Patent Publication Number: US-2019168361-A1

Title: Grinding Disc Device for a Grinding Apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a grinding disc device for a grinding apparatus, in particular to a grinding disc with a carrier disc. 
     2. Description of the Related Art 
     Grinding disc devices or grinding tools are sufficiently well known. In the case of known grinding disc tools, grinding bristles can, for example, be molded on a plastic base essentially constituted of plate-shaped or grinding filaments which can be embedded in a plastic matrix. Such a grinding brush, wherein grinding bristles with abrasive particles are molded on a plastic base, is disclosed for example in U.S. Pat. No. 6,179,887 B1, wherein the grinding surface with this kind of grinding brush is formed by the ends of the bristles at the free-end side. German Patent No. DE 196 50 393 A1 in turn describes a grinding tool, wherein a bundle of grinding monofilaments is attached to a hub and the grinding monofilaments attached to the hub are embedded in an elastomer foam. With their tips facing away from the hub, the embedded grinding monofilaments form an annular or cylindrical grinding surface. 
     Furthermore, a grinding tool is known from PCT Publication No, WO 2005/115716 A1, which is produced by means of an injection molding process. To produce the grinding tool of PCT Publication No, WO 2005/115716 A1, particles of an abrasive granulate, or an abrasive agglomerate are scattered into an injection mold and thermoplastic elastomer material is then injected into the injection mold, so that the particles of the abrasive granulate are embedded in the thermoplastic elastomer material. 
     A drawback, however, is that the aforementioned grinding tools often do not produce the desired grinding performance, especially for specific purposes or in specific applications. 
     Grinding disc devices, i.e. grinding discs with carrier discs, are also known which usually comprise a carrier disc or support disc or a carrier plate with an abrasive grinding disc or grinding layer fastened or connected thereto. Such a grinding disc with a carrier disc is known for example from German Patent No. DE 10 2016 102 037 B4, wherein an abrasive grinding layer is applied to a rigid carrier disc made of polyamide or ABS, the grinding layer comprising grinding lamellas arranged fan-shaped. 
     In order to fasten the grinding layer on the carrier disc, use is made, for example, of an adhesive, which ensures a durable connection between the grinding layer and the carrier disc. Such an adhesive must therefore satisfy a variety of conditions, in particular an unlimited strength even in a continuous operation and at high temperatures. Furthermore, the fastening of the grinding layer by means of the adhesive on the carrier disc requires sufficient hardening, which delays production considerably. 
     Despite the solutions known from the prior art, there is therefore a need for easily and cost-effectively producible, improved grinding disc devices, which are suitable for the most diverse kinds of application and exhibit an adequate grinding performance. 
     SUMMARY OF THE INVENTION 
     The present invention, therefore, provides a grinding disc device, which can easily be produced and provides an improved grinding performance, and with which the drawbacks of the prior art caused by the adhesive are avoided without limitations. 
     The present invention provides a grinding disc device for a grinding apparatus, which comprises at least one grinding layer and a carrier disc fixedly connected to the grinding layer. The grinding layer comprises on a first side at least one connection surface connected to the carrier disc and, with a second side lying opposite, forms an abrasive grinding surface lying opposite the connection surface and facing away from the carrier disc. The carrier disc is made of a plastic material and is produced by means of injection molding. The carrier disc is connected immediately and directly to the connection surface of the grinding layer. The plastic material of the carrier disc is sprayed by means of injection molding immediately and directly onto the connection surface of the grinding layer in such a way that the carrier disc and the grinding layer are connected to one another in a materially-bonded manner. 
     A grinding disc device for a grinding apparatus is essentially understood in the present case to mean a grinding disc with a carrier disc or carrier plate. In the sense of the present invention the grinding disc device is to be regarded as a grinding body, which can also be described as a grinding tool or grinding plate or as a carried or held or supported grinding disc. The grinding disc is designed particularly for rotating surface fine-machining and is configured for use in a grinding apparatus correspondingly driven rotationally or such machine tool, for example a grinding machine, in particular an angle grinder. 
