WO1998008921A1

WO1998008921A1 - Use of bismuth compounds in cooling lubricants

Info

Publication number: WO1998008921A1
Application number: PCT/EP1997/004515
Authority: WO
Inventors: Jürgen Geke; Wiltrud Klose; Matthias Kampmann
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1996-08-28
Filing date: 1997-08-19
Publication date: 1998-03-05
Also published as: DE19634733A1; AU4205697A

Abstract

The invention concerns a friction-reducing additive for water-miscible or non-water-miscible cooling lubricants which contains: a) bismuth compounds of organic acids; and b) sulphurous organic compounds, in a mixture ratio such that the sulphur content of the additive ranges from 2 to 30 wt % and the bismuth content ranges from 1 to 25 wt %. The invention further concerns the use of this additive in the minimal lubricating technique and as a friction-reducing additive for non-water-miscible cooling lubricants and water-mixed cooling lubricants and their concentrates.

Description

"Use of bismuth compounds in cooling lubricants"

The invention relates to non-water-miscible or water-miscible cooling lubricants or their concentrates for metal cutting. The invention relates to an additive for such cooling lubricants, consisting of a mixture of organic bismuth compounds and organic sulfur compounds.

Cooling lubricants are preparations / mixtures that are used in metal cutting and metal forming to cool and lubricate the tools. The most important machining processes, which differ in the type of movements that the machined part and tool perform and in the geometry of the parts to be manufactured, are referred to as milling, turning, drilling and grinding as machining operations, as well as rolling, deep drawing and cold extrusion as non-cutting Deformations.

The common principle of metal-cutting processes is that the cutting edge engages in the material and lifts a chip off the surface, so that a new surface is created. Very high pressures are required to break up the material. The deformation of the chip and the friction that occurs under pressure generate heat that heats up the workpiece, the tool and, above all, the chips.

The desired effect of using cooling lubricants is therefore the lowering of the temperature that would otherwise occur in the chips. B. can rise to 1000 ° C, and which has an influence on the dimensional accuracy of the manufactured parts. Another main task of cooling lubricants is to improve the service life of tools that wear out quickly under the influence of high temperatures. The use of a cooling lubricant reduces the roughness of the surfaces, since the lubricant welds the tool and the workpiece surface prevents surface and prevents particles from sticking. In addition, the cooling lubricant takes on the task of removing the chips that have formed.

With the new version of DIN 51385 No. 1, a clear designation of the cooling lubricants was created, whereby we speak of non-water-miscible, water-miscible and water-mixed cooling lubricants. According to DIN 51385, the terms "water-mixed" mean the final state of the finished medium (mostly as oil-in-water emulsions), but "water-miscible" means the state of the concentrate.

Water-mixed cooling lubricants are produced by the user by 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, which is based on the thermal properties of the water. Due to the good cooling effect, it is possible to achieve very high working speeds and thus increase the productivity of machines. The lubricating effect of the water-mixed cooling lubricants is sufficient for most machining processes in machining. Another advantage is the low cost that can be achieved by mixing the concentrate with water. The disadvantage of water-mixed cooling lubricants is that they are sensitive to attack by microorganisms and therefore require more control and care.

The table shows a summary of the requirements for water-miscible and water-mixed cooling lubricants:

- Cooling and lubricating effects

- rust protection

- no attack on non-ferrous metals

- Toxicological harmlessness, especially skin tolerance

- no foaming

- no attack on paints and seals

- emulsion stability - no sticking or resinification

- good miscibility

- pleasant smell

- clean appearance

- good filterability

- easy disposal.

An overview of the shaping metalworking processes and the aids usually used for this purpose can be found, for example, in Ullmann's Encyclopaedia of Industrial Chemistry, 5th Ed., Vol. A15, 479-486. The spectrum of the forms of supply of the auxiliaries in question ranges from oils to oil-in-water emulsions to aqueous solutions.

