US3557468A - Method and apparatus for drying lumberboard - Google Patents

Method and apparatus for drying lumberboard Download PDF

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Publication number
US3557468A
US3557468A US796338A US3557468DA US3557468A US 3557468 A US3557468 A US 3557468A US 796338 A US796338 A US 796338A US 3557468D A US3557468D A US 3557468DA US 3557468 A US3557468 A US 3557468A
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United States
Prior art keywords
drying
wood
grad
moisture
lumberboard
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Expired - Lifetime
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US796338A
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English (en)
Inventor
Rudolf Keylwerth
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Bauwerk AG
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Bauwerk Bodenbelagsind Ag
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B21/00—Arrangements for supplying or controlling air or other gases for drying solid materials or objects
    • F26B21/30—Controlling, e.g. regulating, parameters of gas supply
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B25/00—Details of general application not covered by group F26B21/00 or F26B23/00
    • F26B25/22—Controlling the drying process in dependence on liquid content of solid materials or objects
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B2210/00—Drying processes and machines for solid objects characterised by the specific requirements of the drying goods
    • F26B2210/16—Wood, e.g. lumber, timber

Definitions

  • the inventive method is directed to the control of the climatic drying sequence in lumberboard drying installations and is characterized by the feature that the psychrometer difference during the drying time is increased in the same manner, i.e., steadily and in a uniformly logarithmic fashion, in which the wood moisture of the wood decreases.
  • the instant invention generally relates to drying methods and apparatus therefor and particularly concerns a drying method wherein the climatic drying sequence in lumberboard drying installations is controlled.
  • the instant invention comes to the fore and has as its primary object the elimination of the disadvantages inherent with prior-art techniques.
  • the object of the instant invention is to achieve a time-depending economical and, so far as is possible, an automated control of the drying climate for 3,557,468 Patented Jan. 26, 1971 any desired wood of different types, thicknesses, and initial wood moistures.
  • the drying time Z Z f -f -f .f log (I) in which a equals the initial wood moisture and J, to i represent different factors which depend upon temperature, type of Wood, thickness of wood, psychrometer difference, air velocity, and the like. Since an equation such as Equation 1 does not provide information concerning the required relative air humidity, such equation is unsuitable for the actual control of the wood drying and is only useful for providing a rough estimate of the entire drying time in conjunction with empirical values and tables.
  • the drying temperature is chosen with consideration being given to the initial wood moisture, the tendency of the wood to crack or discolor, the outflow of sap, and the quality of the wood itself. For example, pin woods and leafy woods, the latter having been pre-dried in the open air, can be dried at a constant drying temperature.
  • psychrometer difference or wet bulb depression relates to the difference of the temperature between a dry bulb thermometer and wet bulb thermometer subjected to the same medium, namely the water vapor-air mixture in the drying area or chamber. It has been shown in the art that the following psychrometer differences are suitable and adequate for drying hardwoods, for example:
  • Psychrometer Initial moisture, percent: difference, C. Fresh from the forest up to 30% 3 Below 20 5 The instant invention provides a solution to the problem posed in such a manner that the psychrometer difference is regulated so that the time-wise increase of the logarithm of the psychrometer difference remains at least approximately constant throughout the drying time.
  • This regulation ensures that the time-wise decrease of the logarithm of the wood moisture also remains constant throughout the drying time such that the psychrometer difference is increased in the same manner as the wood moisture decreases, i.e., steadily and in a uniformly logarithmic fashion. As is explained hereinbelow, this also makes it possible to predetermine the drying time of the wood.
  • the drying installation or chamber is then set into operation.
  • a graphic chart preferably one drawn in double logarithmic ruling, is immediately taken of the abovementioned relationship between grad u and grad T and a suitable guide value is selected when dealing with a yet completely unknown type of wood, for example, for grad T in accordance with the gross density and initial wood moisture of the particular type of wood.
  • This value is set at a special control device provided for the purpose of keeping grad T constant throughout the entire drying time, such control device being aided by and utilized with known mechanical or electrical setting means such as cam plates, for example, or program storage means, such as punch cards.
  • grad T determined from grad u in accordance with the above-mentioned function is taken and the expected drying time for the wood is calculated.
  • the drying chamber is turned off either manually or automatically after this expected drying time.
  • EXAMPLE Assume initially that it is desired to dry Oakwood of 28 mm. thickness, such wood having an initial moisture of 30%, a desired terminal or finished wood moisture of 8% and, accordingly, a customary drying temperature of approximately 70 C. and initial psychrometer difference of 3 C.
  • Oakwood has a medium gross density of 0.62 g./cm.
  • the expected drying time for the wood therefore comprises:
  • the psychrometer difference is increased during the drying time in the same manner in which the wood moisture decreases, i.e., steadily and in a uniformly logarithmic fashion.
  • grad T the uniform intensity or sharpness of drying is obatined during the entire drying time and a faster drying, particularly in the second half or period of the drying time or cycle is achieved.
  • the instant inventive method is particularly advantageous if one desires to develop an economical drying program for a certain material.
  • a preliminary drying of the material would first be carried out with a relatively low guide value for grad T (from the table), and additional dryings would each be carried out with respectively higher values for grad T.
  • the drying would be continued in this manner until such time that a surface crack formation is initiated indicative that a further increase of grad T is no longer permissible. Proceeding further in this fashion, the economical optimum of the drying time would be quickly reached, whereas in the heretofore employed control methods of the priorart, it was very difiicult to learn during which point in time of the drying process it was possible to dry more intensely than before.
  • the drying process can also be controlled 6 with a constant time-wise decrease of the equilibrium wood moisture du dZ instead of with a constant grad T if such is found to be advantageous as far as the measurement or control techniques are concerned.
  • Such installation comprises a dry-bulb thermometer 1 and a psychrometer 2 adapted to be placed in the drying chamber (not illustrated).
  • the measuring values obtained from the thermometer and the psychrometer are fed through a conductor 3 to a control apparatus 5 having a variable drive for program discs.
  • the control quantity or signals derived from the control apparatus 5 is fed through conductor 4 to the actual correcting or final control elements: such as a heat control valve 8 for controlling the drying temperature, a spray evaporation valve 9, and opening and closure flaps 10.
  • a curved disc or cam plate 6 is utilized for the psychrometer difference and a curved disc or cam plate 7 is utilized for the drying temperature as the means for setting the ideal or theoretical values for the control quantity or signal.
  • a drying method for controlling the climatic sequence in lumberboard drying installations comprising the steps of placing the lumberboard to be dried in a drying area, subjecting the lumberboard to a drying operation, and during the drying operation increasing the wet bulb depression steadily and uniformly logarithmically as a function of the logarithmic decrease with time of the moisture content of the wood being dried.
  • drying method for lumberboard as defined in claim 1 further including the steps of regulating the wet bulb depression such that the drying time (Z) can be determined from the function 11,, log us grad u wherein u represents the initial wood moisture content and M the final wood moisture content, and wherein u /u represents the ratio of the initial and final moisture content of the wood, and wherein grad u denotes the decrease with time of the logarithm of the wood moisture.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Drying Of Solid Materials (AREA)
  • Chemical And Physical Treatments For Wood And The Like (AREA)
US796338A 1968-02-09 1969-02-04 Method and apparatus for drying lumberboard Expired - Lifetime US3557468A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CH191068A CH479845A (de) 1968-02-09 1968-02-09 Verfahren und Einrichtung zur Trocknung von Schnittholz

