GB2078164A - Bending of gumwood - Google Patents

Abstract

A wood bending process which is comprised of the following steps: cutting gumwood in such a manner that tension wood is located on the surface to be bent, drying the treated wood rapidly, producing the first-stage bending at the surface where the tension wood is present, heating the treated wood gradually in an aqueous solution containing a very small quantity of a surface active agent which penetrates and diffuses through the wool and a latex solvent, treating the wood in an aqueous solution containing an insecticide for gumwood, clamping the gumwood into a wood bending mold, and then drying the treated wood.

Description

SPECIFICATION A wood bending process utilizing gum wood The present invention relates to a wood bending process utilizing gumwood. The said bent wood is used for high-class furniture, fittings, and fixtures.

Regarding the wood for furniture and fittings, a necessity of producing wood with beautiful bent surfaces or delicate curved surfaces is particularly on the increase recently.

Heretofore, when ordinary wood was subjected to bending processes, breaking strains have occurred inside of the wood, and also the wood fibers have split or cracks have occurred on the outside of the bent wood. For this reason, in producing large volumes of bent wood, laminated wood or plywood is usually subjected to heating and pressing treatments, and the treated wood is utilized as bent wood. However, even when such processed wood such as laminated wood is used, defects such as strains or splits occur inside and outside the wood structure, and moreover, the treating expenses are becoming higher. Likewise, due to limitations on design, there is a strong potential demand for bent wood obtained by treating single pieces of wood, which is not the laminated wood or plywood.

The previous applicant has discovered that the quality of the gumwood was extremely suitable for use as bent wood. The process which is the subject of this patent aims at not merely utilizing gumwood as bent wood as it is. Rather utilizes the intrinsic quality of gumwood and a unique treatment of gumwood, thereby producing high quality bent wood.

Gumwood is produced in countries like Thailand and Malaysia and normally 3040% of the volume is composed of reaction wood. The untreated wood is a tension wood similar to those found in ordinary hard woods.

In cases where the tree is bent due to the wind or the weight of the crown of the tree, tension wood is produced by natural phenomenon that the wood structure of the opposite side of the inclined side tries to grow perpendicular. In the case of gumwood, due to the quality of the wood or the influence of the growing location, the volume of reaction wood generated is particularly great.

In general, tension wood maintains a balance of tension in the log, and there is no distortion of the log itself, but when it is sawed or cut into a board or veneer sheet, contraction occurs rapidly, and the bend or distortion occurs on the side or the direction where the tension wood is present.

When tension wood is present at both sides of a single board, the end occurs at the side where the volume of tension is greatest. The tension wood of the gumwood, in particular, exhibits a high degree of contraction, and the degree of contraction is more than twice that found in other hard woods.

Comparing the tension wood of the gumwood with the other species, the following should be noted: (1) Lignin volume is small.

(2) Capillaries are small.

(3) Clearly recognizable reaction wood is generated which is much wider and longer than other species.

According to the present invention, there is provided a wood bending process which is comprised of the following steps: cutting gumwood in such a manner that tension wood is located on the surface to be bent, drying the treated wood rapidly, producing the first-stage bending at the surface where the tension wood is present, heating the treated wood gradually in an aqueous solution containing a very small quantity of a surface active agent which penetrates and diffuses through the wood and a latex solvent, treating the wood in an aqueous solution containing an insecticide for gumwood, clamping the gumwood into a wood bending mould, and then drying the treated wood.

The present invention will now be described using the accompanying drawings which illustrate, by way of examples, processes related to the present invention and in which: Figure 1 is a cross section showing the state of a gum tree log; Figure 2 is a view in perspective of a square timber which has been sawed in such a manner that the tension wood is distributed disproportionately.

Figure 3 shows the square timber in Figure 2 is being subjected to preparatory drying; Figure 4 is a view in perspective of a board similar to Figure 2; and Figure 5 is a view of bending similar to that in Figure 3.

In the drawings, reference numeral 1 denotes a gum log; numeral 2 denotes a cross section; numeral 3 denotes a tension wood portion; numeral 4 denotes the sawed wood (square timber), and numeral 5 denotes a sawed board.

The present invention utilizes the foregoing quality of the reaction wood existing in gumwood.

However, gumwood cannot be utilized as it is even though the foregoing preferable qualities for use as bent wood are present. Namely, in gumwood, the bacteria which cause discoloring or decaying breed very rapidly because of the latex contained in the tree immediately after it is cut down. These bacteria cause the log to turn blue within several hours. Gumwood also tends to suffer damage from insects and if the untreated wood is used as it is, it will be eaten to pieces.

The present invention can produce bent wood by applying an appropriate treatment to the gumwood as will be described in the following whereby bent wood resembling white oak, having a white surface and clear figure, is produced.

Moreover, the tension wood of the gumwood is always disproportionately distributed at one side of untreated logs, and it is extremely easy to confirm the location of this portion from a cross section of the log so that the sawing of the tension wood so that it will be disproportionately distributed to side of the square timber or the board is technically extremely easy.

