Epoxy

High-Temperature Epoxies: A Guide to Selection and Uses

Standard epoxy softens as it nears its glass transition temperature, often between 50 and 120 degrees Celsius. High-temperature grades hold structural properties from 175 degrees into the range where ceramic-filled formulations survive brief excursions past 1,000 degrees. Understanding High-Temperature Epoxies These are formulations engineered to keep their mechanical and chemical properties at elevated temperature. Compared with general-purpose epoxy, they offer higher continuous-use temperature, better thermal-shock resistance, and stronger chemical resistance. They come in organic epoxy systems for the mid range and inorganic, ceramic-filled compounds for the extreme end. Incure's Epo-Weld epoxy line spans this range, with high-temperature grades such as the HTE series for structural bonding at elevated temperature and ceramic-based products for the highest thermal exposure. Key Selection Factors Maximum operating temperature. Separate continuous exposure from short excursions. A grade rated for continuous 200 degrees Celsius may tolerate brief spikes well above that; a grade for intermittent 1,000 degree exposure may not survive that temperature continuously. Thermal shock resistance. If the part cycles rapidly between temperature extremes, the epoxy must absorb the expansion mismatch without cracking or delaminating. This is governed by the mechanism in how CTE mismatch causes adhesive bond failure. Chemical exposure. Identify every fluid the bond will contact, at temperature. Oils, fuels, solvents, and combustion byproducts each attack some formulations. Mechanical requirement. Structural bonding, gap filling, potting, and surface repair each call for different viscosity and filler content. Cure schedule. Many high-temperature epoxies need an elevated-temperature cure or a post-cure ramp to develop full properties. Confirm your process can deliver it. For help matching a grade to a thermal and chemical profile, Email Us. Viscosity and Application Method Low viscosity flows into tight gaps and porous surfaces, suiting infiltration and thin bondlines. Medium viscosity covers general structural bonding. Paste and thixotropic grades stay on vertical surfaces and fill large gaps for repair and buildup. Ceramic coatings for radiant-heat management are a related category; the Epo-Weld HECC high-emissive ceramic coatings are selected by substrate and service temperature rather than by bond strength. Cure and Post-Cure Follow the manufacturer's cure schedule exactly. Under-cure leaves the glass transition temperature below its rated value, so a bond that should hold at 200 degrees fails at 150. A staged post-cure, ramping slowly to the final temperature, drives full crosslinking and relieves internal stress. Rushing the ramp can crack a filled system. Organic Epoxy Versus Ceramic-Filled Compounds The two ends of the high-temperature range are different materials with different rules. Organic high-temperature epoxies stay true structural adhesives to roughly 200 to 260 degrees Celsius continuous. They keep useful tensile and shear strength, bond a wide range of substrates, and tolerate some flex. Their limit is the organic backbone, which oxidizes and chars above its ceiling. Ceramic and silicate-filled compounds reach 500 to over 1,000 degrees Celsius but behave more like a rigid cement than an adhesive. They carry high compressive load, resist flame and oxidation, and seal against hot gas, but they have low tensile strength and almost no flexibility. Use them…

