Abstract : This paper focuses on the basis weight control requirements of E-glass fiber paper, briefly describing the pulping and sizing processes and the adjustment of the longitudinal and transverse uniformity of E-glass fiber paper. It mainly analyzes the implementation strategies of pulp concentration control, feed motor speed calculation, and online basis weight detection closed-loop control system.
Keywords : E-glass fiber paper; basis weight; closed-loop control; automatic detection
1 Introduction
E-fiberglass paper is a type of nonwoven wet-laid glass fiber paper. Its production process is similar to traditional papermaking. Alkali-free chopped glass fiber yarn (EC9-12mm) is dispersed with water and chemical additives under thorough stirring to form a uniform fiber slurry. This slurry is then formed on an inclined wire, saturated with resin, dried with hot air penetration, and finally wound. E-fiberglass paper is a primary material for manufacturing CEM-3 type copper-clad laminates in the electronics industry. It features uniform fiber distribution, high strength, good solvent resistance, good resin compatibility, and high cost-effectiveness. Copper-clad laminates made from it exhibit excellent machinability, resistance to tracking, and excellent dielectric properties, while also being environmentally friendly. Basis weight is a crucial performance indicator for E-fiberglass paper. The consistency and stability of the product's basis weight are related to factors such as production process adjustments, slurry concentration control, and the control of the slurry valve opening. This article analyzes and discusses the technological principles of basis weight control and the control methods used in actual production.
2. Pulping and Sizing Process
The slurry system has three mixing tanks with a total volume of 75 m³. The three tanks are connected by a connecting pipe, and tank I is equipped with a level sensor. According to the production process requirements, when the softened water level in the mixing tank reaches 240 cm, a thickener is added evenly in the specified amount. After a certain period of stirring and circulation, white water is produced. When the viscosity of the white water reaches approximately 7 centipoise, the feeding and weighing system adds alkali-free EC9-12 mm short-cut fibers to tank I, along with dispersants and other chemical additives in the specified amount. Through continuous stirring in the three tanks and multiple circulations of the slurry system, a homogenized slurry is produced. The sizing system is a closed sub-circulation system. The slurry flowing through the control valve is mixed and diluted with the white water in white water tank 1, and then pumped together to the slurry distributor and the stepped diffuser and perforated plate inside the white water tank for even distribution. The fibers in the slurry are formed on the inclined wire mesh, while the white water flows back to white water tank 1 through the dewatering tank for continued recycling. The process flow of the slurry preparation and sizing system is shown in Figure 1.
Figure 1. Process flow of the pulping and sizing system
The liquid level sensor in the pre-mesh box is interlocked with the frequency converter of the pre-mesh box pump. The sizing speed is adjusted according to the liquid level, ensuring a stable and uniform distribution of the sizing material on the forming conveyor belt, guaranteeing product isotropy. After dewatering on the inclined forming conveyor belt, the sizing material is evenly distributed to form wet E-glass fiber paper. The longitudinal uniformity of the wet E-glass fiber paper is achieved by adjusting the position of the lip plate in the pre-mesh box, thus changing the turbulence magnitude. Lateral uniformity is achieved by computer-controlled dewatering speeds of the water legs in the five dewatering zones within the pre-mesh box.
3. Slurry concentration control
In the E-glass fiber paper product basis weight control system, pulp concentration control is a crucial step. The pulp preparation process must ensure a stable and accurate chopped fiber content that meets process requirements. The main factors affecting pulp concentration include the amount of chopped fiber added, the return water flow rate, and the liquid level in preparation tank I. The amount of chopped fiber added is controlled by the speed of the main belt of the fiber feeding system, which in turn achieves automatic closed-loop control based on the chopped fiber content set in the preparation tank, thus stabilizing the pulp concentration. Figure 2 shows the block diagram of the feeding and weighing closed-loop control system.
Figure 2. Closed-loop control system for feeding and weighing
The return water is metered by an electromagnetic flow meter on the return water pipeline and then added to the pulp mixing tank 1. The pulp mixing tank 1 adopts a closed-loop level control to ensure the stability of the liquid level in the tank. The basis weight of the E-glass fiber paper product is the basis for setting the pulp concentration. The chopped fiber content of different basis weight products is generally controlled within the range of 0.1%-0.3%. The lower the concentration, the more conducive it is to fiber dispersion.
The main belt speed of the feeding system is calculated as follows:
1) Main belt closed-loop control of front speed
Return water value = (average return water value × product width) / 13………(1)
The average return water value is calculated using a flow meter installed in the return water pipeline.
