Worm gear

A worm gearbox is one of the classes of mechanical gearboxes. Gearboxes are classified by type of mechanical transmission . The gearbox is called a worm gear in the form of a worm gear , located inside the gearbox, transmitting and converting torque. The screw that underlies the worm gear looks like a worm, hence the name. The worm gear may be with one or more mechanical planetary gears.

In a worm gearbox, an increase in torque and a decrease in the angular velocity of the output shaft occurs due to the conversion of energy enclosed in high angular velocity and low torque on the input shaft.

An engine with an integrated worm gear is called a worm gear motor .

The most common single-stage worm gearboxes. With large gear ratios, either two-stage worm gears or combined worm-toothed or gear-worm gears are used. In single-stage worm gearboxes, the worm can be located under the wheel, above the wheel, horizontally on the side of the wheel and vertically on the side of the wheel. The choice of worm gear scheme is determined by the layout requirements. Worm gearboxes with the lower location of the worm are used at v ₁ <5 m / s, with the upper gear at v ₁ > 5 m / s. In worm gearboxes with a worm lateral arrangement, the lubrication of the vertical shaft bearings is difficult.

In worm gearboxes, more viscous oils are used to increase sticking resistance than in gearboxes. At sliding speeds V _ck <7 ... 10 m / s, the worm gears of the gearboxes are lubricated by dipping the worm or wheel in an oil bath. With the lower position of the worm, the oil level in the bath should pass in the center of the lower ball or roller of the rolling bearing, and the worm should be immersed in oil at about the height of the turn. If the oil level is set by bearings and the worm is not dipped in oil, then oil spray rings (impellers) are installed on the worm shaft, which supply oil to the worm and wheel. In worm gearboxes V _ck <7 ... 10 m / s, forced-circulation lubrication is used, in which the oil from the pump through the filter and the refrigerator is fed into the engagement zone.

In worm gearboxes, a worm gear is used. A worm gear consists of a screw called a worm and a worm wheel, which is a type of helical gear.

Worm gears belong to gear-screw. If in the gear-screw transmission the tilt angles of the teeth are taken so that the gear teeth cover it around, then these teeth turn into turns of the thread, the gear into a worm, and the gear from a helical gear to a worm gear.

In most cases, the leading link in the worm gear is the worm, and the driven link is the worm gear. Reverse transmission is often impossible - the efficiency of the worm gear in combination with the gear ratio causes the gear to self-lock.

The advantage of a worm gear compared to a helical gear is that the initial contact of the links occurs along a line rather than at a point. The angle of intersection of the shafts of the worm and the worm wheel can be anything, but usually it is 90 °. In contrast to the helical gear, the rim of the worm wheel has a concave shape, which contributes to a certain fit of the worm and, accordingly, an increase in the area of ​​contact surfaces. The direction and angle of the teeth of the worm wheel are the same as that of the threads of the worm. The thread of the worm can be single-start or multi-start, as well as right or left. The most common right-hand thread with the number of entries z1 = 1 ... 4.

There are two main types of worm gears: cylindrical, or simply worm gears (with cylindrical worms) and globoid (with globoid worms).

Compared to ordinary gears, the gear ratio (gear ratio) of the worm gearbox can be significantly larger. So, for example, with a single-start worm (z1 = 1) and a worm wheel with z2 = 100, the gear ratio is u = 100. With the same gear ratio, the worm gearbox is much more compact than an ordinary gear train . The possibility of implementing a large gear ratio with one gear stage, compactness, smoothness and noiseless operation are the main advantages of worm gear reducers. Due to these advantages, worm gears are widely used in hoisting-and-transport machines, various machines and some other machines. The worm gear ratio is usually taken in the range u = 8 ... 90, but in special installations it reaches u = 1000 or more.

In a worm gear, in addition to the transmitted power losses characteristic of a gear transmission, there are power losses characteristic of a screw pair . Consequently, the efficiency of a worm gear is much smaller, which is the main disadvantage of worm gears. The disadvantages also include the tendency of the threads of the worm and the teeth of the wheel to seize and the need to use expensive antifriction materials for the worm wheels. Because of these shortcomings, worm gearboxes are used much less frequently than gear reducers and only for transferring small and medium powers, usually up to 50 kW and less often up to 200 kW.

Due to its design, worm gear motors are characterized by smooth and quiet operation. The advantages of a worm gear motor can also include compactness - a worm gear motor will be significantly smaller in comparison with a similar gear motor with a gear with the same gear ratio. A characteristic feature of a worm gear motor is the self-braking property.

Worm gear motors have an output shaft arrangement deployed at 90 degrees, which is convenient when it is not possible (for example, in size) to locate the entire gear motor with a coaxial shaft arrangement.

• Worm-gear
• Mechanical gear
• Gearbox
• Gear motor

1. Guzenkov P. G. Machine Details: Textbook. for universities, - 4th ed. - M .: Higher. school, 1986
2. A. Ivanov. We construct the machines step by step, part two. - M.: Publishing House of MSTU named after N. E. Bauman, 2003

• Characteristics of worm gears