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September 9, 2024
Epoxy

Fixturing for Epoxy Bonding: How Part Holding Controls Bond Quality

An epoxy joint is only as good as the position it holds while it cures. If parts shift, rock, or spring apart during the green-strength window, the bond line ends up starved, misaligned, or locked in stress, and no amount of adhesive performance recovers it. Fixturing is the quiet variable that decides whether a process is repeatable. What Fixturing Actually Does A fixture does four jobs at once during the cure: Alignment: It holds mating parts in their designed relationship so the finished assembly meets dimensional tolerance. Immobilization: It resists handling, gravity, and vibration until the adhesive develops enough strength to hold on its own. Load distribution: It spreads clamping force evenly so no local area is crushed or left unbonded. Repeatability: It reproduces the same gap, pressure, and orientation on every unit, which is what turns a lab result into a production yield. Getting the Bond Line Right A frequent fixturing mistake is over-clamping. Squeezing a joint hard feels thorough, but it pushes adhesive out and leaves a bond line too thin to carry load or absorb thermal movement. Many structural epoxies perform reliably at a controlled gap in the range of 0.1 to 0.25 mm. Hold that gap with shims, molded standoffs, or a small fraction of glass beads mixed into the adhesive, and let the fixture apply only enough pressure to keep contact. Uniform pressure matters as much as magnitude. A single clamp at one end of a long joint bows the parts and produces a wedge-shaped bond line that is strong at one end and weak at the other. Multiple contact points, a compliant pad, or a vacuum bag distribute force across the whole area. Fixturing for Heat Cure When the schedule includes an oven step, the fixture becomes part of the thermal system. A heavy steel fixture adds thermal mass and delays the moment the joint reaches cure temperature, so oven dwell has to account for ramp time measured at the part, not the setpoint. Thermal expansion is the bigger trap. If the fixture material expands at a very different rate than the parts, it can clamp down or pull away as the assembly heats, distorting the joint or forcing a stressed bond line that relaxes into misalignment on cooling. Choosing a fixture material with an expansion rate close to the parts, or designing in compliant contact, avoids baking stress into every unit. The same thermal expansion mismatch that damages cured joints in service can be introduced at the fixturing stage if it is ignored. Practical Design Guidance Analyze the part first. Map the datum surfaces, the tolerance stack, and where the adhesive needs to be dispensed and, for light-cure systems, where the lamp needs line of sight. Design for access. Leave room for the dispense tip, for inspection of squeeze-out, and for the operator to load and unload without smearing adhesive. Use release coatings. Coat fixture surfaces that contact adhesive with PTFE or a release film so cured squeeze-out does not weld the part…

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August 21, 2024
Epoxy

How Curing Conditions Shape Epoxy Adhesive Performance

Two assemblies bonded with the same epoxy can behave nothing alike if they cure under different conditions. Temperature, humidity, mix accuracy, and time each steer the final crosslink network, and small deviations show up later as weak bonds, tacky surfaces, or poor chemical resistance. Why Cure Conditions Matter Epoxy hardens through a chemical reaction between resin and hardener, not by drying. The reaction builds a three-dimensional polymer network whose density determines strength, stiffness, glass transition temperature (Tg), and resistance to solvents and moisture. A bond that reaches only 80 percent of full conversion can lose a large fraction of its rated shear strength and most of its chemical resistance, even though it feels solid to the touch. Cure conditions influence four properties in particular: Cure speed: Reaction rate roughly doubles for every 10 degrees C increase in temperature, so a part cured at 25 degrees C and one cured at 65 degrees C reach handling strength on very different timelines. Ultimate bond strength: Full lap-shear and peel values require complete conversion, which often needs elevated-temperature post-cure. Mechanical character: Under-cured epoxy stays soft and creeps under load; over-baked epoxy can turn brittle and lose toughness. Environmental durability: Only a fully developed network resists humidity, fuels, and cleaning chemicals. Common Curing Problems Manufacturers repeatedly run into the same failure modes: Temperature drift: Oven zones or bench conditions that swing more than a few degrees produce batch-to-batch variation in hardness and cure time. Amine blush: In cool, humid air, the hardener reacts with carbon dioxide and water to leave a greasy carbamate film on the surface. Anything bonded or coated over that film adheres poorly. Incomplete cure: Short dwell times, low fixture temperature, or a heavy heat-sinking substrate that pulls warmth away from the bond line all leave conversion unfinished. Voids and foaming: Trapped air, moisture on the substrate, or a strong exotherm in a thick pour can generate bubbles that concentrate stress. Mix error: Off-ratio resin and hardener, or incomplete blending, leaves unreacted material that never develops properties. Building a Reliable Cure Process Start with stoichiometry. Measure resin and hardener by weight where possible, mix thoroughly including the sides and bottom of the container, and respect the working life so you apply material while it still wets the surface. Control temperature at the bond line, not just in the room. For heat-cured systems, confirm the joint itself reaches the target with a thermocouple, and account for the time a large metal part needs to come up to temperature. A typical schedule might be a fixture cure to handling strength followed by a post-cure at 80 to 120 degrees C to raise Tg and finish conversion. Manage humidity for room-temperature systems. Keep relative humidity moderate, keep air moving gently, and if blush appears, wash it off with warm water before any downstream step. Allow enough time. Published fixture times assume ideal conditions; add margin when the shop is cold or the parts are massive. Deep sections should be poured in lifts to keep…

