Adhesive bond nonstructural

Advances in the use of TP and TS plastic adhesives have made possible the adhesive bonding of RP structural and nonstructural parts in appliances, automobile, aircraft, medical devices, and so on. Adhesives with strengths higher than some metals are used (epoxy, etc.). The wealth of adhesive technologies that are available could make adhesive selection a task if one does use the proper approach such as determining specifically what performance requirements are needed (as with any selection procedure). The best adhesive for an application will depend on processing considerations and meeting the performance requirements. Tables 5.23 and 5.24 provide information on types and use of adhesives. 

D-0905. Test Method for Strength Properties of Adhesive Bonds in shear by Compression Loading (Fig. 8). A basic compression shear test which is widely used in screening wood glues. It is also used in specifications D-3110 (on nonstructural wood laminating ad hesives), D-2559 and D-3024 (on exterior and interior structural wood laminating adhesives respectively) and D-4317 (on polyvinyl acetate based wood adhesives). 

In contrast to other traditional mechanical joining methods such as riveting, welding, and screwing, adhesive bonding has httle or no adverse affect on the material characteristics of the surfaces to be joined. However, in general, in the area of nonstructural adhesives, designers do... 

The lower frequency creep or creep-rupture tests are time dependant. In these tests joints are subjected to a nominally constant load. The tests may proceed for a chosen time period, or may be continued until complete rupture occurs. For example, the durability of thermoplastic adhesives for nonstructural wood applications is classified in European standards EN 204 2001 and EN 205 2003 according to their ability to withstand various water treatments and relatively rapidly applied loads. However, an additional characteristic that can be specified is resistance to static load, which can be determined using the method described in EN 14256 2007. This method is used to determine the ability of a test piece bonded with a thermoplastic adhesive, to support a given load for up to 21 days without fracture or excessive distortion, and specifies a mean survival time of 14 days. 

Films. Both structural and nonstructural adhesives are commonly available in film form. Adhesives applied in the form of dry films offer a clean, hazard-free operation with minimum waste and excellent control of film thickness. However, the method is generally limited to parts with flat surfaces or simple curves. Optimum bond strength requires curing under heat and pressure, which may involve considerable equipment and floor space, particularly for large parts. Film material cost is high in comparison to liquids, but waste or material loss is the lowest of any application method. 

The distinction between structural and nonstructural bonds is not always clear. For example, is a hot melt adhesive used in retaining a fabric s plies structural or nonstructural One could argue that such an adhesive may be placed in either classification. However, the superglues (cyanoacrylates)... 

There are numerous families of adhesives within the structural and nonstructural types. The most common chemical families of structural and nonstructural adhesive famihes for bonding plastics are identified in Table 7.14. 

Nonstructural adhesives are those having bond strength that is less than 1000 psi but sufficient for applications such as pressure sensitive tapes, labels, laminates, and so on. Nonstructural adhesives are usually employed where production speed, convenience, and high peel strength are required. They generally have sufficient permanence for the applications mentioned. 

Nonstructural adhesives are adhesives with lower strength and permanence. They are generally used for tanporary fastening or to bond weak substrates such as paper and foam. Examples of nonstructural adhesives are pressure-sensitive tapes, wood glue, elastomers, and sealants. These adhesives are sometimes used for temporary fastening or sealing. 

One exception of this statement must be noted. These are the so-called pressure-sensitive adhesives which are normally liquids of very high viscosity which do not cure and which are in some cases poorly cross-linked. They adhere on different substrates only by physical bonds and due to the high mobility of their molecules they can repair destroyed bonds in time. This type of adhesion which is called d5mamic adhesion meaning a centipoid effect is unique for this class of adhesives and can be used partly on untreated PP for nonstructural bonds. The adhesion between the pressure-sensitive adhesive and the PP surface in an untreated state is not very high but relatively unproblematic. 

This large market includes residential housing and commercial building, in addition to roads, bridges, and other elements of the infrastructure. The largest volume of adhesives presently used is for nonstructural applications however, the use of structural adhesives is expected to increase in the future. While some end uses will involve primary structural bonds, most will be semi-structural, in which the adhesive will be used in combination with a mechanical fastener. The use of adhesives is also expected to increase as the trend towards the manufacture of prefabricated sections continues. Laminated beams and trusses are one established use for structural adhesives, typically phenolic, but there is now interest in urethanes for this purpose. Epoxies are also widely used, mostly for the bonding and repair of concrete. 

Other adhesives such as hot melt adhesives (HMA), poly(vinyl acetate) (PVA, catalyzed or uncatalyzed), pressure-sensitive adhesives (PSA), or elastomeric adhesives (based on natural or synthetic rubbers) are also used in wood bonding (7). However, their use is mostly limited to nonstructural applications (eg, secondary manufacturing processes such as kitchen furniture, interior joinery, decorative paper, and packaging) where strength and water resistance are of limited concern. 

This industry does not use large quantities of adhesives. However, the products are expensive, as they are highly specialized and must meet strict specifications. The adhesives are utilized for both structural and nonstructural applications. Indeed, aircraft is the single most well-defined market for engineering/structural adhesives. The most common application is for epoxy hybrid films to bond metal structures (Table 20). 

D-3110. Specification for Adhesives Used in Nonstructural Glued Lumber Products. Employs the D-0905 block shear test and a finger joint test, along with several exposures, to evaluate interior and semi-exterior adhesives, in end, edge and face bonded joints, especially for the molding and millwork field. Most of the applicable adhesives are based on polyvinyl acetate. 

Although thermal welding is ordinarily used for bonding this material to obtain optimum bond strength, adhesives are used under certain conditions. Three types of adhesives are used solvent, structural, and nonstructural. Hexafluoroacetone sesquihydrate is used for solvent cementing. Structural adhesives are generally thermosets. Many of these adhesives can be used continuously at temperatures up to 177°C, which is higher than the recommended continuous-use temperature of 104°C of the copolymer. 

Structural adhesive types recommended are epoxy (up to 71°C), polyester with isocyanate-curing agent (up to 121°C), and cyanoacrylate (up to 82°C). Structural adhesives for bonding acetal copolymer to itself have yielded shear strengths of 4.1—5.5 MPa. Nonstructural adhesives are usually... 

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