WO2022106309A2

WO2022106309A2 - Anchoring a dowel in an object with hollow spaces

Info

Publication number: WO2022106309A2
Application number: PCT/EP2021/081509
Authority: WO
Inventors: Mario Lehmann
Original assignee: Woodwelding Ag
Priority date: 2020-11-17
Filing date: 2021-11-12
Publication date: 2022-05-27
Also published as: WO2022106309A3

Abstract

The invention concerns a method of anchoring a thermoplastic dowel (3) in an object (1) comprising hollow spaces (11). The dowel extends between a proximal end and a distal end and forms a sleeve around an interior space, the sleeve having an initial inner diameter and an outer diameter. The dowel is positioned in a bore in the object. A tool (6) having an activation portion (61) is used, the activation portion having an activation portion diameter being greater than the initial inner diameter of the sleeve. For anchoring, the tool (6) is moved relative to the dowel with the activation portion moving in the interior space (61), and simultaneously mechanical energy is coupled into the tool so as to cause the thermoplastic material of the dowel in a flowable state to be displaced radially into the radial outward extensions at the positions of the radial outward extensions. After removal of the tool, the thermoplastic material forms an expanded sleeve with a final inner diameter larger than the initial inner diameter and with radial projections projecting into the radial outward extensions.

Description

ANCHORING A DOWEL IN AN OBJECT WITH HOLLOW

SPACES

FIELD OF THE INVENTION

The invention is in the field of mechanical engineering and construction and concerns methods for anchoring a dowel in an object comprising hollow spaces.

BACKGROUND OF THE INVENTION For objects with macroscopic hollow spaces, for example bricks with hollow spaces (so-called “hollow bricks”) there exist special dowels that provide some anchoring strength despite the special properties of the objects. Such special dowels are pushed into pre-drilled holes in the objects and have the property of spreading when thereafter a screw is inserted, so as to anchor the screw by the conventional dowel principle. A disadvantage is that the anchoring strength is limited. Especially, given the limited axial extension (extension with respect to an axis of the pre-drilled holes) hollow spaces often have, the extent by which the dowel may expand into the hollow spaces depends on the material strength, with only little expansion being possible if the dowel material is comparably strong. This limits the anchoring strength. SUMMARY OF THE INVENTION

The object of the present invention is to provide a method for anchoring a dowel in an object with hollow spaces, which method overcomes disadvantages of the prior art and which secure a strong anchoring also in objects such as bricks with hollow spaces, in which objects anchoring with sufficient anchoring strength and using prior art dowels was difficult.

In accordance with approaches according to the invention, a method of anchoring a dowel in an object comprising hollow spaces, comprises the steps of:

• Providing the dowel, wherein the dowel extends between a proximal end and a distal end and forms a sleeve around an interior space, the sleeve having an initial inner diameter and an outer diameter (which both may but do not need to be constant over the length of the sleeve), and the dowel comprising a thermoplastic material;

• providing a bore in the object, the bore forming a bore wall, with portions of some of the hollow spaces opening out into the bore and forming radial outward extensions of the bore;

• positioning the dowel in the bore;

• providing a tool having an activation portion, the activation portion having an activation portion diameter being greater than the initial inner diameter of the sleeve;

• positioning the tool in contact with the dowel; • moving the tool relative to the dowel with the activation portion moving in the interior space, and thereby using the activation portion to locally expand the dowel at positions of the radial outward extensions;

• simultaneously with moving the tool, coupling energy, for example mechanical energy, into the tool;

• thereby causing the thermoplastic material of the dowel in a flowable state to be displaced radially into the radial outward extensions at the positions of the radial outward extensions; and

• removing the tool.

After removal of the tool, the thermoplastic material forms an expanded sleeve with a final inner diameter larger than the initial inner diameter and with radial projections projecting into the radial outward extensions.

In this, a “flowable state” implies that the material is at least sufficiently pliable for a permanent (and not only elastic) deformation to occur.