The summary of the present invention will be described in the following. First, the sawing of the gum log begins in the following manner according to the use to which the bent wood is to be put: (1) In the case of circular table frame wood or circular door frame wood, the sawing is carried out to produce square timber or boards in such a manner that the tension wood is present on the lateral surface portion, corresponding to the inside of the bend.

(2) In the case of the back of a chair, the sawing is carried out so that the tension wood is present on the flat surface of the inside of the bend.

(3) In the case of a leg of a chair, the sawing is carried out so that the tension wood is present on a lateral surface of the square timber, corresponding to the inside of the bend.

As described in the foregoing, the gumwood produced by the sawing to cause the tension wood to be present on the required surface according to the use to which it is to be put rapidly dried at high temperatures keeping moisture low if it is required that the gum wood be bent to a high degree. In case bent wood with moderate bending is required, it is either dried for a shorter priod at lower temperatures and with a high amount of moisture present or is dried gradually by natural drying.

During this drying process, bending always occurs, and the bending inclination of the wood appears definitely. The resulting bent gumwood is immersed in a boiling tank filled with hot water, and a surface active agent having special penetration and diffusion characteristics and a latex solvent which is alkaline are added to the hot water in the tank and the wood is boiled for several hours. The rubber latex in the capillaries of the structure of the wood of the gum log by means of this process becomes soft and is dissolved and the wood structure becomes soft. The structure of the wood is cleaned. Prior to the foregoing boiling process, it is preferable that the solution is heated to 600C, and that the wood is softened slowly for several hours, and then the heat of solution is raised.

The surface active agent has penetrates the gum tree effectively and also has a high degree of stability with regard to heat, chemicals, and hard water and, moreover, has effective cleaning action. According to various experiments carried out by the inventor, it has been demonstrated that anionic alkylnaphthalene sulphonic acid sodium or dodecylbenzene sulphonic acid sodium are the most effective. Furthermore, as a solvent for latex, triethylamine, ethylbutylamine, diethylaminoethanol or soda ash having proper alkalinity can be optionally chosen.

With the addition of the surface active agent, deep penetration of the latex solvent into the inner part of the wood structure takes place.

Furthermore, the upper limit to the surface active agent and the latex solvent is in the range of a 1% solution. The lower limit is in the range of 0.1%, with the ideal range between 0.30.4%.

If the strength of the chemicals are increased too much, the physical structure of the wood tends to be damaged.

The treated gumwood is placed in a tank of hot water containing insecticide for about 30 minutes more. As an insecticide, a mixture of the borax and boric acid can be used. The proper concentration is a 10-1 5% solution.

The treated gumwood is subjected to a forming process according to the use to which it is to be put. The treated wood is inserted into a bending device. The bent wood is rapidly pressed into the desired shape. The bending vise consists of a steel wood forming vise of the usual type. The wood which has been bent into the desired shape is placed in drying kiln. Moisture content is then reduced to levels preferably below 7%.

The resulting bent gumwood is used by being glued to the circular edge portion of the furniture, fittings and fixtures.

EXAMPLE 1 Process for bending gumwood for use as circular edge wood for a table with a thickness of 40 mm, width of 50 mm and length of 1,800 mm: The presence of the tension wood portion was confirmed by the observation of the cross section 2 of the gumwood 1. (Easily recognizable because it was white and bright.) The gumwood was sawed to produce a square timber 4 the thickness of which was 40 mm, width 50 mm, and length 1,800 mm so that the tension wood 3 would be present at one side of the thick portion of the circular edge wood.

The sawed square timber 4 was placed immediately in a drying kiln, and was dried for 24-48 hours at a temperature of 900C and 50% moisture. As time elapsed, the square timber 4 slowly bent to the shape shown in Fig. 3. From time to time, the progress of the bending was checked, and the process was stopped when about 7080% of the desired bending angle was obtained.

The square timber, initially bent by drying, was placed immediately in a tank of hot water and the dipping treatment was carried out. An aqueous solution, prepared by mixing a 0.4% concentration of anionic alkylnaphthalene sulphonic acid sodium as the surface active agent and 0.4% concentration of soda ash as the latex solvent, was put in the tank and the wood was treated for 2 hours by elevating the temperature to 600 C.

The solution was gradually heated, and it reached boiling temperature after about 1 hour.

The solution in the tank was kept at boiling temperature for one more hour.

Then, the wood is shifted to treating tank filled with hot water containing a 1 5% solution of insecticide prepared by mixing borax and boric acid uniformly, its temperature being set at 80--900C. The wood was immersed for about 30 minutes.

After the treatment, the treated wood was mounted in the steel wood bending clamp which was previously set to form the bent wood for the table and was pressed to the desired shape.

