DE19949032A1 - Lubricant for metal processing with ferromagnetic or ferrimagnetic nanoparticles - Google Patents

Abstract

An oil-based lubricant for metal machining which comprises 0.1 to 5 wt % ferromagnetic or ferrimagnetic particles based on the ready-to-use product, with a volume weighted average crystallite size ranging from 2 to 80 nm.

Description

The invention relates to oil-based lubricants for forming or machining of metals. These lubricants are called Coolant used. An improvement in the lubricating effect compared conventional cooling lubricants is achieved in that the lubricants contain ferromagnetic or ferrimagnetic nanoparticles. Furthermore concerns the invention method for forming or machining of metals, with oil-based lubricants used as cooling lubricants that contain ferromagnetic or ferrimagnetic nanoparticles.

Lubricants, hereinafter also referred to as cooling lubricants Preparations / mixtures used in grinding or cutting / sawing Metal cutting and metal forming for cooling and lubricating the Tools are used. The main machining processes differ in the type of movements that the machined part and Execute tool through the geometry of the parts to be manufactured and the Machining parameters. A distinction is made between milling, turning, Drilling and grinding as machining and rolling, Deep drawing and cold extrusion as non-cutting formations.  

The common principle of metal cutting processes is that the cutting edge engages in the material and thereby a chip from the Surface lifts so that a new surface is created. For the division of the Very high pressures are required. Due to the deformation of the chip and the friction that occurs under pressure creates heat that the Workpiece that heats up the tool and above all the chips.

The desired effect of using cooling lubricants is therefore Lowering the temperature that would otherwise occur in the chips. B. up to 1000 ° C can increase, and the influence on the dimensional accuracy of the manufactured parts Has. Another main task of cooling lubricants is the service life of the To improve tools that ver quickly under the influence of high temperature wear out. By using a cooling lubricant, the roughness of the Reduced surfaces because the lubricant welds tools and Prevents workpiece surface and avoids particles from sticking. In addition, the cooling lubricant takes over the task, the educated Remove chips.

With the new version of DIN 51385 No. 1, the Cooling lubricants created, with non-water-miscible, water-miscible and water-mixed cooling lubricants. According to DIN 51385, the final state of the finished medium (mostly oil-in-water emulsions), under "water miscible" however understood the condition of the concentrate.

Water-mixed cooling lubricants are manufactured by the user Mixing a concentrate of the water-miscible cooling lubricant with Process water. As a rule, approximately 5% aqueous emulsions are produced. The advantage of this type of cooling lubricant is the good cooling effect on the thermal properties of the water. Because of the good cooling effect it is possible to achieve very high working speeds and thus the Increase machine productivity. The lubricating effect of the water-mixed cooling lubricants are sufficient for most machining processes in machining production. Another advantage are the low ones Costs achieved by mixing the concentrate with water will. The disadvantage of water-mixed cooling lubricants is that they counteract External influences, especially against infestation by microorganisms are sensitive and therefore require more control and care than not water-miscible cooling lubricants such as cutting oils, grinding oils and forming oils.

An overview of the shaping metalworking processes and the corresponding ones Commonly used aids are, for example, Ullmann's Encyclopaedia of Industrial Chemistry, 5th Ed., Vol. A15, 479-486. The spectrum The forms of supply of the aids in question range from Oiling over oil-in-water emulsions up to aqueous solutions.

Non-water-miscible and water-miscible cooling lubricants are common Mineral oil built up. The mineral oil qualities used are mostly com combinations of paraffinic, naphthenic and aromatic Koh hydrogen compounds. In addition to mineral oils, so-called synthetic lubricants ("synthetic oils") such as polyalphaolefins, Polyalkylene glycols and glycol ethers, dialkyl ethers, acetals, natural ester oils as well as synthetic esters and their derivatives meaning.

In order to be able to meet practical requirements, cooling lubricants must be used contain various components in addition to the base oil. The most important Substance groups are the emulsifiers, anti-corrosion additives, biocides, EP- Additives, polar additives, anti-fog additives, anti-aging agents, solid lubricants sets and defoamers.