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August 21, 2024
Epoxy

Epoxy Surface Preparation: Ensuring Strong and Durable Bonds

An epoxy bond fails at the weakest interface, and more often than not that interface is the boundary between the adhesive and a surface that was not properly prepared. The epoxy itself is rarely the problem. Contamination, oxide layers, and the wrong surface profile are what turn a specified 3,000 psi joint into a 500 psi one. Why Preparation Determines Bond Strength Adhesion depends on the epoxy making intimate, continuous contact with the substrate and, ideally, forming chemical or mechanical interlocks with it. Anything between the adhesive and the base material blocks that contact: Oils and mold release create a slip layer the epoxy cannot displace. Oxide and scale on metals are loosely attached and pull away under load, taking the bond with them. A too-smooth surface gives the epoxy nothing to key into. Absorbed moisture in plastics and composites outgases during cure and weakens the interface. Proper preparation removes these barriers and creates a surface the epoxy can genuinely grip. It also makes results repeatable, which matters more than a single high test value. A Working Sequence 1. Clean first. Remove loose dirt, then degrease with a solvent appropriate to the substrate. Wipe in one direction with a clean cloth and change cloths often; a saturated cloth just spreads contamination. Let the solvent flash off completely. 2. Abrade. Create a fresh, roughened surface with abrasive pad, grit blast, or sandpaper. On metals this removes oxide and exposes bright material; on plastics and composites it opens the surface without gouging. Grit-blasting gives the most consistent profile on production parts. 3. Clean again. Abrasion generates dust and debris that must be removed with a second solvent wipe or clean, dry compressed air. Do not touch the prepared surface with bare hands; skin oil is a contaminant. 4. Prime or treat where needed. Low-surface-energy plastics such as polyethylene and polypropylene need a primer, a flame treatment, or plasma to raise their surface energy enough to bond. Some metals benefit from a conversion coating or an adhesion-promoting primer for long-term durability in humid service. 5. Bond promptly. A prepared surface starts re-oxidizing and re-contaminating immediately. Bond within the window the primer or process data specifies, ideally within a few hours. Matching Preparation to the Substrate Aluminum and steel respond well to grit-blast plus solvent wipe, with a primer for wet or outdoor service. Stainless and titanium often need a more aggressive chemical or abrasive treatment. Glass and ceramics bond well after cleaning and, for durability, a silane primer; the guide to matching a glass and metal bonder grade to viscosity and tensile requirement covers those substrates in more detail. Engineering plastics like ABS and polycarbonate need only cleaning and light abrasion, while polyolefins and fluoropolymers need surface activation; matching an adhesive grade to the substrate and mechanical demand is a useful reference there. When the joint bonds two dissimilar materials, preparation quality matters even more because the interface already carries expansion stress; see how CTE mismatch causes adhesive bond failure. Incure supplies Epo-Weld™…

