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32-44 ANALIZA CHIMICĂ ȘI MICROSTRUCTURALĂ A MATERIALULUI UTILIZAT LA TURNAREA UNUI CLOPOT

CHEMICAL AND MICROSTRUCTURAL ANALYSES OF

A MATERIAL USED TO CAST A BELL

 

The present study was setup to determine the chemical composition of a bell material. After 27 years of service, a bell weighting 200 kg was broken. Two solutions were proposed for the repairing: soldering using Ag (cheap, but affecting the sound quality and mechanical properties) and a melting the old bell and casting a new one (approximately 16 times more expensive, but with better properties).  An optical microscope Olympus GX51 was used to study the microstructure. The chemical composition was determined using an XRF device Olympus Delta Element. The analysis showed the presence of lead and tin in composition, close to the upper limits. The presence of lead and eutectic structure, and the porosity produced a large crack on the basis of the bell. Clusters of macro pores were observed near the surface of the bell.  The fatigue could appear on the base of this

 

Keywords: bronze, microstructure, bell material, chemical composition

Cuvinte cheie: bronz, microstructură, material de clopot, compoziție chimică

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32-37 CONTACTE ELECTRICE CU DENSITATE RIDICATĂ PENTRU CURENŢI INTENŞI PRODUSE PRIN METALURGIA PULBERILOR

ELECTRICAL CONTACTS WITH HIGH DENSITY FOR STRONG CURRENTS, MADE BY POWDER METALLURGY

 

Electrical contacts for strong currents by infiltration after sintering, was not satisfactory because the final density is much higher (11,100 kg/m3) and porosity is much lower (10.85 %). The infiltration after sintering contains: powder mixture preparation (W – 52 mass %, Ni – 2 %, Cu – 46 %, zinc stearate – 0,7 %  – 7 g), homogenization, pressing (4,5 MPa), sintering (730 and 780 oC). The green density is almost constant, with an identical porosity of the first after the end of the process (14,28 %). By infiltration the density increased drastically (10,832 kg/m3), its variations were increased also and porosity decreased (at 10.85 %). The attained density is not sufficient for electrical contacts work (11,100 kg/m3), but it is closer. Way to improve density: pressing, sintering, and repressing (10,700 kg/m3).

 

Keywords: sintered electrical contacts, W-Cu

Cuvinte cheie: contacte electrice sinterizate, W-Cu

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32-35 BRAZARE NICHEL-ALUMINIU

BRAZING OF NICKEL-ALUMINIUM

 

The brazing between nickel and aluminium plates is a very sensible process being influenced by type of used materials and by brazing devices which maintain in contact the metal plates. These brazing devices have a very important purpose, their pressure affect directly the capillarity force. If the brazing devices are too tight (like 7 bar pressure), the filler melted metal escape from the grip, causing presence of defects in the joint; if the brazing devices are not tight enough (like 5 bar pressure) the capillarity forces become weak, allowing the voids inside the joint. Therefore, it’ is optimal for a nickel-aluminium brazed joint without defects a 6 bar pressure, created by brazing devices,

 

Keywords: brazing, Ni-Al

Cuvinte cheie: brazare, Ni-Al

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30-16 CONTACTE ELECTRICE PENTRU CURENŢI INTENŞI PRODUSE PRIN METALURGIA PULBERILOR

