Process and device for conveying objects along a circuit and use

Details Process and device for conveying objects along a circuit and use Process and device for conveying objects along a circuit and use

1994-06-09

1996-05-21

Bidwell, James R.

Conveyors: power-driven

Conveyor system for arranging or rearranging stream of items

By longitudinally respacing successive articles in stream

198458, 1984651, 198432, B65G 4726

Patent

active

055181058

DESCRIPTION:

BRIEF SUMMARY
The present invention concerns a method for conveying objects along a circuit whereby each object is placed on a transport pallet and the pallets are moved in steps along the circuit to pass successively through a first work station where they are separated by a first longitudinal interval, and at least one second work station where the objects are separated by a second longitudinal interval, larger than the first interval, said method comprising the step of separating the objects between the first and the second work station.
The invention also concerns a device for moving the objects along a circuit consisting of transport pallets arranged in a line on sections of track forming at least one part of said circuit and successively passing through a loading station where each object is placed on a pallet, a first work station, at least one second work station where the objects are treated in batches, and a discharge station where the objects are removed from the pallets; at the first work station, the objects are separated by a first longitudinal interval and at the second work station, by a second longitudinal interval larger than the first interval. The device also comprises means for advancing the pallets in steps along the track. The invention also concerns a use for such a device: conveying preforms during the thermoplastic blow-molding process.
Conveying objects placed on individual pallets along a production line, assembly line or any type of treatment circuit is a common practice. The circuit is generally closed and the pallets are pushed in steps at a predetermined rhythm depending upon the time required to perform operations at the various posts along the line.
Such devices are typically used in production lines during the manufacture of thermoplastic containers blow-molded from preforms. The lines generally comprise a unit for loading the preforms onto the pallets, a preheating oven through which the preforms pass for whatever time is required to soften the material, a blow-molding station and a discharge station where the molded containers are removed from the pallets. The empty pallets then follow the return track that closes the circuit.
If it is necessary for the objects to remain immobile at one work station longer than at other work stations, that work station must treat several objects simultaneously to avoid slowing the rhythm of the line. This is particularly true with a blow-molding station as described above, which generally consists of two half-molds with several cavities that must be transversely separated for the pallets to be introduced, then closed for blow-molding, cooling, etc. to take place. Thus, if several objects are molded simultaneously, the pallets can move along the circuit at a higher speed.
Devices known in the art that function according to this principle require specialized equipment for temporarily storing the pallets before they are introduced as a batch into the mold while successive pallets continue to advance along the circuit. The spacing between successive objects presents a problem with this type of line. The interval should be as small as possible on the largest portion of the circuit, primarily to reduce excessive acceleration. Furthermore, the interval between objects should be as small as possible while they are passing through the preheating oven in order to control preheating time and reduce it. On the other hand, it is imperative that the interval be larger than a limit determined by the size of the object manufactured so that two successive objects do not touch each other. In actuality, the size of the molds imposes an even stricter limit, particularly when the molding station is designed to blow-mold several objects respectively transported on a group of aligned pallets.
One known solution for varying spacing between objects between two predetermined values (specifically in French Patent Application Publication No. FR-A-2 667 051) consists of using rectangular pallets and placing the pallets either longitudinally or transversely in the line of adjacen

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patent: 5391214 (1995-02-01), Nakagawa
Patent Abstracts of Japan, vol. 7, No. 87 (P--190)(1232) 12 Apr. 1983 & JP, A, 58 014 341 (Pioneer) 27 Jan. 1983.

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