Лако-красочные материалы — производство

Casein and then formaldehyde resin compositions have been used as adhesives and gap fillers in wooden boat construction for many years. The most significant use of resorcinol-formaldehyde resins was for the construction of wooden minesweepers for the Royal Navy, each vessel requiring some 3 to 5 tonnes — used mostly for laminating the hull. Polyester resins were then introduced to the marine industry and in 1950 the Scott-Bader Company recorded the construction of the first polyester-glass vessel. Intense development led to virtually all boat-builders producing moulds or finished GRP (glass reinforced plastic) craft, with wooden boat construction assuming a minority or specialist role. Many GRP-hulled boats, both naval and civilian, now rely significantly on resins for laminating, stiffening, the fabrication of sandwich panels, and for bonding attachments. Indeed the fitting out of many vessels is conducted with the large-scale use of non-structural sandwich — and insulating panels using various bonded skin and core combinations. Epoxides were introduced into the industry for a range of bonding and gap­filling applications, one of the latter being for accommodating the tolerances and consolidating the bearings in large mooring buoys for oil tankers.

The most significant marine use of resins is actually in the form of paint corrosion protection systems for hulls. These include polyurethane and epoxide systems, the latter giving good alkali and solvent resistance in addition to providing superior adhesion to most substrates. Such systems take the form of zinc-rich epoxy and epoxy coal-tar combination hull paints. Epoxy powder coatings are also commonly used for the protection of steel pipelines, both on land and offshore.

A number of interesting structural applications of adhesives lie with the development of bonded stiffened plate structures for hulls, the development of lighter-weight composite superstructures (by bonding fibre-reinforced plastics to steel portals and frames), and with the repair of aluminium superstructures. The latter application arose because fatigue cracking developed in Type 21 Frigates, which was difficult to stop from propagating further by such means as drilling out the crack tips. Instead steel plates, up to 6 mm thick, were bonded over the cracks using a two-part cold-curing epoxide; carbon fibre laminate material was later used in place of the steel. The technique provides a rapid repair method with sufficient strength to contain cracking and minimise water leakage until such time as major replating can be carried out. The possibility of developing the procedure to provide sufficient durability and integrity as a permanent solution is being investigated by the Admiralty.

Many offshore steel structures are subjected to major damage due to accidents and collisions, or through stress fatigue failure of welded joints. As well as damage repair there are instances where it is necessary to modify or to strengthen existing structures. Conventional modification or repair techniques, often involving underwater welding, are extremely expensive and the development of the technique of underwater bonding of steel substrates represents a major technical advance in recent years. Adhesive-assisted repair methods for submerged steel structures have been developed by the Admiralty in conjunction with the Department of Energy, together with industry. This has required the formulation of hydrophobic filled cold-curing epoxides, as well as a sacrificial pretreatment technique; an adhesive-compatible hydrophobic film is deposited on

the surface to be bonded which is then absorbed, or displaced, by the adhesive and enables adhesion to be gained underwater.

Another major offshore application, albeit still potential, lies with the stiff lightweight adoption of aluminium and/or polymer composite topside structures in order to reduce weight. Structural aluminium sections may be created by bonding together individual extrusions, and a most convincing demonstration of the potential has been developed by British Alcan (see Chapter 8).