Maintenence

Leakage problems that led to high cleanup and maintenance costs lead Longview, Wash., mill to convert bottom-entering pulpers to mechanical seal technology

Longview Fibre Improves Pulper Operation with Installation of Split Mechanical Seals

BY DICK MARTINSEN

Maintenance

Sealing bottom-entering pulpers is difficult. These pieces of process equipment must withstand large radial shaft deflections caused by market pulp bales and recycled material striking the equipment's rotor. Traditionally, these pulpers are packed, because few believe anything will work better, including typical mechanical seals. However, packing often allows leakage to occur and, in some cases, loss of valuable product.

For Longview Fibre, braided packing applied to this equipment created undesirable leakage levels. Due to the 112 in. square cross-section packing that is required for this application, a tight fit was difficult to achieve. Leakage of water and paper stock created a messy environment in the pits surrounding the pulpers. Located about 10 ft below ground level, the area is accessible only by climbing down a ladder, making cleanup difficult and sometimes costly.

In addition to cleanup costs and product losses, the company routinely paid for other damage associated with the leakage. Water would flow into the gearbox and motor, requiring gearbox repairs and electric motor rewinds throughout the year. Each motor change would take two people at least half a day-usually longer-costing the company $15,000 each time. During a normal year of operation, the mill would replace one gearbox and two motors because of damage caused by the leakage. Longview has 18 pulpers, making such costs add up.

Routine maintenance was time-consuming and expensive. Packing had to be replaced every 6 to 12 weeks, costing about $400 or $500 in materials and labor each time. Clearly there was a need for a better sealing solution than traditional packing or typical mechanical seals.

CONVERTING TO SPLIT SEALS. Since 1927, when Longview Fibre began operations with a single paper machine, packing was the norm. Seventy years later, packing is no longer appropriate for certain extreme applications such as pulpers at Longview. Choosing to take the leap to mechanical seals was relatively simple. Executive management was convinced that the mill was spending too much on repair and maintenance.

The company started with just one seal and now has eight of the 18 pulpers fitted with highly effective split mechanical seals, with plans for further installations. The company learned the benefits of no leakage-greatly reduced maintenance and labor costs and increased equipment reliability. These benefits are so valuable that they far exceed any investment in the seals. Now, no one-the mill maintenance superintendent, the maintenance staff, the general foreman, the executive management-wants to go back to packing for these pulping applications.

A main advantage is that the split seal life is dramatically longer than traditional packing due to its ability to withstand the heavy shock and vibration of the pulper. The first seals were installed almost three years ago, and are still performing reliably. The problem is solved, and the staff no longer considers sealing the pulpers a major concern.

SIMPLE INSTALLATION. During normal downtime of paper machine No. 11, the first two 7.375-in.-dia John Crane fully split seals were installed. First, however, a split 13-in.-dia bronze bushing was installed to keep the recycled trash away from the seal and to reduce the amount of seal water needed to operate this mechanical seal. The amount of water needed for each seal is monitored at 3 gpm to control dilution in the process.

With only seven components, the split seals are outside-mounted and take less time to install than conventional cartridge mechanical seals. In fact, the maintenance mechanics ultimately found that installation of the split seals takes less time than packing, since the large packing that was required for this application was difficult to align properly and took considerable adjustment. The split seals' rotating assembly self aligns squarely with the shaft and is easily mounted even on worn shafts. The split seals' stationary assembly is designed to fit pitted and out-of-square stuffing boxes effectively.

To install the seals, no modification of the equipment was required. All adaptive parts are supplied so the split seals could be fitted to existing equipment correctly. While severe shaft movement and vibration inherent in the application contributed to packing's diminished sealing power, these severe conditions posed no threat to the split seal. In fact, the seal was designed to accept heavy vibration and shaft motion typical on pulpers and other equipment.

ADVANCED TECHNOLOGY. The fully split seal installed at Longview Fibre can withstand the heavy vibration because of the seal's patented designed compression ring rubber bellows. These bellows add flexibility and shaft deflection, so angular misalignments and runouts are "tracked" by the seal without impairing performance. The seals operate leak-free even with rough, pitted, and rusted stuffing boxes typically found on older equipment. These seals can accept:

• Radial shaft movement of 0.125 in.
• Shaft runout up to 0.020 in.
• Stuffing box waviness up to 0.030 in.
• Axial end play up to 0.060 in.

The nonpusher bellows design is key to the seal's flexibility without hang-up. The seal also has no springs or O-rings, which can clog during operation. The rotating rubber sealing ring's large surface area seals on the shaft to block leakage, even on worn or damaged shafts. Additionally, special clamp rings hold the split seal faces in place securely.

Handling temperatures up to 180F, pressures up to 80 psig, and speeds up to 1,800 rpm, the seals are highly effective for bottom-entering pulpers at Longview. These heavy-duty seals are becoming a necessity for equipment typically used in papermaking, such as pulpers, stock chest agitators, horizontal split case pumps, and vertical pumps.

ENVIRONMENTAL IMPLICATIONS. By evidence of the dry surfaces under the pulpers, Longview Fibre found that water leakage need not be a "normal" part of paper production, as it has been considered in the past. As a valuable natural resource, water should be, and can be, conserved. Split mechanical seals prevent the leakage that packing allows on mill floors and pits.

At the same time, the split seals actually cut downtime because of fast installation and eliminated maintenance. This translates into more uptime and better efficiency and productivity for the mill. So, in the long run, these highly reliable split seals go beyond cutting costs to contributing to the bottom line.