ITVR20000085A1 - PROCESS AND EQUIPMENT FOR THE FINISHING OF A MANUFACTURE BY POWDER COATING - Google Patents

Abstract

The present invention relates to a facing process for at least one manufactured article (2) by means of powder coating comprising laying a first powder coating layer, fixing the first coating layer, laying a second powder coating layer having colour, tonality and/or organolectic properties different from the first coating layer, and final baking of the first and the second coating layers. After laying the second coating layer and before final baking, the process further comprises a relative displacement between the or each manufactured article (2) and a roller (34) having its lateral surface (36) in high- or bas-relief thereby producimg a desired decoration on the or each manufactured article (2), the roller 34 being held, in use, in contact with the or each manufactured article (2) to remove locally by rolling under control part of the second powder coating layer. <IMAGE>

Description

PROCEDURE AND EQUIPMENT FOR ENAMELING AN ARTIFACT BY POWDER PAINTING

DESCRIPTION

The present invention refers to a process for ennobling an article by means of powder coating and to an apparatus for its realization.

Currently, the ennobling process by powder coating finds a wide application in the decoration in imitation of the grain of a wood essence of metal profiles intended, in particular, for the realization of windows and doors.

The metal profiles, after being adequately prepared for painting, are subjected to a processing cycle, which involves the following operating phases: initially a first layer of powder paint or primer is deposited on the profile; then partial polymerization of the first layer of paint is envisaged; subsequently, a second layer of powder paint in a different color or tone than the underlying layer is applied according to a predetermined graphic configuration to conclude with the final firing designed to bring both the first and second layers of paint to total polymerization .

However, the painting process described above has drawbacks which drastically limit its industrial application, both in terms of large-scale production and the final cost of the finished product. The most critical phase of such a processing cycle is the application of the second layer of paint, i.e. the decorative layer, a task that is often entrusted to the experience and skill of qualified personnel capable of reproducing a particular graphic configuration, such as , for example, a fake grain, on any support in metallic or non-metallic material, working manually and with the help of traditional tools, such as, for example, brushes and paintbrushes.

From what has just been said it is easy to understand how it is not possible to carry out an industrial process that involves a completely manual execution operation, as the latter is an inevitable and economically unsustainable bottleneck capable of heavily slowing down the entire production cycle.

Attempts to transform the process of ennobling artifacts from purely manual to automated processing, if on the one hand they managed to speed up the production cycle, on the other hand, however, they proved unable to obtain a satisfactory qualitative result in terms of verisimilitude, therefore requiring continuous manual intervention by specialized personnel downstream of the processing cycle.

The main object of the present invention is to provide a process for ennobling manufactured articles by means of powder coating which is capable of eliminating or substantially reducing the aforementioned drawbacks relating to traditional painting techniques.

An important object of the present invention is that with the aforementioned process it is possible to obtain a faux wood varnish with a particularly high degree of likelihood and in a short time so as to be inserted within a completely automated processing cycle and not to require any intervention. manual by specialized personnel.

Another object of the present invention is that with the aforesaid process it is possible to carry out the faux wood painting of manufactured articles at an extremely competitive cost deriving both from the increase in the productivity of the entire plant and from the reduction of the costs of specialized labor.

Another object of the present invention is that the aforesaid process can be applied both in vertical and horizontal painting systems.

Not the least object of the present invention is to provide an apparatus for vertical faux wood painting capable of guaranteeing a production equivalent to normal single-color painting systems, while at the same time obtaining high quality graphic results in terms of of likelihood to a desired wood essence.

According to a first aspect of the present invention, a process is provided for the ennobling of at least one manufactured article by means of powder coating comprising the application of a first layer of powder paint, the fixing of said first layer of paint, the application of a second layer of paint in powder of different color, tonality or organoleptic properties with respect to said first layer of paint and the final firing of said first and said second layers of paint, said process being characterized by providing, after the application of said second layer of paint and before the final firing, to impose a relative displacement between the or each article and a roller having a lateral surface in bas-relief so as to reproduce on the or each article a desired decoration, said roller being, in use, kept in contact with the or each article. product for removing part of said second layer in a controlled and localized manner by rolling of powder paint.

Advantageously, said method provides for controlling said roller to make linear excursions along the longitudinal direction of the or of each product and to rotate around its own axis with a rotation speed corresponding to a peripheral rolling speed substantially equal to its linear displacement speed so as to obtain the rolling of said roller on or on each article.

