EP2520639A1

EP2520639A1 - Environmental friendly cutting fluid

Info

Publication number: EP2520639A1
Application number: EP12166702A
Authority: EP
Inventors: Anand Kumar; Amit Pandey; Ajay KHONGAL; Subodh DESHPANDE
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 2011-05-04
Filing date: 2012-05-03
Publication date: 2012-11-07

Abstract

The present invention relates to a green cutting fluid which is free from chemicals like amines, boron, chlorine and has no added sulphur, which exhibits superior properties in terms of stability, corrosion resistance, effective lubrication and having reduced mist and no sludge formation. Thus the green cutting fluid of the invention is an environmental friendly cutting fluid. The said green cutting fluid comprising base oil, emulsifier, corrosion inhibitor, and extreme pressure additive (E P additive), water, pH adjuster, couplers, biocides, and defoamer. This invention also relates to a process for the preparation of the said green cutting fluid comprising the steps of mixing the acid ingredients and neutralizing with caustic potash solution, adding base oil, sulfonates, ethoxylates and esters and stirring, adding the remaining ingredients such as biocides, couplers and defoamer and stirring, adding demineralized water and stirring.

Description

Field of the Invention

The present invention relates to a cutting fluid for metal working processes. In particular, the present invention relates to a green cutting fluid which is free from chemicals like amines, boron, chlorine and has no added sulphur, which exhibits superior properties in terms of stability, corrosion resistance, effective lubrication and having reduced mist and no sludge formation.

Background of the Invention

Cutting fluids have been widely used in metal cutting and grinding processes over the conventional method of using a cutting tool due to their ability to overcome various problems such as frictional heat and tool wear which usually result in poor product quality. A wide range of metal working liquids or cutting fluids are known in the art which can be broadly classified into water-soluble and water-insoluble (neat oils) fluids. Among the water-soluble (water-based) fluids are soluble (water-in-oil) oil emulsions, semi-synthetic emulsions and synthetic emulsions. These metal-working fluids usually contain base oil for providing lubrication and other additives which provide other functionality such as corrosion inhibition, extreme pressure functions, regulate viscosity of the fluid and control microbial growth.
However, most of these fluids known in the art suffer from several drawbacks. For example, fluid compositions generally contain boron and/or amine based compounds for corrosion protection and chlorine, sulphur or phosphorus compounds for extreme pressure functions which do not ensure safety for the humans and the environment. For instance, while chlorine based extreme pressure agents are known for its excellent ability to improve cutting performance, it is also a concern for environmental pollution and toxicity issues. Further, while amine based compounds (especially secondary amines) are known for imparting lubrication and corrosion protection, it has been found to cause dissolution and discoloration of the metals which amount to environmental issues and health hazards. Although the products available in the market specify that they are free from secondary amines, there always exist trace levels of secondary amines in primary/tertiary amines which are not safe. Some of the cutting fluid compositions present high mist, oil deposition and sludge formation which causes maintenance problems and environment, health and safety issues (EHS). Also, the high pH of some known cutting emulsions may lead to skin problems to the user. Low hard water stability of the emulsions is another problem. Moreover, some of the metal working fluids are highly expensive. Thus, with the global awareness on the rise to address the environmental problems and the cost issue, there is a need for environmentally safe and low cost cutting fluid.
In view of the foregoing, the aim of the present invention is to provide a cutting fluid with superior properties in a cost effective way and which is free from such environmentally harmful components.

