Modern Steel Products (2014) - Rolling of Steel: lecture 10

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Modern Steel Products (2014) - Rolling of Steel: lecture 10
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10 (2014)
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Professor de Cooman talks about the hot and cold rolling of steel. This is a part of a course of lectures given at the Graduate Institute of Ferrous Technology, POSTECH, Republic of Korea.
Keywords The Graduate Institute of Ferrous Technology (GIFT)
Ship breaking Friction Tin can Lugger Hot working Steel Hot working Machining Machine Scouting Ammunition Surface mining Cartridge (firearms) Tram Rolling (metalworking) Rutschung Plane (tool) Surface mining Hose coupling Flatcar Friction Sheet metal Flatcar
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Fiat 500 (2007) Steel Steel Rolling (metalworking) Volumetric flow rate Surface mining Lader <Verdichter> Screw Material Material
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Friction Lader <Verdichter> Fiat 500 (2007) Semi-finished casting products Hot working Gas compressor Angle of attack Surface mining Rolling (metalworking) Remotely operated underwater vehicle Surface mining Material Mail (armour) Strapping Friction
Friction Fiat 500 (2007) Roots-type supercharger Lugger Volumetric flow rate Surface mining Rolling (metalworking) Surface mining Goldsmith Material Gas compressor
Friction Widerstandsschweißen Semi-finished casting products Steel Mechanical fan Hot working Steel Gemstone Food packaging Barque Gas compressor Roots-type supercharger Angle of attack Sonic boom Volumetric flow rate Rolling (metalworking) Surface mining Rolling (metalworking) Surface mining Goldsmith Material Mail (armour) Friction
Friction Nut (hardware) Hot working Tiefgang Kickstand Angle of attack Volumetric flow rate Alcohol proof Commodore MAX Machine Slip (ceramics) Surface mining Tagesschacht Material Mail (armour) Steel Tiefgang Kickstand Gas compressor Seeschiff Titan Saturn System Mission Volumetric flow rate Rolling (metalworking) Surface mining Cartridge (firearms) Engine Firearm
Kickstand Steel Kickstand Automatic watch Hue Clothing sizes Spant Sizing Surface mining Gentleman Rolling (metalworking) Gate valve Book cover Material Rail transport operations Material Mail (armour) Sheet metal
Steel Hot working Noah's Ark Roll forming Gentleman Rolling (metalworking) Rutschung Book cover Surface mining Sangorski & Sutcliffe Guard rail Material Mail (armour) Cylinder block Engine displacement Snips Tin can Steel Kickstand Gas compressor Ammunition Saw Rolling (metalworking) Surface mining Remotely operated underwater vehicle Material Ship of the line
Ammunition Lugger Surface mining Gemstone Rolling (metalworking) Slip (ceramics) Remotely operated underwater vehicle
right there are 2 general
thinks today about rolling being hot strip mill city cultural analysis some general principles in Riyadh will assume you're aware of when when we start talking about products and how they're being made in practice turned its or L just talk about
playing strained information and flat rolling see few things you can calculate things again 1 go into theory much at all and so on 1 of the things all emphasize this set in many of the year and metalworking processes that are used in the steel industry the friction is very important friction is important and 2 of them and then will also see how and how we go about to keep the dimensions of products constant In the case of common stretch were basically talking about the thickness how that being dumped in in rolling mill but it applies to all the time categories of products where it were you concerned about the dimensions of products Chris again here and you know what of when you GFT student or tuned in materials science you concentrate on the science that well when you produce the new Europe producing things you have to make sure that the dimensions of the problem correct and so on and you know in steel products of these dimensional requirements can be very very high so control of the gage control of the flatness of stripped for but is extremely important control of profile of district is extremely important in practice and if you of end up in the industry will actually see that these things are much more important than the physical melody I you've been dealing with um as a student at so let's have a few things general things considerations relation to metal forming so metal forming breaks are typically 10 to the minus I want to tend to 1st In your slides for some reason it's it's 10 to the minus 12 but there you should teach changes in which there are very very low strain rates that are of importance for materials science a for steel products for instance in creep strain rates are very low but here we're talking about metal forming and so on but the rates their attention minus 110 vest and so I think it's a slow leak extrusions for instance about the extent of 2nd the tent 1st 2nd and 4th fast machine it can go up to a very high values India temperatures we usually talk about cold defamation hot deformation a hot working and also this intermediate term of warm working His Gold wrote working as His room-temperature hot working is above the temperature of free crystallization and warm working his right below the temperature of Rick crystallization extrusions temperature can be much higher and the strains In as plastic strains in metalworking are of course very large plastic strains are in comparison so this is In a general overview here it's just concentrate on a couple of months 2
