advance continuous casting of ag-cu alloy · and roll casting process as a new fabrication method...

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Advance Continuous Casting

Of Ag-Cu Alloy

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DECLARATION

I the M Tech students of Materials & Systems Engineering Design from NIT Warangal

hereby declare that the entire work embodied in this Laboratory “ADVANCE CONTINUOUS

CASTING OF Ag-Cu ALLOY” has been carried out by me.

No part of it has been submitted for the award of any Degree or Diploma at any other

University or Institution.

Vaibhav A. Chilate [143752]

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S.No CONTENTS Page no

1 List of figures 5

2 Abstract 6

3 Aim and Objective 7

4 Introduction to the continuous castig process 8

5 Background theory 9

6 Process and equipment design 10

7 1.1 Induction furnace 11

8 1.2 Insulation parts 13

9 1.3 Graphite crucible 14

10 1.4 Plug rod 15

11 1.5 Temperature sensor 15

12 2.1 Die and water assembly 18

13 2.2 Solid-Liquid interphase 18

14 3.1 Roller and rolling mechanism 19

15 4.1 Control panel function 19

16 Experimental details 21

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17 Calculations 22

18 Microstructure of Ag-Cu 24

19 Thermal Images 24

20 Tesile Test of Ag-Cu alloy 25

21 Conclusion 29

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S.No List Of Figures Page no

1 Continuous casting machine 10

2 Induction furnace 12

3 Electromagnetic Flux in Induction furnace 13

4 Graphite Crucible 14

5 schematic diagram of plug rod 15

6 Schematic diagram of thermocouple 16

7 Circuit diagram of thermocouple assembly 17

8 Die and water jacket assembly 19

9 schematic diagram of rollers and rolling mechanism. 20

10 Microstructure of Ag-Cu. 24

11 Regular Image of Die . 25

12 Infrared image 25

13 Tensile Test specimen 25

14 Schematic diagram of UTM 27

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ABSTRACT:

This study sought to examine the suitability of the Advance Continuous strip

and roll casting process as a new fabrication method for Ag-Cu brazing alloy. In

this, all the stages of casting performed on single machine itself as a automated

controlled system. Indeed, it is more effective and efficient casting method for

continuous product such as planner strip casting, melt dragging, roll strip casting.

In this particularly, the final product gets without any loss of materials, and it

would be almost defect free. Such casting product uses for precise purpose like

brazing in aircraft, missiles, rocket, and supersonic jet etc. In particular,

continuous strip casting was found to realize the best strip shaping ability and

microstrutural homogeneity. The effect on mechanical properties of Ag-Cu strip

was also investigated through tensile test, vicker hardness test, optical

microscopic, And scanning electronic microscopic(SEM) observations.

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Aim and Objectives:

The objective of this technology is to understand the design, operating principle

and mechanical properties of continuous casting machine as a system.

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Introduction to the continuous casting process:

Continuous casting is a process that molten melt is solidified into a semi-

finished bloom, billet or slab. The molten metal solidifies against the mold walls

while it is simultaneously withdrawn from the bottom of the mold at a rate which

maintains the solid / liquid interface at a constant position with time. The process

works best when all of its aspects operate in this steady-state manner.

In this, inductive furnace is used for melting the raw materials ( pure silver

and 99.99% pure copper ) where melting temperature is reached rapidly, because

the heat is directly generated in the metal and in the crucible. As the metal is

poured through the crucible bottom, only pure metal can reach into the die,

whereas contamination stays on the surface and can cover the top of the cast.

Benefits of continuous casting process are:

1) higher yield,

2) semi finished products,

3) less segregation,

4) better surface finish.

Apparatus Required:

Followings are the main apparatus required during operation of continuous

casting process.

Continuous casting machine setup.

Power supply through mains.

Graphite crucible and die.

Thermocouples.

Ceramic wool insulator.

Ejector rod.

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Background Theory:

According to a report from American Iron and Steel Institute in 2005 , it

is estimated that a 1% reduction of scrapped product due to casting related defects

(such as slab cracking from improper cooling, porosity, etc.) can result in an

annual energy saving of 0.147 trillion kJ for a single steel plant in their region of

the United State .In continuous casting process it is possible to control on such

defects ( porosity, macrosegregation ) thus, increase in tremendous saving energy

would be beneficial. Therefore, to predict porosity and macrosegregation defects in

the continuous casting process more sophisticated models are needed.

