Composition for Minimum Quantity Lubrication, and Use of Same

Abstract

The invention relates to a lubricant composition and to the use of same for minimum quantity lubrication in the field of metalworking. The composition comprises 0.05 to 5 wt.% of emulsifier in relation to the total weight of the composition, and an amount of an aliphatic C16-24 alcohol that makes the composition up to 100%. The emulsifier is selected from fatty alcohol polyalkylene glycol ethers or glycolic acid alkoxylate alkyl ethers or mixtures thereof.

Description

The invention concerns a lubricant composition for minimum quantity lubrication in metalworking and the use of the lubricant composition therefor.

In metalworking processes, a differentiation is made between conventional wet machining in which the cutting tool is flooded with a lubricating coolant and dry machining without lubrication in which the heat that is produced in the cutting process is transferred mainly to chip, tool, and workpiece. While dry machining does not employ lubricants, the heat flowing into the workpiece can disadvantageously affect the component precision; also, the tool can wear earlier due to the increased thermal load. The lubricating coolants employed in wet machining provide primarily cooling, lubrication, and chip removal, but at the same time have an effect on auxiliary process times in the production process due to catching, recycling or disposing of the lubricating coolants and thus also on the costs for their purchase, recycling, and disposal. Moreover, care must be taken regarding environmental and health protection.

A compromise between wet machining and dry machining is the minimum quantity lubrication (MQL) or also minimum quantity cooling lubrication (MQCL). Precise definitions for the “minimum quantities” do not exist; depending on the source, up to 20 ml/h, 50 ml/h, 150 ml/h but sometimes even up to 500 ml/h are referred to as MQL—in all cases, there is however a significant difference to the usual quantities for wet machining of 30,000 to 60,000 ml/h, or even significantly more.

Compared to wet machining, minimum quantity lubrication provides a significant reduction of the supply and disposal technology for the lubricating coolant, enables longer service lives and reduced processing duration. Moreover, downstream processes for cleaning the workpieces and also the tool can be reduced. Since the minimum quantity lubrication means loss lubrication, only new, i.e., non-recycled or reprocessed, lubricant is employed so that biocides, fungicides, and other additives are not needed.

However, there are higher demands on the lubricant that must be matched to workpiece material, machine parameters, and tool material in order to achieve optimal results.

In general, for MQL either synthetic ester oils or fatty alcohols are employed which are combined in regard to evaporation and flash point for the desired operating range. In this context, synthetic esters are preferred for cutting processes in which an effective lubrication is most important. When using fatty alcohols, the focus is less on the lubrication but on the cooling action.

A composition on the basis of a fatty alcohol for aluminum machining with minimum quantity lubrication is disclosed in EP 2 397 535 A1. The alcohol compound has 1 to 8 hydroxyl groups and 2 to 27 carbon atoms and is contained in the composition in a quantity of 16 to 100 wt. %. The residual quantity can be a mineral oil or synthetic oil, also ester oil. For improving the lubrication action of this composition, various additives are listed which can be added to the composition.

It has been found that, even in minimum quantity lubrication, minimal quantities of the lubricating coolant remain on the workpiece around the cutting location and on the tool. The lubricant residues on the workpiece, on the one hand, can aid in avoiding corrosion at the machining location but, on the other hand, can also have a disadvantageous effect on downstream production processes such as welding, gluing, painting etc. and therefore may possibly require a cleaning step.

Water-miscible metalworking liquids that can be cleaned off with water are considered unsuitable for minimum quantity lubrication because they do not have the required lubrication action therefor or the required flash point.

For cleaning off a lubricant based on a saturated aliphatic monohydric C_14-18 alcohol that is formed as film on the surface of the workpiece for cold machining of aluminum, WO 91/06619 describes heating of the workpiece so that the lubricant evaporates.

Based on this prior art, it is object of the present invention to provide a minimum quantity lubricant that, without heating, can be cleaned off not only from the workpiece but also from the tool and the machine tool in a simple way.

