Woodworking – Process – Mechanical cutting or shaping
Patent
1996-02-15
1997-11-11
Bray, W. Donald
Woodworking
Process
Mechanical cutting or shaping
100 38, 100 93P, 144380, 34389, B27M 102, B27M 100
Patent
active
056853530
DESCRIPTION:
BRIEF SUMMARY
The invention is related to a method according to claim 1 for compressive shape-drying of wood.
Methods are known in the art in which dry wood is compressed to improve the surface hardness of wood. In these methods the compression operation is preceded by a drying phase which is extremely energy-hungry and time-consuming.
Corresponding methods developed for green wood are applicable to deciduous wood only. Such prior-art methods have caused cracks in the compression set wood that impair the quality of the end product.
It is an object of the present invention to achieve an entirely novel method and apparatus for compressive shape-drying of wood.
The invention is based on a process in which green wood is compressed in a first phase rapidly with a high pressure, and subsequent to said compression phase, the wood is allowed to recover toward its initial dimensions, and after these phases, the compression is continued with a low pressure toward a desired compressed end dimension. At the start of the compression phase the wood is kept at a temperature of approx. 150.degree. C., and at the end of the workphase the temperature is advantageously approx. 125.degree. C.
More specifically, the method according to the invention is characterized by what is stated in the characterizing part of claim 1.
The invention provides significant benefits.
The invention is particularly advantageous in the treatment of nordic grades of coniferous wood. The method is environmentally safe as wood color can be varied by a single process without the use of hazardous chemicals. The present drying process is rapid with reference to conventional drying methods. Furthermore, the variations of the method offer a controlled technique to modify the surface hardness, strength and stiffness as well as color change properties of the wood.
In the following the invention is examined in greater detail with reference to exemplifying embodiments illustrated in the annexed drawing in which:
FIG. 1 is a side view of a compression apparatus suited for implementing the invention;
FIG. 2 is a pressure-time graph of the process according to the invention; and
FIG. 3 is a thickness-time graph of the process represented in FIG. 2.
With reference to FIG. 1, the compression apparatus comprises an upper compression plate 5, top support columns 8 of the upper compression plate, and a lower compression plate 6 with hydraulic actuator cylinders 7. The wood-facing surfaces of the plates are heatable. Both plate surfaces are coated with steam-permeable wires 3 and 4, whose material can be, e.g., perforated sheet metal or metal fabric. The planks 1 to be compressed are placed between the wire fabrics 3 and 4, and the compression stroke is limited by backing gages 2 placed at the edges of the compression platens 5 and 6.
With reference to FIG. 2, compression is commenced with a high initial pressure of 20 kg/cm.sup.2, which is maintained according to the exemplifying embodiment for 10 min. Next, the compression pressure is lowered to 5 kg/cm.sup.2. Compression at this lower pressure level is maintained for 2 h 50 min.
With reference to FIG. 3, the thickness of a plank having a cross section of 50.times.100 mm (height.times.width) is reduced in the first compression phase to the height of the gages 2 (33 mm), then partially recovering toward the initial plank thickness reaching 37 mm thickness when the compression pressure is reduced to 5 kg/cm.sup.2. Subsequently, the low compression pressure gradually compresses the plank toward the final thickness determined by the height of the gages 2. As a rule, the compression pressure used in this phase is such that it permits the thickness recovery of the plank by approx. 10% of the maximum thickness compression attained during the first phase; however, the applied low pressure must be at least so high as to achieve a compression equal to the natural thickness reduction caused by the drying of the wood, whereby the occurrence of internal honeycomb cracks is avoided.
The temperature of the compression plates 5 and 6 is adjusted
REFERENCES:
patent: 1403722 (1922-01-01), Turnbull
patent: 1480658 (1924-01-01), Bostock
patent: 1644801 (1927-10-01), Van Der Werff
patent: 2548336 (1951-10-01), Banninger
patent: 2586308 (1952-02-01), Curtis
patent: 2666463 (1954-01-01), Heritage
patent: 2787306 (1957-04-01), Lundstrom
patent: 2793859 (1957-05-01), Darling et al.
patent: 3166110 (1965-01-01), Hartesveldt et al.
patent: 4428410 (1984-01-01), Stranberg
patent: 5190088 (1993-03-01), Thomasson et al.
Derwent's Abstract, No. 85-247595/40, Week 8540, Abstract of SU, 1144883-A (Voron Forestry Inst.), Mar. 15, 1985.
Kontinen Paavo
Viitaniemi Pertti
Bray W. Donald
Valtion teknillinen tutkimuskeskus
LandOfFree
Method for compressive shape-drying of wood does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for compressive shape-drying of wood, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for compressive shape-drying of wood will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1221998