GB2265915A - Bending and shaping MDF - Google Patents

Bending and shaping MDF Download PDF

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Publication number
GB2265915A
GB2265915A GB9307035A GB9307035A GB2265915A GB 2265915 A GB2265915 A GB 2265915A GB 9307035 A GB9307035 A GB 9307035A GB 9307035 A GB9307035 A GB 9307035A GB 2265915 A GB2265915 A GB 2265915A
Authority
GB
United Kingdom
Prior art keywords
mdf
ammonia
method
preceding
shaped
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB9307035A
Other versions
GB9307035D0 (en
Inventor
David Piers Ross Pratt
Richard Gordon Warren Pratt
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
WOODFORM DESIGN Ltd
Original Assignee
WOODFORM DESIGN Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to GB9207418A priority Critical patent/GB2265914A/en
Priority to GB939306627A priority patent/GB9306627D0/en
Application filed by WOODFORM DESIGN Ltd filed Critical WOODFORM DESIGN Ltd
Publication of GB9307035D0 publication Critical patent/GB9307035D0/en
Publication of GB2265915A publication Critical patent/GB2265915A/en
Application status is Withdrawn legal-status Critical

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Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B27WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27NMANUFACTURE 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
    • B27N7/00After-treatment, e.g. reducing swelling or shrinkage, surfacing; Protecting the edges of boards against access of humidity
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B27WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27KPROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K3/00Impregnating wood, e.g. impregnation pretreatment, for example puncturing; Wood impregnation aids not directly involved in the impregnation process
    • B27K3/16Inorganic impregnating agents
    • B27K3/20Compounds of alkali metals or ammonium
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B27WORKING OR PRESERVING WOOD OR SIMILAR MATERIAL; NAILING OR STAPLING MACHINES IN GENERAL
    • B27KPROCESSES, APPARATUS OR SELECTION OF SUBSTANCES FOR IMPREGNATING, STAINING, DYEING, BLEACHING OF WOOD OR SIMILAR MATERIALS, OR TREATING OF WOOD OR SIMILAR MATERIALS WITH PERMEANT LIQUIDS, NOT OTHERWISE PROVIDED FOR; CHEMICAL OR PHYSICAL TREATMENT OF CORK, CANE, REED, STRAW OR SIMILAR MATERIALS
    • B27K5/00Treating of wood not provided for in groups B27K1/00, B27K3/00
    • B27K5/06Softening or hardening of wood

Abstract

MDF, or medium density fibreboard, is a common replacement for wood. It is usually manufactured as flat sheets, and is a stiff, rigid, inflexible material that is difficult to bend into the sort of complex shapes often required. It has now been found that by impregnating MDF with ammonia (used in anhydrous - that is to say, dry gaseous - form) the MDF can be made relatively plastic, and in its plasticised state can quite easily be pressed or bent into almost any shape required.

Description

Bending and shaping MDF This invention relates to bending and shaping MDF (medium density fibreboard).

Wood is an expensive and rather intractable medium for the construction of articles, and for many years various man-made composites have been used instead, sometimes because of cost and sometimes because of the achievable properties. One such material is that known as MDF, or medium density fibreboard, which has been available since the early 1970s. MDF is basically wood fibres compounded together with amounts of one or more synthetic resin, often one based upon formaldehyde (usually a urea-formaldehyde resin, and sometimes advantageously a melamine-urea-formaldehyde this type of MDF is often known as MUF, or HMR, the latter standing for high moisture resistance], and typical such materials available under the generic name MDF are those sold by Medite, Caberboard and Silverpan, the exact details of which are not generally known.The main present uses for MDF are in the manufacture of furniture and kitchen and bathroom fittings (cupboards and shelves, and so on).

MDF is commonly manufactured as flat sheets or boards of various thicknesses (typically from 3 mm to 25 mm) and densities, and may be supplied with a visually-attractive paper- or wood-veneer or plastics surface coating. It is a stiff, very rigid, practically inflexible material, with almost no plasticity, and unless it is provided as very thin sheets, with some limited degree of flexibility by virtue of that very thinness, it is difficult if not impossible to bend or otherwise form into the sort of complex shapes often required.

It has now been found that by impregnating MDF with ammonia (used in anhydrous - that is to say, dry gaseous - form) the MDF can be made relatively plastic, and in its plasticised state can quite easily be pressed or bent into almost any shape required.

In one aspect, therefore, the invention provides a method of shaping MDF in sheet form, in which the MDF is treated with ammonia so as to impregnate it therewith, causing it to become relatively plastic, the thusplasticised MDF is then shaped as desired, and the ammonia is then allowed to dissipate, whereupon the MDF reverts to its normal, relatively unplastic, form, which it thereafter maintains.

