CH 12 Multiple Choice Q's

As particle size increases, interparticle friction (a) decreases, (b) increases, or (c) remains the same?

decreases

After pressing in the press and sinter PM sequence, the work part is called which one of the following: (a) green compact, (b) pressed piece, (c) software, or (d) unsintered work?

green compact

Which of the following design features would be difficult or impossible to achieve by conventional pressing and sintering (three best answers): (a) outside rounded corners, (b) side holes, (c) threaded holes, (d) vertical stepped holes, and (e) vertical wall thickness of 1/8 inch (3 mm)?

outside rounded corners side holes threaded holes

Which of the following statements are correct in the context of metallic powders (three correct answers): (a) porosity + packing factor = 1.0, (b) packing factor = 1/porosity, (c) packing factor = 1.0 - porosity, (d) packing factor = - porosity, (e) packing factor = bulk density/true density, and (f) packing factor = true density/bulk density?

porosity + packing factor = 1.0 packing factor = 1.0 - porosity packing factor = bulk density/true density

Before pressing and sintering in the conventional PM sequence, the powders are blended and/or mixed. Blending refers to which one of the following: (a) air is largely removed from the powders, (b) ceramic powders are intermingled with the metal powders to create cermets, (c) powders of different chemistries are intermingled, or (d) powders of the same chemistry but possibly different sizes are intermingled?

powders of the same chemistry but possibly different sizes are intermingled

For a given weight of metallic powders, the total surface area of the powders is increased by which of the following (two best answers): (a) larger particle size, (b) smaller particle size, (c) higher shape factor, and (d) smaller shape factor?

smaller particle size, higher shape factor EXTRA -> A/V=K/D D - diameter(particle size) K - shape factor

Which of the following powder shapes would tend to have the lowest interparticle friction: (a) acicular, (b) cubic, (c) flakey, (d) spherical, and (e) rounded?

spherical

Which of the following processes combines pressing and sintering of the metal powders: (a) hot isostatic pressing, (b) hot pressing, (c) metal injection molding, (d) pressing and sintering, and (e) spark sintering?

- hot isostatic pressing - hot pressing - spark sintering

Impregnation refers to which of the following (two best answers): (a) filling the pores of the PM part with a molten metal, (b) putting polymers into the pores of a PM part, (c) soaking oil by capillary action into the pores of a PM part, and (d) something that should not happen in a factory?

- putting polymers into the pores of a PM part - soaking oil by capillary action into the pores of a PM part

Which one of the following most closely typifies the sintering temperatures used in powder metallurgy: (a) 0.5 Tm, (b) 0.8 Tm, or (c) Tm, where Tm = melting temperature of the metal on an absolute scale?

0.8 Tm should be between 0.7 and 0.9

The conventional process for producing parts in powder metallurgy is to simultaneously press and sinter metallic powders in a closed mold: (a) true or (b) false?

False Pressing and sintering are done at different times

In the water atomization process for producing metallic powders, particle size is controlled largely by the velocity of the fluid stream; higher speeds create larger particles: (a) true or (b) false?

False particle size is inversely related to the velocity

The particle size that can pass through a screen is obtained by taking the reciprocal of the mesh count of the screen: (a) true or (b) false?

False statement neglects the constant K and the wire thickness of screen mesh.

A powder can be defined as a finely divided particulate solid: (a) true or (b) false?

True

Powder metal part shaping operations are generally considered to be net shape or near net shape processes: (a) true or (b) false?

True

Repressing refers to a pressworking operation used to compress a sintered part in a closed die to achieve closer sizing and better surface finish: (a) true or (b) false?

True

In cold isostatic pressing, the mold is most typically made of which one of the following: (a) rubber, (b) sheetmetal, (c) textile, (d) thermosetting polymer, or (e) tool steel?

rubber