Both were strong enough. The elongation at the brealting point of the modified type was varying little and was large totally against the conventional type. Fig.7.6 shows the creep properties of both materials. As shown in the figure, the creep rupture elongation and the minimum creep velocity of the modified type are larger than it of the conventional type. Also, as a result of the creep test using a test piece with a notch, lifetime of the conventional type is reduced in this case but one of the modified type becomes longer.
Consequently, it has been clear that the new forging process impeller has excellent creep ductility and high notch-creep rapture strength. By this means, life improvement of the impeller for centrifugal compressors has been achieved.
7.4 Development of Mono-Screw Pump Integrated with Motor4)
HEISHIN ENGINEERING & EQUIPMENT Co.,Ltd. has developed the new "NY Series" mono-screw pump (called Mohno pump in Japan) integrated with a motor, it is able to be more compact than the conventional models which are direct-coupled to a drive unit or driven by a V-belt. Its installation space is reduced about 20% on the basic type or further more on the vertical type than that of the conventional models. The drive unit of it is made use of the constant speed geared motor or the variable speed inverter motor. Fig.7.7 shows the basic construction of mono-screw pump.
The heart of mono-screw pump is made up of simplified / high-reliability rotor and stator. It is an eccentric screw pump with single rotor which is one of rotary displacement type. The rotor, which is corresponds to a male screw, is made of metal, of which cross section is a perfect circle at any point, while providing unique twisting angle created by dedicated cutting machine. It is set in the stator with ellipse female screw. The stator is made of elastic material, and used to envelope the rotor closely. When the rotor is assembled in the stator, a spiral and continuous space is generated between the rotor and stator, which is strictly sealed by the contact line. When the rotor is turned at the eccentric shaft center through the drive shaft and universal joint, it is moved reciprocatedly at any section, while it is turning in the stator. As a result, the liquid filled in the space volume is transferred from the suction side to the discharge side quantitatively without pulsation by the infinite piston motion as shown in Fig.7.8. The fish mark in this figure designates the spiral space which is moving from the suction side to the discharge side.
The main performances of mono-screw pump are as follows: 1] It is possible to ensure the constant discharge quantity without pulsation all the time as long as the rotating speed remains constant. It is possible to secure the flow rate control range of 1:100 or over using the steppless speed change inverter motor and so on. 2] Mono-screw pump makes it possible to transfer the materials from the watery liquid to high-viscosity/ high-concentration liquid, slurry, liquid containing air bubble, and micro powder.
