Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-11-29
2001-08-21
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S244110, C156S244210, C156S244250, C156S244260, C156S292000, C156S500000
Reexamination Certificate
active
06277231
ABSTRACT:
The subject of the present invention is a process for manufacturing a honeycomb structure made of thermally fusible material, such as made of thermoplastic or made of rubber, and a plant for the implementation of this process.
The honeycomb structure according to the invention makes it possible to obtain, for example, sheets in which the cells are perpendicular to the plane of the sheet, these sheets having a simple honeycomb structure or a sandwich structure with a honeycomb core.
It is already known to produce honeycomb structures made of thermally fusible material, which are essentially obtained by four processes.
The first process consists in adhesively bonding films to one another, with the aid of offset sheets of adhesive, and then in carrying out a drawing operation in order to obtain a honeycomb structure. This is a batch manufacturing technique, which is very expensive to implement.
A second process consists in thermoforming a sheet of thermoplastic. This is a batch manufacturing technique, the cells necessarily being tapered and the thickness of the structure obtained being very greatly limited.
Another process consists in injection moulding the structure inside a complex mould. In this case again, this is a batch technique, the size of the parts produced being limited.
A fourth process consists in extruding a thermoplastic profile of greater or lesser complexity, having cut-outs making cells. The cells are therefore oriented longitudinally in the extrusion direction. It is necessary, after extrusion, to cut the profile into slices, to reorient these slices at 90° with respect to the extrusion direction and to fasten the slices to each other, either by adhesive bonding or by thermal fusion, with or without added material, such as woven material, needle-punched material or a sheet of thermoplastic, in order to form a panel.
This technique is therefore complex to implement, as it requires off-line operations in order to end up with a final product consisting of a panel.
The honeycomb structures, such as those that have just been defined, possess very good intrinsic properties resulting, on the one hand, from the honeycomb structure and, on the other hand, from the nature of the thermally fusible material. These properties are, in particular, the mechanical strength in compression, a low weight, recyclability, thermoformability, a beneficial thermal insulation coefficient, their imputrescible character, as well as the permeability to most forms of radiation. These structures therefore find applications in many industries: automobile, naval, aeronautical and railway, as well as in buildings and public works, allowing the production of sandwich structures which advantageously replace cellular foams and elastomers of the rubber type, of conventional design.
Document DE 1,779,330 describes a process for manufacturing a crosslinked tubular net, in which strands of thermoplastic are extruded parallel to each other and are deflected in order to be brought into point contact in pairs due to the effect of hot-air pressure. This technique is not suitable for the production of a honeycomb cellular structure.
The object of the invention is to provide a process and a plant for manufacturing such a honeycomb structure, allowing continuous manufacture of a structure in the form of a panel, without requiring any off-line operations, this panel possibly consisting of a sandwich structure with a honeycomb core. Another object of the invention is to allow easy adjustment of the thickness of the structure obtained, during production, as well as of the density of this structure, with the possibility of varying the shape of the cells while the structure is being obtained.
For this purpose, the process to which the invention relates consists:
in continuously extruding, with the aid of a multislot die, parallel sheets of thermally fusible material inside a cooling chamber, with the creation of a seal between the longitudinal edges of the sheets and the walls of the chamber, the various sheets defining, among themselves and with the walls of the chamber, compartments;
in creating, in this chamber and from the end located on the die side, a vacuum in every other compartment so as to deform and attract, in pairs, the extruded sheets in order to carry out localized welding over their entire height;
in filling, from the end located on the die side, every other compartment, these alternating with the above compartments, with the aid of a coolant; and
in alternating, in each compartment, the creation of a vacuum and the filling with the aid of a coolant in order to obtain a solidified honeycomb structure in the cooling chamber, in which structure the cells are perpendicular to the extrusion direction.
This technique is very beneficial insofar as the structure is output continuously, directly from the extrusion die, with cells that are perpendicular to the extrusion direction. It is therefore possible to output from the die honeycomb structures of very large dimensions, for example in the form of panels, which panels are obtained directly without any off-line operations.
The creation of a vacuum in the compartments defined by two sheets ensures that they come together and are welded over their entire height. Feeding the neighbouring compartments with thermally regulated coolant makes it possible, just after welding, to ensure that the structure solidifies in the cooling chamber.
One advantage over the technology of adhesively bonded or welded films is that, according to the invention, the welded part of the sheets may have approximately the same thickness as the non-welded part, thereby resulting in a reduction in the density of the structure, lightness being an important criterion. For this purpose, the process according to the invention consists in exerting on the structure leaving the cooling chamber a jerked pull so as to reduce the thickness of the sheets in those regions of the latter that have to be welded to each other.
It is possible to vary the shape of the cells, which may be in the form of regular or irregular polygons or have an elliptical, circular or oval shape, with the same die, during operation, by adjusting various parameters, such as the extrusion rate, as well as the alternating vacuum-coolant-feed cycles applied between two neighbouring sheets.
A plant for the implementation of this process comprises an extruder delivering the thermally fusible material in the viscous state to a coat-hanger die having several parallel slots each intended for the continuous formation of a sheet, each slot being defined by two cone-shaped pieces made of thermally insulating material and made in each of the cone-shaped pieces is a groove capable of being connected in succession to a vacuum source and to a coolant source, this plant also comprising a tubular cooling chamber, of rectangular cross section, having a height equal to the height of the structure to be obtained, in the direction of the cells of the latter, and having a width equal to that of the structure, a coolant tank from which the coolant is drawn off with the aid of a pump, a vacuum pump and a directional-control valve which, being linked to these two pumps as well as to a circuit connecting it to the various compartments located on both sides of the sheets, is intended to connect, in succession, each compartment with the vacuum source and with the coolant source.
REFERENCES:
patent: 3932106 (1976-01-01), Vogts
patent: 1779330 (1971-09-01), None
patent: 4208812 (1993-09-01), None
patent: 42-024092 (1967-11-01), None
patent: 8700119 (1987-01-01), None
Ball Michael W.
Cantor & Colburn LLP
Musser Barbara J.
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