Past and Current Status of Eco-Friendly Vegetable Oil Based Metal Cutting Fluids

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ScienceDirect Materials Today: Proceedings 4 (2017) 3786–3795

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5th International Conference of Materials Processing and Characterization (ICMPC 2016)

Past and Current Status of Eco-Friendly Vegetable Oil Based Metal Cutting Fluids Kishor Kumar Gajrani, M. Ravi Sankar* Department of Mechanical Engineering, IIT Guwahati, Guwahati, Assam-781039

Abstract Cutting fluids are most fundamental and important part in metalworking industries. Cutting fluids are widely employed due to their ability to reduce friction, cutting temperature, generated heatand also to enhance workpiece surface quality. But the use of the petroleum based cutting fluid threats to the health of workers and environment. Hence to identify user-friendly and ecofriendly alternatives for conventional petroleum based cutting fluids, industrialist and researchers are working hand in hand. Based on the increasing awareness regarding environmental aspects and awareness to employee health, eco-friendly cutting fluids have to be selected very carefully to minimize the same. This paper is focused on review of composition, physico-chemical properties, advantages, applications and practical use of individual vegetable oils as metal working fluid in environmental conscious machining to make the process environmental friendly and less toxic for operators. ©2017 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Conference Committee Members of 5th International Conference of Materials Processing and Characterization (ICMPC 2016). Keywords:Vegetable oils, eco-friendly cutting fluids, environmental concious machining, metalworking fluids

1. Introduction From the past 200 years, cutting fluids are extensively used in metalworking operation [1]. Survey estimation says that United States uses 100 million gallons of metalworking oil each year [2]. In ancient times, cutting fluids constituted of only water which was used on grindstones. About 100 past years, tallow (animal fat rendered form) was applied as lubricating wax. Then, cutting fluids were comprised of simple oils which were applied with brushes for lubricating the cutting tool. Later lard oil was used but it became rancid. Sometimes, directly whale oil or animal

* Corresponding author. Tel.: +91-361-2582684. E-mail address: [email protected] 2214-7853©2017 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of Conference Committee Members of 5th International Conference of Materials Processing and Characterization (ICMPC 2016).

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fat was included to enhance the cutting fluid lubricating properties. In initial years of 20th century, soap was mixed in water [3]. Straight cutting fluids were the popular choice of certain machining operations in the past. Soluble oils were introduced in 1936 and cutting fluids made of chemicals came into metalworking operation in 1944 [4]. Gradually, compositions of the metalworking fluids became more complicated as the cutting actions became more difficult. These days to fulfill the required performance demands of the manufacturing industries, cutting fluids are enhanced combination of oil, water, emulsifiers and chemical additives [5]. 2. Why vegetableoils? In due course of time, the conventional cutting fluids started causing problems for the manufacturers as the substances present in them caused serious health effects on the workers and the surrounding environment [6]. Along with the economic and technical aspects of the manufacturing processes, the environmental safety of the products has also become an important area of concern and it is triggered by the fact that environmental agencies and government have imposed strict measures when it comes to protecting the employees’ health and environment [7,8]. So there is a need to analyze the measures that can be taken to reduce the harmful effects of metalworking fluids as much as possible. Availability of mineral based oils is limited as they are finite source and decreasing steadily whereas vegetable based cutting fluids are sustainable. Literature studies about machining using vegetable based cutting fluids are limited. Vegetable oils are evolving asmetalworking fluids due to its higher biodegradability and ability to minimize the waste treatment costs. It also reduces the health risks to operators which were quiet common with petroleum based mineral oilsdue to their lower toxicity[9]. Cleaner and healthier work environment having less mist in the air is main point. For above mentioned reasons, vegetable oils as metalworking fluids are eco-friendly and are also better lubricantas compared to others [10].Above all,they are extracted from renewable sources and thus unlimited and sustainable. All these factors have pushed the industries, research centers and universities for studying the process in detail and come up with better optimal solution. Several of them have proposed various methods for reducing the exposures of cutting fluids while some have advised in changing its composition [11]. Huge quantities of metalworking fluids are still in use in the industriesreleasing harmful gases into the atmosphere, causing numerous skin and other diseases in the workers and increasing disposal costs [12]. Thus, a research study has been conducted to analyze the vegetable oils that act as an eco-friendly cutting fluid, so that the industries can find alternative answers and use protective measures. This paper presents in detail all these above mentioned aspects. 3. Vegetable oils In 21st century, keeping in view of environment protection awareness under law and regulation enforced, ecofriendly cutting fluid has become a general trend.The eco-friendly cutting fluid generally comprise of vegetables oils, bio cutting fluid and some chemically synthesized fluids as esters including phosphate esters, polyalklene glycols, polyalphaolefins (PAOs), alkylated aromatics and polybutanes that dominates the market among for the same. 3.1 Chemical structure and rheological properties of vegetable oils With the increasing problems of pollution and health hazards to human by the metal working fluid based on minerals oils based, which were put in limitations, the line of thinking towards the use of vegetables oils based lubricants, generally produced from liquid agriculture cash crops and plants. Vegetable oils mostly consist of triglycerides which are long chain fatty acids having number of unsaturated double bonds [13, 14]. Most vegetable oils have minimum four to maximum 12 different fatty acids. Weather and geo-climate mostly affect the proportion of individual fatty acids. Cutting at high speed and feed generates high temperature. Use of cutting fluid at high temperature has possibilities of smoke formation and fire hazard. Vegetable oils have a higher flash point compares to mineral oils

