EP2032679B1 - Graphite-free high-temperature lubricant - Google Patents

Description

The present invention relates to a high-temperature lubricant for the hot processing of metals.

Background of the invention

In the hot forming of metals, especially steel, in a temperature range of 700-1300 ° C occurs on the heated metal surface in the ambient air to the formation of scale. In hot rolling of steel for the production of seamless tubes, a solid material is pierced and a hollow block is formed, which is then elongated in subsequent rolling steps. Here, the risk of scale formation on the heated metal surface of the hollow block during the transfer to the Elongierprozeß is particularly high. In the subsequent rolling steps, this scale attack can lead to internal defects of the seamless pipe. For this reason, the resulting scale is blown out, for example, with compressed air or inert gas. In addition, a wide variety of substances are applied in powder form as a lubricant or mordant to the inner surface of the hollow blocks. Examples of such lubricants or mordants include graphite, boron nitride, molybdenum sulfide, silicates or alkaline earth phosphates and mixtures thereof.

Many lubricants for hot deformation of metals contain graphite because of its good lubricating properties. However, graphite has significant disadvantages, such. Example, the inclusion of graphite carbon in the machined metal surface, whereby the composition and the properties of the metal surface can be changed. In addition, graphite is undesirable for occupational hygiene reasons because the graphite powder is easily atomized into the ambient atmosphere and poses a health hazard to inhaled graphite powder for nearby workers.

Furthermore, many known lubricants due to their physical properties and grain sizes no good trickle or flow behavior. A coarse material with high particle sizes often leads to an insufficient and uneven coverage of the metal surface and thus to a poor scale reduction. Known fine-grained materials with small particle sizes, for example below 50 microns, often tend to clumping, especially during storage, which is why they can be difficult to spray on the metal surface as a powder. However, a finer grain size would have the advantage that a better layer formation can be achieved, but this advantage is nullified in known compositions with fine grain by the strong tendency to clumping again.

The DD 292678 A5 discloses a coating for reducing the friction in the elastic or plastic deformation of metallic materials, consisting of a homogeneous solid mixture of thermal reaction products, produced by thermal action at 250 to 1600 ° C to a homogeneous mixture of (A) 0.02 to 28 parts by mass (B) 0.09 to 9.1 parts by mass alkali or ammonium borate, (C) 0.18 to 26 parts by mass alkali or ammonium phosphate, (D) 0.02 to 18 parts by mass of a polymeric organic compound and (E) O , 06 to 18 parts by mass of reaction products of the components AC, formed in aqueous solution at a pH> 6.5 and at a temperature <80 ° C.

Object of the invention

The object of the present invention was therefore to provide a high-temperature lubricant with good flow and flow behavior for scaling on heated metal surfaces, applied in powder form allows good occupancy of the metal surface and even after prolonged storage under production conditions still good flow and flow properties without has strong clumping and avoids the use of graphite.

Description of the invention

1. (a) eine sekundäre und/oder tertiäre Calciumphosphatverbindung, ausgewählt unter Hydroxylapatit [Ca₅(PO₄)₃OH] und Tricalciumphosphat [Ca₃(PO₄)₂].
2. (b) eine Fettsäure oder ein Fettsäuresalz,
3. (c) Borsäure, ein Borsäuresalz (Borat) und/oder ein Borsäuresalz (Borat) enthaltendes Mineral und
4. (d) Alkalipolyphosphate und/oder Alkalipyrophosphate und/oder Alkalimetaphosphate in einer Menge von 60 bis 95 Gew.-% in dem Gemisch,

und wobei die Bestandteile des Gemischs eine mittlere Korngröße von ≤ 150 µm aufweisen und der Schmierstoff keinen Zusatz von Graphit enthält.This object is achieved according to the invention by a high-temperature lubricant for the hot processing of metals, consisting of a mixture of pulverulent materials, wherein the mixture contains at least the following constituents:

1. (a) a secondary and / or tertiary calcium phosphate compound selected from hydroxyapatite [Ca ₅ (PO ₄ ) ₃ OH] and tricalcium phosphate [Ca ₃ (PO ₄ ) ₂ ].
2. (b) a fatty acid or a fatty acid salt,
3. (c) boric acid, a borate salt (borate) and / or a boric acid borate containing mineral, and
4. (d) alkali polyphosphates and / or alkali pyrophosphates and / or alkali metal metaphosphates in an amount of from 60 to 95% by weight in the mixture,

and wherein the components of the mixture have a mean particle size of ≤ 150 microns and the lubricant contains no addition of graphite.