Emulsifiers (e.g. surfactants, petroleum sulfonates, alkali soaps, alkanolamine soaps) stabilize the fine distribution of oil droplets in the aqueous Working fluid, which is an oil-in-water emulsion. The emulsifiers make up an important group of additives for the water-miscible cooling lubricants.  

Common anti-corrosion additives (e.g. alkanolamines and their salts, sulfonates, or ganic boron compounds, fatty acid amides, aminodicarboxylic acids, Phosphoric acid esters, thiophosphonic acid esters, dialkyldithiophosphates, mono- and Dialkylarylsulfonates, benzotriazoles, polyisobutene succinic acid derivatives) should Prevent rusting of metal surfaces. Some anti-corrosion additives have emulsifying properties at the same time and are therefore also found as Emulsifier their application. Biocides (e.g. phenol derivatives, form aldehyde derivatives, Kathon MW) are said to grow bacteria and Prevent mushrooms. EP additives (e.g. sulfurized fats and oils, phosphorus-containing Compounds, organochlorine compounds) are said to be micro-welds between metal surfaces at high pressures and temperatures. Polar additives (e.g. natural fats and oils, synthetic esters) increase the Lubrication properties. Anti-aging agents (e.g. organic sulfides, Zinc dithiophosphates, aromatic amines) ensure a long life Service life of cooling lubricants.

In addition to the cooling effect, the second important function of the cooling lubricants is in the lubricating effect. The effect of the lubricating components is based on this on the formation of surface layers opposite the base material have a lower shear strength and thus friction and wear belittle. The spectrum of surface conditions ranges from adsorptive bound layers via chemical sorption to chemical Reaction layers that create a firm bond to the metal surface.

The simplest form of lubricant coating on a surface is adsorptive Lubricant layers. They are, for example, without mineral oils produces special additives. The formation of the adsorption layers can by Additions of polar active ingredients such as fatty alcohols or fatty esters can be strengthened. Here there is an interaction between the physical adsorption the metal surface and the lubricant molecules leading to a partial leads to chemisorptive binding of fatty alcohols or fatty esters.  

Typical representatives of chemisorptive lubricant film formers are fatty acids. The hydrophilic carboxyl group is formed by reaction with the metal atoms chemically bound to the metal surface and the hydrophobic Hydrocarbon residue is aligned perpendicular to the surface. The increased Adhesive strength of the chemisorptive layer does improve that Pressure absorption capacity compared to purely adsorptive lubricant layers, is sufficient for many cases of metal forming for friction and Wear reduction is not yet sufficient. Here are the additions of EP or AW additives (extreme pressure or anti wear additives) a sufficient Improvement of the lubrication performance, so that even difficult forming processes be made possible. These are usually chlorine, phosphorus or sulfur-containing active ingredients. Their effect is based on the training of chemical reaction layers in the form of metal chlorides, metal phosphates or metal sulfides. For disposal reasons, there is now an endeavor to If possible, avoid chlorine-containing EP additives. The on the Reaction layers formed on the metal surface act on the one hand as Solid lubricant layers that constantly during the forming process removed and renewed. On the other hand, they form monomolecular Surface films that can add other lubricant components.

Water-mixed cooling lubricants represent a widespread Cooling lubricant type there. In practice, however, are different water-mixed cooling lubricants in use to the different Corrosion protection requirements for the various machined Materials, lubricating effect at high working speed, service life and not last to meet occupational safety and environmental behavior.

By using nanoparticles, the lubricating properties of targeted improvement of conventional lubricants. In an article by Z. S. Hu, J. X. Dong, G. X Chen (Tribology Intern. Vol. 31, No 7, pp 355-360) becomes the Use of amorphous iron oxide with a particle size of 20-50 nm for Improvement of the abrasion resistance and the coefficient of friction described. This Material is made from ethanol by drying under supercritical conditions receive.

In the patent WO 92/01872 / US 5525246, Fe ₃ O _{4 is used} in a mixture with other oxides in a particle size smaller than 2 μm. WO 9114757 describes iron oxide in a concentration of 1-30% and a particle size of 10 μm. JP 01083309 / US 5468402 describes the use of FeO and Fe ₃ O ₄ (<10 µm) for hot rolling processes. Fe ₃ O ₄ with particle sizes of 1-5 µm is described by SU 765344 in concentrations of 8-15% as a solid lubricant for magnetizable surfaces.

