TITLE: A chemical composition of cast Aluminium bronze tube plate and to a
method of producing the same.
FIELD OF INVENTION:
This invention relates to a chemical composition of cast Aluminium bronze tube
plate and to a method of producing the same.
BACKGROUND OF THE INVENTION:
Generally mild steel tube plates with coating of coaltar pitch epoxide is used as
tube plates for coolers, however sometimes based on site requirement, location
of site and water chemistry, it becomes necessary to use nonferrous tube plate,
which is compatible with non ferrous tubes. 60/40 rolled brass was being used for
this purpose. However, the rolled brass tube plates are not indigenously available
with the technical specification required for the same.
Indigenous tube plates used to have problems such as lamination and surface
defects such as blow holes. Tube plate being a pressure part such defects would
result in the problems of leakages.
These tube plates were thus imported and delivery, in time became a big
constraint.
OBJECTS OF THE INVENTION:
An object of this invention is to propose a chemical composition of cast
Aluminium bronze tube plate;
Another object of this invention is to propose a method for producing Aluminium
bronze castings;
Still another object of this invention is to reduce the time cycle of the method for
producing the Aluminium bronze tube plate;
Further object of this invention is to reduce the cost;
Still further object of this invention is to propose use of non-ferrous tube plate
without comprising with the quality of the product.
BRIEF DESCRIPTION OF THE INVENTION:
According to this invention there is provided a chemical composition of cast
Aluminium bronze tube plate comprises:
87.0- to - 88.0 wt% of copper
0.11-to-0.13 wt% of zinc
7.0- to - 8.0 wt% of Aluminium
0.18- to - 0.20 wt % of silicon
3.0- to - 3.5 wt% of Iron
0.015- to - 0.025 wt% of lead
0.70- to - 0.80 wt% of Nickel
0.60- to - 0.70 wt% of Manganese
0.015- to - 0.01 wt% of Magnesium and
0.025- to - 0.035 wt% of Tin
In accordance with this invention there is also provided a method of producing an
aluminium bronze castings comprising the steps of:
adding manganese in the form of a Cu-Mn alloy to the raw material of high purity
before adding aluminium;
subjecting the copper melt to the step of deoxidation;
adding aluminium to the melt of copper;
adding iron as alloy;
adding nickel while charging copper;
preparing a melt of the alloy in a non-oxidizing atmosphere;
subjecting the melt to the step of degassing;
agitating the melt;
pouring the melt in the mould.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig.1: shows microstructure of the imported rolled (60/40) brass plate.
Fig. 2: shows microstructure of the cast aluminium bronze plate.
DETAILED DESCRIPTION OF THE INVENTION:
Production of consistently sound castings requires an understanding of the
solidification characteristics of the alloys as well as knowledge of relative
magnitudes of shrinkage. The actual amount of contraction during solidification
does not differ greatly from alloy to alloy. Its distribution, however, is a function of
the freezing range and the temperature gradient in critical sections. Aluminium
bronzes have very narrow freezing ranges (about 14°C). In this case, the whole
mass tries to solidify almost simultaneously leading to the formation of a large
and deep central pipe. Narrow freezing ranges make aluminium bronzes high
shrinkage alloys. However, their good fluidity allows them to make high-grade
castings in sand, permanent mold, plaster, die and centrifugal casting processes.
However, for producing good quality castings of the bronzes, careful design is
necessary to avoid internal shrinks and draw. Large castings of the bronzes can
be made by the conventional methods paying proper attention to placement of
gates and risers for controlling directional solidification and feeding the primary
central shrinkage cavity. Al bronzes with a narrow solidification range and good
directional solidification range and good directional solidification are
recommended for castings having section thickness greater than about 25 mm. It
becomes difficult to achieve directional solidification in complex castings. The
most effective and most easily used device is the chill, which can be employed to
initiate or accelerate solidification, and thus promote soundness. For irregular
general, no special difficulties arise in producing Al bronze castings to withstand
a high pressure test provided that shape is simple and there are no sharp
corners or abrupt changes in section due to heavy flanges, bosses etc. Intelligent
use of chills may reduce problems associated with intricate shapes and castings
with varying section thickness. However, chills do not take care of accumulation
of oxides at corners and pockets.
