This paper present some partial result based on this idea (of pollution prevention) the domain of making composite-casting moulds (in time of casting, solidifying, and alloy cooling). Casting process impose temporary or permanent moulds in classical approach, capable to assure the liquid alloy flow and cooling. The moulds made by bound mixtures are considerer the most dangerous sources in foundries. Initially the mould is made only by gasified model and dry siliceous sand, the casting of the alloy concomitant with the thermo-destruction of the model and decomposing the products of thermo-destruction , filtering through the mould wall it makes possible realization the mould composite- siliceous- graphite, favorable the process of interface metal-mould. The elimination of the binder and of the separation plane, the raising of thermal conductivity of the mould and even the retention of thermo-destruction products in inter-granular spaces could be a solution to minimize the contamination in foundry

Ioan MARGINEAN

Mihai TARCOLEA

Sorin-Adrian COCOLAS

Vasile MIREA

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

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FO N D ATĂ
19 76
 
 
THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 1 – 2007, ISSN 1453 – 083X 
 
 
 
 
GRANULARLY UNBIND MATERIALS FOR CASTING  
COMPOSITE MOULDS 
 
Ioan MARGINEAN, Mihai TARCOLEA,  
Vasile MIREA, Sorin-Adrian COCOLAS 
University “Politehnica” Bucharest  
 
 
ABSTRACT 
 
This paper present some partial result based on this idea (of pollution 
prevention) the domain of making composite-casting moulds (in time of casting, 
solidifying, and alloy cooling). Casting process impose temporary or permanent 
moulds in classical approach, capable to assure the liquid alloy flow and cooling. 
The moulds made by bound mixtures are considerer the most dangerous sources in 
foundries. Initially the mould is made only by gasified model and dry siliceous sand, 
the casting of the alloy concomitant with the thermo-destruction of the model and 
decomposing the products of thermo-destruction , filtering through the mould wall 
it makes possible realization the mould composite- siliceous- graphite, favorable 
the process of interface metal-mould.  The elimination of the binder and of the 
separation plane, the raising of thermal conductivity of the mould and even the 
retention of thermo-destruction products in inter-granular spaces could be a 
solution to minimize the contamination in foundry  
 
KEYWORDS: pollution prevention, composite, casting moulds 
 
 
1. Structure of a composite mould at 
casting with gasified model 
 
The principle of casting technologies that use 
gasifiable models is simple and consists in model 
obtaining from an expanded synthesis material, 
covered with a refractory material (in a container) and 
the refractory material consolidation (Figure 1).  
 
There are peculiar problems at gasifiable model 
casting, comparing with casting in chills or classical 
one. In this case the gating has to assure two essential 
conditions: 
- correct filling of the mould cavity with liquid 
alloy; 
- optimum gasification of the model and quick 
evacuation of the gases resulted by thermal-
destruction of the model. 
 
1.
4.
3.
2.
a. Gasified Model b. Making mould 
 Fig.1. Making a full mould with gasified model. 1. Forming 
tank; 2. Sand bed; 3. Gasified model; 4. Consolidation sand. 
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FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 1 – 2007, ISSN 1453 – 083X 
 
 
Thermo-destruction of casting mould lead to 
the appearance of the graphite flake with alongside 
with granularly unbind sand, making the composite of 
the casting mould. 
 
2. Method theoretical fundamentation 
 
Duration of the model thermal-destruction 
phenomenon is about few seconds, depending on 
melted alloy temperature, and size and model density. 
The importance of this phenomenon optimization is 
decisive with implication on quality part and specific 
fabrication. In figure 2 is presented the manner where 
the liquid alloy act over the gasified model in time of 
thermo-degradation and in figure 3 is sketch the 
filtering of the thermo-destruction products through 
form wall.  Here is presented the variation mode of 
the main parameters, depending on the metal alloy 
flow velocity. Practically this principle stays at base 
“filling” of full mould, being the critical stage in 
obtaining of a quality piece. 
 
 
 
Liquid alloy Gasified model   Interstice  
Dm - mold domain, 
granularly material 
Direction of 
thermal destruction 
products in mold 
domain  
 
 
Liquid product 
Refractory crust Fig. 3. Flowing itinerary of thermal 
Product zone of liquid infiltration           destruction products 
Fig. 2. Thermo-destruction of model and filtering the 
gaseous product in mould
 
 
Determination of the volume of gases 
resulted by materials models thermal-destruction can 
be done with equation 1: 
m
topQ a S t= ⋅ ⋅                                           (1) 
where: Q is the volume of thermal-destruction gases; 
a is the coefficient of gasification process, 
proportional to the irradiation surface of model and 
the irradiation duration, in m3/m2×sm; it’s values are 
in the range (17.2…37.6)×10-2m3/m2×sm depending 
on the (calculated) velocity of cavity filling with 
alloy, in the range 4.00…17.30×102m/s; m is a 
coefficient that takes into account the gasifiable 
polystyrene characteristics; it is dimensionless and 
has values in the range  0.824…0.553. 
 
