Development of a simulation tool for torsional vibration of branched power transmission system

In this master's thesis a mechanical model that is driven with variable speed synchronous machine was developed. The developed mechanical model simulates the mechanics of power transmission and its torsional vibrations. The mechanical model was developed for the need of the branched mechanics of a rolling mill and the propulsion system of a tanker. First, the scope of the thesis was to clarify the concepts connected to the mechanical model. The clarified concepts are the variable speed drive, the mechanics of power transmission and the vibrationsin the power transmission. Next, the mechanical model with straight shaft line and twelve moments of inertia that existed in the beginning was developed to be branched considering the case of parallel machines and the case of parallel rolls. Additionally, the model was expanded for the need of moreaccurate simulation to up to thirty moments of inertia. The model was also enhanced to enable three phase short circuit situation of the simulated machine. After that the mechanical model was validated by comparing the results of the developed simulation tool to results of other simulation tools. The compared results are the natural frequencies and mode shapes of torsional vibration, the response of the load torque step and the stress in the mechanical system occurred by the permutation of the magnetic field that is arisen from the three phase short circuit situation. The comparisons were accomplished well and the mechanical model was validated for the compared cases. Further development to be made is to develop the load torque to be time-dependent and to install two frequency converters and two FEM modeled machines to be simulated parallel.

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.

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.

A neural network-based preset generation tool for a steel tandem cold mill

This paper traces the development of a software tool, based oil a combination of artificial neural networks (ANN) and a few process equations. aiming to serve as a backup operation instrument in the reference generation for real-time controllers of a steel tandem cold mill By emulating the mathematical model responsible for generating presets under normal operational conditions, the system works as ail option to maintain plant operation in the event of a failure in the processing unit that executes the mathematical model. The system, built from the production data collected over six years of plant operation, steered to the replacement of the former backup operation mode (based oil a lookup table). which degraded both product quality and plant productivity. The study showed that ANN are appropriated tools for the intended purpose and that by this instrument it is possible to achieve nearly the totality of the presets needed by this land of process. The text characterizes the problem, relates the investigated options to solve it. justifies the choice of the ANN approach, describes the methodology and system implementation and, finally, shows and discusses the attained results. (C) 2009 Elsevier Ltd. All rights reserved

Computer aided process planning (CAPP) for flat rolling of copper alloys

The manufacture of copper alloy flat rolled metals involves hot and cold rolling operations, together with annealing and other secondary processes, to transform castings (mainly slabs and cakes) into such shapes as strip, plate, sheet, etc. Production is mainly to customer orders in a wide range of specifications for dimensions and properties. However, order quantities are often small and so process planning plays an important role in this industry. Much research work has been done in the past in relation to the technology of flat rolling and the details of the operations, however, there is little or no evidence of any research in the planning of processes for this type of manufacture. Practical observation in a number of rolling mills has established the type of manual process planning traditionally used in this industry. This manual approach, however, has inherent drawbacks, being particularly dependent on the individual planners who gain their knowledge over a long span of practical experience. The introduction of the retrieval CAPP approach to this industry was a first step to reduce these problems. But this could not provide a long-term answer because of the need for an experienced planner to supervise generation of any plan. It also fails to take account of the dynamic nature of the parameters involved in the planning, such as the availability of resources, operation conditions and variations in the costs. The other alternative is the use of a generative approach to planning in the rolling mill context. In this thesis, generative methods are developed for the selection of optimal routes for single orders and then for batches of orders, bearing in mind equipment restrictions, production costs and material yield. The batch order process planning involves the use of a special cluster analysis algorithm for optimal grouping of the orders. This research concentrates on cold-rolling operations. A prototype model of the proposed CAPP system, including both single order and batch order planning options, has been developed and tested on real order data in the industry. The results were satisfactory and compared very favourably with the existing manual and retrieval methods.

Computer simulation of form-roll design

Changes in modern structural design have created a demand for products which are light but possess high strength. The objective is a reduction in fuel consumption and weight of materials to satisfy both economic and environmental criteria. Cold roll forming has the potential to fulfil this requirement. The bending process is controlled by the shape of the profile machined on the periphery of the rolls. A CNC lathe can machine complicated profiles to a high standard of precision, but the expertise of a numerical control programmer is required. A computer program was developed during this project, using the expert system concept, to calculate tool paths and consequently to expedite the procurement of the machine control tapes whilst removing the need for a skilled programmer. Codifying the expertise of a human and the encapsulation of knowledge within a computer memory, destroys the dependency on highly trained people whose services can be costly, inconsistent and unreliable. A successful cold roll forming operation, where the product is geometrically correct and free from visual defects, is not easy to attain. The geometry of the sheet after travelling through the rolling mill depends on the residual strains generated by the elastic-plastic deformation. Accurate evaluation of the residual strains can provide the basis for predicting the geometry of the section. A study of geometric and material non-linearity, yield criteria, material hardening and stress-strain relationships was undertaken in this research project. The finite element method was chosen to provide a mathematical model of the bending process and, to ensure an efficient manipulation of the large stiffness matrices, the frontal solution was applied. A series of experimental investigations provided data to compare with corresponding values obtained from the theoretical modelling. A computer simulation, capable of predicting that a design will be satisfactory prior to the manufacture of the rolls, would allow effort to be concentrated into devising an optimum design where costs are minimised.

