Bar Mill Research Articles

A Case Study on Reliability Improvement of New Bar Mill Stand Gearboxes

Abstract: This paper describes the major work carried out in study & analyzing the critical reasons for failure of mill stand drive gearboxes that had occurred in New Bar Mill (Rebar Mill) in past 5 years. Suggest improvement measures and maintenance guidelines to decrease the probability of failure and hence develop an action plan for reliability improvement of New Bar Mill stand gearboxes. In the process, study on basics of gearbox and on rolling process of New Bar Mill has been done. Present production data analysis has been done for actual mill load condition. Based on present mill load data, current running service factor of gearboxes has been calculated. Many gearboxes of New bar mill stand found with low service factor than recommended as per AGMA standards. Accordingly, upgradation of mill drives gearboxes have been done for higher service factor and deployment of mill load alarm system to avoid any abnormal load on mill drive gearboxes has been carried out based on study

Investigation of Gold Recovery and Mercury Losses in Whole Ore Amalgamation: Artisanal Gold Mining in Nambija, Ecuador

Mercury is a highly toxic pollutant that can negatively affect human health and the environment; informal mining is one of the main sources of anthropogenic mercury release due to the separation or concentration by amalgamation that is still used to recover gold directly from ore. In the Nambija mining district, there is still informal mining based on practically no technical knowledge, which uses amalgamation as a processing technique for gold recovery. The production tasks that directly affect the handling of mercury during the in situ grinding–amalgamation process are monitored here. Experimental grinding tests were initially carried out in a “chancha” bar mill for a range of ore sizes and as a function of time; then, experimental tests were performed at the macro-level on grinding cycles in Chilean mills. Considering the characteristics of the ore mineral and the operation of the Chilean mills, it was determined that it is possible to reduce the Hg input to mill by up to 20% (at source). Experimental grinding–amalgamation tests were carried out at different times along with a grain size analysis of the ore; the recovery establishes the grinding time and the fraction in which the gold is extracted in a greater proportion, which affects the control of the amalgamation times. The mercury dosage used by the miners in the amalgamation process should be reduced, considering trials where there is better gold recovery and with the purpose of also reducing mercury losses; eventually, it is possible to jointly achieve an increase in gold recovery.

A study of conditions of surface defects formation when bar rolling at a bar and wire mill and methods of their elimination

Quality of long products surface is an important consumer property of it. In the process of measures elaboration aimed at the increase of long products surface quality, in particular of bars produced at the mill 370/150 of ОJSC “BMZ – managing company of holding “BMK”, studies were accomplished by metallographic laboratory. It was established that defects being revealed at the bars finishing, don’t relate to the quality of continuously casted billet (CCB), but formed in the process of deformation. Studies of the mechanism of surface defects formation on hot-rolled bar of rolling origin – deformation fissure and wrinkles were carried out. Results of numerical simulation of rolling in roughing group of stands at various temperature-deformation parameters presented. Regularities of formation of surface defects on the bar in the finished product were revealed. It was shown that the reason of the surface defects of rolling origin – deformation fissure and wrinkles was a high temperature gradient between the core and the surface of billet, originated from local overheating of surface in the angles zone of CCB resulted in nonuniformity of drawing out of different layers of the billet being deformed. To eliminate the defects, minimum possible temperature gradient between the surface and the core of a billet by controlled rolls cooling should be provided. By calculation, the maximum permissible temperature of the working surface of the rolls of the rough group of stands was established, and empirically the actual temperatures of the rolls with the current production technology, as well as the temperature of the rolls support bearings seats of the rolls were measured. The technical and technological possibilities for improving of rolling technology on a bar and wire mill in order to improve the surface quality of rolled bars were demonstrated. The existing technology was adjusted and new technological modes of rolling with controlled cooling of the rolls were established, which made it possible to significantly reduce the rejection of the finished product due to defects in rolling production. A device was proposed for the roughing group of stands, which enables to minimize the ingress of coolant onto the bar rolled.

