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Study of the EP activity of water-soluble inorganic metallic salts for aqueous cutting fluids
WEAR Wear 193 (1996) 226234
Study of the EP activity of water-soluble inorganic metallic salts for aqueous cutting fluids V.K. Jain, D.S. Shukla Indian Institute of Petroleum, Tribology Laboratory, Dehradun 248005, India
Received 26 August 1994; accepted 25 August 1995
Abstract Various inorganic metallic chlorides, sulfates and phosphates were studied for friction, wear and seizure characteristics in four-ball wear and EP testers. Some metallic chlorides and sulfates in aqueous fluid provide improved tribological activities and the rate at which they act is largely dependent on the metal employed in these salts. The interactions of zinc sulfate-zinc chloride and aluminium sulfate-zinc chloride have been shown to be beneficial in improving the adhesion property. Other aqueous solutions of sodium salts of phosphorus in comparison with sulfur salts show better anti-seize tendencies. In these cases, it is believed that a transfer layer formation can explain the lubrication mechanism. Keywords; EP activity; Cutting fluid; Inorganic
metal salts; Wear and friction; Anti-seize behaviour
1. Introduction
In severe cutting operations, the involvement of a large component of friction forces between the tool and the work piece demands greater lubrication properties. The simple aqueous solutions provide excellent cooling but are not adequate for maintaining the good lubrication. Under such circumstances, a compromise is achieved by the use of soluble oils which consist of mineral oil together with EP compounds. These soluble oils function satisfactorily in most of the operations but their EP activities remain to a limited extent. To obtain the full advantages of EP action, neat oils are preferred in operations such as tapping and broaching. It has been shown by Beiswangeret al. [ 1] that 1% solution of phosphate esters based on ethylene oxide and their triethanolamine salt gave wear reduction in the four-ball and falex machine tests. Shapiro [ 21 also observed that fluorides of sodium and silicon improve the load carrying capacity of the formulation in falex tests. Thus Mould et al. [ 31 studied a series of chlorine and sulfur compounds in aqueous media and observed that chlorine compounds gave only moderate improvement over the base fluid while sulfur compounds were very effective. Hence, a small, chemically active species is desirable in the cutting fluids for introducing EP activity. The activity of sulfur, phosphorus and chlorine compounds in mineral base oils is well known [4-71 but their activity may differ greatly in aqueous media, because the tendency Elsevier Science S.A. SSDIOO43-1648(95)06774-4
of ionisation of active compounds also plays some role in governing the behaviour of lubrication system [ 3,6]. The water-soluble inorganic EP compounds used in the present study become ionised readily in aqueous media. On ionisation, the cation in the metallic form is expected to play a part in lubricating the surfaces by way of transformation in addition to negating the action of the anion [ 3,8]. Considering this phenomena, it was planned to examine the various watersoluble inorganic metallic salts consisting of sulfur, phosphorus and chlorine for their EP activity in aqueous cutting fluid containing various ingredients required for the formulation of a cutting fluid as specified in Section 2.2.
2. Experimental
details
2.1. Equipment Friction and wear properties of inorganic salts were studied on a Rexona four-ball friction and wear tester. Standard EN31 steel balls of 12.7 mm diameter were used. The experiments were conducted at room temperature and the speed of rotation of the top ball was 1450 rev min- ’ (0.56 m s- I). The tests were carried out at different loads of 196 N in step with a duration of 60 s. The friction torque was continuously recorded for each load stage and coefficient of friction was calculated at the end of the experiment. At the end of the test,
V. K. Jain, D.S. Shukla / Wear 193 (1996) 226-234
Table 1 Wear results with water-soluble
inorganic
Sample
WSD (MM) at loads (N)
Aqueous fluid ( 1) 1 + FeCls 1+ CUCI, 1+ CrCl, 1 + SnCl, I+ NaCl I+ BaCl, 1 + CaCl, 1 + M&l> 1 + PbClz 1+ ZnCl,
227
chlorine compounds Weld load (N )
392
588
784
980
1176
1372
0.40 0.36 0.40 0.40 0.35 0.40 0.40 0.42 0.40 0.40 0.37
0.42 0.40 0.40 0.45 0.38 0.42 0.45 0.42 0.40 0.42 0.40
0.45 0.42 0.50 0.48 0.46 0.45 0.46 0.45 0.42 0.46 0.41
0.49
0.52 0.49 0.54 0.51 0.50 0.55 0.85 0.51 s s 0.47
> 2.0 s 0.55 0.55 0.52 0.58 1.42 0.55 _
1380 1548 1548 1380 1744 1380 1380 1380 1744
0.51
1960
0.49
0.5 1 0.48 0.47 0.46 0.47 0.47 0.52 0.65 0.45
S, seizure.
the stationary balls were removed and their mean wear scar diameters were measured. Fresh test-balls were employed for each run. The average value of duplicate tests was taken as the experimental result. The surface topography was undertaken with an optical microscope. As the weld load denotes some significance for the evaluation of cutting fluids [5] with respect to EP activity, this was determined on a four-ball EP tester as per standard-IP239 procedure in which a series of 10 s tests were conducted at prescribed load values until a weld load is achieved. In this test also standard EN-3 1 steel balls of 12.7 mm diameter were used. 2.2. Test materials
.
AOUEOUS
0
I+
F&IS
FLUID
P
I+
ClClS
0
I + BnClg
X
I + PbCI2
+
I + CuCl2
(I
1
k
go.07 5 ’ .06o” f 0.05
Metallic chlorides, sulfates and phosphates, all technical grade, were used in the present study. For making blends in aqueous cutting fluid, the metallic salts of 0.2 wt.% were used unless otherwise specified. The aqueous cutting Auid consists of various ingredients such as polar compounds, antirust additives, biocides, surfactants, coupling agents, etc.
-
I
1
1
400
600
600
0.04 200
LOAD,
I
1
1000
1200
N
Fig. 1. Typical friction vs. load curves with inorganic
.
1 1400
AOUEOUS
FLUID
(I
chlorides.
