manufacturing engineering term paper

7/29/2019 manufacturing engineering term paper

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Gati

BAH

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g and riseringby Tesfaye Girma

R DAR UNIVERSI

(IOT)

OL OF MECHANICAL

STRIALENGINEERIN

M IN MANUFACTURING E

ED FOUNDRY TERM PAPER

FAYE GIRMA ALEMAYEH

I

SUBMITTED TO;-PROF.R1

Y

AND

,

GINEERING

-Msc/00036/04

ATINAM UPPAL


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Gating and riseringby Tesfaye Girma

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Abstract

The design of gating and rise ring, or rigging systems as they are sometimes referred to, has been

a very important task in the manufacture of cast components. This paper presents a compilation

of common rules of thumb used by foundry experts and guidelines suggested by researchers for

better quality castings. The paper is divided into three sections: light alloy, steel and ductile iron

castings. Each section presents heuristics com-monly used for specific metals.


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Acknowledgement

In the world there is no one absolute in his work .I thought from the world so much, the world

teaches me so much .I give my gratitude thanks for those who have been awarding me a great

support above all I would thanks my god who helped me in every ups and down of my work and

in my survival. Of all we shall thrust in God for he had bleed and condemned to clean us from

our sin. This work will not be even stay like this without the support and motivation of many

people around me, so that it is my pleasure to express my appreciation to all of them for standing

in my side. Also I thanks to my adviser prof.RATNAM UPPALA ,who encourages me and

advised me to work about this term paper more thanks for his advice and comments he has

been giving to me throughout my work and also I will thanks all my teachers and my friends

those who helped me in my work.


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Abstract................................................................................................................................................... 2

CHAPTER-ONE ......................................................................................................................................... 5

1. INTRODUCTION ............................................................................................................................... 5

1.1. STATEMENT OF THE PROBLEM ..................... ........................ ........................... .......................... 6

1.2Objective: ................................................................................................................................... 6

1.3. Methodology ............................................................................................................................ 6

CHAPTER-TWO ........................................................................................................................................ 7

2. LITRATURE REVIEW ......................... ...................... ............................... ................... ......................... 7

2.1. GATING AND RISERING ........................ ......................... ............................ ......................... ........ 7

CHAPTER ................................................................................................................................................. 9

3. RISERING ......................................................................................................................................... 9

3.1. Criteria for Riser design ..................... ........................... ........................ .......................... ......... 10

3.2. Increasing riser efficiency ....................... ............................ ................... ............................ ...... 11

3.3. Rise ring System Design ....................... ......................... .......................... ........................... ...... 11

3.4. Inscribed circle method for Riser Calculations. ................................... .................... ................. 13

3.5. Modulus Method .................................................................................................................... 13

3.6. Determination of the numbers of Risers. ......................... .............................. .................... ...... 13

CHAPTER FOUR ..................................................................................................................................... 14

4. Gating System ......................... ...................... .............................. .................... ............................ ... 14

4.2. The members of the gating system............................................. ....................... ...................... 15

Pouring basin. ............................................................................................................................ 15

Sprue. ........................................................................................................................................ 15

4.3. Fluidity of molten metal ..................... .......................... ......................... ............................ ...... 16

4.3.1. Factors influencing fluidity ...................... ............................ ................... .......................... 16

4.4. Design of Sprues ..................................................................................................................... 19

Runner ....................................................................................................................................... 21

CHAPTER-5 ............................................................................................................................................ 23

CONCLUSIONS ....................................................................................................................................... 23

Reference ...................................................................................................................................... 24


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CHAPTER-ONE

1. INTRODUCTION

Casting processes are widely used to produce metal parts in a very economical way, and to

obtain complicated shapes with little or no machining. The manufacture of a part involves

several steps, the first of which is the design of the part itself, and the specification of the

material to be used. This information is passed to the methods engineer, who will choose the

casting process, and then design the rigging system necessary to get the molten metal into all

regions of the part so as to produce a sound casting. Two major considerations in the casting

design are the quality of the final product and the yield of the casting, both of which heavily

depend upon the rigging system used.


