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(!!! Even number of pages )
PHYSICAL PROPERTIES OF THE GRIST FRACTIONS AT THE SECOND REDUCTION
PASSAGE OF A MILLING PLANT (english language)
/
PROPRIETĂȚILE FIZICE ALE FRACȚIILOR DE MĂCINIȘ LA AL DOILEA PASAJ DE
MĂCINARE AL UNEI MORI DE GRÂU (native language)

As. Ph.D. Stud. Eng. Constantin G.A.*1), Prof. Ph.D. Eng. Voicu Gh.1), Lect. Ph.D. Eng. Stefan E.M.1),
Prof. Ph.D. Eng. Paraschiv G.1), Lect. Ph.D. Eng. Mușuroi G.1), Ph.D.Eng.Vlăduț V.2)
1) Universities Polytechnic Bucharest, Faculty of Biotechnical Systems Engineering / Romania;
2)INMA Bucharest
Tel: [anonimizat]; E-mail: [anonimizat] (first author’s address)

Keywords: wheat grinding, grist, ground (4-7 words)

ABSTRACT (In English) (Max.100 words)
Choosing functional and structural char acteristics of the equipment on the technological of any milling unit
is influenced primarily by the physical properties of intermediate products of grist. The paper presents
results of experimental research on the physical properties of grist (coefficient of static friction – on three
types of surfaces, the angle of natural slope, density, density, surface area, porosity) compartment
plansifter of the second grinding mill for a unit of 4.2 t/h of Romania.

REZUMAT (In native language)
Alegerea caracteristi cilor funcționale și constructive ale echipamentelor de pe fluxul tehnologic al oricărei
unități de morărit este influențată în primul rând de proprietățile fizice ale produselor intermediare de
măciniș. În lucrare sunt prezentate rezultatele unor cercetăr i experimentale privind proprietățile fizice ale
măcinișului (coeficientul de frecare static – pe trei tipuri de suprafețe, unghiul de taluz natural, masa
volumică, densitatea, suprafața specifică, porozitatea) la compartimentul de sită plană al celui de-a l doilea
măcinător pentru o unitate de morărit de 4,2 t/h din România.

INTRODUCTION
Manufacture of wheat flour involves repeated grinding and sieving operations, for endosperm to be
separated from the bran. Grinding of wheat is made into two separated technological phases: crushing of
wheat seeds (breakage phase) and grinding of semolina (reduction phase). In wheat milling plant, breakage
/ reduction and sifting are complementary operation forming together individual technological phases. After
each grinding stage is made a sorting on fractions (sifting) of the grist within a plansifter compartment.
According to several papers from the specialty literature (Allen T., 2003; Căsăndroiu and David,
1994; KeShun Liu, 2009; Orășanu et al, 2009; Standish N., 1985) , sifting of intermediate products is
affected by several factors, the most important being: size and shape of the grist particles, character of the
relative motion of the particles on the sieve surface, characteristics of sifting sieve fabric, revolution of
plansifter, and the amount of material that reaches on the sieve.
To properly correlate the technical characteristics of equipment used in the milling process flow is
particularly important to know the granulometric characteristics, as well as physical characteristics of grist
intermediate products. Thus, operating parameters of equipments on the technological flow, and proper
selection of fabrics from inside of plansif ters or semolina machines, are influenced by the physical
properties of grist.
Coefficient of static friction and angle of natural slope of grist, intervene in the movement of grist
particles on different types of surfaces, in the sorting on fractions and in the characterization of se paration
on fractions process (Coskuner and Karababa, 2007) .
As described in the paper (Dziki D., Laskowsky J., 2005) , it is important to know the physical
properties of wheat seeds (size and shape, bulk density, density, and mechanical properties, among
them hardness and elastic modulus) because they influence the processes of grinding and sifting, grist
properties being correlated with those of the seeds from which it came. Among these, wheat seeds
hardness impose functional and constructive characteristics of the roller mills, as well as shape and size
of grist particles which influence the choice of fabrics for sorting on fractions of grist.
Processes or drying, ventilation, heating and cooling of wheat seeds, efficient us e of storage places