The production of magnetic nanoparticles, if desired with a layer organic molecules can be documented, as well as their use for the production Magnetic liquids are from a large number of publications known.

The article V. S. Zaitsev, D. S. Filimonov, J. A. Presnyakov, R. J. Gambino, B. Chu: "Physical and Chemical Properties of Magnetite and Magnetite-Polymer Nanoparticles and Their Colloidal Dispersions ", J. Colloid Interface Sci, 212, 49-57 (1999) deals with the production and properties of polymer coated nanoparticles made of magnetite, which are particularly useful as contrast agents magnetic resonance studies can be used. At the Her position of the particles, which also take place according to a continuous process can, quaternary ammonium salts are used as stabilizers. At A suitable choice of stabilizer is aqueous colloidal suspensions that are stable for months. Separate the magnetic particles and if it dries, the powders obtained can be exposed again to ultrasound be suspended. A polymer coating takes place in that Acrylic acid and hydroxyethyl methacrylate in the presence of those already pre-formed Polymerized nanoparticles.

The German utility model DE-U-93 21 479 discloses a magnetic Water based liquid, being magnetic iron oxide particles which preferably have a size of 5 to 20 nm, by a first monomolecular adsorption layer made of saturated or unsaturated Fatty acids and a second adsorption layer of surface-active alkoxylated fatty alcohols are stabilized.

DE 199 23 625 describes a process for producing redispersible Metal oxides or metal hydroxides with a volume weighted average Crystallite size between 1 and 20 nm, whereby from aqueous solutions of Metal salts by raising the pH with a base in the presence polymeric carboxylic acids metal hydroxide or metal oxide fails and at least part of the aqueous phase of the metal oxide or metal hydroxide obtained separates.

The present invention aims to use lubricants as well To provide lubrication methods that have improved Lubrication effect is achieved.

In a first aspect, the invention relates to oil-based lubricants for the Metalworking, the 0.1 to 5 wt .-% based on the ready-to-use Lubricant with a ferromagnetic or ferrimagnetic particle volume-weighted average crystallite size in the range from 2 to 80 nm contain. The volume-weighted average crystallite size is preferably in Range from 8 to 20 nm. The ready-to-use lubricant can a substantially anhydrous oil or an oil-in-water emulsion act.

The volume-weighted average crystallite size can be determined using X-ray diffraction methods, in particular using a Scherrer analysis. The method is described, for example, in: CE Krill, R. Birringer: "Measuring average grain sizes in nanocrystalline materials", Phil. Mag. A 77, p. 621 (1998). Accordingly, the volume-weighted average crystallite size D can be determined by the relationship
D = Kλ / βcosθ.

Here λ is the wavelength of the X-ray radiation used, β is the full width at half the height of the reflection at the diffraction position 2θ. K is a constant of the order of 1, the exact value of which depends on the crystal shape. This indeterminacy of K can be avoided by determining the line broadening as an integral width β _i , where β _{i is} defined as the area under the X-ray diffraction reflex divided by its maximum intensity I ₀ :

The quantities 2θ ₁ and 2θ _{2 are} the minimum and maximum angular position of the Bragg reflex on the 2θ axis. I (2θ) is the measured intensity of the reflection as a function of 2θ. Using this relationship, the following results as an equation for determining the volume-weighted average crystallite size D:
D = λ / β _i cosθ

Because of the improved dispersibility in the oil phase, preference is given to using such ferromagnetic or ferrimagnetic particles that a Have hydrophobic organic coating. Such Hydrophobic organic coating can be achieved, for example by coating the particles with organic sulfonic or phosphonic acids or with Alcohols, each carrying an alkyl radical with a chain length such that the surfaces of the particles are made hydrophobic and the dispersibility of the Particles in the oil phase is improved. This is the case, for example, with alkyl residues Chain lengths in the range of 8 to 22 C atoms. Preferably you bet however, such ferromagnetic or ferrimagnetic particles whose Hydrophobic organic coating at least partially made of carboxylic acids or whose anions consist of 8 to 44, preferably 12 to 22, carbon atoms.

