Incure Archives - INCURE INC.

UV Curing Systems: Accelerating Manufacturing with Eco-Friendly Technology

UV curing does two things at once for a production line: it compresses the cure step from minutes to seconds, and it removes solvent from the process. The result is higher throughput on a smaller footprint with no volatile organic compound emissions to manage. The Process A UV-curable coating, adhesive, or ink is a liquid blend of monomers, oligomers, and a photoinitiator. Ultraviolet light of the matched wavelength activates the photoinitiator, which starts cross-linking. The liquid becomes a solid polymer network within seconds, with no heat input and nothing evaporating. Because the material only reacts when exposed, it stays workable on the part until the operator or the line is ready. Why It Speeds Up Manufacturing Cure time. Surface-to-solid in one to ten seconds under adequate irradiance, against many minutes in an oven. No dwell. There is no oven mass to heat and hold and no cool-down before the next step. In-line fit. A correctly sized lamp cures at the same pace a dispensing or coating head places material, so the cure step stops being the bottleneck. Immediate handling. Parts come off cured, ready for assembly or packing. Why It Is Cleaner Typical UV formulations are 100 percent solids. There is no solvent carrier, so there are no VOC emissions, no solvent recovery, and a lighter ventilation load. LED sources add to this by drawing a fraction of the power of a thermal line and generating far less waste heat, which reduces the plant cooling burden as well. Choosing a System Wavelength. Match the source to the resin's photoinitiator. LED systems use a single peak of 365, 385, 395, or 405 nm; broadband arc lamps cover the near-UV band at once. The data sheet dictates the choice. Irradiance and dose. Dose (mJ/cm²) is irradiance (mW/cm²) times exposure time. Specify irradiance at the part surface, not at the emitter, because it falls off sharply with distance. Lamp type and configuration. Flood heads for area coverage, spot systems for localized bonds, conveyors for continuous flow. The Incure L-Series UV LED flood lamps map curing area to intensity across a wide range. Part handling. Low volume and prototyping suit an enclosed chamber that contains the light for safe batch work. High volume points to the Incure CDM UV conveyor, where dose becomes a belt-speed setting. If you want help mapping these variables to a specific line, Email Us with the resin data sheet and your cycle-time target. Applications UV curing systems serve coatings and inks in printing and packaging, conformal coatings and bonds in electronics, finishes and adhesives in automotive and appliance work, encapsulants in renewable-energy module assembly, and resin cure in additive manufacturing. For assembly work where the bond competes with fast handling, our comparison of UV adhesive and epoxy for quick repairs shows where each method fits. Our guide to selecting a UV lamp for resin curing covers source selection in detail. Process Control Read the required dose and wavelength from the data sheet. Measure irradiance at the part with a…

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January 29, 2025

Cyanoacrylate

Managing Exothermic Heat in Cyanoacrylate Bonding

Cyanoacrylate polymerizes through an exothermic reaction, releasing heat as it cures. In a thin bond line that heat is trivial. In a thick section, a large fillet, or a pooled excess, it can climb high enough to damage substrates, weaken the bond, or in extreme cases scorch nearby material. Understanding where the heat comes from makes it straightforward to control. The Source of the Heat Cyanoacrylate cures by anionic polymerization, triggered by trace surface moisture. The reaction is rapid and releases roughly 200 to 250 kJ per mole of monomer. Because cure propagates quickly once initiated, that energy is delivered in a short burst. In a 0.05 mm bond line the surrounding parts act as a heat sink and the temperature rise is a few degrees at most. In a 3 mm puddle with poor thermal contact, the core can reach 80 to 150 C, and cotton, tissue, or some foams in contact with a large uncured mass can char or ignite. What Excess Heat Does Substrate damage: Thin thermoplastics warp or discolor. Pre-stressed or molded-in parts relax and lose dimensional accuracy. Reduced bond strength: A fast, hot cure produces a more brittle, more stressed polymer network with higher shrinkage. The joint may pass an immediate pull test but fail early under thermal cycling or impact. Blooming: Rapid cure drives more monomer to vaporize before it can polymerize, and the vapor deposits as white haze on cooler nearby surfaces. Safety hazard: Large uncured quantities against absorbent organic material can generate enough heat to smoke or flame. This is the reason cyanoacrylate should never be used to saturate fabric or loose fiber. Controlling the Reaction Keep the bond line thin. The single most effective control. A uniform gap under 0.15 mm cures with negligible temperature rise and gives the strongest joint. Design parts with defined stand-offs or use a fixture that sets the gap. Do not over-apply. Use the minimum adhesive that fills the joint. Excess that squeezes out into a bead cures slowly and hot. Wipe or control squeeze-out before it pools. Fill deep gaps in stages. Where a large volume genuinely must be filled, apply in thin lifts and let each cure, or switch to a gap-filling grade with an accelerator applied per layer. Better still, use a different chemistry, since cyanoacrylate is not designed for bulk potting. Give the joint a heat path. Bonding to metal or another conductive substrate spreads the heat. When both substrates are insulating, work in smaller increments. Manage the work environment. A cool, moderately humid room, around 20 to 22 C and 45 to 55 percent relative humidity, gives a controlled cure rate. Very high humidity accelerates cure and raises peak temperature. Use accelerators deliberately, not by default. A surface activator guarantees cure on inert or acidic substrates and on exposed fillets, but applied to a thick section it makes the exotherm worse by curing the whole mass at once. Apply activator to the thinnest accessible surface and let the bulk cure more…

