Cylindrical worm gear: The "all-arounder" in mechanical transmission
Classification： Blog
Release time：2025-08-08
In the large family of worm gear drives, cylindrical worm gears are definitely the most "popular." Its worm is a common cylindrical shape, and the tooth surface of the worm gear is like a special shape surrounded by a circle, which can perfectly mesh with the cylindrical worm, silently undertaking the transmission task in various machinery.
Let's talk about the "family members" of cylindrical worms. Classified by tooth profile shape, the Archimedes worm (ZA type) is considered an "entry-level model." The tooth profile in its axial cross-section is a straight line, making it easy to process. However, its transmission efficiency is slightly lower, suitable for light-load, low-speed ordinary occasions, such as some simple small machinery. The involute worm (ZI type) is the "precision type." The end face tooth profile is an involute, making the meshing particularly smooth and efficient. It is indispensable in places with high precision requirements, such as machine tool indexing mechanisms. The normal straight-toothed worm (ZN type) is between the two. The normal cross-section is a straight-line tooth profile, the processing is not troublesome, and the performance is relatively balanced. There is also the conical envelope worm (ZK type), which is ground with a conical grinding wheel. It has a large tooth surface contact area, like a natural "strongman," and is indispensable for heavy-load transmission occasions.
The structure of the worm gear is also important. The integral worm gear is a representative of "small and complete." It is suitable for places with small size and light load. The material is generally bronze or cast iron, which is light and durable. The composite worm gear is more "cost-effective." The rim uses wear-resistant tin bronze, and the hub uses cast iron or steel, ensuring wear resistance while reducing costs, making it the "king of cost-effectiveness."
The transmission characteristics of cylindrical worm gears are very distinct. Its transmission ratio is particularly large, reaching 5 to 100 in a single stage. It is small but can achieve large speed reduction, saving space. Even better, it has the ability to "self-lock." When the worm lead angle is less than the friction angle, the worm gear cannot drive the worm, like an installed "safety lock." Hoists and winches that need to be fixed in position rely on it to ensure safety. However, it also has minor drawbacks. The large sliding friction results in relatively low efficiency, usually between 40% and 90%, which particularly tests the matching of lubrication and materials. Fortunately, it can mesh with multiple teeth simultaneously, making it run smoothly with low vibration and noise, making it a "quiet worker." In addition, the axial position of the worm and worm gear is particularly important. Accurate positioning is required during assembly, otherwise it will affect the meshing effect.
Among the parameters that determine the performance of cylindrical worm gears, the module (m) is the "size," which must be selected according to the standard, and the size of the teeth is determined by it. The number of worm threads (z₁) is like a "speed control knob." A single-thread has a large transmission ratio but low efficiency, while multiple threads have high efficiency but a small transmission ratio. The selection should be matched according to the needs. The number of worm gear teeth (z₂) is generally not less than 28, otherwise it is easy to "damage the teeth"—undercutting will occur. The lead angle (γ) affects the "flexibility" and "self-locking force" of the transmission. It is calculated by the formula γ=arctan(z₁/q) (q is the worm diameter coefficient). The angle size needs careful design. The center distance (a) is the "distance code" between the two, calculated by a=m(q+z₂)/2, ensuring that they can mesh accurately.
In terms of material selection, the worm and worm gear are like the "best partners." For high-speed and heavy-load occasions, the worm is selected as 45 steel (quenched and tempered) or 40Cr (quenched), and the worm gear is matched with tin bronze ZCuSn10P1, which is wear-resistant and durable; for medium-speed and medium-load occasions, aluminum bronze ZCuAl10Fe3 and quenched 40Cr are suitable; for low-speed and light-load occasions, cast iron HT200 and carburized and quenched 20CrMnTi are economical and practical.
However, cylindrical worm gears can also be "temperamental." High-speed, heavy-load, and poor lubrication can cause the tooth surfaces to "stick" together, resulting in adhesion; dust entering or insufficient lubricating oil will damage the tooth surface; long-term stress can also cause pitting, like small pits on the face; overloading or impact can even cause tooth breakage. Fortunately, there are solutions to these problems: "strengthening exercise" for the tooth surface (worm quenching, worm gear using bronze), using extreme pressure lubricating oil with sulfur and phosphorus additives for "maintenance," and adding a "small fan" (forced lubrication or air cooling) for high-power transmission can allow it to work properly.
Its application fields are everywhere. The indexing head and rotary table of machine tools rely on it for precise rotation; the self-locking property of cranes and lifting mechanisms ensures safety; there are also its figures in automotive steering mechanisms and wiper drives; robot joints and conveyor speed control devices are inseparable from its cooperation.
Compared with other worm gears, cylindrical worm gears are superior in their "down-to-earth" nature. Annular worm gears have high load-carrying capacity but complex manufacturing, suitable for heavy machinery; variable lead worm gears can adjust the transmission ratio or eliminate backlash, but they are difficult to process and are mostly used in precision occasions. Cylindrical worm gears have a simple structure and low cost. Although their efficiency is not top-notch, they can meet the needs of most general transmission requirements, making them "all-around players."
During design, just remember a few key points: lubrication is the "lifeline," giving priority to oil bath or pressure oil spray lubrication; do not let it "work hard" under low-speed and heavy-load conditions, as it is easy to wear; high-power transmission needs to do a good job of "cooling"; the axial movement of the worm during assembly is controlled within 0.02~0.05mm, which can allow this "all-around player" to perform at its best.
Cylindrical worm gears are like the "old oxen" in the mechanical world. Their structure is not complex, but their abilities are not small. With their advantages of large transmission ratio and wide application, they firmly occupy a place in various mechanical transmission systems.
keyword：