Sintering process and corresponding sintering system
A process is described for the sintering of powders (D) comprising conductive powders, loose or in the form of powder compacts, that comprises the operations of: inserting said powders (D) in a mold ( 23; 33, 34 ); applying ( 5, 6 ) a pressure (P(t)) to said powders (D) in said mold ( 23; 33, 34 ) commanding ( 4 ) nominal pressure values to pressure application devices ( 5, 6 ) to said powders (D); applying ( 1, 2, 3, 4 ) one or more current impulses (I i ) to said powders (D) in said mold ( 23; 33, 34 ) for a respective time interval of predetermined duration (t f ), wherein said nominal pressure values (P(t)) commanded said pressure application devices ( 5, 6 ) defining an increment of pressure (P 1 ) from a first pressure, value (P 0 ) to a second pressure value (P j ) greater | than said first pressure value (P 0 ) and said increment in the pressure (P 4 ) being applied in a synchronized way with respect to the initiation of said time interval of predetermined duration (t f ) of the current impulse (I i ) o .
1. A sintering process for powders comprising electrically conductive powders, loose or in the form of powder compacts, that comprises the operations of:
inserting said powders in a mould;
applying a pressure (P(t)) to said powders in said mould commanding nominal pressure values to pressure application devices to said powders;
applying one or more current impulses (I 1 ) to said powders in said mould for a respective time interval of predetermined duration (t f ), wherein said pressure (P(t)) is applied to said powders through said pressure application devices in at least two opposing directions, said nominal pressure values (P(t)) are commanded to said pressure application devices defining a pressure increment (P 1 ) from a first pressure value (P 0 ) to a second pressure value (Pi) greater than said first pressure value (Po), said pressure increment (P 1 ) being applied in a synchronised manner with respect to the initiation of said time interval of predetermined duration (t f ) of the current impulse (I 1 ), said increment of pressure (P 1 ) being also distributed in said time interval of predetermined duration (t f ) of the current impulse (I 1 ) so to reach said second pressure value (Pi) in an instant in time included between the time instant (t m ) at which said current impulse (I 1 ) reaches its maximum value and an end instant of said time interval of predetermined duration (t f ).
2. The process according to claim 1 , wherein said operation of exerting an increment of the pressure (P 1 ) comprises reaching said second pressure (Pi) in correspondence with the end of said time interval of predetermined duration (t f ).
3. The process according to claim 1 , wherein said operation of exerting an increment of the pressure (P 1 ) comprises reaching said second pressure (Pi) in correspondence with the time instant (t m ) at which said current impulse (I 1 ) reaches the maximum value.
4. The process according to claim 1 , wherein said mould comprises non-conductive side walls and said pressure is applied, in particular axially, through conductive rams.
5. The process according to claim 1 , wherein said mould comprises conductive portions and said pressure (P(t)) is applied to said powders through non-conductive rams.
6. The process according to claim 1 , wherein it comprises applying a voltage (v(t)) of greater than 30V to said powders.
7. The process according to claim 1 , wherein it comprises operating with specific energies greater than 500 J/g.
8. The process according to claim 1 , wherein it comprises monitoring one or more parameters between the movement of the rams, the pressure (P(t)), a voltage (v(t)) and a current (i(t)) in a continuous way to interrupt the supply of electromagnetic energy in case of uncontrolled fluctuations of the process parameters and/or to provide detailed information concerning a working component.
9. The process according to claim 1 , wherein said increment of pressure (P 1 ) comprises a linear or monotonic increasing ramp from the first pressure (P 0 ) to the second pressure (Pi).
10. The process according to claim 1 , wherein it comprises modulating said increment of pressure (P 1 ) to control porosity, in particular to obtain porosity gradients.