Archimedes screw: The "practical veteran" in worm gear transmission
Classification： Blog
Release time：2025-08-04
In worm gear types, Archimedes worm gears are widely used. Their name originates from the design feature where the worm gear profile is based on the Archimedes spiral, and they have a long and stable history of application in the industrial field.
Structurally, the Archimedes worm is the core component of the transmission. In the axial cross-section, its tooth shape is linear, similar to a trapezoidal thread; the end face profile is distributed along the Archimedes spiral. The machining process is relatively simple, and a linear tooth profile can be formed through turning or grinding. The mating worm gear has a special curve profile that matches the worm, usually machined with a hob matched to the worm parameters to ensure accurate meshing.
Archimedes worm gears have several significant characteristics. First, they have a large transmission ratio; a single-stage transmission ratio can reach 5-100, with a compact structure, making them very suitable for scenarios requiring speed reduction. Second, they have a self-locking characteristic. When the worm lead angle is less than the friction angle, the transmission is irreversible (the worm wheel cannot drive the worm). This characteristic is particularly useful in machinery such as cranes that need to maintain a fixed position. However, the meshing tooth surfaces are mainly based on sliding friction, with a large sliding speed, easily generating heat, and the transmission efficiency is usually between 40% and 90%, so higher lubrication requirements are needed. In addition, the design must follow the standardized center distance (such as GB/T 10085-1988) for convenient engineering applications.
Understanding its main parameters helps to better grasp its performance. The module (m) is a key parameter; the axial module of the worm and the end face module of the worm wheel must be consistent and standard. The worm pitch circle diameter (d₁) matches the module, and standardization is achieved through the diameter coefficient q (q = d₁/m). The lead angle (γ) can be calculated by the formula \(\tan \gamma = \frac{z_1 m}{d_1}\) (where \(z_1\) is the number of worm starts). The transmission ratio (i) is the ratio of the number of worm wheel teeth to the number of worm starts (\(i = \frac{z_2}{z_1}\), \(z_2\) is the number of worm wheel teeth). In terms of application scenarios, Archimedes worm gears are suitable for low-speed, heavy-load applications, such as cranes and winches; they can also play a stable role in precision indexing fields, such as machine tool rotary tables; and because of their compact structure, they are suitable for transmission scenarios with limited space and requiring a large speed reduction ratio.
In terms of material selection, the worm needs to have wear resistance and strength, and commonly used carbon steel (such as 45 steel) or alloy steel (such as 20Cr, 40Cr) are used, and the performance is improved through surface quenching. The worm wheel focuses on reducing friction and is often made of bronze (such as tin bronze ZCuSn10P1) or cast iron. During design, several points need to be noted: lubrication and heat dissipation are crucial; high-viscosity lubricating oil should be used, and heat dissipation fins or forced cooling should be added if necessary; the tooth surface contact fatigue strength of the worm wheel needs to be checked to avoid wear affecting the service life; the number of worm wheel teeth is generally not less than 28 to prevent undercutting.
Compared with other worm gear types, Archimedes worm gears are easy to process and have lower costs, making them widely used in general industry. Involute worm gears have an involute end face profile, better meshing performance, but complex processing; normal straight-toothed worms have a straight line in the normal cross-section and are suitable for high-precision transmission. In high-efficiency or high-speed applications, other types (such as circular arc cylindrical worm gears) may be preferred, but Archimedes worm gears remain the preferred choice for many scenarios due to their practicality.
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