Energy Efficiency Through Precision Lubrication

In today’s increasingly competitive manufacturing business, plant managers face the daunting task of finding ways to reduce cost and increase throughput. Moreover, energy is a significant component of a manufacturer’s cost structure, and its price keeps rising.

Manufacturing processes use energy from such varied sources as coal, natural gas, petroleum and electricity from a generating plant. Plants also put some of these sources to direct use to create other forms of energy, such as pressurized oil, pressurized air, steam and accelerating chemical reactions.

Most practitioners know that one of a lubricant’s key responsibilities is surface separation and protection. When properly selected and maintained, the lubricant provides surface clearance that also enables effective energy use. However, plants often overlook this aspect of machine lubrication, along with human energy use. Human energy expended to replace the lubricant represents approximately 5% of maintenance labor, which is only a small portion of the total labor. Even so, underdeveloped practices squander much of the human energy dedicated to lubrication maintenance.

Opportunities for energy improvement from the machine lubrication process are both obvious and obscure. In this article, we’ll explore some of these opportunities, including:

• The strong theory behind reduced energy consumption through better lubrication practices.
• How most plants could save huge amounts of money by improving their human energy use.
• A six-step lubricant evaluation process that reduces energy consumption.

Tribology—To Coin a Word

The word “tribology” first appeared on March 9, 1966, following the publication of a report by the British Minister of State for Education and Science. The report suggested that British industry stood to gain very big money from improvements in lubrication design and practice [1].

British professor and researcher Dr. H. Peter Jost and his team offered their impression of the potential for improvements in a variety of areas, as shown in Figure 1 [2]. Following this study, Germany, Japan, China and Canada each executed their own studies that have produced insight similar to that of the Jost Report.

Projected Economic Benefits of Improved Lubrication

Figure 1: Dr. H. Peter Jost’s Projected Economic Benefits Associated With Improved Lubrication Design and Practice.

Jost’s study indicated cost reduction potential for several categories including savings on energy purchases (7.5%), general efficiency (1%) and lubricant purchases (20%). In fact, forty-four years after this study, one could argue that even greater savings potential are available in a modern manufacturing economy from most of these categories.

Following are some arguments to consider for these savings opportunities.

Lubrication Program Process Improvements

Before efficiency analysis and optimization, plant lubrication programs typically waste a large amount of time and effort. For this reason, practice improvement considerations could include:

• Using tools and technology (automation) to replace human labor.
• Optimization of each machine’s lubricant requirement.
• Optimization of each selected lubricant totals.
• Elimination of lubricant replenishment via sealed or non-lubricated components.
• Use of advanced eutectic technologies/materials to limit surface roughness.

Labor Utilization

A large percentage of lubrication programs operate inefficiently and on auto-pilot. As a result, the net labor hours required to fulfill practices tend to be high, and yet the results often fail to cover the minimum requirements. Labor-saving practices include the following.

Grease Relubrication Practices

Efficient grease relubrication frequencies (15% to 20%). It is common for grease relubrication practices to be inconsistent with component manufacturer’s requirements. Therefore, calculating intervals based on machine operating environment and characteristics is an important first step. Reliability engineers often discover, to their surprise, that the scheduled frequencies for slow-rotation machines are too short and high-speed (high nDm) applications are too long. In fact, balancing grease relubrication intervals alone may free up labor needed to make other systematic lubrication program improvements.

Use of automation for short-term grease intervals (5%). Plants should certainly evaluate any grease replacement activity with an interval shorter than seven days for automatic lubrication, either in the form of a single-point grease cup or in the form of simple multipoint systems. Ultimately, a cost comparison for installation and long-term maintenance should drive the choice.

Operator Care and Oil Condition Control

Operator-based care, including sump level checks and top-up activities (20%). Operators can and should perform level checks and corrections. Admittedly, operators are always busy; however, part of the operator’s role should be to visit the machines, observe their condition, check the levels and report any observed problems.

Aggressive oil condition control—filtration and cooling (10%). Plants could safely extend lubricant sump change intervals in many applications by a factor of three simply by cooling and cleaning the sumps. After all, research has proven the relationship between wear debris, heat and oil oxidation, and it is intuitively obvious. When integrated into the lubricant analysis program, sump filtration requires effort while the plant is operating; however, it returns labor back to the planning department during outages.