elements which have interest today cold rolling cold working such as rolling Fork forging and in hot were working rolling and forging are done in these temperature ranges of the definition of strain rate this is given here yes when you roll something you have starting thickness and thickness and if you have a contact area and a strip velocity right and so if you put these data points this the state of values into this equation distress with stewardess strained right who so In both in cold rolling and the hot rolling the amounts of strains you can give our are about similar workers and the strain ranges typically set about 10 per cent at most 50 per cent of cases so that's the range of the air there is a a big difference in the the strain rates however so the strain rates tend to be higher in cold rolling then in hot rolling will see that depends very much on the wherein the processes were looking product velocities themselves are much higher cold rolling down and and hopefully so that the stripped velocity at the end of the hot cold rolling process can be 100 meters seconds very high comparison 30 meters per 2nd in the hot milk and of course the yes essentially very different in hot rolling weird above I do not have the melting temperature in Calvin and a we carry out in the cold working without addition of heat but it doesn't mean that there is no heated and remember that at any time you do form steel the indeed the energy you put is converted to heat 90 per cent of it gets converted to heat the rest of the energy is stored in the material under the form of dislocations so but so if you do it defamation very quickly at low temperatures as the temperature rise yes included temperature rises because of that there is no time for the the heat to dissipate right so if you continue deforming the heated that can be considerable so never touch which you hand a "quotation mark cold rolled steel cord you will you will you'll hurt yourself that's because it's very hot yes even tho it's been cold-rolled did the heat from defamation what is that hasn't had the time to dissipate so you have Egypt batik heated Close to idiomatic heating and so you your coiled it's very very hot OK now I why don't we hopped roll everything why don't we call the roll everything well we good reasons for their cold rolling usually Donald higher quality you get much greater precision yes In your products yes and also much better surface finish in Europe than in hot or warm only years very high velocities as I said and the reductions the smaller units of that strain rates of our high that's so you cannot replace him cold rolling by hot rolling just like that sometimes you will hear people give presentations about all but now we don't have to do you don't need cold rolling mills and more we can do everything by direct casting and then 1 1 Mills stand in there we have a product you may have a product that you have a product of very low quality yes in particular very low dimensional quality and very low surface quality yes and if many applications where that means that for instance thin strip direct casting technologies you know have a long way to go before they can reach the quality of cold-rolled materials from just focusing on the cost of making a product this is not the it's is not the end the good approach hot trolling we can do larger reductions because we have lowered the forces material softer basically we have no Francis's deals are typically during the hot rolling use you start to temperatures at 1250 and then you pass to a number of rolling passes they can be very they can be high that information can be high again you can do this because the material is much softer than and and forging is comparable to hot rolling in terms of temperatures and the formation but the defamation In wire drawing and just want to to mention this again but that this is a cold-rolled process but because you have so much adiabatic to very high strain rates and you have very high frictional thank you very high friction between the dying and the material that should afford the temperature is raised rice can be very high has so about a 3rd of the melting temperature and Calif and in very high strain rates as I said so it's important when we make steel wire so again where is the line between hot the and and Coldwell what's the hot mean in the hot strip mill while carbon steel re crystallizes at the about half the melting temperature and Calvin so that corresponds to the 630 degrees C it's a good temperature to remember if you're still expert because at that temperature still worry crystallize it will not request lies at 500 deg you can wait for a very long time and it will not this there will be recovery a rearrangement of the dislocation structure but you'll have to go beyond 630 650 to get rid crystallization so new the grains are by dislocation free soaked in hot working week add energy in the form of heat yes and we deformed steel in the rechristened re crystallization temperature so the material deform the material it will request a loss like that at its at the temperature will do a defamation in cold working we do not add to thermal energy but material can heat up yes as I just said and still does not request or is that just as show you picture of
what this means in hot rolling you start with Austin migraines are they get pancaked as you roll yes In between defamation steps the material re crystallizes there may be a grain refinement yes this there is usually a grain refinement and then you roll again and the material is pancaked again and we crystallizes almost immediately in the cold rolling you you have you France's far-right brains you pancake done nothing happens during the stands and then when you roll again it's you accumulate striding in all the what's that's an important thing so we say we've we've said that a cold rolling you have your Nova crystallization of hot rolling we have we crystallization now what about the mechanical properties the mechanical properties we usually got the assist the cold rolling as at room temperature temperatures may rise to about 200 degrees C no I on the higher end in the in the hot rolling we do the deformation of the range typically of 900 to 1200 degrees so around a thousand degrees in that range for most of the steals that we use are Boston because then you can see what the flow the stresses distress at there's been this case about 20 per cent of the formation but you can see that but we typically in the range 100 to 200 the maker of