Machinery's Handbook, 31st Edition
2638 Transmission Roller Chains Lubrication.— It has been shown that a separating wedge of fluid lubricant is formed in operating chain joints much like that formed in journal bearings. Therefore, fluid lubri - cant must be applied to ensure an oil supply to the joints and minimize metal-to-metal contact. If supplied in sufficient volume, lubrication also provides effective cooling and impact damping at higher speeds. For this reason, it is important that lubrication recommendations be followed. The ratings in Table 9 apply only to drives lubricated in the manner specified in this table. Chain drives should be protected against dirt and moisture and the oil supply kept free of contamination. Periodic oil change is desirable. A good grade of non-detergent petroleum base oil is recommended. Heavy oils and greases are generally too stiff to enter and fill the chain joints. The following lubricant viscosities are recommended: For temperatures of 20 ° to 40 ° F, use SAE 20 lubricant; for 40 ° to 100 ° , use SAE 30; for 100 ° to 120 ° , use SAE 40; and for 120 ° to 140 ° , use SAE 50. There are three basic types of lubrication for roller chain drives. The recommended type shown in Table 9 as Type A, Type B, or Type C is influenced by the chain speed and the amount of power transmitted. These are minimum lubrication requirements and the use of a better type (for example, Type C instead of Type B) is acceptable and may be beneficial. Chain life can vary appreciably depending upon the way the drive is lubricated. The better the chain lubrication, the longer the chain life. For this reason, it is important that the lubri cation recommendations be followed when using the ratings given in Table 9. The types of lubrication are as follows: Type A — Manual or Drip Lubrication: In manual lubrication, oil is applied copiously with a brush or spout can at least once every 8 hours of operation. Volume and frequency should be sufficient to prevent overheating of the chain or discoloration of the chain joints. In drip lubrication, oil drops from a drip lubricator are directed between the link plate edges. The volume and frequency should be sufficient to prevent discoloration of the lu - bricant in the chain joints. Precautions must be taken against misdirection of the drops by windage. Type B — Bath or Disc Lubrication: In bath lubrication, the lower strand of the chain runs through a sump of oil in the drive housing. The oil level should reach the pitch line of the chain at its lowest point while operating. In disc lubrication, the chain operates above the oil level. The disc picks up oil from the sump and deposits it onto the chain, usually by means of a trough. The diameter of the disc should be such as to produce rim speeds of between 600 and 8000 feet per minute. Type C — Oil Stream Lubrication: The lubricant is usually supplied by a circulating pump capable of supplying each chain drive with a continuous stream of oil. The oil should be applied inside the chain loop evenly across the chain width, and directed at the slack strand. The chain manufacturer should be consulted when it appears desirable to use a type of lubricant other than that recommended. Installation and Alignment.— Sprockets should have the tooth form, thickness, pro- file, and diameters conforming to ANSI/ASME B29.1. For maximum service life small sprockets operating at moderate to high speeds, or near the rated horsepower, should have hardened teeth. Normally, large sprockets should not exceed 120 teeth. In general a center distance of 30 to 50 chain pitches is most desirable. The distance between sprocket centers should provide at least a 120 degree chain wrap on the smaller sprocket. Drives may be installed with either adjustable or fixed center distances. Adjust able centers simplify the control of chain slack. Sufficient housing clearance must always be provided for the chain slack to obtain full chain life. Accurate alignment of shafts and sprocket tooth faces provides uniform distribution of the load across the entire chain width and contributes substantially to optimum drive life.
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