Bond Strength of Multicomponent White Cast Iron Coatings Applied by HVOF Thermal Spray Process

Multicomponent white cast iron is a new alloy that belongs to system Fe-C-Cr-W-Mo-V, and because of its excellent wear resistance it is used in the manufacture of hot rolling mills rolls. To date, this alloy has been processed by casting, powder metallurgy, and spray forming. The high-velocity oxyfuel process is now also considered for the manufacture of components with this alloy. The effects of substrate, preheating temperature, and coating thickness on bond strength of coatings have been determined. Substrates of AISI 1020 steel and of cast iron with preheating of 150 A degrees C and at room temperature were used to apply coatings with 200 and 400 mu m nominal thickness. The bond strength of coatings was measured with the pull-off test method and the failure mode by scanning electron microscopic analysis. Coatings with thickness of 200 mu m and applied on substrates of AISI 1020 steel with preheating presented bond strength of 87 +/- A 4 MPa.

Kuparituotetehtaan tuoterakenteen ja logistisen tehokkuuden kehittäminen

Tässä tutkimuksessa on keskitytty tutkimaan kuparituotetehtaan tuoterakennetta ja tilausten kohdistumispisteitä sekä esittämäänparannusehdotuksia näiden suhteen. Valssaamon prosessivarasto on kokenut huomattavan pienennyksen ja tavoitteena on, että tästä huolimatta tuotantoa pystyttäisiin ohjaamaan vähemmin resurssein, materiaalipulasta kärsimättä ja nopeammin läpimenoajoin. Lisäksi työssä esitetään muita tuotantoprosessiin liittyviä kehitysehdotuksia, jotka tukevat tuotannon virtaviivaistamista ja varastosaldojen vähentämistä. Teoriaosuudessa selitetään Lean-tuotannon toimivuuttavalssaamon kaltaisessa toimintaympäristössä. Teoriaosuudessa on käsitelty Lean-tuotannon lisäksi myös Agile- ja Leagile-teorioita, koska myös näiden teorioidenyhteensopivuus valssaamon tuotantoon on merkittävä. Empiirisessä osassa on kuvattu tuotantoprosessin ja tuoterakenteen nykytila sekä esitetty kehitysehdotuksianäiden kehittämiseen esiteltyjen teorioiden pohjalta. Tutkimuksen perusteella esitetään muutoksia tämänhetkiseen tuoterakenteeseen, koska nykyisen kaltainen tuoterakenne on jäänyt osittain turhaksi varastojen siirryttyä tuotannon alkupäähän. Lisäksi ehdotetaan kuumavalssaussuunnitelmasta luopumista ja kuumavalssaimen ohjaussyklin lyhentämistä vuorokauden mittaiseksi, sekä esitetään, miten tuotantoon tulisi välittää nykyistä tarkempaa tietoa tilauksien valmistumisajankohdista.

CO2-päästötaseenhallinta terästeollisuudessa

Tämän diplomityön tavoitteena oli kehittää hiilidioksiditaseen hallintamenetelmää Rautaruukin toiminnoille päästökaupan olosuhteissa. Taseenhallintamenetelmä sisältää päästöjen laskennan sekä päästöoikeuksien hallintaan liittyviä asioita. EU:n laajuisen päästökaupan reunaehdot määrittelee päästökauppadirektiivi ja sen antama päästöjen seurantaa ja raportointia koskeva monitorointiohje. Työssä on tarkasteltu hiilidioksidipäästöhistoriaa ja laskentamenetelmiä niiden Rautaruukin toimipaikkojen kohdalta, joiden oletetaan kuuluvan EU:n päästökaupan piiriin. Toimipaikoista on tarkasteltu erityisesti Raahen ja Koverharin terästehtaita, sillä ne muodostavat merkittävimmän osuuden konsernin Suomen toimipaikkojen hiilidioksidipäästöistä. Muita tarkasteltavia toimipaikkoja ovat Hämeenlinnan ja Dalsbrukin valssaamot Suomessa, Smedjebackenin terästehdas ja Boxholmin valssaamo Ruotsissa, Mo i Ranan terästehdas ja Profilerin valssaamo Norjassa sekä Nedstaalin valssaamo Hollannissa. Kustannustehokkaan ja hallitun päästökaupankäynnin perustaksi yritystasolla tarvitaan päästötaseenhallintamenetelmä, jonka avulla voidaan määrittää syntyneet päästöt komission monitorointiohjeen vaatimalla tavalla, arvioida tulevia päästömääriä sekä hallita päästökaupankäyntiä. Päästökaupanhallintaan sisältyviä asioita ovat saadut ilmaiset päästöoikeudet, ostettavien tai myytävien oikeuksien määrä, kaupankäynnin ajankohta, päästöoikeuksien erilaiset hankintamahdollisuudet, päästöoikeuksien hinnanmuodostus ja riskienhallinta.

