Adhesive bonding is a joining process in which a filler material is used to hold two (or more) closely spaced parts together by surface attachment. The filler material that binds the parts together is the adhesive. It is a nonmetallic substance—usually a polymer. The parts being joined are called adherends. Adhesives of greatest interest in engineering are structural adhesives, which are capable of forming strong, permanent joints between strong, rigid adherends, A large number of commercially available adhesives are cured by various mechanisms and suited to the bonding of various materials. Curing refers to the process by which the adhesive's physical properties are changed from a liquid to a solid, usually by chemical reaction, to accomplish the surface attachment of the parts. The chemical reaction may involve polymerization, condensation, or vulcanization. Curing is often motivated by heat and/or a catalyst, and pressure is sometimes applied between the two parts to activate the bonding process. If heat is required, the curing temperatures are relatively low, and so the materials being joined are usually unaffected—an advantage for adhesive bonding. The curing or hardening of the adhesive takes time, called curing time or setting time. In some cases this time is significant—generally a disadvantage in manufacturing.
(Mikell P. Groover,Fundamentals of Modern Manufacturing,4th Edition,pg.756)
Blast Finishing: 31.03 2011 00.35
Blast finishing uses the high-velocity impact of particulate media to clean and finish a surface. The most well known of these methods is sand blasting, which uses grits of sand (S1O2) as the blasting media. Various other media are also used in blast finishing, including hard abrasives such as aluminum oxide {AI2O3) and silicon carbide (SiC), and soft media such as nylon beads and crushed nut shells. The media is propelled at the target surface by pressurized air or centrifugal force. In some applications, the process is performed wet, in which fine particles in a water slurry are directed under hydraulic pressure at the surface.
(Mikell P. Groover,Fundamentals of Modern Manufacturing,4th Edition,pg.663)
Vibratory Finishing: 31.03 2011 00.44
Vibratory finishing was introduced in the late 1950s as an alternative to tumbling. The vibrating vessel subjects all parts to agitation with the abrasive media, as opposed to only the top layer as in barrel finishing. Consequently, processing times for vibratory finishing are significantly reduced. The open tubs used in this method permit inspection of the parts during processing, and noise is reduced.
Most of the media in these operations are abrasive; however, some media perform nonabrasive finishing operations such as burnishing and surface hardening. The media may be natural or synthetic materials. Natural media include corundum, granite, limestone, and even hardwood. The problem with these materials is that they are generally softer (and therefore wear more rapidly) and nonuniform in size (and sometimes clog in the workparts). Synthetic media can be made with greater consistency, both in size and hardness. These materials include AI2O3 and SIC, compacted into a desired shape and size using a bonding material such as a polyester resin.
(Mikell P. Groover,Fundamentals of Modern Manufacturing,4th Edition,pg.664)
Emulsion Cleaning: 31.03 2011 00.51
This cleaning method uses organic solvents (oils) dispersed in an aqueous solution. The use of suitable emulsifiers (soaps) results in a two-phase cleaning fluid (oil-in-water), which functions by dissolving or emulsifying the soils on the part surface. The process can be used on either metal or nonmetallic parts. Emulsion cleaning must be followed by alkaline cleaning to eliminate all residues of the organic solvent prior to plating.
(Mikell P. Groover,Fundamentals of Modern Manufacturing,4th Edition,pg.662)
No comments:
Post a Comment