Conveniently, said method provides for driving said roller to perform linear excursions along the longitudinal direction of the or each product and to rotate around its own axis with a rotation speed corresponding to a peripheral speed of said matrix lower than its linear displacement speed so as to obtain a rolling with sliding of said roller on or on each article.

A second aspect of the present invention relates to an apparatus for carrying out the aforesaid process, which apparatus comprises at least one conveyor means adapted to support the or each article and to transport it sequentially through the different work stations of a painting plant, said apparatus being characterized in that it comprises a support frame provided at a predetermined distance from or from each conveyor means, at least one slider element slidably mounted on said support frame so as to pass, on command, between one end and the other of the or of each product, at least one roller carried by a respective slider element and having a side surface in bas-relief which reproduces a desired original and is able to reproduce it, in use, on or on each article, said roller being able to pass between a position of work, in which it is in contact with the or each artifact from ennoble, and a rest position, in which it is set back with respect to the or each product, actuation means able to impart to said roller a controlled rotation around its own pin and means for supporting and moving the or each roller mounted movably on the respective element slider and adapted to move the respective roller between said rest position and said working position.

Advantageously, said support and movement means comprise at least one lever pivoted to the respective slider element and adapted to perform controlled angular excursions with respect to it and at least one linear actuator having one end articulated to the respective slider element and the other end articulated to the respective lever and adapted to control said controlled angular excursions of said lever to move the respective roller between said working position and said rest position.

Further aspects and advantages of the present invention will become clearer from the following detailed description of some of its currently preferred embodiment examples, given purely for illustrative and non-limiting purposes, with reference to the accompanying drawings, in which:

Figure 1 is a block diagram representing the sequence of the work stations of an imitation wood painting plant according to the invention;

Figure 2 shows a front elevation view of an apparatus according to the invention;

Figure 3 shows a side elevation view on an enlarged scale of the movable assembly of the apparatus of Figure 2;

Figure 4 is a sectional view of the movable unit, taken along the line IV-IV of Figure 3;

Figure 5 shows a plan view of a layer of elastically deformable material with a surface in bas-relief used as a matrix in the rolling process;

Figure 6 is a sectional view of the layer of Figure 5, taken along the line VI-VI;

Figure 7 illustrates a plan view of a second embodiment of the layer of Figure 5;

Figure 8 shows a sectional view of the layer of Figure 7, taken along the line VIII-VIII;

Figure 9 illustrates a perspective view of a portion of the finished product through the implant of Figure 1;

Figure 10 illustrates a schematic view on a reduced scale of the movable assembly of Figure 3 with roller and brushes in the working phase; Figure 11 shows a schematic view of the movable assembly of Figure 10 with roller and brushes at rest; And

Figure 12 is a schematic view of the mobile unit of Figure 10 with the roller at rest and the brushes in the working phase.

In the accompanying drawings identical or similar parts or components have been marked with the same reference numerals.

Referring first to Figure 1, a plant dedicated to the coating of imitation wood using powder paint according to the invention, represented with a block diagram and indicated with the reference number 1, can have a two-stage or three-stage processing cycle. stages according to whether two or three painting phases of the article 2 to be decorated are respectively provided.

The plant 1 sized to carry out a two-stage processing cycle preferably comprises a first painting center 3 for spreading a first layer of powder paint, a fixing center 4 arranged downstream of the first painting center 3 and suitable for carrying out the partial polymerization of the first layer of paint, a second painting center 5 for spreading a second layer of powder paint and a work station 6 suitable for carrying out the final firing of both the first and second layers of paint.

Advantageously, between the second painting center 5 and the final firing station 6 an apparatus 7 is provided, in correspondence with which the process of ennobling the article 2 takes place, which consists in subjecting the latter to a rolling treatment to obtain on the second layer of paint not yet fixed and uniformly distributed on the article 2, a design imitating the grain of a wood essence.

As shown in Figures 2, 3 and 4, the apparatus 7 is preferably composed of a frame 8 comprising a base 9, a pair of lateral uprights 10 and 12 rising from the base 9 and defining an intermediate processing area 13 which extends vertical, and an upper crosspiece 14 supported by the side uprights 10 and 12 and able to delimit the machining area 13 in height.

