DESCRIPTION

The present invention relates to an industrial brush and a method for making an industrial brush.

The present invention relates to the field of industrial brushes and brushes for non-professionals, i.e. brushes that are used in machining processes (for example in the lapping of surfaces), which are usable in an industrial environment as well as in a non-professional environment (in other words in a private environment, for domestic use).

In this field, known brushes comprise a brush body and a plurality of wires, said wires having a first portion anchored in the brush body and a second portion suitable for carrying out the brushing when set brush body is set in rotation around an own axis. More specifically, such a brush comprises a flange having a central hole and an external portion to which the wires (which can be metallic, or plastic, or natural) are connected.

The brush body also comprises an adapter, or rather a coupling element for connecting the brush to a mandrel. Said adapter is constituted by a metallic block, machined through a turning process, which defines a nut provided with an extension having a cylindrical wall; the adapter defines a central threaded hole having a longitudinal axis.

The adapter is inserted in a central hole of the flange, said flange being arranged in a transversal plane. The brush body also comprises an internal cup and an external cup associated with the flange, which constitute locking elements for the wires.

In the method of making the brushes according to known techniques, the components of the brush (flanges, wires, adapters, internal and external cups) are assembled like described before. After this, one proceeds with the step of drawing of a border of an extension of the adapter protruding beyond the flange. Said drawing produces a flap of the adapter which is folded so as to hold together all the components of the brush (pressing them against the nut of the adapter). It is also foreseen that the brush comprises a retaining ring, associated with an end portion of the external cup and arranged externally to the first portion of the wires for holding them tight, in such a way as to exercise an inward pressure on them, or rather a pressure in the direction of said longitudinal axis, which also constitutes the rotational axis of the brush, when it is associated with a mandrel.

In known brushes, said retaining ring serves for obtaining a better functioning of the metallic filaments (it is used only for brushes of twisted bundles of metallic wires). It is furthermore observed that industrial brushes can be divided into various types, for example according to the way the wires are anchored to the flange and the material used for the wires.

Regarding the way the wires are anchored to the flange, the brushes can be divided into brushes with twisted wires (or rather twisted bundles of wires, also sometimes referred to as twisted tuft brushes or twisted tuft knot brushes) and brushes with undulated wires (also sometimes referred to as crimped wire brushes).

In the brushes with twisted wires (or rather with twisted bundles or tufts of wires), the wires are grouped into bundles and every bundle of wires is associated with a hole defined in the flange in the proximity of its external circumference; each bundle is introduced in a hole and tied to the brush body by twisting the bundles of wires. In this case, the central hole of the flange is of relatively small dimensions.

In crimped wire brushes, the flange is also called a ring nut. In this kind of brush, the flange (or, the ring nut) defines a throat in a lateral external border, in which a first portion (or rather a first extremity) of the wires is inserted. The flange works together with a support ring, around which the wires are folded for holding them in their desired position.

Therefore, the flange and the support ring (which is a metallic ring) tightly hold the metallic wires folded in U, which are distributed around the circumference of the internal support ring. The support ring is provided on the outside of the throat in the flange.

In this case, the central hole of the flange is of considerable dimensions (it has a diameter superior to two thirds of the flange itself, for example around 80 - 90 % of the diameter of the flange). Therefore, in the case of brushes with crimped wires, for the closure of the brush, an internal cup (or rather a locking element) is used, which, through the step of drawing of the adapter, makes the wires come closer to the throat for squeezing them. Regarding the material constituting the wires, the brushes can be divided into brushes with metallic wires, brushes with polymeric wires and brushes with mixed polymeric-metallic wires.

In this respect, it is noted that the brushes with twisted bundles of wires always have metallic wires; or rather, the configuration with twisted wires is not used for brushes with natural wires. Therefore, for the brushes with natural wires the configuration with crimped (or undulated) wires is always used.

Conventional brushes have the following problems.

More than anything, the brushes need to be robust, so as to be able to work at a particularly elevated speed without breaking (typically the wires break or go loose).

Another problem related to the high rotational velocity under which the brushes need to be able to work lies in the stability; that is, the brush always needs to rotate as a rigid body around its longitudinal axis which should remain still when working. Besides, it is required that those characteristics are inherent to brushes of all different kinds, and thus regardless of the material that the wires are made of or the arrangement of the wires itself.

