Citation: Wójcik, Ł.; Gajek, M.;
Rapacz-Kmita, A.; Mastalska-Popławska,
J.; Pacan, R.; Puchyrska, I.; Sacha, P.;
Cegłowski, D. Rheological Properties
of Soft Waste Granulates Produced in
the Fabrication Process of Ceramic
Tiles and the Possibility of Their
Reuse. Materials 2022, 15, 1366.
https://doi.org/10.3390/ma15041366
Academic Editors: Arkadiusz Gola,
Izabela Nielsen and Patrik Grznár
Received: 21 December 2021
Accepted: 10 February 2022
Published: 12 February 2022
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Article
Rheological Properties of Soft Waste Granulates Produced in
the Fabrication Process of Ceramic Tiles and the Possibility of
Their Reuse
Łukasz Wójcik
1,
* , Marcin Gajek
1
, Alicja Rapacz-Kmita
1
, Joanna Mastalska-Popławska
1
, Robert Pacan
2
,
Izabela Puchyrska
2
, Piotr Sacha
2
and Dawid Cegłowski
2
1
Faculty of Materials Science and Ceramics, AGH University of Science and Technology, Mickiewicza 30,
30-059 Krakow, Poland; mgajek@agh.edu.pl (M.G.); kmita@agh.edu.pl (A.R.-K.); jmast@agh.edu.pl (J.M.-P.)
2
Cerrad Sp. z o.o., ul. Radomska 49B, 27-200 Starachowice, Poland; r.pacan@cerrad.com (R.P.);
i.puchyrska@cerrad.com (I.P.); p.sacha@cerrad.com (P.S.); d.ceglowski@cerrad.com (D.C.)
* Correspondence: lukwoj@agh.edu.pl
Abstract:
The paper presents the results of research on the influence of the granulometric composition
on the rheological properties of granulates from soft waste produced in the manufacturing of ceramic
tiles using the Lamgea and Continua methods in terms of the possibility of their reuse. The composi-
tion of the granulates was modified by removing individual grain fractions in three measurement
series. Comparatively, the measurement samples for the production granulates were prepared in the
same way. Microscopic observations and granulometric analysis showed significant differences in the
grain shape and grain size distribution of granulates. The soft waste granulates also showed much
worse flow ability than the production granulates. It was shown that the removal of the smallest
fractions significantly improved the rheological properties of soft waste granulates. This tendency
was also observed in the case of measurements of changes in the bulk density. A Brookfield powder
analyzer was used for rheological tests, and a flow analysis was performed using the numerical
Jenike classification.
Keywords: soft waste granulate; powder flow; rheology; ceramic
1. Introduction
The production of ceramic tiles has recently undergone several significant changes
in the technological process. Starting from the introduction of fast firing, through the
replacement of traditional methods of decorating with digital printing, to the introduction
of new methods, such as continuous strand using the “Continua” method and forming
large slabs using the “Lamgea” method. In both “pressing” technologies, the final size of
the tiles is shaped by cutting the unfired strand or large-size slab [
1
–
3
]. Any major change
in the production process usually entails adjustments to the rest of the production steps. In
the case of the Continua and Lamgea methods, there was a problem with the management
of large amounts of soft waste, (up to 30%), generated when cutting the desired tile formats.
This waste, being a full-value production mass, can be reused in the production process,
but requires reprocessing. Returning waste to the spray dryer would be associated with
high energy expenditure, therefore other, more effective methods of using it are sought [
4
,
5
].
One such method may be the production of granulates by mechanical grinding to obtain
the appropriate particle size.
The obtained re-granulate from soft waste (crushed green body granulate) differs
significantly from the granulates produced in spray dryers [6,7], as it has a different grain
shape, grain size, and rheological properties. The rheological properties of granulates for
the production of ceramic tiles are particularly important due to the stages of the production
process [
1
]. After production, the granulate is transported to silos, where it is homogenized
Materials 2022, 15, 1366. https://doi.org/10.3390/ma15041366 https://www.mdpi.com/journal/materials
