Ball-rolling Mill Research Articles

Tuning Parameters of a Ball-Rolling Mill for Rolling of Grinding Balls

Tuning Parameters of a Ball-Rolling Mill for Rolling of Grinding Balls

Influence of deformation parameters on quality of billets and grinding balls during their production from rejects of rail steels

The conducted studies have determined the regularities of influence of rolling parameters of billets and grinding balls in their production from the rejects of K76F rail steel on probability of defects formation during deformation. Modeling of the rolling process of high-grade billets from the rejects of continuously cast ingots of rail steel of the specified grade in DEFORM-2D software package allowed us to establish a significant effect of such parameters as: partial coefficients of drawing along the transfer bar, frequency of rolling edges, and rolling temperature, on the probability of defect formation, characterized by the maximum value of the Cockcroft-Latham criterion in cross section of the rolls. It is shown that an increase in the coefficients of drawing (compression) along the transfer bar, due to intensification of the rolling mode and an increase in frequency of edging, reduces the likelihood of defects forming during rolling by reducing the temperature inhomogeneity along the rolls section. The established effect of temperature increase on reducing the probability of defects formation is due to an increase in plasticity of the considered rail steel. Based on the data obtained, general recommendations are formulated on the directions of improving the rolling modes of billets from the rejects of rail steels and restrictions on their application in practice. Based on the results of modeling the rolling of grinding balls from the rejects of rail steel on a helical rolling mill, a significant effect of an increase in the deformation temperature on reduction of cracking in the balls axial zone, due to an increase in the steel ductility, was established. Therefore, a new mode of rolling grinding balls from the rejects of K76F rail steel was developed, which provides an increase in impact resistance of grinding balls while maintaining high surface hardness. Effectiveness of this mode is confirmed by the results of its pilot testing in conditions of the ball rolling mill at JSC “Guryevskii Metallurgical Plant”.

Effect of carbon nanotubes on microhardness and adhesion strength of high-velocity oxy-fuel sprayed NiCr–Cr3C2 coatings

NiCr–Cr3C2 coatings are widely used for high temperature and tribological applications due to their high hardness, oxidation, and wear resistance properties. In the present investigation, an attempt is made to further enhance the hardness and adhesion strength of NiCr–Cr3C2 coatings by reinforcing them with multi-walled carbon nanotubes. The carbon nanotubes (3–7 wt%) with varying weight percentages were mixed with NiCr–Cr3C2 using a planetary ball rolling mill and sprayed on SA213 T12 (T12 alloy steel tube) using a high-velocity oxy-fuel spraying process. The microstructures of mixed powder, coating cross-section, and fractured coating surface were characterized using a scanning electron microscope while X-ray diffraction was used for phase identification in the fractured coating surface. The coated samples were subjected to microhardness and adhesion strength tests according to ASTM E384 and ASTM D4541-09 standards. Out of all coatings, NiCr–Cr3C2/7% carbon nanotube composite coating showed the lowest porosity of 1.17%, highest microhardness, and adhesion strength of 563.8 HV and 55.8 MPa, respectively. A fracture analysis after a pull-off adhesion test revealed adhesion failure for NiCr–Cr3C2 coating and combined adhesion/cohesion failure for NiCr–Cr3C2/7% carbon nanotube composite coating.

Theoretical study of the process of balls rolling with a diameter of 40 mm on a ball rolling mill

The following calibration scheme for rolling round steel is used for producing thermally hardened grinding balls with a diameter of 40 mm at JSC SSGPO for 320 variety rolling mill: a round billet with a diameter of 40 mm is produced from the initial billet of 120 × 120 mm. In the last developed scheme the square billet 150x150 mm is used as an initial billet for whole mill where the round steel with diameter of 40 mm is obtained from the above mentioned billet and then this round steel is used for production of balls with a diameter of 40 mm. Computer simulation of the ball rolling process in the Simufact Forming program was performed. The results of strain state distribution showed that the maximum processing level in the surface layers of balls is observed, while the stress state distribution showed that in the surface layers prevail high compressive stresses up to −400 MPa. Such stress-strain state leads to formation of gradient structure in the ball cross-section, where the surface layers will have more high mechanical properties. That is the most optimal result for details worked in condition of high values of friction.

