Gears helical

Screw Pumps A modification of the helical gear pump is the screw pump. Both gear and screw pumps are positive displacement... 

If an intermediate gear is necessary, some manufacturers use single helical gears provided with thrust collars on the pinion shaft, as shown in Figures 4-32 and 4-33. The thrust collars not only neutralize the... 

Figure 4-32. Method of axial thrust transfer in a single helical gear with thrust collar.

This standard API Standard 613 covers special purpose gears. They are defined as gears, which have either or both actual pinion speeds of more than 2900 rpm and pitchline velocities of more than 5000ft/min (27 meters/sec). The standard applies to helical gears employed in speed-reducer or speed-increaser units. 

Top entering mixers are heavy duty equipment. They are usually fixed to a rigid structure or tank mounting. Either radial flow or axial flow turbines may be used. Speeds vary from 50 to 100 rpm and usually require a double set of helical gearing or a single set of worm gears to achieve these low speeds. Therefore, they are more expensive than single reduction mixers. 

The bullgear design uses a direct-driven helical gear to transmit power from the primary driver to a series of pinion-gear-driven impellers that are located around the circumference of the bullgear. Figure 36.4 illustrates a typical bullgear compressor layout. 

In addition, the large helical gear used for the bullgear creates an axial oscillation or thmsting that contributes to instability within the compressor. This axial movement is transmitted throughout the machine-train. 

The helical lobe, or screw, compressor is shown in Figure 36.7. It has two or more mating sets of lobe-type rotors mounted in a common housing. The male lobe, or rotor, is usually direct-driven by an electric motor. The female lobe, or mating rotor, is driven by a helical gear set that is mounted on the outboard end of the rotor shafts. The gears provide both motive power for the female rotor and absolute timing between the rotors. 

Helical gears, which are shown in Figure 39.4, are formed by cutters that produce an angle that allows several teeth... 

Helical, double (also referred to as herringbone) Connects parallel shafts, overcomes high-end thrust present in single-helical gears, compact, quiet and smooth operation at higher speeds (1000 to 12,000 fpm or higher), high efficiencies ... 

The double-helical gear, also referred to as the herringbone gear (Figure 39.8), is used for transmitting power... 

The bullgear centrifugal compressor (Figure 44.7) is a multi-stage unit that utilizes a large helical gear mounted on the compressor s driven shaft and two or more pinion gears, which drive the impellers. These impellers act... 

Screw compressors have two rotors with interlocking lobes and act as positive-displacement compressors (see Figure 44.11). This type of compressor is designed for baseload, or steady state, operation and is subject to extreme instability should either the inlet or discharge conditions change. Two helical gears mounted on the outboard ends of the male and female shafts synchronize the two rotor lobes. 

The gear set should be monitored for axial thrusting. Because of the compressor s sensitivity to process instability, the gears are subjected to extreme variations in induced axial loading. Coupled with the helical gear s normal tendency to thrust, the change in axial vibration is an early indicator of incipient problems. 

Because a bullgear compressor incorporates a large helical gear, the shaft displays moderate to high axial... 

With the exception of helical gears, most gear sets should not generate axial or thrust loads in normal operation. However, at least one axial (Z-axis) measurement point should be placed on each of the gear shafts. The axial point should be located at the fixed, or thrust, bearing cap and oriented toward the gearbox. 

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