Plastic article or earthenware shaping or treating: apparatus – Female mold and means to shape parison directly by internal... – With heating or cooling means
Reexamination Certificate
1998-11-12
2001-02-20
Davis, Robert (Department: 1722)
Plastic article or earthenware shaping or treating: apparatus
Female mold and means to shape parison directly by internal...
With heating or cooling means
C425S534000, C425S547000
Reexamination Certificate
active
06190157
ABSTRACT:
The present invention relates to an ejection device for a discharging tool suitable for the removal of preforms, from a mould tool.
Machines for manufacturing preforms or preform blanks, in particular for the manufacture of drinks bottles of PET, comprise essentially a plastic unit and a mould tool unit. With this discharging tool for the removal of the preforms from the mould tool are increasingly applied in order to reduce the cycle times and in particular the long moulding time of the plastic injection moulding machines caused on account of the long cooling times of the preforms. For this the mould tools after the injection procedure or during the cooling phase are prematurely opened and the preform blanks which are not completely cooled down are automatically accommodated by these discharging devices and cooled further. During this cooling time the mould tools may again be closed and filled again. Modern discharging devices may as a rule accommodate three charges manufactured after one another before they eject the first charge.
For the ejection of the cooled preforms, in this field various devices are known. One of the most commonly used ejection devices comprises in the inside of the coolable removal sleeves a piston which may be ejected outwards with pressurised air. A bolt fixed in the floor of the removal sleeve retains this piston in its end position, whilst the pressurised air, through a bore in the cylinder, may expel the preform blank from the sleeve. This bore through the piston is simultaneously used in order to pump away the air in the removal sleeves via the pressurised air conduit system provided for the ejection, i.e. in order to produce in the removal sleeves a vacuum or suction effect with which the preforms may be pulled into the removal sleeves. Unfortunately it has been shown that the preforms which shrink or contract on cooling do not release uniformly from the walling of the removal sleeves and partly unexpectedly remain firmly adhesed thereto. With known ejection devices this leads to the fact that the cooled preforms cannot be ejected with certainty since the pressurised air provided for ejection escapes at the removal sleeves with easily removable preforms or with already ejected preforms.
It is therefore the object of the present invention to provide a discharging tool with an ejection device, with which the cooled preforms may be securely removed from the mould tool and after their cooling likewise may be securely and completely ejected again from the discharging tool.
According to the invention this is achieved with an ejection device, and in particular with an ejection device which comprises an ejection piston whose piston head is displaceable in the preform holder in a pressure-tight manner. Between the piston head and the floor part of the preform holder there is formed a pressure chamber which communicates with a pressurised air channel system provided in the base plate of the discharging tool. Additionally the ejection piston comprises a piston pin which is guided through a bore in the floor part of the preform holder and in turn is mounted in this bore in a pressure-tight and movable manner. This piston pin projects in a second chamber (subsequently also called vacuum chamber), which communicates with a vacuum channel system provided in the base plate of the discharging tool. This second chamber communicates via a bore leading through the piston pin and the piston head into the inner space of the preform holder. For receiving preforms the removal plate is positioned in the desired manner in the opened mould tool. By way of the suction effect produced with the vacuum system, the individual preforms are pulled into the respective preform holder until this bears on the piston end face of the piston head. By way of the further vacuumisation of the second chamber, the whole ejection piston together with the preform is pulled further against the floor of the preform holder and is held here. With this the vacuum may be controlled in a suitable manner. After the cooling has been effected the pressurised air system is activated and in the pressure chamber between the piston head and the floor part a pressure is built up with which the displaceable piston head is moved outwardly in order to eject the cooled preform out of the preform holder. A flange at the end of the piston pin determines the end position of the ejection piston.
This device ensures that the excess pressure produced in the pressure chamber on ejection of the preforms does not fall, independently of the acting adhesing forces, and is controllable in a simple manner. The individual preforms are safely ejected with this device. For the first time this device permits the pulling in and ejection forces to be controlled and regulated in a suitable manner. Furthermore with the ejection device according to the invention the preform may also be actively cooled in the moulding region.
In further embodiment forms it is taken care of that the piston end face tightly conforms to the outer shape of the preform. Helpfully this surface may be coated with a particularly suitable anti-sticking layer. It has proven to be particularly advantageous when the pressure chamber moving the piston is formed annularly and the piston pin at its end on the side of the base plate comprises a flange for limiting the piston stroke. For permitting a simple assemby and disassembly of the individual preform holders these comprise in each case an outer tubular cylinder housing and an inner cup-like cylinder liner, wherein this cylinder liner on the floor side is provided with a base part which may be inserted into a recess or the base plate. This base part is secured against turning on the base plate by way of positioning pins. The cylinder sleeve of the preform holder comprises a foot plate in a manner such that the base part of the cylinder liner with the help of this foot plate may be held firmly in the recess of the base plate.
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Fernandez Luis
Hofstetter Otto
Davis Robert
Nath Gary M.
Nath & Associates
Novick Harold L.
Otto Hofstetter AG, Werkzeug-und Formenbau
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