Welds dissimilar materials

Dissimilar Material Welds Dissimilar material welds assumed for a transition from superalloy to titanium pressure boundary at cooler. Dissimilar welds assumed to be less reliable than normal welds due to potential brittle phases. Crack/Leak to space. 9990 per weld... 

Stainless steel develops a passive protective layer (<5-nm thick) of chromium oxide [1118-57-3] which must be maintained or permitted to rebuild after it is removed by product flow or cleaning. The passive layer may be removed by electric current flow across the surface as a result of dissinulat metals being in contact. The creation of an electrolytic cell with subsequent current flow and corrosion has to be avoided in constmction. Corrosion may occur in welds, between dissimilar materials, at points under stress, and in places where the passive layer is removed it may be caused by food material, residues, cleaning solutions, and bmshes on material surfaces (see CORROSION AND CORROSION CONTROL). 

Dissimilar Materials. When materials having different preheat requirements are welded together, it is recommended that the higher temperature shown in Table GR-3.5 be used. 

A variety of techniques is available for joining plastics to themselves or to other materials—mechanical fastening, welding, and bonding with adhesives—and all are used extensively. Each method has both advantages and drawbacks for plastics, bonding might be said to be preferable when they are to be joined with dissimilar materials. 

Polymer Engineering and Science 40, No.8, Aug.2000, p.1931-41 FRICTION WELDING OF SIMILAR AND DISSIMILAR MATERIALS. PMMA AND PVC... 

Novikov, V.G., Diffusion bonding dissimilar materials in aerospace technology. Weld. Int. 65 (1995) 477-478. 

In order to facilitate this shift toward lighter materials, designers have had to identify an appropriate method of joining new and dissimilar materials. The joining method must be fast and easy to achieve, and the resultant joints need to be strong and durable (at least on a par with the performance of welding and other traditional methods of joining steel components). This is where structural adhesives have helped to make a big difference. 

LEW is a versatile process and can be used to weld a variety of materials including carbon steels, stainless steel, titanium, aluminium, nickel alloys and plastics. Lasers are often used in high-volume production applications as they have high welding speeds and a level of automation which allows them to be used in numerically controlled machines and robots. They are also used to weld dissimilar metal combinations. 

With these materials, solvent cementing or thermal-welding methods are often preferable alternatives to adhesive bonding. However, where dissimilar materials are being bonded, or where the thermoplastic is relatively inert to solvents, adhesive bonding is recommended. 

Ultrasonic welding is the most common thermal assembly process used with polybuty-lene terephthalate parts. However, heated tool welding and other welding methods have proven satisfactory joints when bonding PET and PBT to itself and to dissimilar materials. Solvent cementing is generally not used to assemble PET or PBT parts because of their solvent resistance. 

Plastics that are readily bonded with induction methods include all grades of acrylonitrile butadiene styrene (ABS), nylon, polyester, polyethylene, polypropylene, and polystyrene, as well as those materials often considered more difficult to bond such as acetals, modified polyphenylene oxide, and polycarbonate. Reinforced thermoplastics with filler levels up to 65 pCTcent have been joined successfully. Many combinations of dissimilar materials can be bonded with induction welding processes. 

Weld Overlay (WOL) Produced by weld depositing a dissimilar material on a base metal surfaee. 

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