Modern Steel Products (2014) - Overview of Conventional Hot Strip Mill (HSM) Design: lecture 12

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Modern Steel Products (2014) - Overview of Conventional Hot Strip Mill (HSM) Design: lecture 12
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12 (2014)
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Professor de Cooman builds on the previous lectures in the sequence, this time dealing with the hot-strip mill. 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)
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Typesetting Cylinder head Typesetting Cylinder head Kopfstütze Surface mining Mechanical watch Alcohol proof Rolling (metalworking) Leitwerk <Flugzeug> Forging Rail transport operations Material Boeing 727
Überschallstaustrahltriebwerk Lugger Typesetting Hot working Pufferlager Book cover Ballpoint pen Book cover Insulator (electricity)
Tin can Rolling (metalworking) Kickstand Cartridge (firearms) Alcohol proof Finishing (textiles) Bow (ship) Material Last
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but so far ,comma started here so we had
already it's given
introduction about
these hopes OK and we
went we were going to throw a number of configurations this review configuration 1 again and no 1 was slightly different layout here you start with 2 furnaces which recalled walking being furnaces in this case and then you have but this is a slightly different the line it's got some really roughing males it in succession that many of the hot strip mill configurations have a from a single roughing mail that works best be reversible male To do the rolling some of the mills have roughing males in succession of that makes the line very long yes and of course there are additional so additional investments in terms of the building but also additional investment in terms of the of the male stance and then you have but many configuration would transfer bar is just exposed 2 the the air is you have also the configurations where the transfer is there can be covered this either passively covered or actively cover will see what I mean the cops here at the scalar finish or and then measuring here of the thickness the temperature of the but coming strip lemon cooling and around table before this week or and you can see that this is the long life this is an
alternative here no alternative configurations of the standard mail which has the advantage of being shorter and it has hired you reduce the length of the male well 1 of the reason was hot strip mill so long is because of the length of the transfer but yes the transfer bars I told you this 100 meters yards so you've you've got to have room for the transfer market if you use coral books technologies you chieftain thanks 1st of all you make the line shorter because you call oil the you a new corralled the transfer this you don't lay it all out yes and those of you achieve 2 things personally you don't have a prolonged transceiver and the 2nd thing is you minimize heat losses of the transfer and that's also a positive and it although the line shorter the investments for the coral box are very important soul if it ends up being a costly solution but anyway this is the the the "quotation mark books here and we will be talking about this in more detail but you can see again furnaces the scaling reversing rougher call box crop share the scaling edging and finishing mill cooling in the run-up to the land and 2 or 3 "quotation mark Ehlers 10
some of this summer features here
so let's look at the different parts quickly Of the reheating furnace reheating furnace why do we need as well we need to start at high temperature has tried to do the hot deformation and the choice of temperature yes yes basically based on metallurgical considerations yes you want to have homogeneous and Austinite and you want to be able to do the processing and so this is about that as you go through the line you get pretty much a linear decreasing temperature "quotation mark here's what some of the material it has entered and you want to make sure that you but you end at the right temperature at the finishing temperatures colder finishing temperature and the temperature should be In the homogeneous Austinite range so that you can carry out the cooling and the transformation in the runout table and the OK so let's start the D types of reheating furnaces for strict product you have what we call a walking beam furnaces pusher type furnaces and tunnel furnaces internal furnaces is a type of furnace that's referred to above and that's used to and in many like the a CSP line which will have separate section on on that so many miles of which usually have a walking beam or pusher being furnaces and the current technology is walking being furnaces so that you avoid damaging the slaps the then the furnace what can we say about the heating zone 12 the the slabs remember they'll be a very high temperatures and so we have to put them on something right and will you basically put him on what we called skids and as a water or other steam cooled rails .period internally cooled knows because they're cooler yes they will leave marks on the slab which we called skid marks these marks can be very pronounced if we if you have a pusher type a pusher type the reheating furnace because in a push retired furnace you basically Bush the the at the slab across but through the furnace over these array Spaniard you you leave a trace Fonda this lapse and will see that you know this is it looks like it's not very cop possibly be opposed a big effect it actually has a big effect on the product and the ERM In these furnaces are heated with 2 heavy oil with LPG because I know they are working around the clock and so will you choose the least expensive with the heating methods and natural gasses that are much cheaper than electricity so you usually use LPG it has 3 zones the preheating to 600 heating the high temperature and a soaking where you home watching eyes the slab this the furnace is at ambient SO you've got a lot of thermal oxidation and new forms scale and that means a loss in yield because you just made steel and now you turning it into iron oxide and so it will cost you in terms of yield it'll cost you in terms of having to remove the this oxide and then to recycle it in the process so the scale that you form how much of it is what type etc. is relate to distill composition and that you can't really change very much but you will form of course more scale at at higher temperatures so that's why I you don't have extremely high temperatures and prefer to work at slightly lower temperatures the heating time has longer you leave the slab at high temperature and the uh more skill uniform and the atmosphere of the furnace was also determined how much skill you forms of and you don't want to have your burners work with the very high oxygen XX it's so few more words
about the so up pusher types and walking beings lunacy here I think in hazardous this is the exit of Of these furnaces you could see the slap coming onto the roles here but so what is important is that you achieve temperature home watching natives would you have these huge blocks of Steele's no waiting waiting up to 20 times as I'm there have to be homogeneously he did too but about 1250 or slightly more than these if you charge them at ambient temperature a and they usually stay In the furnace for 2 and a half hours that's the typical resident residency time that is necessary yes but not for a logical reasons because 1 of the things that matter logically that you want is to France's dissolved all the precipitates as I you'd only 2 and a half hours to dissolve most precipitates that much faster at the reason why you stay there is to achieve a homogeneous temperature and because these blocks these latter so semester right and this is a typical temperature range 1202 12 88 has sold about 1200 to 1300 degrees N almost universally people use 1250 and so on these I don't want to use the pointers is out at then sometimes it's interesting from metallurgical point of view physical metallurgical point of view to use a lower reheating as you may have reasons for instance to not dissolve a precipitate or for other reasons yes or you know that if you don't reheat at higher at these high temperatures you mate be able to have smaller grain sizes then but you cannot do this yes these furnaces are at a stable temperature as you cannot turn the knob and say well and at this level be 100 degrees lower in this slot will let you cannot do this right so this is not it's it is in a laboratory circumstances each parameter to change Industrial Services very difficult to change venue be almost impossible the 1st is a matter of fact a rector of course because it takes 2 and a half hour for slap heat up the debt means that the capacity of about the hot strip mill is dependent on how much slaps you can heat up for how this intent and a typical furnace will will be able to to process about 300 tons of steel per hour there that there is it's usually you lose slab is that the slapped charging is at ambient temperature but there are some slabs which are very sensitive to cracking and those ones will be charged for instance will come straight from the a steel plant To be reheated at a higher temperature yes for instance that applies typically too Hi silicon grades this would be which which tend to be very
