Study of Oiliness Agent for Cold Rolling Oilof Copper and Copper Alloyby Sakae Imaizumi *, Minoru Igarashi *2 and Junichi Shibata *3

Oil for the cold rolling of copper and copper alloys is generally a commercial rolling oil consisting of a low-viscosity mineral oil to which fatty alcohol and fatty
acid ester is added as an oiliness agent. Because knowledge of the influence ofoiliness agent on rolling performance and of how to maintain the rolling oil is considered by eachcompany to be proprietary, there are few reports concerning cold rolling oils for copper and copper alloys. Thus typical copper alloys have been evaluated for an experimental rolling mill using
commercial rolling oil. It has been understood that there is a problem in the lubricity of brass(Cu-Zn alloy) when rolled with commercial rolling oil. To study the oiliness agent in the rolling oil,the adsorption activity of a model oiliness agent component gas was evaluated, and acid andether compounds were found to show the potential for enhancing the adsorption activity of theoiliness agent onto the nascent Cu-Zn alloy surface. In experimental rolling, it was confirmed thatthe lubrication performance of the oiliness agent added to standard oil could be improved byadding the ether compound without other problems. We also studied the type of ether compound and the proper amount of the ether compound, and examined to elucidate the lubrication
mechanism by experimental rolling.

ABSTRACT1.

INTRODUCTION

Oil for the cold rolling of copper and copper alloys is generally a commercial rolling oil consisting of a low-viscosity
mineral oil to which fatty alcohol and fatty acid ester isadded as an oiliness agent. Because knowledge of theinfluence of oiliness agent on rolling performance and of
how to maintain the rolling oil is considered by each company to be proprietary, there are few reports concerning
cold rolling oils for copper and copper alloys. Pure copper (Cu), brass (Cu-Zn alloy) and phosphor bronze (CuSn alloy) as three typical copper alloys were evaluated bystep rolling in an experimental rolling mill using commercial rolling oil. It seemed that examination of an oilinessagent suitable for Cu-Zn alloy was necessary because theroll coating of the Cu-Zn alloy to the work-roll was remarkable, and a scaly pattern was observed on the rolled strip
surfaces after rolling with commercial rolling oil. In order
to select an oiliness agent suitable for Cu-Zn alloy, theadsorption characteristic of oiliness agents on a nascent
Cu-Zn alloy surface was investigated and the values ofadsorption activity were measured by experimental apparatus for adsorption tests. The ether compound and the* Metal Research Center, R&D Div.
* 2 First Research Dept., Metal Research Center, R&D Div.
* 3 Nippon Oil Corp.

fatty acid showed higher adsorption activity for Cu-Zn
alloy.
Because subsequent discoloration was observed on
the surface of strips after rolling with rolling oil containing
fatty acid, we only studied use of the ether compounds.
We also studied the type of ether compound and theproper amount of the ether compound by experimental
rolling of Cu and Cu-Zn alloy. We also examined the reason why the ether compound was effective in increasing
the rolling performance of Cu-Zn alloy.

2.

EXPERIMENTAL

2.1 Rolling Tests with Commercial Rolling Oil
2.1.1 Test Conditions
The specifications and rolling conditions of the test mill
are shown in Table 1.
For the material to be rolled, we selected 70%Cu30%Zn alloy (C2600) as brass, Cu-8%Sn alloy (C5212) as
phosphor bronze and tough pitch copper (C1100) as
pure copper. We adopted a step rolling method, increasing reduction while rolling at a constant rate at regularintervals, and recorded the rolling data for each reduction.
Rolling tension was constant because it could not be
adjusted at each reduction. The rolling oil contained 15-%
ester and about 1-% alcohol in a mineral oil of viscosity
4.6 mm2/s as components. The work-roll roughness was

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Study of Oiliness Agent for Cold Rolling Oil of Copper and Copper Alloy

Table 1120

Test mill specifications and rolling conditions.