Tosca so that is some OK this soft police are so you can see here at the uh few stress-strain curves of the same still at relatively high strain rates strain rates that are higher than the ones you will use a new laboratory tests from the 10 per 2nd and you see that at the thousand degrees so that at spoke on this end of the temperature range this is distressed so you can see that the yield strength is less than 100 years and it doesn't get much higher than 120 this year is very soft however of course as you hot roll it the temperature of history or decreases and distress this is the strength of the material increases also but the amount of increases the risk is small yes hundreds 20 as field strength and tensile strength can reach the 250 at that the you large deformations OK so 100 to 200 megabytes is typically the strength of your material and as I decrease the temperature for instance it's at 700 deg C and material is now for Riddick yes but I have also 300 a makeup Oscar about so even in the Riddick out state at 700 deg C and you I still have a pretty soft material so the it not the court when it interesting questions user what's hard enough variety also tonight at the same temperature in general With low-carbon steels you never have Austinite and far-right at the same temperature in most of you can see this here in the diagram this is the line the flow stressed and any depth as you go through the transformation and increases again OK so this suggested that far-right groups variety is softer than Austinite at the same temperature and that's indeed the case and and I can show this to you as follows take for instance
I cannot make some stainless steels this makes some stainless steels and I can I attended the deformed yes for instance and in portion test should test is heated to 100 carry out this task not a test where you need utensil the defamation which you do but torsion debts and you can see the sample is In the induction course you can heat up at a certain temperature so this is isn't high temperature at 1200 deg C and this is the stress-strain curve for far-right and Austinite with about the same composition at the same temperature again you cannot do this with a low-carbon steel because it's low-carbon steel it's of far-right or its Austin and you can see that the US knives very much stronger then the you can also be friends in this particular Steelers at 1200 it's only 40 mega Pascal and strength in the Austinite is the 140 which is also very small yeah yeah this is a similar
example but this is not data taken from a plant when we measure the don't know the rolling forces and from the rolling forces we can determine of flow stresses Of the material as a function of temperature during the rolling and I we look at the data that's the rolling forces yeah flows trying to determine from these rolling forces for for erratic stainless steels 409 and for Austin stainless-steel and you can see they difference you the Florida grades are softer then the Austin integrates at the same temperature and not and not a little bit again you can see here a forensic trade at around the evil what is that there 11 102 around 50 megabytes of varies from yeah but there what when you
when you you visit the hot strip mill you know you have this very heavy equipment at its it's very happy just because the slabs are very heavy not because the the material is intrinsically very hard to work exactly very soft and and so it can also easily be the deformed hands and damaged case you you are you have to make sure that the roles that role the on the surface are we placed constantly yes also so that you always have nice surfaces yes and you don't damage due the product quality right let's go into this rolling and out in order to introduce this what do we do when we're all things well but we we do something that's a little bit similar to that of of a simple forging so it's a win-win look at this at 1st here we have a 2 flat dies yes and we press a piece of steel in between so what what will happen with this deal is here the middle part will not move go anywhere the part of this part here will gradually move to the left and this 1 will move to the right side of you may have done the experiment yourself so what happens I deformed the material and there is slept a less so and so anytime you have slipped relative motion of this surface doesn't move and this service will build the French president and that's it is also what happens in the In the role gap in the role gap we have apart I think that moves toward entry of them the role gap and a part of steel that moves toward the exits of devoted just like him yet and there is a point at which we call the neutral point where the district doesn't move left or right it moves with the roles surface yes that's which we called a neutral .period depends very very similar to that in the case of forging new to this spot here this direction and this part moves in this direction In terms of the surface right don't
tell so let's have we will use the very many interesting things happening to to the rolled right there in the role so we have a pressure the roles exerted pressure on the district we have yes roll by angle which we call Alpha we have our Neutral point and we have the frictional forces that were in opposite direction on the left and on the right of this neutral .period so the frictional forces the frictional forces of the role on this stretch is in this direction that's because the strip moves backward and the frictional forces that the role exerts on the strip rules In this was moved forward with Our frictional force of the role on the stretch are oriented to the the laughed because the strict moves faster than the role of his right hand side all right look at so if you look at the surface and the strip center the deformation is different In this strip center Umatilla gets basically squashed the squashed and it becomes longer and it goes through a plane what we call a plane strain defamation the plane strain means there is no the formation in the direction perpendicular