DE102006040755B4 - Process for removing stress from dried bamboo canes and circumferentially closed bamboo cane - Google Patents

Abstract

The method involves isolating a bamboo cane (1) after developing tension in the bamboo cane in a longitudinal direction over an entire length in a peripheral point, and optically closing a longitudinal gap (2) that is developed in the bamboo cane. The bamboo cane is dried up to fiber saturation point. Finish-cutting of the bamboo cone is performed by closing the longitudinal gap and processing the bamboo cone at an end point during an air conditioning phase. The bamboo cone is air-conditioned for about 12 hours per day in the air condition phase. An independent claim is also included for an extensively closed bamboo cane.

Description

I. Field of application

The The invention relates to a method of treating bamboo tubes, to at least visually avoid cracks by either a radial View is prevented by appropriate design of the crack or the kerf or an overlap of the gap with a cover strip, so that the opacity even with changing ones Gap width is still maintained. Also an actual crack avoidance by Composing from z. B. half shells is possible.

II. Technical background

bamboo is due to its high elasticity and stability, especially in Asia, in the most diverse Wise used as a constructive element, creating a steeple Scaffolding until used as a material for seating and crockery.

Also In Europe, bamboo, especially for the production of seating furniture, bedsteads and the like used.

there basically exists the problem that the moisture content, as the bamboo tube during the Owns growth, namely about 55-110 Weight%, after cutting off the pipe and ending the capillary water supply from the root system to the humidity of the environment decreases. While in the Asian space due to the usually very high humidity this difference only occasionally to the cracking of the bamboo cane leads, tear such pipes when transporting to Europe or North America and before especially when used in centrally heated or air-conditioned rooms almost regularly, due to then existing very high humidity difference.

Though Cracking also affects the stability of the bamboo cane However, this is not the decisive disadvantage, but the deteriorated visual effect when the bamboo tube as construction material for relative high quality furniture has been used.

Since the bamboo tube has a closed, circular cross-section, and is divided longitudinally at irregular intervals of bulkhead transverse walls, the methods known from the treatment of logs processed solid wood methods of crack prevention (layered gluing the solid wood planes in an angular fiber direction to each other) not Crack prevention can be used. Because on the one hand, bamboo is not biologically a species of wood, but a giant grass and also there are almost opposite behaviors in physical terms:
While wood has the conduction cells for the transport of liquids, especially in the outer areas directly under the bark and therefore has a tree trunk in the outdoor area the highest and the core area has the lowest moisture content, it is exactly the opposite with bamboo:
In the outer third of the tube are the support cells, which give the bamboo its strength, while inwardly follow the Leitzellen and storage cells for the water to be absorbed with the built-up builders. Consequently, the two substances behave absolutely unequal, especially since it is added that the physical behavior of the bamboo is again completely different due to the hollow construction with the transverse walls present in the axial direction.

In addition is the moisture content of bamboo pipes when cutting not only generally higher than in wood, but also varies much more depending on the location, momentary Climate and, considered in the cross-sectional direction of the bamboo pipe as also in the axial longitudinal direction, of the size.

From the DE 43 00 557 A1 it is already known in this context, to slit the bamboo tubes before drying in the longitudinal direction, and this by the subsequent drying usually widening gap thereafter by the insertion of a bamboo strip, consisting of several longitudinal sections of another bamboo cane to close.

Furthermore, it is from the DE 43 00 555 A1 It is known to prevent cracking when drying bamboo closed-section bamboo tubes by chemically treating the bamboo tubes prior to drying and, if necessary, to perform mechanical measures such as partial removal of the transverse walls.

III. Presentation of the invention

a) Technical task

It is therefore an object according to the invention, to create a process using the bamboo pipes, which also include and / or several transverse walls can be treated, that cracks of the bamboo cane are avoided after its processing or at least not visible.

b) solution the task

These The object is solved by the features of claims 1, 3, 4 and 12. advantageous embodiments emerge from the dependent claims.

The described methods are intended to reduce the occurring cause mechanical stresses.

These Tensions are on the one hand by the closed, round cross-sectional contour of the bamboo, resulting in even percentage shrinkage of the bamboo in the outer layer Tensile stresses opposite the inner layer must occur. This is reinforced through the inner structure of the bamboo, which in the outer third more supporting cells and in the inner third more tubular Has water transport cells and memory cells.

A further difficulty in influencing the tensions in the bamboo are the ones present at irregular intervals inner transverse walls, which also revolve around in one on the outside of the bamboo increased Express bead.

There due to growth, the thickness of the wall opposite the Diameter of the tube, the taper of the tube, as well as the inner Structure of bamboo and its initial moisture in almost every one Individual case is different, need Also, the types of influence individually variable.

