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.
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Nominal pitch
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Medium pitch
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Long pitch
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Row pitch or back pitch or transverse pitch
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Diagonal pitch
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Margin
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Marginal distance
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Strap thickness
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Plate thickness
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shank diameter
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tail
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head
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Types of rivets
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Caulking
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Fullering
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Clearance
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Types of riveted joints
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Lap joint-single/double/triple riveted
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Butt joint with single strap—Single/double/triple riveted
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Butt joint with double strap– Single/double/triple riveted
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Chain riveting
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Zigzag riveting
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Strength of one rivet
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Riveted joint efficiency
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Tearing efficiency
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Shearing efficiency
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Crushing efficiency
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Design of riveted joints
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Cold working of rivets
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Hot working of rivets
Q2. List the various assumptions used in the design of riveted joints.
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Neglect Bending of rivets.
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Uniform bending stress over the projected area of the rivet.
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Rivet completely fills the hole after riveting.
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Uniform stresses in the plate.
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There is no friction between the plates.
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Riveted joints joins light metals.
Q3. List the applications of riveted joints.
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Structures
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Pressure vessels
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Ship building
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Tanks
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Bridges
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Boilers
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Air crafts
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Railway wagon and coaches
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Buses and trucks
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Used with wood, metal and plastic
Q4. Advantages and disadvantages of riveted joints.
(a) ADVANTAGES
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Advantages of riveted joints
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Riveting is cheap.
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It is a superior method of fastening.
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Rivets are easy to install.
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Low cost of maintenance
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Available in variety of materials, types and sizes
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Riveted joints are reliable permanent joints.
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These can with stand environmental conditions of heat, rain and dust over a long period.
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Riveted joints are light weight and high strength.
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Used in light materials, wood and steel
(b) Disadvantages of riveted joints
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Needs skilled persons to do riveting.
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Pressure vessels and boilers leak. Leakage is preventive with caulking and fullering
Q5. List the materials of rivets.
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Material of the rivet should be tough and ductile. Boilers use special rivet materials as per CODE. Materials used in different applications are.
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Wrought iron
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soft steel of less hardness
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Copper
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Brass
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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
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Rolled bolt threads have longer fatigue life than normally cut threads.
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HEAT treatment is necessary for threads. This heat treatment induces compressive stresses in the roots of the threads which increases the fatigue life.
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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.
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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.
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By increasing the minimum root radius to 0.15 p instead of normal 0.125 p increases the fatigue life.
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Mounting of bolts straight increases fatigue life. Even a small angle of tilt in mounting reduces the fatigue life significantly.
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Asymmetric thread profile in the nut increases the fatigue life by 20 %.
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Use of different material of nut with higher Young’s modulus increases the fatigue life.
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Tighten the bolt very firmly to increase fatigue life.
Q8. What are the advantages and disadvantages of cotter joints?
A.
ADVANTAGES
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Easy to design and manufacture.
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Assembling and dissembling is easy.
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Tightening force is very high due to wedge action. It prevents the loosening of parts.
DISADVANTAGES OF COTTER JOINTS
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It cannot connect two shafts having rotary motion.
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Rods of rectangular sections cannot be connected by a cotter joint.
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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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