A chain is a series of traveling journal bearings with a means to engage the teeth of a sprocket and transmit force and motion. Because each chain joint is a bearing, proper lubrication is essential to obtain the maximum service life from a chain drive or conveyor.
Chains for Drives
The three most common types of chains used for drives are: precision roller chain, covered by American National Standard ASME B29.1; silent (inverted-tooth) chain, covered by ASME B29.2; and engineering steel offset sidebar chain, covered by ASME B29.10. Roller chains are produced in 0.25 through 3.0-inch pitch and are used for a wide variety of drives in the slow to high-speed range. Silent chains are produced in 0.375 through 2.0-inch pitch, run smoother than roller chains, and are used mainly in high-speed drives. Engineering steel chains are made in 2.5 through 7.0-inch pitch and are used mainly in slow-speed drives.
Pitch - The nominal distance between the centers of consecutive chain joints. That would be the distance between consecutive rollers in roller chain and offset side bar chain, and between consecutive pins in silent chain.
Side Bar - The tension members connecting consecutive joints in an offset sidebar chain.
Link Plates - The tension members connecting
Joint - The place in a chain where the chain articulates to engage the sprocket.
Guide - A plate or rail on which a chain, usually a conveyor chain, rides.
Pin - The innermost member of a chain joint. The pin articulates inside the bushing in roller and offset side bar chains, and it usually is pressed into the outer link plates or the wide end of the side bars.
Bushing - The intermediate member of a chain joint in roller and offset side bar chains (silent chains may not have bushings). The bushing is fitted between the pin and roller, and it usually is pressed into the inner link plates or the narrow end of the side bars.
Strand - In roller chain, multiple rows of link plates, bushings and rollers are sometimes assembled onto a common pin. Each row of links is called a strand.
Chains for Conveyors
Both precision roller chains and engineering steel roller chains are commonly used in slat, apron, pusher and crossbar conveyors. Welded steel chains are widely used in scraper and drag chain conveyors. Forged link chains are frequently used in overhead trolley and floor conveyors. Precision roller chains, engineering steel roller and rollerless chains, cast chains, polymeric chains, flat top chains and silent chains are used in plain chain and carrier chain conveyors. Space limitations will permit covering only a few of the most widely used types of conveyor chains here.
How Chains Fail
The three most common ways that a chain may fail are tensile, fatigue and wear. In a tensile failure, the chain is overloaded in tension until it is stretched so badly it will not function properly, or it is literally pulled apart. In a fatigue failure, the chain is loaded repeatedly in tension, at a load below the yield strength (the chain is not stretched), until microscopic cracks develop in the link plates or sidebars. These cracks continue to grow until the chain breaks. In a wear failure, material is removed by sliding, or sliding combined with abrasion or corrosion, until the chain will not function properly (will not fit the sprockets) or the remaining material is so thin that it lets the chain break. This article covers only the lubrication of commonly used steel bushing and roller chains to reduce the effects of wear.
Most often, wear between the pin and bushing causes the chain to elongate (grow longer but not stretch) until the chain will not fit the sprockets correctly or will not maintain correct spacing or timing. Sometimes wear between the roller and bushing or wear between the link plates or sidebars and guides causes the chain to malfunction.
Chain wear elongation usually progresses through three stages as shown in Figure 2. First, there is a short period of rapid initial, or run-in wear. In this first stage, high spots are worn off the pins and bushings and minor misalignments are quickly worn away. Second, there is a period of constant slow, or lubricated wear. In this second stage, the pins are seated properly in the bushings and the bearing areas are normally well-lubricated. And finally, there is another period of rapid, or terminal wear. In this final stage, lubrication may have become ineffective or failed completely, or the hard case on pins and bushings may have worn through, or chain elongation on the sprocket may have caused loads on individual joints to increase dramatically.
Lubrication Effects on Chain Operation
The majority of chain drives and conveyors will perform better and last longer when timely and adequate lubrication is provided. One rule-of-thumb is that proper lubrication can extend chain life by as much as 100 times (Figure 3).
Even if overall chain life is acceptable, lack of proper lubrication can cause other problems. When a chain is starved for lubrication, wear from one joint to another can vary greatly, causing erratic action. Rapid joint wear can cause early loss of timing in a conveyor. Lack of lubrication can increase friction and power consumption and cause a harmful temperature rise.
Need for Lubrication
Chain lubrication is needed mainly to slow the wear between the pins and bushings in the chain joints, to flush out wear debris and foreign materials, and to smooth the chain’s engagement with the sprocket. Additionally, lubrication may be needed to inhibit rust and corrosion, to carry away heat, and to cushion impact forces.
A chain lubricant should have low enough viscosity to penetrate into critical internal surfaces and high enough viscosity, or necessary additives, to maintain an effective film at the prevailing temperature and pressure. Recommended viscosity for various surrounding temperature ranges are shown in Table 1. The lubricant should have the capability to maintain the desired lubricating qualities under prevailing operating conditions, and be clean and free of corrodents.
A good grade of nondetergent petroleum base oil usually is acceptable. While detergents are not normally needed, antifoaming, antioxidizing and extreme pressure additives are often helpful. Impure oils should be avoided. Acids or abrasives in the oil can permanently damage the chain.
The chain manufacturer often uses grease or petroleum jelly as an initial lubricant. However, users generally should not apply greases to chains in service because they are too thick to penetrate into the internal bearing surfaces of the chain. Users should use grease only when fittings for injecting the grease into the chain joints are provided.
