The topic of this article will be where the worm and worm wheel are used. The areas of use of the worm gear and worm wheel are quite varied. A worm gear can be preferred wherever the direction of motion needs to be changed. Let’s take a look at examples of worm gear use, both from the recent past and today.
Where the Worm and Worm Wheel Are Used
The worm and worm wheel system is used on shafts whose axes form a 90° angle and do not intersect. The worm is a trapezoidal screw. Depending on the magnitude of the power transmitted and the transmission ratio, it is made with a single start, or with two, three, or four starts.
The rim of the worm wheel is made either straight or curved so as to wrap around the worm. Since the worm wheel engages the worm the way a nut does, both have the same helix direction. The lead angle of the screw is equal to the helix angle of the gear.
Worm gears are like other screws. The only difference is that their pitch is expressed in module units.
The worm and worm wheel are used in places where the load is heavy and the speed ratio is small.
They accomplish a great deal of work with a small amount of force. They are used in dividing heads, lifting equipment, automobiles, vacuum cleaners, etc.
In the figure, we see a cross-section of the internal structure of a dividing head (an indexing device used in milling).
The picture below shows a cross-section of a toy car model. With the help of a simple electric motor, a worm, and a worm wheel, the toy car will move forward or backward depending on the direction the motor spins.
When the worm has 40 teeth, a single-start worm is used. For 40-50 teeth, a double-start worm is used, and for other tooth counts, a multi-start worm is used. For good engagement, the worm wheel’s tooth count must always be greater than 30.
A cross-sectional view of a valve used in places such as pipelines and natural gas facilities. When we turn the valve handwheel to the right, the worm will rotate the worm wheel counterclockwise
Above, the internal structure of an advanced valve system is shown as an animation. Here too we find the worm and worm wheel in use.
The worm and worm wheel have a wide variety of uses. They can also be used in speed reducers, which change the axis of motion and force (above).
Use of the worm and worm wheel in speed reducers
Recirculating-ball worm steering gearbox
A view of the mechanism of a pulley-type crane system. Here, the winding of the pulley is provided by the worm and worm wheel.
Video showing a worm and worm wheel used together with a cam (above)
Where the worm is used
A view of the mechanism of a 19th-century British-made heavy muzzle-loading rifled iron cannon. (Istanbul Naval Museum) When the steering-wheel-like handwheel is turned right or left, the worm will rotate the worm wheel clockwise or counterclockwise. This allows the cannon to traverse right and left.
The uses of the worm and worm wheel also show up in the arms industry. Another view of a cannon mechanism from the Istanbul Naval Museum
We also find the worm and worm wheel used in a road-grading vehicle from the past. In this vehicle’s steering mechanism, chains are attached to the right and left of the wheel and used just like a horse’s harness.
When the steering wheel is turned to the right, the worm connected to it will rotate the worm wheel clockwise, and the chain will wind onto the pulley. This will turn the vehicle’s wheel to the right.
High Reduction Ratio
Worm gear systems can achieve very high reduction ratios in a single stage.
Self-Locking
Worm gear mechanisms provide self-locking by preventing motion from being transmitted backward from the output shaft to the input shaft.
Use in Elevators and Cranes
Thanks to their self-locking property, worm gears are preferred for safety in elevator and crane mechanisms.
Related Questions
This system is designed to transmit power between shafts that sit at a 90-degree angle to each other but do not intersect in the same plane. Since many other gear types cannot operate in this kind of arrangement, the worm gear is chosen for this specific situation.
The system provides a high reduction ratio that lets a small force move a large gear. This feature offers a great advantage in applications, such as lifting equipment, that need to move large loads in a controlled way at low speed.
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