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August 20, 2024
Epoxy

Impact-Resistant Bonding for Multi-Substrate Assemblies

A bonded assembly is only as durable as its response to a shock. Many joints that pass a static pull test still split the first time the product is dropped, slammed, or run on a vibrating machine. Impact-resistant bonding is about designing the adhesive and the joint together to survive those events. Why Standard Adhesives Fail Under Impact A rigid, highly crosslinked adhesive can have excellent static strength and almost no toughness. Under a sudden load, energy has nowhere to go, so a crack starts at a stress concentration and propagates through the bond line before the material can deform to absorb it. Vibration does the same thing over time through fatigue: millions of small cycles grow a crack that a single test never revealed. Multi-material joints make this harder. Bonding metal to plastic to ceramic to glass means each substrate has a different stiffness and a different rate of thermal expansion, so the bond line is already under stress before any external load arrives. What an Impact-Resistant Epoxy Does Differently A toughened two-part epoxy carries a dispersed flexible phase within the cured matrix. That phase blunts crack tips and lets the bond line flex slightly under a shock load instead of shattering. The trade-off is a modest reduction in peak rigidity and glass transition temperature compared with an untoughened structural epoxy, which is usually a good exchange for an assembly that has to survive handling and transport. Incure Epo-Weld™ includes two-part epoxy formulations built for impact and vibration resistance across dissimilar substrates, with these typical working characteristics: Substrate range: metals, engineering plastics, ceramics, glass, and cured rubbers Gap filling: accommodates bond lines in the 0.1 to 0.2 mm range Working time: around a 4-hour pot life for unhurried application on larger assemblies Cure: full cure in roughly 24 hours at room temperature, or about 2 hours at 65°C Designing the Joint for Shock The adhesive is half the answer. The joint geometry is the other half: Maximize bonded area so an impact load is spread thin rather than concentrated. Load the joint in shear, not peel or cleavage, wherever the layout allows. Radius internal corners and avoid abrupt changes in section that concentrate stress. Keep the bond line uniform; thick and thin patches cure and flex differently. Add a mechanical backup, such as a rivet or a snap, on joints that see the highest peak loads. Because dissimilar-material joints carry constant expansion stress, review how CTE mismatch causes adhesive bond failure during design. For guidance on where epoxy is the right chemistry for a heavy or structural joint in the first place, see UV glue versus epoxy for heavy-duty repairs. Where Impact-Resistant Bonding Matters Automotive: bonding components in engines, transmissions, and chassis that see continuous vibration and road shock Rail and transit: interior and underframe assemblies subject to coupling shock and track vibration Industrial equipment: machinery housings, guarding, and brackets exposed to impact and cyclic loading Consumer electronics: enclosures and internal structure that must survive drop testing Aerospace: secondary…

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August 20, 2024
Epoxy

Eliminating Voids in Your Epoxy Application

A void in an epoxy bond is a trapped pocket of air where there should be solid adhesive. It looks minor, but each void is a stress concentrator and a missing patch of bonded area. In a structural joint or a potted assembly, voids are a common root cause of premature failure that never shows up until the part is in service. How Voids Form Air gets into an epoxy joint through several routes: Mixing: stirring folds air into the resin, especially with thick or filled systems. Application speed: pouring or spreading too fast rolls air under the leading edge. Substrate texture: porous surfaces and machined grooves hold air that the epoxy has to displace. Outgassing: some substrates release trapped gas as they warm during cure. Pressure changes: a bond made at ambient pressure that later sees vacuum or altitude will expand any dissolved air into a visible bubble. What Voids Cost You A void reduces the load-bearing bond area directly, so a joint with five percent voiding has five percent less adhesive doing the work. Worse, the sharp edge of a void concentrates stress, so cracks initiate there under load or thermal cycling. Voids near a bond-line edge create a path for moisture and chemicals to wick in. And in a potted electronic assembly, a void against a component can trap heat and create a local hot spot. Strategies That Actually Remove Voids Mix to minimize air. Stir slowly and deliberately rather than whipping. Fold the material over instead of beating it. For production volumes, use a planetary or static mixer designed to blend without aeration. Vacuum degas the mixed epoxy. Placing the mixed batch under vacuum for a few minutes pulls entrained air out before application. The mixture will foam up, then collapse; that collapse is the air leaving. This is the most effective single step for critical joints. Apply slowly and from one side. Lay the epoxy down so it pushes air ahead of it toward an open edge rather than trapping it. Pour in a thin stream from a low height. Prepare the surface to release air. Wet out textured or porous surfaces with a thin coat of epoxy first, work it into the texture, then make the full bond. Warming the substrate slightly before bonding drives off surface moisture and reduces outgassing during cure. Use pressure or a controlled clamp. Applying even pressure to the joint during cure collapses small bubbles and pushes them out. A vacuum bag does the same for large bonded areas. Match viscosity to the job. A lower-viscosity epoxy flows into tight joints and releases air more readily than a thick paste. Incure Epo-Weld™ offers grades across the viscosity range for exactly this reason. Where a void-sensitive joint bonds dissimilar materials, an edge void becomes the starting point for the stress cracking described in how CTE mismatch causes adhesive bond failure. For structural joints where epoxy is being weighed against faster chemistries, UV glue versus epoxy for heavy-duty repairs covers where…