Rational redistribution of waste of resources. Manufacturing of equipment for cutting machine

Almost all metal at OJSC «Byelorussian Steel Works» – management company of holding «Belarusian Metallurgical Company» includes today a mandatory physical-mechanical tests which allow to estimate the parameters of the raw materials, to know the reasons for loss of strength and determine operational characteristics. In the Central Factory Laboratory (CFL), laboratory of physical and mechanical tests (LPMT) for the preparation of samples of reinforcement equipment is used of knives in the cutting machine SIMA GEL-30 for cutting rebar from the mill 320 rolling shop № 1 with a diameter from 6 to 24 mm. In the drop-hummer shop annually discards off for scrap waste up to 50 knives. Hydraulic shears of drop-hummer shop used knives set of production of OJSC «Kobrin tool plant «SITOMO», made of steel grade 30ХСНВФА, according to the TU14-1-4461. The staff of the Central laboratory LFMI proposed to use waste knives drop-hummer shop for the manufacture of knives for the chopping of the machine SIMA GEL-30. On the basis of the conducted researches the technological scheme was developed for production of knives for the chopping of the machine SIMA GEL-30 cold cutting of reinforcing bar mill 320 the rolling shop № 1.

STATUS AND PROSPECTS OF DEVELOPMENT OF METALLURGICAL PRODUCTION IN BELARUS

A brief analysis of the status and prospects of development of metallurgical complex of the Belarus Republic is given in the article. Statistics of the structure of manufacturing sector by types of economic activities, including metallurgical production, in the Republic of Belarus as a whole and by regions is provided. It was noted that the largest share in the regional scale – 15.6% of metallurgy exists in Gomel region, due to the location of the main flagship of the Belarusian industry – the Belarusian steel works in Zhlobin city of Gomel region. Thanks to the systematic reconstruction and upgrading of existing equipment, introduction of advanced development in the field of metallurgical equipment and technologies OJSC «BSW – management company of holding «BMC» is dynamically developing in the coming years and it is planned to overcome the 3-million milestone in steel production and a threefold boost in productivity. The large-scale project of building a new bar mill with the capacity of 700 thousand tons of rolled products per year was completed in 2015. This production eliminated the strategic imbalance between the capacity of the steelmaking complex and related industries.The most important projects of the holding companies and the perspectives of further development of the holding «BMC» were described. The year of the science -2017began to JSC «BSW» with very significant event: OJSC «BSW – management company of holding «BMC» for the first time was awarded a Certificate of accreditation as a scientific organization.

Structure and properties of H-beams after accelerated water cooling

The structure and properties of the surface of DP155 H-beams made of 09G2S low-carbon steel are determined on the basis of materials physics, before and after thermomechanical strengthening—that is, accelerated water cooling. Such H-beams are used in monorail tracks. Highly defective structure in the surface layer is created by accelerated cooling of the beam in the line of the 450 bar mill at AO EVRAZ Zapadno-Sibirskii Metallurgicheskii Kombinat, in the following conditions: rolling speed 6 m/s; water pressure in the crosspiece-cooling section 0.22–0.28 MPa; temperature before cooling about 800°C. As a result, the hardness, wear resistance, and scalar dislocation density are higher than in the steel without strengthening. Without thermal strengthening, the microhardness of the samples is 2.70 ± 0.33 GPa, while the Young’s modulus is 269.2 ± 27.1 GPa. Thermomechanical strengthening increases its microhardness to 3.30 ± 0.29 GPa, and decreases the Young’s modulus to 228.2 ± 25.7 GPa. In addition, the microhardness range is increased from 2.20–3.80 GPa to 2.64–4.60 GPa, while the Young’s modulus range is reduced from 208.0–403.0 GPa to 184.1–278.2 GPa on thermomechanical strengthening. It is found that thermomechanical strengthening increases the wear resistance of the steel’s surface layer by a factor of ~1.36 (decrease in wear rate from 5.3 × 10–5 to 2.9 × 10–5 mm3/N m) and increases the frictional coefficient by a factor of 1.36 (from 0.36 to 0.49). Without thermal strengthening, the structure observed is dislocational chaos; the scalar density of the dislocations is (0.9–1.0) × 1010 cm–2. High-temperature rolling and subsequent accelerated cooling of the samples produces dislocational substructure of band type in the ferrite grains and of reticular type in the martensite grains: the mean scalar density of the dislocations in the surface layer is 4.5 × 1010 cm–2. Possible explanations for such behavior are discussed.