It is necessary to know the permeability level 
of the granular material columns that form the mould 
with gasifiable model, because this must be correlated 
with the volume of the resulted gases from thermal-
destruction. 
Permeability determination can be done with 
classical apparatus (with few accessories) existing in 
usual laboratories for molding sand analyses.  
The permeability value can be calculated 
with: 
tpA
hVP
o ⋅⋅
⋅
=                                             (2) 
where: P is the permeability value; V is the air 
volume that passed through sample, in cm3 (usually 
2000 cm3), h is the sample height, in cm (usually 5 
cm), Ao is the surface area of sand sample, in cm2 
(usually 19.66 cm2), p is the pressure difference 
between the two plane surfaces after t time, in cm 
(water column height) – can be read from manometer, 
t is the necessary time for air volume crossing 
through sample, in minutes. 
 
3. Interface process at casting  
with gasified models 
 
Technological elements can be classified in 
some domains: the mould domain, Dm – sand, the 
gasifiable model domain, Dgm – cellular polystyrene, 
liquid alloy domain, Da – aluminum alloy (see 
Figures 4, 5, 6). The model domain and the alloy 
domain modifies in time, from the moment of pouring 
to the moment of complete filling and solidifying of 
the part, the liquid alloy taking the place of the model 
that is gasified. The interfaces and the domains are 
variable in time.  
The gasifying process duration is short and 
directly depending on the model size, density and 
thermo-physical properties.  
The interstice may vary between 5-8 mm and 
consist in a mixture of polystyrene de-polymerization 
products. 
 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 1 – 2007, ISSN 1453 – 083X 
 
 
 
 
Symbols: 
Sa-g = liquid alloy – gas interface, 
Sg = gas – gasifiable model interface; 
Smg-f = gasifiable model – mould interface; 
Sg-f = gas – mould interface; 
Sa-f = liquid alloy – mould interface; 
Dg = interstice domain. 
 
Their state of aggregation is different: 
  Solid – brown-russet pyrolysis carbon in flakes or 
ashes; 
  Liquid – brown-russet; 
  Gas – identified in the working environment. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 7. Thermal-destruction products in sand around the cast part 
 
4. Experimental result 
 
In order to reveal the pyrolysis graphite 
resulted from polystyrene thermal-destruction, we 
used an experimental installation (fig. 8). Pyrolysis 
graphite was collected on a metallic support (fig. 9). 
There was obtained a crust of from pyrolysis graphite 
on the metallic support. In the case of casting moulds, 
the resulted pyrolysis graphite by thermal-destruction 
of the model will depose on sand granules. Pyrolysis 
graphite retaining on sand granules (fig. 7), during 
casting process accordingly with the thermal 
destruction of gasifiable model determines the 
realization of a composite layer at the interface 
metal/mould, composed by sand granules sand and 
pyrolysis graphite flakes. This phenomenon favors a 
behavior specific to filled moulds made of granularly 
unbind material. So, during casting it is accomplished 
a reducing atmosphere in mould cavity and also 
changes mould behavior to thermal flux transfer. 
 
 
Smg-f
Dmg 
Df 
Fig. 4. Technological element that participate, 
before pouring (in which Smg-f is the surface or 
frontier among model and sand) 
 
 
Df
Da
Sa-f 
Fig. 5. Technological element that participate, 
at complete filling of the form (in which Sa-f is 
surface or frontier among alloy and sand 
Figure 6. The variation of technological elements 
that participate at the process of gasification 
models to the contact with liquid alloy 
 
 
Smg-f 
Dmg 
Df Da
Sa-f 
  
Dg 
Sg-f 
Sa-g 
Sg-mg
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 1 – 2007, ISSN 1453 – 083X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Fig. 10. Casting temperature influence on polystyrene density. 
 
Laboratory experiments has followed the 
putting in evidence the composite thickness batch  
from full mould utilized at casting and the 
dependence of this by different agents, as casting 
temperature (nature of casted alloy), duration of 
mould cooling after casting, the position of the wall 
form regarding the front filtering gases. In figures 10, 
11 are presented experimental laboratory result in this 
domain. 
 
