Adhesives

Start here: ten words every newcomer needs

Overheard on the job

Real-sounding lines from the floor, translated into plain English.

• Bead came off clean as a whistle, that's adhesive failure, not cohesive, somebody skipped the IPA wipe.

  TranslationThe adhesive separated from the surface without leaving residue, which points to contamination from a missed cleaning step rather than a weak adhesive.

• Mixed a quart and it kicked in the cup before half of it was out, pot life's gone in this heat.

  TranslationThe two-part adhesive gelled in the mixing container because the large, warm batch generated heat and sped up the cure.

• Open time on the MMA is eight minutes, fixture time twenty, so don't pull the clamps at fifteen.

  TranslationThe structural acrylic must be closed within eight minutes of application and needs twenty minutes before the assembly can be unclamped.

• PP housing reads 30 on the dyne pens, plasma it to 50 or it'll pop off like the last lot.

  TranslationThe polypropylene part has too low a surface energy for the adhesive to wet, so it needs plasma treatment or the bonded parts will separate cleanly again.

• Squeeze-out is still gummy and marbled, that cartridge went off-ratio, purge it and change the mixer.

  TranslationThe excess adhesive has not cured and shows streaks of unmixed components, so the dispense was out of proportion and the mixing nozzle and first material need replacing.

• Tape passed peel but failed static shear at 70, it'll creep right off that heater cover.

  TranslationThe tape grips well when peeled at room temperature but cannot hold a sustained load when hot, so the part will slowly slide off in service.

• Lap shear looks great but ultrasound can't see a kissing bond, so we bond witness coupons every shift.

  TranslationGood test strength and clean inspection results do not rule out contact without adhesion, so the process is proven with test specimens made alongside production.

The main adhesive families, what each bonds well and the names insiders use for them.

• Anaerobic adhesivealso anaerobic, anaerobic sealant
  A one-part liquid that stays fluid in air but cures when sealed between metal surfaces away from oxygen.
• Bluealso blue threadlocker, medium-strength threadlocker
  Shop shorthand for medium-strength threadlocker, the removable kind; red means the permanent kind. Shop talk
• Contact cementalso contact adhesive, contact bond
  An adhesive applied to both surfaces and left to dry before they are pressed together for an instant bond.
• Cyanoacrylatealso CA, instant adhesive
  A one-part instant adhesive that cures in seconds when trace moisture on a surface triggers it.
• Epoxyalso epoxy adhesive, structural epoxy
  A thermoset adhesive cured by reacting epoxy resin with a hardener, the benchmark for strong, rigid structural bonds.
• Film adhesivealso adhesive film, film
  A thin sheet of partly reacted epoxy on a carrier, laid into joints and cured with heat and pressure.
• Five-minute epoxyalso 5-minute epoxy, quick-set epoxy
  A fast two-part epoxy that gels in about five minutes, the bench-repair go-to for quick fixes. Shop talk
• Gluealso adhesive
  The everyday word for any adhesive, used freely on the floor but avoided in engineering drawings. Shop talk
• Hot gluealso hot-melt glue
  Floor and craft name for hot melt adhesive, especially sticks fed through a handheld gun. Shop talk
• Hot meltalso hot-melt adhesive, HMA
  A solid thermoplastic adhesive melted in a tank or gun, dispensed hot and set within seconds as it cools.
• MMAalso methyl methacrylate, methacrylate
  Methyl methacrylate, the monomer behind most structural acrylic adhesives and the shorthand name for them.
• MS polymeralso SMP, silane-modified polymer
  A silane-modified polymer that moisture-cures into a flexible, paintable, isocyanate-free adhesive-sealant.
• Polyurethane adhesivealso urethane, PU adhesive
  An adhesive based on isocyanate chemistry that cures into a tough, somewhat flexible bond.
• PURalso reactive hot melt, RHM
  Polyurethane reactive hot melt, applied molten like a hot melt, then moisture-cured into a heat-resistant bond.
• PVAalso polyvinyl acetate, white glue
  Polyvinyl acetate emulsion, the white or yellow wood glue that sets as its water soaks into the wood.
• RTValso RTV silicone, silicone
  Room-temperature vulcanizing silicone, a rubbery adhesive-sealant that cures without heat, usually from air moisture.
• Solvent weldingalso solvent bonding, solvent cementing
  Joining plastics by softening their surfaces with a solvent cement so the two parts fuse into one.
• Structural acrylicalso acrylic adhesive, methacrylate adhesive
  A fast-curing two-part methacrylate adhesive that bonds metals, plastics and composites with little surface prep.
• Super gluealso CA, crazy glue
  Everyday name for cyanoacrylate instant adhesive, used on the floor for any CA grade. Shop talk
• Threadlockeralso thread locker, thread-locking compound
  An anaerobic adhesive applied to fastener threads to stop them loosening from vibration.
• Toughenedalso rubber-toughened, impact-modified
  Describing an adhesive modified with rubber or soft particles so the bond resists cracking, peel and impact.
• UV-cure adhesivealso light-cure adhesive, UV adhesive
  An adhesive that cures in seconds when exposed to ultraviolet or visible light of the right wavelength.