From Figure 2 it can be seen, in particular, how the processing area 13 of the apparatus 7 is crossed by an overhead conveyor 15 intended to support the product 2 in a vertical position and to transport it through the various work stations of the plant 1. Advantageously, the conveyor 15 is equidistant from the two lateral uprights 10 and 12 so as to force the product 2 to follow, in use, a trajectory coinciding with the center line x-x of the processing area 13.

The lateral uprights 10 and 12 are also equipped with vertical guides 16 and 17 facing the machining area 13, along which a respective mobile unit 18a and 18b is designed to slide between an upper dead center and a lower dead center so as to move respectively , in use, near the upper and lower ends of the article 2 in a vertical position.

As is better illustrated in Figure 3, the mobile unit 18a, like the mobile unit 18b, is preferably composed of a carriage 19 having a body 21 equipped with rollers or wheels 23 for rolling engagement with the respective vertical guide 17 and two extreme upper 24 and lower 25 portions integral with the body 21 and projecting therefrom towards the machining area 13.

A fork 27 comprising a pair of lateral shoulders 28 adapted to support, at their free ends, an oscillation pin 29 acting as an articulation element for a pair of levers 30 with respect to the carriage 19.

Each lever 30, which has a longitudinal end 31 rotatably constrained to the pivot 29 and the other longitudinal end 32 articulated to a shaft 33 with axis of rotation y-y supporting a roller 34, is controlled, in use, to perform excursions angular elements controlled around the oscillation pin 29 by means of a linear actuator 35 so as to move the roller 34 between a working position, in which its lateral surface 36 is in contact with the article 2 to be ennobled (see Figure 3), and a rest position, in which the roller 34 is set back with respect to the product 2 (as shown in Figure 2).

The linear actuator 35 can be constituted, for example, by a cylinder-piston assembly mounted on the carriage 19 with the cylinder 37 pivoted to the lower extreme portion 25 of the same and the free end 38 of the piston 39 articulated to the respective lever 30 in correspondence of a hinge pin 40 arranged at a predetermined distance from the pivot pin 29 of the lever 30 so as to transform, in use, the advancement and retraction of the piston 39 with respect to the cylinder 37, respectively, into a movement towards and away from the roller 34 to and from the product 2.

Advantageously, the roller 34 is constrained to rotate integrally with the shaft 33, which receives, in use, a rotation motion generated by a motor 44 and controlled by an encoder (not shown in the Figures) both arranged coaxial with the axis y-y.

At the longitudinal ends of the shaft 33 from the opposite side with respect to the roller 34 there are also fixed two arms 42 intended to support a horizontal pin 45, which in turn carries a plurality of suction means 49 suitable for removing the powder paint accumulated on the lateral surface 36 of roller 34 during the rolling treatment performed on the product 2.

As shown in Figure 3 and in particular in Figure 4, the suction means 49 comprise a series of suction openings 50 communicating with a suction duct 51 and suitable for removing the powder paint retained, during the rolling treatment, from the lateral surface. 36 of roller 34 and convey it through the suction duct 51 towards a suitable storage and disposal tank (not shown in the Figures).

The use of suction means 49 is essential for the purpose of an adequate cleaning of the lateral surface 36 of the roller 34, since the latter is advantageously worked in bas-relief according to the desired original that is intended to be reproduced on the surface 11 of the product to be ennobled. 2.

As shown in Figures 5 to 8, it is possible to apply on the lateral surface 36 of the roller 34 of an overlay layer 52 made of elastically deformable material having a working face 53 affected by a sequence of peaks 54 and depressions 56 specifically obtained on it based on the graphic result to be obtained on the artifact 2.

In fact, when it is desired to reproduce on the surface 11 of an article 2 to be ennobled a grain 55 in imitation of a wood essence, peaks 54 and depressions 56 extending irregularly substantially in the direction longitudinal of the overlay layer 52 (see Figures 5 and 6). Applied the overlay layer 52 as described above on the roller 34, during the rolling of the latter on the article 2 with a peripheral speed equal to that of the movement of the carriage 19, the work face 53 adheres with only the peaks 54 to the surface to be decorated 11, on which a uniform layer of powder paint has been previously deposited, thus removing the paint in a localized way, i.e. only in correspondence with the peaks 54 and faithfully reproducing on it the design shown on the work face 53.

