Modern requirements for the rational use of raw materials and
energy resources for industrial enterprises, including factories producing
construction supplies, require innovative development and upgrade of their
production facilities. Despite the new types of walling products, the
popularity of ceramic bricks remains at a high level, and technological
complexes for brick production represent a significant share of the industry. It
is important to develop and implement methods and means of controlling the
technological process of ceramic bricks manufacture, as it ensures the required
quality of the products -with the lowest possible specific energy consumption in
each individual case. The creation of algorithms and control systems with
similar properties requires a preliminary analysis of the production cycle
processes, the selection and justification of technological parameters, that
characterize the quality of bricks and determine the causes of defects. The
graphical representation of technological variables dependencies simplifies the
analysis of the technological process and helps to identify hidden patterns. In
this regard, the visualization of the working area of the space of
technological parameters for the processes of brick production is considered an
important task.
The manufacture of ceramic bricks, carried out most often by
plastic shaping, includes several basic steps, at each of which the mechanical,
physical, and chemical properties of the raw materials change in a certain way
[1, 2]: preliminary preparation of raw materials, shaping, drying and firing.
The peculiarity of this technological chain is in the significant impact of
each process on the subsequent stages.
In this paper, we solve the problem of data visualization, that
characterize the stage of shaping the ceramic paste in an auger vacuum extruder
for the paste wetting, mixing, vacuuming and the extrusion itself. The
subsequent analysis of the obtained graphic images will allow to determine the
most effective approaches to the management of the considered technological
process.
The shaping of ceramic paste is one of the most important
stages of brick production, determining the quality of the finished product [3,
4]. The complexity of managing this process is due to its substantial
non-linearity, the non-stationary nature of the mechanical, physical and
chemical properties of the raw materials, the inability to measure certain
technological parameters, and the fact that defects caused by the extrusion
step and the deviation of the products from the required value are detected
only after drying and firing [4‑6]. Nevertheless, rather strict
requirements are imposed on ceramic bricks related to their strength,
deviations of their geometric shape, absence of defects in the internal
structure (concentric and s-shaped cracks, laminated bars, etc.) [7].
The auger vacuum extruder is an aggregated unit that consists of
a clay mixer, a vacuum chamber and the extruder [8]. After preliminary
preparation, clay feedstock is fed into the loading window of the mixer using a
belt feeder for further moistening, steam heating and mixing. Next, the ceramic
paste enters the vacuum chamber where the air is extracted from it, adsorbed by
the surface of clay particles (causing microcracks in the brick). After
vacuuming, the ceramic paste is transported by an auger to the pressure head
where the paste is pressed through the head outlet of a given shape resulting
in a bar of the desired cross section.
It is known [4, 6, 9] that the strength value R of
finished products under compression depends significantly on the shear rate 
and the moister level w of the
ceramic paste in the pressure head, the value of the vacuum pressure Pv
in the vacuum chamber of an auger extruder (Fig. 1). Therefore, these
parameters make up the vector of controlled coordinates
,
where
t is time; T is the transpose mark.
Shear rate is determined
by the auger angular velocity ω and the flow behavior index of the
ceramic paste ψ [10, 11]; Pv is determined mainly
by the vacuum pump flow rate Qvp and the flow area of the
duct, which can vary by ΔF due to dust and pollution in the vacuum
chamber [6, 12]; w depends on the moisture value w0 of
the raw material entering the clay mixer and the flow rate of the water added
to it while mixing Qv [11, 13, 14]. During operation, it is
possible to regulate ω, Qvp, Qv
values by varying the frequency of the voltage ω0a,
supplying the auger driving motor, the frequency voltage ω0vp,
feeding the driving motor of the vacuum pump, voltage U0sv,
supplied to the water metering solenoid valve, respectively. In this case, the
vector of control actions will be as follows:
,
The disturbance vector will take the form:
.
Fig.
1. Influence of the technological parameters of ceramic paste shaping on brick
strength R.
In order to make the most rational management decisions in the
current technological situation, it is necessary to find the optimal position
of the operation point in space 
of the
extrusion technological parameters, the coordinates of which are determined by
the elements of the vector 
. We suggest
that the easiest way for such an approach to be implemented is by visualizing
the dependencies between the controlled coordinates of the process and further
analysis of the obtained graphical representation.
