Plastic article or earthenware shaping or treating: apparatus – Including means advancing continuous length work through...
Patent
1997-11-17
1999-04-06
Ryan, Patrick
Plastic article or earthenware shaping or treating: apparatus
Including means advancing continuous length work through...
2642094, 425325, 425392, B29C 4790
Patent
active
058914811
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tubular calibration unit for calibrating the outer or inner diameter of extruded plastic string bodies such as pipes.
2. Description of Related Art
In the production of extruded plastic pipes it is customary that the hot plastic compound is forced through an extruder nozzle, the diameter of which is somewhat larger than the desired pipe diameter, the extrusion taking place to a calibration tube unit, at the inlet of which the plastic pipe is narrowed to the diameter of this unit, this diameter corresponding fully or almost to the desired pipe diameter. The metallic calibration tube is cooled by cold water such that during its throughflow the plastic compound solidifies sufficiently to be stabilized with a corresponding pipe diameter as it leaves the unit. Thereafter the pipe is passed through a cooling zone, normally of a length larger than that of the calibration tube, such that at the outlet from this zone the pipe is stabilized sufficiently for co-operation with a pulling station effecting the pull out of the pipe from its initial formation in the calibration tube. Thereafter the pipe can be passed further to be reeled or cut into desired lengths.
Normally, the production tolerances should be rather narrow, both for satisfying certain minimum requirements and for achieving this without overdosage of plastic.
In practice it happens that for several reasons changes in the process conditions may occur, such that for the desired optimizing of the produced pipe it may be required to use a slightly changed calibration diameter. In such cases it is necessary to stop the process and replace the calibration tube by another such tube with a diameter deviation of, maybe, only one or half a millimeter.
Such a change, therefore, implies a production stop and often scrapping of many meters of produced pipe, so it would be highly desirable if it was possible to use calibration tubes with adjustable diameter, such that required adjustments could be effected currently, during operation.
The problem has earlier been considered in connection with narrow calibration rings, confer GB-1,349,436, where it has been possible to use a split ring with such a pronounced screw shaped split that the ring, seen in the direction of throughflow, will be unbroken annular, whether it is squeezed to a more or less advaced closing of the oblique split. Also, from U.S. Pat. No. 4,578,025 is known a construction comprising a row of mutually widely separated calibration rings provided at the outer end portions of funnel shaped elements and being controllable to undergo a more or less pronounced, resilient expansion or contraction.
These solutions, however, are unusable when it is a condition that the calibration unit be a heat/cold transferring, regular tube, preferably having a length up to several times its diameter. This is confirmed by practice, where it has been necessary to effect the said problematic total change out of the calibration tubes.
SUMMARY OF THE INVENTION
With the present invention it has been recognised that in fact it is possible to realise a calibration tube with variable diameter, viz. in that this tube is made up of a row of closely juxtaposed, split ring members, the splits of which are generally located mutually staggered in the peripheral direction, such that the tube when seen in the throughflow direction has a fully closed tubular shape; extending along this tube, axially oriented elements are provided which are controllable to effect a collective radial impact on all of the ring members for changing the operative diameter thereof. It will not be required that the splits of the single ring members be oblique, when they are only peripherally offset from each other, and there will be no question of dealing with any total resiliency of entirely closed ring elements.
Thus, a calibration tube according to the invention may, as a unit, extend over a noticeable length in both calibrating and cooling engagement with the extruded p
REFERENCES:
patent: 3596321 (1971-08-01), Upmeier
patent: 4408970 (1983-10-01), Bustin et al.
patent: 5139402 (1992-08-01), Topf
Leyson Joseph
Ryan Patrick
Safran David S.
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