very brittle and this is a cross-section here of a typical furnace you see it's got a different zones in and and this is a pusher that means that the slabs were brought in here and there is a mechanism this is pushing the new slab in and out comes the the the the the 1 that's in the drop so yes so you have a uh preheating heating and and home which in icing parts of the of the furnace of course because you you you heat here that is what a waste their heats and that is the recuperated in the recuperated so typically you have some sizes here about 30 meters the convection zone that's that's that's the the 1st here heating so as of 9 meter and in equalizing was soaking zone of 8 meters of in total about a good 30 meters so are a large units this is a test of
walking being furnace so there you go you basically have a mechanism where to buy you you move this lapse through the furnace a lot of it with a walking beam system so you you have a slap here and it's rests on the skids yes on scared and then there is a mechanism here yes could this be yeah and goes up yes picks up the slack and moves it the head and dropped in and puts it down again the slabs or not pushed against each other years and they are not totally don't touch each other and they don't dare not pushed across the in the supports gets so there is less damage To date on the surface of the the this the more expensive of course because you need to have this mechanical systems but in operation at high temperature and let's have a
look at what's happening inside the furnace Nos so we've got our slaps year very high temperatures so we have but we factories Her factories on the walls of our furnace yes and we burn I have the oil or gas usually it's get its guests natural gas and natural gas the main constituencies method was so and we burn it with the air that's the oxidizing so what will happen have met plus Air Force nitrogen of course in the air that gives me C O 2 that's the heat yes water vapor nitrogen and signatures and we had originally plus a candidate OK so the the relative amount oxygen to the methane yes is important because that you can have a flame that is not neutral you could have a flame that's oxidizing strongly oxidizing or a flame that I reducing has so when we have when you have the exact ratio the example here but you will have 10 volumes of air for force but 1 volume of gas yes and the flame temperature Clinton criterium is close to 2 thousand degrees yes and it's it's very hot and these furnaces and so on 2000 degrees but if you have an excess air France's 12 volumes of air for 1 volume of gas the flame temperatures will be below time because of some of the air some of the oxygen is not used to produce L the heat yes you can also have an excess natural gas and any of your flame is slightly reducing differences 8 volumes of air 1 volume of gas the flame temperature will be lower but why would you do this well for instance if you have a problem of excessive scale formation OK
like so how does that he is the he transferred against you don't actually you don't actually direct the burners on condition on this film the slack yes you don't do that duty it's so the heating is indirect so you get radiation mainly from the walls refractory walls of your furnace and convection yes and and radiation from the flight yes that's how you heat up the the slapped you don't have the burner actually burning on directed to the slaps so the actual transfer of to steal of D energies about 70 per cent and you know you have a considerable amount of a waste heat that's lost the stack about 22 per cent the reason why the slab stay in that in the in this very hot atmosphere for so long is basically to homogenize the temperature right so the if if you look here this is in the furnace this this so you started really cold slabs His and and and a heated up to about 1250 it at the exit of the slab temperature increases gradually yes but the wall and the gas temperature in the in the furnace of very hot don't OK and as I said the flame itself it can be close to 2 thousand
degrees C so what the energetics about about reheating furnace say you you enter with a 100 percent energy good at reheating furnace the actual yield is about 52 per cent I just said it was about 70 per cent of the reason is because we can recuperate some of this of the heat and that that's not you so so we do have a way to increase is with direct and indirect transfers about 50 to 100 heat losses to exhaust gas 20 per cent we lose some of the 2 cooling water and 2 I couldn't learn heat that's transferred to the walls of the furnace about 5 per cent of this year where does this heat loss come from cooling water well mainly from diskettes and this disk is we need to protect them from excessively high temperatures they are water-cooled after steam cool but to that's where this distant cent comes from focus so let's say a few things that important things about what happens metallurgical to the product as you heat up a slap all the major them the most important things that that happens to the Microsoft is a very strong coarsening of 2 cranes from this shows however that the coarsening is very much a function of the type of steel that you process OK and in the Tinkler the edited the reason is because you have particular precipitates in the MicroStrategy so let's look for instance at what happens to a carbon manganese steel yes that is being reheated as of and here shown as a function of the temperature carbon manganese to this this red line here you see that the temperature increases we're in this range as a temperature increases the grain size agreed would typically in this temperature range 200 at 1202 1300 and you see that the corresponding a grain size is of the order of close to 300 if not guests if you have grades that contains small precipitates such as vanadium carbon nitrogen aluminum nite and I tried to Naomi Carbide yes what you see is that the grain size will stay it's as long as the precipitates are present but once you cross the solubility this is the solubility temperature yes the precipitates will go fully into solution yes and they will not be there to prevent grain growth sir when vanadium goes into solution In a vanadium micro alloyed steels suddenly the grain growth starts In an aluminum nitrite containing steel once the aluminum nitrate is in solution the grain growth .period NI albeit Carbide in goes in solution get grain growers will stop and you see this usually happens act for normal steel compositions below 1200 there's so when you reheat slaps most of the time whether or not you have these precipitates at this at this type of temperature they'll be in yes and you'll have a very coarse grain Is that true for all the precipitates what is 1 precipitate in that doesn't go into solution and that's Titaniums nitrite yes and that is what you see here Tania if you have a steel that is micro alloyed with Titaniums yes that tie Tania will form extremely stable Titaniums nitrite with a very low solubility so the solubility of tightening nitrite is very low In other words to dissolve Titaniums I tried you need very very high temperatures temperatures that are even higher than we heating temperatures so Tania Allied Grades while usually not show excessive grain growth 10 and in certain cases it we use this we use this phenomenon that uh tied to the new Micro Alloy Inc it allows us to refine the grain and even at the at the level of due the reheating furnace let's busy lets you know in detail at
what we have here so this this coarsening of course a coarsening of grains is the dynamic phenomena right it takes time yes and it did so depending on the temperature is depending on the type and of course it's depending on this specific composition yes it for instance in the case of Niobe Carbide it depends on how much now be in Carbide you have in other words what is the concentration of myopia and this is illustrated here so the coarsening the type and the amount of precipitate is imported we have a carbon manganese steel no yes and it contains we have 3 1 contains 100 ppm 1 contains 500 ppm and 1 contains about a thousand ppm and you can see of course that if you have only 100 ppm of niobium carbide that niobium carbide will be dissolved yes at lower temperatures you remember what Why is that because so this is my old because we die beyond ,comma this is it this year solubility life so all the compositions Adobe low solubility lines sales at temperatures of temperature want all the compositions of below this line will be In solution so if I have 3 compositions we put 1 here 3 compositions this 1 has a lower now you will be and carbon this 1 has more nail vehement Cobb this 1 has the largest amount so this composition this will be in solutions at the 1 but the still there will still be a certain amount of niobium precipitate so the amount of niobium carbide of niobium is important so you can see here if you have 500 ppm of male the coarsening will only start at 1100 if you have a thousand the coarsening will I start slightly at temperatures slightly below 1200 but again I thousand ppm of nail him for your information is an excessive is a relatively large amount of nails usually microbiologist deals we have about 500 ppm 400 to 500 people so that means that in a nite he'll be a micro alloyed steels which but when they are reheated the denial be is fully in solution has and will have cost cranks yes so the composition is important in terms of the coarsening of but also the temperature and the top OK so what you see here the grain size again the fact that no exploded as a function of the times yes and there are 3 choruses 950 thousand 50 and 11 15 OK so you see that the grain size but if you reheat to 950 nothing much happens against the grain size of course is a little bit Read I have a typical reheating times two-and-a-half hours yes on this scale right so you knew you don't keep score slabs in 4 for 10 hours but let's have a look at what happens at the the thousand 50 by the thousand 50 the grain size increases slightly yes you have to imagine of course that the precipitates don't suddenly into solution it needs some time to dissolve right so so what of between 6 and 10 hours you see that the grain size increases suddenly not suddenly just gradually to 5 thousand 50 or groups that OK so that means that if we have but if if we have a reheating time of 2 and a half hours the grain size you will still be small yes if if we we he 2050 now that's saying of steel yes if we the reheat at 11 15 we see that the coarsening starts within half an hour as you see here the grain size already started and and so we I went and that means that this particular still here which contains aluminum nitrite the precipitates but because we put him 2 and a half hours in the India this slab reheating the coarsening will already have started long before that and so again grain sizes 203 hundred microns will be achieved in the during the separate heating OK topic so
