OA16275A - A method for joining at least two elements and an assembly. - Google Patents

Abstract

A method for joining at least two elements (1, 2), for example solid wood parts, the elements (1, 2) having at least partly mating contact surfaces that are to be connected to each other, wherein a curable adhesive (3) is applied to secure the contact surfaces to each other, wherein friction enhancing means (4) are applied between said contact surfaces for enhancing friction. Also, there is provided an assembly of at least two elements the elements (1, 2) having opposite contact surfaces, the contact surfaces being connected by an adhesive, wherein friction enhancing means are provided between the contact surfaces in addition to said adhesive.

Description

Nederlandse Organisatie voor Toegepastnatuurwetenschappelijk Onderzoek TNO

Title: A method for joining at least two éléments, and an assembly

The présent method relates to a method for joining at least two éléments, for example freshly eut (i.e. relatively wet) solid wood parts, the éléments having at least partly mating contact surfaces that are to be connected to each other, wherein a curable adhesive is applied to secure the contact surfaces to each other.

Such a method is commonly known from the prior art. For example, in a known method, wooden éléments are connected to each other using fînger joints. Such joints usually include opposite mating profiles, providing mating projections and cavities there-between, which are glued with respective contact surfaces to each other. Usually, during production, the éléments are pressed onto each other and transported to another processing station. The resulting connections are relatively strong and durable.

The pressing together of the éléments that are to be joined has the disadvantage that it usually requires the use of a dedicated pressure application system. However, the uncured glue as such can hâve a lubricating effect, such that the éléments slide apart in case pressure or clamping force is relieved too soon. Thus, the pressure will hâve to be maintained for a relatively long period of time before the joined éléments can safely be removed from the pressure application system.

As a resuit, the processing of large quantities of joints will require a relatively large amount of processing time of such a system. In some applications, speeding up the curing of glue can be achieved, for example under the influence of radiation (for example microwave or high frequency radiation) and/or heat, and depending on the type of adhesive. However, such treatment is not always possible, for example due to certain limitations relating to the éléments material, their dimensions and/or other factors, and/or due to a desired type of adhesive for connecting the éléments. In such cases, for example, relatively slow adhesive curing can be desired in order to achieve best bond properties.

US 3,888,715 discloses a process of bonding members with a thermosetting adhesive in a heat generating, dielectric, radio frequency field, providing faster cures. According to column 8 of the publication, discrète particles can be used in the heating pattern, wherein the particles also provide a porous and discontinuous deposit which does not interfère with bonding. Figure 24 of the publication shows boards 170, 171 to be joined by a finger joint 172, wherein a conductive field control pattern of parallel stripes 173 is placed on the surface of one of the finger joints.

US2006/0060296 relates to conductive adhesive bonding. In the bonding process, surfaces are coated with adhesive that is filled with conductive metallic particles, pressed together and an electric current is passed between them to momentarily melt conductive particles. The molten drop le ts aggloméra te and wet the facing surfaces. When the molten clusters re-solidify, electrically conductive paths are formed between the workpieces.

US 6,146,488 relates to a weld bonding method.

The présent invention aims to solve or at least alleviate the problème of the known methods. Particularly, the invention aims to provide an improved method for joining éléments, wherein a durable joint can be obtained in an efficient manner. More particularly, it is desired to provide a method, wherein éléments can be joined without having to provide for long pressure application times, and for example allowing relatively long curing periods.

To this aim, advantageously, the method according to the invention is char acte rised by the features of claim 1.

According to an aspect of the invention, friction enhancing means are applied between said contact surfaces for enhancing friction, wherein the friction enhancing means include locking éléments, wherein at least some of the locking éléments are forced into at least one contact surface by pressing the contact surfaces together.

As a resuit, the éléments, that are to be joined, can simply be held in a joined position using friction enhancing means enhancing friction between / the contact surfaces (for example by locking the éléments to each other at/along the contact surfaces, and before curing of the adhesive). The friction enhancing means can act as slide prévention means, preventing the joined éléments sliding away from each other (before the adhesive has been cured). For example, a clamping force or pressure for joining the éléments can be released swiftly, when the éléments are held in said joined position. Particularly, the friction enhancing means are used to assist the curable adhesive in connecting the éléments together.

