Effects of bottom base shapes on burden profiles and burden size distributions in the upper part of a COREX shaft furnace based on DEM

The shaft furnace plays a very important role in the quantity and quality indexes of the COREX process. However, research on burden distribution in the COREX shaft furnace is still immature and in need of further development and improvement. For instance, only a single ring charging process rather than multiple rings or a burden matrix process has been simulated for the shaft furnace in practical operation. Therefore, a three dimensional model of the upper part of COREX shaft furnace is developed in the present study. The model simulates the charging process with multiple rings and is then used to investigate the effects of different bottom base shapes on the burden profiles and radial size distributions. Results show that the last rings (the inner rings) in the burden matrix needs be carefully chosen, especially for the middle mode. The bottom base shape affects the burden size distribution a great deal but the surface burden profile very little at a fixed burden matrix. A bottom base of M shape is strongly recommended to obtain a uniform burden size distribution. The burden matrix and bottom base shape need to be well matched in order to obtain desired gas distributions.     

Metallurgical re-examination of wear modes II: adhesive and abrasive

Adhesive and (three-body) abrasive wear modes in the interface between a 303 steel shaft and a 52100 steel ball-bearing inner race were studied. Scanning electron micrographs showed significant differences in the different stages of adhesive and abrasive wear modes. Further scanning electron microscopy examinations of the cross section of the worn samples showed severely strained layers on the shafts from adhesive wear and heat-affected transformed surface layers on the bearing races from both adhesive and abrasive wear tests. Transmission electron microscopy examinations also showed a severely strained layer in the case of the adhesively worn shaft. A significant increase in hardness was measured on shafts from both wear modes. Auger analysis of worn surfaces detected the existence of modified layers and material removal. The metallurgical techniques described in this paper can be successfully used to diagnose wear.     

A study of microstructure and tribological behaviour of Al–4.5% Cu/Al3Ti composites

Al–4.5% Cu/Al₃Ti composites with the varying amount of in-situ Al₃Ti were prepared in an induction furnace. The prepared in-situ composites were subjected to mechanical stirring at 700 °C. The composites after stirring have been defined as melt processed composites. Wear tests have been performed to study the influence of Al₃Ti on the sliding wear behavior of in-situ and melt processed composites. The effect of ageing on the wear behavior of both in-situ and melt processed composites has been studied. Wear has been simulated in two different conditions, namely mild and severe. It has been found that the wear resistance of the composites improves with the increase in amount of Al₃Ti as well as with ageing. It has been observed that mainly oxidative and abrasive wear coexist in severe condition, whereas a combination of oxidative, abrasive and adhesive wear exists in mild condition.     

Mechanical and three-body abrasive wear behaviour of PMMA/TPU blends

The blends of poly(methyl methacrlate) (PMMA) and thermoplastic polyurethane (TPU) were prepared by a Brabender co-twin screw extruder. The mechanical and three-body abrasive wear behaviour of PMMA/TPU blends has been studied. Three-body abrasive wear tests were conducted using rubber wheel abrasion tester (RWAT) under different abrading distances at 200 rpm and 22 N load. A significant reduction in tensile strength and tensile modulus with an increase in TPU content in the blend formulation was observed. Three-body abrasive wear results indicate that the wear volume increases with increase in abrading distance for all the samples studied. However, neat PMMA showed better wear resistance as compared to PMMA/TPU blends. The worn surface features, as examined through scanning electron microscope (SEM), show matrix cracking and deep furrows in PMMA/TPU blends.     

Centrifugally cast cylinder lining alloys and their compatibility with cobalt-base and nickel-base hardfacing alloys

Wear- and corrosion-resistant coatings applied to cylinder bores by an in situ melting and centrifugal casting process are widely used in plastics processing machinery. Cylinder lining alloys and the method of manufacturing bimetallic cylinders with these alloys are described. One primary cause of cylinder wear is an internal screw which can bear heavily against the cylinder bore. Since the screw flights are often hardsurfaced with cobalt-base or nickel-base alloys, Alpha LFW-1 wear tests were made to evaluate the relative wear resistance of these alloys and their compatibility with centrifugally cast cylinder lining alloys. The results indicate preferred hardfacing materials and application processes for use with each lining alloy.     

微量Zr对Cu-Ag合金磨损行为的影响

采用真空熔炼的方法制备了CuAg-Zr合金，研究了微量Zr对Cu-Ag合金磨损行为的影响，探讨了合金的磨损机理．结果表明：Cu-Ag合金的磨损率随着Zr含量的增加明显减小，随着受电电流和滑动距离的增大逐渐增大．粘着磨损、磨粒磨损和电侵蚀磨损是主要的磨损机制．微量Zr的加入使合金中形成弥散细小的析出相，使其磨损性能明显优于Cu-Ag合金．     

Effect of abrasive wear on the tensile strength of steel wire rope

Known amounts of external abrasive wear were introduced into a new 6-strand steel wire rope and the effects of this wear on the tensile strength of the rope examined against the rope discard criteria for wear stated in ISO 4309: 1990 and other selected international standards. The variations of strength with degree of wear in the test rope were compared with continuous observations on two haulage ropes which were in service under abrasive wear conditions up to the stage of failure. The results point to a need for greater caution in applying available discard criteria for wear. The results also indicate the existence of two different rapid strength deterioration regimes in strand wire rope under increasing amounts of external abrasive wear and they direct towards test parameter levels which signal the onset of these regimes.     

