Note: Descriptions are shown in the official language in which they were submitted.
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COMPOSITION FOR MINIMUM QUANTITY LUBRICATION,
AND USE OF SAME
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,
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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 Al. 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.
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For cleaning off a lubricant based on a saturated aliphatic monohydric C14-18
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.
Further embodiments of the lubricant composition are disclosed further.
The simple cleaning off when using the lubricant composition is disclosed
herein.
The lubricant composition according to the invention for minimum quantity
lubrication for metalworking is comprised of a main proportion of an aliphatic
C18-
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
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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 C16-24 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*-[(CH2CH20)x -(CH2CH(CH3)0) y]-R1 (I)
wherein R1 is an aliphatic, branched or linear C16-18 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-(CH2CH20)n-R with R = C18 or Cm 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 5 wt.%, wherein smaller proportions, e.g., 1 wt.%, are
preferred in
particular. Advantageously, the lubricant composition with 1 wt.% 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)
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R2 -0-RCH2CH20)X4CF12C1-1(CH3)0)+CF12-COOH (II)
wherein R2 is an aliphatic, preferably branched or linear, C6_20 alkyl or
alkylene
residue. In this context, purely ethoxylated, purely propoxylated, or mixed
ethondated 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-ethanediy1),
a-
(carboxymethyl)-w-hydroxy-, C10-16 and C12-20 unsaturated alkyl ethers (e.g.,
CAS
No. 68954-89-2), poly(oxy-1,2-ethanediy1), a-(carboxymethyl)-w-hydroxy-, C16-
18
and C18 unsaturated alkyl ethers (CAS No. 227310-69-2), poly(oxy-1,2-
ethanediy1), a-(carboxymethyl)-w-hydroxy-octyloxy-, (CAS No. 53563-70-5) or
poly(oxy-1,2-ethanediy1), a-(carboxymethyl)-w-hydroxy-hexyloxy-, (CAS No.
105391-15-9).
The aliphatic C16-24 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 a position relative to the primary OH
residue),
such as e.g. 2-hexy1-1-decanol or 2-octy1-1-dodecanol. The latter Czo 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 C16-24 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 5 wt.%, relative to
the total
weight of the composition, fatty acid alkanolamide or alkoxylated fatty acid
alkanolamide of the formula (111)
R3 -(C0)-NR`-(CH2)2-0-[(CH2CH20) x -(CH2CH(CH3)0) y]-R" (Ill)
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wherein R3 is an aliphatic, linear or branched, C5-23 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) C12-24 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.,
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b) pure fatty acids such as e.g. oleic acid or similar ones with chain lengths
in the
range of C12-24,
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 15 wt.%, wherein the proportion
of the sum of the performance additives relative to the total weight of the
composition does not surpass 30 wt.%.
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.
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