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(especially, at seeds and final products of the grinding process), but also process of modeling of air flow
through the mass of material particles are affected by the porosity of the wheat seeds and intermediate grist
products (Karimi et al, 2009) . Also, porosity of grist fractions and density of particles influence the
stratification of grist on the frames inside of plansifter compartment.
Given the importance of knowing the physical properties of grist products, obtained after each
stage of sifting within a plansifter compartment, this paper presents the results of experimental
research on the physical properties of the fractions separated at compartment of reduction roll 2 of a
milling plant of 4.2 t/h.

MATERIAL AND METHOD
Samples used in the experim ental measurement of the physical characteristics of grist were taken
on the technological flow of unit S.C. Spicul S.A., Roșiorii de Vede, Teleorman, Romania. It was determined
experimentally: coefficient of static friction, angle of slope, bulk density a nd density of particles of each
fraction and was calculated the specific surface and porosity of grist fraction at plansifter compartment C2
for passage M1B from the reduction phase of the milling plant. In fig. 1 is presented the flow diagram for
reduction phase of semolina at the reminded milling plant.

Fig.1 – The flow diagram of the wheat reduction phase in a milling plant with the capacity of 4.2 t/h [12]
(Arial 9pt, Bold )
C1–C6 – plansifter compartments; Break 1–5 – break rolls; MG1, MG2 – semolina machines;
M1A, M1B, M2–M6 – reduction rolls; F, F1, F2 – flour
(Arial 8pt, Italic )

For technological diagram of the analyzed mill, equivalence between number of mesh and
mesh size, as are indicated in the diagram, is presented in table 1.
Bulk density of a granular mixture is defined as the mass of the material reported to the total
volume that it occupies in its natural state.

(Arial 10 pt) Table 1
Equivalence between the mesh number and mesh size (Arial 9pt)
(Table content Arial 9 pt)
Mesh number 18 20 26 36 40 46 48 50 54 56 60 VIII IX X XI
Mesh size [mm] 1.17 1.05 0.78 0.52 0.47 0.39 0.37 0.35 0.32 0.31 0.28 0.18 0.17 0.15 0.13

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This property is considered as one of base qualitative indices used in est ablishing of extraction
flour (Costin I., 1988) . Yield of flour is closely related to the bulk density. To determine the bulk density
was used the method of graduated cylinder.
Density represents between the mass of the sample and the volume occupied by the particles of it.
In paper, dete rmination of density of the grist fractions was made through pycnometric method using xylene
as working fluid (ρ x=825,44 kg/m3).
Methodology for determining the bulk density and density used in this paper is given in detail in the
papers (Căsăndroiu and David L., 1994; Mohsenin, 1986) and corresponds to the standard method.
In the paper was performed also particle size analysis of each grist fraction. Fineness of grist, assessed by
the mean diameter dm of grinded particles, determined with sieve shaker, was calculated with relation:
i i
m
ip ddp×=å
å, [mm] (1)
where:
pi represents percentage of material on the sieve of the sieve shaker (i = 0, 1, 2,…, 5); pi = 100 – sum of
the percentages of material on sieves;
di – average particle size of e ach intermediate fractions, considered as an arithmetic mean of sieves
size apertures surrounding the respective fraction d i = (li+li+1)/2.
Classifier sieves were chosen to meet the estimated relationship12i il l+= ×, from the topper to
the lower sieve.
Knowing the average diameter of newly formed particles, specific surface Se.m of them can be
evaluated with the relation (2):
.e m
m6 = S dr×, [m2/kg] (2)
where  is the density of analysed fraction, determined with the pycnometer.
Porosity represents the property of granular materials not to overlay the whole storage volume,
existing an intergranular space. Knowing the values of bulk density and density of grist, porosity was
determined by the relation (3), (Căsăndroiu and David L., 1994, 8]:
1 100vreræ öç ÷= – ×ç ÷è ø, [%] (3)
The angle of the natural slope is the angle that is make by a free surface of a mass of granular
material poured onto a surface, with the horizontal plane. To determine the angle of natural slope was used
the material cone method (Căsăndroiu and David L., 1994) .
Coefficient of static friction , determined by the usual method of the inclined plane [9], was carried
out on three types of surfaces: fibre glass, steel sheet and cotton canvas.

