Chain drives consist of an endless series of chain links that mesh with toothed sprockets. Chain sprockets are locked to the shafts of the driver and driven machinery. Chain drives represent a form of flexible gearing. The chain acts like an endless gear rack, while the sprockets are similar to pinion gears.
Chain drives provide a positive form of power transmission. The links of the chain mesh with the teeth of the sprockets and this action maintains a positive speed ratio between the driver and driven sprockets.
Chains can be used to perform three basic functions:
Chains and sprockets are used to deliver positive power transmission in the forms of torque and speed ratio from one rotating shaft to another. Chains can be used in many forms to carry, slide, push, or pull a variety of materials found in countless industrial settings.
Different types of chains are used as devices to synchronize or time movements such as valve timing in four-cycle engines.
The six styles of chain used for mechanical transmission are:
The following styles of roller chain will be discussed:
A standard roller chain is made up of alternate roller links, as shown in Figure 1. Roller links consist of two sidebars, two bushings, and two rollers. Pin links have two sidebars and two pins, which are normally riveted.
Figure 1: Standard Roller Chain
A standard roller chain is manufactured with all the rollers evenly spaced throughout the chain. The rollers have the ability to rotate when contacting the teeth of the sprocket.
A roller chain can be of the single-strand type as shown in Figure 1 or multiple-strand type as shown in Figure 2. Roller chains operate effectively on drives up to approximately 2,500 FPM (762 meters/minutes).
Figure 2: Multiple-Strand Roller Chain
A standard roller chain is manufactured to the specifications outlined in the American National Standards Institute (ANSI) B29.1-1975. These specifications refer to the roller chain, attachments and sprockets. Chains of various manufacturers who conform to ANSI standards may be used interchangeably.
Standard dimensions for roller chain parts are provided in Table 1. Refer to Figure 3 and use Table 1 as a reference.
Figure 3: Roller Chain Dimensions
Table 1- Roller Chain Dimensions Chart
Chain Pitch- The distance in inches between the centers of adjacent joint members. Other roller chain dimensions are proportional to the pitch.
Tolerances for Chain Length- New chains, under standard measuring load, must not be under-length. Over-length tolerance is .001/(pitch in inches) squared plus .015 inch per foot. Length measurements are to be taken over a length of at least 12 inches (304.8 mm).
Measuring Load- This is the load in pounds under which a chain should be measured for length. This is equal to 1% of the ultimate tensile strength, with a minimum of 18 pounds and a maximum of 1000 pounds for both single- and multiple-strand chains.
Minimum Ultimate Tensile Strength- For a single-strand chain, minimum ultimate tensile strength is equal to or greater than 12,500 lbs.(pitch in inches, squared). For multiple-strand chain, the minimum tensile strength is equal to that of single-strand chain multiplied by the number of strands.
A roller chain number consists of at least two digits.
The right-hand digit designates style:
1 = Lightweight roller chain
2 = Rollerless chain
(Numbers to the left indicate pitch in 1/8-inch units.)
For a multiple-strand roller chain, a dash and the number of strands is added to the chain number.
Heavy series roller chain has a link plate thickness equal to the next largest pitch standard series chain. This chain is used where space and weight limitations prohibit use of larger chain. The heavy series has higher yield strength than standard roller chain and will withstand greater shock loads. It is available in single- or multiple-strands.
Adding the suffix ΑH to standard roller chain numbers indicates a heavy series chain.
60H = 3/4 inch pitch, heavy series roller chain.
A multiple-strand roller chain consists of two or more single-strand chains placed side-by-side and joined with pins that extend through the entire chain width. Multiple-strand chains are used to transfer maximum power with the smallest pitch size.
High sprocket speeds combined with long pitch sizes are destructive and noisy. This is due to the impact of the chain links on the sprocket teeth. The force of this impact increases in proportion to the weight of the chain. A multiple-strand chain with small pitch size at high speeds gives the chain drive smooth operation, longer life, and high horsepower transmission.
