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Metal casting and joining technologies
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ASSIGNMENT
Module Code AMT 503
Module Name Metal casting and joining technologies
Course M.Sc in Advanced Manufacturing Technology
Department Mechanical and Manufacturing Engineering.
Name of the Student Papineni.Satheesh
Reg. No BVB0911002
Batch Full-Time 2011
Module Leader Mr. K.N. Ganapathi
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M.S.Ramaiah School of Advanced Studies Postgraduate Engineering and Management Programmes(PEMP)
#470-P Peenya Industrial Area, 4th Phase, Peenya, Bengaluru-560 058
Tel; 080 4906 5555, website: www.msrsas.org
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Declaration Sheet Student Name Papineni.Satheesh
Reg. No BVB0911002
Course AMT Batch Full-Time 2011.
Batch FT-11
Module Code AMT-503
Module Title Metal casting and joining technologies
Module Date 19-03-2012 to 17-04-2012
Module Leader Mr. K.N. Ganapathi
Extension requests: Extensions can only be granted by the Head of the Department in consultation with the module leader.
Extensions granted by any other person will not be accepted and hence the assignment will incur a penalty.
Extensions MUST be requested by using the „Extension Request Form‟, which is available with the ARO.
A copy of the extension approval must be attached to the assignment submitted.
Penalty for late submission Unless you have submitted proof of mitigating circumstances or have been granted an extension, the
penalties for a late submission of an assignment shall be as follows:
Up to one week late: Penalty of 5 marks
One-Two weeks late: Penalty of 10 marks
More than Two weeks late: Fail - 0% recorded (F)
All late assignments: must be submitted to Academic Records Office (ARO). It is your responsibility to
ensure that the receipt of a late assignment is recorded in the ARO. If an extension was agreed, the
authorization should be submitted to ARO during the submission of assignment.
To ensure assignment reports are written concisely, the length should be restricted to a limit
indicated in the assignment problem statement. Assignment reports greater than this length may
incur a penalty of one grade (5 marks). Each delegate is required to retain a copy of the
assignment report.
Declaration The assignment submitted herewith is a result of my own investigations and that I have conformed to the
guidelines against plagiarism as laid out in the PEMP Student Handbook. All sections of the text and
results, which have been obtained from other sources, are fully referenced. I understand that cheating and
plagiarism constitute a breach of University regulations and will be dealt with accordingly.
Signature of the student P.Satheesh Date 17-04-2012
Submission date stamp (by ARO)
Signature of the Module Leader and date Signature of Head of the Department and date
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Abstract ____________________________________________________________________________
In this Metal casting and joining technologies assignment we have three different sets of parts.
In the Part-A, it is discussed about a debate topic on “cast components designed for
functionality, regardless of manufacturability is the main reason for high rejections in foundry”.
To support this debate an industrial case study is taken and explained about what actually the
cast product design engineers will do while designing the cast components, and what design
engineer should perform while designing the cast component and the main reason for these
defects is due to the lack of communication between the product designers and casting experts.
To overcome these how to apply the Design for Manufacturability in the cast design is
explained.
In the Part-B, it will be seen about the simulation of casting model using pro cast
software and using this software critical analysis of the fluid velocity, temperature during
filling, solidification time, pressure of liquid metal while filling the mould cavity and fraction
of solid in the gate junction and center of the castings. In the same casting the defects are
identified and explained the reason for the defect and calculated the riser dimensions for the
given model.
In the Part-C, welding process is selected for high alloy steel materials to manufacture
the pressure vessels. The selected welding process is capable of good corrosion resistance and
weld will be able to with stand the pressure given by the pressure vessel and weld should be of
no porosity. By considering all the above factors Sub merged Arc Welding process is selected
and explained about the complete process with process parameters of selected welding process.
For checking the quality of weld a non-destructive testing method is also explained which is
suitable for this application.
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Contents ____________________________________________________________________________
Contents Declaration Sheet ......................................................................................................................... ii
Abstract ....................................................................................................................................... iii
Contents ........................................................................................................................................iv
List of Tables ................................................................................................................................vi
List of Figures ............................................................................................................................ vii
Nomenclature ............................................................................................................................ viii
PART-A ......................................................................................................................................... 1
1.1 Casting: .................................................................................................................................... 1
1.2 Analysis of the case and build of opinion: .............................................................................. 1
1.3 Examples: ................................................................................................................................ 1
1.4 Conclusion: .............................................................................................................................. 3
PART-B ......................................................................................................................................... 4
2.1 Pro CAST: ............................................................................................................................... 4
2.2 Given model: ........................................................................................................................... 4
2.3 Simulation process: ................................................................................................................. 5
2.4 Defects identified: ................................................................................................................. 14
2.5 Riser calculation for given model: ........................................................................................ 16
2.6 Conclusion: ............................................................................................................................ 16
PART-C ....................................................................................................................................... 17
3.1 Welding: ................................................................................................................................ 17
3.2 Suitable welding process for fabrication of pressure vessel from high alloy steel for LPG
storage: ........................................................................................................................................ 17
3.2.1 Process features: ............................................................................................................. 17
3.2.2 Advantages of SAW: ...................................................................................................... 18
3.3 SAW Process and process parameters: ................................................................................. 19
3.3.1 Power source: ................................................................................................................. 19
3.3.2 SAW head: ..................................................................................................................... 20
3.3.2.1 Manual welding: ...................................................................................................... 20
3.3.2.2 Mechanized welding: .............................................................................................. 20
3.3.2.3 Wire stick out or electrode extension: ..................................................................... 20
3.3.2.4 Gun angle: ............................................................................................................... 21
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3.3.3 Flux handling: ................................................................................................................. 21
3.3.4 Electrode wires: .............................................................................................................. 23
3.3.5 Protective equipment: ..................................................................................................... 23
3.4 NDT techniques for pressure vessels: ................................................................................... 24
Comments on learning outcomes ................................................................................................ 25
4.1 Comments on learning outcomes: ......................................................................................... 25
References ................................................................................................................................... 26
Bibliography ................................................................................................................................ 27
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List of Tables ____________________________________________________________________________
Table No. Title of the table Pg. No.