This concept is based on the insight that a making flowable (softening/liquefying) of thermoplastic material is not only suitable for making possible an anchoring by penetration of first object material as for example taught in WO 98/42988, WO 2008/034 278 or WO 2009/052 644 but may also be used for anchoring a dowel in the per se known manner by causing the dowel to expand into spaces of the object in which it is anchored. In contrast to the prior art, however, it is not by resilience or by the screw screwed into the dowel that this expansion is caused but by the activation portion of the tool that acts both, as a means for making the thermoplastic dowel material pliable and even, to some extent, flowable, and to expand it in this pliable/flowable state to at least partially fill the radial outward protrusions, whereby the dowel is anchored in a positive-fit like manner, independent of the screw that is later screwed into it. It has been found by tests that the anchoring strength achieved by this approach is superior than the anchoring strength of conventional dowels, especially in brick material.

The radial outward protrusions are protrusions caused by the bore reaching into the hollow spaces of the first object. In this, the hollow spaces are macroscopic and have defined positions and shapes, in contrast to a mere porosity. The dimensions of the hollow spaces - and of the outward protrusions, are for example larger than 1 mm or larger than 2 mm in any direction/dimension. The hollow spaces thus may have a volume of at least of at least 10 mm³ or at least 100 mm³. The hollow spaces may be closed cavities or open cavities, formed for example by tube-shaped through openings in the first object, as is known for some bricks available on the market. The hollow spaces may for example form a regular pattern.

If the energy coupled into the tool is mechanical energy (mechanical vibration energy and/or rotation), the thermoplastic material of the dowel may become flowable due to one or a combination of: friction between the tool and the dowel; friction between the dowel and the first object.

In addition or as an alternative to mechanical energy, other energy may be coupled into the tool such as electromagnetic energy (laser radiation or the like).

In addition to causing thermoplastic material to expand into the radial outward extension(s), the thermoplastic material may also be caused to interpenetrate structures of the object material itself, such as pores or the like (if present). Such structures will be generally undefined and microscopic (typical dimensions of less than 1 mm) and/or will be generated only due to the pressure caused by the thermoplastic material.

In addition to having the functions of softening and of expanding, the activation portion may also have the function of causing an axial displacement of the thermoplastic material. Especially the thermoplastic material may be displaced axially from positions where the bore has a (usually rotationally cylindrical) wall formed by the first object material (i.e. positions different from the ones of the radial outward extension) to the positions of the radial outward extension. Thereby, the dowel that for example initially has an essentially homogeneous thickness along its length is caused to have a larger cross section area (in a cross section perpendicular to the proximodistal axis) at the axial position of the radial outward extension than at the position where the bore has a defined wall formed by the first object material.

The moving of the tool relative to the dowel in its interior may be a movement into the distal direction (“forward”) and/or into the proximal direction (“backward”). In many embodiments, a forward movement is more convenient. During such a forward movement of the tool relative to the dowel, the dowel may rest against a bore bottom. Especially if the stability of the dowel and/or of the bore bottom is not sufficient or if there is no bore bottom (or the bore is too deep), the dowel may have a retaining portion that prevents the dowel from being pushed deeper into the object. Such retaining portion may especially extend radially outward from a proximal part of the dowel. For example, the retaining portion may be a proximal head (a flange-like structure is considered as an example of such a head in this text). It has a distally facing stop face (for example an underside of the head) that rests against a proximally facing abutment face around a mouth of the bore. A retaining portion may remain as a part of the dowel, or it may be removed after anchoring. The retaining portion may be formed integrally with the sleeve, possibly with a pre-determined separation location, such as a constriction, between the retaining portion and the sleeve.

The energy may be mechanical vibration energy, for example longitudinal vibration, especially ultrasonic vibration. Alternatively, mechanical energy may be rotational energy.

The dowel, namely its sleeve portion, may have a slit. Such slit may run axially or approximately axially, and it may serve for easing the outward expansion. It is possible that the dowel has more than one slit, for example two slits or three slits. In such a case, the slits may optionally run approximately parallel.

