P.S. Misra

A study on the behaviour of M-type barium hexagonal ferrite based microwave absorbing paints

This paper deals with development of single and double-layer microwave absorbing paints using Mn-substituted barium hexagonal ferrite. The comparative studies of both theoretical and experimental results at Ku band have been reported. It has been found that the single layer absorbing paint exhibits peak absorption of 12.3 dB at 17.4 GHz for a thickness of 1.12 mm. Double layer absorbing paint with each layer of different composition of ferrite gives a broad band characteristics, but at the cost of lowered absorption.

Comparisons of Sintered Technology with Powder Forging for Fe-P Soft Magnetic Alloys

Sintered P/M ferrous compacts containing up to 0.8% phosphorous have attractive set of mechanical and magnetic properties. Large phosphorous additions increase the shrinkage during sintering to such a degree that the tolerances of the sintered component may become adversely affected. Further, the sintering process requires more time and energy and is hence costly. To overcome the above problems, powder forging route has been used. In this process encapsulated Fe- P based alloy powder is heated and forged it into slabs. These were hot rolled to produce sheet and wires. Phosphorous addition improves the final density of the resulting product. It also improves the soft magnetic properties. All the alloys exhibited excellent workability.

Magnetic Abrasive Finishing – A Review

Abstract: The magnetic abrasive finishing (MAF) process which was introduced during the late 1940s has emerged as an important non-traditional metal finishing process. The process has found applications in a wide range of fields such as aerospace, medical, electronics, precision dies and moulds as a part of their manufacturing activities. Magnetic abrasive grit size, magnetic field intensity, magnet & workpiece gap, relative speed between workpiece & magnet, vibration of workpiece/magnet are the principal parameters that control the surface characteristics. MAF is the process that is being developed for efficient & precision finishing upto nanolevel of cylindrical or flat workpieces made of hard to machine materials. This review provides an insight into the fundamental parameters and creates a better understanding of this finishing process, with the objective of helping in the selection of optimum machining parameters for finishing of varied workpieces in practice.

Wear Characteristic of Al-Based Metal Matrix Composites Used for Heavy Duty Brake Pad Applications

Wear study of metal matrix composites used as friction material is one of the most important parameter for determining the brake performance. The present investigations relates to the development of Aluminum powder based brake pads; where the back plates are also made of Aluminum based powders respectively. Thus it is aimed to fabricate net-shape Aluminium powder based brake pads in a single forming operation with better characteristics (low wear, low temperature rise, stable coefficient of friction) employing a newly developed technology namely “Hot Powder Preform Forging” technique. Three Aluminum based friction composites which are designated as ALM 01, ALM 02 & ALM 03 were formulated. The dry wear test is carried out using a pin-on-disc tribo-tester at constant sliding speed of 9 ms-1 under a load of 50 N. The counter face disc is made of heat treated grey cast iron. During the test, the cumulative wear (gm), Coefficient of friction, temperature rise (oC) and noise level (dB) were recorded. The effect of load at constant speed on sliding wear, frictional characteristic of aluminum based MMC (rotor / drum) in dry condition is studied. On the basis of initial laboratory tests like density, Hardness, wear test, the samples were qualified for sub-scale dynamometer test at Rejected Take Off condition. Optical microscope was used to investigate the microstructure of metal matrix friction composites surfaces. The results revealed that coefficient of friction was more stable. The Cumulative wear (gm) was low with rise in temperature. It was also observed that distribution of ingredients in matrix was fine and homogeneous.

Study of Magnetic Abrasive Finishing Using Mechanically Alloyed Magnetic Abrasives

The finishing characteristics of mechanically alloyed magnetic abrasives used in cylindrical magnetic abrasive finishing (MAF) are presented in this study. Mechanical alloying is a solid state powder processing technique, where the powder particles are subjected to impact by the balls in a high energy ball mill or attritor at room temperature. After the process, fine magnetic abrasives are obtained in which the abrasive particles are attached to the base metal matrix without any bonding material. The magnetic particle used in the magnetic abrasive production is iron powder and the abrasive is aluminium oxide. Magnetic abrasives play the role of cutting tools in MAF, which is emerging as an important non-conventional machining process. The experiments performed on stainless steel tubes examine the effects of varying the quantity of magnetic abrasives, magnetic flux density, speed of rotation of the workpiece and amount of lubricant. The surface roughness measurements demonstrate the effects of the abrasive behaviour on the surface modification. The surface roughness was analysed in terms of percentage improvement in surface finish (PISF). The obtained maximum PISF was 40 % and the minimum surface roughness was 0.63 μm Ra.

Fe-P Soft Magnetic Properties of Iron for A.C. Applications

Silicon steels and ferrites dominate soft magnetic materials. However, Soft magnetic materials using powder metallurgical techniques are gaining wide spread use in motor, compressors and other rotating devices. High-density Fe-P soft magnetic materials have been developed using hot powder forging route. It was observed that phosphorous addition (ranging from 0.30P-0.80P) enhances the soft magnetic properties of iron for AC applications. This new soft magnetic material offers many manufacturing advantages. Because of its low eddy current loss, it has good high frequency magnetic properties comparable to other soft magnetic materials. Also, it has been observed that phosphorous addition improves the final density of the resulting product.

Manufacturing Brake Pads by Using Hot Powder Preform Forging for Low Duty Applications

To develop a high density brake pad for low duty application, a P/M route based on ‘Hot Powder Preform Forging’ was developed, which is not possible by sintering route. The mechanical properties of these materials were characterized using ASTM standards. The limitations of the conventional technique i.e. Compacting and Sintering for the manufacture of brake pads were tried to remove by adopting this technology. It offers better opportunity for pore free materials with better bonding between metallic and non-metallic constituents. Fade and Recovery test were done by using a Krauss Tester. μfade , μrecovery and μperformance lie within the range of friction materials used for low duty applications.

Role of Silicon in PM Processed Soft Magnetic Alloy

Iron-Phosphorus based soft magnetic materials are known for their hot and cold shortness. The present investigation deals with the development of high-density Fe-P based alloys in the form of very thin sheets (0.1mm) by proper soaking of them at a high temperature so as to eliminate Iron-Phosphide eutectic and bring the phosphorus entirely into solution in the iron. It has also been possible to eliminate the use of a hydrogen atmosphere during sintering by using carbon to form CO gas within the compact by reaction with the oxygen of the iron powder particles. A glassy ceramic coating applied over the compact serves as a protective coating in order to avoid atmospheric oxygen attack over the compact held at high temperature. The Fe-0.3wt% P- 0.4wt% Si alloy so formed yielded coercivities as low as 0.42 Oe, resistivities as high as 28.4 µΩcm and total losses as low as 0.132 W/Kg. Such a combination of properties may make the alloy suitable for application in magnetic relays and transformer cores.