The brake disc includes two first members and at least one second member. Each of the first members has a sliding surface, and has almost a disc shape or an almost annular plate shape. The second member has a plurality of fins and a fin holding part. Each of the two first members and the at least one second member is manufactured by pressing. The brake disc is manufactured as the two first members and the at least one second member manufactured by pressing are joined to each other.

A wheel automatic closed die forging production line includes a sawing machine, a first transfer track, a bar heating furnace, a first manipulator, an oscillating rolling machine, a second manipulator, a primary forging hydraulic machine, an intermediate heating furnace, a third manipulator, a finish forging hydraulic machine, a wheel transfer block, a fourth manipulator, a cutting, expanding and punching hydraulic machine, a second transfer track, a spinning machine, a fifth manipulator, a third transfer track, a heat treatment furnace, a fourth transfer track, a machining unit, a sixth manipulator and a fifth finished product track, and can improve mechanical and the physical properties of the wheel product, the wheel forging effect and the yield. Aluminum and magnesium alloy wheel compression molding is realized, reducing cost, time and labor for secondary machining and reshaping, and improving production safety and efficiency.

A flywheel energy storage system incorporates various embodiments in design and processing to achieve a very high ratio of energy stored per unit cost. The system uses a high-strength steel rotor rotating in a vacuum envelope. The rotor has a geometry that ensures high yield strength throughout its cross-section using various low-cost quenched and tempered alloy steels. Low-cost is also achieved by forging the rotor in a single piece with integral shafts. A high energy density is achieved with adequate safety margins through a pre-conditioning treatment. The bearing and suspension system utilizes an electromagnet that off-loads the rotor allowing for the use of low-cost, conventional rolling contact bearings over an operating lifetime of several years.

A flywheel energy storage system incorporates various embodiments in design and processing to achieve a very high ratio of energy stored per unit cost. The system uses a high-strength steel rotor rotating in a vacuum envelope. The rotor has a geometry that ensures high yield strength throughout its cross-section using various low-cost quenched and tempered alloy steels. Low-cost is also achieved by forging the rotor in a single piece with integral shafts. A high energy density is achieved with adequate safety margins through a pre-conditioning treatment. The bearing and suspension system utilizes an electromagnet that off-loads the rotor allowing for the use of low-cost, conventional rolling contact bearings over an operating lifetime of several years.

Aluminum alloys described herein include silicon, iron, copper, manganese, magnesium, and chromium. In various implementations, the aluminum alloys also include one or more of zinc and titanium. Typically, a total amount of iron and manganese in the aluminum alloys is no less than 0.28% by weight and no greater than 0.45% by weight, and the grains in the aluminum alloys have an average grain length of no greater than 6 mm. Aluminum alloy billets can be forged for wheel production at selected temperatures.

Aluminum alloys described herein include silicon, iron, copper, manganese, magnesium, and chromium. In various implementations, the aluminum alloys also include one or more of zinc and titanium. Typically, a total amount of iron and manganese in the aluminum alloys is no less than 0.28% by weight and no greater than 0.45% by weight, and the grains in the aluminum alloys have an average grain length of no greater than 6 mm. Aluminum alloy billets can be forged for wheel production at selected temperatures.

Various implementations include a ring material used for producing a ring molded article. The ring molded article has two convex portions which respectively protrude on opposite sides of the ring molded article in a direction of a center axis thereof and extend in a direction of a circumference of the ring molded article. A straight line passing through centers of gravity of first and second side regions is inclined by an angle relative to the center axis of the ring material, the first and second side regions are obtained by virtually dividing a one half section of the ring material based on a middle of a maximum height of the ring material in the direction of the center axis of the ring material, and a range of the angle is 7 degrees to 40 degrees.

Various implementations include a ring material used for producing a ring molded article. The ring molded article has two convex portions which respectively protrude on opposite sides of the ring molded article in a direction of a center axis thereof and extend in a direction of a circumference of the ring molded article. A straight line passing through centers of gravity of first and second side regions is inclined by an angle relative to the center axis of the ring material, the first and second side regions are obtained by virtually dividing a one half section of the ring material based on a middle of a maximum height of the ring material in the direction of the center axis of the ring material, and a range of the angle is 7 degrees to 40 degrees.

A flywheel energy storage system incorporates various embodiments in design and processing to achieve a very high ratio of energy stored per unit cost. The system uses a high-strength steel rotor rotating in a vacuum envelope. The rotor has a geometry that ensures high yield strength throughout its cross-section using various low-cost quenched and tempered alloy steels. Low-cost is also achieved by forging the rotor in a single piece with integral shafts. A high energy density is achieved with adequate safety margins through a pre-conditioning treatment. The bearing and suspension system utilizes an electromagnet that off-loads the rotor allowing for the use of low-cost, conventional rolling contact bearings over an operating lifetime of several years.

A flywheel energy storage system incorporates various embodiments in design and processing to achieve a very high ratio of energy stored per unit cost. The system uses a high-strength steel rotor rotating in a vacuum envelope. The rotor has a geometry that ensures high yield strength throughout its cross-section using various low-cost quenched and tempered alloy steels. Low-cost is also achieved by forging the rotor in a single piece with integral shafts. A high energy density is achieved with adequate safety margins through a pre-conditioning treatment. The bearing and suspension system utilizes an electromagnet that off-loads the rotor allowing for the use of low-cost, conventional rolling contact bearings over an operating lifetime of several years.