60 Basic Knowledge of Mechanical Design You Should Know

1. The machine is composed of prime mover part, transmission part, execution part and control part.

2. The main failure forms of belt drive are fatigue damage and slip of belt.

3. The significance of implementing standardization, serialization and generalization in mechanical design:

① Reduce the design workload;

② Standard parts are produced on a large scale by professional factories, with high efficiency, low cost and reliable quality;

③ It is convenient for maintenance and repair;

④ “Three modernizations” is the principle that should be implemented in design, and it is also a national technical policy.

4. The connection can be divided into detachable connection and non detachable connection.

5. Screw connection can be divided into bolt connection, double headed stud connection and screw connection.

6. Anti loosening measures for threaded connection: friction anti loosening, mechanical anti loosening and permanent anti loosening.

7. Pin connection classification: locating pin, connecting pin and safety pin.

8. Key connection is divided into: flat key connection, semicircular key connection and spline connection.

9. Shaft function classification: transmission shaft, spindle, rotating shaft.

10. Couplings are divided into two categories: rigid couplings and flexible couplings.

11. Bearings: sliding bearings and rolling bearings;

Sliding bearings are divided into radial bearings and thrust bearings according to the load they bear.

12. ① Definition of oil bearing: generally, metal powders such as bronze, iron or aluminum are mixed with graphite to form bearing shells, which are sintered at high temperature to obtain non compact and porous bearing shells with ceramic structure.

After it is fully soaked in lubricating oil, the pores are filled with lubricating oil, so it is called oil bearing.

Oil bearing is made of powder metallurgy material.

② Features of oil bearing: low strength, no impact resistance, simple structure and low price.

13. Rolling bearing:


① Small friction resistance, sensitive starting, high efficiency, less heating and low temperature rise;

② Axial dimension is conducive to the compactness and simplification of the whole machine mechanism;

③ The radial clearance is small, and the clearance can be adjusted by pre tightening method, so the rotation accuracy is high;

④ Simple lubrication, low oil consumption and convenient maintenance;

⑤ Standard parts, mass production and supply to the market, cost-effective, easy to use and replace.

Disadvantages: the radial size is large, the ability to bear impact load is not high, the sound is large when running at high speed, and the working life is not long.

14. The composition of rolling bearing: outer ring, inner ring, rolling element and cage.

15. A. code of rolling bearing: it consists of pre code, basic code and post code;

b. The basic code consists of bearing type code, size series code and inner diameter code.

16. Structural form of rolling bearing: Double fulcrum one-way fixed support, single fulcrum two-way fixed support, double fulcrum floating support.

17. Lubricants are divided into: lubricating oil and grease.

18. The sealing of rolling bearings is divided into contact type and non-contact type.

19. Function of spring:

a. Mitigate impact and absorb vibration;

b. Control movement;

c. Storing and releasing energy;

d. Measurement indication;

e. Maintain elastic contact.

20. Springs are divided into spiral springs, plate springs, disc springs, disc springs and ring springs according to their shapes.

21. a. The coil burning method of spring: cold coil and hot coil.

b. Manufacturing process of cylindrical spiral spring: winding forming, end processing or hook manufacturing, heat treatment.

22. The movable connection between the components in the machine, which can not only maintain contact, but also produce a certain relative motion, is called the moving pair.

23. If the relative motion between the components of the kinematic pair occurs in the same plane or in a plane parallel to each other, it is called a planar kinematic pair;

Otherwise, it is a space kinematic pair.

24. Plane motion pairs are divided into plane low pair and plane high pair according to different contact forms.

25. Common space motion pairs are: spiral pair and spherical pair.

26. The low pair can be divided into rotating pair and moving pair according to the relative motion form between the two components.

27. Low associate and high associate in daily life:

① Low pair: door and window hinges and ceiling fans, which are in surface contact, can bear large loads, wear slowly, have long service life and low pressure, so they are low pairs;

② High pair: the meshing of gears, the ball heel ring of rolling bearings, the contact between train wheels and rails, and the contact between cams and push rods are all line or point contact, with high pressure, which can achieve more accurate movement and high manufacturing requirements, so it is a high pair.

28. Three basic forms of hinged four-bar mechanism:

① Crank rocker mechanism (agricultural manual thresher, liquid mixer, rocking horse in children’s playground, sewing machine);

② Double crank mechanism (linkage mechanism of train wheels, umbrella);

③ Double rocker mechanism (electric fan shaking mechanism, automobile wiper).

