60819
Description
Flashcards by Brandon Alcaraz, updated more than 1 year ago
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Created by Brandon Alcaraz
over 11 years ago
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| Question | Answer |
| What are some of the disadvantages of PM methods? | Disadvantages include (1) high tooling costs, (2) metal powders are expensive, (3) difficulties in storing and handling metallic powders, (4) certain limitations on part geometry imposed by the uniaxial press methods, and (5) variations in density in a PM component can be troublesome. |
| In the screening of powders for sizing, what is meant by the term mesh count? | The mesh count of the screen is the number of openings per linear inch. |
| How would one measure the angle of repose for a given amount of metallic powder? | One measure would be to let the powders flow through a small funnel and measure the angle taken by the resulting pile of powders relative to the horizontal. |
| What are the principal methods used to produce metallic powders? | The powder production methods are (1) atomization - the conversion of molten metal into droplets which solidify into powders; (2) chemical reduction - reducing metallic oxides by use of reducing agents which combine with the oxygen to free the metals in the form of powders; and (3) electrolysis - use of an electrolytic cell to deposit particles of the metal onto the cathode in the cell. |
| What are the three basic steps in the conventional powder metallurgy shaping process? | The steps are (1) blending and/or mixing, (2) pressing, and (3) sintering. |
| What is the technical difference between mixing and blending in powder metallurgy? | Mixing refers to the combining of metal powders of different chemistries, while blending means combining particles of the same chemistry but different sizes. |
| What are some of the ingredients usually added to the metallic powders during blending and/or mixing? | The additives include (1) lubricants, (2) binders, and (3) deflocculants. |
| What is meant by the term green compact? | The green compact is the pressed but not yet sintered PM part |
| What are the three steps in the sintering cycle in PM? | The three steps in the cycle are (1) preheat, in which lubricants and binders are burned off, (2) sintering, and (3) cool down. |
| What are some of the reasons why a controlled atmosphere furnace is desirable in sintering? | Some of the purposes of a controlled atmosphere furnace are (1) to protect against oxidation, (2) to provide a reducing atmosphere to remove existing oxides, (3) to provide a carburizing atmosphere, and (4) to remove lubricants and binders from pressing. |
| What are the advantages of infiltration in PM? | Advantages of infiltration are (1) the resulting structure is nonporous structure and (2) toughness and strength are improved. |
| What is the difference between powder injection molding and metal injection molding? | Metal injection molding is a subset of powder injection molding, in which the powders are metallic. The more general term includes powders of ceramic. |
| Why is PM technology so well suited to the production of gears and bearings? | The reasons are (1) the geometries of these parts lend themselves to conventional PM pressing, which consists of pressing in one direction, and (2) the porosity allows impregnation of the PM parts with lubricants. |
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