Application of Hard Chromium Flow Plating Technology on Inner Wall of Mold Copper Tube

Summarizes the application of hard chromium flow plating technology on the inner wall of crystallizer copper tube, and describes the basic principle and operation points of hard chromium flow plating technology on inner wall of mold copper tube. By comparing with the traditional bath electroplating, it shows that the main benefit index and technical index of hard chromium flow plating technology for mold copper tube have been significantly improved.

Key words: mold copper tube; flow plating technology; environmental protection; economic benefits

At present, the main method of electroplating hard chromium layer on the inner wall of the copper tube of the steel continuous casting crystallizer is the traditional tank electroplating method, which is to combine the copper tube and the anode through the fixing and connection support of the hanger, and hang the whole into the plating tank for electroplating , usually called tank plating (immersion plating), its main advantage is that the electroplating equipment is simple, the main body of the equipment is a DC power supply and the plating tank, the production line has low investment, and is easy to build, so this electroplating method has been widely used in the past. , and many companies are still using it. The disadvantages of tank plating are also very significant, mainly as follows: ① The utilization rate of chromic anhydride is low, generally around 30%, mainly due to the carrying out of hangers, anodes, workpieces, exhaust air at the side of the tank, and short service life of the plating solution. ②Low current efficiency, generally 15`18% ③High energy consumption, coating thickness 0.1mm, average power consumption per square decimeter 1.14kwh ④High labor intensity ⑤High risk of environmental pollution ⑥High comprehensive cost, coating thickness 0.1mm, average per The square decimeter is about 67 yuan. Based on these advantages and disadvantages, all relevant enterprises are currently trying to explore new hard chromium electroplating technology for mold copper tubes to overcome the shortcomings of traditional bath plating.

Basic principle of flow plating system

The flow plating equipment and operation principle of chromium plating on the inner wall of the copper tube of the crystallizer are shown in Figure 1:

Figure 1 Schematic diagram of flow plating equipment for hard chromium plating on the inner wall of the crystallizer

As shown in Figure 1, the flow plating equipment system mainly consists of a computer, liquid storage tank, electroplating power supply, infusion pump, pneumatic valve, temperature control device, liquid level monitoring device, trivalent chromium electrolysis device, etc. The entire flow plating equipment system consists of The computer takes control.

Temperature control

According to the hard chromium electroplating process requirements, set the temperature on the computer at 55±2°C, and the computer will send instructions to the temperature control system (in the red rectangle area in Figure 1), and the temperature control system will execute the computer instructions to control the plating solution. Perform heating or cooling work.

Electroplating process

Input the parameters such as the specifications of the copper tube, electroplating time, current density, and flow rate of the plating solution into the computer, assemble the copper tube on the flow plating equipment, and start the electroplating start command through the computer. The computer will send instructions to the infusion pump, frequency converter, and electroplating power supply. At this time, the D1/D3 pneumatic valve will automatically open, and at the same time the D2/D4 pneumatic valve will automatically close. The infusion pump P2 will start, and the plating solution will pass through the D1/D3 pneumatic valve. , between the liquid storage tank, pump, flow meter, and copper tube of the crystallizer, the PVC pipeline forms a closed path to circulate and flow. Under the control of the computer, the electroplating power supply starts the current output work according to the set value until the electroplating set time At the end, the electroplating work is completed. After the current returns to zero, the D1/D3 pneumatic valve will automatically close, and at the same time, the D2/D4 pneumatic valve will automatically open, and the washing pump P3 will start to work, and the cleaning water will pass through the D2/D4 pneumatic valve and PVC pipeline for post-plating washing for 1min. After the washing work is completed, the clamping and sealing device controlled by the pneumatic cylinder is automatically opened, and the copper pipe is removed from the equipment, and the entire electroplating process is over.

Plating solution level monitoring

Since the liquid storage tank is fully enclosed, it does not need to be opened during the daily electroplating process, but the liquid level of the plating solution will also drop during use, so the liquid storage tank is equipped with a liquid level control device. When the liquid level is lower than the set When the value is set, the P4 pump will start to work, and the online cleaning water will be automatically replenished into the liquid storage tank.

Trivalent chromium electrolysis device

Since Cr3+ will be continuously produced during the electroplating process, when the content of Cr3 exceeds a certain limit, there will be problems with the quality of the electroplating coating. In order to overcome this process problem, an online electrolysis device is installed in the liquid storage tank. Electrolysis is carried out continuously to control the stability of Cr3+.