Non-water-miscible and water-miscible cooling lubricants are often based on mineral oil. The mineral oil qualities used are predominantly combinations of paraffinic, naphthenic and aromatic hydrocarbon compounds. In addition to mineral oils, so-called synthetic lubricants ("synthetic oils") such as polyalphaolefins, polyalkylene glycols and glycol ethers, dialkyl ethers, natural ester oils and synthetic esters and their derivatives are also important.

In order to meet practical requirements, cooling lubricants must contain various components in addition to the base oil. The most important substance groups are the emulsifiers, corrosion protection additives, biocides, EP additives, polar additives. Anti-fog additives, anti-aging agents, solid lubricant additives 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. In terms of quantity, the emulsifiers represent an important group of additives for water-miscible cooling lubricants. Usual corrosion protection additives (e.g. alkanolamines and their salts, sulfonates, organic boron compounds, fatty acid amides, aminodicarboxylic acids, phosphoric acid esters, thiophosphonic acid esters, dialkyldithiophosphates, mono- and dialkylarylsulfonates, benzotriazoles, polyisobutene succinic acid surfaces) are intended to prevent rusting of metal surfaces. Some corrosion protection additives also have emulsifying properties and are therefore also used as emulsifiers. Biocides (e.g. phenol derivatives, formaldehyde derivatives, Kathon MW) are intended to prevent the growth of bacteria and fungi. EP additives (e.g. sulfurized fats and oils, compounds containing phosphorus, organochlorine compounds) are intended to prevent micro-welding 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 service life of the cooling lubricants.

In addition to the cooling effect, the second important function of the cooling lubricants lies in the lubricating effect (see the article by W. Klose: "Cooling lubricants on metal surfaces", messages from the Association of German Email Specialists, 41, Issue 11, pages 138-142 (1993)) The effect of the lubricating components on the formation of surface layers, which have a lower shear strength compared to the base material and thus reduce friction and wear. The spectrum of the surface conditions ranges from adsorptively bound layers through 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 produced, for example, by mineral oils without special additives. The formation of the adsorption layers can be increased by adding polar active ingredients such as fatty alcohols or fatty esters. In addition to the purely physical adsorption, there is an interaction between the metal surface and the lubricant molecules, which leads to a partial chemisorptive binding of the fatty alcohols or fatty esters. Typical representatives of chemisorptive lubricant film formers are fatty acids. The hydrophilic carboxyl group is chemically bound to the metal surface by reaction with the metal atoms and the hydrophobic hydrocarbon residue is aligned perpendicular to the surface. The increased adhesive strength of the chemisorptive layer improves the pressure absorption capacity compared to purely adsorptive lubricant layers, but is still not sufficient for many cases of metal forming to reduce friction and wear. It is only when EP or AW additives (extreme pressure or anti wear additives) are added that the lubricating performance is sufficiently improved so that even difficult forming processes are possible. These are usually chlorine, phosphorus or sulfur-containing active ingredients. Their effect is based on the formation of chemical reaction layers in the form of metal chlorides, metal phosphates or metal sulfides. For reasons of disposal, there is an attempt today to avoid using chlorine-containing EP additives wherever possible. The reaction layers formed on the metal surface act on the one hand as solid lubricant layers, which are constantly removed and renewed during the shaping process. On the other hand, they form monomolecular surface films that can attach additional lubricant components.

