What are the differences in failure modes and design guidelines between closed gear drives and open

1. Failure mode:

1) The open transmission is a hard tooth surface, and the failure mode is fatigue breakage. Open gear transmission is not only easy to invade external debris, but also has poor lubrication, so the working conditions are not good, and the gear teeth are also easy to wear, so it is only suitable for low-speed transmission.

2) The closed transmission is a soft tooth surface, and the failure mode is fatigue pitting. Automobiles, machine tools, aero engines.

The gear transmission used in this is packed in a precisely machined and tightly closed box (casing), which is called a closed gear transmission (gearbox). Compared with open or semi-open type, it has the best lubrication and protection conditions, and is mostly used in important occasions.

2. Design criteria:

1) The open gear transmission uses the modulus formula for design calculation.

2) The closed-type gear transmission is designed and calculated according to the calculation formula of the center distance.

The main forms of gear failure are broken teeth, wear, pitting, and gluing.

Broken tooth: In the gear transmission, due to various reasons other than this, one or more gear teeth are broken and the gear fails;

Wear: During gear transmission, the relative sliding on the tooth surface will cause wear;

Pitting corrosion: In the process of gear transmission, the contact stress at each point on the contact surface of the gear changes in a pulsating cycle, and after a period of time, fine fatigue cracks will be formed due to the fatigue of the metal on the contact surface, and the expansion of the crack will cause the metal to peel off and form pitting corrosion;

Gluing: When the gear is in the case of high speed, large load or lubrication failure, the two tooth surfaces are in direct contact to form a local high temperature, and a large area of adhesion occurs in the contact area, which is gluing.

Proper lubrication can significantly delay or prevent the failure of gears. The main failure modes of closed transmission are pitting of the tooth surface and bending fatigue fracture of the gear teeth. When using a soft tooth surface (tooth surface hardness 350 HBS), the tooth surface contact fatigue strength is relatively low.

Therefore, in general, the indexing circle diameter of the gear and its main geometric parameters (such as center distance, tooth width, etc.) should be calculated according to the contact fatigue strength condition of the tooth surface, and then the bending fatigue strength of the gear tooth should be checked. When the hard tooth surface (tooth surface hardness 350HBS) is used, the modulus of the gear and its main geometric parameters should be determined according to the bending fatigue strength of the gear, and then the contact fatigue strength of the tooth surface should be checked.

The main failure modes of open transmission are abrasive wear on the tooth surface and bending fatigue fracture of the gear teeth. Since there is no perfect calculation method for abrasive grain wear on the tooth surface, only the bending fatigue strength is usually calculated, and the method of increasing the modulus appropriately is used to consider the influence of abrasive wear.

1. Failure mode:

1. Tooth breakage: There are usually two cases of tooth breakage: one is due to repeated bending stress.

and fatigue fracture caused by stress concentration; The other is overload fracture caused by the sudden occurrence of severe overload or shock load.

2. Tooth surface pitting: When the gear teeth are working, the front meshing is under the repeated action of alternating contact stress, and several small cracks will occur on the tooth surface close to the joint line. As the crack propagates, it will cause small pieces of metal to peel off, a phenomenon known as tooth surface pitting.

The continued propagation of tooth surface pitting will affect the smoothness of the transmission, and produce vibration and noise, resulting in the gear not working properly.

3. Tooth surface wear: When the gear teeth are meshed, due to relative sliding, especially when the external hard particles enter the meshing working surface, it will lead to the wear of the tooth surface. After the tooth surface is gradually worn, the tooth surface will lose the correct tooth shape, and in serious cases, the gear teeth will be too thin and broken, and the tooth surface wear is an open gear transmission.

The main mode of failure. In order to reduce wear, important gearing should be closed transmission, and care should be taken to lubricate.

4. Tooth surface gluing: in the high-speed and heavy-duty gear transmission, the pressure between the tooth surfaces is large, the temperature rises, and the lubrication effect is poor.

, the sticky place is torn, thus forming a ribbon or a large area of scars along the sliding direction on the tooth surface, and the transmission of low speed and heavy load is not easy to form an oil film, and the friction is heated.

Although it is not large, it can also be cold glued due to heavy loads.

5. Plastic deformation of the tooth surface: the soft tooth surface gear with low hardness is due to the excessive pressure of the tooth surface when the tooth surface is too heavy at low speed and heavy load.

Under the action, the metal on the tooth surface produces a plastic flow and loses its original tooth shape. Improving the hardness of the tooth surface and using a higher viscosity lubricant can help to prevent or reduce the plastic deformation of the tooth surface.

