60 Basic Mechanical Design Principles You Should Know: A Comprehensive Guide

1. The machine is made up of four parts: the main engine, transmission, running and control.
2. The main forms of failure in belt drives are fatigue damage and belt slippage.
3. The importance of implementing standardization, serialization and generalization in mechanical designs:

① Reduces project workload;

② Standard parts are produced in large quantities by professional factories with high efficiency, low cost and reliable quality;

③ Makes maintenance and repair more convenient;

④ The principle of “Three Modernizations” must be followed in design and is also a national technical policy.

4. Connections can be classified into two types: detachable and non-detachable.
5. Bolted connections can be divided into bolted connections, double-headed pin connections and bolted connections.
6. Anti-loosening measures for threaded connections include frictional anti-loosening, mechanical anti-loosening and permanent anti-loosening.
7. Pin connections are classified into locating pins, connecting pins, and safety pins.
8. Key connections are divided into flat key connections, semicircular key connections and spline connections.
9. Axis functions are classified into drive shafts, spindles and rotary shafts.
10. Couplings are grouped into two categories: rigid and flexible couplings.

11. Bearings can be classified into two types: sliding bearings and rolling bearings.

Sliding bearings are divided into radial and thrust bearings based on the load they support.

12. Oil Bearing Definition: Oil bearings are made from powder metallurgy material where metallic powders such as bronze, iron or aluminum are mixed with graphite to form bearings. These bearings are sintered at high temperatures to produce non-compact, porous bearings with a ceramic structure. Once fully soaked in lubricating oil, the pores are filled with oil, hence the name “oil bearing”.

Oil bearing characteristics: low resistance, no impact resistance, simple structure and low cost.

13. Bearings:

Benefits:

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

② The small axial dimension contributes to the compactness and simplicity of the entire machine mechanism;

③ Small radial clearance, which can be adjusted by pre-tightening method, leading to high rotation accuracy;

④ Simple lubrication, low oil consumption and easy maintenance;

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

Disadvantages: large radial size, limited ability to withstand impact loads, high noise when operating at high speeds and short service life.

14. The components of a bearing: outer ring, inner ring, rolling elements and cage.
15. Rolling code: consists of a pre-code, a base code and a postal code. The basic code includes the bearing type code, size series code and inner diameter code.
16. Structural forms of bearings: double pivot unidirectional fixed support, single pivot bidirectional fixed support, double pivot floating support.
17. Lubricants can be divided into lubricating oil and grease.
18. Bearing sealing can be contact or non-contact.
19. Springs functions:

The. Reduce impact and absorb vibrations;

B. Control movement;

w. Store and release energy;

d. Provides measurement indication;

It is. Maintain elastic contact.

20. Springs are classified into different shapes such as spiral springs, plate springs, disc springs and ring springs.

21. The. Spring winding methods: cold winding and hot winding.

B. Cylindrical spiral spring manufacturing process: winding formation, final processing or hook production and heat treatment.

22. A moving pair is a movable connection between components of a machine that allows contact and relative movement.
23. If the relative motion between the components of a kinematic pair occurs in the same plane or in parallel planes, it is known as a planar kinematic pair. Otherwise, it is considered a spatial kinematic pair.
24. Planar motion pairs are divided into low plane pairs and high plane pairs based on their different forms of contact.
25. Common spatial motion pairs include spiral pairs and spherical pairs.
26. Low pairs can be divided into rotating pairs and moving pairs based on the form of relative movement between the two components.
27. Low and high pairs in everyday life:

① Low pairs: door and window hinges, ceiling fans, which have surface contact, can withstand large loads, wear slowly, have a long service life and low pressure, making them low pairs.

② High pairs: the meshing of gears, the spherical ring of bearings, the contact between the train wheels and the rails, and the contact between the cams and connecting rods are all line or point contacts with high pressure. They allow for more precise movements and high manufacturing requirements, making them high pars.

28. Three basic forms of a four-bar articulated mechanism:

① Crank mechanism (e.g. agricultural manual thresher, liquid mixer, rocking horse, sewing machine);

② Double crank mechanism (e.g. train wheel linking mechanism, umbrella);

③ Double oscillating mechanism (e.g. electric fan oscillating mechanism, car wiper).