The new ball-rolling mill of EVRAZ NTMK – new possibilities for customers

In view of increase of ferrous and nonferrous ores mining, the need for grinding balls, used for the ores grinding in the process of concentration, is also increasing. Description of technical solutions, realized at accomplishment of an investment project at JSC EVRAZ NTMK, presented. The investment project on the technical modification of the rail and beam shop included construction of the new ball-rolling mil further to production of steel grinding balls. The new ball-rolling mill, which was put into operation in 2018, has a possibility to produce ball of diameter from 60 up to 120 mm with hardness up to 5th group. The mill is equipped by an automation system of the process and balls stocking control. The ball production section comprises a walking beams heating furnace with automated heating modes to ensure energy-efficient operation; automated hot rolling mill for production grinding balls of 60 ‒ 120 mm diameter; balls thermal treatment line, including temperature leveling facility, quenching machine and tempering furnace. The system of the process automation enables to trace on-line all the technological parameters for production quality products, parameters of the environment to increase the energy efficiency of the section, and control system to create safety working area at the section. Within a year after the ball-rolling mill commissioning, the whole nomenclature series of balls was mastered and the passport productivity at each profile was reached. The maximum mill productivity obtained was 22 t/h. The JSC EVRAZ NTMK mill of grinding balls of 60 ‒ 120 mm diameter production meets all the modern market requirements.

The Exploration of the Possibility of Using Continuous-Cast 55 Grade Steel in the Manufacturing of 40-mm-in-Diameter Grinding Balls of IV and V Hardness Class

Results of a field–experimental study on the applicability of continuous-cast medium-carbon 55 grade steel sparingly alloyed with chromium to the manufacturing of hardness IV and V class grinding balls 40 mm in diameter are presented. The possibility of the stable production of hardness IV class grinding balls is shown since chromium added in small quantities facilitates the hardness stabilization over the half of the ball radius and increases the volumetric hardness by 2–3 HRC figures. The established increase in the volumetric hardness did not allow for the HRC 57 level to be reached to certify the balls as the hardness V class products. Rational process variables have been recommended to ensure the production of 40-mm-in-diameter grinding balls for the V hardness class of continuous-cast medium-carbon 55 grade steel on the ShPS 30–80 ball-rolling mill.

Improvement of Rolling Dynamics to Increase Roller Life in Ball Rolling

The downtime of ball-rolling mills is largely associated with the replacement of worn rollers. In the present work, the degree and location of critical roller wear are studied: the greatest wear is observed at the flanges in the billet-capture zone. The conditions required for billet capture and successful rolling are determined analytically. Variation in roller speed during billet supply is proposed. Tests are conducted with linear and quadratic variation in roller speed. The familiar formulas for the mean deformation rate are modified for linear and quadratic variation in roller speed. Experiments are conducted on the ball-rolling mill of AO EVRAZ Nizhnetagil’skii Metallurgicheskii Kombinat (NTMK), in rolling 60-mm ШЗГsteel grinding balls on a 40–80 rolling mill. In the experiments, the roller speed is varied manually according to a specified program, with billet capture by the rollers. It is found that speed variation significantly affects the mean pressure at the instant of billet capture. Time dependences of the torque and the mean contact pressure are plotted on the basis of calculation results and experimental data. Empirical characteristics with linear and quadratic variation in roller speed are presented. The permissible agreement of the calculated and empirical results is determined. The installation of a thyristor converter is proposed, so as to decrease the roller speed before billet capture and restore the speed to the rated value in specified fashion after capture. That yields a uniform distribution of the mean contact pressure over the roller length during automatic operation of the mill in different conditions. As a result, the roller wear is decreased, without loss of mill productivity. That reduces roller consumption and the mill downtime for roller replacement.

