Investigation on the Surface Coating of Grinding Balls

The surface coating of grinding balls was investigated experimentally. The results show that a coating may form on the surface of grinding balls when Cr or Al powders are subjected to ball grinding. The plastic deformation of the ball surface plays an important role during the coating formation, and the strong binding force between the powders and the balls is a necessary pre-condition. The thickness of coating increases with the plasticity of the powders and the balls. Annealing the balls with coating will result in an obvious diffusion of the elements in the bonding zone of interface.

Effects of austempering temperature on microstructure and surface residual stress of carbidic austempered ductile iron(CADI) grinding balls

The effects of austempering temperature on microstructure and surface residual stress of carbidic austempered ductile iron （CADI） grinding balls were systematically investigated in this work. The microstructures were oberserved by optical metallography and analyized by X-ray diffraction. The surface residual stress measured by the cutting method is mainly composed of thermal stress and phase transformation stress.The thermal stress in grinding balls was determined by ANSYS simulation technique, and the surface phase transformation stress was obtained by subtracting the simulated surface thermal stress from the measured surface residual stress. Results show that all microstructures consist of ausferrite, white-bright zones （mixture of martensite and austenite）, nodular graphite, and carbides. The distribution of ausferrite shows uniform. With the increase of austempering temperature, the volume fraction and carbon content of austenite increase, whereas the amount of white-bright zone decreases. In addition, the surface residual stress increases with the increase of austempering temperature. Only the tension exists at the austempering temperature of 200 ℃, and the pressure exists at the austempering temperature of 220-260 °C. The thermal stress changes from the tension on the inside with the radius of 0-35 mm to the pressure on the outside with the radius of 35-62.5 mm, and the stress balance state presents at the radius of 35 mm. It is also found that the transformation stress is related to the content of carbon-rich austenite, and will reduce by 5.03 MPa accompanied with 1vol.% increase of the austenite.The thermal compressive stress and the transformation tensile stress on the surface both decrease with the increase of the austempering temperature.

Properties of Cross-Rolled Low Alloy White Cast Iron Grinding Ball

The low-energy, multi-impact fracture resistance and the abrasiveness of the cross-rolled low alloy white cast iron grinding balls were studied after heat treatments at residual rolling temperature. Moreover, the means by which they are damaged and characters of the wear surface were analyzed. The results show that high resistance to impact fracture and high abrasiveness can be achieved after appropriate heat treatment at residual rolling temperature. This kind of heat treatment technology has several advantages under low impact and hard abrasive. These results are very useful for determining the optimized heat treatment technology at residual rolling temperatures.

Mechanical Property of Low Chromium Semi-Steel Grinding Ball Prepared by Cross Rolling

The preparing method,rolling technology and mechanical properties of low chromium semi-steel grinding ball by cross rolling were studied.The results show that when the low chromium semi-steel bar is forged from55mm to50mm,cross-rolled into grinding ball at 1 000-1 050℃,air cooled and tempered at 550℃for 2h,the best mechanical properties,especially the abrasive resistance under the action of hard abrasive,can be obtained.

Simulation on stress of large diameter CADI grinding ball based on ANSYS

The falling ball tests were carried out on theΦ125 mm diameter Carbidic Austempered Ductile Iron(CADI)grinding balls with Mn content of 2.0wt.%,2.3wt.%,2.6wt.%and 3.0wt.%,respectively,and the kind of grinding ball with the most serious spalling was selected for stress simulation.The stress distribution between four grinding balls in the elbow of the falling ball test device when they collided with each other was simulated based on ANSYS.Results of the falling ball tests show that the spalling and mass loss of a CADI grinding ball increases with the increase of Mn content,and the CADI grinding ball with 3.0wt.%Mn shows the most obvious spalling and mass loss.The simulation results of stress distribution of a CADI grinding ball show that the maximum impact stress does not appear in the center of the contact area,but in the annular area(inner diameter of^20 mm and outer diameter of^50 mm)in the section with a depth of 5-15 mm below the grinding ball surface.The actual spalling of the ball is consistent with the simulation results,and the oxide-based impurities in CADI grinding ball accelerate the spalling of the grinding ball in service.

A Structural Study of High Cr Cast Iron as a Grinding Ball Material

In present paper, the 3-body abrasion and impact fatigue resistance of a 12％Cr-2.65％C-1.4％Si high Cr cast iron are comprehensively evaluated. The results indicated that the lower the C content of the martensitic matrix, the better the impact fatigue resistance of the iron. The retained austenite is always harmful to both 3-body abrasion and impact fatigue resistances. The low C content martensitic matrix free from retained austenite is suitable for making grinding balls.

Low-Energy Multi-Impact Fracture Resistance of Cross Rolled Low Chromium Cast Semi-Steel Containing Rare Earth Grinding Ball

The low-energy multi-impact fracture resistance of the cross rolled low chromium cast semi-steel containing RE grinding balls was studied. Moreover, its damage mode was analyzed by means of metallographic examination, scanning electron microscopic examination and drop ball test. The results show that it can obtain extractive impact fracture resistance after proper heat treatment. More advantages were obtained for the ball worked in the condition of low-imp ductility act. The main reasons are the function of RE and the change in morphology of eutectic carbide network.

A study on controlled cooling process for making bainitic ductile iron

In the present research, TTT curve of bainitic ductile iron under the condition of controlled cooling was generated. The cooling rate of grinding ball and its temperature distribution were also measured at the same time. It can be concluded that the bainitic zone of TTT curve is separated from the pearlitic zone. As compared to the water-quenching condition, more even cooling rate and temperature distribution can be achieved in the controlled cooling process. The controlled cooling can keep away from pearlitic zone in the high temperature cooling stage and produce similar results to the process of traditional isothermal cooling with a low cooling rate in the low temperature cooling stage.

Influence of Mechanical Activation on Acid Leaching Dephosphorization of High-phosphorus Iron Ore Concentrates

High pressure roll grinding（HPRG）and ball milling were compared to investigate the influence of mechanical activation on the acid leaching dephosphorization of a high-phosphorus iron ore concentrate,which was manufactured through magnetizing roasting-magnetic separation of high-phosphorus oolitic iron ores.The results indicated that when high-phosphorus iron ore concentrates containing 54.92 mass% iron and 0.76 mass% phosphorus were directly processed through acid leaching,iron ore concentrates containing 55.74mass%iron and 0.33mass%phosphorus with an iron recovery of 84.64%and dephosphorization of 63.79% were obtained.When high-phosphorus iron ore concentrates activated by ball milling were processed by acid leaching,iron ore concentrates containing56.03mass%iron and 0.21mass% phosphorus with an iron recovery of 85.65% and dephosphorization of 77.49%were obtained.Meanwhile,when high-phosphorus iron ore concentrates activated by HPRG were processed by acid leaching,iron ore concentrates containing 58.02mass%iron and 0.10mass% phosphorus were obtained,with the iron recovery reaching 88.42% and the dephosphorization rate reaching 88.99%.Mechanistic studies demonstrated that ball milling can reduce the particle size,demonstrating aprominent reunion phenomenon.In contrast,HPRG pretreatment contributes to the formation of more cracks within the particles and selective dissociation of iron and P bearing minerals,which can provide the favorable kinetic conditions to accelerate the solid-liquid reaction rate.As such,the crystal structure is destroyed and the surface energy of mineral particles is strengthened by mechanical activation,further strengthening the dephosphorization.