Summary of the Invention

The objective of the present invention is to provide a green cutting fluid with superior properties in terms of stability, corrosion resistance, and lubrication, and has low mist generation, is free of sludge formation and which is free from chemicals like amines, boron, chlorine and sulphur.
Accordingly one aspect of the present invention is to provide a cutting fluid which comprises base oil and other special additives for imparting enhanced corrosion inhibition and to formulate a clean working product. The above special additives may comprise emulsifiers, corrosion inhibitors, extreme pressure additives (EP additives), water, pH adjuster, couplers, biocides, and defoamers. The ingredients of the present composition interact synergistically to generate a green cutting fluid with superior properties.
According to a further aspect, the instant cutting fluid composition comprises one or more of the following components in the following concentrations

a) base oil, about 30 to 50% by weight
b) emulsifier, about 5 to 20% by weight
c) corrosion inhibitor, about 10 to 15% by weight
d) extreme pressure additive (EP additive), about 5 to 15 % by weight
e) water, about 5 to 15% by weight
f) pH adjuster, about 5 to 10% by weight
g) coupler, about 5 to 10% by weight
h) biocide, about< 1 %by weight and
i) defoamer, about <1 % by weight.

Another embodiment the present invention relates to a process for the preparation of the green cutting fluid comprising the steps of mixing the acid ingredients and neutralizing with caustic potash solution, adding base oil, sulfonates, ethoxylates and esters and stirring, adding the remaining ingredients such as biocides, and defoamer and stirring, adding demineralized water and stirring.
The present invention possesses the following advantages:

Very low mist formation and nearly no sludge in the application thereby directly translating in to clean environment
Comparatively low pH (8) provides skin protection to the user as against already known compositions which has higher pH
Naturally derived esters in replacement of chlorine as extreme pressure additive makes the product biodegradable
Multi metal compatibility wherein this single product can be used for machining of aluminum, iron, steel and copper within the extreme pressure capabilities of this product.

Other features and advantages of the present invention will become apparent as the following detailed description proceeds or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

Detailed Description of the Invention

For the purposes of the following detailed description, it is to be understood that the invention may assume alternative variations and step sequences, except where expressly specified to the contrary. Moreover, other than in any operating examples, or where otherwise indicated, all numbers expressing, for example, quantities of ingredients used in the specification and claims are to be understood as being modified in all instances by the term "about". It is noted that, unless otherwise stated, all percentages given in this specification and appended claims refer to percentages by weight of the total composition.
Thus, before describing the present invention in detail, it is to be understood that this invention is not limited to particularly exemplified systems or process parameters that may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments of the invention only, and is not intended to limit the scope of the invention in any manner.
It must be noted that, as used in this specification and the appended claims, the singular forms "a", "an" and "the" include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a "corrosion inhibitor" includes two or more such corrosion inhibitors. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains.