Calibration of ball-rolling rollers with continuously variable pitch

Presented is the state of ball rolling production, review of existing techniques for roll pass design ball-rolling today development. Possibilities of roll pass design with regard to the existing metal cutting equipment and variation of pitch parameters. The priority is set for the use of rolling rolls with a continuously varying pitch, in comparison with rolls with discretely varying pitch. Possibility of using 5-axis milling equipment for obtaining a given profile, with several variable values, is shown. Model is developed for calculating the roll pass design for rolls with a continuously varying pitch, the save constant amounts of metall of workpiece between the rolls in every moments. Pitch change functions for roll pass design of ball rolling with a constant and variable flange width are derived, using which it is possible to determine the theoretical pitch at any rolls rotation angle. Technique for constructing a 3-D model is developed, based use on obtained curve of the 2nd order, which is the basis helical surface with a continuously varying pitch. Production of profile on a 5-axis machining center, according to the the 3D models suggest. Roll pass design was used ob the experience practical, with production example ball with a diameter of 120 mm, which were calculated from the deduced function for rolls with a constant width of the flange. He was tested in the conditions of the newly introduced ball-rolling mill of JSC "EVRAZ-NTMK". After introduction of a new roll pass design, were resived technical results: the reduction in force rolling, in contrast at use operating rolls with discretely varying pitch, by 25–30%, obtaining ball sizes that are as close to nominal values GOST standard, decreased of defects, uniformity forge along entire length of the rolls forming-part obtaining.The analytical solutions presented in this article, in combination with industrial approbation, make it possible to use a new method roll pass design rolls of a ball rolling mill with a continuously changing pitch for educational and production purposes.

Production of hard (class V) grinding balls at PJSC “DMPZ”

In industrial trials on the 30-80 ball-rolling mill at PJSC “Donetsk Metal Rolling Plant”, operational guidelines are developed for the production of grinding balls (diameter 40 mm) in hardness class V from continuous-cast eutectoid steel 85 provided by LLC “Elektrostal”. Rolling parameters for this process are recommended. Measures are developed to improve ball performance.

Industrial Testing of Group IV Hardness Grinding Balls Produced by Donetsk Metal Rolling Plant

Results are given for a complete processing scheme for manufacturing small diameter grinding balls of hardness groups III and IV produced from small cross-section continuously-cast carbon steel billet. The steel chemical composition and rolling and heat treatment regimes proposed have made it possible to produce balls of grinding hardness groups III and IV since the beginning of mastering ball rolling mill 30–80. Industrial tests of grinding balls 40 mm in diameter of hardness group IV performed under Southern Mining and Processing Plant conditions demonstrate that grinding efficiency of finished class size –0.074 mm is better by 3.1% higher and specific consumption of grinding balls is 8.83% lower than in the case of using grinding balls of hardness group III produced by DMKD or Azovstal Metallurgical Combine.

MATHEMATICAL MODELING OF BALLS ROLLING

The paper presents the results of simulation of rolling of balls precise in mass with diameters of 93 and 125 mm in screw calibers in QForm-3D and DEFORM-3D, the stages and initial data of creating a virtual model of ball-rolling mill are described. The stress state of the metal in characteristic points along the rolling axis was analyzed: stress intensity, stress tensor components, average normal stress. The results of mass measurements of balls rolled on new and worn rolls are presented. The quality check of the inner layers of metal was carried out and the hardness of the rolled balls was measured along the vertical and horizontal axes of ball symmetry. Investigation of metal deformation in simulation of ball rolling has shown that heated billet in form of hot-rolled steel rod is well gripped by rolls, rolling process is stable without slipping. Billet metal fills the gauges completely. There are no gaps observed between metal and gauges walls. Breaker cores connecting molded balls are completely separated in the mill rolls. In this case, core is cut by the rolls flange and is pressed into the ball body. Separated ball continues to roll in gauge finishing section, core remains are smoothed, and completely formed ball with a smooth surface appears from the rolls. It was established that in stress-strain state modeling all components of stress tensor have negative value, that is, all components of stress tensor during balls rolling are compressive. Statistical processing of data on weighing rolled balls with a diameter of 93 mm and 125 mm shows that deviation of mass from the nominal does not exceed 1 %. Measurements of hardness along the balls diametric section shows absence of hardness failures in the inner layers of rolled metal, which indicates a good quality of core zone.

