Hot water modules for calender rolls, recommended maintenance

Calendering involves running the sheet through nips of heated rolls. The rolls are heated via heating modules to provide low-variance accurate roll temperatures. The following are recommended procedures for maintaining the hot water modules.

All strainers should be cleaned or blown down including the following:

1. Strainer on suction side of pump
2. Strainer in fill water line
3. Strainer in cooling water supply
4. Strainer in steam supply line

In addition, check the pump seal, heater and cooler tube bundle, solenoid valve and steam traps. Check the pump seal for leaks and to see if the seal flush operating. Loosen the seal flush coil at the seal end to determine that water is flowing. Repair a leaking seal or coil. Replace a coil if plugged.

Make a check on the heater and cooler tube bundles at system temperature of 200 °F or less. Check the tube bundles by first valving off the steam, condensate, water fill and cooling water supply and drain lines. On the heater, open the tell tale valve immediately after the cooler. In either case, a prolonged flow of water, for a minute or more, will indicate a leak in the tube bundle. If no tell tale valve is present, then the drain or condensate line will have to be disconnected to observe leakage. Replace a tube bundle if leak is found. A temporary fix would be to plug off a leaking tube bundle loop.

Check the solenoids by seeing if they respond to power on and off and if they allow and stop flow of water, steam or air. Replace any bad coils. Clean or replace sticking valves.

If pneumatic valves with positioners are present, check valve operation by moving the temperature setpoint up and down. The controller should be set with a 4 to 5 °F deadband to prevent unnecessary cycling of the valves.

Check to see that auto air vents are working. Clean or repair as necessary.

Check the pipe lines to see that all insulation is still in place. Replace as necessary.

For more information on calender maintenance, contact your Valmet representative.