Prem Engineering

Hard Calender

 

Hard Calendar for Paper Machines

A hard calendar is a machine typically installed at the end of the paper machine (PM) line before the reel. It is designed for both-sided smoothening of paper webs for the production of industrial and cultural papers. A steam box is sometimes installed before the calendar to further enhance the smoothness of the paper surface.

Design Features

Multi or Single-NIP Press:

  • NIP Combinations:
    • Two hard rolls.
    • An oil-heated thermo roll and a hard roll.
    • An oil-heated thermo roll and a swimming roll (hard) with camber control according to the load applied.

Main Parts

  1. Supporting Structure:

    • Composed of structural steel stands.
    • Minimizes operating vibrations.
    • Stands are connected by strengthened bolts and designed for safe handling during installation with a crane or other lifting devices.
    • Provides maximum machine rigidity both at standstill and during operation.
  2. Top Roll:

    • Solid or thermo roll.
    • Fixed or floating with air bellow loading/lifting.
    • Made of cast iron with a chilling depth of 10-12 mm.
  3. Bottom Roll:

    • Solid or swimming roll.
    • Fixed or floating with hydraulic upward loading/lowering.
    • Made of cast iron with a chilling depth of 10-12 mm.
  4. Swinging Doctors:

    • Used to clean the rolls during operation.
  5. Spreader Roll:

    • Ensures even distribution of the paper web.
  6. Web Guiding Roll with Bedding:

    • Guides the paper web through the calendar.
  7. Pneumatic / Hydraulic Loading:

    • Applies the necessary pressure for smoothening.
  8. Heating Station for Thermo Roll:

    • Provides oil heating for the thermo roll.
  9. Hydraulic Station for Swimming Roll:

    • Controls the camber and loading of the swimming roll.
  10. Drive for Both Rolls:

    • Powers the rotation of the rolls.

Advantages

  • Easy Installation and Assembly: Designed for straightforward setup and integration into existing PM lines.
  • Simple Routine Maintenance: Facilitates regular maintenance with minimal downtime.

Additional Features

  • Enhanced Smoothness: The optional steam box installed before the calendar can further improve the smoothness of the paper surface.
  • Load Control: The camber control of the swimming roll adjusts according to the load, ensuring consistent paper quality.

This hard calendar design ensures high-quality smoothening of paper webs, enhancing the final product’s surface quality while maintaining ease of installation, operation, and maintenance.