Experimental research and simulation studies on flow in gating systems and mold cavity

62 Pages·2012·22.85 MB·English

Experimental research and simulation
studies on flow in gating systems and
mold cavity

M.Tech Dissertation

Submitted in partial fulfillment of the requirements
for the degree of
Master of Technology
by
Akash Chavan
(10310069)

Guide
Prof. B. Ravi

Department of Mechanical Engineering
INDIAN INSTITUTE OF TECHNOLOGY BOMBAY

June 2012

Abstract

The pouring of molten metal into the mold is one of the most critical steps in producing
castings, since the behavior of the liquid and its subsequent solidification and cooling
determine whether the cast shape will be properly formed, internally sound and free from
casting defects.
The fluid flow phenomena during mold filling are very complex. It is very difficult to
investigate these phenomena through experimentation, since both the metal and mold are
opaque, and because of the high temperatures involved. Complete, smooth and uniform
filling of mold with clean metal is achieved by an appropriate gating system, which
comprises of one or more pouring basins, sprues, runners and gates. The number, location,
shape and size of the gating elements determine the sequence and rate of flow of molten
metal into the mold cavity. There are however, no mathematical models to estimate the
discharge and volume of flow through each gate. This is needed to balance the flow
through multiple gates (by adjusting their position and cross-sectional area), and to ensure
that the mold cavity is filled in an optimal time. In this work, experimental and simulation
studies on discharge through multiple gates connected to a horizontal runner and an H-
shape mold cavity to observe the filling pattern has been carried out.
Experiments on multi-gate systems have been conducted by tap and collect method using
water and the volume of flow through each gate is observed for two different
configurations: end-sprue and centre-sprue. The results are compared with computer
simulation, providing valuable insights useful for designing multi-gate systems. This study
is to establish the apparatus and procedure for measuring the filling pattern of molten
metal in a mold cavity. A so called contact-time technique has been employed to study the
filling phenomena in a mold cavity. The result of the measurements has provided a great
deal of information with regard to the filling sequence, ratio among the multiple gates and
the last filled areas, which are important to evaluate the appropriateness of the gating
system. Supported by a personal computer version of data acquisition system and software
to record the time data, the measured contact times are transformed to graphical filling
patterns using a computer program.
iv
Table of Contents

Abstract iv
Table of Contents v
List of Figures vii
List of Tables viii

1 Introduction 1
1.1 Mold filling phenomena in castings 1
1.2 Gating system 3
1.2.1 Components of gating system 3
1.2.2 Multi-gate gating systems 5
1.3 Organization of the report 7

2 Literature Review 8
2.1 Experimental Methods to Study Mold Filling 8
2.1.1 Use of water models 8
2.1.2 Use of X-Ray and tracers 10
2.1.3 Use of contact-time technique 11
2.2 Analysis of Gating System 11
2.21.1 Empirical approach 12
2.2.2 Hydraulics based approach 12
2.2.3 Numerical analysis approach 18
2.3 Summary of Literature Review 19

3 Problem Definition 20
3.1 Motivation 20
3.2 Goal and Objectives 21
3.3 Research Approach and Scope 22

4 Flow Through Horizontal Multi-gate System 24
4.1 Introduction 24
4.2 Modular Horizontal Multi-gate Experimental Setup 24
4.3 Experimental Observations 26
4.4 Numerical Prediction of Flow Parameters 31
4.5 Summary of the Chapter 33
v
5 Mold Filling in a H-shape Cavity 34
5.1 Introduction 34
5.2 Experimental Setup 34
5.3 Data Acquisition System (DAS) 36
5.4 Experimental Observations 37
5.5 Computer Implementation of Acquired Data 39
5.5 Numerical Simulation 41
5.6 Summary of the Chapter 46