Especially, the slit(s) may run across a substantial part of the length of the dowel, such as across at least a third or at least half of its length. It may for example run across at least the middle third of the sleeve. These considerations about the slit length may pertain either to an interrupted (by at least one bridge) or uninterrupted portion of the slit; especially the entire slit may be uninterrupted.

The tool, for example sonotrode or rotating tool, may have a shaft that carries the activation portion and is for example formed integrally with it, the activation portion being a distal broadening with a larger cross section (perpendicular to the axis) than the shaft. The activation portion may have a distal taper or be distally rounded.

The dowel may have a proximal receiving portion with an inner diameter larger than the initial inner diameter. In many embodiments, the dowel consists of the thermoplastic material and is present as one single piece. It may for example be injection molded.

The method may further comprise fastening a connector relative to the object by means of the anchored dowel, for example by being screwed into the interior space that has the expanded final inner diameter.

A thermoplastic material suitable for the dowel is, under the conditions prior to anchoring, solid. It preferably comprises a polymeric phase (especially C, P, S or Si chain based) that transforms from solid into liquid or flowable above a critical temperature range, for example by melting, and re-transforms into a solid material when again cooled below the critical temperature range, whereby the viscosity of the solid phase is several orders of magnitude (at least three orders of magnitude) higher than of the liquid phase. The thermoplastic material will generally comprise a polymeric component that is not cross-linked covalently or cross-linked in a manner that the cross-linking bonds open reversibly upon heating to or above a melting temperature range. The polymer material may further comprise a fdler, e.g. fibres or particles of material which has no thermoplastic properties or has thermoplastic properties including a melting temperature range which is considerably higher than the melting temperature range of the basic polymer.

Examples for the thermoplastic material that may be used for manufacturing dowels as described herein are thermoplastic polymers, co-polymers or filled polymers, wherein the basic polymer or co-polymer is e.g. polyethylene, polypropylene, polyamides (in particular Polyamide 12, Polyamide 11, Polyamide 6 (such as PA6 GF30), or Polyamide 66), Polyoxymethylene, polycarbonateurethane, polycarbonates or polyester carbonates, acrylonitrile butadiene styrene (ABS), Acrylester-Styrol- Acrylnitril (ASA), Styrene-acrylonitrile, polyvinyl chloride, polystyrene, or Polyetherketone (PEEK), Polyetherimide (PEI), Polysulfon (PSU), Poly(p-phenylene sulfide) (PPS), Liquid crystal polymers (LCP) etc. LCPs are of particular interest since their sharp drop in viscosity during melting enables them to penetrate in very fine spaces in the penetrable material. Mechanical vibration or oscillation suitable for the method according to the invention has preferably a frequency between 2 and 200 kHz (even more preferably between 10 and 100 kHz, or between 20 and 40 kHz) and a vibration energy of 0.2 to 20 W per square millimeter of active surface. The vibrating tool (e.g. sonotrode) is e.g. designed such that its contact face oscillates predominantly in the direction of the tool axis (longitudinal vibration) and with an amplitude of between 1 and 100pm, preferably around 30 to 60pm. Such preferred vibrations are e.g. produced by ultrasonic devices as e.g. known from ultrasonic welding.

In embodiments in which the energy is rotation energy, the rotational speed of the tool may for example be between approximately 500 and 100’000 rpm, especially between 2’000 and 50’000 rpm.

In this text, the terms “radial” and “axial” are to be understand as relating to the proximodistal axis which may, during the process, coincide with the respective axis of the bore and with the axis of the interior space.

BRIEF DESCRIPTION OF THE DRAWINGS The invention and embodiments thereof are described in further detail in connection with the appended drawings that are all schematical. Same reference numbers refer to same or analogous elements. In the drawings:

Fig. 1 illustrates, in cross section, a configuration of a first obj ect with a bore, a dowel inserted in the bore, and a sonotrode.

