Gears types

FIG. 10-54 Positive-displacement gear-type rotary pump. 

Couplings are a very eritieal part of any turbomaehinery. They must be earefully designed and proper lubrieation must be applied. The most eommon methods of lubrieating gear-type eouplings are (1) grease-paeked, (2) oil-filled, or (3) eontinuous oil flow. 

Flexible element couplings tend to be somewhat heavier than the comparably rated gear coupling. On a retrofit, heed the earlier warning about lateral criticals. The coupling can handle axial misalignment but is more restrictive than the gear type. 

The coupling is required to have a no more than M-inch end-float ul a gear type). 

Type and specifications on fan driver, gear types, pow er voltage, phase, cycles. Motors should at least meet specifications equivalent to totally enclosed, fan cooled, or if in explosive hazardous area, TEFC Class I, Group D (except this not acceptable in hydrogen or acetylene atmosphere). Due to moisture conditions around this equipment, it should be protected against moisture penetration and corrosion. 

There are several different types of gears used in industry. Many are complex in design and manufacture and several have evolved directly from the spur gear, which is referred to as the basic gear. Types of gears are spur, helical, bevel, and worm. Table 39.1 summarizes the characteristics of each gear type. 

Despite its demand for special lubrication, this gear type is in widespread use in industrial and automotive applications. It is used extensively in rear axles of automobiles having rear-wheel drives and is increasingly being used in industrial machinery. 

In positive lubrication systems, a gear-type pump is normally used to provide positive circulation of clean oil within the compressor. In some cases, the main compressor shaft directly drives this pump. In others, a separate motor-driven pump is used. 

Gear couplings When properly installed and maintained, gear-type couplings do not generate a unique forcing function or vibration profile. However, excessive wear, variations in speed or torque, or over-lubrication results in a forcing function. 

The lubrication requirements of gears vary considerably and create the need for specifically formulated products. This, combined with the diversity of automotive and industrial gear types, has led to the introduction of several specifications for gear lubricants (see Figure 52.7). 

Gear type Characteristics Attributes/Positives Negatives... 

Straight bevel gears, also known as plain bevels, are the most commonly used and simplest type of bevel gear (Figure 57.15). They have teeth cut straight across the face of the gear. They are recommended for peripheral speeds up to 1,000 feet per minute in cases where quietness and maximum smoothness are not cmcial. This gear type produces thmst loads in a direction that tends to cause the pair to separate. 

Table 57.2 provides a comparison of the approximate efficiency range of various gear types discussed in this chapter. 

All gear types are comprised of common gear tooth elements, which can be defined in terms of measurements and dimensions (linear, circular, and angular), and ratios. 

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