Energy balance of a belt sinter furnace

Abstract

Controlling the energy consumption in PM processes is becoming increasingly crucial, as in all competing industries. It has been shown that the core PM process of sintering is responsible for most of the energy consumption. To improve understanding of the energy flows, a detailed analysis has been undertaken of a typical belt furnace, involving the mass flow of belt, sinter trays and payload as well as the flow of protective gases, combustible gases and electric energy. Different loading conditions were investigated to generate a complete image of the furnace. Various details have been analysed in a flow canal to understand the physics. The monitored data were matched and checked against a calculated physical balance.     

THE TECHNICAL CONTROL OF THE MANUFACTURE OF AIRCRAFT BRAKE FRICTION LININGS

Abstract

The processes used in the production of friction materials for aircraft brakes are outlined. The stringent quality-control procedures adopted at all stages of raw-material testing, mixing, pressing, and sintering are discussed and examples given that show the necessity for these procedures. The control system results in an end product that gives reproducible friction properties and wear rates and can fulfil the requirements of an emergency stop.     

Powder Metallurgy Group Meeting,Stratford-Upon-Avon, 3–4 November 1975: Report of Proceedings

Abstract

The key steps of a PM technique for manufacturing fully dense near net shape tool steel parts are described. The main production steps are powder preparation, compaction, and sintering. The pre- alloyed powders used in the process are annealed to soften them, making compacting to fairly high green densities possible. Sintering to full density is accomplished at a closely controlled temperature near the solidus of the material. The heat treatment response of sintered high-speed steel parts is similar to that of conventionally produced steels. A model for the calculation of the necessary carbon content to achieve full hardness during the heat treatment of high-speed steels was developed. The model is based on predicting the amount and approximate chemical composition of the carbides present after quenching from the austenitizing temperature and the subsequent calculation of the carbon tied up within the carbides. PM/0207     

Status,technological progress,and development directions of the ironmaking industry in China

ABSTRACT

The ironmaking industry in China is developing rapidly. This paper discusses the status, technological progress, issues, and possible development directions of ironmaking in China. Because the standards for waste discharge and energy consumption have become more redundant, the steel production capacity has decreased by ～145 million tons from 2016 to 2018. New sintering and coking technologies, such as water vapour spray sintering, high-temperature exhaust gas sintering, and semi-coke utilization, have led to distinct energy and efficiency improvements. Moreover, blast furnaces (BFs) are becoming larger and more intensive, due to which labour productivity has increased noticeably. However, some issues still remain, such as high fuel ratios, hot blast temperatures, and BF longevity. Nevertheless, eco-friendly and intelligent ironmaking is gaining importance and could be the development directions of the future.     

Heat-Treatment Response and Cutting Properties of Sintered Type M2 High-Speed Steel

Abstract

The difficulties in the production of steel parts, with a uniform carbon content from the surface to the centre and a constant carbon content from one part to another, are well known. Recent progress on sintering atmospheres with regard to carbon content is assessed and found lacking, especially when compared with the current demands of the automotive industry. The author investigates the operating conditions in a furnace with a good production rate and submits possible explanations for this, as well as suggesting a means by which the sintering atmosphere may be controlled. PM/0142     

The synergy between powder metallurgy processes and welding of metallic alloy: a review

ABSTRACT

Powder metallurgy (PM) technology is an ideal manufacturing process to produce near net shape parts i.e. part that requires little or no machining, examples of PM processes are spark plasma sintering, isostatic pressing and additive manufacturing. PM allows maximisation of materials and produces part with optimised mechanical and physical properties. Also, PM process provides the possibility to further increase the industrial use of PM parts by fabricating it into complex geometrical shapes via joining. Joining is the most important mechanical process necessary for PM parts to perform in actual service conditions expected in automobile parts and structural parts. Despite apparent advantages of PM processes, joining PM parts has been a tedious process, due to challenges associated with inherent characteristics, like porosity, chemical composition and impurities like oil or grease, which tend to impair the weldments property. In this document, a review of PM process is presented, focusing on different welding methods that can be used to effectively join PM components.     

Effect of Al2O3 and B4C particle additions on microstructure of PM copper based brake linings

Abstract

This paper highlights the effect of different ceramic particles on the structure of PM copper based brake linings. The copper based brake linings using a range of ceramic additives (1–6 wt-%) were prepared by powder metallurgy (PM). The optimum conditions for the production of brake linings were determined as compaction under 400 MPa and sintering at 805°C for 20 min in an argon atmosphere. The density of copper based brake linings decreased after sintering with the increase in ceramic powder contents for both Al₂O₃ and B₄C ceramic particles. The microstructural characterisation of produced samples showed that the lower boiling point elements in the as supplied powder vaporise during sintering from the structure and this leads to an increase in the porosity amount of the final component.     