29. a. shape classification of cam mechanism: moving cam, disc cam and cylindrical cam;

b. Classified according to the shape of the follower: pointed follower, roller follower, flat bottom follower;

c. It is classified according to the movement form of the follower: direct moving follower and oscillating follower.

39. Common intermittent motion mechanisms: ratchet mechanism, Geneva mechanism, incomplete gear mechanism.

40. Features of belt drive:


① It can mitigate impact, absorb vibration, drive smoothly and have low noise;

② Simple structure, convenient maintenance and replacement, low cost;

③ It can easily realize the transmission between large center distances;

④ When overloaded, the conveyor belt will slip on the wheel to avoid damage to the machine.


Belt transmission cannot guarantee accurate and constant transmission ratio;

② Low mechanical transmission efficiency;

③ The shaft and shaft are subject to large radial force, which is unfavorable to the operation of the machine.

41. ① V-belt structure: divided into cord core structure and cord core structure, with top rubber layer (1), tensile layer (2), bottom rubber layer (3) and cladding layer (4);

② Neutral layer: it is located between the top rubber layer and the bottom rubber layer, and its length and width do not change due to the tension of V-belt on the pulley;

③ Pitch width: the width of the neutral layer of V-band;

④ There are three types of V-belt pulley according to the size of its benchmark diameter: solid type, spoke plate type and spoke type.

42. The main types of belt transmission: flat belt transmission, V-belt transmission, round belt transmission and synchronous belt transmission.

43. Characteristics of chain drive:

Advantages: ① meshing transmission can ensure constant average transmission ratio;

② There is no need for initial tension, and there is basically no shaft bending force;

③ The strength is greater than that of belt drive, which can transmit greater load;

④ It has strong adaptability and can be used in occasions with poor working conditions.


① It cannot guarantee the constant instantaneous transmission ratio like gears;

② High noise and vibration;

③ Manufacturing and installation requirements are higher than belt drive;

④ The direction of the sprocket shaft is restricted.

44. Characteristics of gear transmission:


① High transmission accuracy;

② . wide scope of application;

③ It can realize the transmission between any two shafts in space;

④ Reliable operation and long service life;

⑤ High transmission efficiency.


① High manufacturing and installation requirements and high cost;

② The requirements for the conditions of the ring mirror are strict, which generally need to be placed in the box cover to prevent dust and scale, and attention should also be paid to lubrication;

③ Not suitable for long-distance transmission;

④ Vibration damping and impact resistance are not as good as belt transmission.

45. In mechanical transmission, in order to ensure the smooth transmission of gears, the profile of gears usually adopts involute;

Involute gear transmission has a constant transmission ratio.

46. The angle between the action direction of the force and the movement direction of the force action point on the object is called the pressure angle.

47. A pair of involute gears must have equal modulus and pressure angle before meshing and transmission.

48. The main failure forms of gear damage: gear fracture from the tooth root, tooth surface fatigue pitting, tooth surface wear and tooth surface gluing.

49. Gear train type: fixed axle gear train and epicyclic gear train.

50. Function of gear train:

① Obtain large transmission ratio;

② Realize variable speed and reversing transmission;

③ Realize multi-channel transmission;

④ Realize gear transmission with large distance;

⑤ Realize the synthesis and decomposition of motion.

51. The transmission system composed of a series of meshing gear mechanisms is called gear train.

52. Screw transmission is composed of screw, nut and machine rod.

53. Chain drive is mainly composed of driving sprocket, chain, driven sprocket, frame and other parts.

54. Common lubrication forms of closed gear transmission: oil immersion lubrication and oil injection lubrication.

55. Common gear structure types: gear shaft, solid gear, spoke plate and spoke gear.

56. The components in the mechanism are divided into three types: frame, prime mover and follower.

57. Clutch is divided into jaw clutch, friction clutch and overrunning clutch.

58. Advantages of cam mechanism: it can accurately realize any motion law, and its structure is simple and compact.

59. Basic form of sliding bearing:

① Integral sliding bearing;

② Partial sliding bearing;

Self aligning sliding bearing;

④ Thrust sliding bearing.

60. The reducer is composed of box, bearing, shaft, shaft parts and accessories.

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