A workpiece holding device for holding a workpiece in a heat treatment system while the workpiece undergoes a thermal expansion and/or contraction includes at least two clamping units configured to apply a radial and/or an axial clamping force to the workpiece to hold the workpiece in the workpiece holding device in a predefined position, and an adjustment mechanism for setting the at least two clamping units to synchronously apply a substantially identical radial and/or axial clamping force to the workpiece.

A workpiece holding device for holding a workpiece having a substantially radial inner surface and a substantially radial outer surface in a heat treatment system while the workpiece undergoes a thermal expansion and/or contraction, the workpiece holding device includes at least two clamping units configured to apply a radial clamping force to the workpiece to hold the workpiece in the workpiece holding device in a predefined position, each of the at least two clamping units including a clamping element configured to abut against the radially inner surface and/or against the radially outer surface of the workpiece and to apply a radial clamping force to the workpiece.

A production method includes a surface-crosslinking step of heating a mixture of a surface-crosslinking agent and a particulate dried polymer obtained with an acid group-containing unsaturated monomer as a main component. A moisture content of the particulate dried polymer is not greater than 15% by mass. A heating device including a rotary container and a plurality of heating tubes that are located within the rotary container, extend in an axial direction of the rotary container, and rotate together with the rotary container, is used in the surface-crosslinking step. The heating device includes a means for introducing and discharging a gas into and from the rotary container.

A production method includes a surface-crosslinking step of heating a mixture of a surface-crosslinking agent and a particulate dried polymer obtained with an acid group-containing unsaturated monomer as a main component. A moisture content of the particulate dried polymer is not greater than 15% by mass. A heating device including a rotary container and a plurality of heating tubes that are located within the rotary container, extend in an axial direction of the rotary container, and rotate together with the rotary container, is used in the surface-crosslinking step. The heating device includes a means for introducing and discharging a gas into and from the rotary container.

A furnace includes: a furnace body; a housing rotary body including a plurality of side walls, a plurality of housing chambers partitioned by the side walls and disposed circumferentially in multiple stages, each including multiple housing chambers, and a space disposed in the central portion of the housing rotary body to provide a donut shape in plan view; a rotary driving device for rotating the housing rotary body; a heating device for heating the air inside the furnace body; a first and a second partition wall which together partition the inside of the furnace body into the first and the second zone; a first flow passage communicating a blowout port of the fan with outer circumference sides of the housing chambers in the first zone; and a second flow passage communicating outer circumference sides of the housing chambers in the second zone with a suction port of the fan.