Patent Application
20240375245
The present invention relates to a grinding plate for a grinding disk of a grinding machine.
Grinding machines for machining substrates are known in the prior art. Such grinding machines have a motor with which a grinding disk can be driven. The grinding disk comprises a grinding plate and a grinding attachment. The grinding attachment comprises an abrasive that is brought into contact with the substrate and machines the substrate by means of a rotational movement of the grinding disk. It is known that the grinding attachment or the grinding means can wear, and so the attachment must be exchanged regularly. In order to enable such an exchange, various connection methods between the grinding plate and the grinding attachment are known in the prior art. In particular, the grinding plate and the grinding attachment can be connected to one another with a Velcro fastener connection. The Velcro hooks are usually attached to the grinding plate and the Velcro fleece is attached to the grinding attachment.
The Velcro hooks usually form a Velcro hook fabric that is adhesively bonded to the grinding plate, with this adhesive connection having turned out to be technically challenging in the past. In particular, there are disadvantages associated with the adhesive connection, such as a complicated pretreatment of the components involved through mechanical reworking, degreasing, application of a primer, low process reliability, the need for manual work steps, and a multipart process chain with injection molding of the basic body of the grinding plate, post-processing of the components and an application of the Velcro tape. As a result, the production process for grinding disks, in which a Velcro hook fabric is fastened to the grinding plate with an adhesive connection, is costly, complex, and labor-intensive.
In order to overcome the disadvantages of an adhesive connection, it has been proposed in the prior art to produce the Velcro hooks integrally using an injection molding method. For example, U.S. Pat. No. 5,656,226 A proposes using layered tool inserts in order to apply the Velcro hooks to a surface of an object. The geometry of the Velcro hooks is repeatedly cut into thin laminations, with these laminations being joined together to form a lamination stack, as a result of which the layered tool insert is obtained. In particular, undercut microstructures can be realized in this way.
However, the disadvantage of using layered tool inserts is that structures or Velcro hooks in the desired order of magnitude can only be produced using so-called “unfilled plastics”. The term “unfilled” preferably means in the context of the invention that the plastic contains no inorganic and/or organic fibers or other fillers in the order of magnitude of the microstructure. The corresponding plastics can preferably also be referred to as “unreinforced plastics” within the meaning of the invention. However, it has been shown in the past that such grinding plates with integrally manufactured Velcro hooks made of unfilled plastics do not have sufficient rigidity for use when grinding hard substrates, such as concrete, for example.
The use of fiber-reinforced plastics is also ruled out in the production of Velcro hooks by the fact that the production of the undercut structures requires forced demolding, which is associated with deformation and elastic deformation of the Velcro hooks. Owing to the low viscosity of the plastic material needed for filling the structures, as well as the high elongation needed for forced demolding, fiber-reinforced plastics cannot be used when using layered tool inserts.
For production-related reasons, the Velcro hooks that are produced with the layered tool inserts are each arranged along straight lines and parallel to one another. Furthermore, usually only part of the surface of the object is provided with Velcro hooks, and so its surface is not completely available for the Velcro connection. This incomplete covering of the surface of the object with Velcro hooks can have a negative effect on the adhesive action of the Velcro fastener connection.
In addition to the grinding plates with integrally formed Velcro hooks, grinding disks are known in the prior art in which a Velcro hook tape is adhesively bonded to the grinding attachment with a foamed adhesive. Such grinding plates often have a soft intermediate layer, which usually comprises a thermoset plastic, such as a polyurethane foam, for example. The intermediate layer serves in particular to compensate for tolerances and for adhesive bonding. Depending on the material used, grinding plates of this type also do not have sufficient rigidity for the application of concrete grinding.
It is an object of the present invention to overcome the above-described shortcomings and disadvantages of the prior art and to provide a grinding plate for a grinding disk of a grinding machine, which has sufficiently high rigidity for performing concrete grinding work. The grinding plate should be simple and inexpensive to produce, it being a further concern of the invention that the exchange of grinding attachments can be carried out quickly and in an uncomplicated manner for the user of the grinding machine. The connection between the grinding plate and the grinding attachment should be robust and strong enough to allow safe and risk-free use in the field of concrete grinding. In a second aspect, the object of the present invention is to specify a production method for such a grinding plate.