that's 1 thing that's 1 important thing that happens to your material very coarse grains 300 microns what the typical grain sizes that we want to have in practice that's a very few very very few steals where we have grain sizes of the the door large typically it there would be electrical steels there you need grain sizes which can be as high as 100 to 150 microns and most of the production will be less than 20 microns considered that's a considerable reduction of grain size that you will need to achieve as you a process system that's 1 thing that have the other thing that happens of course and we talked about this is scale formation no In the hot strip mill you form scale in the reheating furnace and In the rolling section yes the these scale you form in the reheating furnace we call primary scale yes this scale you form In the hot strip mill outside the better reading for call secondary care and so on it's a whole science the formation of scale on steel the ring and it's a pretty complex and the reason is because the oxide later scale later is complex and we have typically at 3 the types of Aaron cup and iron oxide compounds and tide magnetite and was tied in addition of course most of the outlying elements are also oxidized so that adds to the complexity of the types of oxides you have and they may be microscopic old features such as blow holes in your oxides etc Vt a at the 2 203 3 it has is very dense and has good thermal conductivity 53 304 is porous poor thermal conductivity and I feel it is also porous and also poor thermal conductivity and his works have petunias installation almost I this oxide give easily delight mate yes do come off the surface enter wildly if you're familiar with thermal oxidation there are classical series on for the growth of these oxides for instance 1 of the series states that thickness on the weight of the oxide is proportional to the square root of the time no that's not very useful but in practice to study this oxidation we therefore typically to the 3 mm of scale so that's a considerable amount in indeed the secondary scale this about 10 times that no .period 1 2 . 2 5 mm and so there will be a loss IRA lost due to scale formation and that's of deep order of 50 thousand to 100 thousand dollars per year so that is not to be a huge amount of money for a steel company but its bitterness appreciable still right so that the scale thickness will be a function of the temperature now we can't do much about the right because you you want you have your reheating temperature at the time exposed to these high-temperature again you can't do much about it we noticed it will be 2 and a half hours that the slab will have to reside at high temperature but it wouldn't also a function of the air the excess In the 1st of the oxygen success in the 1st instance so typically here this skill formation amount of skill and bounced per square feet and and 1 pound the square feet is about almost 5 kilograms per square meter yes so that as a function of the temperature here that used me as a function of the the time so you can see here and these are typical of the Times for the reheating time and d year so so we will have about it in this particular case 12 18 we look at about 2 and a half kilograms per square meter of scale knows if the temperature is the increased or you increase the uh the excess oxygen you will of course make more oxides at surface what else happens to our well this land is put on the skid skipped pipes and so this is what this is for instance the top of the a what's inside the furnace you can see the Saudis get pipes here skipped pipes of water cooled so around this contact .period you'll have slightly lower temperatures and of course is the skin pipes the distance between the script pipes the missing like it's not very important thing but actually disk pipes I will determine how how short euros the maximum or the minimum length of slaps that you can process live and you you cannot process the slab that will fall in between the skates right obviously and of course there the size of the furnace will determine how long the slaps can be To some
practical thing now they did this kid pipe marks will leave what we call it a thermal profile on the on the sly and that's why we use isolated surrounded by yes but still we get thermal market of the earth Of the SLA and this is the really interesting about this thermal profile stays on the material this is an example here and of the thermal profile that you get From a slab yes In on the bar the use of the material has been rolled and this is a bar no you see the thermal profile has ended after the finisher yes you can still see the same oscillation the same thermal profile June 2 these skipped pipes has if you look at this you'll wall but what are we looking at we we will do this in Fahrenheit so it I would have to to to to recovery and and Fahrenheit tends to be but so so it's not the 28 would I want to say is that he receives about 50 degrees Fahrenheit it insouciance it's much smaller but at this stage you know you'll have to forgive me but I didn't and so it's it's it's a it's a number of sufficient tenths of a degree has mentioned that you also weighed and it means that the properties of the steel very also With this oscillation so and this brings us back to which we would discussing yesterday is when the temperature changes the properties of the material change as and when the property is a material change strip thickness will check right so and that's 1 of the reason Woods is absolutely essential to have the control all males because the temperature differences would always result in In home which in and of course not to speak about the possible metallurgical problems the
important things in the slab reheating just burned steel surfaces yes /slash should never be exposed directly to halt flesh yes very silly and because why is that because the flame is very hot 2 thousand degrees right so what happens the oxide yes this is this is the irony oxygen phase diagram you see here is he was tight and magnetite and I wanted and Tottenham a tight here OK you see that eds about slightly less than 1400 deg C Our oxide start to become liquid and you don't want to have a liquid scale that's because liquid scale give here a crazed not flat bumpy surface appearance which looks while answered this is but no no never I have never say never melt the the scale that's important OK so I /slash comes out you've got to hot rolling yes what are you going to do 1st things 1st you have to take care of the the skills you cannot say role material 2 or 3 millimeters of scale on top of pace of the 1st things you do in the anytime a whether it's string or wire or bar products at high temperatures before the roughing you always to scare right always discussed
White what do you do in the scaling you removed the oxide layers which are formed by thermal corrosion course you if you don't do that you will have poor service quality you have to remove primary scale when you come out of the reheating furnace in and you do this it's a thick oxide that so you start by the and although it the addition of it is not very good you have to make sure it's fully removed so you you start with vertical scale breaker he is being held and by sometimes you can also give it a horizontal skittered pass through horizontal skilled parade and then it's removed basically by high-pressure water well the 2 times to 6 thousand PSI and I will give you some Buttrick numbers animal secondary scale is formed during the rolling itself yes and that is removed only with high-pressure water and and that's essentially before the finish finishing these layers far less thick and easier to remove finally when we closed the material yes we will also form scale yes In the coiled material that scale will also need to be removed but will do that in a separate unit which is called the pickling line the and will talk about the claims animals so it this is a vertical scale breaker it removes primers get so which which is this is the slap here and in here you see a role on on the side isn't as 1 on the left and 1 on the right and it basically roles the sides of the the slap and at basic cracks the scale To make it easier to remove to be removed in addition is that vertical scale break will also is also an engine and and shirt as you may remember but allows you to change slightly change the weather of Europe slap before you do the rough can't I while there's not much to see 2 the did did the high pressure the scalar there's this is seen from the scale of from outside obviously everything looks very rusty and at the end of these units because of lots of fire and oxide it's 1 of the reasons why hot strip mills are not very nice to visit is always a lot of very fine iron oxide flying around us the and you see so you you have had years this where the water high-pressure water comes from you have been shawls that's to avoid that a a lot of the year the scaling water it's sprayed everywhere and you also have a you skill you have the skill on top and the bottom rights you have you did the skill headers the candidates if you look at the inside this from the outside you don't see measures just the district court stripped coming in and out here as well so you have the top sprays yeah Top sprays the that spray on the top and on the bottom of strip and the the water is that is 1 of the reason why you use a box you have to recuperate the water right because of water costs money and then you you recycle this water cannons and there