How adhesives harden and the time windows that govern mixing, assembly, handling and full strength.

• Activatoralso accelerator, kicker
  A liquid applied to one surface to speed or start the cure of an adhesive placed on the other.
• Blushalso amine blush, blushing
  A waxy or greasy film on curing epoxy where amine hardener has reacted with moisture and carbon dioxide.
• Curealso curing
  The chemical reaction or physical change that turns a liquid adhesive into a solid that carries load.
• Exothermalso exothermic reaction, exothermic heat
  The heat released by a curing adhesive, which speeds the reaction and can overheat thick masses.
• Fixture timealso handling time, clamp time
  The time until a bond is strong enough to handle or unclamp the assembly without moving the parts.
• Grabalso initial grab, hold
  Floor word for how quickly and firmly an adhesive takes hold when parts are pressed together. Shop talk
• Green strengthalso initial strength, wet grab
  The hold a bonded joint has in its first seconds or minutes, long before the adhesive reaches full cure.
• Gummyalso undercured, soft
  Describing an adhesive that stayed soft and rubbery instead of curing hard. Shop talk
• Kickalso kick off, kicked off
  To gel or cure suddenly, as in a resin kicking in the cup or a CA kicking with accelerator. Shop talk
• Mix ratioalso ratio, mixing ratio
  The proportion of resin to hardener in a two-part adhesive, given by volume or by weight.
• Moisture curealso moisture-curing
  A cure triggered by humidity in the air or on the parts, used by silicones, urethanes and silane polymers.
• Open timealso open assembly time
  The longest gap allowed between applying adhesive and closing the joint while it can still wet the second part.
• Oxygen inhibitionalso air inhibition
  Air at the surface blocking the cure of free-radical adhesives, leaving them sticky where exposed.
• Post-curealso postcure, post-bake
  Extra time at elevated temperature after the first cure, which finishes crosslinking and raises Tg and heat resistance.
• Pot lifealso working life, work life
  How long a mixed batch of two-part adhesive stays usable before it thickens too much to apply.
• Set upalso set, setting up
  To thicken and start to hold, the point where an adhesive stops being workable. Shop talk
• Tgalso glass transition, glass transition temperature
  Glass transition temperature, above which a cured adhesive turns from hard and glassy to soft and rubbery.
• Two-partalso 2K, two-component
  Describing an adhesive supplied as a resin and a hardener that start curing only once mixed.

Surface energy, wetting, treatments, primers and cleaning steps that decide whether an adhesive can stick.

• Adherendalso substrate
  Each of the parts in a bonded joint; the surface the adhesive has to grip.
• Adhesion promoteralso coupling agent, silane primer
  A chemical, often a silane, that links an adhesive to a surface by bonding to both.
• Corona treatmentalso corona, corona discharge
  High-voltage electrical discharge across a film or sheet to raise its surface energy for bonding or printing.
• Dyne penalso dyne marker, dyne ink
  A marker filled with test fluid of known surface tension, used to check a surface's treatment level. Shop talk
• IPA wipealso alcohol wipe, IPA clean
  Cleaning a bonding surface with isopropyl alcohol on a lint-free wipe just before adhesive goes on. Shop talk
• LSEalso low surface energy, LSE plastic
  Low surface energy, describing plastics and coatings that most adhesives cannot wet or bond without help.
• Mechanical interlockalso mechanical adhesion, mechanical keying
  Adhesion gained by adhesive flowing into pores and roughness and locking in once it hardens.
• Peel plyalso tear ply, peel cloth
  A fabric layer cured onto a composite surface and torn off just before bonding to expose a clean, textured face.
• Plasma treatmentalso plasma, atmospheric plasma
  Exposing a surface to ionized gas to clean it and add reactive groups that raise its surface energy.
• Plasticizer migrationalso plasticizer bleed
  Softening agents moving out of flexible plastics into an adhesive layer and weakening it over time.
• Primeralso bonding primer, surface primer
  A thin first coat wiped or sprayed onto a bonding surface so the adhesive grips better or the fresh prep stays clean.
• Scuffalso scuff sand, abrade
  To roughen a bonding surface lightly with an abrasive pad or paper to remove gloss and contamination. Shop talk
• Surface energyalso surface free energy, dyne level
  A measure of how strongly a solid surface attracts liquids, which decides whether an adhesive can wet it.
• Wettingalso wet-out, spreading
  How well a liquid adhesive spreads over and makes intimate contact with a surface.