The prior art tries to solve the problems by perfecting the finishing and the assembly of all components that together make up the brush. However, this brings an increase in the cost of the brushes, due to the number of components, the complexity of the components, and their assembly.

In this respect, another inconvenience related to the fact of having numerous elements that together make up the brush consists in the necessity, for the companies manufacturing the brushes, of having copious stocks in their storage rooms (with a corresponding waste of money, means and space).

Another inconvenience of the known solutions for the robustness and stability of the brushes lies in the working tolerances of the components, especially of the adapters. Another problem of the known solutions relates to the fact that the brushes, made (for reasons of robustness) of steel components or of other iron containing materials cannot be used in a secure way for brushing metallic surfaces (such as stainless steel surfaces), or in environments that prescribe anti-explosion measures (because there is a risk that sparks may be produced) or in the food sector.

In fact, the brushes according to known solutions do not allow them to be washed and sterilized, so that their use causes particular problems in the food sector.

It is also noted that that other technical solutions are known which foresee the welding together of the wires and subsequently the attachment of a plastic cap (or cup) to the extremities of the welded wires by applying external pressure, or obtained through special plastic resins. In these solutions, it is furthermore known to use a retaining ring as hereinbefore described.

Such plastic caps or cups have the problem of increased fragility of the materials, so that their use is restricted to plastic filaments with the aim of reducing the mechanical strains. Thus, this manufacturing method can absolutely not be used for the construction of brushes with metallic wires.

Furthermore, those solutions do not resolve the problems described above, for example regarding the possibility of using a brush in sterile environments, or in respect of the robustness and the strength when being used at high speeds, because the wires need to be welded and the plastic external cap only works as covering member.

US 2004/0187244 discloses a brush with twisted bundles of wires. The brush comprises a shell which forms the outer surface of the brush. Within the shell, a disk with a plurality of notches is arranged. A plurality of bundles of twisted wires is arranged in said plurality of notches. A center plug or core may be provided to embrace a portion of the wires with a goal to dampen unwanted vibrations.

Such a brush is not suited for use at elevated temperatures, since the outside shell impedes thermal transfer of heat generated in the brush.

In this context, the technical goal at the heart of the present invention is to provide a brush and a system for making a brush that solves the above mentioned problems of the prior art.

In particular, it is an object of the present invention to provide a brush and a method for making a brush which is constructively simple, with cost reduction during its manufacture, while guaranteeing elevated robustness, also when used at high rotational speeds (in particular with metallic wires). Another object of the present invention is to provide a brush and a method for making a brush which is particularly stable when used at high speeds.

Another object of the present invention is to provide a brush and a method for making a brush which can be used in a secure way for working on metallic surfaces (such as for example stainless steel) or in environments that prescribe anti-explosion security measures.

Another object of the present invention is to provide a brush and a method for making a brush which can be easily washed and sterilized, so that it can be used in a secure way in the food sector. The technical task that is specified and the specified objects are achieved by an industrial brush and a method for making an industrial brush comprising the technical features of the attached claims.

In particular, the industrial brush according to the present invention is characterized in that the brush body comprises a matrix of binding material wherein a first portion of the wires is immersed, said matrix encompassing the first portion of the wires for rendering it integral with the brush body, said matrix substantially defining an external surface of the brush body.

The method for making an industrial brush according to the present invention is characterized in that it comprises the following steps, in the following order: - Provision of a mould that defines a volume suitable for receiving a liquid;

- Provision of a plurality of wires arranged in such a way that a first portion of said wires is arranged in the volume of the mould;

- Introduction into said volume of a binding material in a liquid phase, in such a way that the first portion of the wires is immersed in the binding material;

- Solidification of the binding material for forming a matrix that encompasses the first portion of the wires and constitutes in this way a rigid brush body to which a first portion of the wires is anchored. - Removal of said brush body from said mold.

Other characteristics and advantages of the present invention will be more clearly explained in the description for illustrative (and thus non-limiting) purposes of some preferred, but not the only possible, embodiments of industrial brushes according to the present invention, with reference to the appended drawings, in which: - Figure 1 illustrates a brush according to the present invention in cross- section;

- Figure 2 illustrates the brush of figure 1 , according to another aspect of the present invention; - Figure 3 illustrates the brush of figure 2, according to a first preferred embodiment;

- Figure 4 illustrates the brush according to figure 2, according to a second preferred embodiment;

- Figure 5 illustrates the brush of figure 1 in a step of the method of manufacturing of said brush.