 
 
T
h
ic
kn
e
ss
 o
f 
c
o
n
d
e
n
sa
ti
o
n
 b
a
tc
h
, m
m
 
Figure 9. Pyrolysis graphite layer resulted from 
thermal destruction of polystyrene: a) aspect of the 
pyrolysis graphite layer resulted from thermal 
destruction of polystyrene;b) aspect of the deposit of 
pyrolysis graphite on holde;1- holder for pyrolysis 
graphite collection; 2- aspect of the pyrolysis 
graphite deposit 
Fig. 8. Experimental installation for pyrolysis 
graphite revealing as a result of gasifiable model 
thermal destruction: a) equipment for process 
parameters control; b) detail of experimental 
installation. 
AT Si3Cu4 (Tt =700°C) Fc200 (Tt =1250°C) 
Polystyrene density, kg/m3 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 1 – 2007, ISSN 1453 – 083X 
 
 
 
In table 1 and 2 are presented values of 
composite batch thickness in situation of changing 
polystyrene density and position in mould. 
 
Table 1. Values of composite batch thickness at casting aluminum (700oC)  
and grey cast iron (1250oC) for various density of model. 
  
Position (position 1) (position 2) (position 3) (position 1) (position 2) (position 3) 
ρ, kg/m3 Batch thickness, (aluminum), mm Batch thickness, (grey cast iron), mm 
0 5-8 / 6.5 5-10 / 7.5 5-20 /12.5 8-13 / 10.5 10-15 /12.5 10-15 / 12.5 
15 5-10 / 7.5 8-12 / 10 5-25 / 15 18-23 /20.5 20-23 /21.5 20-24 / 22 
18 6-12 / 9 10-15/12.5 7-30 /18.5 20-26 /23 20-34 / 27 25-36 / 30.5 
22 10-15 /12.5 10-18 /14 10-35 /22.5 - - - 
 
Table 2.  Values of composite batch thickness at casting aluminum (700oC)  
for various intervals of time for cooling the piece in mould. 
 
 
 
 
 
 
(position 1) 
 
 
 
 
 
 
(position 2) 
 
 
 
 
 
 
(position 3) 
         
 
                  Position 
 
 
 
 
Time, min Batch thickness, (aluminum), mm (ρ=15 Kg/m3) 
5  5-10 / 7.5 8-12 / 10 5-25 / 15 
10 10-15 / 12.5 10-20 / 15 10-30 / 20 
15 10-17 / 13.5 10-22 / 16 15-32 / 23.5 
20 10-19 / 14.5 12-25 / 18.5 17-34 / 25.5 
25 10-20 / 15 12-27 / 19.5 20-36 / 28 
T
h
ic
kn
e
ss
 o
f 
c
o
n
d
e
n
sa
ti
o
n
 b
a
tc
h
, m
m
 
Fig. 11 Influence of cast part cooling time on condensation batch thickness (different 
positions in mold: 1-beside the horn gate, 2-beside the part, 3-above the part). 
(ρpolystyrene = 15kg/m3) 
AT Si3Cu4 (Tt =700°C) 
Time, min 
  
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 1 – 2007, ISSN 1453 – 083X 
 
 
 
5. Conclusion 
 
Experimental observations revealed that the 
mould walls retain the condensed thermal-destruction 
products, resulting the composite mould.  
The technological behavior of such mould at 
the alloy-mold interface and the reducing atmosphere 
that forms into the cavity of the mold confirm the 
composite mold status, with a reducing atmosphere 
during casting. 
The experimental research revealed enough 
thickness for the impregnated layers with thermal 
destruction products, those layers thickness was about 
5…30mm. Such a thick layer is capable to assure a 
behavior very similar to metallic molds (high cooling 
rates), an overpressure of the alloy during 
solidification, and a very good protection against 
oxidation,  
The presence of pyro-graphite al interface 
metal-mould modified the humectation angle in way 
of diminution the capillary effect due to mould 
porosity.  
 
References 
 
[1]. Marginean Ioan. “Researches concerning increasing 
toughness and improvement quality parts casted” Doctoral 
dissertation 1995, Politehnica University  of Bucharest. 
[2]. Simona Avram. „Studies and researches regarding  at casting 
aluminum alloy in moulds with gasified models” Doctoral 
dissertation 2005, University Tehnica Cluj-Napoca 
[3]. Marginean Ioan, etc, “Experimental model for determination 
of the expanding condition and dimensioning of the horn gates 
utilized in method of obtaining the metallic piece through precision 
casting”, Project INVENT 195/2006. 
 
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Granularly Unbind Materials for Casting Composite Moulds

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Granularly Unbind Materials for Casting Composite Moulds

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