Fig. 2 shows the configuration of Fig. 1 during the anchoring step;

Fig. 3 depicts a detail of Fig. 2;

Figs. 4 shows an alternative configuration;;

Figs. 5 shows a detail of an even further configuration in cross section and a top view of the dowel of this configuration;

Fig. 6 depicts a head of a further dowel;

Fig. 7 shows a head of an other dowel;

Fig. 8 shows a view of an even further dowel; and

Fig. 9 depicts a view of yet another dowel. DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 illustrates the first object 1 being a brick with hollow spaces 11. The brick material is porous and thereby allows interpenetration by thermoplastic material when the same is in a flowable state as explained hereinafter in more detail. The first object is further provided with a bore into which a dowel 3 of thermoplastic material is inserted. The bore has a mouth in the proximally facing surface 14 of the first object. Some of the hollow spaces (the hollow spaces through which the bore extends at least partially) open into the bore, whereby they form radial outward extensions 12 of the bore. The bore has a closed distal end, i.e. it distally ends at a bore bottom.

The dowel is generally sleeve-shaped, i.e. it forms a thermoplastic sleeve around an interior space 33, whereby an initial inner diameter di and an initial outer diameter d_a are defined. A proximal portion of the dowel has a widened receiving portion 34 where the inner diameter is greater than the inner diameter di of the interior space. The outer diameter d_a approximately corresponds to the diameter of the bore or is slightly smaller than this; the outer diameter of the dowel may also be slightly larger than the bore diameter prior to insertion, whereby the dowel is slightly radially compressed when inserted (see also the description of Fig. 7 hereinafter).

For anchoring the dowel in the object, a sonotrode 6 having a shaft 62 and a distal broadening 61 extending distally from the shaft is used. The sonotrode, namely its distal broadening, has an outer diameter d_s that is greater than the inner diameter of the dowel but that is smaller than the diameter of the bore and is for example also smaller than the outer diameter of the dowel. The distal broadening has a distal tapered or rounded end for easier insertion into the interior of the dowel and, if applicable, its receiving portion 34.

In Fig. 1, the depth of the bore and the length of the dowel are adapted to each other so that a proximal end 31 of the dowel is approximately flush with the mouth of the bore when a distal end 32 of the dowel rests against the bore bottom. This is, however, optional. It is well possible that the dept of the bore is larger than the axial length of the dowel, especially if (as is often the case) the bore is drilled by hand. Figure 2 shows the configuration of Fig. 1 towards the end of the anchoring process in which the distal broadening 61 of the sonotrode 6 is moved within (for example into) the interior space towards distally while mechanical vibration is coupled into the sonotrode. As a result of this activation by mechanical vibration, the material of the dowel around the distal broadening is softened and is for example brought to a temperature above its glass transition temperature. Further, due to the fact that the diameter of the distal broadening is greater than the inner diameter of the dowel, the dowel material is caused to be expanded. Due to the softening, this expansion effect is irreversible and remains after the thermoplastic material has hardened again (re- solidification) by cooling. At the end of the process, the sonotrode 6 is removed, in a vibrating or in a non-vibrating state.

Figure 3 schematically depicts the region of the dashed ellipse 40 in Fig. 2 in order to illustrate the dowel, after re-solidification, being anchored in the first object. This is mainly due to two effects:

Firstly, the thermoplastic material of the dowel has been caused to expand into the radial outward extensions 12 where such expansion encounters no resistance. This leads to a positive-fit connection between the first object 1 and the dowel with respect to axial directions: The dowel cannot be removed to proximally (or distally) because of the outward protrusions 38 of the thermoplastic material, which outward protrusions 38 protrude onto the radial outward extensions 12.

Secondly, because the object is porous, its material is interpenetrated by an interpenetration portion 39 of the thermoplastic material. This is illustrated in Figure 3. In alternative embodiments, in which the material of the object is, however, not porous, the thermoplastic material will be pressed against wall portions of the bore, thus ensuring a better clamping action between the dowel 3 and the wall when e.g. a screw is screwed into the dowel.