are developments in the area of the scaling but why is that well the trend is In the scaling is to use less water because of the treatment of the scale the scalar water is expensive but you need to remove particles you need to recyclers and did In the smaller the volume is that you have to treat the less expensive so you you want to have a very efficient deescalate and that's 1 thing the other thing is you out and you know you want to have theory the space where you do the the scaling confide make small so In the particular in many males as the day use wrote to read the scale and there we can we instead of having stationary sprays you have sprays that rotate at very high speeds and very high Water pressure 1 of the very compact again you can see here this is a unit before it gets mounted against and you have to have these rotary arms on top and the bottom and the left and right with very highly skilled efficiencies and low low-temperature losses D
India the advantage of this technology I you again you don't tend to see them in conventional hot strip mill the antecedent in compact strip that melts so where do we do did the DEA Skilling well everywhere where we are and we start to 2 roll so you have your skill breaker and you the scale before the roughing male energy skill before the finishing with and then maybe the killers in between the passes 10 the right is
so what does the 2000 is I mean it's around the 120 bars these these Scala's these deserves some parameters the skill parameters before the offering and D 4 the these killers before the finishing stance news and there may be in the interest and the Scala's and this is what they look like these these conventional so you you've got header and then smaller tubes with spray nozzles that
10 good now about the the scaling some people think yes that you need a lot of water yes to the scale and the water's got to be cold yes and and that is not right the deal scaling is based on pressure yes so there's no effect from the thermal shock knowledge that you use cold water and spray on red-hot scale and so the the thermal shock will results in skilled removal that's that's not how it works so that the scaling forests developed by the skill and also depend on 2 factors the pressure as the the amount both what yes but if you have high pressure you can reduce the amount of water and have been at the same efficiency and effectiveness of the the scaling depends on many things muscle and bone tends to strip strip Spiegel lead angle offset angle etc. yes and the impact forces a parameter that so often use of force divide by the width and length of the impact area you will see that the impact the the these and these nozzles the it's it's not around spray it's like a knife like spray line types spread and you see it at the effectiveness of removing an indeed the scale is a function of the pressures if you have high pressures you don't need so much water yes and that's very advantages actually but you also know there is also a good reason to avoid using too much water is because the more water use the more you cool your strip yes to you you basically wasting heat at the same time so that's why I pressure it is the most important of spoofs such
imports as to how this visited the scaling mechanism actually work in small due to thermal shock from cold water on the strip it's due to the impingement forests that breaks the Gail steel ball if the impinge on costs but or answer the audited with water volume is too high you get in there and desirable stripped cooled and and this will affect strip partners and gage so so what you basically do it is that you like to the the the high-pressure water removed did the scale basically by brute force by breaking the bond between the scale and and the metal and that's why this is the geometry Of the the water spray is so important so did the scaling will work best when you crack when it works on the cracked scale and so that's why I am so the deal because the skill works by breaking oxide metal bond and lift off the scale sowing the impact area the water spray get under the scale and apply enough force on the scale that's why we have we have these oxide breakers ahead of the of the D scale so you can have a horizontal role or the vertical fractures and and they're basically
there too but cracks in the scare you so this is a nice schematic here and a nice figure of this this nozzles IG and you can see the did nozzles are uh the spray pattern you see here yes alinghi Hairspray high uh high pressure lean years prior to in this a scene from the site but again the d scalar looks like you know pretty dirty box and what are the not have to do too much with it but it is essential that it is working correctly if the the of the distance between the 2 header with all the nozzle and district is not good if the on goal is not perfect this article here the 2 and is not seven-and-a-half degrees you will have very poor performance so far but the Skilling may not look like a very young the important thing but it's
important to have the parameters right yes and to have the set up of the d scalar very nice so this is an example here of typical ranges for instance for the distance here this distance here it is in the range of 6 to 14 inch sold that would be about 10 centimeters to 20 centimeters yes and did the nozzles here are this is high-tech yes you cannot I remember visiting a company in India and they have done the change this into something that had bought In some supermarket yes so said the decision this year you can this is not the garden gardens prefect right this is a risky high-tech to achieve the right spray pattern so you have to buy this from from specialized companies and you cannot just replace them and this can have a major influence this and I say this because know some people don't know Duck you know for most people and nozzle is a nozzle right and it's something you you know it's a garden hose nozzle that they're all the same it's not like
this and so on to be aware of this certainly with did the scaling that the right nozzles are used so we come
to do the right thing to the material has been the scales are you going to do reflect a mail so 1st of all the district has a certain with yes your a mail has a certain position you have to make sure that this trip goes right through the middle in the in the correct position so you have centering guides us centering you see here they will make sure that your strength yeah that that's the time do the slap goes through V the middle of the dude
life is so OK so the number of things that happened also steel this is considered a vertical edges vertical edges we talked about it to sigh it's got it can worsen skilled breaker but it also has acts to change the the width of the the slap the with itself is established at the Casa and the edge Europe can control their gives some variation in the the product with us you cannot give large amounts of the reduction US the reason is because you will former dog ball the dog bones so if you if you want to change the way here desire of roles my passing years slabs through the roles of the edges and have you can only do a small amount of reduction and if you do too much reduction you will have this yes and you're slabs will look like a dog bowl yes and so on so there is a limit to how much you can the reduced the way and then I yes and In particular this can generate not only problems at the the at the on the sides but also at the ends of the the bar so after you roll the slab and
giving rise to
tongs and fishtail Sweden's talk about this and the consisted of course the position of the vertical edges right to the head of
the right before the roughing so this is an example here of this venture will so it's basically a mail when the roles are vertical yet and so can be In India usually in the front of the rougher it can be attached to the Sorokin be a stand-alone units and a typical edging capacity is 2 inches the 2 inches that's about 5 cm that's about the amount of change you can give to the west it's not very much and this is that this isn't major here so the area
the answer would which usually have with the edges of the edges assists is seen from the top right from the from the top few him to the edges changes for instance the width of the slapped by a centimeter 2 yes OK and then you you always passed through a vertical horizontal male guests and the reason is this 2 but to flatten this and so it will give you some recovery of the West also Clinton To say you use of much of sedition more detail moment and so that the with control and in particular these effects here are important because they result in this the if if it's too important as you get Tong effects and Fishtail effects see when you when you roll this yes when you roll so suicide you roll this and here it's slightly thicker at the end this slightly thicker parts will be flattened and this will give you this shape yes and depending on the profile you have you can also have a township the fish tales Avery ,comma can so that and it basically depends on the amount of defamation you have given so that's been
