Patent Description:
Plywood is manufactured by laying sheets of veneers on top of each other, adhesive in between, and pressing them to form a plywood panel. When manufacturing plywood, the veneers to be pressed are preferably substantially dry in order to avoid e.g. warping of the panel. Therefore, the veneer sheets are dried. Typically drying comprises at least drying by hot air. Recently it has also been found that a veneer can be pre-dried at least to some extent by pressing aqueous solution out of it. A device for such a purpose is known.

In order to efficiently dry the veneers, preferably the veneers are dried by compression as much as practically possible. Parameters affecting the drying include time and pressure. In principle, the higher the pressure and the longer the time, the more water can be squeezed out from the veneers. However, the pressure for compression must not be too high in order not to break the veneers. Moreover, for process efficiency, the drying time must not be too high. In this way, the dryness after the compressive drying is somewhat limited.

It has been found that the quality of the veneer sheets dried by compression affects the drying. In particular, it has been found that the amount and/or size of the peeling checks affects drying. It seems that by increasing the number and/or size of the peeling checks (i.e. lathe check, peeling cracks, or lathe cracks) improves drying. Moreover, it has been found that the evenness of a surface of a veneer formed by peeling affects drying. It seems that by increasing the surface roughness of the veneers, compressive drying can be improved. Moreover, it has been found that such veneers for compressive drying can be produced using a special type of a veneer lathe. In particular, it has been found that a by using a veneer lathe having a roller nose bar these properties of the veneer are better in terms of compressive drying than for veneers manufactured by some other means.

The invention is disclosed in the independent claim. Preferable embodiments are disclosed in the dependent claims. The description discloses also further embodiments.

Dried veneer sheets are commonly used to manufacture plywood. In order the manufacture veneer <NUM> and/or veneer sheets <NUM> from a wood block <NUM>, various methods are known. Methods to produce veneer may be classified as rotary methods, as shown in <FIG>, and non-rotary methods, as shown in <FIG>.

Parts of a process for manufacturing plywood is shown in <FIG>. Referring to <FIG>, after soaking, de-barking, and cutting the wood, veneer <NUM> is made from a wood block <NUM>. If a rotary method is used to manufacture veneer <NUM>, a veneer lathe <NUM> is used for peeling veneer <NUM> from a wood block <NUM>. Thereafter, the veneer <NUM> is cut to veneer sheets <NUM> including heart wood veneer sheets and other veneer sheets. The veneers are cut in a cutting apparatus <NUM> having a blade <NUM> for cutting the veneer. Thereafter, at least some of the veneer sheets <NUM> are pre-dried by compression. A veneer sheet <NUM> is pre-dried simultaneously with some other veneers in a stack <NUM>. Accordingly, a stack <NUM> of veneer sheets <NUM> is formed. Correspondingly, at least one of the veneer sheets <NUM> manufactured from the wood block <NUM> is arranged into the stack <NUM>. The stack <NUM> may further comprise veneer sheets manufactured from another wood block or other wood blocks. Not all the veneer sheets <NUM> need to be pre-dried, depending on their moisture content. For example, heart wood is typically so dry, that it is dried in a drier <NUM> without compressive pre-drying. Thus, at least one of the veneer sheets <NUM> peeled from the wood block <NUM> is pre-dried by pressing the stack <NUM> of veneer sheets to dry the veneer sheets of the stack <NUM>. The veneers of the stack <NUM> are pre-dried in a press <NUM> for pressing a stack <NUM> of veneer sheets <NUM>. Referring to <FIG>, <FIG>, and <FIG>, the press <NUM> comprises a first surface <NUM> and a second surface <NUM>. The first <NUM> and second <NUM> surfaces are arranged such that the stack <NUM> of veneer sheets can be arranged in between the first surface <NUM> and the second surface <NUM>. The press <NUM> further comprises an actuator arrangement <NUM> configured to move the first surface <NUM> towards the second surface <NUM> in order to press the stack <NUM> of veneer sheets, which has been arranged in between the first surface <NUM> and the second surface <NUM>. The actuator arrangement <NUM> may comprise at least one hydraulic press <NUM>. The first surface <NUM> may comprise a surface of a first planar object <NUM>. The second surface <NUM> may comprise a surface of a second planar object <NUM>. The first surface <NUM> may be formed of surfaces of multiple first planar objects <NUM>. The second surface <NUM> may be formed of surfaces of multiple second planar objects <NUM>.

Referring to <FIG>, the veneer sheets <NUM>, i.e. the pre-dried veneer sheets <NUM>, may be used to manufacture plywood <NUM>. For example, the pre-dried veneer sheets <NUM> may be further dried in an drier <NUM> using heat and gas circulation (i.e. wind). In this way, dry veneers <NUM> are obtained. Thereafter, adhesive <NUM> is arranged onto at least one side of at least some of the dry veneers <NUM>. Adhesive may be applied in an applicator <NUM>. Thereafter, a stack of dry veneers <NUM> and adhesive <NUM> is pressed, in a second press <NUM>, to form plywood <NUM>. The plywood <NUM> is typically thereafter finished, e.g. by sawing the edges and/or by coating the plywood <NUM>.

Several methods for manufacturing veneer <NUM> are known. Referring to <FIG>, veneer <NUM> suitable for plywood may be produced by a non-rotary method from a wood block <NUM>. Such methods include: a method for manufacturing crown cut veneer (<FIG>), half-round slicing (<FIG>), a method for manufacturing quarter cut veneer (<FIG>), rift-cutting (<FIG>), and lengthwise cutting (<FIG>). Referring to <FIG>, <FIG>, veneer <NUM> for plywood may be produced by a rotary method by using a veneer lathe <NUM>.