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September 4, 2024

Cyanoacrylate

Fixturing and Clamping Techniques for Cyanoacrylate Bonding

Cyanoacrylate cures fast, but fast is not the same as forgiving. Because the adhesive fixtures in seconds, any misalignment or movement in that window is locked in permanently. Good fixturing is what turns cyanoacrylate's speed into a production advantage rather than a source of scrap. Why Restraint Matters A cyanoacrylate bond reaches handling strength in 5 to 60 seconds on most substrates and continues gaining strength for 24 hours. During the initial set, the parts must be held in their final position with zero relative motion. Even slight shifting breaks the forming polymer chains at the interface and produces a bond that looks complete but carries a fraction of its rated strength. Restraint also controls bond-line thickness. Cyanoacrylate performs best in a thin, uniform gap, typically under 0.15 mm. Thicker sections cure slowly from the center outward, can trap stress, and are more prone to blooming, the white haze caused by uncured monomer vapor settling on nearby surfaces. Common Fixturing Problems Part distortion: Excess clamping force bends thin walls or flanges, so the bond cures with the part sprung. When the clamp releases, the joint carries a permanent preload that reduces its effective strength. Adhesive contamination: Cyanoacrylate wicks. If it reaches a fixture surface, the fixture becomes bonded to the part or transfers cured residue to the next unit. Accelerated cure from the fixture: Metal fixtures and alkaline surfaces speed cure, sometimes so much that the adhesive sets before parts are seated. Access: Confined assemblies leave no room to apply and release a clamp without disturbing alignment. Fixture cost: Bespoke fixtures for complex geometry take time and money to design and prove out. Recommended Practices Locate before you clamp. Design the fixture so hard stops and locating pins define part position. The clamp should only hold parts against those references, not establish position itself. Distribute clamping force. Use wide contact pads or a compliant layer such as urethane over the clamp face. Aim to hold parts firmly enough to prevent movement and no firmer. For delicate components, a few newtons is often sufficient. Choose non-stick fixture materials. Acetal, UHMW polyethylene, and PTFE resist cyanoacrylate adhesion. Where a metal fixture is needed for rigidity or heat management, mask the contact zone with a replaceable polyethylene tape or a machined insert. Control the local environment. Keep humidity in the 40 to 60 percent range. Below that, cure slows and bloom increases; above it, cure can run away. A gentle extraction near the station removes monomer vapor before it deposits. Use quick-release mechanisms. Toggle clamps, cam levers, and pneumatic hold-downs shorten cycle time and give consistent, repeatable force, unlike a hand-tightened screw clamp. Consider vacuum fixturing. For thin, flat, or irregular parts, a vacuum chuck holds the whole surface without a point load, eliminating distortion and giving unobstructed access to the bond line. For guidance on fixture design for a specific assembly, Email Us with your part drawings and cycle-time target. Matching the Adhesive to the Fixture Strategy Viscosity drives fixturing choices. A…

