An investigation of worn work roll materials used in the finishing stands of the hot strip mill for steel rolling

The surface failure characteristics of different work roll materials, i.e. High Speed Steel, High Chromium Iron and Indefinite Chill Iron, used in the finishing stands of a hot strip mill have been investigated using stereo microscopy, 3D optical profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. The results show that the surface failure mechanisms of work rolls for hot rolling are very complex, involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. Despite the differences in chemical composition and microstructure, the tribological response of the different work roll materials was found to be strongly dependent on the material microstructure and especially the presence and distribution of microstructural constituents, such as the different carbide phases and graphite (in the case of Indefinite Chill Iron). Cracking and chipping of the work roll surfaces, both having a negative impact on work roll wear, are strongly influenced by the presence of carbides, carbide networks and graphite in the work roll surface. Consequently, the amount of carbide forming elements as well as the manufacturing process must be controlled in order to obtain an optimised microstructure and a predictable wear rate.

Modeling precipitation and its effect on recrystallization during hot strip rolling of niobium steels

Using a physically based model, the microstructural evolution of Nb microalloyed steels during rolling in SSAB Tunnplåt’s hot strip mill was modeled. The model describes the evolution of dislocation density, the creation and diffusion of vacancies, dynamic and static recovery through climb and glide, subgrain formation and growth, dynamic and static recrystallization and grain growth. Also, the model describes the dissolution and precipitation of particles. The impeding effect on grain growth and recrystallization due to solute drag and particles is accounted for. During hot strip rolling of Nb steels, Nb in solid solution retards recrystallization due to solute drag and at lower temperatures strain-induced precipitation of Nb(C,N) may occur which effectively retard recrystallization. The flow stress behavior during hot rolling was calculated where the mean flow stress values were calculated using both the model and measured mill data. The model showed that solute drag has an essential effect on recrystallization during hot rolling of Nb steels.

A Cost Model for the Effect of Setup Time Reduction in Stainless Steel Strip Production

Setup time reduction facilitate the flexibility needed for just-in-time production. An integrated steel mill with meltshop, continuous caster and hot rolling mill is often operated as decoupled processes. Setup time reduction provides the flexibility needed to reduce buffering, shorten lead times and create an integrated process flow. The interdependency of setup times, process flexibility and integration were analysed through system dynamics simulation. The results showed significant reductions of energy consumption and tied capital. It was concluded that setup time reduction in the hot strip mill can aid process integration and hence improve production economy while reducing environmental impact.

Tribology in Metal Working

This thesis focuses on the tribological performance of tool surfaces in two steel working operations, namely wire drawing and hot rolling. In all forming operations dimensions and surface finish of the products are of utmost importance. Forming basically includes three parts – forming conditions excluded – that may be changed; work material, tool and (possibly) lubricant. In the interface between work material and tool, the conditions are very aggressive with – generally or locally – high temperatures and pressures. The surfaces will be worn in various ways and this will change the conditions in the process. Consequently, the surface finish as well as the dimensions of the formed product may change and in the end, the product will not fulfil the requirements of the customer. Therefore, research and development in regard to wear, and consequently tribology, of the forming tools is of great interest. The investigations of wire drawing dies focus on coating adhesion/cohesion, surface characteristics and material transfer onto the coated steel both in laboratory scale as well as in the wire drawing process. Results show that it in wire drawing is possible to enhance the tribological performance of drawing dies by using a lubricant together with a steel substrate coated by a polished, dual-layer coating containing both hard and friction-lowering layers. The investigations of hot rolling work rolls focus on microstructure and hardness as well as cracking- and surface characteristics in both laboratory scale and in the hot strip mill. Results show that an ideal hot work roll material should be made up of a matrix with high hardness and a large amount of complex, hard carbides evenly distributed in the microstructure. The surface failure mechanisms of work rolls are very complex involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. This knowledge may be used to develop new tools with higher wear resistance giving better performance, lower costs and lower environmental impact.