1
?? I+ZnClp 0,09
D
I+
0
I + N&l
COCl2
X
I + M&2
0
I + BOCl2
3. Results 3.1. Study of inorganic metallic chlorides A variety of inorganic chlorine-containing compounds are available and they show an increased corrosion tendency in water media. Despite this fact, these were studied for a load bearing capacity that may help in further developing a suitable additive system. The wear results of various metallic chlorides at different loads are given in Table 1 and the corresponding frictional values, calculated at the end of experiments are plotted in Fig. 1 and Fig. 2. The wear results show that, in general, the metallic chlorides showed little or no improvement in reducing wear over the base aqueous fluid. However, some were effective at higher loads showing good anti-seize property, an essential requirement for metal cutting
0.06 i
iii 8
I
O.O?-
0.05
-
8,
0041 200
400
I 600
I 600
I 1000
I
,
1200
1400
L0AD.N
Fig. 2. Friction vs. load curves with inorganic
chlorides.
228
V. K. Jain. D.S. Shukla / Wear 193 (1996) 226-234
processes [ 51. It is of interest to observe that chlorides of magnesium (Mg) and lead (Pb) had an adverse effect. Of the many metallic chlorides, tin (Sn) and zinc (Zn) chlorides showed better anti-seize properties as indicated from their weld load test results. Frictional results show, in general, their frictional properties were improved and the rate at which they differ widely to each other, is dependent on the metal employed as the cation. The frictional curve of copper chloride is interesting as its effectiveness is seen beyond a load of 1000 N whereas Zn chloride becomes effective beyond a load of 400 N showing decreased friction as the load is
Fig, 3. Optical (a) +Cu(NO,),,
increased. Therefore, some chlorides possess mild EP properties. As the anion is common in all the metal salts, the wide difference in their performance could be attributed to the role of the metallic cations. 3.2. Study of inorganic copper compounds It is seen that copper chloride is a moderately effective compound in reducing anti-seize and frictional properties at higher loads. Optical views of wear scars shows the transformation of the soft copper layer at some region in the background (Fig. 3) that may provide the lubrication property.
photographs of wear scars of 4-ball wear test with: (a) and (b) aqueous load 1372 N.
fluid, load 1176 N; (c)
(a) +CuCI,;
(d)
(a) +CuSO.+; (d)
V.K. Jain, D.S. Shukla / Wear 193 (1996) 226-234
Table 2 Effect of sulfur, chlorine and nitrogen compounds Sample
229
of copper on wear and weld load
WSD (MM) at loads (N)
Aqueous fluid ( 1) 1+ CuCl, 1+ cuso, 1 +Cu(N03)a
Weld load (N)
392
588
784
980
1176
1372
0.40 0.40 0.39 0.40
0.42 0.40 0.42 0.45
0.45 0.50 0.46 0.45
0.49 0.5 1 0.50 0.48
0.52 0.54 0.55 0.52
> 2.0 0.55 0.56 0.55
Table 3 Wear and weld load results with inorganic
sulfur compounds
Sample
WSD (MM) at loads (N)
1380 1548 1744 1960
Weld load (N)
392
588
784
980
1176
1372
1+ Na2S04 1+ MgS04 1+ PbSO,
0.40 0.40 0.39 0.37 0.45 0.40 0.40
0.42 0.41 0.40 0.40 0.45 0.44 0.42
0.45 0.44 0.46 0.42 0.45 0.48 0.46
0.49 0.48 0.50 0.48 0.50 0.53 0.47
0.50 0.50 0.55 0.53 1.15 0.51 0.52
> 2.0 0.55 0.56 0.57 1.25 S 1.3
_ _
1 + ZnSO, 1 + LizSOd 1 +ZnClz+Al,(SO,), 1 +ZnCl,+ZnSO,
0.36 0.42 0.35 0.38
0.42 0.46 0.39 0.40
0.45 0.45 0.42 0.44
0.47 0.50 0.46 0.466
0.50 S 0.50 0.50
0.52
1744
0.53 0.54
1744
Aqueous fluid ( 1) 1+ FeSO., 1+ cuso,
1+AMSOd,
(1:l) (1:l)
1380 1744 1744 1744
S, seizure.
The role of the chlorine anion is not very clear at this stage. In order to examine the effect of copper (Cu) on lubrication, other salts of copper such as cupric nitrate (Cu( N03) ?) and copper sulfate (CuS04) were evaluated. The wear results given in Table 2 show that their relative wear properties are similar to each other. The friction coefficients for different loads are compared in Fig. 4. At lower loads, the friction properties differ other but their tendency reverse at higher loads. A comparison with the base fluid shows that they
0.09
t
: 0.06 E 0.
.
AQUEOUS
Cl
I+
Cu
D
I +
C&2
0
I +
cuso4
FLUID
3.3. Study of inorganic metallic sulfates
(II
(No3)2
g ;o.06;i t
0.0-r
0.0!5-
0.04
L 200
I
400
reduce adhesion between rubbing contacts which is also reflected by their weld load values. It can be said that the role of active components such as chlorine and sulfur is not very pronounced for EP activity and thus the transfer layer of the copper cation predominates the lubrication behaviour. Optical views of their wear scars appear to be similar to each other and have some kind of thin lubricating film when the surfaces were compared with the base aqueous fluid (Fig. 3).
I 600
I
000 LOAD,
I
I
I
1000
1200
1400
N
Fig. 4. The effect of anions of copper salts on friction.
To determine the effect of sulfur compounds, various inorganic sulfur compounds having the same metallic cation as the chlorides, were studied for friction, wear and weld load in aqueous fluid. The wear results of various metallic sulfates at different loads are given in Table 3 and the corresponding frictional values, calculated at the end of the experiments are plotted in Fig. 5. These metallic sulfates have shown little or no influence on the wear property. However, the reduction in friction, with sulfates of copper, iron, aluminium and zinc tends to show the effect on the anti-seize property. Weld load values determined on a four-ball EP tester show a moderate improvement of the anti-seizure tendency of sulfates. It can be said that metallic sulfates, in general, are superior in antiseize property than metallic chlorides in aqueous fluid.
V.K. Jain, D.S. Shukla / Wear 193 (I 996) 226-234
230
Table 4 Effect of sulfur compounds of
sodium on wear and weld load
WSD (MM) at loads
Sample
Aqueous fluid ( I ) 1 + Na sulfonate 1 + Na$
I+ Na$,O, I+ Na,SO,
0
AQUEOUS
Weld load (N)
(N)
392
588
784
980
1176
1372
0.40 0.37 0.35 0.40 0.45
0.42 0.40 0.40 0.40 0.45
0.45 0.42 0.42 0.45 0.45
0.49 0.46 0.45 0.47 0.50
0.50 0.50 0.50 0.51 1.15
>2.0 0.56 0.50 0.51 1.25
FLUID
(1)
0 I+ZnSo4 A I+ 0.06
0
0.09
LiSO4
I+No2S04
t
.