Multiple-strand roller chain drives require accurate alignment to ensure that the load is distributed equally over each strand. If alignment cannot be maintained, it may be preferable to use single-strand chains on the multiple-strand sprockets.
Figure 4 shows another type of roller chain. This is a double-pitch roller chain, which is similar to a standard chain, except the link plates have twice the pitch of single pitch chain.
Figure 4: Double-Pitch Roller Chain
Double-pitch drive chain is used in place of standard roller chain when speeds are low, loads are light, and center distances are excessively long.
Double-pitch chain has the same diameter pins and rollers, the same width rollers, and the same thickness of link plates as a standard roller chain. Double-pitch chain is not manufactured in multiple-strand widths.
The number system for double-pitch chain is similar to the ANSI standard roller chain number system. The difference is the addition of 2000 to the base ANSI standard number.
2050 = base number 50 or ε inch pitch x 2, the pitch size is 1.25 inches.
This type of roller chain uses oil-impregnated, sintered, metal bushings for self-lubrication as shown in Figure 5. It is capable of running at the same loads as a standard roller chain, but at the lower end of the speed range.
Figure 5: Self-Lubricated Roller Chain
Self-lubricated chains can be used in industry and abrasive conditions where well-lubricated roller chain would only serve to attract abrasives, which can cause early chain wear.
A lack of lubrication between the pin and bushing of a roller chain is a major cause of reduced chain life. A pre-lubed roller chain uses an O-ring seal located between the roller link plate and the pin link plate. The seal permanently confines the factory lubricant to the critical space between the rollers and bushing. Figure 6 displays how the O-ring seal is located in the roller chain.
Figure 6: Pre-Lubed Roller Chain
This section discusses two types of chain links used on standard roller chain: offset and connecting.
An offset link (Figure 7) is a combination pin and roller link. It is used when there are an odd number of pitches in a roller chain strand.
Figure 7: Offset Link
This link consists of two offset link plates, a single bushing with a roller, and a single pin. The link plates are offset to accommodate the difference between the widths of the pin links and the roller link. The pin has a head on one end and a flat on the other end to prevent pin rotation.
A connecting link is a special type of pin link used to provide easy installation or removal of a roller chain with an even number of pitches.
There are two types of connecting links for roller chain:
The drive fit type is similar to a standard pin link in that each pin is riveted to the link plate at one end. The other end of the pin is an interference in its link plate and is retained by either a spring clip or a cotter pin as indicated in Figure 8.
Figure 8: Drive Fit Connecting Link
The slip fit type is similar in design to the drive fit. Each pin is riveted to the link plate at one end, but the other end of the pin is a slip fit in its link plate. This facilitates easy removal of the link plate for chain assembly or disassembly.
Drive fit connecting links offer the greatest security, but where speeds are slow and maximum convenience for chain coupling or uncoupling is desired, slip fit connecting links may be used.
Detachable chains are designed for low-speed and light load power transmission drives. This chain consists of identical links, which are easily detachable from one another. Each link has a hook-shaped end in which the bar of the adjacent link articulates, as shown in Figure 9.
Figure 9: Detachable Chain
The detachable chain is designed for one-way drives where a steady pull is applied on the load side and some tension on the return side is maintained to help keep the slack from buckling. Normally, this chain bends only one way. The chain is assembled and disassembled by pulling up the slack and flexing the links, then sliding a link sideways.
Detachable chains are made from steel, malleable iron, or cast iron. They are used on drives which operate up to approximately 350 FPM (107 meters/minutes). These chains are not usually lubricated and are not as smooth running as higher precision chains such as roller chains. The direction of travel for this chain is with the hook end forward.
The pintle chain is used as a drive chain for higher speeds (to about 450 FPM or 137 meters/minutes) and heavier loads than detachable chain is capable of transmitting. The pintle chain is made up of individual cast links having a full round barrel end cast integral with offset side bars. These links, as shown in Figure 10, are interconnected with steel pins, which are usually riveted over at both ends. Some applications call for cotter pins to hold the pin in place.
