Cylindrical worm gear: The "invisible force" in mechanical transmission

I. Classification of Cylindrical Worm Gears

In addition to the common types mentioned above, various cylindrical worm gears have more subtle differences in structure and performance.

Archimedes worm gear The tooth profile on both the end face and axial section is an Archimedes spiral. This characteristic allows it to be processed on an ordinary lathe without complex specialized equipment. It is widely used in low-power, low-speed transmission scenarios, such as lifting mechanisms in small lifting equipment and feed systems in ordinary machine tools.

Involute worm gear Because the end face tooth profile is an involute, it has better meshing performance. During transmission, the tooth surface contact is smoother, with less impact and noise. Moreover, its processing precision is easier to ensure, and high-precision hobs can be used for mass production. It is suitable for occasions with high requirements for transmission smoothness, such as the transmission system of precision instruments and the transmission mechanism of high-speed blowers.

Normal straight-toothed worm gear (ZN worm gear) The tooth profile in the normal section is a straight line, and the end face tooth profile is an extended involute. This worm gear is also relatively easy to process and is suitable for medium-speed transmission. The characteristic of a straight tooth profile in its normal section makes the installation and adjustment of the tool relatively simple during processing. Its load-carrying capacity is slightly stronger than that of the Archimedes worm gear, and it performs well in some medium-load mechanical transmissions, such as the transmission part of textile machinery and the paper feeding mechanism of printing machinery.

Conical envelope worm gear (ZK worm gear) It is processed with a conical grinding wheel or tool, and the worm gear tooth surface is the envelope surface of the conical surface family. Its contact line has a larger angle with the direction of relative sliding speed, which is conducive to forming an oil film and has high transmission efficiency. The way its tooth surface is formed determines that it has excellent lubrication conditions. During transmission, the oil film is easier to form and maintain stability, which can effectively reduce tooth surface wear and improve transmission efficiency. Therefore, it is suitable for high-speed and heavy-load transmission occasions, such as the transmission system of large mining machinery and the rolling mill transmission mechanism of metallurgical equipment.

II. Working Principle of Cylindrical Worm Gears

Cylindrical worm gears and worm wheels constitute worm gear transmission. Its working principle is to drive the worm wheel to rotate through the rotation of the worm gear, realizing the movement and power transmission between two intersecting shafts (usually two perpendicular intersecting shafts). In the transmission process of cylindrical worm gears and worm wheels, the angle between the two intersecting shafts is usually 90 degrees, which is the most common case. Of course, it can also be designed into other intersecting angles according to actual needs, but it is less commonly used. The rotational motion of the worm gear is transmitted to the worm wheel through the friction and meshing force between the tooth surfaces, thereby achieving power transmission.

In terms of transmission ratio, the transmission ratio of worm gear transmission is equal to the ratio of the number of teeth of the worm wheel to the number of starts of the worm gear, i.e., i = z₂/z₁ (where z₂ is the number of teeth of the worm wheel, and z₁ is the number of starts of the worm gear). Since the number of starts of the worm gear is generally small, usually 1-4 starts, it can achieve a large transmission ratio. For example, a single-start worm gear and a 60-tooth worm wheel can achieve a transmission ratio of 60. This characteristic makes it very practical in occasions where speed reduction transmission is required, effectively reducing the speed and increasing the torque.

At the same time, worm gear transmission has self-locking properties. When the lead angle of the worm gear is less than the equivalent friction angle between the tooth surfaces, the worm wheel cannot drive the worm gear to rotate. This self-locking performance plays an important role in the safety protection of some lifting equipment, preventing the heavy object from falling automatically when the lifting stops.

III. Advantages and Disadvantages of Cylindrical Worm Gears

Advantages:

Compact structure: Compared with other transmission methods that can achieve a large transmission ratio, such as multi-stage transmission of gear reducers, cylindrical worm gear transmission has a more compact structure and saves installation space under the same transmission ratio. This is crucial for mechanical equipment with limited space, such as automotive steering systems and small medical devices.

Stable transmission The meshing of the worm and worm wheel tooth surfaces is continuous line contact, not point contact as in gear transmission. Therefore, during transmission, the impact and vibration are small, the noise is low, and the operation is smoother. It is suitable for occasions with noise requirements for the working environment, such as transmission mechanisms in office equipment.

Lower manufacturing and installation costs Especially for common types such as Archimedes worm gears, the processing technology is simple, and expensive special equipment is not required. Moreover, the requirements for the error of the center distance during installation are relatively low, reducing the installation difficulty and cost.

Disadvantages:

Low transmission efficiency Due to the large relative sliding speed between the tooth surfaces of the worm and worm wheel, the friction loss is serious, resulting in a transmission efficiency usually between 70% and 90%, which is much lower than the efficiency of gear transmission. In high-power transmission, it will cause significant energy loss and increase operating costs.

Large heat generation Because of serious friction, a large amount of heat will be generated during high-speed and heavy-load transmission. If the heat dissipation is not timely, it will cause the lubricating oil temperature to rise, the viscosity to decrease, increase tooth surface wear, and even affect the normal operation of the transmission. Therefore, good heat dissipation devices, such as heat sinks and cooling fans, need to be equipped.

Worm wheel is prone to wear Worm wheels are usually made of non-ferrous metals such as bronze, while worm gears are mostly made of steel. During transmission, the worm wheel tooth surface is subjected to large friction, which is prone to wear, thus affecting the transmission accuracy and service life. Regular inspection and replacement of the worm wheel are required.

IV. Installation and Maintenance of Cylindrical Worm Gears

Installation points During installation, the center distance of the worm and worm wheel must be accurate, and the intersecting angle of the axes must meet the design requirements, otherwise it will cause poor tooth surface contact and increase wear. At the same time, the meshing clearance of the worm and worm wheel should be adjusted. Too large or too small clearance will affect the transmission performance. Too large clearance is prone to impact and noise, while too small clearance will increase friction and heat generation.

Lubrication and maintenance Appropriate lubricating oil must be used; high-viscosity gear oil is generally used to ensure a good oil film between tooth surfaces, reducing friction and wear. Regularly check the oil level and quality; replenish when insufficient and replace when the oil quality deteriorates.

Regular Inspection Regularly inspect the worm and worm wheel for tooth surface wear, tooth thickness changes, and bearing operating conditions. Repair or replace parts as needed to ensure normal operation of the transmission system.

V. Expanded Application Scenarios of Cylindrical Worm Gears

In addition to the applications mentioned above, cylindrical worm gears are widely used in other fields. In agricultural machinery, such as the power take-off shaft drive of tractors and the conveying mechanism of harvesters, its large transmission ratio and compact structure are used to achieve efficient power transmission. In construction machinery, such as the transmission system of concrete mixers and the slewing mechanism of tower cranes, cylindrical worm gears can also be found. In addition, some precision transmission components in medical devices, such as the adjustment mechanism of X-ray machines and the transmission system of surgical instruments, also use high-precision cylindrical worm gears.

With the continuous development of industrial technology, the performance requirements for cylindrical worm gears are also becoming increasingly higher. By adopting new materials and new processes, such as using high-strength alloy steel for worm gears and surface hardening treatment, and using new wear-resistant alloy materials for worm wheels, the transmission efficiency, load-carrying capacity, and service life of cylindrical worm gears are continuously improved, allowing them to play a role in more high-end fields.