Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting
Patent
1990-01-29
1991-12-24
Silbaugh, Jan H.
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
264 404, 264 406, 425144, B29C 4576, B29C 4792, B29C 4978
Patent
active
050750500
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to methods for manufacturing of plastic articles, and more closely to such a method giving rise to plastic articles having desired wall thickness, weight per meter and/or weight per piece.
The invention is primarily intended to be used in connection with the forming of plastic articles by extrusion, such as blown film and foil extrusion, cable extrusion plastic coating, pipe and rod extrusion, but the invention may also, after modifying of the discharge section, be adapted to processes for blowing of bottles and injection moulding.
By the invention it has been possible to manufacture plastic articles having precise dimensions without use of instruments for measuring the thickness or for measuring some other dimension, or complicated and expensive weighing equipment for batch weight as referred to in e.g. DAS 1 964 386.
An essential problem in connection with the manufacturing of plastic articles is to be able to maintain an even quality of the articles, and then especially with regard to the wall thickness. The thickness variations occurring in connection with e.g. film and foil manufacturing, are resulting in that nominal correct thickness vary above as well as under said thickness. The result thereof is that one either accepts a product the thickness of which is incorrect, or one has to manufacture a product being thicker than the nominal one in order to be able to guarantee desired thickness. In the one case the quality is faulty and in the other case the plastic consumption is unsatisfactory high. The latter case also gives rise to not only increased costs for the consumed plastic but also for heating, extrusion energy, transportation and so on.
To overcome the above problems thickness measuring instruments have been used within the plastic industry, but these instruments have caused problems due to often used additives such as pigments and similar, due to variations of the temperature of the sensed article through the thickness thereof, and due to the fact that plastic temperature variations have appeared caused by conditions depending upon different times of the year and/or product and manufacturing conditions. Accordingly, the result is that a great number of calibration constants have been necessary to identify, which the operator then has had to take into consideration for the continued production. The result thereof is that on-line measuring of the thickness generally is an unpractical and unreliable method which cannot be used successfully for manual or automatic control of the manufacturing process.
Another attempt to get rid of said deficiencies is described in DAS 1 964 386. This attempt includes the development of a weighing method for the batch weight in accordance with which the material is supplied to the extruder or corresponding machine is weighed, batch by batch or continuously, and for a set amount of weighed input material determines manufactured length or time of manufacture. Thereby, it is possible to calculate weight per meter or production per time unit. The weight per length or time unit is then determined by means of a level switch mounted in the lower portion of the extruder funnel or in the pipe between the extruder funnel and the extruder. The closer the extruder and the less area at the place of measuring the better the accuracy of the weighing. However, this leads to the fact that a very small reserve amount of raw material is maintained before the extruder which in connection with trouble in the delivery of raw material or in the weighing equipment for the input material gives rise to production stop and deficiencies in the manufactured product. Production stop means loss of time and reduced profitability and unnecessary deficiencies in the manufactured article and involve extra trouble for taking care of these faulty articles and increased costs.
In the conventional technique in use today for manufacturing of plastic articles, an extruder is used comprising a rotary screw arranged within a cylinder, which screw is responsible for the process
REFERENCES:
patent: 3148231 (1964-09-01), Spencer
patent: 3649147 (1972-03-01), Fritsch
patent: 4171193 (1979-10-01), Rahlfs
patent: 4213747 (1980-07-01), Friedrich
patent: 4613471 (1986-09-01), Harris
patent: 4667852 (1987-05-01), Siemann
patent: 4721589 (1988-01-01), Harris
patent: 4816197 (1989-03-01), Nunn
patent: 4858139 (1989-08-01), Wirtz
Silbaugh Jan H.
Timm Catherine
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