The casting of the cylindrical parts with great diameter and small thickness and intermediary flange is difficult because of the great values of the forced contraction. Thus the value of the tensile stress is very great and can determine the fracture of the part in zone of the thermal knot. For assurance of the quality of these parts some technological solutions are necessary. The paper shows the analysis of this aspect and presents practical solutions

Alexandru CHIRIAC

Nicolae CANANAU

Vasile BRATU

The Annals of “Dunarea de Jos” University of Galati Fascicle IX Metallurgy and Materials Science

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FO N D ATĂ
197 6
 
 
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 3 – 2010, ISSN 1453 – 083X 
 
 
 
 
QUALITY ASSURANCE OF CYLINDRICAL CASTED PARTS  
WITH SMALL THICKNESS  
 
Nicolae CANANAU, Alexandru CHIRIAC,  
Vasile BRATU 
“Dunărea de Jos” University of Galati 
email: ncananau@ugal.ro 
 
ABSTRACT 
 
The casting of the cylindrical parts with great diameter and small thickness and 
intermediary flange is difficult because of the great values of the forced contraction. 
Thus the value of the tensile stress is very great and can determine the fracture of 
the part in zone of the thermal knot. For assurance of the quality of these parts some 
technological solutions are necessary. The paper shows the analysis of this aspect 
and presents practical solutions. 
 
KEYWORDS: casting, solidification, small thickness, flange 
 
1. Introduction 
 
The casting is a very good technological method 
for obtaining complex engineering parts.  
The parts with great diameter and length and very 
small thickness when have intermediate flange 
present a thermal knot (Fig.1). 
 
 
 
 
 
 
 
 
 
The thermal knot has a great influence on the 
solidification process and on the quality of the casted 
part. This can determine a contraction hole (shrink 
hole) in the case of the metallic material with great 
contraction coefficient at the solidification. 
In the case of the metallic material with fragility 
(in the casted state) and great thermal contraction 
coefficient, cracks can be developed. 
Under the practical condition, cracks appear with 
a relatively great frequency.  
In this paper we develop the study in the aim of 
analyzing the casting and solidification processes for 
eliminating the causes that can determine the 
appearance of cracks in zones of the thermal knot. 
 
 
2. Analysis of the solidification process 
 
We will consider that the solidification process 
begins immediately, in the certain point, when the 
casting process is finished. We admit that the material 
of the cast form (mould) is homogeneous and 
uniform. Under these conditions, the heat flux from 
the casted material to the casting mould, at the 
beginning of the solidification process, is constant.  
In the following stage the thermal flux is different 
in the different geometrical points of the thermal knot.  
Admitting a macro-element with the volume V 
and surface area A, we get of the equation of heat flux 
[1]: 
( )[ ]
dt
dTcVQVTtTA gen ρα −=− &0           (1) 
Where: 
 
t
fHQ sfsgen ∂
∂
Δ= ρ&             (2) 
The function fs has the form: 
bTafs +=  
 
and, after the integration, using the initial 
condition, we obtain the time ts of solidification of the 
parts defined by equation: 
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
−
−
⎟
⎠
⎞
⎜
⎝
⎛ Δ−−=
0
0ln1
TT
TT
H
c
b
A
cVt
i
f
fs α
ρ
    (3) 
 
 
Fig. 1. Example of a part with  
thermal knot. 
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FO N D ATĂ
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 3 – 2010, ISSN 1453 – 083X 
 
 
In the above equations we have: 
α -mean heat transfer coefficient, ρ-density, c-
specific heat, ΔHf- latent heat of melting, Tf-melting 
temperature, Ti-casting temperature, T0- temperature 
of the mould.     
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The equation (3) proves that the solidification 
time is greater when the local volume is greater. 
Therefore the greatest solidification time is in the 
centre of the thermal knot. 
The solidification front, in the thermal knot, at 
various moments of the solidification process is 
represented in Figure 2. 
In the first phase of the solidification process, the 
intensity of the heat transfer is constant and, 
consequently, the solidification front is uniform in the 
entire contour of the form walls (Fig. 2a).  
In the following phase (Fig. 2b), the intensity of 
the heat transfer decreases in the points B and C 
because of the peak form of the mould. Consequently 
the thickness of the solid layer in these points is 
smaller than in the points of the uniform thickness of 
the part.  
In the point A, because of the great quantity of 
the melt metallic material, the thickness of the solid 
layer is small, too.  
When solidification finishes, without the thermal 
knot, the two solidification fronts meet in the middle 
of the part wall.  
In the thermal knot rests an important quantity of 
liquid metallic material. The thickness of the solid 
phase is variable with minimum value at the point A. 
Simultaneous with the solidification process, the 
thermal contraction of the solid phase is developed, 
because the cast part has flanged at the both its heads. 
The part has a great length and, consequently, the 
absolute value of the free contraction is great. 
Because we have forced contraction, the tensile 
stress in zone A can be greater than the strength of the 
material, in the given conditions, and the crack 
appears.  
In the practical conditions, we found the cracks at 
the interior surface of the cast parts at the label of the 
point A. 
 