CopperWork roll

φ51×220 mm (SKD-11)
Surface roughness Ra=0.04 µm

Material

Copper (C1100) (t)0.3×(w)50 mm×coil
Brass(C2600) (t)0.3×(w)50 mm×coil
Bronze(C5212) (t)0.3×(w)50 mm×coil
Buffing surface after full annealing

Rolling speed

70 m/minTensionCopperBrass
BronzeRolling oil

Reduction

100

Reversing Z-High type millBrassBronzeRolling load (kN)

Test mill type

80
60
40
20

Entry:
815 N
Entry: 1360 N
Entry: 1360 N

Exit: 490 N
Exit: 1000 N
Exit: 1000 N

Total volume

10

Flow rate
Temperature

7 /min (Entry side)
40°C

0

15

25

35

45

55

65

75

Reduction (%)

Figure 2

Relationship between rolling load and reduction.

Copper 30, 40, 45, 50, 55, 60, 65, 70%
Brass20, 25, 30, 35, 40, 45, 50, 55%
Bronze20, 30, 40, 45, 50, 55, 60, 65%
Rolling for 60 s at each reduction

Ra=0.04 µm and new rolling oil and a new work-roll wasused for each material. Figure 1 shows the schematic of
the experimental rolling mill.
(a) Cu2.1.2 Test Results
In the rolling tests we measured the rolling speed, theentrance and exit speed of the strip, the rolling load, thereduction, the front and back tension, and the temperature of the oil.
The relationship between the reduction and the rolling
load for Cu, Cu-Zn alloy, and Cu-Sn alloy is shown in
Figure 2.
The rolling load did not increase for Cu at a reduction of
50 % or more, even if the reduction increased, but when
the rolling load increased for Cu-Zn alloy and Cu-Sn alloy
as the reduction increased, and when reduction exceeded
45 % in Cu-Zn alloy, this tendency increased.
The strip surface photomicrograph of each material at
50-% reduction is shown in Figure 3. The transferred pattern of the work-roll and the oil pits could be observed on

Rolling direction

P
Heat exchanger
Pump

Figure 1(b) Cu-Zn

0.1 mm(c) Cu-Sn

Figure 3

Microscopic observation of strip surface at 50%
reduction.

Cu and Cu-Sn alloy surfaces, but even at this reduction,
we observed a scaly pattern that seemed to be a metallic
adhesion of Cu-Zn alloy to the work roll, and when reduction exceeded 30 % it became remarkable. This seemed
to be related with the fact that in the observation of rollcoating after rolling, roll coating was not observed at allon the surface of the work roll for Cu and was observed
clearly for Cu-Zn alloy. For Cu-Sn alloy roll coating wasobserved at a level midway between Cu and Cu-Zn alloy.
As shown by the above-mentioned result, the problem
with rolling performance for Cu and Cu-Sn alloy was notseen using the commercial rolling oil, but there was a
problem with Cu-Zn alloy in that there was thought to be
an increase in rolling load by the adhesion of metal to thework-roll even under low reduction. Thus we aimed to
improve rolling performance for Cu-Zn alloy. The oilinessagent was selected measuring the adsorption activity to
the metal, considering that it was important that the oiliness agent be adsorbed to the rolling material or the
work-roll.

Z-high type test mill.

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Study of Oiliness Agent for Cold Rolling Oil of Copper and Copper Alloy

Table 2

Adsorption activity of model oiliness agents on the nascent surface of metal. (Adsorption activity, sec-1)

Model compounds of introduced gas

C1100(0%Zn)

C2200(10%Zn)1-Butanol

0.07

0Dibuthylether

0.05

0.05

Methylpropionate

0.10

0.04

Propionic acid

0.16

0.12

2.2 Measurement of Adsorption Activity
To examine the adsorption activity of the oiliness agent to
the nascent Cu, Cu-Zn alloy and Zn surfaces, and to
study the relationship to the rolling test result, adsorption
activity was measured using the same apparatus used by
Shibata for aluminum 1). To confirm whether adsorption
activity changes in proportion to the amount of zincadded to copper, a total of seven metals were investigated: pure copper, pure zinc, and five alloys of brass inactual use. The alloys tested are shown in Table 2. Figure
4 shows the experimental apparatus for the adsorption
test. Because the oiliness agent does not have enoughvapor pressure to be introduced in the apparatus, small
molecular-weight and high vapor-pressure model gasesof alcohol, ester, fatty acid, and ether were examined torepresent the oiliness agent. The measurement result isalso shown in Table 2.
These results showed that, while the adsorption activityof most kinds of the model gas to nascent metal surfaces
was satisfactory for Cu, that for Cu-Zn alloy was near theadsorption activity for pure zinc and different from Cu,
and Cu-Zn alloy having a Zn content of only 10 % showed
different behavior from base metal, Cu. For zinc, dibutyl
ether and propionic acid showed comparatively good
adsorption activity, corresponding substantially to theresults reported by Mori et al. 2).