For example, in a further élaboration ofthe invention, the friction enhancing means can lock the two éléments when they have been joined with each other (with respective contact surfaces being in suitable connecting positions). In that case, the friction enhancing means are locking means. The locking allows curing of the adhesive without having to apply external pressure onto the éléments during a (subséquent) curing period. Thus, the curing of the adhesive (having been applied to the éléments) can be carried out at another location than a location where the éléments are initially joined to each other. As a resuit, a prolonged use of a pressure application System pressing the parts together can be avoided. Also, as a resuit, relatively long curing periods can be used, for example allowing the adhesive to cure in a natural manner without application of external pressure and/or curing radiation treatment.

It has particularly been found that application of locking éléments, at Ieast some of the locking éléments being forced into the contact surfaces, provides a very reliable anchoring of the éléments that are to be joined, before the adhesive has developed handling strength. Also, it has been found that such locking éléments can be broadly applied, with many different types of adhesive and many different types of éléments and element materials. In fact, locking éléments can be selected such that they do not change or reduce desired mechanical and chemical properties ofthe adhesive that is to be used.

In a further embodiment, said locking éléments can be rigid (and for example massive) locking éléments.

In a preferred embodiment, the locking éléments are applied after the adhesive has been applied to one or both of the contact surfaces. Thus, the locking éléments and the adhesive can be supplied separately from each other (without being mixed prior to application). This provides significant advantages regarding supply and storage of these components (avoiding mixing related ségrégation problème), and regarding the adhesive application process (an adhesive applicator does not hâve to be specifically adapted for handling application of the locking éléments).

The friction enhancing means can hâve various configurations. According to a further embodiment, for example, the friction enhancing means can be friction enhancing éléments, enhancing friction between abutting surfaces of the éléments to be joined (preventing the surfaces sliding apart from one another), preferably by reaching at least partly into at least one contact surface, for example into both contact surfaces. The friction enhancing means can also be configured différéntly, for example by including a second adhesive (i.e. a secondary adhesive) which cures before curing the curable (primary) adhesive

Also, an aspect of the invention provides an assembly of at least two éléments, for example provided by a method according to the invention. Advantageously, the éléments hâve opposite contact surfaces, wherein a layer of friction enhancing means reaches into at least one of the contact surfaces. Thus, above-mentioned advantages can be provided.

Further advantageous embodiments of the invention are described in the dépendent claims. These and other aspects of the invention will be apparent from and elucidated with reference to non-limiting embodiments described hereafter, shown in the drawings.

Figure 1 depicts a plan view of an assembly of joined éléments according to a non-limiting embodiment of the invention; /

Figure 2 depicts a cross-section over line II-II of Fig. 1;

Figure 3 depicts a detail Q of Fig. 2;

Figure 4 schematicaily shows an apparatus for pressing parts together;

Figure 5 is similar to Fig. 3, depicting part of a second embodiment; and

Figure 6 is similar to Fig. 3, depicting part of a third embodiment.

Similar or corresponding features are dénotéd by similar or corresponding reference signs in this application.

Figures 1-3 depict a non-limiting first embodiment of an assembly K of, in this case, two éléments 1, 2 that hâve been connected to each other along opposite contact surfaces la, 2a. Particularly, adhesive 3 has been applied between the contact surfaces (serving as bonding surfaces) to hold the éléments 1, 2 together after curing. According to a further embodiment (not depicted), the element K can be made of more than two parts, wherein ail the parts are joined via respective glue layers between respective contact surfaces.

Each of the éléments 1, 2 as such can hâve various shapes and dimensions, as will be appreciated by the skilled person. Also, the éléments 1, 2 can hâve the same dimensions, or they can hâve mutually different dimensions. For example, the éléments 1, 2 can be solid, massive éléments, for example having closed (for example smooth) contact surfaces facing each other.

In the présent embodiment, the éléments 1, 2 are beams, plates or sheets 1, 2, which form a composite rectangular element K (having a thickness measured in a Z-direction that is relatively small compared to dimensions measured in other orthogonal directions X, Y). The éléments 1, 2 can also be dimensioned differently. The composite element K can hâve various shapes, for example straight, curved, rectangular (as in Fig. 1), square, convex, concave, elongated, beam- or rodlike, and a combination of these and/or other shapes, as will be appreciated by the skilled person. /

A resulting structure K can be used in an advantageous manner in/as construction element. The assembly (i.e. a composite element) K can comprise or be used to provide, for instance, plate material, a wall, laminate, a sandwich construction, a construction block, a construction beam, a door, a window, a window casings, ceiling parts, board, a floor part, a roof box and/or the like.