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PROCESS EQUIPMENT DESIGN:

Continuous Casting Machine consists of separate units basically divided into

four subsystems.

1. Top panel: Induction furnace, Graphite Crucible, Thermocouple, top cover.

2. Middle panel: Die, Die clamping arrangement, Cooling Water supply pipe.

3. Bottom panel: Rollers and pneumatic actuator etc.

4. Control panel: Digital screen, cooling die reader, gear system etc.

Fig:1 Continuous casting machine

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Table No. 1 Machine Details

1.1]Induction furnace: An induction furnace is an electrical furnace in

which the heat is applied by induction heating of metal. The advantage of

the induction furnace is a clean, energy-efficient and well-controllable

melting process compared to most other means of metal melting.

Sr.

No.

Parameter Details

1 Crucible Material Graphite

2 Crucible Volume 1500 cm3

3 Dimensions

Wire

Sheet

Tube

2 x Φ 15mm

100mm x 10mm

Max. Φ40mm

4 Melting Performance

Max. Power input

Mains supply

25 kW

3 phase, 400 v, 35 A,

50/60 Hz

5 Cooling Water supply 2.5 – 5 Bar, atleast 400

LPH

7 Room temperature 10 – 350 c

8 Relative Humidity 20 – 80 %

9 Compressed air Supply 6 – 8 Bar

10 Weight Approx. 250 kg

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Since no arc or combustion is used, the temperature of the material is no

higher than required to melt it; this can prevent loss of valuable alloying

elements. The one major drawback to induction furnace usage in a foundry

is the lack of refining capacity; charge materials must be clean of oxidation

products and of a known composition and some alloying elements may be

lost due to oxidation.

Fig:2 Induction furnace.

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Working Principle of induction furnace:

The principle of induction heating is mainly based on two well-known physical

phenomena:

Electromagnetic induction

ELECTROMAGNETIC INDUCTION :

The energy transfer to the object to be heated occurs by means of

electromagnetic induction. Any electrically conductive material placed in a

variable magnetic field is the site of induced electric currents, called eddy

currents, which will eventually lead to joule heating.

Fig:3 Electromagnetic Flux in Induction furnace

1.2] Insulation Parts:

In induction furnace, a ceramic insulator is provided between water cooled

copper coil and graphite crucible. Ceramic wool insulator provides protection to

the induction coil from high temperature of charge. There are different types of

insulators available such as glass wool, silica wool, ceramic wool etc.

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1.3] Graphite Crucible:

A crucible is a container that can withstand very high temperatures and is used

for metal, glass, and pigment production as well as a number of modern laboratory

processes. While crucibles historically were usually made from clay, they can be

made from any material that withstands temperatures high enough to melt.

Fig:4 Graphite Crucible

It is the inner part of induction furnace. It is made up of graphite because

graphite has very less coefficient of thermal expansion of the order of 3x10-6

m/mk. So it gives very good thermal stability and dimensional accuracy.

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1.4] Plug Rod:

Plug rod controls the flow of molten metal to the die. During the melting

process this plug rod is used to keep the die inlet closed. After the uniform

temperature is achieved in the crucible of the molten metal this is lifted up with

help of a switch provided outside. This is operated by lever mechanism.

Fig:5 schematic diagram of plug rod

1.5] TEMPERATURE SENSOR:

Thermocouple:

A thermocouple is a temperature-measuring device consisting of two

dissimilar conductors that contact each other at one or more spots.

An induction furnace for melting metal has a built-in thermocouple

assembly for continuously measuring the temperature of the molten metal.

A power controller then adjusts the power to the furnace to maintain a

predetermined temperature.

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The thermocouple assembly includes a refractory substrate which forms a

portion of the furnace lining partially coated with thin strips of two

thermoelectric materials so as to form a thermocouple junction.

Working Principle:

When any conductor is subjected to a thermal gradient, it will

generate a voltage. This is now known as the thermoelectric effect or

Seebeck effect.

Fig:6 Schematic diagram of thermocouple

A K – type thermocouple is used to measure the furnace, molten

metal temperature, cooling water temperatures time to time.

Properties of K type thermocouple:

Table No. 2 Properties of Thermocouple

Sr.

No.

Property Range

1 Composition:

Chromel

Alumel

90% nickel and 10%

chromium

95% nickel, 2%

http://en.wikipedia.org/wiki/Chromel

http://en.wikipedia.org/wiki/Alumel

http://en.wikipedia.org/wiki/File:Thermocouple_circuit_Ktype_including_voltmeter_temperature.svg

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manganese, 2% aluminium

and 1% silicon

2 Sensitivity 41 µV/°C

3 Temperature range −200 °C to +1350 °C

4 Wire color standard Yellow (+) and Red (-).

There are four such thermocouples in the whole setup.

