Читать книгу The Death of Reliability: Is it Too Late to Resurrect the Last, True Competitive Advantage? - Nathan C. Wright - Страница 13
ОглавлениеLubrication is a must with respect to reliability, but what exactly is lubrication? Webster’s Dictionary defines lubrication as the application of some oil or grease substance to diminish friction. Although this definition is valid, it does not encompass everything that proper lubrication can achieve. It is this simple definition that often explains why organizations place little or no importance on lubrication. They lack a thorough knowledge of reliability and how lubrication impacts it. I am giving organizations the benefit of the doubt here, because if they understand the importance of lubrication and do nothing to ensure its complete, proper application, they would be criminally liable. Think of your lubrication systems as the circulation system in your body. To stay alive, you need to do a lot of proactive reliability efforts.
The driving force behind the need for a lubrication program is the fact that 70% of all unreliability is caused by a lack of a lubrication program. Improper lubrication causes mechanical wear and premature equipment/component failure, or unreliability. Figure 2.1 illustrates the major causes of unreliability and the breakdown of components.
Figure 2.1 Improper Lubrication.
Mechanical wear of equipment components is common, and this is particularly true where improper lubrication is an issue. Particle and moisture contamination, along with the wrong or degraded lubricants, are the prevalent factors in creating rust on metal components. This increases oxidation rate, which leads to increased acid within the components.
Mechanical wear happens when machine surfaces rub against each other. Abrasive wear happens when particles enter the system, commonly through contaminated lubricants. These particles are usually dirt or wear materials, and they lead to three-body abrasion known as surface fatigue, which pits and scores the machine surfaces. This results in premature failure, also known as unreliability. Adhesive wear results when two surfaces come in direct contact and transfer material from one face to the other. This happens because lubricants cannot support the load, or in areas where the surfaces suffer from lubricant starvation or the use of the wrong lubricant.
Metal fatigue is another form of mechanical wear. An example would be when you work a wire back and forth to cut it without tools. The more you move a wire back and forth, the harder the metal works; the fatigue increases, ultimately resulting in a brittle point that snaps. This is the effect contaminants have on metal surfaces. Over time, this constant flexing will fatigue the metal, resulting in premature failure. The Institute of Mechanical Engineers has found that “every $1,000 invested in proper lubrication yields a savings of $4,000, which is a 3,900% return on investment.” This is a great return on investment in anyone’s book, and an example of how to justify a project and fund your reliability efforts.
Acid is a by-product of the reaction between additives in the oil and water. Lubricant contamination has many paths. The manufacturing process of the lubricants is the first-place contamination enters the system, but it can enter through seals, creating a caustic environment that results in wear. This can also happen if you do not understand the lubricant’s additive package, because you can end up with corrosive damage. An example would be using an extreme pressure additive with yellow metal (copper, brass, etc.) because some of these additives are corrosive to them. This is another example where you need someone on your team who understands this problem and is qualified to review and eliminate it from happening.
Equipment loses its functionality in three ways, but it is the lubrication (life blood) of the parts that is the root cause of much of these failures. Keeping your plant equipment properly lubricated, controlling the contamination, and ensuring the proper installation can extend the equipment life and contribute to a more reliable operation. To proactively address the single most common cause of unreliability, you need to develop a lubrication program.
To start a lubrication program, you need to understand that there are several different substances that can be used to lubricate a surface. The most common are grease and oil. Grease is comprised of oil and a thickening agent. The thickening agent’s job is to retain the desired consistency, while the job of the oil is the actual lubrication. The selection of the proper grease should be done with the utmost diligence to address all equipment needs. Many of the manufacturers sell inferior grease, and the thickening agent and oil separate. This leads to lubrication-based failures because once the oil separates, the grease loses its protective quality. I have seen organizations use extension hoses to make grease points easily accessible. This can be a machine killer depending on your grease. You need to know the amount of time the grease will sit in the line based on the frequency of application and amount. The wrong grease will allow the oil to leach out of the thickening agent and all you will be providing the lubricated asset is the thickening agent, devoid of oil. What would appear to be a great idea to an uninformed organization could be a self-inflicted wound.
Oils come in three common varieties: vegetable, mineralbased, or synthetic. There can also be a combination of these as well. The application dictates which oil, referred to as the base oil should be used. Synthetic oils are designed for extreme conditions while vegetable oil is used where there are environmental concerns. Your decision on which to use needs to go beyond application and should consider your overall program. Resources will play into your decision as the different bases require different proactive approaches. If your organization plan includes in-the-field filtration instead of interval-based replacement, you need to understand the effects on your base and its additives. Reliability leaders need to have experience with this or you will leave this type of decision to a supplier who may be unqualified and most certainly does not have any “skin in the game.” Most organizations leave this important decision up to their supplier because they offer “free” advice. Is it truly “free” if your reliability suffers? Part of your justification for your program start-up is the real cost of “free” advice and its detriment to plant reliability. Suppliers have very little risk in providing free bad advice because if an organization is allowing them to give it, the organization lacks the ability to determine that it is bad.
ADDITIVES
In addition to determining the correct base oil, the selection of additives will enhance, add, or suppress properties within the base, and the lubricant’s performance. The additive package is determined by the type of base oil and the application that it will be used in. An example would be engine oil with a dispersant added. The dispersant keeps insoluble matter conglomerated together so it can be captured by the filter during circulation. Additives can improve anti-wear and extreme pressure performance. It can enhance seal performance and reduce or eliminate start-up wear. Allowing the supplier to dictate such an important decision should never happen. Again, this seemingly “free” advice is costing you thousands or even tens of thousands of dollars in unreliability caused by premature failure of your lubricated assets. Educating yourself on machinery lubrication is vital to the selection of the proper lubrications, as is selecting a lubrication partner who has the same goals you have—plant reliability, not their profits.
