Cleaning agent for ball mills and method for cleaning ball mills

Abstract

The invention relates to a cleaning agent for ball mills, comprising a dispersion of inorganic particles in a liquid dispersion medium. The liquid phase of the cleaning agent contains at least one pH-active compound, a surfactant, and 20 to 70 wt.% inorganic particles. The invention further relates to a method for cleaning ball mills with the cleaning agent.

Description

Field of invention

[0001] The invention relates to a cleaning agent for grinding assemblies of ball mills and a method for cleaning the grinding assemblies.

[0002] Ball mills are suitable for coarse, fine, and ultrafine grinding or homogenization of materials. In the grinding chamber of the ball mill, usually in the form of a grinding bowl, the material is crushed and thus ground by grinding media. For this to occur, the material and grinding media are moved, resulting in impacts between them. Material particles located between the balls are reduced in size by this impact.

[0003] Grinding media consist of spheres or cylinders made of a hard material, such as zirconium oxide, steel, tungsten carbide, or agate. The grinding process contaminates the surfaces of the grinding media and the walls of the grinding chamber with dust from the material being ground. To prevent cross-contamination of different materials, the grinding media and grinding chamber must be thoroughly cleaned between grinding operations.

[0004] Especially with grinding media that have a rough surface, dust can adhere strongly to the surface, so cleaning usually cannot be achieved simply by loosening the contaminants, but rather requires abrasive methods. Grinding media and grinding bowls are typically cleaned with an aqueous suspension containing sand particles. This suspension is added to the grinding bowl, and the ball mill is then operated as if it were a grinding process. This mechanically removes the contaminants from the surface of the grinding media and the walls of the grinding bowl. However, a disadvantage is that such cleaning processes are prone to errors and difficult to reproduce. For example, incorrect amounts of sand and / or sand with an unsuitable grain size can be used.For example, if sand with too small a grain size is used, the mechanical cleaning effect is insufficient, and the grinding media are not completely cleaned. Conversely, if the grain size is too coarse and / or the quantity of sand is too large, abrasion of the grinding media can occur. The resulting roughened surfaces are susceptible to corrosion. For instance, corrosion of the grinding media and / or the grinding bowl can occur during the drying process after cleaning, negatively impacting the service life of these components. Depending on the type of sand used, it may also contain oxidative components as impurities, which can likewise lead to corrosion.

[0005] Since sand, as a natural product, generally does not have standardized grain or particle sizes, these adverse effects are difficult or even impossible to avoid. Consequently, the cleaning process is not reproducible. Another disadvantage of the known sand cleaning method is that coarse sand particles mix with the grinding media during cleaning and are subsequently difficult or impossible to separate. Furthermore, the cleaning effect can be reduced by an incorrect amount of cleaning agent added. Object of the invention

[0006] It is therefore an object of the invention to provide a cleaning agent for ball mills with which effective, material-friendly and reproducible cleaning is achieved. A further object is to provide a method for cleaning ball mills as well as a set comprising a ball mill and a cleaning agent tailored to it. Description

[0007] The object of the invention is already solved by the subject matter of the independent patent claims. Advantageous embodiments and further developments of the invention are the subject matter of the dependent claims.

[0008] The invention relates to a cleaning agent for cleaning ball mills, in particular for cleaning grinding media and / or grinding bowls. The cleaning agent comprises a dispersion of inorganic particles in a liquid, preferably aqueous, dispersion medium.

[0009] The inorganic particles in the cleaning agent act as abrasive particles, mechanically removing contaminants from the surface of grinding media and / or grinding cups. Thus, the inorganic particles, or the dispersed phase of the cleaning agent, constitute a mechanical cleaning component.

[0010] One embodiment of the invention provides that the inorganic particles used for cleaning have a high hardness. Preferably, the inorganic particles have a Mos hardness of at least 5, more preferably at least 7, and most preferably at least 8.5.

[0011] According to one embodiment of the invention, the inorganic particles comprise a metal oxide, a silicate, a nitride, and / or a carbide. Another embodiment provides that the inorganic particles contain a non-oxide ceramic and / or a ceramic. Non-oxide ceramics include, in particular, carbides or nitrides such as boron nitride, silicon nitride, aluminum nitride, silicon carbide, and tungsten carbide.

