Royal Purple Machinery Lubrication Magazine Purple Means Performance

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.

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 contaminants 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 compounded 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 than mineral oil-based lubricants. This isn't necessarily true. A mineral-based lubricant with a superior additive package can out-perform 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.

When is it appropriate to upgrade lubricant quality? Lubricants should be upgraded whenever the upgraded lubricant produces benefits or savings that exceed the additional cost of the oil.

What is a lubricant upgrade and who defines it? Some attempts to make lubricant upgrade decisions are based solely on comparative ASTM test results on various oil candidates. While ASTM tests can be indicators of how oil may perform, there is only one final arbiter for performance—the equipment being lubricated. The equipment will indicate what makes it work best!

Observed changes in oil and bearing temperatures, bearing vibration levels, energy demand, oil life and re-lubrication intervals, equipment cleanliness, how the oil handles water and other contaminants and machine repair frequency and costs are all indicators of lubricant performance. There simply is no substitute for running the candidate oil upgrade in the equipment.

When considering a lubricant upgrade, the lubricant supplier should be able to provide long term user references that can provide information to help determine whether the candidate lubricant is likely to deliver the targeted results.

Too often the cost of the oil becomes the main focus in purchasing decisions. In the absence of empirical evidence to the contrary, cost per gallon becomes the defining measure of value. Though unintentional, this leads to the most myopic view of lubricants possible. It is not the cost per gallon of the oil that is ultimately important. The only meaningful measure of value is the “applied cost” of the lubricant in the equipment it lubricates, which encompasses the lubricant's contribution to increasing or decreasing each of the following:

It is common for 80% of a plant's maintenance efforts to be expended on just 20% of its equipment, commonly called “bad actors.” These machines are the most likely candidates that can benefit from lubricant upgrades. They are also the machines in which the reliability benefits of the upgrade will be most quickly observable. While the need for improved equipment reliability may be the primary motivation for manufacturers to upgrade lubricant quality, the cost reductions attainable through energy savings can be significant and are the most easily documented.

Repairs and unscheduled downtime can drive up costs considerably. The following case illustrates how upgrading lubricants can dramatically reduce maintenance costs.

A major paper mill had experienced five unscheduled bearing failures on two wet ends in a two year time-frame. These failures were very costly and forced a review of the mill's lubrication practices and lubrication selection. The decision was made to test the impact of upgrading lubricants.

Bearing temperatures and vibration readings were monitored on the two paper machines before and after switching to high-performance synthetic grease. Equipment temperatures were taken four weeks after lubrication with the original synthetic grease and then four weeks after lubrication with the high-performance synthetic grease. Changing to the high-performance synthetic grease dropped temperatures an average of 30° F (Figures 1 and 2). The lower temperatures have been stable for 19 months.

Figure 1. Temperature readings on a paper machine press section with original syntheic grease with machine speed at 2,700 fpm.		Figure 2. Temperature readings on the same paper machine press section shown in Figure 1 with upgraded high-performance synthetic grease with machine speed at 2,900 fpm.

For a larger view of these figures, click here.

Vibration levels prior to the lubricant upgrade were normal but since the change, many vibration frequencies have dropped. No bearing vibration reading on either machine increased.

Most importantly, neither paper machine experienced a single unscheduled or scheduled bearing replacement since upgrading lubricants during the first two years of service. The annual production loss in dollars from bearing failures during two years of using the original grease was $64,625 (5 failures x 5.5 hours per failure x $4,700 per hour lost time / 2 years).

In addition to eliminating the downtime expense due to the failed bearings, upgrading lubricants enabled the mill to reduce maintenance expenses by reducing the frequency of lubrication intervals. The plant was originally using forty 120-lb kegs of synthetic grease annually for two machines at a cost of $500 / keg. The annual cost was $20,000.

The high-performance synthetic grease allowed the mill to extend lubrication intervals from four weeks to twelve weeks. Although the high-performance synthetic grease had a higher purchase price at $632 / keg, only sixteen 120-lb kegs were needed annually, for a total cost of $10,112. The combined annual financial impact of reduced maintenance cost and lubrications purchases was significant.