RESULTS
The experimental data which charact erize the physical properties of the grist obtained at reduction
roll M1B of the technological diagram of milling plant, and sorted on fraction in afferent plansifter
compartment, are shown in table 2.
According to the technological diagram, wheat semolin a grinded at reduction roll M1B are sorted on
fractions inside of plansifter compartment C2 (see fig. 1), consisting of four frame packages with metallic
fabric or from plastic material with mesh size in correlation with type of fabric and with number of w ires per
unit length (table 1).
From the analysis of fig. 1 is found that the top five sieves, are disposed within a package, have no.
50 (ie mesh size 0.35 mm) and transmit the packet refusal to reduction roll M3, while the sifting of the
frames is direc ted to second package with eight sieve frames (flour sieves, having the fabric no. IX, ie mesh
size 0.1 mm). Refusal of the second package feeds the frames of the third package that has seven sieve
frames no. X, with mesh size of 0.15 mm (flour sieve). Sif ting of sieve frames from packages 2 and 3 are
evacuated from compartment as flour, and refusal of them pass to fourth package equipped with five frames
no. VIII (also flour sieve), with mesh size of 0.18 mm. Sifting of this frames is a semolina flour and is
evacuated as such, while the refusal of the package is redirected to reduction roll M2.

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All fractions extracted at compartment C2 – afferent to reduction roll M1B was analyzed and was
determined coefficient of static friction and angle of natural slope (table 2).

Table 2
Values of coefficient of static friction and angle of natural slope
Coefficient of static friction, μ
Grist fraction
Steel sheet Cotton canvas Fiber glass Angle of natural
slope, ψ
C2 Entrance 0.576-0.723 >1.470 0.676-1.000 38.320
C2 M3 0.611-0.900 >1.760 0.782-1.535 41.152
C2 M2 0.835-1.176 >1.760 >1.760 49.927
C2 Fgrif 0.688-1.035 >1.760 0.829-1.760 38.767
C2 F2 0.653-0.941 >1.760 >1.760 41.081
C2 F 0.676-1.400 >1.760 >1.760 46.178

From Table 2 it can be se en that the values of the coefficient of static friction, on steel sheet and
fiber glass, are limited is within the limits described in the specialty literature. Values of friction coefficient
obtained for cotton canvas also falls within the range of value s presented in other papers, being somewhat
higher, because of humidity, of equivalent average diameter of particles quite small, which makes them
adhere to work surface used in experiments, and to high content of endosperm of grist fractions analysed.
Us ing experimental values, presented in table 2, were drawn charts of variation of the average
values for the coefficient of static friction and the angle of natural slope for the six grist fractions analysed ,
using MS Excel program version 12 (fig. 2).
Val ues of bulk density, specific surface, porosity and mean diameter of the grist fractions analyzed
are presented in table 3.
Based on the data obtained and presented in Table 3, were drawn, graphic, variations of bulk
density, density, specific surface and porosity of grist intermediate products analysed.
As can be seen from the analysis of data from table 3, and of charts in figure 3, bulk density of
fractions resulted at sorting of grist in plansifter compartment C2 has a random variation, it depends suc h
on the type of sieve frame fabric, and to the size of apertures of the working sieve, but also of the initial
granulation of grist or of shell content adhesive on the semolina particles subjected to grinding.