[0012] Ceramic materials and materials made from non-oxide ceramics are characterized by low abrasion.

[0013] In particular, the inorganic particles contain aluminium oxide (Al 2 O 3 ), steatite, porcelain, zirconium dioxide (ZrO 2 ), silicon nitride (Si 3 N 4 ), silicon carbide (SiC ), tungsten carbide (WC ), boron nitride (BN ), aluminium nitride (AIN ), aluminosilicates, pyrogenic silica and / or agate.

[0014] According to one embodiment of the invention, the grinding media contain Al₂O₃, particularly in the form of corundum. Preferably, corundum particles are used as the grinding media. For the purposes of the invention, corundum particles are understood to be particles that contain Al₂O₃ as their main component. Preferably, the corundum particles contain at least 90 wt.% Al₂O₃, particularly preferably more than 95 wt.% Al₂O₃ or even more than 98 wt.% Al₂O₃. In addition to Al₂O₃, the corundum particles may contain further components, in particular Na₂O, Fe₂O₃, and / or Cr₂O₃. These minor components may be present, in particular, in the form of unavoidable impurities in the starting materials used to produce the corundum particles.

[0015] The use of inorganic particles with high MOS hardness allows for particularly thorough mechanical cleaning, making corresponding embodiments especially advantageous in the case of stubborn contaminants.

[0016] An alternative embodiment provides that the inorganic particles have a Mos hardness of less than 5 or even less than 4. Such cleaners are less abrasive and are therefore particularly advantageous when the grinding balls have fewer firmly embedded contaminants or are sensitive to abrasion. Preferably, in this embodiment, the inorganic particles have a Mos hardness in the range of 3 to 5. These inorganic particles can, for example, contain ground pumice, also known as pumice powder, calcium carbonate, and / or kaolin.

[0017] Unlike sand, for example, the inorganic particles contained in the cleaning agent have a defined particle size and / or particle size distribution. The mean particle size distribution d50 is preferably in the range of 50 to 100 µm, particularly in the range of 65 to 90 µm. The particle size and / or particle size distribution of the inorganic particles can be adjusted depending on the particle size of the grinding media. In particular, the particle size of the inorganic particles can be selected to ensure the most effective mechanical cleaning of the surfaces and, at the same time, to allow for easy separation of the inorganic particles from the grinding media after cleaning. It is especially advantageous if the particle size of the inorganic particles is adapted to the size of the grinding media so that they are small enough to cover the surface of the grinding media as densely as possible and thus completely.One embodiment provides that the following applies to the mean particle size of the inorganic particles d Anorg and the particle size of the grinding media d Mahl:. d Anorg < 0 , 1 * d Mahl .

[0018] According to one embodiment, the inorganic particles have a particle size distribution with d10 in the range of 25 to 52 µm, d50 in the range of 65 to 90 µm, and / or d90 in the range of 105 to 150 µm. Preferably, the inorganic particles have a spherical shape or at least a largely spherical shape. According to one embodiment, the inorganic particles are spherical. This enables uniform mechanical cleaning.

[0019] The total content of inorganic particles in the cleaning agent is 20 to 70 wt.%, preferably 40 to 60 wt.%.

[0020] The cleaning agent comprises, in addition to the inorganic particles, a liquid, preferably polar, and particularly preferably water-miscible or water-containing dispersion medium in which the inorganic particles are dispersed. Within the scope of this disclosure, the dispersion medium is also referred to as a dispersing agent. A polar dispersion medium is understood to be, in particular, a dispersion medium whose components have polar groups such as hydroxyl groups and are preferably miscible with water or contain water. In particular, the dispersion medium is an aqueous dispersion medium. Here, an aqueous dispersion medium within the meaning of the invention is understood to be a dispersion medium that contains at least 50 wt.%, preferably at least 80 wt.% water. Alternatively or additionally, the dispersion medium may comprise further liquid components, which are preferably miscible with water.In particular, the dispersion medium can contain polyalcohols, especially polyglycols. This allows, for example, the adjustment of the dispersion medium's rheological properties.