Referring to <FIG> and <FIG>, a veneer lathe <NUM> in general comprises a rotor <NUM> for rotating the wood block <NUM>. The rotor <NUM> may comprise a spindle <NUM> (or a pair of spindles <NUM>) for rotating the wood block <NUM> from an end of the wood block, as indicated in <FIG>. In the alternative, as indicated in <FIG>, the rotor <NUM> may comprise support rolls <NUM> configured to rotate the wood block <NUM> from such an outer surface of the wood block that has a normal parallel to the radial direction of the wood block <NUM>. A lathe without a spindle <NUM> may be referred to as a spindless lathe.

The veneer lathe <NUM> further comprises a knife <NUM> for peeling veneer <NUM> from the wood block <NUM>, and nose bar (<NUM>, <NUM>) configured to press the wood block <NUM>. The wood block <NUM> is configured to rotate about a first axis of rotation AX1. Typically the wood block is arranged in the lathe such that the grain orientation of the wood is parallel to the first axis of rotation. The spindle <NUM> (if present, or the pair of spindles <NUM>) is configured to rotate about the first axis of rotation AX1. In such a lathe <NUM>, an knife gap <NUM> is left in between the nose bar (<NUM>, <NUM>) and the knife <NUM>. As an alternative term for the knife gap, the term exit gap is sometimes used. In particular the knife <NUM> comprises an edge <NUM>, i.e. a cutting edge <NUM>, which is configured to peel the veneer <NUM> from the wood block <NUM>. The veneer <NUM> is configured to exit through the knife gap <NUM>.

Referring to <FIG>, and <FIG>, it has been found that veneer sheets <NUM> manufactured using a veneer lathe <NUM> having a roller nose bar <NUM> can be dried to a much greater extent by compression than veneers sheets <NUM> formed otherwise. Thus, an embodiment of a method for manufacturing veneers <NUM> comprises producing veneer <NUM> by peeling the wood block <NUM> with a veneer lathe <NUM> comprising a rotor <NUM> (such as a spindle <NUM> or a pair of spindles <NUM>) for rotating the wood block <NUM> and a roller nose bar <NUM> configured to press the wood block <NUM> and rotate. Moreover, an embodiment of an arrangement comprises a veneer lathe <NUM> comprising a rotor <NUM> for rotating the wood block and a roller nose bar <NUM> configured to press the wood block <NUM> and rotate.

As indicated in <FIG>, the in non-rotatory methods a nose bar is commonly not used. However, in the rotatory methods, a nose bar <NUM>, <NUM> is typically used. In contrast to a fixed nose bar <NUM> (see <FIG>), the roller nose bar <NUM> is configured to rotate. In particular, the roller nose bar <NUM> is configured to rotate in a manner independent of the knife <NUM>. In other words, the roller nose bar <NUM> is configured to rotate independently of the knife <NUM>. In other words, the roller nose bar <NUM> is configured to rotate with an angular velocity different from an angular velocity of the knife <NUM>.

Referring to <FIG>, when peeling the wood block <NUM>, the wood block <NUM> rotates about a first axis of rotation AX1 with a first peripheral velocity v1 and the roller nose bar <NUM> rotates about a second axis of rotation AX2 with a second peripheral velocity v2. The peripheral velocity (v1, v2) is, by definition, the radius of the object (wood block <NUM>, roller nose bar <NUM>) multiplied by an angular velocity of the object. During peeling a wood block, the wood block <NUM> and the roller nose bar <NUM> rotate such that the second peripheral velocity v2 is equal to the first peripheral velocity v1. However, when a wood block is not peeled, the roller nose bar <NUM> may rotate with a different peripheral velocity than the wood block. The lathe <NUM> may comprise first rotator <NUM> arranged to rotate the spindle <NUM>. Even if two first rotators <NUM> are shown in <FIG>, one first rotator <NUM> may suffice, and the other end of the wood block may rotate freely. The lathe <NUM> may comprise a second rotator <NUM> arranged to rotate the roller nose bar <NUM>. The second rotator <NUM> is arranged to rotate the roller nose bar <NUM> without rotating the knife <NUM>. Even if two second rotators <NUM> are shown in <FIG>, one second rotator may suffice, and the other end of the roller nose bar <NUM> may rotate freely.

A lathe <NUM> with a roller nose bar <NUM> produces a large piece of veneer <NUM>, whereby the veneer <NUM> is cut to veneer sheets <NUM>, as indicated above.

In order to dry at least a veneer sheet <NUM>, an embodiment of a method comprises arranging at least one of the veneer sheets <NUM> into a stack <NUM> of veneer sheets, and pressing the stack <NUM> of veneer sheets to dry the veneer sheets of the stack <NUM>. Correspondingly, an embodiment of an arrangement comprises a press <NUM> as detailed above.

<FIG> shows, as a first side view, a part of a stack <NUM> of veneer sheets <NUM><NUM>, <NUM><NUM>, <NUM><NUM> under compression. The pressure generating the compression is indicated by the symbol P. As indicated in <FIG>, aqueous fluid is squeezed out of the veneers 120i (i = <NUM>, <NUM>, <NUM>) mainly in the direction of the grains (i.e. Sx) of the veneers <NUM>.

<FIG> shows, as a second side view perpendicular to the first side view of <FIG>, a part of a stack <NUM> of veneer sheets <NUM><NUM>, <NUM><NUM>, <NUM><NUM> under compression. As indicated in <FIG>, the pressing surfaces (only one pressing surface <NUM> is shown in <FIG>) impose a pressure to the stack <NUM> of the veneer sheets <NUM><NUM>, <NUM><NUM>, <NUM><NUM>. In the pressing process, the total pressure P is controlled. As indicated in <FIG>, the pressure is not necessarily constant throughout the surface of the stack <NUM>. Thus, the local pressure Ploc(r) is a function of location r. In <FIG>, the local pressure P(r) and its magnitude is indicated by the vertical arrows. In mechanics, it is conventional to refer to stress when the question is about internal stress (i.e. pressure) and to refer to pressure when question is about external load (i.e. distributed force, i.e. pressure).

