11. Necessary conditions for forming dynamic pressure oil film
(1) There must be a wedge-shaped gap between the two working surfaces. (2) The space between the two working surfaces must be continuously filled with lubricating oil or other viscous fluids. (3) There must be a relative sliding speed between the two working surfaces, and the direction of movement must make the lubricating oil flow in from the large section and flow out from the small section. In addition, for a certain load, the speed, viscosity and gap must be properly matched.
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12. The connection and difference between coupling and clutch
Both are mainly used for the link between shafts, allowing them to rotate together and transmit torque. The two shafts connected by a coupling can only be separated after the machine is stopped and disassembled. The two shafts connected by a clutch can be easily separated or joined during machine operation.
13. Under variable stress, fatigue fracture of parts has the following characteristics:
(1) The maximum stress of fatigue fracture is far lower than the strength limit of the material under static stress, and even the yield limit is lower.
(2) Regardless of brittle materials or statue materials, fatigue fractures appear as brittle sudden fractures without obvious plastic deformation.
(3) Fatigue fracture is the accumulation of damage.
14. Main types of mechanical wear
Abrasive wear, adhesive wear, fatigue wear, corrosion wear.
15． The function of the washer
Increase the support area of the connected parts to reduce the pressure at the contact point and avoid scratching the surface of the connected parts when tightening the nut.
16． Advantages and disadvantages of rolling spiral
Advantages: (1) The wear is very small, and the adjustment method can be used to eliminate the gap and produce a certain pre-deformation to increase the stiffness, so its transmission accuracy is very high. (2) It does not have self-locking properties and can change linear motion into rotational motion.
Disadvantages: (1) Complex structure and difficult to manufacture. (2) In some mechanisms, an additional self-locking mechanism is required to prevent reversal.
17. In gear transmission, the impact of errors on transmission
(1) Affects the accuracy of transmitted movement. (2) The instantaneous transmission ratio cannot be kept constant, which affects the smoothness of the transmission. (3) Affects the uniformity of load distribution.
18． Power loss in gear transmission
Friction losses in meshing, oil resistance losses in churning lubricating oil, friction losses in bearings.
19. Advantages and Disadvantages of Single Arc Gears
Advantages: (1) High tooth surface contact strength. (2) The tooth profile shape is beneficial to lubrication and has high efficiency. (3) The tooth surface is easily saturated. (4) There is no undercut, and the number of tooth surfaces can be small.
Disadvantages: (1) The accuracy requirements of center distance and tooth cutting depth are relatively high, and errors in these two significantly reduce the load-bearing capacity of the transmission. (2) The noise is large and its application in high-speed transmission is limited. (3) Usually the bending strength of gear teeth is low. (4) Different hobs should be used to cut convex arc tooth profiles and concave arc tooth profiles of the same module.
20. Performance of bearing material
(1) The friction coefficient is small. (2) Good thermal conductivity and small thermal expansion coefficient. (3) Wear-resistant, corrosion-resistant and strong glue-resistant ability. (4) It must have sufficient mechanical strength and plasticity.