Table of Contents
Why adhesives- Advantages of adhesive technology over conventional methods
Adhesives bond dissimilar and hard to bond materials
Adhesives can bond hard to bond materials such as low surface energy plastics, oily metal and silicone rubber. Without adhesives, it would be difficult to imagine how to assemble two dis-similar material like plastic to rubber, metal to wood, plastic to metal etc
Adhesives bond and seal simultaneously
Using adhesives to bond two surfaces helps seal out water, moisture, dirt and other environmental contaminants. Because the seal has adhesive properties, there is no need for a separate mechanical fastener.
Adhesives reduce stress concentration at screw and rivet points
Mechanical fastening requires drilling holes, and attachment at each hole concentrates stress at that point. Because adhesives and tapes bond over an area rather than points, they disperse the load over the entire bond area. Eg: entire bus body is made from adhesive and sealants- sheet metal bonding instead of fastening or welding.
Adhesives improves production efficiency
Incorporating adhesives into the manufacturing process can improve efficiency by eliminating process steps, failure rates, and time of assembly. Adhesives can increase speed, reduce cost, reduce labor hours and streamline operations.
Adhesives improves aesthetics
Adhesives provide virtually invisible fastening to keep surfaces smooth and clean with no visible screws, rivet heads or protruding nuts and bolts. Adhesives also save the time and cost of refinishing welding burn marks. Eg: bonding glass to glass with optically clear adhesive.
Adhesives reduce vibration, fatigue and noise
Because adhesives are viscoelastic, they are energy absorptive and improve the impact, vibration and fatigue performance of your design.
Types of adhesives
Adhesives are primarily classified based on their curing mechanisms and chemistry.
Based on curing mechanism
Water based adhesives– cure ( dry ) when water evaporates from the adhesive. Eg: Fevicol white glue used for plywood bonding in interior furnitures
Solvent based adhesives – cure ( dry ) when solvent evaporates from the adhesive. Eg-rubber adhesive used for type puncture repair, shoe repair.
Non curing adhesives : Eg: butyl sealant for bonding car door fabric to metal body.
Reactive adhesive– cures when it reacts due to some external factor( eg- UV curing glue) and chnages phase from liquid to solid. Eg: 2 part araldite cures after expocy and hardener are mixed together.
Based on chemistry
Acrylic adhesive – Generally 2 part adhesive system for structural bonding.
Anaerobic adhesive – one part adhesive used for threadlocking, threadsealing, flange sealing, bonding cylindrical assemblies. Used extensively in manufacturing and maintenance work. It is also called Engineering adhesive.
Cyanoacrylate adhesive – popularly called instant adhesive or super glue. It bonds instantly. It can bond alomost all material except telfon. It is not flexible after curing and generally used for bonding small parts.
Epoxy adhesive – Araldite is a polular household name in India. It is used for bonding any material together. Generally 2 part system which either is mixed manually or used with a special 2 part dispenser.
Methyl methacrylate adhesive – 2 part adhesive system used for structural bonding.
Silicones– Silicone adhesive and sealant is popularly used for glazing applications. Some viscous silicone sealants are used for other bonding purpose also.
Polyurethane adhesive – It is a single component adhesive used for wood working applications, honeycomb bonding and other furniture manufacturing applications.
PVA ( Poly vinyl acetate) – Typical white glue used by students for project work like paper pasting, carboard pasting and sundry home use.
Synthetic rubber adhesive – Dendrite is a poplular SR adhesive used in India. It can bond most substrates. It is also used for bonding solid gasket on the flange.
Hot melt adhesive – There are various types of hot melt adhesives used for book binding, wood working, packaging, automotive interior assembly, diaper and sanitary pad production etc.
MS polymers is the latest generation adhesive and sealant which combines advantages of silicones and polyurethanes. It can be used for bonding almost all materials except pp,teflon,hdpe, ldpe.
Advantages of MS Polymer adhesive
- High initial tack properties reduce the need for initial support.
- Fast curing, a quick build-up of end strength alongwith high sheer strength after full cure (no primer).
- Easy to apply and easy to tool and finish
- Remains elastic after curing.
- No odor.
- Does not contain neither isocyanates, silicones nor solvents.
- Paintable with all water-based paints.
- Excellent color stability. Likewise, weather and UV resistance.
- Good adhesion on wet substrates, bonds underwater.
Adhesive selection parameters
M- Machine – How are you applying the adhesive? How Fast? What type of equipment are you using? S- Substrates – What are you adhering together? E – Environment– What will the bond / finished product be subjected to? (Hot Fill, Cold, Wet, Freezer, Blast Freezer) C- Cost and volume – Ballpark of where you would like this product to fall in your COM. How much & how often do you order? P- Plant conditions– What are the conditions in your plant? (Temp Controlled, Dusty, Wet, ETC.)
Summary of questions to be answered for adhesive selection.
- Details of the substrates to be bonded- low energy substrates like telfon, HDPE, LDPE, PP is diffcult to bond and requires special surface prepration before bonding.
- Gap between the surfaces- for higher gaps than 0.5 mm we need higher viscosity adhesive, else regular CA( cyanoacrylate, instant glue) will work.
- Max Temperature to be sustained by the assembly – If more than 100 Celsius: silicone adhesives are the best else you have to select special high temperature grade from other chemistries.
- Type of loading, stresses on the adhesive joint – instant glue is not good in cleavage, peel or shear strength.
- Production speed: How many assemblies per hour to determine how to dispense the glue.
- Environment: Will the adheive bondline come into contact with water, fuel, gas, harsh chemicals etc. knowing this we need to choose adhesive chemistry that can sustain that environment.