AOUEOUS
U
I +
fJ
I+No2S
0
I+
N02S204
X
I+
No2S04
No
FLUID
1380 1744 2258 2197 1380
(1 1
SULFONATE
IP x
t ::
0.07
I + MgS04
0.06
:
-
k “0 0.07
i
t
/
0 $
0.06-
!3
$ c
E
”
0.06
0.055
o.o4l----_i !
200
400
600
(a)
I
LOAD,
I
/
1200
1400
I
600
1000
I
N 200
0
AOUEOUS
0
I+
o I+
0.08
FLUID
(1)
PbSO4
+
I +
cuso4
t
0.041 200 @I
000
Fig. 6. The role of the sulfur component
AlpIS
I+
600
LOAD,
FeSO4
x
400
I
I
I
600
800 LOAD,
1200
1400
in sodium salts on friction.
property (Table 4). Poor activity of sodium sulfate (Na,SO,) is observed in reducing adhesion while the sodium sulfide (Na,S) appears to be more active beyond a load of 1000 N and thus the friction is low. This activity is also reflected in improving the weld load. The most stable and reactive sodium dithionate (Na&O,) gives low frictional values throughout the given load stages (Fig. 6). It can be attributed that the low frictional value with sodium dithionate is governed by its better action in reducing adhesion at moderate loads resulting in smooth wear marks (Fig. 7 (a) and Fig. 7(b)).
-Y.
400
1000 N
I
I
I
1000
1200
1400
3.5. Study of inorganic sodium phosphate salts
N
Fig. 5. Some typical friction vs. load curves with inorganic metallic sulfates
3.4. Study of water-soluble sulfur-containing
additives
A wide variety of sodium-containing sulfur compounds listed in Table 4 were studied for tribological properties. The activity of sulfur of these sodium based compounds in water is highly active and corrosive except in the case of sulfonate. As a result, they do not tend to show good antiwear property but the active sulfur must have a good influence on seizure
Three sodium phosphate salts, as mentioned in Table 5, were examined for tribological properties. The effect of phosphorus in aqueous systems seems to be poor on the behaviour of the wear reduction tendency whereas its influence on frictional properties is quite evident at moderate loads (Fig. 8). Despite their mild EP action, the high weld load values are not clearly understood. On the contrary, sodium molybdophosphate shows poor reflection on weld load and this tendency could result from the abrasive tendency of molybdenum metal in water [ 91.
V.K. Jain, D.S. Shukla / Wear 193 (1996) 226-234
Fig. 7. Optical view of wear scars of 4-ball wear tests with: (a) Na,S; (b) Na,SO,; Table 5 Wear and weld load results with solutions of phosphates Compounds
Aqueous fluid ( 1) l+l%NazHPO, 1 + 1% Na molybdophosphate 1 + 1% Na tripolyphosphate
(c) Zn Cl&nSO,
231
mixture; (d) Zn Cl,-Al,(
SO,),
mixture, load 1372 N.
of sodium
WSD (MM) at loads (N)
Weld load (N)
392
588
784
980
1176
1372
0.40 0.39 0.37 0.37
0.42 0.42 0.41 0.39
0.45 0.43 0.45 0.45
0.49 0.44 0.47 0.55
0.50 0.45 1.25 0.60
> 2.0 0.98 1.30 0.75
1380 2482 1380 2482
Table 6 Study with typical solution of sodium salts Sodium salts
Aqueous fluid ( 1) 1 + NaOH 1 + Naz CO3
WSD (MM) at loads (N)
Weld load (N)
392
588
784
980
1176
1372
0.40 0.34 0.37
0.42 0.47 0.42
0.45 0.50 0.47
0.49 0.55 0.57
0.50 0.60 1.92
>2.0 0.95 S
1380 1744
S, seizure. Sodium hydroxide (NaOH) and sodium carbonate (Na&O,) are most widely used compounds in metal working processes and these are not found effective in reducing wear and friction properties, but the increased weld load value with sodium hydroxide reflects possessing mild anti-seize tendency (Table 6 and Fig. 9).
3.6. Study of mixture of inorganic salts It has been shown that some metallic chlorides and sulfates are effective as mild anti-seize agents. In these cases, the prime action of anions along with the formation of a transfer layer of metallic cations predominates the behaviour of the
232
V. K. Jain. D.S. Shukla / Wear 193 (1996) 226-234
0
AOUEOUS
0
I+
NaTPP
P
I+
NaMaP04
FLUID
(I
1
0
0.08 0.09
I+
0
I+tnS04
0
I +
ml*
X
I +
MIXTURE
t
Ii
NaHP04
k
0.08
0.07
-
t
5
Il.
P $0.060 a LL 0.05
-
0.041 200
I
I
I
400
600
800 LOAD,
(a)
0.041 196
I
I
392
588
I
,
784
980
I
1
1176
1372
0
compounds
in aqueous fluid on
t
.
AQUEOUS
b
I+Na2C03
o
I+
FLUID
I 1400
N
AOUEOUS
LI)
FLUID.
0 It bl2(50‘,)3 X
0.09
I 1200
0 I + ZnClp
LOA0.N
Fig. 8. Effect of water soluble phosphate friction.
I 1000
(I
I +
MIXTURE
/’
1
NaOH
0.041 200 0)
I
I
I
400
600
800 LOAD,
I
1
I
1000
1200
1400
N
Fig. 10. Beneficial effects of metallic sulfate and metallic chloride mixtures. (a) ZnCl,-ZnSO,, 1:l; (b) ZnCl,AI,(SO,),, 1:l.
4. Discussion 0.041 200
I
I
I
1
400
600
800
1000
LOAD,
I 1200
I 1400
N
Fig, 9. Influence of NaOH and NaZCO, on the frictional aqueous fluid.
behaviour
of an
lubrication mechanism. It was thought that chloride and sulfate anions may produce a better effect on anti-adhesion behaviour by way of eutectic mixture formation. In order to know the proposed formation of a eutectic of chloride and sulfate anions, common metallic salts of zinc were chosen in this study. It can be seen from Fig. 10(a) that the mixture gives better reduction in friction at higher loads. Using a mixture of different metallic salts of chloride and sulfate also produces a similar beneficial effect (Fig. lO( b) ) . Regarding their wear properties, these mixtures show a little improvement in wear prevention at low load conditions (Table 3). Optical views of wear scars support the view of eutectic formation of a chloride and sulfate anion mixture, providing smoother surfaces throughout the wear scars (Fig. 7(c) and Fig. 7(d)).
