Basic Parameters

edit

Modulus m, pressure angle, worm diameter coefficient q, lead angle, number of worm heads, number of turbine teeth, tooth crest height coefficient (taken as 1), and crest clearance coefficient (taken as 0.2). Among them, the modulus m and pressure angle refer to the modulus and pressure angle of the worm shaft surface, that is, the modulus and pressure angle of the turbine end face, and both are standard values; The worm diameter coefficient q is the ratio of the worm pitch circle diameter to its modulus m.

The conditions for correct meshing

1. The end face modulus of the worm gear is equal to the axial face modulus of the worm gear and is a standard value. The end face pressure angle of the worm gear should be equal to the axial face pressure angle of the worm gear and be a standard value, that is, m (rod)=m (wheel), α (rod)=α (wheel).

2. WhenWorm gear machiningWhen the interlocking angle is 90 °, it is also necessary to ensure that the worm wheel and the worm screw are helicalThe rotation direction of the line must be the same.

Geometric dimension calculation is basically the same as cylindrical gears, but there are several issues to be noted

1. The worm lead angle γ is the angle between the tangent of the helical line on the worm indexing cylinder and the end face of the worm. Its relationship with the screw helix angle is that the helix angle of the worm wheel is larger, resulting in higher transmission efficiency. When it is smaller than the equivalent friction angle between the meshing teeth (ψ v=arctan fv, which means the equivalent friction angle is equal to the arctangent value of the friction factor, and when ψ v is less than γ), the mechanism locks itself.

2. The introduction of the worm diameter coefficient q is to limit the number of worm gear cutters and standardize the diameter of the worm indexing circle. When m is constant, q increases, and the stiffness and strength of the worm shaft increase accordingly; When q is small, the lead angle increases and the transmission efficiency correspondingly improves.

3. The recommended values for the number of worm heads are 1, 2, 4, and 6. When the smaller value is taken, the transmission ratio is larger and it has self-locking properties; When taking a large value, the transmission efficiency is high.

Unlike cylindrical gear transmission, the transmission ratio of worm gear mechanism is not equal to the ratio of worm diameter to worm gear diameter.

4. The method for determining the direction of worm gear rotation in worm gear transmission can be based on the direction at the meshing point K, the direction (parallel to the tangent of the helix), and the drawing of a velocity vector triangle perpendicular to the worm gear axis; It can also be judged by "holding the right-handed worm with the left hand, holding the left-handed worm with the right hand, and using the four fingers of the thumb".

Characteristics, Applications, Common Problems, and Solutions

Characteristics of Institutions

1. It can achieve a large transmission ratio and is more compact than a staggered shaft helical gear mechanism.

2. The meshing teeth of the two wheels are in linear contact, and their load-bearing capacity is much higher than that of the helical gear mechanism with staggered shafts.

3. Worm gear transmission processing is equivalent to spiral transmission, which is a multi tooth meshing transmission, so the transmission is smooth and the noise is very low.

4. It has self-locking properties. When the lead angle of the worm is less than the equivalent friction angle between the meshing teeth, the mechanism has self-locking properties and can achieve reverse self-locking, that is, only the worm can drive the worm wheel, not the worm wheel. The self-locking worm mechanism used in lifting machinery can provide safety protection through its reverse self-locking property.

5. Low transmission efficiency and severe wear. When the worm gear is engaged in transmission, the relative sliding speed between the meshing teeth is high, resulting in high friction loss and low efficiency. On the other hand, due to the high relative sliding speed, the tooth surface wear and heat generation are severe. In order to dissipate heat and reduce wear, expensive materials with good anti friction and anti-wear properties, as well as good lubrication devices, are often used, resulting in higher costs.

6. The axial force of the worm is relatively large.

application

Worm gears and worm gear mechanisms are often used in situations where two shafts are interlocked, the transmission ratio is large, the transmission power is not large, or intermittent work occurs.