Right Lubricant for the Right Job Helps Lower Machine Operating Costs, The

Pulp & Paper, Jul 2004 by McFann, Mark

Rather than a "one-size-fits-all" approach, reliability managers should examine major machine sections to determine well-suited oil and grease characteristics

Today's global economy has put many paper facilities under pressure to lower operating costs and increase efficiency. This often means doing more with fewer people in aging facilities using older equipment. The challenge is magnified by the loss of an increasing number of senior reliability managers who retire and take their many years of valuable experience and knowledge with them.

The necessity for improvement has prompted more attention to lubrication and its role in operating equipment safely, reliably, and less expensively. As a result, the industry is focusing more on the two factors that collectively determine the quality of lubrication-lubricant selection and lubrication management.

Lubricant Selection

In its most rudimentary form, lubricant selection is nothing more than selecting the appropriate type and viscosity of lubricant for each piece of equipment requiring lubrication. This information is usually found in the original equipment manufacturer's manuals.

The first step is to compile a list of lubricants for all equipment requiring lubrication (a lubrication survey). The second step is usually to consolidate this list into a more practical and manageable number of different types and viscosities of lubricants to be inventoried and used in the plant.

Lubricant consolidation always involves certain trade-offs. Informed choices must be made regarding how far lubricants can be safely consolidated without materially affecting the performance and reliability of the equipment being lubricated.

There are four distinct sections of paper machines requiring lubrication. They are the forming section, the press section, the drying section, and the reel. Each section performs specific functions and creates particular demands that must be considered in lubricant selection. The first three sections create particular lubrication challenges.

The large volume of water in the forming section puts unusually high demands on a lubricant, which must seal, keep water out, and purge containments from the bearing. Typically, grease is the best choice for forming section bearings. One should seek high-quality aluminum complex grease with high water-repelling qualities and outstanding corrosion protection. Sheer stability-a lubricant's ability to prevent additives from dropping out of the base oil-is also critically important. Lubricants in wet environments are often prone to sheering. A lubricant with poor sheer stability will lose its additives and its ability to lubricate properly and quickly, increasing the likelihood of bearing failure.

In the press section, plain (or "solid") press rolls are common, and heat press rolls are becoming increasingly common. As with the forming section, water is the predominant lubrication challenge. High temperature pressing with heated rolls exacerbates the lubrication challenge. Grease and circulating oil are common in the press section. In addition to repelling water and preventing corrosion, the lubricant must be able to disperse heat quickly.

The dryer section exposes bearings to high temperatures over a long period of time. The trend toward larger, faster machines has compound the temperature challenge even further. Regardless of which combination of rolls and configurations may be found in a dryer section, the circulating paper machine oil chosen should be selected based on real-world data on heat dispersement and/or temperature reductions that lubricant suppliers should be able to provide.

If all lubricants performed equally well, involvement in lubrication selection would end with selecting the appropriate type and the correct viscosity. Recent advances in lubricant technology provide users with a broad range of quality options, and many of these lubricants can provide significantly improved machinery efficiency and reliability.

There are no specific types of lubricants that can be predicted to underperform. Each lubricant manufacturer's unique blend of additive chemistry and base oil gives each lubricant its performance characteristics/capabilities. For instance, the conventional "wisdom" is that synthetic lubricants are better then mineral oil-based lubricants. This isn't necessarily true. A mineral-based lubricant with a superior additive package can outperform a synthetic lubricant with a lesser additive package. Testing lubricants against each other in real-world situations is the only way to determine which works best.

Because high-performance lubricants can cost more, opting to use one of these lubricants almost always involves overcoming the additional hurdle of "price justification." This becomes somewhat of a "Catch 22" situation, wherein the cost justification required for purchase approval cannot be documented until after the lubricant has been purchased and put to use. Thus a commitment to lubricant upgrades often requires a leap of faith.