Patent Application
20100098895
The present invention relates to folding solid wood blockboard.
Curved wood panels are used in backrests for wooden chairs, casket lids, boat shells, and wood furniture, cabinet doors and drawers, to only give some examples. Some curved wood panels, such as the backrests of chairs, are folded on the length of the grain, i.e. longitudinally arched. We can say that other curved wood panels such as casket lids, have boards parallel to the axis of the vault, i.e. are transversely arched.
The production of longitudinally arched wood panels implies folding, or curving, the wood. Curving or folding wood is a delicate operation which requires to master the process and to have a good knowledge of the solid wood properties. The green wood, that is wood freshly cut, is generally easier to curve then the wood which was dried in an oven. The wood can be exposed to vapor, or be immersed in the water, before it is curved to reduce the probability of checking or cracking. Curving the wood can be made by different ways, for example using a custom jig or using a press.
The production of longitudinally arched wood panels implied, until this day, assembling several parts previously curved side by side, by any way, to form a panel. For the transversely curved panels, the machining of at least one edge of each of the wood boards is necessary to give it an angle to assemble the boards, and to assemble them to give them a transversely shaped curve. The radius of the vault is thus predetermined by the angle at which the edges of the wood parts are machined.
Curving or folding solid wood by vapor has allowed so far the use of parts of wood of a single cut, that is, unique parts, which have to have at the onset the wished final dimension. This thus limits the dimension of the possible curved parts and often causes a lot of wood loss.
The known processes of production to obtain curved solid wood panels were satisfactory to a certain extent. However, there is still place for improvement.
It is possible to obtain a curved panel, using a flat panel composed of boards rectified on their edges and transforming it, by pressing, into a bent panel.
We can also use a bent wood panel fabrication method starting from a flat panel formed of boards glued edge on edge to transform it from a flat panel into a panel bent transversely, longitudinally or bothwise.
We can use a bent wood panel fabrication method starting from a flat panel formed of boards glued edge on edge using a glue resisting to the vapor; this method will allow the use of warm vapor which will increase the flexibility of the wood boards and facilitate the folding of the panel.
We can use a bent wood panel fabrication method starting from a flat panel formed of boards glued edge on edge which have between 8 and 30% of hygroscopic humidity and which are glued using a glue resisting to the vapor, then steaming them during 2 to 60 minutes. This technique allows to fold panels of thickness of ⅛″ to 1⅞″ and to have a radius larger than 2 inches.
We will be able to bend the panel longitudinally, transversely, or bothwise.
It is also possible to fold panels formed of wood boards assembled in a longitudinal way, a transverse way, or bothwise.
The wood panels can be panels of solid wood.
In the appended figures:
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A set of tests was so made to validate the principle of the longitudinally folding and of the transverse folding. For each of the tests, panels were curved using a similar process. Each of the tests was realized according to the processes illustrated in
For the longitudinal bending, the general process used in each of the 4 tests is represented in
During the stage of panelling, each panel is made by gluing a variable number of boards of varied widths edge on edge with the glue indicated in the above Table. It is good to note that all the panels are flat after they are glued, before being curved. The panels are glued directly in the steaming room. The heat, 85-90 degrees Celsius, in the steaming room, contributed to harden the glue during the steaming stage of 15 or 30 minutes depending on the test. A total of about ten panels were made for each test.
The panelling was followed by a panel sizing stage. Panels were trimmed at 13/16 inch and cut at a precise length to fit to the compression steel sheet when such a device is used.
Each panel was then folded in a hydraulic press on a mould. The type of press used is indicated in the above Table. When a compression steel sheet was used during the folding step, it is also indicated in the column “compression when folding” in this Table.
The folded panels were, afterward, let to dry naturally, in normal atmospheric situation (hygroscopic balance from 6 to 8%).
The folded panels were then inspected to verify the condition of the glued joints, the appearance of the panels, both on the concave and on the convex faces. The results of this inspection for each test appear in the Table presented below.
For the transverse folding, the general process used in each of 4 tests is represented in
During the stage of panelling, each panel is made by gluing a variable number of boards of varied widths, edge on edge, with the glue indicated in the above Table. The panels are glued in a spider-type press. It is good to note that all the panels are flat after being glued, before being curved. The time it takes for the glue to dry and harden is according to the manufacturer's data sheet of the glue used. A total of about ten panels were made for each test.
The panelling is followed by a stage of panel sizing. Panels were trimmed at 13/16 inch and cut to a precise width to fit to the compression steel sheet when used.
Every panel was treated with vapor with a free steam steaming pit. This operation was made at 85-90 Celsius degrees for 15 or 30 minutes depending on the test.
Each panel was then folded in a hydraulic press on a mould. The type of press used is indicated in the above Table. When a compression steel sheet was used during the folding, it is indicated in the column “compression when folding”, also in this Table.