Publications (1)

Publication Number Publication Date
US3557468A true US3557468A (en) 1971-01-26

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ID=4221453

Family Applications (1)

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US796338A Expired - Lifetime US3557468A (en) 1968-02-09 1969-02-04 Method and apparatus for drying lumberboard

Country Status (5)

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US (1) US3557468A (de)
AT (1) AT286880B (de)
CH (1) CH479845A (de)
DE (1) DE1906160C3 (de)
FR (1) FR2001605A1 (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3245282A1 (de) * 1982-12-07 1984-06-07 KNIPISM "Savodproekt", Sofia Verfahren und vorrichtung zum trocknen von gegenstaenden
EP2278241A1 (de) * 2009-07-22 2011-01-26 Jevgenijs Gordijs Anlage und Verfahren zur Wärmebehandlung von holzartigem Material
WO2025087877A1 (en) * 2023-10-23 2025-05-01 Cee-Engineering Sprl Drying method and apparatus

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1982002439A1 (en) * 1981-01-07 1982-07-22 Lynch Gary Michael Misting control apparatus

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3245282A1 (de) * 1982-12-07 1984-06-07 KNIPISM "Savodproekt", Sofia Verfahren und vorrichtung zum trocknen von gegenstaenden
EP2278241A1 (de) * 2009-07-22 2011-01-26 Jevgenijs Gordijs Anlage und Verfahren zur Wärmebehandlung von holzartigem Material
WO2025087877A1 (en) * 2023-10-23 2025-05-01 Cee-Engineering Sprl Drying method and apparatus
BE1032081B1 (fr) * 2023-10-23 2025-05-26 Cee Eng Sprl Procede et appareil de sechage

Also Published As

Publication number Publication date
DE1906160A1 (de) 1969-08-21
AT286880B (de) 1970-12-28
CH479845A (de) 1969-10-15
FR2001605A1 (de) 1969-09-26
DE1906160C3 (de) 1974-08-08

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