Method and device for rounding fibres of brushes

Abstract: Method for rounding brush fibres of thermoplastic material, characterized in that the ends of the brush fibres are heated up thanks to friction, caused by a relative movement between these ends and a friction element which is equipped with a suitable friction surface, up to a temperature at which they are rounded in cooperation with this friction surface.

Description: The present invention concerns a method and device for rounding fibres of brushes. It is known that during the manufacturing of brushes, after the brush fibres have been inserted in the brush body, the free ends of the brush fibres are warped even or are milled off to smooth away the unevennesses which arise during the insertion of the fibres. As a result, certain types of brush fibres obtain sharp edges at their fibre ends, which is unacceptable for certain brushes. This is for example the case for tooth brushes, where the sharp edges could harm the gums, or for hair brushes, where the sharp edges could harm the scalp. In order to remove these sharp edges, the ends of the brush fibres are rounded by putting them in contact with a moving grinding element. This grinding element can be a grinding strip or a grinding disc as described in EP-A-0.019.944. The grinding is usually carried out in a relatively large number of steps, for example some five to ten steps, with an increasing grain fineness of the grinding surface, and it is usually followed by a polishing stage. Consequently, these methods applied until now are time-consuming. Moreover, a lot of dust is produced during the grinding. In order to obtain reasonable results, rather sophisticated devices are used whereby the relative movement of the grinding surface in relation to the brush fibres is carried out according to a relatively complicated pattern. As a result, these devices are relatively expensive and, even with such devices, a relatively large amount of brush fibres of a brush will not obtain a perfectly rounded shape, whereas the ends of those which were rounded sometimes are still relatively coarse when seen under a microscope. An even greater problem arises during the rounding when the brush is provided with a profiled cut, as a result of which the ends of the brush fibres are not all situated in one plane. With the known methods whereby the'brush fibres are polished, the long brush fibres are usually polished too much, in order to make it possible for the grinding element to also reach the short brush fibres. This problem is described in detail in DE-A-4.425.231 and DE-A-4.138.777. From US-A-2.554.777 it is known to round fibre ends by means of a disc which is provided with pins or blade elements which do not only provide in friction but also provide in a substantial hammering and impacting action, having the disadvantage that the fibre ends may become damaged. The invention aims a method and a device used with it with which the rounding process can be carried out in a simple and a relatively fast manner with a very good result. To this end, the invention concerns a method for rounding brush fibres of thermoplastic material, by bringing the ends of the fibres in contact with a treatment surface which moves relative to the brush fibres and by heating the ends of the fibres up to a temperature at which they are rounded by thermoplastic deformation due to the contact with said treatment surface, characterised in that the rounding of the fibre ends is essentially realised by using a friction element which is provided with a friction surface which is less coarse than the surface of abrasive or grinding elements and in that the rounding of the fibres is created mainly through the heat developed by the contact between the fibres and said surface. In this way, practically all brush fibres of a brush can be perfectly rounded, even when the brush fibre ends are situated in different planes. The required rounding can be obtained in one step or in a limited number of steps which is significantly lower than the number of steps required for the grinding. It is hereby very important that very little or no dust is produced with this method according to the invention. It was found that a friction surface made of a material which does not conduct the heat well, for example made of a synthetic material, is particularly suitable. The speed at which the heating up caused by friction takes place not only depends on the friction surface of the friction element, but also on the speed of the relative movement which can be selected relatively fast. In order to carry out this method, use can be made of a device comprising a friction element which is provided with a friction surface, means to put the thermoplastic brush fibres and the friction element in contact with one another and means to create a relative movement between the friction surface and the brush fibres, said device being characterised in that the friction surface is less coarse than the surface of abrasive or grinding elements and provides in that the rounding of the fibres is created mainly through the heat developed by the contact between the fibres and said surface. According to a preferred embodiment, the device mainly consists of a frame which is equipped with one or several slidable carriages, whereby one or several supports are fixed on each carriage, displaceable in the longitudinal direction of the brush fibres, and whereby one or several supports are coupled to the frame by means of a cam drive and whereby a friction element is mounted in a rotatable manner on each support. In order to better explain the characteristics of the invention, the following preferred embodiments of a method and device for rounding brush fibres according to the invention are described as an example only without being limitative in any way, with reference to the accompanying drawings, in which: figure 1 schematically represents a finishing unit for brushes which contains a device for rounding brush fibres according to the invention; figure 2 shows a view according to F2 in figure 