HK1133033A - Graphite-free high-temperature lubricant - Google Patents

Description

Graphite-free high-temperature lubricant

The present invention relates to a high temperature lubricant for heat treatment of metals.

Background

In hot working of metals, especially steel, in the temperature range of 700-. In the case of hot rolling processes for producing steel for seamless pipes and tubes, the solid material is perforated to form a hollow block, which is then elongated in a subsequent rolling step. Here, the risk of scale formation on the heated metal surface of the hollow block during the transfer to the elongation step is very high. The formation of scale in the subsequent rolling step may lead to internal defects of the seamless tube or pipe. For this purpose, the contained dirt is blown off, for example, by compressed air or inert gas. In addition, a very different substance in powder form is applied as a lubricant or mordant to the inner surface of the hollow block. Examples of such lubricants or mordants contain graphite, boron nitride, molybdenum sulfide, silicates or alkaline earth phosphates and mixtures thereof.

Many lubricants used in hot working of metals contain graphite due to its good lubricating properties. It should be noted, however, that graphite has many disadvantages, such as graphitic carbon absorbing into the surface of the processed metal, thereby altering the composition and properties of the metal surface. In addition, the undesirable cause of graphite is also related to work hygiene, since graphite powder is easily atomized into the ambient atmosphere, and people working nearby run the risk of health hazards due to breathing of the graphite powder.

In addition, many known lubricants do not have good drip and flow characteristics due to the physical properties and particle size of the lubricant. The inclusion of coarse material of large particle size often results in insufficient and uneven coverage of the metal surface and thus less effective reduction of fouling. Known fine-grained materials of small particle size (e.g. less than 50 microns) generally have a tendency to form agglomerates, particularly on storage, so that they can only be sprayed onto metal surfaces with difficulty in the form of a powder. However, smaller particle sizes provide the advantage of forming better layers, but in known compositions of small particle size this advantage becomes ineffective again due to the severe tendency to form agglomerates.

Object of the Invention

It is therefore an object of the present invention to provide a high temperature lubricant with good dripping and flow characteristics for dissolving the scale formed on heated metal surfaces, which lubricant, when applied in powder form, is able to cover the metal surfaces well and maintain good dripping and flow properties even after prolonged storage under production conditions without severe lump formation phenomena, avoiding the use of graphite.

Detailed Description

According to the invention, this object is achieved by a high-temperature lubricant for heat treatment of metals comprising a mixture of fine powder materials, wherein the mixture comprises at least the following components:

(a) a second and/or third generation of calcium phosphate compounds,

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

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

(d) the condensed alkali metal phosphate is a salt of an alkali metal,

wherein the components of the mixture have an average particle size of 150 μm or less and the lubricant does not contain any added graphite.

It has surprisingly been found that the mixtures according to the invention containing components (a), (b), (c) and (d) are particularly suitable as lubricants for the heat treatment of metals. It is to be understood that the lubricants of the present invention may contain other components so long as they do not substantially adversely affect the desired advantageous properties.

Surprisingly, secondary and/or tertiary calcium phosphate compounds have proven to be particularly suitable trickle flow aids in high temperature lubricants of the type of the present invention used for heat treatment of metals. Monocalcium phosphate is not suitable because it can lead to the formation of lumps in the presence of moisture in the air. The calcium phosphate compound in the high-temperature lubricant according to the invention is particularly preferably selected from hydroxyapatite [ Ca ]₅(PO₄)₃OH]And tricalcium phosphate [ Ca ]₃(PO₄)₂]More preferably hydroxyapatite.

The mixture of high temperature lubricants according to the present invention also comprises a fatty acid or fatty acid salt in combination with other components. It has surprisingly been found that the use of a fatty acid or fatty acid salt means that the formation of lumps from fine-grained powder can be greatly reduced, increasing the storage-resistance. Without the applicant itself being bound thereby by theory, it is hypothesized that the fatty acid or fatty acid salt adheres to the particles of one or more of the other components in the mixture, thereby preventing or reducing the formation of clumps of the particles, keeping moisture away from the particles, and thereby improving the storage durability and lubricant dripping or flow characteristics.

In a preferred embodiment of the high-temperature lubricant according to the invention, the fatty acid or fatty acid salt is selected from saturated and unsaturated fatty acids having 6 to 26 carbon atoms or salts thereof. It is particularly preferred that the fatty acid or fatty acid salt is selected from: caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, eic acid, erucic acid, nervonic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, 4, 7, 11-docosatrien-18-ynoic acid, and salts thereof. It is particularly preferred that the fatty acid or fatty acid salt is stearic acid or a salt thereof, especially magnesium stearate. A prerequisite for the selection is that the fatty acid or fatty acid salt is in solid form at a temperature >30 ℃.