     In the present case, the carrier disc can also be described as a carrier plate and is essentially to be understood as a support body, a support disc, or a support plate. A grinding layer, in the sense of the invention, is to be understood as an essentially flat or planar disc-like element or a flat or planar disc-like structure with a first side or side face and an opposite second side or side face. The first side face forms the connection surface, which is immediately and directly connected to the carrier disc, and the opposite second side face forms the outwardly orientated grinding surface which defines an underside of the grinding disc device. The grinding layer may consist of a single part, or also of a plurality of assembled parts, which together form the flat or planar disc-like structure. According to the present understanding, therefore, the connection surface and the grinding surface can also be constituted as non-planar surfaces and can for example comprise steps or graduations, offset edges or protruding regions, which may perhaps arise if a plurality of parts are arranged together in a preferably fan-shaped arrangement to form a flat structure. 
     To solve the aforementioned problem, according to the invention, the carrier disc made of plastic is sprayed by means of an injection molding process immediately and directly onto the grinding layer, i.e. onto the connection surface of the grinding layer, without an intermediate layer, in particular without an adhesive or bonding agent applied in between. 
     Compared to the prior art, this solution has the considerable advantage of a straightforward and quick production, which essentially requires only one process step, i.e. the injection molding process or the forming by means of injection molding and takes place without the frequently impracticable influences of an adhesive, because the plastic material of the carrier disc is sprayed directly onto the grinding layer. The essentially liquid, i.e. plasticised, plastic material connects in an integrally, materially-bonded manner with the connection surface of the grinding layer. As a result, after only a short hardening time of less than a minute, a firm, durable connection between the two parts arises, which is also extremely durable at high speeds of the grinding disc device and therefore at high temperatures. 
     Due to the immediate and direct connection of the grinding layer to the carrier disc according to the invention, the present grinding disc device particularly advantageously has an improved grinding performance, since the bonding of the grinding layer to the carrier disc is thereby improved and is thus much more stable. This leads to an overall harder grinding disc device, in particular to a stabilised grinding surface with a greater degree of hardness. The grinding disc device according to the invention can thus advantageously be operated in a rotating manner in a grinding apparatus with the avoidance of disruptive vibrations, i.e. particularly advantageously vibration-free. This proves to be particularly advantageous, since such grinding apparatuses are operated at high speeds, for example in a range from 10,000 to 15,000 revolutions per minute, and the avoidance of vibrations at such high speeds leads to a particularly reliable and efficient operation. 
     In order to further improve the stability, in particular the dimensional stability and/or the rigidity of the grinding disc device, reinforcing structures can optionally be provided in the carrier disc, and more precisely at an upper side of the grinding disc device, which reinforcing structures can be constituted for example in the form of annular ribs. In addition, or alternatively, structures for improving the elasticity of the grinding disc device, in particular for improving the elasticity during application when grinding, can also be provided, which structures can for example be constituted in the form of annular grooves. 
     According to a preferred embodiment, the grinding layer of the grinding disc device may consist of a flat, circular grinding disc, in particular a sanding disc. The grinding layer can then preferably be formed by a conventional, commercially available grinding disc, which usually comprises a carrier or carrier material and an abrasive medium applied thereon. In accordance with such a construction, paper carriers, fabric carriers, or vulcanised fiber carriers are used as carriers and the abrasive medium can for example be a ceramic grain. The side of the carrier which is loaded with the abrasive medium represents the grinding surface and the opposite, unloaded side of the carrier represents the connection surface. In this embodiment, the connection surface is thus essentially formed from the material of the carrier of the grinding disc. 
     Preferably, the grinding layer is formed by a fiber disc, in particular a vulcanised fiber disc, and the grinding surface is formed preferably by a scattered ceramic grain abrasive medium. Such grinding discs are produced and marketed for example by the firm “VSM Vereinigte Schmirgel- and Maschinen-Fabriken AG” and are available in the market under the trade name “VSM CERAMICS Fiberscheiben”. 
     In these particularly preferred embodiments, the carrier material of the vulcanised fiber carrier of the grinding disc forms the connection surface of the grinding layer for direct connection to the plastic material of the carrier disc. 