Strength class M is one of the brick's main
characteristics [7]. Based on the analysis of the requirements described in
GOST 530-2012 (Ceramic Brick and Stone. General Technical Conditions) we can
suggest that a certain class M is assigned to a brick (provided that the
requirements for flexural strength are met) in accordance with the following
logical rule:
(1)
In studies [4, 9], the authors present an assessment of the
influence of the shear rate in samples made of
non-vacuum ceramic paste (Pv = 0 %) on their strength R′
under compression after drying and firing. Every curve 
of the
represented family of functional dependencies, corresponding to some fixed
moisture value w, has approximately the same shape with a pronounced
extremum at 
. We assume that these curves absolutely
coincide in shape and are located at the same level relative to the R′
axis, and as w changes, they shift only along the axis. The
analysis of the dependencies presented in studies [4, 9] makes it possible to
describe the shifting extremum with moisture level variations in the
technologically justified range by a quadratic function
,
(2)
where
k1, k2, c3 are constants.
Based on the data [4, 9] for ceramic samples from Cambrian
clay, and taking into account expression (2), we construct a family of curves
for five moisture values (Fig. 2).
Fig.
2. The dependence of the compressive strength of a brick on the shear rate when
shaping a non-vacuum ceramic paste:
1
– w = 15.5 %; 2 – w = 17.1 %; 3 – w = 19.9 %;
4 – w = 22.5 %;
5
– w = 25.5 %.
In the case under consideration, k1 = 0.1457 s–1,
k2 = 4.4815 s–1, c3 = 34.778 s–1.
Studies of the effect of vaccum processing of the extruded
ceramic paste [6] revealed that no increase in strength R was observed
at vacuum level of 40÷60 %, at 80÷90 % the
strength increased by 70 %. Based on these conclusions, we
introduce the concept of hardening coefficient Kh [12], which
is described as the ratio of the strength R of a finished brick obtained
from a vacuum processed paste (where R depends on the vacuum level) to
the strength R' of a brick made of non-vacuum paste
.
(3)
Let us construct the dependence of the hardening coefficient Kh
on the vacuum level Pv (Fig. 3), and select the area of
acceptable variation in the vacuum level (on the condition of excluding
defective products by appearance), which is in the range 
. Based on [6] - 
= 70 %,
= 100 %, optimal
value 
.
Fig.
3. Dependence of the hardening coefficient of ceramic bricks on the vacuum
pressure in vacuum chamber of an auger extruder.
It can be noted that the change in the hardening coefficient Kh
can occur between the abcc′d and abb′c'd polylines,
and according to the data in [6] it is not possible to identify the pattern
that more accurately determines the increase in strength of ceramic bricks
during vacuuming of raw materials used for their production. Therefore, for
further analysis here, we will use the option that requires a higher vacuum
level, that is, the abcc′d polyline, which will increase the
likelihood of obtaining the expected hardening effect. The polyline abcc'd
is a graph of a non-linear function 
.
The presented dependences illustrate the influence of the
vector elements of controlled coordinates separately,
but do not provide a holistic picture and do not allow to determine the optimal, w, Pv values,
ensuring the operation of the unit in the most rational mode for the current
technological situation. In this regard, it is advisable to create a
generalized space of technological parameters of the ceramic paste extrusion
process 
.
A structural diagram is one of the options for representing
the space of technological parameters of the ceramic paste extrusion process 
. This method makes sense if the space need to be embedded in the computational
model of the brick production process. In this case, to reduce the number of
manipulations with data arrays, we advise to use only one family curve in the
structural diagram at some selected base
value of moisture wb, and cast the current value of the shear
rate to an equivalent value 
according to the expression
,
(4)
where
is the value of the shear rate correction,
;
(5)
is the curve extremum,
corresponding to the moisture value wb.
Thus, the extrusion process can be modelled at any moisture
value of the ceramic paste using only one curve of the dependence of the brick
strength on the speed of shear deformations.
The combination of expressions (1) ‒ (3) and
non-linear functional dependencies of Φ1 and Φ2
allows to create a structural representation of the space of technological
parameters of the ceramic paste shaping process (Fig. 4). However, this
form of display, convenient for use in computational experiments, does not
allow for a thorough analysis of this three-dimensional dependence, or to
reveal its hidden properties. Therefore, it is obviously necessary to introduce
the space in the form of three-dimensional
graphic design in the coordinates of technological variables ‒ , w, Pv. The
solution of this problem is accomplished by graphic synthesis with several
stages.
Fig.
4. Structural representation of the space of technological parameters of the
ceramic paste extrusion process.