to my picture here but that the surface the material gets sheared Is this good undergoes shear deformation took the strip surface and that this is the surface here this trip surface moves backwards but before the neutral point and then it moves forward In Texas In the past the neutral point so In hot rolled products this is not very important this sharing of the surface because that gives information the formation of dislocations dislocations that drive the disagrees Nancy Drive the week slight station so it's pretty much washed away but in cold-rolled products yes you get the same phenomena and so the texture development at the surface can be very different from 2 textured development In the material inside so always be very careful when you measure you make texture measurements yes if the texture measurements come from the surface and they will be influenced by this deformation content and that's why I usually if you want to buy I want to get correct texture former information on U.S. Steel's you should remove yes we move this surface layers which has gone through the Sheri alternatively of course you know you may want to study this in this layer here now OK
so you're probably familiar with what I've just said from the you from mechanics or a materials science undergraduate classes this there's lots more complexity to 2 rolling in practice for instance L always have stripped tension there's tension to be tension for word on the street and tensions backwards very often in this tension is natural the result of the process Prince if you have a attended mail the strip has to leave 1 of stands and going to the next step is very often that results in tension In distress again will talk about this in more detail later wrong at the entrance and the that there are elastic the last thing the disturbances outside the gap where for instance when the roads and you can easily understood when when the stress comes out of the it said the role gap it will rebound elastically but that's the kind of disturbances were talking about V role you know when we say In the yet the role has a diameter of say 370 mm what we actually have it we are saying is this is that's the the role diameter in they're not mounted not Inc service in service will you do actually rolling the ball surface is flattened yes it is clear and the Rangers can be much larger then the radius of your role In this so there is an elastic deformation of the role surface which causes a very tremendous flattening of the surface the other thing is right and we we have /slash so the distraught moves which is good but not much rested a few per cent faster than the role surface at the thank you you can already see that this will complicate matters as in the rolling process now we would just stay saying that 1 of the there Due to rolling it's plane strain defamation yes that there is no defamation perpendicular to the plane of rolling is that true what is the pants if you do very large amounts of thickness reductions yes you will get a widening of the strip the strip will get wider use of friends this is the side view of the role have topped with those of the other 2 were crossing the street With entry and exit thickness the West can also change this and the amount of change is a function of the amount of reduction you give to the Delta W. The with change increases with the thickness changes that you might and you can see here that the larger you make your thickness of change the larger the wits change can be so I'm very important not to to do excessively large changes In into thickness In 1 step and it can only not only lead to L with changes of distant but it can also lead to edge cracking which corrects In case let's now have a look at the the context of the but the rolling process rehearsed that so so when you role and materials in the role so did that gap here's how pressure this the pressure that's exerted Binder role yes this pressure
here it is a function of position yes varies as a function of position Texas and this is what theory tells us what it looks like the pressure has looks like this is busily looks like a hunk of hump-shaped curve that goes down up and no the and this role pressure variation can be divided in 2 the To segments yes the disagreeing segment this and this blue segments in and the surface of the Greens segment that is related to the force needed to do the plastic deformation whereas the blue segment yes if the is related to the forest required to overcome frictional forces yes that's really energy that spending for nothing right not 4 to deform the material I I don't think so this is simple case if we want to have an idea of what the role pressure is as what we will do what do you elementary theories do as we say Well 1st of all we'll will consider this there contact length here yes this will consider this a straight line in will consider this very much a straight line so we can say that the contact claimed the square root of the radius of the role times the difference and thickness and square root of our times Delta age if an equation which gives me the mean value Of this pressure so the mean value of depression instead of the pressure variation it is the mean value and I multiplied this with did Wang said of the contact and do this help and the weather of the mail yes then that'll give me an idea of the rolling low notes pocket so let's see that's 1 thing the order of point that D theory tells us the condition for engagement in the role by why is this important it's whenever you start rolling U.S. District has to enter the rollback yes no the condition for this very much related to the the fracture because this condition is very simply put the frictional coefficient coefficient of friction should be equal to Tangent alfalfa were Alpha is the opening on goal for did contact area so what does it mean for as if if I don't have friction yes the attention of elsewhere will be of his allotted and 0 yes and so there will not be engagement what does it mean if you have a very very very but extremely low 0 friction roles you will not even be able to start rolling right so that makes sense but it's a general formula here that's your friction should be large enough to start rolling there is another thing that illustrates the importance the thing that illustrates the importance of friction of the 1st act 1st was the friction helped the the 2nd 1 is the a condition for engagement the 3rd 1 is the maximum amount of reduction that you can give theory tells us I'm not going to prove it but I am maximum reduction that I can give Delta each maximum is related date the radius of the roles N this car the square of the friction coefficients yes where Delta ages h 0 minus each 1 here in the figure of so the the friction