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1.1. STATEMENT OF THE PROBLEM

To gate fast pouring to: Minimize temperature loss during mould filling. To maximize Minimize metallurgical fade. To minimization Minimize oxidation. To clean pouring to: Avoid slag (dross) generation during pouring. To Screen out slag from first iron poured into mould. For Economic Design: .Maximize casting yield

1.2Objective:

The main objective of this experiment is to enhance the practical knowledge of thestudents in the field of metal casting technology and to review the basic principles for

the design of casting patterns, feeding systems and gating systems, in addition to the

investigation of the m

Castings without shrinkage defects Economic production maximize casting yield in factors affecting the

function of such casting elements.

1.3. Methodology

Design is an integral part of any product or process. Designers go through a number of processes

to achieve the final specification from an initial list of requirements known as a design brief.


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Available books journals AutoCAD Internet Different books Drawing

CHAPTER-TWO

2. LITRATURE REVIEW

2.1. GATING AND RISERING

The assembly of channels which facilitates the molten metal to enter into the mold cavity is

called the gating system. Alternatively, the gating system refers to all passage ways through

which molten metal passes to enter into the mold cavity. The nomenclature of gating system

depends upon the function of different channels which they perform.

-Richard W Hein Though we have a number of scientific approaches to the design of the gating

and rise ring most foundries still prefer to have the traditional way of designing gating & feeding

systems by trials and experimentations. Designing a gating system in a purely scientific way

demands through knowledge in the thermal and fluid dynamics field. Well this assignment

utilizes a classic fluid dynamical approach to design the gating with limited amount of empirical

results concluded by the leading researchers of 1960s. An empirical way of rise ring is also

formulated with some little success without following the results concluded by prior researchers.As it is a completely theoretical try, the concluded results may not match with the real time

situations. And this is where we take the aid of simulation programs.


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Riser always blind (closed top). Riser contact generally as short as possible. Designed dimensions always measured at the Notch. Gate thin and wide for fast freezing. Vents to assist fast mould filling


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CHAPTER

3. RISERING

Carbon steel experiences shrinkage of about 3% during solidification. Additional volume

reduction occurs during the cooling of the liquid metal after pouring. These contractions will

create internal unsoundness (i.e., porosity) unless a riser, or liquid metal reservoir, provides

liquid feed metal until the end of the solidification process. The riser also serves as a heat

reservoir, creating a temperature gradient that induces directional solidification. Without

directional solidification, liquid metal in the casting may be cut off from the riser, resulting in the

development of internal porosity. Two criteria determine whether or not a riser is adequate: 1)

the solidification time of the riser relative to that of the casting, and 2) the feeding distance of the

riser. To be effective, a riser should continue to feed liquid metal to the casting until the casting

has completely solidified. Thus, the riser must have a longer solidification time than the casting.

Since the critical factor affecting solidification time is heat loss, minimizing heat loss from the

riser is an important consideration. For a rise of fixed volume, a minimum amount of heat loss

will occur when the riser geometry has the smallest possible surface area. A sphere represents

the maximum volume-to-surface-area ratio (V/A, the solidification modulus), and therefore

freezes at the slowest rate according to Chorinovs rule. However, spherical risers present

molding problems. A cylinder with a height, H, equal to its diameter, DR, is the typically

recommended riser geometry, since it is a simple, easily moldable shape having a high volume-

to-surface-area ratio. Various insulating or exothermic riser sleeves are available to reduce the

heat loss from a riser. Regardless of its shape, the riser must be large enough to provide


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sufficient feed metal without the shrinkage pipe in the riser extending into the casting. As shown

in Figure 1, there are two common riser configurations: the top riser, which is typically more

efficient, and the side riser. The hemispherical bottom on the side riser prevents premature

freezing of the riser/casting junction [1]. It is also recommended to gate the casting through the

side riser for maximum effectiveness [1]. The feeding distance (FD) is the maximum distance

over which a riser can supply feed. The feeding distance depends in part on the temperature

gradient, which is the change in the temperature per unit length during solidification. Figure 5b

illustrates how a steep temperature gradient facilitates the feeding of a casting [4]. The shape of

the solid skin surrounding the liquid metal varies with the steepness of the temperature gradient

during freezing. Steep gradients provide open, more accessible feeding passages. There exists a

critical tapering angle for the liquid pool feeding the solidification shrinkage. For liquid pool

angles smaller than this critical angle, centerline shrinkage will form in the isolated pools of

liquid that are cut off from the feeding path.

