(A superior and economical antifriction alloy)
ZA-27 is a Zn-Al-Cu-Sn etc. alloy with unparalleled bearing properties and silver in colour. The unusual anti-friction properties of ZA-27 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 qualified for bushings for low and high speeds with light and/or heavy loads. ZA-27 can stand extreme conditions of shaft deflections and emergency starting and stopping conditions.
It is an ideal bearing material for heavy and light load pressures with low and high surface speeds.
The main factor in making ZA-27 economical is the fact that it has a specific gravity of 4.8 only as compared to 8.7 of other bronzes, which entails a considerable savings.
ZA-27 has all the qualities of bearing alloy i.e.
| COMPATIBILITY
LOAD CAPACITY
HARDNESS |
CONFORMABILITY
FATIGUE STRENGTH
STRENGTH |
EMBEDABILITYCORROSION RESISTANCE |
Hence ZA-27 is a technically superior and economically cheaper anifriction alloys 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 .
- Higher Tensile Strength.
- Double thermal conductivity.
- Lower specific weight.
- Easy machinability.
- Four to Five times longer life than Phos. Bronze.
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 10 Kgs then the identical bush in ZA-27 will weigh only 5.6 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 hetrogenous 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 diffussion of copper into journal does not arise as :-
- It has a low content of copper.
- Copper is not present in free state as it forms intermetallic compound with Zn and Al.
- Easily oxidised surface of ZA-27 prevents diffusion.
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.
ZA-27
- Mechanical and Physical Properties
- Bearing Capacity Table of ZA-27
- Comparison of ZA-27 with other Non-Ferrous bearing alloys
- Comparison of wear on ZA-27 Bushings and other bronzes
- Stress – Strain characteristic (CREEP)
Mechanical and Physical Properties.
| Ultimate Tensile Strength MPa. |
420-490 |
| Yield Strength MPa. |
378 |
| Elongation % in 51mm. |
2-8 |
| Hardness BHN |
90-120 |
| Shear Strength MPa. |
290-305 |
| lmpact Strength Joules (6.35 x 6.35mm. Un notched bar) |
15.2 |
| Creep Strength MPa. (Stress to produce Creep rate of 0.01%/1000 Hrs. at 25º C) |
70 |
| Creep rate at 138 MPa. Stress (%1000 Hrs. at 20º C) |
0.04 |
| Density gms/Cm3 at 20° C. |
4.7-4.9 |
| Solidification Shrinkage % |
1.26 |
| Solidification Temperature range ° C. |
480-580 |
| Thermal Conductivity mm/mm/° C at 20-100° C (x 10-6.) |
136 |
| Thermal expansion W/m/°C at 70-140°C. |
25 |
| Electrical Conductivity %IACS |
30.2 |
| Endurance Limit (Fatigue Strength) MPa. |
59 |
| Fracture Toughness MPa. m½ |
22 |
| Energy to Fracture N M-1. |
11×103 |
| Stress to Fracture MPa. |
149 |
| Co-efficient of friction. |
0.01-0.30 |
Bearing Capacity Table of ZA-27.
(This table indicates the maximum bearing pressure permissible at specific sliding speeds with gravity drip feed lubrication)
| Sliding Speeds |
Bearing Pressure |
| Metric |
British |
Metric |
British |
| 1 Metre/Sec |
200 Ft/Min |
400 Kgs/Cm2 |
5690 Lbs/Sq. In. |
| 2 Metre/Sec |
400 Ft/Min |
360 Kgs/Cm2 |
5120 Lbs/Sq. In. |
| 3 Metre/Sec |
600 Ft/Min |
230 Kgs/Cm2 |
3270 Lbs/Sq. In. |
| 4 Metre/Sec |
800 Ft/Min |
140 Kgs/Cm2 |
2000 Lbs/Sq. In. |
| 5 Metre/Sec |
1000 Ft/Min |
40 Kgs/Cm2 |
570 Lbs/Sq. In. |
| 6 Metre/Sec |
1200 Ft/Min |
25 Kgs/Cm2 |
350 Lbs/Sq. In. |
| 7 Metre/Sec |
1400 Ft/Min |
14 Kgs/Cm2 |
200 Lbs/Sq. In. |
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.
| Specification |
Specific
Gravity |
Yield
Strength
Tons/Sq.In. |
Tensile
Strength
Tons/Sq.In. |
Elongation |
Brinell
Hardness |
| ZA-27 |
4.8 |
15 |
20 min. |
2 min. |
90/100 |
| Gun Metal Lg2-C |
8.7/8.8 |
8 |
12 min. |
2 min. |
55/66 |
| Phos. Bronze 2B8 |
8.7 |
10 |
16 min. |
1.5 min. |
100 |
| Phos. Bronze Pb 2-C |
8.7 |
11 |
17 min. |
3 min. |
90 min. |
| Leaded Phos. Bronze LPB1-C |
8.7 |
9 |
14 min. |
1.5 min. |
65/75 |
| Leaded Bronze LB3 |
8.9 |
– |
12 |
5 min. |
60/70 |
Comparison of wear on ZA-27 Bushings and other bronzes.
|
JOURNAL |
BEARING WEAR-INCH DURATION OF TEST IN HOURS. |
| Material |
Speed
Ft/Min. |
Load Pressure
Lbs/Sq.In. |
100 |
200 |
300 |
| ZA-27 |
555 |
135 |
0.0005 |
|
|
| 850 |
175 |
|
0.0009 |
|
| 1420 |
200 |
|
|
0.001 |
| Phos. Bronze |
500 |
130 |
0.0024 |
|
|
| 850 |
175 |
|
0.0039 |
|
| 1420 |
200 |
|
|
0.004 |
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 is ideally suited as a bearing alloy as the brinell hardness fails gradually with increase in temperature.
This insures longer life due to reduced wear.
| Temperature |
Brinell Hardness |
| 50 ºC |
90 Min. |
| 100 ºC |
80 Min. |
| 140 ºC |
60 Min. |
| 200 ºC |
33 Min. |
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
- Machine Tools
- Presses
- Smelters
- Internal Combustion Engines
- Oil Lubricated Pumps
- Generators
- Rubber Industries
- Heavy Engineering Industries
- Refineries
- Power Plants
- Paper & Pulp Industries
- Mining, Iron and Steel Works
- Cement and Building industry
- General Engineering Industries
- Agricultural Machinery
- Transport Industry
- Oil Industries
- Textile Industries
- Chemical Industries
- Railways
- Aeronautics