Figure 10: Pintle Chain
The pintle chain link pitches range from 1.5 inches (38 mm) to 6 inches (152 mm). These chains are not normally lubricated and weigh more than standard roller chains or detachable chains. The direction of travel for pintle chain is usually with the barrel forward as shown in Figure 10.
The term silent chain has been adopted to describe the inverted tooth link-type of chain that is commonly used for high speeds, over 4,500 FPM (1,372 meters/minutes), and for smooth, vibration-free operation.
Silent chain consists of a series of toothed link-plates assembled on pin connectors, as shown in Figure 11, permitting smooth joint articulation.
Figure 11: Silent Chain
In operation, the silent chain passes over the face of a spur gear-like sprocket. The sprocket teeth do not protrude through the chain as with roller chains. Instead, the chain meshes with the sprocket by means of teeth extending across the width of the chains underside. The links have no sliding action, either on or off the teeth, thus providing a quiet and smooth rolling operation.
Figure 12 shows a section of silent chain. The pitch of a silent chain is measured by the distance between adjacent connecting pins, from center-to-center.
Figure 12: Silent Chain
The silent chain's designation number provides information on chain pitch in 4/8 inch increments, and chain width in 1/2 inch increments.
SC 408 = Silent chain, 4/8 inch or 1/2 inch pitch, 08/4 inch or 2-inch chain width.
Standard pitch sizes for silent chain include:
The silent chain number followed by a hyphen and the number of teeth on the sprocket.
SC 620-25 = Silent chain, 6/8 inch or 3/4 inch pitch, 20/4 inch or 5-inch chain width, 25 tooth sprocket.
The hub construction and details about the bore are the only additional specifications normally required when ordering replacement silent chain sprockets.
The silent chain is manufactured in five basic types to provide effective operation for a variety of drive requirements.
For standard drives, the side guide chain is recommended for all chains up to and including 9/16 inch (12.7 mm) width. Figure 13 identifies the sprocket face profile for side guide chain. This chain has a side guide link, also shown in Figure 13, which acts to maintain the chains position on the sprocket.
Figure 13: Side Guide
This silent chain design is recommended for standard drives from .748 inch (19 mm) to 7 inch (178 mm) width. Figure 14 shows the sprocket profile for a center guide silent chain.
Figure 14: Center Guide
This silent chain design is used for serpentine drives, for reversing a secondary shaft's rotation, or if an adjustable idler is required for tensioning the chain. Figure 15 shows a section of duplex silent chain.
This type of silent chain is used for standard drives from 3-inch (76.2 mm) to 20-inch (508 mm) widths. Figure 16 shows the sprocket face profile for a two-center guide silent chain.
Figure 16: Two-Center Guide
Figure 17 shows a silent chain with no guide links or plate. This type of silent chain assembly is normally used on flanged sprockets.
Figure 17: No Guide
The concentric pin and rocker joint is used in some designs of silent chain. This joint, together with the involute sprocket tooth reduces chordal action to a minimum. The joint consists of a pin and rocker, each with identical cross-sections and concentric radii. When the chain engages the sprocket, the curved surfaces roll on one another, thus eliminating sliding friction and joint galling.
Before the chain engages the sprocket, the contact point of the pin and rocker remains below the pitch line as shown in Figure 18 Top . As the chain engages the sprocket, the contact point moves upward and the pitch of the chain elongates as shown in Figure 18 Bottom.
Figure 18: Rocker Joint
Chordal action is a serious limiting factor in silent chain performance. It is the vibratory motion caused by the rise and fall of the chain as it goes over a small sprocket. This motion produces pulsations, vibrations and limits high-speed, load-carrying capability.
The silent chain with concentric pin and rocker joints can minimize chordal action. Smooth chain/sprocket engagement reduces shock loading and stresses in the links, as well as noise, vibration, and heating. Figure 19 shows how the silent chain enters tangent to the pitch circle and maintains this position as it travels around the sprocket.
Figure 19: Silent Chain Chordal Action
This is possible because of two features:
A leaf chain is used in applications requiring a strong, flexible linkage for transmitting reciprocating motion, or lift, rather than rotative power. Leaf chain is used on applications such as:
Leaf chains are built of interlaced plates held together by rivet pins as seen in Figure 20. The plates are heat-treated for toughness and the pins are case hardened to combine a wear-resistant bearing surface with a strong resilient core.