has fundamental role to play in rolling you because and it cannot be 0 yes so what what will influence the rolling friction and that many parameters years and but let's have a look 1st at values so this is a friction coefficients I don't know if you familiar with friction coefficient but say arms typical values are No . 0 5 2 . 5 to discuss a range I've I've collected some data on friction at high temperature for frantic steals and 4 Austin intake of low-carbon steel friction coefficient and you can see here that for 4 hot rolling you've got quite a wide range so it's not it's not a parameter that's easy to use determined in practice and it's kind of temperature dependence you can see that the measurements of the room measurements the slight got in the mean higher than that higher temperatures but you know we have a range of 2 . 2 . 5 9 that's a high fractions situation so in hot rolling we we are in much higher friction coefficient situation than in cold friction coefficient in cold rolling is of the order .period won last that's what they what is of of influence here where 1st of all there's this speech yes this is the relative speeds when you have the work role speed increase that we have an increase of the friction yes I lubricants we use 1 of the reasons why there is a big difference in In friction coefficient between the 2 cold rolling out is because we use lubricants yes in cold rolling mill the roughness Of the surface is important if you have roles that are rougher you'll have higher friction so it's important to control the roughness in cold rolling it's not that difficult but in hot rolling it's difficult because you have additional thermal effects very strong temperature variations at the surface there are out of this box new high-temperature oxidation and and and damage to the surface of the role so you can use it's difficult to could control the roughness of the role so you have more I where at high temperature to the temperature influences the friction coefficient pressure will have a new type of steel in case of hot strip mill of course the scale the oxide layer that gets formed at high temperatures and and so you get an idea how are on hold important friction is but also how difficult and complexity of the parameters and certainly in in hot rolling and that's again 1 of the reasons why it's so difficult to make very high-quality products in a just by by heart strip processing but that's so again friction very important primary we knew we know this because the maximum reduction and condition for engagement is a function of the this coefficient and remember that in the hot strip mill we have high friction so we have kind of sticky friction whereas in the Colstrip strip mill we have lubrication and are the but the mn coefficient of friction as is much smaller . 0 5 2 for 1 it's that I have a few of examples here so let's have an example of which the maximum reduction I can give them in the hot strip mill and using our little formula that we just wrote to the maximum reduction is part New Square we are In the briefing milk and we had high friction coefficient so roughing mill the radius of a role will be of the order of 600 millimetres guns friction coefficient .period 2 so my Delta is H is maximum 24 mm I can give in terms a reduction in the hot strip mill In the finishing also have high friction but I have a smaller roles yes same friction coefficients 12 mm height is my maximum reduction in the Colstrip mail my friction is even lower I have similar the role radio 250 the friction coefficient it's appreciably lower .period all 8 for instance mine thickness reduction is maximum is 1 . 6 seconds so that let's have a look at the measurements actual measurements of but reductions in hot strip mill you go from 25 the 250 mm 2 about 5 mm Yesalis a lot has been you do this in about 14 passes 14 times you roll the material so that means about 70 millimetres per pack so that's that's exactly within the range but I've found shown here In the Colstrip mail you go from 6 mm 2 1 millimeter yes you can hardly see it when I show it with my fingers here so the reduction and you do this in about 7 passes reduction is slightly less than a millimeter preposterous and agrees With and the the order of magnitude former that last year focus so In the rolling the 1st of all we have a working assumption is that the defamation is a plane strained information that we have a constant rolled diameter again this may not be the case because the role flattening and the steel has a certain resistance to defamation which is related to its composition it's Mike MicroStrategy the temperature and the deformation wrecked that's In general the case we don't have a very important parameter that's friction coefficient and we always have or in general we have forward and backward attention on district took in the in the following slide will assist and we'll just have a look at some of the important parameters OK so and will for instance here
