Effect of friction between powder and a mandrel on densification of iron powder during cold isostatic pressing

The effects of friction between the powder and the mandrel on densification behavior of metal powder were investigated under cold isostatic pressing. The friction coefficients between the powder and the mandrels with different surface roughness were determined from the relationship between the compaction pressure and the ejection pressure of the mandrel from powder compacts. The elastoplastic constitutive equations based on the yield function of Shima and Oyane were implemented into a finite element program (ABAQUS) to simulate compaction responses of metal powders during cold isostatic pressing. Finite element results were compared with experimental data for pure iron powder under cold isostatic pressing.     

机械合金化FeS/Cu复合材料的摩擦磨损性能

以FeS和CuSn8Ni1粉末为原料,利用机械合金化技术和粉末冶金技术制备了FeS/Cu复合材料,探讨了不同载荷情况下所制备的FeS/Cu复合材料的摩擦学性能及润滑膜与转移膜特征。结果表明：机械合金化提高了FeS与铜合金基体界面结合性能,进而提高了材料减摩耐磨性能;当载荷较小时,摩擦副表面接触不稳定,复合转移膜不连续,摩擦因数波动大;载荷较大时,复合转移膜易破损,材料的减摩耐磨性能变差;当载荷为150 N时,载荷适宜,材料表面软化,复合转移膜更加完整,摩擦因数较小。     

Modification with metals: an efficient method of improving wear resistance of phenol carboplastic pcp in friction with “viscous” corrosion-resistant steels

We study the effects of modification with metal powders on the triboengineering characteristics of carboplastic PCP under friction with “viscous” corrosion-resistant steel. It is shown that B83 habbitt is the best modifier among those studied because its application simultaneously reduces the wear rate of the carboplastic and steel and the friction coefficient of the couple. From the standpoint of improving the wear resistance of the couple, modification with nickel is most effective. The positive effect of modification with metals is that metals can effectively heal surface defects and smooth the surface relief of the counterbodies, thus reducing the wear rate and friction coefficient. In carboplastics modified with metals, the most dangerous wear mechanism (ploughing) does not occur.     

Simulation of microscopic shrinkage behaviour in sintering of powder compact

A method for simulating microscopic shrinkage behaviour of powder particles in sintering of a compact is proposed on the basis of the granular element method. In this method, the powder particles are modelled as many circular elements undergoing viscoplastic deformation due to surface tension during the sintering, and the microscopic shrinkage is calculated by equilibrating forces acting on the elements. The variation in shape of necks between the elements during the sintering is taken into consideration. Plane-strain shrinkage in sintering is calculated under regular and irregular dispositions of powder particles. In the regular disposition of powders having the same diameter, the obtained shrinkage behaviour is compared with the experimental one using glass rods and the calculated one by the viscoplastic finite-element simulation respectively. It is shown from the simulation of irregular disposition that the densification due to the sintering is accelerated by mixing powders having different diameters.     

石墨种类对铜基粉末冶金摩擦材料性能的影响

采用柔性石墨、造粒石墨和鳞片石墨分别制备粉末冶金烧结摩擦材料，研究不同种类片状石墨对摩擦材料摩擦磨损性能的影响。结果表明：不同种类石墨制备的摩擦材料的密度和力学强度差异，将影响材料基体在制动过程中的组织形态，使摩擦界面呈现不同的磨损形式，其中柔性石墨摩擦材料的主要磨损机制为氧化磨损，造粒石墨摩擦材料的主要磨损机制为犁削磨损和磨粒磨损，鳞片石墨摩擦材料的主要磨损机制为犁削磨损和黏着磨损；造粒石墨制备的摩擦材料在不同速度下制动和重复单次制动时的摩擦因数波动值较小，摩擦因数稳定性好，且具有适中的磨耗量，综合摩擦磨损性能最佳。     