The bent wood fixed in the steel frame was placed in the drying kiln while still in the clamp - and the wood was kiln dried at temperatures of 70-1 000C. The drying was carried out to reduce moisture content of the bent wood below 7%. The dried bent wood was cured at ambient temperatures for 5-7 days. The bending device was opened and the bent wood was used as circular edge wood 4'.

EXAMPLE 2 Process for making bent wood for the back of a chair with thickness of 20 mm, width of 60 mm and length of 450 mm, with a distance perpendicular to the chord of 250 mm: The presence of the tension wood 3 was confirmed by examining a cross section of the gumwood 1 as shown in Fig. 1, and the wood was sawed to produce a board the thickness of which was 20 mm, width 60 mm, and length 450 mm as shown in Fig. 4 so that the tension wood 3 was present at the inside surface of the back board 5.

The sawn board 5 was immediately subjected to natural drying. In this case, since the bent portion perpendicular to chord was large, the reaction surface was on top. In cases where the bent portion perpendicular to chord is small, the reaction surface is turned down and natural drying is carried out. This natural drying is varied depending upon the type of bending required by checking the degree of bending during the drying process which lasts 1-3 days. In the case of the back board, as described in the EXAMPLE 1, it was necessary to hold it to 7080% of the bending perpendicular to chord that was desired.

In case of boards as well, as in this EXAMPLE, attention is invited to the fact that sharp bending tended to occur in the direction where the reaction wood was present by natural drying only.

Furthermore, in cases where the amount of reaction wood was small and the bending was limited, preparatory bending was carried out by kiln drying as described in EXAMPLE 1.

The bent wood was placed immediately in a tank containing hot water and was subjected to the dipping treatment. A solution containing a 0.3% concentration of anionic dodecylbenzene sulphonic acid sodium as the surface active agent and a 0.3% concentration of ethylbutylamine as the latex solvent was added to the hot in the tank and the wood was soaked at a temperature of 60"C for 30 minutes.

Then, the water in the tank containing the wood was heated gradually, and it was gradually caused to boil over a period of 30 minutes kept boiling for 30 minutes.

The heat treated wood was shifted to the insect control tank filled with hot water at a temperature of 800C-900C The concentration level of the insecticide was 15% and it was prepared by mixing borax and boric acid in equal parts. The wood was immersed for about 1 5 minutes.

As described in the foregoing, the wood, after undergoing a series of warm and hot water treatments, was mounted on a steel wood bending mold set to form the back of a chair, and was pressed, and bent in the desired shape. The bent wood, clamped in the steel mold, was heated and dried by releasing the steam through a pipe in the steel mold, and the drying was carried out to lower moisture content below 7%. The dried bent wood was subjected to curing at ambient temperatures for 5-7 days, and then removed from the mold. The resulting treated wood was used as bent wood 5' for back of a chair.

Claims (12)

1. A wood bending process which is comprised of the following steps: cutting gumwood in such a manner that tension wood is located on the surface to be bent, drying the treated wood rapidly, producing the first-stage bending at the surface where the tension wood is present, heating the treated wood gradually in an aqueous solution containing a very small quantity of a surface active agent which penetrates and diffuses through the wood and a latex solvent, treating the wood in an aqueous solution containing an insecticide for gumwood, clamping the gumwood into a wood bending mold, and then drying the treated wood.

2. A wood bending process as claimed in claim 1 wherein the surface active agent is chosen either anionic alkylnaphthalene sulphonic acid sodium or dodecylbenzene sulphonic acid sodium.

3. A wood bending process as claimed in claim 1 or claim 2 wherein the latex solvent is chosen from among triethylamine, ethylbutylamine, diethylaminoethanol, or soda ash with proper alkalinity.

4. A wood bending process as claimed in any preceding claim wherein the insecticide is sodium borate.

5. A wood bending process as claimed in any one of claims 1 to 3 wherein the insecticide is a mixed solution of borax and boric acid.

6. A wood bending process as claimed in any preceding claim wherein the surface active agent is present in a proportion of 0.11.0% and preferably 0.30.4%.

7. A wood bending process as claimed in any preceding claim wherein the latex solvent is present in a proportion of 0.11.0% and preferably 0.30.4%.

8. A wood bending process as claimed in any preceding claim which comprises the steps of heating the gumwood, the bending of which is caused by initial drying, gradually to about 60 C first to soften the wood structure, and then raising the temperature to boiling for 1-2 hours.

9. A wood bending process as claimed in any preceding claim wherein the insecticide is 10%--15% and the treatment is carried out with hot water at 800C-1 00cC.

10. A wood bending process as claimed in any preceding claim wherein the gumwood is in the desired shape by means of a bending wood mold, and drying is carried out to lower the moisture content below 7% as a final step in finishing the gumwood bending process.

11. A process as claimed in claim 1 and substantially as herein described with reference to the accompanying drawings.

12. A process as claimed in claim 1 and substantially as described in the specific examples hereinbefore set forth.