(i) Thermocouple which measures the temperature of molten metal.

(ii) Thermocouple which measures the temperature of crucible.

(iii) Thermocouple which measure the temperature of die.

(iv) Thermocouple which measure the temperature of water assembly.

Fig:7 Circuit diagram of thermocouple assembly

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2.1] Die and Water jacket assembly:

Die is fixed in bottom of crucible and inserted through the furnace

in die chamber. Die chamber consists of a cooling water circulatory system that

maintain the die temperature. Die is designed according to output casting. Die has

holed (rectangular or Circular) throughout its length through which desired casting

product such as billet, bloom or slab draw out by the help of puller rod. Die is

made up of brass, cast alloy, cast steel etc. Cooling water is circulated outside the

die chamber to maintain the temperature of die at 75 oC.

Fig:8 Die and water jacket assembly

2.2] SOLID- LIQUID INTERPHASE IN DIE:

solid – liquid interface between the metal is formed in the die. This

interface plays a crucial load while selecting draw rate. If draw rate is high, the

interface is get shifted to lower level, creating threat of splashing the molten metal.

If draw rate is low, the interface can enter crucible making die cavity blocked due

to solidification.

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3.1] ROLLER AND ROLLING MECHANISM:

To draw the cast properly from the bottom, there is one special arrangement.

This is called as puller mechanism. On the bottom portion of machine rollers are

provided to draw the casting product and enhance the mechanical properties. Puller

rod is fixed between the rollers. There are two parallel heavy rollers are provided

to the left side of plug rod. These rollers are operated by single motor with helical

gear mechanism. On the right side of puller rod, generally three small rollers are

provided which are used to press and fixed the rod by pneumatic pressure.

Fig:9 schematic diagram of rollers and rolling mechanism.

4.1] Control Panel Functions:

Crucible Temperature –This temperature can be adjusted with the help of the

buttons “+” or “-”. This buttons could be pressed at least 5 seconds, to change the

values to the set point values. The set point values can be altered with the help of

“+” or “-” buttons.

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Die Temperature –

Similarly, Die cooling temperature can also be set with the help of following

buttons. We have to press the “+” or “-” buttons for at least 5 sec. an active set

point value can be adjusted with the help of red decimal point.

Power (Start/ Stop) –

These buttons are provided to turn on / turn off the generator. After turning the

generator on, we can keep the temperature adjusted to the set point value.

Water –

Water pressure is needed to be kept at appropriate levels (2 bars). Then the signal

lamp illuminates. If water pressure falls at very low values, the error signal comes.

Air –

Signal lamp illuminates when entry pressure of the compressed air is more than 4

bar. If air pressure is too low, the signal extinguishes and generator is stopped.

Draw length –

Set point level of the drawing length is indicated in this field.

Drawing Mode –

Manual Mode: As long as button is pressed, material is drawn.

Auto Mode: automatic drawing cycle is operated with this button.

Time – Set point for pausing is indicated in this field.

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EXPERIMENTAL DETAILS

Aim: To find the length of the casting product.

Material: Ag-Cu alloy

Composition: Copper-99.99% , Silver-99.99%

Procedure:

1) Take 72% Ag and 28% Cu by weight i.e. 2.992 kg Ag & 1.64 kg Cu, Total wt. is

4.56 kg

2) Cut this metal into small pieces on shearing machine.

3) Clean these metal pieces with acetone.

4) Dry metal pieces as well as graphite crucible by air pressure.

5) Take all these clean pieces into induction furnace.

6) Seal it with glass wool insulation.

7) Attach a metal bar for dragging purpose at the bottom of die, coated with Sic

powder.

8) Tighten the stainless steel plate and set thermocouple and closed the bell.

9) Turn on cooling water and compressed air supplies, push the main switch.

10) Supply power, and set the furnace temperature at 1085 deg ( M.P of Cu is 1083

deg & Ag-962 deg) .

11) Also Set water flow meter (die cooling) to approx. 75 deg.

12) Alloy to heat the furnace gradually in three or four stages upto its capacity

(25 Kw).

13) After getting steady state, set the temperature of induction furnace to get down to

900 deg due to lowering of M.P of alloy.

