Design and application of multidimensional decision system for aluminum electrolysis
Aluminum electrolysis is a complex process, the outputs of the controller are hard to decide. This paper described a system for the decision of the setting voltage, AlF3 addition and aluminum tapping amount in aluminum electrolysis process according to the equivalent superheat which is regarded as the main parameter. The system has four sub-systems, which are the fault diagnosis, equivalent superheat calculation, control extent decision, decision quantity correction. The cell state diagnosis was implemented based on the frequency characteristics of cell resistance, which helps to select the decision strategy. The superheat soft measurement model was given by the analysis and calculation of electrolyte composition after the aluminum fluoride volatilization rate model was built, and it was on-line corrected by the actual measured value. The outputs of the controller were got by the equivalent differential diagram. At last, the decision content was corrected by the prediction of temperature. This system have been applied in a 300kA aluminum production control system, and the results showed that the temperature can be controlled between 945 degree celsius and 960 degree celsius, and the superheat can be controlled within 12 degree celsius, the current efficiency increased and power consumption reduced.
Calculation and control of equivalent superheat for 300kA prebake aluminum electrolysis
The superheat is one of most important technical parameters in aluminum electrolysis. Based on the principle of material and energy equilibrium, this paper analyzed the effect of superheat on the aluminum industrial process. By combination of the dairy decisions of the aluminum reduction, the vaporization model of aluminum fluoride was built with selecting the temperature and free aluminum fluoride, and the model for superheat soft measurement was given by use of the data from chemical analysis and computation of the compounds of electrolyte. This model can be periodically revised on line in the practical uses. This paper also divided the cell status by three parameters which are temperature, superheat and aluminum level, on which the control charts were plotted and decision system was designed. This technique was applied in Baotou Hope aluminum limited, and results showed that temperature was largely controlled 950–960 centigrade degree, the superheat was controlled between 5–10 centigrade degree, and the current energy consumption has been lowered obviously.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.