Failure Investigation of a Locomotive Turbocharger Main Shaft and Bearing Sleeve

A failure investigation was conducted on a locomotive turbocharger main shaft and a bearing sleeve which had been assembled with the main shaft. The fracture of the main shaft took place at a sharp edged groove between two journals with different cross-sectional areas. The dominant failure mechanism of the main shaft was low-cycle and rotation-bending fatigue. Wear failure occurred on the bearing sleeve through a mixed mode of abrasive and adhesive wear. Detailed metallurgical analysis indicated that the bearing sleeve and the journal surface assembled with the sleeve had been subjected to abnormally high temperatures which led to increased friction between the bearing sleeve and the bearing bush, the sleeve, and the journal surface. In addition, the abnormally high temperature softened the induction-hardening case on the journal surface and decreased the fatigue strength. Fatigue crack initiation occurred at the root fillet of the groove because of the stress concentration in that area.     

马氏体基体含碳量对马氏体球铁磨损性能的影响

针对马氏体球铁,研究了马氏体基体不同含碳量(不同奥氏体化温度)对两体磨损和冲击磨料磨损耐磨性的影响。结果表明:在软磨料作用下的高应力两体磨损中,马氏体球铁以疲劳机制破坏,硬磨料作用下以切削机制破坏;在有较大冲击载荷作用的动载磨料磨损中,马氏体球铁存在有抗冲击疲劳剥落的最佳马氏体含碳量;石墨球的存在对耐磨性有害。     

真空热压烧结制备Mo10/Cu-Al_2O_3复合材料及其载流磨损性能研究

在VDBF-250真空热压烧结炉中,采用真空热压烧结工艺制备了Mo10/Cu-Al2O3复合材料,观察显微组织,并测试性能。在HST100载流高速摩擦磨损试验机上研究了载流磨损机理。结果表明,该材料致密度为98.23%,组织较为致密;显微硬度为116 HV,导电率为41.33%IACS;Mo10/Cu-Al2O3复合材料的磨损形式为粘着磨损、磨粒磨损和电弧烧蚀磨损。     

Effect of processing parameters and graphite content on the tribological behaviour of 3D printed acrylonitrile butadiene styrene

3D printing is nowadays used not only to rapidly produce prototypes, but is further applied for the fabrication of functional parts. Amongst other factors, processing parameters such as scaffolding angle and raster gap greatly affect the behaviour of such printed parts. Little attention has been given so far to the tribological behaviour of such prints. In this study the above mentioned parameters on the friction behaviour, in terms of friction coefficient and wear rate, is investigated. For this purpose the Fused Deposition Modelling is used as one of state of the art 3D printing methods. Graphite flakes were further added to the reference acrylonitrile butadiene styrene (ABS) matrix in an attempt to enhance the properties. Results show that the scaffolding angle only affects the behaviour, if a positive printing gap is applied – when a negative gap is used, the angle has no significant effect on properties. Maximum coefficient of friction at acceptable values of specific wear rates can be attained at a scaffolding angle of 90° with negative gap. The incorporation of graphite further increases the friction coefficient on the expense of reduced wear properties.     

电弧喷涂Al,Zn涂层和Al-Zn伪合金涂层的磨损性能

采用电弧喷涂制备了Al涂层、Zn涂层和Al-Zn伪合金涂层,在Falex试验机上测试了3种涂层的磨损性能。利用扫措电镜（SEM）、X－射线衍射分析（XRD）、能谱分析（EDX）等手段,地试样磨痕形貌及悄进行了分析。结果表明：Al涂层的磨损主要为粘着磨损和磨粒磨损,Zn涂层的磨损主要为氧化磨损,Al-Zn伪合金涂层的磨损兼有Al,Zn2种涂层磨损特征,但更接近于Zn涂层的磨损机理。3种电弧喷涂层中,Zn涂层的耐磨性能优于其他2种涂层,Al-Zn伪合金涂层的耐磨性能介于两者之间,但更接近于Zn涂层。在140℃以下,温度对3种涂层的磨损性能影响不显著。     

Failure Analysis of AISI 440C Steel Ball Screws Used in the Actuator System of a Satellite Launch Vehicle

In view of its excellent wear and corrosion resistance, AISI 440C steel is the material of choice for the fabrication of ball screws used in actuator systems of satellite launch vehicles. During the routine acceptance test of a ball screw, longitudinal cracks were observed at the shaft location of the ball screw. The optical microstructure of the ball screw material (AISI 440C) revealed the presence of aligned carbides (carbide banding). Fractographic observations revealed the cracking to be along the carbide bands. Based on detailed optical and scanning electron microscopic observations, the cracking of the ball screws was attributed to the carbide bands.     

