Лако-красочные материалы — производство

An adhesive may be defined as a material which, when applied to surfaces, can join them together and resist their separation. Thus adhesive is the general term used for substances capable of holding materials together by surface attachment and includes cement, glue, paste, etc. There is no universally accepted definition of a structural adhesive, but in the following chapters the term will be used to describe monomer compositions which polymerise to give fairly stiff and strong adhesives uniting relatively rigid adherends to form a load-bearing joint.

The term adhesion refers to the attraction between substances whereby when they are brought into contact work must be done in order to separate them. Adhesion is an important phenomenon in science as well as in engineering, but it is used in a different sense. The engineer uses experimentally determined values, which describe joint behaviour under specified conditions, in order to classify the bond or adhesion between two phases. To the physical chemist adhesion is associated with intermolecular forces acting across an interface, and involves a consideration of surface energies and interfacial tensions. The modern science of adhesion is concerned at a fundamental level with increasing our knowledge of the nature of the forces of attraction between substances, determining the magnitude of such forces and their relation to measured joint strengths. For many adhesive/substrate interfaces of practical import­ance, however, there are still unresolved debates concerning the detailed mechanisms of adhesion and the mechanics of joint rupture.

The materials being joined are often referred to as the adherends or substrates. The properties of the composite made when two adherends are united by adhesive are a function of the bonding, the materials involved and their interaction by stress patterns. It can be appreciated that adhesive bonding technology presents some very unfamiliar concepts to all engineers and, in particular, to civil engineers.

The science of adhesion is truly multi-disciplinary, demanding a consideration of concepts from such topics as surface chemistry, polymer chemistry, rheology, stress analysis and fracture mechanics. It is, nevertheless, important for the technologist to possess a qualitatively correct overall picture of the various factors influencing adhesion and controlling joint performance in order to make rational judgements concerning the selection and use of adhesives.

As with any new technology there are both advantages and disadvantages so that when considering the use of adhesives the merits of the main alternative means of joining (e. g. by welding, bolting, riveting and brazing) should be assessed. The main advantages and limitations of adhesive bonding are given in Table 1.1. The opportunities for increased design flexibility and innovation in design concepts is very real, provided that due consideration is given to balancing the needs of the various materials in a bonded assembly. However, the difficulties of ensuring a good standard of surface pretreatment, particularly to enhance long-term joint durability, are very real, as are the difficulties inherent in verifying the integrity of bonded joints.

Structure of the book

Table 1.1. Advantages and limitations of adhesive bonding

Advantages Limitations