Sheet Cladding

Generally, cladding is needed to protect materials from corrosion in hostile environments, e.g., concrete in chemical plants. Two of the most widely used construction materials today are concrete and mild steel. There are, however, two things known for certain, namely concrete will crack, and steel will rust. 

Polymers are favored as cladding materials since there is a wide range of substrates to choose from, with different chemical resistances, operating temperatures, and thicknesses. There is the added advantage that a complete liquid-proof lining can be constructed in new or old structures. Applications include bunded areas in chemical plants and linings for sewage pipes. 

Two factors are very important for adhesion to polyolefins with epoxy adhesives, i.e., (a) the surface activation method, and postactivation cleaning of the surface. 

The surface activation method, especially the gas mixture used, determines the chemistry of the surface and can thus promote the adhesion properties with epoxy adhesives. The following example illustrates the importance of the correct activation gas mixture. As is clearly illustrated by Table 16.6, oxyfluorination induces better adhesive properties than fluorination on PE with Pro-Struct 30/71. 

Postactivation cleaning of the surface can be vital in cases where the polyolefin sheeting is transported and subjected to contamination. The contaminants, e.g., oils and dust, have to be successfully removed prior to adhesion to ensure a strong bond. The effect of certain organic solvents on the adhesion to PE with Pro-Struct 30/71 can be seen in Table 16.7. 

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Our houses are built of wood (cellulose and lignin), sheathed with particleboard (wood chips pressed with plastic resin), wrapped with plastic sheeting, clad with siding (vinyl), and decorated with plastic shutters. Buildings with wood siding are covered with paint. Inside, water flows through plastic pipes, the floors are covered with tiles (vinyl) or carpeting (polyester, nylon), the walls are covered with wallpaper (vinyl) or painted (acrylics), and the... 

Irrigation channels, reservoir linings Interior panels, exterior panels, door frames, windows Sheet cladding, plain roof tiles, fire-resistant pads, molded shapes and forms, pipes... 

Cement sheet and boarding materials such as roofing sheets, cladding, flat sheeting, rainwater services, water tanks, moulded decorative panels or containers, pipework/flue pipes, non-slip external floor tiles etc. 

Multilayered composite sheets and plates can be bonded in a single explosion, and cladding of both sides of a backing metal can be achieved simultaneously. When two sides are clad, the two prime or clad metals need not be of the same thickness nor of the same metal or alloy. 

Explosion-bonded metals are produced by several manufacturers in the United States, Europe, and Japan. The chemical industry is the principal consumer of explosion-bonded metals which are used in the constmction of clad reaction vessels and heat-exchanger tube sheets for corrosion-resistant service. The primary market segments for explosion-bonded metals are for corrosion-resistant pressure vessels, tube sheets for heat exchangers, electrical transition joints, and stmctural transition joints. Total world markets for explosion-clad metals are estimated to fluctuate between 30 x 10 to 60 x 10 annually. 

AJ—Zn. Aluminum-rich binary ahoys (Fig. 18) are not age hardenable to any commercial significance, and 2inc [7440-66-6] Zn, additions do not significantly increase the abhity of aluminum to strain harden. Al—Zn ahoys find commercial use as sacrificial claddings on high strength Al—Cu—Mg—Zn aircraft ahoy sheet. The eutectoid composition near 78% Zn has found use as a superplastic sheet ahoy. 

The resistance to corrosion of some alloy sheet is improved by cladding the sheet with a thin layer of aluminum or aluminum alloy that is anodic to the base alloy. These anodic layers are typically 5—10% of the sheet thickness. Under corrosive conditions, the cladding provides electrochemical protection to the core at cut edges, abrasions, and fastener holes by corroding preferentially. Aircraft skin sheet is an example of such a clad product. 

In a chemical vapor deposition (CVD) variant of conventional powder metallurgy processing, fine chromium powder is obtained by hydrogen reduction of Crl2 and simultaneously combined with fine thorium(IV) oxide [1314-20-17, H1O2, particles. This product is isostaticaHy hot pressed to 70 MPa (700 atm) and 1100°C for 2 h. Compacts are steel clad and hot roUed to sheets (24). 

Cladding may be less expensive than selective electro deposition when coatings greater than 1 p.m of a noble metal are required, but may be more expensive than electro deposition for thinner coatings. Selective techniques are most easily used for sheet metal substrates that are to be machine stamped and formed into contacts. Clad noble metals are considerably more ductile (and less hard) than comparable electro deposits and, therefore, are better suited to forming operations. Contacts that are made into separate parts from rod by screw machining are usually coated on all exposed surfaces by barrel electroplating. 

Clad Tube Sheets Usually tube sheets and other exchanger parts are of a solid metal. Clad or bimetallic tube sheets are usecito reduce costs or because no single metal is satisfactory for the corrosive conditions. The alloy material (e.g., stainless steel, Monel) is generally bonded or clad to a carbon steel backing material. In fixed-tube-sheet construction a copper-alloy-clad tube sheet can be welded to a steel shell, while most copper-alloy tube sheets cannot be welded to steel in a manner acceptable to ASME Code authorities. 

Ferrous-aUoy-clad tube sheets are generally prepared by a weld overlay process in which the alloy material is deposited by welding upon the face of the tube sheet. Precautions are required to produce a weld deposit free of defects, since these may permit the process fluid to attack the base metal below the alloy. Copper-aUoy-clad tube sheets are prepared by brazing the alloy to the carbon steel backing material. 

Profiling - Sheet steel may be pressed into the correct shape for crash barriers or the cladding of buildings (known as profiling). 

Platten-gewebe, n. lamellar tissue, -glimmer, m. sheet mica, -gummi, n. plate rubber sheet rubber, -kaik, m. slab limestone, -kautschuk, n. plate rubber sheet rubber, -kondensator, m. (Elec.) plate condenser, -kultur, /. plate culture, -kupfer, n. sheet copper, -pulver, n. (Expl.) rolled powder, flake powder, -achale, /. flat dish, specif. Petri dish, -turm, m. plate column, plate tower, -zink, n. slab zinc, plattgedriickt, a. flat-pressed, flattened, plattieren, jj.t. plate clad. 

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