Aerospace structures adhesives manufacture

The increasing amount of research in waterborne systems should some day overcome technological difficulties. Howeverr the change-over from some solvent-borne to waterborne systems has presented difficulties (107), for exampler poor coating quality, excessive foam, insufficient water resistance, and even some corrosion and clean-up problems. Despite the problems, some waterborne systems have already been adopted for the manufacture of PSA s, contact adhesives, laminating adhesives, and wood adhesives. However, few applications of the waterborne systems as structural adhesives, especially as aerospace structural adhesives have been found. 

For both small boats and racing yachts, the adhesive bond line thickness is rather variable it is not possible to maintain tight composite tolerances with this type of hand layup or oven manufacture, so adhesive thickness can reach several millimeters. This is much thicker than for aerospace structures, produced using film adhesives with carrier fabric in autoclaves, for which a typical bond line thickness is less than 0.2 mm. The consequences of this larger bond line thickness may be significant, resulting in ... 

Composites Both UV and EB cures are employed for the production of wood composite materials and in fiber-reinforced composites for aircraft and aerospace applications. The EB technology has been successful in the manufacture of large structures that exceed the size of autoclaves, and in curing adhesive joints in cases where uniform radiation can be provided more easily than uniform heat. In industrial and consumer applications, multiple combinations of different reinforcing fibers can be co-cured in one cycle by EB with considerably lower residual stresses than those introduced by thermal cure.16... 

In contrast to aluminum and titanium structural bonds where performance can be optimized for most aerospace applications, steel bonds are often designed to minimize cost as long as certain performance standards are met [47]. If feasible, many manufacturers prefer to select adhesives or primers that provide adequate strength and durability with untreated steel rather than to prepare the surface for bonding. 

In addition to the preforms and pellets mentioned in Section II.A.l.c., there are other forms of solid adhesives that have much versatility of use. Films and tapes have long been used in the manufacture of bonded flat structures. In particular, the aerospace industry has used a wide variety of film adhesives. In general, these products are handled manually. Occasionally such equipment as tape dispensers are used as assists to manual applications. Work is presently in progress to develop an automatic device to apply strips of film adhesive to automobile hoods. This device will be a curve-following robot that will place the adhesive in the hemming flange around the outer edge of the hood. 

We will study the formulation and manufacturing of these films in the relevant chapters. For instance thermosetting structural films based on epoxies are studied in the chapter Epoxy Adhesives in Volume 5, and also in chapter Aerospace Bonding in Volume 1. 

Epoxy resins are widely used as protective coatings and adhesives, for structural applications such as adhesives to bulk out structural components, with extensive use in the aerospace, dental and other medical fields. Moreover, epoxies are widely used as insulating and structural materials in manufacturing microelectronic devices and components such as computer chip packing and circuit boards, due to their excellent combination of chemical and corrosion resistance and good electrical properties. On the other hand, unsaturated polyester (UPE) resin, a resin prepared from a polyester synthesized by esterification of glycol, unsaturated acid and saturated acid dissolved in styrene monomers, is widely used in many applications, such as electronic equipment, containers, automobiles, and cultured marble because of its clarity, and excellent chemical and corrosion resistance. 

Polymeric adhesives and sealants are finding increased use in aerospace and automotive applications. This is due to the benefits they offer enabling the manufacture of structures with high strength yet low weight. Readers are referred to the chapter Sealants for Aerospace in this Handbook. 

Epoxy resins see large applicability in the aerospace and defense sector for a large number of structural applications as adhesives, as coatings, and in composite forms. Epoxies are used in composite manufacture and repair, missile manufacture, and bonding of aluminum skins to the aircraft body. 

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