Patent Application
20240293914
The invention relates to a grinding means and a method for producing the grinding means.
Grinding means of this type are used, in particular, for processing metal workpieces and are available in various grain sizes. Generally, the grinding means comprises a carrier, e.g., a carrier disk or a carrier strip made of a rigid or flexible material, onto which a binder layer and abrasive grains included in the binder layer are applied. The abrasive grains may be made from α-alumina or other materials.
The abrasive grains may, be, for one thing, crushed abrasive grains sein; furthermore, shaped abrasive grains are known which are shaped, dried and burned individually, e.g., by means of a sol gel process, and, by virtue of their consistent shapes, allow for a consistent grinding operation when suitably aligned.
For production the binder layer and the abrasive grains are applied, whereby the abrasive grains are scattered, e.g., by gravitation or electrostatically, such that they are received in the binder layer. Hereby, the abrasive grains may be aligned, e.g., using an electrostatic DC field. Subsequently, the binder layer is cured. Hereby, e.g., thermally initiated, radiation curing, as well as chemical curing using corresponding binders or curing agents/initiators are known.
In “Magnetocuring of temperature failsafe epoxy adhesives, Chaudhary, Ramanujan, Steele, Applied Materials Today 21 (2020)” the magnetic curing of epoxy resins is known. Thus, it is possible, e.g., to attach soles of sneakers and other heat sensitive materials by means of a binder layer which contains superparamagnetic nanoparticles with a defined Curie temperature. Using an alternating magnetic field or variable magnetic field the superparamagnetic nanoparticles are selectively excited and enable a thermal curing of the binder layer.
The document US 2020/0071584 A1 shows magnetizable abrasive particles that comprise ceramic particles with outside surfaces, wherein the outside surfaces comprise a layer of unfilled polyion and magnetic particles bound by the polyion. The magnetizable particles may be ferrimagnetic or ferromagnetic.
From the citation AT 368054 B a method for producing shaped pieces, in particular, disc-like shaped pieces, from an abrasive material in a powder or granulate state is known, wherein the abrasive material is dispersed in a matrix of glass melt or organic material. Hereby, the initial mass is brought into the required shape and subsequently subjected to thermal treatment first for drying and then for melting or curing of the matrix material, where the thermal treatment is carried out by means of microwave heating.
The document US 2014/0299268 A1 describes an adhesive binder film comprising at least one layer of a thermally curable synthetic resin. The thermally curable synthetic resin in turn comprises embedded metal particles suitable for being excited for the purpose of generating heat for curing the synthetic resin. The metal particles may be, in particular, iron nanoparticles.
The citation WO 2020/165709 A1 describes an abrasive article with a fabric substrate comprising threads or strings in-between which gaps are formed, where a laminate is connected to the fabric substrate and where a cured synthetic resin composite is connected to the laminate opposite the fabric substrate.
The invention is based on the object of creating a grinding means and a method for producing of a grinding means allowing for a secure and material-efficient formation of the grinding means.
This task is solved by a grinding means and the method for producing of a grinding means according to the independent claims. Advantageous further developments are described in the sub-claims.
The grinding means according to the invention may be manufactured, in particular, using the producing method according to the invention; the producing method according to the invention serves, in particular, for making the grinding means according to the invention.
Thus, the grinding means includes at least one binder layer comprising a thermally curing binder and magnetic nanoparticles. Thus, it is possible to first apply the binder layer and the abrasive grains in the usual manner and using the known process parameters and tools. The subsequent curing happens not or not exclusively by thermal admission but by means of selective excitation of the magnetic nanoparticles which, thereby, heat up and/or, by virtue of their interior change in polarity, heat up the surrounding binder, in particular, endogenously. Thus, it is possible to selectively excite the thermally curing binder without, e.g., compromise the carrier. Thus, it is possible to utilize even carrier materials such as plastics, paper and textile fibers which could otherwise be damaged by the temperature applied under conventional application of thermal energy, e.g., in a furnace. This selective curing compared to industry standard thermal curing is also advantageous under environmental considerations.
A further advantage lies in the consistent temperature distribution during the endogenous heating because the heat emanates from the nanoparticles. Thus, temperature gradients within the layer can be kept to a minimum.
The magnetic nanoparticles have a primary particle size of 2 to 100 nm, in particular, 10 nm to 70 nm, in particular, 10 to 50 nm, preferably 10 to 30 nm. In particular the range from 10 to 30 nm is particularly well suitable because of the complex relaxation ratio of the nanoparticles in the magnetic field.