studied use tongs and Fishtail standby the 1st them subsidies newsstands and facial referred to the bar rights after the roughing it but the reason why Curtis is because the poor is sick basically poor control of the edges so so what you want is to have a square pants and white To me why do
you want a square and because you don't want to start the rolling wait the strip the people who admire that's not straight yes you want you have to start rolling with this with the Bardot's straight line of fire and you also don't want to have this yes because you need to scrap it yes sold that I told you this is where you can get your samples so we don't know this is a research you don't think you actually don't mind these things but for the process people you you you want to forward so rights so that's basically what happened was a set at the end of this last year has this the edging will result in the free flow of the material used in the rolling direction rather than the spread in the thickness and deformed and the formation of this dog bone so deep depending on the size relative change in width and height you can have tongue shape or fish and they need to be removed so you'll have to cut this off them and and that means you will have a material loss so what is this Delta W Delta W said the difference in the the West you realized and the differences in thickness that you realize India edges tilts normally you want to have a few this is your use last year's you want you wanted to know when you squash said you wanted to deform homogeneously into a thicker slab that's not as narrow right however depending on the the relative amount of thickness change and with change you will have Fish Tales for tongues on your body 10 this is a more detailed this
vertical edges so you based have these grooved roles they are here you see here and then Of course you you need to position them for so you have forced cylinders In the press and everything is a horizontal and if they're driven and so you need a motor spend all the motor here a gearbox Excuse me spend that goes from the the gearbox 2 the because of this and you can see here this is the there are new technologies that's where I found instead of using roles too change the way you for each you use forecheck if you actually do the /slash yes and those so-called the sizing presses there are considerable cost but there were sent because you minimize Fish tailings and so on it allows you to get more variety in and that's important for because the the the inventories this the slab weights that you have to produce you you can do with only 4 to 5 slab weights to cover all the weights you need to produce right so that simplifies the processing right and so again so and you don't have as much lost the ability to cut off materials so much to me To removed to fish tales of the Thompsons costly and of course that is an issue so but what you
do is basically instead of rolling the edges you the materials now the problem is when you forge the the good thing the easy thing which rolls yes is that the product can move that's when you forage at the moment you you had the material that the products the moves yes most mostly the latter so on the that's why this sizing press has to be of flying press so got to had the material and move with it yes so did the product can continues to move fast and basically as I said it's a forging operation has so you can't be you work with them and fell and the and Villa shaped this has a particular 1 profile years and every time the anvil heads the slab yes it will it will reduce the the width of the of the slab and increase the thickness of course and it does that because it's not so because it's not so localized yes you don't get this dog born effect Clinton this is an
example here and a lot it's been conceded that it's basically a flying press you can know the units can go up to 2 months to thousands of mm right so what's important here is the the with reductions so it 30 this remember when we're talking about the the the edges can mention Elijah Wood talking about interests 5 centimeters here it 30 centimeters by right so we're talking about a big difference right and then we come to the
roughing the Ruffin mail is usually up 2 or 4 or higher stand up and down and it's it's basically used as a reversing a mail so you know the the slab goes through and then is rolled back through the this is rolled back and forth through the role gap till you achieve the the thickness that you want can this example here and you can see here I that the this is this is the rough wrote Ruffin male and in front of it you have the the vertical edges right so it's depending on the choices that people make when they designed the lines yes either others many varieties of choices that people make but you can have the edge of very close to the Ruffin mail or or or not the number of passes is always an even of course because you need to do to move in a certain direction and here you have some some parameters here about diameters of the the role
the barrel less means that the length of the total length of the of the role rather than a the the actual product yes the
text so what do we do In the roughing prepare this land yes to make a bar which will be finished rolled in so we make we get thickness and width reduction and we're usually going from as I said here I from 25 centimeters about 25 cents to 25 millimetres rounds of its considerable reduction and is 25 mm 238 mm that will go into the finish Akerman and that's the end typical and thickness the with reductions that we can give typically are of the order of India edges 5 centimeters 0 2 inches yes that's for a standard vertical and sure if you use of flying sizing press you can go up to 30 what we also need to do keep in mind when you do the roughing mail is that the temperature control rights so we need to deliver the bar to do finishing mill at the right temperature which is about 2 thousand 50 degrees C. yes and uh remember the material may be very heavy as it is relatively soft at this temperature so we want to avoid surface defect skill removal of course happens before the end of the year and stable positioning and and minimum minimizing hook and camper that is the general shape of the strip right if you know your your mail is not well aligned you're strapped can move this way and or it can have this state of that ship yes so that would mean would Hoke and Qambar and of course that's a nightmare when that happens and we'll talk about this later on when we talk about it the profile of strips and flatness aspects but I'm
so usually roughing males are too high or for high types of males this is an example where is too high a mail you conceded the slab passing through a mail user for high you have to work rules and to backup role
and here you have an example of what types of roles and 4 different a conventional hot strip mill I guess what is important for you is to diameter after the the roles and things like that don't carry will love will talk in a moment
about daily the fact that these roles operate at high temperatures so but they're subject to wear the way and so you need to replace them yes and Out the work roles .period direct contact with the she'd need to review replaced every about 2 thousand 500 Thomas so if you say that that we would produce 20 Toms 20 times coils yes that means that about yes it's about about a thousand every thousands coils you need to to make the replacement get this on the Net the which it looked a little bit too much just 25 2005 look too much of it's more reason to every every about 100 100 150 coils you need to replace the were crops and so that's that's actually rather frequent the backup roles too they can say about these concern about a thousand Tong hours every 25 thousand to 30 thousand pounds of steel process they need to be replaced as quickly we don't replace them we remove the reprocessed the surface we reworked the surface we removed the damaged and UK's can use the same role 4 for a while but not not forever wrecked so we this so now we have we're out of the way roughing we made a bar and we're going to transfer this bartered to finish a mail to the finish so let's 1st look at but temperatures again this is a more detailed view of what the temperature variations look like let's look at what is temperature at the In this century of our material so that would be this medal gray lying so I see the temperature reducing and then passing through the 7th roughing passes yes right in mind when they come out of the rough roughing past my temperature should be around 1100 so that at the thousand 50 I started rolling don't know what's funny you notice here is that the temperature actually increases why does a temperature increase the temperature increase because I'm deforming the material and so I adding energy yes and it heats up the material the surface against the surface at 0 sorry I'm looking at this as a strip middle this is between the surface to strip red here sorry about that and waded into the message is the same inside inside the material the and you basically heat up every time you do the the surface it's at the surface story because there you touching these role surface as and so you get every time you roll you get a a big debt indeed In the temperature of the surface of the strip yes but because the center is warm you reheat you reheat dissenter you you and you reheat should make the uh the surface as you go you see also that between the steps that the the rolling past there is considerable amount of of time there's 20 30 seconds and if you compare now too the finishing process yes there much that is of much faster