May 3, 2022
To operate your paper machines at today’s high speeds, at longer operation periods between shutdowns and at a total higher operating efficiency - a planned maintenance policy must be adopted.
Paper machine rolls are the most numerous and often the most complicated components of the machine. Standards of performance for paper machine rolls are higher, making maintenance increasingly important in several areas:
The standards of performance have to be maintained to compete in today’s world market. Paper machine efficiency and product quality depend directly on roll maintenance.
In addition to the requirement that rolls be maintained to give acceptable standards of performance, the maintenance program must be cost effective as well. Both product quality and cost effectiveness are necessary to promote something very dear to all of us: Job Security.
There are four approaches you can take to maintenance programs.
Reactive, also called corrective, run to failure, or fix it when it breaks. This will maximize the run time between repairs but it is also costly as unplanned shutdowns equal lost production and you must gather parts and people at the last minute. You need to stock more spare parts as you do not know what will break, when it will break and, if a catastrophic failure occurs, other components will be damaged. This is also considered dangerous and affects off quality production.
Routine preemptive wear repair, replacement or overhaul is done based on a schedule. Component life is determined by theory and experience. The problem here is that machines do not always follow schedules and this leads to needless repairs or failures ahead of schedule.
Preventive maintenance that maximizes component life through lubrication, alignment and roll grinding or balancing. This will extend the component life but does not prevent failure. Preventive maintenance can be compared to preventive medicine, the only
difference is the type of patient.
Predictive maintenance that is based on observation or measurement of the machine condition. This is performed while the machine is running versus while the machine is down. It includes vibration analysis, temperature and lube oil checks, visual (stroboscope) and audible (stethoscope). Combined with preventive maintenance, this is the best approach because it maximizes up time, improves quality and prevents catastrophes.
Maintenance - either scheduled or unscheduled - is an essential aspect of paper mill operations. It must be done and its cost is the price you pay for efficiency. The maintenance department is expected to maintain rolls so that they operate at the highest speed possible, for the longest period possible between shutdowns; and the shutdown itself must be as short in time as possible.
It is usually much easier and less time consuming to remove a completely assembled roll in need of repair and install a new unit than it is to attempt to make the repairs during a shut down. The repairs can then be done with attention to detail under the best possible conditions while the machine is running.
There are cases however, when this is not possible, such as when there is no spare available.
It is important that records are kept regarding the condition of rolls as they are removed from the machine and again when they have been refurbished and are again installed in the machine. These records help you analyze a reoccurring problem or operating conditions that are causing poor operating efficiency of the paper machine. Press and calender rolls are prime examples where good and accurate record keeping can help with solutions to operating problems.
When planning roll maintenance work to be done during a shutdown, there can be many jobs which interrelate, and the best way to coordinate is to plot them out.
One way of doing this is with a bar chart. This is particularly important when operations or the complete job depends on outside vendors or factory services.
With the sequence and timing thus indicated, those involved in the repair operations and those depending on the completion time have a graphic picture of how the work will progress.
A meeting should be held with key personnel that are involved in the shutdown. There should be one coordinator and they should use the chart to coordinate the various activities according to their proper sequence. The coordinator would also monitor the efforts of the vendors and service people who do not attend the scheduling meeting. Items that should be discussed in the meeting include:
NOTE: The installation and removal of mill maintenance crew safety locks can cause serious delays if not watched closely.
The maintenance departments of today’s paper mills have become more than a machine shop of the past. To keep the machine operating for longer periods of time and on-machine downtime at a minimum, the maintenance person must:
For assistance with your roll maintenance process, contact your Valmet representative.