The total pressure P is related to the compressing force by F=P×A, wherein A is the area of that surface of the stack <NUM> that is pressed, and F is the force applied to the surface. Moreover, the total pressure P is an average of the local pressure Ploc(r). The unit of pressure in this field is conventionally bar or N/mm<NUM>, which equals to MPa (i.e. <NUM> N/mm<NUM> = <NUM> MPa = <NUM> bar).

As indicated in <FIG>, the veneer sheets <NUM> include imperfections. Imperfections include checks <NUM>, such as checks 112b that are open on top (i.e. open checks) and checks 112a that are closed on top (i.e. closed checks). Typically, the closed checks 112a are only closed when the stack <NUM> is formed, and optionally the stack <NUM> is also compressed. A single veneer, separated from a stack, typically comprises only or at least mainly open check 112b. As detailed below, in a measurement process, wherein colouring substance is used to colour the checks, the colouring substance penetrates into such open checks 112b. Imperfections further include valleys <NUM> in between elevations <NUM>. Checks <NUM> are commonly also referred to as cracks. In the stack <NUM>, the valleys <NUM> form stack cavities <NUM>. Despite of these imperfections, a part of a veneer <NUM> can be considered as integral wood substance <NUM>.

The total compressing force F is spread as the internal stress within the stack <NUM>. The internal stress of the stack includes stresses within the integral wood substance <NUM> (i.e. wood material without checks, i.e. cracks). Within the integral wood substance <NUM> the stress is distributed to stress of wood cell walls and stress (or pressure) in wood cell voids i.e. cell lumens. Inside the veneers <NUM>, the cell wall stress has to be sufficiently high to cause enough volume chance in wood substance and cause internal water pressure in cell lumens. Furthermore the internal stress of the stack includes stresses in the checks 112a and 112b. Furthermore some of the stress is distributed as pressures within veneer stack cavities <NUM>.

Compression drying has been found to be particularly efficient when there is enough difference between pressure within the cell voids (in the material <NUM>), pressure at the checks <NUM>, pressure at the veneer stack cavities <NUM>, and the ambient pressure. Preferably, the pressure within the cell voids (in the material <NUM>) is higher than the pressure at the checks <NUM>, which is higher than the pressure at the veneer stack cavity <NUM>, which is higher than the ambient pressure.

Compression drying has been found to be particularly efficient, when both checks <NUM> (in particular open checks 112b) and veneer stack cavities <NUM> are present. Even more preferably, in the stack <NUM> there is not much hydraulic resistance from middle parts of the veneer stack to vertical edges of the veneer stack. Some of those cavities become closed, when compression pressure is increased. Thus it is advantageous to use, as the drying pressure P, an pressure P of from <NUM> MPa to <NUM> MPa depending on the wood material and its density, to make sure that there is enough open cavities 112b.

It has been observed that especially by peeling using lathe <NUM> having a roller nose bar <NUM>, it is possible to obtain veneer and veneer stack structure consisting proper continuous cavities <NUM> to make efficient and fast compression drying possible. By peeling with a lathe having a roller nose bar it is possible to produce proper peeling checks <NUM>, enough variation in surface profile of the veneer, and the form of variation is such that continuous cavities are formed.

As for the variation in surface profile of veneer, <FIG> shows a veneer <NUM> manufactured using a lathe <NUM> with a roller nose bar <NUM>. The figure shows dark areas <NUM> and light areas <NUM>. The dark areas are the result of colouring the veneer <NUM> with a planar part of a crayon. Thus, the dark areas correspond to elevations <NUM> in the veneer <NUM>. Correspondingly, the light areas <NUM> correspond to valleys <NUM> in between the elevations <NUM>. In a direction Sy that is perpendicular to the thickness of the veneer and to the grain direction, an average distance (i.e. spacing) between the elevations <NUM> is typically from <NUM> to <NUM>. The roughness of the surface is measured as described in the standard ISO <NUM>:<NUM> using a measuring tip with a radius rtip of <NUM> and from a sampling length lri <NUM>. As indicated in the <FIG>, the sampling length and the direction in which the measurements are made is, in an embodiment, perpendicular to the grain direction. Moreover, in an embodiment, the greatest height of the roughness profile, Rz, as measured from a bottom of a deepest valley to a top of a highest elevation is from <NUM> to <NUM>. The depth Rv of a deepest valley, as measured from an average surface level of the surface of the veneer, was in the range of from <NUM> to <NUM>.

As an average roughness value, the roughness average Ra of a surface of the veneer <NUM> may be e.g. from <NUM> to <NUM>, or from <NUM> to <NUM>, when the roughness is measured as indicated in the standard ISO <NUM>:<NUM> along the direction Sy, as defined above from a sampling length lri of <NUM> and using a measuring tip having a radius rtip of <NUM>. At least such variations from the planarity of a surface of the veneer <NUM> seem to be sufficient from the point of view of compression drying. It is also noted that surface of veneer produced with a lathe having a fixed nose bar is typically much more even. Surface roughness of several such veneers were also measured, and the Ra surface roughness was only from <NUM> to <NUM> as measured with the same method and equipment. Reasons for this difference will be discussed below.