This object is solved by a lubricant composition with the features of claim 1.

Further embodiments of the lubricant composition are disclosed in the dependent claims.

The simple cleaning off when using the lubricant composition is disclosed by the features of independent claim 8.

The lubricant composition according to the invention for minimum quantity lubrication for metalworking is comprised of a main proportion of an aliphatic C_16-24 alcohol to which is added a minimal proportion of an emulsifier so that the lubricant can be emulsified with water. In this way, not only the workpiece but also the tool and the machining space (e.g., interior of the machine) can be simply removed from the residues of the lubricant composition according to the invention by emulsifying with water. However, care must be taken that the lubricant composition during storage and supply to the tool does not come into contact with water.

A preferred emulsifier can be a fatty alcohol polyalkylene glycol ether which is contained in the composition with 0.05 to 5 wt. % relative to the total weight of the composition. Alternatively, the emulsifier can be a glycolic acid alkoxylate alkyl ether whose proportion in the composition lies in a range of 0.05 to 5 wt. % relative to the total weight of the composition. However, it is also conceivable that mixtures of fatty alcohol polyalkylene glycol ether and glycolic acid alkethoxylate alkyl ether are used as emulsifier with a weight proportion of 0.05 to 5 wt. % relative to the total weight of the composition. The aliphatic C_16-24 alcohol is then present in a proportion that supplements the composition to 100%, respectively.

The fatty alcohol polyalkylene glycol ether has the formula (I)

R*-[(CH₂CH₂O)_x(CH₂CH(CH₃)O)_y]-R¹   (I)

wherein R¹ is an aliphatic, branched or linear C_16-18 alkyl or alkylene residue. R* can be a hydroxyl group. The variables x and y can be 0 to 10 with the condition that the sum of x+y is from 1 to 10. The fatty alcohol polyalkylene glycol ether, also by trivial name fatty alcohol alkoxylate or alkoxylated fatty alcohol, can be comprised only of ethylene oxide units (y=0) or only of propylene oxide units (x =0). The polyalkylene glycol ether may however also contain ethylene oxide units as well as propylene oxide units. In this context, the respective proportions as well as sequence of the units (e.g., alternating or in blocks) can vary. A non-limiting exemplary purely ethoxylated fatty alcohol can be based on oleyl or cetyl alcohol: HO-(CH₂CH₂O)_n-R with R=C₁₈ or C₁₆ with n=5, for example. Deviations with regard to the base alcohol, type and number of alkoxy units are conceivable, of course.

Preferably, the weight proportion of the fatty alcohol polyalkylene glycol ether can amount to 1 to 5wt. %, wherein smaller proportions, e.g., 1wt. %, are preferred in particular. Advantageously, the lubricant composition with 1wt. % fatty alcohol polyalkylene glycol ether exhibits a suitable emulsifier balance with sufficiently good emulsifying properties without negatively affecting the separation behavior in the cleaning device (demulsifying behavior) in this context. While an emulsifier concentration that is too low causes a reduced cleaning action on tool, workpiece, and machine space, concentrations that are too high prevent the oil separation in the cleaning device.

The glycolic acid alkoxylate alkyl ether (also ether carboxylic acid) as an alternative to the fatty alcohol polyalkylene glycol ether has the formula (II)

R² -O-[(CH₂CH₂O)_x-(CH₂CH(CH₃)O)_y]-CH₂-COOH   (II)

wherein R² is an aliphatic, preferably branched or linear, C_6-20 alkyl or alkylene residue. In this context, purely ethoxylated, purely propoxylated, or mixed ethoxylated and propoxylated compounds are also conceivable so that x and y can be selected from 0 to 10 with the condition that the sum x+y=1 to 10. The glycolic acid alkoxylate alkyl ether is preferably a glycolic acid ethoxylate alkyl ether.