succession and because the tender but you have the same story every time you touch they for all the surface will that's considerably however in the center you get heated and that the defamation you look at so the important message about this but I figure here is that you have in home watching in defamation you also have strain rates that can be in Homewood unions and we have continuous temperature changes and we also have the temperature in unity so we need to have very strict temperature control that's the best thing to achieve this because but if we do that we can get the right Mike restriction and the properties and the different ways in which we do this in the hot strip mill and the hot strip mill because we do defamation and thermal cycle we talk about thermal mechanical process and so they're are basically 3 simple ways it's more than actuality more complex and will talk about this as we go so you can build what we call a high-temperature role as it's basically everything is impossible Semitic and you always fully we crystallized the grains yes these Rico lies Grace McAuslan between did the deformation steps and eventually you get if you working with constructional steals a relatively coarse verite perlite might rastructure and you can the way you control the grain size is by by this request crystallization you up you can reduce the grain size you can do normalizing rolling yes there you are is trying to stay close to the finishing rolling close to the transformation so that the Austinite is full array crystallized but it's a smaller also denied career it's not costs and then you have many types of different ways to do thermal mechanical process and it's it's very important for plates steals it there we are doing the finishing by the very close to the transformation or sometimes even In the two-phase region the Austinite grains may not crystallized and that happens when we add these Michael Allen additions such as albeit yes and we have to obtain an extremely fine might rastructure and that's that's the realm of the real thermal mechanical process and this is a very often combined with what we call accelerated cooling so you do not get a fair I perlite Microsoft about the Benedict Microsoft or in some cases marked acidic MicroStrategy again and so
this this is kind of the range of temperatures where you would work for High high-temperature normalizing and so usually you know you're in the normalizing range for in the thermal mechanical range from
10 temperature variations so we already saw that in function of the thickness there at a temperature variations but there's also temperature variation along the length of your material and so this is a picture you have to imagine this is very was 500 meters right but the image has been compressed as it's compressed and you basically look at the temperature distribution also while Spadea a strict along its length and also along the way so what you see the head this 817 so this is what comes out of the finish and this is what comes out of the Finnish or at the end it's 800 accidents 60 degree difference that's 1 of the other thing you can see is that I'm not well the the edges of black so that means the edges are cooler then are the rest of the material so In other words we have not only temperature variations in the thickness which we have temperature variations in the end with and in the length directions and then we talking about you know here we talk about 60 degrees you know considerable amounts of temperature difference so I. so we will try to minimize these differences and so and in particular will do that at the at the level of the transfer and of course the achieving high levels of temperature homogeneity implies that you need additional equipment that's when you need equipment additional equipment it means that investments operation costs and maintenance costs so you always have to balance this with the type of products that you make the cancel let's have a look at the solutions was 1
of the solution is and is a transfer table With a coffin and so this is where you see here the bar coming out of what looks like a tunnel it's actually a basic you cover yes still the steel construction which some refractory has so that was the radiant heat you don't lose so much heat so this is insulated basically cover but you
can have active covers in these active covers the actually have burners has so the day will they're able to avoid heat loss so that Prince which should give you constant in uniform bar temperature and option also add work as a buffer which was buffer well is is is is a place where you you keep the ball for a while yes and if you have an active cover you can keep it longer because there is no risk for a lot loan which means less risk for large temperature losses again typical temperatures for the start of the rolling thousand 50 1090 here OK In the new
technologies are due coil box technologies because the coil box technologies are really really good in home which analyzing the temperature and the reason is very simple if I have a BA that's a 100 meter long yes but that's 23 mm take and 16 100 mm wide yes I have a surface exposed of 325 square meters yes that's a lot of surface where you can lose heat yes if I take the same bar and I roll it into a coral the total surface it's 11 square meters yes sir the heat loss will be minimized and on top of that because I have a massive coral I will have less than temperature in Homewood Unity's
yes and this is shown here for instance you have a constant temperatures and so when you roll you temperatures unchanged so you don't have to correct 4 the fact that the material becomes harder of forensic if you have the conventional rolling and you measured the power the ruling power as a function of the times yes you have to increase steadily increased the rolling load because your material becomes stronger and stronger and if you have a coral box the temperatures much flatter yes and you don't have to increased the rolling and there is no difference in rolling load last difference in from the start to the end of the coils of the barked brought against and this is a temperature measurements here is coming out of the box into the finisher the temperature should be at around while here in this particular case around thousand 15 years he conceded what comes out of the coil box the temperature differences about 12 degrees as in the case of the conventional 80 degrees with the example I showed was 870 on 1 side the 10 on the other side was about 60 degrees so that so that's now reduced to from more than 50 degrees to less to buy up to about 10 degrees so very stable rolling conditions there and of course everything translates into more homogeneous Mike rastructure you can so this is
basically what a coil box looks like it's position between the roughly and a finishing stand conserves the transfer bar temperature and you get the whole genius transfer temperature doctor basically like a Correla yes With it an
you were and there were there are served by the witnesses lied about this you know for certain a high quality high quality grades was mostly in the stainless steel area yes you will have not not only coiled boxes but actually coil box furnaces that's where you can actually we he the bomb the coral bark to specific temperature has it's a very important investment of course but the next and you only do this for really high end products where you don't want to make too much scrap and have losses in high value-added products this is an example of what went score a box furnace would look like looks like so the big advantage of being an additional advantage of the coil box is that you you have a shorter I was shorter the the line also so he noted that D so when you are these units you consist of a unit that coils that did bar and the unit that uncoils and substance not there's always 1 1 a unit that court makes do the coil and 1 unit that uncosted so you can call calling on 1 end and the calling on the other hand against otherwise you would keep the finisher you know doing nothing while you calling this can so there is an increased productivity but now that there are some interesting which usually the original classic Mandrell the thing is to be classical choral books had has a Mandarin this minerals basically this uh this axis didn't the disease body here around which you form the the court units now of course this Mattel here this Mandrell here this is "quotation mark yes so that means that when you use a man's role the inner wraps are actually not at the right temperature the cold colder so in order to avoid this there they the the latest coil box technology is called Manjural less yes and so you will wraps the coral without the central Mandarin and the big advantage of having a Mandrell that it's very simple then to transport the corals from the calling opposition to the UN calling position because and this is barges goes From this position to this position and Europe you're in business if you don't have a Amanda all you need to more complicated system to transfer transferred the coral From the coiling position to the UN coiling position so it kind of gets rolled soldier these these roles here and but the big advantage is