It has surprisingly been found that the mixture according to the invention with the components (a), (b), (c) and (d) is particularly suitable as a lubricant for the hot processing of metals. It is understood that the lubricant of the invention may contain other ingredients, as far as they do not significantly adversely affect the desired advantageous properties.

Secondary and / or tertiary calcium phosphate compounds have surprisingly proven to be particularly suitable flow aids in a high-temperature lubricant of the type according to the invention for the hot processing of metals. Monocalcium phosphate is unsuitable because it leads to clumping when humid. The calcium phosphate compound of the high-temperature lubricant according to the present invention is selected from hydroxy diaxbutate [Ca ₅ (PO ₄ ) ₃ OH] and tricalcium phosphate [Ca ₃ (PO ₄ ) ₂ ], with hydroxy diaxapatite being particularly preferred.

The mixture of the high-temperature lubricant according to the invention further contains a fatty acid or a fatty acid salt in combination with the other constituents. It has surprisingly been found that by using a fatty acid or a fatty acid salt, the agglomeration of the fine powder can be significantly reduced and the storage stability can be improved. Without the applicant's being bound by theory, it is believed that the fatty acid or fatty acid salt attaches to the granules of one or more other constituents of the mixture and thus prevents or reduces clumping of the granules, preventing moisture from the granules and thereby improves the storage stability and the flow or flow behavior of the lubricant.

In a preferred embodiment of the high-temperature lubricant according to the invention, the fatty acid or the fatty acid salt is selected from saturated and unsaturated fatty acids having 6 to 26 carbon atoms or their salts. Particular preference is given to the fatty acid or the fatty acid salt among caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachic acid, behenic acid, lignoceric acid, cerotic acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, icosenoic acid, erucic acid, nervonic acid, linoleic acid, Linolenic acid, arachidonic acid, timnodonic acid, clupanodonic acid or salts thereof. Most preferably, the fatty acid or the fatty acid salt is stearic acid or its salt, in particular magnesium stearate. Prerequisite for the selection is that the fatty acid or the fatty acid salt is present at a temperature> 30 ° C as a solid.

The high-temperature lubricant according to the invention contains as further constituent boric acid, a boric acid salt (borate) and / or a mineral containing boric acid (borate). Particular preference is given to boric acid [H ₃ BO ₃ ], borax [Na ₂ B ₄ O ₅ (OH) ₄ 8H ₂ O or Na ₂ B ₄ O ₇ · 10H ₂ O], further sodium borates, such as Na ₂ B ₄ O ₇ 5H ₂ O, Na ₂ B ₄ O ₇ (anhydrous), sodium metaborate [NaBO ₂ 4H ₂ O] and boric anhydride [B ₂ O ₃ ]. The use according to the invention of boric acid, a boric acid salt (borate) and / or a mineral containing a boric acid (borate) improves the uniform distribution of the lubricant on the metal surface and reduces scale formation. At high metalworking temperatures, the high temperature lubricant forms a melt.

The high-temperature lubricant according to the invention contains as further constituent alkali polyphosphates and / or alkali pyrophosphates and / or alkali metal metaphosphates, preferably of sodium or potassium. Very particularly preferred are disodium pyrophosphate [Na ₂ H ₂ P ₂ O ₇ ], trisodium pyrophosphate [Na ₃ HP ₂ O ₇ ], tetrasodium pyrophosphate [Na ₄ P ₂ O ₇ ], sodium tripolyphosphate [Na ₅ P ₃ O ₁₀ ], sodium trimetaphosphate [(NaPO ₃ ) ₃ ], sodium polyphosphate [(NaPO ₃ ) _n ], dipotassium pyrophosphate [K ₂ H ₂ P ₂ O ₇ ], tripotassium pyrophosphate [K ₃ HP ₂ O ₇ ], tetrapotassium pyrophosphate [K ₄ P ₂ O ₇ ], potassium tripolyphosphate [K ₅ P ₃ O ₁₀ ], potassium trimetaphosphate [(KPO ₃ ) ₃ ] and / or potassium polyphosphate [(KPO ₃ ) _n ], most preferably sodium tripolyphosphate [Na ₅ P ₃ O ₁₀ ]. It has been found that the use of a polyphosphate and / or a pyrophosphate and / or a metaphosphate in the mixture of the high-temperature lubricant according to the invention advantageously contributes, inter alia, to the scale dissolution.