Examples of glycolic acid alkoxylate alkyl ether are poly(oxy-1,2-ethanediyl), α-(carboxymethyl)-ω-hydroxy-, C_10-16 and C_12-20 unsaturated alkyl ethers (e.g., CAS No. 68954-89-2), poly(oxy-1,2-ethanediyl), α-(carboxymethyl)-ω-hydroxy-, C_16-18 and C₁₈ unsaturated alkyl ethers (CAS No. 227310-69-2), poly(oxy-1,2-ethanediyl), α-(carboxymethyl)-ω-hydroxy-octyloxy-, (CAS No. 53563-70-5) or poly(oxy-1,2-ethanediyl), α-(carboxymethyl)-ω-hydroxy-hexyloxy-, (CAS No. 105391-15-9).

The aliphatic C_16-24 alcohol which is used in the lubricant composition according to the invention can be a branched alcohol, preferably a Guerbet alcohol (long-chain alcohol that is alkyl-substituted in α position relative to the primary OH residue), such as e.g. 2-hexyl-1-decanol or 2-octyl-1-dodecanol. The latter C₂₀ alcohol can be employed preferably. Due to the low pour point and the reduced adhesion tendency as a result of complete saturation, such alcohols can be used at lower temperatures of use compared to natural linear alcohols.

A lubricant composition embodied according to the invention can thus be comprised of only two components, the basic C_16-24 alcohol and the emulsifier.

In a further embodiment of the invention, it can however be provided also that the lubricant composition contains in addition from 0.05 to 5wt. %, relative to the total weight of the composition, fatty acid alkanolamide or alkoxylated fatty acid alkanolamide of the formula (III)

R³ -(C0)-NR′-(CH₂)₂-O-[(CH₂CH₂O)_x -(CH₂CH(CH₃)O)_y]-R″   (III)

wherein R³ is an aliphatic, linear or branched, C_5-23 alkyl or alkenyl residue and R′, R″ independent from each other are hydrogen or an aliphatic, linear or branched, substituted or unsubstituted alkyl or alkenyl residue. x and y can be each selected from 0 to 10 so that, as above, purely ethoxylated, purely propoxylated, and mixed ethoxylated and propoxylated compounds are encompassed, wherein here the sum x+y can be from 0 (non-alkoxylated) to 10. The addition of a fatty acid alkanolamide or alkoxylated fatty acid alkanolamide contributes to an improved corrosion protection action of the lubricant composition and can positively affect the cleaning action of the workpiece or of the machine as a result of the emulsifying properties.

Moreover, a lubricant composition according to the invention can additionally comprise at least one performance additive that can be selected from a group that encompasses

a) sulfurized compounds such as sulfurized olefins, sulfurized esters, sulfurized triglycerides, and sulfurized natural ester oils,
b) C_12-24 fatty acids,
c) ethoxylated natural oil,
d) KOH-saponified rapeseed oil,
e) ethoxylated acidic phosphoric acid ester.

In the following, examples are disclosed that explicitly are not to be understood as limiting:

Non-limiting examples for

a) sulfurized compounds comprise

• • sulfurized olefins such as di-tert-dodecyl-polysulfides (EC No. 270-335-7), e.g., di-tert-dodecyl-trisulfide or di-tert-dodecyl-pentasulfide,
  • sulfurized esters such as fatty acids, vegetable oil, methyl ester, sulfurized (EC No. 276-337-4),
  • sulfurized triglycerides/sulfurized natural ester oils such as e.g. sulfurized rapeseed oil, sulfurized lard oil, sulfurized castor oil etc.,
    b) pure fatty acids such as e.g. oleic acid or similar ones with chain lengths in the range of C_12-24,
    c) ethoxylated natural oils such as e.g. castor ethoxylate with 1 to 10 ethylene oxide units,
    d) KOH-saponified rapeseed oil,
    e) acidic phosphoric acid ester ethoxylated, such as e.g. oleyl alcohol ethoxylated phosphate (CAS No. 39464-69-2).

