Metalworking emulsions from industrial vegetable oils

Copyright © 2008 John Wiley & Sons, Ltd.

Metalworking emulsions from industrial vegetable oils

Anuj Jain1,*† and R. P. S. Bisht2

1Harcourt Butler Technological Institute, Department of Oil & Paint Technology, Kanpur 208002, India2Indian Institute of Petroleum, Dehradun, 248005, India

ABSTRACT

In the present work, an attempt has been made to develop the indigenous formulation for metalworking lubricants by replacing mineral oils partially with non-edible industrial oils like rapeseed and karanja oil. Metalworking formulations consist of vegetable oil, mineral oil, an emulsifi er and commercial additives for better performance. Non-edible vegetable oils such as karanja and rapeseeds are renewable, biodegradable and cheaper than synthetic fl uids. The constituent vegetable oils and mineral oils were evaluated for physico-chemical characteristics and blended as per the saponifi cation value and viscosity requirements of the reference oils. The so formulated oils are taken as 5% oil-in-water emulsion and tested for lubricity, load bearing capacity, particle size distribution, wear test, weld load test and plate-out test. Performance of all formulated oils was compared with that of the reference oils, and optimized to meet the market requirements. Copyright © 2008 John Wiley & Sons, Ltd.

KEY WORDS: metalworking lubricants; rapeseed oil; karanja oil; soluble oil; tribology; vegetable oils

INTRODUCTION

Metalworking lubricants are important and in fact necessary production aids to the engineering indus-try. Petroleum lubricating oils have established themselves as major constituents of such lubricants.

Petroleum or mineral oils usually do not have the lubricity possessed by animal-and vegetable-type materials. The less chemically active petroleum oil molecules adhere more loosely to the metal sur-faces, and therefore being unable to withstand the shearing stresses exerted in the metalworking process [1].

The principal virtue of vegetable oils as lubricants is their superior ability to cling to metal surfaces in the form of very thin fi lms. Actually, this property appears to be due largely to the surface activity conferred by the small amount of free fatty acids occurring in the oils. The free acids are polar and tend to become adsorbed in layers of molecular dimensions at metal–oil interface. The interpo-sition of such fi lms is effective in preventing metal seizure under conditions of extreme pressure. Fatty oils are less easily displaced from metal surfaces by water than mineral oils, and hence are valuable ingredients for lubricants.

JOURNAL OF SYNTHETIC LUBRICATIONJ. Synthetic Lubrication 2008; 25: 87–94Published online 21 April 2008 in Wiley InterScience(www.interscience.wiley.com) DOI: 10.1002/jsl.51

*Correspondence to: A. Jain, C/o Sunil Kumar Sachin Jain, Kamal Colony, Gali No. 1 Jain Degree College Road, Saharanpur-247001, India.†E-mail: [email protected]

88 A. JAIN AND R. P. S. BISHT

Copyright © 2008 John Wiley & Sons, Ltd. J. Synthetic Lubrication 2008; 25: 87–94 DOI: 10.1002/jsl

In rolling mills, mixed lubrication regime prevails but mostly dominated by boundary lubrication and asperities contact.

The effi cacy of any formulated cold rolling oil is to be fi nally evaluated by conducting long duration tests on actual production rolling mill. However, such testing is not only expensive and time consum-ing, but also involves great risk in terms of loss of production, wastage of material, change of rolls and cleaning of oil systems, etc. Therefore, before actual roll mill tests, the lubricants are screened for different characteristics on laboratory scale.

In recent years, attempts have been made [2–6] to use both water-soluble and highly emulsifi ed materials as metalworking lubricants.

EXPERIMENTAL

Materials

Base vegetable oils, that is, karanja and rapeseed oil and paraffi nic basestock (N150 and N500), emulsifi er and additives like antioxidants, corrosion and rust inhibitors, defoamer were used as such.

Preparation of Basestock

As no specifi cations are laid down for the cold rolling lubricants for steel, so a meaningful comparison could be made by including products of proven service in the screening process. So, two commercial formulations having low and two commercial formulations having medium saponifi cation value were taken as reference oils.

The requirements of low saponifi cation formulations were kinematic viscosity at 40 °C = 40 cSt and saponifi cation value = 60 ± 5, while the requirements of medium saponifi cation formulations were kinematic viscosity at 40 °C = 60 cSt and saponifi cation value = 100 ± 5.