The present invention provides a grinding plate for a grinding disk of a grinding machine is provided, wherein the grinding plate has a basic body and a Velcro hook layer with Velcro hooks. The basic body comprises a fiber-reinforced plastic, while the Velcro hook layer comprises a nonreinforced plastic. It is preferred within the meaning of the invention that the Velcro hook layer can be attached to the basic body in one process. It is particularly preferred within the meaning of the invention that the Velcro hook layer can be molded as a thin layer of the unreinforced plastic onto the basic body. The Velcro hook layer is formed from integrally produced Velcro hooks, with the Velcro hooks being able to be connected to the basic body either in a form-fitting or integrally bonded manner. It is particularly preferred within the meaning of the invention that the grinding plate can be produced in a so-called two-component injection molding method. In a first work step of the production process, the basic body is produced from a fiber-reinforced plastic and in a second work step of the same process, the Velcro hook layer is produced from a nonreinforced plastic. It is particularly preferred within the meaning of the invention that the Velcro hooks of the Velcro hook layer are molded onto the basic body as part of the two-component injection molding method. The Velcro hook layer is preferably referred to as a soft component, with the Velcro hook layer comprising or being formed from a nonreinforced plastic as the soft component of the grinding plate. The basic body comprises a fiber-reinforced plastic or can be formed from this. Within the meaning of the invention, this can be achieved in particular in that the basic body is produced from the fiber-reinforced plastic.
In other words, the invention relates to a grinding plate that comprises a basic body as the supporting structure and an injection-molded layer that is preferably substantially completely covered with Velcro hooks on the surface of the grinding plate. The basic body is preferably produced from a rigid material, while the Velcro hook layer represents a soft component and consists of a softer, nonreinforced plastic material. The grinding plate serves for receiving a grinding attachment with a fleece underside and a functional side, the functional side preferably being provided with an abrasive.
Tests have shown that grinding plates in which the basic body comprises a fiber-reinforced plastic and the Velcro hook layer comprises a nonreinforced plastic have a surprisingly high flexural rigidity and are therefore very well suited for grinding, especially of hard substrates, such as concrete. In addition, the proposed grinding plates can be produced particularly easily and inexpensively using the two-component injection molding method, with the labor effort and the number of manual process steps in particular being able to be significantly reduced.
It is preferred within the meaning of the invention that the grinding plate comprises an abrasive as a grinding attachment, which is brought into contact with the substrate and machines the substrate by means of a rotational movement of the grinding plate. Within the meaning of the invention, the term “rotational movement” is preferably to be understood in such a way that it means a relative movement between the abrasive and the substrate to be machined. In particular, this wording should also include such grinding machines in which the abrasive does not perform any rotating movements. An example of such a grinding machine is, inter alia, a so-called orbital grinder.
It is preferred within the meaning of the invention that materials, such as fiber-reinforced polyamide 6 (PA6) or polyamide 66 (PA66) with a mass fraction of glass fibers greater than 30%, are used as the fiber-reinforced plastic for the basic body. Within the meaning of the invention, it is particularly preferred to use the fiber-reinforced plastic PA6GF30 for the structural basic body. The soft component, from which the Velcro hook layer with the Velcro hooks is preferably formed, can be produced from PA6, for example. It has been shown that this material combination is particularly well suited to producing the components of the proposed grinding plate, preferably in a single process. In particular, the material combination of PA6GF30 for the basic body and PA6 for the Velcro hook layer allows a strong, robust connection between the components of the proposed grinding plate, as well as flexibility during production. It is possible, for example, to connect the components of the grinding plate to one another in a form-fitting or integrally bonded manner.
With the proposed grinding plate and in particular the proposed material combination, in particular grinding plates with a high degree of rigidity in the region of the basic body can be provided, while the proposed grinding plates have a sufficiently high elongation at failure in the region of the Velcro hook layer to allow forced demolding of the Velcro hooks.