00.20.40.60.811.21.41.61.82
C1 Entrance C1 M3 C1 M1B C1 M2 C1 F C1 FgrifStatic friction coefficient, μ
Grist fractionsSteel sheet Cotton canvas Glossy fiberglass
01020304050
C2 Intrare C2 M3 C2 M2 C2 Fgrif C2 F2 C2 FAngle of natural slope , ψ [ °]
Grist fractions
Fig. 2 – Variations of the average values of static friction coefficient for six grist fractions,
on 3 types of surface (steel sheet, cotton canvas and fiber glass) and of natural slope angle

Table 3
Values of: density, bulk density, specific surface, porosity and average diameter
for grist fractions resulting at C1 compartment (from technological diagram)
Average
diameter Bulk
density Density Specific
surface Porosity Grist
fractions [mm] [g/dm3] [g/dm3] x 103
[m2/kg] [%]
C2
Entra
nce 0.160 499.000 1371.970 27.333 63.629

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Average
diameter Bulk
density Density Specific
surface Porosity Grist
fractions [mm] [g/dm3] [g/dm3] x 103
[m2/kg] [%]
C2
M3 0.420 463.000 1334.897 10.702 65.316
C2
M2 0.210 426.000 1389.644 20.560 69.345
C2
Fgrif 0.140 463.000 1371.312 31.253 66.237
C2
F2 0.130 460.000 1377.551 33.504 66.607
C2 F 0.090 440.000 1382.717 48.214 68.179

0100200300400500
C2 Intrare C2 M3 C2 M2 C2 Fgrif C2 F2 C2 FBulk Density [g/dm3]
Grist fraction 010203040506070
C2 Intrare C2 M3 C2 M2 C2 Fgrif C2 F2 C2 FPorosity, ε [%]
Grist fraction

13001310132013301340135013601370138013901400
C2 Intrare C2 M3 C2 M2 C2 Fgrif C2 F2 C2 FDensity, ρ [g/dm3]
Grist fraction 05101520253035404550
C2 Intrare C2 M3 C2 M2 C2 Fgrif C2 F2 C2 FSpecific surface , Ss [m2/kg]
Grist fraction
Fig. 3 – Variations of bulk density, porosity, density and specific surface values,
depending on six grist fractions analyzed
(Arial 9, English language )

Also, at separation on fractions of the grist, porosity of each fraction is changing, and this will
influence the bulk density value of the resulting material.
However, is observed that fractions C2-M3 and C2- Fgrif have the highest bulk density value
(about 463 kg/m3 for both). It appears, but, that porosity of flours has relatively high values, in the in verse
relationship with bulk density (about 65.3% for C2-M3, respectively 66.2% for C1-Fgrif).
It is noted, also, that fraction which has the lowest bulk density (fraction C2- M2, which is a dunst)
presents the higher porosity (having 426 kg/m3 bulk densit y and 69.3% porosity), in the same inverse ratio
as the other fractions of compartment.
Related to the surface area of the grist fractions of compartment C2 of the second reduction roll,
it is found that the flour fractions have the highest values (31.2 for m2/kg pentru C2-Fgrif, 33.5 m2/kg for
C2-F2 respectively 48.2 m2/kg for m2/kg).
It is found that fraction C2- M3 (with a high content of shell) has a lower specific surface (about 10.7
m2/kg), even if the porosity is high.
Regarding the fraction C2-M2 c lassified as dunst, it has a specific surface, with value of about