It is known from EP-A-675 192 and the literature cited therein to add certain bismuth compounds to lubricating oils and greases for the lubrication of bearings. The bismuth compounds serve as EP additives. These are preferably selected from naphthenates and / or carboxylates of the general formula (R-C0 ₂ ) ₃ Bi, in which R is a linear, branched or cyclic alkyl radical having 1 to 30 C atoms or an aryl, alkylaryl or arylalkyl radical with 5 to 20 carbon atoms. In addition to bismuth naphthenates, bismuth alkyl carboxylates having 6 to 10 carbon atoms in the alkyl radical and especially bismuth octoate are particularly preferred. These bismuth compounds are intended in particular to replace the lead compounds which have the same effect but are toxicologically unsafe. The object of the invention is to provide non-water-miscible or water-mixed cooling lubricants or their water-miscible concentrates with an improved lubricating effect. In this case, an additive which improves the lubricating effect must be designed in such a way that it is compatible with the other components of the cooling lubricants or their concentrates. For example, it must be soluble in an oil-based, non-water-miscible and water-miscible cooling lubricant. In the case of water-mixed cooling lubricants, which are usually in the form of an emulsion, it must also not adversely affect the stability of the emulsion.

In a first aspect, the invention relates to a friction-reducing additive for water-miscible or non-water-miscible cooling lubricants, comprising

a) Bismuth compounds of organic acids b) Sulfur-containing organic compounds

in a mixing ratio such that the sulfur content of the additive is in the range from 2 to 30% by weight and the bismuth content is in the range from 1 to 25% by weight. The mixing ratio is preferably chosen such that the sulfur content of the mixture is in the range from about 5 to about 25% by weight and the bismuth content is in the range from about 4 to about 20% by weight. Additives in which the ratio of sulfur content to bismuth content are in the range from 1: 0.1 to 1: 2, preferably in the range from 1: 0.15 to 1: 1, are particularly preferred.

According to the teaching of EP-A-675 192, the bismuth compounds are preferably selected from naphthenates and / or from carboxylates of the general formula (R-CO ₂ ) Bi, in which R is a linear, branched or cyclic alkyl radical with 1 to 30 C. -Atoms or an aryl, alkylaryl or arylalkyl radical having 5 to 20 carbon atoms. The bismuth compounds are preferably selected from Naphthenates and / or from alkyl carboxylates with 6 to 10 carbon atoms in the alkyl radical. Bismutoctoate is particularly preferred. For better compatibility with water-mixed cooling lubricants, these bismuth compounds can be reacted with ethylene oxide and / or propylene oxide.

Organic sulfur compounds are generally known in the lubricant field as so-called extreme pressure additives (EP additives). Examples of these are organic sulfides and disulfides, sulfurized paraffins, sulfurized fatty oils, sulfurized polyisobutene, sulfurized polypropylene or sulfurized polystyrene. These can be used together with phosphorus-containing organic compounds to further increase the activity. Sulfurized fatty oils and sulfurized paraffins are particularly preferred for the purposes of the present connection.

The additive according to the invention can furthermore contain up to 5% by weight, based on the total mass of the additive, of compounds selected from the group of the esters and / or the polyglycols. Examples of esters are di- and triglycerides such as turnip oil. Further examples are polymer esters such as butanol esters of α-olefin-dicarboxylic acid copolymers. Polymer esters of this type, which can have a molecular weight of around 1,800, for example, are sold by Akzo under the name Ketjenlube 135. An example of a usable polyalkylene glycol is the Emkarox VG 180 from Erbslöh.

In a further aspect, the invention relates to the use of the additive described above as a friction-reducing additive in water-mixed or non-water-miscible cooling lubricants. The additive is preferably used in a concentration range such that the ready-to-use water-mixed cooling lubricants, which are usually in the form of an oil-in-water emulsion, are prepared by adding a concentrate to water , the bismuth content is in the range from 0.01 to 0.2% by weight, preferably in the range from 0.02 to 0.15% by weight. In the case of ready-to-use, non-water-miscible cooling lubricants, the additive is used in a concentration range such that the bismuth content is in the range from 0.2 to 4% by weight, preferably in the range from 0.4 to 3% by weight.