Moreover, wetting of such a veneer was studied by arranging an edge of the veneer <NUM> to a bath of coloured water. The edge had a surface normal parallel to a grain direction of the veneer. As indicated in <FIG>, the elevations <NUM> were not further coloured by the coloured water, indicating that water absorption in those regimes in small or negligible. However, as indicated by the reference numeral <NUM>, a lot of the coloured water was absorbed in the valleys <NUM>. Thus, it seems that the valleys <NUM> provide for channels for water to flow. It also seems that during compression, the aqueous solution is squeezed out of the veneer <NUM> at least through such valleys <NUM>. Thus, the presence of the valleys seems beneficial from the point of view of compression drying.

As indicated above, it seems that the peeling checks <NUM> provide for additional channels for the aqueous solution to flow during compression. To test this, first, two types of veneers <NUM> having different checks <NUM> were produced. As for characterizing the quality and/or amount of peeling checks <NUM>, the checks <NUM> were measured. <FIG> indicate measurement of properties of the checks <NUM>.

The amount and quality of peeling checks <NUM> from a veneer <NUM> or a veneer sample <NUM> is measured by applying textile colouring solution onto the veneer <NUM> (or veneer sheet <NUM> or veneer sample <NUM>), cutting an edge of the veneer <NUM>, <NUM> to expose the colouring of the checks of the veneer, and observing the cut edge. As the colouring solution, diluted colouring substance is used. In an embodiment, Dylon® Tulip Red is used as the colouring substance, even if also other colouring solutions, preferably water soluble colouring substances, could be used. However, the purpose of the colouring substance is only to make the check visual, whereby the any suitably dark textile colouring substance may be used. Textile colouring substances, when diluted, have sufficiently low viscosity for filling the checks <NUM>. The colouring solution is diluted as indicated below.

Referring to <FIG> the test is performed to test samples <NUM> of veneer <NUM> having a length LS of <NUM> and width WS of <NUM>, wherein the width WS of the sample is directed in the grain direction DG of the sample <NUM> of veneer <NUM>. Such a sample <NUM> may be cut from a veneer <NUM> or veneer sheet <NUM>, or the veneer <NUM> or the veneer sheet <NUM> may be otherwise of proper size.

The textile colouring substance is mixed with water in a ratio of <NUM> of colouring substance per <NUM> of water in order to form the colouring solution. Typically this amount is sufficient for colouring at least two test samples <NUM>.

An amount of <NUM> ± <NUM> of the colouring solution is spread onto the sample to form a <NUM> wide coloured stripe <NUM> extending throughout the whole length of the test sample <NUM> as indicated in <FIG>. A suitable dispenser and/or brush may be used for the purpose.

The sample <NUM> with the stripe <NUM> is let dry for an hour at room temperature (T = <NUM>) in regularly dry air (relative humidity approximately <NUM> %RH). The sample <NUM> is dried so that it feels dry. After drying the test sample <NUM>, the sample <NUM> is cut lengthwise in the middle of the aforementioned stripe <NUM>. A cutting line CL is shown as a dotted line in <FIG>.

The cut edge of the sample <NUM> is observed visually using a microscope. <FIG> illustrates a cut edge of the sample showing peeling checks <NUM>. <FIG> also shows the stripe <NUM> on a surface of the veneer sample <NUM>.

<FIG> illustrates measures of the peeling checks <NUM>. The figure indicates in detail four checks <NUM><NUM>, <NUM><NUM>, <NUM><NUM>, and <NUM><NUM>. For each check 112i, (i = <NUM>, <NUM>, <NUM>, or <NUM>) four parameters are measured:.

As for the measuring the angle Ci, the angle Ci is defined by inverse tangent of the ratio Wi/Bi, wherein Wi is the width of the check 112i in the planar direction of propagation of the check 112i, wherein the planar direction of propagation is a direction of the plane of the sample <NUM> and directed from the surface of the stripe <NUM> to an end of the check 112i in the cut edge (see <FIG>).

To test the effect of a roller nose bar <NUM> used in the veneer lathe <NUM> on the quality of the veneers <NUM> to be dried, veneers <NUM> were produced by [i] using a lathe <NUM> with a roller nose bar <NUM> (cf. <FIG>) and [ii] using a lathe <NUM> with a fixed nose bar <NUM> (cf. It is also noted that the non-rotatory methods shown in <FIG> typically produce veneer <NUM> with even less peeling checks <NUM>, since the veneer <NUM> in those methods need not to bend after peeling. Thus, for comparative purposes, a veneer that could be anticipated to have also a lot of checks <NUM>, was chosen.

Samples from ten veneer sheets <NUM> produced by using a lathe <NUM> with a roller nose bar <NUM> were produced; and the check dimensions were measured as indicated above. In addition samples from ten veneer sheets <NUM> produced by using a lathe <NUM> with a fixed nose bar <NUM> were produced; and the check dimensions were measured as indicated above. Referring to <FIG>, veneer <NUM> can be cut to veneer sheets <NUM>, whereby veneer <NUM> comprises multiple regions Rk, of which the regions R<NUM> and R<NUM> are shown in <FIG>. Even if not shown in the figures, the different regions correspond to parts of different veneer samples <NUM> (for their size, see above). However, multiple samples <NUM> may be formed from one veneer. Each sample k of Table <NUM> corresponds to a region Rk of veneer <NUM> (herein k = <NUM>, <NUM>, <NUM>,. The region may be a part of the aforementioned sample. In an embodiment, each region has a length of <NUM> in a direction that is perpendicular to the grain direction. Moreover, the regions do not overlap, i.e. comprise same points of the veneer.

