Powder Metallurgy Multiple Choice Questions on “Production of Sintered, Non Porous Bearings and Composition”.
1. For bronze bearings, the amount of shrinkage _______ as the particle size of powder mix decreases.
a) decreases
b) increases
c) constant
d) moderate
Answer: b
Clarification: In the production of bearings by P/M route, powder characteristics like particle size and distribution, and particle shape play an important role. In the bronze bearings, decrease in the particle size of elemental tin or copper powder increases the amount of shrinkage.
2. Which of the following material on addition to the powder mix lowers the strength of the bearing?
a) Oil
b) Lead
c) Bismuth
d) Graphite
Answer: d
Clarification: The addition of graphite improves lubrication but also results in growth and lowers the strength of the bearings. Lubricants used in the mix have significant effect on the apparent density and flow rate but very little influence on the dimensional change.
3. Which of the following bearing doesn’t belong to the class of non-porous bearing with steel backing?
a) Copper-antimony alloy
b) Aluminum based alloy
c) Copper based alloy
d) Babbit
Answer: a
Clarification: The major types of bearings which belong to the class of non-porous bearing with steel backing include: aluminum-based alloy, copper-based alloy, and babbits. Bronzes and aluminum alloys are more common than babbits because of their higher load carrying capacity.
4. Which of the following powder production method is used for the production of non-porous bearing with steel backing?
a) Mechanical alloying
b) Gas atomization
c) Water atomization
d) Electrolysis
Answer: b
Clarification: The pre-alloyed powders for the production of non-porous bearing with steel backing are manufactured by gas atomization. In this process the molten metal stream is disintegrated using high velocity argon, nitrogen or helium gas jets and the atomized powders are collected in a water bath.
5. Lower lead content in copper-lead alloy is undesirable.
a) True
b) False
Answer: a
Clarification: Copper with 30wt% and 40wt% lead is commonly used for production of bearings. Lower lead content gives better strength but poor surface (anti-seizure) characteristics whereas higher lead contents (40wt%) ensure better lubrication.
6. What should be amount of tin in copper-lead alloy containing 25% lead for production of non-porous bearing?
a) 14 – 20wt%
b) 4 – 10wt%
c) 1 – 5wt%
d) 11 – 15wt%
Answer: b
Clarification: The amount of tin in copper-lead alloy containing copper with up to 25% lead for production of non-porous bearing is 4 – 10wt%. Addition of tin not only improves the strength but also increases the seizure resistance, and oil corrosion is reduced.