Table 3. 1 Maximum stick out lengths and wire diameters [12] ................................................. 21
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List of Figures ____________________________________________________________________________
Figure No. Title of the figure Pg. No.
Figure 1. 1 Part designing features which affects quality [1] ........................................................ 2
Figure 2. 1 Gravity casting process, given casting model with complete mold and casting
assembly ........................................................................................................................................ 5
Figure 2. 2Actual given casting model with gating system .......................................................... 5
Figure 2. 3 Material assigning tool bar .......................................................................................... 6
Figure 2. 4 Interfacing tool bar ...................................................................................................... 7
Figure 2. 5 Boundary conditions assigning tool bar ...................................................................... 8
Figure 2. 6 Flow rate and filling time calculator ........................................................................... 8
Figure 2. 7 Initial gravity condition assigning tool ....................................................................... 8
Figure 2. 8 Initial conditions tool bar ............................................................................................ 9
Figure 2. 9 Run parameters tool bar .............................................................................................. 9
Figure 2. 10 Simulation status window ....................................................................................... 10
Figure 2. 11 Fluid velocity in the gating junction ...................................................................... 10
Figure 2. 12 Critical fluid velocity of casting ............................................................................. 11
Figure 2. 13 Molten metal filling temperature during filling ...................................................... 11
Figure 2. 14 Solidification temperature ....................................................................................... 12
Figure 2. 15 Solidification time of casting .................................................................................. 13
Figure 2. 16 Fraction of solid in the casting ................................................................................ 13
Figure 2. 17 Molten metal pressure while filling the casting ...................................................... 14
Figure 2. 18 Shrinkage porosity defect in the casting ................................................................. 14
Figure 2. 19 Shrinkage porosity in the casting ............................................................................ 15
Figure 2. 20 Casting volume and surface area ............................................................................ 15
Figure 3. 1 Schematic diagram of submerged arc welding process [11] .................................... 18
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Nomenclature ____________________________________________________________________________
Acronyms Description
AC Alternate Current
DC Direct Current
DFM Design for Manufacturability
DECN Direct Current Electrode Negative
LPG Liquid Petroleum Gas
OEM Original Equipment Manufacturer
SAW Submerged Arc Welding
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PART-A
1.1 Casting:
Metal casting is one of the direct methods of manufacturing the desired geometry of
component. The method is also called as near net shape process. It is one of the primary processes
for several years and one of important process even today in the 21st century. The principle of
manufacturing a casting involves creating a cavity inside a mould and then pouring the molten
metal directly into the mould. Casting is a very versatile process and capable of being used in mass
production. The size of components is varied from very large to small, with intricate designs. Out of
the several steps involved in the casting process, moulding and melting processes are the most
important stages. Improper control at these stages results in defective castings, which reduces the
productivity of a foundry industry.
1.2 Analysis of the case and build of opinion:
I agree with given stance, cast components designed for functionality regardless of
manufacturability is the reason for high rejections in foundry.
Casting rejections as high as 8-15% in jobbing foundries cannot be attributed to poor
methoding and process variability alone. Most castings are designed for manufacture, not for
manufacturability. Many defects like shrinkage porosity, hot tear, and cold shut originate from
poorly designed part features like isolated junction, constrained internal feature, and long thin
section, respectively. Foundry engineers partially tackle the problem by tweaking the part design
for example; increasing a fillet radius or padding a thin wall, but incur additional and avoidable
costs of machining and productivity loss [1].
To overcome these, design for manufacturability (DFM) should be carried out early by
product design engineers, instead of late DFM. In practice, casting product designers need to
communicate with casting experts in order to ensure that the casting being designed is
manufacturable and the most appropriate casting process is chosen. Lack of communication
between these parties or lack of expertise support can lead to erroneous design and extensive design
lead times. The problems originated in such scenarios are considerably magnified when the design
engineer is as yet inexperienced [2].
1.3 Examples:
(1) According to technical paper for 59th
Indian foundry congress, a series of industrial
studies and discussions with major original equipment manufacturers (OEMs) revealed that most
parts are designed for manufacture, not for manufacturability [1]. The origin of major casting
defects like shrinkage porosity, crack, and cold shut discovered at the manufacturing stage can be
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traced back to part design. This is because product designers usually limit their focus to achieving
the desired functionality through a suitable combination of part material, geometric features and
manufacturing tolerances. They may not be aware of the extent to which part features affect quality
and cost issues later. In the figure 1.1, we can see some of the part design features which cause the
defect in casting.
Figure 1. 1 Part designing features which affects quality [1]
Foundry engineers try to achieve the desired quality through appropriate design of tooling
and process parameters. Minor changes to part design is needed in most cases: draft for faces along
draw direction, plugging drilled holes, increasing fillet radius, padding thin walls, and other
changes. These increase the weight of as-cast parts by 10-15% compared to the original design.
Machining the additional volume leads to an unnecessary increase in cost. Still, a large number of
castings are rejected, recycled or repaired, implying further avoidable costs. The above mentioned
wastage of resources could be avoided by early evaluation of part design in terms of product quality
and cost, and modifying the design to achieve the desired manufacturability without compromising
the required functionality. [1]
(2) Case study on Brock Metal Company limited, Zinc die casting defects. The need for
high quality decorative finishes will invariably mean that the finishing criteria will become more
critical and this will affect the cost and the prospect of higher reject rates must be taken into
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account. It therefore follows that the elimination of surface defects is a key requirement when
manufacturing parts which require high quality surface finishes [3].
In the zinc die casting, casting design is a major controlling factor in the instigation of
casting defects. Section thickness changes, lack of fillet radii, surface textures and profiles may all
promote surface defect problems if the casting design does not follow recognized design guidelines.
Here the some of the cast design guidelines for achieving better surface finish in the casting, lack of
these knowledge only most of the casting defects occurring in the zinc die casting [3].
Failure to use adequate fillet radii and soft external edges.
Failure to control section changes, and adopt the accepted guidance.
Failure to adopt curved surfaces and other design aids which disguise plating and polishing
blemishes.
Deep blind pockets or holes.
Gate scars and part line defects.
Vertical part line changes.