These However, mechanical treatment must be supported by special, gradual drying processes, also in European climatic conditions not tearing To get bamboo product:

pretreatment:

A Possibility, to reduce the tendency to crack in bamboo cane, on the one hand The lower 50 to 200 cm of the grown bamboo cane stand let and just harvest the top of the tube as with increasing height of Starting moisture content of the bamboo tube decreases sharply.

By the most extensive removal a few weeks before harvesting the branches and branches of bamboo will be added the water transport through the bamboo cane reduces and thus the Initial moisture content at harvest.

Pre-drying:

Supporting becomes the cut tube still stored upright after harvesting, best directly in the bamboo grove, leaving the remaining branches, whereby a kind of pre-drying by moisture release over the leaves and evaporate over the cut surfaces takes place, supports by the sinking of moisture in the bamboo tube by gravity.

Active drying:

The Active drying of the bamboo is carried out in several stages:

1st stage:

In the first stage, the bamboo is preferably dried outdoors from the initial moisture content (50 to 100%) to the so-called fiber saturation limit. This is bamboo between 14 and 21 wt .-% water in contrast to wood, where this value is 23 to 35%. Also, bamboo already begins to shrink in this first drying phase in contrast to wood, which only after Falling below the fiber saturation value begins to shrink. Unless otherwise stated, all percentages are by weight.

These first phase is by upright storage in partial shade outdoors for 2 to 10 weeks, especially from 3 to 4 weeks. there the moisture content decreases to a value of about 17%. This Value corresponds to the moisture balance, as it is sufficient long storage due to the ambient humidity in the tropics established.

there the bamboo shrinks in diameter by 4 to 14%, making it beneficial is to open the transverse walls already before this first drying phase. This can be by poking or a diameter adjustable drill head happen.

This is necessary because in this first drying phase especially the free water from the water pipes, which are increasingly located on the inner circumference is discharged and open transverse walls better to the outside can escape.

If it cracks in this first stage, these arise mainly from inside, as by evaporation of the free water in the capillaries the inner wall-near areas of the tube the strongest shrinkage and tension occurs. With the above measures are in this drying phase However, cracking is largely avoidable.

2nd stage (drying chamber / climatic chamber):

In the second stage is ideally based on the fiber's saturation content Moisture, dried to 7% to 10% final moisture. In this second drying phase of the bamboo is preferably the in the outdoor areas bound waters, which is why these outer layers contract want, but what due to the differently behaving inner Pipe areas is not possible. This will - much like with a bimetal - the Tube diameter bent so that the circumference increases and possibly at one point of the pipe circumference a longitudinal gap is formed or increased.

2.a drying chamber

During the Chamber drying is the air temperature between 30 ° and 60 ° C and the relative humidity is 75% to 33%.

Farther is during the chamber drying regularly with a moisture meter the drying checks what while the second drying phase every 2 hours, at the previous first Outdoor phase happens every 2 days.

The drying in the drying chamber is started with cool air and high humidity, during the drying process, the temperature is increased and the humidity in the drying oven is lowered. Preferably, it is dried in several chamber phases. Typical for 3 m long bamboo tubes with the usual 5-year growth period, taken from the middle stem area and with chemical pretreatment are the following values:
1st stage = 30 ° Celsius / 75% relative humidity
2nd stage = 38 ° Celsius / 60% relative humidity
3rd stage = 49 ° Celsius / 45% relative humidity
4th stage = 60 ° Celsius / 35% relative humidity.

In this case, preferably during the first phase, the outside, especially in the node area, the bamboo tube regularly sprayed with water to prevent cracking especially there. The total time of the chamber drying (eg, the 1st to 4th phase shown above) is 3-7 days, with the total time and the individual times of the individual phases differ depending on the wall thickness of the pipe to be dried approximately as follows: Wall thickness 1st phase (x) 2nd phase (x) 3rd phase (x) 4th phase (x) 10 mm 20 22 24 22 12 mm 20 22 33 27 14 mm 20 22 43 31 16 mm 22 26 49 35 18 mm 22 26 55 42 20 mm 22 26 62 50 (x) = length of stay in hours

2.b climate room:

To about 3 to 7 days Residence time in the drying chamber is conditioned the climatic conditions carried out by the exporting country, So an acclimatization at about 40 to 50% humidity and 20 to 25 ° C Temperature for European Countries.