Paper mill reliability staff determined that the first press section roll drive side bearing was stage failing. This was determined by a temperature rise from the normal 165° F to 175° F to a temperature of 265° F and excessive vibrations.

Reliability staff decided to attempt to prolong the life of the equipment without making immediate repairs. Instead, they elected to simply upgrade lubricants. Although they were already using a major brand synthetic grease, they believed they would be better served by trying a synthetic grease from a manufacturer who specialized in high-performance lubricants.

Upon making the change, the bearing temperature went from 265° F to 160° F in less than one hour, and the vibrations decreased. The mill continued to run until its next scheduled downtime and changed the bearing even though all indications were that the bearing was no longer problematic. Reliability staff concluded that the upgraded grease prevented an approximate 12-hour downtime, which saved the mill in excess of $36,000 in downtime expense.

Energy costs for rotating equipment are many times higher than maintenance costs. Even a small percentage energy savings can quickly exceed the total cost of a lubricant purchase.

Production employees at a paper mill had attempted to put a higher pli load on a control crown (CC) roll in the calendar stack due to some new grades of paper now being made. The limiting factor had been the temperature rise of the oil in the CC roll with increased pli. The oil temperature was causing concern as it was reaching a level at which the oil viscosity and lubrication limits were being compromised. The plant had never been able to go above 650 pli.

Lubrication quality was determined to be the factor limiting equipment performance. Reliability staff made the decision to seek a better performing lubricant in an attempt to resolve the issue. They elected to upgrade from their current brand name petroleum-based paper machine oil to a high film strength paper machine oil. The high-performance synthetic lubricant allowed them to increase machine speed, reduce temperatures, and achieve a pli level they had never been able to attain: 873 pli (Table 1).

	Conventional oil	High- performance synthetic oil

Machine speed average	1,600 fpm	1,780 fpm
Oil temperature to roll average	130° F	130° F
Oil temperature from roll average	194° F	194° F
CC roll PLI average	650 PLI	873 PLI

After 15 months, the oil condition had remained exceptional, with iron wear metals remaining nearly nonexistent. The vast improvement in equipment operation created annual energy savings of $27,945. Energy savings were calculated using the data in Table 2. The energy savings alone exceeded the total cost of upgrading the lubricants within a few months and created substantial cost savings long-term.

Data

	Gallons oil flow through roll per minute	11.8
	Temperature difference between standard and upgraded oil	32
	Specific gravity (SG) of petroleum-based oil	0.893
	Specific heat (SH) of petroleum-based oil	0.505
	No.of BTUs to raise one lb of water 1° F	1
	No. of BTUs per hour to equal one hp	2,547.16
	Annual energy cost per hp at mill	$213
	Weight gallon of water	8.345

Calculation

11.8 gpm x 8.345 lb / gallon of water x 0.893 SG = 87.93 lb / min 87.93 lb / minute x 60 minutes = 5,275.8 lbs / hr (oil flow) 5,275.8 x 32° = 168,825.6 BTU / hr 168,825.6 / .505 SH = 334,308.11 334,308.11 / 2,547.3 = 131.2 hp 131.2 hp x $213 cost per hp = $27,945 in annual energy savings

Lubrication management encompasses all of the lubrication practices and procedures attentive to properly storing, applying, monitoring, and taking care of the selected lubricant. It includes making sure the right oil gets into the right equipment in the right place in the right amount at the right time. It also encompasses used oil analysis programs, visual inspections and maintenance of fluid levels, timely oil changes, and attention to contamination control from water, etc.

The elements that constitute good fluids management are far too extensive to address in this article, but they are essential to achieving quality lubrication. It is important to note however, that good lubrication practices are not a substitute for selecting high quality lubricants with the performance properties necessary for optimum performance in equipment.

Good lubrication practices simply cannot make a poor lubricant become a high-performance lubricant. Good lubrication practices are important in helping to preserve the original lubricating properties of the selected oil.