Projecting function graphs (Fig. 2),
where the boundaries of brick strength classes M are also indicated in
accordance with expression (1), on 
plane allows
to get a group of curves 
, each of which corresponds to a specific
value of R′. Further, we use only some of these curves, which will
be boundary in terms of the separation of plane into
class areas. We should also take into account that for Cambrian clay the
optimum shaping moisture value ws is about 23.5 %
[5], and we will take Δwacc = ± 1 %
[15] as the acceptable range. Minding these limitations, we obtain a set of
work areas of an auger extruder (in terms of and w)
(Fig. 5), within which it is possible to ensure the production of a brick of a
certain class from a non-vacuum ceramic paste. In fact, the formed image is a
cross-section of space with Pv = 0% - 
.
Fig.
5. The cross-section of the space of technological parameters of the ceramic
paste extrusion process in plane.
We should find the sought space by
multiplying the elements of the set by the
hardening coefficient, which lies in 
range.
According to the above data, 
, 
. Thus, given the expression (3), we
synthesize a three-dimensional space:
.
Let us present in the form of
a set of surfaces 
(Fig. 6), limiting ourselves to the
consideration of four values of Pv.i from the allowable range
of changes in the vacuum pressure of the vacuum chamber of an auger extruder in
the process of shaping ceramic paste for brick production: Ðv.1
= = 70 % , Ðv.2
= 80 % , Pv.3 = 
= 90 % , Pv.4
= = = 100 %. This
series of values determine the values of the hardening coefficient Kh.i
– Kh.1 = 1.23, Kh.2 = 1.47, Kh.3
= Kh.4 = 
= 1.7.
Using this kind of visualization clearly shows the areas of constant values of
brick strength classes in space (Fig. 6).
Sections in 
plane (Fig. 7) record working range of the
unit, which provide for the production of bricks of a certain class with fixed
values of w.
Fig.
6. Three-dimensional visualization of the space of technological parameters of
the ceramic paste extrusion process.
Fig. 7. The cross-sections of the space of
technological parameters of the ceramic paste extrusion process in 
plane.
Based on the analysis of the surfaces obtained (Fig. 6, 7), we
proposed an automatic control system structure for an auger vacuum extruder
(ACS for AVE) to manufacture the ceramic stones [11]. The structure consists of
three separate channels and includes a multi-dimensional object of control, by
which we understand the combination of hydrodynamic and electromechanical
processes in the preparation of clay raw materials and the shaping of bars and
subsequent drying and firing processes. The state of the object is determined
by vector. We use the following as converting
elements: in shear rate control channel –
frequency converter to power the extruder drive; in the control channel for the
Pv value – frequency converter for the vacuum pump motor; in
the moisture control channel w – pulse-width modulators for powering the
coils of the solenoid valves supplying water and steam to the extruder mixer.
The synthesized space of technological parameters of the
ceramic paste extrusion is incorporated into the vector of master
signals for the ACS for AVE and can be adjusted depending on the data obtained during
production. The arrangement and implementation of such an automation system
allows to establish the competitive brick production, to ensure an increase in
productivity and to reduce the specific energy consumption along with
stabilizing the brick strength matching the given class requirements.
The paper describes the technique allowing the visualization
of the space of technological parameters of the ceramic paste extrusion
process. At first, this stage was considered using the approaches of system
analysis, identification of objects of control and automatic control theory,
which allowed to isolate the vectors of control and disturbing influences, the
vector of controlled variables, elements of which were taken as coordinates of
the multidimensional parameter space of the extrusion process.
The authors analyzed the results of few and scattered studies
to assess the impact of the main parameters, most characterizing the efficiency
of an auger vacuum extruder (shear rate and moisture levels of the ceramic
paste in the pressure head and the level of vacuum pressure in the vacuum
chamber), on the quality of the finished product, and first of all on its
strength. This made it possible to represent the sought space in the form of a
three-dimensional graphic design, in which the iso-areas of brick classes are
visually displayed in coordinates corresponding to the elements of the vector
of controlled variables. It should also be noted that a structural
representation of the multidimensional relationship between the shear rate, the
moisture of the ceramic paste, the vacuum pressure and the strength class was
obtained, which is essential in preparing and conducting computational
experiments.
Studying sections of the found space of technological
parameters has greatly facilitated the creation of the structure of the
automation system for an auger vacuum extruder and the algorithms for its
rational work.