The significance and use of the friction coefficient

The quantity known as the friction coefficient (or ‘coefficient of friction’) has long been used in science and engineering. It is easy to define, but not easy to understand on a fundamental level. Conceptually defined as the ratio of two forces acting, respectively, perpendicular and parallel to an interface between two bodies under relative motion or impending relative motion, this dimensionless quantity turns out to be convenient for depicting the relative ease with which materials slide over one another under particular circumstances. Despite the fact that both static and kinetic friction coefficients can be measured with little difficulty under laboratory conditions, the time- and condition-dependent characteristics of friction coefficients associated with both clean and lubricated surfaces have proven exceedingly difficult to predict a priori from first principles.The shaky nature of friction's fundamental underpinnings, has not prevented investigators from compiling lists of friction coefficients and publishing them for general use. Problems often arise, however, when engineers attempt to use tabulated friction coefficients to solve specific problems in mechanical design or failure analysis. The systems-dependence of frictional behavior is sometimes ignored, leading to misapplication of published data. This is particularly true for applications in nano-technology and others that differ from typical laboratory size scales. This paper will review the measurement and use of static and kinetic friction coefficients, discuss their usefulness, and describe the sources of frictional resistances in terms of shear localization.     

催化剂对蛇纹石粉体减摩抗磨性能的影响

采用UMT 3摩擦磨损试验机,在高接触压力下考察蛇纹石粉体及其与催化剂组合作为润滑油添加剂对45#钢的减摩抗磨作用.结果表明:在高接触压力下,润滑油中添加蛇纹石粉体后摩擦因数和磨损量都变大;相对于蛇纹石粉体,以蛇纹石和某种催化剂组合作为润滑油添加剂,可有效地降低摩擦因数和磨损量,并提高摩擦因数的稳定性.     

Model for compaction of metal powders

A new yield criterion for metal powder compaction based on continuum mechanics has been proposed. It includes three parameters to characterize the geometric hardening of powder compact and strain hardening of incompressible metal matrix. The elasto-plastic finite element method to describe compaction of metal powders has been formulated using the new yield criterion. The values of parameters in the yield criterion could be determined through cold isostatic pressing (CIP). The finite-element method was used to simulate compaction behaviour of copper powders of different shape and mean particle size.     

用正交设计优化半金属摩擦材料的配方

介绍了半金属摩擦材料的组成，用二水平七因素的正交设计对半金属摩擦材料的配方进行优化设计。通过对试验结果和极差值的分析，得出了各组分对摩擦系数和磨损率影响的重要次序，为优化配方、提高材料质量、调整摩擦系数提供了依据。经综合评分，推荐出较好的配方组合：13．9％腰果壳油改性树脂，32．4％钢纤维，7．4％海泡石纤维，11．1％石墨，2．8％二硫化钼，13．9％碳化硅，5．6％高岭土，7．4％硫酸钡，2．8％氧化镁，1．8％氧化铁，0．9％轮胎粉。     

高载荷条件下的材料表面摩擦因数测量

针对材料表面高载荷条件的要求，提出了测量摩擦因数的方法，并进行了相应测试装置的设计，该测试装置由正向加载装置、侧向加载装置和数据处理装置3部分组成。可以用来测量高载荷条件下材料表面的静摩擦因数和滑动摩擦因数，同时得到整个滑动过程中摩擦因数变化情况。利用该装置对某国防减摩涂层进行了测试，结果表明在高载荷条件下该涂层对碳钢表面具有较好的减摩效果。     

A new test method for measuring the galling resistance between metal powders and die tool materials in powder compaction

The friction characteristics and galling resistance between metal powder and die tool material in metal powder compaction is of outmost importance since they will influence the porosity and surface quality of the green body and consequently the porosity, tolerances and surface quality of the final sintered product. In the present study, a new test method for evaluating the tribological performance of die tool materials aimed for powder compaction is presented. The test method is based on controlled scratch testing using a commercial scratch tester but instead of the commonly used Rockwell C diamond stylus a sample holder with a small green body of compacted powder particles is drawn over the surface in a well controlled multi pass linear reciprocating sliding contact. The capability of the test method was evaluated for different types of tool materials including two PVD coatings in contact with different types of metal powders to determine the friction characteristics and the adhesion and material transfer tendency at the sliding interface. Post-test examination of the tool surfaces using FEG-SEM and EDS were performed in order to evaluate the mechanisms controlling the friction behavior and the material transfer tendency. The results show that the proposed test is a simple and fast method to obtain relevant data regarding the friction and galling characteristics of die tool materials in metal powder compaction. The mechanisms prevailing at the green body/die tool material interface, e.g. cold welding, can easily be monitored by the friction and acoustic emission signals. Of the die tool materials investigated the low friction PVD a-C:Cr coating displayed the lowest friction and highest galling resistance.     

