GENERAL COMMENTS
While handling and processing coal and other bulk solids,
transfer points are used to change the momentum of the
material flow writes Carlos Alberto Llanes Leyva – Professional
Mechanical Engineer – Master of Science and Marcio Bomfim
Dessaune – Professional Mechanical Engineer – CREA 8757/D - MG.
Transfer points usually consist of belt conveyors, chutes, silos,
transfer houses, etc. The transfer should be properly designed to
centralize the unloading of the material over the receiving belt,
to reduce the wear of the chute wall and the degradation of the
material handled, and to avoid plugging, fugitive material and dust
generation. Chutes often require complex tri-dimensional
geometry with customized design in order to control the flow
velocity.
Braco Consultant and Selpeco Resources are sister
companies focused on material handling. This work describes
some of the design capabilities of these companies, by reviewing
the concepts and technologies involved in the modern design
process of transfer points.
 
OPERATIONAL PROBLEMS DUE TO POOR TRANSFER DESIGN
Poor transfer point design may be a major cause of several
operation and maintenance problems (and their related
costs) in material handling facilities:
plugged chutes, material spillage, dust generation, belt damages,
accelerated belt and chute wear, etc.
Braco Consultants and Selpeco Resources take advantage of
the state-of-the-art theoretical basis for flow analysis and chute
design, the know-how developed from practical experience of its
engineering team for decades, as well as the modern tools for
computational modeling and simulation of material flow.
In addition to lab test, some fundamental equations have been
described in technical literature for assuring free flow in chute
design. In curved chutes design, special care must be taken in
determining the critical cut-off angle, i.e: the angle from chute
tangent at discharge to horizontal. The proper choice of cut-off
angle will assure that the chute is ‘self-cleaning’ so no material
build-up happens when stopping and restarting the operations.
The impact angle of material flow on the deflecting plate is also
very important, as well as the chute valley angles.
Braco Consultants and Selpeco Resources make intensive
usage of computer aided design via CAD/CAE tools. After a
preliminary layout based on design experience and fundamental
models, the engineered concept comes from a 3D mock-up built
in parametric software. The 3D mock-up goes through an
optimization process in specific software for flow simulation of
bulk solids. The optimized model goes back to the detailed
design process, and a complete detailed 3D model is used to
generate the final 2D shop drawings, or even the 3D model of
specific parts for CAM manufacturing. Fig. 3 illustrates a typical
design case.
Additional computer-based tools are used for Finite Element
Analysis (FEA), structural calculation, belt conveyors design, etc.
They help through the calculation and dimensioning of structural
members and mechanical components. For instance, an actuator
can be properly specified after the deflector inertia is found
from the 3D model and the impact force has been calculated
from flow simulation; then FEA analysis of the actuator arm and
supports can be conducted, etc.
This approach allows for better design reliability and short
time-to-market.
 
CONCLUSIONS
Despite the fact that the modern design process takes important
advantage of computer based design tools, the designer’s
expertise is the key-aspect for a successful design. In Braco
Consultants, great value is given to the past experience and
know-how of both its engineering team and the client, from the
first concept of the transfer point to the final analysis and
discussion of the detailed model.