The invention further relates to the use of cooling lubricants which contain the additive according to the invention for the so-called minimal lubrication technology. This is sometimes, albeit misleadingly, referred to as low-quantity lubrication. For example, it is explained in the article by A. Walter: ..Minimal lubrication technology and dry machining; possible fields of application ", German Industry Forum for Technology 10/95 (DIF 17/21 / WA). In the case of minimal lubrication technology, compared to the conventional use of cooling lubricants, cooling lubricant quantities are significantly reduced. This leads to a greatly reduced cooling of the tool and workpiece Increased importance is attached to the lubrication to reduce the frictional heat in the process. The lubrication can only be carried out by using a suitable cooling lubricant when using minimal quantity lubrication. The cooling lubricant is sprayed onto the tool and workpiece. For this type of use the additive mixture according to the invention can be used as such, ie without mixing with other components, but it is also possible to use the additive in a mixture with mineral oils, vegetable oils or synthetic polar compounds, the proportion of the additive in the total mixture being at least 10 Ge % w.

In a further aspect, the invention relates to a water-miscible concentrate for preparing a water-mixed cooling lubricant which contains the additive described above, preferably in an amount of about 2 to about 20% by weight, based on the total concentrate. In addition to the additive mentioned the concentrate contains at least one base oil, an emulsifier and a selection from the additives listed above. To prepare the ready-to-use water-mixed cooling lubricant, the concentrate is usually mixed with about 50 to about 10, for example with about 20, parts by weight of water. A suitable concentrate emulsifies spontaneously and forms a stable oil-in-water emulsion.

The invention further comprises a water-immiscible cooling lubricant which contains about 2 to about 20% by weight, for example about 10% by weight, of the additive described above.

Execution examples

The following standard tests were carried out to check the lubricating effect:

Testing in the shell four-ball apparatus ("VKA") according to DIN 51350 part 1-3

According to the DIN 51350 standard, a distinction is made between short and long-term tests.

Short-term attempt

The method according to this standard is used to determine the good and weld strength of liquid lubricants with active ingredients that should allow high surface pressures in the mixed friction area between surfaces that move relative to each other (EP behavior). For this purpose, the lubricant is tested in a four-ball system, which consists of a rotating ball (running ball) that slides on three balls of the same size (standing balls) under selectable test forces. The test force is gradually increased until the four-ball system is welded.

Before the start of the test, the test balls and the ball cup are cleaned with mineral spirits in order to obtain reproducible and thus meaningful results. Three test balls are firmly clamped in the cleaned ball cup. The ball cup is then filled with the lubricant to be tested so that the test balls are completely covered.

A test ball is carefully pressed into the ball holder and inserted into the test spindle. After inserting the ball cup, the test force is applied. The test force is set by moving a barrel weight on the balance beam. This pressure generated in this way corresponds to the test ball load. The duration of the test run is one minute, unless it is interrupted by welding the test balls.

If welding does not occur, further test runs with increased test force and new test balls are required until the welding force is reached. The force at which welding does not yet occur is called the good force.

Long-term trial

Long-term tests are carried out to obtain information about the wear protection behavior of a lubricant (AW behavior).

For this purpose, the lubricant is tested in a four-ball system, which consists of a rotating ball (running ball), which is applied to three of it under a specified test force same balls (standing balls), exists. According to method B, a test load of 300 N is set as the test force. The test time is one hour. The calotte diameters of the three standing balls are then measured and averaged.

The wear diameter is measured with a Brinell magnifying glass or with a measuring microscope. The value determined in this way is regarded as a measure of the strength of the wear and is referred to as the average wear diameter (“AW wear”).

