CH 10 1364

What is the technical difference between blending and mixing in powder metallurgy?

Blending- powders same chemical compistion but dif size Mixing- powders of dif chemistry

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 e) vertical wall thickness of 1/8 in

a b c

Disadvantages of PM

Can be expensive high tool costs,powders variation density

What are the three steps in the sintering cycle in PM

preheat sinter cooldown

repressing

press in closed die to inc density

coining

pressing to add details to surface

sizing

pressing to improve accuracy

What are some of the reasons why a controlled-atmosphere furnace is desirable in sintering?

protect from oxidation reduce atmosphere to remove oxides provide a carbuzing atmosphere(add carbon) assist removing lubricants and binders

conventional sequence used after powders are made are.. (Primary operations)

(1) blending and mixing of the powders;(2) compaction, in which the powders are pressed into the desired part shape; and(3) sintering, which involves heating to a temperature below the melting point to causesolid-state bonding of the particles and strengthening of the part. The three steps,sometimes referred to as primary operations

What are some of the ingredients usually added to the metallic powders during blending and/or mixing?

(aluminum,zinc lubricants) deffloculants binders

Largest tonnange for PM (common metals)

aluminum steel iron

Which of the following most closely typifies the sintering temperatures in PM: ( Tm = melting temperature of the metal)

0.8tm

What are the principal methods used to produce metallic powders?

1)atomization-molten metal is siphoned and then sprayed(high velocity) into container. tend to be spherical. Gas water centifugual. 2)chemical-uses reducing agents to free metallic elements produces iron tungsten and copper. Precipitation-metallic elements from salts dissolved in water copper nickel cobalt 3)electrical-eleytrosis anode dissolves transfers to cathode deposit is washed off dried yields metal. berriluim copper iron silver talnumun titanuim

What are the two basic classes of metal powders as far as chemistry is concerned?

Elemental and pre alloyed

Why PM is important?

Good for medium-high production Can be mass produced to net shape little waste can be made to a specific level of porosity good for certain metals difficult to fabricate ex tungsten filaments better dimensonal control over casting.

Describe liquid phase sintering.

In this process, the two powders are initially mixed, and then heated to a temperature that is high enough to meltthe lower-melting-point metal but not the other.

What is meant by the term green compact?

The green compact is the pressed but not yet sintered PM part.

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 d) something that should not happen in a factory

b c

other common metals for PM

copper, molbdeunum,tungsten,nickel tungsten carbide

machining (secoundary op)

for geometric features such as threads or side holes

What is the difference between impregnation and infiltration in PM?

impreg-fill with oil or resin infiltration-fill with molten metal

How is isostatic pressing distinguished from con-ventional pressing and sintering in PM?

isostatic all directions conventional only 2

Why is PM technology so well suited to the pro-duction of gears and bearings?

need for pores geometry is 2D

Describe what happens to the individual particles during compaction.

they get pressed together