The casting (pouring) temperature should be least possible ensuring free flow of
the melt in all parts of the castings. Interestingly, good fluidity of Al bronzes
enables the application of low casting temperatures for producing sound
castings. Higher casting temperatures are bound to lead to greater possibility of
gas absorption in the course of melting and greater shrinkage or contraction. It
also delays the solidification of the castings, which is detrimental especially to Al
bronzes. Avoidance of slow cooling is one of the important requirements of
casting Al bronzes to take care of the problem of self annealing; coarse brittle
structure otherwise forms. To reduce this problem, castings thicker than 25 cm
should be knocked off the mould just after solidification and allow the castings to
cool in air or even in the spray of water. However, this calls for a careful
judgment and should not by any means approach a quenching treatment leading
to the retention of excess quantities of the (3 phase, thereby making the
machining operation difficult. It has been observed that rapid cooling of Al bronze
castings containing 9.5-10.5% Al is just as dangerous as self annealing. Al
bronzes containing less than 9.5% Al are not so susceptible to the influence of
rapid cooling. Addition of 3% iron or other grain growth inhibitor further helps to
reduce the susceptibility of the Al bronzes towards self annealing. The adverse
effect of self annealing could also be eliminated by heat treatment. For this
reason, it is preferred in some cases to omit the use of chills in the moulds,
especially if these are costly to use, and to allow castings to self anneal and then
to subject them to quenching and tempering/ageing heat treatment. However,
heat treatment may not be possible for large size castings due to handling
problems and because stress of an undesirable character may remain in
quenched castings.
Shrinkage and contraction are responsible for many production problems.
Accordingly, special attention needs to be paid to risering in order to prepare
sound castings. The necessity to provide large feeding heads and risers with Al
bronze castings arise from high (liquid-to-solid and solid-to-solid) contractions.
The level of shrinkage of Al bronzes (~11.2%) is less than that of brasses
(~12.4%). However, despite less shrinkage than many copper-based alloys like
gun metals, the mode of shrinkage in Al bronzes is more dangerous since long
central pipe formed extends almost to the bottom of their castings. On the
contrary, the shrinkage pipe is limited to the top most regions of gun metal
castings, although the remainder of the castings shows a fine pin hole type
porosity. By carefully designing the riser and feeding system, it is possible to take
care of shrinkage problems in Al bronze castings. In fact the casting so prepared
could have the same level of density as that of the worked material.

Shrinkage problems could be attributed to the very short freezing range of Al
bronzes as their liquids and solids are not separated by more than a few
degrees. A further reason is that the primary a dendrites, which freeze first, are of
such form and dimension that they hinder the gravitational flow of liquid metal.
The use of chills in Al bronze sand castings becomes of great help to overcome
both shrinkage defects and tendency to obtain coarse and brittle structure due to
slow cooling of heavy sections. The chills have been reported to also allow
oxides to be collected on their surfaces, so that only light machining or grinding
suffices to give clean sound castings. Without the chills, the defects become
deep rooted needing heavy machining. The chills should be clean (Free of rust)
and dry otherwise they may lead to porosity or blow holes in the castings.
Another way to overcome shrinkage difficulty is to provide large feeding heads
and risers to Al bronze castings. The metal in the feeding heads and risers
should be the last to freeze to compensate for shrinkage in different portions of
the castings. As a general practice, the mass of the feeding heads and risers
may quite frequently far exceed the weight of the castings. Use of chills in
heavier sections can also enable to properly feed the metal in the mould. One of
the best methods to realize good feeding is to put bushes over the risers and to
feed with super heated melt, the degree of super heating should at least be
150°C. This enables to flow the melt into and through the semi solid castings,
thereby filling up shrinkage cavities and pores. The covering of feeder heads with
an insulating material, such as chopped straw, retards their freezing and thus
assisting in feeding. However, this may be associated with the danger of forming
folds. Use of heat insulating pads and risers moulded in gypsum have also been
found fruitful to solve the problem.
Gating Arrangements
Gating arrangements should be such that turbulent flow of the melt in the mould
is avoided to the greatest possible extent with a view to produce sound castings.