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August 20, 2024
Epoxy

Epoxy Mixing Ratios: A Guide to Consistent Cures and Results

An epoxy is only as good as its mix. Get the resin-to-hardener ratio wrong by ten percent and the cured material can end up soft, brittle, tacky, or slow to develop strength, no matter how good the formulation is on paper. Accurate mixing is the single most controllable factor in a reliable bond. Why the Ratio Is Not Negotiable Epoxy cure is a stoichiometric reaction: each resin molecule needs a matching number of reactive sites on the hardener to build a complete network. The published ratio is set to balance those sites. Deviate from it and some molecules never fully react, leaving unreacted resin or excess hardener trapped in the matrix. The result is a measurable loss in these properties: Cure time: off-ratio mixes often cure slower and may never reach full hardness. Bond strength: an incomplete network has lower shear and peel strength. Thermal and chemical resistance: the glass transition temperature drops and solvent resistance falls. Consistency: every off-ratio batch is off in a slightly different way, so results scatter. Note that epoxy ratios are specified either by weight or by volume, and the two numbers are usually different because resin and hardener have different densities. Use the basis the data sheet gives, and do not convert casually. Where Mixing Goes Wrong Manual measurement error. Eyeballing volumes in a cup, or using uncalibrated pumps, introduces ratio drift. Incomplete blending. Even a correct ratio fails if the two parts are not fully combined. Unmixed streaks cure differently from the bulk. Container scraping. Resin clinging to the sides and bottom of the mixing vessel, transferred late or not at all, shifts the effective ratio. Viscosity mismatch. A thick resin and a thin hardener resist blending. Cold material makes this worse. Pot life pressure. Rushing the mix to beat the working time leaves it under-blended. Best Practices for Accurate Mixing Weigh components on a calibrated scale for the tightest control, or use metered dispensing equipment for production volumes. Mix deliberately for the full recommended time, scraping the sides and bottom of the container at least once and transferring to a second clean container to catch unmixed material on the walls. For thick or filled epoxies, use a mechanical mixer at a speed that blends without whipping in air. Bring components to about 20–25°C before mixing so viscosities are in their intended range. Degassing under vacuum after mixing removes entrained air before it becomes a void in the finished bond. Incure Epo-Weld™ epoxies are supplied with defined mix ratios and, for many grades, pre-measured or cartridge packaging that removes the measurement step entirely. Ratio, Strength, and Substrate A correct mix matters most when the joint is already working hard. For heavy structural bonds where epoxy strength is the deciding factor, see UV glue versus epoxy for heavy-duty repairs. When the epoxy bonds two dissimilar materials, an under-cured matrix has less capacity to absorb the stress that expansion mismatch adds, so review how CTE mismatch causes adhesive bond failure as well. Symptoms That Point…