The depth of the checks were measured as a proportional depth, i.e. as the ratio Bi/(Ai+Bi) for each check <NUM>i. In table <NUM>, the average of the proportional depth is denoted by <Bi/(Ai+Bi)>. The distance Di between a check 112i and a neighbouring check <NUM>i-<NUM> was also measured. Moreover, in some parts of this text, the distance is denoted by Di,k, wherein k denotes the number of the sample (i.e. region) from which the checks are measured. A practice, an average distance <Di> (or <Di>k) was determined by dividing the length of the observed part of the veneer <NUM>, <NUM>, <NUM> (typically <NUM>) by the number of checks within the observed part. In table <NUM>, the average of the distances Di is denoted by <Di>k, since the average distance <Di>k varies from sample to sample. The average (AVE), standard deviation (STD), minimum (MIN) and maximum (MAX) of the average distances <Di,k> are also shown in Table <NUM>. The veneers of Table <NUM> had a thickness of <NUM>.

As indicated in Table <NUM>, the average depth of the checks <NUM> is much greater when a lathe <NUM> with a roller nose bar <NUM> is used.

To test the effect of the checks <NUM> and/or the use a roller nose bar <NUM> on the drying by pressing the veneers, stacks <NUM> of veneer sheets <NUM> were pressed. Some primary stacks, wherein in the veneers were peeled using a lathe having a roller nose bar <NUM> were pressed. Moreover, some secondary stacks, wherein in the veneers were peeled using a lathe having a fixed nose bar <NUM> were pressed. In both cases, pressing was performed by first pressing the stack of veneer sheets with a pressure of <NUM> bar for <NUM>. Thereafter the stack of veneer sheets was pressed with a pressure of <NUM> bar for <NUM>. Finally, the stack of veneer sheets was pressed with a pressure of <NUM> bar for <NUM>. Such a pressure profile resembles a pressure profile that is anticipated to function well also in the production of plywood. The stack that was compressed comprised five or ten veneers. The results are shown in Table 2a for veneers peeled with a lathe having a roller nose bar; and in Table 2b for veneers peeled with a lathe having a fixed nose bar.

For the primary stacks, veneers were peeled with a veneer lathe comprising a roller nose bar <NUM> (see <FIG>). Typically, the moisture content (i.e. content of water in grams divided by dry mass in grams) was from <NUM> % to <NUM> %. On the average, the mass reduction of the veneers of the primary stacks during pressing was <NUM> %.

For comparison, veneers were peeled with a veneer lathe comprising a fixed nose bar <NUM> (see <FIG>). Typically, the moisture content (i.e. content of water in grams divided by dry mass in grams) was from <NUM> % to <NUM> %. On the average, the mass reduction of the veneers of the secondary stacks during pressing was <NUM> %.

Thus, already from these numbers it seems that compressive drying was much more efficient for the veneers manufactured with a lathe having a roller nose bar <NUM>.

In principle, some of the difference could be due to a different initial moisture content. However, the mass reduction of veneers having an initial moisture content of about <NUM> % was about <NUM> %, when a roller nose bar <NUM> was used. In contrast, the mass reduction of veneers having an initial moisture content of about <NUM> % was about <NUM> %, when a fixed nose bar <NUM> was used. This confirms that compressive drying was much more efficient for the veneers manufactured with a lathe having a roller nose bar <NUM>.

In terms of initial density, i.e. density before pressing the veneers, the density being indicative of moisture content, for veneers having the density from <NUM>/m<NUM> to <NUM>/m<NUM> and having been made using a lathe with a roller nose bar <NUM>, from <NUM> to <NUM> wt-% of aqueous liquid was squeezed out from the veneers. In contrast, for veneers having the density from <NUM>/m<NUM> to <NUM>/m<NUM> and having been made using a lathe with a fixed nose bar <NUM>, from <NUM> to <NUM> wt-% of aqueous liquid was squeezed out from the veneers.

The veneers of table <NUM> were made from spruce. Before compressing the stack <NUM>, the veneers <NUM> are wet, whereby their density is significantly higher than after drying. For example, when veneers <NUM> of spruce are dried, the density of at least some of the wet veneers <NUM>, before the compressive drying, may be in the range from <NUM>/m<NUM> to <NUM>/m<NUM>. The mass of the veneer <NUM> before compression is denoted by m1. When the veneers <NUM> of the stack <NUM> are compressed, aqueous liquid is squeezed out from the veneer <NUM>. Thus, the mass of the veneers <NUM> is reduced. The mass of the veneer <NUM> after compression is denoted by m2. In an embodiment, the stack <NUM> is pressed in such a way that the second mass m2 is at most <NUM> % or at most <NUM> % of the first mass m1.

As indicated in Table 2a, such values have been found applicable also to more than one veneer in the average. However, for the average value, the mass reduction may be slightly less. An embodiment comprises forming ten veneer sheets <NUM> from spruce (from one or more wood blocks <NUM>) with a veneer lathe <NUM> having a roller nose bar <NUM>; and arranging the veneer sheets <NUM> to a stack <NUM>. In the embodiment, such wet spruce is peeled that the average density of the ten veneers <NUM> before pressing the stack <NUM> is from <NUM>/m<NUM> to <NUM>/m<NUM>. A first total mass of the ten veneer sheets <NUM> before pressing is m1T. In the embodiment, the stack <NUM> is pressed in such a way that the ten veneer sheets <NUM>, after pressing, have a second total mass m2T, wherein the second total mass m2T is at most <NUM> %, at most <NUM> %, or at most <NUM> % of the first total mass m1T. It is noted, than in table 2a, for the primary stacks of five or ten veneers, this ratio ranges from <NUM> % to <NUM> %; while for the secondary stacks of five or ten veneers (table 2b), this ratio ranges from <NUM> % to <NUM> %.