     The grinding layer can also be composed of grinding lamellas, which are arranged for example in a fan-shaped manner to form the flat structure of the grinding layer. In all cases, the plastic material for the carrier disc can be injected in the desired manner into the molding tool of the injection molding machine and sprayed directly onto the connection surface of the grinding layer. 
     The connection surface and the grinding surface lying opposite the connection surface are each preferably constituted at least as annular, essentially continuous surfaces. In the present case, this is understood in particular to mean that the two aforementioned surfaces, in at least one annular section, form a continuous, closed surface without interruptions. The annular, essentially continuous surface or the annular, continuous surface section preferably occupies more than half, particularly preferably more than 60% and with particular preference more than 70% of the total area of the underside of the grinding disc device. More preferably, the annular, continuous surface section has a surface segment area of more than 80% or more than 90% of the total area of the underside of the grinding disc device. On the one hand, the connection surface, onto which the plastic material of the carrier disc is sprayed, is thus constituted at least in an annular section as a continuous surface, which ensures a uniform and reliable connection between the grinding layer and the carrier disc. On the other hand, the grinding surface is sufficiently large to permit a good grinding performance and efficient use. 
     Particular advantages arise from the fact that the grinding surface of the grinding disc device, i.e. the grinding surface of the grinding layer connected to the carrier disc, is constituted dish-shaped. This is understood to mean that the grinding surface does not run even or flat in a plane, but rather has an arch or curvature. For example, the grinding surface is arched in a radial direction, starting from an edge of the grinding disc device in the direction towards the center, and more precisely for example with a gradient angle in a range from approximately 3° to 10°, preferably in a range from approximately 4° to 7°, and more preferably of around 5°. 
     According to a preferred embodiment of the present invention, slots distributed over its periphery for the passage of cooling air are designed or formed in the carrier disc. Such slots are known for example from the aforementioned German Patent No. DE 10 2016 102 037 B4. These slots provide, especially at high speeds, for an effective cooling air flow in the direction of the grinding layer and the machined workpiece, without the durability and service life thereby being adversely affected. In a continuous operation, temperatures over 100° C. can be tolerated over a long period. 
     In a development of the invention, the carrier disc is constituted in one piece with a hub part, from which ventilation ribs extend radially outwards. By means of the latter, a cooling air flow is additionally generated, which markedly reduces the working temperature. 
     Preferably, the hub part comprises an inner thread for the fastening of the grinding disc device on a drive shaft of the grinding apparatus. Cooling air passage slots can also be fashioned into the hub part, which again assist efficient and effective cooling. 
     The carrier disc is preferably produced from a thermoplastic plastic, in particular from a thermoplastic polymer. For example, the carrier disc can be made from a thermoplastic terpolymer, preferably from an acrylnitrile-butadiene-styrene copolymer (ABS). According to an alternative variant of embodiment, the carrier disc can be made from a polyamide, preferably from polyamide PA6, in particular from a glass fiber-reinforced PA6. Polyamide PA6 is a thermoplastic, partially crystalline construction plastic, which can be processed as a tough, hard industrial material. The main properties are a high impact resistance, rigidity, and a good damping capacity, as well as a relatively high dimensional stability. As a result of a possible glass fiber reinforcement, for example with a glass fiber content of 30%, the plastic is ultimately even firmer and more rigid. As a result of the use of PA6 or PA6-GF30, the production of the grinding disc device can take place in the optimum manner by means of injection molding, wherein the stability, strength, and hardness of the grinding disc device are at the same time also matched in the optimum manner to the technical requirements. 
     The present invention also includes a method for producing a grinding disc device for a grinding apparatus by injection molding. In the method, a grinding layer with a connection surface and an opposite abrasive grinding surface is first provided and introduced into a suitable molding tool of an injection molding machine. The grinding layer is introduced into the suitable molding tool of the injection molding machine in such a way that the connection surface of the grinding layer points in the direction of a predefined cavity of the molding tool. A carrier disc directly connected to the grinding layer is then formed, wherein a plastic material suitable for producing the carrier disc is injected into the closed molding tool at a predefined temperature and under pressure. More precisely, the plastic material of the carrier disc is sprayed immediately and directly onto the connection surface of the grinding layer and the grinding disc device is thus produced. 