Fluoriditasetarkastelu ja päästöjen hallinta ferrokromi- ja terästeollisuudessa

Työn alkuosassa kartoitettiin AvestaPolarit –yhtiöiden Tornion tehtaiden keskeiset fluoridilähteet kuten fluspaatti, valukuonat, valupulverit ja fluorivetyhappo. Valupulverien ja kuonien haihtumis- ja liukoisuuskäyttäytymistä valaistiin kotimaisten ja kansainvälisten tutkimusten avulla. Tutkimustuloksia sovellettiin pääpiirteittäin Tornion tehtaiden tilanteeseen ottamalla huomioon tekijät, jotka saattoivat lieventää tai vahvistaa fluoridien vaikutusta ympäristöön. Yleisesti fluoridien ympäristö- ja terveysvaikutukset arvioitiin vähäisiksi. Työn kokeellisessa osassa määritettiin Tornion tehtaiden ferrokromitehtaan, terässulaton, kuumavalssaamon ja kylmävalssaamon fluoriditaseet. Jokaisen osastojen syötteiden fluoridipitoisuudet selvitettiin tuottajien ilmoittamien tuotekoostumuksien, spesifikaatioiden ja fluoridianalyysien perusteella. Fluoridien kokonaismäärät laskettiin jokaiselle syötteelle ja ne suhteutettiin kunkin osaston vuoden 2001 tuotantotasoon. Tasetarkastelussa suurimpina fluoridisyötteinä nousivat odotetusti esiin terässulaton käyttämä kuonanmuodostaja-aine fluspaatti (CaF2) ja kylmävalssaamon peittaushappo, 70 prosenttinen fluorivetyhappo (HF). Lisäksi muita merkittäviä syötteitä olivat kylmävalssaamon käyttämä kalkkipitoinen sekakuona ja ferrokromitehtaan sulatuskoksi. Tuotoksien eli päästöjen fluoridipitoisuudet saatiin selville päästömittauksin. Jätevesistä otettiin pääosin viikoittaisia kokoomanäytteitä, jotka analysoitiin tehtaan laboratoriossa. Kaasumaiset tuotokset oli määritetty kertamittauksien perusteella. Kiinteiden tuotoksien eli sakkojen ja kuonien fluoridimittaukset suoritettiin 3 sulatuksen kuonanäytteistä ja sakan vuosinäytteestä. Tuotoksista suurimmat ominaispäästökertoimet olivat juuri terässulaton AOD-konvertterin ja senkkauunin kuonilla ja kylmävalssaamon neutraloidulla regenerointisakalla ja neutralointisakoilla. Näistä ei aiheutunut varsinaista päästöä lähiympäristöön, koska sakat ja kuonat loppusijoitetaan tehtaan kaatopaikalle tai niitä käytetään liukenemattomassa muodossa. Tornion tehtaiden fluoridisyötteiden ja -tuotoksien mittausepätarkkuudet vaikuttivat fluoriditaseeseen. Ferrokromitehtaan fluoridisyötteet olivat kokonaismäärältään selvästi suurempia kuin tuotokset. Terässulaton fluoriditaseen tuotokset olivat suurempia kuin syötteet ja kylmävalssaamon syötteet sekä tuotokset olivat karkeasti arvioiden samaa suuruusluokkaa. Kuumavalssaamon fluoridisyötteet ja -tuotokset olivat mitättömiä. Fluoriditaseen epävarmuustekijöitä voidaan vähentää suorittamalla esimerkiksi useita fluoridimittauksia kaasumaisista päästöistä.

