Globally, about 30% of energy is consumed in industrial sector, mainly due to the electric motors, that produce more than 2/3 of these consumptions. The most environmental industrial sectors are chemical and petrochemical (33%), iron and steel (17%), cement (9%) and cellulose and paper (9%). If industrial system starts to use the most sustainable technologies available they could reduce 75% of emissions and limit energy consumption, also with a considerable economic advantage. Efficiency is one of the most important characteristics of industrial sector, it is good to make a comparison when you buy the technical equipment, and is one of the advantages of use of gearboxes.
The advantages of using gearboxes on consumption
Gearboxes are effective mechanisms because they help to handle the motors' power without dispersions. They increase torque (power transmitted through the gearbox as usable work) (for more information see article How to limit energy consumption thanks to the advantages of using the gearboxes) How to manage the lubrication of the gearboxes), while they reduce the rotational speed of the prime motor. This is an advantageous use of energy, that allows a great energy saving, developed thanks to advantages of use gearboxes.
There are other factors that contribute to raising the percentages of efficiency, like the production methods of the gearbox and the lubricant used. It is not uncommon for gearboxes to incorporate more than one set of gears (called stages) to achieve the desired overall reduction ratio. In such cases, the overall efficiency of the gear train is the product of the individual efficiencies of each gear reduction stage.
Relationship between seals maintenance and consumption
Seals maintenance and proper lubrication reduce efficiency losses and limit energy consumption, making gearboxes like sustainable gearboxes. Bearings are devices that have the purpose to maintain the lubricant within the bearing and/or to prevent the ingress of foreign matter into the race, in most cases they contribute at the creation of friction and efficiency losses. Bearings are a component common to all gearboxes, they allow for a smooth, low-friction, motion between two components, accepting external loading, and accommodating the internal forces generated by the gears. However, if these devices are carefully designed and manufactured, they can contribute to attracting and producing energy savings.
Bearing and oil maintenance
These seals can be found on both the input and output shafts as well as internally within the unit, and their primary function is to retain the lubricant within the gearbox while eliminating the ingress of dirt and water into it. There exist a variety of different types of seals for a variety of different applications, based on the use of the machinery and the system in which it is positioned. Through operation, the seal lip will gradually wear so, in some cases, a garter spring is incorporated into the oil seal in order to maintain adequate seal lip pressure against the shaft, additionally, in some cases, a secondary lip may be utilized on the seal to prevent the ingress of contaminants into the system and the oil losses.
Since these seal lips are riding against a rotating shaft, friction at this interface is developed, hence, an energy loss is realized. It depends on shaft speed, shaft diameter, and the surface finish/roughness against which the seal lips are in contact, and may develop frictional losses exceeding 100 Watts.
Lubrication as a method to limit energy losses
The use of the appropriate lubricant is crucial to obtaining maximum energy saving from the gearboxes (for more information see article Complete guide to the most common types of gearboxes), preventing direct metal-to-metal contact and providing a median in which heat, developed through normal unit operation, is dissipated. The type of lubrication utilized in a gearbox plays a role in the overall efficiency of the unit, indeed a gearbox lubricated with grease would be less efficient than if it were to be lubricated with oil. Intuitively, this makes sense since grease is typically thicker than oil and it requires a greater amount of power to move the gearing through it. Imagine, for a moment, what it would be like to swim in syrup as opposed to swimming in water.
Another venue for loss in efficiency specifically related to gearing and lubricant is what is known as wind age loss, that is when a certain amount of lubricant adheres to the surface of the gear itself. Since the gear is rotating, centrifugal forces cast the lubricant adhering to the gearing into the enclosed atmosphere of the gearbox casing. This action may serve to create a lubrication “mist” through which the gearing must pass, and this mist is another barrier for the gear to pass through thereby requiring (or diverting) power which otherwise could have been utilized as usable output torque.
Several tests have been conducted on the types of lubricant, one of them is an efficiency test, that was conducted twice: once with the gearbox lubricated with a moderately soft grease with the approximate consistency of peanut butter, and again with a semi fluid grease. Post-test results revealed that the gearboxes lubricated with the semi fluid grease had an efficiency of 92.1%whereas the same unit lubricated with the butter grease was 90.9% efficient.
Analysis necessary before choosing the ideal gearbox
The greatest loss in efficiency is typically associated with the interaction of the gears in mesh, other factors and components also serve to influence the overall efficiency of the system. When you evaluate an efficiency gearboxes, you have to compare these characteristics:
- The use of high quality gears
- The manufacturer's recommendations on the correct type of lubricant
- The frequency to change the lubricant
- How the reducer is connected to the shaft motor
- The surface of the gear teeth
- Low friction seals
- The bearings
- The size of the unit
- The adaptability of the gearbox to the system and to the application power supply
If you neglect the last characteristic, you may have two different disadvantaged situations: If the power capacity of the gearbox greatly exceeds the power of the applied motor combined with the application service factor, much of the motor power will be used to overcome the constant losses within the gearbox there by leaving little additional usable power/torque for the application itself. Conversely however, a gearbox undersized for an application runs the risk of low life expectancy due to overload conditions despite a seemingly high efficiency.
The choice of the best gearbox can bring great earnings both for consumption and for productivity. The quality of gearbox and its energy performance can increase the performance of the entire system.