Friction wear scales according to Reichert

This method is used to determine the pressure absorption capacity (EP behavior) and to determine the adhesive strength of liquid lubricants. Here, a test roller is adapted to a rotating slip ring by means of a lever system, the lower third of which is immersed in the lubricant to be tested. Before the start of the test, the test roll, which has been cleaned in white spirit, is installed in the swiveling holder. The holder is swung in and clamped. The slip ring remains clamped in the device for several test runs, where it is also cleaned with white spirit after each test run. The test roller is placed on the slip ring by slowly applying the load weight (1.5 kg). The counter on the Reichertwaage is set to 0. When the motor is switched on, the rotating slip ring immersed in the lubricant continuously supplies the contact point with lubricant. When the number 100 is reached on the counter (100 meter friction distance), the test roller is removed from the slip ring. The test roller is removed and the cut mark is measured using a magnifying glass. The ellipse area is calculated as 0.785 * length * width, or is read off using a number table. So many test runs are carried out until the ellipse surfaces of the last 3 test runs do not differ from one another by more than 10%. The smaller the elliptical area, the greater the pressure absorption capacity. 1. Non-water-mixed cooling lubricants

By mixing base oil and additives according to Table 1, comparative examples and examples according to the invention for water-immiscible cooling lubricants were produced. The lubricating effect of the mixtures was checked using the four-ball device. The results are also shown in Table 1. % Figures for base oil and for additives are% by weight with respect to the total mixture. Sulfur and bismuth contents are also given as% by weight with respect to the total mixture.

Table 1: Coolants that are not mixed with water

No. of base oil additives S-content Bi-content good strength AW-Ver. (% By weight) (% by weight) (% by weight) (% by weight) VKA (N) wear (mm)

Cf. 1 80% mineral oil 20% mixture of chlorinated paraffin + beet oil - - 2800 0.5

Compare 2 95% mineral oil 5% Bi-Octoat - 1, 2 3500 1.0

Cf. 3 95% mineral oil 5% sulfurized fat oil 1.3 - 2900 0.9

Ex. 1 90% mineral oil 5% bi-octoate 1.3 1.2 10500 0.5

5% sulfurized fat oil

Ex. 2 88% mineral oil 4% bi-octoate 1.3 1.0 8500 0.8 4% beet oil 4% sulfurized hydrocarbon (32% S)

Example 3 90% beet oil 5% bi-naphthenate 1.65 0.85 9000 0.8

5% sulfurized fat oil (26% S)

Ex. 4 80% mineral oil 10% Bi-Octoat 2.6 2.4> 12000

10% sulfurized fat oil

Ex. 5 80% beet oil 10% Bi-Octoat 2.6 2.4> 12000

10% sulfurized fat oil

Table 1: continued

No. Base oil additives S content Bi content Good strength AW packaging

(% By weight) (% by weight) (% by weight) (% by weight) VKA (N) wear (mm)

Ex. 6 95% mineral oil 2.5% bi-octoate 0.65 0.6 4800

2.5% sulfurized fat oil

Ex. 7 88% mineral oil 2% bi-octoate 1.6 0.5 8500 0.8 5% beet oil 5% sulfurized hydrocarbon

Ex. 8 89% mineral oil 1% bi-octoate 1.6 0.25 6500 0.7 5% beet oil 5% sulfurized hydrocarbon

2. Water-miscible cooling lubricants

The following concentrates of water-miscible cooling lubricants were produced, which in their composition resemble common commercial products. 90 parts by weight of these concentrates were mixed with 10 parts by weight of additive. Ready-to-use water-mixed cooling lubricant emulsions were prepared from these mixtures by adding 95 parts by weight of water to 5 parts by weight of the concentrate / additive mixture. The lubricating effect was measured with the Reichert balance. The results are shown in Table 2.

Concentrate 1 (composition in% by weight) 36% paraffinic mineral oil

6% monoethanolamine

4% triethanolamine 8% boric acid

7% tall oil fatty acid

8% tall oil fatty acid monoethanolamide 2% glycerin

7% oleyl / cetyl alcohol x 10 ethylene oxide balance: demineralized water

Concentrate 2

45% paraffinic mineral oil

5% beet oil

14% tall oil fatty acid

2.5% potassium hydroxide

7% tall oil fatty acid monoethanolamide

2% triethanolamine

6% hexanediol-2,4 12% oleyl / cetyl alcohol x 2 ethylene oxide

3% Benzylhemiformal rest: demineralized water

Concentrate 3

21% paraffinic mineral oil 16% tall oil fatty acid 5% dimer fatty acid 15% potassium hydroxide