1.4 Conclusion:
Casting design and manufacture is, however, a complex problem and involves the
interactions of many interdependent casting process variables. Designing cast components and
determining the correct casting process requires extensive knowledge of various casting processes
and their practical capabilities and limitations. Quite an extensive experience curve is necessary in
order for one person alone to be able to acquire all the knowledge and experience needed. It is,
therefore, highly unlikely that a casting product designer will have all the knowledge needed to
solve a whole range of casting design problems. Product designers usually design the cast
components for functionality; regardless of manufacturability is the reason for high rejections in
foundry. To overcome these Design for Manufacturability should be carried out early by product
design engineers, instead of late DFM.
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PART-B
________________________________________________________________________________
2.1 Pro CAST:
The Pro CAST is leading Finite Element solution for casting process simulation software.
Throughout the manufacturing industry, casting process simulation is now widely accepted as an
important tool in product design and process development to improve yield and casting quality.
Based on powerful Finite Element solvers and advanced specific options developed with leading
research institutes and industries, Pro CAST provides an efficient and accurate solution to meet the
casting industry needs. Compared to a traditional trial-and-error approach, Pro CAST is the key
solution to reduce manufacturing costs, shorten lead times for mold developments and improve the
casting process quality. [4]
Pro CAST provides a complete software solution allowing for predictive evaluations of the
entire casting process including mold filling, solidification, and microstructure and thermo-
mechanical simulations. It enables to rapidly visualize the effects of mold design and allows for
correct decision making at an early stage of the manufacturing process [4].
Pro CAST covers a wide range of casting processes and alloy systems including:
High and low pressures die casting.
Sand casting, gravity die casting and tilt pouring.
Investment casting, shell casting.
Lost foam and centrifugal casting.
2.2 Given model:
Gravity casting process in a sand mold:
Filling time 9sec.
Material to fill the casting AlSi7Mg03-A356.
Percentage of filling should be 95%.
Given model shown in the figure number 2.1.
Given actual casting and gating system shown in
the figure number 2.2.
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Figure 2. 1 Gravity casting process, given casting model with complete mold and casting
assembly
Figure 2. 2Actual given casting model with gating system
2.3 Simulation process:
Here the given file to simulate the model is complete assembly of casting and mold
in the meshed file.
These meshed file to assign the material properties, boundary conditions opened in
the precast tool in the pro cast software.
In the precast tool by the use of material assigning tool applied given materials to the
given model and here in the assigning of material to the casting that casting area
should be kept empty and mold area should be filled. Material assigning tool with
assigned materials shown is in the figure number 2.3
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Figure 2. 3 Material assigning tool bar
After assigning the material give interface between mold, internal cores and casting.
In the interface tool the model will be pre grouped before in the mesh cast only.
Here we have to define the interfacing type like if it is equal material in the casting
and gating should give EQUIV connection and it is not equal the material like mold
and casting should give COINC connectivity and in the COINC interface should
assign temperature variation heat coefficient.
In the given model (1) Mold (2) Casting (3) Gating system (4) Internal cores (5)
Internal cores.
Here the interfacing between 2 & 3 that is casing and gating system is given EQUIV
connection because of its same material in the interface of both.
Interface between 1 & 5 and 1 & 4 given EQUIV connection because mold and
internal core material are same.
Interface between 2 & 1, 2 &4, 2 &5, 3 & 1 given COINC connection because of
casting, mold, cores having different materials and here given the temperature
variation heat coefficient given as h=500.
The interfacing of given model assigned tool shown in the figure number 2.4
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Figure 2. 4 Interfacing tool bar
After interfacing we should specify the boundary conditions and this is done with
boundary conditions menu.
In the boundary condition menu with use of surface boundary tool can be applied
mold cooling type and inlet conditions.
By using add option in the side menu, add the heat and select the entire model and
add the cooling medium like air cooling or water cooling and assign the properties.
Next should add the inlet conditions, here by add option, add the inlet and select the
inlet portion in the given model and store it and next should give inlet parameters.
Inlet parameter can be applied by add option in the down menu; add the inlet give
the inlet parameters like material flow rate and temperature at which material should
flow and here only we can able to calculate the fill time and according to that we can
able to assign the proper flow rate to the metal.
After giving the all inlet conditions should assign to the inlet conditions to the
model.
In the figure number 2.5 & 2.6 shows the boundary condition tools and flow rate
calculator.
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Figure 2. 5 Boundary conditions assigning tool bar
Figure 2. 6 Flow rate and filling time calculator
After assigning of boundary conditions should apply the material filling process.
In the process menu by selecting the gravity option add the initial gravity to the
model according to the axis of filling. The gravity tool shown in the figure number
2.7.
Figure 2. 7 Initial gravity condition assigning tool
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After applying the gravity conditions next should apply the initial conditions to the
model.
In the initial conditions menu by selecting constant option should give initial
temperatures to the assigned material.
Hear in the given model I assigned initial temperatures as mold and cores 30 deg C
and casting metal 780 deg C. The figure number 2.8 shows the initial condition tool
bar.
Figure 2. 8 Initial conditions tool bar
After assigning the initial conditions we should run the given conditions in the run
parameters.
In the run parameters menu we should select the gravity filling option in the
preference of filling the material and should give final temperature to stop and
should give time step in general tool bar. Figure number 2.9 shows the run
parameters tool bar.
Figure 2. 9 Run parameters tool bar
By assigning all the above options pre casting will be finished then it should be
saved.
After saving the precast should run the data cast for error checking in the assigned
properties.
If there are no flaws in the assigned parameters we should run the pro cast for actual
simulation of the casting.
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Next in the status window we can able to see the percentage of filled material,
percentage of solid fraction and time step.
In the figure number 2.10 shows the status of given model filling details.
Figure 2. 10 Simulation status window
After the completion of percentage of filling and solid fraction we can able to
simulate the model in the visual cast tool.
In the visual cast tool we can able to simulate the model in different conditions like
thermal flow, fluid velocity, solidification time, temperature during solidification
and temperature during filling.
In the simulation itself we can able to find out the shrinkage porosity and other
defects.
Fluid velocity of the given model in the gating junction shown in the figure number
2.11.