29. The. Classification of cam mechanisms based on shape: movable cams, disc cams and cylindrical cams.

B. Classification based on follower shape: pointy followers, roller followers and flat-bottomed followers.

w. Classification based on the form of follower movement: direct moving followers and oscillating followers.

39. Common mechanisms for intermittent motion: ratchet mechanism, Geneva mechanism, and incomplete gear mechanism.
40. Features of belt drives:

Benefits:

① They can reduce impact, absorb vibration, provide smooth operation and have low noise;

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

③ It can easily achieve transmission between large central distances;

④ When overloaded, the conveyor belt will slide on the wheel to prevent damage to the machine.

Disadvantages:

① Precise and constant gear ratio cannot be guaranteed in belt drive;

② Low mechanical transmission efficiency;

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

41. ① V-belt structure: divided into cord core structure and cord core structure, with upper rubber layer (1), elastic layer (2), lower rubber layer (3) and coating layer (4) ;

② Neutral layer: located between the upper and lower rubber layers, its length and width do not change due to the tension of the V-belt on the pulley;

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

④ There are three types of V-belt pulleys based on the size of their reference diameter: solid type, spoke plate type and spoke type.

42. Main types of belt transmissions: flat belt transmission, V-belt transmission, round belt transmission and synchronous belt transmission.
43. Characteristics of chain drives:

Benefits:

① Mesh transmission can guarantee a constant average transmission rate;

② No initial tension is required and there is minimal shaft bending force;

③ Greater resistance compared to belt drives, allowing the transmission of larger loads;

④ Strong adaptability, can be used in challenging working conditions.

Disadvantages:

① Constant instantaneous transmission ratios such as gears cannot be guaranteed;

② High noise and vibration;

③ Higher manufacturing and installation requirements compared to belt drives;

④ The direction of the sprocket axis is restricted.

44. Features of gear transmissions:

Benefits:

① High transmission precision;

② Wide range of applications;

③ Can achieve transmission between any two axes in space;

④ Reliable operation and long service life;

⑤ High transmission efficiency.

Disadvantages:

① High manufacturing and installation requirements and high cost;

② Strict requirements for ring mirror conditions, generally need to be placed in a cover to prevent dust and scale, and attention must be paid to lubrication;

③ Not suitable for long-distance transmission;

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

45. In mechanical transmission, involute profile is generally adopted for gears to ensure smooth transmission, and involute transmission has a constant gear ratio.
46. The angle between the direction of the force and the direction of movement of the point of action of the force on an object is called the pressure angle.
47. A pair of involute gears must have equal modulus and pressure angle before meshing and transmission can occur.
48. Main forms of gear damage: tooth root fracture, tooth surface fatigue corrosion, tooth surface wear and tooth surface adhesion.
49. Types of gear trains: fixed shaft gear train and epicyclic gear train.
50. Functions of gear trains:

① Get large gear ratios;

② Get variable speed and reverse transmission;

③ Achieve multi-channel transmission;

④ Achieve gear transmission over long distances;

⑤ Synthesize and decompose motion.

51. A transmission system made up of a series of gear mechanisms meshed together is called a gear train.
52. The screw transmission consists of a screw, a nut and a machine rod.
53. Chain drives mainly consist of a driving sprocket, chain, driven sprocket, frame and other parts.
54. Common forms of lubrication for closed gear transmissions: oil immersion lubrication and oil injection lubrication.
55. Common types of gear structures: gear shaft, solid gear, spoke plate and spoke gear.
56. The components of a mechanism are divided into three types: frame, main motor and follower.
57. Clutches are divided into jaw clutches, friction clutches and overrunning clutches.
58. Advantages of cam mechanisms: they can accurately realize any law of motion and have a simple and compact structure.
59. Basic shapes of sliding bearings:

① Integral sliding bearings;

② Partial sliding bearings;

③ Self-aligning sliding bearings;

④ Thrust sliding bearings.

60. Reducers consist of a housing, bearing, shaft, shaft parts and accessories.