The MDF may be any of those materials commonly known as MDF, including especially that known as MUF.

The MDF sheet shaped by the process of the invention may intrinsically be of any appropriate shape, size and thickness. As noted above, typical thicknesses for MDF range from 3 to 25 mm, and the method of the invention can successfully be applied to any of these.

Moreover, perhaps slightly surprisingly the MDF sheet may already have a previously indented surface, giving it in section a shaped profile, and this will be substantially undistorted even when the sheet has thereafter been bent and shaped by the method of the invention.

In the process of the invention the MDF is treated - conveniently at room temperature (around 15"C) - with gaseous ammonia so as to impregnate it therewith, causing it to become relatively plastic. The ammonia reacts with the MDF, and with the moisture in the MDF, in an exothermic reaction the heat from which raises the MDF's temperature 5 or 10 C. It is believed that the reaction of the ammonia enables the cellulose molecules making the wood, as well as the wood fibres made therefrom, to release their grip one on another and on the bonding agent (typically a urea-formaldehyde resin), and so separate to allow them to be re-positioned as required while any applied bending or impressing occurs.

In other words, the altered chemical (and physical) nature of the MDF, coupled with the rise in temperature, causes the MDF to become rather more plastic - that is, able to have its shape changed by an applied force without immediately recovering its original shape when that force is removed - than in its original state. Of course, once the ammonia has been removed, or dissipates, the molecules/fibres re-bond in their new positions, without any distortion of the MDF.

The ammonia, which is preferably in dry (anhydrous) gaseous form, may be applied to the MDF in a variety of ambient physical circumstances. For example, it may be applied in a sealed pressure chamber (which may take the form of a standard autoclave, but can also be nothing more complicated than a sealed plastic bag [albeit one capable of withstanding the pressures and temperatures involved] under a slight pressure of up to 4 Bar (about 4 atmospheres). However, the higher the pressure the more likely the ammonia will be absorbed into the MDF, reacting with it and the moisture therein, so quickly and in such amounts that localised overheating occurs to cause swelling and bubbles in the MDF as it expands, distorting the MDF and even leading to surface unevenness and possibly explosive disintegration of the MDF.Most preferably, therefore, the applied pressure is kept low, and is about 1 Bar (1 atmosphere).

It may be advantageous to evacuate the pressure chamber containing the MDF prior to feeding in the ammonia, for by doing so the applied pressure of the ammonia can be kept low and yet the treatment period can be reduced (but without fear of distorting the MDF as mentioned above).

The rate at which the treatment ammonia is absorbed into the MDF depends to some extent upon the moisture in the MDF, the rate being higher the wetter it is.

Accordingly, ensuring that the MDF is moist will result in a shortening of the time of treatment - but as observed elsewhere too rapid an impregnation can cause surface blemishes and deformation, and care should be exercised when speeding treatment up in this way.

The period during which the MDF is so treated will also depend to some extent upon the density and thickness of the MDF, and upon the temperature. The higher the density and thickness the longer a treatment is required, while the higher the temperature the shorter the treatment needed. Thus, for example, a 6 mm sheet can successfully be treated for a period of 1 hour and a temperature of 15"C, while a 16 mm sheet might need a longer and/or hooter treatment - maybe for 3 hours and/or at 20or.

Once impregnated with ammonia the MDF becomes relatively plastic, and the thus-plasticised MDF is then shaped as desired. The shaping may be done in any convenient manner, and may cause the MDF to have any suitable form. Typically, a sheet (or part thereof) of MDF can be stamped or impressed with surface patterns so that it looks embossed, while a strip of MDF can be clamped to and bent round a former into a curve.

Although the plasticised MDF sheet may be bent and shaped entirely by hand, one suitable bending and shaping method involves the use of a jig - that is, a pre-shaped surface or set of points around which the MDF sheet can be bent and clamped into place while it "sets". The art of jig construction and use is in general well-known, and no more need be said about it here.

If the bending or shaping is to involve a stamping or pressing operation, then this can be accomplished in any convenient way - in a conventional press, or using rotating rollers, for instance. This type of shaping method is in general well-known, and needs no further comment here.