These results indicate that pressing dries the veneer sheets that are peeled with a lathe comprising a roller nose bar <NUM> much better than the veneer sheets that are peeled with a lathe comprising a fixed nose bar <NUM>. As indicated above, it seems that this effect is at least partly due to the checks <NUM> and the valleys <NUM> of the veneers. Moreover, since the non-rotatory methods of <FIG> most likely produce even less checks <NUM> and valleys <NUM>, it seems that compression drying for such veneers would be even worse.

As seen from Table <NUM>, the check depth is greater in veneer <NUM> produced using a lathe with a roller nose bar <NUM>. It seems that the such deeper checks <NUM> provide for more fluid channels within the veneers to enable drying by compression. Consequently, as indicated above, veneers produced using a lathe having a roller nose bar <NUM> dried more than veneers produced using a lathe having a fixed nose bar <NUM>.

Moreover, even if the average distance between neighbouring checks was about <NUM> in both tests of Table <NUM>, it is noted that the standard deviation of the distances between neighbouring checks was smaller when the veneers were produced using a lathe having a roller nose bar <NUM>. For example, In table <NUM>, the standard deviation of the average distances <Di>k from ten samples was <NUM> when a fixed nose bar was used and <NUM> when a roller nose bar was used. Given that the average of the average distances <Di>k was <NUM>, when a roller nose bar was used, the standard deviation of the average distances was less than <NUM> %, and even less than <NUM> %, of the average of the average distances. The average of the averages may be denoted e.g. by <<Di>k>. A smaller deviation implies that the checks <NUM> are more evenly distributed in the veneer <NUM>. Therefore, drying by compression takes place in a more even manner in case the veneers are produced using a lathe having a roller nose bar <NUM>. This not only increases drying, but also makes the moisture content of the pre-dried veneers (i.e. veneer dried only by compression) more even. The final drying step (e.g. by hot air) is therefore easier to control in such a way that the veneers do not dry too much.

<FIG> shows the lathe <NUM> in a side view. The direction Sz refers to upward vertical direction. The directions Sx and Sy refer to horizontal directions. The directions Sx and Sz are perpendicular. The direction Sz is perpendicular to both Sx and Sy. The direction Sx is also used to denote a grain orientation of the veneer <NUM> or veneer sheet <NUM>, when the veneer <NUM> and/or the veneer sheets is/are oriented horizontally. Correspondingly, the direction Sx is parallel to the first axis of rotation AX1. Thus, when the veneer <NUM> and/or the veneer sheets is oriented horizontally, the direction Sy is perpendicular to the thickness of the veneer <NUM> and to the grain orientation. As indicated in <FIG> (and <FIG>), when a veneer lathe <NUM> is used, the wood block <NUM> surrounds the first axis of rotation AX1. Thus, the veneer <NUM> would naturally bend about the first axis of rotation AX1. However, in the lathe <NUM>, the veneer <NUM> is bent in the opposite direction. Because of this bending, checks <NUM> are formed into the veneer <NUM>. They are formed typically on the lower side of the veneer <NUM> as indicated in <FIG>.

The formation of checks <NUM> may also be somewhat dependent of other process details. Preferably, the wood block <NUM> is peeled such that the first peripheral velocity v1 is from <NUM>/min to <NUM>/min. As indicated above, during peeling, the second peripheral velocity v2 equals the first peripheral velocity v1. Typically, before peeling, i.e. when the wood block is rotated, but the knife is not used to form veneer, the second peripheral velocity is slightly more than the first peripheral velocity. At that time, the second peripheral velocity may be e.g. up to <NUM> % higher than the first peripheral velocity. It has been noticed, that peeling with a large peripheral velocity produced more peeling checks that peeling with a lower peripheral velocity. Thus, from the point of view of compressive drying, a peripheral velocity from the higher end is used. In an embodiment, the wood block <NUM> is peeled such that the first peripheral velocity v1 is from <NUM>/min to <NUM>/min; or from <NUM>/min to <NUM>/min.

Referring to <FIG>, in an embodiment, the lathe <NUM> comprises a first rotator <NUM> configured to rotate the wood block <NUM> (and the spindle <NUM>, if present) with such a first angular velocity that the peripheral velocity of the wood block is within the aforementioned limits. In an embodiment, the lathe <NUM> comprises a second rotator <NUM> configured to rotate the roller nose bar <NUM> with such a second angular velocity that the peripheral velocity of the roller nose bar is within the aforementioned limits. A diameter of a typical wood block is from <NUM> to <NUM>, and decreases during peeling. More precisely, a wood block is typically peeled until the diameter of the remaining wood block (i.e. core) is about <NUM>.

Typically, the peripheral velocity v1 is constant while peeling the wood block <NUM>. The peripheral velocity v1 may be e.g. constant and within the limits given above. Correspondingly, the angular velocity of the wood block (and spindle <NUM>, if present) increases during peeling. For a wood block having a diameter <NUM>, whereby the cutting edge <NUM> of the knife <NUM> is arranged <NUM> apart from the first axis of rotation AX1, the angular velocity of the wood block (and spindle, if present) may be e.g. from <NUM> rad/min to <NUM> rad/min, i.e. from <NUM> rpm to <NUM> rpm. Herein rpm stands for revolutions per minute, i.e. <NUM>×π radiands (rad) per minute. Considering the aforementioned minimum peripheral speed (<NUM>/min) for a large wood block (diameter <NUM>), a lower limit for the angular velocity is about <NUM> rpm. Considering the aforementioned maximum peripheral speed (<NUM>/min) for a small wood block (diameter <NUM>), an upper limit for the angular velocity is about <NUM> rpm. Thus, the rotor <NUM> may be configured to rotate the wood block <NUM> with an angular velocity of from <NUM> rad/min to <NUM> rad/min. It is also possible to have a constant angular velocity for the wood block, whereby the first peripheral velocity v1 would decrease while the radius of the wood block decreases during peeling.