The invention can advantageously ensure that a surface of the grinding plate is substantially completely covered by the Velcro hook layer or with Velcro hooks. Thus, substantially the entire surface of the grinding plate is available for creating the Velcro fastener connection with the grinding attachment, as a result of which a better adhesive action between the grinding plate and the grinding attachment can be made possible. This significantly reduces the risk of an undesired detachment of the grinding attachment from the grinding plate. The wording “substantially completely” does not represent an unclear wording for a person skilled in the art, because a person skilled in the art knows that the wording “substantially completely” means that practically the entire surface of the grinding plate, apart from any isolated, small partial areas, is covered with the Velcro hook layer and thus Velcro hooks. In the case of a Velcro connection, the Velcro hooks of the Velcro hook layer interact with a Velcro fleece, with the Velcro fleece being able to be arranged, for example, on an underside of a grinding attachment. This grinding attachment can be attached to the upper side of the grinding plate by means of the Velcro connection. The Velcro fleece comprises loops that cooperate with the hooks of the Velcro hook layer in such a way that a connection between the components having the hooks and loops is produced. By using a Velcro connection between the basic body and the grinding attachment, the connection can withstand a particularly high load under a plane shear load without the connection becoming detached.
It is preferred within the meaning of the invention that the term “surface” describes the side of the grinding plate that faces the grinding attachment or the side of the grinding plate on which the grinding attachment with the abrasive is attached or applied. The other side of the grinding plate is preferably referred to as the “rear side of the grinding plate” within the meaning of the invention, this rear side of the grinding plate preferably facing the grinding machine. The surface of the grinding plate preferably forms an active surface for producing a Velcro connection between the grinding plate and the grinding attachment.
It is preferred within the meaning of the invention that the active surface of the basic body of the grinding plate is substantially annular. The annular surface is preferably delimited outwardly by an outer circumference of the basic body, the outer circumference of the basic body having a substantially circular shape. Inwardly, the annular active surface of the basic body is delimited by a central circular surface inside the basic body. Within the meaning of the invention, the “active surface of the basic body” is understood to mean that surface which is in contact with the grinding attachment, with this active surface of the basic body in particular being “substantially completely” covered with the Velcro hook layer.
It is preferred within the meaning of the invention that a surface of the grinding plate has a planarity in a range of less than 0.5 mm, preferably in a range of less than 0.3 mm, particularly preferably a planarity of 0.2 mm. In the context of the invention, the planarity is defined in terms of a shape tolerance in such a way that an actual surface of the grinding plate does not intersect virtual surfaces parallel to the ideal surface of the grinding plate at the distance of the tolerance dimension.
Owing to this low planarity, the ability of the grinding plate to be connected to the grinding attachment, which preferably has a Velcro fleece, can be significantly improved. In addition, the planar surface of the grinding plate allows particularly even wear of the grinding attachment or abrasive. This particularly even wear of the grinding attachment is achieved in particular by the fact that the grinding attachment rests equally on the substrate to be machined at all points due to the particularly planar configuration of the surface of the grinding plate and is therefore also subjected to equally high stress and wear. Owing to the particularly planar surface of the grinding plate, a particularly good utilization of the abrasive used on the grinding attachment can thus be achieved. In addition, the intervals at which the grinding attachment needs to be replaced can be significantly increased by the invention.
It is preferred within the meaning of the invention that the Velcro hooks of the Velcro hook layer are arranged oriented substantially in the circumferential direction of the grinding plate.
The orientation of the Velcro hooks in the circumferential direction advantageously corresponds to the load direction when the torque of the grinding machine is transmitted to the grinding plate. By orienting the Velcro hooks in the load direction, the transmitted torque can be significantly increased compared with a grinding disk with linearly oriented Velcro hooks.
The orientation of the Velcro hooks of the Velcro hook layer “substantially in the circumferential direction” preferably means within the meaning of the invention that the opening of the Velcro hooks is oriented substantially tangentially to an imaginary circle concentric to the annular geometry of the grinding disk. It is particularly preferred within the meaning of the invention that the radial rows are arranged between the outer and the inner boundary of the preferably annularly shaped surface of the basic body. Preferably, the radial rows are present at uniform spacings between the outer and the inner boundary of the surface of the grinding plate. It is preferred within the meaning of the invention that the radial rows are arranged substantially equidistant from one another. In other words, this means that the spacings between the radial rows are substantially identical. Preferably, the radial rows have a spacing in a range from 0.3 to 2 mm, preferably a spacing in a range from 0.5 to 1.5 mm, particularly preferably a spacing of 0.7 to 1.0 mm and most preferably a spacing of 0.8 mm.