Blending Procedure

In a cleaned three-neck fl ask with stirrer and heating system, measured quantities of component fatty oils and mineral oils based on their required ratio (by volume) were poured and the mixture was heated under agitation to a temperature of 50–60 °C for 30 minutes. Then, the required quantity of emulsifi er was added in small dosages followed by other additives. The blend was then stirred vigor-ously for 30 minutes under controlled temperature (50–60 °C) conditions. The blend was then allowed to cool down to ambient temperature. The following additives were blended with the basestock:

• Lubrizol® 5620 (Lubrizol Wickliffe, Ohio, US) (Nature: non-ionic; HLB: 10.8; use level: 5–15% by wt; uses: O/W emulsifi er package for wide

range of parrafi nic basestock; chemical description: proprietary). This additive was added 10% w/v in each basestock.

• Zinc dialkyl dithiophosphate (Viscosity at 100 °C: 10.2 cSt; specifi c gravity: 1.125; phosphorus, wt%: 7.8; sulphur, wt%: 16;

zinc, wt%: 8.2; use: mainly as an antioxidant but also has anti-corrosion and load-carrying proper-ties). This was used 1% w/v in each basestock.

METALWORKING EMULSIONS FROM VEGETABLE OILS 89


• Silicone defoamer (Specifi c gravity: 0.87; viscosity at 100 °C: 31.9 cSt; use level: 1–500 ppm). This was used at

500 ppm in each basestock.

• Fynol AC 28 (Appearance: clear viscous liquid at room temperature; water content: 2%; characteristic: non-ionic;

dilution: 1:80; dispensability: complete; composition: fatty acid complex derivatives; use: rust and corrosion inhibitor). This was added 0.5% w/v in each basestock.

The 5% oil-in-water (o/w) emulsion of the fi nished oils were made by emulsifying 5 mL of each fi nished oil in tap water (CaCO3, 179 mg) by mechanical shaking. The emulsions were then kept at 50 °C in oven.

The performance of so prepared emulsions was evaluated on tribotesters, which can simulate the conditions prevailing in rolling mills, for lubricity (coeffi cient of friction µ), load bearing capacity (LBC), wear scar diameter (WSD) and weld load (WL). Plate-out test and particle size distribution analysis were also done for monitoring emulsion stability.

Lubricity Test

This test determines the lubricity property of cold rolling oils for steel. The coeffi cient of friction (µ) at the end of the test is the criteria for determining the lubricity property of the oil. A pair of En31 and mild steel disc rotates in circumferential contact under the load as shown in Figure 1.

This test was carried out on Amsler type A135 machine in which a pair of discs rotates under a load of 150 kg, thus creating microplastic deformation conditions. The test lubricant was supplied through rotating lower disc partially immersed in the oil. The lubricant temperature was maintained at 50 ± 5 °C thermostatically. The frictional torque was continuously recorded with the help of a torque dynamometer. The pair of hard alloy and mild steel discs simulates the plastic deformation conditions

Figure 1. Arrangment of oil feeding into contact zone.



prevailing in the deformation process. The load applied causes generation of contact stresses which are well above the yield strength of mild steel leading to superfi cial deformation of mild steel.

The operating conditions were: rpm (200), load (150 kg), disc (M.S + EN 31), motion of discs (opposite and double sliding) and temperature (50 ± 5 °C).

WL Test

This test was carried out on shell four-ball E.P. machine in which a sliding motion under high pressure is produced between steel test specimens; the contact conditions, therefore, to a great extent simulate those which occur in metalworking process.

Procedure

(i) We ran the motor unloaded for some minutes before commencing a series of tests in order to remove the possibility of under-friction from the motor and bearing lubricants. (ii) We used a set of four new steel balls for each operation which are 12.7 mm (1/2 inch) in diameter. Then, we cleaned the new balls with hexane and then with acetone. We also cleaned the ball pot and chuck assemblies. (iii) We pressed one ball by hand into the male chuck, care being taken that the ball is snapped right into the position with an audible click. (iv) Then, the chuck was positioned in the male clutch holder. (v) Three balls were put in the ball pot, and lock ring was placed over them and screwed down the lock nut tightly. (vi) We poured the test lubricant over the balls until they were covered. (vii) The weight tray, which weighed 1 kg, was suspended from the desired notch on the horizontal arm, and weights were placed upon it. (viii) The lever was released and the load was gently applied to the balls. (ix) The main motor was started and machine was allowed to run for 10 seconds. (x) As the seizure did not occur, load was increased stepwise until the welding of the four balls takes place owing to the great intensity of the heat generated. (xi) The load at which the lubricant failed was called WL for that test lubricant.

