Joining using adhesives

Joining using adhesives does not present particular difficulties and is used to assemble thermoplastics with plastics, composites or metals. Joining avoids damaging the parts by drilling and allows an excellent distribution of the stresses. The parts can have structural functions if the adhesive is correctly chosen, and if care is taken to ... 

Definition of Adhesives and Adhesive Bonding Functions of Adhesives Classification of Adhesives Advantages and Disadvantages of Joining Using Adhesives... 

Many current production materials can only be successfully joined using adhesives. The emergence of fibre-reinforced plastics as structural materials has meant that adhesive... 

Adhesive Disadvantages. There are some limitations in using adhesives to form assemblies. The major limitation is that the adhesive joint is formed by means of surface attachment and is, therefore, sensitive to the substrate surface condition. Another limitation of adhesive bonding is the lack of a nondestructive quality control procedure. Finally, adhesive joining is still somewhat limited because most designers of assemblies are simply not familiar with the engineering characteristics of adhesives. 

Plywood requirements—includes wood species used, synthetic repair requirements, veneer grades, veneer layers and thicknesses, panel grades with respect to end-use, adhesive bond requirements, panel construction and workmanship, scarf and finger-join ted panels, dimensional tolerances, moisture content, and packaging and loading... 

There are several claims in the literature regarding the maximum speed of microwave curing of epoxy adhesives. Claims have been made of ten- to twenty fold cure time reduction when compared to conventional thermal heating. A more practical estimate, however, is that microwave joining using epoxy-based adhesive will significantly reduce the curing time... 

These plastics are quite inert thus, compatibility with other substrates does not pose major problems. The terephthalates have high tensile and tear strengths, excellent chemical resistance, good electrical properties, and an operating temperature range from —55 to 200°C. These materials are generally joined with adhesives, and surface treatments are used to enhance adhesion, if required. 

Carbon nanotubes can be used in reinforcing polymer matrix composites in two ways a) as the sole reinforcing phase (CNTRP), or b) as an additional reinforcing phase in conjunction with carbon fibers (CF+CNT) in a hybrid composite. Carbon nanotubes reinforced plastics (CNTRP) can be prepared by several methods, as described in section 15.1.3. Both CFRP and CNTRP composite structures can be joined using structural adhesives but machining and drilling are difficult as a result of the widely different properties of their constituents. 

Thermosetting Foam Substrates Most thermosetting plastics are not particularly difficult to bond. Obviously, solvent cementing is not suitable for bonding thermosets to themselves, since they are not soluble. In some cases solvent solutions can be used to join thermoplastics to thermosets. In general, adhesive bonding is the only practical method of joining a thermoset to itself or to a non-plastic material. Epoxies or modified epoxies are the most widely used adhesives for thermosets (1). 

LDPE coating to polyester film, clay-coated liner board, and aluminum foil was improved by an addition of calcium carbonate. Adhesion increases as the amount of calcium carbonate is increased and at a 30% level it is doubled. The adhesion of SBR to a polyurethane adhesive was substantially improved (400%) by the addition of silica but only when the surface was roughened. The amount of silica did not affect adhesion of unroughened SBR. The use of MgO with silane coupling increased adhesion of bromobutyl liner by a factor of four. Generally, in the reported data, surface roughening of the filled composite contributes to a better adhesion to other substrates joined by adhesives. 

Table 7.6 Refractive indices (Rl) of piastics and commonly used adhesives. A join is invisible if the adhesive matches the Rl of the object 0.01. A consolidant or coating should match the Rl of a surface 0.06 to give optimum saturation ...

State four advantages of using adhesives instead of mechanical or heat joining methods. 

It has often been observed that the application of adhesives to metal fabrication, in common with many other technological innovations, was pioneered by the aircraft industry. It is ironic that this industry, in which safety and reliability command paramount attention, should lead the departure from traditional methods of joining. Today adhesives are used to bond critical parts in commercial and military aircraft and helicopters, spacecraft, rockets, missiles and the US Space Shuttle. The American Primary Adhesively Bonded Structure Technology (PABST) Programme, which ran from 1976-81, was an imaginative attempt to advance significantly the use of bonded... 

Dissimilar materials, including plastics, are readily joined by many adhesives, provided that proper surface treatments are used. Adhesives can be used to join metals, plastics, ceramics, cork, rubber, and combinations of materials. Adhesives can also be formulated to be conductive. The focus of this book is on adhesives for bonding plastics, thermosets, elastomers, and metals. 

Adhesion is an interfacial phenomenon that occurs at the interfaces of adherends and adhesives. This is the fact underlying the macroscopic process of joining parts using adhesives. An understanding of the forces that develop at the interfaces is helpful in the selection of the right adhesive, proper surface treatment of adherends, and effective and economical processes to form bonds. This chapter is devoted to the discussion of the thermodynamic principles and the work of adhesion that quantitatively characterize the surfaces of materials. Laboratory techniques for surface characterization have been described which allow an understanding of the chemical and physical properties of material surfaces. 

Groups of holes for non stmctural or lightly loaded connections or where the bolting is used in conjunction with adhesives may, with the approval of the designer, be formed separately in the components to be joined, using a template. Such holes (made separately in the parts to be joined) should be 2 mm greater in diameter than the bolt(s) used for the connection. 

Flexible Plastics and Elastomers. Thin or flexible polymeric substrates may be joined using a simple or modified lap joint. The double strap joint is best but also the most time-consuming to fabricate. The strap material should be made out of the same material as the parts to be joined, or at least have approximately equivalent strength, flexibility, and thickness. The adhesive should have the same degree of flexibility as the adher-ends. 

The applications described are but a few of the many thousands of joints that are assembled using adhesives. They illustrate the varied applications and some detail of the benefits of using adhesives compared to other joining methods. 

---