In the figures, the industrial brush according to the present invention has been indicated with reference sign 1.

The brush 1 comprises a brush body 2 and a plurality of wires 3.

The wires 3 have a first portion 3a anchored in the brush body 2 and a second portion 3b suitable for carrying out the brushing when the brush 1 (or rather the brush body 2) is put into rotation along its longitudinal axis 4.

Unconventionally, the brush body 2 comprises a matrix 5 of binding material in which the first portion 3a of the wires 3 is immersed; said matrix 5 of binding material encompasses the first portion 3a of the wires 3 such that it is rendered integral with the brush body 2.

In this way, as can be seen in figure 1 , said matrix 5 defines the external surface of the brush body 2. In some embodiments of the present invention, the brush body 2 may be partially or completely provided with a thin coating to improve mechanical or thermal properties of the brush body. However, the shape of the brush body is substantially defined by the matrix.

Said binding material consists of an originally liquid material which subsequently is solidified around the first portion 3a of the wires 3 for encompassing them in said solid brush body 2.

Preferably, said matrix is a matrix of plastic material. For example, the matrix comprises solidified polyurethane around the first portion 3a of the wires 3 such that it constitutes a rigid block 2 (which however is not fragile) encompassing said first portion 3a of the wires 3 for fixing them.

Therefore, the brush body 2 unconventionally comprises a rigid block 2 which encompasses the wires, obtained by solidification of a liquid plastic material in a mould 6 (for example introduced by casting or by injection molding). Preferably, matrix 5 of binding material comprises an internal socket 7. The socket 7 has the function of facilitating a connection between the brush 1 and a mandrel or a rotating shaft for putting the brush into rotation during its functioning. It should however be noted that the presence of socket 7 is not essential. The brush 1 could namely be connected to the brush' rotation means through clamps or other connection means.

Nevertheless, the presence of the socket is advantageous in that it facilitates the coupling of the brush 1 to a mandrel; besides, there are no tolerances in the centering of the brush when it is fixed to the mandrel.

Preferably, the socket 7 comprises a through-hole. This facilitates the manufacturing of the socket itself.

For the making of the socket 7, the mould 6 can be provided with a projection (not illustrated in the figure) corresponding to the cavity. Alternatively, it is foreseen for example to provide the matrix 5 of binding material with a hole in a subsequent step.

Consequently, in the preferred embodiment illustrated in figure 1 , the brush 1 comprises a particularly reduced number of components, or rather only comprises the wires 3 anchored to the brush body 2 defined by the binding matrix 5.

Consequently, the brush does not have an adapter, and also no flanges and cups.

This is made possible by the matrix of solidified binding material which constitutes the anchoring means for the wires 3 and constitutes fixing means for all possible extra components.

In this light, it is also foreseen that the socket 7 may define a thread 7a for allowing the brush body 2 to be screwed on the mandrel.

It is also foreseen that the brush 1 may comprise a holding element for wires 3, provided around the first portion 3a of the wires for pressing on them, said holding element being unconventionally encompassed in matrix 5 of binding material (preferably plastic material).

Said holding element of the wires 3 is formed, in the preferred illustrated embodiment, by a ring 9 provided around the first portion 3a of wires 3 for pressing on them, said ring 9, in an unconventional way, being encompassed in matrix 5 of binding material. The ring 9 preferably (but not necessarily) is a metallic ring and has the function of guaranteeing a secure fixing of the wires 3 (guaranteeing thus an improved robustness of brush 1 ) at high rotational speeds and at elevated temperatures (arisen through the action of brushing); temperatures at which matrix 5 (being made of plastic material) softens and looses mechanical strength.

The presence of the ring 9 is particularly advantageous in brushes with metallic wires; however, also in brushes with polymeric wires, the presence of ring 9 is important when the temperature of the brush is particularly high. The ring 9 also serves for having a better positioning of the wires (or bundles of wires) with respect to the rotational axis, insofar the plastic material of the matrix 5 binds in a indissoluble way with the wires 3, so that the brush 1 maintains robustness also at particularly elevated temperatures.

It is noted that the holding element (or the ring 9) can also have a polygonal shape (it does not necessarily have to be circular).