Production of Al–Cu and Al–Cu–Si Alloys by PM Methods

Abstract

The possibilities of the production of aluminium-base copper and/or silicon alloys by conventional powder compaction and sintering methods have been studied. The effects of various lubricants, pressing, and sintering conditions on the behaviour of Al–Cu and Al–Cu–Si alloys were evaluated systematically. The role of copper and silicon additions during compaction and sintering and their advantages or disadvantages are discussed. All alloys underwent large dimensional changes (sudden swelling followed by rapid contraction) during sintering at temperatures greater than Al–Cu eutectic temperature and it is suggested that a process of particle rearrangement is largely responsible for this behaviour. The mechanical properties of the alloys were highly dependent on the sintering temperature. PM/0215     

烧结工序节能降耗新技术发展趋势

通过分析节能降耗的意义和国内烧结能耗现状,从改善原料条件、回收利用及降低电耗方面总结了国内外常用烧结节能降耗的技术措施,并阐述了部分技术措施的实际运行效果;结合设计经验及考察部分烧结厂实际运行情况,通过分析部分设计和生产参数,探讨了近几年国内采用的烧结节能降耗技术及实际运行效果,提出了烧结节能降耗技术未来发展的建议。     

Electrical Conductivity and Strength Changes in Green Compacts of Iron Powder When Heated in Range 50–400°C in Air

Abstract

Based on considerable technological development and comprehensive work in process engineering, a method has been developed for short-time induction sintering of hardmetals which combines increased production throughput with savings in treatment time and improvement of the final product. The process is applicable to conventional WC–Co and WC–TiC–Co hardmetals and can be readily transferred to other cemented carbide systems. PM/0217     

烧结生产添加粘结剂的实验研究

进行了烧结生产添加粘结剂的实验,并分析了实验结果.结果表明,烧结生产添加粘结剂可提高混合料制粒效果,改善烧结料层透气性,提高烧结矿产量,降低能耗.     

PM Nickel Alloys for Thermionic Emitters

Abstract

An introduction explains the principles for substrates of oxide thermionic emitters. A method of fabrication, alternative to the traditional fusion processes, is described, employing roll compaction of mixed metal powders, with the recognized advantages over conventional ingot pressing and sintering for medium-scale production with modest equipment investment. Especially valuable is the capability to sinter continuously, rapidly, and at relatively low temperatures, which confers extra control over contents of volatile and reactive additives. Protection of these additives during sintering and preliminary fabrication is effected by prealloying and coating the alloy powders with a layer of the matrix metal-nickel. The equipment and process is described with attention to controlling uniformity of thickness and density transversely and along the strip length, which is essential in minimizing edge cracking during the early rolling stages. Purity and compositional control is held to much tighter tolerances than for cast alloys, but a microheterogeneity obtains: a method for demonstrating this feature is illustrated. This microinhomogeneity modifies the diffusion characteristics of the additives and is a factor in restricting grain growth during fabrication and operation. PM/0240     

Electrochemical behaviour of sintered,yttria reinforced ferritic stainless steels

Abstract

The electrochemical behaviour of 434L ferritic stainless steels produced by the powder metallurgy (PM) route has been studied. The effects of sintering temperature (1250 and 1400°C) and dispersoid addition (10%Y₂O₃) have been investigated by potent iodynamic polarisation and electrochemical impedance studies in 0·05 M H₂SO₄ solution. All the alloys exhibited active-passive behaviour in the electrolyte. The critical current density for passivation was lower in the case of the PM samples when compared with 430, which has been attributed to the presence of Mo in the samples. The passive current density of the PM samples correlated with the sintered porosities. All the other passivation parameters were similar for the materials. The nature of passive film was investigated using electrochemical impedance spectroscopy. A lower capacitance (i.e. more corrosion resistant) surface film was obtained after sintering at the higher temperature. Yttria dispersoids in ferritic stainless steel decreased the corrosion resistance of the surface film after sintering at the higher temperature, whereas they did not significantly affect the surface film behaviour after lower sintering temperature. The results have been correlated to microstructural parameters of the PM materials.     

Effectiveness of reducing agents during sintering of Cr-prealloyed PM steels

Abstract

Development of strong inter-particle necks requires successful removal of surface oxides, present on the powder particles, during the initial stages of sintering. In the case of water-atomised powder prealloyed with chromium, the surface oxide consists mainly of an iron oxide layer with some more stable fine particulate oxides. The formation of sufficiently strong inter-particle necks requires as a minimum full removal of the iron surface oxide layer. This can be achieved by gaseous reducing agents (e.g. H₂, CO or a mixture of both) or by carbon, typically admixed in the form of graphite. The reducing power of various sintering atmospheres (active gas content ≤10 vol.-%) and their combined effect with graphite has been investigated by a thermal analysis technique. Results indicate that a combination of a dry hydrogen-containing atmosphere and fine graphite allows successful sintering of chromium alloyed PM steels.     