ELECTRICAL CONTACTS FOR STRONG CURRENTS
MADE BY POWDER METALLURGY
It was tested to be produced electrical contacts for strong currents by
infiltration after sintering, because the final density is much higher (11.100
kg/m3) and porosity is much lower (10.85 %). The infiltration after sintering
variant contains the steps: powder mixture preparation (W – 52 mass % – 520 g,
Ni – 2 mass % – 20 g, Cu – 46 mass % – 460 g, zinc stearate – 0,7 mass % – 7
g), homogenization, pressing (4.5 MPa), sintering (730 and 780 oC) and
infiltration (the green part is layed down on an electrocorindon EC 120 bed,
then the Cu green is on top of it, 1100 oC). In this variant the green part density
is almost constant (s = 0.062), with an identical porosity of the first after the end
of the process (14,28 %). By infiltration the density increased drastically (at
10,832 kg/m3), but its variations were increased also (s = 0.174) and porosity
decreased (at 10.85 %). The attained density is not sufficient for electrical
contacts work (11,100 kg/m3), but it is closer. The final composition of the
electrical contact was: W – 48.69 mass %, Ni – 1. 87 mass % and Cu – 49.44
mass %.
Keywords: sintered electrical contacts, W-Cu
Cuvinte cheie: contacte electrice sinterizate, W-Cu

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28-58 ASPECTE PRIVIND OBŢINEREA MATERIALELOR POROASE ARMATE

ASPECTS OF REINFORCED POROUS MATERIALS OBTAINING
The sintered materials of metal powders have low mechanical properties, which is why a reinforced process can improve these properties. The reinforcement is made of steel webs with square cell and particle size distribution of the powder deposited on these elements must be within the network parameter data. The materials obtained by sintering at 800 0C for 30 minutes in a hydrogen atmosphere have a uniform structure with a good pores distribution. The metal network influences the development of breakage and increases the tensile strength.
Key words: porous materials, powders, powder metallurgy
Cuvinte cheie: materiale poroase, pulberi, metalurgia pulberilor

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28-56 CERCETARE PILOT PENTRU PRODUCEREA CONTACTELOR ELECTRICE PENTRU CURENŢI INTENŞI PRIN METALURGIA PULBERILOR

PILOT RESERARCH FOR PRODUCTION OF
ELECTRICAL CONTACTS FOR STRONG CURRENTS
BY POWDER METALLURGY
There were experienced three pilot versions for electrical contacts for strong currents, W – Cu, by powder metallurgy. Based on these it was selected the following variant: Cu matrix composite reinforced with W, starting from the powder: W – 50.18 mass %, Ni – 1.02 %, Cu 48.06 %, and 0.74 % zinc stearate. 8 GPa pressed, sintered at 875 °C for 15 minutes, then infiltrated with Cu to fill the pores, resulting in a product that has a density of 11.738 kg/m3, similar to the theoretical density. It is noted that often remain additions of no infiltrated Cu and sometimes may appear craters in place of infiltration. It is preferred the version with as little as possible infiltrated Cu.
Keywords: sintered electrical contacts, W-Cu
Cuvinte cheie: contacte electrice sinterizate, W-Cu

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28-52 CARACTERIZAREA LIANTULUI FOLOSIT PENTRU FORMAREA PRIN INJECŢIE A MATERIALELOR COMPOZITE CU MATRICE DIN ALUMINIU ŞI PARTICULE DE CARBURĂ DE SILICIU ŞI GRAFIT

CHARACTERIZATION OF BINDER UTILIZED FOR INJECTION MOLDING OF ALUMINIUM MATRIX COMPOSITE WITH GRAPHITE AND SILICON CARBIDE PARTICLES
Powder Injection moulding is considered a novel technique for the manufacture of complex shape samples of ceramic or metal powders. It consists in: powder mixing with a binder, injection into a form; binder removal, and sintering. Injection moulding technology is characterized by high stability and productivity. It makes possible to use uncomplicated and inexpensive equipment. The most important for a binding agent is to be thin to reduce the force of attraction between solid particles of different sizes in order to reduce the viscosity. By adding a small quantity of binder it should provide a good formation of the mixture, ready for separation of the preform to retain the shape and strength of injection moulded sample. The sample is quickly removed and does not contaminate the carbon material contained in waste, or other products.
Keyword: binder, injection moulding, sintering, preform
Cuvinte cheie: liant, formare prin injecţie, sinterizare, preformă

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26-64 EFECTUL CUPRULUI ŞI A DEFORMĂRII MATERIALELOR SINTERIZATE PE BAZĂ DE FIER ASUPRA UNOR PROPRIETĂŢI MECANICE