Definitions

Cutting fluid: Cutting fluid is a type of coolant and lubricant designed specifically for metalworking and machining processes. There are various kinds of cutting fluids, which include oils, oil-in-water emulsions, pastes, gels, aerosols (mists), and air or other gases. They may be made from petroleum distillates, animal fats, plant oils, water and air, or other raw ingredients. Depending on context and on which type of cutting fluid is being considered, it may be referred to as cutting fluid, cutting oil, cutting compound, coolant, or lubricant. Cutting fluids are used in metal machining for a variety of reasons such as improving tool life, reducing workpiece thermal deformation, improving surface finish and flushing away chips from the cutting zone.
Green cutting fluid: This term is used to refer to the environmental friendly cutting fluids.
Metal working fluids: Metalworking fluid (MWF) is the name given to a range of oils and other liquids that are used to cool and/or lubricate metal workpieces when they are being machined, ground, milled, etc. MWFs reduce the heat and friction between the cutting tool and the workpiece, and help prevent burning and smoking. Applying MWFs also helps improve the quality of the workpiece by continuously removing the fines, chips, and swarfs from the tool being used and the surface of the workpiece. (Swarfs are the small pieces of metal removed from a workpiece by a cutting tool.)
Mist: Metalworking fluids can form a mist of small droplets that are suspended in the air and can be inhaled and ingested. When these fluids form into a mist during the machining process, they can be very irritating to the eyes, nose, and throat. Therefore it is highly desirable to reduce mist.
Sludge: Sludge results from breakdown of emulsions due to bacterial soap formation with metallic content (for example calcium, magnesium from water or metal chips from the machining process). Sludge leads to bad odour, depletion of useful additives and/or oil and dirty working conditions. Therefore it is highly desirable to reduce and if possible eliminate sludge.
Base oil: Base oil is the name given to lubrication grade oils initially produced from refining crude oil (mineral base oil) or through chemical synthesis (synthetic base oil). Base oil is typically defined as oil with a boiling point range between 290 and 570°C (550 and I 050 °F), consisting of hydrocarbons with 18 to 40 carbon atoms. This oil can be either paraffinic or naphthenic in nature depending on the chemical structure of the molecules.
Corrosion inhibitor: A corrosion inhibitor is a chemical compound that, when added to a liquid or gas, decreases the corrosion rate of a material, typically a metal or an alloy.
Emulsifier: An emulsifier (also known as an emulgent) is a substance that stabilizes an emulsion by increasing its kinetic stability.
Extreme pressure additives (EP additive): Extreme pressure additives, or EP additives, are additives for lubricants with a role to decrease wear of the parts of the gears exposed to very high pressures. They are also added to cutting fluids for machining of metals.
Couplers: Couplers assist in stabilizing water dilutable metal working fluids in the concentrate to prevent separation of components.
Biocides: A biocide is a chemical substance or microorganism which can deter, render harmless, or exert a controlling effect on any harmful organism by chemical or biological means.
Reichert wear tester: The testing of materials for load bearing capacity is tested by means of Reichert wear tester. Extreme pressure properties of lubricants in terms of film formation, wearing out and load carrying capacity are evaluated by Reichert wear tester.
Four Ball WSD: The Four Ball Wear Test determines the wear protection properties of a lubricant. Three metal balls are clamped together and covered with the test lubricant, while a rotating fourth ball is pressed against them in sliding contact. This contact typically produces a wear scar, which is measured and recorded. The smaller the average wear scar, the better the wear protection provided by the lubricant.
IP 125: Test for the determination of cast iron corrosion characteristics of petroleum products.
IP 287: Test for the determination of rust preventive characteristics of water mix metal working fluids-chip / filter paper method.
ASTM D130: Standard test method for corrosiveness to copper from petroleum products by copper strip test. In ASTM D130, ratings are specified from 1A to 4C; 1A being no corrosion and 4C very high corrosion.
ASTM D 4172: Standard test method for wear preventive characteristics of lubricating fluid (four ball method)
In a preferred embodiment, the green cutting fluid of the invention comprises base oil, emulsifier, corrosion inhibitor, EP additive, water, coupler, biocides, pH adjuster, defoamer etc.
Base oil imparts better lubricity to the cutting fluid. The base oil used in the invention may be selected from paraffinic or naphthenic oil. In a preferred embodiment of the invention, the base oil used is naphthenic base oil.
The green cutting fluid composition comprises anionic or non-ionic surfactants, such as sulphates, sulphonates or ethoxylates, as emulsifiers. In a preferred embodiment, the emulsifier used is selected from sulphates, sulfonates and ethoxylates of vegetable origin. The preferred sulfonates and ethoxylates used are sodium dodecyl sulfonate or sulphate, oleyl cetyl alcohol ethoxylates and sorbitol mono oleate.
Corrosion inhibitors used in the invention are preferably selected from long chain fatty acid or succinic acid derivatives. The preferred corrosion inhibitor is selected from succinic anhydride derivatives for. e.g., alkenyl succinic anhydride and tall oil fatty acid.
EP additives prevent the tool from welding by forming metal complexes at elevated temperatures. In particular, the fluid composition of the present invention comprises naturally derived esters such as fatty acid esters and glycol or glycerol esters as EP additives for extreme pressure additive property over the conventionally used chlorines. This feature of the present invention imparts biodegradability to the product. The preferred EP additive used in the invention is selected from esters of ricinoleic acid.
The pH adjuster controls the pH of the composition to about pH 8, which provides skin protection to the user. pH adjuster that could be used in this invention is potassium hydroxide.
Couplers are used to keep the concentrate stable. Couplers used in the present composition are selected from glycols and ethers. Some examples of specific couplers used in the invention are butyl diglycol and hexylene glycol
Biocides are used to control fungus and mold growth. Biocides used in the invention are selected from isothiazole derivatives and methyl oxazolidine. Isononane acid amide could be used as a defoamer in the invention.
In a preferred embodiment, the cutting fluid of the invention comprises base oil in an amount of 30 to 50% by weight, emulsifier in an amount of 5 to 20% by weight of, extreme pressure additive (EP additive) in an amount of 5 to 15% by weight, corrosion inhibitor in an amount of 10 to 15% by weight, water in an amount of 5 to 15% by weight, pH adjuster in an amount of 5 to 10% by weight, coupler in an amount of 5 to 10% by weight, biocide in an amount of <1% by weight and defoamer in an amount of <1% by weight.
In a preferred embodiment the green cutting fluid of the invention comprises naphthenic base oil in an amount of 30-50% by weight, sodium dodecyl sulfonate (or sulphate) in an amount of 4-15% by weight, oleyl alcohol ethoxylate in an amount of 4-15% by weight, sorbitol oleic acid ester in an amount of 3-8% by weight, ricinoleic acid ester in an amount of 5-15% by weight, tall oil fatty acid in an amount of 2-6% by weight, alkenyl succinic anhydride in an amount of 5-12% by weight, demineralized water in an amount of 5-10% by weight, caustic potash solution in an amount of 3-8% by weight, hexylene glycol in an amount of 1-5% by weight, butyl diglycol in an amount of 1-5% by weight, octyl isothiazol in an amount of <2% by weight, methyloxazolidine in an amount of <1% by weight and isononane acid amide in an amount of <1 % by weight.
In a further preferred embodiment the green cutting fluid of the invention comprises naphthenic base oil in an amount of 45 % by weight, sodium dodecyl sulfonate (or dosium dodecyl sulphate) in an amount of 5 % by weight, oleyl cetyl alcohol ethoxylates in an amount of 7 % by weight, sorbitol mono oleate in an amount of 4% by weight, ricinoleic acid ester in an amount of 7% by weight, tall oil fatty acid in an amount of 4% by weight, alkenyl succinic anhydride in an amount of 8% by weight, demineralized water in an amount of 8.2% by weight, caustic potash solution in an amount of 6% by weight, hexylene glycol in an amount of 2% by weight, butyl diglycol in an amount of 3% by weight, octyl isothiazol in an amount of 0.4% by weight, methyloxazolidine in an amount of 0.2% by weight and isononane acid amide in an amount of 0.2% by weight.
The following examples merely illustrate certain aspect of the invention and not to be construed as limiting the scope thereof.

