Loading

Module 1: Multipoint Machining Processes

Notes
Study Reminders
Support
Text Version

Rheology and Thermal Characterization of Cutting Fluids

Set your study reminders

We will email you at these times to remind you to study.
  • Monday

    -

    7am

    +

    Tuesday

    -

    7am

    +

    Wednesday

    -

    7am

    +

    Thursday

    -

    7am

    +

    Friday

    -

    7am

    +

    Saturday

    -

    7am

    +

    Sunday

    -

    7am

    +

Video 1: Introduction to RheologyTill now we have seen the ah various cutting fluids in the previous class. So, now, wehave to study about their one of the important characteristics that are rheological characteristics,as well as thermal characteristics of this various cutting fluids. Among the cuttingfluids that we have seen we are most interested towards 2 cutting fluids; one is the mineraloil cutting fluid, another one is a bio cutting fluid.So, the mineral oil place a datum where it is as a reference and how we can improve inthe bio cutting fluid that we will see from the point of rheological characteristics,that is a flow and deformation size as well as thermal characteristics.Till now what we have seen in the previous classes is advantages of Eco-friendly cuttingfluids and ah like vegetable oil based cutting fluid over the mineral oil based cutting fluids.We have also seen the machining performance comparison of vegetable oils, cutting fluidversus the mineral oil ok; that means, we have seen the performance of a metal cuttingfrom the point of biological cutting fluid, from the point of mineral oil also. How toimprove performance of eco-friendly cutting fluids? Just in order to increase the performanceof existing bio cutting fluids, if the performance is approximately similar as since we are workingin this area and we have to improve. So, the research somebody is taking up inthis ah area what they have to do they have to continuously strive hard to improve theperformance, improve the rheological performance, improve the thermal performance of that particularfluid, how to do that we will see? So, overview of this lecture we will see aboutthe rheological characterization of cutting fluid coming to the first one that is a introductionto rheological various flows of the fluid various rheological characterization, andthe measurement techniques followed by the flow studies of cutting fluid, that is a concentriccylinder as well as a parallel plate and all those things we will see, then activationenergy and all those things we will see from the point of rheological characterization.Then we go to the thermal characterization of the cutting fluids, thermogravimetric analysiswe will see then followed by thermal conductivity and followed by the specific heat of the emulsions.What is the emulsion and all those things you have seen it, but we will see what isthe optimum emulsion for ah better thermal properties and all those things we will see?The rheological characteristics of the fluids rheological characteristics is the most important,because if at all I want to study the flow properties of that one because cutting fluidhas to penetrate or it has to flow into the cutting region. So, that is the main function,if it cannot flow nooks and corners of the complex machining region it cannot extract.So, the first and foremost thing that it should possess from the cutting fluid point of viewis the rheological properties it can enter then the thermal properties can extract theheat that is generated in the machining . So, that is why we have divided into 2 sectors1 is rheology let it enter into the machining zone then thermal properties. So, that itcan extract that is why these 2 play a major role in the machining arena for cutting fluids.So, introduction to rheology as you all see the fluid flow in this particular picture;how the fluid is flowing and how the wave is taking place and all those thing thesetype of things? Whenever you ah shake your glass with water and all those things if itis a transparent glass and all those things that you can also observe this one, at thesame time if you see the rheology normally Rheo means the flow logos means the scienceand ology means the study. Basically the rheology is nothing thing, butthe science of flow deformation. The science of flow deformation is nothing, but for thefluids you are ah studying up the flow for the solids or semi-solid you study about thedeformation for the semi solids you can also study the flow properties. So, that is nothing,but the rheology. So, if at all I want to see the flow characteristics as well as deformationcharacteristics of any particular fluids, whether it is a semi solid or a liquid 1 hasto do the rheological characterization. If you see the rheology of the fluids thefluid behaviors normally it can be divided into 2; 1 is Newtonian as well as non-Newtonianfluid Newtonian fluid normally it will have a proportionally increment with respect toshear rate the shear stress will be proportional increase with shear rate, but ah it will notin terms of non-Newtonian fluids the non-Newtonian fluids most of the fluids are non-Newtonianfluids. That is why the non-Newtonian fluids again divided into 2 sectors that