In an application that experiences extreme temperature, from hot to cold, a viscosity index (VI) additive would be used. The molecular construction of these additives has long, organic molecules that stay together in cold conditions, but they unravel in hot environments. This allows the oil to change its viscosity and flow better when it is cold while maintaining its high-temperature properties. The main concern most organizations should have with additives is that they can be depleted, requiring the oil to be changed to restore them to required levels. This was the “old school,” or supplier-preferred approach. In reality, you can re-infuse additives without a complete oil change. Working with a lubricant partner, you can determine what portion of transfusion is required to return the additives to desired levels. The combination of in-the-field filtration, base oil, and infusion is another cost savings. Most supplier representatives are not qualified to assist you in this decision so they will focus their efforts on sales and not your performance or cost savings. This is another aspect of reliability where you can save money to fund other reliability efforts.
FRICTION
The key objective of lubrication is to reduce friction, but it has a lot of other benefits. The lubricating film helps to prevent corrosion by shielding the metal surfaces from water and other substances. It also has a role in controlling contamination within the system. It serves as a conduit to move the contaminants to the filter for removal. Another aspect of lubrication is that it aids in controlling the temperature by absorbing heat and transferring it to where it can be dissipated. Accordingly, the selection of your lubricants needs to align with your reliability strategy and is key to its success. Selecting your supplier cannot be left to purchasing agents and supply chain managers. They are not qualified to make this decision. Selling the importance of lubrication is the job of Reliability Managers, and they can only do so if they have the experience and education to communicate this at all levels of the organization. Do not entrust this solely to your supplier; educate yourself in machinery lubrication so you can instruct your suppliers and not just hope they get it right.
Lubrication has three different types: boundary, mixed, and full film. Each of these is different, and they rely on both the lubricant and the additives to protect against wear.
There are two forms of full-film lubrication: hydrodynamic and electrohydrodynamic. Hydrodynamic is when two surfaces, relative to each other, in a sliding motion, are completely (fully) separated by a fluid film. Electrohydrodynamic differs from hydrodynamic in that the surfaces, relative to each other, are in a rolling motion. An additional difference between the two is that while electrohydrodynamic has a much thinner film layer, the pressure on the film is much greater. This is called electrohydrodynamic because the film elastically deforms the rolling surface to properly lubricate it. If you want to test your supplier, ask a basic question about this and see if they can answer it.
ASPERITIES
No matter how polished or smooth the surface appears, there are always irregularities present. At a microscopic level, they jut out from the surface like peaks and valleys. The peaks and valleys are called asperities. It is the peaks of these asperities that carry the load. To achieve a full film condition, the lubricating film must be thicker than the asperities. This type of lubrication is the most desired and protects the surfaces most effectively. By filling in the peaks and valleys, you can spread the load across the entire surface area, reducing friction.
In applications where there are shock loading and frequent starts and stops, boundary lubrication is preferred. Additives like extreme pressure (EP) or anti-wear (AW) protect surfaces where a full film cannot be accomplished because of load, speed, or other factors. These additives form sacrificial layers of protection by clinging to the surfaces, preventing wear. When surfaces are contacting in such a way that only an EP or AW layer will protect them, boundary lubrication must be used. However, this is not the ideal situation because of high heat, friction, and other undesirable effects.
In applications where you need both boundary and hydrodynamic lubrication, you can employ mixed lubrication. In this application, most of the surfaces are separated by a lubricating layer but the asperities will still come in contact. Because of this, you will need to employ additives.
Only with an understanding of the process will it be easy to determine which lubricants to use. The determination is between separating the surfaces or protecting them from friction, heat, wear, and other issues. Using oils, grease, gas, or other fluids will accomplish this. Next time you change the oil in your car, understand that there is a lot more going on than meets the eye.
When making the decision to undertake any project, you must understand what constraints you have. The constraint can be displayed as a triangle. A graphical representation of this decision making is shown in Figure 2.2. One leg of the triangle is costs, the next is time, and the final one, quality. The middle of the triangle is traditionally risk. I like to look at these projects with an eye on the opportunity and not the risk. All projects have associated risk and opportunity. Your job is to look at the risk and mitigate it to the best extent possible, or to look at the opportunity and maximize it.
My recommendation to all organizations is to never compromise on quality. This is always the approach I take. If I cannot do it with the quality I set, then I will not undertake the project. For me, the decision on how to approach the project comes down to cost and time. If cost is the determining factor in your organization, then it will take more time. The reverse is also true: if you want results in a quicker time, then the costs will increase. The decision on costs and time needs to be made by looking at the opportunity. Organizations that keep their eye on the opportunity will gain a competitive advantage over their competitors.
Figure 2.2 Project Decision Making.
When determining how much the potential savings will be when you undertake a lubrication project, you can use detailed information from your computerized maintenance management system (CMMS) or other cost tracking system or industry standards. Most organizations lack the detailed information to calculate the cost of not having a strong lubrication program, so I normally use percentages I have gathered throughout my experience. If your organization does not gather this information, you will need to determine potential savings.
ROI CALCULATION