Calucaltion of waste heat from hot rolled steel coils at SSAB and its recovery

Hot rolling process is heat input process. The heat energy in hot rolled steel coils can be utilized. At SSAB Strip Product Borlänge when the hot rolled steel coils came out of the hot rolling mill they are at the temperature range of 500°C to 800°C. Heat energy contained by the one hot rolled steel coil is about 1981Kwh whereas the total heat energy for the year 2008 is 230 GWh/year.The potential of heat is too much but the heat dissipation rate is too slow. Different factors on which heat dissipation rate depends are discussed.Three suggestions are proposed to collect the waste heat from hot rolled steel coils.The 2nd proposal in which water basin is suggested would help not only to collect the waste heat but to decrease in the cooling time.

Finite element analysis of hot rolling in the blooming mill

During this thesis work a coupled thermo-mechanical finite element model (FEM) was builtto simulate hot rolling in the blooming mill at Sandvik Materials Technology (SMT) inSandviken. The blooming mill is the first in a long line of processes that continuously or ingotcast ingots are subjected to before becoming finished products. The aim of this thesis work was twofold. The first was to create a parameterized finiteelement (FE) model of the blooming mill. The commercial FE software package MSCMarc/Mentat was used to create this model and the programing language Python was used toparameterize it. Second, two different pass schedules (A and B) were studied and comparedusing the model. The two pass series were evaluated with focus on their ability to healcentreline porosity, i.e. to close voids in the centre of the ingot. This evaluation was made by studying the hydrostatic stress (σm), the von Mises stress (σeq)and the plastic strain (εp) in the centre of the ingot. From these parameters the stress triaxiality(Tx) and the hydrostatic integration parameter (Gm) were calculated for each pass in bothseries using two different transportation times (30 and 150 s) from the furnace. The relationbetween Gm and an analytical parameter (Δ) was also studied. This parameter is the ratiobetween the mean height of the ingot and the contact length between the rolls and the ingot,which is useful as a rule of thumb to determine the homogeneity or penetration of strain for aspecific pass. The pass series designed with fewer passes (B), many with greater reduction, was shown toachieve better void closure theoretically. It was also shown that a temperature gradient, whichis the result of a longer holding time between the furnace and the blooming mill leads toimproved void closure.

Koldiffusionens inverkan på utmattnings-hållfastheten hos varmvalsade sexkantsstänger;The influence of carbon diffusion on the fatigue strength of hot rolled hexagonal rods

Helstångsborr och konstång kallas bergborrverktyg, som tillverkas av sexkantiga stänger med inre hål för ledning av spolvatten. Dessa spolhål är klädda med ferritiskt rostfritt stål. Innan valsning borras ett centrerat hål i stålämnet som ska valsas. I det borrade hålet appliceras ett rör av ferritiskt rostfritt stål och i det röret skjuts en manganstålskärna in. Efter valsning dras kärnan ut och ett spolhål med invändigt foder av rostfritt stål bildas. Under uppvärmningen och valsningen av stålämnet sker normalt en koldiffusion från manganstålskärnan till det rostfria fodret. Fodrets syfte är att skydda spolhålets yta mot erosion och korrosion.Syftet med arbetet var att hitta en metod som garanterar uppkolning av det invändiga fodret, samt att utreda vad uppkolningen betyder för den mekaniska hållfastheten i stängerna. Ett laboratorieförsök visade att det var bra, med avseende på uppkolning, att blanda stearat i kärnbestrykningsmedlet. Kärnbestrykningsmedlet penslas på manganstålskärnan innan den förs in i stålämnet som ska valsas, dess syfte är att minska friktionen vid kärnutdragningen efter valsning.Ett försök utfördes i valsverket med stearat i kärnbestrykningsmedlet. En grundlig undersökning utfördes på två hetor som valsats med stearat-bestrykningsmedel, samt på en traditionellt tillverkad heta för att ha som referens. Hetorna kapades till provstänger om 1,5 m, totalt undersöktes 55 st.Utvärderingen av verksförsöket visade att stängernas kvalitet blir tillräckligt bra om ingenting oförutsett händer i produktionen, oavsett om koltillskott är tillsatt i bestrykningsmedlet eller inte. Arbetet gav inte en garanterande metod, men visade att stängerna normalt håller hög kvalitet.

