Here is a comprehensive explanation of mechanical knowledge, including nuts, bolts, screws, bearings and other information. There are also various mechanical design knowledge. mechanical
1. What are the reasons and measures for the anti-loosening of threaded connections?
Answer: The reason is that under the action of shock, vibration and variable load, the pretightening force of the threaded connection may disappear at a certain moment, and the connection may be loose. The threaded connection at high temperature may also occur due to the difference in temperature deformation. Loosening phenomenon, so the anti-loosening must be considered in the design. Measures – use additional friction to prevent loosening, such as using slot nuts, cotter pins, stop washers, etc., and other methods to prevent loosening, such as punching point method and bonding method. mechanical
§2. Measures to Improve Bolt Connection Strength
Answer: (1) Reduce the variation range of the total tensile load Fa of the bolt: a. In order to reduce the stiffness of the bolt, the diameter of the polished rod of the bolt can be reduced or the hollow screw can be used, and the length of the screw can also be increased. b. The rigidity of the connected part itself is relatively low Large, but the joint surface between the connected parts needs to be sealed and the stiffness will be reduced when the soft gasket is used. If the metal thin gasket or the O-ring is used as the sealing element, the original stiffness value of the connected parts can still be maintained. mechanical
(2) Improve the load distribution between thread teeth,
(3) Reduce stress concentration,
(4) Avoid or reduce additional stress.
Answer: (1) Tooth fracture generally occurs at the root of the tooth, because the root bending stress is the largest when the tooth is stressed, and there is stress concentration, which can be divided into overload fracture and fatigue fracture. mechanical
(2) Pitting corrosion on the tooth surface.
(3) Tooth surface gluing.
(4) Tooth surface wear.
(5) Plastic deformation of tooth surface.
§4. Lubrication of gear drives
Answer: The open gear transmission is usually manually lubricated regularly, and lubricating oil or grease can be used. Generally, the lubrication method of the closed gear transmission depends on the size of the peripheral speed V of the gear. When V<=12, the oil pool is often used. For lubrication, when V>12, it is not suitable to use oil pool lubrication. This is because (1) the peripheral speed is too high, and most of the oil on the gears is thrown out and cannot reach the meshing area; The temperature rise increases and the lubricating performance is reduced. (3) It will stir up the impurities deposited at the bottom of the box and accelerate the wear of the gears. Oil injection lubrication is often used. mechanical
5. Why do worm drives need heat balance calculations and cooling measures?
Answer: Due to the low efficiency of the worm transmission and the large heat generation, if the heat is not dissipated in time, the oil temperature in the box will rise, the lubrication will fail, and the gears will be more worn and even glued. calculate.
Measures: 1), increase the heat dissipation area, rationally design the box structure, cast or weld the heat sink, 2) improve the surface heat transfer coefficient, install a fan on the worm shaft, or install a serpentine cooling water pipe in the oil pool of the box .
§6. Advantages and disadvantages of belt drive
1) Suitable for transmission with large center distance
2) The belt has good flexibility, which can alleviate impact and absorb vibration
3) Slip occurs between the belt and the pulley during overload, which can prevent damage to other parts
4) Simple structure and low cost.
1) The outer dimension of the transmission is larger
2) Tensioner is required
3) Due to the slippage of the belt, a fixed transmission ratio cannot be guaranteed
4) The life of the belt is short
5) The transmission efficiency is low.
§7. Definitions of elastic sliding and skidding
Answer: Elastic sliding refers to sliding due to the elastic deformation of the material. Slipping refers to full-scale sliding due to overloading. Elastic sliding is caused by the difference in tension. As long as the circumferential force is transmitted and tight edges and loose edges appear, elastic sliding will definitely occur, so elastic sliding is inevitable, and V2 is always greater than V1. mechanical
§8. Advantages and disadvantages of chain drive compared with belt drive and gear drive
Answer: Compared with the belt drive, the chain drive has no elastic sliding and slipping, can maintain an accurate average transmission ratio, requires less tension, and has less pressure on the shaft, which can reduce the friction loss of the bearing and has a compact structure. , can work under harsh environmental conditions such as high temperature and oil pollution. Compared with the gear transmission, the manufacturing and installation precision requirements of the chain transmission are lower, and the transmission structure is simple when the center distance is large. Disadvantages of chain transmission – the instantaneous chain speed and instantaneous transmission ratio are not constant, the transmission stability is poor, and there are certain impacts and noises during work.