Putting Freed Labor to Work

The few items noted above account for 50% of the labor expected for machine lubrication. Of course, freeing this labor for other purposes may require capital (for tools and systems). Meanwhile, during the evaluation of practice efficiencies (for a safe return of labor to the maintenance department), the plant engineering department should redefine inefficient practices to reflect the best practices of the plant.

Material Conservation

If the plant engineering department executes the previous improvements, it will already have achieved the potential for material conservation (reduced lubricant consumption).

Beyond that, three highly visible targets for lubricant consumption improvements stand out:

Friction Reduction

There is a strong theoretical basis for reducing energy consumption by improving lubricant effectiveness. Personal experience suggests that the 7.5% potential for energy reduction noted in the Jost Report may be attainable for some types of applications but not all. The challenge for the reliability engineer, however, is measuring the improvement with some degree of repeatability and overcoming skepticism from engineering and operations managers.

With that in mind, there are a few things to consider.

Figure 2: All machine surfaces have a significant amount of roughness and potential for frictional energy losses.

Figure 3: Oil films must be greater than the combined maximum asperity heights to avoid contact and parasitic energy losses.

Inadequate film conditions occur as a consequence of changes in load and machine operating temperatures, changes in lubricant condition (particularly contamination with gases or fluids) and accidents in lubricant handling and application, which lead to viscosity errors. Unfortunately, these condition changes often occur simultaneously, resulting in film collapse, machine component interaction, greatly increased frictional resistance and greatly increased energy and machine component consumption.

In addition, several lubricant manufacturers have made energy conservation claims. These companies create specialized additives that accomplish a variety of end-results from friction reduction to surface improvement. Most of these companies consider their additive technologies to be central to their survival and are tight-lipped about product composition. However, there is no debating that there are additive agents that improve lubricity and reduce energy consumption.

However, it is less well-known that the type of base oil (molecular composition) influences energy consumption in a couple ways. Some polar stocks, specifically esters and polyglycols, have lubricity properties superior to conventional mineral oil and unconventional hydrocracked stocks. These fluids provide better surface protection with less bulk oil requirement. Consequently, a lower viscosity grade may be adequate to provide similar levels of component protection vs. a mineral oil option. Lower viscosity also enhances flow rate, an important characteristic for heat removal that further enhances energy efficiency [3].

For this reason, the combined lubricity and polarity of ester stocks make them an ideal choice for lubricants for reciprocating compressor cylinders. Users can reduce volumes and viscosities, which cuts parasitic energy losses from friction and viscous drag. High-hp machines benefit the most.

Evaluation Factors

Documenting energy improvement results is not difficult, but it does warrant careful planning and measurements. Above all, compare similar conditions before drawing final conclusions.

With that in mind, consider these six factors during the evaluation process:

1. Identify machines that operate with a narrow range of load, speed and throughput variability. Otherwise, fluctuations will complicate test cycle comparisons.
2. Verify that the lubricant in use for the select machine (Product A) is in fact the correct type and grade of product for the application.
3. Collect process data. At the very minimum, conduct energy readings (amps) for a period of at least 30 days. Also, record ambient temperatures, operating temperatures vs. ambient, machine loads, machine throughput (speed, units of production, RPM, etc.) and/or other process values. In addition, observe and document mechanical conditions and changes, as well as all maintenance conducted on the machine during the test period.
4. Collect mechanical data including sump, motor, drive and bearing temperatures (thermal images), vibration levels and oil analysis data. All of the sample collection methods must be highly repeatable in order for the data to be dependable. Also, a sample set of less than 30 readings can bring the results into question. In short, it is better to have too much data than too little.
5. Make the conversion to the alternate product (Product B). Make sure that the sump is completely clear of Product A and that no other mechanical or electrical changes have occurred that might impact the operation of the machine.
6. Finally, repeat the data collection activity and compare the results.

Summary

Precision lubrication practices support machine reliability interests, produce best use cost and improve labor efficiency. As a result, plants can reduce electrical energy consumption by using high-performance lubricants and a careful measurement plan.

In addition, they can reduce human energy consumption through careful evaluation and improvement of machine lubrication requirements including the application of high-performance lubricants for critical production machines.