RIVETED, BOLTED & COTTER JOINTS SHORT QUESTION ANSWERS

RIVETED, BOLTED & COTTER JOINTS

SHORT QUESTION ANSWERS

Question answers make the concept clear.

Joints play an important role in

manufacturing. Different joints used

in different applications. No assembly

is possible without a joint.

Riveted joints used in sheet work.

These used in boilers. These are

easily made leak proof. These can

withstand higher temperatures.

SHORT QUESTION ANSWERS

JOINTS

Q1. Write down the important terms used in the design of riveted joints.

  1. Nominal pitch

  2. Medium pitch

  3. Long pitch

  4. Row pitch or back pitch or transverse pitch

  5. Diagonal pitch

  6. Margin

  7. Marginal distance

  8. Strap thickness

  9. Plate thickness

  10.  shank diameter

  11.  tail

  12.  head

  13. Types of rivets

  14. Caulking

  15. Fullering

  16. Clearance

  17. Types of riveted joints

  18. Lap joint-single/double/triple riveted

  19. Butt joint with single strap—Single/double/triple riveted

  20. Butt joint with double strap– Single/double/triple riveted

  21. Chain riveting

  22. Zigzag riveting

  23. Strength of one rivet

  24. Riveted joint efficiency

  25. Tearing efficiency

  26. Shearing efficiency

  27. Crushing efficiency

  28. Design of riveted joints

  29. Cold working of rivets

  30. Hot working of rivets

Q2. List the various assumptions used in the design of riveted joints.

  1. Neglect Bending of rivets.

  2.  Uniform bending stress over the projected area of the rivet.

  3.   Rivet completely fills the hole after riveting.

  4. Uniform stresses in the plate.

  5. There is no friction between the plates.

  6. Riveted joints joins light metals.

Q3.  List the applications of riveted joints.

  1. Structures

  2. Pressure vessels

  3. Ship building

  4. Tanks

  5. Bridges

  6. Boilers

  7. Air crafts

  8. Railway wagon and coaches

  9. Buses and trucks

  10. Used with wood, metal and plastic

       Q4. Advantages and disadvantages of riveted joints.

(a) ADVANTAGES

  1. Advantages of riveted joints

  1. Riveting is cheap.

  2. It is a superior method of fastening.

  3. Rivets are easy to install.

  4. Low cost of maintenance

  5. Available in variety of materials, types and sizes

  6. Riveted joints are reliable permanent joints.

  7. These can with stand environmental conditions of heat, rain and dust over a long period.

  8. Riveted joints are light weight and high strength.

  9.  Used in light materials, wood and steel

(b) Disadvantages of riveted joints

  1. Needs skilled persons to do riveting.

  2.  Pressure vessels and boilers leak. Leakage is preventive with caulking and fullering

         Q5. List the materials of rivets.

  1. Material of the rivet should be tough and ductile. Boilers use special rivet materials as per CODE.  Materials used in different applications are.

  2.  Wrought iron

  3.  soft steel of less hardness

  4.  Copper

  5.  Brass

  6.  Aluminum

Q6. What are the methods to increase the fatigue strength of bolted joints?

A.

Bolted joints are very common in the construction of structures and machines. Mostly Bolts are under fluctuating tension which causes fatigue. But there fatigue strength is less. Therefore chances of crack initiation and propagation are bright. Thus fatigue strength needs to be increased.

Q7. Steps to increase fatigue strength

  1. Rolled bolt threads have longer fatigue life than normally cut threads.

  2.  HEAT treatment is necessary for threads. This heat treatment induces compressive stresses in the roots of the threads which increases the fatigue life.

  3. On the larger size of bolts, initial compressive stresses is easily achieved by shot peeing. It is more costly by rolling on larger size of bolts.

  4. Nuts should have two or more than two thread pitches distance from threads run out region to increase fatigue life. It normally doubles the fatigue life.

  5. By increasing the minimum root radius to 0.15 p instead of normal 0.125 p increases the fatigue life.

  6. Mounting of bolts straight increases fatigue life. Even a small angle of tilt in mounting reduces the fatigue life significantly.

  7. Asymmetric thread profile in the nut  increases the fatigue life by 20 %.

  8. Use of different material of nut with higher Young’s modulus increases the fatigue life.

  9. Tighten the bolt very firmly to increase fatigue life.

Q8. What are the advantages and disadvantages of cotter joints?

A.

ADVANTAGES

  1.  Easy to design and manufacture.

  2.  Assembling and dissembling is easy.

  3. Tightening force is very high due to wedge action. It prevents the loosening of parts.

DISADVANTAGES OF COTTER JOINTS

  1. It cannot connect two shafts having rotary motion.

  2. Rods of rectangular sections cannot be connected by a cotter joint.

  3. It does not allow any angular alignment between the two rods being connected.

Q9. State the differences between Caulking and Fullering.

A.

Table Differences between Caulking and Fullering
Sr. No.
Caulking
Fullering
1.
 makes the riveted joint leak proof
Used to make the riveted joint leak proof
2.
Caulking tool thickness is much less than the thickness of the plates. Thickness is roughly 5 mm.
 Fullering tool thickness is equal to the thickness of the plates.
3.
Caulking tool is a blunt tool.
Fullering tool is not a blunt tool.
4.
It is for low pressure vessels.
 Used for making joint leak proof joint in high pressure vessels.
5
It can harm the plates
There is no harm to the plates being connected.
6.
Less surface finish is obtained.
More surface finish is obtained.

 

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