《机械设计(双语)》试卷

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华南理工大学期末考试

《机械设计（双语）》试卷2009 A

注意事项：1. 考前请将密封线内填写清楚；

2. 所有答案请直接答在试卷上；

3．考试形式：开卷；

4. 本试卷共 5大题，满分100分， 考试时间120分钟。

题 号一二三四五总分

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FINAL EXAMINATION OF MACHINE ELEMENTS IN MECHANICAL DESIGN 2009

(VERSION A)

1. Filling the blanks with the correct words or phrases (10)

(1) Both of chain drive and belt drive are flexibility, by comparison， chain drive transmits larger tensile forces， __belt_ drive transmits higher speed，and __belt_ drive transmits more smoothly and steadily.

(2) For parallel keys, the working faces are the two side_ faces, and for taper keys and gib head keys, the working faces are the __top_ face and the __bottom_ face.

(3) The popular methods of machining the gear teeth are form milling of gears, gear shaping, and gear hobbing.

(4) For V belt drive, there are three types of working stresses, they are tensile

stress，bending stress and ____centrifugal stress____ .

2. Answer the following questions briefly (20)

(1) What are three main types of lubrication for plain surface bearing?

Which are recommended to be used or avoided by designer?

A. Three main types of lubrication for plain surface bearing are

boundary lubrication ,mixed film lubrication and hydro-dynamically

film lubrication or full-film lubrication

B. Boundary lubrication and full-film lubrication are recommended, and

mixed film lubrication should be avoided by designer.

(2) For chain drive, the average speed ratio is constant, is the

instantaneous speed ratio variable? why?

For chain drive, the average speed ratio is constant, but the instantaneous speed ratio is variable, because profile of chain sprocket is regular-polygon

(3) Briefly explain the maximum clamping load, proof load and tightening

torque of bolted joints.

The maximum clamping load: when a bolt or a screw is used to clamp two parts, the force exerted between the parts is the clamping load .The maximum clamping load is often taken to be 0.75 times the proof load

The proof load: is the product of the proof stress times the tensile stress area of the bolt or screw.

Tightening torque: T =KDP

Where: T=torque, lb in

D=nominal outside diameter of threads, in

P=clamping load ,lb

K=constant dependent on the lubrication present

(4) What are the three necessary conditions for full-film hydrodynamic

lubricated bearing in sufficiently oil supply?

A. Enough relative motion velocity and one of correct motion

directional;

B. The converging wedge-shaped area above the region of contact;

C. Proper viscosity of lubrication.

3. Forces analysis problems (10)

Fig.1 shows a double wormgearing chain, the helix direction of worm 3 is dextrorotation, shat I is input shaft, and the direction of axial force applied on wormgear 2 is inverse to that of worm 3. Please answer following problems,

（1）what are the rotational directions of shaft I and shaftⅡ?

（2）what are the helix directions of worm 1, wormgear 2 and wormgear 4?

（3）what are the force directions applied on worm2 and worm 3?

Solution: