Glossary of Terms
The following list of technical terms will help in understanding the adhesive bonding process.
Adhesion: The state of two surfaces held together by interfacial forces, to be stuck or clinging together.
Adhesive: A substance that holds or bonds together two surfaces by mechanical or chemical forces.
Ambient Temperature: The temperature surrounding or in the room where an object rests.
Bleed-Through: The migration of an adhesive through a surface so that it becomes visible.
Bond: The attachment of an adhesive to a surface or surfaces.
Bond Strength: The force or load that can be applied to a bonded joint before it will fail or break.
Catalyst: A substance added in small amounts to an adhesive to speed up the cure time.
Cement: Another word for adhesive.
Cohesion: The state in which the particles of the adhesive are held together.
Cohesive Failure: A term used to describe bond failure within the glue line without failure of either bonded surface.
Cold Flow: Dimensional change of a material under load at room temperature. Also known as Creep.
Contact Adhesive: An adhesive which when coated on two surfaces for bonding and dried will adhere only to itself. May be solvent or waterborne.
Coverage: The amount of adhesive required to cover a specific square foot area for proper bonding.
Crazing: The creation of fine cracks or dull haze in substrates caused by solvent or adhesive compounds attacking a surface. The effect may also appear in the adhesive.
Creep: A change in size of a material under load. Movement at room temperature is often called creep.
Cross Linking: The union of two large molecules by means of chemical reaction resulting in a random network of molecules which no longer have mobility.
Cure: The change in physical property of an adhesive caused by a chemical reaction which may be by condensation, polymerization or vulcanization. This is usually produced by the action of heat and a catalyst alone or in combination with or without pressure. In common terms, it is the process in which an adhesive dries or changes to bond two substrates together.
Cure Temperature: Ideal temperature for maximum cure to take place for a specific adhesive.
Delamination: The separation of layers of a laminate to failure within the adhesive itself or the bond between the adhesive and the substrate.
Dry: The change in state of an adhesive by loss of evaporation, absorption or both.
Elastomer: A material which, at room temperature, can be stretched repeatedly beyond its original size and when released return to its former size. (Rubber)
Emulsion: A suspension of particles of liquid or solid in a normally incompatible liquid.
Fatigue: The internal weakening of a dried or cured adhesive resulting from constant static or dynamic force acting on it.
Flash Point: The temperature at which the vapors of an adhesive or other chemical will ignite when exposed to an open flame.
Full strength or full cure: The time an adhesive takes to build up to its full, final strength. Remember with all these terms, figures quoted on technical datasheets will vary depending on temperature, gap and surface reactivity, so exercise caution with these figures.
Green Strength: The amount of strength in an adhesive before achieving full curing or drying.
Handling Time: After the adhesive has been applied and the joint assembled and clamped, the handling time is the point at which the clamps can be removed and the joint is strong enough to hold itself in position. The bond strength after the handling time is often understood as approximately 100 psi.
Hardener: Added to an adhesive to promote or control curing. See Catalyst.
Latex: A very fine particle size emulsion.
Non-Structural Bond: A bond that is required to bear little or no load other than to hold two parts together.
Open time: The time between the application of an adhesive to a surface and assembly of the two parts.
Pot life: The period of time during which an adhesive may be used satisfactorily after being mixed or exposed to drying air (also known as Working time or Work time).
Shelf life: (Same as storage life) The period in which an adhesive may be stored in its original, unopened container at a specific temperature and still be usable.
Substrate: The material surface to which an adhesive is to be spread for bonding.
Tack: The stickiness or ability of an adhesive to cling to an object.
Thermoplastic: A material that will repeatedly soften when heated and harden when cooled.
Thermoset: A material that after being exposed to heat will remain in a fixed or infusible state.
Thixotropic: A property in which a chemical's viscosity will lessen after being agitated such as in stirring or pumping.
Viscosity: The thickness or heaviness of a liquid and its resistance to flow, such as the difference between a 10 weight oil and a 40 weight oil.
Wetting: The ability of an adhesive to adhere to a surface immediately upon contact.