In an embodiment, the first rotator <NUM> is configured to rotate the spindle <NUM> with an angular velocity of from <NUM> rad/min to <NUM> rad/min.

In an embodiment, a diameter d1 of the roller nose bar <NUM> is from <NUM> to <NUM>, such as from <NUM> to <NUM>. The roller nose bar <NUM> is configured to rotate about a second axis of rotation AX2, which is parallel to the first axis of rotation AX1. The roller nose bar <NUM> is configured to rotate with the same peripheral speed v2 as the wood block <NUM>. From the value given above, the roller nose bar <NUM> may be configured to rotate with an angular velocity of from <NUM> rpm to <NUM> rpm, such as from <NUM> rpm to <NUM> rpm (for a nose bar diameter of <NUM>).

<FIG> is a top view of the lathe of <FIG>, whereby most of the knife <NUM> remains behind the wood block <NUM> or the roller nose bar <NUM>. <FIG> is a bottom view of the lathe of <FIG>, whereby most of the roller nose bar <NUM> remains behind the knife <NUM>. The arrows in <FIG> indicate direction of rotation and the direction of the veneer as coming out from the lathe <NUM>.

<FIG> shows peeling a wood block <NUM> in more detail. Typically the lathe <NUM> comprises a pressure head <NUM>, which is configured to press the roller nose bar <NUM> against the wood block <NUM>. The knife gap <NUM> is left in between the cylindrical roller nose bar <NUM> and the knife <NUM>. In particular, the knife <NUM> comprises a first surface <NUM> that faces the roller nose bar <NUM>. The first surface <NUM> may be planar or comprise a planar part. The knife gap <NUM> is left in between [a] the first surface <NUM> or the planar part of the first surface <NUM> and [b] that part of the roller nose bar <NUM> of which tangent surface is parallel to the first surface <NUM> or the planar part thereof. The dotted lines of <FIG> indicate the direction of the planar first surface <NUM> and the aforementioned tangent surface of the roller nose bar <NUM>. As indicated in the figure, the width GW of the knife gap <NUM> is parallel to a normal of the first surface <NUM> or the planar part thereof. Thus, and also in a more general situation, the width GW of the gap is a minimum distance between the first surface <NUM> of the knife and the surface of the roller nose bar <NUM>.

It has been found that from the point of view of forming the valleys <NUM> and/or the checks <NUM>, the roller nose bar <NUM> should be pressed against the wood block <NUM>. Moreover, it has been found, that the mutual location of the roller nose bar <NUM> and the edge <NUM> of the knife <NUM> affect the formation of the valleys <NUM> and/or the checks <NUM> into the veneer. The edge <NUM> of the knife <NUM> refers to that edge of the knife that is configured to separate the veneer <NUM> from the wood block <NUM> (or the rest of the wood block <NUM>) as indicated in <FIG>. In an embodiment of the method or the arrangement, the edge <NUM> of the knife <NUM> is arranged at a height ΔH apart from a plane P1 comprising the first axis AX1 of rotation and the second axis AX2 of rotation. Moreover, the knife <NUM> is arranged such that it does not penetrate the plane P1.

Because the wood block <NUM> and the roller nose bar <NUM> takes up most space on the plane P1, most compression within the wood block <NUM> occurs at this plane P1. It seems that as the knife <NUM> (or the edge <NUM> thereof) peels the veneer <NUM> from the wood block, a crack starts to propagate from the edge of the knife more or less towards the plane P1. However, because of the compression formed by the roller nose bar <NUM> within the plane P1, the compressive pressure prevents the crack from propagating through the plane. The precise direction of the crack is determined, among other things, by the internal structure of wood, and is, therefore, somewhat random. Therefore, it seems the propagation of such a crack for only such distances forms the aforementioned valleys <NUM> and elevations <NUM> to the surface of the veneer <NUM>. This phenomenon can be controlled e.g. by the distance ΔH between the edge <NUM> of the knife <NUM> and the plane P1.

In an embodiment, the height ΔH is at least <NUM> % of a diameter d1 of the roller nose bar <NUM>. In an embodiment, a diameter d1 of the roller nose bar <NUM> is at least <NUM> and the height ΔH is at least <NUM>. In an embodiment, a diameter d1 of the roller nose bar <NUM> is at least <NUM> and the height ΔH is at least <NUM>.

In an embodiment, the height ΔH is at most <NUM> % of a diameter d1 of the roller nose bar <NUM>. In an embodiment, a diameter d1 of the roller nose bar <NUM> is at most <NUM> and the height ΔH is at most <NUM>. In an embodiment, a diameter d1 of the roller nose bar <NUM> is at most <NUM> and the height ΔH is at most <NUM>.

Referring still to <FIG>, in a preferable embodiment, the veneer <NUM> has space for being peeled from the wood block <NUM> in such a way that such a crack can propagate within the wood block. In order to facilitate the aforementioned crack propagation and to ensure proper surface roughness of the veneer <NUM>, in an embodiment, the width GW of the gap <NUM> if greater than the thickness t1 of the veneer <NUM>. The width GW has been defined above and indicated in <FIG>. The thickness t1 of the veneer <NUM> may be measured e.g. at least one meter away from the knife gap <NUM>. The thickness t1 of the veneer may be e.g. at least <NUM> % or at least <NUM> % less than the width GW of the knife gap <NUM>. As an absolute value, the width GW of the knife gap <NUM> may be e.g. less than <NUM> or less than <NUM>, such as less than <NUM>.