Besides, the ring 9, in a preferred non-illustrated embodiment is unconventionally provided with through-holes for improving the adhesion and encompassing of the ring by the matrix of binding material.

Figure 2 illustrates a brush 1 provided with the socket 7 and the ring 9. In a first preferred embodiment of the present invention (illustrated in figure 3), the brush comprises a flange 10 which defines a central hole and is included in said matrix, the wires 3 being connected to flange 10.

In the first preferred embodiment illustrated in figure 3 the brush is a brush with twisted wires (or rather with twisted bundles of wires). Unconventionally, flange 10 has a central portion 10a which is folded and threaded so as to define a threaded portion of a lateral wall of the socket 7.

This facilitates, in an advantageous manner, the coupling of the brush to a mandrel, without a need for providing a thread in matrix 5 of binding material (and avoiding also the presence of the adapter). Therefore, the fact that the threaded part is situated on the inside of the brush improves its stability notably.

The brush that is illustrated in figure 3 also comprises the ring 9, but the presence of the ring is not essential (it is particularly advantageous if the wires 3 are metallic). In a second preferred embodiment of the present invention (illustrated in figure 4), the brush comprises a flange 10 that defines a central hole and a fixing element for fixing the wires 3 connected to the flange (also called internal cup).

In the second preferred embodiment illustrated in figure 4, the brush is a crimped wire brush, having crimped (or undulated) wires 3.

The fixing element 11 , in an unconventional way, is included in the matrix 5 of binding material; besides, the fixing element 11 unconventionally comprises a central portion (not illustrated in the figure) which is folded and threaded for defining a threaded portion of a lateral wall of said socket 7. This allows, in an advantageous manner, to facilitate the coupling of the brush 1 to a mandrel, without the need for providing a thread in the matrix 5 of binding material directly (and anyhow avoiding also the presence of a adapter).

Also the brush illustrated in figure 4 comprises the ring 9, but the presence of the ring is not essential (but is particularly advantageous if the wires are metallic).

The metallic ring serves for achieving a particularly precise centering of the wires with respect to the rotational axis, for holding the wires still during the moulding step (using casting or injection molding) and for achieving increased mechanical strength during the use of the brush at high rotational velocities. In the second preferred embodiment illustrated in figure 4 (referring to a brush with undulated wires, also called a crimped wire brush), the brush comprises also a support ring 12 (which preferably is metallic), which is also unconventionally included in the matrix 5 of binding material.

The flange 10 cooperates with said support ring 12, around which the wires 3 are folded (said folding defining said first portion 3a of the wires), to hold the wires in their desired position.

Therefore, the flange 10 and the support ring 12 tightly hold the wires 3 folded in U and distributed along the circumference of the support ring.

The support ring is provided on the outside of the throat of the flange 10. According to another aspect of the present invention, the external surface of matrix 5, or rather of the brush body 2, unconventionally defines a plurality of ridges (not illustrated in the figures).

Said ridges increase the robustness of the brush, insofar as they allow the redistribution of the loads on the brush during its use in a more efficient way. Besides, said ridges increase the surface for thermal exchange of the brush body 2, improving the strength of the brush 1 at high temperatures.

Naturally, these ridges may be provided in brushes according to the present invention regardless of the exact shape of the brush, regardless of the type or material of wires used and regardless of which other components the brush may comprise.

It is noted that the wires 3 (or rather the first portion 3a of the wires 3) are encompassed in the matrix 5 of binding material thanks to the immersion of said first portion 3a of the wires 3 in the binding material when it is in its liquid phase; therefore, the liquid binding material, before solidifying and fixing the first portion 3a of the wires 3 on the inside of the brush body, first impregnates the portion 3a of the wires 3 also because of the principle of capillarity, thanks to which it penetrates in the interstices between one wire and another.

In this light, it is also foreseen, unconventionally, to impregnate all the wires 3 with the binding material in their entirety (so the first portion 3a and also the second portion 3b); the portion of the wires that is not directly immersed in the liquid binding material is reached by the liquid binding material through capillarity.

Therefore, the present invention also provides a brush 1 , wherein also the second portion of the wires 3b is impregnated with said binding material.

The present invention also foresees, in a preferred, but non-illustrated embodiment, the possibility that the brush body comprises a metal threaded adapter, unconventionally included in matrix 5 of binding material.