a
c

d

e
b
b

f
a: Reaction chamber, b: Variable leak valves,c: Magnetic drive assembly, d: Cutting tool,
e: Metal specimen, f: Mass spectrometer

Figure 4

Experimental apparatus for adsorption test.

C2400(20%Zn)C2600(30%Zn)C2680(35%Zn)C2801(40%Zn)

Zn

0

0

0.03

0.04

0.02

0.08

0.04

0.06

0.08

0.07

0

0.05

0.02

0.04

0.03

0.07

0.09

0.05

0.08

0.07

Table 3

Test lubricants (I).

Oil No.

Viscosity @40 C(mm2/s)

Butyl stearate(%)

Oleic acid
(%)

Ether
(%)

S1

10

5.2

̶

̶

S2

5.2

0.5

̶

S3

5.2

̶

0.5

As a result the rolling test was carried out using theoleic acid as the fatty acid and alkyleneglycol diol as theether compound.
2.3 Rolling Tests to Consider Types of Oiliness Agent
The chemical composition of the oils tested is shown in
Table 3. It was decided to add 0.5-% fatty acid and ether
compound from the experience of aluminum rolling. The
rolling conditions were the same as in Table 1, and Cu(C1100) and Cu-Zn alloy (C2600) were used as the rolledmaterials.
Figure 5 and Figure 6 show the relation between reduction and rolling load for Cu and Cu-Zn alloy using each of
the oils tested.
It was a purpose in this rolling test to examine an additive suitable for use with the Cu-Zn alloy, but it is understood that a decrease in rolling load was seen from theseresults by adding the fatty acid and the ether compound
effective for both Cu and Cu-Zn alloy, compared with thestandard oil S1 which had only buthylstearate added.
Test oil S2 had 0.5-% fatty acid added and the test oil
S3 had 0.5-% ether compound added to the standard oil.
The rolling load for test oils S2 and S3 was lower thanfor standard oil S1 at each reduction in the rolling of Cu.
Moreover, the rolling load for test oil S2 showed a tendency to be higher than that of the standard oil S1 at low
reduction of the Cu-Zn alloy, but rolling load decreased
more than for the standard oil S1 at high reduction.
Because the rolling load tendency for test oil S2
decreased more than for the standard oil S1 at highreduction, it was thought that the fatty acid achieved aneffect under the severer rolling condition. Rolling loads
lower than the standard oil S1 were shown under all
reductions for test oil S3, the effect of a decrease in rolling
load for test oil S3 was larger than for test oil S2, and theeffect of test oil S3 was also admitted under a light reduction.
Strip surface photomicrographs at 55-% reduction of
Cu-Zn alloy rolled with oils S1, S2, and S3 are shown in
Figure 7. Heavily scaly patterns, which seemed to be due

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Study of Oiliness Agent for Cold Rolling Oil of Copper and Copper Alloy
30

Rolling load (kN)

25
20
15
10
S1
S2

5

S3
0

20

Figure 530

4050Reduction (%)

60

70

Relationship between rolling load and reduction
for Cu (I).