is timedependent and time independent. In the time dependent if you see again there are 2 thingswhat is thixotropic and rheopectic, in the time independent again it will divide into2 things one is pseudo plastic as well as dilatant. Normally we study mostly about thetime independent one that is called shear thining fluids shear thickening fluids andall those things in the upcoming slides. So, the rheology particularly about this cuttingfluids helps in proper mixing, as well as proper flow and deformation, whenever theintricate, complex regions of chip tool interface or work piece flank surfaces comes into picture.So, this is the beauty about the rheology. So, introduction to rheology we are continuingnormally if you see Issac arise at Newton ah 1643 to 1727. So, he published the scientificbook called principia and where if you see in the 19th century scientist discovered thesolids with liquid like responses and liquids with solid like responses these are the changesthat one can see. For example, if you see take the water if you go to the freezing temperaturebasically it will convert into solid. At the same time the deformation characteristicsof this when it is solid when it is a liquid is completely different, that is what to onewant to say. At the same time today the rheology is an integral part of the industry, basicallyif you take any industry; like pharmaceutical industry or any other industry. It is forexample, if you see the plastics or paints, you have how to spread the paint accordingto your wish, if the paint is not spreading as per your wish and it is the delaminatingthen there is no requirement or if you are facing a lot of problem you take a brush andyou take you just deep into the paint bucket and then you just put on the wall assume thatit is very difficult. Because the energy required to paint on the wall is very high; that means,that you do not prefer the type of thing, why because you need better flow ability onthe wall at the same time it has to spread easily on the wall and your energy consumptionshould be very less. So, you need to study the flow characteristicsof this paint. For example, if you see the pharmaceutical industry mostly the fairnesscreams everybody want to become a beautiful person or something. So, lot of creams arethere. So, whenever a person want to apply the cream on their face what will happen youhave to apply at uniformly, the cream has to deform uniformly it has to flow uniformly,because it is a semi solid normally this a ah semi solid complex suspension. So, hasto flow deform and uniformly spread and the look of particular person, whether it is amale or a female does not matter that is ah it appearance should be beautiful or a handsome.That is why always rheology play major role in the pharmaceutical industry also like bioinks and inks also there. Now, a day's people are talking about 3 dprinting people talk about 3 d bio printing. So, you have to deform or you want to flowthe ink along with the cells properly, otherwise you cannot make a complex surface. Similarlythe cutting fluids also are one type of the suspensions because people now a days aretalking about Nano fluids and other things if you take the Nano fluid that is what youhave seen in the previous classes, these are the cutting fluids or the emulsions with Nanoparticles ok. So, this also resemble similar to your paint or your pharmaceutical creamsand all those things, but with low viscosity that is why it is more important to studyabout the cutting fluids from the point of rheology.Categories of flow and deformation there are 2 categories one is Newtonian fluid and non-Newtonianfluid that we have seen already the Newtonian fluid the higher the viscosity of the liquidthe greater the force per unit area is required, that is shear stress required is very high;that means, you always should put the less energy as a customer.So, ah if you see the non-Newtonian for the liquids tau equal to n to gamma are some peoplethey say n Newtonian viscosity into gamma dot. So, tau stands for shear stress betsstands for viscosity and gamma stands for shear rate. So, people also say ah that theseare the gamma or gamma dots some of the books, if you are following about the ah basic rheologybooks ah if you see there some people give the gamma dot also. So, gamma or d comma dotplease considered as a ah shear rate shear rate indirectly ah means the full name forthis one is shear strain rate for the ah liquids this is a equation, which you may ah see inthe fluid mechanics also. For the ah solids and other things this isa equation shear stress is nothing, but you are e into e epsilon. So, ah since we aretalking about the ah liquids we are more worried about our cutting fluid, that is why we alwaysthink about the shear stress equal to the viscosity multiplied by the shear strain rateit can be grammar or gamma dot. The Newtonian and non-Newtonian fluid as perthe continued mechanics is considered the Newtonian fluid is a fluid in which the viscoustraces arising from it is flow at every point are linearly proportional to it is local strainrate that mean that, the stresses are linearly proportional to the local strains in the non-Newtonianfluid it is not. So, so if it the fluid is not following this ah Newtonian principalif the fluids are not following the ah the fluids which are not Newtonian fluids areall not Newtonian fluids.