This complies with possible particular assembly requirements. It is also noted that such an adapter can be formed by a pin which can be inserted in a drill (instead of coupling to a mandrel).

It is also noted that the present invention, described for a brush, at the same time also regards paint brushes or other similar tools as brushes, or other tools comprising wires which are anchored in a brush body suitable for being put into rotation around its proper axis for carrying out a machining process.

Besides, according to a second aspect of the present invention, the brush 1 comprises a microchip (or other means for electronic recognition), unconventionally encompassed in the matrix 5 of binding material, for forming a single block with the brush body. In an advantageous manner, this allows a recognition and an efficient and quick reading (through electronic means) of the single brush, or the information relating to the brush itself, serial number etc.

The present invention also provides a method of making an industrial brush. Said method comprises, unconventionally, the following steps, in the following order:

- Provision of a mould 6 which defines a volume suitable for receiving a liquid;

- Provision of a plurality of wires 3 provided in such a way that a first portion 3a of said wires is provided in the volume of the moulding;

- Introduction in said volume of a binding material in a liquid phase, in such a way that the first portion 3a of the wires 3 is immersed in said binding material;

- Solidification of the binding material so as to form a solid matrix 5 which encompasses the first portion 3a of the wires 3 and in this way constitutes a rigid brush body 2, to which the first portion 3a of the wires 3 is anchored.

After these steps, the mould may be removed to liberate the brush body 2 from the mould.

Preferably, said binding material is a plastic material with a high elasticity and a low fragility.

Preferably, said binding material is a plastic material such as polyurethane, or a thermoplastic or an elastomer, or a silicone or a natural rubber (for example rubber from the Caoutchoua rubber tree).

It is noted that the step of introduction of the binding material can be carried out either by casting or by injection molding.

Preferably, said method also comprises a step (before the step of introducing the liquid material in the mould 6) of providing a ring in said volume around said first portion 3a of the wires 3 for pressing on them.

The ring 9 also serves for achieving a better positioning of the filaments in the step of providing the wires and in the subsequent steps of the introduction and solidification, guaranteeing a correct positioning and centering of wires with respect to the central rotational axis of the brush. Therefore, in the subsequent step of the introduction of binding material, the ring is immersed in the liquid binding material; in the subsequent step of solidification, the ring 9 is included in the matrix 5 of binding material.

In this light, it is noted that it is unconventionally foreseen that the ring is provided with holes for facilitating its inclusion in the matrix of binding material.

Besides, the method also preferably comprises, another step, after the solidification step, of machining of the brush body 2 (or rather of the matrix 5 of solid binding material), for obtaining a socket 7 which extends along a longitudinal axis 4. Said step can comprise for example a puncture of the brush body 2 to make a through-hole.

Said machining step can be substituted by the steps of introduction and solidification, in a case wherein the mould 6 defines a central projection that corresponds to the socket 7.

In the step of machining it is also preferably foreseen, to make a threading in the wall of the socket 7 for facilitating the coupling of the brush to a mandrel which is suitable for putting the brush into rotation around longitudinal axis 4.

In another aspect of the present invention, the surface of the mould 6 which receives the liquid material comprises a plurality of grooves, in such a way that the solidification step provides a plurality of ridges defined in the surface of matrix 5 that defines the brush body 2 (not illustrated in the figures).

Such ridges increase the robustness of the brush because they allow a more efficient redistribution of loads applied to the brush body 2 during the use of the brush 1.

Besides, said ridges increase the surface for thermal exchange of the brush body 2, thus improving the strength of the brush at elevated temperatures.

The ridges particularly make the cooling of the brush efficient, also thanks to the fact that they generate a turbulent motion in the area of the external surface of the brush body during its rotation, making thermal exchange through convection possible. With respect to the introduction step of binding material in a liquid phase into the volume defined by the mould, the following is observed.

The liquid binding material, before solidifying and fixing the first portion 3a of the wires 3 in the inside of the brush body, first impregnates the portion 3a of the wires 3 also thanks to the principle of capillarity, thanks to which it penetrates in all interstices between one wire and another. In this respect, it is also foreseen, unconventionally, to impregnate all wires 3 in their entirety (so the first portion 3a and also the second portion 3b) with binding material; the portion of the wires that is not directly immersed in the liquid binding material is reached by the liquid binding material through capillarity.