§9. The role of the shaft, the difference between the shaft, the transmission shaft and the spindle
Answer: A shaft is a mechanical part used to support rotation. The shaft not only transmits torque but also bears bending moment. The transmission shaft only transmits the torque without bearing the bending moment or the bending moment is very small. The mandrel only bears the bending moment and not transmits the torque.
§10. The main requirements for the structural design of the shaft
Answer: 1) The shaft should be easy to process, and the parts on the shaft should be easy to assemble and disassemble.
2) The shaft and parts on the shaft must have accurate machining positions
3) All parts should be firmly and reliably fixed relative to each other
4) Improve stress conditions and reduce stress concentration.
§11. Necessary conditions for the formation of a hydrodynamic oil film
Answer: 1) There must be a wedge-shaped gap between the two working faces
2) The gap 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 movement direction 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 clearance must be properly matched.
§12. The connection and difference between coupling and clutch
Answer: Both are mainly used for the link between shafts, so that they rotate together and transmit torque. The two shafts connected by couplings can be separated only after the machine is stopped and disassembled. The two shafts connected by a clutch can be easily separated or engaged during machine work.
§13. The characteristics of fatigue fracture of parts under variable stress
Answer: 1) The maximum stress of fatigue fracture is much lower than the strength limit of the material under static stress, and even the yield limit is low. 2) No matter the brittle material or the statue material, the fatigue fracture is a brittle sudden fracture without obvious plastic deformation. 3 ) Fatigue fracture is the accumulation of damage.
§14. Main types of mechanical wear
Abrasive wear, adhesive wear, fatigue wear, corrosive wear
§15. The role of the gasket
Increase the supporting area of the connected part to reduce the pressure at the contact point and avoid scratching the surface of the connected part when tightening the nut
§16. Advantages and disadvantages of rolling spiral
Answer: Advantages: 1) The wear is very small, and the adjustment method can be used to eliminate the gap and generate a certain pre-deformation to increase the rigidity, so its transmission accuracy is very high. 2) It is not self-locking, and it can change linear motion into rotary motion.
Answer: Disadvantages: 1) The structure is complex and difficult to manufacture, 2) In some mechanisms, an additional self-locking mechanism is required to prevent reversal.
§17. In gear transmission, the influence of error on transmission
Answer: 1) Affect the accuracy of the transmission movement,
2) The instantaneous transmission ratio cannot be kept constant, which affects the stability of the transmission.
3) Affect the uniformity of load distribution.
§18. Power loss in gear transmission consists of
Friction losses in meshing, oil drag losses in churning lubricating oil, friction losses in bearings.
§19. Advantages and disadvantages of single circular arc gear
Answer: Advantages: 1) High contact strength of the tooth surface, 2) The shape of the tooth profile is good for lubrication and high efficiency, 3) The tooth surface is easy to be saturated, 4) There is no undercut, and the number of tooth surfaces can be reduced.
Answer: Disadvantages: 1—) The accuracy of the center distance and the cutting depth is relatively high, and the error of the two will significantly reduce the bearing capacity of the transmission. 2) The noise is large, and its application in high-speed transmission is limited. The bending strength of the tooth is low. 4) The same hob should be used to cut the convex arc tooth profile and the concave arc tooth profile of the same modulus.
§20. Properties of bearing material
1) Small coefficient of friction.
2) Good thermal conductivity, small thermal expansion coefficient.
3) Wear-resistant, corrosion-resistant, strong anti-gluing ability.
4) There must be sufficient mechanical strength and plasticity.
This article comes from BTMA Company —– Grease Machinery and Equipment Processing.