[0021] According to one embodiment, the aqueous dispersion medium comprises a water-soluble polymer. The water-soluble polymer can be dissolved in the aqueous dispersion medium or be present as a water-miscible, liquid component of the dispersion medium. Polyethylene glycols, especially those with an average molar mass in the range of 200 to 600 g / mol, have proven particularly advantageous in this regard. These can be, in particular, polyethylene glycols with an average molar mass of at most 400 g / mol, such as polyethylene glycol 400 (CAS number 25322-68-3). The cleaning agent can also contain mixtures of various water-soluble polymers, especially different polyethylene glycols. According to one embodiment of the invention, the cleaning agent contains 0.2 to 1 wt.% of a water-soluble polymer, in particular a polyethylene glycol.

[0022] One embodiment provides that the dispersion medium contains or even consists entirely of polyethylene glycols. The use of liquid polyethylene glycols with relatively low viscosities has proven particularly advantageous in this context. One embodiment provides that the dispersion medium contains or consists of a polyethylene glycol with a viscosity at 20°C of no more than 150 mPas. Alternatively or additionally, the dispersion medium contains a polyethylene glycol with an average molar mass of < 400 g / mol, preferably < 300 g / mol. In particular, polyethylene glycols with an average molar mass of < 300 g / mol, preferably PEG 200, can be used as a dispersion medium or dispersing agent without the addition of any further solvents. Thus, polyethylene glycols with very low molar masses, such as PEG 200, can be used as a dispersion medium without the addition of water.According to one embodiment, the dispersion medium or dispersing agent therefore contains no water or is anhydrous.

[0023] The proportion of the dispersion medium in the cleaning agent is preferably 30 to 80 wt.%, in particular 40 to 60 wt.%. One embodiment provides that the total water content in the cleaning agent is 30 to 80 wt.%, in particular more than 40 wt.%.

[0024] According to one embodiment, the dispersion medium contains polar organic solvents, such as alcohols, preferably low-molecular-weight alcohols with a maximum of 5 carbon atoms, in particular ethanol, propanol, or isopropanol. These are used in an aqueous dispersion medium. The use of the organic solvents described above as additional components allows, for example, the influencing of physical properties such as surface tension or boiling point of the dispersion medium. One embodiment provides that the dispersion medium has a boiling point of at least 90°C, preferably at least 100°C. Since the cleaning agent or the dispersion medium can heat up during the cleaning process due to friction, high boiling points of the dispersion medium are advantageous because they allow for a long cleaning time. However, it is also possible to use dispersion media or dispersion mediums with lower boiling points.to use individual components of the dispersion medium with lower boiling points, provided that the duration of a cleaning process is limited accordingly and / or several cleaning cycles are carried out with pause intervals to cool the dispersion medium.

[0025] The cleaning agent contains substances that exhibit a chemical cleaning effect. These substances can be present as liquids and be part of the dispersion medium, or as solids dissolved or dispersed within the dispersion medium. The cleaning effect of the cleaning agent is thus based not only on mechanical cleaning by the inorganic particles but also on chemical cleaning processes. This occurs when the substance(s) to be removed are dissolved and / or dispersed on the surface of the grinding media and / or the grinding bowl by components of the cleaning agent within the dispersion medium. The chemical cleaning effect is primarily achieved through the aqueous or liquid phase of the cleaning agent.

[0026] The cleaning agent comprises at least one pH-active substance. For the purposes of this invention, a pH-active substance is understood to be a substance or compound that influences the pH value of the dispersing, in particular aqueous or water-containing, phase of the cleaning agent through acid and / or base reactions. The pH-active substance can be either an acid or a base. Preferably, the cleaning agent contains at least one polyprotic acid or polyprotic base as the pH-active substance. This gives the cleaning agent a buffering effect, so that the pH value is not affected, or not as strongly affected, by the dissolved or dissolved contaminants. This, in turn, can have an advantageous effect on the cleaning action.

[0027] According to one embodiment, the cleaning agent, or the dispersing, preferably aqueous, phase of the cleaning agent, has a pH value of ≤ 6. Another embodiment provides that the pH value of the dispersing phase, preferably the aqueous phase, is ≥ 8. In these embodiments, the dispersing phase of the cleaning agent is thus either acidic or alkaline. By selecting and concentrating the pH-active substance, the pH value of the dispersing, preferably aqueous, phase of the cleaning agent can, for example, be adjusted to increase the solubility and / or dispersibility of the substance to be removed from the surface of the grinding media and / or the grinding bowl, or substances to be removed from the dispersion medium. Alternatively or additionally, the pH value of the dispersing, preferably aqueous, phase is in the range of 3 to 10, preferably 4 to 9.