Faktorer som påverkar uppkomsten av hot och våld inom psykiatrin

Syftet med denna systematiska litteraturstudie var att beskriva faktorer som påverkade uppkomsten av hot och våld inom psykiatrin. Till resultatet har författarna använt sig av tjugoen vetenskapliga artiklar som hämtats ur Högskolan dalarnas databaser ELIN, Academic Search Elite samt Cinahl. Sökord i olika kombinationer har använts för att få fram relevant litteratur till studien. De sökord som användes var violence, nursing, mental health nurses, aggressive patients, aggressive behaviour, psychiatric units, patients, factors, prevention, aggression, nurses, psychiatric, management, psychiatry och causes. Även manuell sökning i tidskrifter har gjorts. Artiklarna skulle vara publicerade tidigast år 2000 om inte tidigare studier ansågs innehålla relevant fakta för studien. Granskning av artiklarna genomfördes med hjälp av granskningsmallar. Resultatet visade att bemötandet av patienter inom psykiatrisk vård var av stor betydelse för om hotfulla och våldsamma incidenter skulle inträffa. Att som vårdpersonal försöka förstå anledningen till den uppkomna situationen kunde leda till att dessa situationer kunde undvikas. Patienterna upplevde ofta att personalen inte lyssnade och detta var en vanlig orsak till att våldsamma incidenter uppstod. Vårdpersonalen ansåg istället att patientens sjukdom var orsaken till uppkomsten av hot och våld. På avdelningar där patienter med paranoida och psykotiska tendenser var intagna ökade risken för våldsamma situationer. Patienterna upplevde ofta tiden på den psykiatriska avdelningen som långtråkig och det påverkade stämningen. Både vårdpersonal och patienter ansåg att mer aktiviteter skulle minska aggressionen på avdelningen.

Haren. Ett hot mot idrottens värde?

Inom friidrottens löpgrenar kan man idag se vid de stora galorna att det finns en person som har till uppgift att springa före övriga deltagare och springa i en viss fart som har beställts antingen av arrangörerna eller någon löpare. Denna person kallas för "hare" vars huvuduppgift är att se till att ett visst tempo hålls under loppet. Men vad har detta fenomen för effekt på idrottens värde? Detta arbete ger en beskrivning av fenomenet "haren" både ur historiskt perspektiv samt hur det ser ut i nutida läge. Genom diverse teorier om vad som skapar värde inom idrott och hur idrott bör utföras för att uppfattas som mer "äkta" har fenomenet sedan analyserats för att bestämma om fenomenet är något positivt eller negativt för idrottens värde. Prestationer är något som ska genomföras på egen hand och idrottaren skall besitta de resurser som krävs för att kunna genomföra ett lopp helt på egen hand och kunna hantera både interna och externa påfrestningar. Att inte veta vem som kommer att vinna är den ovisshet som skapar spänning och därmed värde inom idrott. Med haren har man eliminerat denna ovisshet för att i stället få spänning genom att fokusera loppen på att slå rekord. Detta sätt att skapa prestationer har en mycket negativ påverkan på idrottens värde vilket får en detaljerad analys i detta arbete.

Hot och våld i socialarbetares yrkesutövning : Threats and violence in the socialwelfare secretary occupation.

2004, the SSR, Akademikerförbundet, made a study on the threats and violence as a social secretary in the municipal social services are exposed in their occupation of the "social secretary of threats and violence at work" (T-110192), conducted by Temo ab. We have chosen to use the study on a smaller scale and then made contact with five municipalities in the middle of Sweden to investigate social secretaries experiences of threats and violence. Using the cross-sectional design and a convenience sample, we have gained access to data from 56 people. From a sociological perspective, we have chosen to use Norbert Elias theory of universal configuration and interdependence, and Michel Foucault’s theories concerning power search explanation for the existence of threats and violent situations in the contact between social workers and their clients.

