US3429055A - Method for heat treatment - Google Patents

Method for heat treatment Download PDF

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US3429055A
US3429055A US709856A US3429055DA US3429055A US 3429055 A US3429055 A US 3429055A US 709856 A US709856 A US 709856A US 3429055D A US3429055D A US 3429055DA US 3429055 A US3429055 A US 3429055A
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boards
air
temperature
heat
board
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US709856A
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Lars-Gunnar Bergh
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Svenska Flaktfabriken AB
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Svenska Flaktfabriken AB
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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 or duct systems, e.g. in combination with pallet boxes, for supplying and controlling air or gases for drying solid materials or objects
    • F26B21/004—Nozzle assemblies; Air knives; Air distributors; Blow boxes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B27—WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27N—MANUFACTURE BY DRY PROCESSES OF ARTICLES, WITH OR WITHOUT ORGANIC BINDING AGENTS, MADE FROM PARTICLES OR FIBRES CONSISTING OF WOOD OR OTHER LIGNOCELLULOSIC OR LIKE ORGANIC MATERIAL
    • B27N7/00—After-treatment, e.g. reducing swelling or shrinkage, surfacing; Protecting the edges of boards against access of humidity
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
    • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
    • B29C35/04—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould using liquids, gas or steam
    • B29C35/06—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould using liquids, gas or steam for articles of indefinite length
    • D—TEXTILES; PAPER
    • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
    • D21J—FIBREBOARD; MANUFACTURE OF ARTICLES FROM CELLULOSIC FIBROUS SUSPENSIONS OR FROM PAPIER-MACHE
    • D21J1/00—Fibreboard
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F26—DRYING
    • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
    • F26B15/00—Machines or apparatus for drying objects with progressive movement; Machines or apparatus with progressive movement for drying batches of material in compact form
    • F26B15/10—Machines or apparatus for drying objects with progressive movement; Machines or apparatus with progressive movement for drying batches of material in compact form with movement in a path composed of one or more straight lines, e.g. compound, the movement being in alternate horizontal and vertical directions
    • F26B15/12—Machines or apparatus for drying objects with progressive movement; Machines or apparatus with progressive movement for drying batches of material in compact form with movement in a path composed of one or more straight lines, e.g. compound, the movement being in alternate horizontal and vertical directions the lines being all horizontal or slightly inclined
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
    • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
    • B29C35/04—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould using liquids, gas or steam
    • B29C35/045—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould using liquids, gas or steam using gas or flames
    • 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 good
    • F26B2210/16—Wood, e.g. lumber, timber

