Up and Running articles
Up and Running articles
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Field Report - Chronic dryer drive oscillation, a case study
The clack-clack-clack noise warned of heavy oscillation in the drive, subjecting the machine to potentially damaging duress. The only known cure was a shutdown and restart, costing the mill productivity and dollars. The shift supervisor calls in a drive technician for assistance...
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Field Report - Cleaning VacRolls
VacRoll suction holes and the grooves of all rolls should be cleaned regularly, as they may get completely clogged due to web moisture, particularly at the start of the dryer section. Bearing housings also need attention. Proper handling of the rolls is also important.
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Increase dewatering, reduce vacuum needs with Valmet Hard Coating Solid and Valmet Uhle Box Cover
The new coating and uhle box cover also improve runnability, moisture profiles and felt lifetime. The technology is unbeatable and several references prove it.
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Field Report - Care and handling of Uhle boxes
Reliable operation of a press section uhle box requires attention to care and handling, as well as routine maintenance. Blades and covers are susceptible to costly damage if improperly handled and maintained.
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Field Report - Screen cylinder troubleshooting
Once a screen cylinder's holes plug or its raised plating or coating is worn smooth, a host of operational problems can occur affecting runnability, capacity, pulp quality and cylinder life. There are three warning signs of excessive wear to monitor.
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Field Report - Common hydraulic valves, pressure reducing valves
Pressure reducing valves are used to create and hold a pressure setpoint in a downstream hydraulic branch. Valmet uses sandwich style valves because they are easy to fit in a stacked hydraulic valve block circuit.
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Field Report - Reel primary arm nip relief
Excessive bottom waste occurs during turn-ups where there is insufficient primary arm nip relief at the reel. To avoid this, primary arm nip force control should start before turn-up and continue smoothly as the building parent reel travels down along the reel drum to the secondary arms at the kickout rails.
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Common evaporator issues and solutions
Evaporators are used to evaporate black liquor from approximately 15% dry solids to 70-85% dry solids. Operating issues include scaling, corrosion, liquor carry-over, vacuum, condensate segregation and foaming liquor. Each can be mitigated with process and technology changes.
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Field Report - Dynamic balancing of rolls
Although a roll is statically balanced, it may have an eccentric center of gravity which cannot be detected by simple static balance. This will become noticeable when the roll speed is increased, and an end-for-end motion occurs. Dynamic unbalance requires investigation to determine which end, or both, require counter-weighting.
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Field Report - Roll structure analysis (wound-in tension)
Among the most important factors determining the quality of a finished paper roll is consistent roll structure. Wound-in tension is the most important component of roll structure. The WIT-WOT and Gap Test are methods of measuring wound-in tension.