Joint geometries, bondline control and the stresses that make bonded joints succeed or fail.

• Bondlinealso glue line, bond line
  The layer of adhesive between two bonded parts, and in shop talk the thickness of that layer.
• Butt jointalso end-to-end joint
  A joint where two parts are bonded end to end, with only the small end area carrying the load.
• CTE mismatchalso thermal mismatch, differential expansion
  Coefficient of thermal expansion mismatch, the different growth of bonded materials with heat that stresses the bond.
• Filletalso adhesive fillet, spew fillet
  The bead of adhesive left around the edge of a joint, which smooths stress at the ends of the bond.
• Gap fillingalso gap fill, gap-filling ability
  The ability of an adhesive to bond parts with a loose or uneven fit and still cure fully across the gap.
• Lap jointalso single lap, overlap joint
  A bonded joint where two parts overlap face to face, loading the adhesive mainly in shear.
• Peel stressalso peel loading
  Tension pulling one adherend away from the other at the edge of a bond, concentrated along a thin line.
• Scarf jointalso scarf, scarf repair
  A joint where both parts are tapered to long matching slopes and bonded along the taper.
• Spacer beadsalso glass beads, bondline control beads
  Small glass or plastic spheres mixed into an adhesive to hold a set bondline thickness under clamp pressure.
• Squeeze-outalso squeeze out, ooze-out
  The excess adhesive that oozes out along the joint edges at clamp-up, read as proof the joint is full.
• Starved jointalso starved bond, dry joint
  A joint left short of adhesive, with bare patches or voids where the glue soaked in, squeezed out or never reached.

Strength tests, specimens and the failure modes read from a broken bond.

• Adhesive failurealso interfacial failure, AF
  A break at the interface between adhesive and part, leaving one surface clean or nearly clean.
• Cleavagealso cleavage strength, cleavage loading
  Loading that pries a rigid joint open from one end, concentrating stress along the leading edge of the bond.
• Cohesive failurealso cohesion failure, CF
  A break that runs through the adhesive itself, leaving adhesive on both parts.
• Couponalso test coupon, witness coupon
  A small standard test piece, usually a metal or plastic strip, bonded to check adhesive strength or prep. Shop talk
• Creepalso creep deformation
  Slow, continuing deformation of an adhesive under a constant load, which can end in failure over time.
• Dog bonealso dogbone, tensile bar
  A cast or cut tensile specimen with wide ends and a narrow middle, used to test bulk adhesive properties. Shop talk
• Fiber tearalso fibre tear, percent fiber tear
  Paper or wood fibers torn out and stuck to the adhesive when a bond is pulled apart, showing the bond beat the substrate.
• Kissing bondalso zero-volume disbond
  A bond where adhesive and part are in full contact but have little or no real adhesion.
• Lap shearalso lap shear strength, single lap shear
  The standard strength test for adhesives, pulling apart a single overlap joint and reporting load over bond area.
• Peelalso peel strength, peel adhesion
  The force needed to strip a flexible bonded layer off a surface, given per unit width.
• Pop-offalso popped off clean
  A part that lets go with a snap, leaving the adhesive cleanly on one side and nothing on the other. Shop talk
• Substrate failurealso adherend failure, material failure
  A joint failure where the bonded material itself breaks before the adhesive or the interface gives.
• T-peelalso T-peel test
  A peel test where two flexible strips bonded face to face are pulled apart in a T shape.
• Tackalso quick stick, initial tack
  The stickiness of an adhesive surface: how quickly it grabs another surface with light pressure and short contact.
• Zipperingalso zipper, unzipping
  A bond peeling open fast and continuously once it starts, like a zipper running down. Shop talk

Pressure-sensitive adhesives, tape construction and the properties that make tapes and labels hold.

