This article takes an in-depth look at lubrication systems.
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Lubrication systems distribute the lubricant to the moving machine parts in contact. Lubricants reduce the friction between sliding or rolling machine elements, such as gears, spindles, bearings, chains, dies, screws, cylinders, valves, and cables, in order to prevent wear, heat generation, and premature failure and prolong the service life of the machine elements. Lubricants may also function as a coolant that prevents thermal expansion, which consequently degrades the accuracy of the machine element.
Lubrication systems control the volume and pressure of the lubricant to be applied to the surfaces of the moving machine parts in contact. They promote the smooth and healthy operation of the machinery. Through lubrication systems, the lubricant is applied and distributed efficiently and regularly. These systems are widely used in the automotive, industrial manufacturing, oil and gas, power generation, and steel processing industries. Lubrication systems are also present in automotive engines. The complexity of lubrication systems ranges from manually operated grease guns to automated and centralized lubricant dispensing systems.
The basic components of industrial lubrication systems are the following:
The types of industrial lubrication systems are the following:
Single line resistance (SLR) lubrication systems consist of a central pump that distributes the lubricant to single or multiple supply lines parallel to each other (multi-line systems). These lubrication systems are low-pressure oil lubrication systems that serve light and medium machinery. The oil pressure ranges from 100 to 250 psi. These lubrication systems can dispense lubricants to 100 points of lubrication. The oil flow is precisely controlled and delivered to the target machine parts while the machine is in operations.
SLR lubrication systems can deliver the lubricant by manual or automatic operation. Manual SLR lubrication systems use a hand-actuated pump that dispenses oil in an intermittent or occasional manner. Automatic SLR lubrication systems are safer and more efficient than manual systems and are ideal for machine parts that require continuous or regularly timed lubrication. Automatic SLR lubrication systems are actuated by a timing mechanism or a mechanical drive mechanism that dispenses the oil in a continuous or regular timing, respectively. These mechanisms eliminate operator intervention when there is a need for lubricant replenishment.
SLR lubrication systems are compact, cost-efficient, and have a simple design. They are suitable for closely configured bearing clusters or groups.
Single point (SP) lubrication systems apply lubricant to only one lubrication point. These lubrication systems are practical if there are few lubrication points spread over a wide area. These systems are also used when the lubrication points are in remote or restricted areas. SP lubrication systems are typically automatic, though manual systems can still be found. They have compact sizes in which the components such as reservoir, metering devices, and supply and feed lines are contained in a small, protective housing. The types of single-point lubrication systems are the following:
Spring-loaded lubricators have chambers commonly constructed from polycarbonate or borosilicate, which can withstand temperatures of up to 2500F and 4500F, respectively. Their volumes range from 2 to 18 ounces and can handle lubricant pressure from 2 to 65 psi.
Since grease flow is dependent on temperature, spring-loaded lubricators are not suitable for environments with wide temperature variations. The viscosity of the grease is directly proportional to its temperature. Also, since grease consistency increases with applying shear forces (i.e., thixotropic nature), these lubricators cannot be used in environments with high vibrations.
Gas-Charged Automatic Lubricators: Gas-charged automatic lubricators consist of a cylinder with the pressure generator and lubricant stored in different chambers. The piston, which separates the two chambers, pushes the lubricant to respond to the pressure build-up caused by the pressure generator.
The pressure generator of the gas-charged automatic lubricator is composed of an electrolytic solution and a galvanic strip contained in a plastic tube. The activating screw breaks the plastic tube after the injector is installed, which exposes the galvanic strip to the electrolytic solution. This exposure results in an electrochemical reaction that produces hydrogen gas. As more hydrogen gas is produced, the internal pressure within the generator increases, which pushes the piston. The piston then ejects the lubricant out of its chamber. The rate of lubricant discharge can be designed or set by the manufacturer depending on the nature of the customer’s application.
The electrochemical reaction inside the pressure generator is dependent on temperature. As the ambient temperature increases, consequently increasing the lubricant discharge rate. The flow properties of the lubricant also vary with the ambient temperature.
Since hydrogen gas is flammable, gas-charged automatic lubricators should not be used in areas with ignition sources.
Positive Displacement Single Point Lubricators: Positive displacement single point (PDSP) lubricators are electromechanical single point lubricators consisting of a follower plate that ejects the grease from its canister. The follower plate is powered by a battery or an electric motor. The rate of grease ejection can be precisely controlled and is not dependent on ambient temperature. PDSP lubricators can be controlled such that a specific volume of grease is dispensed at regular time intervals. The capacity of PDSP lubricators ranges from 60 cc to 600 cc.
Dual-line lubrication systems, also known as “dualine” or double line lubrication systems, operate in a two-phase alternating cycle. In the first cycle, the lubricant is pumped from the reservoir to the first supply line and moves the inlet and discharge pistons of all injectors in one direction. The lubricant is also released in one direction. The injectors are arranged in modular styles and are shared by the two supply lines. Once the preset pressure on the end-line pressure switch is reached, the first supply line is relieved, and the lubricant is pumped to the second supply line. The inlet and discharge pistons will now move and dispense lubricant in the opposite direction.