Fig.3.1. feature of riser

Rise ring is a process designed to prevent shrinkage voids that occur duringsolidification contractions

Aluminum 6.6% Steel 2.5 to 4%

3.1. Criteria for Riser design

Riser must remain molten until casting is completely solidified Riser should have enough liquid metal to feed casting


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Gati

Riser should be kept a

3.2. Increasing riser efficien

1. Blind riser Good for narro Create a partia

from riser

Smaller riser - better y2.

Add exothermic comp

3.3. Rise ring S

Risers are elements of the

shrinkage cavity and porosit

The thinner sections of a casti

at the top. The latter commu

g and riseringby Tesfaye Girma

proper distance from the casting

fig.3.2.fo

y

w freezing range

l vacuum in the casting due to shrinkage that

ield

ound on riser

stem Design

gating and feeding system, which are in

outside of the casting. By the principle of

ng should preferably be located at the botto

icate with risers above them. If this is im

11

m of riser

can draw liquid metal

tended for displacing

directed solidification.

and the thicker ones,

ossible, side risers are


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provided for the hot spots. Using internal and external chills can also bring about directed

solidification. Drawings of castings are checked for the probability of formation of shrinkage

defects by the method of inscribed circle (Figure 1 a), which should freely roll out, as it were,

from lower sections of a casting into the upper ones and further into the riser. For the casting

shown in Figure 1 a, this condition is not satisfied (R1> R2), and therefore, shrinkage cavity 1 is

likely to appear in the hot spot. After marking the machining allowances, draft 2 and fillet 3 in

the drawing (Figure 1 b), the inscribed circles will roll out freely (R1< R2) from the bottom of

the casting up wards into the riser, which will ensure the directed solidification, and therefore,

the absence of shrinkage cavity in the casting.

Fig 3.3.riser system design

However, the basic requirement of a riser is that is should:

1. Be the last portion to solidify;2. Be effective in establishing a pronounced temperature gradient within the casting to

promote directional solidification towards the risers;

3. Have sufficient volume to compensate for shrinkage in the casting;4. Completely cover the casting section that is to be fed;5. Ensure the maximum yield possible. Apropos maximum yield, one has to know the

different shapes of risers in common use - spherical, hemispherical, elliptical, cylindrical,

square, rectangular and that, for a particular volume of the riser, the one having the

minimum surface area is the most effective.


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3.4. Inscribed circle method for Riser Calculations.

Heuvers was developed this method. The riser diameter is obtained by multiplying the diameter

of the largest circle (hot spot) that can be inscribed in the section to be fed by an arbitrary factor

which normally ranges from 1.5 to 3, i.e. riser diameter D = 1.5 TO 3 times diameter of the hot

spot. Though this method is empirical, it is still very much in use because of its simplicity.

3.5. Modulus Method

The Modulus of a casting M is given by:

aofcastingsurfaceare

stingVolumeofca

AV

Mc

c

c== .3.1

In view of the fact that the shrinkage cavity of a riser can amount to a maximum of 14% of its

original volume, the modulus of the riser must be at least 1.2 times the modulus of the casting.

To ensure that the riser solidifies later than the casting, (theoretically the solidification of the

riser will be about 1.44 times that of the casting) after obtaining the modulus, the size of the riser

can be calculated by assuming a suitable height to diameter ratio.

MM cr 2.1= .3.2

3.6. Determination of the numbers of Risers.

Number of required Risers can be calculated using the following formula

3.3............................................................................)(.)(

)(

mmTFDmm

mmL

dn

F

F+

=

Where: nF : Risers numbers required.

L : Casting length or mean circumference.

F d: Is the riser diameter.

T : IS the thinnest casting section through which to feed.

FD: Feeding distance factor, which is (4-5 for steel), (5 for malleable iron), (10 for

AL),(5-6 Al alloys), etc.