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which reduce smoke formation and fire hazard [15, 16]. Vegetable oils have high viscosity index. Viscosity of oil also effect machining productivity [15]. As viscosity index of vegetable oil is high, viscosity drops more slowly than that of mineral oils with increase in temperature. So with fall in temperature, vegetable oils remain more viscous than mineral oils, leads to early drainage from workpiece and chips. Vegetable oils higher viscosity ensures more stable lubricity across the operating temperature range [16]. Molecules sizes of mineral oils are varying but vegetable oil molecules sizes are quite homogeneous resulting in less variation of its properties with respect to physical parameters [15]. Vegetable oil has greater molecular weight and higher boiling point and this reduces misting and vaporization [17]. They are much better substitutes of petroleum based cutting fluids which make them probable candidate for industrial use. Apart from above mentioned properties, oxidation stability of vegetable oils depends on amount of present unsaturated products. For high melting point and even better oxidation stability, the presence of unsaturated product should be low. To reduce friction and wear, long and polar fatty acid carbon chains perform better to strongly interact with metallic surfaces.Figure 1.shows life cycle of chemical products based on renewable resources [18]. Micro-organisms have ability to metabolized and ingest vegetable oils base stock which creates problems toxic mists environment affecting operators health.Various researchers are investigating and exploring oils from vegetables and seeds such as canola, rapeseed, palm, jatropha, olive, neem and coconut to use for metal working fluids as base stock.Table 1 shows length of carbon chain for various fatty acids chemical structure while table 2 shows the physico-chemical or rheological properties of various vegetable oils [19].

Figure 1.Life cycle of chemical products based on renewable resources [18]

3.2 Merits and applications of vegetable oils Vegetable oils have numerous advantages over petroleum based mineral oils apart from being sustainable in nature. Table 3 shows merits and demerits of vegetable oils over mineral oil properties. Demerits of vegetable oils can be tackled using chemical and genetic modification as well as reformulation of base stock. Potential practical applications of particular vegetable oils are shown in Table 4.

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Table 1 Fatty acid structure of various vegetable oils [19] Fatty acid

Soybe an [20]

C 14: 0 C 16: 0 C 16:1 C 18: 0 C 18: 1 C 18: 2 C 18: 3 C 20: 0 C 20:1 C 22: 0 C 22: 1 Others a

Sunflower [22]

Rapeseed [23]

Palm [24]

Pongammia pinnata [25]

Jatropha curcass [26]

Olive [27]

Castor [22]

Neem [28]

-

High oleic Soybe an [21] -

-

-

1.50

7.90

-

0.10

-

-

1.50 10.4 4.30 24.4 51.6 7.7 0.5 -

6.0 3.0 85.0 4.0 2.0 -

6.0 3.0 17.0 74.0 6.0 Traces Traces -

9.8 1.6 18.4 16.8 6.5 9.2 37.7 -

43.0 5.0 40.0 10.0 0.5 -

4.0 2.0 62.0 12.0 10.0 4.0 -

12-17 6.7 37-63 19-41 -

17.3 2.7 60.7 4.40 0.5 -

2-3 3-5 3-5 80-90 -

15.0 22.0 19.0 49.0 9.50 -

Lauricacid

Linseed [24]

Coconut [29,30]

5.0

9.0

3.0 22.0 17.0 52.0 -

2.0 7.0 1.0 72.0a

Table 2Rheological properties of vegetable oils [19]