Dual-line lubrication systems are used to supply lubricants to the lubrication points continuously. They are found in every industry requiring continuous lubrication. They are typically used in medium- to large-sized machinery and equipment and can operate in harsh environments. They are cost-efficient if there are more than 20 lubrication points, and more points can be added easily without modifying the whole system. If blockage between the supply line and lubrication occurs, the remaining lubrication points will continue to be lubricated. Lastly, dual-line lubrication systems can handle lubricants with a wide range of flow properties, from light oil to grade-2 grease.
The types of small-scale and/or manual lubrication systems are enumerated as follows. These types typically supply lubricant only on a single point in one application and are preferred for occasional and intermittent usage.
Like industrial lubrication systems, automatic chain oilers are composed of a reservoir, pump, metering device, and an injector; these components are installed in bicycles and motorcycles which do not appear bulky. These integrated components are connected to a controller in which the release of the lubricant can be set or adjusted. The lubricant is usually released when the bicycle or motorcycle is running.
Grease Gun: Grease guns are one of the commonly found tools in machine shops and garages. They are used to inject grease to a lubrication point. They are also used in maintaining light to heavy machinery and equipment in industrial plants. The lubricant is contained in a canister and is dispensed through an aperture by the following methods:
Positive displacement injector (PDI) lubrication systems are driven by a central pump that generates pressure (greater than 55 bars) to distribute the lubricant over several supply lines. The lubricant is then distributed to the feed lines wherein PDIs are installed. Once the operative pressure is reached, the fixed displacement piston inside the PDIs is moved hydraulically against spring pressure to discharge a fixed amount of lubricant into the lubrication point. PDI lubrication systems are used in small- to medium-sized machinery and are preferred if the machinery requires an accurate and precise dispensing of lubricant in multiple lubrication points. PDI lubrication systems can be controlled to dispense lubricants at regular time intervals.
In series progressive lubrication systems, the pump is connected to the master divider block, which distributes the lubricant to secondary divider blocks. Divider blocks contain a series of hydraulically actuated spool valves arranged in a modular style, delivering the required lubricant. The lubricant is dispensed from each valve in series, which means that the lubricant on one valve will be released after the lubricant release in the previous valve. If the last valve will release the correct amount of lubricant, it means the divider block is working perfectly. However, if one valve is malfunctioning, the whole divider block will not dispense the lubricant correctly and causes pressure build-up. A pressure switch can be installed to monitor the lubrication system by detecting faulty divider blocks. Series progressive lubrication systems are commonly used in medium- to heavy-duty industrial equipment.
The types of industrial lubricants are the following:
Oil is the main component of lubricant that reduces friction and wear between machine elements in contact. Oil lubricants have a wide range of viscosities and can be synthetic, vegetable, and mineral-based.
Oil lubricants are the “purest” form of lubricants, though several additives can be added. Antioxidant and corrosion inhibitor additives can be mixed with the lubricant to prevent oxidation and corrosion. Detergents prevent deposits from forming. Viscosity index improvers, such as polyacrylates and butadiene, are added in order for the lubricant to remain viscous at high temperatures.
Oil lubricants are commonly used in lubricating hinges, bearings, and sharpening blades. However, it is not advisable to use oil lubricants on dirty, dusty, and/or wet surfaces.
Grease is a mixture of oil, thickening agent, and additives with self-lubricating properties such as PTFE, graphite, and molybdenum disulfide particles. Grease lubricants have extra stickiness which enables them to stick to surfaces better. They also protect the surfaces of the lubricated machine elements from corrosion and damage.
Grease lubricants are used if the desired lubricant application is less frequent, as they can stay for longer times. Since grease lubricants generally have high viscosities and densities, they create more resistance; hence, they are not suitable for small and fast-moving parts.
Penetrating lubricants are used for lubricating machine parts covered in rust and debris. These lubricants seep into tiny cracks present in the metal surface and break up rust. However, they do not last long on surfaces and should not be used as a substitute for other types of lubricants.
Dry lubricants are made up of tiny particles with self-lubricating properties such as PTFE, graphite, and molybdenum disulfide. These particles create a microscopic, slippery film when they are sprayed onto the surface of the machine part. Dry lubricants can be mixed and sprayed together with water, alcohol, or solvent, eventually evaporating, leaving the thin lubricating film on the surface. Unlike oil and grease, dry lubricants do not attract dust and dirt.
Dry lubricants are used for machine parts requiring high accuracies, such as actuating ball screws and lead screws and gears. They can be used in threaded rods, locks, bearings, and hinges. They are the best option for high-temperature applications since oils oxidize at elevated temperatures. However, they are not ideal when the lubrication point is exposed to liquids and solvents because these lubricants can be washed away.
Gear lubricants are specially formulated to protect the gears and their gear teeth from abrasion. These lubricants must be thermally stable to prevent sludge formation on the gears. Special additives can be mixed with gear lubricants to protect the gear teeth from pitting and localized corrosion. Extreme pressure (EP) additives are incorporated in some gear lubricant formulations to protect the surfaces from high pressure during shock loading; EP additives are required for lubricants for gears inside heavily loaded gearboxes.
Compressor oils lubricate the rotating parts to reduce friction and prevent friction. Aside from lubrication, it also serves as a coolant, which removes heat generated during compression of air, and as a sealant for the compression chamber. Hence, compressors should only use compressor oils; other lubricant types cannot be used as a substitute for compressor oils.
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