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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 “Watanabe Theory” ?

“Watanabe Theory” considers shear-rate of back-flow speed for the estimating polymer viscosity inside of gear pump. The shape of DEX gear pump has been designed based on “Watanabe Theory” and DEX gear pumps has achieved over 95% volumetric efficiency of PS polymer at pressuring between 150 and 180 Bar.





Molten polymer, whose viscosity decrease with the increasing shear rate, are Non-Newtonian fluid. Polymers such as PS, PE, PP, PMMA. are shear-sensitive polymer, and those viscosities decline drastically as the shear rate increase.







                 ると急激に移送効率の低下がみられ、ポンプの効                 率計算結果と実際の運転結果に大きな差が出てい                 ました。



                                                  これは、図-2のように溶解樹脂がギアポン                   プ内部の隙間から逆流する為であり、逆流                    する流速に従って見かけ粘度が低下した結                    果です。つまり、ギアポンプ内部で逆流 が                   発生すると、逆流速度に従ったシアレート                    に粘度が低下していき、更に、粘度が低下                    するからまた逆流量が増加し、逆流速度が                    増します。そうして、この見かけ粘度の低                    下現象は、あるシアレートまで続きます。この粘度特性を理解して、ギアポンプ内部での逆流量を最小になるようにポンプ形状を工夫したポンプが、「渡辺理論」を適用したポンプです。






(Figure- 3)

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.


図-3 従来型ギアポンプとDEX-GPポンプの吐出量変動幅を比較した事例
図-2 ギア速度を考慮した剪断速度

図-2 ギア速度を考慮した剪断速度

図-1 従来の剪断速度の考え方

図-1 従来の剪断速度の考え方

As Fig.1 shows, the conventional calculation of pump’s performance only considers shear rate of gap S and gear face speed. However, there used to be a greart difference in results between conventional way and actual practice of gear pump's performance due to the rapid decreases in volumetric efficiency at pressuring over 100Bar, in case of tranferring shear-sensitive polymers.

Refer to Fig.2. This differrence occurs due to the increasing   back-flow amount of molten polymer through the gaps inside of gear pump, and the polymer viscosity decreases with the increasing back-flow speed. The back-flow occurs inside of gear pump, and the polymer viscosity decreases according to the shear rate of back-flow speed, and the back-flow increases with the decreasing viscosity. And the polymer viscosity continues at a certain shear-rate . 

DEX gear pump, based on Watanabe Theory, has been designed in consideration of the  viscosity characteristic to minimize the back flow within the gear pump.


As shown in figure 3, optimizing volumetric efficiency results in different running efficiency of gear pump itself, and it enables to keep the stable flow rate against increasing resistance of discharge side as well. Under pressuring over 100Bar discharge, conventional gear pump cannot be operated since the flow rate show a steep decline, however, DEX-GP pump is able tobe in proper working order with little decline in volumetric efficiency.


This means that screen changer can be installed downstream of DEX-GP gear pump with keeping high volumetric efficiency and needs less filter replacement in addition.



DMAG deals with a various kinds of components for extrusion system and internally-designed gear pumps, and provide maintenance service.


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Dragon Manufacturing and Automation Gears Co., Ltd.


Mimuro 2607-9, Midori-ku, Saitama-shi, Sitama, Japan



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