Figure 20: Leaf Chain
The leaf chain is characterized by link plates having the contour and pitch of the roller link plate equivalent to the pitch of an ANSI standard roller chain. However, the link plate thickness is of the next larger pitch ANSI standard roller chain.
The leaf chain consists of both odd and even lacings and its nomenclature indicates type, pitch and lacing. A ΑBL≅ prefix is used followed by three or four digits. The last two digits indicate the lacing combination (2 x 2, 2 x 3, etc.),while the digit(s) to the left indicate pitch in χ inch increments.
BL423 = Leaf chain, 4/8 inch or 2 inch lacing, as shown in Figure 21.
Figure 21: 2 x 3 Leaf Chain
A laminated metal chain consists of thin strips of resilient metal that extend on each side of the link and conform to the ribbed sides of a sheave face. This action produces a positive link engagement for variable speed drive units.
Figure 22 shows a section of a laminated metal chain. Its appearance is similar to that of a timing chain, except sheave engagement is made by the thin metal strips sliding and conforming to the grooves rather than an actual tooth/sprocket engagement of typical roller or silent chain.
Figure 22: Laminated Leaf Chain
Figure 23 shows a complete variable speed drive unit using laminated metal chain. These units are a fixed shaft center drive. As one sheave is actuated to increase or decrease its pitch diameter, the other sheave automatically increases or decreases its diameter to provide for positively infinite speed control.
Figure 23: Complete Variable Speed Drive with Laminated Metal Chain
Sprockets can be made of fabricated steel, cast steel, cast iron, or synthetic materials such as nylon. Sprockets may be of solid plate design, or be of the open design using spokes. Larger fabricated steel or cast iron sprockets often use the open/spoke design to help reduce weight.
The teeth on most fabricated sprockets are hardened. This provides for:
Some roller chain drives have restricted spaces or machine design limitations for installation or removal of the drive sprocket. Sprockets are designed with four distinct hub classes and are designated Type A, B, C, D.
Figure 24 shows a Type A, which is flat and has no hubs. They are mounted on flanges or hubs of the device they will be driving. The bore of the hub must be located in the center of the bolt hole circle and in the center of the sprocket itself. Type A sprockets can be welded to hubs or collars for mounting purposes.
Figure 24: Type A Sprocket
Type B sprockets have one hub protruding from one side of the sprocket. The hub is extended to one side, as shown in Figure 25. This design allows the sprocket to be fitted close to the machinery it is to be mounted on and helps to reduce a large overhung load on the machine's bearings. Type B sprockets are usually used on the driver or smaller sprocket of the drive set.
Figure 25: Type B Sprocket
Type C sprockets (Figure 26) have hubs extended to both sides of the sprockets plate surface. This hub design is usually used on the driven sprocket where the pitch diameter is larger and it has more surface area in contact with the shaft.
Figure 26: Type C Sprocket
Both Type B and Type C sprockets are designed with either straight or tapered bores. Tapered bore hubs can be fitted to tapered shafts or installed on straight shafts with tapered bushings.
Straight bore sprockets can be supplied with either:
Figure 27: Chain Drive with Type B and Type C Hubs
A fourth type of sprocket occasionally used on chain drives is the Type D sprocket. This sprocket as indicated at the top of Figure 28 has a split hub, which could be of Type B or Type C design. This design permits installation or replacement of the sprocket without disturbing shafts or bearings. The sprocket halves are held together by heavy bolts.
Figure 28: Type D Sprocket
A variation of a Type D sprocket is shown in the lower portion of Figure 28. This design has a detachable rim that permits replacement of the tooth sections without disturbing shafts or bearings. Variation of the number of teeth to change speed ratios, or for replacing worn tooth sections is also possible with this design. The detachable rim sections can be reversed when teeth become worn, thereby doubling sprocket life.
