Inducing Unreliability

Operating and maintaining a paper machine is a complex task.

Most of the problem is the issue of variability.

Yes, the machine was designed by the manufacturer to produce x number of tons at a speed of x feet per minute with a paper weight of x grams per meter.

The design is complex as well simply because the size of the continuous web is changing as it progresses through the different ‘sections’ of the machine, albeit as moisture is driven out through gravity, vacuum and heat. The sheet shrinks from side to side, or cross direction (CD) and end to end, or machine direction (MD).

Add in the influences of ambient air, the effects of chemicals added to the cellulose fibers and human intervention and the variability becomes almost infinite.

It is not uncommon for the operators, especially aggressive technical management types to push the design parameters, e.g., speed, paper properties, furnish characteristics.

Increasing speed beyond the original design alone is a huge culprit for unreliability, yet it is a very common practice within the paper industry.

Paper machines built a century ago, designed for maximum speed of 300 feet per minute are now operating at speeds exceeding 1000 feet per minute and likely producing a grade of paper never even imagined at the time of design. Much of the experimenting is done as a so-called ‘trial’, a proof of concept that by changing this parameter, or that part of the process or equipment will result in increased production, or improved quality.

When the operating goal is more production (throughput) with existing equipment something must suffer and that something is asset performance, usually effecting reliability.

For example:

The newly promoted paper machine superintendent, former process engineer – paper is motivated and encouraged to produce more paper, in this case common 20lb uncoated free sheet, in the same amount of time with the same equipment, which is a vintage 1960’s Beloit newsprint machine with straight through presses.

Of course, the paper produced must meet, or exceed the market’s quality requirements to be saleable, so that is an important consideration.

The machine produces 250 tons per day of 20# UFS/UWF without too much stress on the equipment, quality is another story and will require a major rebuild of the wet end and stock delivery system.

Formation, two sidedness and curl being a few of the major issues for this paper market segment.

The higher weight paper (than originally designed) now being made requires more moisture removal in order to speed up the machine to make more paper. A situation typically called dryer-limited where there is not enough dryer capacity to remove the moisture in the sheet as it enters the drying sections. Adding dryers is not an option in this case due to building constraints.

A proven solution is to increase the press section removal of water.

A strategy develops

This is the option the new manager studies.

He contacts his preferred fabric supplier to ask a myriad of questions about the potential clothing, cleanliness and water removal characteristics, ultimately ordering a set of newly designed felts for the first and second presses, top and bottom. Felts are expensive and have a limited, yet variable life cycle.

He contacts the area assigned engineer to research the first press bottom suction roll for its designed loading (pounds per linear inch – PLI) capabilities.

His basic solution concept being to increase load on the press to squeeze more water from the sheet to the felt and then squeegee and vacuum the water from the felt through the bottom suction roll and added vacuum sources.

A new press section designed to do this can be a solution, but is months, perhaps years in the future and a large capital expenditure allocation. Proof of concept will improve the chances of funding approval.

Placement of cleaning showers and additional vacuum sources (uhle boxes) is evaluated with the felt supplier.

All these evaluations and ultimately, decisions, are made without any input from maintenance and only the ‘loading’ research by the area engineer.

The engineer delivers the chart indicating the design limitations of PLI for the suction press roll, a drilled brass shell that rotates while supported on each end with bearings on a stationary core to collect the water removed by vacuum as the felt and sheet are pressed between it and its matching solid roll loaded with pneumatic cylinders. The roll is designed for 150 PLI.

The paper machine manager wants to load it to 400 PLI.

The engineer explains that too much pressure will damage the suction roll, for which there is no spare, and confirms he has had a conversation with the OEM who agrees.

The paper machine manager flat states that the process to load the roll is already started, money is spent on clothing, work orders to the area assigned maintenance have been written to rearrange showers and add uhle boxes as required. Work to be performed during upcoming scheduled machine downs.

The engineer is stunned and reports this to the e&m manager, the highest authority in his chain of command.

The e&m manager approaches the paper machine manager about this developing disaster but is told that they will proceed, because the paper machine manager suspects there is sufficient ‘safety factor’ built into the design of the suction press roll shell to withstand the added linear pressure imposed by the pneumatically loaded solid top roll.

