Production of Bonded Joints

Applied Adhesive Bonding A Practical Guide for Flawless Results. Gerd Habenicht Copyright 2009 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 978-3-527-32014-1 

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With a few exceptions (e.g., body-in-white manufacturing), the production of bonded joints requires surface treatment of the adherends as an additional production stage. 

In the production of bonded joints, the time required for the relevant reaction kinetics of curing has to be taken into consideration. 

Figure 7.1 Process steps for the production of bonded joints.

For the production of bonded joints with metal materials, appropriate surface pretreatment is of priority. In the technical literature, various formulations of pickling solutions are to be found, their application, however, is limited for reasons of occupational safety and due to the disposal problem. Therefore, we refrain from describing them here. 

Perhaps, the earlier materials found to have a useful capacity for adhesive bonding underwater depended upon the use of a stoichiometric excess of water-scavenging polyamide hardener in an epoxide-based adhesive. This approach can lead to the production of effective joints in the short term, but formulations of this type, which are hydrophilic in the uncured state, are also likely to absorb significant amounts of water in the cured condition. It is a widely accepted view that the extent of joint weakening in susceptible joints, quite apart from the consequences of plasticization, is a function of the water-uptake characteristics of the adhesive (see Glass transition temperature). The consequence is therefore likely to be that such joints will show poor durability in the presence of water, when rapid uptake of water may lead to equally rapid degradation of both cohesive and interfacial properties (see Durability fundamentals). 

Adhesive product data sheets and the literature often cite the vulnerability of bonded joints in contact with various organic solvents. Because most adhesives tend to have polar compo-... 

For the design of bonded joints, basic information is required on available adhesives and their characteristics. This provides an indication of the capabilities of potential adhesives and also serves as a basis of comparison between commercially available products. However, finding and acquiring this information can be a difficult and very time consuming process. This book will greatly simplify this process for the reader. 

Kuenzi, E. W. and Stevens, G. H. (1963) Determination of Mechanical Properties of Adhesives for use in the Design of Bonded Joints, FPL Report No. Oil, US Forest Products Laboratory. 

Kuenzi EW, Stevens OH (1963) Determination of mechanical properties of adhesives for use in design of bonded joints. US Forest Products Service Researdi Note FPL-011. US Department of Agriculture, Madison... 

It is quite difficult to check visually the adequateness of adhesion bonding after the joining process. Therefore, design of bonded joints, process optimization, and its control are very important. In this chapter, some important aspects are discussed to obtain practically good adhesion in the fabrication lines of products having adhesively bonded joints. The quality control in adhesives production is not treated here. This aspect is, for example, treated in Petrie (2007). 

It is true the repair of bonded joints is different from that of bolt-on parts. But in comparison with riveted, spot welded, or welded structures, the removal of bonded parts may be even easier. When repairing bonded metal structures, the removal of a damaged part is done by mechanical abrasion or with hammer and chisel. The adhesive is then removed by abrasion like it is done with painted surfaces. More challenging in the repair case is to bond a new part on the old structure. It is not possible to use the same adhesive as in the production line since the process conditions are different. In this case, 2-C high strength adhesives with improved impact resistance can be used as published by Lutz (2009). And to process these adhesives correctly, well-educated personnel is required. 

As no totally effective NDT method has yet been devised for the assessment of bonded joints, the process of quality assurance must be carried out indirectly. Table 7.12 lists the more significant aspects of a quality monitoring system for primary safety critical structures. Table 7.13 cites the primary causes of production difficulties, though it should be added that established production lines rarely give rise to problems and when they do the cause is usually found to be an imposed change in working methods or materials. 

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