Sharp corners and edges should also be avoided in the pouring system. The aim
should be to fill the mould cavity by displacement rather than by a stream falling
through air. Use of inverted horn gates in which the diameter of the gate
increases towards the casting give best all round results in the case of Al
bronzes. Other suggested gates consist of a spiral or series of inclined planes
leading the melt down to the lowest level of the mould without undue churning.
The gate can be connected to the thick sections of Al bronze castings (so that
the melt in gate will also act as a feeder), as far from the cores as possible.
Putting small runners around the mould and double pouring should be avoided
as far as possible. This is in view of the fact that two streams seldom unite
perfectly owing to the enveloping effect of the oxide films, forming folds and or
cold shuts, to which the Al bronzes are quite sensitive. Putting a pouring basin on
the sprue head or a down gate with a pouring basin. Producing castings of Al
bronzes is not a difficult job provided required precautions are taken at different
stages of the process. With good casting techniques, it is possible to attain
consistently satisfactory results in terms of excellent finish, dimensional accuracy
and superior mechanical properties. This can be achieved in general through:
• Use of raw materials of high purity (99.95% and above) with less (15-30%)
of scrap;
• Use of thick and large pieces and not the chips or turnings
• Use of copper with least possible content of oxygen
• Adding (~0.3%) manganese in the form of a Cu-30% Mn master alloy
immediately before adding Al to the melt of copper to remove copper
oxide (Mn added to the melt of copper prior to adding Al removes copper
oxide even in the case of Al bronzes not meant to contain any Mn as an
essential constituent)
• Deoxidation of the copper melt may also be carried out with commercially
available deoxidizers (like E3 tube of Greaves Foseco or Cu-15%P master
alloy)
• Addition of Al to the melt (of copper) as virgin element (of 99.95%
minimum purity) or as 50/50 master alloy of Al and Cu; use of the master
alloy also reduces overheating otherwise forming more of dross
• Adding Fe as master alloy (e.g. AI:Cu:Fe = 20:60:20); or sheets of iron in
the melt of copper together with Al
• Adding nickel (wherever needed) as shots or shots of 50/50 master alloy
of Nickel-copper while charging copper
• Preparing the alloy melt by directly melting ingots of required composition
in place of adding virgin elements/master alloys may be more effective in
terms of cutting down the time and number of processing steps involved
and closely controlling the alloy composition
• Use of non-oxidizing atmosphere (by covering the melt with commercially
available chemicals like Albral of Greaves Foseco, or charcoal powder if
possible) during melting
• Proper degassing of the alloy melt using commercially available
degassers (like Logas 50 of Greaves Foseco) and/or by passing nitrogen
• Minimum agitation to the melt and turbulent-free pouring
• Completing the process of melting in the shortest possible duration
• Use of least possible casting (pouring) temperature (but sufficient to
ensure free flow of the melt in all parts of the mould, preferable
temperature ~1100°C);

• Effective skimming of the melt before pouring
• Adopting bottom pouring arrangement preferably
• Allowing the melt to fill the mould from down below or close to bottom
• Avoiding double pouring and moisture pick up by the melt
• Avoiding abrupt changes in cross section and notches in the casting
• Liberal use of risers or exothermic compounds and making provision for
adequate feeding and risering to combat high shrinkage by ensuring
adequate molten metal to feed all sections of the casting, the volume of
risers may constitute ~40% of the weight of the casting while their length
to diameter ratio should be ~1.5. The volume of the feeder may also be of
the same order as that of the risers.