In Figures 2 and 3, also another possible characteristics of the method is illustrated: Namely, initially (Fig. 1) the thickness of the sleeve formed by the dowel may be essentially constant along its length (with possible exceptions, such as the receiving portion, a distal taper and/or the features illustrated in Fig. 7 explained hereinbelow), and is especially essentially the same at the positions of the radial outward extensions and at positions where the outer surface is in contact with first object material. Nevertheless, after the anchoring process, there is more thermoplastic material at the positions of the radial extensions than elsewhere: the thickness of the wall formed by the dowel is greater at these positions. This means that during the process, thermoplastic material is not only displaced to radially outwardly but also axially: it is dragged along by the movement of the sonotrode in the interior space, from positions where only little material can flow radially outwardly (because the bore is confined by the porous but usually relatively dense and stable first object material) to positions where such radial outward flow has no or only little resistance (because of the radial outward extensions 12). This causes the macroscopic positive-fit connection illustrated in Figures 2 and 3 and that functions in some way like the principle of a blind rivet. . In addition, the additional material in the outward extensions 12 make the dowel stronger at positions where it is not supported, thus where such strength is needed most.

Figure 4 shows a variant of a configuration similar to the one of Fig. 1. In contrast to the embodiment of Fig. 1, the dowel has a proximal head 35 serving as retaining portion by defining a distally facing stop face 41 that abuts against the proximally facing abutment face 14 at the mouth of the bore. Due to this, the method is suitable also for situations in which the bore is a through bore, in which the bore has unknown depth, e.g. when it is drilled by hand, in which the depth of the bore is not defined sufficiently and/or in which the material at the bore bottom and/or the dowel material does not have sufficient stability for the bottom serving as a stop as illustrated in Figs. 1 and 2.

Fig. 4 also illustrates the (proximodistal) axis 30.

In embodiments, the retaining portion (such as the proximal head 35) is removed after the anchoring process. To this end, the dowel 3 of Figure 5 is illustrated to have a constriction 36 between the sleeve-shaped portion and the proximal head, where the head may be sheared off or severed from sleeve-shaped portion in an other way after the anchoring process, for example using a removal tool 51. In addition or as an alternative to such constriction, the proximal retaining portion may have an other shape so as to be separable from the rest of the dowel along a pre-determined breaking location - for example by having a cut 67 and being separable similar to the closure of a tin can by pulling in the direction of the arrow in Fig. 5.

Returning to Fig. 4, the dashed arrow 8 in Fig. 4 illustrates a further option, which is independent of the specifics of the connector of Fig. 4: Namely, instead of being a sonotrode, the tool may also be a rotation tool such as a drilling machine set into rotation around the axis. The energy is than coupled into the tool as rotation energy. Similarly to the embodiments in which the energy is vibration energy, the material of the dowel is locally heated by friction between the tool and the thermoplastic dowel material.

In embodiments that comprise rotation of the tool relative to the dowel, measures need to be taken that the dowel does not rotate together with the tool. Figure 6 schematically illustrates a head with a shape that deviates from circularly symmetrical by being hexagonal. A holding tool such as a wrench or similar may then be used to prevent the dowel from rotating.

In addition or as an alternative to having a head portion with a not fully circularly symmetrical shape for a tool to engage, the following measures may be taken for preventing rotation:

The distally facing stop face 41 and the proximally facing abutment face 14 may be adapted to each other for the friction being high enough to impede rotation of the dowel, for example by the head having a coating of an elastomeric material like rubber or a silicone.

The sleeve portion of the dowel may have outer elements, for example near its proximal end, that are pressed into material of the first object to cause a locking of the dowel, for example by a press-fit or by the elements cutting into the first object-material in a blade-like manner, as for example illustrated in Figure 7. For example, especially if such elements are wedge- shaped, with the broader end proximally, the dowel may be hammered into the first object. Such outer elements may also prevent rotation if they, for example by resilience, protrude into a radial outward extension that does not extend around the full periphery of the bore, as is often automatically the case due to the anisotropic shape of the hollow spaces of bricks (often the hollow spaces are vertically extending, tube-shaped cavities).