For example, the assembly K can be relatively large, made of relatively large massive components 1, 2 (this contrary to, for example, composites that are made of fiber reinforced of wood chips material). As a nonlimiting example, each of éléments 1, 2 can hâve a length, measured along a first orthogonal direction X, of at least 1 cm, particularly at least 10 cm, for example 0.5 me ter or more. Also, each of the éléments 1, 2 can hâve a width, measured along a second orthogonal direction Y, of at least 1 cm, particularly at least 10 cm, for example 0.5 meter or more. A thickness measured along a third orthogonal direction Z, of each element 1, 2 can be at least circa 1 mm, for example at least 1 cm, or a different thickness.

Various types of adhesive 3 can be applied. Depending on the éléments used, good results can be obtained with adhesive that is or contains a curable epoxy resin, and alternatively with adhesive that is or contains a curable polyuréthane adhesive. Also, for example, the adhesive can be of a phénol formaldéhyde type, or a resorcinol formaldéhyde, or a phenolresorcinol formaldéhyde type. Other examples of suîtable adhesives are or include: ureum formaldéhyde, melamine, melamine formaldéhyde, melamine ureum formaldéhyde, melamine ureum phénol formaldéhyde, isocyanate (PDMI), ethylene vinyl acetate (EVA), polyvinylacetate (PVAc), acrylate, cyanoacrylate, methy le méthacrylate, silicones, and Modified Silane or Modified Silyl polymers.

Each of the éléments 1, 2 can be made of various materials. The éléments 1, 2 can be made of the same material, but that is not essential. Good results hâve been achieved in case each element 1, 2 is made of wood (i.e. each element is a lignocellulosic part). According to a further embodiment, each of / the parts 1, 2 is made of hardwood, for example having a dry wood density of at least 800 kg/m³ or having a different (lower) dry wood density.

Also, good results hâve been achieved when the éléments 1, 2 are relatively wet wooden parts, for example freshly eut hardwood (i.e. lignocellulosic éléments having a dry wood density of at least 800 kg/m³ and having a water content of for example 25 w% or more). In case of joining wet (for example wooden) éléments 1, 2, preferably, an adhesive 3 is used that can cure and connect such éléments 1, 2, for example (but not limited to) a curable epoxy resin glue 3, and altematively with a curable polyuréthane adhesive 3.

Altematively, one or both parts 1, 2 can be (a) plastic, fibre reinforced plastic, métal, rubber, concrète, stone, brick, or ceramics part(s). Other materials can be applied as well.

The mating contact surfaces of the éléments 1, 2 can hâve various configurations, as will be clear to the skilled person. The contact surfaces can be fully mating (as in Fig 1), or partly mating (for example in case voids are présent between the surfaces, after having joined the two éléments 1,2).

In the présent example, the mating contact surfaces are provided by mating projections (i.e. convex parts) and cavities (i.e. concave parts) of the opposite sides of the éléments 1, 2. In this example, each of the éléments 1, 2 includes a plurality of such projections and cavities, at least partly engaging each other when the éléments 1, 2 hâve been joined. Altematively, a single projection and mating cavity can be provided to defîne a single mating contact surface between the two éléments 1, 2 that are to be joined.

More particularly, in the présent example, the mating projections and cavities of the éléments 1, 2 define a fînger joint structure, in this case having tapered contact surfaces (with V-shaped cross-sections, as follows from Fig. 1). Each contact surface can also be shaped différéntly, for example substantially conical, frusco-conical, wedge-shaped, U-shaped (in crosssection), cup-cone shaped, a combination of such shapes and/or différéntly shaped. /

Figure 4 depicts a non-limiting example of a (preferably automated) positioning System 20 that is configured to hold or support the éléments 1, 2, and to press the éléments 1, 2 with the contact surfaces towards each other, for joining the éléments 1, 2. For example, the System 20 can include two supports 21, 22 to hold the parts 1, 2, wherein the System 20 can move the supports 21, 22 towards each other and away from each other. The System 20 can include a glue application device that is configured to apply the curable adhesive 3 (usually being in a liquid -i.e. wet- state before curing) to one or both of the bonding surfaces la, 2a, before the surfaces la, 2a are moved towards each other. The applied adhesive can be pressed and spread between the contact surfaces la, 2a when the éléments 1, 2 arejoined by the System 20, thereby forming a relatively thin curable bonding layer for bonding the surfaces la, 2a.