Definitions

  • the present invention relates to a method for the heat treatment of dry wood fibre boards or similar material and more particularly the treatment by hot air at temperatures exceeding 160 C.
  • An important object of the invention is to prevent a harmful overheating of the dry wood fibre boards or similar material during the heat treatment.
  • FIG. 1 is graphical representation showing the relationship between the swelling and the heating time at various temperatures of typical wood fibre boards
  • FIG. 2 is a graphical representation showing the relationship between the moisture absorption and the heating time at various temperatures of typical wood fibre boards
  • FIG. 3 is a vertical section through a heat treatment apparatus constructed in accordance with the present invention.
  • FIG. 4 is a longitudinal section taken along the line 4-4 in FIG. 3.
  • Compressed wood fibre boards for example hardboards, are heat-treated or hardened in their dry state in order to impart to them certain properties of strength, water absorption, swelling, etc.
  • This heat treatment is usually carried out with the aid of hot air, which is maintained in circulation around the boards. If the heat treatment is to produce the desired eifect, it must be carried out at a high temperature above 160 C. At a temperature of approximately 140 C. an exothermic reaction occurs in dry wood fibre board which gradually increases the temperature of the board above that of the ambient air.
  • the present invention is based on the discovery that the present high demands for quality properties in the above stated respects cannot be met by a conventional treatment in known apparatus, operating with parallel flow of treatment medium along the surface of the boards, Since the high temperatures necessary to fulfill the said requirements could not be used in this apparatus without the risk of ignition and fire.
  • the risk of ignition and fire is too great, because a completely uniform air dis tribution is never obtained in said known apparatus, and, within reasonable pressure limits, only a relatively low heat transmission coefiicient between air and boards is attained.
  • the heat transmission coefiicient is of decisive importance after the exothermic reaction has set in and, for control of the temperature gradient in the board, it is necessary to maintain as low a temperature difference as possible between board and air.
  • the quantity of heat to be supplied for heating the board to the required temperature and the quantity of heat which then must be removed after the board has been brought to the treatment temperature is dependent on the product of the heat transmission coefiicient and the temperature difference between board and air.
  • a high heat transmission coefiicient permits a short heating-up time and a small temperature difference when the board has reached the treatment temperature.
  • a high heat transmission coefficient is obtained while a harmful increase in the exothermic reaction occurring in the boards is prevented, by supplying hot air of regulated temperature in the form of uniformly spaced jets at a high velocity and substantially at right angles against both sides of the boards.
  • the heat transmission coefiicient value is approximately five times that obtained by supplying the air in the form of parallel streams.
  • My invention is accompanied by other advantages. It provides a very uniform air distribution across the board, both in the lengthwise and crosswise directions.
  • the drawing illustrates an apparatus for carrying the method into practice.
  • the apparatus consists of a treatment channel provided with elements for the transport of the boards and equipped with elements for heating and circulation of the treatment medium.
  • Characteristic of the apparatus is that air distribution boxes are arranged on both sides of each transport plane and the walls of these boxes facing the transport plane are provided with a large number of evenly-spaced discharged openings for blowing-on treatment medium in the form of jets substantially directed at right angles to the dry boards.
  • an outer housing 1 of the apparatus has inspection panels or doors 2.
  • Blower boxes 3 and 4 are mounted in the housing from which air is blown through slots or perforated plates at right angles, or possibly slightly inclined, against the material 11.
  • the material is supported on rollers 5 mounted in bearings 6 and driven by means of sprockets 7 and chains (not shown).
  • Circulation of air in the apparatus is produced by a fan 8 driven by a motor 9.
  • heaters 10 are supplied with hot oil from a source of heat (not shown).
  • Circulating air can also be heated by means of air from an oil-fired heat exchanger; possibly it is conceivable that flue gases could be used directly. During heat treatment, gases are generated, some of which are poisonous (CO) and the housing must therefore be ventilated. This takes place through a flue 12 fitted with a controllable damper 13.
  • the location of the fan shown in FIG. 3 provides the advantage that the static pressure on the housing of the apparatus is low. It can even be negative in relation to the static pressure outside the housing of the apparatus. This makes the risk of external leakage very small.
  • the apparatus is supported by a stand 14. FIG.
  • blower box 4 shows that the upper blower box, which is located nearest to the material, is fitted with normal perforations 15, and the lower box, which must be located further away from the track due to the rollers 5, is fitted with nozzles 16.
  • the apparatus may also be fitted with double rollers, if desired, in which case both of the blower boxes 3 and 4 are fitted with nozzles.
  • a method of heat-treating dry hardboards of wood fibre and the like which are subject to localized overheating in random areas due to exothermic reactions occurring within the boards at temperatures above C., and are subject to charring at temperatures above 235 comprising the steps of:
  • said supplied air in the form of uniformlyspaced jets at high velocity substantially at right angles against both sides of the boards, said air serving to heat the boards up to a temperature approximating the temperature of the air and serving to cool said random areas of localized overheating wherein the board temperature has started to rise above said air temperature.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Thermal Sciences (AREA)
  • Oral & Maxillofacial Surgery (AREA)
  • Health & Medical Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Manufacturing & Machinery (AREA)
  • Wood Science & Technology (AREA)
  • Forests & Forestry (AREA)
  • Dry Formation Of Fiberboard And The Like (AREA)
  • Drying Of Solid Materials (AREA)
  • Chemical And Physical Treatments For Wood And The Like (AREA)