A Complex Use of the Materials Extracted from an Open-Cast Lignite Mine

Abstract The company Sokolovská uhelná, was the largest producer of city gas in the Czech Republic. After its substitution by natural gas the gasification technology became the basis of the production of electricity in the combine cycle power plant with total output 400 MW. For the possibility of gasification of liquid by- -products forming during the coal gasification a entrained-flow gasifier capable to process also alternative liquid fuels has been in installed. The concentrated waste gas with these sulphur compounds is conducted to the desulphurisation where the highly desired, pure, 96 % H2SO4 is produced. Briquettable brown coal is crushed, milled and dried and then it is passed into briquetting presses where briquettes, used mainly as a fuel in households, are pressed without binder in the punch under the pressure of 175 MPa. Fine brown coal dust (multidust) is commercially used for heat production in pulverized-coal burners. It forms not only during coal drying after separation on electrostatic separators, but it is also acquired by milling of dried coal in a vibratory bar mill. Slag from boilers of classical power plant, cinder form generators and ashes deposited at the dump are dehydrated and they are used as a quality bedding material during construction of communications in the mines of SUAS. Fly ash is used in building industry for partial substitution of cement in concrete. Flue gases after separation of fly ash are desulphurized by wet limestone method, where the main product is gypsum used, among others, in the building industry. Expanded clays from overburdens of coal seams, that are raw material for the production of “Liapor” artificial aggregate, are used heavily. This artificial aggregate is characterized by outstanding thermal and acoustic insulating properties.

Design and Development of Rasp Bar Mill for Size Reduction of Maize

Particle size affects many characteristics in the manufacturing process. Controlling the particle size helps to assure that the milled material will be consistent and repeatable with respect to firstly color, that is, uniform particles assure batch-to-batch color consistency, Secondly, flowability that is critical to packaging, tableting, weighing. Thirdly, uniformity, that is , consistent bulk density. Fourthly, density - helps control shipping costs and minimize dust. Fifthly, reconstitution, that assures the desired dissolution rate, Sixthly, chemical reaction that is vital for uniform, controlled chemical change. Finally, taste that allows precise portion control for consistent taste. The aim of this project is to design and develop a rasp bar mill for size reduction of maize seeds for different purposes. The fabricated rasp bar mill is capable of feeding maize around 60-180 kg/h, delivering of grits 60-90%, with sieve effectiveness 90-100% at a power requirement of 800-1400W,for different sieve perforation sizes of 5, 6, 7, 8 mm respectively. ENGINEER, Vol. 47, No. 03, pp. 39-47, 2014

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M2(B,C), (W,Mo)2(B,C), M3(B,C), M23(B,C)6 type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm2. The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K1 mill housing of bar mill.

Effect of Heat Treatment on Structure and Wear Resistance of High Chromium Cast Steel Containing Boron

The microstructure, mechanical properties and wear resistance of high chromium cast steel containing boron after different heat treatments were studied by means of the optical microscopy (OM), the scanning electron microscopy (SEM), X-ray diffraction (XRD), hardness, impact toughness, tensile and pin-on-disc abrasion tests. The results show that as-cast microstructures of boron-free high chromium steel consist of martensite and a few (Cr, Fe)7C3 carbide, and the macro-hardness of boron-free high chromium steel is 55–57 HRC. After 0.5 mass% B was added into high chromium cast steel, as-cast structure transforms into eutectic (Fe, Cr)2B, (Cr, Fe)7 (C, B)3 and martensite, and the macro-hardness reaches 58–60 HRC. High temperature quenching leads to the disconnection and isolated distribution of boride, and there are many (Cr, Fe)23 (C, B)6 precipitated phases in the quenching structure. Quenching from 1050 °C, high chromium steel obtained the highest hardness, and the hardness of high chromium cast steel containing boron is higher than that of boron-free high chromium steel. The change of quenching temperature has no obvious effect on impact toughness of high chromium steel, and the increase of quenching temperature leads to tensile strength having an increasing tendency. At the same quenching temperature, the wear resistance of high chromium cast steel containing boron is more excellent than that of boron-free high chromium steel. High chromium cast steel guide containing boron has good performance while using in steel bar mill.