In the high-temperature lubricant according to the invention, the constituents of the mixture have an average particle size of ≦ 150 μm. Preference is given to an average particle size of the constituents of the mixture of ≦ 100 μm, particularly preferably ≦ 50 μm. Due to the small mean particle sizes of the constituents of the mixture according to the invention, the flow and flow behavior of the high-temperature lubricant according to the invention compared to known lubricants is significantly improved, facilitates the spraying on surfaces as a powder and ensures better and more uniform layer formation or occupancy on the metal surface. At the same time, the combination of the constituents of the mixture according to the invention prevents or reduces clumping which has regularly occurred in the case of lubricants according to the prior art with small particle sizes and has led to considerable disadvantages.

It is furthermore preferred if the constituents of the mixture of the high-temperature lubricant according to the invention have an average particle size of ≥ 3 μm, preferably ≥ 10 μm, particularly preferably ≥ 15 μm. It has been found that too small average grain sizes can only be produced very costly and under relatively high costs and, on the other hand, they also increase the tendency to clumping again. An average grain size in the range of 20 to 50 microns has therefore proved to be optimal.

In a preferred embodiment of the high temperature lubricant of the present invention, the secondary or tertiary calcium phosphate compound (a) is in an amount of 0.1 to 15% by weight, preferably 0.5 to 10% by weight, more preferably 1 to 5 Wt .-% in the mixture.

In a further preferred embodiment of the high-temperature lubricant according to the invention, the fatty acid or fatty acid salt (b) is present in an amount of from 0.1 to 15% by weight, preferably from 1 to 10% by weight, more preferably from 3 to 7 Wt .-% in the mixture.

In a further preferred embodiment of the high-temperature lubricant according to the invention, boric acid, boric acid salt (borate) and / or a mineral (c) containing boric acid (c) are present in an amount of from 5 to 30% by weight, preferably from 10 to 25% by weight. %, more preferably from 15 to 20 wt .-% in the mixture.

In a further preferred embodiment of the high-temperature lubricant according to the invention polyphosphate and / or pyrophosphate and / or metaphosphate (d) in an amount of 70 to 85 wt .-%, particularly preferably from 75 to 80 wt .-% in the mixture.

Storage behavior, agglomeration and moisture absorption

To test the tendency to agglomerate under production conditions, storage trials of various mixtures were carried out under production conditions. For this purpose, 150 g of sample were stored in a climate chamber (type 3821/15 from Feutron) at a constant 30 ° C. and 80% relative humidity for 0 h, 67 h and 96 h and then their agglomeration (free-flow) in a sieve test and their moisture absorption the weight gain compared to the original weight determined.

Only the overall assessment of combined storage and trickling behavior of a particular mixture can be a statement about their quality and suitability under production conditions. The results of the examination of various mixtures are shown in Table 1.

Particle size determination

The average particle size of the mixture or components of the mixture of the high-temperature lubricant according to the invention is determined by means of a Cilas Model 715/920 laser granulometer from Cilas US Inc. About 80 mg of sample are suspended in 2-propanol and the measurement taken for one minute after preparation of the suspension according to the instructions of the manufacturer. <b><u> Table 1 </ u></b> Free-flowing and moisture absorption after different storage periods under production conditions Sample number composition Storage duration under production conditions; 30 ° C, 80% rel. humidity Sieve residue at mesh or hole width of 250 μm ¹⁾ moisture absorption (Wt .-%) (%) of weight (%) of weight 1 82% sodium tripolyphosphate 0 h 5 0 18% boric acid (technical powder) 67 h 89 17 (State of the art) 96 h 87 20 2 74% sodium tripolyphosphate 0 h 2 0 16% boric acid (technical powder) 67 h 67 11 5% tricalcium phosphate 5% magnesium stearate 96 h 57 11 3 72% sodium tripolyphosphate 0 h 3 0 16% boric acid (technical powder) 67 h 73 12 10% tricalcium phosphate 2% magnesium stearate 96 h 71 10 4 72% sodium tripolyphosphate 0 h 4 0 16% boric acid (technical powder) 67 h 59 12 2% tricalcium phosphate 10% magnesium stearate 96 h 53 8th 5 74% sodium tripolyphosphate 0 h 16 0 16% borax (technical powder) 67 h 14 8th 5% tricalcium phosphate 5% magnesium stearate 96 h 13 13 ¹⁾ Screening conditions: sample quantity 2 g + wet pickup amount; Vibration amplitude 1 scale part; Vibration duration 70 sec.