Video 2: ViscosityThe viscosity is nothing, but theresistance to flow of the cutting fluid, if you see here in this particular picture theviscosity is low here and the viscosity is high here. For the same inclination or somethingwhatever is given the flow rate that is falling from the test tube is gradually increasingfrom this to this that is why the ah viscosity is gradually increasing.So, if you see here the inclination is same, but the thing is that of fluid inside thetest tubes is different ok. So, if you see here the liquid is different if you see issecond one the liquid is different as you move here, it is clearly you can see it isa semi solid. Here the semi-solid similar semi solid is there, but deformation is thereok. So, the viscosity is increasing if the viscosity is increasing. For example, fromthe cutting fluids itself we can say that grease is one type of lubricant and mineraloil is one type of lubricant the mineral oil has a low viscosity, but the grease whateveryou use for your applications that is nothing, but high viscosity lubricant.So, viscosity characteristics that it changes with respect to temperature most of the cuttingfluids will change with respective temperature. As the temperature goes into the cutting fluidwhat will happen the ah molecules gain the energy this is called as a thermal energyand it try to move apart. That is why always the cutting fluid fumes whatever you haveseen which is going to the operator nose and all those things these are because, it gainsa energy and move apart and distance between 2 molecules will gradually increase and theforce of attraction between those 2 molecules as a distance increases will goes down. Thatis why mostly the cutting fluids viscosity will decrease with respect to temperaturethis cutting fluid significantly reduces when the temperature increases that is what I said.So, the temperature as it increases inter molecular distance of this molecules willincrease. So, inter molecular force of attraction willdecrease that is why the liquid will become gas and it force various methods to test theviscosity. So, simple test in the previous olden ageare whenever the standard reo meters are not there the people used to use trowel test,that is called just to take the ah viscosity of the high viscosity of the fluids thickand they say low viscosity of the fluids as a thin fluids for the dispersion just thetake a ah strip wooden strip or metallic strip and just they put into the liquid or semi-solidand just they take out and they say depend on the visibility test they can say that,whether it is a thin or whether it is a thick fluid.But only thing you have to observe here is it is a qualitative statement there is noquantity, whether it is viscosity is x or y you cannot say you can say only this isthick fluid this is a thin fluid you hope you understand what is the difference betweena qualitative statement and a quantitative statement? The qualitative statement goesby like this Ramu is a good boy that is a qualitative statement Ramu is 80 percent goodboy is a quantitative statement ok. So, if you are quantifying by particular valuethat is nothing, but quantitative value here the people can say whether it is a thick orthin, but they cannot say the viscosity is this much or viscosity is this much quantitativevalue they cannot say. The second one is finger test take this one and just move on or movea part both thumb and index finger. So, you can feel the ah tacky which is nothing, butthe long less tacky then it is short for example, paints and offset printing inks and pigmentpastes these are all done. Normally by the finger test in olden daysnow a days everything is ah used to by the commercial rio meters to test the rheology,but these are the old test ok again this is also the qualitative statement only one cangive ok. These people during our childhood be might have also played with our bubblegum after chewing sometime sometime just take like this and like this so, but do not dothat people might have done. In fact, I have done it at childhood sinceour childhood we do not have very good exposure to the bubble gums or whenever we get we usedto make bubbles and all those things, but particularly from the health point of viewdo not make the bubbles or do not going fit into your fingers and the just expand, thenafter that you just put into your mouth and chew again do not do all this things, becausebacteria or the microorganisms, which are in the atmospheric conditions will easilystick on the bubble gum if it comes out like you just blow the bubble and it will blastand again you take inside. So, organisms will come and it will go into your intestine andcauses lot of problems. So, that is a practical point of you, butah from the course point of you this you can do ah by the finger test anyhow, I want toconvey that these 2 techniques are the qualitative techniques, but not quantitative techniques.To standard viscosity measurement, if you see there are oscillation viscometer theseare the second versions or the primary versions for the quantitative