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August 17, 2024
Epoxy

How to Extend Epoxy Pot Life for Better Productivity

Pot life is the working window after resin and hardener are mixed, before viscosity climbs too high to apply the adhesive properly. A short pot life forces small batches, rushed application, and discarded material. Extending it, without slowing the final cure, directly improves throughput and reduces waste. What Pot Life Actually Measures Once mixed, an epoxy begins cross-linking immediately. Pot life is the point at which viscosity has roughly doubled, or the material has warmed and thickened enough that it no longer wets surfaces or dispenses cleanly. It is not the same as cure time. A system can have a 20-minute pot life and still take hours to reach handling strength. Pot life depends on: Hardener chemistry. Fast aliphatic amines give short pot lives; cycloaliphatics, polyamides, and latent hardeners give longer ones. Mixed mass. A large batch retains its own reaction heat, which accelerates the reaction and shortens pot life. The same formulation in a thin film lasts far longer. Temperature. Reaction rate roughly doubles per 10 degree Celsius rise, so a warm shop halves pot life compared with a cool one. Mix ratio. Excess hardener shortens pot life and can embrittle the cured bond. Why a Short Pot Life Costs Money Material is discarded when it gels before it is used. Mixing and application are rushed, which invites ratio errors and trapped air. Production stops and starts around each small batch. And adhesive applied near the end of its pot life has already partly reacted, so it wets poorly and the bond is weaker. Ways to Extend Pot Life Lower the temperature of the components. Cooling the resin and hardener to 10 to 15 degrees Celsius before mixing can double the working window. The parts being bonded can then be at room temperature to keep the cure on track. Mix smaller batches, more often. Less mass means less self-heating and a longer effective window per batch. Meter-mix-dispense equipment takes this to its limit by mixing only what is dispensed each second. Spread the mixed material. Pouring a fresh batch into a shallow tray instead of leaving it in a cup dissipates reaction heat and slows the viscosity rise. Choose a longer-pot-life hardener. If the process needs 45 minutes of open time, specify a system rated for it rather than fighting a 15-minute product. Confirm the slower hardener still meets your cure-time and temperature-resistance requirements. Refrigerate component stock. Storing resin and hardener cold extends their shelf life and means they start each batch at a lower temperature. If you need a system that balances a long pot life against a specific handling time, Email Us with both targets and the batch size you mix. Keep the Final Cure on Target Extending pot life by cooling the mix should not slow the cure of the finished joint, as long as the parts and the cure environment are at the proper temperature. If you extend pot life by switching to a slower hardener, plan for a longer cure or add a post-cure…

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August 17, 2024
Epoxy

How to Reduce Epoxy Shrinkage

Epoxy loses a small amount of volume as it cures, usually only a few percent. But that contraction builds internal stress that can crack the bond line, distort a precision part, or pull the adhesive off a substrate weeks after assembly. Controlling shrinkage is central to a durable joint. Why Epoxy Shrinks Curing converts a loosely packed liquid into a densely cross-linked solid. The molecules end up closer together, so the material occupies less space. Two mechanisms are at work: chemical shrinkage from the cross-linking reaction itself, and thermal shrinkage as a heat-generating or heat-cured epoxy cools back to room temperature. The consequences show up as: Stress cracks in the adhesive or at the interface, where locked-in tension exceeds the bond strength Dimensional change in bonded assemblies, affecting fit, flatness, and optical alignment Delamination as the cured epoxy peels from a substrate it can no longer grip evenly Warpage of thin or unbalanced parts pulled out of shape by a shrinking bond line Factors That Control Shrinkage Formulation. Epoxy chemistries vary widely in cure shrinkage. Cycloaliphatic and filled systems shrink less than unfilled aliphatic ones. Choosing a low-shrinkage grade is the most direct fix. Filler content. Inert fillers do not shrink, so they dilute the shrinking resin fraction. A filled grade can cut effective shrinkage substantially, though it raises viscosity and can lower toughness. Section thickness. Thick pours generate and hold more reaction heat, cure hotter, and then shrink more on cooling. They also cure unevenly, top to bottom. Cure schedule. A fast, hot cure produces more thermal shrinkage stress than a slow, cool one because the material vitrifies at a higher temperature and has further to contract. Cure completeness. An under-cured epoxy continues to shrink slowly in service as the reaction finishes. Practical Ways to Reduce It Select a low-shrinkage grade. Start here. If dimensional stability is critical, specify a filled or cycloaliphatic system formulated for the purpose. Cure cooler and slower. A room-temperature cure followed by a gentle post-cure builds less thermal stress than a single hot cure. Ramp temperature gradually. Limit bond line thickness. Keep the joint as thin as the fit allows. Where a deep fill is unavoidable, pour and cure in lifts so each layer shrinks against a stable base rather than one thick mass shrinking at once. Cure fully. Follow the recommended schedule so no residual shrinkage is left for the service life. Verify hardness through the section. Design the joint to tolerate movement. A joint with some compliance and a modest bonded area distributes shrinkage strain instead of concentrating it at an edge. If you are seeing shrinkage cracks or distortion on a current part, Email Us with the geometry and cure schedule and we can suggest changes. Shrinkage and Dissimilar Substrates Shrinkage stress and thermal expansion mismatch add together. When epoxy bonds two materials with different expansion coefficients, the cured joint already carries shrinkage tension, and every subsequent temperature change loads it further. The combined effect is the common cause of edge…