• Properly placing gates and risers
• Fast cooling of the melt/ casting to avoid brittleness otherwise achieved
through self annealing), if possible
• The use of chills to overcome both shrinkage defects and tendency to
obtain coarse and brittle structure due to slow cooling of heavy sections
• Avoiding sharp corners and edges in the pouring system
• Putting a pouring basin on the sprue head or a down gate with a pouring
basin allowing quiescent flow of the melt in the mould
• Using a stopper/plug and box at the head of the down sprue, if possible
• Use of dry sand/CO2 /no bake sand moulds
• Appropriate venting of the mould in all sand castings
• Use of dry cores having sufficient strength and permeability
• Covering of feeder heads risers with heat insulating pads or exothermic
powder

Table 1: Chemical composition of the brass and bronze samples
Table 2: Density and mechanical properties of the rolled brass and cast Al
bronze
Characterization of the received plates of rolled 60/40 brass and cast Al bronze
in terms of chemical composition, microstructure, density, hardness, ultimate
tensile strength, yield strength, elongation, impact strength, fatigue strength and
corrosion and erosion-corrosion resistance has been carried out. This section
would highlight the experimental techniques adopted and the observations made
as follows:
Experimental Techniques
Chemical composition of the samples (size 25 mm x 25 mm) was analyzed
using a spark met machine. Microstructure of the samples was analyzed using
an optical microscope. The samples were polished metallographically and etched
with potassium dichromate solution prior to their microstructural characterization.
Density was measured by water displacement technique. Hardness was
determined with a Vickers' hardness tester at an applied load of 30 kg. An
average of five observations has been reported in this study. Tensile tests were
carried on round samples having 12 mm gauge diameter and 60 mm gauge
length using a Shimadzu make universal testing machine at a strain rate of
1.61x10-3 s-1. Impact tests were carried out with an impact testing machine. An
average of three observations are reported in this study in the case of hardness,
density, tensile strength and elongation and impact properties. Fatigue tests were
conducted on a fatigue testing machine at the stresses of 150 and 350 Mpa. Two
samples at each stress for each material were tested for characterizing the
fatigue behaviour of the brass and bronze. Chemical properties of the samples
were characterized by immersion, sacrificial/ bimetallic and sample rotation
techniques. The medium used in each case was tap water while all the tests
were conducted at ambient temperature (~38°C) on (15 mm diameter, 4 mm
thick) metallographically polished samples. Immersion tests were carried out for
a total duration of 2496 hrs, while weight losses were determined at definite

intervals. For sacrificial/ bimetallic corrosion testing, a sample of brass/ bronze
was interfaced with that of mild steel with an insulating (rubber) sheet in between.
The assembly so prepared was dipped in the medium for a total duration of 984
hrs. For erosion-corrosion testing, the samples were fixed on a disc and rotated
in the medium using an erosion-corrosion testing machine. The total test duration
in this case was 500 hrs.
Observations made in this study were as follows:
Chemical Composition
Table 1 shows the chemical composition of the brass and bronze plates. The
composition of the brass suggested it to be a naval brass inhibited with Sn (close
to UNS No. 46400 except Ni). The Al bronze conformed closely to UNS No.
61400 (except Ni).
Microstructure
Figure 1 shows the microstructure of the imported rolled 60/40 brass. Primary
dendrites of a-phase along with ß in the interdendritic regions may be noted in
the figure (regions marked by A&B respectively). Flow of microconstituents in the
direction of rolling may also be noted in the figure. The aluminium bronze
revealed primary a dendrites surrounded by a+?2 eutectoid and/or retained ß
(Fig. 2, regions marked by A& B respectively). Fine particles of iron and some
spherical particles of a glassy phase may also be noted in Fig.2 (regions marked
by arrow and C respectively).
Density and Mechanical Properties
Table 2 shows the density and various mechanical properties like hardness,
tensile, impact and fatigue of the samples. The aluminium bronze was observed
to be lighter than that of the brass. Further, the hardness and tensile strength
and elongation of the bronze were higher than that of the brass while yield stress
followed a reverse trend. The impact strength of the bronze was comparable with
that of the brass. At the stress of 350 Mpa, the number of fatigue cycles
withstood by the bronze prior to failure was more than that of the brass while
both the materials could sustain 106 cycles at the stress of 150 MPa.
Corrosion and Erosion-Corrosion Properties
Negligible material loss was observed in case of either of the materials i.e. the
rolled brass and cast Al bronze over the test duration of 2000 hrs during
immersion corrosion. A similar trend was also noted for the samples during
sacrificial corrosion (1000 hrs) and erosion-corrosion (500 hrs) tests. However,
there was considerable weight loss in the case of the steel part of the assembly
during sacrificial corrosion tests. Observed weight losses in different cases/tests
are shown in Table 3.