Friction, wear and weld load results of metallic chlorides, sulfates and phosphates obtained on four-ball wear and EP testers show their potential as mild EP agents in aqueous fluid system. Of the many metallic chlorides, zinc, and chromium chlorides show good anti-seize properties at all loads employed whereas copper chloride becomes effective at higher loads. In general, metallic chlorides in aqueous media show good anti-adhesion properties, but their tendency to protect the surfaces against adhesion differs significantly at higher loads. It appears that the rate at which they protect the surfaces against adhesion is a function of the metal employed in chlorides and some are, therefore, useful as a mild aritiseizure. Of the many metallic sulfates, zinc, copper, iron and aluminium sulfates are effective in reducing frictional properties in aqueous media and are therefore, considered useful as mild anti-seizure compounds. On the contrary, lead and sodium sulfates show poor behaviour. A comparison between the effectiveness of chloride and sulfate anion groups in aqueous media shows no appreciable difference in their activity on the adhesion property. It has been observed [ 31 that the sulfur compounds are better than chlorine compounds in load bear-
V.K. Jain, D.S. Shukla / Wear 193 (1996) 226-234
Fig. 11. Optical view of 4-ball test wear scarswith: (a) SnCI,; (b) CrCl,; (c) and (d) ZnCl,; (e) and (f) Fe&;
ing capacity. This difference was attributed to the solubility of iron chloride in water resulting in poor protection. This
233
(g) FeSO,, load 1372 N.
trend is not observed with other inorganic metallic chlorides. This suggests that the lubrication behaviour is significantly
234
V. K. Jain, D.S. Shukla / Wear I93 (1996) 226-234
governed with the metal employed in their salts. This hypothesis was supported by examination of the wear scars with an optical microscope (shown in Fig. 11) in which water dissolved the chloride part of the coating leaving behind the metallic part in the form of net. The processes of transfer soft layer formation with zinc and iron chlorides at low magnification can be better visualized (Fig. 11 (c) and Fig. 11 (e) ) and the details are more clarified at higher magnification (Fig. 11 (d) and Fig. 11 (f) ). On the other hand, similar behaviour is not observed with metallic sulfates (Fig. 11 (g) and Fig. 3(d) ). In a further attempt to know the eutectic behaviour of mixtures of these metallic chlorides and sulfates on adhesion, a better protection against adhesion was afforded. It can be seen from Fig. 7(c) and Fig. 7(d) that interaction between them produces stable and smoother surfaces. The examination of sulfur salts of sodium for friction and wear show that sodium sulfide and sodium dithionate are better at reducing adhesion and thus possess higher weld load values than other metallic sulfates whereas phosphorus salts of sodium tend to show a better anti-adhesion property. Despite poor wear and friction properties at higher load conditions, the peculiar behaviour of phosphorus salts in improving the weld load is not well understood. This tendency may relate to the quick action of the phosphorus component in forming the protective film over the heavily loaded contacts. Other sodium salts of hydroxide and carbonate do not produce a good effect on tribological properties in an aqueous system. However, all these inorganic salts show little or no effect on the wear properties of the aqueous fluid used.
Acknowledgements We wish to thank Dr. T.S.R. Prasado Rao, Director, Institute of petroleum, for permission to publish this We also wish to thank Shri S. Singhl, Head, Petroleum ucts Application Division and Dr. P.C. Nautiyal, Leader, Tribology, for useful suggestions.
Indian work. ProdGroup
References [l] John PG.
121
[3]
[4]
[S]
[6] [7] [ 81
[ 91
Beiswanger, William Katzenstein and Freed Krupin, Phosphate ester acids as load carrying additives and rust inhibitors for metalworking fluids, ASLE Trans. 7 ( 1964) 398-405. Arthur M. Shapiro, Fluorides and silicofluorides as extreme pressure additives in lubricating fluids for titanium, ASLE Trans., 12 ( 1969) SO85. R.W. Mould, H.B. Silver and R.J. Syrett, Investigation of the activity of cutting oil additives. Part V-The EP activity of some water-based fluids, Lub. Eng., 33(6) (1977) 291-298. R.W. Mould, H.B. Silver and R.J. Syrett, Investigation of the activity of cutting oil additives-II organochlorine containing compounds, Wear, 22 (1972) 269-286. R.W. Mould, H.B. Silver and R.J. Syrett, Investigation of the activity of cutting oil additives-I organ0 sulfur containing compounds, Wear, 19 (1972) 67-80. Milton C. Shah, On the action of metal cutting fluids at low speeds, Wear, 2 (1958/59) 217-227. W.L. Brown, The role of Polyalkylene glycols in synthetic metal workingfluids,Lub. Erg., 44(2) (1988) 168-171. V.K. Jain and D.S. Shukla, The role of carrier fluid on the tribological behaviour of metallic stearates, Wear, 157 (1992) 127-139. Masao Uemura, Koichi Saito and Kenji Nakao, A mechanism of vapour effect of friction coefficient of molybdenum disulfide, ASLE Trans., 33 (1990) 551-556.
Biographies 5. Conclusion
Four-ball wear and EP test results have shown the capability of inorganic metallic chlorides and sulfates to act as mild EP agents in aqueous media, in general. The role of the metal employed in these salts appears to be significant in protection against adhesion. The interaction of some metallic sulfates with metallic chlorides such as zinc sulfate-zinc chloride and aluminium sulfate-zinc sulfate provide better protection against adhesion at moderate loads.
V.K. Jain: after obtaining a degree in mechanical engineering in 1965, he has been working at Indian Institute of Petroleum, Dehradun in tribology area. His current areas of interest include non-conventional metal working lubricants, fuel efficient oils and technique design for performance evaluation of lubricants. He is the author of 32 papers. D.S. Shukla: received his doctorate in chemistry from Agra University in 1980. Since then he has been working at Indian Institute of Petroleum, Dehradun in tribology area. His current area of research include development of non-conventional aqueous based metalworking fluid systems.