Mastering the Production of 40- and 60-mm-Diam. Grinding Balls in Hardness Classes III and IV at the Donetsk Metal-Rolling Plant

Information is presented on the development of a new technology for the production of small-diameter grinding balls that have class-III and class-IV hardness ratings and are made from continuous-cast carbon steel semifinished products with a small cross section. Recommendations are given on the chemical composition of the high-carbon steel, which has superior hardenability. The regimes established for the rolling and heat-treatment operations have made it possible to produce class-III and class-IV-hardnessrated 40-mm-diam. grinding balls and class-III-hardness-rated 60-mm-diam. grinding balls since the successful introduction of the ShPS 30-80 ball-rolling mill. The balls meet the requirements of the standards GOST 7524–89 and DSTU 3499–97.

Heat treatment of rollers in the ShPS 30-80 ball-rolling mill at JSC DMPZ

In the production of steel rollers, surface decarburization may occur in the course of heating before quenching. Means of more effective protection against such decarburization are considered in the case of the 35X CA steel barrel of wrapped rollers for the ShPS 30-80 ball-rolling mill. A technological protocol for the heat treatment of the rollers is developed. It is shown that protection by means of nitrogen + a carburizing agent + a muffle increases the likelihood of the desired outcome (no decarburized surface layer and hardness no less than 45 HRC) by 31.9% in comparison with protection by means of Barier protective compound + a carburizing agent + a muffle. On average, 450–470 t of grinding balls (diameter 40 mm; hardness groups III and IV) may be rolled in a complete run (to regrinding) on rollers heat-treated by the proposed protocol.

ROLL PASS DESIGN OF A BALL-ROLLING MILL. PART 2

In making balls for ball mils the metal is deformed in rolling balls in rolls with helical pass grooves. Insofar as the character of the deformation is concerned, the pass can be divided into the forming section, where the rolls bite the billet and reduce it gradually into the ball shape, and the finishing section where the ball is rolled to the final size and severed from the rest of the billet. A normal process of rolling is provided for by designing the forming section of the pass groove. In the article outcomes calculation roll pass design for rolling of balls. Calculation is made for roiling of ball of125 mm. Initial data for ball-rolling mill design are given.

CALIBRATING ROLL OF THE BALL-ROLLING MILS. PART 1

During the rolling of balls on ball-rolling mill deformation of the metal is in the rolls with screw gauges. In view of such a character of the rolling of deformation is concerned, and can be divided into the forming section, where the rolls bite the billet and reduce it gradually into the ball shape, and the finishing section, where the ball is rolled to the final size and severed from the rest of the billet. A normal process of rolling is provided for by designing the forming section of the pass groove. In the article outcomes the calculation of roll pass designed for rolling of balls. The calculation outcomes for roiling of balls 125 mm. The article provides the initial data for roll pass design of a ball mill.

Characterisation of multi-walled carbon nanotube reinforced epoxy resin composites

The main theme of this paper is to describe the mechanical properties of multi-walled carbon nanotube (MWCNT)/epoxy resin composites with the variation of MWCNT fillers. The work tried to achieve a uniform distribution of MWCNT filler in the epoxy matrix by modifying the hardener and mixing conditions. The MWCNT fillers were used to fabricate the MWCNT/epoxy resin composites with the variation of weight percentage of 0⋅5, 1, 2 and 3%. The dispersion of MWCNT in epoxy resin was carried out with the help of three ball rolling mill process. A significant improvement in tensile strength, compressive strength and elastic modulus was observed due to the excellent dispersion of the MWCNT filler in the epoxy resin that give higher values of tensile strength, compressive strength and elastic modulus at 3% MWCNT.