Undersökning av steady state och utvärdering av valskraft och friktion vid kallvalsning av aluminium

The purpose with this thesis was to examine the cold rolling mill located at Högskolan Dalarna and to stabilize the rolling process, to achieve steady state. Experiments with cold rolling of an aluminium strip have given results for rolling force, friction, reduction, strip tension and strain hardening. Results show that steady state has been found for the experiments with roll force and strain hardening, and not been found for the experiments with friction and reduction. Results show that increased strip tension gives lower roll forces. The roll force equation of Stone shows comparable results with reality for dry contact with reductions up to 30 %, but starts being incomparable with higher reductions. The roll force equation of Stone shows a bit higher roll forces than reality gave, but was comparable within reductions from 13 to 50 %. Experiments have shown that the aluminium strip has gone through strain hardening. Experiments show how the set roll gap did not yield the desired thickness reduction, there for the elastic spring constant for the rolling mill was examined and determined to be 417 N / mm for the specific alloy band. The influence of tension strip for roll force was examined and Results confirm the theory about how the roll force is decreased by increasing tension strip. The work rolls started to slip against the alumina strip as high tension strip; 70 N/mm2, gave low roll force; < 15kN.

Pedagoger i det sociala uppdragets gränstrakter : Att hantera familjerättsliga processer, hot och våld

Pedagogues in the borderland of their social task: dealing with family law proceedings, threats and violence Drawing upon an explorative study of family law proceedings from a school perspective, the aim of this paper is to examine the school staff’s strategies for solving or coping with problematic situations in this context. Gendered conflicts between adults and violence are extreme cases for pedagogues in school and preschool. How do the staff cope with their own and the children’s vulnerability? Based upon interviews with 22 informants, the staff’s strategies are outlined and discussed in relation to organizational and professional circumstances and intersecting social relations of power. An analytical construction of six types of proactive and reactive strategies, ranging from distance keeping to normalization of own exposure, is utilized in the analysis. Findings suggest that the staff’s strategies to handle challenging events in this context vary with the parent’s gender, class position and ethnicity. Further, it is argued that creating a sense of safety and promoting learning among the children may be obstructed by lack of support from the school’s organization, demands on staff to perform customer oriented attitudes towards parents and lack of clarity concerning the limits of the social task. Conflicts between the organization and profession on the one hand and the educational and the social task on the other hand, are thus illuminated. In conclusion, a further aim of this article is to contribute to broader discussions on men’s violence against women and children – in families as well as in workplaces and in the intersection between these two areas. 

Ökat hot och våld i arbetslivet – en följd av förändrade arbetsförhållanden? : En studie utifrån de svenska Arbetsmiljöundersökningarna 1991–2005

Increase in work related violence. A reflection of changes in working conditions? An analysis based on the Swedish Work Environment surveys. Victim surveys from Sweden show that the proportion reporting exposure to work related violence has increased. On the basis of the Swedish Work Environment surveys 1991–2005 this article focuses on the following questions: What kind of situations and working conditions are related to workplace violence? And, has the number of employees exposed to these working conditions increased parallel to the rise of reported workplace violence? Logistic regression analysis shows that some situations and working conditions are indeed related tothe risk of violence. To some extent exposure to these working conditions co-varies with exposure to violence. This result is more prominent for women than for men. Further research is needed to understand how changes in working conditions affect the risk of violence and the development thereof, not least from a gender perspective. Even so, changes in working conditions can not alone explain the increase of reported workplace violence in Sweden during this period. It seems that the influence of changed working conditions offers an interesting complement to criminological theories of broadened definitions and decreasing tolerance against violence in problematizing how an increase in reported workplace violence should and could be understood.