1.
Spiral groove depth
The depth of screw
groove is an important parameter of the twin - screw extruder. Usually it is
expressed indirectly by the ratio of screw diameter and screw root diameter.
The value is an important parameter to indicate the technical level of the twin
screw extruder. At present, the ratio of the external diameter of the screw to
the root diameter of the screw in the latest generation (sixth generation)
coaxial twin-screw extruder represented by WP of Germany is D/Di = 1.55.There
are many factors limiting D/Di, in addition to the center distance of the
gearbox output shaft of the driving screw, the screw itself also has a greater
impact on D/Di: such as the shear resistance of the screw mandle-shaft, the
torque transfer mode between the screw element and the mandle-shaft, the
structure of the screw element itself, etc.
(1)
The breakthrough in material
selection, processing technology and heat treatment performance of mandrel
makes the torque capacity of mandrel bearing greatly improved, and the
length-diameter ratio of screw increases from the initial 36 to 50, or even
higher.
(2)
The technological breakthrough
of the special gear drive system of the co-directional twin-screw extruder
provides the power transmission guarantee for the torque input required by the
deep groove screw under the condition of the constant center distance, making
the screw D/Di goes to 1.55.
(3)
The torque transfer mode
between screw and mandrel is the key to realize the deep screw groove. The
torque transfer between the screw element and the mandrel was initially connected
by flat keys, which not only limited the deepening of the screw groove and
increased the free volume of the screw, but also the strength of the flat keys
could not meet the requirements of some production operations. Using multi -
key torque transmission in the form of involute can greatly improve the depth
of the screw groove under the same outer diameter of the screw. In recent
years, while learning from foreign advanced technologies, China has made great
breakthroughs in processing and manufacturing. At present, it has been able to
manufacture involute spline structure with the same connection form with
foreign screw, thus making great breakthroughs in the depth of screw groove.
(4)
The breakthrough of element
structure. The structure of the kneading block solves the key technology of
manufacturing, its structure changes from the original single piece type, the
assembling type to the present integral type, thus guarantees the deepening of
the screw groove from the strength of the element, also makes the adjustment of
the screw combination and the assembly of the screw more reliable and
convenient.
To sum up,
breakthroughs in the aspects of gear transmission system, shear strength of
mandrel, torque transmission form of screw element and mandrel, and design and
manufacture of screw element ensure the successful development of a new
generation of high-speed and deep screw slot extruder.
2.
New screw element
Synthetic twin screw
extruder is the core part of the screw, after the advent of synthetic double
screw extruder, and development of screw and screw element has always been a
developer research and the main direction, screw structure from the integral
development early to "building block", three thread from single head
to head, later when the double structure, type of screw elements, structure and
function differences. Develop self-cleaning type mixer type screw element, edge
type mixer type screw element, toothed screw element, pressure regulating screw
element, etc., of the twin screw extruder screw element made greater
innovation, supplement and perfect, strengthen and improve the direction of the
twin screw extruder mixing and plasticizing effect, dispersion, shear,
pressure, and adjustable.
3.
Gear box torque rating
parameters
The torque grade
parameter M/A3 of the gear box is an important performance indicator parameter
of the coaxial twin-screw extruder. Its value represents the technical level of
the coaxial twin-screw extruder and represents the torque output capacity of
the gear box under a certain screw center distance. Due to the particularity of
the transmission form of the coaxial twin-screw extruder, the torque of the
gear is input into the gear box by a high-speed shaft. Through deceleration and
torque distribution, the torque is transmitted to the twin-screw by two output
shafts with limited center distance under the condition of great axial force. Therefore,
the ratio parameter M/A3 between the center distance of the output shaft and
the output torque has become an important symbol to measure its technical level.
So the design of gear box of twin screw extruder is very difficult compared
with the design and development of general gear transmission system. At
present, China has made great breakthroughs in gear transmission mode, torque
uniform distribution and axial force solution. The torque grade parameters of
the experimental extruder have been changed from 4.Seven goes up to eight.8. It
lays a good foundation for the development of high speed and high torque gear
box of production extruder.
In terms of the
service life of the gear box, by improving and driven by new type of
multi-channel way, not only greatly improve the transmission capacity, and
through the reasonable arrangement of the axis, solved the gear and thrust
bearing load distribution, greatly reduced the gear drive and work process of
the additional force, making long-term restricting the service life of the gear
box of the anti-fatigue performance of the gear, thrust bearing system
performance are greatly improved, after adopts multiplex drive, output the
stress of the bearing diameter of axle direction decrease greatly, therefore,
in many ways to improve the gear, the thrust bearing system, the torque
distribution part of the bearing service life, Designed life up to 10 a.
4.
Screw speed
Screw speed is
another important parameter to measure the performance grade of the extruder
with the same direction and it is an important way to improve the performance
index of the extruder. It directly affects the torque grade parameters and
production capacity of the equipment. The screw rotation speed increase mainly
depends on the innovation and development of gear transmission system drive,
the ability of the screw torque under and anti-fatigue performance, by
developing a new type transmission way and optimize the innovation design,
selection of key parts imported bearing, means, the strict screening of screw
spindle materials and the improvement of heat treatment process, and the screw
element and spindle, involute spline breakthrough made in the form of uniform
stress distribution, making it possible to screw rotation speed increase, has
been in a small high-speed experimental synthetic twin-screw extruder machine
through industrial test.
5.
Production capacity
The technical level
and performance of the equipment are aimed at improving production capacity,
reducing energy consumption and improving reliability. Production capacity is
the main factor to evaluate the performance of a unit:
(1) improve the screw
speed, the same type of production can be doubled;
(2) the use of deep screw
groove screw, increase the screw free volume, improve the unit speed and unit
time transport capacity;
(3) the use of twin screw and gear pump combined
technical route, improve the reliability of the transmission box, reduce the
axial force borne by the gear, eliminate the limit of the axial force to reduce
the output of the factor, improve the output of the extruder.