It is also possible to use a two-step procedure: in a first step, the dowel is rotated relative to the object, until thermoplastic material of the dowel is caused to become flowable and interpenetrates structures of the object. Such material may be material of the head and/or material of the sleeve portion. Then, the rotation is stopped and the flowable material is allowed to re-solidify. Thereafter the process is continued with the rotational tool having the activation portion that is inserted into the dowel - the resolidified material of the previous step impedes rotation in this second step.

Combinations of rotation and vibration are possible also, i.e. the tool is a vibrating sonotrode that also is caused to rotate, simultaneously with the vibration or sequentially therewith.

If the mechanical energy comprises mechanical vibration energy, the sonotrode may vibrate longitudinally (as illustrated by the double arrows in Figs. 1, 2, and 4) and/or may be set into rotational vibration around the axis.

Figure 8 illustrates a dowel that has the following features: in addition to features described referring to previous embodiments:

The dowel has a slit 42 extending along a large portion of its length. In the embodiment of Fig. 7, the slit runs axially; it would be possible for the slit to run slightly helically also. Instead of just one slit, the dowel can have a plurality of slits, for example two slits at positions opposed to each other. The slit(s) reduce the mechanical resistance against outward deformation.

The dowel has a plurality of circumferentially running ribs 43. In the shown configuration, the ribs have a double function: Firstly, they serve as energy directors in the process of causing the thermoplastic material to soften and become pliable/flowable also on its outer surface. Secondly, they are shaped in a barb-like manner, so that the resistance against insertion is smaller than the resistance against a pulling out. This approach assists the anchoring effect achieved by the approach according to the invention.

The features of the slit and of the circumferentially running ribs are completely independent of each other. It is thus possible to provide a dowel that does not have the ribs with a slit, and vice versa.

In embodiments, the at least one slit may be enforced by one or more bridges 100 subdividing the slit(s) into segments.

The invention is not restricted to these embodiments. Other variants will be obvious for the person skilled in the art and are considered to lie within the scope of the invention as formulated in the following claims. Individual features described in all parts of the above specification, particularly with respect to the figures may be combined with each other to form other embodiments and/or applied mutatis mutandis to what is described in the claims and to the rest of the description, even if the features are described in respect to or in combination with other features.

Claims

WHAT IS CLAIMED IS: A method for anchoring a dowel in an object comprising hollow spaces, the method comprising the steps of:

• Providing the dowel, wherein the dowel extends between a proximal end and a distal end and forms a sleeve around an interior space, the sleeve having an initial inner diameter and an outer diameter, and the dowel comprising a thermoplastic material;

• providing a bore in the object, the bore forming a bore wall, with a portion of at least one of the hollow spaces opening out into the bore and forming a radial outward extension of the bore;

• positioning the dowel in the bore;

• positioning the tool in contact with the dowel;

• moving the tool relative to the dowel with the activation portion moving in the interior space, and thereby using the activation portion to locally expand the dowel at a position of the radial outward extension;

• simultaneously with moving the tool, coupling energy into the tool;