Example 1: Preparation of the green cutting fluid of the invention

The composition of the green cutting fluid according to a preferred embodiment is shown in table 1.

Table1

Components of the green cutting fluid of the invention	% by weight of the composition
naphthenic base oil	45
sodium dodecyl sulfonate	05
oleyl cetyl alcohol ethoxylate	07
tall oil fatty acid	04
sorbitol mono oleate	04
alkenyl succinic anhydride	08
ricinoleic acid ester	07
demineralized water	8.2
caustic potash solution	06
hexylene glycol	02
butyl diglycol	03
octyl isothiazol	0.4
methyloxazolidine	0.2
isononane acid amide	0.2

To prepare the green cutting fluid with the above composition, the following process is used.
All acid ingredients viz. alkenyl succinic anhydride, ricinoleic acid ester and tall oil fatty acid were taken in a kettle and neutralized with caustic potash (50% KOH) solution for 1 hr. To this mixture, naphthenic base oil, sodium dodecyl sulfonate (or sodium dodecyl sulphate), oleyl cetyl alcohol ethoxylate and sorbitol oleic acid ester were added and stirred for 30 minutes. Then the remaining ingredients such as octyl isothiazol, methyloxazolidine, hexylene glycol, butyl diglycol and isononane acid amide were added and stirred for 30 minutes. Then demineralized water was added and stirred for 30 minutes. Blend was ready to be discharged and for use.