Effect of aging on the abrasive wear properties of AlMgSi1 alloy

In this paper, the wear performance of the aged AlMgSi1 alloy was investigated. Great improvements in mechanical properties of Al alloys can be achieved by suitable solution treatment and aging operations. A pin-on-disk wear machine was designed and developed for abrasive wear tests. The wear resistance was evaluated using a pin-on-disk wear testing method with a SiC abrasive paper counterface. The variation of wear volume is presented as a function of applied normal load, abrasive grit size and sliding distance for running speed. Mass losses were measured within a load range of 6.45–11 N, a sliding velocity range of 0.078–0.338 m/s and abrasive grit size of 5–30 μm. The effects of different sliding speeds and loads on wear resistance and surface roughness were also examined. It was measured amounts of mass loss and examined worn surfaces. Metal microscope was used to study the microstructures of the wear scars. Natural aged specimen observed maximum wear resistance.     

Effect of fracture toughness on abrasive wear resistance of steels

Various abrasive wear mechanisms were reviewed and an abrasive wear modeling experiment is assessed. Abrasive wear resistance of non-heat treated and heat treated steels has been determined by using a pin-abrasion machine with five abrasive papers, which grinds on a small pin of test materials. The mass loss of test material during abrasive wear was determined gravimetrically. A correlation between abrasive wear resistance and Mode II fracture toughness of materials was established. The effect of fracture toughness on abrasive wear resistance of steels was outlined.     

Effect of WC Particle Size on the Abrasive Wear of Thermally Sprayed WC-Co Coatings

Four types of WC-Co powders with different WC particle sizes are sprayed to produce WC-Co coatings with a Jet-Kote gun using a gas mixture of C₂H₂-30% C₃H₆ and pure propylene as fuel gases. The carbide size in sprayed high velocity oxy-fuel (HVOF) WC-Co coatings is measured from the microstructure. The abrasive wear of the coatings is characterized using a Suga abrasive wear tester. The abrasive wear mechanism of thermally sprayed WC-Co is discussed. The relationship between the relative wear of WC-Co coatings and carbide sizes is established according to the strength theory on hard alloy. The correlation with experimental data proves that the relative abrasive wear of WC-Co coating is proportional to square root of relative carbide size.     

Effects of temperature on the tribological behavior of Al0.25CoCrFeNi high-entropy alloy

The tribological behavior of Al_0.25CoCrFeNi high-entropy alloy (HEA) sliding against Si₃N₄ ball was investigated from room temperature to 600 ℃. The microstructure of the alloys was characterized by simple FCC phase with 260 HV. Below 300 ℃, with increasing temperature, the wear rate increased due to high temperature softening. The wear rate remained stabilized above 300 ℃ due to the anti-wear effect of the oxidation film on the contact interface. The dominant wear mechanism of HEA changed from abrasive wear at room temperature to delamination wear at 200 ℃, then delamination wear and oxidative wear at 300 ℃ and became oxidative above 300 ℃. Moreover, the adhesive wear existed concomitantly below 300 ℃.     

Investigation of the abrasive wear behaviour of ZA-27 alloy and CuSn10 bronze

In this study, abrasive wear behaviours of ZA-27 alloy and CuSn10 bronze were investigated using a purpose-built wear tester. The ZA-27 alloy was produced by permanent mould casting. The abrasive SiC particles having 63 μm grit size was added to the lubricant oil. The wear rate and friction coefficient of alloys were determined at the different test conditions such as sliding distance, applied load, linear velocity and percentage SiC weight content. The wear surfaces of alloys were examined using SEM and EDS analysis. The results showed that the wear rate of alloys decreased with the increasing of applied load and increased with the increasing linear velocity and abrasive SiC content. It was found that the SiC particle fracture was an important mechanism determining the friction and the wear rate of alloys. CuSn10 bronze showed higher wear resistance than ZA-27 alloy under abrasive test conditions except at high linear velocities.     

Effects of graphite particle addition upon the abrasive wear of polymer surfaces

The abrasive wear performance of vinyl ester resins modified with various volume fractions (5, 10, 15, 20 and 30%) of graphite powder has been measured. Using a conveyor belt driven testing machine developed locally, it has been possible to realistically simulate the effect of three-body abrasive wear upon these graphite modified polymer samples. A comparison of the calculated dimensionless wear rates obtained for these surfaces reveals that the effect of the graphite powder depends strongly upon the volume fraction of particles in the resin matrix. It appears that, for intermediate volume fractions, the presence of graphite powder in the resin matrix reduces the abrasive wear of the polymer surface. Scanning electron microscopy has been used to probe the mechanisms of abrasive wear of the pure resin and graphite modified surfaces. It appears that the embedded graphite particles can act as a lubricant during the abrasion process thus reducing the wear rate. The effect of increasing graphite powder volume fraction upon the abrasive wear mechanism is discussed.