Image fixing device for image forming apparatus

A fixing device for fixing an image on recording paper, comprising:

• a fixing roller including a cylindrically shaped core and a heater;
• a pressure roller held in pressured contact against said fixing roller;
• and
• a circular plate having a contacting portion held in contact with the inner surface of the cylindrically shaped core for reinforcing and preserving the cylindrical shape of said core,
• wherein a specific heat capacity of said circular plate is less than that of a specific heat capacity of said cylindrical core.

A fixing device for fixing an image on recording paper, comprising:

• a fixing roller including a cylindrically shaped core and a heater;
• a pressure roller held in pressured contact against said fixing roller;
• and
• a circular plate having a contacting portion held in contact with the inner surface of the cylindrically shaped core for reinforcing and preserving the cylindrical shape of said core,
• wherein a thickness of said cylindrically shaped core t.sub.r0 satisfies the equation:
• t.sub.r0 >3.times..sigma..sub.th .times.D.sub.in /(2.times..sigma..sub.s)
• where .sigma..sub.th denotes a thermal stress of the reinforcing means, t.sub.r0 denotes a thickness of said cylindrical core, D.sub.in denotes an inner diameter of said cylindrical core, and .sigma..sub.s denotes a yield stress of said cylindrical core.

A fixing roller comprising:

• a cylindrically shaped core and a heater;
• a pressure roller held in pressured contact against said fixing roller;
• and
• reinforcing means for preserving the cylindrical shape of said core, said reinforcing means comprising a circular plate having a contacting portion held in contact with the inner surface of the cylindrically shaped core, said reinforcing means further comprising a shoulder connecting said cylindrically shaped core to a surface parallel to an axis of the cylindrical shape and having a diameter smaller than that of said cylindrically shaped core.

A fixing roller comprising:

• a cylindrically shaped core and a heater;
• a pressure roller held in pressured contact against said fixing roller;
• and
• a circular plate having a contacting portion held in contact with the inner surface of the cylindrically shaped core for reinforcing and preserving the cylindrical shape of said core,
• wherein a specific heat capacity of said circular plate is less than that of a specific heat capacity of said cylindrical core.

A fixing roller comprising:

• a cylindrically shaped core and a heater;
• a pressure roller held in pressured contact against said fixing roller;
• and
• a circular plate having a contacting portion held in contact with the inner surface of the cylindrically shaped core for reinforcing and preserving the cylindrical shape of said core,
• wherein a thickness of said cylindrically shaped core t.sub.r0 satisfies the equation:
• t.sub.r0 >3.times..sigma..sub.th .times.D.sub.in /(2.times..sigma..sub.s)
• where .sigma..sub.th denotes a thermal stress of the reinforcing means, t.sub.r0 denotes a thickness of said cylindrical core, D.sub.in denotes an inner diameter of said cylindrical core, and .sigma..sub.s denotes a yield stress of said cylindrical core.

An image forming apparatus for forming an image on a sheet of paper, comprising:

• a fixing roller including a cylindrically shaped core and a heater;
• a pressure roller held in pressured contact against said fixing roller;
• and
• reinforcing means for preserving the cylindrical shape of said core, said reinforcing means comprising a circular plate having a contacting portion held in contact with the inner surface of the cylindrically shaped core, said reinforcing means further comprising a shoulder connecting said cylindrically shaped core to a surface parallel to an axis of the cylindrical shape and having a diameter smaller than that of said cylindrically shaped core.

An image forming apparatus for forming an image on a sheet of paper, comprising:

• a fixing roller including a cylindrically shaped core and a heater;
• a pressure roller held in pressured contact against said fixing roller;
• and
• a circular plate having a contacting portion held in contact with the inner surface of the cylindrically shaped core for reinforcing and preserving the cylindrical shape of said core,
• wherein a specific heat capacity of said circular plate is less than that of a specific heat capacity of said cylindrical core.

An image forming apparatus for forming an image on a sheet of paper, comprising:

• a fixing roller including a cylindrically shaped core and a heater;
• a pressure roller held in pressured contact against said fixing roller;
• and
• a circular plate having a contacting portion held in contact with the inner surface of the cylindrically shaped core for reinforcing and preserving the cylindrical shape of said core,
• wherein a thickness of said cylindrically shaped core t.sub.r0 satisfies the equation:
• t.sub.r0 >3.times..sigma..sub.th .times.D.sub.in /(2.times..sigma..sub.s)
• where .sigma..sub.th denotes a thermal stress of the reinforcing means, t.sub.r0 denotes a thickness of said cylindrical core, D.sub.in denotes an inner diameter of said cylindrical core, and .sigma..sub.s denotes a yield stress of said cylindrical core.

A fixing device for fixing an image on recording paper, comprising:

• a heat emitting fixing roller including a thin cylindrically shaped core whose inner surface has a cylindrical shape;
• a pressure roller held in pressured contact against said fixing roller;
• and
• a reinforcing device having a circular plate and a contacting portion which is extended at an angle of substantially 90.degree. from an outer edge of said circular plate portion along the inner surface of said cylindrically shaped core.