Worm gear mechanisms are commonly used to transmit motion and power between two staggered shafts. The worm gear and worm are equivalent to gears and racks in their mid-plane, and the worm is similar in shape to the screw.
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So, how does a worm gear work? Today we will share it.
The worm gear mechanism usually has two axes with a staggered angle of 90°, and generally uses a worm as the driving component. In appearance, the worm is similar to a bolt, and the worm gear is similar to a helical cylindrical gear. During operation, the worm gear teeth slide and roll along the helical surface of the worm. In order to improve the contact of the gear teeth, the worm gear is made into an arc shape along the tooth width direction so that it partially covers the worm, so that when the worm and worm gear mesh, there is line contact instead of point contact.
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Worm gear transmission is composed of a worm and a worm gear. Generally, the worm is the driving part. Like threads, worm gears can be divided into right-hand and left-hand worm drives, which are called right-hand worm and left-hand worm respectively. If there is only one helix on the worm, it is called a single-head worm, that is, the worm rotates once, and the turbine rotates one tooth; if there are two helices on the worm, it is called a double-head worm, that is, when the worm rotates once, the turbine rotates two teeth. .
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Characteristics of worm gear:
1. A large transmission ratio can be obtained, which is more compact than the staggered shaft helical gear mechanism.
2. There is line contact between the meshing tooth surfaces of the two wheels, and its load-bearing capacity is much higher than that of the staggered-axis helical gear mechanism.
3. Worm transmission is equivalent to screw transmission and is a multi-tooth meshing transmission, so the transmission is stable and the noise is small.
4. Self-locking. When the lead angle of the worm is less than the equivalent friction angle between the meshing gear teeth, the mechanism is self-locking and can achieve reverse self-locking, that is, the worm can only drive the worm gear, but not the worm gear. For example, the self-locking worm mechanism used in lifting machinery has a reverse self-locking function that can provide safety protection.
5. The transmission efficiency is low and the wear is serious. When the worm gear is engaged in transmission, the relative sliding speed between the meshing gear teeth is large, so the friction loss is large and the efficiency is low. On the other hand, the relative sliding speed increases the tooth surface wear and heat seriously. In order to dissipate heat and reduce wear, more expensive materials with good friction reduction and anti-wear properties and good lubrication devices are often used, so the cost is high. .
6. The axial force of the worm is large.
Let's learn more about it through a video
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In worm gear transmission, the failure modes of worm gear teeth include pitting, wear, gluing and tooth bending and breakage. However, the general worm transmission efficiency is low, the sliding speed is large, and it is easy to generate heat, so gluing and wear damage are more common.
In order to avoid gluing and slow down wear, the materials of the worm gear transmission must have anti-friction, wear-resistant and anti-gluing properties. Generally, the worm is made of carbon steel or alloy steel. The spiral surface should be heat treated (such as quenching and carburizing) to achieve high hardness (HRC45~63), and then ground or honed to improve the load-bearing capacity of the transmission. Worm gears are mostly made of bronze. For low-speed transmissions that are not important, brass or cast iron is sometimes used. In order to prevent gluing and slow down wear, good lubrication should be selected and lubricants containing anti-gluing additives should be used.
There is no mature calculation method for the gluing and wear of worm drives. Tooth surface contact stress is an important factor causing tooth surface gluing and wear, so the calculation of tooth surface contact strength is still the basic calculation of worm transmission. In addition, the bending strength of the gear teeth should sometimes be checked. Generally, worm teeth are not easily damaged, so it is usually not necessary to calculate the strength of the teeth, but the strength and stiffness of the worm shaft should be checked if necessary. For closed transmissions, thermal balance calculations should also be performed. If the heat balance calculation cannot meet the requirements, add heat sinks on the outside of the box or use forced cooling devices.
Turbine and worm gear transmission is often used in situations where two shafts are staggered, the transmission ratio is large, the transmission power is not too large, or the work is intermittent.
When the worm gear transmission is required to transmit larger power, in order to improve the transmission efficiency, Z1=2~4 is often taken. In addition, since the transmission has self-locking properties when γ1 is small, it is often used in hoisting machinery such as winches for safety protection. It is also widely used in machine tools, automobiles, instruments, metallurgical machinery and other machines or equipment. The reason is that the use of wheel and axle motion can reduce force consumption, so it is vigorously promoted.