It is preferred within the meaning of the invention that the Velcro hooks of the radial rows are oriented in an alternating manner in the clockwise direction and in the counterclockwise direction. In the context of the invention, this preferably means that the Velcro hooks are present in rows from the outside to the inside, with, for example, in the outermost layer the Velcro hooks being oriented in the clockwise direction (orientation A), while the Velcro hooks in the second outermost layer are oriented in the counterclockwise direction (orientation B). This advantageously results in an orientation pattern of alternately A- and B-oriented, radially arranged Velcro hook rows.
It is preferred within the meaning of the invention that the Velcro hooks have a height in a range from 0.4 to 1.2 mm, preferably a height in a range from 0.5 to 0.9 mm, particularly preferably a height in a range from 0.6 to 0.8 mm and most preferably a height of 0.7 mm. Tests have shown that Velcro hooks made of nonreinforced plastic with a height of 0.7 mm can be produced particularly easily and in an uncomplicated manner and at the same time have a good adhesive action with an adhesive fleece that is attached to the grinding attachment, for example. It is preferred within the meaning of the invention that the Velcro hooks have substantially the same height.
In the context of the invention, this preferably means that the Velcro hooks of the different radial rows are each of the same height and that the height of the Velcro hooks does not change from the outside to the inside, or vice versa. In particular, the Velcro hooks of the Velcro hook layer are not present in groups but in radial rows. These radial rows can in particular be arranged equidistantly from one another.
It is preferred within the meaning of the invention that the Velcro hooks have a width in a range from 0.05 to 5 mm, preferably a width in a range from 0.1 to 0.3 mm and particularly preferably a width of 0.2 mm. Tests have shown that Velcro hooks made of nonreinforced plastic with a width of 0.2 mm can also be produced particularly easily and in an uncomplicated manner and also have a good adhesive action with an adhesive fleece. The same advantageously also applies to a Velcro hook layer with a total thickness in a range from 0.3 to 3 mm, preferably a total thickness in a range from 0.5 to 2 mm, particularly preferably a total thickness of 0.8 to 1.5 mm and most preferably a total thickness of about 1 mm.
In a second aspect, the invention relates to a method for producing a grinding plate. The terms, definitions and technical advantages introduced for the grinding plate preferably apply analogously to the production method. The method for producing the grinding plate is characterized by the following method steps:
It is preferred within the meaning of the invention that the method is carried out as a two-component injection molding method. Preferably, the Velcro hook layer can be attached to the basic body in a form-fitting or integrally bonded manner. It is preferred within the meaning of the invention that the method comprises a method step of countering in order to avoid any distortions. The term “distortion” is to be understood within the meaning of the invention as a deviation from a geometry of the tool cavity due to process-induced stresses. Usually, such an unwanted deformation has to be “countered” in an iterative process, i.e. the deformation of the component is introduced into the tool in an inverted manner. To do this, the surface of the injection molding tool must be machined. In this way, surfaces functionalized with Velcro hooks can undesirably lose their microstructuring that supports the functionality.
In the context of the invention, the term “countering” preferably means that a geometry of the injection mold used in the production of the grinding plate is adapted in such a way that any distortions and/or shrinkage of the material, as well as thermal and/or mechanical changes that can occur or are expected when the material cools down are taken into account when shaping the geometry of the injection mold. In other words, it may be that a shape of the injection mold does not coincide with the desired shape of the finished, cooled grinding plate, but that the injection mold is designed in such a way that the grinding plate, after it has cooled and after any distortions, shrinkage or thermal and/or mechanical changes have occurred, assumes or has its desired shape. Countering thus represents a measure to combat changes that occur in reality in an object produced by an injection molding method, which can occur when the object cools.