that you know are you have absolutely perfect home which in 80 in the temperature you can have a look at this pectorals here that shows you how the the Boris transfer is done very carefully because you you don't want to damage to coral and you don't want you know it has to remain nice circle Australia who wanted to come now is the there is a certain people are very concerned about the the fact that the edges of your of district loose a lot of heat and power cold hands and for the big their products where it's important that there is no edge cooling has so there is a possibility to mount induction heaters on the line the and basically this induction heating using doctors produce eddy currents in the strip the bench and the Andes currents will he ducked the strict edge was so this is what it looks like the from the outside his no strip going in since this is a an edge heater In operation is busily non-contact heating matter most and this is how it works you basically have 80 make a magnet and the Petunia coil and you while you generate a deep currents in the strip as it passes the heating is is very fast so that is no problem in with the fact that the strippers is moving by so this is some
parameters here and you can also reheat considerable thickness of material good so we've got this
bar it's still active but the temperature at the right temperature and the right thicknesses of entry thickness about 25 mm the temperature about 50 but thousand 50 degrees C and you're ready to do go into officials the 1st thing you do it is the bar will pass through the shares the shares an
hour removed the fish tales order talks you you arrive at 2 finishing mill with a straight edge as examples of the
equipment the end the share it is called the crop here OK and that it can I be either a flying sheer or a drum shearer the reason is that this sharing operations is spot are made you don't want to stop the bar to share as you what you cut this year you share offer the crop the Abacha's me as it as it goes so you have to have a flying it goes goes with the 2 goes down with the with the Borodin and cuts it as it comes by this but when you have a flying or drum she wasn't so denies are a drum and and as the district passes it gets caught on to the bar is not stationary again why do we do this because we want continuous operation we don't want temperature losses etc but again this is a very simple I think I'm but it's very important this is very important to have the right to shared profile because if your profile is not correct you may be damaging the ropes yes so the sheer profile has has looks like this I don't know if you've ever done sharing in the laboratory which usually use a kind of pensioners and you have terrible edge let's that stick out yes on which you can cut yourself well this this and in the end conventional in and in sharing you don't want this kind of a profile don't have that kind of proof and consult sharing very important and this
is an example here of crops wikis that amounted on on drums a slightly different system OK again due to the entry equipment will involve a guide world now you're seeing the guy in the direction of the day would district would move you have with adjuster and in a position duchesses so because you want to to the bark moved in the correct directions toward the the finishing the men OK right so what do we want to do in the finishing mill required the finishing temperature obtained their did the thickness of course maintained the with achieved a profile the 2 women with profile admitted the shape of distress and we want to avoid cobbles squabbles are this kind of thing and that is the problem during the the role that this is a particular unit the type of cobalt that occurs when you rolling there the hot strip but you can also have cobbles between 2 stance where the material where there is a problem with tension control and then you accumulates struck between 2 stance yes and it means that you get 3 400 meters of red-hot metal between 2 stands and its total disaster you can imagine this because it has to be removed and this also has to be removed so that so that the rolling stability is important thing again there are lots of improvements in technologies nowadays hydraulic gage adjustments rule-bending CVC technologies to control the shape of the stripper will talk about this in later in separate session and crossed roles and then hydraulic bloopers and those are the type of Lopez which control the tension between the steps but in an example of
this this squabble here where does this come from well when the strip the last and stand yes there's basically nothing holding onto it yes and it will have to travel there that the front and will have to travel from the finisher to the Correla yes on its on its own and of course it will pass the cooling section has but it's basically this is not a know nothing is holding it it's got to go straight to the Correla if you have strip yes there is a possibility that this district will move will start to fly basically yes will start to basically float in the air fares and found it'll come come back down yes so you will you'll have the rollers it will rebound and it'll start forming waves yes forming had the head Colonel flies the and then by the time the do the disturbance can be so important but by the time you arrive at the corners there are those that the place where you have to engage the strike and is missed yes and then you get this the material that comes out 10 meters per 2nd and it's nothing to pick it up and it's a disaster that's very important to know that's so this is very much a function of district thickness so you get very high waves a of instability waves when you you make thin strip definitely 1 of the reasons why the people in the hot strip mill they do not like to make very thin products because of the year there is no basic metallurgical reason other mothers and but there 2 other reasons is that the risks of this happening and and that the fact that the productivity goes down so cobbles so a finishing
mill around in general will look like this that you have stands in tandem yes and the strip goes through each stand and finally to the Correla of course the temperature is reduced as you go through each stand this
is a typical of you here Of the temperature distribution in the thickness of the strip as you roll it so what do we see 1st look at the middle again the middle every time you roll increases the temperature that's because you dump energy in your material has had most of it is turned into the at the surface is an entirely different story now we have the effect of for instance here what is this here you have temperature lost at the surface but no temperature increase in the middle and that's because the weird the scaling would the scaling and that we do with what every time he passes through the role bite we touch the the cold surface Of course Gold the surface of the work rules and so you get the temperature drops and in between the roles you also have an interest in and analysts braced for a for a variety of reasons the owner the strain rates in the the strip production are I'm pretty important yes but what is also important body Inter past yes so the India pastimes In an instructor production since the strict this system the stripped this use reprocessed between a thousand and 900 degrees seeing this and the Inter past times against can be you can see here less than 1 2nd and the reason is the history and and that is very important because that means that we can have very optimal thermal mechanical process we can accumulate the formation at high temperature and achieve grain refined and that's very important thing In the case of plate material you I that is much more difficult because in case of a plate processing we usually work which reversing males yes because we have the and Pic yes we have reversing males yes and are inter pastimes are usually at least 10 seconds to play goes back and forth in the reversing singles so it's not difficult to achieve thermal mechanical processing on plate products than it is on the strip products and will come back to that when we can we talk about plate products and the and how they do produced the
other hot strip mill sir the finishes are usually for high that type of stuff a mail the diameter of the roles typically around 700 mm the setting gaps setting nowadays in modern facilities a hydraulic automatic gage control and and this is a typical the values of the reductions that you get in the 7th the Stanton mail so you you start by relatively high reductions in as you remember and then as you goes on the line you reduce the amount of reduction yes so what happens here it's also interesting this speech of the stressed coming in and and coming out is very different In fact you have the speed of about 2 . 5 meters the 2nd coming in and the speed that can be 20 meters the 2nd coming out so very large differences in spins and speed yes and so on but let me out so few words whether it means that there this the the end of your strip yes and the start of history it goes through a different thermal cycles yes the the the the end of the trip has has a lot more time to cool so even if you strip was perfectly homogeneous in the bar against an even if you was but you know you everything went perfect yet still that they can be even if the cooling rate was the same everywhere right still there the end would always be cooler than the then there the start because it's got to wait yes it's got to wait till all the material that goes before it is processed yes so it's it's it's it takes more time for the ends pieces to go through the life basically should always be cooler so how do we work with this this will then there are the ways in which the finishing nails can address this problem and that's called speed up yes which basically happens is that the male roles not wait days this stable the rolling speed but with an accelerating rolling speed yeah so you start to roll at relatively low speeds and use speed up the rolling yes so that you compensate for this temperature for this time difference since and again minimized temperature differences and so far as you can only do this if if you have a very clever and models mechanical and thermal models for your for your process and again it's something you don't see when you visit a hot strip mill they're all daily the fact that there's a lot of intelligence needed to achieve that you can use to achieve high product home which energy and and as a consequence hot product quality OK so basically sound we've already talked about the basic structure of these mills you have no housing you have to work rules and you have the top and the bottom backup roles in on the top you can have the the screwed down and hydraulic or hydraulic cylinders to control them pressure the mode on the rolls standard role gap and on the bottom here for instance for this particular configuration you have a load cell then you have and so this is that the basic stance but very
