1. Gated Pa
Many tim
cavities a
gates. Th
as gated
Sweep P
For axi-s
sweeping
Such pat
shaped ca
attern
mes it is des
are created
his arrange h
pattern. A ty
Pattern
symmetrical
g the pattern
tterns are kn
astings. A ty
CO
M
Patter
sired to prod
in one mou
helps to achi
ypical gated
l castings su
around the
nown as sw
ypical sweep
OURSE: M
Module No
Lec
rn types an
duce the mul
uld and thes
ieve higher p
pattern is sh
uch as bells
spindle. The
weep pattern
p pattern is sh
METAL C
o. 6: PATT
cture No-2
d Design Co
ltiple small
e cavities a
productivity
hown in Fig.6
s, the full c
e pattern is a
and are pre
hown in Fig
CASTING
TERNS
onsideration
parts in one
are joined by
y. Such type
6.2.1.
cavity of the
a part of the f
eferred for p
g.6.2.2.
ns
e go. In such
y the system
e of pattern
e casting ca
full shape of
producing la
h case, smal
m of runners
system is kn
an be create
f the end pro
arge symme
l part
s and
nown
ed by
oduct.
etrical
2.
3. Loose Pi
Sometim
pattern w
or underc
from the
shown in
iece Pattern
mes loose pie
withdrawal fr
cuts. the proj
mould. Hen
n Fig. 6.2.4.
n
ces need to b
rom the mou
jections and
nce loos piec
be added wi
uld. This typ
d undercuts m
ce pattern is
th the patter
pe of pattern
may create h
s sued in suc
rn. These loo
n is used whe
hindrance in
ch cases. A
ose piece hel
en the castin
the withdraw
typical loos
lp to facilitat
ng has projec
wal of the pa
e piece patte
te the
ction,
attern
ern is
4.
5. 4. Distortion or camber allowance
5. Rapping allowance
Shrinkage or Contraction Allowance
The metal when solidifies shrinks volumetrically. The metal shrinkage is of two types:
i. Liquid shrinkage:
After pouring the liquid metal in a mould, metal starts solidifying. When metal solidifies
from liquid state to solidus temperature, there is reduction in volume of the liquid metal.
This reduction is known as liquid shrinkage. The reduction in volume is compensated by
the riser, which stores liquid metal and the metal in riser remains liquid later than that of
metal in cavity.
ii. Solid shrinkage:
Once the casting is solidified in the mould cavity, the contraction in volume, when the
temperature of the casting moves from solidus to room temperature, of the casting occurs.
This contraction in volume is taken care by providing the shrinkage allowances in the
pattern.
The rate of contraction with temperature is dependent on the material. For example steel
contracts to a higher degree compared to aluminum. To compensate the solid shrinkage, a shrink
rule must be used in laying out the measurements for the pattern. The various rate of contraction
of various materials are given in Table 6.2.1.
Material Dimension Shrinkage allowance
(mm/mm)
Grey Cast Iron Up to 610 mm
610 mm to 1220 mm
0.010
0.009
6. over 1220 mm 0.007
Cast Steel Up to 610 mm
610 mm to 1830 mm
over 1830 mm
0.021
0.016
0.013
Aluminum Up to 1220 mm
1220 mm to 1830 mm
over 1830 mm
0.013
0.012
0.010
Magnesium Up to 1220 mm
Over 1220 mm
0.014
0.013
Table 6.2.1 Rate of Contraction of Various Metals