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September 3, 2024

Cyanoacrylate

Mastering Cyanoacrylate Cure Time Variability

A cyanoacrylate joint that sets in five seconds on a humid morning can take a minute on a dry winter afternoon. On a production line, that swing turns into inconsistent fixture times, parts moved before they are ready, and rework. Cyanoacrylate cure speed is not a fixed property; it responds to conditions on the floor. Controlling those conditions is what makes the process repeatable. What Drives Cure Speed Cyanoacrylate cures by anionic polymerization initiated by surface moisture and weak bases. Anything that changes the amount of initiator, the diffusion path, or the reaction rate changes cure time. Relative humidity. More ambient moisture means faster initiation. Below roughly 40 percent RH, cure slows noticeably; above 70 percent it accelerates and working time drops. Temperature. Higher part and ambient temperature speed the reaction, within limits. Cold parts pulled from storage cure slowly until they warm. Surface chemistry. Slightly alkaline surfaces (bare steel, many ceramics) speed cure. Acidic surfaces (some woods, certain treated metals, acid-stabilized coatings) slow or stall it. Bond gap and volume. Thin films between close-fitting parts cure fast. As the gap grows, the center is starved of surface moisture and cure time climbs sharply. Large fillets and puddles can stay uncured in the middle indefinitely. Substrate porosity. Porous surfaces absorb adhesive and can either speed skinning or starve the joint, depending on the material. Symptoms of Poor Cure-Time Control Fixture times that vary by shift or season Parts that shift after being released because the bond was not fully developed Blooming and frosting when working time is longer than expected and vapor spreads Bond strength that drifts lot to lot despite no change in adhesive Strategies for Consistency Stabilize the environment. Hold the bonding area in a controlled band, for example 21–24°C and 45–55 percent RH. This single step removes most seasonal variation. Condition the parts. Bring substrates to room temperature before bonding. Do not bond parts straight from a cold store or a hot process. Standardize the deposit. Use a metered dispenser so every joint gets the same volume, and design fitted joints so the gap is thin and repeatable. Use an activator or accelerator when you need speed or gap cure. Spray or wipe the accelerator on one surface, let the carrier solvent flash, then assemble. This gives fast, consistent cure on large gaps, porous surfaces, and acidic substrates, at the cost of some ultimate strength if over-applied. Use a surface-insensitive or slow grade when you need working time. For complex assemblies that take time to position, a longer-setting grade prevents premature lock-up. Monitor. Run a periodic set-time check on a standard coupon under line conditions and chart it. A drifting number flags a humidity, temperature, or material-lot problem before it reaches product. When Another Chemistry Fits Better If the assembly needs a guaranteed cure-on-demand rather than a condition-dependent set, a light-cure adhesive removes the variability entirely: it does not cure until the lamp triggers it, and the dose is measurable. The trade-offs are covered in UV glue…

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August 31, 2024

Cyanoacrylate

Cyanoacrylate and Material Degradation: A Closer Look

Cyanoacrylate is prized for bonding in seconds, but that speed comes from a reactive chemistry that does not always leave the surrounding material untouched. On the wrong substrate, cyanoacrylate can embrittle a plastic, soften a rubber, discolor a surface, or accelerate corrosion on a metal. Knowing which materials are at risk, and how to protect them, prevents a bond that succeeds while the part around it fails. How Cyanoacrylate Attacks Materials Three mechanisms account for most degradation: Chemical interaction with the polymer. Cyanoacrylate monomer and its acidic stabilizers can react with or plasticize certain polymers. In plastics that already contain mobile plasticizers, the adhesive can draw them to the surface or disrupt the polymer network, leaving the region near the bond brittle or crazed. Exothermic cure heat. Polymerization releases heat. In a thick deposit or a confined joint, the local temperature rise can be enough to soften a thermoplastic, relieve molded-in stress, or trigger crazing in a stressed part. Acidic byproducts and moisture at a metal interface. On some metal alloys, the acidic cure environment combined with trapped moisture accelerates localized corrosion under the bond line, which shows up later as a weakening interface or visible staining. Materials Most at Risk Plasticized PVC and other filled or plasticized plastics: softening, embrittlement, or surface crazing near the joint. Polycarbonate and acrylic under stress: environmental stress cracking, especially where the part carries molded-in or assembly stress. Natural and synthetic rubbers: hardening or loss of elasticity in the affected zone. Sensitive metal alloys: accelerated corrosion under humid conditions with prolonged exposure. Painted and coated surfaces: discoloration or lifting of the coating. Preventing Degradation Run compatibility tests first. Bond a representative sample, age it under the real service conditions, then inspect the material next to the joint, not just the bond strength. Minimize contact area and volume. Use the smallest deposit that makes the joint. Less monomer means less chemical interaction and less exothermic heat. Control the exotherm. Avoid thick sections. If a gap must be filled, build it up in thin passes or use a gap-filling grade formulated for lower reactivity. Choose a low-acid or surface-insensitive grade for coated and sensitive surfaces. Apply a barrier where necessary: a thin compatible primer or coating between the cyanoacrylate and a vulnerable substrate. Use an accelerator carefully. Accelerators speed cure but can raise the local exotherm; test the combination. When to Switch Chemistries If the substrate is inherently sensitive, or the joint needs a thick bond line, a wide temperature range, or long-term load in peel, another adhesive is usually the safer choice. A light-cure acrylate cures without a strong exotherm and without solvent attack; a two-part epoxy cures slowly and gently. The trade-offs are laid out in UV glue versus epoxy for quick repairs and UV glue versus epoxy for heavy-duty repairs. For joints that also see elevated temperature in service, Incure's Heat-Resist™ cyanoacrylate grades hold strength where standard grades soften. The Role of Stress Material degradation and mechanical stress compound each other. A part…