Study of the EP activity of water-soluble inorganic metallic salts for aqueous cutting fluids V.K. Jain, D.S. Shukla Indian Institute of Petroleum, Tribology Laboratory, Dehradun 248005, India
Received 26 August 1994; accepted 25 August 1995
Abstract Various inorganic metallic chlorides, sulfates and phosphates were studied for friction, wear and seizure characteristics in four-ball wear and EP testers. Some metallic chlorides and sulfates in aqueous fluid provide improved tribological activities and the rate at which they act is largely dependent on the metal employed in these salts. The interactions of zinc sulfate-zinc chloride and aluminium sulfate-zinc chloride have been shown to be beneficial in improving the adhesion property. Other aqueous solutions of sodium salts of phosphorus in comparison with sulfur salts show better anti-seize tendencies. In these cases, it is believed that a transfer layer formation can explain the lubrication mechanism. Keywords; EP activity; Cutting fluid; Inorganic
metal salts; Wear and friction; Anti-seize behaviour
1. Introduction
In severe cutting operations, the involvement of a large component of friction forces between the tool and the work piece demands greater lubrication properties. The simple aqueous solutions provide excellent cooling but are not adequate for maintaining the good lubrication. Under such circumstances, a compromise is achieved by the use of soluble oils which consist of mineral oil together with EP compounds. These soluble oils function satisfactorily in most of the operations but their EP activities remain to a limited extent. To obtain the full advantages of EP action, neat oils are preferred in operations such as tapping and broaching. It has been shown by Beiswangeret al. [ 1] that 1% solution of phosphate esters based on ethylene oxide and their triethanolamine salt gave wear reduction in the four-ball and falex machine tests. Shapiro [ 21 also observed that fluorides of sodium and silicon improve the load carrying capacity of the formulation in falex tests. Thus Mould et al. [ 31 studied a series of chlorine and sulfur compounds in aqueous media and observed that chlorine compounds gave only moderate improvement over the base fluid while sulfur compounds were very effective. Hence, a small, chemically active species is desirable in the cutting fluids for introducing EP activity. The activity of sulfur, phosphorus and chlorine compounds in mineral base oils is well known [4-71 but their activity may differ greatly in aqueous media, because the tendency Elsevier Science S.A. SSDIOO43-1648(95)06774-4
of ionisation of active compounds also plays some role in governing the behaviour of lubrication system [ 3,6]. The water-soluble inorganic EP compounds used in the present study become ionised readily in aqueous media. On ionisation, the cation in the metallic form is expected to play a part in lubricating the surfaces by way of transformation in addition to negating the action of the anion [ 3,8]. Considering this phenomena, it was planned to examine the various watersoluble inorganic metallic salts consisting of sulfur, phosphorus and chlorine for their EP activity in aqueous cutting fluid containing various ingredients required for the formulation of a cutting fluid as specified in Section 2.2.
2. Experimental
details
2.1. Equipment Friction and wear properties of inorganic salts were studied on a Rexona four-ball friction and wear tester. Standard EN31 steel balls of 12.7 mm diameter were used. The experiments were conducted at room temperature and the speed of rotation of the top ball was 1450 rev min- ’ (0.56 m s- I). The tests were carried out at different loads of 196 N in step with a duration of 60 s. The friction torque was continuously recorded for each load stage and coefficient of friction was calculated at the end of the experiment. At the end of the test,
V. K. Jain, D.S. Shukla / Wear 193 (1996) 226-234
Table 1 Wear results with water-soluble
inorganic
Sample
WSD (MM) at loads (N)
Aqueous fluid ( 1) 1 + FeCls 1+ CUCI, 1+ CrCl, 1 + SnCl, I+ NaCl I+ BaCl, 1 + CaCl, 1 + M&l> 1 + PbClz 1+ ZnCl,
227
chlorine compounds Weld load (N )
392
588
784
980
1176
1372
0.40 0.36 0.40 0.40 0.35 0.40 0.40 0.42 0.40 0.40 0.37
0.42 0.40 0.40 0.45 0.38 0.42 0.45 0.42 0.40 0.42 0.40
0.45 0.42 0.50 0.48 0.46 0.45 0.46 0.45 0.42 0.46 0.41
0.49
0.52 0.49 0.54 0.51 0.50 0.55 0.85 0.51 s s 0.47
> 2.0 s 0.55 0.55 0.52 0.58 1.42 0.55 _
1380 1548 1548 1380 1744 1380 1380 1380 1744
0.51
1960
0.49
0.5 1 0.48 0.47 0.46 0.47 0.47 0.52 0.65 0.45
S, seizure.
the stationary balls were removed and their mean wear scar diameters were measured. Fresh test-balls were employed for each run. The average value of duplicate tests was taken as the experimental result. The surface topography was undertaken with an optical microscope. As the weld load denotes some significance for the evaluation of cutting fluids [5] with respect to EP activity, this was determined on a four-ball EP tester as per standard-IP239 procedure in which a series of 10 s tests were conducted at prescribed load values until a weld load is achieved. In this test also standard EN-3 1 steel balls of 12.7 mm diameter were used. 2.2. Test materials
.
AOUEOUS
0
I+
F&IS
FLUID
P
I+
ClClS
0
I + BnClg
X
I + PbCI2
+
I + CuCl2
(I
1
k
go.07 5 ’ .06o” f 0.05
Metallic chlorides, sulfates and phosphates, all technical grade, were used in the present study. For making blends in aqueous cutting fluid, the metallic salts of 0.2 wt.% were used unless otherwise specified. The aqueous cutting Auid consists of various ingredients such as polar compounds, antirust additives, biocides, surfactants, coupling agents, etc.
-
I
1
1
400
600
600
0.04 200
LOAD,
I
1
1000
1200
N
Fig. 1. Typical friction vs. load curves with inorganic
.
1 1400
AOUEOUS
FLUID
(I
chlorides.
