In my last blog, I raised the question about zero breakdowns and if it was possible to achieve that state of equipment reliability. This blog starts the first of five steps to achieving zero breakdowns. The first step is to maintain basic conditions. The three components to this step are:
- Equipment cleaning
- Tightening procedures
Equipment cleaning activities in many companies today are primarily motivational activities. And while motivation is a good reason to clean equipment, there are also technical reasons to clean equipment. For example, consider an electrical motor. If electrical motor is allowed to become contaminated, the contamination acts as an insulator, interfering with the thermal transfer process or heat dissipation. This results in excessive temperature rise of the motor. As the temperature increases, the design life of the motor decreases. One study showed that in some motors the useful life was reduced by ½ for every 10 degree C rise in operating temperature above the designed operating temperature. This can be a self-destructive problem, since in some annealed copper wire; a 50 degree C temperature rise causes a 20% increase in resistance in the wiring. This leads to even more heat, more resistance, more heat, until the motor fails.
Even if this does not result in an immediate failure of the motor, it may result in getting six months of life out of a motor, when it was designed to provide 6 to 10 years of life. This means that unnecessary maintenance will be performed.
Also, consider that gear cases have a similar problem. If gear case exteriors are allowed to become contaminated, the internal temperature of the gear case will rise. As the temperature rises, the manufacturer’s suggested lubricant for the gear case is incorrect. The higher temperatures will result in thinning viscosity of the lubricant, creating metal to metal contact between components in the gear case. This will result in rapid wear, again shortening the life of the gear case.
As with the motor, the gear case and components will not fail immediately: however it may need to be replaced after two or three months of use, rather than seven or eight years of use. This leads to excessive maintenance cost and lower availability of the equipment.
Hydraulic systems also have a problem with cleanliness and heat. A hydraulic system is equipped with a reservoir that is designed to dissipate the heat in the hydraulic fluid as it returns to the tank. This cooling function may be enhanced by coolers to lower the temperature of the fluid. If the tank becomes dirty or the coolers become clogged and the temperature of fluid begins to rise. Once it reaches about 140 degrees, the hydraulic fluid will begin rapid degradation. Once study shows that the hydraulic fluid will oxidize twice as fast for every 20 degree F temperature rise above 130 degrees. At 215 degrees F the oil life expectancy will drop to 3% of original design.
As the hydraulic oil reaches the end of its life, it loses its lubricating quality, allowing rapid wear of system components, such as pumps, valves and actuators. This rapid wear produces particles and contaminants that will further damage the hydraulic system and degrade its performance.
Another problem related to overheated hydraulic fluids is inlet air leaks or cavitation. As the air bubbles transfer from the suction side of the pump to the pressure side of the pump, the air bubbles implode, producing temperatures of up to 2100 degrees F.
Regardless of how the oil is overheated, it will take on a varnished and sticky quality. The varnish particles travel downstream through the pump and other components such as control valves and actuators clogging lines and causing sticking valves that burnout solenoids and other components. This results in the system failure and downtime or erratic operation and the related minor stoppages.
Tightening or torquing procedures.
When considering proper torquing procedures, one must first consider the proper tools. In many organizations technicians are observed using crescent wrenches, channel locks, or other improper tools to tighten hex-headed fasteners. The proper tool, of course is a torque wrench. A torque wrench can measure the proper amount of torque applied to a fastener. This is important, since all threaded fasteners are two inclined planes wedging against each other. When a fastener has the proper amount of torque applied, it is distorted, locking the threads so they will not loosen.
If fasteners are not torqued sufficiently, the faster is not deformed, it will not lock, and eventually works loose, creating a vibration, wear, and ultimately failure. Conversely, if a fastener is over tightened, it can exceed the elasticity of the fastener material, deforming the fastener so that is weakened. Then the fastener, when re-tightened will loosen quickly or break.
Also, it is not just enough to understand the amount of torque to a size of fastener, the amount of torque is also determined by the grade of the fastener. There are many grades of fasteners available and even in the same size; each requires a different amount of torque.
Consider how many failures at a plant or a facility have the root causes simply because a mechanical device was not fastened correctly. The fasteners would begin to work lose, creating vibration, creating wear, which increases the vibration, which increases the wear, until a failure occurs. This scenario is all too common in plants today. What percent of all failures at a specific plant or facility could be eliminated by paying attention to proper fastening procedures? One study in the petrochemical industry showed that 50% of all fastener failures occur due to improper assembly and incorrect torque.
Proper lubrication would include the following items:
- the right lubricant
- the right quantity of lubricant
- the right application method
- the right frequency of application
The question might be asked, how often do individuals get all four of the requirements correctly performed? Do some individuals use power grease guns to lubricate bearings and continue until the bearing is filled with grease is then forced out of the seals? Is completely full the correct level of lubricant for a pillow block bearing? In reality, a pillow block bearing is designed to be filled only one-third full of oil or grease to allow for heat dissipation during operation. So when the bearings are over lubricated, they over heat, and their life is shortened dramatically.
Lubrication also needs to be monitored for contamination. Any solid contaminants in the lubricant will eventually come between the components in a drive and accelerate the wear on the components.
Water is also a contaminant, but it acts differently. Water has no load carrying capability. As water molecules move between the components of a drive, the fluid film barrier or is ruptured and metal to metal contact occurs. This accelerates wear in the gear case or drive. For example, water content does the following:
.03% water content reduces bearing life to 50% of L-10 rating
.2% water content reduces bearing life to 17% of L-10 rating
1% water content reduces bearing life to 6.3% of L-10 rating
2% water content reduces bearing life to 4% of L-10 rating
By these figures, it is quite easy to see the dramatic impact even the slightest water content has on the life of the lubricated components.
Mixing lubricants can also create problems. Since different vendors use different additives to their lubricants, mixing incompatible lubricants will cause a chemical reaction. This leads to the formation of acids, alkaloids, thinning viscosity, thickening viscosity, coagulation, etc. It is important to always understand the interchange requirements and consequences of mixing lubricants.
So there it is- the first step to zero – How does it apply to your plant or facility? If you were to perform a true root-cause analysis of all of your equipment failures, what percent of them would be related to cleanliness, fastening procedures, and lubrication? What if your technicians suddenly started performing these tasks as described in this blog? Would your failure rate drop? By how much? 50%? 75%? More? Less?
The next blog will discuss step 2 on the journey to zero breakdowns.