Figure 29 shows a shear pin attachment for a chain sprocket. When this unit is used as the driven sprocket, suitable provision is made for positive power transmission under normal load conditions. The shear pin device provides immediate disengagement of the drive by shearing the pin, when an overload or jam occurs.
Figure 29: Shear Pin Sprocket
Two mounting methods for tapered bushings are commonly used for roller chain sprockets. Figure 30 (left) shows the standard mounting style and Figure 30 (right) shows the reverse mounting style.
Figure 30: Tapered Bushing Sprocket
The installation procedure for tapered bushings and sprockets is as follows:
Figure 31 shows how either the standard or reverse-mounted tapered bushing is removed.
Figure 31: Tapered Bushing Removal
For correct sprocket and chain mesh, and to have the sprocket carry the loads imposed, the design of the sprocket must follow certain fixed dimensions:
This is the diameter of the pitch circle that passes through the centers of the link pins as the chain is wrapped on the sprockets.
The bottom diameter is equal to the pitch diameter minus the chain roller diameter. It allows the chain roller center to follow the sprocket pitch circle. This diameter should not be oversize as destructive loads can be imposed on chains, shafts and bearings. This dimension is used for measuring the diameter on sprockets having even numbers of teeth.
The caliper diameter is used for measuring roller chain sprocket diameters having an odd number of teeth. Caliper diameter is measured from the bottom of one tooth gap to the bottom of the nearest opposite tooth gap.
This is determined by the necessity for a clearance between the hub and the chain link plates when the chain is engaged with the sprocket.
The face width is limited in its maximum dimension to allow proper clearance to provide for chain engagement and disengagement.
This is determined by the required hub wall thickness for proper strength. Allowances must be made for the keyway and setscrews.
Sufficient hub length must be provided to allow a long enough key to be installed to withstand the torque transmitted by the shaft. This also assures stability of the sprocket on the shaft. Figure 32 shows various sprocket dimensions.
Figure 32: Roller Chain Sprocket Diameters
The rate of wear in sprocket teeth can be reduced by the use of double-cut sprockets with the hunting tooth design, as shown in Figure 33.
Figure 33: Hunting Tooth Sprocket Design
This arrangement provides an extra set of teeth, as well as an odd number of teeth, so that each tooth contacts the chain only every other revolution. Less contact results in proportionately less wear. Hunting tooth design can only be used with double-pitch chain.
The location of power transmission shafts are important considerations when planning and installing chain drives. Shaft location will effect chain lubrication, the fit of the chain on the sprocket, and overall chain performance.
Each chain drive is different due to machine requirements, therefore, specific factors must be considered for the chain drive arrangement.
Factors that influence shaft locations are:
The slack in the chain should be on the bottom strand. The chain should wrap the sprocket at least 90 degrees. Chain wrap of 120 degrees is more desirable.
With vertical chain drives, the chain tends to hang away from the lower sprocket, especially when the driver sprocket is in the lowest position. Arrange the shaft centers so that they are at least 20 degrees off of true vertical. If room permits, install a chain tightening mechanism to help maintain proper chain tension.
Figure 34 shows the recommended method for installing a vertical chain drive.
Figure 34: Recommended Vertical Chain Drive Installation Method
Figure 35 shows installations that are not recommended because the chain tends to hang away from the sprocket, resulting in chain and tooth misengagement.
Figure 35: Non-Recommended Installations
Figure 36 Left shows a close-center horizontal chain drive. The rotation of the sprockets should be such that the slack resulting from wear and stretch is on the lower strand. This prevents the chain from grabbing between the sprockets as indicated in Figure 36 Right.
Figure 36: Close-Center Distance
Figure 37 Top identifies a chain drive with an extremely long center distance. The rotation of the sprockets should be such that accumulating chain slack will fall away from the tight strand, rather than fall onto it as shown in Figure 37 Bottom.
Figure 37: Long-Center Distance
On chain drives where it is not practical to have adjustable shaft centers, or where longer center distances may cause the chain to whip, the installation of a chain tightener is recommended. One of the most common types of chain tightener is an idler sprocket mounted on an adjustable bracket, either manually adjusted or spring loaded.
