Cadmium Substitution - garteur

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