[0028] According to one embodiment, the cleaning agent contains at least one acid as a pH-active substance. In this embodiment, the cleaning agent preferably has a pH value of ≤ 6, preferably in the range of 3 to 6, and particularly preferably in the range of 3.5 to 5.8. In particular, the pH value of the cleaning agent is ≥ 4. Thus, acid-induced corrosion reactions on the materials of the grinding media and / or grinding cups can be avoided.

[0029] According to one embodiment, the cleaning agent contains at least one inorganic acid, for example hydrochloric acid or ammonium chloride, as the pH-active substance. Another embodiment provides that an organic acid or a carboxylic acid is used as the at least one pH-active substance. Acids with a pKa value in the range of 2.5 to 5, preferably from 2.5 to 4, have proven particularly advantageous. Cleaning agents with carboxylic acid contents in the range of 0.1 to 0.5 wt.% have proven particularly advantageous. According to a particularly preferred embodiment, the cleaning agent contains a polyprotic organic acid, in particular a triprotic acid, as the pH-active substance. It has proven particularly advantageous if the following pKa values ​​apply to the respective pKa values: 1.9 ≤ pKa1 ≤ 4; 4 ≤ pKa2 ≤ 6 and / or 6 ≤ pKa3 ≤ 10.It can be assumed that acids with the pKa values ​​described above, in particular, exhibit a buffering effect and can thus stabilize the pH of the cleaning agent throughout the cleaning process. Buffering the pH ensures that the cleaning agent maintains a constant or largely constant pH throughout the entire cleaning process, even if compounds or substances with acidic or basic properties are dissolved during the cleaning process. For example, substances to be removed from the surface of the grinding media and / or the grinding bowl can be acidic or basic and thus influence the pH of the cleaning agent after being removed from the surfaces. The use of a suitable buffering acid counteracts this effect.One embodiment provides that the cleaning agent contains a polyprotic organic acid as a pH-active substance, and that its concentration is in the range of 0.005 to 0.05 mol / l, preferably in the range of 0.01 to 0.03 mol / l.

[0030] A further development provides that, in addition to the pH-active substance, the cleaning agent contains a pH buffer comprising an acid and its salt as the conjugate base. Preferably, the acid in the buffer corresponds to the pH-active component of the cleaning agent. Furthermore, the cleaning agent contains the acid's salt in addition to the acid, so that the acid not only constitutes the pH-active component but is also part of the buffer system. In particular, the cleaning agent contains citric acid and / or a citrate as the pH-active component, so that the dispersed phase of the cleaning agent comprises a citrate buffer. Alternatively or additionally, the cleaning agent can also contain a buffer in addition to the pH-active component. For example, the cleaning agent can contain citric acid as the pH-active component and also a phosphate buffer.

[0031] A further development provides that, in addition to an acid as a pH-active substance, the preparation contains components that can raise and / or stabilize the pH value. For example, the preparation can contain surfactants with basic groups or corrosion inhibitors that raise the pH value. Another embodiment provides that, in addition to an acid as a pH-active substance, the preparation contains the salt of a diphosphate, preferably a dialkali hydrogen diphosphate, and particularly preferably disodium hydrogen diphosphate. The diphosphate content in the preparation is preferably 0.3 to 1.1 wt.%, and particularly preferably 0.7 to 1 wt.%.

[0032] Alternatively or additionally, according to one embodiment, the preparation for pH adjustment contains, besides an acid, at least one amphoteric oxide, preferably Al₂O₃. The amphoteric oxide can be present in the preparation in the form of inorganic particles. Alternatively or additionally, according to another embodiment, the amphoteric oxide can be present in the preparation as a powdered, dispersed, or dissolved component, in addition to the inorganic, abrasive particles. It has proven particularly advantageous if the amphoteric oxide has a high surface area, for example, in the case of certain γ-Al₂O₃ phases or when using nanoparticles.

[0033] Through proton binding to the amphoteric oxide, the acid is partially neutralized, resulting in an increase in pH. This effect can be further enhanced by the use of complexing acids such as citric acid and / or the addition of complexing agents.