Locate the chain tightener near the drive sprocket on the slack span of the chain. Figure 38 shows the proper idler position on a horizontal drive, while Figure 39 shows the proper idler position for a vertical drive.
Figure 38: Chain Tightener Position
Figure 39: Chain Tightener Position
The correct amount of slack in the chain drive is essential for proper operation. Unlike belts, chain requires no initial tension and should not be tightened around the sprockets, as shown in Figure 40. When the chain is too tight, the working parts carry an extra load and work harder without delivering any more power than a properly installed chain drive. This causes chain wear due to increased pressure in the joints. Over-tightening also overloads the shaft and support bearings.
Too much slack, as shown in Figure 41, is also harmful to the drive. Excessive chain slack causes vibration, whip, and reduced chain life because of the flexing condition.
Figure 40: Correct Tension
Figure 41: Excessive Slack
For most horizontal and inclined drives, the chain should be installed with a sag in the unloaded span of approximately 2% of the sprocket center distance.
Figure 42 shows correct slack for a horizontal chain drive.
Figure 42: Correct Slack
To measure the actual amount of sag, one side of the chain should be pulled up taut, allowing all of the excess chain to accumulate in the opposite span. A straight edge over the sprockets, and a scale can be used to determine the sag, as shown in Figure 43.
Figure 43: Measuring Sag
Vertical center chain drives, or those subject to shock loads, rotation reversals, or dynamic braking should have the chain installed quite taut. Regular inspections for proper tension and adjustments are recommenced. Table 2 indicates approximate chain sag values for sprocket centers ranging from 20 inches to 150 inches.
Proper alignment of sprocket and shaft is necessary to provide long wear life of the drive unit. Increased wear results from misalignment, due to rubbing of chain parts against the sides of the sprocket teeth and excessive friction wear in the joints caused by whipping and twisting of the chain. Figure 44 shows the dimension for shafts and mounted sprockets.
Figure 44: Correct Alignment
To ensure correct alignment, the following steps are recommended:
Figure 48: Align Sprockets
Shafts having end play are best aligned by having them in their usual operating position. One method used to determine this running position is to chalk the shaft, then scribe a line in the chalk opposite a convenient fixed point. Adjust the alignment with the shaft fixed in this position.
Secure each keyed sprocket against axial movement by means of a setscrew, or by collars located on the shaft.
When inspecting roller chain drives, look for the following conditions:
Also, inspect for excessive chain elongation. This condition is indicated by the tendency of the chain to jump the sprocket teeth, as shown in Figure 49.
Figure 49: Excessive Elongation of Chain
Chains cannot operate efficiently if used with worn or faulty sprockets. Regular sprocket inspection and maintenance should include the following:
Figure 50: Excessive Tooth Wear
To break a roller chain where no form of connecting pin or pin link exists, it is advisable to use a proper chain breaker as shown in Figure 51.
Figure 51: Chain Breaker
This tool is designed to prevent chain damage during disassembly. The chain is clamped into the fixture while a tapered conical plunger pushes the pin out. These chain breakers are manufactured for all standard sizes of roller chain.
The purpose of chain lubrication is to provide a clean film of oil at all load carrying points where motion occurs. To maintain chain efficiency and long service life, oil must be delivered to the chain to assure that sufficient oil reaches the joints. Oil of the proper viscosity must be used to penetrate the close clearances and to fill the spaces between the links, as indicated in Figure 52.
Figure 52: Roller Chain Lubrication
Reduced chain life is usually the result of poor or ineffective lubrication. More damage is caused by relatively short periods of operation with faulty lubrication than by years of normal service. Factors such as windage, centrifugal force, and temperature rise must be considered to provide adequate chain lubrication.
When chain drives operate at high speeds, windage, or the air stream induced by the moving chain, blows the oil from the chain. At a given speed, the larger the chain, the greater the amount of windage. The critical velocity usually occurs only at speeds where forced lubrication is indicated, as in Table 3, and its velocity must be overcome by the jet velocity of the oil spray.