The Residence time in the climatic room is 2 to 4 days, whereas opposite the last phase in the drying chamber in turn a diameter reduction of the bamboo cane by 5 to 12%, due to the higher relative Humidity in the climatic room compared to the last phase in the Drying chamber. This is used selectively, as it turns out has that this under-drying in the drying chamber the subsequent crack resistance of the processed bamboo cane, as it later becomes one have lower swell. This could collapse with the sustainable related to individual capillaries.

The mechanical processing is done in addition as follows:
When drying whole bamboo tubes, stresses occur in the circumferential direction of the tube, which can cause the tube to rupture on the circumference.

By the separation of the bamboo tube in the longitudinal direction over the whole length can such stresses are dissipated by the pipe cross-section then according to the existing stresses in the circumferential direction can deform, so after the separation C-shaped cross-section widens or in a few cases also contracts under overlapping the free ends of the circumference.

• a)

As a result of the subsequent optical closing, the gap is at least as such no longer visible, or actually no longer present, if an actual, mechanical closing takes place instead of only an optical shutter. In this case, the transverse walls of the bamboo cane before the drying down of the moisture content of the bamboo tubes, in which yes build up the tensions open, so pierced or pierced, but preferably not completely removed, but introduced an opening only in the center of the transverse wall, which is one size of twenty to thirty percent of the outer diameter of the bamboo cane.

• a)

A Method of closing concerns only the optical, not the actual closure of the longitudinal gap: The longitudinal gap is closed by placing a strip of material over the Width of the longitudinal gap - and of course its entire length - away, however, the strip of material does not have to be flush with the longitudinal gap the adjacent outer surfaces and Complete with original bamboo look: The material strip a foreign material.

• b)

As foreign materials in particular metal or plastic comes in a flexible, thin form, so metal foil or deformable, but still form-retaining, plastic film in question. The film is inserted into a groove in the cut surface of the bamboo tube and pressed against the opposite cutting surface, for example, with slight curvature of the strip of material outwards, so that when changing the joint width by the bias of the strip of material in the circumferential direction continues to concern the other edge of the strip the opposite cut surface is guaranteed. It is also possible to protrude into a slot in the cut surface in the bamboo.

• b)

• c)

A second method is to make the longitudinal gap optically not appear by through the longitudinal gap in normal, radial viewing of the tube can not see inside the tube. This is achieved by the longitudinal gap is produced by a section which is not radially, but so much obliquely guided to the radial direction, namely at least thirty degrees obliquely thereto, that when viewed radially, although a part of the one sectional surface of the gap is seen but can not be seen inside the tube.

• c)

One third method is that the separation of the bamboo tube longitudinal takes place at least two separate locations of the circumference and thereby the bamboo tube into at least two separate segments, For example, two half-shells, is separated.

by virtue of the residual stresses present in the material will become both segments, z. B. both half shells, with regard to their cross-sectional contour something change, usually rise, so their radius of curvature increase a little.

Subsequently - after one Waiting time dependent from a state of a bamboo from several hours to several days - segments or half shells of the same tube reassembled, in particular by gluing, possibly also by means of additional mechanical fasteners like dowels, Nailing, screws.

Of the Advantage is that due to the division into at least two different segments a better release of tension in the individual Segments possible is, as in a split at one place, otherwise whole tube, and thus the remaining residual stresses accordingly lower are.

Accordingly is the probability that such a segmented separated, and joined together after relaxing the segments tube in the future much less often gets such strong tensions that tear it becomes.

One Another advantage is that by separating into several Segments work on the inner surfaces easily performed these segments can be For example, the removal of the transverse walls or their still existing Remains very easily complete can happen and also a layer removal of the bamboo from the Inner side, so the innermost layers, in a simple way and Way can be done.

The latter According to experience, the later tendency to crack reduces as well as the complete one Removing the transverse walls and give it over In addition, a weight reduction without significant loss of stability.

In addition, you can also the fine internal bamboo dust and any mold are easily removed.

Regarding the transverse walls is preferably moved so that before drying the transverse walls only open become, so in the center a hole with a fifth to a quarter of the Outside diameter of the Pipe in the transverse walls is introduced, and the rest of the transverse walls only after splitting of the pipe is removed into segments.

disadvantage This method is that the segments, especially the two Half shells, while relaxing under different circumstances deform, and then no longer match seamlessly, for example because their free edges are at a different distance from each other taking. At least, however, the bending radius of the reduced individual segments, so that juxtaposed cut surfaces one outward cuneiform would reveal gaping fugue, which can be closed by adhesive, but then visually are visible.

Around To avoid this, the cut surfaces or gap surfaces of the individual segments before joining, in particular bonding, mechanically pretreated that subsequently no outward opening Wedge joint, but a flat abutment of the machined cut surfaces or Cleavage surfaces or even an inward opening Keilfuge arises, the outer edges the cut surfaces but close together. Also there protruding fibers of the When gluing together, bamboo will either be found in the finest available there cavities pressed or glued in Nutinnenraum.