1 to a larger scale. In order to round the ends of the warped or milled brush fibres of thermoplastic material, in particular of thermoplastic synthetic material, of a brush, these ends are heated up in one or several steps by means of friction as a result of a fast relative movement of a friction element with a suitable friction surface against these brush fibres, up to a temperature at which these ends obtain a rounding due to the contact with the friction element. Preferably, the friction element hereby makes such a movement that the frictional direction changes continuously and evenly, such as for example a movement as described in Belgian patent application No. 9400745 of 17 August 1994, or such that all points on this friction element simultaneously follow identical circular courses as described in Belgian patent application No. 9500402 of 4 May 1995. Surprisingly, it was found that in this manner, the ends which were sufficiently heated up thanks to the friction, as they make contact with the friction element, are rounded in an almost perfect way with a microscopically smooth surface. In order to heat up the ends sufficiently by means of friction, these ends are preferably heated up until they soften, and, to the limit, possibly slightly melt on the surface. A very large percentage, even more than 95% of the brush fibres of a thus treated brush obtain such a rounding, even when the brush fibres of one and the same brush body have different lengths. Both the brush and the friction element can be moved, but the brush is preferably maintained stationary whereas the friction element is moved. This friction element can be a rotating disc, a rotating drum, a moving flat plate or an endless belt as described in Belgian patent No. 1.007.111. In the case of a rotating drum, the drum barrel will be preferably cylindrically shaped, barrel-shaped and/or profiled, for example fluted. Moreover, the brush fibres can be directed for example vertically with their ends up or with their ends down. It is essential that this friction element touches the brush fibres with a friction surface which has the appropriate structure to sufficiently heat up the ends of these brush fibres by means of friction, at the selected relative speed of the friction element on the spot where contact is made with the brush fibres, and to round the heated ends, thanks to an appropriate variation of the frictional direction. This friction surface is usually less coarse than the surface of abrasive or grinding elements and is preferably made of a material which does not conduct the heat well, such as for example a material on a synthetic basis, so as not to remove the created frictional heat prematurely. If a friction surface is used which is made of a material which is too heat-conducting, the required heat level can be obtained or maintained by supplying heat from outside, for example by heating the friction body. Provided the speed is sufficiently high, the surface of certain polishing discs would also do. The friction element can be entirely made of the appropriate material, or it can be provided with a layer or covering of such material on the outside. Said friction element may also have obtained the required friction surface thanks to a special treatment of its surface. The speed and thus the time required for the heating up naturally also depend on the relative speed of the movement of the friction element, which is selected as fast as possible. This speed varies as a function of the nature of the brush fibres to be rounded and the friction surface of the friction element. The frictional heat can also be supported by a directed heat supply from outside. When the rounding is carried out in more than one step, the brush fibres can be either or not cooled between the steps. It is very important that, during the treatment, little or almost no dust is produced, as opposed to what happens with grinding or abrasive treatments whereby many fine dust particles are produced. In a relatively fast way and with a simple device can be obtained an excellent result. The figures represent a device which applies the method according to the invention and which mainly consists of a complete finishing unit 1 for brushes which contain a series of holders 2 for brush bodies 3 in which brush fibres 4 are fixed. Every holder 2 can hereby hold one brush body 3, but according to another embodiment, also two or more brush bodies 3 can be provided per holder 2. The above-mentioned holders 2 are provided on a frame 5 upon which are mounted an endless conveyor belt 6, a device 7 for warping the brush fibres 4 and a device 8 for rounding the free ends of these brush fibres 4. The devices 7 and 8 are erected along the conveyor belt 6, for example as represented in the figures along the lower end thereof. The holders 2 are applied on the conveyor belt 6. The device 7 for warping the ends of the brush fibres 4 consist of one or several moveable warping units 9 which may be of a known construction. These warping units 9 are equipped with control elements 10, such that the warping plane 11 of each warping unit 9 can be adjusted in height. By means of these control elements 10, the brush fibres 4 can be warped according to a certain length. By providing the appropriate knives on the warping units 9, brushes can be either cut off flat or with a certain profile. By providing additional devices as described for example in EP-A-0 078 569 of the applicant, fibres can also be cut off at two or more different length levels. The device 8 for rounding the ends of the brush fibres 3 contains one or several rounding units 12 which each contain a friction element 13 provided with a suitable friction surface 14 and means 15 to put the friction surfaces 14 and the brush fibres 4 in contact with one another in an appropriate way, and means 16 to create a relative movement of the friction surfaces 14, when in contact with the brush fibres 4, in relation to the brush fibres 4. In the embodiment shown, the friction element 13 consists of a round drum 17 whose perimeter