before they reach full chemical cure, and confusing the two is a common source of premature seal failure. A joint may be stable enough to move to the next station within minutes, but full cure — the point at which the sealant reaches its rated chemical and pressure resistance — can take considerably longer, particularly at lower ambient temperatures or on passive metal surfaces without an activator. Pressurizing or loading a joint before full cure is reached can permanently compromise the seal even though it appeared solid when handled. Production schedules should build in the manufacturer's specified full-cure…

A leaking flange rarely means the anaerobic sealant chemistry was wrong for the job — in most cases it means something in the assembly process undermined a perfectly good product, and the fastest path to a permanent fix is matching the actual symptom to its real cause. For background on how anaerobic chemistry cures and where it fits against gasket alternatives, see our overview of anaerobic flange sealants for industrial metal-to-metal sealing. Symptom: Weeping Appears Within the First Few Days of Startup An early leak, showing up before the assembly has accumulated meaningful service hours, points to an incomplete cure rather than a sealant selection problem. Anaerobic chemistry cures in the absence of air and in the presence of metal ions at the mating surfaces, and disturbing the joint — pressurizing it, running the equipment, or even revisiting the torque — before the manufacturer's specified cure window has elapsed removes the polymer's chance to reach full cross-link density. Checking the cure-time log against the actual time the assembly went into service is the first thing to verify before questioning the product itself. Symptom: The Leak Only Appears on One Side of the Flange A leak concentrated at one section of an otherwise sealed flange face is a strong signal of an uneven clamping pattern rather than a sealant failure. Tightening bolts in a random order instead of a specified crossing sequence leaves one part of the flange face under-compressed while the sealant is still curing, so that section never achieves full surface contact even though the rest of the joint looks perfectly sealed. Re-torquing the assembly in the correct sequence on the next rebuild — rather than switching sealant formulations — resolves this failure mode in most cases. Symptom: Lubricant or Process Fluid Shows Contamination After Assembly Particles or a film in the lubricant or process fluid downstream of a newly sealed flange, misdiagnosed as a sealant chemistry problem, is frequently a squeeze-out issue instead. Excess sealant applied beyond what the joint's gap-filling requirement calls for gets pushed into the bore of a pump or gearbox housing during assembly, where it can break off after cure and travel downstream. Reducing bead size to match the actual gap, rather than applying a generous margin "to be safe," prevents this without needing a different product. Symptom: A Seal That Held for Years Suddenly Starts Leaking A joint that performed reliably for an extended period before failing usually points to accumulated thermal-cycling stress rather than a sudden chemistry breakdown, particularly on assemblies where dissimilar metals expand at different rates across repeated heating and cooling. Each cycle adds a small amount of stress at the flange interface, and a rigid sealant chemistry that seemed adequate at installation can eventually reach its fatigue limit years into service, especially on equipment that runs through frequent startup-shutdown cycles rather than staying at a stable operating temperature. Symptom: The Same Flange Keeps Leaking After Repeated Rebuilds If a specific flange location fails repeatedly despite reapplying sealant correctly each…