Inhomogeneous density distribution, which destroys the mechanical properties of the parts. In order to investigate the friction behaviour of powder d Wear of the tool. during compaction, a new method has been developed.Losses of the press forces, etc. Compaction is a complicated process and direct and All these problems are caused by the friction that occurs continuous measurement of the coeYcient of friction during the process. Unfortunately there is neither a generally is not easy, because the coeYcient of friction varies accepted method to measure friction nor a generally accepted due to changes in such process parameters as pressure friction law. The lack of an accepted test method and a distributions, powder surface deformation etc. In this friction law impedes the communication between the powder paper, a new device for measuring the coeYcient of producer and the part producer. friction between metal powder particles in contact with A major problem is the lack of equipment that would the die wall during compaction is presented. Using the allow continuous measurement of the coeYcient of friction conventional methods for direct measurement of during compaction. There is an increasing interest in the radial pressure during compaction is very diYcult.modelling powder compaction, and the need for correct The new device oVers the possibility of investigating input data must be met. The powder compaction process the normal pressure on the powder particles directly is complex and diYcult to understand, since for example and continuously by keeping the green density conit is a combination of powder rearrangement and elastic stant. The measurements are performed using strain and plastic deformation of the particles. gauges mounted on the upper punch. The upperThe answers to even simple questions are not at all punch surface in the new device corresponds to the obvious. When does powder rearrangement occur and die wall in a conventional press. The sliding velocity, compaction velocity, normal load and temperature when do elastic and plastic deformation processes begin to can be monitored and controlled. Measurement of dominate? Is it possible to distinguish between the diVerent the coeYcient of friction at low densities is one of the stages during compaction? Do ow and deformation occur advantages and possible applications of this apparatus.simultaneously? Clearly, these questions require detailed The investigation shows that the powder compaction study using equipment which is capable of monitoring is controlled by a combination of powder rearrangethe process closely and producing data which help us to ment and elastic and plastic deformation of particles.understand what is going on. In order to obtain answers At densities below 4 g cm -3 the dominant process is to some of these questions, a new device has been designed particle rearrangement. No plastic deformation occurs and manufactured. at such low values of density. At densities aboveThe coeYcient of friction is not a constant material 4•5 g cm -3 the plastic de...

The coef cient of friction is a system response parameter, which is affected by a number of parameters such as normal load and sliding distance. Experimental results describing the in uence of these parameters are presented in this study. These parameters have a crucial role in the modelling of the compaction process and also provide an in depth understanding of the mechanism of friction in powder compaction. The powder surface characteristics change continuously during the pressing, making friction measurement quite dif cult. An attempt has been made to identify and separate the powder behaviour during compaction. The experimental results show that the plastic deformation of the surface in contact with the die wall occurs at an early stage of the compacting. At densities above 5 g cm 3 the plastic deformation is completed and the variation of the coef cient of friction is minimal. It has been observed that most changes of the powder surface occur at low densities. The nature of the friction has also been discussed.MST/5506

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Effect of cooling rate during sinter hardening on the microstructure and wear behavior of sintered steel grade Distaloy HP has been studied. Wear performances are closely related to macro and micro hardness of the materials. Dry sliding wear tests have been conducted using a reciprocating pin on flat wear testing machine under normal loads of 25, 35 and 45N and at a constant speed of 0.3 m/s. The samples were sinter hardened at different cooling rates 0.5–3 °C/s in order to investigate the influence of microstructure and hardness on wear behavior. It has been shown that, sintering process and cooling rate change the microstructure and hence the hardness and wear behavior of the material. The best wear resistance was detected at a cooling rate of 3 °C/s. At this cooling rate the material had an almost martensitic microstructure and the wear rate was some how independent of the applied load.