forms the above-mentioned friction surface 14 and whose axial length or width practically coincides with the length of the part of the brush body 3 which is provided with fibres 4. The drum 17 is fixed on a shaft 18 which can rotate in a drum 19. This shaft 18 is situated in a plane which is parallel to the part of the brush body 3 which is equipped with brush fibres 4 to be rounded. The support 19 is in turn fixed on a shaft 20 which can rotate in a casing 21. This shaft 20 is parallel to or almost parallel to the direction of the above-mentioned brush fibres 4 and preferably runs through the centre of the above-mentioned drum 17. The casing 21 of each rounding unit 12 is fixed to a carriage 23 by means of a connecting element 22 which can be moved in the longitudinal direction of the brush fibres 4. To each connecting element 22 are fastened one or several casings 21, such that each casing 21 can be adjusted individually by means of a control element 24 in the longitudinal direction of the brush fibres 4. Several or all connecting elements 22 of the device 8 can be coupled to one another. The above-mentioned carriage 23 is provided in a slidable manner on a guide 25 which is fixed on the frame 5, such that the carriage 23 can slide in a direction which is parallel to the longitudinal direction of the part of the brush bodies 3 which is filled with brush fibres 4. The connecting elements 22 can be moved in the longitudinal direction of the brush fibres 4 in relation to the carriage 23 by means of a cam drive 26 consisting of a buffer shaft 27 which is mounted slidable in the longitudinal direction of the brush fibres 4 to the carriage 23 and which is equipped with a cam follower 28 which cooperates with a cam 29 fixed on the frame 5. With a group of coupled connecting elements 22, as represented in the figures, several cam drives 26 can be provided whose cams 29 have the same active surface. Between the carriage 23 and the frame 25 is provided a crank mechanism 30 whose crankshaft is driven by an electric motor 31 which is fixed to the frame 5. On the carriage 23 are fixed two or more electric motors 32 and 33 whose outgoing shafts are coupled via transmissions 34 and 35 to the shaft 20 of one or several supports 19 and to the shaft 18 of one or several drums 17 respectively. The transmissions 34 and 35 are for example a couple of belt transmissions. The transmissions 35 are preferably made such that the drums 17 of neighbouring rounding units 12 turn in the opposite sense. The conveyor belt 6 and the cam drive 30 are part of the above-mentioned means 15 to put the friction surface 14 in contact with the brush fibres 4. The casing 21 with the support 19, the connecting element 22 and the motors 32 and 33 with the transmissions 34 and 35 are part of the above-mentioned means 16 which make it possible to realize a relative movement of the friction surface 14 in relation to the brush fibres 4. The carriage 23 which can slide over the guide 25, the crank mechanism 30 and the motor 31 are common to the above-mentioned means 15 and 16. The working of the finishing unit 1 is simple and as follows. By means of the conveyor belt 6, the brush bodies 3, filled with brush fibres 4, are successively provided opposite the warping units 9, where the brush fibres 4 are put in contact with the warping planes 11 and are warped in one or several steps, and are subsequently provided opposite the rounding units 12, where they are rounded in one or several steps. During the rounding of the brush fibres 4 of a brush body 3, the drum 17 of the corresponding rounding unit 12 is rotated via the transmission 34 through the motor 33 around the shaft 18, whereas the drum 17 is rotated via the transmission 34 through the motor 32 around the shaft 20. The combination of the above-mentioned rotary movements will cause the necessary friction between the friction surface 14 and the ends of the brush fibres 4 to obtain the required rounding. The drum 17 and thus the friction surface 14 are also moved in the longitudinal direction of the part of the brush body 3 which is filled with brush fibres 4 thanks to the to-and-fro movement of the carriage 23 which is caused via the crank mechanism 30 by the motor 31. Thanks to this to-and-fro movement of the carriage 23, the cam follower 28 is moved over the cam 29, such that the connecting element 22 and consequently also the drum 17 with the friction surface 14 make a movement in the longitudinal direction of the brush fibres 4. By giving the active side of the cam 29 a certain profile, brush fibres 4 of one and the same brush body 3 which have several lengths can be rounded in this manner. If only brush fibres are rounded which have the same length or whose ends are situated in one and the same horizontal plane, the cam drive can be omitted, whereby the connecting element 22 is then firmly fixed to the carriage 23. The rotational speed of the motors 31-32-33 can be controlled separately and continuously by means of for example a frequency regulator. The invention is by no means limited to the embodiment described above; on the contrary, such a method and device can be made according to several variants while still remaining within the scope of the invention. Thus, for example instead of erecting the warping units and the rounding units in groups, whereby a brush is first subjected to all cutting operations, and then to all rounding operations, the warping units and the rounding units can be alternately erected at random. Hereby, for example one or several warping units can be each time followed directly by one or several rounding units, and then again one or several warping units can be followed by rounding units, etc. According to yet another embodiment, the brush fibres can be spread such by means of spreading elements that the operating units can be adjusted for the short fibres without touching the long fibres. Naturally, the above-described method can also be used for rounding loose brush fibres, either in bundles or wound on bobbins, before fixing them in or on a brush body.