Straightening Technology of Round Bars Using 2-roll Rotary Straightener

In order to improve the productivity and quality of round bar products, the finishing area of the round bar mill was revamped at Kobe Works, Kobe Steel Ltd. in 2011. Various pieces of equipment were newly installed, such as a high-speed rotary straightener, a magnetic leakage flux testing system and an ultrasonic testing system. Among them, the straightener was the key device and was expected to soon be in actual operation. In addition, it was necessary for this straightener to correct the round bar shape of the product, widening its diameter from 17 to 80mm more than the conventional one. To decide the proper setting of the roll gap, the roll skew angle and the rotation speed of the top and bottom rolls of the straightener, a simple 3-point bending model was applied, and the inside of the working straightener was observed by an infrared camera. This paper describes the synergistic effect of the above mentioned three straightening factors and the applied result of these straightening conditions in actual operation.

Cracking of a Tool Steel Guide Roller in a Bar Mill

Failure analysis of a guide roller used in a bar mill of an integrated steel plant has been presented. The guide rollers are positioned at the entry of rolling stands and act as guide in the multi-grooved pass for aligning the hot bars and hold the twisted oval bar while it enters a round pass. The hot bar is at a temperature of ≈1100°C, and the rollers are water cooled. The component is subjected to cyclic thermal stress depending on the mill operating conditions. The rollers are cracking longitudinally leading to failure. The investigation consists of visual inspection, chemical analysis, fractography, characterization of microstructures using optical and scanning electron microscopes (SEM), energy dispersive spectroscopy (EDS) analysis, and measurement of micro-hardness. The chemical analysis indicates the material as AISI D2 grade of cold work tool steel. Visual observation of the failed component shows multiple longitudinal cracks on the roller surface associated with a dark circular band of oxidation. The fracture surface shows a dark oxidized area propagating from the roller surface followed by flat bright appearance indicating final brittle fracture. Fractography of the dark surface from where the crack initiates shows fatigue striations. Microstructural examination under optical and SEM shows a network of coarse carbide particles at the grain boundary as well as uniformly distributed fine carbide precipitates within the martensite matrix. Multiple cracks are observed to initiate and propagate from the surface through the clusters of grain boundary carbides. EDS analysis and elemental mapping suggest the carbides to be chromium carbides. SEM shows micro-cracking of carbide particles associated with the crack. Clustered distribution of carbides deteriorates toughness and initiates cracking at the roller surface subjected to thermal cycling because of their differential thermal expansion coefficient leading to the failure of the component.

Cracking of tungsten carbide rolls during hot rolling of branded rebars in a bar mill

Premature failure of Tungsten Carbide (WC) rolls, due to cracking during hot rolling of branded rebars was found to raise the cost of rolling due to unscheduled stoppage of the mill. Hence, a detailed investigation was conducted to reduce above problem using non-destructive analytical technique such as Ultrasonic velocity measurement, X-ray diffraction (XRD). Finite Element Analysis (FEA) was carried out to know the rolling stress and its adverse effects. Optical technique Scanning Electron Microscopy (SEM) and fractography also carried out to know the root cause of the cracking problem. XRD results indicated high tensile residual stresses at branded area (420.5MPa) and unbranded area(279.2MPa). FEA results revealed that the rolling stress was much lower than the yield stress of WC roll. SEM and Fractography revealed beach and striation marks which confirmed fatigue failure. Whereas ultrasonic velocity measurements indicated density variations of 0.49g/cm3 which is very high in comparison to the desired permissible variation of 0.05g/cm3. The rolling stress together with the impact stresses developed in the branded area due to surface unevenness and causes variation in compactness (density) which in turn causes fatigue failure. This phenomenon was also confirmed with SEM and fractography.

Heat treatment of centrifugally cast high carbon high vanadium high speed steel mill roll

The effects of austenitising temperature and temper treatment on the microstructure, hardness and abrasive wear resistance of a high carbon high vanadium high speed steel roll of composition 2·2–2·4C, 5·5–6·5V, 4·5–5·5Cr, 14·0–16·0(W+2Mo), 1·0–1·4Ni and 1·2–1·5Nb (wt-%) were investigated by light optical microscopy, scanning electron microscopy, backscattered electron image, X-ray diffraction and hardness and wear testing. It was found that the hardness increases as the austenitising temperature increases to a maximum of 1050°C, and then begins to decrease because of the increase in retained austenite. Moreover, retained austenite begins to transform into martensite with increasing tempering temperature. The retained austenite in the quenched structure leads to the temper hardening of the rolls, which promotes improved abrasive wear resistance. The roll life of high carbon high vanadium high speed steel compound rolls austenitised at 1050–1080°C and tempered at 540–560°C increased by 400% (single groove trials) compared to high nickel–chromium white cast iron rolls when the rolls were used in a K1 mill housing of a bar mill.