Rotation speed = (slurry concentration × return water value × speed coefficient) / 1000………(2)
2) Determine the speed correction factor
R = (average fiber weight × 10) / weighing coefficient………(3)
Coefficient a = (R1 + R2 + R3 + ... + R30) / 30 ... (4)
Coefficient b = average fiber weight / weighing coefficient………(5)
The speed correction coefficients for the main belt during operation, derived from the above formulas, are shown in Table 1.
Table 1 Correction coefficients during main belt operation
3) After the main belt is under closed-loop control, the speed is as follows, based on the above analysis:
Rotational speed = Speed correction coefficient × Rotational speed before main belt closed-loop control
The frequency converter controls the main belt motor to operate at its calculated speed under closed-loop control, thereby achieving effective control of stable slurry concentration.
4. Sizing control
Figure 3 shows the closed-loop control principle of sizing pressure and basis weight detection for E-glass fiber paper products.
Figure 3. Schematic diagram of closed-loop control principle for sizing pressure and weight detection.
The closed-loop control of the slurry pipeline pressure sensor and the slurry pump frequency converter in the diagram ensures the stability of slurry delivery. The slurry pressure closed-loop control is achieved through a PLC program. The program execution sequence is as follows:
PB40 (Making pump motor starter)
PB43 (Closed-loop control, transmission, and PC display) PB131 (A/D conversion)
PB132 (D/A converter)
OB15 (Execution)
Figure 4 shows the block diagram of the closed-loop control for sizing pressure. As can be seen from the figure, the PID controller is invoked during program execution. The PID control algorithm is embedded in the system program; the user only needs to call the organization blocks OB250 (PID algorithm initialization) and OB251 (PID algorithm execution). The closed-loop control system for sizing pressure uses PI regulation with no disturbance setting. The control algorithm is a position algorithm. At time tk, the control variable Yk = dY1 + dY2 + ... + dYn (n = 0, 1, 2...k). According to the PLC parameter settings of the E-glass fiber paper product production line control system, dYk = 1.5(2XWk – XWk-1), thus ensuring that the sizing pressure remains stable between 0.25 and 0.3 bar.
Figure 4. Block diagram of closed-loop control of sizing pressure
5. Product weight control
The online basis weight detection closed-loop control enables the basis weight control range of E-glass fiber paper products to approach the target value, ensuring the uniformity and consistency of product basis weight. Figure 5 is a schematic diagram of the HY138 type glass fiber paper basis weight and binder content measurement and control system. Before the formed E-glass fiber paper products enter the winding process after impregnation, drying and curing, the device achieves automatic control of the unit area weight (g/m2) of the E-glass fiber paper products.
Figure 5. Schematic diagram of the HY138 type glass fiber paper basis weight and binder content measurement and control system.
The measurement and control device employs advanced microprocessor and laser technology. It uses the radioactive element Kryton 85 to perform non-contact measurement of the E-glass fiber paper product's basis weight, detecting the data and converting it into a corresponding voltage output. The basis weight detection device is equipped with a transverse reciprocating mechanism. The E-glass fiber paper product passes through the gap in the middle of the measuring disk. The measuring probe at the center of the disk acts as a scanner, moving laterally back and forth within the material's width to scan and measure the basis weight at different points on the material. It calculates the average basis weight of the sampled points and uses the average deviation between the calculated result and the target value as a PLC input control signal to control the opening of the slurry valve (as shown in Figure 3). If a basis weight deviation occurs, the feedback signal from the basis weight detection device automatically adjusts the opening of the slurry valve through the PLC to eliminate the deviation, achieving closed-loop basis weight control. The block diagram of the E-glass fiber paper product's basis weight closed-loop control is shown in Figure 6.
Figure 6. Block diagram of closed-loop control for gram weight
Depending on the system configuration, the scanning width of the weight detection device can be preset in the product data or determined automatically by the product width recognition system. The number of sampling points per scanning cycle can be manually set. The sensor scanning speed is synchronized with the machine speed.
6 Conclusions
This paper takes the basis weight control system of E-glass fiber paper as the research object, analyzes several factors affecting the basis weight of E-glass fiber paper, and adopts closed-loop control of feeding and weighing, closed-loop control of pulp pressure, and closed-loop control of online measurement of E-glass fiber paper basis weight. It can effectively control the basis weight index. The application results show that the system operates stably and reliably, and the basis weight control effect is good.
References
[1]S5-90U/S5-95UProgrammablecontrollerSystemManual
[2] Instruction Manual for HY138 Glass Fiber Paper Basis Weight and Binder Content Measurement and Control System. Third Research Institute of China Nuclear Power Research and Design Institute. 2008.9
About the Author
Feng Jianxiu is a senior engineer engaged in the research and practical application of automatic control systems.
Contact Information Address: Technology Center, Shaanxi Huatai New Materials Co., Ltd., Xingping City, Shaanxi Province
Postal code: 713100
Telephone: 029-38362022
Email: [email protected]
