Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Controlling fluid pressure in direct contact with molding...
Patent
1997-02-03
1999-05-11
Timm, Catherine
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Controlling fluid pressure in direct contact with molding...
425136, B29C49/78
Patent
active
059025271
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an apparatus and method for blow moulding.
Extrusion blow moulding is a technique that is used for moulding hollow plastics articles such as plastics cases and the like. A thermally plasticised thermoplastic tubular parison is first extruded. A two part moulding die is then closed around the parison. Air is injected into the parison enclosed by the die to blow mould the parison into the shape of the cavity of the die. The mould is then opened and the blow moulded article is removed.
There are several problems in blow moulding to a high standard of quality in a cost efficient manner. One of the problems is to minimize the cycle time to produce a moulded article.
This invention is directed towards providing an improved apparatus and method for blow moulding to a high quality standard while minimizing cycle time.
According to the invention there is provided a blow moulding apparatus comprising: blown during blow moulding; and pressurized air is delivered; moulding station; vessel to the blowpin; moulding station if the pressure in the vessel is below a preset pressure.
In one embodiment of the invention the volume of the vessel for holding air is at least 10 liters. The volume may be typically 10 or 25 liters.
Preferably the preset pressure in the vessel is approximately 10 bar. In a particularly preferred embodiment of the invention the air control system includes temperature sensing means for sensing the temperature of air for delivery to the blowpin and temperature control means for preventing operation of the dedicated blow moulding station if the temperature of the air is not within a preset temperature range. In this case preferably the temperature sensing means is located to sense the temperature of the air in the air supply vessel.
Preferably the preset temperature range is from 8.degree. C. to 10.degree. C., especially approximately 8.degree. C.
In another preferred embodiment of the invention the air control system includes water level sensing means for sensing the level of condensate in the supply vessel and a drain system for removing condensate from the supply vessel.
Preferably the control valve on the delivery line for delivery of air to the blowpin is a fast acting directional control valve having ports for maximum flow of air to the blowpin with minimum pressure drop across the control valve.
In a preferred arrangement the inlet to the air supply vessel is supplied with air at a pressure of at least 8 bar through an inlet pipe having a diameter of at least 15 mm preferably at least 25 mm.
In one embodiment of the invention the apparatus includes an exhaust vessel maintained at a negative pressure into which exhaust air is delivered before exhausting to atmosphere. Preferably the exhaust vessel is maintained at a negative pressure of from 0.2 to 0.8 bar by a vacuum pump. Usually the air is exhausted from the exhaust vessel through a non-return valve. Preferably the exhaust vessel has a capacity larger than that of the air exhausted in the blow moulding cycle.
The invention also provides a method of blow moulding including the steps of: station, the supply vessel having an air inlet and an air outlet; blowpin of a blow moulding station; in the supply vessel is below a preset pressure.
Preferably the method includes the steps of: temperature of the air is not within a preset range.
In a preferred embodiment of the invention the method includes the step of exhausting air from the blowpin into an exhaust vessel maintained at a negative pressure prior to exhaust to atmosphere.
The invention also provides a blow moulded article whenever produced using the apparatus and/or method of the invention.
The invention will be more clearly understood from the following description thereof given by way of example only with reference to the accompanying drawings, in which:
FIG. 1 is a schematic view of part of a blow moulding apparatus according to the invention.
Referring to FIG. 1 there is illustrated portion of a blow moulding apparatus according to the invention which comprises a b
REFERENCES:
patent: 3841555 (1974-10-01), Lilja
patent: 4120924 (1978-10-01), Rainville
patent: 4946366 (1990-08-01), Dundas et al.
patent: 5007817 (1991-04-01), Wallis
Kunststoffberater, vol. 30, No. 4, Apr. 1985, Germany, R. Hegele, "Blasluftsteuerung und Nachkuhlung . . . ".
D.V. Rosato, "Blow Molding Handbook", 1989, Hanser, pp. 412-415, Figures 11.8 and 11.10.
Menza Limited
Timm Catherine
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