The degree of bending attainable without damaging the MDF depends to some considerable extent of the thickness of the MDF, thin sheets being understandably more bendable than thick ones. In tests using the method of the invention it has been possible reliably to bend sheets as follows to make commercially-useful products: Sheet Normal Bend Extreme Bend Thickness (mm) outside diameter (mm) 18.7 300 155 16 230 120 12 190 90 6 50 40 Once the plasticised MDF has been shaped as desired, the ammonia is then allowed to dissipate, whereupon the MDF reverts to its normal, relatively unplastic, form, which it thereafter maintains. For example, a strip of MDF clamped to and bent around a former in a jig may simply be left there for several hours, during which the ammonia diffuses out of the strip and away, and when removed from the former the strip will then hold its new shape.However, it may be desirable to accelerate this "drying", setting, stager and various techniques can be employed, including the application of heat (as by radiant heat, or even radio frequency induction, as in a microwave oven) and/or vacuum, and the passing of air currents across the surface (hot air heats, while moist air extracts chemically). It may be desirable, in order to improve the drying effect, if possible to release those parts of any jig (or other former device) that would otherwise occlude one or more of the sheet;s surfaces.

The surface of an MDF sheet treated by the method of the invention may be roughened slightly as a result of moisture absorption. This roughening can usually be removed by a simple buffing operation once the bent and shaped sheet has been dried and thus "fixed" into the required shape.

Although the ammonia treatment of the method of the invention may cause a small amount of swelling of the MDF sheet, this is not significant, and should not cause any noticeable distortion of the finished product.

The invention extends, of course, to shaped MDF articles whenever made by a process according to the invention.

The following Examples are now given, though by way of illustration only, to show details of an embodiment of the method of the invention.

Example 1: Bending and shaping of MDF Staae 1: Plasticisation of the MDF Using a purpose-built circular-section autoclave of dimensions 4.2 m by 250 mm internal diameter, there were plasticised a dozen strip-like sheets of MDF each of dimensions 150 mm by 18.7 mm and various lengths from 1.5 m to 3.6 mm. This MDF was obtained from Nelson Pine <img class="EMIRef" id="026754160-00070001" />

Industries, of Auckland, under the name THINLINEl(this is an MUF material).

First, the sheets were placed in the autoclave, and the latter was evacuated down to a pressure of 0.1 Bar and stabilised at ambient temperature. The sheets were held at this low pressure for 2 mins, whereupon gaseous ammonia (from a cylinder of anhydrous liquid ammonia) was allowed in over a period of 4 mins, all the while maintaining the temperature more or less constant, until the internal pressure had risen to 4 Bar.

Once all the ammonia had been introduced, the sheet was kept in the ammonia atmosphere for 4z hours at the same temperature and pressure. During this time the chemical action of the ammonia caused the binding forces between the MDF constituents to become less, so that the MDF itself became plastic.

Stage 2: Bending the MDF At the end of the specified time the ammonia remaining free in the autoclave was drawn off for disposal, the pressures were equalised, and the autoclave was opened to allow the plasticised MDF sheet to be removed.

The sheets were taken out and placed in a variety of bending jigs of standard form as appropriate. In this way one, for example, was bent into a semicircle outside diameter 800 mm. Thus bent, the sheets were then secured in place in the jigs and allowed to "dry" that is, the absorbed ammonia was allowed to evaporate off (this evaporation was encouraged by blowing warm air over the sheet). For the first half-an-hour or so each sheet was retained clamped in its jig, but at the end of this time it sheet was unclamped and removed from the jig, and allowed to dry "free-standing" for another four or five hours.

At the end of this drying stage each sheet had recovered its normal physical properties, but retained its new shape and resisted any ordinary attempts to unshape it.

Example 2: More bending and shaping MDF Two further batches of MDF (this time the non-MUF <img class="EMIRef" id="026754160-00080001" />

material xH;vlL7, available rrom Mealte Local were Dent and shaped in much the same overall manner, but with the following significant differences:a) The container used was a large heavy-duty plastic bag.

b) No initial vacuum was applied to one batch, while a 0.1 Bar vacuum was applied to the other.

c) The pressure of ammonia in the container was no more than 1 Bar.

d) For the pre-evacuated batch the treatment time was hour, while for the other it was 1 hour.

e) Drying was effected under ambient conditions for 24 hours.

A third batch was treated in much the same way except that it was subjected to a 0.1 bar vacuum after the ammonia withdrawal to hasten the "drying" stage and in fact the product needed no further drying at all.

The shaped MDF products made in these ways were all quite satisfactory.