These are chain lengths that you usually find with fatty acids or so-called Dimer fatty acids are found.

The ferromagnetic or ferrimagnetic particles can be selected from doped or undoped cobalt ferrite, manganese ferrite, zinc ferrite, nickel ferrite and γ-Fe ₂ O ₃ . The latter is particularly preferred.

The lubricant in which the ferromagnetic or ferrimagnetic Nanoparticles dispersed can be a substantially anhydrous oil represent. Such oils are in the technical field concerned as cutting or forming oils known. They can contain other additives, as introductory were exemplified. Because the ferromagnetic or ferrimagnetic As a lubricant, nanoparticles can contribute significantly to the lubricating effect Oil used contains much less EP additives than usual or even free of such additives.

In an alternative embodiment, the lubricants are an oil-in-water Emulsion, the ferromagnetic or ferrimagnetic particles in the Oil phase are dispersed. Such emulsions are usually made prepared that with low or anhydrous emulsion concentrates Mixed water, usually 10 to 50 per part by weight of concentrate Parts by weight of water are used. For the purposes of the invention can be used for production of the oil-in-water emulsions are used from that known in the art and commercially available Only differentiate concentrates in that they are ferromagnetic or contain ferrimagnetic nanoparticles. Otherwise they can Emulsion concentrates and the oil-in-water emulsions that can be produced from them contain customary components in the technical area concerned, which were enumerated above by way of example. However, even in this Embodiment on the addition of conventional EP additives at least be largely dispensed with.  

The oil used as a lubricant or the oil phase of the oil-in-water Emulsions can consist of any oil as it is on the affected one Field of application is common. Paraffinic or naphthenic mineral oil, synthetic oils such as polyolefins, Acetals or dialkyl ethers or bio-based oil, for example ester oils, the triglycerides occurring in plants or animals or Modification products thereof, wax esters and fatty acid esters of Monoalkanols with 4 to 12 carbon atoms, for example tallow fatty acid ethylhexyl ester or transesterified rapeseed oil, and also fatty acid esters of polyols, in particular trimethylolpropane being used as the polyol component can. Mixtures of such oils can of course also be used will.

The invention further relates to the use of a dispersion of ferromagnetic or ferrimagnetic particles with a volume weighted average crystallite size in the range from 2 to 80 nm, preferably from 8 to 20 nm in oil for the production of a lubricant according to the above Description. Regarding the manufacturing process for such particles and their optional surface coating, the above statements apply. A dispersion is preferably used to prepare the lubricants of ferromagnetic or ferrimagnetic particles in oil, which are about 10 to 35 % By weight of the ferromagnetic or ferrimagnetic particles based on the Contains total weight of the dispersion.

Another aspect of the invention lies in a method for forming or for machining metals using a Tool and an oil-based lubricant, being an oil-based Lubricant as described above, the ferromagnetic or contains ferrimagnetic nanoparticles. Examples of the above Working methods "forming" and machining "have been introduced called.

A particular advantage of the invention is shown when the tool during the forming or machining of metals is magnetized or if, e.g. B. in non-magnetic metals, the location of Chip generation is exposed to a permanent magnetic field. This can for example electromagnetically. The magnetized tool pulls the due to the presence of the ferromagnetic or ferrimagnetic Nanoparticles ferromagnetic or ferrimagnetic oil phase and keeps them so at the processing location, i.e. in the tribo zone. A shear off of the oil phase this makes it more difficult. This aspect of the process is particularly advantageous if if an oil-in-water emulsion is used as the cooling lubricant, the Oil phase contains ferromagnetic or ferrimagnetic nanoparticles. By Applying the magnetic field to the tool binds the ferromagnetic or ferrimagnetic oil phase on the tool. There is therefore one in the tribo zone desired particularly high oil concentration before, while in the periphery of the Tribozone sufficient water phase is available for cooling. To The magnetic (electromagnetic) field can be switched off Remove the resulting chips well with the cooling lubricant.

