What is the difference between open pores and closed pores in metallic powders?
ID: 2326900 • Letter: W
Question
What is the difference between open pores and closed pores in metallic powders? Angle of repose (write larger or smaller in blanks): ___ with more friction, ____ for smaller particle size, ___ for more spherical shapes. What is the aspect ratio of a cubic particle shape? In air or water atomization of metal powders, ___ velocity of stream produces a smaller particle size. What is the main driver for the sintering process and its connection to particle size? Jeopardy: Ingredient added to metallic powders to inhibit agglomeration of powders. What is ___ ? A bearing of simple geometry is to be pressed out of bronze powders, using a compacting pressure of 200 MPa. Outside diameter of the bearing = 35 mm, inside diameter = 20 mm, and length =18 mm. What is the required press tonnage to perform this operation?Explanation / Answer
Open pores are air spaces between particles, while closed pores are voids internal to aparticle.
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The aspect ratio is the ratio of the maximum dimension to the minimum dimension of theparticle shape.The minimum dimension is the edge of any face of the cube; call it L. The maximum dimension is the diagonal of the cube, which is given by (L2+ L2+ L2)0.5= (3 L2)0.5=(3)0.5L = 1.732 L. Thus, theaspect ratio = 1.732:1.
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Higher
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The driving force for sintering is a decrease in the surface free energy of powdered compacts, by replacing solid-vapor interfaces (of surface energy SV) with solid-solid ( SS) interfaces, where SS < SV.
Surface energy can be increased with decrease in the sie of the particle.
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Deflocculants are added to metallic powder to inhibit deflocculants thus increasing flow characteristics
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Projected area of part (Ap),
Ap = pi* (do2-di2)/ 4 = 3.14*(352-202)/4
= 648 mm2
F = AP * PC
= 648 * 200 = 129600 KN
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