In early 1980's, various steel companies developed a steel with both ferritic and austenitiv microstructure called duplex stainless steel. It contains the characteristics of ferritic steel such as high yield strength and good weldability with resistance to generak corrosion, pitting and stress corrsion cracking Duplex steels from different mills each have slightly have diffrent chemical copmpositions.,
C(max)= %0,03
Si (max)=%1
Mn(max)= %2
P(max)= %0,03
S(max)= %0,02
Cr=%22
Ni=%5.5
Mo= % 3
Pitting and crave corrosion protection depends on chromium and molydenum present in the steel. Because its ferritic properties duplex steel has high resistance to erosion corosion. The relatively low nickel content may make duplex steel more economical than austenitic steels. That of course, depend on pricing policies of the steel mills: Duplex stainless steels resist the cavitation and caviation corrosion.
Uno Wahren,Practical introduction to pumping technology P.98
Transverse Cracking
Transverse cracks in weld metal formed when predominanr contraction are in directionof the weld axis They can be hot cracks which seperates intergranularly as the result of hot shortness or localized planar shrinkage, or thet can be transgranular separations produced by stresses exceeding the strength of the material. Tranverse cracks lie in a plane normal to the axis of the weld. and are usually open to the surface. They usually extend across the entire face of weld and usually open the surface. They usually extend the across the entire face of weld and sometimes porpagete into the base metal.
Tranverse cracks in base metal occur on surface in or near the HAZ. They are result of the high residual stresses induced by thermal cycling during welding. high hardness excessive restraint and the precense of hydrogen promote theri formation. Such crack propoganete ino the weld or beyond the HAZ into the base metal. as far as needed to relive the residual stresses.
Steve Lampman,ASM International, Weld integrity and performance: a source book adapted from ASM international
Poke Yoke (Poka Yoke)
Althought the concept of poka yoke has existed for a long time in various forms, iı was japanese manufacturing engineering Shigeo Shingo who developed idea into the formiable tool for achieving zero defects and evantually eliminating quality control inspection.The method he avocates were formerly called "fool-proofing" reconizing that this is label could often many workers, Shingo came up with the term poka-yoke generally translated as " mistake proofing" or " fail safing". The idea behind the poka-yoke is to respect the intelligence of workers. By taking over respetitive tasks or actions that depend on vigilance or memory, poka-yoke can free a worker's time and mind to pursue more creative and value-adding activities
Many thing can go wrong in complex enviroment of workplace; every day there are opportunities to make mistake that will result in defective products. Defects are wastefull and if they are not discovered they disappointed the costumer expectations of quality. Behind poka- yoke is the conviction that is not accepteable to produce small number of defective goods.. To become world class competitor. a company mus adopt not only philosophy but a producing zero defects. Poka-yoke methods are simple concepts for achieving this goal.
Poka-yoka, Improving Product Quality by Preventing Defects, P. XI
Flux Cored Arc Welding
 |
| http://www.robot-welding.com/arc_weld_processes.htm |
Although the process was introduced in 1950's it represented less than % 5 of the total amount of welding done in 1965. In 2005 it passed the %50 of mark and still is rising
Advantages.
High Deposition Rate
Minimum Electrode aste
Ecellent controll.
No comments:
Post a Comment