This force, which increases with chain speed, throws oil off the chain. Centrifugal force can be used to an advantage if the lubricating oil is applied to the inside of the chain strands, preferably evenly across the chain width on top of the lower span. Enough oil could be provided to flood the chain.
With some drives, the temperature rise will be barely perceptible, while others could exceed the maximum recommended operating temperature of 160 degrees Fahrenheit. To hold the temperature rise within the recommended maximum, it may be necessary to increase the casing area or equip the drive with an oil cooler.
Most chains receive some factory pre-lubrication. This helps to extend the chain operating life by providing the lubricant that is needed until the regular method of lubrication has had sufficient time to become effective.
Viscosity is an important physical property of a lubricating oil. It is a measure of an oil resistance to flow. A low viscosity oil will flow into a chain joint easier than a high viscosity oil. To be effective, the viscosity of the lubricant selected for a chain drive must be low enough to have sufficient film strength to support the load between pin bushing joint components.
Most drive chains should be lubricated with one of the neutral grades of mineral oil indicated in Table 4.
Several methods have been developed for lubricating chain drives. Each suits a particular range of operating conditions. Horsepower, chain speed, and shaft position are primary considerations.
The following are common ways of lubricating chain drives:
This method is used for open running drives operating in a non-abrasive environment. Manual lubrication should be confined to low horsepower drives with chain speed under those listed in Table 3. The lubricant may be applied with a brush or oil can, as shown in Figure 53.
Figure 53: Manual Lubrication
This is a semi-automatic method of chain lubrication adaptable to low horsepower drives with a chain speed under those listed in Table 3. Open-running drives lubricated by this method should be operated in a non-abrasive atmosphere. Drip-cups should be mounted so the oil will drip on the lower span of the chain. Approximately 4 to 10 drops per minute are sufficient to lubricate low speed drives, while a minimum of 20 drops per minute are recommended for higher speeds. Figure 54 shows an example of a drip-cup lubricator.
Figure 54: Drip-Cup Lubricator
Splash lubrication is the simplest automatic method of chain lubrication. This method is satisfactory for low or moderate speed drives. The chain dips about 1/2 inch into an oil reservoir or casing, forcing the lubricant into the chain joints.
Only a short length of chain should run through the oil, preferably a portion of the bottom of the lower sprocket. The relative shaft positions as shown in Figure 55 are recommended for splash lubrication.
Figure 55: Splash Lubrication
This method is effective for moderately high-speed drives and is used when the drive arrangement is not suited for splash lubrication. An oil disc mounted on the lower sprocket dips about 2 inch into an oil reservoir, throwing the oil off the disc by centrifugal force and lubricating the chain.
Disc speed is usually above 300 RPM. This method of chain lubrication is ineffective when peripheral disc speeds reach 8,000 FPM, as well as when the speed drops below 600 FPM. Oil disc lubrication is applicable to the shaft positions shown in Figure 56.
Figure 56: Oil Disc Lubrication
Forced lubrication is recommended for large horsepower drives, heavily loaded drives, high speed drives, or where splash or disc lubrication cannot be used. An oil pump is provided to supply a continuous spray of oil to the inside of the lower span of the chain. The circulation of the lubricant aids in the dissipation of heat and results in a well lubricated, cooler operating chain drive.
The lubricant pump can be directly connected to an electric motor drive as shown in Figure 57. It can also be a chain driven pump operating from either the driver or driven shaft where electric power is not available. The relative position of the shaft is not a factor when forced lubrication is used.
Figure 57: Forced Lubrication Method
Determining whether or not to lubricate open running chain drives under abrasive conditions has been the subject of debate for many years. There are many variables and considerations to analyze between one application and another. The success of chain lubrication may depend on how much abrasive material accumulates on the chain, how well it is cleaned off before lubricant is applied, and how successful the oil penetration is to adequately reach the pin-bushing joints.
Attempt lubrication with a straight mineral oil (SAE 30) using a suitable technique to assure success. If wear life under this method is considered to be less than desirable, then the drive should be run without lubrication to establish a basis for comparison, analysis and conclusion.