Example 2: Evaluation of the performance.

The composition of the present invention was subjected to various tests to evaluate the performance of the said composition in terms of corrosiveness to iron, copper and aluminum, rust prevention characteristics, anti-wear properties, stability of the cutting fluid in the form of aqueous solution and load bearing capacity as per the known methods. The results are enumerated in table 2 below:

Table 2

Test	Method	Results
pH 5% in distilled water (DW)	pH meter	7.9
Corrosion	IP 125
3% emulsion in 200ppm hard water (HW)		0% staining
5% emulsion in 200ppm HW		0% staining
Corrosion	IP 287
3% emulsion in 200ppm HW		0% staining
5% emulsion in 200ppm HW		0% staining
Reichert Test (5% emulsion in DW)	1.5kg/100metre run	26.3 mm²
Aluminum Corrosion (At 55 °C / 4 hrs)	5% emulsion in 200 ppm hard water	0% staining
Copper Corrosion	At 50°C as it is concentrate sample	0% staining
4 Ball WSD- as it is sample 40kg/RT/1200RPM, 1hr	ASTMD4172	0.601 mm
4 Ball WSD- 5% emulsion in DW 40kg/RT/1200RPM, 1 hr	ASTMD4172	0.663 mm

As evident from the above table, the green cutting fluid of the present invention exhibited excellent properties with regard to corrosion prevention, anti-wear, rust prevention and stability. Further the invented composition has very low mist formation and no sludge in the application thereby translating in to clean environment.

Example 3: Comparative evaluation showing the superior performance of the green cutting fluid of the invention

The superior performance of the present invention over a commercially viable "comparative prior art fluid" is experimentally proved by the following evaluation. This mimicked the actual metal working set up except machining is not done. The performance level of the "comparative prior art fluid" and the green cutting fluid of the present invention has been measured. The following steps were performed.

Step 1: 25 liters each of 5% emulsion of the present Invention and "comparative prior art fluid" were prepared in 400ppm hard water.
Step 2: These emulsions were circulated (300liter/hour) in separate fish tanks for 30 days with temperature being maintained at 45°C.
Step 3: Volume is exactly marked in the fish tanks at the start of the test.
Step 4: After 30 days volumes were measured; sludge quantified and corrosion test
(IP 287) was conducted for day 1 & 30 emulsions.

Details of evaluated parameters are given in the table 3:

Table 3

Properties of present invention - Green cutting fluid versus a Comparative prior art fluid
S.No	Test	Method	Comparative prior art fluid	Cutting fluid of the invention
1	pH 5% in Distilled Water	pH	8.3	7.9
2	Emulsion Stability	IP 263, 20:1/ 40degC/24hrs	0mL 'oil, 0mL' sludge	0mL 'oil, 0mL' sludge
3	Corrosion	IP 125
	3% Emulsion in 200 ppm HW		Pass	Pass
	5% Emulsion in 200 ppm HW		Pass	Pass
4	Corrosion	IP 287
	3% Emulsion in 200 ppm HW		Slight corrosive	Slight corrosive
	5% Emulsion in 200 ppm HW		Pass	Pass
5	Reichert Test 5% Emulsion in DW		28.4 mm²	26.3 mm²
6	Aluminum Corrosion	55 degC/4hrs 5% Emulsion in 200 ppm hard water	Pass	Pass
6	Aluminum Corrosion	55 degC/4hrs 5% Emulsion in 200 ppm hard water	No corrosion	No corrosion
7	Copper Corrosion	At 50°C as it is concentrate sample, ASTM D130	1A	1A
8	Copper Corrosion	5% Emulsion/copper trip/48hrs/ 55degC, ASTM D130	1A	1A
9	4 Ball WSD - As it is sample	ASTM D 4172; 40kg/RT/1200RPM, 1 hr	0.674 mm	0.601 mm
10	4 Ball WSD - 5% emulsion in DW	ASTM D 4172; 20kg/RT/1200RPM, 1 hr	0.650 mm	0.559 mm
11	Circulation test	5% Emulsion, 200ppm hard water, 30 days, 250 litres/hour	Sludge observed	No sludge
		Volume decrease after 30 day circulation	3 litres	1.5 litres