• Aggressivealso high-tack, grabby
  Describing a tape or adhesive with high tack and strong immediate grab that is hard to reposition. Shop talk
• Carrieralso backing, core
  The film, foam, paper or fabric layer inside a tape that the adhesive is coated onto.
• Cold flow
  Slow flow of a soft adhesive at room temperature under its own weight or light pressure.
• Dwellalso dwell time, build-up time
  The time a pressure-sensitive bond sits after application while it builds toward full strength.
• Edge oozealso ooze, oozing
  Adhesive squeezing out from the sides of a tape roll or die-cut part, making edges sticky and dirty. Shop talk
• Flaggingalso flag
  The end of a tape or label lifting off a curved surface and standing up like a small flag.
• Foam tapealso double-sided foam tape, mounting tape
  Double-sided tape with a foam core, used to mount and bond parts with gaps, vibration or thermal movement.
• Peel-and-stickalso self-adhesive, pre-applied adhesive
  Describing any product with a ready-coated pressure-sensitive adhesive under a liner that goes on without tools. Shop talk
• PSAalso pressure-sensitive adhesive, pressure-sensitive
  Pressure-sensitive adhesive, the always-tacky layer on tapes and labels that bonds under finger pressure with no cure step.
• Release lineralso liner, backing paper
  The silicone-coated paper or film that protects a tape or label adhesive until it is peeled off for use.
• Static shearalso shear holding power, holding power
  A tape test that hangs a weight from a bonded strip and records how long it holds before sliding off.
• Tackifieralso tackifying resin
  A resin added to rubber or acrylic adhesives to raise their tack and peel.
• Transfer tapealso adhesive transfer tape, ATT
  A layer of pressure-sensitive adhesive on a release liner with no carrier, which transfers entirely to the part.
• Wet-outalso wetout
  How fully a tape's adhesive has flowed into contact with a surface, often visible through clear parts.

Mixers, cartridges, metering equipment, bead application and the problems that show up on the line.

• Angel hairalso stringing, cobwebbing
  Fine threads of hot melt that string off the nozzle and drift across machines and products. Shop talk
• Beadalso glue bead, adhesive bead
  A continuous line of adhesive laid on a part, specified by its diameter or cross-section.
• Butteringalso butter, double spread
  Spreading adhesive on both mating surfaces rather than one, to ensure full wetting and coverage. Shop talk
• Charalso charring
  Dark, degraded hot melt that builds up in tanks and hoses from long time at temperature. Shop talk
• Dual cartridgealso twin cartridge, dual-barrel cartridge
  A twin-barrel package that holds both parts of an adhesive and pushes them through a static mixer in fixed ratio.
• Glue-upalso glueup, clamp-up
  The stage of assembly where all parts get adhesive and are clamped together, or the clamped assembly itself. Shop talk
• Marblingalso streaking, swirling
  Swirls and streaks of separate colors in a two-part adhesive that show it has not mixed thoroughly. Shop talk
• Meter-mixalso meter-mix-dispense, MMD
  Dispensing equipment that pumps two adhesive components from bulk containers in a set ratio and mixes them on demand.
• Off-ratioalso out of ratio, bad ratio
  Describing a two-part adhesive dispensed with the wrong proportion of resin to hardener. Shop talk
• Purgealso purge shot, waste shot
  To run adhesive through a mixer or dispense valve and discard it, clearing old, unmixed or off-ratio material. Shop talk
• Sagalso slump, sagging
  An adhesive bead slumping or running down a vertical or overhead surface before it sets.
• Shelf lifealso storage life, expiry
  The use-by window for a sealed container of adhesive, tied to the storage conditions on the label.
• Static mixeralso mixing nozzle, mix tip
  A disposable nozzle full of fixed baffles that mixes two adhesive components as they are pushed through.
• Wickingalso wicking grade, penetrating grade
  Describing very thin adhesives that run into already assembled joints by capillary action.

Frequently asked questions

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