Working Time: See “Pot life”
Useful Adhesives Info
Information on Adhesive Technology
- Definition of Adhesives
- Types of Adhesion
- Adhesive Advantages
- Adhesive Disadvantages
- Adhesive Technology
- General information on using adhesives
- Understanding joints and stress
- Adhesive selection guide
- Adhesive characteristics
- Hot Melts
- Epoxy Adhesives
- Urethane Adhesives
- Acrylic Adhesives
- Emulsion Adhesives (white glues)
- Contact Adhesives
- Anaerobic Adhesives
- UV Cure Adhesives
- Ceramic Adhesives
- Special Adhesives
Definition of Adhesives
Any substance, inorganic or organic, natural or synthetic, that is capable of bonding two objects together by surface attachment or adhesion.
Types of Adhesion
Mechanical - Results when one surface is roughened and offers something for the adhesive to grab mechanically.
Chemical - Reaction or attraction of the molecular forces between the adhesive and the surfaces to be bonded.
- Ability to bond different materials to each other.
- Attach thin and small parts with ease.
- Equal distribution of stress not possible with screws.
- High environmental resistance- heat, cold and the elements.
- Non-electrically conductive
- Fast, easy assembly
- Reduced cost
- Acts as a sealant and moisture barrier.
- Many adhesives require extended curing times to reach full bond strength.
- Bonded components cannot be easily disassembled.
- Parts may require design change for adhesive application.
- Parts must mate well and provide bond area.
- Adhesive may be attacked by some chemicals.
- Most adhesives are limited to temperatures below 400°F
Adhesives have become an important part of modern industry. From the tiles on the Space Shuttle to bonding parts on many home appliances, they encompass every area of our lives. Having some knowledge of what adhesives are and how to properly use them will be an asset to the technician as well as any handy person.
Adhesive Dispensing Systems
Manual Application Methods Brush - Available in various sizes, a brush offers the simplest method of applying adhesive when limited control is required.
Trowel - Specially designed for spreading adhesives evenly on broad surfaces.
Rollers - (paint type) For fast application of adhesive on large areas.
Squeeze Bottles - (with nozzles) For limited application of small amounts of adhesive.
Cartridge Guns - (air/manual) For applying a bead of single part adhesives.
Dual Pack Cartridges - These Deliver two part adhesives through a static mixing nozzle and eliminate the need to hand mix and the problem of achieving proper mix ratios.
Syringes - (air/manual) For applying small amounts of low viscosity adhesives.
Valves - (auto/manual) Available with nozzles for multiple heads and tips for special applications.
Spray Valves - For fast coating of large areas with sprayable adhesive. The applicator to use will depend on the type of adhesive, the amount to be applied, the area to cover, the difficulty of application and production requirements.
Automatic and Semi-Automatic Systems - Automatic adhesive dispensing systems are used when precise control of the amount and placement of adhesive is required. Fully automatic systems are completely "hands off" operations and range from simple trigger mechanical control to complex electronic and computerized robotic systems. Semi-automatic systems indicate some manual function involved in the cycle of operation.
Semi-Automatic Systems - These offer a considerable increase in efficiency at moderate cost over manual systems. Manual actuation involves foot pedal or push button control of application cycle.
Manual placement - Nozzle or substrate manipulated for application of the adhesive.
Fully automatic systems - Though expensive, these provide precise control of all operations thereby reducing labor costs, improving quality control, and reducing waste.
Actuation - This involves an adhesive application that automatically dispenses the correct amount, in timed intervals, at the right location.
Placement - The substrate is automatically positioned for proper placement of adhesive.
Adhesive Dispensing Equipment Micro Air Dispensing - Electro-Pneumatic controllers for dispensing solder masks, sealants, lubricants, epoxies, cyanos, or solvents. These units are used for precision application of small amounts of product usually through syringes.
Pressure Tanks - When moderate quantities and pressures are needed in a dispensing system, pressure tanks are ideal. These are available in steel and stainless steel, and in one gallon or larger sizes.
Air Powered Reciprocating Pumps - These pumps are required when high pressure and volume are needed to supply large production adhesive systems. Pumps are available in stainless steel for long service life.
Dispensing Nozzles - Nozzles or tips provide for precise application of an adhesive. Beading, roller, spray, cleat and needle are a few of the standard nozzles. Custom tips can be designed to meet special applications.
Manual and Air Powered Guns - Compact, lightweight, air powered or manual guns for field applications are available for one or two component materials. Most guns are adaptable to various size cartridges.
Diaphragm Pumps - Stainless steel diaphragm pumps are high volume, self priming material suppliers for any fluid system. A well designed pump will provide stall free, low maintenance operation for adhesive systems
Meter & Mix Systems - Complete systems designed to automatically dispense one, two or more component materials.
Automatic Dispensing Valves - These valves are the heart of any automatic adhesive system, providing the precision metering necessary for most operations.
Control Systems - Electronic and pneumatic control systems including logic packages, timers, sensors, limit switches and actuators provide for the ultimate in design for any production need.
General information on using adhesives
What can be bonded?
Nearly every material, natural or synthetic, may be bonded with adhesives. What adhesive to use for the best bond is directly related to the material. Some materials bond easily and others require special preparation to achieve a good bond.
Points to consider when selecting an adhesive
- Substrate Materials Are they the same or different, porous or nonporous, rigid or flexible, plastic or metal?
- Joint Design - Join design is based on the type of stress the joint must be resistant. Types of joints are covered later in this section.
- Gap Filling - This is required when mating poorly fitting parts.
- Environment The temperature, moisture, and chemical and shock resistance must be evaluated.
- Handling Bond The time for the adhesive to "set" or hold the assembly together must be considered.
- Cure Time The importance of the period of time required for the adhesive to reach its full strength.
- Appearance The color or clarity of the adhesive may affect the appearance of the product.
- Cost The quantity of adhesive, its packaging, shelf life and method of dispensing affect cost.
- Preparation Is it a one or two part adhesive? If it is a two part adhesive, how difficult and critical is the mix ratio?
- Dispense Method - This is relative to the adhesive used and the area to be covered. It may be manual, semi or fully automatic. The selection of an adhesive for your application can be a complex matter of meeting many needs. Therefore, it is advisable to consult the manufacturer or adhesive distributor for technical guidance.
Points to consider when using adhesives
- Storage Life Adhesives do not last forever, therefore, do not buy in quantities greater than needed. The storage life of some adhesives may be extended by refrigeration at 40ºF. Do not freeze. Storage life ranges from six months to a year unopened.
- Preparation - Other than selecting the proper adhesive, preparing the resources substrate for bonding is of great importance. Surface contamination is the frequent cause of bond failure. When possible, clean the surfaces with a solvent or cleaner that will not leave a residue of any kind. Be sure the surface is dry. Roughen the surface to help the adhesive grab the material and wipe away any loose particles. Some materials require the application of a primer to improve bondability. The temperature limits of most adhesives falls between - 40ºF and 400ºF. However, it is important to check each adhesive for its specific temperature range. There are special ceramic adhesives available for ultra high temperature applications to 4000ºF. The ideal temperature for using an adhesive is 70ºF. The lowest recommended temperature for using an adhesive is 55ºF. In general, raising the temperature of many adhesives will shorten their working life. Keep in mind that the working time given by the manufacturer is normally 70ºF and a summer time temperature of 95ºF may reduce the open, set, and cure times of the adhesive.
- Electrical Conductability - Most adhesives are good insulators, however, there are some available that are made into conductors for special applications by the use of silver fillers. The chemical and environmental resistance of most adhesives is very good. One of the most common elements that an adhesive must resist is moisture, in the form of humidity and water. Check with the manufacturer for this kind of resistance. The adhesive industry does not usually give a chemical resistance chart for its adhesives, but each user must do his/her own testing to arrive at the suitability of an adhesive for each application. How adhesives cure should be understood by the user. In two part adhesives a chemical cure is created by mixing the resin with the hardener or accelerator. With single part moisture cure adhesives react to surface moisture or the humidity of the surrounding air. Other solvent or water based adhesives cure with evaporation. Anaerobic adhesives cure in the absence of air. Actural full cure is a chemical process that varies with each type of adhesive. Setting, or the initial grabbing of the adhesive, is only the beginning of the curing process and the assembly should not be subjected to stress or test until the time of full cure has passed.
Understanding joints and stress
The simple lap joint: On loading, the adhesive and the adherent react to the applied forces. There is a shear force along the plane of the joint and a peel force at right angles to it. These stresses are at a maximum at the edges of the bond where they cause high levels of strain and twisting as illustrated in the drawing.
Basic bonded joints between sheet metal. In practical structures two or more basic types may be used in combination, and the relative dimensions of the joints may vary from those shown.
Adhesive selection guide
A= strongest bonds
B= Good bonds - with limitations
C= Non-structural bonds
D= Poor bonds - not recommended
@= Special treatment required * Includes UV adhesives
Acrylics - Fast, strongest bonds on metals and plastics
Anaerobics- Metal sealing and locking
Contact- Quick grab, non-structural bonds
Cyanoacrylates- Speed & Strength with limitations
Emulsion- Strong bonds on porous substrates
Epoxies- Strong bonds on most substrates
Hot melts - Fast, non-structural bonds on most materials
Sealants- Flexible joint sealing
Urethanes- Strength with flexibility
Hot Melts are 100% solid thermoplastic adhesives. They liquefy by being heated and bond after being applied to the substrate; they then cool and re-solidify. Hot melts are available in a number of formulations for specific applications. They are not recommended for high strength or high temperature applications.
Using Hot Melt adhesives
Unlike most other adhesives, which when activated cannot be reused, hot melts being made of thermoplastic polymers can be repeatedly heated and cooled without a significant chemical change.
Benefits of Hot Melts
- Low Cost - More economical to use than cold glue systems or tape, staples, nails or screws.
- Fast - High production speeds, no cure or dry cycles…
- Clean - No mixing and no clean up…
- Compact - 100% solid, provides for long shelf life and not affected by freezing…
- Sealing - Gap filling and caulking effect possible…
- Strong - Bonds dissimilar substrates and are stronger than the substrates themselves…
- Resilient - Flexible and can dampen vibrations…
- Versatile – They permit new manufacturing techniques not possible with cold glues, fasteners or solvent based adhesives…
- Safe - Less pollution and fire hazards than solvent based adhesives…
- Moisture resistant - Do not absorb moisture that will weaken bonds…
Disadvantages of Hot Melts
- Limited toughness and heat resistance…
- Lack of high structural strength…
- Subject to degradation and charring by overheating…
Hot melt application equipment
Manual hand operated guns are designed to meet the needs of the user. Light duty guns are economical for intermittent use in craft work, repairs and light assembly jobs. Medium duty guns provide the industrial user with a reliable adhesive tool. Heavy duty, high capacity production guns meet the needs of the manufacturer...
Reel-fed hot melt applicators provide hands free application of adhesive. There is no need to manually supply glue sticks to the gun. The applicator may be part of a semi or fully automatic system...
Bulk melt applicators are used when the amount of adhesive required exceeds the capacity of stick feed systems. A heated tank holds a large amount of melted adhesive, which is supplied to a manual or automatic gun by pumping through a heated hose.
The capacity of hot melt applicators is rated in pounds per hour of adhesive it can deliver. Light duty means four to five pounds per hour. Medium duty is eight to nine pounds per hour. Heavy duty bulk units deliver 10 to 15 pounds per hour.
Tips for using hot melts
- Clean surfaces if necessary and wipe plastics and metals with a solvent.
- Apply adhesive to only one bond surface.
- Hard, smooth surfaces are more resistant to bonding than rough porous surfaces.
- Mate surfaces quickly after applying adhesive.
- Use firm pressure and do not adjust substrates after contact is made.
- For best performance of metals, preheat surfaces to at least 95°C/ 200°F.
- Generally, a hot melt will achieve 50% of its full strength in one minute, 75% after one hour and 100% after 24 hours.
Hot Melt applications:
Bonding wood, cardboard, paper and any porous materials. Use for fabrics, vinyls and leather products. Hot melts may be used on most plastics with good results. Use hot melts when you need fast, clean, no mix bonding.
Cyanoacrylates were discovered by accident in the laboratory when parts containing it could not be separated. It is commonly known as "crazy glue." It is also known as the “instant adhesive” because of its ability to set and achieve a high level of bond strength quickly. Cyanoacrylates have been modified and improved for industrial usage and a broad selection is now available for many different applications. This adhesive has its limitations and commercial advertisements can be misleading.
Using Cyanoacrylate adhesives
To ensure a good and lasting bond, the surface must be clean and free from rust inhibitors, mold release agents, grease and oil. Bond strength on painted parts will be determined by how well the paint adheres to the substrates.
Optimum results with Cyanoacrylates are obtained with the minimum quantity of adhesive needed to fill the joint. In general, one free-falling drop spreads over one square inch. Apply firm hand pressure to mated surfaces until the adhesive sets. The thinner the bond line the quicker the set and stronger the bond.
Durability is affected by surface conditions, bond area, service temperature, environment and stress. Each application must be evaluated individually. Moisture and temperature resistance are dependent on the substrates bonded and the particular cyanoacrylate used. There are many different grades of this adhesive available, tailored for each special application.
When bonding dissimilar materials or when the surface contains an acidic residue, a slow or inhibited cure may result. This condition is most effectively corrected with the use of an accelerator.
Storage and shelf life
It is best to use cyanoacrylates from original containers and stored in a cool, dry location at a temperature below 80°F. The useful shelf life of the adhesive will be six months. This expected useful life may be extended by refrigeration storage at 40°F. Material in use should be stored at room temperature and the container should be tightly sealed at all times when not in use because this adhesive reacts to moisture in the air. When removing products from refrigeration, allow the adhesive to reach room temperature prior to opening the container. Do not refrigerate an adhesive that has been opened.
Cyanoacrylates adhesives have been used in various industries for many years and have an excellent safety record. Cyanoacrylates are non-toxic. The vapors can cause eye irritation in poorly ventilated areas or low humidity environments. Accidental skin bonding is best handled by passive, non-surgical first aid. Hot soapy water aids separation of skin tissue. Use a peeling, not pulling action to separate bonded tissue. In case of eye contact, the eye should be washed with copious quantities of water. When large quantities of cyanoacrylates are accidentally spilled, the area should be flooded with water, which will cause the liquid to cure. The material can then be scraped from the surface.
Note: The liquid adhesive should not be wiped up with rags or tissue. The fabric will cause polymerization and large quantities of the adhesive will generate heat on cure causing smoke and strong irritating vapors. Always flood the area with excess water to clean up spill conditions.
Cyanoacrylates do not act as void-filling adhesives and are limited to gaps under .020”, unless an accelerator is used. Strong bonds are initially formed on glass, ceramics and stone, but will often rapidly decrease in strength. Cyanoacrylates are not recommended for high moisture or submerged applications or situations requiring high shock resistance.
Eye irritant - bonds skin in seconds. Do not get adhesive on your skin or another part of your body, or that of others. In case of body contact, flush with water. Get medical attention for eye or internal contact. To avoid skin contact, use the applicator nozzle when provided. Wear gloves when possible. Use with adequate ventilation. KEEP AWAY FROM CHILDREN.
Epoxy is one of the most common general purpose, high strength adhesives that the average person will have reason to use. Most true epoxies are two part and are available in various viscosities or thicknesses to meet specific applications. This adhesive will give strong bonds on most materials with the proper preparation. Epoxy is ideal for metals, plastics, rubber, wood, glass and ceramics. Epoxy will fill the gaps between poorly fitting parts and can be sanded, cut and painted after curing.
General purpose two part epoxies generally require mixing in a 1:1 ratio or equal parts of both components. However, variation in temperature resistance and flexibility may require a different mix ratio. Check the manufacturer’s instructions. Carefully measure by weight or volume and mix well for the best performance of the adhesive. Do not mix more than can be used during the pot life of the adhesive. Do not use an adhesive that has begun to set.
Surfaces must be free from all contaminants such as soil, oil, grease, fingerprints, dust, and mold release agents. Wipe the surface with a solvent that will completely evaporate. Do not use a soap or other cleaner that will leave a film when dry. Roughen the surface when possible to increase bond strength. Special primers are available to improve the bonding of cured rubber.
Adhesive may be applied to one or both surfaces and use only enough to cover the surface and fill the gap as needed. Use a trowel or spreader for large surfaces. Assemble the parts in a way to avoid entrapped air. Some squeezing out of a little adhesive is a sign of proper assembly. Clamping is necessary only if the assembly is subject to movement before achieving a handling bond.
Curing the adhesive:
Nearly all adhesives go through a curing process measured in minutes, hours and days to reach the full bond strength. Some fast bond epoxies will grab and hold in a few minutes, however, they may take hours before achieving full bond strength. Most regular epoxies take hours at room temperature to reach a strong handling bond and 24 to 48 hours to reach full strength. Speed and strength of the bond can be increased by baking or raising the bond temperature. A 24 hour curing time may be reduced to as little as one hour or less. Check with the manufacturer for recommended baking temperatures.
It is necessary to clean up hands, equipment and any excess adhesive before it sets. Hot water and a detergent or a solvent will remove the adhesive. It is difficult to remove cured adhesive because of its resistance to solvents and other cleaning agents. The adhesive will soften at a temperature above 400°F and a bond can be broken or an adhesive can be removed by scraping. There are some commercial epoxy strippers available.
Care must always be taken when using any chemical. Adhesives can be a danger to the eyes and skin. Epoxies are usually heavy or thick materials and not subject to splash or spilling, but care must be taken not to touch the eyes or wipe or spread the adhesive on your own or other people's clothing. A cured adhesive may be disposed as any plastic material. Adhesive containers must be tightly closed and kept from the reach of children. Follow any special instructions of the manufacturer. Industrial users are required to have Material Safety Data Sheets on hand.
Select epoxy for high strength structural applications on metals, plastics or porous materials. It is ideal for combinations of different substrates. They work well in bonding rubber to other materials. These are not instant adhesives unless you can use heat. Many epoxies are available in dual cartridge dispensers that eliminate the mess and problem of mixing.
Urethane adhesives are available in one part moisture cure systems or two part 100% reactive room temperature or heat cure systems. Urethane adhesives are designed primarily for industrial usage and are not usually available to the handy person because of high flammability and limited shelf life. The leading characteristic of urethanes is their flexibility. This adhesive is available in a wide range of viscosities from a paste to a sprayable liquid. Urethanes will bond prepared metals, plastics, wood, foam, rubber, fabrics and leathers.
Substrates must be free from all contaminants. Prepare the surface by wiping with a solvent. Abrasion is recommended for metals and thermosets plastics. Two part urethanes require careful combining of fractional mixing ratios for specific applications. The adhesive is moisture sensitive and open containers must be capped with dry nitrogen for storing. Check with the manufacturer for specific mixing and storage guidelines.
The adhesive needs to be applied to only one surface. Open time and cure time will vary depending on the specific urethane used. Single part, high grab urethanes should be applied to one surface and the solvent permitted to evaporate for up to 15 minutes before bringing together the other bonding surface and the adhesive will give an almost immediate handling bond. Heat may be used on urethanes to speed curing and improve bond strength. Check with the manufacturer for heating guide lines. Clamping is necessary only if the joint is subject to movement.
Select urethanes for broad area structural bonding suction. Urethanes are ideal for structural wood bonding applications and foam bonding. They also give structural strength for rubbers and other materials requiring flexibility.
Acrylics are high strength, structural adhesives that equal or exceed the strength of epoxies. The advantages of this adhesive is a handling bond in minutes and 90% of full cure strength in about two hours without heating. An additional advantage is the ability to bond substrates with minimal preparation, including oily metals. Acrylics are two part adhesives consisting of a resin and accelerator to promote the cure. These are ideal for metals, plastics, and ceramics. This adhesive does not work particularly well on porous materials and elastomers.
Mixing & Application:
Acrylics may be used as a mix-in or no mix product. For bond lines up to 25 mils the accelerator may be applied to only one surface. From 25 to about 50 mils it is necessary to apply the accelerator to both surfaces. Permit the accelerator to dry and then add the resin to one surface and bring the two substrates together. For large gap filling applications or over 50 mils, the accelerator must be mixed with the resin using the proper mix ratio supplied by the manufacturer. Acrylics are now available in dual cartridge dispensers with static mixers that eliminate the mixing problems by dispensing the adhesive ready for application.
Surfaces must be free from all grease or loose materials that may affect the bond. Metals with thin films of oil may be bonded. Some plastics require little preparation and others may require a solvent wipe or primer and need to be roughened.
Curing the adhesive:
Acrylics are available in various viscosities and set times. Follow the instructions for the one you are using. Do not use the material after setting has begun. A handling bond may be achieved in as little as two minutes or up to 30 minutes. It is not recommended that heat be used on acrylics.
Follow standard safety measures for using any chemical. Uncured acrylics have a strong odor and adequate ventilation should be provided during mixing and bonding operations.
Select acrylics for speedy, high strength structural bonding of metals, plastics and ceramics.
Emulsion Adhesives (white glues)
Emulsion Adhesives are water dispersions of small particles of high strength adhesive materials such as polyvinyl acetate polymers, copolymers and resins. The bond is formed by the absorption of water by the substrates. This adhesive is primarily used on porous materials such as wood and wood products. However, other combinations of materials may be bonded, such as plastics and metals, as long as one surface will absorb water. Though very strong, these adhesives should not be used in high stress post forming.
Except with tightly fitting parts, joints should be clamped during the setting period, which is about 30 minutes and full cure or strength will develop in 24 hours. This adhesive may be applied to only one surface. Various formulations of this adhesive are available for industrial use other than the general purpose products found in retail stores. Emulsions are not gap filling and should be used only on well fitting tight joints. Joints are water resistant but not water proof.
Select emulsions for quick setting, strong joints on wood and other porous materials.
Contact Adhesives are given this name because instant bonding is made on contact after the adhesive has been properly applied. Solvent-borne adhesives are elastomeric polymers (Neoprene rubber) modified with synthetic resins and stabilizers dissolved in solvents. Water-borne adhesives are also based on Neoprene, acrylics or other polymers in emulsion or latex form. This adhesive will adhere to and give strong bonds on most materials. Not being creep resistant, it should not be used in high stress, shear applications.
All types of contact adhesives must be applied to both surfaces, permitted to dry, and then pressed together. At the moment of contact a bond is formed. Proper drying of the adhesive before assembly and sufficient pressure applied after assembly is required to create a good bond. Proper alignment of the substrates before contact is necessary because the adhesive will grab instantly and adjustments will not be possible after touching. Industrial grade contact adhesives are available in various formulations for specific application methods such as roller coating, spray, hand brushing or other special methods. Materials to be bonded must be free from all contaminants and moisture before applying the adhesive.
Solvent-borne contact cements are highly flammable and proper precautions must be taken to prevent fire and or explosion. Many water-borne contact adhesives are now available that eliminate this problem and perform comparably with the solvent adhesive in most applications.
Select contact adhesives for broad surface bonding of sheet materials of various combinations. Contact adhesives are ideal for wood, plastics and metals in nonstructural applications that require instant bonding.
Adhesives/Sealants are formulated primarily to seal and protect rather than create strong bonds, even though most have some bond strength to adhere to the surfaces to which they are applied. Sealants are created to resist water or moisture, temperature, sunlight and other environmental conditions. Most sealants are designed with some flexibility to allow for some joint movement. Sealants are made from various materials, each of which will perform best in certain applications. The following is a list of the most common materials available.
Urethane - Excellent adhesive properties, very flexible, excellent resistance to water, humidity and weather.
Butyl - Economical, general purpose sealant.
Polysulfide - Flexible, tough, and water resistant - permits disassembly.
Acrylic - General purpose, paintable and easy to clean up.
RTV silicone - High temperature resistance to (450 °F), quick cure, high strength with good flexibility and weatherability.
MS Polymer – MS Polymers, or hybrid adhesives, are a family of high strength adhesives/sealants that combine many of the best properties of silicone and polyurethane based products including – primerless adhesion to most substrates, excellent environmental resistance, paint-ability, and flexibility.
Various formulations of the above sealants are available for specific applications. Check with the manufacturer for the best sealant to use in your application. Construct and prepare the joint properly for the sealant. The joint must be clean, dry and free from loose materials. Clean up the excess sealant before curing. Most cured sealants are difficult to remove.
Select sealants for construction projects, marine applications, and equipment protection. Sealants have many applications around the average home.
Anaerobic adhesive/sealants are formulated for use in thread locking, sealing, fastening and retaining of metal components. This material is designed to eliminate the need for mechanical locking devices such as lock washers, set screws, lock nuts and cotter pins. Units assembled with this type of adhesive resist vibration and seals against corrosion, seizure, solvents, and other chemicals that might lead to a loose joint or assembly. Because anaerobics cure in the absence of air, they harden in the spaces between the bolt threads or other tight fitting assemblies, locking the parts in place.
Anaerobics are manufactured by a number of companies, the most common of which is Permabond. Adhesives are available in a number of different strengths and viscosities. Selection is based on the type of assembly, be it small screws that need to be removed for maintenance, or locking a bearing on a shaft, or holding a bolt on a high strength assembly of a vehicle. Refer to the manufacturer's catalog as a guide to selection.
Mating surfaces must be clean and dry before applying the adhesive. Very little is needed so use sparingly. Torque the assembly immediately after application before adhesive begins to cure. Thread lockers may be used in temperatures from -65ºF to 300ºF and resist most automotive fluids and common solvents. Anaerobics are formulated primarily for use on metals. Other types of thread lockers are available for plastics and similar materials.
UV Cure Adhesives
UV Cure Adhesives are adhesives designed to cure when exposed to ultra-violet light. They are transparent, clear acrylics that can be used to bond transparent materials to themselves or to other materials. Specially designed UV lamps are available to activate these adhesives.
Surfaces to be bonded must be clean and transparent enough to pass the light. Instant cure is achieved with exposure to the properly powered light. This adhesive is ideal for bonding glass, including fiber optics, and clear plastics. Because of the precautions necessary with UV light, this adhesive is available for industrial use only.
Adhesives with a thermoplastic base are usually limited to temperatures below 350° F. Adhesives with a ceramic base raise this limit to over 5000 °F. These adhesives are comparable in strength to epoxies and acrylics and are available in many different formulations for various applications.
- Adhesive bonds
- Other high temperature materials
Use for ovens, burners, electrical sealing, potting and any application requiring high temperature resistance. Consider the difference in expansion rates between different materials when bonding for high temperatures.
Pressure sensitive adhesives are applied to a surface and permitted to dry. That surface will then adhere to most other materials on contact with pressure. Bonds may be temporary or permanent. These adhesives are usually made from natural or synthetic rubber.
Self-seal or cohesive (cold seal) latex adhesives – This is an adhesive that will adhere only to itself. Bond strength is variable and may be permanent or re-sealable. These may be used as a protective coating that will not transfer to the material being coated.
Heat seal adhesives are waterborne resin heat seal adhesives. Heat seals are applied to one surface and dried. The adhesive is then activated for bonding by applying heat. Temperatures required vary from 175°to 300°F depending on adhesive.
Fugitive adhesives form a temporary bond between two materials. The two materials may then be separated without damaging either surface. Made from natural rubber latex, it has no tack, dries clear, and is non-staining.
Non-fray adhesives are used to prevent fabrics from unraveling or to give fabrics a firmer feel. These adhesives are high gloss, water resistant, and clear when dry.