1
?? I+ZnClp 0,09
D
I+
0
I + N&l
COCl2
X
I + M&2
0
I + BOCl2
3. Results 3.1. Study of inorganic metallic chlorides A variety of inorganic chlorine-containing compounds are available and they show an increased corrosion tendency in water media. Despite this fact, these were studied for a load bearing capacity that may help in further developing a suitable additive system. The wear results of various metallic chlorides at different loads are given in Table 1 and the corresponding frictional values, calculated at the end of experiments are plotted in Fig. 1 and Fig. 2. The wear results show that, in general, the metallic chlorides showed little or no improvement in reducing wear over the base aqueous fluid. However, some were effective at higher loads showing good anti-seize property, an essential requirement for metal cutting
0.06 i
iii 8
I
O.O?-
0.05
-
8,
0041 200
400
I 600
I 600
I 1000
I
,
1200
1400
L0AD.N
Fig. 2. Friction vs. load curves with inorganic
chlorides.
228
V. K. Jain. D.S. Shukla / Wear 193 (1996) 226-234
processes [ 51. It is of interest to observe that chlorides of magnesium (Mg) and lead (Pb) had an adverse effect. Of the many metallic chlorides, tin (Sn) and zinc (Zn) chlorides showed better anti-seize properties as indicated from their weld load test results. Frictional results show, in general, their frictional properties were improved and the rate at which they differ widely to each other, is dependent on the metal employed as the cation. The frictional curve of copper chloride is interesting as its effectiveness is seen beyond a load of 1000 N whereas Zn chloride becomes effective beyond a load of 400 N showing decreased friction as the load is
Fig, 3. Optical (a) +Cu(NO,),,
increased. Therefore, some chlorides possess mild EP properties. As the anion is common in all the metal salts, the wide difference in their performance could be attributed to the role of the metallic cations. 3.2. Study of inorganic copper compounds It is seen that copper chloride is a moderately effective compound in reducing anti-seize and frictional properties at higher loads. Optical views of wear scars shows the transformation of the soft copper layer at some region in the background (Fig. 3) that may provide the lubrication property.
photographs of wear scars of 4-ball wear test with: (a) and (b) aqueous load 1372 N.
fluid, load 1176 N; (c)
(a) +CuCI,;
(d)
(a) +CuSO.+; (d)
V.K. Jain, D.S. Shukla / Wear 193 (1996) 226-234
Table 2 Effect of sulfur, chlorine and nitrogen compounds Sample
229
of copper on wear and weld load
WSD (MM) at loads (N)
Aqueous fluid ( 1) 1+ CuCl, 1+ cuso, 1 +Cu(N03)a
Weld load (N)
392
588
784
980
1176
1372
0.40 0.40 0.39 0.40
0.42 0.40 0.42 0.45
0.45 0.50 0.46 0.45
0.49 0.5 1 0.50 0.48
0.52 0.54 0.55 0.52
> 2.0 0.55 0.56 0.55
Table 3 Wear and weld load results with inorganic
sulfur compounds
Sample
WSD (MM) at loads (N)
1380 1548 1744 1960
Weld load (N)
392
588
784
980
1176
1372
1+ Na2S04 1+ MgS04 1+ PbSO,
0.40 0.40 0.39 0.37 0.45 0.40 0.40
0.42 0.41 0.40 0.40 0.45 0.44 0.42
0.45 0.44 0.46 0.42 0.45 0.48 0.46
0.49 0.48 0.50 0.48 0.50 0.53 0.47
0.50 0.50 0.55 0.53 1.15 0.51 0.52
> 2.0 0.55 0.56 0.57 1.25 S 1.3
_ _
1 + ZnSO, 1 + LizSOd 1 +ZnClz+Al,(SO,), 1 +ZnCl,+ZnSO,
0.36 0.42 0.35 0.38
0.42 0.46 0.39 0.40
0.45 0.45 0.42 0.44
0.47 0.50 0.46 0.466
0.50 S 0.50 0.50
0.52
1744
0.53 0.54
1744
Aqueous fluid ( 1) 1+ FeSO., 1+ cuso,
1+AMSOd,
(1:l) (1:l)
1380 1744 1744 1744
S, seizure.
The role of the chlorine anion is not very clear at this stage. In order to examine the effect of copper (Cu) on lubrication, other salts of copper such as cupric nitrate (Cu( N03) ?) and copper sulfate (CuS04) were evaluated. The wear results given in Table 2 show that their relative wear properties are similar to each other. The friction coefficients for different loads are compared in Fig. 4. At lower loads, the friction properties differ other but their tendency reverse at higher loads. A comparison with the base fluid shows that they
0.09
t
: 0.06 E 0.
.
AQUEOUS
Cl
I+
Cu
D
I +
C&2
0
I +
cuso4
FLUID
3.3. Study of inorganic metallic sulfates
(II
(No3)2
g ;o.06;i t
0.0-r
0.0!5-
0.04
L 200
I
400
reduce adhesion between rubbing contacts which is also reflected by their weld load values. It can be said that the role of active components such as chlorine and sulfur is not very pronounced for EP activity and thus the transfer layer of the copper cation predominates the lubrication behaviour. Optical views of their wear scars appear to be similar to each other and have some kind of thin lubricating film when the surfaces were compared with the base aqueous fluid (Fig. 3).
I 600
I
000 LOAD,
I
I
I
1000
1200
1400
N
Fig. 4. The effect of anions of copper salts on friction.
To determine the effect of sulfur compounds, various inorganic sulfur compounds having the same metallic cation as the chlorides, were studied for friction, wear and weld load in aqueous fluid. The wear results of various metallic sulfates at different loads are given in Table 3 and the corresponding frictional values, calculated at the end of the experiments are plotted in Fig. 5. These metallic sulfates have shown little or no influence on the wear property. However, the reduction in friction, with sulfates of copper, iron, aluminium and zinc tends to show the effect on the anti-seize property. Weld load values determined on a four-ball EP tester show a moderate improvement of the anti-seizure tendency of sulfates. It can be said that metallic sulfates, in general, are superior in antiseize property than metallic chlorides in aqueous fluid.
V.K. Jain, D.S. Shukla / Wear 193 (I 996) 226-234
230
Table 4 Effect of sulfur compounds of
sodium on wear and weld load
WSD (MM) at loads
Sample
Aqueous fluid ( I ) 1 + Na sulfonate 1 + Na$
I+ Na$,O, I+ Na,SO,
0
AQUEOUS
Weld load (N)
(N)
392
588
784
980
1176
1372
0.40 0.37 0.35 0.40 0.45
0.42 0.40 0.40 0.40 0.45
0.45 0.42 0.42 0.45 0.45
0.49 0.46 0.45 0.47 0.50
0.50 0.50 0.50 0.51 1.15
>2.0 0.56 0.50 0.51 1.25
FLUID
(1)
0 I+ZnSo4 A I+ 0.06
0
0.09
LiSO4
I+No2S04
t
.