Figure 2. 11 Fluid velocity in the gating junction
In the figure number 2.11 shows the fluid velocity of the gating junction, here we
have to select a node point on the gating junction, at that node point we can able to
see the critical fluid velocity with respect to Z-direction of 0.531 m/sec.
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In the figure number 2.12 shows the fluid velocity of the casting, here we have to
select one node point to show the fluid velocity of the casting, that node point shows
the critical fluid velocity of the casting with respect to the Y-direction of 0.349
m/sec.
Here in the both places compare to fluid velocity in the casting and fluid velocity in
the gating junction, inlet entry in the gating junction fluid velocity is high.
By this we can able to tell that gating system can able to control the inlet fluid
velocity to avoid turbulent flow of liquid metal.
Figure 2. 12 Critical fluid velocity of casting
In the figure number 2.13 shows that temperature during filling.
Figure 2. 13 Molten metal filling temperature during filling
In the figure number 2.13 we can able to observe that molten metal filling
temperature and here we have selected one node point to show the temperature
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where it is decreased below the melting point while filling. The node temperature
shows 740.6 deg C this temperature is below the melting temperature.
In the figure number 2.14 shows the solidification temperature.
Figure 2. 14 Solidification temperature
In the figure 2.14 we are able to observe that solidification temperature. Here in the
model casting area is reached the temperature up to 558 deg C and raiser
temperature reached up to 422 deg C.
From these temperatures the casting starts solidification.
In the figure 2.15 we can able to see the total solidification time of the casting and
gating system.
In the solidification time of casting, we are able to observe where exactly maximum
time as taken to solidify the casting.
In the figure 2.15 we have selected the node point where exactly the casting
solidification time taken more, as much as 1593.5 sec. Because at this node area of
casting where it‟s having more material and in-gates are coming contact with this
point and this point is last to fill area compare to other areas in casting because of
these reasons this area will solidify last.
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Figure 2. 15 Solidification time of casting
Figure 2.16 shows the fraction of solid in the casting. Here in the selected node point
we can able to see the where exactly fraction of starts.
Figure 2. 16 Fraction of solid in the casting
In the figure 2.17 we can see the fluid pressure differences in filling the casting.
Here in the bottom portion of the casting we can observe that it‟s having more
pressure compare to the top portion.
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Figure 2. 17 Molten metal pressure while filling the casting
2.4 Defects identified:
In the figure 2.18 we can able to see the shrinkage porosity in the casting area.
In the figure 2.18 we can observe that shrinkage occurs where the area of
solidification has taken more time and in the same area we can see the shrinkage
porosity. Here proper riser is not available to compensate this shrinkage, because of
this shrinkage porosity came in the casting area.
Here in the figure 2.18 & 2.19 selected node areas we can see the shrinkage porosity
percentage as maximum as 81.94 to 85.31%
Figure 2. 18 Shrinkage porosity defect in the casting
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Figure 2. 19 Shrinkage porosity in the casting
Figure 2. 20 Casting volume and surface area
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2.5 Riser calculation for given model:
According to given drawing and pro cast results casting volume 5730.03 CC and surface
area of casting 2.280 e+5 mm2. In the figure 2.20 we can see the pro cast results for volume and
surface area.
Modulus of casting = casting volume /surface area
Mc=5730030/228000=25.13 mm.
The modulus of casting =25.13mm, according to this modulus of riser is 1.2 of Mc.
Mr= 25.13*1.2= 30.156 mm.
The diameter of the riser is 4 times of modulus of riser.
d= 30.156 * 4 = 120.624mm.
The length of the riser is l/d=1.5.
L = 1.5 * 120.624 = 180.936 mm.
According to this for given casting model (d) 120 mm * (l) 180 mm riser should be used.
2.6 Conclusion:
For the given casting model major defect occur in the casting because of no riser in the
casting to avoid the shrinkage porosity and for the given model we should use 120 mm diameter.
By observing the simulation details where the defect has occurred, at the same area solidification
time has taken more and this is the place of last to fill area and thick ness of the casting here is high
compare to other. In the entire casting area first solidification is started on the gating system and
gradually it moved to the casting. Here the most of the incoming velocity of the molten metal is
reduced in the gating system to avoid turbulent flow in the casting.
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PART-C
________________________________________________________________________________
3.1 Welding:
The process of joining together two pieces of metal`s so that bonding accompanied by
appreciable interatomic penetration takes place at their original boundary surfaces. The boundaries
more or less disappear at the weld, and integrating crystals develop across them. Welding is carried
out by the use of heat or pressure or both and with or without added metal. The integrity of a
welded component, which has metallurgical continuity across the joint, is also characterized by
properties such as pressure tightness or heat and corrosion resistance. These properties have
contributed to the rapid development, both technical and economic, in all fields including nuclear
power, chemical engineering, bridge building, offshore engineering, shipbuilding and the
manufacture of cars, railway locomotives and rolling stock, aero engines, domestic appliances, and
military hardware from small arms to main battle tanks. There are many types of welding including
Metal Arc, Atomic Hydrogen, Submerged Arc, Resistance Butt, Flash, Spot, Stitch, Stud and
Projection.
3.2 Suitable welding process for fabrication of pressure vessel from high alloy steel for LPG
storage:
Here I suggest a suitable welding process for fabrication of pressure vessel from high alloy
steel for LPG storage as Submerged Arc Welding process with reference to the below case studies,
Process features and advantages of Submerged Arc Welding process (SAW).
PPS group of companies, one of the leading manufacturers of LPG cylinders. In the LPG cylinder
manufacturing process they first take high alloy steel sheet and deep draw on the hydraulic press by
two half cylinder bodies. Then both the top and bottom halves are joined by the backing strip and
are welded together by submerged arc welding process by using 3.15mm MSCC wire [5].
In the Case study of Raya Technical services, they prefer submerged arc welding process for
fabrication of petro chemical pipelines and gas cylinders because of its various advantages [6].
In the Case study of BOC India limited leading manufacturers of pressure vessels, they use
submerged arc welding process for LPG cylinder welding [7].