The Separation of the bamboo tube into segments does not take place by means a saw, but by means of a splitting tool, so a knife, so that no material is cut. This has the advantage, among other things, that the splitting follows the fiber course of the bamboo, so fibers not be interrupted, even if the resulting gap thereby not necessarily rectilinear along a surface line of the tubular tube runs, but under certain circumstances aslant For this. As well as the outer surfaces of the Bamboo pipes at the joint after joining in certain circumstances no longer be aligned with each other, a leveling of the joints on the outer circumference made so that at the joint no paragraph remains. In particular, a material removal via the entire outer circumference take place, ie the removal of a continuous layer around the whole outer circumference around.

c) embodiments

embodiments according to the invention are closer in the following example described. Show it:

1 : a bamboo tube with foil cover,

2 a slotted bamboo cane,

3 : the process of segment decomposition, and

4 : a restored bamboo cane.

1 shows a bamboo tube 1 in cross-section, in which the transverse wall 5 is largely removed and the bamboo cane 1 was cut along a generatrix, creating a longitudinal gap 2 originated.

In this case, due to the cutting process, which was completed with a circular saw or the like, the side walls of the longitudinal gap 2 parallel to each other and extending substantially radially.

Here is a strip of material 3 made of elastic material in a groove 17 inserted in the cut surface 18a of the bamboo cane 1 and thus only to the longitudinal gap 2 is open.

The fixation of the material strip takes place 3 only in one of the grooves 17 while the opposite edge of the strip of material 3 in the other groove 17 the opposite cut surface 18b free ends and there still has game for stretching or shrinkage of the bamboo tube in the circumferential direction.

2 shows a solution in which the longitudinal gap 2 in the bamboo tube 1 de facto not closed at all, but only optically insofar not as a longitudinal gap noticeable, as by this longitudinal gap 2 with normal viewing of the bamboo cane 1 , namely radially from the outside, no longer inside the bamboo cane 1 can be seen in:
For this purpose, the longitudinal gap 2 generated by an oblique to the radial direction 19 guided cut, so that the resulting cut surfaces 18a . 18b also obliquely to the radial direction.

If the inclination is chosen sufficiently strong, so that in relation to the thickness of the bamboo tube, the cut edges 18a , B overlap in the circumferential direction, no view into the interior of the tube is possible when viewed radially. As a rule, inclinations are at least 30 ° to the radial direction for this purpose 19 sufficient.

The 3 on the other hand, show a way of avoiding cracking:
This is the bamboo tube 1 as in 3a shown in the longitudinal direction in several, in this case two segments 1a , b separated by cutting by means of a knife along the fiber direction. It is not necessary to hit exactly the middle of the cross section, or in the case of a long bamboo tube, a cut at one end in the middle of the cross section may lead to an uneven and not even split due to the fiber flow at the other end.

Before dividing into segments, the transverse walls become 5 at least partially removed, for example, by piercing in the middle and thereby at least about a quarter of the area of the transverse walls 5 each removed.

In the subsequent waiting period of a few hours to several days, the Seg turn mente 1a , b usually something on, so change z. B. their original semicircular shape to a circle segment with less than 180 °.

In addition, the z. B. two segments 1a , b one and the same original bamboo cane 1 often in different ways, so that the two segments thereafter have a different diameter, that is, a different width.

However, possess the so deformed segments 1a , b now much less internal stress than the previously entire bamboo cane 1 , so that when joining, for example gluing, the segments 1a , b to a re-closed new bamboo cane 1' , as in 3d shown, the risk of subsequent re-breaking is only very low.

However, in order to achieve a closed pipe shape during assembly, several measures are generally necessary:
For one, the no longer radially running cut edges 18a , b are processed. From the cut surfaces material is removed, preferably by means of a knife, planer or a grinder, the outer edge of the cut surface 18a , B is preferably not processed or impaired, but the material removal from there wedge-shaped towards the inner surface of the segment 1a , b increases, so that the resulting new cut surfaces 18'a and 18'b placed against each other, as in 3c , d shown, touching at the outer edge and an inwardly open wedge-shaped glued joint 6 resulting, which can be closed by adhesive, such as epoxy resin.

Due to the unaffected outer edge of the cut edges 18a , b the two segments fit together again without a heel and optically very inconspicuously or invisibly, according to the original cut and fiber course.