measurement, vibrationalviscometer and there are called falling piston viscometer there are ah this is a third oneand the fourth one is rotational viscometer, which nowadays mostly people uses it the advancedversion and falling sphere viscometer there are different, different types of there andamong these rotational is very common. If you see the rotational viscometer or ahthe standard viscometer what currently what we are using at our laboratory to test therheological properties of the fluids is Anton Paar MCR ah 1 0 2, and we can also use AntonPaar series that is a Anton Paar is a company which produces the rheometers just do nottake in other way that I am advertising or something, there is a t a instruments alsoproduces this viscometers. So, many companies are there who produces this for instance whatI am showing in this picture is Anton Paar rheometer this is the schematic view of theah rheometer this one is the schematic view of the ah rheometer.This is the fixed bottom this is this one is a fixed bottom one and this is the rotatingplate 2 and in between there is a medium this is called 3. And the the bottom one havingtemperature increment or decrement options also, because some of the cutting fluids orsome of the fluid that one want to check may be interested to check at higher temperaturesalso. So, for that purpose there is a ah temperatureah increment and decrement options and you give the rotation to the top plate by keepingthe bottom plate constant that is about the shears strain rate, if at all I as I alreadysaid that my bottom plate is there my top plate is there in between I am having my samplenot this it has to cover the complete space of the top plate, because the top plate issmaller one compared to the bottom plate that is why always it should occupy the circleor if you go to concentric cylinders it has to fill upto certain point what do you dois you just give rotation to the top plate, but bottom plate is fixed that is about therheology that you do. If you see this one the second picture showsthe ah commercial rheometer this is a head that is a movable head and this is the bottomyou can see here, but we are not using the same cutting fluid here to explain the rheometeror the rheology physics we are using a semi solid in this particular.So, this is the tool master which is a small and this is the fixed bottom plate and inbetween you have a sample this is the sample ok. So, of you give the rotational speed tothe ah top plate that is this one. So, that it will rotate and this is a fixed bottomend and will assist for keeping your sample. So, this is how the ah experiment will takesplace, but this is for the semi solids and all those things normally you will use theparallel plate rheometer, but if at all somebody want to do the radiology of the liquid normallyplan parallel plate is not used. Whatever we have shown in this particular slide isto explain you how the physics of the rheometer goes on? That is what we want to say for thatpurpose easily understanding is by the parallel plate rheometer ok.The same thing we can extend to the concentric cylinders in the current viscosity measureusing rotational viscometers whatever we have done at our laboratory for explaining you,the materials which we have taken in this particular conditions are 2; one is Bio-cuttingfluid, another one is commercial mineral oils. As I said this is a liquid or a liquid emulsion,because you have to mix with water and also things you cannot use a parallel plate rheometry,because it may splash out when the you give the shear rate and all those things for thatpurpose we have to move to some of the advanced tool masters that is ah one of them is concentriccylinders. If you see here in this picture you have aah concentric cylinders, where the cutting fluid is filled beyond the tool master thetool master looks like this. This is the tool master and ah you have a hollow at the bottom.So, just you go and put here and so, that it should cover completely then you give theshear rate; that means, that you give rotation to the tool master. So, you can calculatethe viscosity. How the viscosity will be calculated. Normallyif you see the figure one this figure one what will happen there will be a torsionalsensor will be there on the top, assume that you have given certain RPM assume 15 RPM or20 RPM it has to rotate at that particular RPM at the air.Whenever you are putting a certain liquid in it what will happen it cannot rotate whateverthe given RPM, for that purpose it need because it is resisted by the fluids viscosity forthat if at all I want to rotate at the given RPM it has to put extra torque to rotate.That extra torque it has a internal software to calculate and it will you in terms of theviscosity shear stress and also those things, that is how probably this type of rheometersare working. Shear stress if you see the shear stress ahversus shear rate in for the mineral oil as well as bio cutting fluid, the ah shear stressrequired for the bio cutting fluid is higher compared to the shear stress required forthe mineral oil based cutting fluids. Normally it required around 55 ok and this requiresabout ah 120 or something ok 120 Pascal and this is 55 around 55 