     In injection molding, which numbers among the primary shaping processes, a suitable material, in particular a plastic material is liquefied, i.e. plasticised, and injected under pressure with an injection molding machine into a cavity of a corresponding mold, i.e. into the molding tool or injection molding tool. The cavity represents the shaping hollow space. In the molding tool, the plastic material transforms back into the solid state by cooling or a cross-linking reaction and can be removed as a finished part after the opening of the molding tool. 
     With the method according to the invention, the grinding layer, and more precisely for example in the form of a grinding disc, in particular a vulcanised fiber disc, is first introduced or placed into the cavity of the molding tool of the injection molding machine prior to the injection of the plastic material. The grinding layer is placed into the cavity of the molding tool in such a way that the connection surface of the grinding layer is facing the hollow space, i.e. the cavity or the lumen of the hollow space. That is to say that the side of the grinding surface lies against an inner wall or hollow-space wall of the molding tool. As a result, the grinding surface is facing outwards in the finished molded part of the grinding disc device. 
     During the injection of the plastic material into the shaping hollow space, which injection takes place for example under a pressure in a range from 500 bar to 2000 bar and at a temperature in a range from 200° C. to 330° C., the plastic material is sprayed directly onto the connection surface of the grinding layer, which is formed for example by the vulcanised fiber material of the vulcanised fiber carrier of the grinding disc. No prior treatment of the connection surface whatsoever is required, i.e. any kind of use of additional binder or adhesive agents or adhesives, bonding agents or such can be completely avoided. 
     As a result of the hardening in the injection molding machine, the plastic material of the carrier disc hardens and is directly bonded or fixed to the connection surface of the grinding layer. In particular, it is connected in a materially-bonded manner to the latter. 
     The carrier disc is preferably constituted in one piece with a hub part by the injection molding. In addition or alternatively, slots distributed over the periphery of the carrier disc for the passage of cooling air can also be formed by the injection molding. 
     Preferably, an inner thread is formed in the hub part for the fastening of the grinding disc device on a drive shaft of the grinding apparatus. 
     In addition, or alternatively, the hub part can also be formed with corresponding cooling air passage slots. 
     With the method, a flat, circular vulcanised fiber disc with a scattered ceramic grain abrasive medium can, for example, be used as a grinding layer. At the same time, a glass fiber-reinforced polyamide PA6 as a plastic material for the carrier disc is sprayed onto the grinding layer. The preferred glass fiber-reinforced polyamide PA6 has for example a glass fiber content of 30%. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained below in greater detail with the aid of examples of embodiment in connection with the drawings. 
         FIG. 1  shows a diagrammatic plan view of a first example of an embodiment of the grinding disc device according to the invention; 
         FIG. 2  shows a cross-section through the grinding disc device of  FIG. 1 ; 
         FIG. 3  shows a perspective view of the grinding disc device of  FIG. 1 ; 
         FIGS. 4-6  show an alternative embodiment of the grinding disc device according to the invention in plan view, in a cross-sectional representation, and in a perspective view; 
         FIGS. 7-9  show a further alternative embodiment of the grinding disc device according to the invention, wherein the grinding layer comprises grinding lamellas, in plan view, in a cross-sectional representation, and in a perspective view; 
         FIGS. 10-12  show a further alternative embodiment of the grinding disc device according to the invention, wherein the grinding layer comprises grinding lamellas, in a view from beneath, in a cross-sectional representation, and in a perspective view from beneath; 
         FIGS. 13-15  show a further alternative embodiment of the grinding disc device according to the invention, wherein the grinding layer comprises grinding lamellas, in a view from beneath, in a cross-sectional representation, and in a perspective view from beneath; 
         FIGS. 16-18  show yet another embodiment of the grinding disc device according to the invention, in plan view, in a cross-sectional representation, and in a perspective view and 
         FIGS. 19-21  show yet another embodiment of the grinding disc device according to the invention, in plan view, in a cross-sectional representation, and in a perspective view. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     All the examples of embodiment described below have in common that grinding disc device  10 , according to the invention, comprises an essentially circular carrier disc  12  provided with an abrasive grinding layer  14 , such that grinding layer  14  and carrier disc  12  are immediately and directly connected to one another without an intermediate layer. The side of grinding disc device  10  on which abrasive grinding layer  14  is arranged represents an underside U of grinding disc device  10 . Opposite underside U of grinding disc device  10  lies an upper side O defined by carrier disc  12 . 