3.2.1 Process features:
Similar to MIG welding, SAW involves formation of an arc between a continuously-fed
bare wire electrode and the work piece. The process uses a flux to generate protective gases and
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slag, and to add alloying elements to the weld pool. A shielding gas is not required. Prior to
welding, a thin layer of flux powder is placed on the work piece surface. The arc moves along the
joint line and as it does so, excess flux is recycled via a hopper. Remaining fused slag layers can be
easily removed after welding. As the arc is completely covered by the flux layer, the molten weld
and the arc zone are protected from atmospheric contamination by being “submerged” under the
blanket of granular fusible flux, heat loss is extremely low. Distortion is much less and welds
produced are sound, uniform, ductile, and corrosion resistant and have good impact value. Single
pass welds can be made in thick plates with normal equipment. The arc is always covered under a
blanket of flux, thus there is no chance of spatter of weld. This produces a thermal efficiency as
high as 60% (compared with 25% for manual metal arc). There is no visible arc light, welding is
spatter-free and there is no need for fume extraction [8,9]. The Schematic representation of
submerged arc welding process is shown in the figure 3.1.
Figure 3. 1 Schematic diagram of submerged arc welding process [11]
3.2.2 Advantages of SAW:
High deposition rates (over 100 lb/h (45 kg/h) have been reported).
High operating factors in mechanized applications.
Deep weld penetration.
Sound welds are readily made (with good process design and control).
High speed welding of thin sheet steels up to 5 m/min is possible.
Minimal welding fume or arc light is emitted [10, 8].
Practically no edge preparation is necessary.
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The process is suitable for both indoor and outdoor works.
Distortion is much less.
Welds produced are sound, uniform, ductile, and corrosion resistant and have good impact
value [10, 8].
Single pass welds can be made in thick plates with normal equipment.
The arc is always covered under a blanket of flux, thus there is no chance of spatter of weld.
50% to 90% of the flux is recoverable.
3.3 SAW Process and process parameters:
Essential equipment components for SAW are:
Power source
SAW head
Flux handling
Electrode wires
Protective equipment
3.3.1 Power source:
SAW can be operated using either a DC or an AC power source. DC is supplied by a
transformer-rectifier and AC is supplied by a transformer. Current for a single wire ranges from as
low as 200Amp, (1.6mm diameter wire) to as high as 1000Amp (6.0mm diameter wire). In practice,
most welding is carried out on thick plate where a single wire (4.0mm diameter) is normally used
over a more limited range of 600 to 900A, with a twin wire system operating between 800 and
1200A [12].
In DC operation, the electrode is normally connected to the positive terminal. Electrode negative
(DCEN) polarity can be used to increase deposition rate but depth of penetration is reduced by
between 20 and 25%. For this reason, DCEN is used for surfacing applications where parent metal
dilution is important. The DC power source has a 'constant voltage' output characteristic which
produces a self-regulating arc. For a given diameter of wire, welding current is controlled by wire
feed speed and arc length is determined by voltage setting [12].
AC power sources usually have a constant-current output characteristic and are therefore not self-
regulating. The arc with this type of power source is controlled by sensing the arc voltage and using
the signal to control wire feed speed. In practice, for a given welding current level, arc length is
determined by wire burn off rate, i.e. the balance between the welding current setting and wire feed
speed which is under feedback control [12].
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Square wave AC square wave power sources have a constant voltage output current characteristic.
Advantages are easier arc ignition and constant wire feed speed control.
3.3.2 SAW head:
SAW can be carried out using both manual and mechanized techniques. Mechanized
welding, which can exploit the potential for extremely high deposition rates, accounts for the
majority of applications [12].
3.3.2.1 Manual welding:
For manual welding, the welding gun is similar to a MIG gun, with the flux which is fed
concentrically around the electrode, replacing the shielding gas. Flux is fed by air pressure through
the handle of the gun or from a small hopper mounted on the gun [12]. The equipment is relatively
portable and, as the operator guides the gun along the joint, little manipulative skill is required.
However, because the operator has limited control over the welding operation (apart from adjusting
travel speed to maintain the bead profile) it is best used for short runs and simple filling operations.
3.3.2.2 Mechanized welding:
Single wire: - As SAW is often used for welding large components, the gun, wire feeder
and flux delivery feed can be mounted on a rail, tractor or boom manipulator. Single wire welding
is mostly practiced using DCEP even though AC will produce a higher deposition rate for the same
welding current. AC is used to overcome problems with arc blow, caused by residual magnetism in
the work piece, jigging or welding machine [12].
Twin wire: - SAW can be operated with more than one wire. Although up to five wires are
used for high deposition rates, the most common multi-wire systems have two wires in a tandem
arrangement. The leading wire is run on DCEP to produce deep penetration. The trailing wire is
operated on AC which spreads the weld pool, which is ideal for filling the joint. AC also minimizes
interaction between the arcs, and the risk of lack of fusion defects and porosity through the
deflection of the arcs (arc blow). The wires are normally spaced 20mm apart so that the second wire
feeds into the rear of the weld pool [12].
3.3.2.3 Wire stick out or electrode extension:
The distance the wire protrudes from the end of the contact tip is an important control
parameter in SAW. As the current flowing between the contact tip and the arc will preheat the wire,
wire burn off rate will increase with increase in wire stick out. For example, the deposition rate for
a 4mm diameter wire at a welding current of 700A can be increased from approximately 9 kg/hr at
the normal 32mm stick out, to 14 kg/hr at a stick out length of 178mm. In practice, because of the
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reduction in penetration and greater risk of arc wander, a long stick out is normally only used in
cladding and surfacing applications where there is greater emphasis on deposition rate and control
of penetration, rather than accurate positioning of the wire [12]. Recommended and maximum stick
out lengths shown in the table no 3.1
Table 3. 1 Maximum stick out lengths and wire diameters [12]
3.3.2.4 Gun angle:
In manual welding, the gun is operated with a trailing angle, i.e. with the gun at an angle of
45 degrees (backwards) from the vertical. In single wire mechanized welding operations, the gun is
perpendicular to the work piece. However, in twin wire operations the leading gun is normal to the
work piece, with the trailing gun angled slightly forwards between an angle of 60 and 80 degrees.
This reduces disturbance of the weld pool and produces a smooth weld bead profile [12].