Properties

Soybean [21]

Sunflower [20]

Rapeseed [23]

Jojoba [31]

Pongammiapinnata [32]

Jatrophacurcass [23,33]

Neem [25]

Castor [23,34]

32.93

High oleic soyabean [22] 41.34

Kinematic viscosity@40 1C (cSt) Kinematic viscosity@100 1C (cSt) Viscosity index Saponofication value(mgKOHg _1) Total acidvalue(mgKOHg _1) Iodine value(mglg _1) Pour point(0 1C) Flash point(0 1C)

40.05

45.60

24.9

43.0

47.48

68.03

220.60

8.08

9.02

8.65

10.07

6.43

8.30

8.04

10.14

19.72

219 189

-

206 -

216 180

233 94.69

172 179

208 196.80

135 166

220 180

0.61

0.12

-

1.40

1.10

22

3.20

23

144

85.9

-

104

98

78

97

66

87

-9.0 240

-

-12.0 252

-12.0 240

9.0 -

-9.0 -

0 240

9.0 -

-27.0 250

1.40

3.3 Performance of vegetable oils as metal cutting fluids: turning applications Vegetable based cutting fluids associated machining literatures are presented in this section. Combined influence of MQL using vegetable oil as cutting fluid in turning of AISI 1060 steel were observed and found that the tool wear, surface roughnessand cutting temperaturereduced in comparison to dry machining. At an average of 5-12% reduction of cutting temperature was observed while using MQL with vegetable oil as compared to dry machining. Cutting forces were also reduced by using MQL with vegetable oil [17, 35]. Table 3 Merits and demerits of vegetable oils over mineral oils [21,36,37,38] • • • • • • •

Merits Suistainable and highly biodegradable Least toxic compare to mineral oils High viscosity and viscosity index Environmental friendly High flash point Additives compatible Less volatile

• • •

Demerits Low thermal and oxidative stability High pour point More corrosive behaviour

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Table 4 Potential practical applications of vegetable oils [27,39,40,41] Soyabean

Vegetable oil type

Application Lubricants,chain bar fluid,greases,marine and automotive,metal working fluids, industrial and food grade hydraulic fluids, bio-diesel fuel, sources of oleic acid for oleochemical production, paints, soaps, coatings

Sunflower Palm

Cooking oil, lubricants, grease substitutes, sources of oleic acid for oleochemical production Two stroke engine oil, chain bar lubricants, metal working fluids, textile lubricants, antiwear hydraulic fluid, food processing machines lubricant

Pongammiapinnata

Cooking lamp fuels, water-paint binder, pestisides, soap, tanning industries, herbal medicines

Jatrophacurcass

Bio-diesel, cooling lubricants, base stock for metal working fluids

Castor

Greases, metal working lubricants base stock, gear lubricants

Neem

Medicines, cutting fluids, coolants,

Coconut

Chain bar fluids, grease, engine oils

Jojoba

Surfactants, colour dies, surfactants, emulsifiers, resins, protective coatings, fibers

Experimentally performance of sunflower oil, canola oil, semisynthetic and mineral based cutting fluids including different concentration (8 and 12%) of extreme pressure additives were compared in turning of AISI 304L stainless steel. Machining forces, tool life and surface roughness with all four types of cutting fluids were measured and found that vegetable oils have shown better machining performance. Due to long chain of fatty acid content in vegetable oils they have shown better machining performance. Canola based cutting fluids are found to be best as compare to all three including sunflower oil based cutting fluids, as canola oil has three more carbons in its fatty acid chain which are able to perform better at higher cutting temperature. Moreover canola oil has high viscosity which provides more effective lubrication at the tool-chip interface, reducing cutting temperature and removing heat easily. Higher concentration of pressure additives in vegetable oils results in higher surface roughness values. Canola based cutting fluid with 8 % of extreme pressure additive has shown better performance than others [42]. Four different vegetable based cutting fluids (coconut oil, palm kernel oil, groundnut oil and shear butter oil) were used while turning of copper, mild steel and aluminium. Cutting forces were measured and compared with four different cutting fluids during cutting of various materials. If was found that the effect of vegetable based cutting fluid are material dependent. Out of the four, groundnut oil showed best machining performance [44]. Tool wear and surface roughness were analysed in turning of AISI 304 stainless steel using coconut oil as cutting fluid and compared with an emulsion as well as neat cutting oil. Reduction in tool wear and better surface finish was observed with coconut oil as cutting fluid compared to other oils. Figure2(a) shows variation of surface roughness with respect to feed rate and Figure 2(b) shows variation of tool wear with respect to cutting speed, comparing three cutting oils. They measured cutting forces and temperature in other study. Coconut oil was able to perform much better in terms of reducing cutting forces and temperature compare to other two cutting fluids. Figure3 shows scanning electron microphotographs of tool wear. During turning of mild steel, neem oil, karanja oil and conventional cutting fluid were used. Vegetable based cutting fluids shows better surface finish and lesser cutting temperature as compared to dry machining as well as conventional cutting fluids. Neem oil has shown best abilities to reduce cutting temperature because of its lower viscosity compare to karanja oil [47].

