Double helical gearing

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

Fig. 6.39 Double helical gears. [Photograph courtesy of Farrel Corp., Ansonia, CT.]...

Double-helical gears Gears have both right-hand and left-hand teeth on each gear. The teeth are separated by a gap between the helices (Fig. 5.19). Where there is no gap, they are known as herringbone gears. 

Gears, wherever used, can be a major source of problem and downtime. This standard specifies the minimum requirements for special-purpose, enclosed, precision, single- and double-helical one- and two-stage speed increasers and reducers of parallel-shaft design for refinery services. Primarily intended for gears that are in continuous service without installed spare equipment. These standards apply for gears used in the power industry. 

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. 

A double-helical design should be considered, particularly for critical service. Rotation of the helices should be such that they will be apex leading, that is, teeth engage at the centers with mesh progressing to the tooth outer ends. Additionally, rotation should permit the force from the gear mesh to cause the gear to load the lower half of its bearings. The... 

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 ... 

FIGURE 5.27 Double-reduction helical gear drive. (Flender Corporation.)... 

FIGURE 5.31 THple-reduction spiral bevel-helical FIGURE 5.32 Shaft-mounted double-reduction gear gear drive. (Falk Corporation.) drive. (RockwellAutomation.)... 

Y14.7.1-197KR1998) Gear Drawing Standards— Part 1 For Spur, Helical, Double Helical and Rack... 

Fig. E6.16 Output versus gear frequency of rotation for a 5.6-in-diameter 4.5 in wide, double (30°) helical, 14-teeth 0.67-in-deep gear pump, and with LDPE (circles) and PS (triangles). Smooth curves are the theoretical ones at the respective densities. [Reprinted with permission from C. Y. Cheng, Farrel Corp., Ansonia, CT, private communication, 1972.]...

Figure 13.21 presents the picture of the dielectric ellipsoid orientation within each unit cell that is at the nanometer scale. The weak molecular chirality results in additional weak twisting of all structures with characteristic pitch of about Po 0.1-1 pm. An example of a such twisted structure is shown in Fig. 13.22 it is an antiferroelectric double-layer cell describing two geared helices upon rotation about z-axis. The helices are shifted in phase by (p = 7t and have the same handedness. On the molecular scale, due to molecular chirality, the c-director turns from layer to layer by a small angle 5cp = 2nllPo, therefore, for / Inm,... 

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