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Asian Journal of Current Engineering 1 (2), 2016, 01-03.
Scabbing Defect: Gate Modification
Anup Latane*, Rohan Yadav, Tejas Salunkhe, Dhrumit Patel
Department of Mechanical Engineering, Keystone School of Engineering, Pune, Maharashtra, India.
Abstract
At the entrance of in-gate, the temperature of mould material is very high (about 1440°C). Due to this
high temperature, the compressive stresses are induced on surface layer of mould which produces
scabbing defect. Also, for reducing the heat dissipation from fluid to mould sand surface, the
convective heat transfer is considered. In this paper, the effect of gating design on scabbing defect
was investigated by pouring molten metal. Also, heat dissipation is less in laminar flow than turbulent
flow. The direct observations and trials were taken. These experimental results indicate that the
change in gate design reduced the compressive, tensile stress, turbulence and hence scabbing
defect.
Keywords: Tensile and compressive stress, turbulence.
1. Introduction
Casting is one of the most desirable and
widely used processes for manufacturing of
components like exhaust manifold, cylinder
head etc. During this process, various failures
occur because of improper mould material,
temperature of mould material, mould cavity
etc. Hence, various defects occur. So it is
necessary to reduce defect while
manufacturing process because plant
efficiency is totally depends upon the rate of
rejection of product. The scabbing defect
occurs due to high temperature created and
turbulence created in the mould cavity. The
silica expands at 573°C which causes the
formation of compressive stress on surface
layer of mould and this leads to formation of
shell. Tensile stress occurs at boundary layer
between highly heated shell and sand inset
core which is relatively cool.
*Corresponding author
E-mail address: -
(Anup Latane)
© 2016 AJCE. All rights reserved.
The compressive stress is counteracted by
moulding material and strength of adhesion to
the surface. i.e. height of tensile strength in
layers of mould material lies behind. Top
scabs thus develop from the condensation
zone in the mold surface as a result of the
compression stress that occurs there and that
pushes up the wall of the mold and lifts it off.
This process is generally referred to as shell
formation. Scabbing is also caused by the
formation of a shell. However, the shell does
not break open, so that a burr-like elevated
seam becomes visible on the cast part. This
scabbing can be removed by means of
increased cleaning work, and the cast part can
possibly be saved. Bottom scabs form in the
mold cavity below a flow of casting metal and
thus on the bottom of the mold. The
condensation zone that effects the formation of
a shell is the cause here, too. If the sand shell
remains attached to the bottom of the mold,
the protruding edges of the shell cause either
scabbing or rat-tails. In contrast, if the sand
shell bulges and breaks apart under the weight
of the metal that flows across it, a typical
Research Article
R E D IF IN IN G R E S E A R C H

2. Anup Latane et al / Asian Journal of Current Engineering 1(2), 2016, 01-03.
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bottom scab forms at the underside of the cast
piece.
Also, the molecules of mould material
dissipate more heat in turbulence than laminar.
In laminar flow, the outermost molecules come
in contact with sand surface only dissipate
heat to the sand. But while in case of
turbulence, large number of molecules come in
contact with core and dissipates more heat
which results into scab.
2. Experimental
Most of the Indian foundry use rectangular
profile for designing the in-gate. Due to sudden
enlargement in cross-section, the turbulence
occurs. Hence, instead of allowing sudden
enlargement, the entrance of the in-gate is
provided a gradually increasing cross-section
with 60° angle. The Schematic diagram of
typical in-gate shape and modified in-gate
shape is shown in figure below.
Figure 1. Typical rectangular profile.
Figure 2. Modified profile.

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3. Results and Discussion
By using this experiment, the turbulence was
reduced. The flow of molten metal which was
turbulent previously, turned into laminar flow
and hence loosening of the sand was reduced.
4. Conclusion
In conclusion, it can be seen that the
modification of in-gate directly affects the
scabbing defect. The 60° taper reduces the
turbulence, compressive stress and tensile
stress as well.
5. References
1. M. Masoumi ‘Effect of gating design
on mould filling’, Iran University of
technology, Tehran, (2005).
2. Sunil Chaudhari ‘Review and analysis
of foundry defects for quality
improvement in sand casting’, Gujrat
technological university, Gujrat,
(2014).
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Source of Support: Nil.
Conflict of Interest: None declared