纳米CaCO3半金属摩擦材料摩擦磨损性能的研究

使用定速摩擦试验机研究了纳米CaCO3对半金属摩擦材料性能的影响。结果表明：在半金属材料中，用纳米CaCO3代替普通的CaCO3粉体，在混料过程中，纳米CaCO3粒子粘附在其他颗粒和钢纤维表面上，热压成型过程中，作为粘结剂的树脂材料与这些材料之间的结合强度降低。在摩擦过程中，造成表面颗粒在剪切力的作用下，很容易与基体脱离，从而使得摩擦材料的摩擦因数偏小，而磨损率却大大增加。     

半金属基粉末摩擦片摩擦磨损性能研究

在不同工况下研究半金属基粉末摩擦片与淬火45#钢配副时,载荷和转速对其摩擦磨损性能的影响,并分析其磨损机制。结果表明,在油润滑和水润滑下,半金属基摩擦片高速下的磨损量要明显低于低速下的磨损量,而干摩擦下其高载高速下的磨损要高于高载低速时的磨损量。油润滑下随载荷的增大,半金属基摩擦片的摩擦因数逐渐升高;水润滑下随载荷的增大,高速时摩擦因数先增大后减小,低速时则逐渐降低;干摩擦下随载荷的增大,高速时摩擦因数呈现出先升高后降低再升高的趋势,低速时则先升高后降低。干摩擦时摩擦面十分粗糙,有比较明显的沟状磨痕和硬质颗粒脱落后残留的凹坑;而水润滑和油润滑时摩擦面较为光滑。     

Determination of the coefficient of friction in forging of porous metals from ring compression

An analysis of ring compression of porous metals was made on the basis of the plasticity theory for porous metals previously proposed by the authors. The change in geometry of rings with various porosities was obtained for various coefficients of friction. Experiments on ring compression were carried out using sintered copper powder metals. The coefficient of friction was determined for various lubricants and a proper lubricant for forging of porous metals was found.     

铁基粉末冶金刹车材料加压烧结冷却水流量研究

对于铁基粉末冶金刹车材料而言,加压烧结冷却过程中冷却水流量是保证材料获得优良综合性能的关键参数之一.通过粉末冶金方法制备了铁基刹车材料,研究了空冷和不同水流量(12 L/s、27 L/s、40 L/s)条件下,材料组织、力学性能及摩擦磨损性能的变化规律.通过光学显微镜和扫描电镜分析了材料性能变化规律的形成原因.结果表明:冷却水流量与冷却时间及冷却速度并不是简单的正比例关系,当冷却水流量为27 L/s时,冷却所用时间最短,材料冷却速度最大,材料组织以片状珠光体和粒状珠光体为主,其它条件下材料的组织主要为片状珠光体,但材料力学性能随冷却水流量变化不显著,同时,当冷却速度为27 L/s和40 L/s时,材料具有最大的密度;摩擦因数比较稳定,材料表面形成了完整的氧化膜,磨损量最小.     

A Study of the Static/Kinetic Friction Behavior of PTFE-Based Fabric Composites

Three different polytetrafluoroethylene (PTFE)-based fabric composites were prepared. The static/kinetic friction behaviors of these composites under different loads and speeds were studied. A 3D laser microscope and profile measurement apparatus were used for analysis of the morphology and weave structure of the composites, and the contact temperature of these composites under different loads and speeds was monitored continuously using a high-precision thermal resistor. In addition, a dynamic mechanical analysis (DMA) apparatus was used to explore the thermal and mechanical properties of PTFE-based fabric composites. The results demonstrated that speed/load, weave structure, and fiber form have an important influence on static and kinetic friction behavior of the fabric composites. Generally, the static friction coefficient is greater than the kinetic friction coefficient, except when considering light load conditions. Under light load conditions, the static friction coefficient is equal to the kinetic friction coefficient. In addition, the kinetic friction coefficient first increased and then decreased with increased speed, but the static coefficient increased first and then remained at an almost constant value. At all sliding speeds, the static and kinetic friction coefficients of tape yarn composites are better than those of the multifilament yarn composites. Weave structure has no effect on the static friction coefficient, but it has a significant influence on the kinetic friction coefficient.     