Figures 7 and 8 instead illustrate an overlay layer 52 with working face 53 presenting a sequence of peaks 54 and depressions 56 in concentric semicircles, by means of which it is possible to obtain a distribution by rolling and sliding the roller 34 on the product 2 powder paint on the surface to be decorated 11 such as to reproduce a plurality of knots 57 in imitation of a wood essence (as shown in Figure 9).

Advantageously, both the movable groups 18a and 18b can comprise one or more brushes 22 fixedly mounted on the respective oscillation pin 29 integral in rotation with it and a motor 66 adapted to impose, on command, a desired position on the brushes 22 in order to make that they work, in use, with a correct inclination of their bristles sliding against the surface to be ennobled 11 of the article 2.

The operation of the apparatus 7 is illustrated in Figures 10 and 11, representing respectively the forward stroke of the carriage 19, during which the rolling and brushing operation of the surface to be decorated 11 is performed, and the return stroke, in which the carriage 19 has the roller 34 and the brushes 22 in rest position.

The forward stroke starts preferably when the carriage 19 is at the top dead center. Subsequently, the roller 34 is brought into contact with the surface 11 to be decorated by means of an angular excursion of the levers 30 controlled by the cylinder piston assembly 35 around the oscillation pin 29.

If it is intended to perform a rolling by rolling the roller 34 on the product 2, in combination with the linear movement downwards obtained by sliding the carriage 19 along the respective vertical guide 17, the motor 44 is commanded to impart, in use, to the roller 34 a rotational motion around its y-y axis such as to obtain a peripheral rolling speed at the point of contact between roller 34 and article 2 equal to the vertical translation speed of the carriage 19.

The rolling without sliding of the roller 34 on the article 2 causes the working face 53 of the overlay layer 52 to adhere without scratching to the face to be decorated 11 and that the powder paint, previously deposited uniformly on the surface to be decorated 11, is retained by the peaks 54, thus leaving an imprint faithfully reproducing the original design obtained on the working face 53.

On the other hand, to obtain a rolling with sliding of the roller 34 on the article 2 it is sufficient for the motor 44 to impart to the roller 34 a rotation around the y-y axis, which corresponds to a peripheral rolling speed lower than the vertical translation speed of the carriage 19. in this case, the imprint obtained on the face to be decorated 11 does not faithfully reproduce the original obtained on the working face 53 of the overlay layer 52, but rather a distorted effect thereof adapted to reproduce the nodes 57 of a desired wooden essence.

As highlighted in Figure 9, the equipment 7 is able to perform a faux wood varnish on a product 2 presenting both the veins 55 and the nodes 57 typical of a milled surface of a wood essence.

This result can be obtained by associating the rolling treatment obtained by means of the roller 34 with a brushing treatment by means of the fixed brushes 22 with bristles sliding, in use, against the surface to be decorated 11.

A two-stage processing plant 1 can provide for the execution of the brushing treatment at the same time as that of rolling, arranging, during the forward stroke of the carriage 19, the brushes 22 in contact with the surface to be decorated 11 with the roller 34 already in working position. When the carriage 19 has reached the bottom dead center, a control unit (not shown in the Figures) blocks the brushes 22 in an angular position indicated by an encoder (not shown in the Figures), in which their bristles do not interact. with the article 2 and to keep them in the aforementioned position during the entire return stroke of the carriage 19.

For the realization of the veins 55 on the surface 11 to be decorated, the apparatus 7 can be provided, instead of the brushes 22, with a comb (not shown in the Figures) mounted on each carriage 19 and integral with its alternating rectilinear movement. The aforesaid comb has a plurality of prongs made of flexible material distributed with a uniform or irregular pitch and having a pointed or flattened free end, which are able to slide, in use, against the article 2.

The powder coating process, the plant and the apparatus for its realization as described above are susceptible of numerous modifications and variations within the scope of protection defined by the content of the claims.

Thus, for example, as shown in Figure 1, the plant 1 can provide a three-stage painting processing cycle, the realization of which is made possible by interposing between the apparatus 7 described above and the final firing station 6 a fixing station 60 able to perform the partial polymerization of the second layer of paint just treated, a third painting center 61 for the application of a third layer of powder paint of different color, tonality and / or organoleptic properties compared to the underlying second layer and a second apparatus 7 for treating the third layer of paint that has just been deposited with an imitation wood.