3.3.3 Flux handling:
Flux should be stored in unopened packages under dry conditions. Open packages should be
stored in a humidity-controlled store. While flux from a newly-opened package is ready for
immediate use, flux which has been opened and held in a store should first be dried according to
manufacturer's instructions. In small welding systems, flux is usually held in a small hopper above
the welding gun. It is fed automatically (by gravity or mechanized feed) ahead of the arc. In larger
installations the flux is stored in large hoppers and is fed with compressed air. Unused flux is
collected using a vacuum hose and returned to the hopper [12]. Care must be taken in recycling
unused flux, particularly regarding the removal of slag and metal dust particles. The presence of
slag will change the composition of the flux which, together with the wire, determines the
composition of the weld metal. The presence of fine particles can cause blockages in the feeding
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system. The flux has to be designed and selected to incorporate Thermodynamics, Kinetics &
Transport phenomenon.
It must [6]:
Melt just below the temperature of the steel being welded via Material balance & phase
diagrams to achieve the ideal eutectic point (Thermodynamics).
Mix with the parent material in the molten zone & refine the weld metal, adding elements
such as Mn, Si, Cr, etc & removing rust & nonmetallic oxide inclusions from the heat
affected weld zone, by enveloping the oxides in a Silicate-aluminate matrix (Kinetics).
Float up (Transport the oxides) to the surface before the steel solidifies & to peel off
automatically (self-lifting slag).
Two main types of fluxes are available: fused and agglomerated. Fused fluxes are manufactured by
fusing together a mixture of finely ground minerals, followed by solidifying, crushing and sieving
the particles to the required grain size. Fused fluxes do not deteriorate during transportation and
storage and do not absorb moisture. Agglomerated fluxes are manufactured by mixing finely
ground raw materials with bonding agents such as sodium or potassium silicates followed by
baking to remove moisture. This type of flux is sensitive to moisture absorption and may require
drying before use. Agglomerated fluxes are more prone to mechanical damage which can cause
segregation of some of the constituents [13].
Fluxes are classified as acid, neutral, or basic, the last being subdivided into semi-basic or
highly basic. The main characteristics of the fluxes are as follows [13]:
Acid fluxes: High content of oxides such as silica or alumina. Suitable for high welding currents
and fast travel speeds. Resistant to porosity when welding rusty plate, Low notch toughness, and
not suitable for multi pass welding of thick material`s.
Neural fluxes: High content of calcium silicate or alumina-rutile. Suitable for fairly high welding
currents and travel speeds and also for multi pass welding.
Basic fluxes: High content of chemically basic compounds such as calcium oxide, magnesium
oxide and calcium fluoride. Highest weld metal quality in respect of radiographic soundness and
impact strength. Lower welding currents and travel speeds are suitable for multi pass welding of
thick sections.
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3.3.4 Electrode wires:
The electrode for submerged-arc welding is a bare wire in coil form usually copper coated.
They two types are available solid wire and tubular wire. The solid wire is widely used for general
fabrication of mild and low-alloy steels, stainless steels and non-ferrous metals. The tubular wire
(made by forming narrow strip into a tube) carries alloy powders which permit the economical
production of a wider range of weld compositions than is possible by using the solid wire type.
Tubular wires are widely used for hard-facing [13]. With coated manual electrodes, wire and
coating is one unit so that such electrodes can be classified according to the type of coating and its
effect on weld mechanical properties. In submerged-arc welding, any wire may be used with a
number of different fluxes with substantially different results in respect of weld quality and
mechanical properties. Consequently, BS 4165 grades wire flux combinations according to the
tensile and impact strengths obtained in the weld metal. A number of tubular wires are available,
particularly for surfacing and hard-facing. These contain alloy powders which produce weld metals
consisting of low-alloy steels, martensitic and austenitic stainless steels, chromium and tungsten
carbides, and various cobalt- and nickel-based heat- and corrosion-resistant alloys. Some corrosion-
resistant alloys, including stainless steel, are available in the form of coiled strips from 100 mm to
150 mm wide, 0.5 mm thick for high deposition rate surfacing by a submerged-arc welding process
known as strip cladding [13].
ASTM A240 Type 316 or 316L, electrode wire is best suitable for joining the more
common austenitic stainless steel grades referred to as "18-8" steels for very good corrosion
resistance in acid environments [14].
3.3.5 Protective equipment:
Unlike other arc welding processes, SAW is a clean process which produces minimum fume
and spatter when welding steels. Normal protective equipment is required for ancillary operations
such as slag removal by chipping or grinding. Special precautions should be taken when handling
flux - a dust respirator and gloves are needed when loading the storage hoppers [12, 15].
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3.4 NDT techniques for pressure vessels:
The following welds shall be tested by NDT process:
All butt welds in the pressure structure shall be subjected to X-ray radiographic
inspection over their entire length. In addition, at least 10 % of the weld length shall
be tested for surface cracks.
Fillet welds at the joint between the central longitudinal bulkhead and the tank
casing of twin tanks or similar structures shall be subjected to ultrasonic or, where
this is not possible, X-ray radiographic inspection over their entire length. In
addition, at least 10% of the weld length shall be tested for surface cracks.
10 % of the butt-welded joints of supporting rings in tanks shall be subjected to X-
ray radiographic inspection. In the case of fillet welds between the web and the
tank wall and between the web and the girder plate, at least 10 % of the weld
length shall be tested for surface cracks.
All butt and fillet welds of nozzles weldments, e.g. sockets, domes, sumps, rings,
and of reinforcing plates around cutouts shall be tested for surface cracks over their
whole length.
Fillet welds of fitments welded to the tank which may induce stresses in the tank
wall, e.g. lifting lugs, feet, brackets, shall be tested for surface cracks over their
whole length.
Full root penetration nozzle connections in the pressure structure shall undergo
ultrasonic or radiographic inspection if the attachment wall thickness at the
pressure structure is > 15 mm and the inside diameter of the nozzle is ≥ 120 mm.
If pressure vessels are to be mechanically de stressed, all points with geometry-
related stress concentrations, such as the seams of socket weldments or fitments,
shall afterwards be tested for cracks by the magnetic particle or dye penetrant
method [16].
