Process analysis:

Alkali liquor degreasing

The electroplating process is a method to lay a layer of metal on the conductor by using the principle of electrolysis. The chemical action (saponification) of alkali is used to remove the grease and slight rust on the metal surface. This method is often used to remove ferrous metals such as steel, nickel, copper, and nonferrous metals insoluble in alkali solution. The main components of alkali liquor include sodium hydroxide, trisodium phosphate, sodium silicate, sodium carbonate, sodium sulfate, etc. Among them, sodium hydroxide plays the role of saponification and washing. The concentration of sodium hydroxide determines the washing effect and has a great impact on the subsequent process. Therefore, PH detection is very important in this process!

Model selection: PH controller+PTFE electrode

Function: After the alkali liquor is degreased, the workpiece needs to be carefully rinsed. The common alkali cleaning aids are sodium hydroxide, soda ash, sodium silicate, and sodium tripolyphosphate. As alkali agents, sodium hydroxide and soda ash are the cheapest, and wastewater is difficult to treat. Sometimes the washing objects are damaged due to the strong alkalinity. On the other hand, sodium hydroxide and soda ash have no emulsification effect on the cleaning of mineral oil, so online PH is needed to monitor the PH value of the detergent aid

Note: The PH electrode needs to be a tetrafluoro electrode, not a conventional plastic shell electrode, or it will be corroded

Advantages: in the process of alkaline washing, alkali is directly added for cleaning, and a small amount or excessive amount will lead to a poor cleaning effect, so the online PH can well regulate the PH value to achieve a better effect of oil removal.

Three-stage countercurrent rinsing (wastewater containing chromium and zinc)

The so-called multi-stage dynamic countercurrent rinsing has three characteristics: first, the cleaning tank is not a single tank, and the workpiece needs to go through multiple cleaning steps one after another; Secondly, the cleaning water is not static but in a series of cleaning tanks, supplying water from the last cleaning tank and draining water from the first cleaning tank; Third, the direction of the workpiece to be cleaned is opposite to the direction of the water flow, which is in reverse motion. Although multi-stage dynamic countercurrent rinsing can not achieve zero discharge of cleaning water, three-stage countercurrent dynamic rinsing has an obvious water-saving effect. Of course, this process will involve sewage discharge! A flowmeter is required.

Model selection: PTFE lining+titanium alloy electrode

Function: During wastewater discharge, it is necessary to detect the flow of wastewater, and an electromagnetic flowmeter is required

Note: The discharge of wastewater is mostly self-flowing. To ensure full pipe, attention should be paid to the installation position of the electromagnetic flowmeter

Advantages: The wastewater treatment in the electroplating park needs to be metered if it is charged. The electromagnetic flowmeter meets the needs of most sites in terms of corrosion resistance and high accuracy.

Hydrochloric acid pickling activation

A processing method that uses chemical methods to remove rust and oxide film on the surface of the substrate and make the workpiece surface in an activated state

Although sulfuric acid or hydrochloric acid can be used as a pickling solution, hydrochloric acid is mostly used in hot galvanizing production. The reason for this is that hydrochloric acid pickling can be carried out at room temperature. Hydrochloric acid has strong chemical dissolution on metal oxides, and can effectively perform pickling on multiple metals. In the greenhouse, hydrochloric acid dissolves and pickles the iron matrix of the steel workpiece faster than sulfuric acid, and the pickling time is shorter, so it is easy to effectively control the pickling process. Therefore, it is not easy to cause "over corrosion" and "hydrogen embrittlement" when using hydrochloric acid to pickle steel workpieces.

Model selection: PH controller+PTFE electrode

Function: Because the acid solution is required to remove oxide skin and rust on the metal surfaces, PH is required to control the amount of acid added to avoid excessive corrosion. There is also acid mist generated, which needs to enter the acid mist spray tower for neutralization.

Note: The acid pickling inhibitor must be added during acid pickling to prevent the acid from corroding the metal.

Advantages: The range of PH to be controlled can be precisely set to effectively control the amount of acid added.

Model selection: PTFE lining+tantalum electrode.

Function: The amount of acid liquor needs to be measured in the process of pickling. In the later stage, it can save costs and can be combined with the PH meter to achieve a better pickling effect.

