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Advantages Microstructure Properties Comparison Application
ZA-27 [Zinc Bronze] It has unusual anti-friction properties that brings about a
very fine running surface and low temperature, whereby pivots and shafts are
protected. Frictional load dissipation of energy is reduced in the use of
bushings made of ZA-27, therefore this alloy is suitable and qualifies for
bushings for low and high speeds with light and/or heavy loads.
Hence ZA-27 is a technically superior and economically cheaper Anti-Friction alloy as compared to Gun metal, Phos. Bronze, Leaded Bronze, Aluminium Bronze, Other Traditional Bronzes, Brasses, White Metal and Nylon. ZA-27 is technically superior to the traditional bronze because of the following properties of ZA-27 .
ZA-27 is cheaper even at initial purchase as its specific gravity is only 4.8. Thus if a particular bush in Phos. Bronze or Gun Metal weighs 100 Kg then the identical bush in ZA-27 will weigh only 56 Kgs. Over and above the above stated fact ZA-27 is economical as its working life is 4 to 5 times longer than Phos. bronze. Microstucture: ZA-27 has a heterogeneous structure i.e. hard particles in soft matrix In this case the hard ternary eutectic Cu-Al-Zn etc is in a soft binary matrix of Zn/Al. The microstructure is similar in form to the tin bronzes. In case of ZA-27 the question of diffusion of copper into journal does not arise as :-
It is claimed that in the event of lubrication failures, bushings of ZA-27 will not score the shaft, no welding of bearing to the shaft will occur and the shaft will not suffer any embrittlement due to copper penetration. There is no change in the texture even when ZA-27 is remelted several times, borings, turnings, scrap pieces can be remelted and recast without under going any deterioration in quality. ZA-27 is less sensitive to load fluctuations thus suggesting its suitability as a bearing material for heavy static loads and those subjected to sudden and high impact loadings as are found in the case of cranes, road rollers, tractors, earth moving machinery, etc. Mechanical and Physical Properties.
Bearing Capacity Table of ZA-27.
The above table indicates that ZA-27 can be used in preference to Phosphorus Bronze, Gun Metal, Leaded Bronze and other alloys for both low and high speed applications and goes to prove its economy and efficiency in heavy and light engineering services. Comparison of ZA-27 with other Non-Ferrous bearing alloys.
Comparison of wear on ZA-27 Bushings and other bronzes.
Stress - Strain characteristic (CREEP). The ASME Boiler Code
defines the allowable design stress as the load required to produce a secondary
creep rate of 1%. in 1,00,000 Hrs. (11.4 Years). On this basis the design stress
for ZA-27 is 70 MPa and thus
ZA-27 can be recommended for many stressed
applications at temperatures upto 150 ºC.
==> ZA-27 has better castability, lower density, improved strength, less wear in service, with regard to Brass and Bronze alloys.
==> ZA-27 has an as Cast U. T. S. of @ 425 MPa at room Temp. and drops to 380 MPa at 80 ºC and to 200 MPa at 150 ºC.
==> Temp. ageing also has no effect on the U.T.S. ageing at 95 ºC for 10,000 Hrs. (425 Days) results in a decrease to 370 MPa.
==> Elongation of ZA-27 shows a gradual rise with increase in Temp. and increases sharply above 100 ºC.
Applications of ZA-27 · Cement and Building industry · General Engineering Industries · Paper & Pulp Industries · Heavy Engineering Industries · Mining, Iron and Steel Works · Machine Tools · Presses · Textile Industries · Agricultural Machinery · Smelters · Internal Combustion Engines · Oil Lubricated Pumps · Generators · Rubber Industries · Refineries · Power Plants · Transport Industry · Oil Industries · Chemical Industries · Railways · Aeronautics
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