Anode Technical Proposal

A. Anode Process/Technology Description

1.1 Process Diagram

1.2 Anode Technology Description

1. Anode Plate Specifications

The composition of lead-alloy anode for copper electrowinning is made from Pb-Sn-Ca-Sr and rare earth alloy.

The default effective surface area of the plate is two square meters, and the conductive rod is about 1.3 meters. Furthermore, as one of our customers can also provide us with your design, and we will produce the anode plate according to your drawings.

We sent our alloy sample to a third-party metal research facility for metallography analysis. The result is that our alloy shows our alloy has smooth edges and the gap between each crystal structure. Meanwhile, the Vickers hardness of our alloy is 46.41HV, but the Vickers hardness of other companies’ alloy is 37.92HV.

2. Plates Surface Processing

To improve the performance and service life of the lead-based alloy anode plates, the surface area of the anode plates was increased. The purposes are as follows: firstly, by doubling the surface area of lead-based alloy anode plates, under the same electric current, the surface current density of the new anode plates is halved compared to the other alloy anode plates with a normal surface area. As a result, the rate of surface electrochemical erosion is significantly lowered. Thus, the service life of the anode plates can be prolonged. 

Secondly, by increasing the surface area of the anode plates, the adhesion of the following oxide, such as lead dioxide, cobalt dioxide, and manganese dioxide, can be strengthened on the surface of the anode plate. Therefore, lead-alloy anode can be better protected against the acidic environment. Hence, the quality of cathode copper can be improved. The enhanced anode plate that was used in the copper smelter is shown in figure 1. 

3. Manufacturing of Hanger Bar

The Conductive rods consist of copper rods coated with a layer of special alloy. The process is as follows. First, the grease and oxide on the copper rod are removed by using detergent and acid, respectively. Then, the copper rod is coated with a layer of special alloy. The purpose is to achieve better adhesion between lead-alloy and the copper rod, this is our leading technology. The final step is to cover the copper rod with lead-alloy. Figure 2 & 3. illustrates the three phases of coating process of the conductive bar.

Figure 2. The coating process of the hanger bar (from top to bottom: copper bar coated with special alloy 1, copper bar coated with special alloy 2, original copper bar)
Figure 3. The coating of lead-alloy on the copper rod

4. Welding Between Hanger Bar and Plates

To ensure a firm bond between the plate and the conductive rod, we use a trapezoid-shaped connection point to combine the plate with the conductive rod (as shown in Figure 4). This method can increase the contact area of the plate and the hanger bar. Thus, the plate could tightly weld to the hanger bar. As for the welding method, we use argon-oxygen welding.

Figure 4. Trapezoid-shaped connection illustrations

1.3 Packaging Plan

To adapt to long-range shipping, we use steel racks to hang the anode vertically inside the racks. Between each plate we use plastic foam to protect the surface from scratching. Lastly, we use plastic wraps to wrap around the plate to protect the plate from shifting around during shipping (illustrate in figure 5-9).

Figure 5.  Anode Packaging (front view)
Figure 6.  Anode Packaging (side view)
Figure 7.  Anode Packaging (inside view)
Figure 8.  Anode Packaging (outside view)
Figure 9.  Anode Packaging (with shipping marks and lifting signs)

1.4 Drawing of Anode Plate

B. Anode Inspection Plan

1.1 Raw Material Inspection and Testing Plan:

1. Lead Ingot:

The grade and batch number are guaranteed to be consistent with the suppliers’ quality inspection report. The purity of lead ingot meets the requirement of the Grade one lead. Every batch is randomly surveyed with a weight of about 400g, where the chemical analysis is conducted to investigate the chemical elements for the 200g sample. The analysis results are filled in the lead ingot inspection form and archived to trace the source.

2. Tin:

The grade and batch number are guaranteed to be consistent with the quality inspection report from the suppliers, and the the purity of the silver ingot meets the requirement of >99.9%. The sample is examined, and the analysis results are filled in the Sn ingot test certificate.

3. Copper:

The grade, batch number and quantity are guaranteed to be consistent with the quality inspection report from the suppliers, and the chemical composition meets the production requirement. The dimension, appearance, purity, and hardness inspections for above 5% of the samples are randomly conducted. The analysis results are filled in the copper bar inspection form.

1.2 Process Control and Quality Inspection Measures of Lead-tin Alloy

1. The mold temperature during casting is controlled at 180℃±20℃. Also, the mold is pre-heated for the first time before the work.

2. The alloy casting control form is filled to record the front and back temperature to achieve the traceability, where the front surface temperature of the billet during the casting is controlled at 240-270℃, the back temperature of 230-280℃. We measure the temperature with the infrared thermometer via 5 points method, and the distance is 30cm. If the temperature is not in the required range, we should regulate the lead ingot’s cooling time and mode correspondingly.

3. The hot billets are put into the mold to keep warm.  Then the mold is re-heated when the temperature of the mold is below 160℃.

4. Sampling: The alloy sample is taken from every furnace, which is immediately delivered to the analysis laboratory to determine the chemical composition. The subsequent process can be carried out after the test results are qualified.

5. We identify the Sn, Ca, Sr contents in the sample, and the analysis results are filled in the casting billet alloy report form. If the alloy’s content is unsatisfied, we will take measures to ensure the alloy composition is qualified.

