Maganese - Nickel Aluminum Bronze (Aqualloy) vs. Stainless Steel in Marine Propellers

The superiority of Mn - Ni Al bronze (Aqualloy) has been convincingly demonstrated by its characteristics of service, in which has been demonstrated to be the good enough, for the work in marine environment.

The consumption of use (Aqualloy) bronze has increased quickly in the United States, and other countries its their property of being nonrusting in marine environment as well as also its resistance to the corrosion in highly aggressives environments.

Propeller efficiency: It is important to highlight that propellers made of Aqualloy bronze as well as those of stainless steel, retain their original smooth machined surface over a long period of time, conserve the factor of efficacy the time over.

Numerically the increase in efficiency would lie in the order of 1.5- 3.0%, in the Aqualloy bronze and decrease in the stainless steel for its higher weight due to bigger material density, approximately a 10% heavier than Aqualloy bronze propellers would have an advantage in fuel savings due to its weight, also efficiency will also depend on the size of the propeller, factors of design and time of service.

Less weight will reduce, loading stresses on the tailshaft and bearings permitting smaller shafts.

MECHANICAL RESISTANCE: Because the ability of the Aqualloy bronze to resist failure under cut impact it is the reason why it is a material widely used to manufacture propellers.

And stainless steel behaves with less resistance, and similar elongation.

REPAIRABILITY: Aqualloy bronze is easily repairable by the process of MIG weld, or anyone, could also require or not of small preheating in order to weld, to difference of the stainless steel that if doesn't have a preheating adapted before welding, it will be subject to fractures for resistance for what it necessarily require a treatment for relief of efforts, as well as a treatment of heating for passivation of carbides and to avoid the oxidation process.

PROPELLERS COST. The reduction of weight of  Aqualloy bronze in conjunction with the increased in strength of the material, allows the design propellers approximately of 10 % less weight than a stainless steel propeller.

Although or in spite of the fact that the propellers of stainless steel is more expensive in price for kilogram, they for the high cost of their elements like him are the chromium and the nickel, the reduction of cost for a long period of time is appreciable.


Stainless steel propeller


Manganese - nickel aluminum bronze (aqualloy) propeller

TABLE 1- CHART OF PROPERTIES OF MANGANESE -  NICKEL ALUMINUM BRONZES (AQUALLOY), AGAINST STAINLESS STEEL

ITEM AQUALLOY 
manganese - nickel aluminum bronze

STAINLESS STEEL
 
(CF3 CF8)

Chemical composition %    
Copper 71 78 -
Manganese 10.0 14.0 1.5
Aluminum 7.0 8.5 -
Nickel 1.5 3.0 8.0 12.0
Iron 2.0 4.0 Rem.
Carbon - 0.03
Silicon - 2.00
Sulphur - 0.04
Phosphorus - 0.04
Chromium - 17.0 21.0
All Others 0.50 -
Physicals properties - -
Density

0.252 lb/cu. in.@68F
6.97 gm/cu. cm @20C

0.28 lb/cu. in @68F
7.75 gm/cu. cm @20C

Specific gravity 7.53 7.75
Coefficient of Thermal Expansion

0.0000098/F, de 68F 72F
0.0000176/C de 20C 300C

0.000009F de 68F 1000F
0.0000162/C de 20C 300C

Conductivity Electrical

3.1 % IACS @ 68F
0.018megahom/cm @20C

2.5 % IACS
Mechanical properties    

Tensile Strength
Kg/mm2 (psi)

56.47
(80,000)

49
(70,000)

Yield Point
Kg/mm2 (psi)

24.5
(35,000)

21
(30,000)

Elongation in 50 mm
(2 in.) percent
30 % 30 %

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