Detection and Control of Surface Treatment Liquid in PS Plate Manufacturing Process (Part 2)

Detection and Control of Surface Treatment Liquid in PS Plate Manufacturing Process (Part 2)

1. Manual control.

This is the common practice of most small and medium-sized PS version manufacturers in my country. It is mainly manifested in the fact that the data management system of the entire production line has not yet been formed. The degree of automation is low, and the detection of various acid-base treatment liquids in the surface treatment process section is often only displayed by the instrument. However, there is no automatic real-time monitoring, in which the concentration detection is completed by manual laboratory titration, and the supplementary solution is also performed manually by experience. Therefore, it is greatly affected by human factors. The manual control process is shown in Figure 3:

(1) Regular inspection. In the production line, the storage tanks of each acid-base solution in the surface treatment process section are equipped with corresponding acid-base concentration detection instruments. There are box-type or wall-mounted display panels. Displays the real-time concentration of acid or lye in the tank. during normal production. As the reaction proceeds. The concentrations of various acid-base solutions have different degrees of reduction and change. therefore. Workers will follow certain shifts. Regularly check the display number of each instrument. After regular inspection. The worker will notify the inspector to take a sample to check the actual concentration of the treatment liquid. also. If there is a problem in the production process. When the quality of the finished plate is affected. Workers will also take samples of surface treatment fluids for inspection.

(2) Laboratory titration detection. The concentration detection of the solution is done in the laboratory by titration. The inspector determines the end point of the titration based on the color change of the indicator. Then according to the volume of standard solution consumed. Calculate and analyze the results. Obtain the exact concentration of the treatment solution.

(3) Manual supplementation. Workers who are responsible for replenishing the stock solution. After receiving the additional notice from the inspector. According to the corresponding concentration difference. Add a certain amount of stock solution to the treatment box. To restore the solution concentration required by the process. The specific amount of stock solution added is often based on the practical experience of workers for many years. Gradually find out a certain experience value.

2. Semi-automatic control.

Currently. Some enterprises are based on the experience of manual control. A set of "semi-automatic solution concentration control device" was designed, the schematic diagram is shown in Figure 4.

In the production line, each surface treatment liquid circulation tank is equipped with corresponding acid-base concentration detection instruments. An external display panel is connected by wires. Real-time display of the acid or lye concentration in the circulating tank.

at the same time. There are pipes leading from the raw liquid storage tank to the treatment liquid circulation tank. A certain amount of liquid outflow is controlled by a valve. The stock solution was continuously added dropwise to the treatment tank to keep the concentration of the treatment liquid in the tank stable.

The real-time dripping amount of the stock solution. It is based on many years of actual production experience by workers, and with different speed conditions and production conditions, a set of empirical data is gradually formed, which is generally measured and controlled by "drops per minute".

3. Automated detection and control.

At present, some large-scale PS plate manufacturers at home and abroad have adopted an automatic detection system for the concentration of the treatment solution, which is controlled and displayed by a computer to realize the automatic detection of the solution concentration and the automatic replenishment of the original solution.

This kind of system adopts advanced solution concentration sensor, solution temperature sensor and corresponding intelligent instrument to detect the concentration and temperature of each surface treatment liquid online. It is connected with the main control cabinet of the computer through the interface that automatically controls the concentration and temperature of the liquid medicine, and the test results are transmitted to the central controller. After calculation, the controller sends out control commands to drive acid and alkali resistant solenoid valves to control hydrochloric acid and sulfuric acid. And the automatic replenishment of treatment liquids such as lye in the degreasing section, so as to achieve automatic control of the concentration and temperature of the chemical section. Due to the real-time and accuracy of automatic control, the stability of the quality of the base grit and the quality of the oxide film is well guaranteed.

4. existing problems.

At present, the concentration of the surface treatment solution of the production line of the medium and small PS plate manufacturers in my country is generally controlled manually. The data management system of the entire production line has not yet been formed, the degree of automation is relatively low, and it is greatly affected by human factors. The disadvantages of manual control are mainly manifested in:

(1) There is a time lag. It usually takes half an hour or even an hour to delay from the regular inspection of the workers to the notification of the laboratory personnel for sampling and testing until the final addition of the original solution. In this process. The concentration of the surface treatment liquid cannot be controlled in real time, and the process conditions in the actual production have already changed, which will definitely affect the quality of the surface roughening treatment of the plate, thereby affecting the final plate quality.

(2) The influence of human factors. First, the titration operation is manual operation. When the indicator comparison is performed to determine the titration end point. It is bound to be affected by human factors and thus affect the accuracy of the test results. Secondly, when adding the stock solution, it is also done by manual operation, and different people will implement different experience standards. The implementation standards of each shift are also different, so that the production process conditions cannot be controlled stably and consistently.

(3) Consume acid and alkali. A standard acid-base solution is required for titration detection. With the operation of the production line for many years. Increased raw material consumption. Increased production costs. (4) Occupy human resources. Because the titration detection is done by manual operation. Therefore, each shift must be equipped with a full-time inspector. This increases labor costs. Increased production costs.

Semi-automatic control adopts the method of real-time dropwise addition of stock solution, which to a certain extent makes up for the "time lag" defect of manual control, but the amount of real-time replenishment is also determined by years of production experience, and it is difficult to guarantee the accuracy. . In addition, the semi-automatic control also includes the detection link, so there are also the influence of human factors and the consumption of standard acid-base solution.

At present, although some large-scale Ps board production enterprises with Sino-foreign joint ventures in China have applied automatic detection and control devices, the development and design of the entire system have not yet been localized. Generally, the foreign party determines the process conditions and specific control requirements, and the domestic professional manufacturers complete the hardware design of the corresponding control system, and the control software is generally designed by the foreign party.

Therefore, for the relevant technical data of the automatic control system and the key issues of the control system design, all enterprises maintain an attitude of keeping it secret. It brings a certain difficulty to the self-developed control system.

4. Main directions and difficulties in the research of automatic control system

1. Selection of acid and alkali concentration detection sensor.

Sensors for online detection of acid and alkali concentrations in liquids. It is commonly used to detect the conductivity of the liquid, which indirectly reflects the concentration of the liquid. Since the chemical composition of acid and alkali determines that the acid and alkali concentration of the liquid is proportional to its conductivity value, the concentration of acid and alkali can be determined by detecting the conductivity value of the liquid. Currently. Most of the domestic acid-base concentration meters are of the contact type, that is, in the form of electrodes, they are in contact with the liquid to be measured to measure the conductivity value, and use this to determine the acid and alkali concentrations of the liquid. The most fatal disadvantage of this method is that the electrode is easily corroded and contaminated, which will seriously affect the accuracy of the measurement and the service life of the electrode.

In the selection of electrodes, titanium alloys, stainless steel sprayed anti-corrosion coatings, etc. are more commonly used. In addition, there are annular electrodeless probes, but their prices are high and difficult to be accepted by some small and medium-sized enterprises.

2. Design and selection of system control algorithms.

The surface treatment solution in the PS plate manufacturing process involves a variety of acids and alkalis, and each acid or alkali treatment solution becomes a multi-component and large-hysteresis system, so there is not only a large concentration detection. Difficulty, there are also difficulties in the design and selection of the concentration control algorithm.

Currently. Generally, PID (proportional, integral, differential) control algorithm and Smith prediction control are used. Ideal results have been achieved in practical applications. With further research. It can also introduce the more popular fuzzy control technology and expert system in the field of control. ■(The author is from the School of Printing and Packaging Engineering, Xi'an University of Technology)