In such a plant 1 it is therefore possible to obtain the veins 55 and the knots 57 in two separate phases and on two different paint layers, with the advantage of distinguishing one from the other by using paints of different colors or shades.

Preferably, the veins 55 are produced in the first apparatus 7 by means of a brushing treatment or by means of a rolling treatment without rubbing of the second layer of paint just deposited on the article 2.

To carry out the brushing treatment, the apparatus 7 has an arrangement like that of Figure 12, in which the roller 34 is moved away from the surface to be decorated 11 and the brushes 22 are commanded to move to the working position and to move in the vertical direction by means of the sliding of the carriage 19 along the respective guide 17 so as to slide against the surface to be decorated 11 and remove part of the second layer of paint to obtain on it a plurality of veins 55.

In the second case, on the other hand, the veins 55 are obtained by rolling the roller 34 on the manufactured article 2, on which a coating layer 52 of the type illustrated in Figure 5 is applied.

Once the second layer of paint thus worked has been fixed and the third layer of powder paint has been applied, the rolling treatment with sliding takes place in correspondence with the second equipment 7, for the realization of which a coating layer 52 is applied to the roller 34 of the type shown in Figure 7.

In practice, the materials as well as the dimensions can be various according to the requirements.

Claims (22)

CLAIMS 1. A process of ennobling at least one product by powder coating comprising the application of a first layer of powder paint, the fixing of said first layer of paint, the application of a second layer of powder paint of color, tone and / or having different organoleptic properties with respect to said first layer of paint and the final firing of said first and said second layers of paint, said process being characterized by providing, after the application of said second layer of paint and before the final firing , to impose a relative displacement between the or each article and a roller having a side surface at the top or a bas-relief so as to reproduce a desired decoration on the or each article, said roller being, in use, kept in contact with the or each article to remove in a controlled and localized way by rolling part of said second layer of powder paint. 2. Process according to claim 1, characterized by the fact of controlling said roller to perform linear excursions along the longitudinal direction of the or of each manufactured article and to rotate around its own axis with a rotation speed corresponding to a peripheral rolling speed substantially equal to its speed of linear displacement so as to obtain the rolling without sliding of said roller on or on each article. 3. Process according to claim 1, characterized by the fact of controlling said roller to perform linear excursions along the longitudinal direction of the or of each manufactured article and to rotate around its own axis with a rotation speed corresponding to a peripheral rolling speed lower than its rotation speed. linear displacement so as to obtain a rolling and sliding of said roller on or on each article. 4. Process according to any one of the preceding claims, characterized in that it provides for the application of said side surface at the top or bas-relief on said roller, which comprises a layer of elastically deformable material affected by a plurality of bas-reliefs delimiting a sequence of peaks and of depressions so as to interact, in use, with said second layer of paint and to remove it in a localized way from or from each manufactured article by means of said peaks. 5. Process according to any one of the preceding claims, characterized in that after the application of said second layer of paint and before said rolling treatment: - a brushing treatment of said second layer of paint by means of at least one brush with bristles sliding against said product; - fixing said second layer of paint; - the application of a third layer of powder paint having a different color, tonality and / or organoleptic properties than said second layer of paint, said third layer of paint being intended to undergo said rolling treatment. 6. Process according to any one of claims 1 to 4, characterized by providing, after the application of said second layer of paint: - a first rolling treatment by means of a roller with a side surface at the top or a bas-relief affected by a multiplicity of substantially parallel incisions or grooves so as to reproduce on said product a grain imitating a wood essence; - fixing said second layer of paint; - the application of a third layer of powder paint; - a second rolling treatment with sliding by means of a roller with a lateral surface affected by a plurality of concentric semicircles at the top or bas-relief capable of reproducing on or on each product a multiplicity of knots in imitation of a wood essence. 7. Plant for carrying out the process according to any one of the preceding claims, said plant comprising a first painting center for spreading a first layer of powder paint, a center for fixing said first layer of paint downstream of said first painting center, a second painting center for the spreading of a second layer of powder paint and a work station able to carry out the final firing of said first and said second layers of paint and being characterized in that it comprises, between said second painting center and said final firing station an apparatus suitable for performing a rolling and / or brushing treatment on the surface of the or each article so as to reproduce a desired decoration on them. 8. Plant according to claim 7, characterized in that it comprises in sequence between said apparatus and said final firing station a second fixing center suitable for carrying out the partial polymerization of said second layer of paint just treated by means of said apparatus, a third center coating suitable for spreading a third layer of powder paint of different color, tonality and / or organoleptic properties with respect to said second layer of paint and a second apparatus intended to perform a rolling and / or brushing treatment on said third layer of paint. 