The capillary effect may be influenced, especially when the binding material is introduced using injection molding by controlling the temperature and the pressure of the molding process.

Thus, the present invention also provides a method of making a brush 1 in which the second portion 3b is also impregnated with said binding material.

Said result can be achieved by prolonging a resting step, subsequent to the insertion step, in which the wires are immersed in the liquid binding material, before said material solidifies.

In that respect, it is noted that introduction step of binding material (for example by injection moulding) may be carried out with volumetric dosing of the liquid material introduced into the mould. For example, the use of a volumetric pump is foreseen.

Preferably, it is foreseen to carry out a constant dosing of the liquid binding material, if necessary with a feedback control. A control of the insertion speed of the liquid binding material (for example controlling the transport of the liquid material introduced into the mould, with a feed-back in the control) allows, advantageously, to obtain a particularly efficient penetration of the liquid material in the wires (or rather in the portion of the wires that one wants to be encompassed by the matrix 5). As a matter of fact, if the injection speed is too high or too low, the binding material that forms the matrix penetrates the wires through capillarity in a non- optimum way.

Therefore, said control step also advantageously allows, the making of the matrix 5 of binding material with a minimum quantity of binding material with the consequent reduction in manufacturing cost of the brush.

Said method also provides, in a preferred embodiment, the possibility in the step of providing the wires, to also provide also a metallic threaded adapter, with the goal that also said adapter is encompassed in the matrix 5 of binding material in the introduction step. This satisfies possible assembly requirements. It is also noted that the step of providing the wires and introduction of the liquid binding material in the mold are not necessarily sequential, since it is possible, in an embodiment of the present invention, that the introduction step precedes the provision step. On the other hand, the solidification step is necessarily subsequent to the steps of providing the wires in the mold and introduction of the liquid binding material.

According to another aspect of the present method, it is foreseen, in the introduction step or in a subsequent step (but before the solidification step) to submerge a microchip in the matrix of binding material.

In this way, said microchip (or other electronic recognition means) is encompassed in the matrix of 5 of binding material, so as to form a single block with the brush body.

This allows, advantageously, a particularly efficient and quick recognition and reading (through electronic means) of the brush, or rather of the information relating to said brush, serial number etc.

Therefore, the present invention has the following advantages.

The brush 1 is particularly easy to make and particularly robust, since the presence of matrix 5 of solidified plastic material encompassing the first portion of the wires allows obtaining an increased robustness and at the same time makes possible the avoidance of adapters and possibly of other components, amongst which the internal and external cups. This leads to a cost reduction in the manufacturing and storing, apart from eliminating the uncertainties related to working tolerances. The fact that the matrix 5 of plastic solidified material encompasses all components (that may be present), amongst which for example ring 9, renders the brush free from metallic parts protruding on the outside; therefore the brush 1 is particularly secure when being used in environments with anti- explosive norms or in the machining of stainless steel surfaces; naturally, in those cases, the wires of the brush will be made of appropriate materials, free of iron, for example aluminum, brass, or phosphor bronze.

The fact that the brush comprises a flange with a tubular threaded protrusion

(in the case of brushes with twisted wires) or an internal cup with a tubular threaded protrusion (in the case of a brush with crimped wires) which is immersed in matrix 5 makes it possible to maintain the previously mentioned advantages (for example avoiding adapters and not having metallic protruding parts) when at the same time using the flange.

The fact that the brush comprises a wire retaining ring immersed in the matrix 5 guarantees an increased robustness (apart from all the previously mentioned advantages) also at elevated temperatures; besides it improves the centering of the wires with respect to the rotational axis of the brush.

It is noted that the presence of the ring in the brush does not exclude the presence of some other component in the brush.

Besides, the ring has a stabilizing effect on the wires and generates robustness (allowing a functioning of the brush at particularly high velocities and temperatures). For this reason it interacts synergistically with the matrix of binding material, which has an intrinsic structural limit, since it tends to soften at particularly high temperatures; besides, the ring favors the encompassing of the wires in the correct position because it fixes them during the making of the brush.

It is furthermore noted that even though in the attached figures, the shape and dimensions of the brush bodies shown is the same in all figures, it should be clear that this shape and its dimensions may be varied freely in accordance with the circumstances. The shape and dimension may e.g. be adapted to the intended use of the brush.