Hereby, primary particle size of a nanoparticle is to be understood as a sphere-equivalent diameter of a single nanoparticle. The sphere-equivalent diameter may also be referred to as a volume-equivalent diameter of a sphere.
The magnetic nanoparticles may be, in particular, ferromagnetic, ferrimagnetic or even superparamagnetic. Superparamagnetic nanoparticles are made, in particular, of a ferromagnetic or ferrimagnetic material which maintains no permanent magnetization even at temperatures below the Curie temperature when a prior applied magnetic field has been switched off.
It is a particular advantage of the invention that the Curie temperature of the magnetic nanoparticles, above which the magnetic nanoparticles lose their magnetic properties, can be adjusted to the process temperature for curing the binder, i.e., the curing temperature. Thus, the Curie temperature may selectively lie above the curing temperature or process temperature respectively, but below a critical upper temperature that may cause damage. This guarantees a particular level of process reliability (fail safe) because the product cannot be overheated. This is the case, in particular, because at a higher process temperature the magnetic nanoparticles can no longer be activated or excited respectively and, therefore, no further heating can occur.
Alternatively, instead of the controlling by means of the Curie temperature, it is possible, e.g., to regulate the energy amount via the system parameters, i.e., in particular, for one thing, via the field strength and/or the exposure time and/or the frequency of the variable magnetic field, and/or the electrical induction field.
Further, it is also possible to selectively adjust the concentration of the nanoparticles. When multiple binder layers are formed with magnetic (in particular, metal) nanoparticles it is possible, e.g., to adjust the concentration and material differently. For purposes of the invention, in particular, the range of concentration between 3 and 30% by weight, preferably, 10 to 25% by weight, has proven to be most advantageous.
The different binder layers may have different concentrations of nanoparticles and/or different Curie temperatures of their nanoparticles.
The binder layers may comprise, in particular, a lower binder layer or basic bond and a top layer. Hereby, it is also possible for one of the layers, i.e., the lower binder layer or the lower top layer, to have a concentration of zero %.
Furthermore, e.g., a second top layer may be applied onto the first top layer. Hereby, the second top layer may be formed with or without the nanoparticles. Moreover, in this case, one or two of the three layers may also be formed, e.g., with a concentration of zero % nanoparticles.
Owing to the different Curie temperatures of the binder layers the following advantages may be attained:
Furthermore, the concentrations of the nanoparticles in plurality of layers may vary. Thus, it is possible, e.g., to heat a layer having a lower concentration to a smaller extent than a layer having a higher concentration of nanoparticles, and this may of advantage in term of process parameters. Thus, e.g., the lower binder layer may be made from epoxy resin and the top layer from phenolic resin, or vice versa. Hereby, due to the different concentrations, it may be possible, e.g., to attain a stronger heating of one of the two layers.
Furthermore, advantageously, a combination of the methods of thermal curing and endogenous curing, i.e., curing in a magnetic, induction, and/or microwave field, is provided, where this combination may happen simultaneously, for one thing. Furthermore, these methods may also be carried out successively. Thus, it is possible, in particular, to carry out a subsequent optional curing of products which have been cure already, i.e., post-curing of the grinding means in a magnetic, induction, and/or microwave field.
Furthermore, the method is suitable, e.g., for curing large rolls in that, prior to rolling up, heat is again introduced directly into the grinding means thereby creating a consistent temperature distribution in the large roll during curing.
The magnetic nanoparticles may be activated, for one thing, by an alternating magnetic field. Furthermore, however, it is also possible to utilize electromagnetic microwave radiation, e.g., in a frequency range between 1 and 10 GHZ, in particular, 2 and 7 GHZ, because the invention recognizes that an activation of the magnetic nanoparticles can be attained also by such an electromagnetic field or, respectively, electromagnetic radiation without an additional alternating magnetic field, and this activation is sufficient to create a heating excitation, and in particular, for heating the binder.
In the alternative or in addition, an induction field may be applied and utilized for the polarity switch of the nanoparticles, e.g., with frequencies in a range between 1 and 1500 kHz, e.g., 10 and 1000 kHz, in particular, 20 and 800 KHz. This, too, may lead to a heating of the binder according to the invention.
The abrasive grains may, in particular, as shaped abrasive grains include a defined support length and a defined tip. Hereby, in particular, embodiments with triangular, in particular, plane-parallel triangular abrasive grains are advantageous, because these provide a sufficient edge for contact with the carrier as well as a suitable tip. Also, equilateral triangles are of particular advantage because they will always create an equal support on one of the three edges upon spreading. Furthermore, in particular, in the alternative or in addition, non-shaped abrasive grains may be utilized.