Claims (11)

1. A high-temperature lubricant for the hot processing of metals consisting of a mixture of fine-powder materials, wherein the mixture includes at least the following constituents:

   (a) a secondary and/or tertiary calcium phosphate compound selected from hydroxyapatite [Ca₅(PO₄)₃OH] and tricalcium phosphate [Ca₃(PO₄)₂],

   (b) a fatty acid or a fatty acid salt,

   (c) boric acid, a boric acid salt (borate) and/or a mineral containing boric acid salt (borate), and

   (d) alkali polyphosphates and/or alkali pyrophosphates and/or alkali metaphosphates in an amount of 60 to 95 % by weight in the mixture,
   and wherein the constituents of the mixture have a mean grain size of ≤ 150 µm and the lubricant does not contain any addition of graphite.
2. A high-temperature lubricant according to one of the preceding claims characterized in that constituent (c) is selected from boric acid [H_aBO₃], borax [Na₂B₄O₅(OH)₄8H₂O or Na₂B₄O₇10H₂O], sodium borates such as Na₂B₄O₇5H₂O, Na₂B₄O₇ (water-free), sodium metaborate [NaBO₂4H₂O] and boric acid anhydride [B₂O₃] and mixtures thereof.
3. A high-temperature lubricant according to one of the preceding claims characterized in that constituent (d) is selected from polyphosphates and/or pyrophosphates and/or metaphosphates of sodium or potassium, preferably from disodium pyrophosphate [Na₂H₂P₂O₇], trisodium pyrophosphate [Na₃HP₂O₇], tetrasodium pyrophosphate [Na₄P₂O₇], sodium tripolyphosphate [Na₅P₃O₁₀], sodium trimetaphosphate [(NaPO₃)₃], sodium polyphosphate [(NaPO₃)_n], dipotassium pyrophosphate [K₂H₂P₂O₇], tripotassium pyrophosphate [K₃HP₂O₇], tetrapotassium pyrophosphate [K₄P₂O₇], potassium tripolyphosphate [K₅P₃O₁₀], potassium trimetaphosphate [(KPO₃)₃], potassium polyphosphate [(KPO₃)_n] or mixtures thereof, wherein constituent (d) is most preferably sodium tripolyphosphate [Na₅P₃O₁₀].
4. A high-temperature lubricant according to one of the preceding claims characterized in that the fatty acid or the fatty acid salt is selected from saturated and unsaturated fatty acids with 6 to 26 carbon atoms and salts thereof, preferably from capronic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachic acid, behenic acid, lignoceric acid, cerotic acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, icosic acid, erucic acid, nervonic acid, linoleic acid, linolenic acid, arachidonic acid, timnodonic acid, clupanodonic acid and salts thereof, provided that the fatty acid or the fatty acid salt is present as a solid at a temperature > 30° C.
5. A high-temperature lubricant according to one of the preceding claims characterized in that the fatty acid or the fatty acid salt is stearic acid or salt thereof.
6. A high-temperature lubricant according to one of the preceding claims characterized in that the secondary or tertiary calcium phosphate compound (a) is contained in the mixture in an amount of 0.1 to 15 % by weight, preferably 0.5 to 10 % by weight, particularly preferably 1 to 5 % by weight.
7. A high-temperature lubricant according to one of the preceding claims characterized in that the fatty acid or the fatty acid salt (b) is contained in the mixture in an amount of 0.1 to 15 % by weight, preferably 1 to 10 % by weight, particularly preferably 3 to 7 % by weight.
8. A high-temperature lubricant according to one of the preceding claims characterized in that boric acid, boric acid salt (borate) and/or a mineral (c) containing boric acid salt (borate) is contained in the mixture in an amount of 5 to 30 % by weight, preferably 10 to 25 % by weight, particularly preferably 15 to 20 % by weight.
9. A high-temperature lubricant according to one of the preceding claims characterized in that polyphosphate and/or pyrophosphate and/or metaphosphate (d) is contained in the mixture in an amount of 70 to 85 % by weight, particularly preferably 75 to 80 % by weight.
10. A high-temperature lubricant according to one of the preceding claims characterized in that the constituents of the mixture have a mean grain size of ≤ 100 µm, preferably ≤ 50 µm.
11. A high-temperature lubricant according to one of the preceding claims characterized in that the constituents of the mixture have a mean grain size of ≥ 3 µm, preferably ≥ 10 µm, particularly preferably ≥ 15 µm.