According to a preferred embodiment, the éléments 1, 2 are joined by a method (for example using the System 20 shown in Fig. 4), wherein the curable adhesive 3 is applied between the respective contact surfaces to secure the contact surfaces la, 2a to each other, wherein friction enhancing means 4 are applied between said contact surfaces as well, for enhancing friction after application (and during curing) of the adhesive 3. Examples of embodiments of such friction enhancing means 4 are shown in the detail of Fig. 3.

The friction enhancing means 4 (which differ from the adhesive, i.e. are not the curable adhesive 3) can hâve various configurations. Good results hâve been achieved by friction enhancing means 4 that provide a clamping or locking engagement between the éléments 1, 2, at the contact surfaces la, 2a, thereby holding the éléments 1, 2 together at the opposite contact surfaces (and preventing the surfaces to slide away from each other). Thus, any subséquent application of external pressure to hold the éléments 1, 2 together during curing of the adhesive can be reduced or avoided. As a resuit, the éléments 1, 2 can be transported to another location (for example away from a joining/pressing system 20), to be processed further. Various subséquent >

processing steps can be carried out, for example (but not limited to) a curing and/or drying step, coating, imprégnation, cutting, sawing, and the-like.

In the présent first embodiment, rigid, massive, friction enhancing means 4 are applied between the contact surfaces la, 2a for mechanically locking the main éléments 1, 2 to each other (the respective friction enhancing means can then be called ‘locking means’ or ‘blocking means’). For example, the friction enhancing means can include relatively small rigid locking éléments 4, for example rigid particles, beads. Particularly, at least one of the contact surfaces la, 2a can be provided with a layer of a plurality of such friction enhancing mean 4, to lock the éléments 1, 2 to each other during a pressing step. The rigid locking éléments 4 can remain rigid during the joining ofthe éléments 1, 2, i.e. during pressing the éléments 1, 2 with their contact surfaces towards each other (and during curing of the adhesive).

The rigid locking éléments 4 can be made of various materials, for example rigid lignocellulosic material, for example hardwood material, métal, alloy, stone or stone-like material, for example sand, or any combination of such materials. Preferably, when the éléments 1, 2 are both lignocellulosic éléments, lignocellulosic locking éléments 4 are used. One or more ofthe rigid locking éléments 4 can be electrically and/or thermally conducting éléments. Also, one or more of the rigid locking éléments 4 can be electrically insulating éléments.

Each ofthe friction enhancing locking éléments 4 can hâve various shapes, for example regularly and/or irregularly, as follows from Fig. 3. Locking éléments 4 can be applied that ail hâve the same shape, and the same dimensions. Also, mutually different locking éléments 4 can be used, for example having different shapes and/or different dimensions.

The locking éléments 4 can be relatively small, compared to the dimensions of the éléments 1, 2. For example, each locking element 4 can hâve a crosS'Section measured in parallel with the respective contact surfaces la, 2a that is at least ten times smaller than the surface area of the respective / ίο contact surfaces la, 2a, for example at least fifty times smaller than the surface area of the respective contact surfaces la, 2a.

Alternatively, for example, each locking element 4 can hâve a crosssection measured in parallel with the respective contact surfaces la, 2a that is in the range of about half the surface area of the respective contact surfaces la, 2a to a tenth of that surface area.

Also, for example, in a non-limiting embodîment, a maximum size of each of the locking éléments 4 can be 1 mm, particularly 0.5 mm.

Alternatively, a maximum size of each of the locking éléments 4 can be larger than 1 mm, for example about 4 mm or larger.

Besides, for example, a minimum size of each of the friction enhancing éléments can be 0.1 mm, for example about 0.4 mm, or smaller than 0.1 mm, for example a minimum size of 0.01 mm.

