Optimal Operational Conditions during Production of Lead-Calcium-Tin Anodes for Improve Their Mechanical Properties

Abstract

Previous works have shown that a minimum yield strength s0 of 58 MPa for leadcalcium- tin anodes of 6 mm thickness and a nominal composition of 0.7% Ca and 1.3% Sn are required to avoid early deformations and distortions during their operation in copper electrowinning cell. This s0 value for the anodes is associated with a terminal cold rolling process and a further precipitation hardening prior to their installation in the electrowinning cells. The objectives of the present work are to determine the alloy recrystallization temperature according to Ca and Sn contents, the maximum cold rolling temperature and the aging time required to obtain the desired mechanical quality. The results indicate that recrystallization temperature ranges between 120 and 150°C, according to the anode composition. To reach the desired deformation and precipitation hardening and consequently a yield strength of 58 MPa, the maximum cold rolling temperature is 45°C and the minimum aging time, 30 days.

Study of precipitation hardening in lead calcium tin anodes for copper electrowinning

“…without deformation hardening. 2 Figure 5 shows a typical optical micrograph of our anodes Figure 5a shows a recrystallised structure consistent with the annealing process, while in Fig. 5b, some deformed grain was observed.…”

“…The recrystallisation temperature of the anodes varies between 120 and 180uC according with Ca and Sn contents, being of 150uC for the nominal composition of 0?07%Ca and 1?3%Sn. 2 The hot rolling is done in three passes with an average strain rate of 2?5 s 21 and a total rolling time of 1-2 min, so no enough time is available for a complete recrystallisation and as a consequence some deformed grain appears, as shown in Fig. 5b.…”

“…By means of a semiempirical theory it has been possible to establish, as the minimum mechanical quality standard, that 6 mm thick anodes should have a yield stress of 58 MPa to obtain a standard working life of 3-4 years. 1,2 The catastrophic deformation of some anodes after a few months of operation has been shown to be due to low values of the yield stress, around 40 to 45 MPa. This effect can be seen in Fig.…”

“…The yield stress s 0 of the anodes depends on the deformation hardening generated during their final cold rolling process, about 20 MPa of the final value of s 0 , and on the precipitation hardening induced after their metal forming. 2,3 Since precipitation hardening depends on distribution and size of precipitates, in general associated with the cooling rate and temperature at which hot rolling is done, the aim of the present work is to optimise these variables from the point of view to perform the highest possible yield stress.…”

Optimal Deformation Hardening in Lead Base Anodes for Copper Electrowinning for an Appropiate Working Life

“…If this loss of thickness is combined with a low yield stress of the anodes, dependent on its precipitation and deformation hardening, these are much more likely to suffer premature deformations and distortions in cells, being not compatible for the optimal process due to over voltages, short circuits and other related problems which affect the cathodic copper quality. Regarding the yield stress of 6 mm thick anodes, Camurri et al [1][2][3][4][5] demonstrated that a minimum value of 58 MPa is needed to assure a working life of 4-5 years, if working at a typical current density of 300 A/m 2 . It was also demonstrated [1][2][3][4][5] that to achieve the appropriate minimum value of 58 MPa for the yield stress of aged anodes the contribution associated to the deformation hardening must be at least 20 MPa, reached with a 50% of area reduction during the final cold rolling process, from 12 to 6 mm of thickness.…”