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Comments on learning outcomes ________________________________________________________________________________
4.1 Comments on learning outcomes:
By undertaking this assignment now I am able to justify that what are all the casting defects
and by which process these casting defects will occur. The main casting defects arise from the
foundry because of inefficient communication between product designer and foundry engineer and
product design engineers who don‟t perform DFM early in the product design. This debate helped
me to get the complete knowledge about casting and casting defects.
By doing simulation of given model I have understood that how the simulation software is
helpful in the foundry to eliminate the casting defects and here we can able to see the virtual model
of casting and simulate the model in different conditions like fluid velocity, fluid pressure,
solidification time and fluid flow in the casting where the turbulence effect appears.
In the selection process of welding high alloy steel for the manufacturing of pressure
vessels I came to an understanding that the conditions essential for selecting the welding process
,suitable weld quality that can be identified, process parameters for selected welding process and its
limitations in carrying out the welding.
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References
________________________________________________________________________________
1. Author unknown, http://www.foundryinfo-india.org/images/pdf/TS-2C-II.pdf, retrieved on
25th March 2012
2. Author unknown, http://www.sciencedirect.com/science/article/pii/S0950705100000757,
retrieved on 25th March 2012
3. Author unknown,
http://www.brockmetal.com/downloads/documents/EB4IB5ELA9_Web_Tech_Resource__
_Zinc_die_casting_defects_cause_and_elimi.pdfl, retrieved on 25th March 2012
4. Author unknown, http://www.esi.com.au/Software/ProCAST.html, retrieved on 26th March
2012
5. Author unknown, http://www.pps-india.com/lpg.htm, retrieved on 27th March 2012
6. Author unknown, http://rayatechnicalservices.com/case_studies, retrieved on 28th Mar 12
7. Author unknown, http://www.boc-india.com/business_area/case_study.php, retrieved on
28th March 2012
8. Author unknown, http://www.wolfrobotics.com/products/images/SAWbro.pdf, retrieved on
29nd March 2012
9. Author unknown, http://www4.hcmut.edu.vn/~dantn/TWI/jk5.html, retrieved on 29th
March 2012
10. Author unknown,
http://cmapspublic2.ihmc.us/rid=1151380771906_867522767_14912/Submerged%20Arc%
20Welding.doc, retrieved on 30th March 2012
11. Author unknown, http://www4.hcmut.edu.vn/~dantn/TWI/jk5.html, retrieved on 30th March
2012
12. Author unknown, http://www4.hcmut.edu.vn/~dantn/TWI/jk16.html, retrieved on 30th
March 2012.
13. Edward H. Smith, Mechanical engineers Reference book, Twelfth edition.
14. Author unknown, http://www.lincolnelectric.com/en-us/consumables/submerged-
arc/Pages/submerged-arc.aspx, retrieved on 4th Apr 2012.
15. Author unknown, http://www4.hcmut.edu.vn/~dantn/TWI/jk20.html, retrieved on 4th Apr
2012.
16. Author unknown, http://www.gl-group.com/infoServices/rules/pdfs/english/werkstof/teil-
3/kap-3/englisch/abschn03.pdf, retrieved on 5th Apr 2012.
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Bibliography
________________________________________________________________________________
1. Edward H. Smith, Mechanical engineers Reference book, Twelfth edition.
2. Author unknown,
http://www.twi.co.uk/services/technical-information/job-knowledge/job-knowledge-87-
submerged-arc-welding-consumables-part-1/.
3. Dr.N.S.Mahesh, Weld metallurgy Weld design, AMT 503, MS Ramaiah School of
Advance Studies.
4. Mr.K.N. Ganapathi, Casting process, AMT 503, MS Ramaiah School of Advance Studies.
5. Author unknown,
http://www4.hcmut.edu.vn/~dantn/news/Jk-view.
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Industrial visit Report on Bangalore Metallurgical Pvt, Ltd ___________________________________________________________________________
Bangalore metallurgical Pvt Ltd is one of the leading cast component manufacturing
industries. It produces a wide variety of sand castings ranging from 0.5 kg to 3000kg which
includes housing clutches ,motor parts, flywheel housings, eccentric housings, bearing shields
etc.,.
In the sand casting process they use silica sand for mould making and in the mould
making 70% old sand and 30% new sand. The process they use in the binding of sand is no-
bake binder system. The binding process is based on the ambient temperature cure of two or
more binder components on sand. The resin binder used at this industry is the fural-alcohol.
The concentration of this fural alcohol is about 0.9-1 percent of the sand. Along with this the
sulphonic acid is mixed around 30-40 percent of one percent fural alcohol. All these
ingredients are mixed with silica sand and water in right proportion. Curing of the binder
system begins immediately after all the components are combined. Furon binder can be
modified with urea, formaldehyde, phenol and wide variety of other reactive and non-reactive
additives. The choice of specific binder depends on the type of metal to be cast. The speed of
the curing action can be adjusted by changing the catalyst type. Furon or No bake binder
process provides high dimensional accuracy and high degree of resistance to sand or metal
interface casting defects. After the completion of all the above processes now the sand is
ready for mould making. After making of required mould geometry, the mould surface
should be applied the refractory coatings like zirconia and graphite coating of 20 microns.
For curing and removal of water content from zirconia and graphite coatings preheating will
done to the mould for easy removal of pattern from the mould strip coating will done to the
pattern. Here the compaction process of moulds will do manually for the small moulds and
for the big moulds hydraulic gaggers will be used for achieving the better strength in the
moulds.
Next after preparation of mould cope and drag they will arrange the internal cores
with the help of chaplets to support and hold the cores at the right position during the taping
of molten metal to the mould. After arrangement of all the cores in the mould cope and drag
the cope and drag portion will be assembled. After arrangement of all the cope and drag
assembly next process will be the pouring of molten metal to the mould. Here for melting of
metal done using of induction furnace and here the sum amount of pure iron and scrap will be
used for ingot. This molten ingot will be transferred to the crucible and through the crucible
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molten metal will be poured in to the mould. After solidification of metal the casting will be
removed and the broken mould will be collected in to the vibrator or reclamation impeller. In
the vibrator or impeller this material will be further broken into fine particles and refined.
Here the refined sand will be reused for mould making again for reduction of cost. This
process is called as the reclamation of the sand.