In a further preferred embodîment, the rigid locking éléments 4 can hâve a hardness that is higher than the hardness of at least one (for example each) of the two éléments 1, 2 (at least at a respective contact surface of the element 1, 2). For example, a différence in hardness between a locking element’s hardness and the hardness of a main element 1, 2 can be at least one, measured on the hardness scale of Mohs (commonly known).

Alternatively, the rigid locking éléments 4 can hâve a hardness that is about the same as the hardness of at least one (for example each) of the two éléments 1, 2 (at least at a respective contact surface of the element 1,2).

As follows from Fig. 3, according to an embodîment, at least some of the locking éléments 4 may in dent at least one (for example both) of the two éléments 1, 2 at respective contact surfaces, to be at least partly embedded in the element(s) 1, 2. As a resuit, a fîrm mechanical locking can be achieved.

The locking may be achieved by application of the locking éléments 4 between the main éléments 1, 2, and by bringing the éléments 1, 2 towards each other in a first direction R (such as in Fig 4). In that case, the éléments 1, may be positioned such that their contact surfaces extend substantially in at / least one second direction that differs from said first direction R (for example a second direction that includes an angle with said first direction R, for example but not limited to an angle in the range of 10 to 80 degrees). In an alternative embodiment, during movement of the éléments 1, 2 towards each other, the éléments 1, 2 may be positioned such that their contact surfaces extend at least partly in said first direction R.

At least some of the hard, rigid locking éléments 4 can be forced (for example substantîally normally) into both contact surfaces la, 2a of the éléments 1, 2 by pressing the surfaces together. Fig. 3 shows an example of a resulting product, the hard locking éléments 4 having been pressed into both contact surfaces la, 2a, and showing a glue line of adhesive 3 between the éléments (the adhesive providing a final connecting force after curing). Since the locking éléments 4 are harder than the éléments 1, 2 at their contact surfaces, the locking éléments 4 (of the présent example) as such hâve not, or substantîally not, been deformed during the pressing step. This contrary to the two locally indented contact surfaces la, 2a. In the example, locking éléments 4 can partly reach into each of the éléments 1, 2 (without entirely penetrating the element), see Fig. 3. Thus, from the drawing it follows that the présent éléments 4 are thicker than the adhesive’s glue line thickness. Also or alternatively, one or more of the éléments 4 can hâve other dimensions, for example one or more éléments 4 having a thickness that is about the same as or smaller than the adhesive’s glue line thickness.

In a further embodiment, at least some of the hard rigid locking éléments 4 can deform during the pressing step. In that case, still, deformed rigid locking éléments can reach into at least one of the contact surfaces la, lb for locking the éléments 1, 2.

In one embodiment, the locking éléments 4 are applied simultaneously with application of the adhesive 3. For example, the locking éléments 4 can be mixed in the curable adhesive 3 before the adhesive is being applied. Alternatively, for example, the curable adhesive 3 can be applied to at least one contact surface la, 2a of the main éléments 1,2, after which the friction enhancing éléments 4 are applied (for example to the adhesive 3).

Also, for example, a bonding medium can be used to bond the locking éléments 4 to at least one of the contact surfaces la, 2a. Said curable adhesive 3 can be the bonding medium. Alternatively, a dedicated bonding medium can be applied, different from the curable adhesive 3.

Example

An experiment was carried out, wherein two hardwood éléments 1,

2, having a configuration as shown in Fig. 1, 2 were fïnger jointed to each other by a method according to the invention. A curable epoxide glue was applied, wetting the contact surfaces la, 2a, for bonding the éléments 1, 2 to each other. Also, in experiments, a polyuréthane glue was used. Locking éléments 4, consisting of small ground hardwood parts, had been applied to the glue as well. In the experiment, a minimum dimension of the parts was 0.4 mm, and a maximum dimension 1 mm.

After application of the glue and the hardwood parts, the éléments 1, 2 were pressed onto each other (as in Fig. 4). It has been found that as a resuit, the éléments 1, 2 were locked together, and could be jointly transported to another location, before the glue was allowed to develop handling strength. Also, after further inspection of a bonding line between the éléments, it was found that the hardwood parts had been pressed into each of the two wooden éléments, leading to the locking effect.