THE EFFECT OF COPPER AND DEFORMATION ON SOME MECHANICAL PROPERTIES OF IRON BASED SINTERED MATERIALS
The behaviour of materials to static solicitations and especially to dynamic solicitations is very influenced by the presence of pores in the structure. Their effect on the concentration of stresses is greater the more the pores are situated closer to the surface. It greatly depends on the type of solicitation that material is subjected to. The processing by plastic deformation can have a double effect. On one hand, it can lead to the hardening of the material; on the other hand, it leads to a favourable tension state in rapport with these types of solicitations. Experimental results show that the effect of superficial deformation of sintered materials on the mechanical properties is different according to the type of solicitation and the structure of the material. It has been observed that it has an important positive effect on the hardness, Young modulus and the behaviour to fatigue of sintered materials.
Keywords: plastic deformation, powder metallurgy, material properties

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24-20 CERCETǍRI PRIVIND OBŢINEREA PIESELOR INJECTATE DIN PULBERE DE FIER

RESEARCH FOR OBTAINING OF IRON POWDER
INJECTED PARTS
Complex shape parts of small size and made in mass production may
be economically produced by metallic or ceramic powder injection. This modern
technology considers using a multi-component binder added to a small grain
size powder (less than 40 μm). During spraying iron powder process results a
small grain size fraction, which can be used in obtaining of injected parts. There
are presented the results of our research for obtaining of parts by injection
moulding technology in present paper. Present results are referring to used
binder properties, injection conditions, resulting shrinkage after injection and
de-binding, as well as the causes of defects may appear in injected parts. It is
noticed that, in addition to the binder characteristics, the knowledge of injection
process parameters and the de-binding conditions are very important in the
injection moulding technology design in order to obtain parts without defects.
Cuvinte cheie: formarea prin injecţie, deliere, metalurgia pulberilor
Keywords: injection training, debinding, powder metallurgy

20 CERCETǍRI PRIVIND OBŢINEREA PIESELOR INJECTATE DIN PULBERE DE FIER


21-111 INFLUENCE OF GRAİN SİZE ON MECHANICAL PROPERTIES OF Al2O3 – SiC COMPOSİTES

INFLUENCE OF GRAIN SIZE ON MECHANICAL
PROPERTIES OF Al2O3 – SiC COMPOSITES
Composite material of Al2O3/SiC was prepared by pressing Al2O3 and
SiC powders. The mechanical properties, including flexural strength,
compression strength, hardness, and resilience were studied. The amount of
SiC was 20, 30, and 40 vol. %. Sintering was done at 1650 oC for 1 h soaking
time in air. Porosity decreases as grain size of SiC is increasing. As increasing
the particle size the resistance of flexion decreases, the resistance of
compression is decreasing, HRA is highest for 20 % vol. SiC, and resilience is
highest for 40 vol.% SiC.
Keywords: Al2O3/SiC composites, flexural strength
Cuvinte cheie: compozite Al2O3/SiC, rezistenţă la încovoiere

111 INFLUENCE OF GRAİN SİZE ON MECHANICAL


22-36 INFLUENŢA PARAMETRILOR DE SINTERIZARE ASUPRA DURITĂŢII SINTERIZATELOR DIN PULBERE DE FIER DWP 400

The present paper is focused on the hardness of iron powder DWP
400 parts sintered in endogas. The effect of sintering parameters is studied.
There were prepared cylindrical specimens pressed at 600 MPa and sintered in
endogas at the temperature of 1120 0C and 900 0C for 30/60 minutes. Sintered
specimens were analyzed by optical microscopy, micro-hardness test and
macrohardness measurements. Increasing the temperature and duration of
sintering leads to a linear increase of hardness of specimens, influencing
strongly the density and the microstructure.
Cuvinte cheie: sinterizare, duritate, pulbere fier
Keywords: sintering, hardness, iron powder

36 INFLUENŢA PARAMETRILOR DE SINTERIZARE