so there With this is actual cops don't theoretical calculation this is the the the the pressure as a function of position in the role gap in and it's divided by the equivalent stressed so you don't have to do this is like a it's a universal curve if you want to do so so we have our well known friction Hill here then you can see that the amount of energy that goes into friction is it is really important yes you can decrease the friction yes and of course the friction held decrease Kent and art lowered the pressures and loads are of smaller another very efficient way of reducing the friction health is too increases the tension on the straps and this is an example where you have the back tension this is increased you get and a decrease in the Back tension but of course you can reduce the and rolling loads by decreasing the role of radius but what happens there of course is that the amount of defamation you may be smaller look at this as a d yes effect of the past reduction the amount of production that you give that constant radius grows so 50 per cent that will of course have an influence on the magnitude of the friction here there it so the I don't know whether we work with larger diameter roles for instance to high a mail or wit smaller diameter work roles in 4 Hi mail for the same thickness reduction it is related to the condition for engagement so the which tells us that we need a higher friction when we I want to achieve a larger reduction in In general what holds is that larger diameters as as a result will allow I figure strips to be used in general too high males or rather uncommon on last you you working with really I just think materials slabs are typically rolled with it too high a mail but even then you for highs are quite useful
so when I basically saying is that the reduction of the role diameter yes reduces the load and contact like an example here where we compare the the role pressure 4 a larger role in a small in the smaller frictions less contact linked of course and the reduction of of the load in general but then
the differences of course is that the bungalow also right and so that that will
impact the engagement can so let's have a look at the this weekend calculate what demean the pressure is remind you of the fact that as a function of position the pressure in the role goes through a maximum and decreases so this would be the pressure In the role as a function of position and we can replace this by I mean pressure the impression that the formula for pressure is this analytical equation here and underwear where that this parameter Chiu this is given bye this equation and in this equation you see the effect of the friction that contract the length the thickness and entry to thickness of exits divided by 2 that's the mean thickness as you can and as there is a new parameter here here that is Sigma and and segment and that is the flow stress of your material this obviously the the pressure in the rolled gap will depend on the strength of your material became so if we have a strip of which W here's a D rolling load isn't very simply given by 6 PM this is theirs the at times With of the those strict times the contact like and therefore the contract lengths we can replace this by Delta each time's up because it's very convenient little formal that allows you to determine the rolling along with the rolling lowered in as I want if you would look at this formal in more detail you'd see that the rolling load is proportional the the square root of the radius and can and can't that's 1 thing so that's similar to what we said previously smaller diameters role allow you to reduce the rolling loads because we have more or less the contract length and also because of this relation here but what is also very important yes and then you would see this if there is that there lowered increases the trip becomes thinner yes it's very important so
so that is why you see that he ceded the ruling load increases when the strip because the offensive there are some steel products yes all of which require very thin struck for instance packaging steal its packaging silvery fan as and so how do work because it's very thin and the rolling loads become very high so you reduce the rolling load yes by using very thin very very small diameter roles because the ruling was proportional to the square root of our rights so and that explains why you get these would call cluster cluster of mills that you have a very small diameter work yeah and the problem is of course when you have very small diameter but it's very easy to it will benefit so you need to supporters yeah and of course the end of it can also it will easily go we'll be bent forward and backward and an event like this so you need many roles to make sure that this will work role has been the constant position because that's where you get will cost roles this around the work this is the work role is very small diameter role as why because the ruling forces us so high that you have been stripped and you need to reduce the rolling forces by making use of the a formula that the pressure required is proportional to the square root of the world I Of the role expressed and so this kind of roles the cluster rose you don't see very often for carbon steels and you're talking about really I think products that but is a very common for stainless steel stainless steels think products thing and stainless steel products you will love very often see cluster mills being used so that lets have an example here of the use of this formerly you say you have 40 millimeter bark of a bar remember that's this the between the slab and the the final hot strip its reduced by 30 per cent in the mail yes and this mail has work roles of 800 mm we have with the strip with is 1400 mm and the friction coefficient the high friction point too and we work with the carbon steel at high temperature it's soft 100 Pascal the temperature changes yes so the material increases in strength so when it comes out it's 150 men so 1st we start by calculating the defense did the parameters we need in our equation for peace so the we know that the reduction is 30 per cent so if we have starting thickness and we also haven't we can calculate our In the end thickness Our mean thickness and our thickness the reduction then we calculate the mean strength of the material that's the demeaning of between 100 and 150 is 125 and this allows us to calculate and then we can tell calculate to friction times LP divided by the mean sickness and we find this value .period 34 and then we calculated b USA Inc Our formula yes times the width of distress times the contact the angle and we find 15 major Newton's also pressure you do so so what does this mean we could you won't get physical picture of this fall to the mail we said that is 15 Megan new terms 15 major Newton's is 15 million new Thomas yes but if you have an elephant ears 1 elephant is 5 times since is 5 thousand kilograms Sears is close to 15 new terms so in that mail the pressure that you you work latest kind of equivalent to do the same the pressure you would get if you you know stacked 306 elephants yes so it's a