70

Rolling load (kN)

60
50

2.4

40
30
20

S1
S2

10
0

to the adhesion of metal to the work roll on the surface ofstrips rolled with standard oil S1, were observed to be as
same as in the rolling test with commercial rolling oil.
Scaly patterns weakened in test oil S2, and they were
obviously small and weak on the surface of strips rolledwith test oil S3. Partial oil pits were observed when using
test oils S2 and S3. The reduction at which the scaly pattern appeared under microscopic observation on the surface of strips at each reduction was 30 % for standard oil
S1 but 45 % for test oil S3.
It was confirmed that the fatty acid and the ether compound, which seemed to exhibit high adsorption activity
to Cu-Zn alloy, were effective in improving rolling lubricity
for Cu-Zn alloy, but it was found that the rolling loaddecrease was effective for both Cu-Zn alloy and Cu. With
the rolling oil containing fatty acid, however, discoloration
was observed on the surface of strips after subsequentrolling, so that we only studied use of ether compounds.
Therefore as the next step we investigated the type of
ether compound.

S3
15

25

35

45

55

65

Reduction (%)

Figure 6

Relationship between rolling load and reduction
for Cu-Zn alloy (I).

0.1 mm(a) S1(b) S2

Rolling Test for Selecting Type of Ether
Compound
The chemical composition of the test oil is shown in Table
4. Each ether compound was added in the amount of 0.5% using the same standard oil S1 as in the test on thetype of oiliness agent. The rolling conditions were thesame as in Table 1 and Cu (C1100) and Cu-Zn alloy(C2600) were used as the rolled work. Figure 8 and
Figure 9 show the relation between the reduction and therolling load for Cu and Cu-Zn alloy. When 0.5 % of theether compound was added to standard oil S1 in Cu rolling from Figure 9, it was found that any kind of ether compound had an effect in decreasing the rolling load. The
rolling load reduction effect was comparatively large for
ester type test oils S2 and S3 and was larger for ether
type test oil S5. For test oil S3 however, blue-green oil discoloration occurred after rolling and since this was similar
to the discoloration that occurred with the addition of thefatty acid in the previous experiment, it is thought that
non-esterified fatty acid was present. The change in rolling load at reduction of 40 % or less was relatively small
among test oils for Cu-Zn alloy in Figure 9, but when the
reduction exceeded 45 % it was large.
Table 4No.

(c) S3Figure 7

Microscopic observation of strip surface at 55%
reduction for Cu-Zn alloy.

Test lubricants (II).
Content

S1

Base oil+Butylstearate 10 mass% (Standard)

S2

S1+Alkyleneglycol monooleate 0.5 mass%

S3

S1+Alkyleneglycol diester 0.5 mass%

S4

S1+Alkyleneglycol monoether 0.5 mass%

S5

S1+Alkyleneglycol monolaurylether 0.5 mass%

S6

S1+Alkyleneglycol diol 0.5 mass%

S7

S1+Alkyleneglycol monoglycerilether 0.5 mass%

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Study of Oiliness Agent for Cold Rolling Oil of Copper and Copper Alloy
25

Rolling load (kN)

23
21

S1
S2
S3
S4

S5
S6
S7

19

S1

S2

S3

S4

S5

S6

17
15
13
11
25

35

45

55

65

Reduction (%)

Figure 8

Relationship between rolling load and reduction
for Cu (II).

0.1 mmS7

100

Rolling load (kN)

80

Figure 10 Microscopic photograph of strip surface at 45%
reduction for Cu-Zn alloy, x180 (I).

S5
S6
S7

S1
S2
S3
S4

Table 560

Oil No.
40
20
0
15

25

35

45

55

Reduction (%)

Figure 9

Relationship between rolling load and reduction
for Cu-Zn alloy (II).

In Figure 10 a scaly pattern was observed on the surface of Cu-Zn alloy with standard oil S1, test oil S2, test oil
S4, and test oil S5, but transferred patterns of the workroll and oil pits were observed with test oil S3, test oil S6and test oil S7. A larger number of oil pits were observedon the surface of Cu-Zn alloy with test oil S6, and virtuallyno scaly pattern was seen.
2.5

Examination of Amount of Ether Compound
Added
Despite the fact that the amount added was only 0.5 %,the ether compounds evaluated in Section 2.4 were effective in decreasing the rolling load for Cu-Zn alloy with thestandard oil. This effect was also shown in decreasing therolling load for Cu. To determine the proper amount of
ether compound to be added, we varied the amount ofalkyleneglycol diol, which in the previous experiment hada large effect in decreasing rolling load, and alkyleneglycol monooleate, which had an intermediate effect, andthe effect was examined. The rolling test conditions were
the same as in the previous experiment. As in the previous experiment a mineral oil with viscosity of 5.2 mm2/s at
40 C was used as the base oil, and an oil with 10-% buthylstearate added was used as standard oil S1. The composition of test oils is shown in Table 5.
The relationship between reduction and rolling load for

Test lubricants (III).

