Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2002-10-03
2004-11-16
Von Buhr, Maria N. (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S197000, C162S218000
Reexamination Certificate
active
06819970
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to moulding machines and has been devised particularly but not solely to provide moulding machines for the manufacture of articles from fibrous suspensions, such as suspensions of cellulose or synthetic polymer fibres or mixtures of such fibres, and especially from lignocellulose fibres such as are used in papermaking, and the fibre recovered from recycled waste paper.
The invention may also be used in the manufacture of moulded articles generally, wherein the moulded articles are formed upon, and take their shape from a die or a set of dies, using materials such as fibrous suspensions and thermoplastic sheet.
The invention and prior art is described by way of example, using the manufacture of articles by moulding from fibrous suspensions, but the invention may also be employed to advantage in manufacture by thermoforming from thermoplastic polymer sheet.
2. Description of the Related Art
In background articles may be moulded from fibrous suspensions, the fibre or fibrous mixture suspended in a fluid, to be deposited on the surface of a porous mould or die, the fluid passing through the pores, leaving the fibres behind to form the desired shape on the working surface of the mould or die.
The fluid commonly used to suspend the fibre is water, in a so-called wet forming process, with the suspension loosely referred to as pulp. Steam and/or air and/or other gases may also be used as the fluid, in which case the process is described in the art as a dry or semi-dry forming process. An advantage of water is that it has the ability to suspend the fibre reliably in the form of a pulp feedstock during preparation and storage, and delivery to the moulding machine, enabling the convenient inclusion of various additives both to advantageously modify the moulding process on the moulding machine and also the properties of the moulded article to suit various end uses. When the fibre is or contains lignocellulosic fibre such as papermaking fibre which may be recovered from waste paper for example, another advantage of water is that it enables hydrogen bonds to be developed between the fibres, either as the only bond or in association with other adhesives so connecting the fibres together at junctions in the completed article, hydrogen bonds being the principle bonding means used by papermakers.
In a dry forming process, additional adhesive is invariably required unless the article is held under pressure at a temperature high enough to fuse the natural polymers (principally the lignin) in the formed mass, because significant hydrogen bonding is not developed in a dry forming process.
While water is the most common medium used to transport fibres for moulding it also has some disadvantages and the main disadvantage of water is that when the fibres have been deposited on the mould or die surface, substantial energy is required to remove the water again to produce a usefully rigid article.
The source of lignocellulose fibre most commonly used is recycled waste paper although virgin fibre or a fibre mixture may also be used, including various polymer fibres which of course do not develop hydrogen bonds. When present in large proportions or as the sole fibre, polymer fibres may be bonded by fusing with heat.
After removal of sufficient water by draining, pressing, and the like, to enable the moulded article to be further processed it is transferred directly or by means of a co-acting transfer die or dies of a shape generally matching the moulding die, to a drying facility, where further water is removed using heat. In a dry forming process the dies may be heated to cure a bonding agent. A drying facility may be used, which is typically an oven, including a conveyor onto which the moulded article is deposited, to be conveyed through the oven, to emerge as the dried or cured rigid article of a substantially predetermined moisture content.
In practice, although the moulding process can be accomplished with a single moulding die with or without a single transfer die, the moulding machine more usually includes a plurality of moulding dies and a plurality of transfer dies to effect moulding and transfer of the articles more or less continuously at a satisfactory production rate. Sometimes a lesser number of transfer dies than moulding dies is used, each transfer die serving more than one moulding die, but nevertheless with generally matching shapes and the dies co-acting in sets. The plurality of moulding dies are arranged to move on a path which includes immersing them into a vat of the suspended pulp feedstock to collect or form the moulded article on the porous moulding surface of the die, and the plurality of transfer dies (where used) are also arranged to move on a separate path which includes engaging in co-acting sets with the moulding dies to effect transfer of the moulded articles prior to drying them, or in the case of a dry forming process, to press the article and apply heat to cure a bonding agent.
During engagement of co-acting sets any separate paths must be parallel for a time, and the die sets must be moving at similar speeds to remain properly engaged and this necessity places significant limitations on prior art moulding machines of the continuous-path type, especially where the article requires moulding of deep cavities.
Separate pressing dies may be used either to improve the shape or finish of the article or to provide conditions to bond the moulded material together. When the pressing process is performed on the moulding line the separate pressing dies also have to be coordinated with the other functions of the moulding machine.
The simplest form of a moulding machine arrangement is a reciprocating system with the moulding die or dies reversing repeatedly on a path to accomplish the process. This form of moulding machine is relatively simple to control as the path is usually linear and there are end positions at each end of the path. The reciprocating moulding machine solution is usually applied to comparatively low volume production, often for deep cavity mouldings, and has an advantage of simplicity and low capital cost for such purposes.
For large scale production the common prior art solution is to provide continuous-paths for the dies to follow by mounting them on a rotating framework or rotor, for example a moulding die rotor and a transfer die rotor, which are permanently mechanically interconnected so as to keep them in the correct relative positions throughout the sequences, the rotors usually moving continuously at a constant speed during the production process. The essential sequences of operations required for moulding machines with continuous-path mounted dies become much more difficult to provide and control and the prior art versions of these machines are not suited to deep cavity mouldings, mainly because of interference between moulding and transfer dies as they enter and leave cavities while moving on a non-linear path. Irrespective of whether or not transfer dies are used, the wet articles may also be required to be deposited accurately on a conveyor passing through a drying oven, especially where dryer trays are used. This requires yet further co-ordination. Often a subsidiary function of the transfer dies is pressing to achieve mechanical compaction and accuracy of shape of the article and removal of some water by squeezing prior to a further drying stage, or application of heat in a dry forming process.
Associated with the need for correct register of the moulding and transfer dies are functions such as the application of alternating vacuum and pressure to the moulding dies at the appropriate time to draw fluid through holes provided in order to form the pulp feedstock on the porous working face and effect transfer of the moulded article respectively, and application of alternating vacuum and pressure pulses to the transfer dies (which are also provided with holes), at the appropriate times to effect transfer of the moulded article, and release of the article for placement for drying
Knobbe Martens Olson & Bear LLP
Ludowici Packaging Limited
Von Buhr Maria N.
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