[0034] Another embodiment provides that at least one organic acid with a maximum of 6 carbon atoms is used as the pH-active component. According to one embodiment, this is a monoprotic carboxylic acid such as acetic acid or formic acid.

[0035] The use of hydroxycarboxylic acids, such as citric acid or lactic acid, has proven particularly advantageous. Besides their good environmental compatibility and low toxicity, cleaning agents containing these acids exhibit exceptionally good cleaning performance. It can be assumed that these acids not only act as pH-active substances but also increase the solubility or dispersibility of the substance(s) to be removed through complex formation, for example, by complexing polyvalent metal ions. Alternatively or additionally to the use of complexing carboxylic acids, the cleaning agent can contain other complexing agents, especially for the formation of complexes with polyvalent metal ions.

[0036] According to an alternative embodiment of the invention, the cleaning agent contains a base as the pH-active substance. In this embodiment, the cleaning agent preferably has a pH value of ≥ 7, particularly preferably a pH value in the range of 8 to 10, or in the range of 8 to 9. One embodiment provides that the cleaning agent contains amino alcohols, in particular triethanolamine, or a dissolved ammonium salt, preferably ammonium hydroxide, as the pH-active substance.

[0037] In addition to at least one pH-active substance, the cleaning agent contains at least one surfactant. The surfactant reduces the surface tension of the dispersion medium. Furthermore, the surfactant allows nonpolar compounds, especially organic substances with low or no water solubility, to be transferred into the dispersion medium and thus removed from the surface of the grinding media and / or the grinding bowl.

[0038] According to one embodiment, the cleaning agent contains at least one nonionic surfactant, preferably at least one nonionic surfactant selected from the group consisting of: polyalkylene glucosides, fatty alcohol propoxylates, alkyl glucosides, alkyl polyglucosides, octylphenol ethoxylates, nonylphenol ethoxylates, ethylene oxide-propylene oxide block copolymers, and ethylenediamine-ethylene oxide-propylene oxide block polymers. According to another embodiment, the cleaning agent contains at least one long-chain, alkoxylated alcohol. This may, in particular, be an oligomer or polymer with oxirane monomer units and / or 2-propylheptyl ether monomer units. Suitable surfactants are available, for example, under the name Dusazin 901 from Ehserchemie.

[0039] The cleaning agent may also contain a mixture of different surfactants. Preferably, the cleaning agent contains a non-foaming or low-foaming surfactant. One embodiment provides that the cleaning agent comprises a betaine surfactant, a sugar surfactant, and / or an amphoteric surfactant as a low-foaming surfactant. For the purposes of the invention, a low-foaming surfactant is understood to be, in particular, a surfactant that has a low cloud point. All surfactants contained in the cleaning agent are preferably non-foaming or low-foaming surfactants. Non-ionic surfactants have proven to be particularly advantageous, as they tend to produce only minimal foam and thus belong to the group of non-foaming or low-foaming surfactants.

[0040] Alternatively or additionally to non-ionic surfactants, the cleaning agent can also contain anionic and / or cationic surfactants. According to one embodiment of the invention, the cleaning agent contains at most 1 wt.% or even less than 1 wt.% surfactant. By limiting the surfactant content, undesirable effects on the cleaning process can be avoided. One embodiment provides that the cleaner contains 0.01 to 0.5 wt.% surfactant.

[0041] When using surfactants that tend to foam, pressure can build up in the grinding bowl during the cleaning process. This can be avoided by adding a defoamer or foam inhibitor. Defoamers and foam inhibitors are understood to be compounds or substances that suppress foam formation by lowering the surface tension or contribute to the dissolution of existing foam. In particular, the cleaning agent contains water-soluble monoglycerides, diglycerides, triglycerides, alcohols, silicone oils with silica particles, and / or phosphate esters as a defoamer. According to one embodiment, the cleaning agent contains a low-molecular-weight alcohol as a defoamer, in particular an alcohol with fewer than 5 carbon atoms, most preferably isopropanol. The added defoamers or foam inhibitors can be dissolved or dispersed in the dispersion medium.According to one embodiment, the cleaning agent contains 0.001 to 0.6 wt.% defoamer.