As a further component, the high-temperature lubricant according to the invention contains boric acid, a borate and/or a mineral containing a borate. Particularly preferred is boric acid [ H ]₃BO₃]Borax [ Na ]₂B₄O₅(OH)₄·8H₂O or Na₂B₄O₇·10H₂O]Other sodium borates, such as Na₂B₄O₇·5H₂O、Na₂B₄O₇(anhydrous), sodium metaborate [ Na ]₂BO₂·4H₂O]And boric anhydride [ B ]₂O₃]. Use of boric acid, borate and/or borate containing minerals according to the invention improves lubricationThe agent is uniformly distributed on the metal surface and fouling formation is reduced. In high temperature metal processing operations, the high temperature lubricant forms a molten material.

As a further component, the high-temperature lubricants according to the invention contain condensed alkali metal phosphates, preferably condensed sodium or potassium phosphates or mixtures thereof, particularly preferably polyphosphates and/or pyrophosphates and/or metaphosphates or mixtures thereof. Particularly preferred is disodium pyrophosphate [ Na ]₂H₂P₂O₇]Trisodium pyrophosphate [ Na ]₃HP₂O₇]Tetrasodium pyrophosphate [ Na ]₄P₂O₇]Sodium tripolyphosphate [ Na ]₅P₃O₁₀]Sodium trimetaphosphate [ (NaPO)₃)₃]Sodium polyphosphate [ (NaPO)₃)_n]Dipotassium pyrophosphate [ K ]₂H₂P₂O₇]Tripotassium pyrophosphate [ K ]₃HP₂O₇]Tetrapotassium pyrophosphate [ K ]₄P₂O₇]Potassium tripolyphosphate [ K ]₅P₃O₁₀]Potassium trimetaphosphate [ (KPO)₃)₃]And/or potassium polyphosphate [ (KPO)₃)_n]Most preferred is sodium tripolyphosphate [ Na ]₅P₃O₁₀]. It has been found that the use of polyphosphates and/or pyrophosphates and/or metaphosphates in the mixture of the high-temperature lubricant according to the invention can particularly advantageously promote scale dissolution and the like.

In the high temperature lubricant according to the invention, the components of the mixture have an average particle size of 150 μm or less. It is preferred that the components of the mixture have an average particle size of 100 microns or less, with an average particle size of 50 microns or less being particularly preferred. The low average particle size of the components of the mixture according to the invention makes it possible to greatly improve the dripping and flow properties of the high-temperature lubricants according to the invention compared to known lubricants, to spray the same more easily onto surfaces in powder form, and to ensure a better and more uniform layer or coating on the metal surface. At the same time, the combination of the components of the mixture according to the invention prevents or reduces the formation of lumps, which often occur in the case of lubricants with small particle size levels according to the prior art, leading to serious disadvantages.

It is more preferred that the components of the mixture of the high temperature lubricant according to the invention have an average particle size of 3 microns or more, preferably 10 microns or more, more preferably 15 microns or more. It has been found that too small an average particle size on the one hand is very difficult to manufacture, requires complicated processes and high costs and on the other hand also increases the tendency to form agglomerates. Thus, average particle sizes in the range of 20-50 microns have proven to be optimal.

In a preferred embodiment of the high-temperature lubricant according to the invention, the content of the dibasic or tribasic calcium phosphate compound (a) in the mixture is from 0.1 to 15% by weight, preferably from 0.5 to 10% by weight, particularly preferably from 1 to 5% by weight.

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

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

In a further preferred embodiment of the high-temperature lubricant according to the invention, the polyphosphate and/or pyrophosphate and/or metaphosphate (d) is contained in the mixture in an amount of from 60 to 95% by weight, preferably from 70 to 85% by weight, particularly preferably from 75 to 80% by weight.

Storage characteristics, lump formation and hygroscopicity

Storage tests were performed on each mixture under production conditions to test for the tendency to form lumps under production conditions. To this end, 150 g samples were stored in an air-conditioning cabinet (model 3821/15, from Feutron) constant at 30 ℃ and 80% relative air humidity for 0 h, 67 h and 96 h, and then determined in a sieve test whether lumps were formed (trickle flow behaviour) whose hygroscopicity was determined from the weight gain compared to the original weight.

This is merely an overall evaluation of the storage and trickle flow characteristics of the respective mixtures combined, which evaluation can give information about the quality and suitability of the samples under production conditions. The results of the tests on each mixture are shown in table 1.