Another advantage of using ferromagnetic or ferrimagnetic Nanoparticles for the production of oil-based lubricants lies in the fact that these Nanoparticles can have biocidal, in particular bactericidal, effects. Hereby the service life and the service life of the lubricants are improved without that an addition of conventional preservatives, for example based on Formaldehyde releasing, is required. Accordingly, another aspect of the Invention in a process for forming or for machining Machining of metals using an oil-based lubricant, the oil-based lubricant is not mixed with a common biocide. This is particularly advantageous in terms of occupational and environmental protection.

The ferromagnetic or ferrimagnetic nanoparticles can be produced by known processes and provided with a hydrophobic coating. For example, the method described in DE 199 23 625 may be mentioned. According to this document, the manufacturing process can also be operated continuously, which means increased efficiency of the process. The procedure is such that metal hydroxide or metal oxide is continuously precipitated from aqueous solutions of metal salts by raising the pH with a base in the presence of polymeric carboxylic acids by:

• a) a first container with the aqueous solution of the metal salts and a second Container with an aqueous alkaline solution of a base and a polymer Carboxylic acid provides
• b) continuously taking solution from both containers and the two Solutions mixed in a mixing section and if desired
• c) the precipitation reaction is completed in a pipe behind the mixing section.

Special processes for the production and hydrophobization of ferromagnetic or ferrimagnetic nanoscale γ-Fe ₂ O ₃ are the following:

Example a

6.48 g FeCl ₃ are dissolved in 40 g water. 3.97 g of FeCl ₂ .4H ₂ O are dissolved in a mixture of 8 ml of deionized water and 2 ml of 37% hydrochloric acid. Shortly before the solutions are used in the precipitation process, they are combined to form a mixture.

10.0 g of NaOH are dissolved in 400 ml of water in a template. After cooling down Pour the iron salt solution at room temperature with vigorous stirring, whereby deposits nanoscale iron oxide. The precipitate is centrifuged off and washed several times with deionized water. Then the Precipitation is added to a stirrable suspension in water and with 1.11 g of lauric acid heated to 80-90 ° C for half an hour with stirring. After the coating has taken place, the precipitate settles out and the excess Water is decanted off.

The residue is taken up with 70 g soybean oil. By shaking and adding the coated magnetic particles are transferred from water into the oil phase.

Example b

6.48 g FeCl ₃ are dissolved in 40 g water. 3.97 g of FeCl ₂ .4H ₂ O are dissolved in a mixture of 8 ml of deionized water and 2 ml of 37% hydrochloric acid. Shortly before the solutions are used in the precipitation process, they are combined to form a mixture.

80.0 g of NH _{3 are} mixed with 320 ml of water in a template. After cooling to room temperature, the iron salt solution is poured in with vigorous stirring, nanoscale iron oxide separating out. The precipitate is centrifuged off and washed several times with deionized water. The precipitate is then taken up in a stirrable suspension in water and heated with 2 g of isostearic acid to 80-90 ° C. for half an hour with stirring. After coating has taken place, the precipitate settles out and the excess water is decanted off.

The residue is taken up with 65 g soybean oil. By shaking and adding the coated magnetic particles are transferred from water into the oil phase.

Embodiments

A friction wear test according to Reichert was carried out as a suitability test carried out. This procedure is used to determine the Pressure absorption capacity (EP behavior), as well as to determine the adhesive strength of liquid lubricants. Here, a test role is created using a Lever system adapted to a rotating slip ring, the with his immersed the lower third in the lubricant to be tested. Before the start of the test, the Test roll cleaned in special-grade petrol installed in the swiveling holder.

The holder is swung in and clamped. The slip ring remains several test runs clamped in the device, where he also after each Test run is cleaned with mineral spirits. The test roll is slow Apply the load weight (1.5 kg) to the slip ring. That on the counter located on the Reichertwaage is set to 0. By switching on the Motors is supplied by the rotating slip ring immersed in the lubricant Point of contact continuously with lubricant. When the number reaches 100 am Counter (100 meter friction distance) the test roller is removed from the slip ring. The test roll is removed and the cut mark created using a Measuring magnifier measured. The ellipse area is calculated to be 0.785. or is read using a number table. There are so many test runs performed until the ellipse surfaces of the last 3 test runs do not exceed 10% differentiate from each other. The pressure absorption capacity is the greater, ever the elliptical area determined is smaller.