4% diethylene glycol monobutyl ether

5% dodecyl succinic anhydride 5% beet oil

10% ethylene glycol monophenyl ether 19% oleyl / cetyl alcohol x 12 EO

17

Table 2: Water-miscible cooling lubricants

(The indicated S and Bi contents refer to the total mixture)

Base (90%) additive (10%) friction wear acc. To Reichert (mm ² )

Comp. 1 concentrate 1 sulfurized hydrocarbon 18 and polymer ester (3% S)

Example 1 concentrate 1 sulfurized fat oil, bi-octoate 1.3 (1.3% S, l, 2% Bi)

Compare 2 concentrate 2 polyalkylene glycol, fat 32

Example 2 concentrate 2 sulfurized fat oil, Bi-Octoat 25 (1.3% S, 1.2% Bi)

Compare 3 concentrate 3 phosphoric acid esters, fatty substances 32

Compare 4 concentrate 3 sulfurized fat oil (2% S) 20

Comp. 5 concentrate 3 polyalkylene glycol, bi-octoate 1 1 (2.4% Bi)

Example 3 concentrate 3 sulfurized fat oil, bi-octoate 2.0 (1.3% S, 1.2% Bi)

Example 4 concentrate 3 sulfurized fat oil, bi-octoate, 1,3

Polyalkylene glycol

(0.65% S, 0.5% Bi)

Claims

claims

1. Low-friction additive for water-miscible or water-immiscible cooling lubricants, containing

a) Bismuth compounds of organic acids b) Sulfur-containing organic compounds

in a mixing ratio that the sulfur content of the additive is in the range from 2 to 30% by weight and the bismuth content in the range from 1 to 25% by weight.

2. Additive according to claim 1, characterized in that the ratio of sulfur content to bismuth content of the additive is in the range from 1: 0.1 to 1: 2.

3. Additive according to claim 1 or 2, characterized in that the bismuth compounds are selected from naphthenates and / or carboxylates of the general formula (R-C0 ₂ ) ₃ Bi, in which R is a linear, branched or cyclic alkyl radical with 1 to 30 C. -Atoms or one

Aryl, alkylaryl or arylalkyl radical having 5 to 20 carbon atoms.

4. Additive according to claim 3, characterized in that the bismuth compounds are selected from naphthenates and / or from alkyl carboxylates having 6 to 10 carbon atoms in the alkyl radical.

5. Additive according to one or more of claims 1 to 4, characterized in that the sulfur-containing organic compounds are selected from organic sulfides and disulfides, sulfurized paraffins, sulfurized fat oils or sulphurised polyisobutene, sulphurised polypropylene or sulphurised polystyrene.

6. Additive according to one or more of claims 1 to 5, characterized in that it additionally contains up to 5% by weight, based on the total mass of the additive, of compounds selected from the group of

Contains esters and / or the polyglycols.

7. Use of an additive according to one or more of claims 1 to 6 as a friction-reducing additive in water-mixed or non-water-miscible cooling lubricants.

8. Use according to claim 7, characterized in that the bismuth content of the ready-to-use water-mixed cooling lubricants in the range from 0.01 to 0.2% by weight, the bismuth content of the ready-to-use non-water-miscible cooling lubricants in the range from 0.2 to 4% by weight. % lies.

9. Use of an additive according to one or more of claims 1 to 6 alone or in a mixture with mineral oils, vegetable oils and / or synthetic polar compounds for minimal lubrication technology.

10. Water-miscible concentrate for preparing a water-mixed cooling lubricant which contains 2 to 20 wt .-% of an additive according to one or more of claims 1 to 6.

1 1. Non-water-miscible cooling lubricant containing 2 to 20 wt .-% of an additive according to one or more of claims 1 to 6.