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0.12

2.8

0.11

2.6

0.10 Tool wear (mm)

Surface roughness (µm)

3.0

2.4 2.2 2.0

Soluble oil Straight cutting oil 0.21

0.23 0.25 0.27 Feed rate (mm/rev)

0.09 0.08 0.07 0.06

Coconut oil

1.8 1.6 0.19

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0.29

Coconut oil Soluble oil Straight cutting oil

0.05 0.04

30

50 70 90 Cutting speed (m/min)

110

Figure 2.(a) Surface roughness vs feed rate at cutting speed: 38.95 m/min, 61.35m/min and 97.38m/min and (b) tool wear vs cutting speed at feed rate: 0.2mm/rev, 0.25mm/rev, 0.28mm/rev [45]

3.4 Performance of vegetable oils as metal cutting fluids: drilling applications Conventional flood lubrication (mineral oil and semisynthetic oil), MQL (vegetable oil and mineral oil) and dry machining were used for drilling and burr heights were measured. Largest burr height was obtained with MQL and smallest with dry machining. MQL with vegetable oil shown lesser burr height compared to MQL with mineral based cutting fluids [48]. Vegetable oil was used as lubricant in MQL during silicon alloys and cast aluminium drilling. Different cutting fluid application techniques were used such as flood lubrication, MQL, compressed air and dry while drilling. Vegetable oil as MQL lubricant performed best in terms of cutting forces, torque and better surface finish. However, flood lubrication technique with mineral based cutting fluid was able to reduce maximum cutting temperature among all [49]. In high speed drilling of Ti-6Al-4V, effect of MQL (with palm oil (MQLPO) and synthetic ester (MQLSE)), flood lubrication and dry air as cutting fluids were investigated. Lower tool rate were measured using MQLPO than MQLSE. However with flood lubrication, flank and corner wear rate were found in between MQLPO and MQLSE. MQLPO has outperformed others in terms of wear rate. Long carbon chain fatty acid are present in palm oil might be the reason for significant reduction in friction and wear. Fatty acid reacts with metallic oxide and form a low friction lubricant layer leads to smooth sliding. Fatty acids having long carbon chain are capable of resisting higher cutting temperature to protect the work surface. During drilling under MQLPO, reduction in friction and tool wear was observed due to presence of molecular thin film lubricant. Palm oil has high viscosity and tendency to resist the flow to provide better lubrication at tool-chip interface resulting in friction reduction and tool wear. With flood lubrication technique lowest torque and thrust forces was obtained, while approximate similar performance was showed by MQLPO to the flood condition in respect of maximum workpiece temperature [50].

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Coconut oil: 100X magnification

Coconut oil: 200X magnification

Soluble oil: 100X magnification

Soluble oil: 100X magnification

Straight cutting oil: 100X magnification

Straight cutting oil: 100X magnification

Figure3. Microphotographs of tool wear at: cutting speed = 38.95 m/min, depth of cut= 0.5mm and feed rate=0.25mm/rev [45]