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August 30, 2024

Cyanoacrylate

Cyanoacrylate Adhesion Failures: Understanding Material Compatibility Issues

Cyanoacrylate bonds in seconds, which makes it easy to reach for and easy to misapply. When a cyanoacrylate joint fails, the cause is usually not the adhesive itself but a mismatch between the adhesive and the surfaces it was asked to bond. Understanding which materials cooperate with cyanoacrylate, and which fight it, is the difference between a reliable process and intermittent field returns. How Cyanoacrylate Cures, and Why That Matters Cyanoacrylate polymerizes through anionic initiation, triggered by trace surface moisture and weak bases. A thin film between two close-fitting, slightly humid surfaces cures almost instantly. That same mechanism explains most compatibility problems: acidic surfaces slow or stop the cure, very dry surfaces starve it, and thick gaps leave the center uncured. The ideal cyanoacrylate joint is a thin bond line between clean, non-porous, chemically neutral surfaces. Common Material Compatibility Problems Polyolefins and other low-energy plastics. Polyethylene, polypropylene, PTFE, acetal, and silicone rubber have surface energies below what cyanoacrylate can wet. Without treatment, the adhesive beads up and the joint peels cleanly. A dedicated polyolefin primer, or plasma or corona treatment, raises the surface energy enough to bond. Metals. Cyanoacrylate generally bonds bare metal well, but oxide layers, passivation, chromate conversion coatings, and residual drawing lubricant interfere. Acidic oxide films on some aluminum and copper alloys can also inhibit cure at the interface, producing a bond that looks set but has no interfacial strength. Rubbers and elastomers. EPDM, natural rubber, and nitrile bond acceptably; the issue is usually the mismatch in stiffness. A rigid cyanoacrylate bond line on a flexing rubber part concentrates peel stress at the edge and fails progressively. Porous materials. Wood, leather, paper, and unglazed ceramic wick the liquid adhesive away from the joint before it can cure, starving the bond line. A gel grade or a two-application technique helps. Acidic or coated surfaces. Some paints, inks, and acid-stabilized coatings slow the cure. Test on the actual production surface, not a bare coupon. Failure Signatures and What They Tell You Clean interfacial separation, no adhesive transfer: surface energy or contamination problem. Fix with treatment or cleaning. Adhesive stays soft in the center: gap too large, or the joint is starved of the moisture that initiates cure. Reduce the gap or use an accelerator. Bond fine, then fails after weeks: often plasticizer migration from a flexible plastic, or moisture and thermal cycling working on a stress concentration. This is where a joint that passed initial pull testing still comes back from the field. Bloom or frosting near the joint: cyanoacrylate vapor condensing and curing on the surface. Improve ventilation or use a low-bloom grade. Preventing Adhesion Failures Prepare the surface. Degrease with isopropyl alcohol, remove oxide and release films, and treat low-energy plastics. Use a primer or activator where the substrate needs it, and let solvent flash off before bonding. Control the gap. Cyanoacrylate is a thin-film adhesive. Design fitted joints, or switch to a gap-filling grade or a different chemistry for loose tolerances. Match stiffness to the joint.…

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August 29, 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

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