PRODUCTION AND EQUIPMENT
EXPERIENCE FROM COMPUTER DESIGN
AND SELECTION OF THE GEOMETRY OF THE FORMING SURFACES
OF A TOOL FOR DRAWING OF ROD BILLETS ON SCREW EXTRUDERS
G. V. Perel’man
Translated from Novye Ogneupory, No. 2, pp. 9 – 17, February, 2012.
Original article submitted November 29, 2012.
Alternative applications of a mathematical model of the process of drawing of ceramic materials for computer
design of molding tools with diaphragms for screw extruders are proposed. A technique of determining the pa
rameters of the plasticity function of molded materials and the friction coefficients of the material against the
surface of the tool with the use of production equipment is developed. Flow conditions of materials through
different types of tools the working molding surfaces of which are upright are analyzed. It is shown how vary-
ing the form of the surface of a channel, the drawing ratio of material in the zone of local reduction in the chan-
nel cross-section, and the cross-sectional area of the billets enables selection of an optimal combination of
these factors for the drawing process.
Keywords: screw extruder, diaphragm, extrusion, stress, mathematical model, optimization
Problems related to molding of billets of required overall
dimensions and shape and to partial or complete welding
with large and small defects in the structure of material, as
well as to the creation of textures that extend along the axis
of the article (since such textures possess the best strength in
dicators in the elements of structures that function under con
ditions of tension (compression) and flexure) are solved in
the course of extrusion processes.
The use of such highly efficient equipment as screw ex
truders (Fig. 1a ) significantly complicates the problem of
creating a high-quality uniform structure across the entire
cross-section of oblong billets. The material in the screw
channel of an extruder travels along the helical surface of a
rotating screw conveyor as a female screw, hence it is present
in the molding channel of the tool in the form of a
thick-walled “tube” (Fig. 2a ) the central cavity of which is
filled with material as the tube is pressed through the con
verging channel of the tool due to axial (subsidence) and ra
dial compression of such a “two-layer” cylindrical aggregate.
Welding of the defect zone of the material in the central cav
ity of the billet in particular always remains a critical prob
lem for all shops that utilize screw equipment. This naturally
follows from the fact that such flaws in articles as S-shaped
cracks, burrs, cross cracks, etc. (Fig. 2b, c) which are the re-
sult of the shrinkage gradients that arise in the operation of
the billet’s thermal process stages are a direct consequence of
the gradient of the structural and texture characteristics of the
material in extruded billets.
Experience has shown that a drawing ratio of the mate
rial (ratio of cross-sectional area of extruder to cross-sec
tional area of billet) of 4.5 – 5.0 is needed to achieve good
compaction of the central zone of the material, the diameter
of which is specified by the diameter of the “body” of the
worm feeder (38 – 43 hundredths of the diameter of the ex
truder) when molding billets from highly plastic materials.
But high-quality molding of billets from nonplastic bodies is
possible only with drawing ratios of 7 or higher. This places
a substantial limitation on the overall dimensions (dimen
sions of cross-sectional area) of rod-like billets that are
molded on screw conveyors as well as requiring significant
compacting pressures with such drawing ratios.
A shop is generally interested in reducing the gage of the
existing equipment and in its efficient use by expanding the
range of articles fabricated on each extruder. The latter in
cludes the possibility of increasing the overall dimensions of
Refractories and Industrial Ceramics Vol. 54, No. 1, May, 2013
1083-4877/13/05401-0017 © 2013 Springer Science+Business Media New York
FGAOU VPO Moscow Lomonosov State University, Moscow,