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20.5 m2/kg, in linear relationship with the porosity of the material.
It also notes that flours (consisting of the endosperm of the wheat seeds) have high values of density
with values over 1371 kg/m3.
CONCLUSIONS
The physical characteristics of grist intermediate products determine the functional
characteristics of the passages technological equipment (breakage or reduction) from milling plant.
From the analysis and interpretation of data obtained for the 6 samples, coming from the input
and 5 outputs of the plansifter compartment C2 (fig. 1), shows the following:
– fraction C2- M2, having a high content of shell (bran), compared with the other analyzed fractions that
have a high content of endosperm, has a lower bulk density ( 426 g/dm3);
– semolina flour extracted at this compartment (C2-Fgrif) together with fraction C2- M3 have the highest
bulk density (both 463 g/dm3);
– also, can be observe that, although the mass of grist mixture that feeds the plansifter compartment C2
has a porosity of 63.62 %, after sorting, the porosity changes considerably reaching 68.18 % for flour
fraction C1-F and 69.35 % for dusnt that feeds reduction roll M2 (fraction C2-M2).
For all plansifter compartments of a mi lling plant, from the wheat reduction phase, it is important to
know the average size of particles of separated fractions, because it re- enters into the grinding process,
and structural characteristics of the roller mills and their operating parameters mus t be correlated with
these.
At the analysed mill, physical properties of grist, average size of particles of fractions at plansifter
compartments and particle size distribution of them fall within the limits shown in other specialty papers.
The data pres ented can be important for all specialists and workers in the milling and grinding of
wheat, referring, firstly, at reduction phase of technological process.

ACKNOWLEDGEMENT
The work has been funded by the Sectori al Operational Programme Human Resources
Development 2007- 2013 of the Romanian Ministry of Labour, Family and Social Protection through the
Financial Agreement POSDRU/107/1.5/S.76903.

REFERENCES
(In alphabetical order, in English and in the original publication language).
Minimum 10 references, last 10 years, minimum 3 references from the last 2 years
[1] Allen T., (2003), Particle size analysis by sieving. Powder Sampling and Particle Size Determination ,
London/U.K., Ed.Elsevier;
[2] Căsăndroiu T., David L., (1994), Equipments for primary processing and preservation of agricultural
products. (Echipamente pentru procesarea primară și conservarea produselor). Guidelines for
laboratory work, ch.4, Bucharest/Romania, Ed. Politehnica University of Bucharest;
[3] Coskuner Y., Karababa E., (2007), Physical properties of coriander seeds (Coriandrum Sativum L.) ,
Journal of Food Engineering , Los Angeles/California, Vol. 80, Issue 2, pp.408-416;
[4] Costin I., (1988), Miller book (Cartea morarului), Bucharest/Romania, Technical Publisher House;
[5] Dziki D., Laskowsky J., (2005), Wheat kernel physical properties and milling process ( Właściwości
fizyczne ziarna pszenicy a proces przemiału), Acta Agrophysica. 6(1), Lublin/Poland, Institute of
Agrophysics, Polish Academy of Sciences, pp.59-71;
[6] Karimi M., Kheiralipour K., Tabatabaeefar A., et al., (2009), The efect of moisture content on physical
properties of wheat, Pakistan Journal of Nutrition, Faisalabad/Pakistan, Vol.8, Issue1, pp.90-95;
[7] KeShun Liu, (2009), Some factors affecting sieving performance and efficiency , Powder Technology ,
London/U.K., Ed. Elsevier, Vol.193, Issue 2, pp.208-213;
[8] Mohsenin N.N., (1986), Physical properties of plant and animal materials, Gordon and Breach
Science Publishers , New York/U.S.A.;
[9] Orășanu N., Voicu Gh., Ungureanu N., (2009), Determination of the static and dynamic friction
coefficients for the milling products and their variation with respect to some parameters (Determinarea
coeficientului de frecare dinamic pentru produsele de moră rit și variația lui în funcție de anumiți
parametri) , Modelling and Optimization in the Machines Building Field – MOCM, Bacău/Romania,
Vol.15/3, ISSN:2068-7559, pp.44-50;

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[10] Standish N., (1985), The kinetics of batch sieving, Powder Technology , London/U.K., E d. Elsevier,
Vol.41, Issue 1, pp.57–67.