Lubrication of Chain Drives
The recommended method of lubrication for chain drives is indicated in the power rating tables published in ASME B29 Series Standards and in various manufacturers’ catalogs. The methods normally listed are manual, drip, oil bath, slinger disk and oil stream. In all methods, the oil should be applied to the upper edges of the link plate or sidebar in the lower span of the chain. This enables gravity and centrifugal force to carry the lubricant into the critical bearing areas.
In manual lubrication, the user applies oil periodically with a brush or spout can. The preferred frequency is once every eight hours, but a longer interval may be used if experience shows it is adequate for that particular drive. The amount of oil and the frequency of its application must be adequate to prevent the formation of a reddish brown discoloration in the chain joints. That discoloration indicates that red iron oxide (rust, hematite, etc.) is being generated in the chain joints because they are not receiving sufficient lubrication.
In drip lubrication, oil is dripped between the link plate or sidebar edges at a rate from four to 20 drops per minute, depending on speed. Again, the amount of oil and the frequency of its application must be adequate to prevent the formation of a reddish brown discoloration in the chain joints. In drip lubrication of multiple strand chains, a wick-packed distribution pipe may be used to uniformly distribute oil to all rows of link plates or sidebars.
Oil Bath Lubrication
In oil bath lubrication, a short section of the chain runs through the oil in the bottom of the chain casing. The oil level should extend only to the pitch-line of the chain at its lowest operating point. Having long sections of chain run through the oil bath can cause oil foaming and overheating.
Slinger Disk Lubrication
In slinger disk lubrication, a rotating disk picks up oil in the bottom of the casing and slings it against a collector plate. The oil is then directed into a trough that drops it onto the upper edges of the link plates or sidebars in the lower strand of the chain. The chain should always run above the oil level in the casing.
Oil Stream Lubrication
In oil stream lubrication, the oil is pumped under pressure to nozzles that deliver a stream or spray onto the lower span of the chain from the inside of the loop. The oil spray should be distributed uniformly across the entire width of the chain.
The excess oil is collected in the bottom of the sump and returned to the pump via a reservoir. An oil cooler may be used to keep oil temperature below the maximum limit.
For manual lubrication, ensure that the designated schedule is followed and the specified grade of oil is used. If the chain is dirty, wipe it clean with kerosene or a nonflammable solvent before relubricating.
For drip lubrication, ensure that the flow rate is as specified and that oil is properly directed onto the chain. Check the oil level in the reservoir at least daily and refill as necessary.
For oil bath, slinger disk and oil stream lubrication, check the oil level in the casing or reservoir at least daily and add oil as necessary. At that time check for leaking, foaming or evidence of overheating. Ensure that all orifices and nozzles are clear and that oil is properly directed onto the chain. Change the oil after the first 50 operating hours and then after every 500 operating hours.
Lubrication of Chain Conveyors
The method of lubricating chain conveyors is generally governed by speed, environment and accessibility. Some method of continuously or periodically lubricating the chain conveyor in service should always be considered. Not lubricating a chain conveyor is a reasonable option only if one of the special chains (sealed joint, etc.) is used.
Manual lubrication is normally sufficient for slow-speed conveyors. Manual lubrication may sometimes be adequate for moderate-speed conveyors, but drip or brush lubrication is often needed. Drip lubrication is often required for high-speed conveyors, and continuous oil stream lubrication may sometimes be needed. Whatever the method, the oil should be applied to the upper edges of the link plate or sidebar in the lower span of the chain. This enables gravity and centrifugal force to carry the lubricant into the critical bearing areas.
In reasonably clean, dry, nonabrasive environments, drip or oil stream lubrication is quite acceptable. However, in dirty, abrasive environments, where the combination of continuous lubrication and abrasive grit can cause rollers and joints to stick, periodic cleaning and manual lubrication may be better. In extremely high or low temperatures, special synthetic lubricants may be required. In wet environments, special lubricants or coatings may be needed.
When accessibility is limited, special remote-fed drip or intermittent-spray lubrication systems may be necessary. Also, special remote-controlled chain cleaning systems may be needed.
In manual lubrication, oil is applied to the chain with a brush or spout can. The preferred frequency is at least once each day, but the interval may be longer if experience shows it is adequate for that particular application. The amount of oil and the frequency of its application must be adequate to prevent the formation of a reddish brown discoloration in the chain joints. That discoloration indicates that red iron oxide is generated in the chain joints because they are not receiving sufficient lubrication.
In brush lubrication, oil is continuously brushed on the lower span of the chain from the inside of the loop. The amount of oil and the frequency of its application must be adequate to prevent the formation of a reddish brown discoloration in the chain joints.
In drip lubrication, oil is dripped between the link plate or sidebar edges at a rate from four to 20 drops per minute, depending on speed. Again, the amount of oil and the frequency of its application must be adequate to prevent the formation of a reddish brown discoloration in the chain joints.
Oil Stream or Spray Lubrication
In oil stream lubrication, the oil is pumped to nozzles that deliver a stream or spray onto the lower span of the chain from the inside of the loop. The oil spray should be distributed uniformly across the entire width of the chain.
The same guidelines given for periodic maintenance of manual and drip lubrication of chain drives apply to chain conveyors.
For oil stream lubrication, check the oil level in the reservoir at least daily and add oil as necessary. Ensure that all orifices and nozzles are clear and that oil is properly directed onto the chain.
Much of the information for this article was extracted from two publications by the American Chain Association. For more information on chain lubrication, please refer to the following publications:
American Chain Association. (1993). Identification, Installation, Lubrication and Maintenance of Power Transmission Roller Chains in ANSI B29.1 and ANSI B29.3. American Chain Association, Naples, FL.
American Chain Association. (1982). Chains for Power Transmission and Material Handling, Design and Applications Handbook. Marcel Dekker, New York, NY.