• thereby causing the thermoplastic material of the dowel in a flowable state to be displaced radially into the radial outward extension at the position of the radial outward extension; and removing the tool; • whereby after removal of the tool, the thermoplastic material forms at least locally an expanded sleeve with a final inner diameter larger than the initial inner diameter and with a radial projection projecting into the radial outward extension. The method according to claim 1, wherein the steps of moving the tool relative to the dowel and coupling energy into the tool are carried out to further cause thermoplastic material of the dowel in a flowable state to be radially pressed into material of the object in addition to portions being displaced radially into the radial outward extension. The method according to claim 1 or 2, wherein the steps of moving the tool relative to the dowel and coupling energy into the tool are carried out to further cause thermoplastic material to be displaced axially from positions different from the positions of the radial outward extension to a position of the radial outward extension. The method according to any one of the previous claims, wherein the dowel has a proximal radially outwardly extending retaining portion, wherein the step of moving the tool relative to the dowel comprises moving the tool relative to the dowel towards distally while a distally facing stop face of the retaining portion rests against a proximally facing abutment face at a mouth of the bore or the retaining portion has a larger diameter than the bore and gets pressed into the bore delimiting the axial movement of the dowel by an interference fit. The method according to claim 4, further comprising the step of removing the retaining portion after the step of moving the tool. - 19 -

6. The method according to claim 5, wherein the step of removing the retaining portion is carried out after the step of removing the tool.

7. The method according to any one of claims 4-6, wherein the retaining portion is a proximal head of the dowel. 8. The method according to any one of claims 4-7, wherein the retaining portion is formed integrally with the sleeve.

9. The method according to claim 8, wherein the dowel has predetermined breaking point, for example a constriction between the sleeve and the retaining portion.

10. The method according to any one of the previous claims, wherein the energy is mechanical energy.

11. The method according claim 10, wherein the tool comprises a sonotrode, and wherein the mechanical energy is mechanical vibration energy.

12. The method according to claim 10, wherein the step of coupling the mechanical energy into the tool comprises causing the tool to rotate relative to the dowel. 13. The method according to claim 12, and comprising using a holding tool for preventing the dowel from rotating. - 20 - The method according to claim 12 or 13, using outer elements that are pressed into material of the first object to cause a locking of the dowel relative to the first object to for preventing the dowel from rotating. The method according to any one of claims 12-14, wherein in a first step, the dowel is rotated relative to the object, until thermoplastic material of the dowel is caused to become flowable and interpenetrates structures of the object, whereafter rotation is stopped and the flowable material is allowed to re-solidify and wherein in a second step a rotational tool having the activation portion that is inserted into the dowel is used to cause the thermoplastic material of the dowel to become flowable and to be displaced radially into the radial outward extension at the position of the radial outward extension, wherein the resolidified material of the first step impedes rotation in the second step. The method according to any one of the previous claims, wherein at least one of the hollow spaces has a hollow space volume of at least 10 mm³ or at least 100 mm³ or at least 500 mm³. The method according to any one of the previous claims, wherein at least one of the radial outward extensions has an axial dimension of at least 2 mm, preferably at least 5 mm. The method according to any one of the previous claims, wherein the first obj ect is a brick with a pattern, especially regular pattern, of the hollow spaces and/or the hollow spaces extend all the way through the brick, preferably perpendicular to the axial direction. - 21 -

19. The method according to claim 18, wherein the steps of moving the tool relative to the dowel and coupling mechanical energy into the tool cause an interpenetration of pores of the brick at the positions different from the positions of the radial extensions. 20. The method according to any one of the previous claims, wherein the dowel has at least one slit.

21. The method according to claim 20, wherein the dowel comprises at least one bridge across the slit.

22. The method according to claim 20 or 21 , wherein the at least one slit runs axially. 23. The method according to any one of claims 20-22, wherein the at least one slit has an axial length of alt least a third of a length of the sleeve.

24. The method according to any one of the previous claims, wherein the tool has a shaft portion, the activation portion extending distally of the shaft portion, wherein the activation portion diameter is greater than an outer diameter of the shaft portion.

25. The method according to any one of the previous claims, wherein the activation portion has a distal tapered and/or rounded end. - 22 - The method according to any one of the previous claims, wherein the dowel has a proximal receiving portion with an inner diameter larger than the initial inner diameter. The method according to any one of the previous claims, wherein the dowel consists of the thermoplastic material. The method according to any one of the previous claims, comprising the further step of fastening a connector relative to the dowel. The method according to claim 25, wherein the connector is a screw screwed into the interior space with the expanded final inner diameter.