14) On pressing auto draw, alloy gets solidified and comes out in desire shape of strip

with constant speed of 1 mm/sec.

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15) Push drawing bar up t the mark and press. Start drawing process and check if the

drawing bar moves, than immediately open the sealing rod. This should be done

rather quickly so that the drawing bar will not be exposed to the heat more than

necessary.

16) In calculated time, entire molten metal gets solidified into strip without any

losses.

17) After getting final product, make sure that power should be off.

Safety Precautions:

1. In order to produce wire, sheet or tube of various dimensions, only die, drawing

rollers and drawing bar have to be exchanged.

2. Before casting, check if crucible, sealing rod, die and insulations etc. are clean and

undamaged.

3. Put sand on bottom to protect the fallen metal injury.

Calculations:

Table 3:

Sample Weight(kg) Density(gm/cc) Melting

Point(oC)

Silver 2.992 11.01 962 oC

Copper 1.64 8.9 1083 oC

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Table 4:

Time(min) Crucible

temperature(oC)

Die

temperature(oC) Power(kW)

0 146 69 9

5 230 68 9

10 422 74 15

15 627 72 15

20 990 73 25

25 1100 74 25

30 1138 75 20

35 1145 75 17

Metal Proportioning:

As we need 72 % silver and 28 % copper,

Silver available for casting = 2.992 kg

Amount of Copper required = 2.992×0.28

0.72 = 1.64 kg

Total weight of cast = 2.992+1.64 = 4.632kg

Length Calculations:

Estimated Length:

Cross section area of Die = 50mm x 5mm

Density of CuSil = 10g/cc

Length = 4.632

.5×.5×.10 = 185.28 cm

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Actual length of cast:

As per observation, the length of the cast has been found out to be 184.7 cm.

Hardness Value of Cusil = 232VHN

Weight of the casting = 4.56 kg.

Microstructure:

5X:

Fig: 10 Microstructure of Ag-Cu.

Thermal Imaging Photographs (IR) :

Here, with these pictures, it is demonstrated that how the gradual change in die

temperature can be measured with the help of IR Imaging Technique. It is a non –

contact type sensing technique. Although thermocouples and sensors can be used

to measure the required temperatures, but after certain range of the temperature, the

material loses its thermal stability.

Thus IR imaging technique comes of help to measure the temperatures without

having contact with the body.

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Fig11: Regular Image of Die . Fig:12 Infrared image

TENSILE TESTING

Aim:

To determine strength and ductility parameters of the given material by tensile

testing and comparing the properties before and after thermo mechanical processes.

Specimen Details:

Fig:13Tensile test specimen

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Table No. Specimen Details

Sr.

No.

Parameter Details

1 Total Length 80mm

2 Gauge Length 35 mm

3 Gauge Diameter 7.46mm

4 Temperature Set point 300c

1.4 Universal Testing Machine Details:

Table No. 8 Machine Details

Sr.

No.

Parameter Test

Value

Maximum

Value

1 Cross Head

Speed

20mm /

min

500

mm/min

2 Temperature 6000c 11000c

3 Capacity -- 25 Ton

CONSTRUCTIONAL FEATURES OF THE UNIVERSAL TESTING

MACHINE:

Universal Testing Machine consists of two pillared frame in which there is a cross

head. Crosshead can move in vertical direction up and down with the help of

hydraulic force. The specimen can be held in a column with the help of knurl

heads.

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Fig:14 Universal testing machine

Test Procedure:

1. The specimen is held fixed between two head jaws.

2. The load is given and specimen necking at ultimate tensile load and finally

leads to failure.

3. Simultaneously the loading and elongation is recorded as the Universal

Testing Machine is interfaced with computer. It takes the data and simulates

the stress – strain curve. The strength and ductility parameters are readily

displayed with the help of software.

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Tensile Test Report of Ag-Cu alloy at RT

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Results:

Material: Ag-Cu alloy

Table No. 9 Results for the Tensile Testing

Sr.

No.

Parameter Value

1 Ultimate Tensile Strength 367.75 MPa

2 Yield Stress 168.75 MPa

3 Fracture stress 239.95 Mpa

4 Percent Reduction in area 64.45%

5 Young’s Modulus 9.772 GPa

Conclusions:

higher yield.

semi finished products.

less segregation.

better surface finish.

Clean process as no metal spillage and sticking.

Near – net shape can be achieved with this process.

Less production time as casting process is continuous.

advance continuous casting of ag-cu alloy · and roll casting process as a new fabrication method...

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