Unlike the non-rotatory methods for manufacturing veneer, a veneer lathe <NUM> produces large veneer pieces. Referring to <FIG>, after peeling the veneer <NUM> with a lathe <NUM>, the veneer <NUM> is transferred to a cutting apparatus <NUM>. The cutting apparatus <NUM> comprises a conveyor <NUM> and a blade <NUM>. The cutting apparatus is configured to cut the veneer <NUM> to veneer sheets <NUM> with the blade <NUM>. The conveyor <NUM> is used to transfer veneer <NUM> to the blade and veneer sheets <NUM> from the blade.

Referring to <FIG>, thereafter, at least one of the veneer sheets <NUM> is arranged into a stack <NUM> of veneer sheets. Moreover, the stack is arranged in between two pressing surfaces <NUM>, <NUM> of a press <NUM>. An embodiment of the method comprises arranging at least twenty or at least hundred veneer sheets to the stack <NUM> of veneer sheets and pressing the stack <NUM> to dry the veneer sheets. In an embodiment of the arrangement, the press <NUM> is configured to receive a stack <NUM> of at least twenty or at least hundred veneer sheets <NUM> in between the first surface <NUM> and the second surface <NUM>. Typically, the thickness of a veneer is from <NUM> to <NUM>. Therefore, in an embodiment, the first surface <NUM> is movable relative to the second surface <NUM> to such a position that the surfaces <NUM>, <NUM> are parallel, a surface normal of the first surface is directed towards the second surface, and a distance d<NUM> from the first surface <NUM> in the direction of the normal of the first surface to the second surface <NUM> is at least <NUM>; preferably at least <NUM>.

In an embodiment, also veneer sheets from another wood block or other wood blocks are arranged in the same stack <NUM> together with the veneer sheet <NUM> from the wood block <NUM>. In an embodiment, the stack <NUM> of veneer sheets is formed such that the stack <NUM> comprises only such veneer sheets that have been peeled from a wood block or wood blocks with a veneer lathe <NUM> comprising a roller nose bar <NUM> as detailed above.

By using the press <NUM>, the stack <NUM> is pressed with a pressure P to dry the veneers <NUM>. In an embodiment, the pressure P is at least <NUM> bar. The pressure refers to the compressing force F as divided by the area A of the stack's surface that is pressed. The pressure P need not to be constant temporally. As indicated above the pressure P is distributed as a local pressure Ploc(r), which needs not be constant spatially. In an embodiment, the pressure P is from <NUM> bar to <NUM> bar at least at some point of time. In an embodiment, the pressure P does not exceed <NUM> bar at any point of time.

In an embodiment, the stack <NUM> is pressed only for a period of time that is less than an hour or less than <NUM> minutes. This improves the process efficiency.

As a specific example, in an embodiment the stack is only pressed for <NUM> minutes such that.

These values of time and pressure have been found to be particularly suitable for softwood, such as spruce. In an embodiment of the method, the wood block <NUM> is a block of softwood, such as spruce. As is conventional, the term softwood refers to wood from coniferous trees, such as spruce, pine, fir, and hemlock. When softwood is pressed, in an embodiment according to the invention, the pressure P does not exceed <NUM> bar at any point of time. This has been found sufficient, in particular, when such veneer sheets <NUM> are pressed that they comprise a proper amount of proper checks <NUM> and/or proper valleys <NUM>, as discussed above.

Higher pressures may be needed for veneers of hardwood, such as birch. For example, in an embodiment, wherein hardwood is pre-dried by pressing,
the stack <NUM> of veneer sheets is pressed, at least at some point of time, with a pressure of at least <NUM> bar.

Referring to <FIG> and <FIG>, to realise such pressures, in an embodiment, the actuator arrangement <NUM> of the press <NUM> is configured to generate a pressure of at least <NUM> bar, more preferably at least <NUM> bar, and most preferably at least <NUM> bar, on a stack <NUM> of veneers arranged in between the first surface <NUM> and the second surface <NUM>. The actuator arrangement <NUM> may comprise e.g. four, five, six, nine, at least four, at least five, or at least nine hydraulic cylinders <NUM>.

Claim 1:
A method for manufacturing veneers (<NUM>), the method comprising
- receiving a wood block (<NUM>),
- producing veneer (<NUM>) by peeling the wood block (<NUM>) with a veneer lathe (<NUM>) comprising
• a rotor (<NUM>) for rotating the wood block (<NUM>),
• a knife (<NUM>) for peeling veneer (<NUM>) from the wood block (<NUM>), and
• a roller nose bar (<NUM>) configured to press the wood block (<NUM>) and rotate in a manner independent of the knife (<NUM>), wherein
• a knife gap (<NUM>) is left in between the roller nose bar (<NUM>) and the knife (<NUM>) and
• the veneer (<NUM>) is configured to exit through the knife gap (<NUM>),
characterized in that the method is further comprising
- cutting the veneer (<NUM>) to form veneer sheets (<NUM>) including heart wood veneer sheets and other veneer sheets,
- arranging at least one of the veneer sheets (<NUM>) into a stack (<NUM>) of veneer sheets, and
- pressing the stack (<NUM>) of veneer sheets with a pressure (P) to dry the veneer sheets of the stack (<NUM>) to obtain pre-dried veneer sheets (<NUM>), wherein
- the wood block (<NUM>) is a block of softwood,
- the pressure (P) is at least <NUM> bar, and
- the pressure (P) does not exceed <NUM> bar, the method comprising
- further drying the heart wood veneer sheets, which are not pre-dried, and the pre-dried veneer sheets (<NUM>) in a drier (<NUM>) using heat and gas circulation to obtain dry veneers (<NUM>).