Description

1969 LARS-GUNNAR BERGH 3,429,055
METHOD FOR HEAT TREATMENT Filed Feb. 12, 1968 I Sheet of 2 I I I I l T IO 20 so 40 so 60 TIME IN MINUTES TIME IN MINUTES mvsmon: LA RS. GUN NAR BERGH AT TYS.
2 1969 LARS'GUNNAR BERGH 3,429,055
METHOD FOR HEAT TREATMENT Sheet Filed Feb. 12, 1968 FIGB.
INVENTOR LARS GUNNAR BERGH ATTYS.
United States Patent 01 I 3,429,055 Patented Feb. 25, 1969 Bee 10,102/ 63 US. Cl. 3413.8 Int. Cl. F26b 3/04; B29j /00 2 Claims ABSTRACT OF THE DISCLOSURE A method for heat treatment of dry fibre boards in which the heating medium is blown perpendicularly against the boards and is maintained between 160 C. and 235 C. to heat the boards and at the same time prevent local overheating in random areas due to exothermic reactions occurring within the boards.
The present application is a continuation-in-part of my application No. 606,458 filed Dec. 30, 1966 as a continuation of my earlier application S.N. 360,302 filed Apr. 16, 1964, both now abandoned.
The present invention relates to a method for the heat treatment of dry wood fibre boards or similar material and more particularly the treatment by hot air at temperatures exceeding 160 C.
An important object of the invention is to prevent a harmful overheating of the dry wood fibre boards or similar material during the heat treatment.
Other objects and a more detailed understanding of the invention may be had by referring to the following description and claims, in conjunction with the accompanying drawings in which:
FIG. 1 is graphical representation showing the relationship between the swelling and the heating time at various temperatures of typical wood fibre boards;
FIG. 2 is a graphical representation showing the relationship between the moisture absorption and the heating time at various temperatures of typical wood fibre boards;
FIG. 3 is a vertical section through a heat treatment apparatus constructed in accordance with the present invention; and
FIG. 4 is a longitudinal section taken along the line 4-4 in FIG. 3.
Compressed wood fibre boards, for example hardboards, are heat-treated or hardened in their dry state in order to impart to them certain properties of strength, water absorption, swelling, etc. This heat treatment is usually carried out with the aid of hot air, which is maintained in circulation around the boards. If the heat treatment is to produce the desired eifect, it must be carried out at a high temperature above 160 C. At a temperature of approximately 140 C. an exothermic reaction occurs in dry wood fibre board which gradually increases the temperature of the board above that of the ambient air.
To prevent the temperature of the board from rising sorption, and that for a constant time, both swelling and absorption will decrease with increasing temperature.
The present invention is based on the discovery that the present high demands for quality properties in the above stated respects cannot be met by a conventional treatment in known apparatus, operating with parallel flow of treatment medium along the surface of the boards, Since the high temperatures necessary to fulfill the said requirements could not be used in this apparatus without the risk of ignition and fire. The risk of ignition and fire is too great, because a completely uniform air dis tribution is never obtained in said known apparatus, and, within reasonable pressure limits, only a relatively low heat transmission coefiicient between air and boards is attained. The heat transmission coefiicient is of decisive importance after the exothermic reaction has set in and, for control of the temperature gradient in the board, it is necessary to maintain as low a temperature difference as possible between board and air. The quantity of heat to be supplied for heating the board to the required temperature and the quantity of heat which then must be removed after the board has been brought to the treatment temperature is dependent on the product of the heat transmission coefiicient and the temperature difference between board and air. A high heat transmission coefiicient permits a short heating-up time and a small temperature difference when the board has reached the treatment temperature.
In the method of the present invention, a high heat transmission coefficient is obtained while a harmful increase in the exothermic reaction occurring in the boards is prevented, by supplying hot air of regulated temperature in the form of uniformly spaced jets at a high velocity and substantially at right angles against both sides of the boards. In this manner, with the same pressure loss (10-40 mm. Hg) the heat transmission coefiicient value is approximately five times that obtained by supplying the air in the form of parallel streams. My invention is accompanied by other advantages. It provides a very uniform air distribution across the board, both in the lengthwise and crosswise directions. This is even more pronounced, if the board is kept in motion at right angles in relation to the discharged direction of the air jets during the treatment process; the movement can be continuous, progressive or oscillating. In this manner, local excessive temperature in the board is avoided. The risk of the occurrence of partial excessive temperature is especially great at the so-called flash or burr, i.e., the uneven edge portions arising outside the pressing plate during the pressing. With a treatment according to the invention, it is therefore advisable that this flash is removed before heat treatment. With right-angle blowing, boards have been treated at a temperature of 215 C. for a period of six hours without ignition taking place. In the areas where the exothermic reaction occurs, the temperature of the board is then only about 5 above that of the air. A completely satisfactory result was obtained after a treatment time of only 30 minutes, which means that there is an adequate margin of safety as regards ignition. The treatment time can be varied within wide limits depending on the properties it is desired to impart to the treated board.
This invention is applicable to dry boards, i.e., boards in which there is no free moisture and in which the hygroscopic moisture is at a minimum. The drawing illustrates an apparatus for carrying the method into practice. The apparatus consists of a treatment channel provided with elements for the transport of the boards and equipped with elements for heating and circulation of the treatment medium. Characteristic of the apparatus is that air distribution boxes are arranged on both sides of each transport plane and the walls of these boxes facing the transport plane are provided with a large number of evenly-spaced discharged openings for blowing-on treatment medium in the form of jets substantially directed at right angles to the dry boards.
In the apparatus shown in FIG. 3, an outer housing 1 of the apparatus has inspection panels or doors 2. Blower boxes 3 and 4 are mounted in the housing from which air is blown through slots or perforated plates at right angles, or possibly slightly inclined, against the material 11. The material is supported on rollers 5 mounted in bearings 6 and driven by means of sprockets 7 and chains (not shown). Circulation of air in the apparatus is produced by a fan 8 driven by a motor 9. When the air strikes the material, it is deflected sideways and is returned through the ducts 17 and 18 to the circulating fan 8. The quantity of heat necessary for the heating-up period is supplied by heaters 10. These could suitably (with regard to the relatively high air temperature being used) be supplied with hot oil from a source of heat (not shown). Circulating air can also be heated by means of air from an oil-fired heat exchanger; possibly it is conceivable that flue gases could be used directly. During heat treatment, gases are generated, some of which are poisonous (CO) and the housing must therefore be ventilated. This takes place through a flue 12 fitted with a controllable damper 13. The location of the fan shown in FIG. 3 provides the advantage that the static pressure on the housing of the apparatus is low. It can even be negative in relation to the static pressure outside the housing of the apparatus. This makes the risk of external leakage very small. The apparatus is supported by a stand 14. FIG. 4 shows that the upper blower box, which is located nearest to the material, is fitted with normal perforations 15, and the lower box, which must be located further away from the track due to the rollers 5, is fitted with nozzles 16. The apparatus may also be fitted with double rollers, if desired, in which case both of the blower boxes 3 and 4 are fitted with nozzles.
I claim:
1. A method of heat-treating dry hardboards of wood fibre and the like which are subject to localized overheating in random areas due to exothermic reactions occurring within the boards at temperatures above C., and are subject to charring at temperatures above 235 comprising the steps of:
supplying air at a temperature exceeding C. and
below 235 C. where chanring starts, and
directing said supplied air in the form of uniformlyspaced jets at high velocity substantially at right angles against both sides of the boards, said air serving to heat the boards up to a temperature approximating the temperature of the air and serving to cool said random areas of localized overheating wherein the board temperature has started to rise above said air temperature.
2. A method according to claim 1 wherein said dry hardboards have an absence of free moisture and in which the hygroscopic moisture is at a minimum.
References Cited UNITED STATES PATENTS 835,843 11/1906 Baetz 34l3.8 XR 2,591,621 4/1952 Shegda 34160 XR 3,099,541 7/1963 Hildebrand 34-23 XR 3,199,213 8/1965 Milligan et al. 34-13.8
KENNETH W. SPRAGUE, Primary Examiner.
U.S. Cl. X.R. 34--23
US709856A 1963-09-16 1968-02-12 Method for heat treatment Expired - Lifetime US3429055A (en)