The operating conditions were: speed (1450 rpm), load (starting load 40 kg step load procedure until welding), duration (10 seconds at each load stage) and temperature (room temperature).

Four-ball Wear Test

This test was carried out on Roxana four-ball wear tester. The average size of the scar diameter of the balls was calculated for each test lubricant. In this test, the same procedure was adopted as in the WL test. The arrangement of the balls was the same, but in this test 40 kg load was applied through air pressure and the top ball was pressed into the cavity made by the lower three balls to make three-point contact. After running the motor for a specifi c time of 30 minutes, the lower three balls were washed with hexane and acetone, and the average size of WSD was calculated for each test lubricant.

The operating conditions were: speed (1450 rpm), load (40 kg), temperature (50 ± 5 °C) and time (30 minutes).

LBC Test

This test was also carried on Amsler machine. This test was devised for evaluation of load-carrying capacity of rolling oils. In this test, a stationary conical alloy disc rubs mild steel disc generating



severe plastic deformation conditions causing fresh surface generations which are highly adhesive in nature. The loads were applied in steps until the lubricant failed, which was indicated by the sudden rise in the frictional torque. The load at which lubricant failed was called failure load for test lubricant.

The operating conditions were: rpm (200) and temperature (50 ± 5 °C).

Plate-out Test

The plate-out characteristics of test oil emulsion were required to know about the tendency of oil to come out of the emulsion and form a thin lubricant fi lm over the strip surface. A test was devised for evaluation of plating-out characteristics of o/w emulsion. A polished steel strip was cleaned with hexane followed by acetone and dipped in the emulsion for 1 minute; the strip was then air-dried for 4 hours. It was then dipped in 1% CuSO4 solution for 10 seconds. The strips were then observed for the area attacked by the copper.

Particle Size Distribution

The particle size distribution is the most important parameter in characterization of any emulsion. The oil globule size was determined by laser particle size analyser, GALAI-CIS-100 (Galai, Israel).

RESULTS AND DISCUSSION

For developing the potential formulations, six blends of different compositions of vegetable oils and mineral oils were prepared. To meet the required viscosity of reference oil, percentage volumes of N150 and N500 paraffi nic lubestock were calculated and blended as mentioned in Table I.

Now, to meet both specifi cation value and viscosity of the commercial reference oil, percentage volume of mineral oil and vegetable oil was calculated as mentioned in Table II.

Physico-chemical properties of the component vegetable oils were determined as per IS: 548 (part I) as shown in Table III. It indicates that crude karanja and rapeseed are in accordance with AOCS specifi cations, and rapeseed oil is high in erucic acid content.

Table IV shows the physico-chemical properties of the component mineral oils (as per ASTM methods) used in the preparation of basestock for the fi nished oils. It indicates that both the high

Table I. Blending of high-viscosity and low-viscosity mineral oil.

Oil code N150 (mL) N500 (mL)

A 92.5 7.5B 93.5 6.5C 92.9 7.1D 28.9 71.1E 18.1 81.9F 24.4 75.6



viscosity and low viscosity oils are highly paraffi nic in nature and are solvent refi ned to acquire the wide temperature range, low staining property, less foaming tendency, etc.

Table V gives the composite performance of the o/w emulsions of six formulated oils (F1L, F2L, F3L, F1M, F2M, F3M) in comparison to the commercial reference oils (R1L, R2L, R3M, R4M, where L stands for low saponifi cation and M for medium saponifi cation value).

Formulation F1L and F3L are giving less values of coeffi cient of friction (µ) in comparison to commercial reference oils, whereas formulation F2L approaches very close to the reference oils. Similarly, formulations F1M and F3M are showing better results in comparison to F2M in lubricity. Overall, the formulated oils lack in LBC in comparison to the reference oils; formulation F3L reaches close to formulated oils at 1400 N. This parameter seems to be governed by the compactness of the

Table II. Blending of vegetable and mineral oils.