Key Points of Operation of Flow Plating Equipment for Hard Chromium Plating on the Inner Wall of Crystallizer

Since the flow plating equipment is an equipment with high system coordination, each module may cause quality problems if there is a problem in the electroplating process. Therefore, we must pay attention to the key points of operation during the use process. After a long-term use summary, the flow chrome plating equipment needs daily attention. The main points are: ① Pay attention to the sealing of the plating solution. During the electroplating process, the plating solution is fully sealed and circulated. When there is slight leakage of the plating solution at the upper and lower ports of the copper tube, pay attention to the use of the sealing material. When the voltage fed back on the computer is too high, pay attention to whether the clamping of the cathode and anode is normal. ③Pay attention to the uniformity of the coating thickness. When the thickness of the coating is uneven, it is generally caused by the uneven distance between the anode and the inner wall of the copper tube. Pay attention to the anode Whether the positioning board is abnormal. ④ Pay attention to the stability of the plating solution temperature. When the plating solution temperature is high or low, first determine whether the temperature sensor is normal, and verify it with a standard mercury thermometer. If there is no abnormality, check whether the heating pipe and cooling water delivery pump are normal one by one. . ⑤ Pay attention to the stability of the flow rate of the plating solution. When the flow rate of the plating solution is unstable, check whether the pneumatic solenoid valve on the pipeline is working normally or check whether the plating solution delivery pump is working stably.

Comparison and analysis of main electroplating benefits and technical indicators

After long-term use, the production data of convective chromium plating have been statistically summarized. In this paper, similar data of flow plating and traditional tank plating are compared, as shown in Table 1:

Table 1 Comparison table of hard chrome plating flow on the inner wall of the crystallizer and traditional tank plating index comparison table

Main Indicator                  TypePlating methodflow platingbath platingCompared
Comprehensive cost (1dm2, 0.1mm thick plating)52 yuan67 yuan22% drop
Chromic acid consumption (1dm2, 0.1mm thick plating)0.016kg0.028kg42% increase
Comprehensive power consumption (1dm2, 0.1mm thick plating)1.02kwh1.14kwh10.5% reduction
Plating solution life (from preparation to replacement time)1.5 years1 year50% increase
current efficiency20%18%11% increase
Wastewater generation (average per copper pipe)150kg194kg22% reduction
Plating solution inventory (according to 20,000 pieces of output/year)12 tons28.5 tons57% reduction
Manpower demand (according to 20,000 production/year)12 people15 people20% reduction

It can be seen from the comparative data in Table 1 that compared with the traditional tank plating, the main benefits and technical indicators of the hard chromium flow plating on the inner wall of the crystallizer have been significantly improved, and the purpose of overcoming the shortcomings of the traditional tank plating has been achieved. Analysis as follows:

The consumption of chromic acid is low, because flow plating is copper pipe plating outside the tank, so the amount of chromic acid carried out is very small; the liquid storage tank is fully sealed, no side exhaust is required, and there is no loss of chromic acid mist; flow plating does not need Put the copper pipe into the plating solution, so the maintenance of the plating solution is better, the service life of the plating solution will be extended, and the usage of the prepared plating solution will also be reduced; no chromium deposition will occur on the hanger, and these are the consumption of chromic acid main factor in the decline.

The comprehensive power consumption is reduced, mainly because there is no chromium deposition on the hanger, and the current is not dispersed; the number of liquid storage tanks is reduced, and the power consumption of electric heating is significantly reduced; the cylinder is used to clamp and conduct electricity, and the conductive line has fewer contacts and good contact. Less power loss; do not draw air at the edge of the tank, and reduce power consumption. These are the main factors for the reduction of power consumption.

The current efficiency is improved, mainly because the hanger does not produce chromium precipitation, which reduces the dispersion of the current and improves the utilization rate of the current; in the traditional tank plating, the inner wall of the hole is plated with chromium, the mass transfer rate of the liquid phase of the plating solution is poor, and the current efficiency is low. Plating is carried out through the infusion pump to enhance the flow rate of the plating solution in the inner hole, which improves the speed of liquid phase mass transfer and improves the current efficiency.

The reduction in the amount of waste water is mainly due to the fact that the outer surface of the copper tube does not adhere to the plating solution during flow plating, so the amount of cleaning water is reduced; the hanger is fixed on the flow plating equipment and does not need to be rinsed, so the amount of cleaning water is reduced.

The decrease in the amount of plating solution is mainly due to the fact that after the flow plating equipment is adopted, each liquid storage tank can supply 4 copper tubes for electroplating at the same time. In the traditional tank plating, each liquid storage tank can supply 2 copper tubes for simultaneous electroplating at most. Therefore, during flow plating, the amount of plating solution is greatly reduced, and the amount of plating solution in the production workshop is reduced, which is also the main factor to reduce the risk of environmental pollution.

The reduction in manpower demand and the improvement of the automation level of hard chromium plating flow plating equipment on the inner wall of crystallized copper tubes are the main reasons for the reduction in manpower demand.

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