9. Apparatus belonging to the plant according to claim 7 or 8, which comprises at least one conveyor means adapted to support the or each manufactured article and to transport it sequentially through the different work stations of a painting plant, said apparatus being characterized in that it is comprising a support frame provided at a predetermined distance from or from each conveyor means, at least one slider element slidably mounted on said support frame so as to pass, on command, between one end and the other of the or each product, at least one roller carried by a respective slider element and having a side surface at the top or bas-relief which reproduces a desired original - and is adapted to reproduce it on or on each article, said roller being able to pass between a working position, in which it is in contact with the or each artifact to be ennobled, and a rest position, in which it is set back resp or to or to each product, actuation means suitable for imparting to said roller a controlled rotation around its own pin and means for supporting and moving the or each roller mounted movably on the respective slider element and adapted to move the respective roller between said position of rest and said work position. 10. Apparatus according to claim 9, characterized by the fact that said side surface at the top or bas-relief comprises a layer of elastically deformable material affected by a sequence of peaks and troughs delimiting a desired original to be reproduced on or on each product by removing controlled and localized by said peaks of a layer of powder paint deposited and not fixed on a surface to be decorated. 11. Apparatus according to claim 10, characterized by the fact that said layer of elastically deformable material is affected by a plurality of bas-reliefs extending, in use, in a circumferential direction so as to reproduce on or on each product a grain in imitation of a wood essence . 12. Apparatus according to claim 10, characterized in that said layer of elastically deformable material has a plurality of bas-reliefs with concentric semicircles capable of reproducing on or on each product by rolling with sliding a multiplicity of knots in imitation of a wood essence . 13. Apparatus according to any one of claims 8 to 12, characterized in that said support and movement means comprise at least one lever pivoted to the respective slider element and adapted to perform controlled angular excursions with respect thereto and at least one linear actuator having a one end articulated to the respective slider element and the other end articulated to the respective lever and adapted to control said controlled angular excursions of said lever to move the respective roller between said working position and said rest position. 14. Apparatus according to claim 13, characterized in that said linear actuator comprises a cylinder-piston assembly. 15. Apparatus according to any one of claims 9 to 14, characterized in that said frame comprises guide means for the or each slider element, which is provided with means for rolling engagement with the respective guide means. 16. Apparatus according to claim 15, characterized in that the or each slider element comprises a carriage. 17. Apparatus according to any one of claims 9 to 16, characterized in that it comprises at least one brush carried by the or each slider element and control and command means for the or each brush suitable for alternating a working phase, in which the or each brush crawls with its bristles against the or each article, at a rest phase, in which the or each brush is in a position that does not interact with the or each article to be ennobled. 18. Apparatus according to claim 17, characterized in that the or each brush is mounted on the respective slider element and commanded to move to the working position by rotating around a pin with a substantially horizontal axis and, in the rest phase, to arrange itself in a predefined angular position, in which its bristles do not interact with the or each artifact. 19. Apparatus according to claim 17 or 18, characterized in that the or each brush is interchangeable and in that it comprises means for supporting the or each brush on the respective slider element. 20. Apparatus according to any one of claims 17 to 19, characterized in that said control and command means comprise a motor adapted to impart to the respective brush a rotational motion around the respective pin and an encoder electrically connected to said motor and act to check the angular position of the or of each brush both in the working phase and in the resting phase. 21. Apparatus according to any one of claims from 9 to 20, characterized in that it comprises suction devices fixedly mounted on or on each slider element and able to be arranged, with the respective roller in the working position, in proximity to its lateral surface thus to remove the powder paint removed from the surface to be ennobled of the or each manufactured article by said roller and accumulated in correspondence with said side surface in bas-relief. 22. Product obtained by the process according to any one of claims 1 to 6, characterized in that it comprises a surface decorated with imitation wood in two or more colors having a plurality of veins extending in a substantially longitudinal direction and / or knots in imitation of a wood essence,