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CHAPTER FOUR

4. Gating System

The assembly of channels which facilitates the molten metal to enter into the mold cavity is

called the gating system. Alternatively, the gating system refers to all passage ways through

which molten metal passes to enter into the mold cavity. The nomenclature of gating system

depends upon the function of different channels which they perform.

Down gates or sprue Cross gates or runners

In gates or gates

The metal flows down from the pouring basin or pouring cup into the down gate or sprue and

passes through the cross gate or channels and in gates or gates before entering into the mold

cavity.

The metal flows down from the pouring basin or pouring cup into the down gate or sprue and

passes through the cross gate or channels and in gates or gates before entering into the mold

cavity.

Function

Trap contaminants Regulate flow of molten metal Control turbulence To establish directional solidification


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The ideal optimum gating system should:

1.

Fill the mold quickly.2. Fill a mold with a minimum of turbulence.3. Establish thermal gradients, which promote soundness.4. Avoid re-oxidation of metal in the gating system.5. Remove slag and dross from the metal as it flows through the gating system.6. Not distort the casting during solidification.7. Maximize casting yield.8. Be economical to remove.9. Be compatible with the pouring system used

4.2. The members of the gating system.

In the following, the individual members of gating systems and of their assembly will be briefly

presented:

Pouring basin.

Pouring basins that contain a well deeper than their depth at the sprue junction to effectively

absorb the impact of the arriving stream, and flow velocity will be governed by sprue height

only. Another advantage of this design is that pouring may start out slowly without iron entering

the sprue. Once the proper location of the ladles lip has been established, fast pour and sprue

filling begins with minimum slag entry.

Sprue.

Circular cross sections are being used most commonly. Tapering the sprue downwards is always

a good practice. Straight or nearly straight sprues may be used in all pressurized systems.

Chocked at the bottom (or sprue basin) of the sprue must be used in a non-pressurized gating

systems.


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Fig.4.7.Step of flow of fluid


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Measuring fluidity

A test for measuring fluidity using a spiral mold

The fluidity index of the material is the length of the solidified metal in the spiralpassage

The greater the length of the solidified metal greater is the fluidityTwo Principles of fluid flow

Bernoullis theorem

Law of mass continuity

Will help in design of gating system

Bernoullis Theorem

h + (P/rg) + (v2/2g) = constant fig.4.3.sprue and runnerh: elevation from reference plane

P: pressure at the elevation h1 + (P1/rg) + (v12/2g) = h2 + (P2/rg) + (v2

2/2g) + f

r: density of fluid

v: velocity of the fluid

g: gravitational constant

F : frinction

Laws of Continuity fig4.3.flow For incompressible liquids the rate of flow is constant Q = A1V1 = A2V2 Q: rate of flow m3/s A: cross sectional area


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Fig.4.7. Fluid flow

V: velocity if fluid flow Factors Affecting

Permeability Gas loss

4.4. Design of Sprues

As the liquid flows down the croaper is provided in the sprue Liquid loses contact if sprue is straight-causes Aspiration P1 = P3, Level 1 is constant V1 = 0, assume no frictional loss ght =(v3)2/2

Time to fill mold

Tf= V/ AgV3

Ag : cross sectional area

V: volume of mold cavity

Flow Characteristics

1

2

2

1

h

h

A

A=


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Important characteristics in fluid flow is Turbulence as opposed toLaminar Flow

Reynolds number

Re = vDr/

V: velocity

D: diameter

r: density

: viscosity

Re is usually between 2000 and 20000For Re above 20000

dross formations occur caused by air and gases Scum on top can get mixed with alloys

4.5. Elimination techniques

Avoid sudden changes in fluid flow Avoid sudden changes in cross section dross can be reduced by filters ( ceramic, mica) Also with proper pouring basin and gating system

4.5. Heat Transfer: Chvorinovs Rule

Solidification time is proportional to volume of casting and its surface area

C: constant reflects mold metal properties

2

=

asurfaceare

volumeCtime


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Runner

A straight runner is the best choice of space permits it. If bending the runner is unavoidable, it

should be done with as large radius as space permits, because curvatures introduce additional

turbulence. A minimum distance of 4 inch between the end point of the runner and the next gate

us recommended. The cross section of the runner is almost always rectangular with thickness to

height ratio of 1:2 in a pressurized system.