Position sensorless electrically excited synchronous motor drive for industrial use based on direct flux linkage and torque control

Synchronous machines with an AC converter are used mainly in large drives, for example in ship propulsion drives as well as in rolling mill drives in steel industry. These motors are used because of their high efficiency, high overload capacity and good performance in the field weakening area. Present day drives for electrically excited synchronous motors are equipped with position sensors. Most drives for electrically excited synchronous motors will be equipped with position sensors also in future. This kind of drives with good dynamics are mainly used in metal industry. Drives without a position sensor can be used e.g. in ship propulsion and in large pump and blower drives. Nowadays, these drives are equipped with a position sensor, too. The tendency is to avoid a position sensor if possible, since a sensor reduces the reliability of the drive and increases costs (latter is not very significant for large drives). A new control technique for a synchronous motor drive is a combination of the Direct Flux Linkage Control (DFLC) based on a voltage model and a supervising method (e.g. current model). This combination is called Direct Torque Control method (DTC). In the case of the position sensorless drive, the DTC can be implemented by using other supervising methods that keep the stator flux linkage origin centered. In this thesis, a method for the observation of the drift of the real stator flux linkage in the DTC drive is introduced. It is also shown how this method can be used as a supervising method that keeps the stator flux linkage origin centered in the case of the DTC. In the position sensorless case, a synchronous motor can be started up with the DTC control, when a method for the determination of the initial rotor position presented in this thesis is used. The load characteristics of such a drive are not very good at low rotational speeds. Furthermore, continuous operation at a zero speed and at a low rotational speed is not possible, which is partly due to the problems related to the flux linkage estimate. For operation in a low speed area, a stator current control method based on the DFLC modulator (DMCQ is presented. With the DMCC, it is possible to start up and operate a synchronous motor at a zero speed and at low rotational speeds in general. The DMCC is necessary in situations where high torque (e.g. nominal torque) is required at the starting moment, or if the motor runs several seconds at a zero speed or at a low speed range (up to 2 Hz). The behaviour of the described methods is shown with test results. The test results are presented for the direct flux linkage and torque controlled test drive system with a 14.5 kVA, four pole salient pole synchronous motor with a damper winding and electric excitation. The static accuracy of the drive is verified by measuring the torque in a static load operation, and the dynamics of the drive is proven in load transient tests. The performance of the drive concept presented in this work is sufficient e.g. for ship propulsion and for large pump drives. Furthermore, the developed methods are almost independent of the machine parameters.

Ristinivel nelivalssaimen voimansiirrossa

Nelivalssaimia käytetään yleisesti metallinauhojen ja -levyjen kylmämuovaukseen. Valssaimissa ristinivel siirtää vääntömomenttia kahden kulmassa olevan akselin välillä. Tässä tutkimuksessa haettiin ratkaisuja nelivalssaimessa esiintyvään epäsymmetriseen taivutustarpeeseen. Valssattavat kuparinauhat alkavat aaltoilla valssaajan puolelta noin yhden millimetrin paksuudessa. Tutkimuksen tarkastelu rajattiin koskemaan vain voimansiirrossa olevaa ristiniveltä, jonka epäiltiin olevan yksi mahdollinen ongelman aiheuttaja. Tutkimuksessa selvisi, että ristinivel ei aiheuta pystysuuntaisia voimia, jotka vaikuttaisivat suoraan nauhan poikkipintaprofiiliin. Kuitenkin ristinivelen aiheuttamat vaakasuuntaiset voimat voivat vaikuttaa epäsuorasti nauhan poikkipintaprofiiliin. Laatupoikkeamien taloudellinen merkitys havaittiin pieneksi, mutta myöhemmissä prosessivaiheissa kuparinauhan epäsymmetrinen poikkipintaprofiili aiheutti ongelmia.

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.

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.

Induktiv provning av ferritiskt rostfritt stå

The report examines the factors which may be a contributing cause to the problems that are present when ferritic stainless steel are eddy current tested in a warm condition. The work is carried out at Fagersta Stainless AB in Fagersta which manufactures stainless steel wire. In the rolling mill there is an eddy current equipment for detection of surface defects on the wire. The ferritic stainless steels cause a noise when testing and this noise complicates the detection of defects.Because of this, a study was made of how the noise related to factors such as steel grade, temperature, size and velocity. By observing the signal and with the possibilities to change the equipment settings the capability to let a signal filter reduce the noise level were evaluated. Theories about the material's physical properties have also been included, mainly the magnetic properties, electrical conductivity and the material's tendency to oxidize.Results from the tests show that a number of factors do not affect the inductive test significantly and to use a filter to reduce the noise level does not seem to be a viable option. The level of noise does not relate to the presence of superficial particles in form of oxides.The ferritic stainless steels showed some difference in noise level. Which noise level there was did match well with the steels probability for a precipitation of a second phase, and precipitation of austenite may in this case contribute to noise when using an eddy current instrument.The noise is probably due to some physical material property that varies within the thread.