Second, the design criteria:

1. For closed soft tooth surface (hardness 350HBW) gear transmission, the lubrication conditions are good, and tooth surface pitting will be the main failure mode, and the tooth surface contact fatigue strength is usually used in the design.

design, and then check the bending fatigue strength of the tooth root.

2. For the closed hard tooth surface (hardness: 350HBW) gear transmission, the pitting resistance is strong, and the energy of the gear tooth fracture is large.

3. The main failure mode of open gear transmission is tooth surface wear. However, due to the complexity of the mechanism of wear, there is no mature design calculation method, so it can only be calculated according to the bending fatigue strength of the tooth root, and the tooth thickness is increased by increasing the modulus by 10% to 20%, so that it has a long service life, so as to consider the influence of wear.

1.Tooth breakage: There are usually two cases of tooth breakage, one is fatigue fracture caused by repeated bending stress and stress concentration, and the other is overload fracture caused by sudden severe overload or shock load; 2. Plastic deformation:

The failure form of closed soft tooth surface is pitting corrosion, which is designed according to the contact strength and the center distance formula. The failure mode of the hard tooth surface is wear, and the modulus formula is selected for design calculation.

The following are the main failure modes of closed soft tooth surface gear transmission: 1. Gear tooth breakage: There are usually two cases of gear tooth breakage: (1) One is due to repeated bending stress.

and fatigue fracture caused by stress failure; (2) The other is overload fracture caused by sudden serious overload or shock load. 2. Tooth surface pitting: When the gear teeth are working, the front meshing is under the repeated action of alternating contact stress, and several small cracks will occur on the tooth surface close to the joint line.

As the crack propagates, it will cause small pieces of metal to peel off, a phenomenon known as tooth surface pitting. The continued propagation of tooth surface pitting will affect the smoothness of the transmission, and produce vibration and noise, resulting in the gear not working normally. 3. Tooth surface wear

During tooth meshing, the tooth surface will be worn due to relative sliding, especially when external hard particles enter the meshing surface. After the tooth surface is gradually worn, the tooth surface will lose the correct tooth shape, and in severe cases, the gear teeth will be too thin and broken, and the tooth surface wear is the main failure of the open gear transmission. In order to reduce wear, important gearing should be closed transmission, and care should be taken to lubricate.

4. Tooth surface gluing: in the high-speed and heavy-duty gear transmission, the pressure between the tooth surfaces is large, the temperature rises, and the lubrication effect is poor.

, the sticky place is torn, thus forming a ribbon or a large area of scars along the sliding direction on the tooth surface, and the transmission of low speed and heavy load is not easy to form an oil film, and the friction is heated.

Although it is not large, it can also be cold glued due to heavy loads. 5. Plastic deformation of the tooth surface: the soft tooth surface gear with low hardness is due to the excessive pressure of the tooth surface when the tooth surface is too heavy at low speed and heavy load.

Under the action, the metal on the tooth surface produces a plastic flow and loses its original tooth shape. Improving the hardness of the tooth surface and using a higher viscosity lubricant can help to prevent or reduce the plastic deformation of the tooth surface.

The teeth are broken, the tooth surface is turbid, the tooth surface is glued, the tooth surface is worn, and the plastic on the tooth surface is deformed.

Under normal circumstances, it is mainly the bending fatigue fracture of the tooth root, because when the gear tooth is loaded, the bending stress generated at the tooth root is the largest, coupled with the stress concentration caused by the cross-section mutation of the tooth root transition part and the processing knife marks, when the tooth is repeatedly loaded, the fatigue crack will be produced at the tooth root, and gradually expand, resulting in the fatigue fracture of the gear tooth, in addition, when the gear tooth is suddenly overloaded, overload fracture or shear may also occur.

1. Gear tooth breakage: including bending fatigue fracture and overload fracture

2. Tooth surface failure: including tooth surface wear, tooth surface pitting, and tooth surface gluing.

3. Plastic deformation of gear teeth.

Generally, the main disadvantage of renting a bird hit-type gear transmission is the failure mode ().

a.Tooth fatigue breaks.

b.The tooth surface is worn out of the field.

c.Tooth surface fatigue pitting.

d.Tooth surface gluing.

Correct answer: ab

Answer]: The gear of the open gear transmission is exposed, which can not protect the lubrication of the Zen stool and is easy to make dust and impurities invade the meshing part of the gear teeth, so the tooth travel surface is easy to wear, and is mostly used for low-speed transmission.

The main failure modes of open gear transmission are ().

a.Tooth flank wear causes tooth breakage.

b.Tooth surface pitting hall belt.

c.Tooth surface gluing.

d.Plastic deformation of the tooth barrage mountain surface.

Correct answer: Tooth surface wear causes tooth fracture in the middle of the war.