Fig.4.4.runner

Sprue runner junction.

The first rule in shaping the sprue-runner junction is that it must not locally decrease the

calculated sprue bottom cross-section area. If then, the sprue cross section is largely in any

dimension than the horizontal section of the runner, the sprue bottom should extend to the

bottom of the runner, see the previous figure.

Gates.

Gates are the most delicate members of the system, Gates should be thin and correspondingly

wide, and should be easy to remove. The optimum gate cross section is rectangular with a little

draft as condition permit.

Runner-gate Junction.


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A gate must never be placed in straight continuation of the runner. Gates must branch off the

side(s) of the runner at near right angles.

Gate-Casting junction

The gates need to join the thinnest sections of the casting as much as layout limitations permit.

The aim is to equalize cooling rate between the different segments of the casting. If delicate

cores or soft mold wall would be damaged by the impact of entering stream of iron, gates may be

flared out or their cross section increased nearing the casting. Such precaution is seldom used

because it increases cleaning room cost, and the reffduction in linear velocity is not significant.

4.6.Classifications of Gating Systems.

According to the hydrodynamics of flow of metal Gating system are divided into open and

closed. Closed or pressurized gating systems are characterized by gradually decreeing cross-

sectional areas of the sprue, slag traps and runners:

Gaterunnersprue SSS AAA >> ..4.5

Better separation of slag, the metal enters the mold cavity with a high linear velocity, which canlead to splashing and oxidation of the molten metal, capture of air, and washout of the mould

walls. Closed gating systems are especially popular in the manufacturing of iron castings.

Open or non-pressurized gating system is characterized by gradually increasing cross-

sectional areas of the sprue, slag traps and runners:

Gaterunnersprue SSS AAA


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CHAPTER-5

CONCLUSIONS

A new set of feeding distance and riser sizing rules has been developed for high alloy steel

grades CF-8M, CA-15, HH, HK and HP. By comparing casting trial results with corresponding

casting simulation a result, a correlation was developed between the Niyama criterion (a local

thermal parameter) and casting soundness. Using this information, extensive casting simulation

was used to develop feeding distance rules for a wide range of casting conditions. It was found

that the feeding distance rules developed in an earlier analogous study for carbon and low-alloy

steels could also be used for the high alloy steels considered, provided that the feeding distance

was modified by the appropriate high alloy steel grade multiplier. Other multipliers for these

feeding distance rules account for superheat, sand mold material, and the use of chills. The new

high alloy feeding distance rules, which are valid for section thicknesses ranging from 2.54

to30.5 cm (1 to 12 in.), are shown to be less conservative than existing feeding distance rules,

and are more tailored to the actual casting conditions. In another part of this study, high alloy

riser sizing rules were investigated. It was determined that if open top risers are used, the C&LA

riser sizing rule (which is less conservative than previously published high alloy riser sizing

rules) is applicable for high alloy steels as well. This study also determined that riser size is

independent of alloy grade for blind top risers.


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Reference

1. Kalpakjian, S., Manufacturing Processes for Engineering Materials, 3rd ed., Menlo Park, CA,

Addison Wesley, 1997

2. Kathie, S. , Chung C.W, Ramani K. & Tomovic M. Methodology for Metal-Casting Process

Selection Society of Automotive Engineers, Inc., 2002

3. Mikell P. Groover. Fundamentals of modern manufacturing materials,process, and systems.

Prentice Hall.Inc;1996 Schey, J. A. Introduction to manufacturing process.3 rd ed. NY: McGraw

Hill ; 2000.

4. Peter Beeley, Foundry TechnologyFirst published 1972 Reprinted 1979, 1980, 1982 Secondedition 2001

5. Ravi B. Metal casting computer-aided design and analysis. New Delhi: Prentice Hall of India;

2005.

6. Steve Hurst,metal casting Appropriate technology in the small foundry, IntermediateTechnology Publications 1996

7. John Campbell the new metallurgy of cast metals,Second edition 2003,First published

1991,Paperback edition 1993

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