In this context, a proportion of each performance additive relative to the total weight of the composition amounts to maximally 15wt. %, wherein the proportion of the sum of the performance additives relative to the total weight of the composition does not surpass 30wt. %.

A lubricant composition according to the invention can thus be used for minimum quantity lubrication in metalworking wherein residues of the lubricant composition remaining on surfaces of workpiece and tool can be washed off with water.

Claims

1.-8. (canceled)

9. A lubricant composition for minimum quantity lubrication in metalworking, the lubricant composition comprising:

an emulsifier in a quantity of 0.05wt. % to 5wt. % of a total weight of the lubricant composition;

an aliphatic C16-24 alcohol in a quantity of a remaining balance of the total weight of the lubricant composition;

wherein the emulsifier is selected from the group consisting of fatty alcohol polyalkylene glycol ethers; glycolic acid alkoxylate alkyl ethers; or mixtures thereof.

10. The lubricant composition according to claim 9, wherein the emulsifier comprises a fatty alcohol polyalkylene glycol ether of the formula (I)

R*-[(CH2CH2O)x-(CH2CH(CH3)O)y]-R1   (I)

wherein R1 is an aliphatic, branched or linear C16-18 alkyl residue or alkylene residue,

wherein R* is a hydroxyl residue,

wherein x=0 to 10, y=0 to 10, and x+y=1 to 10.

11. The lubricant composition according to claim 9, wherein the emulsifier comprises a glycolic acid alkoxylate alkyl ether of the formula (II)

R2-O-[(CH2CH2O)x-(CH2CH(CH3)O)y]-CH2-COOH   (II)

wherein R2 is an aliphatic, branched or linear C6-20 alkyl residue or alkylene residue,

wherein x=0 to 10, y=0 to 10, and x+y=1 to 10.

12. The lubricant composition according to claim 9, wherein the aliphatic C16-24 alcohol is a branched alcohol.

13. The lubricant composition according to claim 12, wherein the aliphatic C16-24 alcohol is a Guerbet alcohol.

14. The lubricant composition according to claim 12, wherein the aliphatic C16-24 alcohol is a C20 alcohol.

15. The lubricant composition according to claim 9, further comprising 0.05wt. % to 5wt. %, relative to the total weight of the composition, of a fatty acid alkanolamide or an alkoxylated fatty acid alkanolamide of the formula (III)

R3 -(CO)-NR′-(CH2)2-O-[(CH2CH2O)x-(CH2CH(CH3)O)y]-R″   (III)

wherein R3 is an aliphatic, linear or branched C5-23 alkyl residue or alkylene residue,

wherein R′, R″ independent of each other is hydrogen or an aliphatic, linear or branched, substituted or unsubstituted alkyl residue or alkenyl residue, and

wherein x=0 to 10, y=0 to 10, and x+y=0 to 10.

16. The lubricant composition according to claim 9, further comprising one or more performance additives selected from the group consisting of:

a) sulfurized compounds selected from the group consisting of sulfurized olefins, sulfurized esters, sulfurized triglycerides, and sulfurized natural ester oils,

b) C12-24 fatty acids,

c) ethoxylated natural oil,

d) KOH-saponified rapeseed oil, and

e) ethoxylated acidic phosphoric acid ester.

17. The lubricant composition according to claim 16, wherein a proportion of each one of the one or more performance additives, relative to the total weight of the lubricant composition, amounts to 15wt. % and wherein a proportion of the sum of the one or more performance additives, relative to the total weight of the composition, amounts to 30wt. %.

18. A method of minimum quantity lubrication in metalworking, the method comprising employing a lubricant composition according to claim 9 during machining of a workpiece and washing off, with water, residues of the lubricant composition remaining on surfaces of the workpiece and on surfaces of a tool.