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SE10102/63A SE309900B (en) 1963-09-16 1963-09-16

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CH (1) CH429172A (en)
ES (1) ES299096A1 (en)
FI (1) FI47434C (en)
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SE (1) SE309900B (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120058279A1 (en) * 2008-12-01 2012-03-08 Johannes Schmid Method and appratus for coating workpieces
US10105900B2 (en) 2013-08-14 2018-10-23 Homag Holzbearbeitungssysteme Gmbh Coating unit

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3044221A1 (en) * 1980-11-25 1982-06-03 Rütgerswerke AG, 6000 Frankfurt METHOD FOR THE DIMENSIONAL STABILIZATION OF PRESS-COMPRESSED WOOD MATERIALS
ES2113263B1 (en) * 1994-08-01 1999-01-01 Barragan Amelia Gomez CONTINUOUS LONGITUDINAL OVEN FOR DRYING AND VULCANIZING OF RUBBER PROFILES.

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US835843A (en) * 1906-07-12 1906-11-13 Henry Baetz Feed mechanism for drying apparatus.
US2591621A (en) * 1951-01-08 1952-04-01 Proctor & Schwartz Inc Tenter drier
US3099541A (en) * 1961-03-24 1963-07-30 Hildebrand Robert Treating veneers
US3199213A (en) * 1961-07-12 1965-08-10 Crown Zellerbach Canada Ltd Method of changing the moisture content of wood

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US835843A (en) * 1906-07-12 1906-11-13 Henry Baetz Feed mechanism for drying apparatus.
US2591621A (en) * 1951-01-08 1952-04-01 Proctor & Schwartz Inc Tenter drier
US3099541A (en) * 1961-03-24 1963-07-30 Hildebrand Robert Treating veneers
US3199213A (en) * 1961-07-12 1965-08-10 Crown Zellerbach Canada Ltd Method of changing the moisture content of wood

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120058279A1 (en) * 2008-12-01 2012-03-08 Johannes Schmid Method and appratus for coating workpieces
US10105900B2 (en) 2013-08-14 2018-10-23 Homag Holzbearbeitungssysteme Gmbh Coating unit

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SE309900B (en) 1969-04-08
CH429172A (en) 1967-01-31
ES299096A1 (en) 1964-12-01
GB1013066A (en) 1965-12-15
FI47434C (en) 1973-11-12
FI47434B (en) 1973-07-31

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