THE CONTINUOUS SINTERING OF COPPER-LEAD TO STEEL

Abstract

Bimetal strip consisting of copper-lead bonded to steel is produced by sintering uncompacted powder on to the steel, compacting by rolling, and resintering. The mechanism of the process is considered in the light of published work on liquid-phase sintering and of some experiments in which material at various stages of processing has been examined physically and metallographically. It is concluded that the process differs from normal liquid-phase sintering in that interparticle welding is brought about by the intermediate rolling process.     

Comparison of Mn,Cr and Mo alloyed sintered steels prepared from elemental powders

Abstract

Molybdenum, chromium and manganese offer considerable potential as alloy elements in sintered steels, especially for PM precision parts used, for example, in automotive engines and transmissions. This holds in particular for recycling and health/safety aspects. Within this work, the influence of these elements as admixed alloy metals on the sintering behaviour and the properties of structural PM steels is discussed. The considerable differences in the homogenisation behaviour during sintering are described as well as the respective advantages and drawbacks. It is shown that for high density PM steels, Cr and Mo are better suited while for conventionally produced mass products Mn is attractive, its affinity to oxygen being less of a problem today than commonly assumed and since Mn addition promotes swelling, this element might be a replacement for Cu. For Mn, admixing is the more attractive route, for Cr, in contrast, prealloying offers advantages, while for Mo both alloying techniques are feasible.     

PILOT STUDY OF PREFORM DESIGN FOR SINTER FORGING

Abstract

An important difference between sinter forging and conventional forging is that of consolidation of the PM preform. It therefore follows that sinter forging would seem to be a hot-compaction process with some bulk metal plastic flow. The permitted amount of plastic flow is considerably less for a PM preform than for a preform produced from wrought material of equivalent composition, since PM preforms exhibit poor ductility and are therefore more prone to cracking. The purpose of this study is to produce some guidelines to assist in designing preforms for sinter forging and to attempt to minimize the ‘trial and error’ approach. This has been undertaken by the production and study of a component suitable for PM forging, which at present is produced by conventional forging.

The lateral flow of metal was observed and investigations undertaken as to how density variations across the preform might assist the consolidation process. An iron powder containing 1% graphite and 1% zinc stearate was used in the production of components.     

Powder metallurgy materials in hot forming

Abstract

The purpose of the present paper is to determine the apparent yield stress of powder metallurgy (PM) materials at high temperatures. A brief introduction concerning the theory of yielding of PM materials is included. The models of loading functions for porous materials are recalled. The experiments have been undertaken by the author to identify the parameters of PM materials in hot forming. Two materials are considered: pure iron and aluminium powders.     

SINTERING KINETICS IN IRON-COPPER ALLOYS WITH AND WITHOUT A LIQUID PHASE

Abstract

Sintering of iron-copper alloys has been studied in the temperature range 950–1250°C. The factors involved include compacting pressure, sintering temperature, sintering time, and atmosphere. The results are interpreted as a decrease in pore volume due to the filling of voids between particles by a diffusion mechanism. An empirical equation of the Arrhenius type, based upon volume change as a function of sintering time, has been derived in order to evaluate the rate constant of the sintering process.

Volume diffusion is considered to be the primary mechanism of material transport in alloys containing 0·5–2·0% copper, when sintered in the range 950–1250°C, and in alloys containing 5·0–10·0% copper, when sintered in the range 950–1050°C. The activation energy derived for the sintering process is 53·4 kcal/mole. Surface diffusion appears to be the operative mechanism of material transport in alloys containing 5·0–10·0% copper, when sintered above the melting point of copper. The activation energy for this sintering process is 32·6 kcal/mole.     

Fatigue crack growth in some PM low alloy steels consolidated by rotary forging and sintering

Abstract

Fatigue crack propagation rates under plane strain conditions have been investigated for three PM low alloy steels consolidated to high densities by rotary compaction followed by sintering and heat treatment. It is shown that the densities and properties are intermediate between those of pressed and sintered materials and of powder forged materials. Threshold stress intensities compare satisfactorily with those for wrought counterparts, but resistances to crack growth are inferior to those of wrought steels. Possible reasons for the properties of the rotary compacted materials are considered in the light of their microstructures and the behaviour of other PM materials.