[0042] The cleaning agent can be supplied as a ready-to-use single dose. A ready-to-use dose means that the user does not need to process the dose further. For example, the addition of other components such as water is unnecessary. Preferably, the volume of the single dose is adapted to the specific volume of the grinding system to be cleaned, consisting of the grinding bowl and grinding media. Therefore, measuring the volume by the user is unnecessary. Providing ready-to-use single doses thus reduces the likelihood of application errors and enables good reproducibility of the cleaning process. With single doses, in addition to the volume, the composition of the cleaning agent, especially the particle size of the inorganic particles it contains, can also be adapted to the properties of the grinding system to be cleaned, consisting of the grinding media and grinding bowl.This ensures that the user employs the optimal composition and volume of cleaning agent for the respective grinding system. A further aspect of the invention therefore relates to a system consisting of a ball mill with the cleaning agent according to the invention, particularly in the form of at least a single dose.

[0043] Furthermore, the invention relates to a method for cleaning a ball mill with grinding media and at least one grinding cup, comprising at least the following method steps a) to d).

[0044] In step a), the cleaning agent according to the invention, particularly in the form of a single dose, is provided and, in the subsequent step b), filled into the grinding bowl containing the grinding media of the ball mill to be cleaned. In step c), the grinding bowl is closed, and the ball mill is operated according to a cleaning protocol at a predetermined speed for a predetermined cleaning duration t. The speed during the cleaning process is adjusted depending on the volume, number, and size of the grinding media to be cleaned. The cleaning duration t depends on the degree and type of soiling to be removed.One embodiment provides that the cleaning process is carried out at a speed that is at least half of the maximum permissible speed of the device to be cleaned or even the maximum permissible speed, and / or that the cleaning process has a cleaning duration of 1 to 5 minutes.

[0045] Step c) can be performed continuously for a cleaning duration t. Alternatively, the cleaning duration t can be divided into several cleaning cycles, each comprising a cleaning duration tcleaning and a break duration tbreak. Preferably, the grinding bowl and grinding media are not moved during the breaks. In these embodiments, the breaks can, for example, serve to cool the cleaning agent and / or to allow the chemically active cleaning components to take effect.

[0046] Once the cleaning process in step c) is complete, the grinding bowl is removed from the ball mill and opened. The cleaning agent, along with the dissolved or dispersed contaminants, is removed from the grinding bowl and separated from the grinding media. This separation can be achieved, in particular, by mechanical separation methods such as sedimentation or filtration. One embodiment provides for the use of a filter whose pore size allows for the separation of the grinding media from both the dispersion medium of the cleaning agent and the cleaning particles. Detailed description of the invention

[0047] The invention will now be described in more detail with reference to the Figures 1 to 7 and further explained with examples. They show: Fig. 1 shows a photograph of grinding media contaminated with silicon after cleaning with a sand-water mixture compared to grinding media cleaned with the cleaning agent according to the invention, Fig. 2 a photograph of ZrO₂ grinding media contaminated with textile dye, Fig. 3 a photograph of the in Fig. 2 The grinding media shown are after cleaning with a sand-water mixture or after cleaning with the cleaning agent according to the invention. Fig. 4 shows a photograph of a grinding cup after the cleaning method according to the invention, and Fig. 5 shows a photograph of grinding balls that were cleaned with the cleaning agent according to the invention. Fig. 6 shows a photograph of a grinding cup with surface corrosion, and Fig. 7 shows a photograph of grinding balls that were cleaned with a sand-water mixture.

[0048] According to a first embodiment, the cleaning agent comprises the following components: corundum 40 to 60 wt.% distilled water 40 to 60 wt.% citric acid 0.2 to 0.5 wt.% Dusazin 901 0.01 to 0.03 wt.% 2-Methyl-1-propanol 0.005 to 0.01 wt.% Polyethylene glycol 400 0.25 to 0.7 wt.%