Pascal at a 20 degrees.What it shows it shows that bio cutting fluid is much viscous compared to your mineral oilok. So, in order to improve the viscosity youhave to play with respect to the water, water is a Newtonian fluid if you put it what willhappen the viscosity will come down. So, how much water you have to put to make the emulsionthat, you have to see and check with respect to thermal properties and then you have tocome back to the rheological properties. Striking balance between thermal properties and therheological properties from this particular point of you flow ability of mineral oil isbetter compared to the bio cutting fluid. However if you see from the other point thelubricating characteristics of the bio cutting fluid is much better than this one, becausethe viscosity is very high means the lubricating characteristics is very high, probably thesecond one is shear rate verses shear stress at at 100 degrees .So, at room temperature or this is at room temperature or 20 degrees temperature approximatelywe are seeing, if you see both the fluids both the fluids are following the Newtonianrent ok. So, what will happen this cutting fluids wheneverit is exposed to the machining conditions, like with respect to shear rate; that means,that shear stress verses shear rate at 100 degrees it is not following the Newtonianrent like gradual straight line increment like the figure 1 . It is not going like astraight line one it is going like a non-Newtonian fluid that is called shear thickening fluid,but at particular temperature. So, I am not talking about the temperaturevariation at his particular moment, but I am talking about the shear rate variationwith respect to shears stress the shear rate is increasing at 100 degrees temperature theshear stress is gradually increasing, because at elaborator temperatures whatever the volatilethings are gone and it is increases it is thickness or it increases it is thixotropy,it becomes some thickly liquids that is why at higher temperatures the viscosity graduallyincreases; that means, it follows the ah shear thickening fluids.
Video 3: Thermal Characterization of Cutting FluidsNow, we move on to the thermal characterization.Here we will see the thermal conductivity and specific heat about the emulsions andall those things, thermal gravimetric analysis of the cutting fluid, if you see TGA is amethod of thermal analysis, which changes the physical and chemical properties of materials,measured the function of increasing with respect to temperature.Whenever you have certain cutting fluid you just put this cutting fluid and change withrespect to temperature and measure the mass as well as you can also measure what are thegases that is availing out. If you see here with respect to temperature the mineral oilstarted changing with respect to as soon as the temperature is increasing the red oneis starting to change, but if you see the bio cutting fluid there is no change up tothis particular portion; that means, that it is still stable at that particular rangeof temperature like up to 120 130 degrees there is no change. If you see the table columnhere up to 100 degrees there is no change in BCF that is 0 and, but the mineral oilhas already consumed or it is gone about ah 11 to 13 percent or a 10 9 to 13 percent.If you see up to 4 hundred degrees temperature what is happening 79 plus or minus 3 percentis gone, but various other thing is maximum of 88 percentage is gone receive 550 degreesapproximately both are same; that means, the degradation with respect to temperature havingbetter from the bio cutting fluids compared to the mineral oil.So, now we have to check which is having the good thermal properties for that purpose whatwe have done here is the emulsions are mixed from 2 to 20 a percent of the that is oneis to 2 to 1 is to 20. So, 1 litre of cutting fluid to the 2 litres of water ranging fromthat to 1 is 1 litre of cutting fluid to 20 litres of cutting fluid. Now my major ambitionfor this particular slide is what amount of water that I can add to the cutting fluidis the question mark. For that purpose we have used k d 2 pro thermal properties analyzerwhich will give the thermal conductivity of the cutting fluid as well as the specificheat. Thermal conductivity of the lubricants normallymineral oil if you see mineral oil thermal conductivity of the mineral oil is 0.126,but the bio cutting fluid is 0.151. However water is very high. So, now, how muchwater one has to add for making the emulsion with respect to the water increment what willhappen; obviously, the thermal conductivity will increase, because 0.6 is going to sithere and 0.15 or it is going to sit on 0.121 it is going to increase. That is why the thermalconductivity of the emulsion gradually increases, but it reaches to a optimum value at 1 isto 8 after 1 is to 8 the thermal conductivity of the cutting fluid is approximately sameso; that means, that from this particular experiment one can say; if you go for oneis to 8 you have optimal thermal conductivity plus since 1 litre of cutting fluid is mixingwith 8 litres of water compared to other one assume that I am going to take 1 is to 20here 1 is to 8 here 1 is to 20 here the water content is very high.