Page 38 - Handbook of Adhesives and Sealants
P. 38

8   Chapter One


            TABLE 1.1 Factors Influencing Selection of an Adhesive or Sealant (Continued)
            Low.................  May cause crystallization or embrittlement, detected by
                                strength test. Cyclic testing with low or high temperatures
                                may detect lack of durability
            Biological Factors
            Bacteria or mold .....  Usually warm, humid tropical conditions. Can affect bond
                                strength, and cause emission of odor or discoloration
            Rodents or vermin....  Adhesives of animal or vegetable origin may be attacked by
                                rats, cockroaches, etc.
            Working Properties
            Application ..........  Brushing, spray, trowel, or knife-spreader application
                                characteristics are usually determined by trial and error.
                                Consistency or viscosity may be adequate indications.
                                Mechanical stability of emulsions and dispersions, and
                                foaming tendency, can be important for machine
                                application
            Bonding range .......  Minimum drying or solvent-reactivation time before
                                suitable bond can be obtained. Maximum allowable time
                                before assembly. Permissible temperature range with heat-
                                activated adhesives
            Blocking .............  Tendency of surfaces coated for storage before assembly to
                                adhere under slight pressure, or changes in humidity or
                                temperatures
            Curing rate ..........  Minimum curing time, and effect of overcuring. May be
                                determined as a shear or tensile-strength vs. curing-time
                                curve at a specific curing temperature
            Storage stability......  Physical and chemical changes in original unapplied state
                                as a result of storage for extended time periods at
                                representative storage temperatures
            Coverage ............  Area of bond that can be formed with unit weight or
                                volume of adhesive; expressed as pounds per 1,000 ft of
                                bond line, or square feet per gallon. Depends on method of
                                application; dimensions of work or of adhesive-coated area
                                in relation to part size may affect coverage


            be very difficult to know exactly the composition of the joint at any
            point in time. The possibility of these transformations resulting in an
            unacceptable material within the joint or in altering the mode of fail-
            ure is great. In some applications, they could result in a catastrophic,
            premature joint failure.


            1.2.4  Nature of the technologies related to
            adhesives and sealants
            A multi-disciplined set of rules and a field-tested methodology are nec-
            essary to successfully negotiate the minefield of obstacles listed above.
            This requires consideration of fundamental concepts from a number
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