6 Summary and Future Scope 47
5.1 Summary of Work Done 47
5.2 Limitations and Future Scope 48

References 50
Bibliography 53
Acknowledgement 54

vi
List of Figures
Figure Description Page
1.1 Defects during mold filling (a) cold shut and (b)misrun 02
1.2 Parts showing defects due to (a) solid inclusions and (b) gaseous 02
entrapments
1.3 Basic components of simple gating system for horizontally parted molds 04
1.4 Horizontal multiple ingates (a),(b) parallel finger ingates, (c) 06
circumferentially placed ingates (Johnson et al., 1950)
Vertical multiple gate gating systems (a) simple system, (b) inclined steps
1.5 07
with common junction, (c) reversed down runner (Johnson et al., 1950)
2.1 Flow behavior in horizontal gating systems (a) central Sprue (b) end 11
sprue (Johnson et al., 1950)
2.2 Model used in development of equation for flow ratio from a runner with 14
two gates (Berger et al., 1951)
2.3 Simplified pipe-node-path representation of pouring cup plus sprue- 16
runner-two-ingate horizontal gating system. (Bradley et al., 1993)
4.1 Horizontal multi-gate experimental setup - end sprue arrangement 25
4.2 Horizontal multi-gate experimental setup –centre sprue arrangement 25
4.3 Schematic diagram of End-sprue arrangement 26
4.4 Discharge through gates in centre sprue arrangement 29
4.5 Velocity trend in centre sprue arrangement (video grab) 29
4.6 Multiple gates, pressure and velocity variation 30
4.7 Velocity distribution corresponding to color plot shown in legend for end 32
sprue
4.8 Velocity distribution corresponding to color plot shown in legend for 32
centre sprue
5.1 H-shape mold experimental setup 36
vii
5.2 Schematic diagram of sensor locations (grid points) along the H-shape 37
mold cavity
5.3 Experimental snapshots of the H-shape cavity at eight instances 38
5.4 Filling pattern drawn from the measured contact times at eight instances 41
Velocity profile inside H-shape mold cavity; (a) to (h) at different time
5.5 41
instance

List of Tables
Table Description Page
2.1 Kinematic and dynamic viscosities of liquid metals and various other 9
fluids
4.1 Results of experiments with end sprue arrangement 27
4.2 Results of experiments with centre sprue arrangement 27
4.3 Discharge through different gates in the two setups 28
Comparison of discharge through different gates from experiment and
4.4 33
simulation
5.1 Contact-time data from DAS 39
5.2 Comparison of fill volume in percentage at different instances for 47
experimental, processed and simulation results

viii
Chapter 1
Introduction
Metal casting may be defined as a process of obtaining a ‘metallic object by allowing the
molten metal to solidify in a mold’, the shape of the object being determined by the shape
of the mold cavity. This is a near-net shape process as it manufactures a desired geometry
of component in a single step, requiring very little post processing. It is one of the most
ancient techniques used for manufacturing metal parts. Early applications of casting are in
making jewellery items and golden idols. Today, the casting applications include
automotive components, spacecraft components and many industrial and domestic
components, apart from art and jewellery items.
Although the manufacturing path from liquid to the finished shape is most direct, this
directness involves the greatest difficulty. This is because so much needs to be controlled
simultaneously including melting, alloying, molding, pouring, solidification, finishing etc.
Every one of these aspects has to be correct since failure of any one will probably cause
the casting to fail.
1.1 Mold Filling Phenomena in Castings
Throughout the casting operation, mold filling is a very important step, which influences
the quality of the castings. The fluid flow phenomena during mold filling are very
complex. It is highly transient and the flow domain keeps expanding. The extent of the
flow domain, and thus the locations of its free surfaces, vary with time and need to be
determined theoretically. The flow of molten metal during casting process is accompanied
by turbulence, splashing, separation of streams near change of sections, branching off and
rejoining of streams, vortex formation, splashing against walls and changes in melt
properties such as density, viscosity and surface tension and the onset of solidification
(Ravi B., 2008). The defects caused by disturbed flow of molten metal during mold filling
may include cold shut, misruns, ripple mark, solid inclusions and air and dross
entrapments as shown in Figure 1.1 and 1.2. It is thus very desirable to be able to
understand the flow behavior of molten metal during mold filling to gain a better insight
on design of the casting in a more systematic and scientific way.

Figure 1.1: Defects during mold filling (a) cold shut and (b)misrun
(Atlas of Casting Defects, Institute of British Foundrymen)

Figure 1.2: Parts showing defects due to (a) solid inclusions and (b) gaseous
(Atlas of Casting Defects, Institute of British Foundrymen)
The production of castings free from defects is dependent on combination of many factors.
One of the important factors is the channel by which the molten metal is transferred from
the ladle to the mold cavity called gating system. Poorly designed gating systems are a
major cause of casting defects.
2