|
ADHESIVE BONDING AND MECHANICAL FASTENING
ADHESIVE BONDING
Ideal Adhesive
- bonds to any material
- needs no surface preparation
- cures rapidly
- maintains a high bond strength under all operating conditions
- DOESN’T EXIST! ...
Adhesive Materials and Their Properties
Adhesive Bonding
- a nonmetallic material (adhesive) is used to create a joint between two surfaces
Adhesives
- span a wide range of material types and forms and can be applied as drops, beads, pellets, tapes, or coatings (films)
- available in the form of liquids, pastes, gels, and solids
- curing can be induced by the use of heat, radiation of light (photoinitiation), moisture, activators, catalysts, multiple-component
reactions, or combinations thereof
- intended applications range from full load bearing (structural adhesives), to light-duty holding or fixturing, to basic sealing (the forming of liquid- or gas-tight joints)
Structural Adhesives
- selected for their ability to effectively transmit load across the joint and
include:
o epoxies
o cyanoacrylates
o anaerobics
o acrylics
o urethanes
o silicones
o high-temperature adhesives
o hot melts
1. ... Anaerobics
* are one-component, polyester acrylics that remain liquid when exposed to air and becomes unstable when confined to small spaces and shut off from oxygen, as in a joint to be bonded
* polymerizes into a bonding-type resin without the need for elevated temperature in the presence of iron or copper
* are extremely versatile and can bond almost anything, including oily surfaces
4. Acrylics
* good strength, toughness, and versatility, and are able to bond a variety of materials, including plastics, metals, ceramics, and composites, even through oily or dirty surfaces
* most involve application systems where a catalyst primer (curing agent) is applied to one of the surfaces to be joined and the adhesive is applied to the other
* offer strengths comparable to the epoxies, good resistance to water and humidity, and the added advantages of room temperature curing and a no-mix application system
* limitations include low high-temperature strength, flammability, and an unpleasant odor when still uncured
5. ... Hot Melts
* can be used to bond dissimilar substrates, such as plastics, rubber, metals, ceramics, glass, wood, and fibrous materials like paper, fabric, and leather
* can produce permanent or temporary bonds, seal gaps, and plug holes
* are usually applied as heated liquids and form a bond as the molten adhesive cools
* provide reasonable strength within minutes, but do soften and creep when exposed to elevated temperatures and become brittle when cold
Nonstructural and Special Adhesives
Nonstructural Adhesives
- have limited load-bearing capabilities
- still play roles in manufacturing through a variety of uses, such as labeling and packaging
1.
Approximate Word count = 1937
Approximate Pages = 7.7
(250 words per page double spaced)
|
|
