Cadmium Substitution - garteur

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GARTEUR LIMITED Additional data obtained by DERA in earlier research [I3] is given in figure I3 for PVD aluminium and PVD aluminium - 5% magnesium coated bolts and nuts. The data points represent the torque values required to achieve each incremental bolt load. For each coating type, data are presented for lubricated and dry fasteners recorded on the first and fifteen nut runs. The scatter in results indicates that the bolt to bolt variation in torque-tension characteristics, are greatest for non-lubricated fasteners. Repeated installations upto 15 nut runs resulted in the degradation of the torque-tension relationship for the PVD coatings. In some instances seizure of the fasteners occurred and often very high torque levels were required to achieve a modest 2kN preload. I.4 Coefficient of friction Values for the coefficients of friction for the various coatings examined in this programme are compared in table I4. Data obtained from earlier work carried out at DERA [I2,I3] is included together with some published values. With the exception of the Delta-tone coating, the coefficient of friction measured is higher than for cadmium plating. The value of the coefficient of friction is sensitive to the measurement method employed. This is reflected in the range of values obtained for electroplated cadmium. I.5 Conclusions 1. For a given locking torque, the preload level recorded is dependent on the coating system. 2. All the coatings examined resulted in pre-loads on Hi-Lok fasteners greater than the minimum 4kN required. With the ED cadmium, ED aluminium, ED Zn-Co-Fe and ED Zn-Ni coated steel fasteners the maximum preload of 10kN was exceeded. 3. With the exception of the Delta-tone coating, coefficients of friction greater than that found for cadmium plating have been measured. 4. Torque-tension tests conducted on combinations of cadmium and Delta-tone coated bolts and nuts have shown that with repeated loading, the greatest change in properties occurs when both the nut and bolt are cadmium plated. The change in coefficient of friction and preload is small if one of the elements is plated with Deltatone. 5. Previous work indicates that PVD aluminium coatings may be ineffective on bolts subjected to repeated loading. I.6 References [I1] [I2] L Magnusson, "Electroplated coatings of Zn-Co-Fe and Zn-Ni. Effect on fatigue properties and tension-torque", SAAB report TUDL R-4015 (1993) V C R McLoughlin, "An evaluation of coatings for steel and titanium alloy fasteners for aircraft applications", AGARD Conference Proceedings No.256, Advanced Fabrication Processes Florence, Italy (1978) [I3] P L Lane and C J E Smith, “Development of aluminium-alloy coatings for the protection of steel”, published in Surface Engineering Practise (ed. K N Strafford, P K Datta and J S Gray) pp566-577 Ellis Horwood Ltd. Chichester (1990) Page 98 GARTEUR SM/AG17 TP128
GARTEUR LIMITED [I4] C A Boose and R J A Blankers, "Investigations of the properties of electrodeposited SIGAL® galvano aluminium coatings", TNO Report 85M/016089 BLA/AKU (1984) GARTEUR SM/AG17 TP128 Page 99
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GARTEUR LIMITED Coating Thickness
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GARTEUR LIMITED A.2.4 Delta-tone/De
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