The folded panels were left, afterward, to dry naturally, in normal atmospheric conditions (hygroscopic balance from 6 to 8%).
The folded panels were inspected to verify the condition of the joints of glue, the appearance of panels, both on the concave face and on the convex face. The results of this inspection for every trial appear in the Table presented below.
A compression steel sheet has for objective to prevent the stretching of the wood fiber on the convex face of the piece of wood or the panel to bend. On both extremities of the steel sheet, we find a stop plate; the panel is then cut in a precise dimension at the exact distance between these two stop plates. In the stage of the folding, the steel sheet follows the panel in the press until the final shape.
In conclusion, the more the radius of curvature is small, the more it is recommended to use a compression steel sheet. The radius of curvature is influenced by the thickness of the wood to be folded: the greater the thickness of the wood is, the greater the radius of curvature must be. Every panel was folded with a hydraulic bending press. The folded panels were, afterward, let to dry naturally, in normal atmospheric conditions (hygroscopic balance from 6 to 8%).
The deformation produced on the bent panels, after drying, is very small. A recovery occurred on the folded panels, but no more than what is normally foreseen for a unique part, that is, without being glued. A very interesting fact is that the folding of a glued wood panel tolerates some defects that the folding of individual parts would not accept at the risk of breaking during the folding step. For example, knots and wood with an oblique thread support the effect of the folding when these parts are glued together. Given that these defects are not often found facing one another, boards exempt of defects support those who do have defects. We can thus expect a better and bigger use of wood resources.
It is normally easier to fold a panel transversely than longitudinally. During a longitudinal folding, the joints of glue are subjected to important longitudinal shears. On the other hand, during a transverse folding, the effort acts between the fibers of the wood rather than on the length of the wood fibers, and the effort on the joints of glue is mainly felt by the tension between the wood boards.
The experiments above described demonstrate that the folding of panels made of solid wood boards is doable and gives satisfactory results while allowing the recovery of the wood, transversely as well as longitudinally. These results imply that the oblique folding of the panels is as well doable because to bend obliquely is the combination of a transverse and longitudinal folding.
If we try to make a folded panel using individual boards then assembled together, the uneven recovery of each individual board will result in panels of uneven surfaces. The radius of the folding of each board can be uneven and the panel which will result will have to be worked on again to obtain a satisfactory product.
Trimming the panel flat on its thickness, before folding it, is much simpler and will require no additional operation after the folding, except a light sanding.
Folding the panel, rather than folding individual boards and assembling them afterwards, can save a considerable quantity of time and decrease a lot the wood loss, given that the glued boards can be of varied widths, even narrow. This can eliminate operations which do not contribute to added value and allows new applications. For example, chair backs, which were usually made with a unique part, can now be made with a glued panel. Panels bent of bigger dimension can also be made, because the panelling allows a lot of flexibility in the size of the finish parts, simply by assembling more or less boards together.
In the case of panels folded transversely, the folding of the panel can advantageously save the step to have to manufacture an angle on the edges of the components. In other terms, assembling a flat panel then folding it can be realized in a short time, according to a process simpler than assembling boards with angular edges and, afterward, gluing them in a mould, and leveling them respecting the target curvature.
Besides the examples above-mentioned in this document, several other alternatives can be considered.
For example, although the examples described above apply to panels folded regularly on their entire surface, it is as well possible to bend only part of the surface.
The folding of the panel can be made with other appropriate tools. For example, the use of rollers rather than a press can be suited in certain situations.
An appropriate choice of glue plays an important role to prevent the appearance of faults in the joints of glue. The glue should be able to resist heat and humidity to which the panel is exposed during the steaming, and should also be able to resist the folding operation. Adequate glue can be polyurethane glue, melamine containing some formaldehyde urea with a catalyst, a white glue of PVA type with a catalyst, to give only some examples. Certain glues must be avoided. In particular, the outside glue PVA of Lepage™, as well as the white glue PVA without catalyst is not suited, at least in some applications.
Hard wood indicated as broad-leaved trees generally give better results than conifer. Wood such as the African mahogany and the eucalyptus or lyptus is to be avoided. The wood species advisable is the wood which we use normally in panelling and industrial folding. For some applications, we can begin the process with already dry wood, dried with a dryer, rather than to use wood naturally dried in air.
After the folding, panels can finish to dry freely, at ambient air, or in an artificial dryer with controlled heat and humidity.
Panels made of solid wood boards having a hygroscopic humidity comprised between 8 and 30% and between ⅛ and 1⅞ inch of thickness, were bent after having been warmed in vapor for between 2 and 60 minutes before the folding and having a radius of curvature higher to 2 inches, for example.
This new way of making opens nice perspectives in the technical and economic point of view for the manufacturers of curved articles, such as wood sport articles, backrests of chairs or cabinet doors and drawers, in solid wood, for example.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2 641 628 | Oct 2008 | CA | national |