If the so juxtaposed segments in cross-section because of the bend the segments too lenticular, deviating from the circular shape Cross-section, can - preferably before fixing, for example gluing, the segments against each other - the area the largest half-knife this lens or ellipse shape of the cross section by means of grinding or cockroaches are flattened.

Likewise, in addition to the complete removal of the inner transverse walls 5 also a removal of material layers, in particular on the inner skin 12 of the single segment 1a , b, possibly also from the outer skin 13 ago, take place.

4 shows a bamboo tube restored in this way 1'' , which consists of four initially divided segments 1a -D was created.

1, 1 ', 1' '

bamboo

1a, b, c, d

segment

2

longitudinal gap

3

strips of material

5

partition

6

bonded joint

10

longitudinal direction

12

inner skin

13

shell

17

groove

18'a, b, 18a, b

section

19

radial direction

21

central hole

Claims (15)

Method for removing stress from dried bamboo tubes, wherein - the bamboo tube ( 1 ) after drying in the longitudinal direction ( 10 ) is separated over the entire length at a circumferential location, and - the resulting longitudinal gap ( 2 ) is closed by arranging a strip of material ( 3 ) across the width of the longitudinal gap ( 2 ), characterized in that - the strip of material ( 3 ) consists of a flexible metal or plastic film and - with its longitudinal edges in grooves ( 17 ) in the cut surfaces ( 18a , b) on both sides of the longitudinal gap ( 2 ) and in one of the grooves ( 17 ) is attached. Method according to claim 1, characterized in that the strip of material ( 3 ) is formed integrally in the longitudinal direction. Process for removing stress from dried bamboo tubes, the bamboo tube ( 1 ) after drying in the longitudinal direction ( 10 ) is separated over the entire length at a peripheral location, characterized in that the longitudinal gap ( 2 ) by a cut with at least 30 ° oblique to the radial direction ( 19 ) is produced, so that not into the interior of the bamboo tube ( 1 ) can be looked into. Method for removing stress from dried bamboo tubes, wherein - the bamboo tube ( 1 ) after drying in the longitudinal direction ( 10 ) is separated over the entire length at a peripheral location, characterized in that - before drying the transverse walls ( 5 ) all pierced, but only partially removed, and - after drying down to the desired residual moisture the bamboo cane ( 1 ) in the longitudinal direction at at least two opposite points of the circumference to at least two segments ( 1a , b) is separated, and - after a waiting period of at least 5 hours after separation, the segments ( 1a , b) again to a circumferentially closed bamboo tube ( 1' ). Method according to claim 4, characterized in that in the separated segments ( 1a , b) the transverse walls ( 5 ) completely removed and on the insides of the tube walls either in the longitudinal direction ( 10 ) running grooves are introduced or to reduce the wall thickness surface material is removed. Method according to one of the preceding claims 4 or 5, characterized in that the bamboo tube ( 1 ) into two segments ( 1a , b), in particular two half-shells, is split by means of a knife extending over the entire pipe cross-section. Method according to one of the preceding claims 4 to 6, characterized in that the segments ( 1a , b) after a waiting period of at least eight hours, in particular at least 24 hours, in particular at least three days, are joined together. Method according to one of the preceding claims 4 to 7, characterized in that when partially removing the transverse walls ( 5 ) only one central hole ( 21 ) in the center of the transverse wall with 1/4 to 1/5 of the outer diameter of the tube ( 1 ) is introduced. Method according to one of the preceding claims 4 to 8, characterized in that the bamboo tube ( 1 ) is separated along the fiber path. Method according to one of the preceding claims 4 to 9, characterized in that before joining the segments ( 1a , b) on the adhesive surfaces ( 18a , b) material is increasingly removed from the adhesive surface to the inner circumference of the tube. Method according to one of the preceding claims 4 to 10, characterized in that the outer edge of the adhesive surface left unchanged becomes. Completely closed bamboo tube ( 1' . 1'' ), which consists of - at least two complementary segments ( 1a , b), and - the segments ( 1a , b) in the longitudinal direction ( 10 ) of the bamboo tube ( 1 ), characterized in that - the joints between the segments ( 1a , b) are wedge-shaped from outside to inside, - the segments ( 1a , b) the same bamboo cane ( 1 ) along the fiber path of the bamboo tube ( 1 ) are glued together. Bamboo tube according to claim 12, characterized in that the segments ( 1a , b) are two half-shells. Bamboo tube according to one of claims 12 to 13, characterized that the transverse walls Completely are removed. Bamboo tube according to one of claims 12 to 14, characterized in that on the insides of the segments ( 1a , b) in the longitudinal direction ( 10 ) extending grooves and / or a flat material decrease to reduce the wall thickness is present.