Manufacture of reconstituted wood products

Details Manufacture of reconstituted wood products Manufacture of reconstituted wood products

1999-08-09

2002-02-05

Tentoni, Leo B. (Department: 1732)

Plastic and nonmetallic article shaping or treating: processes

Direct application of fluid pressure differential to...

Bulk deposition of particles by differential fluid pressure

C264S109000, C264S122000, C425S080100, C425S406000

Reexamination Certificate

active

06344165

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to the timber industry, and particularly to methods and apparatus for use in the manufacture of reconstituted or reconsolidated wood products. More particularly, the present invention relates to methods and apparatus for use in the manufacture of reconstituted wood products using steam pressing methods and apparatus, particularly steam injection pressing methods and apparatus. Even more particularly, the present invention finds application in making SCRIMBER® type wood products, particularly large beams of SCRIMBER or laminated typed products using a steam injection press.
Although the present invention will be described with particular reference to the manufacture of SCRIMBER wood products using steam pressing methods, particularly steam injection pressing methods, it is to be noted that the present invention is not limited in scope to the described arrangement, but rather the present invention is more extensive so as to include other methods and apparatus of producing similar or related products using similar or related methods and for other applications.
It is known to employ steam in methods and apparatus used in the timber industry generally, and in making reconstituted wood products. Such methods involve a “steam pressing” step or a “steam injection pressing” step and are used in the processes of making reconstituted or reconsolidated wood products such as particle boards (chipboards), oriented strand boards, medium density fibre boards, in the form of panels or beams or the like involving the use of adhesives or binders to bind the wood component materials together. Steam pressing is employed not only to compress the wood components, such as for example wood particles, chips, fibres, scrim, flakes, shavings or the like, but also to apply heat to cure the bonding agent or adhesive with which the component materials are mixed. Generally a charge of the wood components and adhesive or binder such as a suitable thermosetting resin is compressed between two platens to form a mat to which steam is introduced to form the wood product. The steam supplies the heat for plasticising the wooden components of the mat and for curing the thermosetting resin binder so that a panel, beam or similar of desired shape and size is formed. In methods and apparatus using steam injection methods, the steam is injected through perforations supplied in the platen or platens so that steam is passed into the mat at various locations over the surfaces of the mat. Examples of steam injection pressing are disclosed in, for example, U.S. Pat. No. 4,393,019 (Geimer) and U.S. Pat. No. 4,517,147 (Taylor and Reid).
The use of steam is well known in the timber processing industry to relieve stresses in both softwoods and hardwoods. Steam pressing of reconstituted timber-based products is regarded as being not only a method of supplying heat to a substrate but also as a means of improving stability of panel products by relieving stresses within the wood product. Such steaming has the effect of reducing the incidence and degree of checking and warping in timber products, for example.
Although known reconstituted wood products are usually manufactured as panels of relatively thin sectional thickness, such as for example a thickness of up to about 40 mm, it is more usual for such methods to be used in the manufacture of panels of thickness from 3 to 25 mm. When heating and pressing is used to manufacture these thinner panels, edge sealing of the mats is not normally necessary because the panel itself is of sufficient density and uniformity to prevent the lateral escape of steam, which is to say that the panel itself acts as its own seal to contain the steam within the bulk of the material in order to allow pressure and temperature to build up within the compressed mat. In steam injection pressing, this “self-sealing” property can be improved by leaving a relatively wide margin between the edges of the mat and the outside edge of the steam holes in the perforated platens compressing the mat to act as a steam seal, or by including a circumferential lip on the face of each platen which increases the compression in the surrounding edge region of the mat and thus seals the edges of the mat during compressing and steaming.
However, the lateral escape of steam from the external edges of the mat may become a problem for panels having thicknesses beyond about 50 mm. Also, the structure of some reconstituted wood products is unsuitable for providing the above-mentioned “self-sealing” property. For example, products manufactured from coarsely splintered wood may not provide a sufficient degree of homogeneity or uniformity to provide an adequate seal. An example of one such reconstituted product, which is perhaps more accurately described as a reconsolidated wood product, is that which is disclosed in Australian patent no. 510845 (Coleman).
U.S. Pat. No. 3,891,738 (Shen) describes a method of steam injection pressing in which the lateral escape of the stream from the fibre mat is prevented by using a sealing frame which is placed circumferencially around the edges of the mat between the platens. When the platens are pressed together against the sealing frame, a sealed chamber is formed which encloses the mat. The amount the platens are spaced apart from each other in the direction normal to the planes containing each of the platens determines the thickness of the resultant board or reconstituted wood product since the material being compressed is contained within the sealing frame, located between the two platens. Although this method and apparatus are said to be applicable to boards of thicknesses greater than 5 inches (125mm), they suffer several disadvantages. Firstly, the compressive force and the steam pressure applied to the mat are not independent of each other. The chamber cannot pressurise (via the lateral escape of steam from the mat) unless and until a seal has been formed between the surface of each platen and the adjacent end surface of the frame, and further, once the chamber does pressurise, the maintenance of this pressure depends in turn on the compressive force being maintained as this determines the seal being maintained. Secondly, it will be very difficult in practice, given the environment in which such apparatus is to perform, to ensure an acceptable seal is maintained between the platens and the frame. For example loose wood particles or splinters will almost certainly become lodged between the sealing surfaces of the platens and the side of the frame, thereby preventing these surfaces from coming into sealing engagement with each other to form the required seals. In addition, resin accumulation or resin build-up on the walls of the apparatus, frame, platen or the like can contribute to the lack of sealing of presses using such arrangements.
SUMMARY OF THE INVENTION
Therefore, it is an aim of the present invention to provide a method and apparatus which at least in part overcomes the disadvantages of existing methods and apparatus for forming wood products, particularly methods and apparatus using steam injection pressing to form reconstituted or reconsolidated wood products of relatively thick section. By their nature, such sections or products are relatively more permeable than the more finely comminuted elements used in, for example, thin panel products.
Another aim of the present invention is to provide a method and apparatus for use in steam pressing, particularly steam injection pressing of reconstituted or reconsolidated wood products of relatively thick sections of from 50 to 300 mm in depth.
It is another aim of the present invention to provide an improved method and apparatus using steam pressing to make reconstituted or reconsolidated wood products made form non-homogeneous starting materials or components, particularly from components which have a wide range of strand or particle sizes.
According to a first aspect of the present invention, there is provided a method of manufacturing a wood product comprising applying a

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