1.3 Process Control and Quality Inspection Measures of Hanger Bar

The conductive copper bar’s raw material comes from the USA ASTM#B-187-92, UNS#C11000 standard copper with the resistance below 1.7593×10-6Ω at 20℃, which corresponds to the Chinese standard GB: T2. We introduced Chile’s advanced technology to improve special alloy coating after exchanging and cooperating with anode plate manufacturers in Chile in recent years. We indeed achieved the metallurgical combination between a lead beam and a copper bar. The lead and copper are not separated without bulging during employment. Besides, the transition resistance between lead and copper is low, possessing a strong binding force. The detailed production process is described as follows. The oil and oxides on the copper surface are cleaned after welding stainless steel hangers on the conducting bar. Then, the conductive copper bar is dipped into the hot plating bath with a temperature of 230-260 ℃ to deposit the alloy layer. After that, the copper beam is cast with hot lead after the copper beam is pre-heated to 230 ℃. The transition alloy between the lead and copper melts and realizes the metallurgical combination. Besides, the casting control temperature is below the softening temperature of Cu (350℃), which effectively guarantees the mechanical strength and hardness of conductive copper beam.

1. The welded junction on the conductive copper beam should be less than 0.2mm, and straight without deformation

2. The exposed copper is polished with a fiber wheel.

3. The conductive copper beams are stacked neatly and placed conveniently for lifting and handling. Each pallet’s total weight is below three tones, and the height of each pallet is below 0.8 m above the ground. Each pallet must be clearly marked to achieve trace ability.

4. We examine the casted conductive beam according to the casting process flow chart. The casting confirmation must be carried out before each shift, and the quantity production proceeds after qualified. The testing results are filled into the hanger bar casting control.

1.4 Process Control and Quality Inspection Measures During Rolling Process

The alloy casting is carried out flat mold casting under cool oil, and the alloy cooling is consistent with uniform composition and fine grain. Thus, the effective strength of the anode plate, alloy uniformity, and compactness is ensured. The plate’s rolling adopts the first hot rolling and then cold rolling process, where the 200 mm thick hot alloy plate is hot-rolled to 25 mm, and finally cold-rolled to 12 mm through 4~5 times repeatedly rolling after 24 hours.

1. The thickness of the hot-rolled billet is 200 mm with the pressure amount of 20-30 mm per round, and the hot rolling temperature is 200-250℃.

2. We recorded the hot rolling production process in the hot rolling control report according to the requirements.

3. Every plate is marked with the furnace number at about 50 mm from the edge mark. Every stack should be less than three tons, and the direction of all plates in each stack keeps the same while cleaning the lead slag during stacking. The lead slag shall not contain between the plates.

4. The cold rolling thickness starts from 25 mm with a pressure amount of 5-8 mm per round. The finishing rolling can be carried out after cooling for 24 hours. The last rolling pressure amount is less than 1 mm, and then the final rolling thickness is confirmed. The finishing process control is filled into the finishing rolling control report.

5. Alloy inspection after finishing rolling: After finishing rolling in each furnace, left, middle and right parts of the plate are randomly taken and marked, which is then send to the analysis center to measure the alloy composition. The analysis results are filled into the cold rolling alloy control report according to the requirements.

1.5 Process Control and Quality Inspection Measures During Resizing

1. The tolerance of the dimension standard (length, width) is less than 3 mm, the diagonal tolerance is within 10 mm.

2.  The production process is filled into the resizing control report to achieve the product’s traceability according to the requirements.

3. The plate surface is smooth and clean without scratches, pits, layers, bubbles, cracks, inclusions, oil, large waves and other defects. Every stack is placed in an orderly manner, and the logo is clear to achieve the traceability of the product.

1.6 Process Control and Quality Inspection Measures During Welding and Packing

1.  Process Control During the Plate Welding

a) The argon arc welding method is adopted to weld the plate and conductive beam.

b) After welding of the anode plate, a piece of anode plate from each batch is extracted to conduct the stretching, metallographic for welding samples to ensure no false welding, leakage welding and other unqualified conditions.

2.  The Quality Assurance Measures

a) The tolerance of the dimension standard (length, width) after the welding is less than 3mm, the diagonal tolerance is within 10mm. The thickness error between the conductive beam and the plate is below 0.25mm. The plate surface is smooth and clean without scratches, pits, layers, bubbles, cracks, inclusions, oil, large waves and other defects. Every stack with weight less than three ton is placed in an orderly manner.

b) Identification of the anode plate: The steel stamp identification ( furnace number blank number board number) is located at the conductive beam’s corresponding position. The packing inspection is conducted according to the packing requirement, and the final dimension inspection is strictly filled to ensure the traceability of the production process.

1.7 Inspection Equipment List During the Production of the Anode Plate

The production process’s quality control fully implements the ISO9001 quality management system, strictly inspects the composition and physical properties of the required raw materials before and during the production process. The advanced testing equipment, high-quality analysts, and accurate analysis methods effectively support product quality during the production process. We employ the atomic absorption spectrometer/ EDM direct-reading spectrometer to examine the alloy elements. A metallographic microscope analyzes the lead alloy’s homogeneity. Moreover, The Brinell hardness tester is employed to explore the alloy plate’s hardness and conductive copper beam. The mechanical properties of the alloy plate are evaluated via a hydraulic universal testing machine. Physical specifications, performance strictly follows the enterprise standards. The equipments are attached in the following.

Figure 10. Atomic absorption spectrometer
Figure 11. Spark direct reading spectrometer
Figure 12. Brinell Hardness Tester
Figure 13. Hydraulic universal experimental unit
Figure 14. Metallurgical microscope

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