Determination of particle size

The operation of determining the average particle size of the mixture of high temperature lubricants according to the present invention or of the components of the mixture is carried out by a laser particle sizer model seeles 715/920 from the american company seelas u.s.inc. About 80 mg of the sample was suspended in 2-propanol according to the manufacturer's instructions and measured 1 minute after the suspension was prepared.

TABLE 1

Drip flow behaviour and hygroscopicity after different storage times under production conditions

¹⁾And (3) screening conditions: sample size 2 g + moisture pick-up; amplitude 1 scale portion; the vibration period was 70 seconds.

Claims (12)

1. A high temperature lubricant for use in the heat treatment of metals comprising a mixture of fine powder materials, wherein the mixture comprises at least the following components:

(a) a second and/or third generation of calcium phosphate compounds,

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

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

(d) the condensed alkali metal phosphate is a salt of an alkali metal,

wherein the components of the mixture have an average particle size of 150 microns or less and the lubricant does not contain any added graphite.

2. The high temperature lubricant of claim 1, wherein component (c) is selected from the group consisting of: boric acid [ H ]₃BO₃]Borax [ Na ]₂B₄O₅(OH)₄·8H₂O or Na₂B₄O₇·10H₂O]Sodium borates such as Na₂B₄O₇·5H₂O、Na₂B₄O₇(anhydrous), sodium metaborate [ Na ]₂BO₂·4H₂O]Boric anhydride [ B ]₂O₃]And mixtures thereof.

3. A high temperature lubricant according to any preceding claim, wherein component (d) is selected from: condensed sodium or potassium phosphate or mixtures thereof, preferably polyphosphate and/or pyrophosphate and/or metaphosphate or mixtures thereof, particularly preferably selected from disodium pyrophosphate [ Na ] Na₂H₂P₂O₇]Trisodium pyrophosphate [ Na ]₃HP₂O₇]Tetrasodium pyrophosphate [ Na ]₄P₂O₇]Sodium tripolyphosphate [ Na ]₅P₃O₁₀]Sodium trimetaphosphate [ (NaPO)₃)₃]Sodium polyphosphate [ (NaPO)₃)_n]Dipotassium pyrophosphate [ K ]₂H₂P₂O₇]Tripotassium pyrophosphate [ K ]₃HP₂O₇]Tetrapotassium pyrophosphate [ K ]₄P₂O₇]Potassium tripolyphosphate [ K ]₅P₃O₁₀]Potassium trimetaphosphate [ (KPO)₃)₃]And/or potassium polyphosphate [ (KPO)₃)_n]Or a mixture thereof, wherein component (d) is most preferably sodium tripolyphosphate [ Na ]₅P₃O₁₀]。

4. The high temperature lubricant of any one of the preceding claims, wherein the calcium phosphate compound is selected from hydroxyapatite [ Ca [ ]₅(PO₄)₃OH]And tricalcium phosphate [ Ca ]₃(PO₄)₂]Particularly preferred is hydroxyapatite.

5. The high temperature lubricant according to any one of the preceding claims, wherein the fatty acid or fatty acid salt is selected from saturated and unsaturated fatty acids having 6 to 26 carbon atoms and salts thereof, preferably from caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, eic acid, erucic acid, nervonic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, 4, 7, 11-docosatrien-18-ynoic acid, and salts thereof, with the proviso that the fatty acid or fatty acid salt is present in solid form at a temperature of >30 °.

6. The high temperature lubricant of any one of the preceding claims, wherein the fatty acid or fatty acid salt is stearic acid or a salt thereof.

7. High temperature lubricant according to any of the preceding claims, characterised in that the content of the dibasic or tribasic calcium phosphate compound (a) in the mixture is 0.1 to 15 wt. -%, preferably 0.5 to 10 wt. -%, particularly preferably 1 to 5 wt. -%.

8. High temperature lubricant according to any of the preceding claims, characterised in that the content of fatty acid or fatty acid salt (b) in the mixture is 0.1-15 wt. -%, preferably 1-10 wt. -%, more preferably 3-7 wt. -%.

9. High-temperature lubricant according to one of the preceding claims, characterized in that the boric acid, borate and/or borate-containing mineral (c) is present 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.

10. The high-temperature lubricant according to any of the preceding claims, characterized in that the amount of polyphosphate and/or pyrophosphate and/or metaphosphate (d) in the mixture is 60 to 95% by weight, preferably 70 to 85% by weight, particularly preferably 75 to 80% by weight.

11. High temperature lubricant according to any of the preceding claims, characterised in that the components of the mixture have an average particle size of 100 microns or less, preferably 50 microns or less.

12. High temperature lubricant according to any of the preceding claims, characterised in that the components of the mixture have an average particle size of 3 microns or more, preferably 10 microns or more, more preferably 15 microns or more.