a lot Of course it when we calculate the forests the In that's not enough To calculate our energy needs to operate b the mills specific that we will have to take into account the frictional effects yes we will take into account also the tension that we apply on the Strip the defamation power the losses yes all these things need to be added together if you want to see what it needs is a new power needs of our 4 the rolling I
thought just for your information in the out and materials you'll see that there's some examples of calculation of rolling forces for a stainless steel at the thousand degrees C with typical values 4 a role radius and with the thickness in and out and and and you can see the grass here and what's interesting for instance again these are the pressure distributions in the role again you can see that the reduction in the pressure as that which translates automatically in the reduction in force that you need to have there's no and energy requirements for the rolling so a decrease in friction coefficient of course works well but an increase in tension on the Strip has an influence and the backs tension also has an influence 2 larger reductions and a larger role diameters usually give you a slight increase but tensions and frictions where you the best methods to reduce or control the ruling forces and you can see here what is the the effect of each parameter all the rolling forests that's key the rolling toward yes D /slash so usually when you so if we increase the coefficient of friction you get an increase in forward but what's interesting here is is that and of course when you pull on the strip you have the more you pull the higher you forward it becomes but if you pull you reduce your forwards yes if you pull Baxter back you have a really strong reduction in the yes but you reduce your /slash the same happens with the but the rolling force a rolling forests is reduced as you increase for attention and the back attention but there is a difference in the talk if I increase the forward tension that poor on the roles decreases so what does this illustrates this illustrates that in a rolling mill changing 1 parameter often has an effect on all the parameters yes control of a rolling mill in practice is actually quite an advanced science that's it doesn't look like much when you visit the plant again look like over nothing to do it but actually it's highly controlled very intelligently control because so many things are interactive OK
again and the typical example here is an example in inches and things like this end I but this again here France's this is an example you just go through it and you have this this would be a cold rolled cold mill example you have a fight stand mill these are the stance this is the diameter this is that the speed Of the an there were Kroll this is the tension on the rolls maximum this is the role forests maximum that you can apply His and these are some RPS this is the base speed and this is the maximum speed In an if received usually going constraint on on arms 3 before I move on let's let's instance have a look at what happened to the speed is to speed increases as you go through from 1 role to the other because you reduce your reducing the 6 yes and OK so let's have a look here so this is stand 3 typical base conditions so I have the entry thickness and exit thickness but my material strength of course material if you are in a cold milk when you start rolling you have a certain soft materials has but by the end it's been hardened by the defamation right so every time you come out of 2 Of the mail of 1 stand the strength has increased but there is usually strip tension has on the inside and the entry and on the excess 10 France and and and the unknown than as a dessert the conditions here so we have for this particular case .period draft drafted again nothing to do with beer or going to bar draft beer it's to do with the reduction of it's a way of but the work roles is 200 AD I have a diameter of 280 the actual diameter yes because of the role flattening his 400 8 it considerable the /slash 1 per cent in the role forests is this and the shaft power and this is the power you actually have to supply to the the roles is given here so let's make some changes for condition 3 years I was and use of the base conditions again if we have 25 per cent higher tension what we see is that the the forward slipped it's now reduced we have an entry tensions this week 25 % entry retention and the role forests which used to be In about 80 500 to Newton is now reduced by 500 :colon Utils knows about the effect of that is that of the entry tension if we do eggs attention yes we see also a reduction of the role force and an increase in the forward slept Of course because I'm pulling this notice that the amount of role force reduction is not more considerable if you do backcourt tension but if I make my material stronger 25 per cent higher the flow stress not much happens to the forward slope but the rolling forces increase of course as a result of the material witness to this is this is also important but when you introduce you develop the new materials yes but they will also influence the rolling conditions some nowadays that leads to some challenges for some steelmakers is that the mill the males when you buy a mail it's of is a very long-term investment has soul you don't just change a mail because a very expensive but the decisions are often made for certain steel products yes nowadays good there is a huge push in the steel industry and research area to increase there the strength of steals massively go to giggle Pascal steals etc. This is of course very big impact also on the on the steals on the on the processing yeah because if you've developed a 1 digger Pascal steel units is very different rolling behavior than 80 you know and I have steal a low-carbon steel you can that's another consideration here 2 of