Sample number Oil code Karanja (mL) Rapeseed (mL) Mineral oil (mL)

1 F1L 32.0 — 68.0 (A)2 F2L — 37.0 63.0 (B)3 F3L 17.0 17.0 66.0 (C)4 F1M 53.2 — 46.8 (D)5 F2M — 61.3 38.7 (E)6 F3M 28.5 28.5 43.0 (F)

Table III. Physico-chemical properties of vegetable oils.

Sample number Properties Rapeseed Karanja

1 Specifi c gravity at 30 °C 0.904 0.9282 Reference index at 40 °C 1.467 1.4763 Kinematics viscosity cSt, 40 °C 49.19 44.294 Saponifi cation value, mg KOH/g 163.3 188.15 Acid value, mg KOH/g 4.29 9.846 Iodine value, g I2/100 g 111.0 88.0

Table IV. Physico-chemical properties of mineral oils.

Sample number Properties N150 N500

1 Density at 15 °C 0.8812 0.89172 Kinematics viscosity, cSt

at 40 °C 33.30 95.66at 100 °C 5.49 10.81

3 Viscosity index 100 964 Pour point, °C −3 05 Carbon residue, % wt 0.001 0.046 Flash point, °C 208 2567 Ash, % wt — —8 Foam — —



Table V. Comparative performance of o/w emulsions (reference and formulated).

Sample number Oil code µ LBC (N) WSD (mm) WL (kgf) Particle size 10–20 µm (%)

1 RIL 0.096 1600 0.666 150 52.02 R2L 0.092 1200 0.781 130 47.73 R3M 0.098 1300 0.781 150 43.54 R4M 0.088 1900 0.625 140 23.55 F1L 0.086 1100 0.725 130 36.26 F2L 0.099 900 0.750 130 19.77 F3L 0.089 1400 0.719 130 42.78 F1M 0.086 1100 0.781 160 32.09 F2M 0.092 1000 0.719 140 29.2

10 F3M 0.089 800 0.812 130 17.4

emulsion. The WSD of the formulated oils is satisfactory, but it is not able to reach as low as 0.666 and 0.625 mm of the commercial reference oils. The WL of all the formulated oils is in accordance with the commercial reference oils. The high percentage of particle size of the commercial reference emulsions in the range of 10–20 µm indicates the metastable nature of the oils. So, this range is also important in the formulated oil emulsions, and formulation F3L seems to be promising for stability factor among all formulated oils.

In plate-out test, the formulation F3L has less area attacked in comparison to formulations F1L and F2L. Similarly, in oil F2M, area attacked was less than formulations F1M and F3M.

CONCLUSION

• The results obtained in the present study show that the formulated oils are close to the commercial reference oils in lubricity, WSD, WL and particle size.

• The narrower the particle size distribution, the more is the LBC.• Formulation F3L (mineral oil and vegetable oil in the ratio of 2 : 1; karanja and rapeseed in

equal amounts) may prove much more potential and economical as well among all other formulations.

• Based on the performance tests, the performance rating of the formulated oils is F3L > F1L > F2L in the low saponifi cation region, and F2M > F1M > F3M in the medium saponifi cation region.

In the area of performance evaluation of rolling oils, the rolling process involves too may parameters so only comparisons can be made with the reference oils. However, the overall perfor-mance will be adjudged by the laboratory mill study and later on to ultimate study on actual produc-tion mills. Other non-edible/non-traditional vegetable oils can also be taken into consideration for such studies.

ACKNOWLEDGEMENTS

The authors are highly thankful to director I.I.P. Dehradun for providing facilities for the project.



REFERENCES

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of Synthetic Lubrication 2007; 24(4):181–197.3. Shukla DS, Jain VK. Water-based lubricants for metalworking. CHEMTECH 1997; 27(5):32–36.4. Durak E, Karaosmanoglu F. Using of cottonseed oil as an environmentally accepted lubricant additive. Energy Sources

2004; 26(7):611–625.5. Singh AK, Gupta AK. Metalworking fl uids from vegetable oils. Journal of Synthetic Lubrication 2006; 23(4):167–176.6. Lightcap DV Jr. Water-dispersible metal working fl uid. US Patent 6204225, 2001.

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Metalworking emulsions from industrial vegetable oils