[0049] In this embodiment, the cleaning agent contains corundum particles as inorganic particles with an Al₂O₃ content of more than 99 wt.% and the following particle size distribution: d10: 28.5 to 49.4 µm, d50: 70.6 to 86.8 µm, d90: 114 to 146 µm. Corundum particles of this type are available, for example, under the name Edelkorund F220 (CAS number 344-28-1). In this embodiment, the dispersion medium consists mainly of distilled or demineralized water; it is therefore an aqueous dispersion medium or an aqueous dispersing phase. Citric acid is dissolved in the dispersion medium as a pH-active compound, and the pH of the aqueous phase is 5.5. In the exemplary embodiment, the pH value of the cleaning agent or the aqueous phase is influenced by the concentration of citric acid in the aqueous phase as well as the basic properties of the corundum contained.The use of citric acid as a pH-active component is particularly advantageous from several perspectives. As a polyprotic, weak acid, citric acid has a buffering effect and can thus contribute to stabilizing the pH value throughout the entire cleaning process. Additionally, citric acid can complex multivalent metal ions, such as calcium ions, and therefore also acts as a complexing agent.

[0050] In this embodiment, the cleaning agent contains Dusazin 901 as a surfactant, which is available, for example, from Ehserchemie. This is a non-ionic surfactant with low foaming properties, i.e., a low-foaming surfactant.

[0051] Polyethylene glycol 400 (CAS number 25322-68-3) is included as an additional component in the cleaning agent. Polyethylene glycol is used here as a rheology additive to adjust the viscosity of the aqueous phase and due to its hygroscopic properties. The cleaning agent is preferably supplied as a ready-to-use single dose. The volume of each single dose is tailored to the volume of the grinding bowl to be cleaned. For a grinding bowl with a volume of 500 ml, the single dose has a total volume in the range of 200 to 250 ml.

[0052] Fig. 1Figure 1 shows a photograph of grinding balls contaminated with elemental silicon, which were cleaned either with a sand-water mixture (reference numeral 1) or with the cleaning agent according to the invention (reference numeral 2). For cleaning, the same volume of sand-water mixture or cleaning agent was added to the grinding bowl containing the grinding balls. The grinding bowl was closed, clamped into the ball mill, and rotated in the ball mill at 1100 revolutions per minute for 5 minutes. Subsequently, the sand-water mixture or cleaning agent was removed from the grinding bowl and separated from the grinding balls. Fig. 1It becomes clear that the grinding balls 1, which were cleaned conventionally, i.e., with a sand-water mixture, still exhibit elemental silicon on their surface. This is recognizable as a dark discoloration. In contrast, the grinding balls 2 cleaned with the cleaning agent according to the invention are white, which suggests that the silicon deposits have been removed from the surface.

[0053] Fig. 2 Figure 1 shows grinding balls made of zirconium dioxide which were contaminated with a textile dye for 24 hours. Subsequently, as a further embodiment, a portion of these grinding balls were mixed with the cleaning agent according to the invention. The grinding balls and cleaning agent were moved in the grinding bowl of the ball mill for 5 minutes at 650 revolutions per minute, and then the grinding balls were separated from the cleaning agent. The other portion of the Fig. 2The grinding balls shown were placed in a grinding bowl with a sand-water mixture for comparison and milled in a ball mill at 650 revolutions per minute for one hour. After cleaning, the grinding balls were separated from the sand-water mixture.

[0054] The spheres of the exemplary embodiment and the comparative example are in Fig. 3 shown. While the grinding balls of comparison example 4 still show clearly visible residues of textile dye on the surface despite a significantly longer cleaning time, no traces of textile dye are visually discernible on the grinding balls 3 cleaned with the cleaning agent according to the invention.

[0055] From the Figs. 1 to 3It becomes clear that both inorganic and organic contaminants can be removed from the grinding balls using the cleaning agent and the cleaning method according to the invention. Furthermore, the cleaning process with the cleaning agent according to the invention does not attack the material of the grinding media or the grinding bowl. In particular, no corrosion occurs.

[0056] This can also be seen from the Figs. 4 and 5 be shown. Fig. 4 This shows a grinding cup and Fig. 5 Grinding balls of a ball mill after a cleaning process according to the invention. Neither the grinding cups nor the grinding balls show any recognizable signs of corrosion. In contrast, grinding cups cleaned with a sand-water mixture show clear signs of surface corrosion. This is demonstrated by the Fig. 6 and 7 clearly. Fig. 6The image shows a grinding cup that was cleaned for one hour with a sand-water mixture. Clearly visible signs of corrosion are present on both the grinding cup and its lid. Fig. 7 shows grinding balls which are in the Fig. 6 The grinding cups shown were cleaned with a sand-water mixture. The surface of these grinding balls has been roughened by the sand grains and also shows signs of corrosion.