3. The solution of the problem 
 
The solving of the objective, the elimination of 
the cracking rescue, entails the control of the 
solidification process by the control of the heat 
transfer in the junction of the walls.  
We consider the solidification module defined by 
the expression: 
S
VM =                           (4) 
In this relation, V is the volume of the melting 
material and S is the surface of the heat transfer. 
The solidification time is correlated with the 
solidification coefficient through the relation: 
2Mkt ⋅=                           (5) 
Definitely, in the above relations it is supposed 
that the intensity of the heat transfer is constant on the 
interface cast material-mould. In the real conditions, 
the heat transfer intensity has dynamic character and 
the evaluation of the correct value of the local 
intensity of the heat transfer is necessary.  
For ensuring the control of the solidification time, 
respectively a correct value of the solidification 
module in the thermal knot, it is chosen one of the 
following methods: 
- changes in the local form and thickness of 
the cast part, 
- use of cooling elements, 
- use of thermo-insulating sleeves included in 
the mould walls, 
- modification of some mould walls by the 
forced heating or cooling. 
Through the use of cooling elements in the 
construction of the casting mould, the real partial 
A 
a 
b 
c 
d 
Fig. 2. Evolution of the solidification front. 
C B 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 3 – 2010, ISSN 1453 – 083X 
 
 
solidification modules change. For the calculus of the 
real solidification modules, in this case, the 
knowledge of the cooling coefficient ki for the 
surfaces with the cooling elements or thermo-
insulating sleeves is necessary. In this aim is used the 
equation that describes the heat quantity extracted by 
the mould from the cast part through unity of contact 
surface mould-cast part, in function of temperature 
gradient liquid alloy – mould and time, used by 
Chvorinov, at the definition of the exterior geometric 
solidification module, for the multiplication of real 
solidification module with the factor n in the 
conditions of the given thermo-physical 
characteristics of the available materials. 
In Table 1 the thermo-physical characteristics of 
the various materials are showed. They are materials 
with small and great values of thermo-physical 
characteristics.  
 
 
Table 1. Thermo-physical characteristic of some materials 
 
Material  Density kg/m3  
Specific 
heat 
J/(kg K) 
Thermal 
conductivity 
coefficient 
W/(m K) 
Heat 
accumulating 
coefficient 
Ws/m K 
Mould mixture (95% quartz sand + 5% 
sodium silicate)  1700 1312 1.5 1856 
Mould mixture (97.8% quartz sand + 1.8% 
furfurol + 1% ortophosphoric acid) 1700 1356 1.35 1761 
55.6% quartz powder + 22.8% quartz sand + 
16.6% ethyl–silicate and catalyser 1600 1232 1.12 1579 
46% zircon powder + 39% zircon sand + 
16.6% ethyl–silicate and catalyser  2700 968 1.35 1881 
Raw mould mixture (quartz sand and 
bentonite) 1800 1050 0.29 740 
Dried mould mixture (quartz sand and 
bentonite) 1700 840 0.17 492 
Low carbon steel 7850 840 50" 18157 
Medium carbon steel 7850 800 46 16996 
Cast iron 7200 540 40 12470 
Siluminum (86-89% Al + 14-11% Si) 2600 880 160 19133 
Bronze (90% Cu + 10% Sn) 8760 360 42 11508 
Copper 8900 440 380 38575 
Diatomite (brick) 550 840 0.17 280 
Vermiculite  300 830 0.14 186 
 
It is observed that the metallic materials, used as 
cooling elements, have the heat accumulating 
coefficient 10-30 times greater then of the mould 
mixture, and thermo-insulating materials have the 
heat accumulating coefficient 2-10 times smaller of 
than the mould mixture.  
The exterior cooling elements for the casting of 
steel parts are worked frequently from steel (sheet or 
rod), in case of the complex form they are cast form 
cast iron, and in very complex form, the cooling 
elements form magnesite mixture are used.    
The forms of the metallic cooling elements are 
showed in Figure 3.  
Solving the problem is possible through the use of 
exterior or interior cooling metallic elements.  
The interior cooling element can be used, but is 
important to establish very exactly its volume for 
ensuring complete melting. Otherwise the part may be 
rejected. 
 
