Plastic and nonmetallic article shaping or treating: processes – Mechanical shaping or molding to form or reform shaped article – Forming plural articles
Patent
1995-07-19
1998-04-28
Tentoni, Leo B.
Plastic and nonmetallic article shaping or treating: processes
Mechanical shaping or molding to form or reform shaped article
Forming plural articles
2642978, 2643288, 264334, 425444, 425556, 425577, B29C 4500, B29C 4540
Patent
active
057440883
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a method for manufacturing hollow objects, in particular plastic preforms for subsequently processing to PET objects.
BACKGROUND
In a known production process PET granules are predried and subsequently processed in the injection moulding process to semi-finished products such as preforms. In this case the injection moulding process comprises a series of successive operations, namely metering and injecting the raw materials into a mould, subsequent pressing thereof by means of a mould, and cooling and unmoulding. In the case of preforms it is customary to remove the products from the mould by means of one gripper element provided with sleeves which are directly or indirectly cooled. The gripper element is provided in order to simplify the ejection process in which the preform is unmoulded. Subsequent cooling is necessary in this case, in order to minimize the deformation of or damage to the preforms. This can also be applied to other production of plastics. During the injection phase into the mould the liquid raw material is injected into the mould between its mandrel and cavity. The mandrel and the cavity are cooled during the injection moulding process. In order to give the preforms to be unmoulded sufficient stability, the cooling time must be accurately set. The cooling time is therefore an important parameter in the injection moulding cycle.
The cooling time will in fact influence the total cycle time of the process. The longer the cooling time, the longer the cycle time will be, and there will thus be a reduced output.
One gripper element means that there can be cooling for virtually one cycle time. However, this is still too little to reduce the cooling time during the injection moulding process, and production continues with cycle times which are too long.
In a known method, one gripper element which is provided with different sleeves as accommodation elements is used. The preforms remain two or more cycles in the sleeves on said one gripper element. The disadvantage in this case is that the gripper element is very heavy, so that more water has to be used, with a resulting increasing so-called shot weight or impulse, and with an increasing number of sleeves. This results in loss of time and a length adjustment and precision problem for the gripper, for the latter has to assume a number of different positions in the mould in each case during the takeover. Early wear also occurs, and the unmoulding time increases, through the heavy handling due to the higher inertia of the apparatus. In addition, the gripper element emerges from the machine laterally, with the result that a considerable surface area is taken up and rendered useless, so that rather a large amount of space is required for the apparatus. Access to the mould is consequently made very difficult, owing to the lateral removal of the gripper element, and this is quite inconvenient for maintenance.
The use of one gripper element with sleeves, in the case of which after a cycle the preforms are discharged and deposited on an air-cooled conveyor belt with pins is also known. A first disadvantage in this case is that cooling after one unmoulding time cycle is not sufficiently intensive.
A further disadvantage of this method is that the positioning of the mandrels increases the complexity of the production process.
In another known method, use is made of a gripper element with sleeves, in the case of which the preforms are cooled and conveyed to an external cooling station, which is external to the actual apparatus for carrying out the method.
In addition to inadequate cooling, there is the disadvantage here of the greater complexity of the cooling stations. For, the cooling moulds generally no longer correspond to the shrinkage of the preforms during cooling. This leads to uneven cooling of the preforms and to possible damage of the preforms. For, it has been found that preforms, in particular PET preforms, have the best cooling properties on the outside wall (heat expands outwards), and the gr
REFERENCES:
patent: 4209290 (1980-06-01), Rees et al.
patent: 4592719 (1986-06-01), Bellehache et al.
patent: 4721452 (1988-01-01), Delfer, III
patent: 4836767 (1989-06-01), Schad et al.
Patent Abstracts of Japan, vol. 11, No. 302 (M-629) (2749) 2 Oct. 1987 & JP,A,62-094,319 (Fanuc) 30 Apr. 1987.
Simeco
Tentoni Leo B.
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