The présent invention is not limited to application of rigid, hard locking éléments. According to an alternative embodiment, the friction enhancing means can include résilient locking éléments 104, for example elastic particles. This is shown in Figure 5. The résilient locking éléments 104 can be used instead of the above-mentioned locking éléments 4 (or in addition there-to), and can provide an internai clamping force between the two M éléments 1, 2 when they are pressed together. For example, when the éléments

1, 2 are both lignocellulosic éléments, résilient lignocellulosic éléments 4 can be used, for example éléments made of softwood.

Also, in an alternative embodiment, the friction enhancing means can include adhesive dispersing éléments, for example breakable adhesive containing éléments, for locally dispersing a second adhesive between the éléments 1, 2 when they are pressed onto each other. The second adhesive has a different composition than a composition ofthe (main) curable adhesive 3. The second adhesive can be configured to cure (and to locally connect the two éléments 1, 2 to each other) before curing the curable adhesive 3. Such adhesive dispersing/containing éléments can be used instead ofthe abovementioned locking éléments 4, or in addition there-to. For example, in a nonlimiting embodiment, the second adhesive can be configured to cure within about one to five minutes or faster, for example within 10 seconds (such as one to five seconds).

The second adhesive can achieve a first (relatively) connecting force to hold the éléments 1, 2 together, after which the main adhesive 3 can be cured to provide a final connecting force (being significantly higher than the first connecting force).

Figure 6 shows a further alternative embodiment, which differs from the above-mentioned examples in that the friction enhancing means includes a second adhesive 204 which may cure (and locally connect the two éléments 1, 2 to each other) before curing the curable adhesive 3, at Ieast part of the second adhesive being applied at a different location between the surfaces than the curable adhesive 3.

The présent invention provides various advantages, such as achieving improved bonding of the éléments, strong and reliable bonds, and higher throughput of a System 20 for pressing the éléments together.

Moreover, the invention is well suited for interconnecting hardwood éléments, using a suitable adhesive, wherein the friction enhancing means can prevent slipping the éléments from each other after the adhesive has been applied there-between. Optionally, the friction enhancing means 4, 104, 204 as such may serve as spacer means as well, for holding the opposite bonding surfaces la, 2a of the éléments 1, 2 at a certain (small) glue line receiving space from each other.

It is to be understood that in the présent application, the term comprising does not exclude other éléments or steps. Also, each of the terms a and an does not exclude a plurality. Any reference sign(s) in the claims shall not be construed as limiting the scope of the claims.

For example, according to a further embodiment, one or both éléments can be made of a métal or alloy.

Besides, according to a further embodiment, each element can be made of a magnetically attractable material. In that case, good results are expected by application of friction enhancing means that are configured to enhance friction using magne tic force (for example friction enhancing means consisting of or including magne tic parts).

Also, the method can include connecting two parts to form a composite element K, or more than two parts. In case the element K, to be manufactured, contains more than two parts, for example, the method can include joining the parts when they are ail moist, wherein spaced-apart bonding surfaces are provided between ail the parts, to be connected using a respective glue layer. Besides, a method for joining a plurality of parts can involve a sequence of gluing two parts to provide a composite element, and subsequently gluing a further part to the resulting composite element, until a desired number of parts has been joined together.

Besides, the pressing together of the éléments 1, 2 can be achieved în various ways, for example by a System 20 that is specifically adapted to apply such a pressure, or in a different manner, for example by manual pressure. s- T4 DEC 2012

Claims (11)

Claims

1. A method for joining at least two éléments (1, 2), for example solid wood parts, the éléments (1, 2) having at least partly mating contact surfaces that are to be connected to each other, wherein a curable adhesive (3) is applied to secure the contact surfaces to each other, wherein friction enhancing means (4) are applied between said contact surfaces for enhancing friction, wherein the friction enhancing means include locking éléments (4), wherein at least some of the locking éléments (4) are forced into at least one contact surface by pressing the contact surfaces together.

2) to each other and before the curable adhesive (3) has been cured, wherein the éléments (1, 2) are subjected to at least one treatment step, for example a curing and/or drying step, at the second location.

2. The method according to claim 1, wherein the friction enhancing means include rigid particles.

3. The method according to any of the preceding claims, wherein the friction enhancing means hold the éléments (1, 2) in a joined position, and act as slide prévention means, preventing the joined éléments (1, 2) sliding away from each other before the adhesive has been cured.

4. The method according to any of the preceding claims, wherein the curable adhesive (3) is applied before the friction enhancing means (4) are applied.

