Cu Alloy Foundry

8/13/2019 Cu Alloy Foundry

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BY:ANJALI SAHU

ARCHANA BEHERA

ARUNI SAHUNEHA JAIN


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Copper melting and casting is known to have occurred as early as3000 B.C.

Pure copper shows low mechanical and casting properties andthus finds limited application for cast parts.

In more common use are alloy based copper.

Copper makes no. of alloys with elements such as Sn, Zn, Be, Cr,Mn, Pb, Al, Ni, Si, etc

Some of the commonly used copper base alloys are:

1.Tin Bronze 6.Leaded tin bronze

2. Aluminium bronze 7.Leaded nickel bronze3. Red Brass

4.Silicon brass

5.yellow brass


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Alloys of Cu readily oxidizes in the liquid state,henceto avoid oxidation of Cu alloys during pouring gating

system must secure quite filling of the mould cavity.

A skim bob is provided in the cope. For the purpose of controlling the rate of filling the

casting , a gating arrangement with choke in the

ingate is provided. A choke is a restriction controlling the rate of liquid

metal flow into the mold.


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GATING SYSTEM FOR COPPER ALLOYS


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As many Copper alloys: Posses high solidification contraction Have long freezing range Freeze dendriticallyThis freezing makes the transfer of molten metal

from risers to casting difficult.Because of dendritic solidification Cu castings posses

many shrinkage cavities

Risers of sufficient amount and size eliminates theabove problem.


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Pouring basin in the gating system is preferredto permit the molten metal to be pouredstraight down the sprue.


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SPRUE

CSA of the sprue should not be larger than therequired.

A sprue should have a sump or well at the base to

reduce the velocity of the vertical flow of metal.RUNNER It provides uniform flow into the casting cavity.

Runners should be rectangular and the CSA canshould be 4-6 times that of sprue exit.


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Copper alloys melt at temperature higher than Al, Mg, Zn

& Pb alloys.

Tapping temperatures for Cu alloys are often as high as

13150c.

Molten Cu alloys get contaminated from refractories as

well as the atmosphere.

Cu casting alloys are subject to fuming from vapourization

of zinc which is a major alloying element.


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Metal charge employed for melting consists of foundry

scrap and ingot of desired analysis.

Gates , risers, casting rejects should be properly cleaned

of molding sand and other contaminants.

There is melting loss of the charge due to burning out,

oxide formation and interaction between the alloy and

lining of the melting furnace. The melting loss varies in quantity with the kind of charge,

type of melting furnace, melting procedure etc.


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Furnaces used for melting Cu based alloys:

Crucible furnace

Reverberatory furnace

Induction furnace

Indirect arc furnace

Selection of a furnace depends on the quantity of

metal to be melted, the degree of purity required and

the variety of alloys to be melted.


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Charge must be weighed accurately. Furnace being charged must be cleaned of slag and be empty.

Furnace temperature at the time of charging must becontrolled.

Melting is done under oxidizing or reducing conditions, gasabsorption is kept at a minimum, as the absorbed gas must beremoved prior to pouring.

When Cu alloys having Zn content are melted oxidizingatmosphere is used to prevent the loss of Zn by

vapourization. Speed is required to minimize contamination from the

atmosphere & vapourization of volatile alloying elements.


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Alloy Pouring temperature 0CLeaded tin bronze 1070-1260

Leaded red brass 1070-1290

Manganese bronze 970-1120

Aluminum bronze 1095-1205

Silicon brass 980-1150

The pouring temperatures for a number of copperalloys are given below:


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Copper alloys such as aluminium bronze & manganesebronze form tight, adherent, non fluid slags oroxides.

Molten aluminium bronze & manganese bronze:

I. Should not be stirred or agitated to minimise oxideentrapment.

II. Pouring should be smooth and even to avoidsplashing and separated metal streams.

Fluxing and Flushing is carried outI. To separate molten metal & dross.II. To remove dissolved gases & dross.


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Lithium is a very effective deoxidizer and removes

hydrogen by forming lithium hydride.

Another effective deoxidizer is zinc alloyed with 2%

sodium.

High leaded tin bronze and leaded red brass form

fluid slags or oxides .


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Bronze pour


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Natural sand is used for most molds for the casting ofcopper alloys. Foundry producing bronze tablets and statues - fine

sand Plumbing goods industries - coarse sand

Synthetic sand is employed to overcome the deficienciesof natural sand. Bonding clays western bentonite, southern bentonite

and fire clay. Synthetic sand includes additives such as cereals, wood

flou and carbanaceous materials like sea coal. The moisture of green sand should be kept at a minimum

and permiability at a maximum. Any of the available types of cores used for metal casting

can be used in the casting of copper alloys


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Best suited to the casting of tin, silicon, aluminium,and manganese bronze and yellow brasses.

Molds are made of gray iron having Ni, Cr, or Mo insmall quantities to improve its high temperature

properties. The mold temperature for the casting of copper

alloys ranges from 120 to 3700C. The permanent cores which project into the metal

stream should be cooled to increase their life. In order to prevent the metal from shrinking and

clinging to mold components , it is necessary to pullthe cores , open the mold , and eject the casting as

rapidly as possible.


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Best suited for yellow brass. Close dimensional control, good surface finish & high

rate of production can be achieved but die life isshort.

Gas fired stationary crucible furnace is used formelting and holding the Cu alloys. Cold chamber die casting machines are used for this

process. Ram pressure 215 to 715 kg/cm2

Speed of injection plunger25 to 625 cm/sec

Water/oil is circulated through cores and dies tocontrol their temperatures.


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Very little lubricant is applied to dies because it burn

into the casting, resulting in defects. Mixture of oil &

graphite is sprayed on the plunger & sprues where

release is a problem.

Defects encountered are cracks, misruns, cold shuts,

porosity etc. caused due to improper pouring

temperature, die temperature, gating, vent, die

design.


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It ensures close dimensional control , smooth surface

finish, and low cost in high volume production.

Since pouring temperature is lower than those of

ferrous metals, silica sand is entirely satisfactory for

making the shell molds and cores.


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Good Castability In-built Corrosion Protection Low Frictional Properties and Good Resistance to

Wear Non-Sparking Characteristics High Electrical and Thermal Conductivity Good Mechanical Properties at Ambient and High

Temperatures Enhanced Low Temperature Properties Machinability Recycling Cost-Effectiveness


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Electrodes of resistance welding machines

Turbine runners

Water-meter housings

Bearings Gears and corrosion resistant pumps

Marine equipment

Plumbing goods

Valves and fittings

Steam pipe fittings


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Cu Alloy Foundry