The magnetic material of the magnetic nanoparticles may include, in particular:
The concentration of the nanoparticles in the binder may lie, in particular, in the range of:
3 to 30% by weight, preferably 10 to 25% by weight
Hereby, the concentration and the utilized alternating magnetic field may be adjusted to one another.
The magnetic nanoparticles may, e.g., also be provided with a coating and/or functionalization, which may possibly be held in the binder. Hereby, the coating may consist, in particular, of oleic acid, silicon dioxide and/or a diglycidyl ether. This may improve characteristics of dispersibility, stability against agglomeration, and integration into the binder.
As thermally curing binder a suitable composition may be prepared which possesses the appropriate process temperature.
Advantageously, for a binder, resins are mixed with a hardening agent.
As resin system, among other things, one or more of the following substances may be provided:
As hardening agent, in particular, one or more of the following substances may be used:
As resin systems alternative to this, one or more of the following systems may be provided
The application of binder may be carried out, advantageously, using one of the following methods:
The grain scattering of the abrasive grains may, advantageously, be carried out using one or more of the following methods which may also be combined.
Variant 1 of grain scattering-electrostatic, where the grain is scattered electrostatically in a constant electric field or an alternating field and aligns in flight and/or in the binder.
Variant 2 of grain scattering-gravimetric or, respectively, by gravitation, which is preferred for grain agglomerates or stabilizing grain scattering
Variant 3; the grain is applied together with the binder as a mass or mixture.
Thus, the grain scattering may be carried out by means of various methods and may, in particular, happen separately from the curing of the binder layer.
Also, the electric or, respectively, electrostatic scattering does not influence the magnetic nanoparticles so that, according to the invention, advantageously, there are broad liberties in choosing the materials and process parameters.
Furthermore, suitable fillers may be introduced into the binder, e.g., chalk (20 to 70% by weight), cryolite (20 to 70% by weight), potassium tetrafluoroborate (20 to 80% by weight), wollastonite (1 to 10% by weight), pyrogenic silica (0.1 to 5% by weight), kaolin (0.5-10% by weight).
Furthermore, suitable additives may be introduced into the binder, e.g., silanes (0.1 to 3% by weight), film formers (0.05 to 2% by weight), dispersing additives (0.1 to 5% by weight), defoamers (0.1 to 2% by weight), plasticizers (0.5 to 10% by weight), rheology modifiers (0.1 to 10% by weight).
These complementary fillers and additives as such exhibit no particular magnetic properties and can therefore, in principle, be utilized at will in addition to the magnetic nanoparticles without influencing the magnetic behavior.
The hardening or curing respectively of the binder may happen under one or more of the following conditions:
For the curing, e.g., one or more of the following curing programs and process temperatures may be utilized:
In principle, the material of the abrasive grains can be selected freely. It may be, in particular, α-alumina sein, e.g., with suitable additives formed, in particular, in a sol-gel process. Furthermore, e.g., zirconia alumina, silicon carbide may also be utilized as material for the abrasive grains.
In principle, any coating of the abrasive grains is possible. According to the embodiments with additional magnetic coating, grain pretreatments may be provided, e.g.,
According to a further development a plurality of binder layers may be provided, e.g., a lower binder layer, in which the abrasive grains are held, and an upper top layer, where multiple binder layers exhibit different concentrations of nanoparticles and/or different Curie temperatures. This allows the top layer to be formed, e.g., even without nanoparticles, i.e., with a concentration of zero. In the alternative, even the lower binder layer may be formed without nanoparticles and the upper binder layer and/or top layer with nanoparticles.
Thus, according to the invention, certain advantages are attained:
A high degree of energy efficiency is attained. The energy introduced is converted to thermal energy directly in the binder where it is evenly utilized for curing. Thus, what happens is an in-situ curing. Thus, the energy is introduced into the binding directly at the site of the chemical curing reaction and not additionally at further regions such as, e.g., the carrier and the grains, or supplementary layers provided. This also helps to avoid or minimize unnecessary thermal loan in other areas or process rooms or buildings.
The Curie temperature of the magnetic nanoparticles limits the maximum process temperature thereby precluding overheating.
The method is environmentally friendly because, compared to thermal curing methods in, e.g., a furnace or autoclave, less energy is required for magnetic curing. Thus, it is also possible to purposefully and effectively position the devices for creating the magnetic fields.
