Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Patent
1991-09-04
1993-01-12
Tentoni, Leo B.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
26421112, 264564, 425141, B29C 4792, B29C 5528
Patent
active
051788063
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a national phase of PCT/DE 91/00007 filed Jan. 9, 1991 and based upon German national application P 40 00 530.5 filed Jan. 10, 1990 under the International Convention. It is also related to my copending application Ser. No. 07/688,927 filed Apr. 19, 1991 and the commonly owned copending application Ser. No. 07/686,824 filed Apr. 17, 1991 by Hartmut Halter.
FIELD OF THE INVENTION
The invention relates to a process for the production of a plastic foil made of a thermoplastic material, as well as for the winding of this plastic foil into a coil, whereby the produced plastic foil has a thickness-error profile with systematic plus and minus thickness errors, the thickness-error profile of the produced plastic foil being measured prior to the winding of plastic foil into a coil so that the coil is practically free of thickness errors added up during the winding process.
BACKGROUND OF THE INVENTION
The expression "systematic thickness error" refers to the thickness errors which are determined by the system, for instance as a result of tool tolerances. They are unavoidable and occur without any intervention in the cross-sectional profile of the produced plastic foil, and in the installation for the production of the plastic foil always at the same locations. If no special steps are taken, these systematic thickness errors add up during the winding of the coil to positive or negative barrel-hoop formations in the roll of foil which is produced.
In the known processes which are the starting point of this invention, the attempt is made to avoid the summation of the thickness errors by displacement and statistical distribution of the thickness-error profile over the entire width of the plastic foil, so that during winding the summation of the thickness errors is replaced by an error distribution, so that the coil is practically free of the effects resulting from the local summation of thickness errors during coil winding.
Layer after layer, the thickness errors are in different locations in the coil. To achieve this in the production of so-called blown film, wherein at first a thermoplastic tube is produced, this tube is then blown to a tubular film and the tubular film is then flattened, either the blowing head with the tool for the tube extrusion must be given a periodic to and fro oscillating motion or the bubble or balloon flattening device must be correspondingly periodically moved. This requires an expensive construction and the results are often not fully satisfactory, because the resulting coil still has irregularities, even if it does not show pronounced barrel hoops.
In order to achieve the described error distribution when operating with a wide-slot nozzle it is known to reduce the magnitude of thickness errors, i.e. to level the thickness-error profile, according to a measured thickness-error profile, by adjusting the gap width of the wide-slot nozzle. The superposition and distribution of intended singular thickness errors is also known. As a result, these known steps the thickness tolerances can be reduced. However a disturbing thickness-error profile with a disturbing error addition are still be present in the coil.
OBJECT OF THE INVENTION
It is the object of this invention to so carry out the process that a coil results which is cylindrical to a much higher degree of precision than was heretofore possible with the known means.
In order to solve this problem the invention teaches that a number n of layers of the plastic foil produced with systematic plus thickness errors and/or minus thickness errors are wound to a coil, whereby n=1 or is greater than 1 and that afterwards with a correspondingly programmed computer the inverse thickness-error profile is established and a plastic foil with the inverse thickness-error profiles is produced and a number of layers of the plastic foil with the inverse thickness-error profile is wound on the coil, and so on and so forth alternately layers of plastic foil with thickness-error profile and furt
REFERENCES:
patent: 4758390 (1988-07-01), Henze
Dubno Herbert
Reifenhauser GmbH & Co. Maschinenfabrik
Tentoni Leo B.
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