The rod for collector brushes with higher electrical and thermal conductivity.

Ungur, Petru ; Pop, Adrian Petru ; Gordan, Mircea 等

Abstract: The paper has presented a composite material with matrix and metallic reinforcing, with higher electrical and thermal conductivity. It has created by processing from liquid form by infiltration of vertical and descending capillary with binary eutectoid alloy-Ag72Cu, of reinforcing from bidimensional and bidirectional twisting cupper wire under roll forming multiple capillary spaces in 3D, located within cylindrical cavity of cupper tube. The composite material process is consisted from certain phases: initial moistening, infiltration of eutectoid alloy and matrix solidifying.

Key words: binary, composite, eutectoid, multiple capillary.

1. INTRODUCTION

The paper is presented a composite material (CM) with matrix and metallic reinforcing, with higher electrical and thermal conductivity, withstand of worn and its fabrication by processing from liquid form by infiltration of vertical and descending capillary of binary eutectoid alloy-Ag72Cu, from bi-dimensional and bidirectional cupper wire in 3D, with multiple capillary spaces. The process was been extended at reinforcing textures wire of soft Iron (Fea), ARMCO, Ni, Co.

It has well known CM with ferrous or non-ferrous matrix, in which is lied at least one material under particle forms, fibers, layers, foils, that assured mechanical and physics-chemicals properties. The metallic matrix are compound from binary eutectoid metallic matrix, and its reinforcing from metallic wires (Ti, W, Mo, Cu, Al) or alloys, being constructed in a variety dimensional scale with diameter between (10-150)[micro]m and each greater.

The fabrication method is processing from liquid form allowing pre-arrangement reinforcing in a desired configuration with liquid metallic matrix, both by infiltration from immersion following by a pressing and diffusion, or a vertical descendent capillary infiltration and next diffusion. These infiltrations had disadvantage that fibers reinforcing must be orientated and maintained in desired position in such a way to keep orientation during infiltration, required a final calibration phase, assembly and diffusion with multiple process phases which are expensive.

The goal is determination of CM with metallic reinforcing from binary eutectoid alloy-Ag72Cu and a reinforcing with texture of bi-dimensional and bi-orientation cupper wire in 3D, with higher electrical and thermal conductivity, having enhanced performance and lower costs.

2. THEORETICAL FUNDAMENTALS

At CM with matrix and metallic reinforcing is required a combatively between them. Common crystalline structure of metallic reinforced are: face-centered cubic, body-centered cubic and hexagonal close-packed [Rufe,2002]. The alloys are created in a variety compositions, the arranged is done by setting of metal elements (Tab.1) in four groups: [T.sub.1]-strong electro-positive, [T.sub.2]-transition elements (3d,4d,5d,1f,5f), B1soft metallic elements, and [B.sub.2]-elements with lower metallic character.

[FIGURE 1 OMITTED]

The most usually alloys are binary alloys, which can be impaired in: mechanic mixtures, in which the compounds didn't dissolve reciprocal; solid solutions, in which the compounds are dissolved partial or total; inter-metallic compounds. The alloys of solid solutions are widely used at matrix of CM, ones of them are binary eutectic alloy-Ag72Cu, with face-centered cubic structure, and its balance diagram is showing in fig.1.

This alloy is suffered transformations in solid form accompanied by chemical reactions [Carp,Ungur,2003; Constantin,1997]. The brazing of Cu in hydrogen medium with eutectic alloy-Ag72Cu [Million,1975], assuring the base of fabrication of CM with matrix of metallic reinforced by nonconventional methods. The brazing tests with eutectoid alloyAg72Cu of cupper with higher purity-CuOFHC and ARMCOiron, in reducer hydrogen medium had been realized at Oradea University [Roman,1997; Maghiar,2000; Ungur,2003], allow creating of CM with matrix of Ag72Cu and reinforcing wires of Cu, Ni, Fe for electrical collector brushes. Infiltration of CuOFHC reinforcing has assured by vertical descendent capillarity (fig.2), and relation gives capillary force-P:

P = 2T cos [alpha]/s (1)

Where: T [g/cm] -is superficial stress of matrix material, a-is contact angle, s [cm]-kerf width.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Specifically this infiltration is that self-weight of eutectoid alloy-G, acting in same direction with capillary force:

P + G 2T cos [alpha]/s + [gamma]h (2)

Where: a-is specific weight of matrix material, h-height of capillary reinforcing. At infiltration of multi-capillary reinforcing of cupper with Ag72Cu are realized solid solutions between Cu-Ag, and Ag-Cu. During moistening of base reinforcing material with matrix is starting an atomic diffusion process. The intimate contact between Cu matrix and Ag-Cu matrix has supported by reducer hydrogen gas, which reducing cupper's oxides:

CuO + [H.sub.2] [??] Cu + [H.sub.2]O [Cu.sub.2]O + [H.sub.2] [??] 2Cu + [h.sub.2]O (3)

By removing of oxides is encouraged fast diffusion process, which due to infiltration during some tens seconds, resulting diffusion layers with 1im width. In fig.3 is depicted the diagram of control solidification process of Ag72Cu by vertical descendent capillarity with multiple reinforcing.