Note: The flow rate in the process of adding acid solution will not be too high, so the electromagnetic flowmeter needs to be calibrated specifically for a low flow rate.

Advantages: electromagnetic flowmeter measurement, which can monitor the flow in real-time and optimize the production process.

Chloride zinc plating

Chloride zinc plating was put into production in China at the end of the 1960s and developed rapidly after the 1980s. The plating solution of this process is a single salt plating solution without the complexing agent, and the wastewater is easy to be treated; The brightness and flatness of the coating are better than those of other zinc plating processes, and the blue and white passivation films are almost comparable to those of chromium plating; High current efficiency (up to 95%), fast deposition speed; With high hydrogen overpotential, it can be conveniently plated on high carbon steel, castings and forgings, which has significant advantages over cyanide zinc plating and alkaline zincate zinc plating. In recent years, significant progress has been made in the development of additives. The temperature range and current density range are wide, and the dispersion ability and deep plating ability are equivalent to that of zincate zinc plating.

Low chromium passivation

The zinc coating becomes thinner after being corroded, which not only damages the appearance of the coating but also loss of the protection ability of the steel substrate. If the zinc coating is passivated in a certain chromic acid solution to form a chromate film (i.e. passivation film) with fine structure and high corrosion resistance on the surface of the zinc coating, the corrosion resistance of the zinc coating can be significantly improved.

Drying

The drying process in the electroplating process is used to prevent residual water stains on the product surface and oxidation discoloration. If the electroplating process is not good, the coating will fall off and discolor when it is dry. The higher the temperature and the longer the time, the higher the requirements for your electroplating process. If you are not confident, it is recommended not to dry, or the drying time should be shorter

Acid mist purification

The acid mist will be generated in the process of acid pickling activation and low chromium passivation. If the acid mist is directly discharged, it will seriously damage the atmosphere, cause acidification of the atmosphere, and endanger people's life safety. Therefore, the acid mist generated in the process of industrial production must be treated by the acid mist purification tower. The principle of the acid mist purification tower is to neutralize through alkali liquor, and the neutralization and removal effect can reach 95%. This requires that the pH value of the lye should be controlled within a certain range. The pH value is low, the neutralization effect is poor, and the acid mist treatment is insufficient. A high PH may cause crystallization, block the filler layer and demist layer, and may also attach to the fan impeller, resulting in low efficiency and short service life of the equipment.

Model selection: online PH controller+PTFE electrode

Function: measure the PH value in the alkali solution tank, and control the output through the relay of the controller to control the alkali dosing. Stable control PH within the required range.

Note: The PH electrode needs to be a tetrafluoro electrode, not a conventional plastic shell electrode, or it will be corroded.

Advantages: Automatic control is realized through the PH controller's real-time monitoring of the pH value of alkali liquor, which reduces manual operation, and can control the pH value more accurately, with a better acid removal effect.

Model selection: pressure transmitter

Function: The induced air pressure of the induced draft fan needs to be controlled to stabilize the pressure difference, so as to ensure that the acid gas can pass through the acid mist tower at a stable speed and achieve the best neutralization efficiency in combination with the speed of alkali liquor spraying.

Note: The induced air pressure is generally negative pressure. The pressure is measured by the acid mist negative pressure transmitter and outputs 4-20mA to the frequency converter. The fan is controlled by the PID algorithm. Moreover, the acid mist is corrosive, and it is highly corrosive in the case of water vapor condensation.

Classic case

The environmental protection electroplating base under a certain environmental protection industry limited company in Guangzhou is the largest and most complete environmental protection electroplating professional park in China. Relying on famous universities and scientific research institutions in China, such as Tsinghua University, Sun Yat-sen University, and the Chinese Academy of Sciences, the Base integrates various advanced wastewater treatment processes and adopts the patent technology route of "wastewater diversion, classified treatment, purified water reuse, and metal recovery" to uniformly classify and collect electroplating wastewater and domestic wastewater discharged by enterprises in the Park. Our online PH detector, liquid level sensor, flowmeter, etc. are needed in the whole process of sewage treatment, which has a good monitoring and control effect.