     Carrier disc  12  is produced by means of injection molding and is directly sprayed onto grinding layer  14  thereby constituting grinding disc device  10  according to the invention. Carrier disc  12  is made of plastic, for example ABS, since the material is food-safe, has a sufficient elasticity, and has a long life. Other injectable plastics can also be used for carrier disc  12 . More preferably, carrier disc  12  is made of a polyamide, in particular of polyamide PA6, and even more preferably of glass fiber-reinforced polyamide with for example a 30% glass fiber content, such as for example PA6-GF30. 
     In injection molding, which numbers among the primary shaping processes, the plastic for carrier disc  12 , for example ABS or PA6, is plasticised and injected under pressure with an injection molding machine into a shaping hollow space, i.e. the cavity of the molding tool. The plastic material transforms back into the solid state by cooling. For the production of grinding disc device  10  according to the invention, grinding layer  14  is first placed into the cavity of the molding tool prior to the injection of the plastic material, in such a way that the side of grinding layer  14  forming a grinding surface F S  lies against an inner wall of the cavity and a connection surface F V  of grinding layer  14  is thus facing the hollow space. The subsequent injection of the plastic material into the shaping hollow space takes place under pressure in a range from 500 bar to 2000 bar and at a temperature in a range from 200° C. to 330° C. The plastic material is thus sprayed directly onto connection surface F V  of grinding layer  14 . As a result of the hardening in the injection molding machine, the plastic material of grinding disc  12  solidifies and is directly bonded to connection surface VF of grinding layer  14  or is connected in a material-locking manner to the latter. 
     In the example of the embodiment of  FIGS. 1 to 3 , grinding layer  14 , comprising a connection surface F V  and a grinding surface F S , consists of a flat, circular sanding disc  16 , wherein carrier disc  12  is sprayed directly by injection molding onto connection surface F V  of grinding layer  14  or sanding disc  16  without plastic being applied between the two latter. This takes place by means of injection molding in a suitable injection molding machine as described above. 
     Grinding layer  14  is first introduced or placed into the hollow space of the molding tool. More precisely, grinding layer  14  is placed into the hollow space of the molding tool such that connection surface F V  of grinding layer  14  is facing the hollow space, i.e. grinding surface F S  is facing an inner wall or hollow-space wall of the molding tool and in particular lies against the latter. The plasticised plastic material of carrier disc  12  is then injected into the cavity under pressure and at raised temperature. Following a short hardening time of less than one minute, the plastic of carrier disc  12  is hard and firmly connected in a durable manner to sanding disc  16  or grinding layer  14 . 
     In the example of the embodiment of  FIG. 1  to  FIG. 3 , a hub part  18  is formed in one piece with carrier disc  12  at upper side O of grinding disc device  10 , from which hub part ventilation ribs  20  extend radially outwards. The ventilation ribs  20  provide for a sufficient cooling air flow over the surface of carrier plate  12  at the speeds generated during operation. 
     As  FIGS. 2 and 3  show, hub part  18  comprises an inner thread  22 , which is also formed in the injection molding, so that carrier disc  12  can be fastened on a drive shaft of a grinding apparatus, in particular a grinding machine, such as for example an angle grinder. 
     Essentially annular grinding layer  14 , which comprises a central perforation in the region of hub part  18 , comprises an annular, continuous connection surface F V  and an annular, continuous grinding surface F S , wherein the circular surfaces extend over more than 90% of the total area of underside U of grinding disc device  10 . 