The Multi-object Optimal Pass Design based on MOGA

The optimal pass design is based on Multi-Object Genetic Algorithm (GA) with the objective of the least of total energy consumption and loads balance on bar mill. By optimization, in condition of normal rolling, the less total energy consumption and relative balanced bar mill loads. Genetic Algorithm Toolbox with Matlab software is adopted to search optimum parameters, which is a new method for the multi-object optimal pass design.

"DREAM STEEL" the Stefana bar mill: efficiency and throughput optimization, an aggregate of the most recent technologies

The Stefana Bar Mill (Nave, Brescia, Italy) was commissioned in April 2008. The production rate, on a 3-shift basis is 750,000 t/y. The product mix includes straight rebars from 8 mm to 40 mm diameters and compact coils from 8 mm to 16 mm diameters. The salient features of this plant are strictly related to improvement of profitability on low-added value products, concentrating on efficiency and throughput optimization.

Sustainable high productivity electric steelmaking

Badische Stahlwerke (BSW) operates a high productivity steelshop with two 90 t ac arc furnaces that produced 1.97 Mt billet in 2004, coupled with a wire rod and a bar mill. The company has evolved an integrated environmental protection strategy to fulfil the objective of economic operation while complying with legal emissions requirements and adapting an active approach to environmental issues more broadly.

A Study of Modification of M2 Cast High Speed Steel

AbstractM2 cast high speed steel was inoculated by addition of rare earth(RE)‐Al‐N, network eutectic carbides were eliminated, matrix structures were refined and the segregation of tungsten and molybdenum elements were relieved. In the condition that the hardness did not decrease, impact toughness obviously increased. Quenching at 1180 °C and three‐times tempering at 560 °C, the hardness of M2 cast high speed steel kept 65~66HRC, impact toughness reached 21.3J/cm2. Modified M2 cast high speed steel had excellent thermal fatigue resistance and high temperature wear resistance. Roll made in modified M2 cast high speed steel had excellent service effect using in slit rolling mill stand of hot rolling bar mill.

Evaluation of friction in the hot rolling of steel bars by means of on line forward slip measurements

In spite of the importance of friction it is still a weak point in the analysis of rolling. Most studies assume that a coefficient of friction (μ) is representative for the roll gap. Forward slip measurements under normal production conditions in a bar mill have been used to evaluate the coefficient of friction, completed by laboratory measurements in a high‐temperature test rig, and stability measurements in oval–square and flat–edge oval pass sequences. Coefficients of friction in the range 0.35–0.40 have been evaluated from the forward slip measurements. The rolling speed did not exceed 0.2 m/s and measurements were made in the temperature range 1000–1150°C. No clear influence of temperature on friction could be observed. The stability measurements show similar results. However, no tests have been made at temperatures other than 1000°C, and no influence of temperature on friction can be evaluated. In the high‐temperature test rig the influence of temperature on friction is strong at temperatures exceeding 900°C, and probably the mechanism of friction changes in the test rig at higher temperatures, due to the lack of plastic deformation in the contact zone. Further investigations are necessary to formulate a relevant model for friction, valid for the entire range of parameters in a bar or wire rod mill.

Plasticity of Tool Steels as a Function of the Deformation Heating Conditions

The effect of the heating method and temperature on the processes of structure formation during hot plastic deformation of tool steels of the carbide class (R6M5, Kh6VF) is investigated. Special features of formation of structure and properties of the steels due to electrocontact and furnace heating under conditions imitating the operation of a 200 EKN bar mill designed by VNIIMETMASh Company are considered. A method for performing high-temperature tensile tests with the use of electrocontact heating of specimens directly in the clamps of the studied machine is suggested.