Dragon Manufacturing and Automation Gears Co., Ltd.
Ask DMAG for any inquiries about gear pump and extrusion system
Mimuro 2607-9, Midori-ku, Saitama-shi, Sitama, Japan
What is a GEAR PUMP？
◎A gear pump is rotating positive-displacement pump.
◎A gear pump is used to transport a high viscosity
liquid with high pressure.
◎A gear pump, which works in the same volumetric efficiency as a diaphragm pump and a piston pump, enables a continuous transportation in a non-fluctuation flow.
◎From small as laboratory to big as commercial production, gear pump works for transportation of high viscousviscosity liquid, such as molten polymer, elastomer, adhesive, hot melt and etc.
◎Application of gear pump = Pressurizing, Transporting, Metering (Accurate steady flow)
At a suction side of a gear pump, the space between each gear tooth creates vacuum by an opening of gear teeth meshing. And liquid goes into space between each gear tooth by this vacuum and suction pressure.
At a suction side of a gear pump, vacuum
Liquid between gear teeth rotate along the housing’s wall and is transported from suction side to discharge side.
Liquid is discharged through meshing gear teeth and transported to ejection outlet.
Function of gear teeth
Inside of gear pump
1. Gear shafts are turned and transported liquid from suction side to discharge side by driving unit, and this transportation generate the pressure at discharge side.
2. Gear shafts, which generate discharge pressure, are supported by bearings.
3. Gear teeth, shafts and bearings work in the transported liquid, and are lubricated by transported liquid.
4. The pressure, which rotating gear shaft creates between suction and discharge sides, makes back-flow of liquid which rubricate shaft, gear teeth, bearing, and which is at the gap between gear side and bearing. And a large amount of the back-flow decreases volumetric efficiency as a result.
Volumetric Efficiency of GEAR PUMP
Transported amount by gear（liter/min）
Actual transported amount （liter/min）
Transported amount by gear（liter/min）
Transported amount by gear （liter/min）
Back-flow in pump（liter/min）
Transported amount ＝
Specific volume(cc/rev)× pump’s speed(rpm)
Functions of gear pump
Functions of extruder line are categorized into melting, mixing & kneading, pressurizing, metering, filtering, and sharping of polymers.
EAlthough each equipment has some overlapping functions, the extruder line is able to be constructed productive and effective in case of combining and maximizing superior functions of each equipment.
Function of each equipment
Extruder : Melting function, mixing & kneading function,
pressurizing function, metering function
Gear pump : pressurizing function, metering function
breaker plate ：Filtering function
Die : Shaping function
Comparison of conventional gear pump and DEX-GP gear pump :
With the increasing pressure from 110 to 130 Bar, conventional gear pump 7% decrease in volumetric efficiency, while DEX-GP gear pump experience less than 1 % decrease.
Proposal by DMAG
DEX-GP gear pump, which is 5 times superior than the extruder main unit in volumetric efficiency, should serve a function of pressurizing primarily, and the whole of the extruder line should be configured totally-balanced in efficiency.
Conventional gear pumps have no applicability of putting more than 100 Bar of pressure, due to the tendency to decrease volumetric efficiency significantly. (Refer to Fig. 1)
Original design of DEX-GP gear pump can perform more than 90% volumetric efficiency at pressurizing more than 150 Bar.
(DEX-GP gear pump is designed based on the “Watanabe Theory”, whose pump is considered with the all shapes of pump in the details and is determined the shape, tolerance and clearance.)
DMAG’s Technical Proposal
(1) To adopt DEX-GP gear pump
(2) To install screen changer on the down-stream of gear pump
(3) To make functions of extruder main unit specialized only in melting
and mixing & kneading.
(i) To maintain inlet pressure configuration of 30 bar or less for the gear
(ii) To change the design of extruder’s screw only for melting, mixing
(iii) To adopt smaller L/D design of the extruder
(4) To take the PID values and control parameters for extruder speed in
order to be run the very stable rpm.
There are many cases that screen changers have been installed on the upper stream,
because conventional gear pumps are not good at pressurizing more than 100 Bar.
However DEX-GP can perform good more than 90% volumetric efficiency at pressurizing
more than 150 Bar.
Fig. 2 & 3 indicate pressure and temperature of the polymer at the extruder line in case that screen changer is installed at the upper and downstream of gear pump.
The extruder’s pressurizing ability is not good, so the pressurizing by extruder for screen changer causes additional friction energy.
And to increase the extruder’s speed for necessary discharge pressure for extruder causes to go up polymer temperature and same time to make lower the polymer viscosity. So additional extruder’s speed-up is required. These are caused the fluctuation of extruder’s discharge pressure.
In the detail description, to increase extruder’s screw speed for pressurizing makes to create the friction energy, not only at pressurizing zone, but also at mixing & kneading zone, all together. The results are polymer’s temperature-up.
However screen changer is installed on the down-stream of gear pump, and the setting 30 Bar suction pressure of gear pump can make inhibit the polymer temperature-up and make stable polymer viscosity. And, at this condition, suction pressure of gear pump can use for speed control for extruder in more directly. The results are that DEX-GP gear pump can work in the stable condition of polymer and can pressurize and meter in a stable.
Fig.3 S/C’s installation on the down stream of G/P
Fig.2 S/C’s installation on the upper stream of G/P
Another meaning of optimized volumetric efficiency
Above Figure 1 is the comparison of performance between DEX-GP gear pump and conventional gear pump. Note:Performance of conventional gear pumps are assumed by some experiences.
The difference of volumetric efficiency between conventional gear pump and DEX-GP gear pump is more than 20% at 120 Bar difference pressure. DEX-GP gear pump can be operated 30% smaller rpm and 40% smaller friction energy in the pump.
There are many cases that the conventional gear pump, whose combination is installed screen changer in the upper stream of gear pump, must be selected one size bigger, even if the pressurizing amount of the conventional gear pump is smaller than that of DEX-GP gear pump.
And the resistance value of screen changer is changed. To say other words, the discharge pressure of gear pump changes 20 Bar from 110 Bar to 130 Bar, the meaning of 20 Bar difference of discharge pressure indicates the difference of volumetric efficiency of each gear pump, which is same meaning of difference of discharge volume.
The results are that DEX-GP gear pump is only less than 1% difference of volumetric efficiency, but the conventional gear pump is more than 7% difference of volumetric efficiency. This difference is that the conventional gear pump must be adjusted the pump’s speed.