Observations

• Volume in the "comparative prior art fluid" tank was reduced by 20% whereas, in the tank of the present invention water reduction was almost half of that in the prior art tank i.e. by 10%. Conclusion: Low mist generation; Lower the water evaporation means lower is the mist generation (as oil is emulsified) and directly correlates to low oil consumption. Low oil top up is required. During machining process, emulsion evaporates (normal phenomenon) and to top up, water is added with relative amount of cutting fluid. If the emulsion is tight the evaporation gets reduced which translates to low mist generation and thus less water addition and relatively less oil top up is required.
• Moderate sludge is generated in "comparative prior art fluid" tank whereas the present invention tank is free of sludge. Conclusion: Clean work environment; no material loss.
• After 30 days "comparative prior art fluid" showed <5% corrosion area in IP 287 test whereas present invention product clearly passed. Conclusion: Excellent corrosion inhibition.

Conclusion: The green cutting fluid of the present invention is a synergistic composition showing excellent performance which is superior over the state of the art technologies.

Claims

A cutting fluid comprising base oil, emulsifier, corrosion inhibitor, extreme pressure additive (E P additive), water, pH adjuster, couplers, biocides, and defoamer.
The cutting fluid as claimed in claim 1 comprising:
a) base oil in an amount of 30 to 50% by weight;

b) emulsifier in an amount of 5 to 20 % by weight;

c) E P additive in an amount of 5 to 15 % by weight;

d) corrosion inhibitor in an amount of 10 to 15 % by weight;

e) water in an amount of 5 to 15 % by weight;

f) pH adjuster in an amount of 5 to 10% by weight;

g) coupler in an amount of 5 to 10 % by weight;

h) biocide in an amount of < 1 % by weight; and

i) defoamer in an amount of < 1 % by weight of the composition.
The cutting fluid as claimed in claim 1 or claim 2 wherein the base oil is selected from paraffinic oil and naphthenic oil.
The cutting fluid as claimed in any of claims 1 to 3 wherein the emulsifier is selected from sulphonates and ethoxylates, preferably of vegetable origin, more preferably selected from sodium dodecyl sulphonate and oleyl cetyl alcohol ethoxylates.
The cutting fluid as claimed in any preceding claim wherein the corrosion inhibitor is selected from long chain fatty acids and succinic acid derivatives, preferably selected from alkenyl succinic anhydride and tall oil fatty acid.
The cutting fluid as claimed in any preceding claim wherein the E P additive is selected from fatty acid esters and glycol, glycerol and sorbital esters.
The cutting fluid as claimed in claim 6 wherein the E P additive is a ricinoleic acid ester.
The cutting fluid as claimed in any preceding claim wherein the pH adjuster is potassium hydroxide solution.
The cutting fluid as claimed in any preceding claim wherein the pH is 8 or less.
The cutting fluid as claimed in any preceding claim wherein the coupler is selected from hexylene glycol, glycol ethers and butyl diglycol.
The cutting fluid as claimed in any preceding claim wherein the biocide is selected from isothiazol derivatives and methyl oxazolidine.
The cutting fluid as claimed in any preceding claim wherein the defoamer is isononane acid amide.
A metal-working process in which a metal is contacted with a tool in the presence of a cutting fluid whereby heat generated by friction between the tool and the metal is absorbed by the cutting fluid and/or friction is reduced, wherein the cutting fluid is a fluid according to any preceding claim.
A process as claimed in claim 13 wherein the working of more than one metal is carried out, said metal comprising any or all of aluminium, iron, steel and copper.
A process as claimed in claim 13 or 14 wherein the cutting fluid is collected after use and re-circulated at least in part into the process.