Claims: Method for rounding brush fibres of thermoplastic material, by bringing the ends of the fibres (4) in contact with a treatment surface (14) which moves relative to the brush fibres (4) and by heating the ends of the fibres (4) up to a temperature at which they can be rounded by thermoplastic deformation, characterised in that the rounding of the fibre ends is essentially realised by using a friction element (13) which is provided with a friction surface (14) which is less coarse than the surface of abrasive or grinding elements and in that the rounding of the fibres (4) is created mainly through the heat developed by the contact between the fibres (4) and said surface (14). Method according to claim 1, characterized in that the ends are heated up to a temperature at which these ends soften on their surface. Method according to claim 2, characterized in that the ends are heated up to a temperature at which these ends start to melt lightly on their surface. Method according to any of the preceding claims, characterized in that the friction element and the relative movement are selected such that the frictional direction of the relative movement of the friction surface is continuously and evenly changed in relation to the brush fibres. Method according to any of claims 1 to 3, characterized in that the friction element and the relative movement are selected such that all points of the friction surface simultaneously follow identical paths. Method according to any of the preceding claims, characterized in that the friction on the brush fibres is caused by a friction surface made of material which does not conduct the heat well. Method according to claim 6, characterized in that the friction is caused by a friction surface on a synthetic basis. Method according to any of the preceding claims, characterized in that the relative movement is carried out at a relatively high speed, depending on the friction surface of the friction element and the nature of the brush fibres. Method according to any of the preceding claims, characterized in that the brush fibres are maintained stationary while the friction element is moved. Device for rounding brush fibres of thermoplastic material comprising a friction element (13) which is provided with a friction surface (14), means (15) to put the thermoplastic brush fibres (4) and the friction element (13) in contact with one another and means (16) to create a relative movement between the friction surface (14) and the brush fibres (4), characterised in that the friction surface (14) is less coarse than the surface of abrasive or grinding elements and provides in that the rounding of the fibres (4) is created mainly through the heat developed by the contact between the fibres (4) and said surface (14). Device according to claim 10, characterised in that the friction surface (14) and the means (16) to create a relative movement or such that the frictional direction changes continuously and evenly. Device according to claim 10 or 11, characterised in that the friction element (13) has a friction surface (14) which does not conduct the heat well. Device according to any of claims 10 to 12, characterized in that it mainly consists of a frame (5) which is equipped with one or several slidable carriages (23), whereby one or several supports (19) are fixed on each carriage (23), displaceable in the longitudinal direction of the brush fibres (4), and whereby one or several supports (19) are coupled to the frame (5) by means of a cam drive (26) and whereby a friction element (13) is mounted in a rotatable manner on each support (19). Device according to claim 13, characterized in that one or several supports (19) are fixed in a rotatable manner to the carriage (23) according to an axis (20) which is parallel to or almost parallel to the longitudinal direction of the brush fibres (4), whereby on each support (19) is fixed a friction element (13) in a rotatable manner according to an axis (18) which is situated in a plane which is parallel to the part of the brush body (3) which is provided with brush fibres (4). Device according to claim 13 or 14, characterized in that the cam drive (26) mainly consists of a buffer shaft (27) which is mounted slidable in the longitudinal direction of the brush fibres (4) to the carriage (23) and which is equipped with a cam follower (28) which cooperates with the active surface of a cam (29) fixed on the frame (5).

Inventors: BOUCHERIE BART G, BOUCHERIE, BART G.
Applicants: BOUCHERIE NV G B, FIRMA G.B. BOUCHERIE, NAAMLOZE VENNOOTSCHAP
Application year: 1996
Main classification: A46D9
IPC codes: A46D9