It is preferred within the meaning of the invention that the Velcro hooks of the Velcro hook layer are produced with laminar tool inserts, the laminar tool inserts being able to comprise, for example, alternatingly stacked lamination assemblies. The grinding plate can be produced in particular with a laminar tool insert, with the tool inserts serving as molds for the injection molding method. In this case, the laminar tool insert can comprise a multiplicity of individual laminations which form a lamination stack or a lamination assembly. Individual laminations can be removed from this lamination stack, which later serve as spacers. The remaining laminations can be functionalized by introducing microstructures into the laminations. These microstructures can form the molds for the Velcro hooks of the Velcro hook layer that are to be produced. The microstructures preferably form depressions into which the unreinforced plastic can penetrate. After cooling and forced demolding of the grinding plate, the material that was present in the depressed microstructures of the laminar tool insert forms the Velcro hooks of the Velcro hook layer. After the depressed microstructures have been introduced, the lamination stack can, for example, be assembled in an alternating manner, as a result of which the orientation pattern can be formed by radially arranged Velcro hook rows with an alternating A and B orientation. This advantageously allows for an arrangement of the radial rows in which the rows are oriented in an alternating manner in the clockwise direction and in the counterclockwise direction. For example, the lamination stack can contain a sequence of laminations arranged as follows: 1) lamination with a microstructure that creates Velcro hooks with an A orientation, 2) spacer lamination as a spacer, 3) lamination with a microstructure that creates Velcro hooks with a B orientation, 4) spacer lamination as a spacer, etc.
The wording “lamination assembly” or “lamination” is to be understood in the context of the invention in such a way that the individual components that form the layers in the “lamination assemblies” of the tool inserts can of course not only be formed from or compise sheet metal, but can also be formed from or comprise other materials, alloys and/or metals. The term “lamination” is therefore to be understood in the context of the invention as a preferably metallic component of a laminar tool insert, into which, for example, microstructures can be introduced or which can serve as spacers between functionalized “laminations” within the tool insert. In the context of the invention, the term “lamination assembly” is to be understood as an arrangement of a large number of such laminations, with a laminar tool insert comprising at least one lamination assembly made of individual laminations that are preferably arranged in an alternating manner.
It is preferred within the meaning of the invention that the tool inserts also have at least one distortion cushion in addition to the lamination assemblies. The use of a distortion cushion allows countering of the grinding plate to be produced. The advantage of using a distortion cushion is in particular that the once produced lamination assemblies do not have to be changed if iteratively minimal corrections or changes to the grinding plate to be produced or the Velcro hooks to be produced are required. Rather, the provision of a distortion cushion makes it possible that only the distortion cushion itself has to be machined and changed in order to make minimal corrections or changes to the object to be produced by the injection molding method, here the grinding plate.
It is preferred within the meaning of the invention that the lamination assembly is arranged in an insert frame, with the lamination assembly forming the laminar tool insert in the insert frame. When using a distortion cushion, it is preferred within the meaning of the invention that the distortion cushion is arranged between the insert frame and the lamination assembly. The distortion cushion preferably represents the surface line of the desired surface of the grinding plate or of the object to be produced. Since the laminations of the lamination assembly butt against the distortion cushion, the laminations or the lamination assemblies represent this surface—preferably in a stepped manner. All that is required to rework or iterate the distortion is to adapt the distortion cushion without having to rework the lamination assembly or the tool insert.
An alternative possibility of producing complexly shaped components, such as a grinding plate for a grinding disk of a grinding machine, is for the insert frame to have concavely or convexly curved surfaces that can act like a distortion cushion. The curvatures of the surface of the insert frame are transferred to the lamination assembly, which—as described—is inserted into the insert frame. In the context of this embodiment of the invention, it is preferred that the lamination assemblies are braced between two contour-defining surfaces, for example, so that the desired microstructures, such as the Velcro hooks of the Velcro hook layer, can be produced by targeted shaping of the insert frame. In addition, the microstructures can be freely oriented in the plane using the method.
Further advantages will become apparent from the following description of the figures. The figures, the description and the claims contain numerous features in combination. A person skilled in the art will expediently also consider the features individually and combine them to form useful further combinations.
Identical and similar components are denoted by the same reference signs in the figure, in which:
| Number | Date | Country | Kind |
|---|---|---|---|
| 21177172.0 | Jun 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/063401 | 5/18/2022 | WO |