According to an embodiment the energy supply may happen in a combined manner by exciting the nanoparticles and further by another energy source, e.g., thermal heating from outside with low output, where the thermal output is preferably dimensioned such that it alone presents no relevant thermal load after termination of the excitation of the nanoparticles, e.g., above the Curie temperature. This allows, e.g., the expenditure for a alternating magnetic field to be kept at a minimum.
Aligned or upright abrasive grains are quickly fixated by means of the method and are then unable to tip over due to potential mechanical stress on the contact or from their support length on the carrier.
In particular, it is even possible in terms of process engineering to carry out the curing at a specific point in time, i.e., on demand; the process parameters can be adapted within a short period of time, in particular, in a matter of seconds.
The method according to the invention can be combined at will with conventional methods, e.g., even with thermal curing and/or radiation curing methods, i.e., thermal energy and/or radiation is supplied in addition to the curing.
The magnetic particles are not influence by the method of grain scattering, e.g., even using electric fields, so that there is a high degree of freedom in choosing process parameters.
Suitable applications are, among other things:
According to an embodiment even two or more top layers or, respectively, coating bond layers may be provided which may exhibit, in particular, different concentrations and/or different Curie temperatures of the nanoparticles.
According to an embodiment a plurality of binder layers with different Curie temperatures and/or curing temperatures may be provided. Thus, e.g., a middle binder layer having a Curie temperature of 100° C. may be provided which is provided, in particular, for curing, where the abrasive grains are then held, e.g., in a lower binder layer having a different curing temperature, and a higher Curie temperature existing in a later applied upper binder layer, in particular, the top layer.
According to an embodiment the magnetic nanoparticles may be utilized for post-curing. Thus, according to one embodiment one or more binder layers, e.g., even all binder layers including the top layer, may be cured in the conventional manner, e.g., thermically, i.e., by heating. Then, subsequently, a post-curing may be carried out by excitation of the magnetic nanoparticles.
The invention is further illustrated in the following by means of the accompanying drawings by example of certain embodiments. It is shown in:
A grinding means 1 comprises a carrier 2, e.g., a carrier strip or a carrier disk, e.g., made from a fabric material, technical paper, in particular, fiber, or plastic material, further a binder layer 3 applied onto the carrier 2, abrasive grains 4 and, preferably, a top layer 5 partially drawn in
The binder layer 3 comprises a thermally curing binder 6, in particular, epoxy resin, e.g., a bisphenol A resin, e.g., Hexion Epikote Resin 828, Ipox ER 1022, and/or a bisphenol F resin, e.g.,: Hexion Epikote Resin 862 or Ipox 1054 (Bisphenol A/F Resin).
In the thermally curing binder 6 magnetic nanoparticles 8 are evenly distributed, e.g., made of MnxZn1-xFe2O4, e.g., where x=0.1 to 0.5, preferably 0.2 to 0.5. Further materials of the magnetic nanoparticles 8 may also be made even without manganese/zinc, e.g., on the basis of iron oxide, e.g., as Fe3O4 or alternatively as Fe2O3. Thus, the abrasive grains 4 are held in the binder layer 3 by the regions which are their lower regions in the direction of the orientation, i.e., upwards in the Figures, their respective underside 4a being in contact with the carrier 2, their tips 4b projecting upwards. Their orientation may be parallel, as shown in the Figures; in principle, however, they may be aligned in a manner with their upper sides and undersides non-parallel with one another. Furthermore, the abrasive grains 4 may also be arranged inclined in relation to the vertical, in particular, uniformly tilted in a preferred direction to facilitate abrasive operation in this direction.
In the three layers 3, 5, 7 different or equal binders 6 may be provided. Further, in the three layers 3, 5, 7 equal or different concentrations of nanoparticles 8 may be provided, where, e.g., in one of the layers 3, 5, 7 a concentration of zero may be provided, and/or in the three layers 3, 5, 7 nanoparticles 8 with equal or different Curie temperatures T8 may be provided.
In
The production of the grinding means 1 happens according to the method shown in
Step ST1 of providing or producing the starting materials: The nanoparticles 8 may be produced, e.g., by means of a modified hydrothermal method which is known as such, e.g., from Chaudhary, Ramanujan, Steele, Applied Materials today-Magnetocuring of temperature failsafe epoxy adhesives, 2020.
As binder 6, in particular, epoxy resins with DICY (dicyandiamide) can be utilized.
According to Step ST2 the nanoparticles 8 are introduced or mixed in respectively into the binder 6 to attain an even distribution.
