tailieunhanh - Handbook Corrosion (1992) WW Part 5

Tham khảo tài liệu 'handbook corrosion (1992) ww part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Table 10 Some standard galvanized fasteners Description ASTM specification Grade or type Carbon steel bolts A 307 Grade A B High-strength bolts A 325 Type 1 Transmission tower bolts A 394 Type 0 1 Quenched-and-tempered alloy steel bolts A 354 Grade BC Galvanized coatings in bearing-type connections which develop shear resistance by allowing the bolts to bear on the plates are not detrimental to performance and have along history of use--for example in electrical utility transmission line towers. In friction-type connections all loads in the plane of the joint are transferred by the friction developed between the connected surfaces. The load that can be transmitted is determined from the clamping force applied to the bolts and the coefficients of friction of the faying surfaces. Clean galvanized mating surfaces have a coefficient of friction that is slightly lower than that of as-rolled steel. The coefficient of friction of galvanized surfaces can be made equal to that of uncoated steel surfaces by wire brushing or light grit blasting Ref 40 41 . Neither treatment should be severe enough to produce breaks or discontinuities in the galvanized coating. The fatigue behavior of galvanized steel connections equals that of uncoated steel connections regardless of whether the galvanized surfaces were wire brushed or gritblasted after galvanizing Ref 40 41 42 . Welding. Zinc-coated steel can be satisfactorily welded by all common welding methods but attention must be given to the possible generation of zinc fumes. Adequate ventilation operator respiration units or a fume-extracting welding unit should be used to avoid potential harmful effects. Extensive tensile bend radiographic and fatigue tests show that the properties of sound metal inert gas or metallic are welds on galvanized steel are equivalent to those on uncoated steel Ref 35 Penetration of molten zinc into the weld metal is the primary factor in cracking of galvanized steel weldments. The crack begins at the root