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August 16, 2024
Epoxy

How to Improve Epoxy Flow Consistency

An epoxy that flows differently from batch to batch, or from morning to afternoon, produces bond lines that vary in thickness, wetting, and strength. Flow consistency, holding viscosity and rheology within a narrow band, is what makes an epoxy process repeatable. Why Flow Behavior Matters Viscosity governs how an epoxy performs at every step: Dispensing. A stable viscosity gives a consistent bead weight through the same valve and needle. Drift changes the amount of adhesive delivered per part. Wetting. The resin must spread into the surface texture of both substrates and displace air. Too thick and it bridges over roughness, trapping voids; too thin and it runs out of the joint before gelling. Gap fill. A wide bond line needs a body that resists slump. A tight joint needs a resin thin enough to fill it fully. Position holding. On vertical or overhead joints, the epoxy has to stay put until it gels. What Makes Epoxy Flow Vary Temperature. This is the dominant factor. Most epoxies lose several percent of viscosity per degree Celsius near room temperature. A drum stored on a cold dock and one in a warm shop dispense very differently. Mix ratio and blend quality. Off-ratio epoxy has the wrong viscosity from the start and gels unpredictably. Incompletely mixed material has streaks of resin-rich and hardener-rich adhesive with different flow. Working time elapsed. Viscosity climbs steadily from the moment resin and hardener meet. Adhesive applied at minute two flows differently from adhesive applied at minute twenty. Filler settling. In filled grades, fillers can settle during storage. Material drawn from the top of an unstirred container is thinner than material from the bottom. Lot-to-lot variation. Incoming batches can sit at different points within the datasheet range. Controlling Flow on the Line Condition the material. Hold epoxy and dispensing equipment at a controlled 20 to 25 degrees Celsius. A jacketed reservoir or a temperature-controlled dispense head removes seasonal and shift variation. Let cold parts warm to shop temperature before bonding. Use metered dispensing. Cartridge systems with static mixers, or meter-mix-dispense equipment, deliver a consistent ratio and a consistent blend, removing the largest sources of variability. Work within a defined open time. Mix batch sizes that can be applied before viscosity rises past the point where wetting suffers. For hand mixing, that often means small, frequent batches. Stir before drawing filled grades. Re-disperse settled filler at the start of each shift so viscosity is uniform through the container. Check incoming lots. Measure viscosity against the datasheet and flag any batch near the edge of the range. For guidance on how viscosity fits into overall grade selection, see our overview of matching a bonder grade to substrate and mechanical demand. Do Not Thin the Epoxy Adding solvent or an unqualified diluent to lower viscosity changes cure chemistry, raises shrinkage, and lowers final strength and temperature resistance. If a different flow is needed, specify a different grade. If you need help choosing one, Email Us with the joint geometry and dispensing method.…

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August 16, 2024