Shui
Fong
Shui
Fong
| 1. | A production method for producing structural layered board formed of bamboo, the method comprising cutting bamboo into elongate thin strips, feeding and holding the strips side by side on a conveyor and joining the strips together to form sheets, drying the sheets to reduce the moisture content to less than 20%, immersing the sheets in a bath of resin, drying the resin impregnated sheets, laying down the dried sheets face to face to form the board with alternative sheets having their strips orientated at right angles to one another, and hot pressing the board. |
| 2. | A method according to claim 1. including placing southward and northward cut strips alternatively side by side to form the sheets. |
| 3. | A method according to claim 1 or 2. including trimming the strips after cutting to a precise uniform thickness and using the trimmed strip sheets as at least one outside sheet of the finished board. |
| 4. | A method according to any one of claims 1 to 3. including joining the strips together by applying thin tapes of adhesive material on one or both sides of the sheet . |
| 5. | A method according to any one of claims 1 to 3. including joining the strips together by stitching. |
| 6. | A method according to any one of claims 1 to 3. including joining the strips together by stapling. |
| 7. | A method according to claim 1 in which some of the sheets are formed by wood ply sheets, compressed wood chips or cork or combinations thereof. |
| 8. | A mu 11 i 1 ayered structural board forme by the method of any one of claims 1 to 7. |
The invention relates to structural board.
The invention relates particularly to structural boards formed of bamboo for use in buildings, shipping containers, and the like. It is known to make boards by saving timber, usually hard wood, into suitable lengths and thicknesses but this is expensive and currently extensive use of diminishing supplies of such timber means that alternative methods must be sought. It is also known to make up boards by using thin plies of wood and gluing them together to form "plywood". Some inner layers may be relatively thick. board so-formed is often referred to a "block board". It is also known to compress and glue wood shavings into laminar board shapes. Some simple boarding for dividing screens have been made of strips of bamboo but so far suitably strong structural boards have not been successfully produced and certainly no satisfactory mass-production methods have been proposed .
It is an object of the invention to overcome or at least reduce these problems.
According to one aspect of the invention there is provided a production method for producing structural
layered board formed of bamboo, the method comprising cutting bamboo into elongate thin strips, feeding and holding the strips side by side on a conveyor and joining the strips together to form sheets, drying the sheets to reduce the moisture content to less than 20'". immersing the sheets in a bath of resin, drying the resin impregnated sheets, laying down the dried sheets face to face to form the board with alternative sheets having their strips orientated at right angles to one another, and hot pressing the board.
The method may include placing southward and northward cut strips alternatively side by side to form the sheet s .
The method may include trimming the strips after cutting to a precise uniform thickness and using the trimmed strip sheets as at least one outside sheet of the finished board.
The method may include joining the strips together by- applying thin tapes of adhesive material on one or both sides of the sheet, by stitching or by stapling.
Production methods of producing a bamboo ply board according to the invention will now be described by way of example.
Suitable lengths of mature bamboo are cut into strips. typically 10 to 30 mm in width and 1 to 3 mm thick. The strips are held side by side on a conveyor and joined together to form sheets.
The joining is preferably formed by passing the sheet between rollers which roll thin adhesive tapes on to each side of the sheet. The tapes are generally previous to resin, or capable of absorbing resin, and stick to the strips to hold them together side by side. The strips may alternatively be stitched together in which case the strips are passed along a production line on the conveyor and through a punch, to form stitching holes, and a sewing machine. The strips may also be joined together side by side by sta les.
The sheets are then rolled up and placed in an oven and heated to a temperature of 100° to 160° (the oven may also be pressurised) until the moisture content of the sheets reduces to at least below 20% and preferably to 12% or less. The sheets, are then cooled before being immersed in a bath of resin, such a water-soluble phenol formaldehyde resin, to allow the resin to fully impregnate into the bamboo.
The sheets are then removed and allowed to drip dry and may be heated in an oven to a temperature around
50° to 90°. The sheets are then normally dehumidified.
The sheets are then unrolled and cut to a required overall size and placed against one another face to face with the strips of alternative sheets extending at right angles to one another. Typically, five or seven sheets will be used at one time to form a five- ply or seven-ply board, respectively. The board is then placed in a hot press for a few minutes to cure the resin and complete the method.
The described method is typically carried using production line techniques and machinery and equipment general ly already available in wood manufacturing plants. By ensuring the sheets are first dried to have a low moisture content, well-below the usual moisture content in normal environmental conditions, before being placed in the resin bath, the resin impregnates fully into and throughout the bamboo. This ensures the finished board is totally bonded together by the resin and substantially ensures that the finished board is significantly resistant to corrosion in use. Further, because in the described method the sheets can be rolled up for drying and resin impregnation, these operations can be carried out using minimum manufacturing space or capacity.
To improve the quality of the described board the
method may include one or other (or both) refinements as described below.
Mature bamboo is naturally thicker and wider along its length closer to its base when it grows. This means that when the strips are formed by a cutting machine, each strip tends to be thicker and wider at one end. In order to ensure that each strip is precisely the same thickness (within normal acceptable tolerances) along its length, the strips can be trimmed after cutting, by a planar for example. The trimmed strips are then used in the final board to provide the external plies of the board. Of course, if the board is to be knowingly used with only one face exposed, it may be sufficient to form only the exposed face with a sheet of trimmed strips.
The second possible refinement is to place so-called "southward cut" and "northward cut" alternatively together side by side when forming the sheet. This means that the slightly thicker and wider ends of each strip is placed adjacent the somewhat thinner and narrower ends of another strip next to it. Overall this provides a natural compensation for the variations is the widths and thicknesses of the strips in the overall sheet made up in this way.
Boards made according to the methods described above
are suitable for a normal structural applications including shelving, flooring, panelling and so on. In particular, the boards are particularly adaptable or useful for use in shipping containers because the boards can not only be very strong but can withstand significantly adverse environmental conditions with minimum pos t -manufactur ing treatment. As such, the described bamboo boards are superior to normal plywood in hardness, strength. resistance to abrasion and moisture absorption. It will also be appreciated that the supply of bamboo is more readi ly and currently available than wood and that mature bamboo can also be grown more qui kly.
The method may include for some applications replacing some of the intermediate layers with sheets of plywood, blocks of woods, sheets of compressed wood chips, and cork chips. The replacement sheets or prepared alternative materials are placed between some of the bamboo sheets to form the board before the board is hot pressed. Preferably, such replacement layers are impregnated or generally treated with resin which is cured during the hot pressing.