AOUEOUS
U
I +
fJ
I+No2S
0
I+
N02S204
X
I+
No2S04
No
FLUID
1380 1744 2258 2197 1380
(1 1
SULFONATE
IP x
t ::
0.07
I + MgS04
0.06
:
-
k “0 0.07
i
t
/
0 $
0.06-
!3
$ c
E
”
0.06
0.055
o.o4l----_i !
200
400
600
(a)
I
LOAD,
I
/
1200
1400
I
600
1000
I
N 200
0
AOUEOUS
0
I+
o I+
0.08
FLUID
(1)
PbSO4
+
I +
cuso4
t
0.041 200 @I
000
Fig. 6. The role of the sulfur component
AlpIS
I+
600
LOAD,
FeSO4
x
400
I
I
I
600
800 LOAD,
1200
1400
in sodium salts on friction.
property (Table 4). Poor activity of sodium sulfate (Na,SO,) is observed in reducing adhesion while the sodium sulfide (Na,S) appears to be more active beyond a load of 1000 N and thus the friction is low. This activity is also reflected in improving the weld load. The most stable and reactive sodium dithionate (Na&O,) gives low frictional values throughout the given load stages (Fig. 6). It can be attributed that the low frictional value with sodium dithionate is governed by its better action in reducing adhesion at moderate loads resulting in smooth wear marks (Fig. 7 (a) and Fig. 7(b)).
-Y.
400
1000 N
I
I
I
1000
1200
1400
3.5. Study of inorganic sodium phosphate salts
N
Fig. 5. Some typical friction vs. load curves with inorganic metallic sulfates
3.4. Study of water-soluble sulfur-containing
additives
A wide variety of sodium-containing sulfur compounds listed in Table 4 were studied for tribological properties. The activity of sulfur of these sodium based compounds in water is highly active and corrosive except in the case of sulfonate. As a result, they do not tend to show good antiwear property but the active sulfur must have a good influence on seizure
Three sodium phosphate salts, as mentioned in Table 5, were examined for tribological properties. The effect of phosphorus in aqueous systems seems to be poor on the behaviour of the wear reduction tendency whereas its influence on frictional properties is quite evident at moderate loads (Fig. 8). Despite their mild EP action, the high weld load values are not clearly understood. On the contrary, sodium molybdophosphate shows poor reflection on weld load and this tendency could result from the abrasive tendency of molybdenum metal in water [ 91.
V.K. Jain, D.S. Shukla / Wear 193 (1996) 226-234
Fig. 7. Optical view of wear scars of 4-ball wear tests with: (a) Na,S; (b) Na,SO,; Table 5 Wear and weld load results with solutions of phosphates Compounds
Aqueous fluid ( 1) l+l%NazHPO, 1 + 1% Na molybdophosphate 1 + 1% Na tripolyphosphate
(c) Zn Cl&nSO,
231
mixture; (d) Zn Cl,-Al,(
SO,),
mixture, load 1372 N.
of sodium
WSD (MM) at loads (N)
Weld load (N)
392
588
784
980
1176
1372
0.40 0.39 0.37 0.37
0.42 0.42 0.41 0.39
0.45 0.43 0.45 0.45
0.49 0.44 0.47 0.55
0.50 0.45 1.25 0.60
> 2.0 0.98 1.30 0.75
1380 2482 1380 2482
Table 6 Study with typical solution of sodium salts Sodium salts
Aqueous fluid ( 1) 1 + NaOH 1 + Naz CO3
WSD (MM) at loads (N)
Weld load (N)
392
588
784
980
1176
1372
0.40 0.34 0.37
0.42 0.47 0.42
0.45 0.50 0.47
0.49 0.55 0.57
0.50 0.60 1.92
>2.0 0.95 S
1380 1744
S, seizure. Sodium hydroxide (NaOH) and sodium carbonate (Na&O,) are most widely used compounds in metal working processes and these are not found effective in reducing wear and friction properties, but the increased weld load value with sodium hydroxide reflects possessing mild anti-seize tendency (Table 6 and Fig. 9).
3.6. Study of mixture of inorganic salts It has been shown that some metallic chlorides and sulfates are effective as mild anti-seize agents. In these cases, the prime action of anions along with the formation of a transfer layer of metallic cations predominates the behaviour of the
232
V. K. Jain. D.S. Shukla / Wear 193 (1996) 226-234
0
AOUEOUS
0
I+
NaTPP
P
I+
NaMaP04
FLUID
(I
1
0
0.08 0.09
I+
0
I+tnS04
0
I +
ml*
X
I +
MIXTURE
t
Ii
NaHP04
k
0.08
0.07
-
t
5
Il.
P $0.060 a LL 0.05
-
0.041 200
I
I
I
400
600
800 LOAD,
(a)
0.041 196
I
I
392
588
I
,
784
980
I
1
1176
1372
0
compounds
in aqueous fluid on
t
.
AQUEOUS
b
I+Na2C03
o
I+
FLUID
I 1400
N
AOUEOUS
LI)
FLUID.
0 It bl2(50‘,)3 X
0.09
I 1200
0 I + ZnClp
LOA0.N
Fig. 8. Effect of water soluble phosphate friction.
I 1000
(I
I +
MIXTURE
/’
1
NaOH
0.041 200 0)
I
I
I
400
600
800 LOAD,
I
1
I
1000
1200
1400
N
Fig. 10. Beneficial effects of metallic sulfate and metallic chloride mixtures. (a) ZnCl,-ZnSO,, 1:l; (b) ZnCl,AI,(SO,),, 1:l.
4. Discussion 0.041 200
I
I
I
1
400
600
800
1000
LOAD,
I 1200
I 1400
N
Fig, 9. Influence of NaOH and NaZCO, on the frictional aqueous fluid.
behaviour
of an
lubrication mechanism. It was thought that chloride and sulfate anions may produce a better effect on anti-adhesion behaviour by way of eutectic mixture formation. In order to know the proposed formation of a eutectic of chloride and sulfate anions, common metallic salts of zinc were chosen in this study. It can be seen from Fig. 10(a) that the mixture gives better reduction in friction at higher loads. Using a mixture of different metallic salts of chloride and sulfate also produces a similar beneficial effect (Fig. lO( b) ) . Regarding their wear properties, these mixtures show a little improvement in wear prevention at low load conditions (Table 3). Optical views of wear scars support the view of eutectic formation of a chloride and sulfate anion mixture, providing smoother surfaces throughout the wear scars (Fig. 7(c) and Fig. 7(d)).