often these there you have it systems here that will have to make sure that the bolts yet admitted that district a profile In control became so what do I mean when you roll it stress you have to imagine desire work roles and here is Europe stretch and uh you remember the pressure it is applied on the chops and in the trucks in Europe you have the the bearings the bearings like this yeah and then your your your role because of this there is a slight bending Of these roles yes when the roll bands that means that there the material actually is not not flat but it has a shape a profile has meant of course you need to you want to control that's in 2 days at nowadays very largest gold crown yes or it's it's a profile defect as we so you need to control and there different ways in which you can do this with 1 of the ways in which you can do this is by compensating the bending that's given this way by having for instance this is 1 of the ways the system that will calls bending in the other way that will bend the cylinders in the other direction this and so these bending cylinders are mounted in Inwood in was specific case in what we call Mae West blocks us and so these abandoned deserve basically hold the bending cylinders 10 there's a lot
of equipment associated with a mail in the the mill stands out just to give you an idea of what would you typically have on a finishing milk you have cooling equipment and there may be lubrication equipment for instance here and I want to point out the system here which is called role term ground controllers yes and it these are special units that control which called the thermal crop against you what is thermal crap at the same time as you rolling new bending this would happen does that you're rolling the very people of hot piece of material what happens when you it material it expects so what does it mean is on top of having this I expansion and abandoning this part here of distress but the city of the role will have a different diameter it will be because it's what it'll be whatever the heating and the expansion can be different depending on if this is for instance a hotspot of the hot hotter part for some reason it's hotter than the diameter will be that will be different and so you will also have what's called thermal crown so you your profile will not only have profiling this but it will also have slight differences which are due the thermal variations on the on the Raul surface so how do you address this will you address this for instance by having role thermal ground control so what is this before he looks sideways it's basically a header His went lots but we put it this way With losses nozzles yes lots of nozzles and each another controls the temperature of a segment of the role yes so if you need more cooling there there will be more the a source of water coming out of debt particular also and that way you can achieve or minimize minimize the effect of thermal cracker very important a again to achieve quality you can in their assistance to blow oxides away you have unity you may want to cool the strip in between the interstate Of course 1 of the things you absolutely need to do is also the surface of the cool the surface of your there also just cooling systems that so for the for the backup role the stand for the work all
you have cooling system so so what happens in With 2 With this this interaction between the hot strip and the work of the role for instance and so when when they come into contact before they come into contact this some radiation heat to the surface of the role and then in contact there is he transfer and then again radiation heat transfer when they're at the exit you use the cooling heaters yes before and after the the rolling to make sure that the role don't doesn't he up the temperature variations yes did it at the surface of the role it's quite considerable news so the year the surface gets heated by the hot strip and then get schooled by the thermal spray so let's have a look at . 1 2 3 4 and 5 years so what does the temperature and look like at the surface so when when you go from . 1 2 point to the temperature raises yes 500 degrees yes and then as we come out 4 the temperature drops and as we come to fight you then you come to the cooling spray headed the temperature is back to normal and that is we didn't last and 2 seconds the loader surface 25 millimetres below the surface writes about an inch below the serve you get a temperature increase of about 100 5 centimeters below the surface is not so much effect so you get a lot of thermal stresses at the surface there's a lot of thermal fatigue yes so what is the result of that it is damage to the surface damage to the surface so we we need again this 1 of the reasons why are in addition to this is where this thermal fatigue requires us to change the rules so frequently this is and in between the Inter stance so you have so did the district goes from 1 out of 1 a melt into the next 1 and just to strip tension is controlled by what we call this ever look into more
details and so we have some cooling of distress In between the air mail it the 2 smell stands and and we had a single cobble God the area what do we have here a cooling of the cooling headers here :colon headers that spray the water on the the work rules here yes and the other thing
that's important between those 2 Nelson's is due Bloomberg and the looper is basically the the mechanism that controls the tension between those 2 2 ships he couldn't success of Mel stance was basically consists of role yes and there is way to Mordor here it is the server water it's pressed against this the stripped so anytime succeed you don't want In 9 in the mail and there are velocity differences and since the last 2 different so the exits In perfect conditions the exit velocity is equal to the entry velocity right then the mass is you have mass balance yes but any change in this Will cause either an increase in tension when you take into much more which comes out or you'll get the decrease in tension where it won the velocities the velocity in is much smaller yes and you can get cobbles so the the year the mechanism that controls you know make sure detentions stays the same is this it is this before I finish all finishing at 2 2 2 3 minutes now and I just want to finish with 2 year With to finish a mail the finishing millions found about his role changes now so did we need to replace them because a a lot aware and they usually you don't throw them away millions you recycle them and you transfer them to grinding shop and backup roles several days to several weeks there will be replaced work rules we grind and much more frequently yes and so they replaced every few hours or so for few days depends on how much production you have by the end of finishing mills and I think as I said to to thousand 500 tons of steals 70 thousand for the backup roles yes and of course when you replace their roles knew that you cannot roll right OK so that has to be minimized so you have 10 to 15 minutes time to replace the roles and then you bring them to the grinding jobs usually they're set up there ready there and if you visit if few ever visited a hot strip mill you will see that in front of every else and they're up there as a pair of roles ready to place the used the worlds here than they usually pretty mounted in the trucks so you just slide men and and it's it's quick so in the grinding shoppers use roles will then go they will be ground you will take out In removed the damaged layers on the special CNC machines yes and it's a lot of work the again it's 24 look good on threat if it's 24 hours a day but it's you know you process typically about you know hundreds of rolls yeah and it takes you about 30 20 to 30 minutes to process and you can read write and how often can you reused as well about 100 times after that you've removed either of the diameters to is this change too much so that I the units diameters has become too small right or you have removed too much of the hard surface layer of the very hot surface layer to about 100 times 2 France's if you have a 600 the about 700 millimetre diameter role will be placed when it's 6 630 mm was so OK so this is an
example here this is the role it's mounted on the CNC machine it's you it's you it's you so you removed a warren of surface with this grinding wheels it's a grinding wheel and write a you removed of the Order of and half a millimeter too few millimeters the it depends very much on the amount of damage and on the road and
here you see the work rules being the replaced and these are the backup roles being
replaced and the variety of schemes where are you if you want 2 single work rules most of the
times you do work or a prepackaged and you can never replace him very quickly Clinton right so
alone all stuck here because I'm already over time and found that is the main thing will do but Monday at 4 o'clock


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