Manufacturing Processes written test Questions & Answers on “Abrasive Jet Micromachining – 7”.
1. During the first half cycle in pressurized powder feed system, powder that has entered the mixing chamber is _____
a) forced out of the nozzle
b) heated to a specific temperature
c) mixed with air
d) mixed with cutting fluid
Answer: a
Clarification: It is during this first half cycle that any powder that has entered the mixing chamber is forced out of the nozzle. In the second half of the cycle, the oscillating valve is closed, stopping air flow through the system.
2. During first half cycle, mixing chamber is at ___________
a) atmospheric pressure
b) 2 atm
c) 2 bar
d) vacuum
Answer: a
Clarification: During the first half cycle the powder in the chamber is forced out of the nozzle. At this point, the reservoir is still pressurized, but the mixing chamber is at atmospheric pressure due to the open nozzle. This creates a pressure differential that forces the powder down through the orifice at the bottom of the reservoir and into the mixing chamber.
3. Powder mass flow rate is controlled by _____________
a) regulating the air flow rate
b) nozzle diameter
c) size of the mixing chamber
d) cycle time
Answer: a
Clarification: Limited control of the powder mass flow rate is possible by regulating the air flow rate through the reservoir, by changing the orifice bypass, and the size of the reservoir orifice.
4. In fluidized bed powder spray system, the air flow from the bottom of the reservoir creates_____
a) pressure in the system
b) a cloud of powder particles
c) vacuum in the system
d) high turbulence to increase the effectiveness
Answer: b
Clarification: In this system, upward high-speed air flow from the bottom of the reservoir through the powder bed created a cloud of suspended particles. Some of which settled into a collection funnel at the top of the reservoir that is connected to the air stream leading to the nozzle.
5. Which of the following is true about powder flow rate in fluidized bed powder system and other systems?
a) First has higher flow rate the other
b) First has lower flow rate the other
c) There is no relation as it is dependent on nozzle parameters
d) Powder flow rate in is not a measurable parameter
Answer: a
Clarification: Fluidized bed powder spray is operated at significantly higher powder mass flow rate than the pressurized powder feed system. The mass flow rate could be regulated to some extent by changing the diameter of the funnel.
6. The powder mass flow rate is dependent on_____
a) fineness of powder particles
b) type of mask used during the process
c) carrier gas
d) amount of powder
Answer: d
Clarification: The powder mass flow rate is dependent on the amount of powder in the reservoir. The powder mass flow rate obtained by fluidized system decreased rapidly as the powder in the reservoir chamber is consumed.
7. Powder compaction is desirable during AJMM.
a) True
b) False
Answer: b
Clarification: This phenomenon usually happens in the pressurized powder feed system. The powder is firmly compacted during the course of AJMM process. Due to this cavities are formed in the supply line, which is not at all desirable.
8. There are variations in the powder mass flow rate due to_____
a) powder compaction
b) size of the powder particles
c) air flow rate inside the mixing chamber
d) pressure build-up in the chamber
Answer: a
Clarification: Due to powder compaction, cavities often form in the vicinity of the orifice, likely causing variations in the powder mass flow rate as the cavity walls collapse randomly, injecting bursts of powder into the nozzle.
9. Mounting a variable speed rotary electric mixer above the reservoir can reduce powder compaction.
a) True
b) False
Answer: a
Clarification: In order to reduce powder compaction in the reservoir of the pressurized powder feed system, the system can be modified by mounting a variable speed rotary electric mixer above the reservoir with the shaft passing through a pressure-seal bearing that had been mounted into the reservoir cap.
10. The degree of powder stratification is not affected by_____
a) mixing time
b) powder mass flow rate
c) air flow velocity
d) diameter of the funnel in the mixing chamber
Answer: a
Clarification: Powders stratify as they flow and it depends on particle size. Mixing time did not appear to affect the degree of particle stratification significantly.
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