Over the past decades, structural adhesives have developed into effective and dependable alternatives to conventional joining techniques such as bolting, riveting, and welding. They can bond effectively almost all commonly employed materials in industrial manufacturing. With notable properties, structural adhesives have been creating significant benefits to a great number of different industries, particularly Automotive, Electronics and Construction.
Structural adhesives definition
A structural adhesive is any adhesive designed to create strong, durable bonds. Hence, the ‘structural’ in structural adhesives means that it will physically become a part of the structure.
Of course, these adhesives are totally different from other types of adhesives, such as DIY glues or tapes. Structural types are designed to provide a sturdy bond and often used in place of mechanical fasteners such as bolts or screws. Sometimes, they can also be employed in lieu of welding.
How many types of structural adhesives are there?
Manufacturers are often confused to pick out the most suitable adhesive since there are thousands of options with different pros and cons. However, we can simplify and narrow it down to three main kinds.
Considered as one of the most common structural adhesive chemistries, epoxy adhesives are typically two-component systems with one side is the epoxy resin and the other is a hardening agent. When these components are mixed, their reaction would form a strong and durable bond. Be noted that the cure speed varies massively depending on the formulation.
Nevertheless, one-component systems are also available for epoxy adhesives. As they only have one component, they require an external factor such as a heated oven to initiate the curing process.
Not only are epoxy most common adhesives, they also are the strongest type of adhesive out there with good chemical and heat resistance. However, surface preparation is required to ensure a strong bond and flexibility is limited.
Common users of epoxy adhesives are aerospace, manufacturing, and automotive industries.
Another type to mention in the list is polyurethane. Similar with epoxy adhesives, this type has both one-component and two-component systems. However, one-component polyurethanes cannot meet the required strength to be used in structural applications.
Structural polyurethane adhesives are a mixture of polyurethane resin with a hardening agent. Though they are highly flexible and durable, they contain harmful chemicals (isocyanates) and usually require longer cure time than other adhesive chemistries.
Marine, mass transportation, and automotive industries are primary users of polyurethane adhesives.
Acrylic adhesives are the newest type of structural adhesive with only two-component systems – they are a mixture of acrylic resin and a hardening agent. Acrylic adhesives can bond all substrates with fast cure times and no requirement of surface preparation. Nonetheless, these adhesives often don’t have much flexibility and contain a distinct odor.
Mass transportation, decorative surface manufacturing, and automotive can be named as the top frequent acrylic adhesive users.
FIND OUT MORE: How Epoxy and Acrylic structural adhesive are replacing mechanical fasteners
Structural adhesives in Automotive bonding
The principal use of structural adhesives in Automative is to reduce vehicle’s weight. Why is it necessary? The answer lies in the body of the car – which accounts for 40% its weight and is made of steel for advanced impact resistance, overall strength, and long term durability. This requires manufacturers to be smart and creative about their choices in materials of the vehicles to reduce weight but also increase performance.
The method to make those enhancements possible are bonding plastics, polymers, and aluminum to various steel components. Not only does bonding brings out greater resourcing flexibility, it can also apply to join heat-sensitive parts (carpets, interior design elements, electronic equipment,etc), or join pieces that are difficult or impossible to reach using traditional welding tools.
Electronics and Structural Adhesives
The basic building block in electronics industry is the printed circuit board (PCB), which makes use of adhesive materials in bonding surface-mount components (chip bonding), wire tacking, conformal coatings and encapsulating (potting) components.
Besides the main usage mentioned above, there are three different processing phases to consider in selecting an adhesive for electronics applications: uncured or liquid-resin phase, curing (transitional) phase and cured or solid-material phase. Above all, cured adhesive is the most important as it affects reliability.
Some major types of structural adhesives employed in electronics manufacturing procedures are: Electrically conductive adhesives, Thermally conductive adhesives and Ultraviolet-curing adhesives.
- Basically, electrically conductive adhesives are converted from non-conductive adhesives by adding filler to the base material. They are required in many applications, such as integrated circuits and surface-mount devices.
- Thermally conductive adhesive helps to provide a heat-conducting path, diodes, fastening transistors or other power devices to ensure heat build-up does not happen.
- Ultraviolet-curing adhesives are simple to use with fast cure time and do not require temperature acceleration. The use of these adhesives is increasing because they meet the requirements of the industry – which include environmental demands, manufacturing-yield improvement and product cost
Adhesives for Building and Construction
Adhesives are actively applied in construction and civil engineering as they adhere large surfaces and thick joints. Structural adhesives are required for structural parts, such as bonding of concrete to concrete, ceramic tiles to concrete, construction panels, masonry, outside doors, civil engineering, composite bonding, metal bonding, structural glass, sealing metal parts into concrete.
Since they can give at least 5 to 8 MPa tensile shear strength, adhesive bonding is the best option for large surface assembly that can reduce stress concentrations. The adhesive layer also protects materials from corrosion and is waterproofed depending on specific requirements. Aesthetically, bonding provides flat and smooth surfaces through the elimination of mechanical fasteners like screws, rivets, nuts and bolts or nails heads. Thus, the design is greatly improved.
Structural Adhesives in Medical Applications
Structural adhesives are widely used in medical applications. Typical employment can be bonding surgical instruments together, rubber bumpers on the bottom of crutches or walking canes, plastic soles and the bottom of cast boots. Traditionally, nails, screws, or rivets are used to perform these applications.
The most commonly used adhesive in medical field is cyanoacrylates – instant adhesives – are solvent-free and fast curing so they help to create thin film bonds between attached surfaces. Should the applications require durable and dependable bonds, cyanoacrylates are the perfect option. Currently these adhesives are employed IV Tube sets manufacture, needle bonding or plastic tubing attachment to a blood bag.
WIDER YOUR KNOWLEDGE with 101 Basic Guide to Medical Device Adhesive Solutions
Summary
Adhesives offer a wide variety of advantages over other fastening systems. It is crucial to possessa deep knowledge of the properties involved, be able to define bond requirements, identify all environmental conditions the bond will encounter, select the appropriate list for testing and narrowing down the options. In this sea of knowledge, let us be the partner with thorough understanding that you can trust along the way.
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