The purpose of production line control is to reduce all possible deviations. The mass of the film is maintained at dimensions and time stability. For example, the thickness of the film is in the same position in the production line, and it does not change in the time. This is a more complex problem due to many affected factors.
Creating a very complex control system around the production line, while ensuring high production capacity. Compared to manual control, there is nowday that there are many process processes that have been automated. The automation system is very effective to help production lines improve energy efficiency and reduce costs. This chapter introduces four aspects to control the dimensions and performance of the film:
- Melt quality
- Thin film thickness
- Width
- Cream height
How to get high quality in these four aspects? High quality melt is the main objective of extruder design. The melt mass can be characterized by continuously stable and uniform temperature and pressure. Uniformity is derived from several aspects: the uniformity of the raw material, the appropriate melting ability, and the mixing ability. The feedstock ensures fluidity by sampling. The supply instability causes the melt to be uneven, so that the feed is stable is the main design goal of the feeding system. Finally, the screw design is the most important, to ensure that the solid melt stabilizes the melt is completely mixed.
The stability of the melt temperature also requires two factors in position and time. Location factors such as the difference in contact surfaces of the melt post and the cartridge and the temperature of the core.
If the melt temperature distribution is different, the flow rate difference between the finish is entered, resulting in uneven extrusion. This will bring uneven thickness. The solution to this problem is the design of the screw mixing element, static mixer and mold internal flow path. Temperature changes in time, requires an extruded temperature control system for compensation. In addition, the screw speed and the amount of feeding are also a large effect on the temperature.
High melt quality also requires pressure to continue to stabilize. The pressure depends on three aspects: mold design, yield and melt viscosity. The hardware is unchanged, so pressure changes are mainly caused by changes in viscosity and yield. The exception is in the filter, and as the stack resistance of impurities becomes large. Therefore, the filter should be replaced on time to avoid excessive pressure to bring security issues and extrusion efficiency.
If the screw extrusion is stable, the yield will be stable. This requires solid delivery efficiency, and the melt pumping efficiency remains stable. For recovery, the stability of extrusion will be relatively poor. Melt viscosity changes come from feedstock changes and system temperature changes. The temperature control system has a higher precision.
Next, talk about the thinness of thin film thickness. Thickness detection can be online or offline. Online detection requires a laser source, such as gamma rays. The apparatus calculates the thickness of the film by detecting the reflection distance difference of the light source on the two surfaces of the film. The probe can be mounted on a fixed position or a trolley rotating around the membrane (Fig. 3.21). Thickness detection units can also be mounted on the membrane flow behind the membrane bubble compression, and measured the thickness of the two thin films at this time. Offline detection often uses capacitive devices without considering the safety of laser light sources
There are several ways to adjust the thickness of the film. The most effective way is that there is a quality and excellent die. Before booting, the operator should confirm the formation of the mold ring and the export clearance. Although there is still some adjustments after booting, you can have a better foundation at first. Final adjustment is based on the shape of the membrane shape and the detected thin film thickness distribution. If there is an asymmetric behavior in the membrane, it can be slightly moved by locking or relaxing the adjustment screw, thereby obtaining a better thickness distribution.
The dome gap adjustment often has some confusing concepts. Sometimes the film is unevenly caused by uneven wind rings, sometimes caused by the operator error adjustment. Worse, sometimes the die design lock adjustment screw is to reduce the outlet gap, and sometimes the lock screw is an increase in the outlet gap, making the operator more confusing. Therefore, it is best to have a special person to be responsible for training the operator to adjust the adjustment of a mold and enable it to cooperate with each other according to the power-on condition. Sometimes in order to get a symmetrical membrane shape, it is also necessary to set the temperature of each of the modules on the circumference. High yield lines typically need to install automatic film thickness control. A part of the machine is installed in a turn near the mouthmount. There is a thick detector at the downstream, and feedback to the controller, controls a heating zone to heat or not heaten.
The temperature in the mouth of the mouth is high and low affects how much is the part. Another part of the machine uses the air volume valve or the heating device to adjust the air volume or wind temperature surrounding a region of the membrane. This type of machine also has a detecting head to give a signal, thereby performing a single control of the air temperature, and changes the thickness of a certain angle range in the membrane bubble.
The control of a width or membrane diameter is also an important process. The width can be measured with a tape measure, but it is usually measured with a laser metric (Figure 3.22). Measurement detection of membrane diameters is often mounted on the guiding structure of the membrane bubble or a membrane measurement in the blown film video surveillance. The adjustment of the diaphragm diameter is carried out by adjusting the contents of the membrane content or internal pressure. The IBC system can perform the automatic operation of the process, or manually open the intake valve to increase the diameter of the membrane, and open the small port on the membrane to reduce the diameter of the membrane.
The last important process is the control of the cream. The cream height is very sensitive to the change of process parameters. Therefore, whether the production stability can be evaluated with this parameter. Process temperature, line speed, screw speed or feed amount change can cause movement of the cream. Thereby also affects the uniformity and width of the film thickness.
When measuring the crepe height, the tape measure can be used to manually measure, or the electronic visual scanning membrane can also be used to determine the height of the bubble neck, or the infrared temperature detection. (Figure 3.23) To control the cream height, you can adjust the air supply of the blower or the cooling temperature. The process is preferably closed. Experienced operators can quickly complete this process.
Shanghai Duxia Industry and Trade Co., Ltd. is an enterprise focusing on manufacturing plastic packaging machinery.The main products of Shanghai Duxia Industry and Trade Co., Ltd .: film blowing machine,stretch film blowing machine, printing machine, plastic bag making machine, plastic recycling machine.If you need any of the above machines, please leave your information. Our sales will contact you as soon as possible.