Wire Flattening Using a Ball Rolling Mill

AbstractIncreasing requirements towards narrow and thin strips necessitates research concerning technology improvements and changes in construction of flattening devices. Wire flattening between the balls is an efficient manufacturing method of thin and narrow strips made of steel non‐ferrous metals and their alloys. The study presents an analysis of the effect of flattening process in a ball rolling mill on widening of X10CrNi 18‐8 steel wire. Performed tests proved that flattened strips feature uniform thickness throughout their width, narrow dimensional tolerance and high surface quality. This innovative method of wire flattening in a ball rolling mill means a step ahead in the development of production technologies of extremely narrow and thin metal strips for many modern applications.

Steel Strips Flattening in Ball Rolling Mill

An effective and efficient production method of narrow and thin strips made of steel, non-ferrous metals and their alloys is wire flattening in a ball rolling mill. In this device cylindrical rollers have been replaced with balls of diameter ca. 15 mm. Proper selection of deformation process parameters enables to obtain strips with the required geometrical characteristics. Experimental planning method was applied to evaluate the influence of flattening process technological parameters on strip geometrical features. Statistical analysis enabled to determine mathematical models of stainless steel 5XCrNi18-10 strips flattening. It was established that strip widening depends on ball roughness, draft applied, relation of wire diameter to ball diameter, back-tension stress. Strips flatness depends on draft applied. It was observed that strips feature uniform thickness over their width, parallel flat surfaces, narrow dimensional tolerance, high quality surface and naturally rounded edges.

Stamping axisymmetric forgings

As a rule, cylindrical blanks are used in hot bulk stamping of axisymmetric parts. However, cutting the rod into measured lengths is associated with fluctuation in mass of the blank on account of distortion of its end geometry and change in its length. Therefore, seams arise in the stamping of such blanks. A promising approach to the deformation of axisymmetric parts (gears, disks, flanges, etc.) is stamping from spherical blanks obtained by hot rolling of rod on a ball-rolling mill. In the present work, experiments on the seamless stamping of axisymmetric forgings from a spherical blank (diameter 60 mm) are conducted for flanges and lids. The forgings are illustrated in Fig. 1, with the relevant dimensions. In the first stage of our research, the stamping of these forgings is simulated on a computer by the finiteelement method [1]. In the second stage, the model is verified. Computer simulation permits study of the filling of the die’s contours by metal and the deformation over the diametric cross section of the forging; evaluation of the nonuniformity of deformation; and the identification of points of possible defect formation in stamping. By computer simulation, new products may be introduced more rapidly, with smaller outlays. Simulation of the filling of the stamp cavity indicates that it is completely filled with metal; there is no burring. No pinching or cracking of the metal is observed. The distribution of the accumulated strain in the axial plane is shown on the right side of Figs. 1a and 1b for a flange and lid forging, respectively, in the form of lines of equal strain. As is evident from Fig. 1a, the strain distribution over the cross section of the forging is nonuniform. The surface layers of the upper and lower plates in the flange experience the least strain e i = 0.49. The central layers of the hub experience the greatest strain. In stamping the lid (Fig. 1b), the surface layer of the central projection experiences the least strain e i < 0.14, while the internal layers of the forging closer to the bottom experience the greatest strain e i = 1.7. On the basis of the computer simulation, the strain distribution in different cross sections of the forging is plotted. The continuous curves in Fig. 2a denote the strain intensity in cross sections A , B , and C . In cross section C , the least strain is observed in the upper region of the concave hub. In the central part of the hub, the strain rises to a maximum, beyond which it falls. In cross section B , the maximum strain is again in the central region. In horizontal cross section C , the strain falls from e i = 2.48 in the central region to e i = 0.72 in the crown at the edge of the forging.

New industrial technology for producing mill balls in a continuous-casting deformation complex

The fields of application of grinding steel balls are in ore processing and the cement industry (material grinding in ball mills); large-size rolling bearings, etc. In mass machine production, for the manufacturing of axisymmetric forgings, cylindrical billets can be effectively replaced by balls. Balls are now produced by casting, die forging, and rolling. Cast grinding balls find a limited application. Hot-rolled balls are produced according to a power-consuming technology, as the ball-rolling mill employs pre-deformed (rolled) billets. The process of ball die-forging is inefficient, as it requires great power and material consumption, etc. In this paper a new technology for producing ball-shaped billets out of continuously cast ingots is presented.