After all, it is the only way to increase production with existing equipment and that is the paper machine manager’s prerogative under existing cultural norms.

The e&m manager is overruled when he approaches senior management. It is a trial after all, a proof of concept. The operators will monitor the suction shell’s condition.

The increased dewatering/speed up trial begins.

After a couple of weeks of increasingly more loading and speed and tons of paper per day improvement, the on-call maintenance person calls the e&m manager at home to announce, in a panic, the bottom first press roll has failed, tearing the top and bottom felts and damaging the second press felts and rubber covered press rolls with debris.

The machine is down and he has people coming to the mill to evaluate the situation.

The e&m manager heads to the mill to be part of the evaluation.

There is no spare bottom first press roll.

A new roll will take 18-24 months to fabricate by the OEM. A fact confirmed by the area engineer during his PLI research.

Contingency planning

A ‘contingency’ plan is devised.

A bottom solid roll might be adapted to fit in the position and additional vacuum sources added to both sides of the nip to simulate the suction roll, but the machine will operate at a much reduced speed because much less water will be removed from the sheet and the dryers will be overwhelmed with their moisture evaporation capability at what had been a normal operating speed before the trial.

In the meantime.

The e&m manager has connections to the OEM and finds that several other very similar sized machines had been built at the same time. His contact informs him that yes, there is an almost exact duplicate, e.g., bearing centers, face length at a mill west of his location and provides a contact name.

The contact explains that, fortunately, that machine has since been rebuilt and the old press section was the major part of the rebuild.

The old suction roll is in that mill’s ‘boneyard’ and is unused. It is available, with conditions, e.g., pay for the shipping preparations, freight and guarantee its return after the new replacement roll is received (18-24 months).

A dedicated truck and trailer with drivers are sent on the nearly 3000-mile roundtrip in order to expedite the shipment.

In the meantime, a lot of experimenting has been occurring to find the optimum configuration and speed of the cobbled-together, temporary solution, two solid rolls squeezing the felt and sheet, numerous vacuum boxes before and after the nip. The machine is making paper, but not nearly as much and with lower quality of previous runs. Paper breaks are plentiful and troublesome.

Frustration rises, fingers pointed, CYAs everywhere.

Of course, the newly appointed paper machine superintendent, former process engineer is the center of attention and blame.

But can he really be blamed for doing his job, the job described to him by his manager and the manager above?

Not really. They expected him to figure out ways to improve the production capacity and quality, using his process knowledge.

His job is a time-honored tradition.

It’s his job, and time-honored tradition.

Did his training include reliability, mechanical failure modes, mechanical engineering?

If any, very little.

Was he told to include reliability as a consideration when he formulated his ideas?

Not likely.

When focused on a task agreed to by your superiors and not given all the parameters to consider, a culture develops. In this case, a production at all costs culture, which in turn leads to a reactive maintenance culture blind to any and all other possibilities.

But in the end, in this situation what was gained and what was lost?

• An asset was ruined, beyond salvage.
• Production ceased and then limited.
• Unbudgeted costs increase.
• Unnecessary expenses incurred.
• Ill feelings and mistrust linger.

All the costs of unreliability that were preventable.

A lot of progress has been made in the field of asset reliability and optimization.

Most of the progress has been in process (RCM, RCA, Basic Care, planning & scheduling, skills training among others) and technology (vibration monitoring, thermography, ultrasound, web break monitoring, lubrication delivery among many others), but how much progress has been embraced, enacted and adopted in mill cultures?

It’s publicized that there is much emphasis on these much-needed cultural improvements among the more enlightened, world-leading companies, but what is the reality on the shop floor, and how was this validation performed?

Asset reliability is everyone’s business but does everyone, from the top down and bottom up participate?

Or, is a position designated, briefly acknowledged and supported, only to revert to the same old ‘caretaking’ culture of old after the flavor of the month loses its taste.

You can have all the right process in place, and many do.

You can have all the appropriate technologies procured, people trained, and many do.

But if the third leg of that three-legged stool, cultural change, is missing you will spend an inordinate amount of time and energy compensating.

Isn’t it time, instead, to focus a little time and effort on cultural reliability and optimization?