Base oil
Butyl-stearate(mm2/s @40 C)(wt%)

Alkylene-glycol
monooleate(wt%)

Alkyleneglycol diol
(wt%)

S1

5.2

10.0

0.0

0.0

S2-1

5.2

10.0

0.25

0.0

S2-2

5.2

10.0

1.0

0.0

S2-3

5.2

10.0

3.0

0.0

S6-1

5.2

10.0

0.0

0.25

S6-2

5.2

10.0

0.0

1.0

S6-3

5.2

10.0

0.0

3.0

Cu when alkyleneglycol monooleate and alkyleneglycol
diol were added changing the concentration is shown in
Figure 11 and the relationship for Cu-Zn alloy is shown in
Figure 12.
From Figure 11 we see that for Cu the rolling loaddecreased with test oil S2-1 which has 0.25-% alkyleneglycol monooleate added compared to standard oil S1.
The same tendency was shown for test oils S2-2 and S23. Even for test oils S6-1, S6-2 and S6-3, with added alkyleneglycol diol, the decrease in rolling load was the same
as for test oil S2. In particular for test oil S6-3 the rolling
load decreased at all reduction ratios by 20~25 % compared with standard oil S1.
For Cu-Zn alloy in Figure 12, the decrease in rolling
load for test oils S2-1, S2-2 and S2-3 with alkyleneglycol
monooleate added and test oils S6-1, S6-2 and 6-3 withalkyleneglycol diol added was no larger than for standard
oil S1 at reductions 40 % or less, but a large decrease inrolling load was seen at reductions of 40 % or more compared with standard oil S1. Moreover, there was a tendency with test oils S2 and S6 that the rolling load did notincrease in the high-reduction range the larger the added
amount of the additives.
Figure 13 shows the photomicrograph of Cu-Zn alloy
after rolling. The strip surface of Cu-Zn alloy showed acompletely scaly pattern with standard oil S1 at 45-%

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Study of Oiliness Agent for Cold Rolling Oil of Copper and Copper Alloy
26
S1
S2-1
S2-2
S2-3

24

Rolling load (kN)

22

S6-1
S6-2
S6-3

20
18
16
14
12
10
25

35

45

55

65

Reduction (%)

Figure 11 Relationship between rolling load and reduction
for Cu (III).

Figure 14 Microscopic photograph of roll surface after rollingfor Cu-Zn alloy, x600.

90
S1
S2-1
S2-2
S2-3

80

Rolling load (kN)

70
60

S6-1
S6-2
S6-3

metal adhesion was observed on the work roll after Cu-Zn
alloy rolling with test oil S6-3, and this may be attributable
to the large decrease in rolling load with test oil S6-3.

50
40
30
20
10
0
15

20

25

30

35

0.02 mm

40

45

50

55

60

Reduction (%)

Figure 12 Relationship between rolling load and reduction
for Cu-Zn alloy (III).

0.1 mmFigure 13 Microscopic photograph of strip surface at 45%
reduction for Cu-Zn alloy, x180 (II).

reduction, but only a weak scaly pattern with a certain
amount of oil pitting with test oil S2-3, and oil pitting onlywith no scaly pattern for test oil S6-3.
Figure 14 shows photomicrograph of the work roll surface after rolling of Cu-Zn alloy. Metal adhesion to thework roll surface was observed after the rolling of Cu-Zn
alloy using standard oil S1 and test oil S2-3. However little

