C - Lublin

STRENGTH PARAMETERS OF FOOD POWDERS
Horabik J., Molenda M.
The strength characteristics of food powders were examined. Experiments were
performed using the Jenike shear tester according to the Eurocode 1 recommendations.
The tester was 60 mm in diameter and the displacement velocity was
0.03 mm⋅s-1. A reference normal stress ranging from 30 to 100 kPa was applied.
The following strength parameters were determined: the effective angle of internal
friction, the angle of internal friction, the cohesion and the flow index. There was
no clear influence of the consolidation pressure on the effective angle of internal
friction and the angle of friction. In the case of fine milk, agglomerated milk and
potato starch a significant shear stress vibration was observed. The frequency of
these vibrations were found to decrease with an increase in normal stress. Two
components of the total strength were considered: the physical friction strength and
the extra component of strength due to dilation.
INTRODUCTION
Automation and increased scale of operation in the food industry in recent
decades has led to an increase in the amount of raw materials. ingredients and food
products used in a more convenient granular form. At the same time handling bulk
solid materials is one of the least understood areas associated with solid processing
plants. An important part of powder production and processing is maintaining the
consistency of the product such that in-plant powder flow problems which could
effect packaging or the use of die-filling machine do not occur. Strength characteristics
of powders and flow behaviour are essential for better design of those type of
processes [6]. To explain the fundamentals of particulate solids consolidation and
flow behaviour a reasonable combination of particle and continuum mechanics are
frequently used. This behaviour depends on the nature of the acting binding
mechanisms at the contact areas among particles [8].
Jenike’s [5] publication is the best known work on determining the strength
and flowability characteristics using shear strength testing. This technique is the
most popular and widely accepted by researchers and knowledgeable practitioners
as a definitive mean of flowability characterisation. Eurocode 1 [3] recommends
using the Jenike shear tester to determine the strength of granular materials. The
objective of this study was to compare shear strength parameters of typical food
powders.
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