Friction, wear and weld load results of metallic chlorides, sulfates and phosphates obtained on four-ball wear and EP testers show their potential as mild EP agents in aqueous fluid system. Of the many metallic chlorides, zinc, and chromium chlorides show good anti-seize properties at all loads employed whereas copper chloride becomes effective at higher loads. In general, metallic chlorides in aqueous media show good anti-adhesion properties, but their tendency to protect the surfaces against adhesion differs significantly at higher loads. It appears that the rate at which they protect the surfaces against adhesion is a function of the metal employed in chlorides and some are, therefore, useful as a mild aritiseizure. Of the many metallic sulfates, zinc, copper, iron and aluminium sulfates are effective in reducing frictional properties in aqueous media and are therefore, considered useful as mild anti-seizure compounds. On the contrary, lead and sodium sulfates show poor behaviour. A comparison between the effectiveness of chloride and sulfate anion groups in aqueous media shows no appreciable difference in their activity on the adhesion property. It has been observed [ 31 that the sulfur compounds are better than chlorine compounds in load bear-
V.K. Jain, D.S. Shukla / Wear 193 (1996) 226-234
Fig. 11. Optical view of 4-ball test wear scarswith: (a) SnCI,; (b) CrCl,; (c) and (d) ZnCl,; (e) and (f) Fe&;
ing capacity. This difference was attributed to the solubility of iron chloride in water resulting in poor protection. This
233
(g) FeSO,, load 1372 N.
trend is not observed with other inorganic metallic chlorides. This suggests that the lubrication behaviour is significantly
234
V. K. Jain, D.S. Shukla / Wear I93 (1996) 226-234
governed with the metal employed in their salts. This hypothesis was supported by examination of the wear scars with an optical microscope (shown in Fig. 11) in which water dissolved the chloride part of the coating leaving behind the metallic part in the form of net. The processes of transfer soft layer formation with zinc and iron chlorides at low magnification can be better visualized (Fig. 11 (c) and Fig. 11 (e) ) and the details are more clarified at higher magnification (Fig. 11 (d) and Fig. 11 (f) ). On the other hand, similar behaviour is not observed with metallic sulfates (Fig. 11 (g) and Fig. 3(d) ). In a further attempt to know the eutectic behaviour of mixtures of these metallic chlorides and sulfates on adhesion, a better protection against adhesion was afforded. It can be seen from Fig. 7(c) and Fig. 7(d) that interaction between them produces stable and smoother surfaces. The examination of sulfur salts of sodium for friction and wear show that sodium sulfide and sodium dithionate are better at reducing adhesion and thus possess higher weld load values than other metallic sulfates whereas phosphorus salts of sodium tend to show a better anti-adhesion property. Despite poor wear and friction properties at higher load conditions, the peculiar behaviour of phosphorus salts in improving the weld load is not well understood. This tendency may relate to the quick action of the phosphorus component in forming the protective film over the heavily loaded contacts. Other sodium salts of hydroxide and carbonate do not produce a good effect on tribological properties in an aqueous system. However, all these inorganic salts show little or no effect on the wear properties of the aqueous fluid used.
Acknowledgements We wish to thank Dr. T.S.R. Prasado Rao, Director, Institute of petroleum, for permission to publish this We also wish to thank Shri S. Singhl, Head, Petroleum ucts Application Division and Dr. P.C. Nautiyal, Leader, Tribology, for useful suggestions.
Indian work. ProdGroup
References [l] John PG.
121
[3]
[4]
[S]
[6] [7] [ 81
[ 91
Beiswanger, William Katzenstein and Freed Krupin, Phosphate ester acids as load carrying additives and rust inhibitors for metalworking fluids, ASLE Trans. 7 ( 1964) 398-405. Arthur M. Shapiro, Fluorides and silicofluorides as extreme pressure additives in lubricating fluids for titanium, ASLE Trans., 12 ( 1969) SO85. R.W. Mould, H.B. Silver and R.J. Syrett, Investigation of the activity of cutting oil additives. Part V-The EP activity of some water-based fluids, Lub. Eng., 33(6) (1977) 291-298. R.W. Mould, H.B. Silver and R.J. Syrett, Investigation of the activity of cutting oil additives-II organochlorine containing compounds, Wear, 22 (1972) 269-286. R.W. Mould, H.B. Silver and R.J. Syrett, Investigation of the activity of cutting oil additives-I organ0 sulfur containing compounds, Wear, 19 (1972) 67-80. Milton C. Shah, On the action of metal cutting fluids at low speeds, Wear, 2 (1958/59) 217-227. W.L. Brown, The role of Polyalkylene glycols in synthetic metal workingfluids,Lub. Erg., 44(2) (1988) 168-171. V.K. Jain and D.S. Shukla, The role of carrier fluid on the tribological behaviour of metallic stearates, Wear, 157 (1992) 127-139. Masao Uemura, Koichi Saito and Kenji Nakao, A mechanism of vapour effect of friction coefficient of molybdenum disulfide, ASLE Trans., 33 (1990) 551-556.
Biographies 5. Conclusion
Four-ball wear and EP test results have shown the capability of inorganic metallic chlorides and sulfates to act as mild EP agents in aqueous media, in general. The role of the metal employed in these salts appears to be significant in protection against adhesion. The interaction of some metallic sulfates with metallic chlorides such as zinc sulfate-zinc chloride and aluminium sulfate-zinc sulfate provide better protection against adhesion at moderate loads.
V.K. Jain: after obtaining a degree in mechanical engineering in 1965, he has been working at Indian Institute of Petroleum, Dehradun in tribology area. His current areas of interest include non-conventional metal working lubricants, fuel efficient oils and technique design for performance evaluation of lubricants. He is the author of 32 papers. D.S. Shukla: received his doctorate in chemistry from Agra University in 1980. Since then he has been working at Indian Institute of Petroleum, Dehradun in tribology area. His current area of research include development of non-conventional aqueous based metalworking fluid systems.