Flywheel Rotor

Abstract

A solid steel flywheel rotor having improved material properties offers improved energy storage at reduced cost. A process for manufacturing the rotor is also provided.

What is claimed is: 
     
         1 . A flywheel rotor comprising a rotationally symmetric mass made of a single piece of steel having:
 a yield strength of at least 900 MPa;   a fracture toughness of at least 40 MPa·m 0.5 ; and   a maximal intrinsic defect size that is 2 mm or smaller,   wherein the mass has a diameter that is greater along a first axis than its widest thickness along a second axis, the widest thickness being between 8 inches and 14 inches, the mass configured to rotate about the second axis.   
     
     
         2 . The flywheel rotor of  claim 1 , wherein the mass does not include a hole through a center axis of the mass. 
     
     
         3 . The flywheel rotor of  claim 1 , further comprising a plurality of journals protruding from the mass, each journal shaped to physically couple to a shaft. 
     
     
         4 . The flywheel rotor of  claim 1 , wherein the rotor has a mass in a range from 2 tons to 10 tons. 
     
     
         5 . The flywheel rotor of  claim 1 , wherein the mass has an outer diameter in a range from 36 inches to 94 inches. 
     
     
         6 . The flywheel rotor of  claim 1 , wherein the mass is formed of through-hardened and tempered 300M steel, formed using at least one of:
 a vacuum-arc-remelting (VAR) process,   an electro-slag-remelting (ESR) process, or   a vacuum induction melting (VIM) process.   
     
     
         7 . The flywheel rotor of  claim 1 , wherein the mass has a fishtail shape. 
     
     
         8 . The flywheel rotor of  claim 1  wherein the fracture toughness is in a range from 150 MPa·m 0.5  to 300 MPa·m 0.5 . 
     
     
         9 . A flywheel rotor comprising:
 a rotationally symmetric body made of a single piece of through-hardened and tempered steel, the mass having a diameter greater along a first axis than its widest thickness along a second axis, wherein the mass is in a range between 2 tons and 5 tons; and   a plurality of journals protruding from the body, each journal shaped to physically couple to a shaft,   wherein the body is configured to rotate about the second axis.   
     
     
         10 . The flywheel rotor of  claim 9 , wherein the body has a yield strength of at least 900 MPa. 
     
     
         11 . The flywheel rotor of  claim 9 , wherein the body has a fracture toughness of at least 40 MPa·m 0.5 . 
     
     
         12 . The flywheel rotor of  claim 9 , wherein the body has a maximal intrinsic defect size that is equal to or smaller than 2 mm. 
     
     
         13 . The flywheel rotor of  claim 9 , wherein the body does not include a hole through a center axis of the body. 
     
     
         14 . The flywheel rotor of  claim 9 , wherein at least some portion of the body is greater than 4 inches from an outer surface of the mass. 
     
     
         15 . The flywheel rotor of  claim 9 , wherein the widest thickness is in a range between 8 inches and 16 inches. 
     
     
         16 . The flywheel rotor of  claim 9 , wherein the diameter is at least 48 inches. 
     
     
         17 . The flywheel rotor of  claim 9 , wherein the body has a fishtail shape. 
     
     
         18 . A method for manufacturing a flywheel rotor comprising:
 alloying a plurality of elements to form a single mass of steel, the mass having a diameter greater along a first axis than its widest thickness along a second axis, the widest thickness being between 8 inches and 14 inches, the mass configured to rotate about the second axis;   refining the mass using one of:
 a vacuum-arc-remelting (VAR) process, 
 an electro-slag-remelting (ESR) process, and 
 a vacuum induction melting (VIM) process; 
   performing a multi-step forging process to align grain size and direction within the mass;   heating and quenching the mass to through-harden the mass;   tempering the mass; and   machining the mass.