2.6 Rolling Tests to Confirm Lubrication Mechanism
The roll coating for Cu-Zn alloy was limited, and an oiliness agent that decreased rolling load was found. Thisoiliness agent has the ether bonds in its molecules, and it
is supposed that this portion has the property of adsorbing strongly to copper-based materials. However, because
the mechanism by which the ether compound contributes
to lubricating in the rolling of copper-based materials is
unclear, further examination was carried out by rolling
tests.
The rolling conditions were in accordance with Table 1,
and only Cu-Zn alloy was rolled at a constant reduction of
45 %. The standard oil was mineral oil of viscosity 5.2
mm2/s at 40 C with 10-% buthylstearate added and theconcentration of alkyleneglycol diol was varied. The
chemical composition of the test oils is shown in Table 6.
Figure 15 shows a comparison of rolling loads. All test
oils with alkyleneglycol diol added showed rolling loads
lower than the standard oil, and the effect on the amountadded became substantially constant at 2.0 % or more.
Figure 16 shows a comparison of amount of wear
debris produced. Wear debris when alkyleneglycol diol
was not added was greater than when it was. A larger difference was seen in the amount of wear debris adheringto the strip than in the amount of wear debris in the oil.
The amount of wear debris produced when alkyleneglycol
diol was added was substantially the same irrespective of
the concentration of alkyleneglycol diol in the test oil, andno effect was found due to alkyleneglycol diol concentration in the range of this examination.
Table 6Composition of oiliness agents (mass %).

Coolant No.

1

2

3

4

5

Butyl stearate

10

10

10

10

10

Ether

0

0.5

1.0

2.0

3.0

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Study of Oiliness Agent for Cold Rolling Oil of Copper and Copper Alloy
560

Elementary ratio (O/Cu)

Rolling load (kN)

50
40
30
20
10
0

0

0.5

1.0

2.0

0 mass%2.0 mass%

4

3

2

1

3.0

Concentration of ether compound (mass%)
0

Figure 15 Relationship between ether concentration and rollingload.

Total amount of debris (mg/m2)

30

On sheet
In coolant

6
5
4
3
2
1
0

0.5

1.0

2.0

3.0

Concentration of ether compound (mass%)

Figure 16 Relationship between ether concentration and total
amount of debris.
1.8

Amount of roll coating (mg)20

Figure 18 Relationship between sputtering time and O/Cu
elementary ratio by XPS.

7

that the ratio of the amount of debris in the oil to theamount adhering to the strip was changed by the additionof alkyleneglycol diol.
The chemical composition of the roll coating was measured by using X-ray photoelectron spectroscopy. The
ratio of oxygen to copper (O/Cu) was determined and isshown in Figure 18. Roll coating became richer in oxygen
content by the addition of alkyleneglycol diol. It has not
yet been possible to verify whether this oxygen was fromthe atmosphere or from the ether compound, but at any
rate it is thought that the nascent metal surface producedby rolling was effectively oxidized and adhesion was prevented.

3.

1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0

10

Sputtering time (min)

8

0

0

0.0

0.5

1.0

2.0

3.0

Concentration of ether (mass%)

Figure 17 Relationship between ether concentration andamount of roll coating.

The amounts of roll coating after the rolling test werecompared, and are shown in Figure 17. The amount ofroll coating decreased with the addition of alkyleneglycol
diol, and showed a constant value by adding approximately 1.0 %. Because the roll coating was due to adhesion of the rolled metal to the work-roll and the amountdecreased, it is thought that alkyleneglycol diol had theeffect of preventing adhesion during rolling. It is thoughtthat the decrease in the amount of wear debris was dueto the prevention of metal adhesion and it is of interest

SUMMARY• Rolling load, the amount of wear debris, and theamount of the roll coating were decreased by theaddition of ether compound.
• It is thought that the addition of ether compound limits the adhesion of Cu-Zn alloy to the work-roll.
• Lubricity can be improved by ether compound not
only for Cu-Zn alloy but also for Cu.
It is postulated that the limiting of the above-mentioned
adhesion is due to the effective oxidation of the nascentmetal surface produced by rolling.
A problem for future consideration is to collect data on
whether the condition of the strip surface and other characteristics of the rolled product are changed by the addition of ether compound.

REFERENCES
1) J. Shibata, S. Ogura and T. Wakabayashi: Tribologist 47-4 (2002)
313-3192) Y. Shidara and S. Mori: Journal of Surface Science 14-6 (1993) 336341

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