In Step ST3 the binder layer 3 is applied onto the carrier 2. To that end, the binder layer 3 may be applied, e.g., using a squeegee, e.g., knife-over-cylinder or knife-over-air, or roll coating, or even by spraying, e.g., compressed air spraying or even airless. The applied amount may be, e.g., 20 to 300 g/m2, depending on the grain size of the abrasive grains 4 to be introduced later, or, in the case of a cream mass, even 200 to 1.600 g/m2, depending on the grain size.
In Step ST4 the abrasive grains 4 are applied, i.e., grain scattering. The abrasive grains 4 may be applied gravimetrically and/or electrostatically, i.e., as electrostatic scattering. In the case of electrostatic scattering and electrostatic alignment an constant or alternating electric field E is applied.
According to Step ST5 the abrasive grains 4 are aligned. Hereby, the Steps ST4 and ST5 may be carried out in a combined fashion, i.e., the abrasive grains 4 are scattered in an aligned manner.
Upon aligning the abrasive grains 4 in Step ST5, advantageously, the positioning of the abrasive grains 4 on an edge as underside 4a is attained, as shown in
In Step ST6 the binder 6 is cured, thereby forming the solid binder layer 3. The curing of the binder 6 for forming the binder layer 3 happens by applying an alternating magnetic field 10, which principally may initially have any direction or orientation respectively. Thus, the direction or orientation respectively of the magnetic field may even change.
By virtue of the alternating magnetic field 10 the nanoparticles 8 are heated directly thereby creating heat, whereby, therefore, the entire binder layer 3 ism heat from the inside. This cures the binder 6 so that the solid binder layer 3 is formed.
The alternating magnetic field 10 may be formed, in particular, using a tunnel magnetizer. The frequency may be, e.g., 100 to 1.000 kHz. The field strength may be, e.g., 4.000 to 21.000 A/m.
Upon magnetic curing the process temperature T reached may preferably by determined by the Curie temperature T8 of the magnetic nanoparticles 8. As soon as the temperature T exceeds the Curie temperature T8 the magnetic nanoparticles 8 become non-magnetic or, respectively, will no longer be ferromagnetic, ferrimagnetic or superparamagnetic, in particular, the nanoparticles 8 become paramagnetic, and, therefore, will no longer continue to heat the binder or at least not to a relevant extent.
Further, however, even when using the alternating magnetic field process can be controlled by means of regulating the amount of energy so that possibly the Curie temperature T8 may be no longer applicable or not to a relevant extent.
Hereby, according to an embodiment the regulation the amount of energy may be carried out by measuring a surface temperature, e.g., that of the binder layer, e.g., in that the currently introduced energy is deduced from the surface temperature, and the introduced amount of energy is deduced from a process time and the measured surface temperature.
In order to attain a sufficient dwell time an array of multiple magnetic coils may be provided.
According to an embodiment alternative hereto the curing of the binder layer 3 happens not by means of an alternating magnetic field but, rather, by means of microwave radiation 11, e.g., in a frequency range from 1 to 5 GHZ, e.g., at 2.4 GHZ. By virtue of the microwave radiation 11, which, thereby, constitutes electromagnetic radiation in this frequency range, it is possible, in particular, to attain an induced excitation and thereby polarity shift of the nanoparticles 8 which, thereby, in turn leads to a heating of the nanoparticles 8 themselves as well as of the binder 6.
When using microwave radiation 11 power can be controlled process-based, and/or for a controlling function the temperature of the binder 6 may be measured, e.g., by means of an infrared sensor.
Subsequently, in a Step ST7 according to
Furthermore, in Step ST7 according to
In the case of the variant involving grain scattering by gravitation, the abrasive grains 4 are scattered from above into the carrier 2 with the binder layer 3. Thus, the abrasive grain 4 will align rather arbitrarily. Such embodiments are relevant for grain agglomerates or even stabilizing grain scattering, where part of the abrasive grains 4 serves as stabilizing grains for the further abrasive grains 4.
Hereby, e.g., in addition, smaller abrasive grain particles may be introduced in-between the abrasive grains 4 as so-called gravel which, in particular, supports the shaped abrasive grains 4.
In the alternative or in addition to a magnetic curing of the binder layer 3 holding the abrasive grains 4, even another binder layer, e.g., a top layer 5, 7 or, respectively, top layers may be magnetic cured. Thus, it is possible, to selectively cure one or more layers 3, 5, 7, e.g., even with different Curie temperatures T8, the process-related regulation of the energy amount, and/or even with different concentrations of the nanoparticles 8.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2021 116 139.8 | Jun 2021 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2022/100457 | 6/22/2022 | WO |