Cooling lubricant emulsions in the form of an oil-in-water Emulsion used. For this purpose, a concentrate was made as follows Composition in the following amounts with water offset:

Emulsion concentrate

13.8% by weight water 8.0% by weight Monoethanolamine 5.0% by weight Triethanolamine 8.0% by weight Boric acid 0.2% by weight Benzotriazole, 1 H, 2, 3- 36.0% by weight Mineral oil, paraffinic 1.5% by weight Fatty alcohol (= FA) + 10 ethylene oxide (= EO), oleyl / cetyl, iodine number (= JZ) 45/50 2.0% by weight Fatty acid (= FS), capryl 5.5% by weight FS, tall oil, 25-30% resin 2.0% by weight Ether carboxylic acid mixture 90.0% 1.0% by weight Glycerin 1.0% by weight Diethylene glycol monobutyl ether 8.0% by weight FS-monoethanolamide + 1.5 EO, tall oil 5.0% by weight FA + 2 EO, oleyl-cetyl, vegetable 3.0% by weight FA, octyldodecyl, 2-

5% by weight of the ready-to-use emulsion Concentrate and according to Table 1 0.63 to 5 wt .-% ferromagnetic or ferrimagnetic nanoparticles mixed in oil, which according to preparation example a) were obtained. The mixture of emulsion concentrate and ferromagnetic or oil containing ferrimagnetic nanoparticles is made up to 100 with water % By weight filled. The results of the friction wear test at the Reichert Scales are included in Table 1.  

Table 1 Friction / wear test on the Reichert balance (Filling volume 25 ml, 100 meter measuring section)

The samples are set up as follows:
The emulsion concentrate is 5% based on the finished emulsion, here 3 g. The ferrofluid is added in concentrations of ferromagnetic or ferrimagnetic nanoparticles of 0.63% -5%, also based on the finished emulsion. It is filled up with water so that a total of 60 g of emulsion is formed.

Result: The lubrication performance improves significantly when a magnet is placed on the test specimen. The lubricant (γ-Fe ₂ O ₃ ) is thus fixed at the site of action (in this case, test cylinder).

The information in the "Noise" column indicates the running distance of the test roller where there is a rubbing noise due to insufficient lubrication.

Claims (11)

1. Oil-based lubricants for metalworking, the 0.1 to 5 wt .-% based on the ready-to-use lubricant ferromagnetic or ferrimagnetic particles with a volume weighted average crystallite size contained in the range from 2 to 80 nm. 2. Lubricant according to claim 1, characterized in that the ferromagnetic or ferrimagnetic particles a volume weighted have average crystallite size in the range from 8 to 20 nm. 3. Lubricant according to one or both of claims 1 and 2, characterized characterized in that the ferromagnetic or ferrimagnetic particles have a hydrophobic organic coating. 4. Lubricant according to claim 3, characterized in that the hydrophobic organic coating at least partially Carboxylic acids or their anions with 8 to 44, preferably with 12 to 22 C- Atoms. 5. Lubricant according to one or more of claims 1 to 4, characterized in that the ferromagnetic or ferrimagnetic particles are selected from in each case doped or undoped cobalt ferrite, manganese ferrite, zinc ferrite, nickel ferrite and gamma-Fe ₂ O ₃ . 6. Lubricant according to one or more of claims 1 to 5, characterized characterized as being an essentially anhydrous oil. 7. Lubricant according to one or more of claims 1 to 5, characterized characterized in that they are an oil-in-water emulsion, the ferromagnetic or ferrimagnetic particles dispersed in the oil phase are. 8. Use of a dispersion of ferromagnetic or ferrimagnetic Particles with a volume weighted average crystallite size in the range of 2 to 80 nm in oil for the production of a lubricant according to one or several of claims 1 to 7. 9. Process for forming or machining metals using a tool and an oil-based lubricant, characterized in that a lubricant according to a or more of claims 1 to 7 is used. 10. The method according to claim 9, characterized in that the tool during the forming or machining of metals is magnetized, or that the location of the chip production is permanent magnetic field is exposed. 11. The method according to one or both of claims 9 and 10, characterized characterized in that the oil-based lubricant is not mixed with a biocide is moved.