Compaction pressure,wall friction and surface roughness upon compaction strength of Andrographis paniculata tablets

A well-known Malaysian herb, Andrographis paniculata was used in this study. This herb is famous at reducing sugar levels for diabetic patients. In this study, the herb was compressed into tablets. A compressed tablet, which is a universal form in modern medicine, needs to meet certain mechanical strength criteria in order to withstand post-compaction loading such as coating, handling, packaging and storage. The objectives of this work were to investigate the effects of compaction pressure, wall friction and surface roughness upon compaction strength of A. paniculata herb during compression. A universal testing machine with pressures ranging from 15 to 30 MPa was used to compact the herb using a 20-mm-diameter cylindrical stainless steel uniaxial die. The tensile strength of the tablet increased as the compaction pressure increased. During compression, as the amount of powder being compressed increased, the tensile strength increased, and from the surface roughness test, the coefficient of wall friction and angle of wall friction decreased. In general, the compaction pressure, the wall friction and surface roughness plays a significant role in tabletting; hence, in producing a tough and coherent tablet.     

纹理表面滑动摩擦稳态摩擦学性能

基于稳态滑动摩擦系统模型,采用球-盘摩擦副定量分析研究法向载荷、滑动速度、初始表面纹理和摩擦副材料对稳态摩擦因数的影响,得到稳态摩擦因数在不同工况下的变化规律。结果表明：滑动摩擦的稳态摩擦因数与磨损率正相关,周向纹理表面的稳态摩擦因数最大,无纹理表面的稳态摩擦因数次之,径向纹理表面的稳态摩擦因数最小;无论何种初始表面形貌,随着转速的增加,稳态摩擦因数先减小后增大,随着法向载荷的增大,稳态摩擦因数呈增长趋势;较深较宽的表面纹理具有更大的稳态摩擦因数和更大的瞬时波动;稳态摩擦因数也与摩擦副材料的选取有关。     

Effect of two different rubbers as secondary binders on the friction and wear characteristics of non-asbestos organic (NAO) brake friction materials

Binder provides structural integrity by holding all ingredients in the composition of a brake friction material. The modified binders have played a major role in improving the frictional performance and thermal resistance of the friction material. The present research work evaluates the influence of secondary binders (Nitrile Butadiene rubber (NBR) and Styrene Butadiene rubber (SBR)) on the tribological performance of the friction material using a full-scale inertia brake dynamometer as per JASO C406 standard. Three brake pads were developed by varying the type and composition of secondary rubber binder (5%NBR, 5%SBR and 2.5%NBR + 2.5%SBR) with rest of the ingredients kept unaltered. It was found that the quantity of SBR rubber powder present as secondary binder improved dry and wet recovery. Friction coefficient (μ) exhibited better stability during the fade with the inclusion of both the rubber powders. The friction material with the inclusion of both the NBR and SBR rubber powders exhibited overall better performance than compared to the inclusion of only one secondary binder rubber in the composition. The worn-out surface of the developed friction materials and the counter discs were characterised using FESEM.     

聚四氟乙烯基减摩复合材料配方优化

以聚四氟乙烯为主体材料,加入石墨、铜粉、碳纤维等粉末作为填充剂,进行减摩复合材料配方优化设计。采用均匀设计法确定了聚四氟乙烯基减摩复合材料各配料实验点的分布,用样条函数对均匀设计法所设计配方得出的摩擦因数进行拟合,找出配料与摩擦因数的关系,建立配方优化拟合曲线,最后在拟合曲线上选取具有代表性的试验点进行验证试验,达到优化的目的。试验结果表明：配方中单独添加铜粉或石墨时,减摩复合材料的摩擦因数均较高,说明石墨和铜粉必须配合使用;当铜粉和石墨各为30份时,及铜粉为60份,石墨为15、25、30份时,材料的摩擦因数在整个配方体系中均较低;得到的配方优化拟合曲线趋势符合实际,可以用于指导生产。