The conducted survey reflects the results of one of the stages
of research work on the synthesis of the structure and the formation of the
software for the digital automatic control system for the production of ceramic
bricks.
1. Khimicheskaya tekhnologiya keramiki [Chemical technology of
ceramics] / edited by I.Ya. Guzman. Moscow, Stroymaterialy, 2003. 496 p.
[in Russian].
2. Zolotarskiy A.Z., Sheynman E.Sh. Proizvodstvo
keramicheskogo kirpicha [Ceramic brick production]. Moscow, Vysshaya shkola,
1989. 264 p. [in Russian].
3. Tolkachev V.Ya. Tekhnologiya kachestvennoy ekstruzii
izdeliy iz glin [Technology of high-quality extrusion of clay products].
Krasnoyarsk, Kompyuternyye tekhnologii, 2009. 220 p. [in Russian].
4. Barabanshchikov Yu.G. Vliyaniye skorosti formovaniya na
prochnost stroitelnykh izdeliy [The effect of shaping speed on the strength of
building products] // Nauchno-tekhnicheskiye vedomosti SPbGPU, ¹ 6-1, 2006, pp. 170-175.
[in Russian].
5. Avgustinik A.I. Keramika [Ceramics]. Leningrad, Stroyizdat
(Leningr. otd-niye), 1975. 592 p. [in Russian].
6. Tretiakov I.M., Golubovich S.R. Shnekovyye vakuum-pressy i vakuumnyye
ustanovki [Auger vacuum extruders and vacuum systems]. Moscow, Gosudarstvennoye
izdatelstvo literatury po stroitelnym materialam, 1953. 92 p. [in Russian].
7. GOST 530-2012 Kirpich i kamen keramicheskiye. Obshchiye
tekhnicheskiye usloviya [Ceramic brick and stone. General technical
conditions]. Moscow, Standartinform, 2012. 39 p. [in Russian].
8. Handle F. Extrusion in Ceramics. Berlin, Springer, 2007.
468 p.
9. Barabanshchikov Yu.G. Formirovaniye struktury i prochnosti
stroitelnykh materialov pri trenii vodosoderzhashchikh syryevykh smesey
[Formation of structure and strength of the building materials in friction raw
water containing mixtures]. Sankt-Peterburgskiy gosudarstvennyy
politekhnicheskiy universitet, Saint-Petersburg, 2006. 292 p. [in
Russian].
10. Silenok S.G. Mekhanicheskoe
oborudovanie predpriyatiy stroitelnyikh materialov, izdeliy i konstruktsiy [Mechanical
equipment of enterprises of building materials, products and structures] / S.G.
Silenok, A.A. Borschevskiy, M.N. Gorbovets. Moscow, Mashinostroenie, 1990. 416 p.
[in Russian].
11. Galitskov S.Ya., Nazarov M.A., Galitskov K.S. Structure of
Intelligent Control System of Auger Vacuum Extruder for Ceramic Bricks'
Manufacturing // International Journal of Applied Engineering Research,
2015, Volume 10, Number 20, pp. 40846-40852.
12. Nazarov M.A., Kantseva A.M. Matematicheskoye opisaniye
protsessa vakuumirovaniya keramicheskoy massy pri proizvodstve kirpicha kak
obyekta upravleniya [Mathematical description of vacuuming ceramic paste
process in bricks production as an object of control] // Traditsii i innovatsii
v stroitelstve i arkhitekture. Stroitelnyye tekhnologii: sbornik statey /
SGASU, Samara, 2016, pp. 455-460. [in Russian].
13. Galitskov S.Ya., Ivanov K.A., Nazarov M.A., Sabanov P.A.,
Pimenov E.K. Matematicheskoye opisaniye protsessa podgotovki keramicheskoy
massy v dvukhvalnom glinosmesitele kak obyekta upravleniya [Mathematical
description of ceramic paste preparing process in a two-shaft clay mixer as an object
of control] // Nauchnoye obozreniye, 2014, ¹ 6, pp. 84-89. [in Russian].
14. Leisenberg W. Moisture measurement on ceramic raw
materials // Zigelindustrie International, 2000, ¹ 8, pp. 25-32.
15. Nichiporenko S.P. Osnovnyye voprosy teorii protsessov
obrabotki i formovaniya keramicheskikh mass [The main issues of the theory of
processing and shaping ceramic pastes]. Kiyev, Izdatelstvo akademii nauk
Ukrainskoy SSR, 1960. 112 p. [in Russian].