5 a method according to any of the preceding claims, the éléments (1, 2) having opposite contact surfaces, the contact surfaces being connected by an adhesive, wherein locking éléments (4) are provided between the contact surfaces in addition to said adhesive, wherein at least some of the locking éléments (4) reach into at least one of the contact surfaces, and preferably into both contact 10 surfaces.

27. An assembly according to claim 26, wherein a maximum size of each ofthe locking éléments (4) is 4 mm, particularly 1 mm, wherein a minimum size of each of the locking éléments (4) is 0.1 mm, for example about 0.4 mm. /

5. The method according to any of the preceding claims, wherein the friction enhancing means include adhesive dispersing éléments, locally dispersing a second adhesive which cures before curing the curable adhesive (3).

6. The method according to any of the preceding claims, wherein the friction enhancing means includes a second adhesive which cures before curing the curable adhesive (3), at least part of the second adhesive being applied at a different location between the surfaces than the curable adhesive (3).

7. The method according to any of the preceding claims, wherein the joined éléments (1, 2) are transported from a first location to a second location S after the friction enhancing means hâve been applied to lock the éléments (1,

8. The method according to any of the preceding claims, wherein the friction enhancing means are rigid friction enhancing éléments having a hardness that is equal to or higher than a hardness of at least one of the éléments (1, 2) that are to be joined.

9. A method according to any of the preceding claims, wherein at least one of the éléments (1, 2) is a lignocellulosic part.

10. A method according to any of claims 1-9, wherein at least one of the éléments (1, 2) that are to be joined, is made of a métal or alloy.

11. A method according to any of claims 1-10, wherein at least one of the éléments (1, 2) that are to be joined, is made of a magnetically attractable material, wherein the friction enhancing means are configured to enhance friction using magnetic force.

12. The method according to any of the preceding claims, wherein the contact surfaces are surfaces of a finger joint structure.

13. The method according to any of the preceding claims, wherein the friction enhancing means do not melt during the pressing together of the contact surfaces or during the curing of the curable adhesive.

14. The method according to any of the preceding claims, wherein the mating contact surfaces are provided by matin g projections and cavities of the opposite sides of the éléments (1, 2).

15. The method according to any of the preceding claims, wherein the adhesive is or contains a curable epoxy resin

16. The method according to any of claims 1-15, wherein the adhesive is or contains a curable polyuréthane adhesive. X

17. The method according to any of daims 1-15, wherein the adhesive is of a phénol formaldéhyde type, or a resorcinol formaldéhyde, or a phenolresorcinol formaldéhyde type.

18. The method according to any of daims 1-15, wherein the adhesive is selected from the group including: ureum formaldéhyde, melamine, me lamine formaldéhyde, melamine ureum formaldéhyde, melamine ureum phénol formaldéhyde, isocyanate (PDMI), ethylene vinyl acetate (EVA), polyvinylacetate (PVAc), acrylate, cyanoacrylate, methylemethacrylate, silicones, and Modified Silyl polymère.

19. An method according to any of daims 1-18, wherein the locking éléments (4) hâve a cross-section measured in parallel with the respective contact surfaces that is about half the surface area of the respective contact surfaces, or smaller.

20. A method according to any of the preceding daims, wherein the adhesive is cured without using radiation.

21. A method according to any of the preceding daims, wherein the adhesive is cured without application of external pressure onto the éléments during a respective curing period.

22. A method according to any of the preceding daims, wherein the friction enhancing means include locking éléments that are made of lignocellulosic material, for example hardwood material.

23. A method according to any of the preceding daims, wherein the friction enhancing means include rigid locking éléments that are made of stone or stone-like material, for example sand.

24. A method according to any of the preceding daims, wherein a maximum size of each of the locking éléments (4) is 4 mm, particularly 1 mm, wherein a minimum size of each of the locking éléments (4) is 0.1 mm, for example about 0.4 mm.

25. A method according to any of the preceding daims, wherein a clamping force or pressure is applied for joining the éléments after the curable adhesive and the friction enhancing means (4) hâve been applied, wherein the a clamping force or pressure is released when the éléments are held in said joined position and before curing of the curable adhesive.

26. An assembly of at least two éléments (1, 2), for example provided by

11 4 DEC 20124