Cadmium Substitution - garteur

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GARTEUR LIMITED The adhesion of conventional epoxy based primers to passivated coatings was examined using a standard cross hatch test. In each case the primer was applied to the complete coating scheme. For example in the case of the electrodeposited zinc – nickel and zinc – cobalt –iron coatings these were passivated prior to painting. Further details of the test procedures employed are given in Annex H. 3.8 Tribological properties The low coefficient of friction of cadmium plating makes it an ideal coating for use on fasteners and threaded parts. Much of the torque used in tightening up a bolt is expended in overcoming the frictional constraints. Coatings with a high lubricity are therefore necessary if adequate pre-loads are to be achieved without the application of excessive torque levels. Another advantage obtained with cadmium plated fasteners is reproducible torque-tension characteristics. During the assembly of an aircraft, parts are often bolted into place and then removed for adjustment or modification. This process may be repeated a number of times and it is essential that there is no significant change in the torque-tension behaviour of the fasteners employed. In the current programme the effect of repeated tightening and untightening on the torque – tension behaviour of coated steel bolts and nuts was determined. Details of the tests are given in Annex I. 3.9 Coating repair Trials have been undertaken to examine the repair of coatings damaged in service. Brush plating techniques, for instance, were evaluated as a method of re-plating areas on zinc – nickel electroplated parts. In preliminary work bath plated test panels have been exposed to neutral salt fog and any corroded areas, after cleaning, re-protected by brush plating. The panels were then further exposed to a salt fog environment. Repair methods for other coating systems were also be evaluated (See Annex J). Page 6 GARTEUR SM/AG17 TP128
GARTEUR LIMITED 4 Summarised results 4.1 Coating characteristics Three aspects were evaluated • Microstructure and composition • Electrical conductivity • Coating adhesion 4.1.1 Microstructure and composition The microstructures of the commercially produced coatings were consistent with those described by the various supply houses and reported in the open literature. Table 3 briefly summarises the general appearance of the microstructures and gives details of the coating thicknesses and compositions. The thickness measurements refer to the unpassivated coatings and give the range of values determined by the partners. 4.1.2 Electrical conductivity Results of the electrical conductivity measurements are summarised in table 4. Electrical resistance values were obtained for type B measurements made on joints made using both Hi-Lok fasteners and countersink screws. With the exception of the Delta-tone coatings, values of electrical resistance of less than 1mΩ were obtained. For the type A measurements resistance values could only be determined for ED cadmium, ED zinc-nickel and ED zinc-cobalt-iron coated Hi-Lok fasteners and ED zinc-nickel coated countersink screws. No measurements were made on either the ED aluminium or UMS aluminium – magnesium coatings but it is likely that their performance will be similar to PVD aluminium. The SermeTel 984 coating was not included in the electrical conductivity test as it is not intended as a coating for fastener applications. 4.1.3 Coating adhesion Tests conducted by NLR on ED cadmium, ED zinc-cobalt-iron, ED zinc-nickel and SermeTel 984 coated test specimens indicated that adhesion to grit blasted steel substrates was very good. 4.2 Resistance to corrosion The detailed corrosion test results are given in Annex C. Two aspects of coating performance have been assessed:- • Coating barrier properties • Sacrificial properties 4.2.1 Electrochemical measurements The true barrier properties of the coatings may only be determined using electrochemical methods, which allow the corrosion rate of a coating in contact with a corrosive environment to be measured. In accelerated corrosion and outdoor exposure trials the time to first rust on undamaged coated panels is dependant on both the barrier GARTEUR SM/AG17 TP128 Page 7
Page 2 and 3: GARTEUR LIMITED This page is intent
Page 6 and 7: GARTEUR LIMITED Executive summary B
Page 8 and 9: GARTEUR LIMITED nickel coatings cou
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Page 12 and 13: GARTEUR LIMITED G.1 Introduction 89
Page 16 and 17: GARTEUR LIMITED The various aims of
Page 18 and 19: GARTEUR LIMITED 3 Summary of work p
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Page 26 and 27: GARTEUR LIMITED coatings showed an
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Page 30 and 31: GARTEUR LIMITED 5.3 Conclusions The
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Page 36 and 37: GARTEUR LIMITED 11 Tables Coating t
Page 38 and 39: GARTEUR LIMITED Coating Thickness
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Page 42 and 43: GARTEUR LIMITED As plated Passivate
Page 44 and 45: GARTEUR LIMITED Coating Potential r
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Page 48 and 49: GARTEUR LIMITED Properties ED Zn-Co
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Page 56 and 57: GARTEUR LIMITED A.4 Tables Coating
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Page 64 and 65: GARTEUR LIMITED B.3.3 Coating Adhes
Page 66 and 67: GARTEUR LIMITED Type A Measurements
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GARTEUR LIMITED ED Cadmium IVD Alum
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GARTEUR LIMITED the salt spray was
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GARTEUR LIMITED c) Exposure to 100%
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GARTEUR LIMITED [C7] Baldwin K.R.,
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GARTEUR LIMITED Coating rust (hours
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GARTEUR LIMITED Post plating treatm
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GARTEUR LIMITED DBAA DERA NLR NLR B
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GARTEUR LIMITED C.7 Figures Figure
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GARTEUR LIMITED D.3 Results and dis
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GARTEUR LIMITED D.6 Tables Time hou
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GARTEUR LIMITED D.7 Figures Figure
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GARTEUR LIMITED Figure D4; Current
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GARTEUR LIMITED E.3 Results and dis
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GARTEUR LIMITED E.6 Tables Laborato
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GARTEUR LIMITED Figure E2; S-N curv
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GARTEUR LIMITED compared with cadmi
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GARTEUR LIMITED F.6 Figures Figure
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GARTEUR LIMITED British Aerospace S
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GARTEUR LIMITED This page is intent
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GARTEUR LIMITED immersion was poor
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GARTEUR LIMITED Coating Dry After i
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GARTEUR LIMITED Additional data obt
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GARTEUR LIMITED I.7 Tables Coating
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GARTEUR LIMITED I.8 Figures Cadmium
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GARTEUR LIMITED Cadmium coated bolt
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GARTEUR LIMITED cadmium although it
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GARTEUR LIMITED Garteur main coatin
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GARTEUR LIMITED This page is intent
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GARTEUR LIMITED D-28183 Bremen, GER
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