Claims

1. Cleaning agent for cleaning ball mills, comprising a dispersion of inorganic particles in a liquid dispersion medium, wherein the liquid phase of the cleaning agent contains at least one pH-active compound, the cleaning agent comprises at least one surfactant, and wherein the content of inorganic particles in the cleaning agent is 20 to 70 wt.%.

2. Cleaning agent according to the preceding claim, wherein the dispersion medium is an aqueous dispersion medium.

3. Cleaning agent according to one of the two preceding claims, wherein the inorganic particles have a Mos hardness of ≥ 5, preferably ≥ 7 and particularly preferably ≥ 8.

5.

4. Cleaning agent according to any of the preceding claims, wherein the inorganic particles comprise a metal oxide, preferably a ceramic, a carbide or nitride, preferably a non-oxide ceramic and / or a silicate.

5. Cleaning agent according to the preceding claim, wherein the inorganic particles contain aluminium oxide (Al2O3), steatite, porcelain, zirconium dioxide (ZrO2), boron nitride (BC), silicon nitride (Si3N4), aluminium nitride (AIN), silicon carbide (SC), tungsten carbide (WC), pyrogenic silica, aluminosilicate, pumice, calcium carbonate, kaolin and / or agate, preferably aluminium oxide, particularly preferably corundum.

6. Cleaning agent according to any of the preceding claims, wherein the inorganic particles have a mean particle size distribution d50 in the range of 50 to 100 µm, a particle size distribution d10 in the range of 25 to 52 µm and / or a particle size distribution d90 in the range of 105 to 150 µm.

7. Cleaning agent according to one of the preceding claims, wherein the cleaning agent comprises a non-ionic surfactant, preferably a long-chain alkoxylated alcohol, particularly preferably an oligomer or polymer with oxirane monomer units and / or a low-foaming surfactant.

8. Cleaning agent according to one of the preceding claims, wherein the cleaning agent comprises a water-soluble polymer, preferably a polyethylene glycol, particularly preferably a polyethylene glycol with a mean molar mass in the range of 200 to 600 g / mol.

9. Cleaning agent according to one of the preceding claims, wherein the cleaning agent has a pH value in the range of 4 to 9, preferably a pH value ≤ 6, particularly preferably a pH value in the range of 3 to 6 and / or contains at least one acid as a pH-active substance, preferably an organic acid with a pKa value in the range of 2.5 to 4.

10. Cleaning agent according to the preceding claim, wherein the cleaning agent contains a polyprotic organic acid as a pH-active substance and the concentration of the polyprotic organic acid in the dispersion medium of the cleaning agent is preferably in the range of 0.005 to 0.05 mol / l, particularly preferably in the range of 0.01 to 0.03 mol / l.

11. Cleaning agent according to any of the preceding claims, wherein the cleaning agent is in the form of a ready-to-use single dose.

12. Cleaning agent according to one of the preceding claims, wherein the cleaning agent comprises a complexing agent for polyvalent metal ions and / or a buffer, preferably a buffer based on the pH-active component.

13. Cleaning agent according to one of the preceding claims, wherein the cleaning agent has a proportion of inorganic particles of 40 to 60 wt.%, a water content in the range of 30 to 80 wt.%, a content of an organic acid in the range of 0.1 to 1 wt.% and / or a content of nonionic surfactants of 0.01 to 0.5 wt.%.

14. Method for cleaning a ball mill, comprising at least the following steps: a) providing a cleaning agent according to one of the preceding claims, b) providing the grinding bowl with the grinding balls to be cleaned, c) filling the grinding bowl with the cleaning agent provided in step a), d) moving the grinding bowl through the ball mill, preferably at a speed of revolution that corresponds to at least half of the maximum permissible speed of revolution of the respective device for a period of time of 1 to max. 5 minutes, e) separating the dispersed phase of the cleaning agent and the inorganic particles from the grinding balls.

15. Method according to the preceding claim, wherein the cleaning agent provided in step a) is provided in the form of a single dose.

16. Ball mill with a cleaning agent according to any one of the preceding claims 1 to 13 for cleaning the grinding balls in the grinding bowl.

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