Adhesive, selection surface preparation

JOINEXCELL (from AJI - The American Joining Institute). An adhesive selection expert system for use with composite materials. The system consists of a job-planner subsystem which creates a joint schedule, complete joint description, adhesive selection, surface preparation, etc. Also a recorder for Quality Assurance criteria. JOINADSELECT is part of the expert system and identifies appropriate adhesives from 15 major classes of engineering adhesives, given information about adherends and adhesives. Databases for composite adherend properties are included. 

Consideration of all the above energy relationships and derived values can be of great help in selecting adhesives and surface preparation conditions for attaining predictable, strong adhesive bonds. Several examples are presented here. 

As already stated, the durability or permanence of a bonded assembly is dependent on the intended use and service conditions to which the bond will be exposed. However, the joint design, choice of substrates, adhesive selection, substrate preparation, and primer selection, where appropriate, plus the method of application and assembly all have significant impact on the service life of adhesively bonded materials. Most or all of these considerations are interdependent, for example, the joint design and substrates chosen will limit the range of suitable adhesives that can be employed. In a similar way, the durability of a sealed joint is only as good as the adhesion of the sealant (and primer) to the surfaces forming the joint. Primers and/or sealants will adhere to surfaces only if those surfaces are properly prepared. A very large proportion of all sealant joint failures result from poor or inadequate surface preparation. 

It is impossible to avoid a discussion on prebond surface preparation since it is one of the most important factors in the fabrication of a durable and consistent epoxy adhesive joint. Selection of a proper surface preparation is not an easy task, and the actual implementation of the surface treating process in production is equally daunting. 

Morris, C. E. M., Strong, Durable Adhesion Bonding Some Aspects of Surface Preparation, Joint Design, and Adhesive Selection, Materials Forum, vol. 17, 1993, pp. 211-218. 

Adhesion, whether the bonding of polymers or the adhesion of coatings to polymer surfaces, is a recurring and difficult problem for all industries that use these materials as key components in their products. Designers must often select specially formulated and expensive polymeric materials to ensure satisfactory adhesion (albeit even these materials often require surface preparation). In some cases, entire design concepts must be abandoned due to the prohibitive cost of the required polymer or the failure of crucial bonds. 

Selection of adhesive, surface preparation, cleaning and bonding should follow the same principles as applicable for the replacement of decayed beam ends. This technique has low intrusiveness and visual impact, and although not reversible, it allows keeping in place the original element that would otherwise have to be replaced. 

Based on the data shown in Figs. 1-8 and similar results obtained on the other candidate adhesives CAA (10 Volts) was selected as the surface preparation for use in the remaining studies of this program. These data were also used to select the adhesive systems for continued evaluation. 

Because of the large number of factors that influence the durability of adhesive-bonded joints, a durability test should be conducted on all systems before they are selected for any particular application. This test should include the adherends, surface preparation, adhesive, and cure parameters needed for each application. ... 

Importantly, for a particular application, and where the metals to be joined have been specified, an overall metal bonding system should be considered. Typically, this will include selection of a suitable adhesive and possibly primer or coupling agent in combination with appropriate methods of surface preparation or pre-treatment. Organofunctional silanes (see Silane adhesion promoters) are commonly used coupling agents, which have been demonstrated to provide covalent chemical bonds with steel or aluminium surfaces and possess epoxide or amine functionality for reaction with Epoxide adhesives. 

Adhesive gluing Difficult to bond plastic, surface preparation very crucial. Proper selection of glue necessary. Consider improved design to avoid the need for gluing or use welding. 

To eonfirm the theoretical predictions that the 7-stress affects the directional stability of cracks, DCB specimens with adhesive C and adherend thicknesses of 4.8 mm were prepared. The surface preparation for the adherends was simply an acetone wipe, and various levels of residual stress were achieved among the specimens using the stretching method. Specimens were then tested quasi-statically according to the procedure discussed earlier. The resulting fracture surfaces of the specimens were carefully examined and three representative specimens were selected as shown in Fig. 9, from which, the effect of the 7-stress on the directional stability of cracks can be inferred. The initial residual stress... 

Over the past several decades, much study has been focused on surface energetics, wetting, adhesion, etc., and some generalizations have been developed. These can be useful guides to the adhesive selection and surface preparation needed to form reliable, strong adhesive bonds. Only a brief exposure to some of this valuable information can be presented here, but further reading is available in Chapter 3 and other chapters of this Handbook, and in listed references. 

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