Process and device for controlling the thickness of extruded flat films or sheets of thermoplastic

    公开(公告)号:DE3107701A1

    公开(公告)日:1982-01-14

    申请号:DE3107701

    申请日:1981-02-28

    Applicant: BASF AG

    Abstract: In this process measured values and data are recorded by a thickness measuring instrument traversing perpendicularly to the extrusion direction, digitised into pulses and the actual values determined are compared with digitised set point values. At the same time a local transverse profile and a longitudinal profile, temporarily superimposed on said transverse profile, of the flat films or sheets are recorded. In said process, the measurement path is subdivided, parallel to the extrusion direction, into a plurality of zones, correlating with control zones of an extrusion die. A mean thickness value is formed from each accepted zone on the flat films or sheets, is compared with the computed set point values and the result is used in the production process for control purposes. An overall mean value is then generated from the mean values of all zones, this overall mean value is compared with the overall mean value of a previous or subsequent traverse of the thickness measuring instrument and the take-off rate of the flat films or sheets is varied corresponding to the differences ascertained. A device for carrying out the process consists of a slit die which is subdivided, parallel to the extrusion direction of the flat films or sheets, into a plurality of control zones which can be temperature-controlled independently of one another and of a thickness measuring instrument which is traversable perpendicularly to the extrusion direction and is connected to a power setting unit and/or a process computer controlling a take-off device.

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