 
 
 
 
 
 
 
 
 
 
 
 
d 
s
b
a d 
b
m
g 
a d 
s 
b 
m 
g 
a 
Fig. 3. Forms of the exterior cooling elements. 
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FO N D ATĂ
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 3 – 2010, ISSN 1453 – 083X 
 
 
Table 2. Dimensions of the cooling elements 
Dimensions of the cooling space, 
mm 
Dimensions of the cooling elements,  
mm Cooling mod 
a b g s m 
Thermal knot cooled with 
two elements 
from 20 
from 20 
to 20 
to 20 
to 20 
from 20 
to 20 
from 20 
- 
0.5-0.6 d 
0.3-0.4 d 
0.5-0.6 d 
0.3-0.4 d 
- 
Thermal knot cooled with 
one element 
from 20 
to 20 
to 20 
to 20 
from 20 
to 20 
from 20 
0.5-0.6 a 
0.5-0.6 a 
0.6-0.8 a 
0.6-0.8 a 
- 
2.5-3 b 
2-2.5 b 
2.5-3 b 
2-2.5 b 
Thermal knot cooled with 
three elements 
from 2 
from 20 
to 20 
to 20 
to 20 
from 20 
to 20 
from 20 
0.4-0.5 a 
0.4-0.5 a 
0.5-0.6 a 
0.5-0.6 a 
0.4-0.5 d 
0.3-0.4 d 
0.4-0.5 d 
0.3-0.4 d 
2.5-3 b 
2-2.5 b 
2.5-3 b 
2-2.5 b 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
The exterior cooling element, included in the 
mould kernel (Fig. 4), is the favorable method for 
intensifying of thermal flux in zone of the metal 
agglomeration.  
The heat transfer between the cast metal and the 
mould is intensified, in the metal agglomeration 
zone, because the heat conduction coefficient 
increases.  
Here it makes heat transfer through thermal 
conduction metal-metal more intense of thermal 
conduction metal-casting mould mixture. 
Consequently, the evolution of the solidification front 
is reversed in comparison with the before case 
mentioned.  
As a result, the thickness of the solid phase in the 
point A is greater than the one in zones of the 
uniform thickness of the part walls. The dimensions 
of the cooling element are established in function of 
the dimensions of the part wall and intermediary rib.  
Thus, for a equal of 25mm and b equal to 30mm, 
we must use a cooling element with dimensions: 
m=60-75mm and g=12.5-15mm.  
4. Conclusions 
 
The casting process of the parts with great 
diameter and length and small thickness, relatively, 
two marginal flanges and one intermediary flange is 
difficult because of three reasons: 
- firstly it occurs a great thermal contraction 
after the solidification of the part, 
- secondly the great fragility of the steel in the 
cast state, 
- thirdly small value of the solidified crust. 
As a result, these can appear a crack in the plan 
of the intermediate flange, in the thermal knot of the 
cast part. 
This rescue may be diminished or eliminated by 
using exterior metallic cooling elements assembled in 
the kernel of the mould. 
The dimensions of the cooling element are 
calculated in function of the characteristic 
dimensions of the part in zones of the thermal knot. 
 
References 
 
[1]. Stefanescu D.M. - Stiinta si ingineria solidificarii pieselor turnate, 
Ed. AGIR, Bucuresti, 2007. 
[2]. Flemings M.C. - Solifification Processing, McGraw-Hill, 1974. 
[3]. Ciobanu I., Munteanu S.I., Crişan A. - Un nou concept în 
turnătorie: modulul de solidificare real al pieselor turnate.- Revista de 
turnătorie, nr. 1-2, 2005, pag 27 - 33 
[4]. Ciobanu I., Munteanu S.I., Crişan A. - Modulul de solidificare 
al barelor cu secţiune U.Partea I: Modulul de solidificare ideal.- 
Revista de turnătorie, nr. 3-4, 2005, pag3-7 
[5]. Ciobanu I., Munteanu S.I., Crişan A. - Modulul de solidificare 
al barelor cu sfecţiune U.Partea II: -Modulul de solidificare real.- 
Revista de turnătorie, nr. 5-6, 2005, pag 9 -16, ISSN 1224-21-44 
[6]. Ciobanu I., Munteanu S.I., Crişan A. - Caracterizarea 
solidificării pieselor turnate prin modulul de solidificare real .- 
Metalurgia, nr.5, 2005, pag. 15- 25, ISSN 0461/9579. 
[7]. Chvorinov N. - Teoria solidificării pieselor turnate. - Giesserei 17 
mai 1940, pag.177-186, Giesserei 31 mai 1940, pag.201-208, Giesserei 
17 iunie 1940, pag. 222-225. 
[8]. Defretin G. - Calcul des modules de solidification apparents des 
pieces de fonderie. - Fonderi 384, decembrie 1978, pag. 355-361. 
[9]. Siegel A., Howell J.R. - Thermal Radiation Heat Transfer, 
Hemisphere Publ. Co., New York, 1981. 
 
Fig. 4. Solidification with cooling 
element: 1-casting mould, 2-mould 
kernel, 3-cooling element, 4-liquid 
phase, 5-solid phase. 
1 
2 
3 
4 
5 
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Quality Assurance of Cylindrical Casted Parts with Small Thickness

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Quality Assurance of Cylindrical Casted Parts with Small Thickness

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