Claims (11)

1. A method of shaping medium density fibreboard (MDF) in sheet form, in which the MDF is treated with ammonia so as to impregnate the MDF therewith, causing it to become relatively plastic, the thus-plasticised MDF is then shaped as desired, and the ammonia is then allowed to dissipate, whereupon the MDF reverts to its normal, relatively unplasticr form, which it thereafter maintains.
2. A method as claimed in Claim 1 applied to that form of MDF known as MUF (melamine-urea-formaldehyde).
3. A method as claimed in either of the preceding Claims, in which the MDF is treated with dry gaseous ammonia.
4. A method as claimed in any of the preceding Claims, in which the ammonia treatment is effected at ambient temperature.
5. A method as claimed in any of the preceding Claims, in which the ammonia is applied to the MDF in a sealed chamber.
6. A method as claimed in any of the preceding Claims, in which the ammonia treatment is effected at a pressure of from 1 to 4 bar.
7. A method as claimed in any of the preceding Claims, in which prior to the ammonia treatment the MDF is subjected to a reduced pressure.
8. A method as claimed in any of the preceding Claims, in which the ammonia-plasticised MDF is thereafter shaped using a jig.
9. A method as claimed in any of the preceding Claims, in which, once the plasticised MDF has been shaped as desired, the ammonia is then encouraged to dissipate by the application of heat.
10. A method as claimed in any of the preceding Claims and substantially as described hereinbefore.
11. A shaped MDF article whenever made by a method as claimed in any of the preceding Claims.
GB9307035A 1992-04-04 1993-04-02 Bending and shaping MDF Withdrawn GB2265915A (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB9207418A GB2265914A (en) 1992-04-04 1992-04-04 Method of plasticising medium density fibre board
GB939306627A GB9306627D0 (en) 1992-04-04 1993-03-30 Bending and shaping mdf

Publications (2)

Publication Number Publication Date
GB9307035D0 GB9307035D0 (en) 1993-05-26
GB2265915A true GB2265915A (en) 1993-10-13

Family

ID=26300653

Family Applications (1)

Application Number Title Priority Date Filing Date
GB9307035A Withdrawn GB2265915A (en) 1992-04-04 1993-04-02 Bending and shaping MDF

Country Status (3)

Country Link
AU (1) AU3898193A (en)
GB (1) GB2265915A (en)
WO (1) WO1993019910A1 (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005007968A1 (en) * 2003-07-16 2005-01-27 Fira International Limited Recycling of lignocellulose based board materials
CN1836069B (en) 2003-07-16 2010-08-11 Fira国际有限公司 Recycling of lignocellulose based board materials
WO2011031223A1 (en) * 2009-09-11 2011-03-17 Design Force Ab Method for manufacturing a panel

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE1010487A6 (en) 1996-06-11 1998-10-06 Unilin Beheer Bv Floor covering, consisting of hard floor panels and method for manufacturing such floor panels.
SE514645C2 (en) 1998-10-06 2001-03-26 Perstorp Flooring Ab Flooring material comprising sheet-shaped floor elements intended to be joined by the separate joining profiles
SE518184C2 (en) 2000-03-31 2002-09-03 Perstorp Flooring Ab Flooring material comprising sheet-shaped floor elements which are joined by interconnection means
BE1013569A3 (en) 2000-06-20 2002-04-02 Unilin Beheer Bv Floor covering.
US7617651B2 (en) 2002-11-12 2009-11-17 Kronotec Ag Floor panel
EP1420125B1 (en) 2002-11-15 2008-05-14 Flooring Technologies Ltd. System consisting of two interconnectable building panels and an insert for locking these panels
DE102005063034B4 (en) 2005-12-29 2007-10-31 Flooring Technologies Ltd. Panel, in particular floor panel
DE102006007976B4 (en) 2006-02-21 2007-11-08 Flooring Technologies Ltd. A process for upgrading a building panel
DE102010004717A1 (en) 2010-01-15 2011-07-21 Pergo (Europe) Ab Set of panels comprising holding profiles with a separate clip, and methods for introducing the clips
WO2011141043A1 (en) 2010-05-10 2011-11-17 Pergo AG Set of panels

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3282313A (en) * 1964-11-24 1966-11-01 Research Corp Method of forming wood and formed wood product
US3642042A (en) * 1970-06-17 1972-02-15 Robert W Davidson Method of forming wood
AT326339B (en) * 1971-09-14 1975-12-10 Inst Khim Drevesiny Akademii N A method for compressing vollholz
CA1236255A (en) * 1985-03-15 1988-05-10 Peter Favot Process for densifying low density woods
CN1017881B (en) * 1987-12-16 1992-08-19 库特·赫尔德·法布里肯特 Apparatus and method for manufacturing wood plank

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2005007968A1 (en) * 2003-07-16 2005-01-27 Fira International Limited Recycling of lignocellulose based board materials
CN1836069B (en) 2003-07-16 2010-08-11 Fira国际有限公司 Recycling of lignocellulose based board materials
WO2011031223A1 (en) * 2009-09-11 2011-03-17 Design Force Ab Method for manufacturing a panel

Also Published As

Publication number Publication date
AU3898193A (en) 1993-11-08
WO1993019910A1 (en) 1993-10-14
GB9307035D0 (en) 1993-05-26

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