3. COMPOSITE MATERIAL FABRICATION

The CM with metallic matrix of binary eutectic alloyAg72Cu with higher conductivity has a higher molten temperature-7800C and metallic reinforcing from texture of cupper wire, soft iron-Fea, Ni or Co, obtaining a minimum process phases, best quality and lower costs.

The metallic matrix is building up from texture of bidirectional and bi-dimensional cupper wire with diameter greater that 100im. It has pre-formed by rolling in roll shaped like this forming multiple wrist layers in 3D with multiple capillary spaces, which enable easy infiltration by vertical capillarity of alloy-Ag72Cu in liquid form, in reducer hydrogen medium within of electrical oven at temperature of (830-850)[degrees]C. The process phases of this new CM are:

* cut off of cupper wire texture at desire size, following by mechanical-chemical cleaner;

* obtaining of multi-capillary structure by wrapping in roll shaped;

* compacting by get in of pre-formed into an inner cylindrical cavity of cupper tube, having inner diameter greater that exterior diameter of pre-formed and its length greater with 1/3;

* light clamped by radial mechanical pressing;

* locking the loading of matrix material from alloy-Ag-Cu has determined by tests in superior zone of cupper tube;

* get in of pre-formed in vertical position within of warm electric oven in a reducer hydrogen medium;

* molting, priming, infiltration, locking and solidification of eutectoid alloy Ag-Cu, having parameters: heating speed-[v.sub.h]=80[degrees]C/h, at molten temperature-T=830-850[degrees]C

[FIGURE 4 OMITTED]

* and maintain time-[tau]=60-90min, cool speed-[v.sub.c]=50[degrees]C/h, in same time with oven;

* trimming of semi-finished by cutting off of blank end of cupper tube due to a metallic composite material CuAg72Cu-Cu.

The infiltration process is doing in reducer hydrogen process, which assured higher superficial stress of alloy-Ag72Cu, lower viscosity, a maximal fluidity a greater moistening rate of multi-capillary pre-formed, and temperature of process is going under 1063[degrees]C due to avoid brittle of cupper.

The proceeding has been extended for other composite materials with matrix of Ag72Cu, with reinforcing of soft iron (Fea), ARMCO, Ni, Co, had obtained enhance performance.

4. CONCLUSIONS

The composite metallic materials of Ag72Cu-Cu, Ag72CuFea, and Ag72Cu-Ni had presented structural and functional properties for contact brushes, electrical contactors and materials with higher electrical conductivity.

An adequate choice of matrix-reinforcing combination due to a very well behavior at higher temperatures, good worn withstand, higher electrical-thermal conductivity, enhance toughness and transversal stiffness.

The manufacturing process by infiltration from liquid form assimilated by descendent capillary brazing in reducer hydrogen medium is simple, easy adaptable due to materials with lower costs.

5. REFERENCES

Carp, V.; Ungur, P. (2003). The Study of Materials, Didactical & Pedagogical Editor, Bucharest

Constantin, G.; Stefanescu, M. (1997). Handbook of Metals. Obtaining, Properties, Using, Technical Editor, Bucharest

Maghiar, T.; Ungur, P. & al. (2000). Magnetron. Elements of Theory, Construction, Technology, Oradea University Editor, Oradea, Romania

Million, A; Million, C. (1975). Soldering and Alloys of Soldering, Vol. I-II, Technical Editor, Bucharest

Roman, S. (1997), Research and Self-Contributions at Realizing the Generators of Microwaves Type Magnetron, PhD Thesis, Oradea University.

Rufe, P. (2002). Fundamentals of Manufacturing, Society of Manufacturing Engineers Editor, ISBN-087263524-4, Dearborn, Michigan, USA

Ungur, P.; Maghiar, T.; Pop, M.T. & al. (2003). Capillary Strong Brazing of ARMCO Alloy with CuOFHC Using an Anticorrosive Intermediary Build-up Layer, Annals of DAAAM 2003, Proceeding of 14th International DAAAM Symposium, B. Katalinic Editor, pp.447-479, ISSN 17269676, ISBN 3901-509-34-8, DAAAM International Vienna Publisher.

Table 1. Classification of metallic elements by properties alloy

 Metals Elements of B group

[T.sub.1] [T.sub.2] [B.sub.2] [B.sub.2]

Li Be
Na Mg Al Si S
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ad Cd In Sn Sb Te
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg T1 Pb Bi Po