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Factors affecting BOPP film thickness measurement

Chinese figure classification number: tm206 tm215.3 document identification code: B article number: (1999) measurement principle radioactive particles of radioactive elements (such as β Ray), which is partially absorbed through the film, enters the ionization chamber (the ionization chamber is equipped with a ray probe and filled with inert gas). Radioactive particles ionize the inert gas and produce positive and negative ions. Under the action of an applied electric field, ions move to the opposite plate, forming a small current on the external circuit and generating a voltage drop on the high resistance. Through the small current amplifier amplification, output a voltage. The system processes the voltage to obtain the thickness of the film. In the biaxially oriented polypropylene (BOPP) film production line, a driving motor synchronously drives the measuring head and the radiation source to move along the direction perpendicular to the film. The film is measured by the thickness gauge system, and a series of thickness data are obtained. 2. The factors affecting the measurement are in the BOPP film production line. The thickness gauge is not only a measuring instrument for measuring and displaying the thickness and uniformity of the film, but also the main equipment for controlling the production line. The quality of the film (mainly thickness and uniformity) depends on the accuracy of the measurement. Therefore, it is very necessary to understand the main factors that affect the accuracy of measurement. The following is an analysis of several main factors that affect the accuracy of measurement

2.1 the accuracy of the thickness gauge itself. Thickness gauges with different radioactive sources have different measurement accuracy. The accuracy of pm147 thickness gauge is 0.03 μ m。 With the decay of radioactive elements, the measurement accuracy will change. Therefore, when the radiation decays to a certain extent, the amplification factor of the measuring head amplification circuit must be adjusted. In the normal production process, it is also necessary to often carry out standardized calibration for thickness measuring instruments due to the numerous types of well cover pressure testing machines

2.2 in order to facilitate the film penetration, the general BOPP production line adopts a C-shaped frame. The parallelism of the upper and lower beams of the frame directly affects the measurement effect of the thickness gauge, and the parallelism should be less than 0.3 mm

2.3 the relative position between the measuring head and the radioactive source. Under normal circumstances, the relative position deviation of them active in the fields of health, nutrition and materials worldwide is: longitudinal 0.2 mm; Transverse 0.4 mm; 0.3 mm up and down. As the equipment will produce vibration, it will produce displacement under long-term operation, so it should be corrected regularly

2.4 the transmission belt of measuring head and radioactive source in the industrial development elongation will change in tension due to long-term operation, which should be adjusted frequently. The copper wheel running on the track will be worn and should be replaced in time

2.5 the longer the measurement time of the thickness gauge is, the more radiation particles enter the detector, the smaller the fluctuation of the measurement result and the higher the accuracy, but there should be limits. Not too long, because the measuring head is moving. If the measurement time is too long, the measurement result will be an average over a long distance. In this case, the thickness profile is completely smooth and cannot correctly reflect the film profile. The general measurement time is 20 ~ 100 ms, and the author chooses 40 ms

2.6 film flattening effect in the production process, if the film is not fully expanded or jittered, it will also have a certain impact on the thickness measurement, because the scattering of rays on the film is related to the position of the film in the air gap. When the film is close to the measuring head, the number of ray particles entering the measuring head is more than when the film is far away from the measuring head

2.7 environmental conditions (temperature, humidity, air pressure, degree of purification, etc.) of pm147 thickness gauge β Keep a distance of 12 mm between the radiation source and the measuring head so that the film can pass through. In this space, the film and air coexist, and the air pair β Rays have a certain absorption effect, and the amount of absorption is related to the air density. The air density changes with the change of ambient temperature, humidity, pressure and purification degree. Although the influence of environmental conditions is considered and compensated when designing the thickness gauge, when the environmental conditions change greatly, the measurement results will still be affected, which should be guaranteed by a better air conditioning system

2.8 zero profile the so-called zero profile is to put a film of standard thickness on the measuring head, let the measuring head move laterally, and measure a profile, which we call zero profile. The zero profile is used to compensate the profile measured by the thickness gauge in production. Its accuracy has a great impact on the accuracy of the profile. The zero profile should be updated frequently. 3 conclusion in the production of BOPP electrical film, there are many kinds of thickness gauges. This paper mainly analyzes the pm147 thickness gauge used in BOPP production line, which has many similarities with other thickness gauges. The main factors that affect the accuracy of the thickness gauge are the accuracy of the equipment itself, the accuracy of mechanical installation and the accuracy of process adjustment. A full understanding of these factors is conducive to controlling the uniformity of film thickness and improving product quality in actual production. About the author: Shu Changqing (1965 -), male, from Tongcheng, Anhui Province, graduated from Changchun Institute of geology, engineer, mainly engaged in film production

Author: Tongling Tongfeng electronic group company, Tongling 244000, Anhui

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