them let's have a L a look at the way we control thickness I think this is a very important dimension in 4 straight years and there are during rolling continuous variations things change all the time they don't change in future uh in large numbers temperatures changes a little bit but it's it's enough to result in thickness changes for instance so there continues variations in materials property sizes thermal profile and the response of the mill stance 10 if you want to have a constant thickness yes you have to take care Of the impact of these changes on the thickness and you have to do this constant otherwise you're is Exhibit thickness will not I have the required value and this is done with what's called automatic gates control yes and the gage control enables a stand to react quickly to changes and that conditions will will have a look at the rolling conditions OK so what we are just introduced here we notice here that the role gaps after is not equal to distribute exit thickness in practice so when when you set rolled opening at a certain value has and you don't do anything as you start rolling the role gap that you measure here In operation is not the same anymore and that's the reason why um and of course if it's not the same it also means that what's my thickness I need to know something about how the role down this changed when I'm I'm rolling and so that's the results we will you know this this this change in the role gap is a result of the male stretch in which Woods smell stridency elastic deformation of the roles the Mittelstand frame to frame on which the bearings etc. and the properties of the material you are rolling so the rumor the rolling them in general this is shown as In grass that's used to for automatic gates control where you plot the rolling forests rolling load as a function of the gaps the role gap and the working .period yes which defines the rolling load and do the exit gap this is defined by 2 properties do mail properties which recalled the mail stretch of the mill modulus it's this straight line here at this properties of the steel you rolling called it the plastic cover this must occur and that's dislike you where intersect that's going to be the working .period of your so let's
have a look at how the studio Our but
these 2 properties yes are obtained those so we start with a static rolled out there so this is what I mean I have with a for-hire middle years and have opened a gap To distance past 0 and so it's like here and this is a mail visit there's nothing here he conceded the roles the role here surfaced work work-rule surface here and there is no script no stress so on this graph of rolling load versus the gaps yes this condition is this point as yes at a load of 0 OK now the next step we are arriving here with a material that has been the thickness H is 0 the 10 and I'm bringing it in front of the the melon and nothing I'm not deforming and so this is Starting conditions in terms of the material mean it .period on the x axis where H 0 Is the entry strip thickness so these are the 2 starting point next we passed 8 straight through the 2 roles from care and what happens elastic deformation of the mail and that's everything the roles they form elastically do the whole a mail framed the forms elastically yes well Bush these 2 rolls away from each other when when I'm rolling hills and the way it does this is Lynn nearly so you get this line here and the equation of this line is S 1 and this 1 this 1 isn't new the gap Rowland is equal to the exit thickness is equal to S A 0 times please light forced divided by appeasers forests this load pressure has defined by S & S is 80 constant which we call the mill modulus the mills typical value would be for instance 5 mega Newtons per millimeter look at and you can determine this in practice and you can measure as you just measure the pressure here for the force rather as a function of this gap when you are rolling something became so the mill modulus this is a straight line going through as 0 and basically the result of the elastic deformation of the material so very very managers want to finish this is just 1 or 2 more slides and the other a parameter is the material behavior 10 and that's the plastic so that starts at age 0 and how do we obtain this classical world wheat take a material a block of this material put it between 2 died have a displacement transducer measure thickness the measure of this distance H 0 and has put pressure yeah and I measure along the motorists so as this pressure the thickness of this material decreases and so I did this cover for instance was a plastic curved plastic force on the rolled peace basically this an example here how this curve would look like for low-carbon steel yes if the Steelers more the Halloween elements may have high won't work hardening so this is a typical measured plastic curve Clinton so the working .period that we obtain has this is it where these 2 lines intersect In the intersection of the male modulus and the plastic of that gives me the rolling lowered extra thickness care for this particular situation really and the plastic curved us at the higher rolling Loza required Will if we need to make higher reductions and a mill modulus tells us that higher rolling loads will cause larger males distortion Clinton and we'll
see on on on Thursday the child
we use the service 2 curves to control the thickness so thank you very much Soriano .period that over time here


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