     For further, improved cooling, slots  24  are designed or formed distributed over the outer periphery or over upper side O of carrier disc  12 . The slots  24  provide for the passage of cooling air both against connection surface F V  of grinding layer  14 , which can also be seen as the inner surface, as well as against the machined workpiece. Cooling air slots  24  are fashioned according to the teaching known from German Patent No. DE 10 2016 102 037 B4, which is incorporated herein by reference. 
       FIGS. 4 to 6  show a variant of the embodiment of  FIG. 1  to  FIG. 3 , wherein carrier disc  12  is also sprayed directly and without adhesive onto grinding layer  14 . Diverging from the example of  FIG. 1  to  FIG. 3 , central hub part  18  is constituted with a flat dish-shaped and has ventilation ribs. In this example of the embodiment of  FIGS. 4 to 6 , the central perforation of grinding layer  14  in the region of hub part  18  is larger than in the example of  FIGS. 1 to 3 , so that the surface segment area of annular, continuous connection surface F V  and grinding surface F S  in the total area of underside U of grinding disc device  10  is smaller than in the example of  FIGS. 1 to 3 . 
     In the alternative, also preferred variant of  FIGS. 7 to 9 , grinding layer  14  comprises grinding lamellas  26  arranged fan-shaped. The plastic of carrier disc  12  is also sprayed without an intermediate adhesive onto grinding lamellas  26  arranged fan-shaped. Grinding lamellas  26  arranged fan-shaped again form a flat grinding layer  14  with connection surface F V  and grinding surface F S , which are also constituted in this embodiment as respective annular, continuous surfaces on account of the overlaps of grinding lamellas  26  arranged fan-shaped. 
     In the embodiment of  FIGS. 10 to 12 , hub part  18 , in the same way as in the example of the embodiment of  FIGS. 4 to 6 , does not have any ventilation ribs. The air slots at the outer periphery of carrier disc  12  are also absent in this example of the embodiment. 
       FIGS. 13 to 15  show a modified embodiment with a carrier disc  12  constituted similar to the example of  FIGS. 4 to 6 , wherein here, as also in the example of  FIGS. 10 to 12 , grinding layer  14  comprises grinding lamellas  26  arranged fan-shaped, onto which carrier disc  12  is directly sprayed. 
     Finally,  FIGS. 16 to 18  show an embodiment with a carrier disc  12 , which has cooling air slots  24  at the outer periphery for the passage of cooling air. The flat, roughly dish-shaped hub  18  of carrier disc  12  also comprises, in addition to ventilation ribs  20 , cooling air passage slots  28  for the passage of cooling air. Grinding layer  14  comprises grinding lamellas  26  arranged fan-shaped. 
     In  FIGS. 19 to 21 , an example of the embodiment of grinding disc device  10  is shown, wherein grinding layer  14  is formed by a grinding disc or a sanding disc  16 . The grinding disc is a vulcanised fiber disc, wherein grinding surface F S  is formed by a scattered ceramic grain abrasive medium. 
     In the case of grinding disc device  10  of the example of  FIGS. 19 to 21 , hub part  18  is constituted with ventilation ribs  20  and with an inner thread  22 . No cooling air slots are provided, however, in carrier disc  12 . 
     For the additional improvement of the stability, rigidity, and bending strength, reinforcing structures are constituted on carrier disc  12  at upper side O of grinding disc device  10 , and more precisely in the represented example in the form of an annular rib  30 . Furthermore, an annular groove  32  is provided, which serves to improve the elasticity during grinding. 
     LIST OF REFERENCE NUMBERS 
     
         
           10  grinding disc device 
           12  carrier disc 
           14  grinding layer 
           16  grinding disc or sanding disc 
           18  hub part 
           20  ventilation rib 
           22  inner thread 
           24  cooling air slots 
           26  grinding lamellas 
           28  cooling air passage slots 
           30  annular rib 
           32  annular groove 
         F S  grinding surface 
         F V  connection surface 
         O upper side 
         U underside