Method for setting the sizes of blown film tubes as well as a blown film system with a control device for carrying out the method

Abstract

The invention describes a method for setting the sizes of film tubes ( 1 ), which are extruded by blow film plants ( 15 ), in which method the film tube size is changed from an initial size of a film tube ( 1 ) to a final size of a film tube ( 1 ), and in which the location of the frost area ( 3 ) is optimized during the size change by setting the output of the cooling fan. Physical parameters of the initial and final size of the film tube ( 1 ) are stored in the control device ( 31 ). The control device ( 1 ) takes these physical parameters into account when generating control signals. Furthermore, these control signals form the basis for the control of the cooling fan output

1 . Method for setting the sizes of film tubes ( 1 ), which are extruded by blown film plants ( 15 ),
 in which method the size of the film tube size is changed from an initial size of a film tube ( 1 ) to a final size of a film tube ( 1 )   and in which method the location of the frost area ( 3 ) is optimized during the size change by setting the output of the cooling fan ( 20 ,  23 ,  27 ),   said method being characterized in that   physical parameters of the initial and final size of the film tube ( 1 ) are stored in the control device ( 31 ),   the control device ( 31 ) takes these physical parameters into account when generating control signals,   these control signals form the basis for controlling the cooling fan output.   
   
   
       2 . Method according to  claim 1  characterized in that the control device ( 31 ) determines physical parameters of the intermediate sizes based on physical parameters of the initial and final sizes. 
   
   
       3 . Method according to  claim 1  characterized in that the physical parameters include the surface area of the film bubble ( 1 ) and/or the extrudate flow rate per unit of time and/or the take-off speed and/or the desired position of the frost line ( 3 ) in the axial direction (z) of the film bubble ( 1 ). 
   
   
       4 . Method according to  claim 1  characterized in that in a memory of the control device ( 31 ) there is stored information, which is assigned to defined values of the physical parameters, and which is taken into account when generating the control signals in the presence of these values of these physical parameters. 
   
   
       5 . Method according to the preceding claim characterized in that the information stored in the memory is programmed based on empirical values or acquired with the help of calculation rules. 
   
   
       6 . Method according to  claim 1  characterized in that an arithmetic unit follows defined calculation rules to generate from the values of the physical parameters instructions for generating control signals. 
   
   
       7 . Method according to  claim 1  characterized in that at least one of the fans ( 20 ,  23 ,  27 ) involved in cooling the film bubble ( 1 ) is connected without flaps to its air outlet. 
   
   
       8 . Method according to the preceding claim characterized in that all fans ( 20 ,  23 ,  27 ) involved in cooling the film bubble ( 1 ) are connected without flaps to their air outlets. 
   
   
       9 . Method according to  claim 1  characterized in that a machine operator implements fine adjustments of the fan output after the control device ( 31 ) uses the control signals to set the fan values, which the control device associates with the final size. 
   
   
       10 . Method according to  claim 1  characterized in that when determining the control signals, the control device ( 31 ) takes into account the fan settings adjusted during the production of the blown film in the initial size. 
   
   
       11 . Method according to the preceding claim characterized in that when determining the control signals, the control device ( 31 ) acts on the basis of the fan settings adjusted during the production of the blown film in the initial size and implements changes of the fan settings based on the physical parameters of the final state. 
   
   
       12 . Method according to  claim 1  characterized in that for implementing a size change, at least one part of those plant components, the settings of which are changed during the size change, experience these changes in a time-shifted manner. 
   
   
       13 . Method according to the preceding claim characterized in that the size change is implemented during the extrusion of the film material in the blown film plant. 
   
   
       14 . Method according to  claim 12  characterized in that at least one part of those plant components, the settings of which are changed, are subject to these changes successively, the sequence in which changes are implemented on the different plant components, corresponding to the sequence in which these plant components influence the plastic extrudate or the extruded film in the conveying direction (z) of the film. 
   
   
       15 . Method according to the preceding claim characterized in that the period of time elapsing between changes on the different plant components largely corresponds to the period of time, which a defined section of film material requires at the current plant speed for covering the distance between the spheres of influence of the related plant components. 
   
   
       16 . Method according to  claim 1  characterized in that the plant components on which changes are implemented in a time-shifted or successive manner, also include the fans assigned to the different cooling devices. 
   
   
       17 . Method according to  claim 1  characterized in that the control device emits a warning signal if a size change causes the width of the flattened film to exceed the maximum working width of the winding device. 
   
   
       18 . Method according to  claim 1  characterized in that at least two classes of physical parameters are stored in the control device, which two classes are each assigned to defined final sizes, the first class of physical parameters comprising desired values for the ongoing production process of an order, and the at least one second class of physical parameters comprising desired values for the start-up operation of the related order. 
   
   
       19 . Method according to  claim 1  characterized in that currently adjusted physical parameters are stored temporarily before a temporary shutdown, and that these temporarily stored physical parameters are either reset when production resumes, or form the basis for determining physical parameters for the start-up operation. 
   
   
       20 . Blown film plant ( 15 ) at which sizes of film tubes ( 1 ), which are extruded by the blown film plant ( 15 ), can be set from an initial size to a final size and at which the output of the cooling fan ( 20 ,  23 ,  27 ) can be set said blown film plant being characterized by a control device ( 31 ),
 in which ( 31 ) physical parameters of the initial and final size of the film tube ( 1 ) can be stored and   using which control signals can be generated based on these physical parameters,   it being possible to perform at least one part of the control of the cooling fan output by using the control signals.