Drying and gas or vapor contact with solids – Process – Gas or vapor contact with treated material
Patent
1998-04-16
2000-08-22
Wilson, Pamela A.
Drying and gas or vapor contact with solids
Process
Gas or vapor contact with treated material
34264, 34536, 34202, 219697, F26B 3347
Patent
active
061052787
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to the drying or so-called seasoning of timber.
Freshly cut wood typically has a moisture content (by weight on a dry weight basis) of about 80%. If such wood were to be used immediately for the making of a timber product such as a piece of furniture, the wood would gradually dry out and in so doing would change shape and thereby distort the timber product. To avoid this problem, wood is dried to somewhere in the region of 20% to 8% moisture content for soft and hard woods respectively, before it is used for making a timber product.
Traditionally, wood has been seasoned by stacking the cut wood and leaving it to dry in the air for several years. Alternatively wood can be dried in a few weeks using a kiln.
Both of the above methods of seasoning are unsatisfactory. Since the production of seasoned timber using air drying or kiln drying takes a considerable time large stocks of wood must be held in order to ensure a constant supply of seasoned timber. The storage of large stocks of wood over a long period of time is expensive. Furthermore both processes usually require periodic restacking of the timber and, in addition, much of the wood is unusable after seasoning as a result of splits and severe distortion. Beech wood for example typically has a wastage rate of between 30% and 40% using either of the above processes.
It is an object of the present invention to provide an improved apparatus and process for drying timber.
According to a first aspect of the present invention there is provided a timber drying apparatus comprises a housing for containing a quantity of timber, temperature sensing means arranged to sense the temperature of timber within the housing, means for heating timber contained within the housing and control means for varying the means for heating the timber in response to the sensed temperature characterised in that the housing comprises or includes a cavity (4), the means for heating is a microwave generator (1) coupled to the cavity (4) by at least two ducts (2) for introducing microwave energy into the cavity (4) and weight sensing means (8) for sensing the weight of timber within the cavity (4).
Apparatus according to a first preferred version of the first aspect of the present invention is characterised by ventilation means (10, 11) arranged to displace air through the cavity (4) to regulate humidity and/or air temperature within the cavity (4). Typically the ventilation means (10, 11) includes a humidity sensor (9, 12) at an air inlet (10) to or an air outlet (11) from the cavity, the humidity sensor (9, 12) being adapted to provide a signal output representing the humidity of air in the vicinity of the sensor; the signal output being used as an input to regulate operation of the ventilation means (10, 11).
Apparatus according to a second preferred version of the first aspect of the present invention or the first preferred version thereof is characterised by a timber carriage (16) arranged to support timber within the cavity (4).
Apparatus according to a third preferred version of the first aspect of the present invention or of any preceding preferred version thereof is characterised by means (7) for the carriage (16) whereby an oscillatory and/or rotatory motion can be imparted to timber supported by the carriage (16) within the cavity (4).
Apparatus according to a fourth preferred version of the first aspect of the present invention or of any preceding preferred version thereof is characterised by stirring means (3) within the cavity (4) operable to vary spacial distribution of microwave energy within the cavity (4).
Apparatus according to a fifth preferred version of the first aspect of the present invention or of any preceding preferred version thereof is characterised by an aperture and a closure (5) therefor, the closure being openable to provide access to the interior of the cavity (4) by way of the aperture whereby timber can be inserted into or removed from the cavity. There typically there is provided a plurality of apertures (5') and closures (5
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patent: 2567983 (1951-09-01), Wood
patent: 3721013 (1973-03-01), Miller
patent: 4176464 (1979-12-01), Randolph
patent: 4485564 (1984-12-01), Iverland et al.
patent: 5109595 (1992-05-01), Wickersheim et al.
patent: 5325604 (1994-07-01), Little
patent: 5399314 (1995-03-01), Samuel et al.
Gerrish Philip
Shute Ralph
Wakefield Francis
Microwave Drying Limited
Wilson Pamela A.
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