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Tool life and efficiency of vegetable based cutting fluids while drilling austenitic stainless steel (AISI 316L)were quantitate analysed. For reference and comparison, a commercial mineral based cutting fluid was opted. Vegetable based cutting fluid have shown best performance by reducing 7 % thrust force and giving 177 % increment in tool life as compare to mineral based cutting fluid. In other study, authors have examined power and cutting force in tapping, reaming, drilling and core drilling of austenitic stainless steel (AISI 316L). In all above operations, vegetable based cutting fluid performed better or comparable to commercial mineral based cutting fluid [51,52]. Crude and refined sunflower based cutting fluids were extracted and evaluated.There effect over surface finish and thrust force was analysed. Crude sunflower based cutting fluids have performed better and reduce more thrust force compare to refined sunflower based cutting fluid. However, refined sunflower based cutting fluids have shown better surface finish compare to other [53,54]. 3.5 Performance of vegetable oils as metal cutting fluids: grinding applications 45 % diluted biodegradable castor oil based cutting fluids were used during grinding operation and it was observed that the grinding forces, wheel wear were reduced and better surface finish was obtained as compare to mineral based cutting fluids [55]. In other study, authors have used vegetable oil based emulsions (sulfonate vegetable oil in water) to meet environmental requirements as well as grinding performance. Sulfonate castor oil was extracted from a plant called mamona. Cutting fluid extracted from mamona is free from chlorine and nitrosamines substances which are harmful for environment. Sulfonate castor oil is biodegradable and can be disposed easily. SAE 8640 was selected as workpiece material for CBN grinding. Semi-synthetic cutting fluids and mineral based neat cutting oil are taken as reference to evaluate performance of sulfonate castor based cutting fluid at three different concentrations (35, 45 and 70 % in volume). Grinding ratio (material removal volume/wheel worn volume) of sulfonate castor oil at 45 % concentration performed almost equal (high G ratio) to mineral based neat cutting oil. Surface finish was obtained much better with 45 % concentrated sulfonate castor oil, however lowest grinding forces were obtained while using neat oil [56]. In another study, same authors have used three different concentrations (15, 21, and 32%) of sulfonate castor oil based emulsion (oil in water). Highest and lowest wheel wear were obtained with using semi-synthetic cutting fluid and sulfonate castor oil based emulsions respectively. Out of the three concentrations, 21 % outperformed other two in terms of surface finish and shows similar performance to neat cutting oil [57]. 4. Future prospects Current trends in metalworking industries have seen shift in product specifications and viscosity grades of lubricants used. In fact it has been observed that eco-friendly vegetable oils performance is better as compared to petroleum based mineral oil in most terms, especially machining performance, stability, viscosity, additives response and oxidation stability. Environmental and ecological conditions have forced industries to develop ecofriendly metalworking fluid to use for manufacturing technology which can be used even at high speed, bearing higher pressure and temperature changes. Despite enough evidences that vegetable oils can cut ecological pollution and is sustainable in nature, manufactures/industries are still making its use more economical. Eco-friendly vegetable oil performance as metal working fluids will become more effective if appropriate base stock for particular application will be selected to enhance efficiency and make it more economical. However, above target can be achieved by optimize combination of vegetable oils and specific additives to enhance fluids properties as required. In fifties, correct viscosity was most important requirement of metalworking fluids. In sixties, specific additives were mixed to enhance properties of lubricants while in seventies few synthetic fluids stated challenging mineral oil for performing even better, but former were challenged due to its high cost. In eighties, hydrocracked quasi synthetic oils made by BP, Shell, Fuchs was economical and also enhanced working performance. In nineties, criteria for working fluids took significant shift towards environment and eco-friendly fluids. In 21st century, even more compatible working fluids with greater performance trend is in continuation with many more development to come in future to make it more environmental friendly and economical.

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5. Conclusions Development of universal vegetable oil base stock which can replace petroleum based mineral oil is biggest challenge in new metalworking fluid industry. Manufacturers and industries have started appreciating as well as accepting vegetable oils as new eco-friendly sustainable metal working fluids with slight chemical modifications. Efforts are going on to make it more economical and easily available. In many forums, need of eco-friendly metal working fluid has been discussed. Eco-friendly vegetable oils have ecotoxicological characteristics and are highly biodegradable. An optimize selection of vegetable oil for particular application is needed to make it economical and performance enhancer. Keeping government enforced environmental law and ASTM standards for lubricants in mind, few eco-friendly vegetable oil products are already commercially available for specific use and performance criteria. Metalworking industries are rapidly shifting towards vegetable oils which are able to protect operators from health hazard and to reduce environmental pollution. Vegetable oils are also able to withstand at high pressure and temperature which make its application even easier in industries. Research and development is directly influenced by above mention factors. For upcoming next 10-15 years, vegetable oils are ready to replace petroleum based mineral oil and can take over 15 to 30 percent worldwide volume share. Lubricant industry will face many challenges in upcoming years to meet environmental laws and vegetable oils will help industries to achieve it. Acknowledgement Authors are thankful to “ELSEVIER (Licence numbers: 3764610869423,3764611083638, 3764611241853)” for providing the copy right permission to various figures in the current paper. References 1.

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