Concluding Remarks
Various activities under the project have been carried out in terms of literature
survey dealing with different aspects of concern in connection with brasses and
bronzes, development of aluminium bronze plates, and laboratory scale studies
on the samples of brass and bronze. Available information and various properties
evaluated so far give a positive indication of the possibilities of using the cast Al
bronze in place of rolled brass for cooler plates in hydro applications. However,
due attention needs to be paid especially in terms of taking precautionary
measures during preparing the (Al bronze) plates by foundry technique (as
discussed in section 3.3.1 and 3.3.2) in order to make good quality products. The
overall developments under the project are enable BHEL to fabricate cast
aluminium bronze plates in place of using imported rolled (60/40) brass for cooler
tube applications indigenously.
Table 3a: Material loss in brass and bronze during immersion corrosion tests
Table 3b: Material loss in brass and bronze during sacrificial corrosion tests
Table 3c: Material loss in brass and bronze during erosion-corrosion tests
WE CLAIM:
1. A chemical composition of cast Aluminium bronze tube plate comprises:
87.0- to - 88.0 wt% of copper
0.11-to-0.13 wt % of zinc
7.0- to - 8.0 wt% of Aluminium
0.18- to - 0.20 wt % of silicon
3.0- to - 3.5 wt% of Iron
0.015- to - 0.025 wt% of lead
0.70- to - 0.80 wt% of Nickel
0.60- to - 0.70 wt% of Manganese
0.015- to - 0.01 wt% of Magnesium and
0.025- to - 0.035 wt% of Tin
2. The chemical composition as claimed in claim 1, wherein the preferred range
are:
87.0- to - 88.0 wt% of copper
0.11- to -0.13 wt% of zinc
7.0- to - 8.0 wt% of Aluminium
0.18- to - 0.20 wt % of silicon
3.0- to - 3.5 wt% of Iron
0.015- to - 0.025 wt% of lead
0.70- to - 0.80 wt% of Nickel
0.60- to - 0.70 wt% of Manganese
0.015-to-0.01 wt% of Magnesium and
0.025- to - 0.035 wt% of Tin
3. A method of producing an aluminium bronze castings comprising the steps of:
adding manganese in the form of a Cu-Mn alloy to the raw material of high purity
before adding aluminium;
subjecting the copper melt to the step of deoxidation;
adding aluminium to the melt of copper;
adding iron as alloy;
adding nickel while charging copper;
preparing a melt of the alloy in a non-oxidizing atmosphere;
subjecting the melt to the step of degassing;
agitating the melt;
pouring the melt in the mould.
4. The method as claimed in claim 3, wherein the raw material used is of high
purity 99.95%.
5. The method as claimed in claim 3, where the manganese is added in the form
of copper manganese master alloy and the amount of copper is 30%.
6. The method as claimed in claim 3, wherein aluminium is added as a virgin
element or as 50 / 50 master alloy of Al & copper.
7. The method as claimed in claim 3, wherein iron is added as master alloy
Alxn.Fe -20:60:20.
8. The method as claimed in claim 3, wherein nickel is added as shots or shots of
50/50 master alloy of Nickel-copper.

9. The method as claimed in claim 3, wherein the melt is covered with chemical
like Albral of greaves Foseco or charcoal powder to provide a non-oxidizing
atmosphere.
10. The method as claimed in claim 3, wherein the step of degassing is preferred
by passing degassers selected from logas 50 of Greaves Foseco and nitrogen.
11. The method as claimed in claim 3, wherein the temperature of the melt is
~1100°C.

A chemical composition of cast Aluminium bronze tube plate comprises:
87.0- to - 88.0 wt% of copper
0.11-to- 0.13 wt% of zinc
7.0- to - 8.0 wt% of Aluminium
0.18- to - 0.20 wt % of silicon
3.0- to - 3.5 wt% of Iron
0.015- to - 0.025 wt% of lead
0.70- to - 0.80 wt% of Nickel
0.60- to - 0.70 wt% of Manganese
0.015- to -0.01 wt% of Magnesium and
0.025- to - 0.035 wt% of Tin