The poured material properties will be checked using a spectro meter. The use of
electrical supply produces a high spark in the sample material and by reading of this spark
light the spectro meter will be able to display the different composition of the metals in the
material according to this display the material ingot properties will be changed in the shop
floor by the engineer to achieve the better material properties in the casting. For the achieving
of better surface finishes in the casting they will pre check the sand properties like moisture
content, sand strength and grain size controlling in the frequent manner.
These are the observations made by me during the visit to the Bangalore metallurgical
Pvt Ltd.Hoskote. By visiting of this foundry I got the clear knowledge about the how the
foundry functions and where actually the chaplets, chills will be used how it will helpful in
achieving directional solidification process.
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M. S. Ramaiah School of Advanced Studies 1
Metal casting and joining process
Module leader:
M.r. K.N. Ganapathi
MSRSAS, Bangalore
Avoid turbulent entrainment
(the critical velocity requirement)
Papineni.Satheesh BVB0911002
Bushan Yadav.B BVB0911003
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M. S. Ramaiah School of Advanced Studies 2
Contents
Maximum velocity requirement
The `no fall' requirement
Surface tension controlled Filling
Filling system design
Gravity pouring of open-top moulds
Gravity pouring of closed Moulds
Pouring basin and down sprue design
Horizontal transfer Casting
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M. S. Ramaiah School of Advanced Studies 3
The key aspect of the critical velocity is that at velocities
less than the critical velocity the surface is safe. Above the
critical velocity there is the danger of entrainment damage.
The criterion is a necessary but not sufficient condition for
entrainment damage.
If the whole, extensive surface of a liquid were moving
upwards at a uniform speed, but exceeding the critical
velocity, clearly no entrainment would occur.
Maximum velocity requirement
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M. S. Ramaiah School of Advanced Studies 4
If the melt is travelling at a high speed, but is constrained
between narrowly enclosing walls, it does not have the room to
fold-over. Thus no damage is suffered by the liquid despite its
high speed, and despite the high risk involved. This is one of the
basic reasons underlying the design of extremely narrow
channels for filling systems (Gating system).
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M. S. Ramaiah School of Advanced Studies 5
The `no fall' requirement
the no-fall requirement applies to the design of the
filling system downstream of the base of the sprue.
The critical fall heights for all liquid metals are in the
range 3 to 15 mm.
For example, if liquid aluminium is allowed to fall
more than 12.5mm then it exceeds the critical 0.5m/s.
with a good sprue and pouring basin design this initial
fall damage can be reduced to a minimum.
The `no fall' requirement may also exclude some of
those filling methods in which the metal slides down a
face inside the mould cavity, such as some tilt casting
type operations.
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M. S. Ramaiah School of Advanced Studies 6
Narrow filling system geometries are valuable in their
action to conserve the liquid as a coherent mass, and so
acting to push the air out of the system ahead of the
liquid.
A good filling action, pushing the air ahead of the
liquid front as a piston in a cylinder, is a critically
valuable action. Such systems deserve a special name
such as perhaps `one pass filling (OPF) designs'
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M. S. Ramaiah School of Advanced Studies 7
Surface tension controlled filling
This is interesting situation that the liquid may not be able to enter the
mould at all.
This is to be expected if the pressure is too low to force melt into a narrow
section. It is an effect due to surface tension.
If the liquid surface is forced to take up a sharp curvature to enter a non-
wetted mould then it will be subject to a repulsive force that will resist the
entry of the metal.
Even if the metal enters, it will still be subject to the continuing resistance
of surface tension, which will tend to reverse the flow of metal, causing it
to empty out of the mould if there is any reduction in the filling pressure.
These are important effects in narrow section moulds (i.e. thin-section
castings) and have to be taken into account.
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M. S. Ramaiah School of Advanced Studies 8
Filling system design
The liquid metal as it travels through the filling system
indicates that most of the damage is done to castings by
poor filling system design.
The filling system design can be of two types:
Gravity pouring of open-top moulds.
Gravity pouring of closed moulds.
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M. S. Ramaiah School of Advanced Studies 9
Gravity pouring of open-top moulds
Generally moulds consists of cope and drag but in open-top moulds
only drag is required. This means the mould cavity is open so that
metal can be poured directly.
The skill of the foundry man plays vital role in the gravity
pouring system
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Gravity pouring of closed moulds
Gravity pouring of closed moulds consists of pipes, channels
to guide the metal from the ladle into the mould.
In poor filling system designs, velocities in the channels can
be significantly higher than the free-fall velocities.
There fore it encourages surface turbulence, bubbles and bi-films.
In the gravity pouring system of closed moulds, bottom gating system
design is much efficient compared to top gating system.
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Pouring basin and down sprue design
The offset blind end of the basin is important in bringing the vertical
downward velocity to a stop. The offset also avoids the direct inline type of
basin, such as the conical basin, where the incoming liquid goes straight
down the sprue, its velocity unchecked, and taking with it unwanted
components such as air and dross, etc.
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M. S. Ramaiah School of Advanced Studies 15
An oversize sprue that has suffered severe erosion damage because of air
entrainment during the pour.
A correctly sized sprue shows a bright surface free from damage.
Greater the sprue diameter greater the turbulence.
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M. S. Ramaiah School of Advanced Studies 16
Runner
The runner is that part of the filling system that acts to distribute the melt
horizontally around the mould, reaching distant parts of the mould cavity
quickly to reduce heat loss problems.
For products whose reliability needs to be guaranteed, the arrangement of
the runner at the lowest level of the mould cavity, causing the metal to
spread through the running system and the mould cavity only in an uphill
direction is a challenge that needs to be met.
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Horizontal transfer Casting
Tilt casting is a process with the unique feature that, in principle, liquid
metal can be transferred into a mould by simple mechanical means
under the action of gravity, but without surface turbulence.
The problem of horizontal transfer is that it is slow, sometimes resulting in
the freezing of the `ski jump' at the entrance to the runner, or even the non-
filling of the mould. This can usually be solved by increasing the rate of
tilt after the runner is primed.
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M. S. Ramaiah School of Advanced Studies 18
References
1. John Campbell, Castings Practice, The 10 Rules of Castings,
published 2004.